Patent Application
20070048855
This invention relates to X-ray crystal data for phenylalanine ammonia-lyase (PAL), PAL analogs, compositions thereof, and optimization of such compositions to enhance PAL stability and to reduce immunogenicity and/or proteolytic sensitivity of PAL. The invention further relates to the use of such optimal compositions of PAL for therapeutic and industrial purposes. This invention also relates to histidine ammonia-lyase (HAL) analogs, compositions containing such analogs, and related compositions.
PAL is a non-mammalian enzyme widely distributed in plants (Koukol, et al., J. Biol. Chem., 236, pp. 2692-2698 (1961); Hanson, et al., The Enzymes (Boyer, P. D., Ed.), Academic Press, New York, Vol. 7, pp. 75-166 (1972); Poppe, et al., (2003) ibid.) some fungi (Rao, et al., Can. J. Biochem., 4512), pp. 1863-1872 (1967)) and yeast (Abell, et al., Methods Enzymol. 142, pp. 242-253 (1987)) and can also be recombinantly produced in Escherichia coli.
A representative list of PALs includes: Q9ATN7 Agastache rugosa; 093967 Amanita muscaria (Fly agaric); P35510, P45724, P45725, Q9SS45, Q8RWP4 Arabidopsis thaliana (Mouse-ear cress); Q6ST23 Bambusa oldhamii (Giant timber bamboo); Q42609 Bromheadia finlaysoniana (Orchid); P45726 Camellia sinensis (Tea); Q9MAX1 Catharanthus roseus (Rosy periwinkle) (Madagascar periwinkle); Q9SMK9 Cicer arietinum (Chickpea); Q9XFX5, Q9XFX6 Citrus clementina x Citrus reticulate; Q42667 Citrus limon (Lemon); Q8H6V9, Q8H6W0 Coffea canephora (Robusta coffee); Q852S1 Daucus carota (Carrot); 023924) Digitalis lanata (Foxglove); 023865) Daucus carota (Carrot); P27991) Glycine max (Soybean); 004058) Helianthus annuus (Common sunflower); P14166, (Q42858) Ipomoea batatas (Sweet potato); Q8GZR8, Q8W2E4 Lactuca sativa (Garden lettuce); 049835, 049836 Lithospermum erythrorhizon; P35511, P26600 Lycopersicon esculentum (Tomato); P35512 Malus domestica (Apple) (Malus sylvestris); Q94C45, Q94F89 Manihot esculenta (Cassaya) (Manioc); P27990 Medicago sativa (Alfalfa); P25872, P35513, P45733 Nicotiana tabacum (Common tobacco); Q6T1C9 Quercus suber (Cork oak); P14717, P53443, Q7M1Q5, Q84VE0, Q84VE0 Oryza sativa (Rice); P45727 Persea americana (Avocado); Q9AXI5 Pharbitis nil (Violet) (Japanese morning glory); P52777 Pinus taeda (Loblolly pine); Q01861, Q04593 Pisum sativum (Garden pea); P24481, P45728, P45729 Petroselinum crispum (Parsley) (Petroselinum hortense); Q84L12 Phalaenopsis x Doritaenopsis hybrid cultivar; P07218, P19142, P19143 Phaseolus vulgaris (Kidney bean) (French bean); Q7XJC3, Q7XJC4 Pinus pinaster (Maritime pine); Q6UD65 Populus balsamifera subsp. trichocarpa x Populus deltoides; P45731, Q43052, 024266 Populus kitakamiensis (Aspen); Q8H6V5, Q8H6V6 Populus tremuloides (Quaking aspen); P45730 Populus trichocarpa (Western balsam poplar); 064963 Prunus avium (Cherry); Q94ENO Rehmannia glutinosa; P11544 Rhodosporidium toruloides (Yeast) (Rhodotorula gracilis); P10248 Rhodotorula rubra (Yeast) (Rhodotorula mucilaginosa); Q9M568, Q9M567 Rubus idaeus (Raspberry); P31425, P31426 Solanum tuberosum (Potato); Q6SPE8 Stellaria longipes (Longstalk starwort); P45732 Stylosanthes humilis (Townsville stylo); P45734 Trifolium subterraneum (Subterranean clover); Q43210, Q43664 Triticum aestivum (Wheat); Q96V77 Ustilago maydis (Smut fungus); P45735 Vitis vinifera (Grape); and Q8VXG7 Zea mays (Maize).
Histidine ammonia-lyase (HAL, E.C. 4.3.1.3) is found in mammalian as well as bacterial sources (Taylor, et al., J. Biol. Chem., 265(30), pp. 18192-18199 (1990); Suchi, et al., Biochim. Biophys. Acta, 1216(2), pp. 293-295 (1993)) and the crystal structure of histidase from Pseudomonas putida is known (Schwede, et al., Biochemistry, 38(17), pp. 5355-5361 (1999)). HAL from Corynebacteriaceae has been proposed to be used for combination therapy with L-histidinol to treat histidine- and/or histamine-dependent pathologies such as human respiratory syncytial virus (HSV), herpes simplex virus (HSV), human immunodeficiency virus (HIV), and cancer (U.S. Patent Application No. 20020052038).
A representative list of HALs includes: Q9 KWE4 (Agrobacterium rhizogenes), Q8U8Z7 (Agrobacterium tumefaciens), Q6 KPK9, Q81Y45 (Bacillus anthracis), Q733H8, Q81AC6 (Bacillus cereus), Q9 KBE6 (Bacillus halodurans), P10944 Bacillus subtilis), Q8A4B3 (Bacteroides thetaiotaomicron), Q8G4X5 (Bifidobacterium longum), Q89GV3 (Bradyrhizobium japonicum), Q8YD10 (Brucella melitensis), Q8FVB4 (Brucella suis), Q20502 (Caenorhabditis elegans), P58082 (Caulobacter crescentus), Q7P188 (Chromobacterium violaceum), Q891Q1 (Clostridium tetani), Q9RZ06 (Deinococcus radiodurans), Q8RFC2, Q8RDU4, Q7P5N4 (Fusobacterium nucleatum), Q7NCB3 (Gloeobacter violaceus), Q9HQD5 (Halobacterium sp.), P42357 (Homo sapiens (Human)), P35492 (Mus musculus (Mouse)), Q7N296 (Photorhabdus luminescens), Q6L2V9 (Picrophilus torridus), Q7MX86 (Porphyromonas gingivalis), Q9HU85 (Pseudomonas aeruginosa), Q9HU90 (histidine/phenylalanine ammonia-lyase, Pseudomonas aeruginosa), Q8VMR3 (Pseudomonas fluorescens), Q88CZ7, P21310 (Pseudomonas putida), Q87UM1, Q87UM2, Q87V42 (Pseudomonas syringae), Q8XW29 (Ralstonia solanacearum, Pseudomonas solanacearum), P21213 (Rattus norvegicus (Rat), Q98310, Q987B4, Q98JY1, Q98NG3 (Rhizobium loti, Mesorhizobium loti), 031197 Rhizobium meliloti (Sinorhizobium meliloti), Q8Z896 (Salmonella typhi), Q8ZQQ9 (Salmonella typhimurium), Q8E9B0, Q8EKJ4 (Shewanella oneidensis), Q99XG3, Q8NYY3 (Staphylococcus aureus), Q93TX3 (Stigmatella aurantiaca), Q9EWW1 (Streptomyces coelicolor), P24221 (Streptomyces griseus), Q8K5L, Q8NZ46, P58083 (Streptococcus pyrogenes), Q9HLI6 (Thermplasma acidophilum), Q8RBH4 (Thermoanaerobacter tengcongensis), Q978N8 (Thermoplasma volcanium), Q73Q56 (Treponema denticola), Q9KSQ4 (Vibrio cholerae), Q87Q77 (Vibrio parahaemolyticus), Q8DA21, Q7MK58, Q7MMJ6, Q8DFZ8 (Vibrio vulnificus), Q8PLZ8 (Xanthomonas axonopodis), Q8PAA7 (Xanthomonas campestris), Q8ZA10 (Yersinia pestis).
Enzyme Substitution Therapy for PKU Treatment
Numerous studies have focused on the application of the enzyme phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) for enzyme substitution treatment of PKU (Hoskins, Lancet, i(8165), pp. 392-394 (1980); Gilbert, et al., Biochem. J., 199(3):715-723 (1981); Hoskins, et al., (1982) ibid.; Sarkissian, et al., (1999) ibid.; Liu, et al., Artif. Cells Blood Substit. Immobil. Biotechnol., 30(4):243-257 (2002); Wieder, J Biol Chem., 254(24):12579-12587 (1979); Gamez, In press; Ambrus, et al., J. Pharmacol. Exp. Ther., 224(3):598-602 (1983); Ambrus, et al., Science, 201(4358):837-839 (1978); Kalghatgi, Res. Commun. Chem. Pathol. Pharmacol., 27(3):551-561 (1980); Ambrus, Res. Commun. Chem. Pathol. Pharmacol., 37(1):105-111 (1982); Gilbert, et al., Biochem. Biophys. Res. Commun., 131(2):557-563 (1985); Pedersen, Res. Commun. Chem. Pathol. Pharmacol., 20(3):559-569 (1978); Marconi, et al., Biochimie, 62(8-9):575-580 (1980); Larue, et al., Dev. Pharmacol. Ther., 9(2):73-81 (1986); Ambrus, C. M., et al., (1987) ibid.; Bourget, et al., Appl. Biochem. Biotechnol., 10:57-59 (1984); Bourget, et al., FEBS Lett., 180(1):5-8 (1985); Bourget, et al., Biochim. Biophys. Acta, 883(3):432-438 (1986); Chang, et al., Artif. Cells Blood Substit. Immobil. Biotechnol., 23(1):1-21 (1995); Chang, et al., Mol Biotechnol., 17(3):249-260 (2001); U.S. Pat. No. 5,753,487).
Phenylketonuria (PKU) is an inborn error of amino acid metabolism that results from impaired activity of hepatic phenylalanine hydroxylase (PAH), the enzyme responsible for the metabolism of phenylalanine. Patients with PAH mutations that lead to PKU and hyperphenylalaninemia (HPA) display impaired neurophysiological functioning and reduced cognitive development. For patients that have severe PKU, there is the potential for irreversible mental retardation unless phenylalanine is controlled at low levels using dietary restrictions. PAL converts phenylalanine to ammonia and trans-cinnamic acid, a harmless metabolite, which is further metabolized and excreted in the urine as hippurate ((Hoskins, et al., (1980) ibid; Hoskins, J. A., et al., “The metabolism of cinnamic acid by healthy and phenylketonuric adults: a kinetic study”, Biomed Mass Spectrom, 11(6), pp. 296-300 (1984)).
Current treatment for PKU involves the adherence to a restricted diet for life that is low in proteins and the amino acid phenylalanine (Levy, Proc. Natl. Acad. Sci. U.S.A., 96(5), pp. 1811-1813 (1999)). This dietary therapy is difficult to maintain (Matalon, et al., Genet. Med., 6(1), pp. 27-32 (2004); Woolf, et al., Arch. Dis. Child., 33(167), pp. 31-45 (1958); Kim, Mol Ther., 10(2), pp. 220-224 (2004)) and does not always eliminate the damaging neurological effects that can be caused by elevated phenylalanine levels (Sarkissian, et al., Mol. Genet. Metab., 69, pp. 188-194 (2000)); less than ideal dietary control during pregnancy can lead to birth defects (Levy, H. L., (1999) ibid.). In addition, it is very difficult for PKU/HPA patients to live a normal life while following the restrictive diet, and the dietary therapy can be associated with deficiencies of several nutrients, some of which are detrimental for brain development (Levy, H. L., (1999) ibid.). Most low phenylalanine diet products have organoleptic properties sufficiently unsatisfactory that compliance with this treatment is compromised (Levy, H. L., (1999) ibid.). Therefore, development of a therapeutic treatment would assist the current dietary treatment and prevent the neurological damages inflicted on those individuals with PKU, particularly for those patients with the most severe forms of the disease.
In 1999, Scriver and colleagues reported their initial studies on the use of the enzyme PAL from Rhodosporidium toruloides (Sarkissian, C. N., et al., 1999 ibid.) for PKU enzyme substitution applications. Mouse PKU and HPA model studies demonstrated that PAL administration (either by i.p. injection or orally using either PAL in combination with aprotinin protease inhibitor or PAL recombinantly expressed and present inside E. coli cells) was able to successfully lower blood plasma phenylalanine levels. In addition, preliminary studies describing the use of PAL with PKU patients have shown reduction in phenylalanine levels using PAL administered in enteric-coated gelatin capsules (Hoskins, J. A., et al., (1980) ibid.) or using an extracorporeal enzyme factory (Ambrus, et al., Ann. Intern. Med., 106(4), pp. 531-537 (1987)). However, the sensitivity of PAL to protease inactivation (low activity in gastric conditions due to protease degradation) and the reduced half-life found after repeated in vivo injection (due to elicitation of an immune response) limits further development of the native PAL protein as a clinical therapeutic.
Other Therapeutic Uses
The use of PAL for cancer treatment has also been suggested based on its ability to limit the nutrient supply of phenylalanine to cancer cells and thereby inhibit neoplastic growth (Fritz, et al., J Biol Chem. 251(15):726 (1976); Roberts, et al., Cancer Treat Rep., 60(3):261-263 (1976); Shen, et al., Cancer Res. 37(4):1051-1056 (1977); Shen, et al., Cancer Treat Rep. 63(6):1063-1068 (1979); Wieder, et al, J Biol Chem., 254(24):12579-12587 (1979)). However, intravenously injected pegylated PAL was cleared rapidly from circulating blood after the 13th injection. In addition, PAL-mediated reduction in phenylalanine prevented the proliferation of murine leukemia and metastatic melanoma (Abell, et al., Cancer Res. 33:2529-2532 (1973)), Roberts, et al., ((1976) ibid) Shen, et al., ((1977) ibid)).
PAL has also been used for tyrosinemia (Marconi, W., et al., (1980) ibid.). Histidine ammonia-lyase (HAL) has been used in enzyme substitution therapy for histidinemia treatment. Histidinemia is an autosomal recessive disorder of histidine metabolism due to defective HAL, and is traditionally a benign condition (Taylor, R. G., et al., (1990) ibid.).
Additional Uses of PAL
PAL has an important industrial use for the synthesis of L-phenylalanine methyl ester (for Aspartame production (D'Cunha, et al., Enzyme and Microbial Technology, 19(6), pp. 421-427 (1996); Hamilton, et al., Trends in Biotechnol., 3(3), pp. 64-68 (1985)) and other substituted L-phenylalanine derivatives that are used as pharmaceutical precursors (U.S. Patent App. 20020102712).
PAL also has agricultural importance, being the initial enzymatic process leading to the phenylpropaniods that produce lignins, coumarins, and flavaniods in plants, fungi, and bacteria. All phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) produce cinnamic acid, which is a precursor for lignins, flavonoids, and coumarins in plants (Alunni, et al., Arch Biochem Biophys., 412(2), pp. 170-175 (2003)). Hence, modulation of PAL activity can influence a number of agricultural phenomena such as the browning of fruit. In addition, structure-based drug design of active site PAL inhibitors could lead to effective herbicides (Poppe, L., et al., ibid.).
Although PAL potentially has various industrial and therapeutic applications, the use of PAL may be limited by reduced specific activity and proteolytic instability. Similar to other therapeutic proteins, use of PAL as an enzyme therapy is accompanied by several disadvantages such as immunogenicity and proteolytic sensitivity. Further, a delicate balance is required between substrate affinity and enzyme activity to achieve and maintain control of plasma phenylalanine levels within a normal somewhat narrow range in disorders characterized by hyperphenylalanemia. As yet, a concerted effort toward improving these parameters has not been made due to a paucity of structural and biochemical knowledge regarding this protein.
Protein Therapeutics and Effective Redesign for Therapeutic Advantage
Numerous proteins are used therapeutically to alleviate metabolic deficiencies caused by genetic disorders. Among the most notable examples are parenterally administered insulin for the treatment of diabetes, alpha-glucosidase for enzyme replacement therapy in Pompe's disease (and other enzymes that are used for other lysosomal storage diseases (“Enzyme Therapy In Genetic Diseases”, Birth Defects Original Article Series, Volume 9, E. D. Bergsma, Ed. Baltimore: Williams and Wilkins Company (1973))), interferon-alpha for hepatitis C or cancer treatment, and adenosine deaminase for severe combined immunodeficiency (SCID) therapy (Russell, et al., Clin. Genet., 55(6): pp. 389-394 (1999)). Unfortunately, the lifetimes of these injected foreign proteins are usually diminished due to acute allergic reactions and rapid clearance from the bloodstream.
The efficacy of protein therapeutics can be improved with protein engineering methods, including rational design, directed evolution, chemical modification, and combinatorial optimization strategies. Rational design requires the availability of three-dimensional structural information and consideration of side-chain orientations and mobilities in the context of the structure, combined with generic properties such as side-chain hydrophobicity, polarity, charge, electronic contributions, and propensities to form specific secondary structures. Among rational protein modification methods, a most promising solution involves producing variants using structure-based protein engineering.
Numerous examples of structure-based protein engineering exist, wherein improved properties have been designed into proteins using structure-based design techniques (Lazar, et al., Curr. Opin. Struct. Biol., 13(4), pp. 513-518 (2003); Marshall, et al., Drug Discov. Today, 8(5), pp. 212-221 (2003)). Site-directed mutagenesis of proteins can be used to generate protein variants containing truncations, insertions, and/or point mutations, leading to improved stability, activity, and/or altered activity (Brannigan, et al., Nat Rev Mol Cell Biol., 3(12), pp. 964-970 (2002)). Chimeras, or combinations of two proteins, have been successfully exploited for a number of therapeutic antibody and protein examples. Additional effective protein engineering approaches have used specific protein loop re-engineering (Chen, et al., Proc. Natl. Acad. Sci. U.S.A., 90(12), pp. 5618-5622 (1993)), loop swapping (Wilks, et al., Biochemistry, 31(34), pp. 7802-7806 (1992); 36 Hedstrom, et al., Science, 255(5049), pp. 1249-1253 (1992)), and subdomain shuffling (Hopfner, et al., Proc. Natl. Acad. Sci., U.S.A., 95(17), pp. 9813-9818 (1998)) approaches.
Immunologic Response Reduction for Protein Therapeutics
Numerous strategies have been devised for minimizing immune responses of therapeutically-administered proteins (Chirino, et al., Drug Discov. Today, 9(2), pp. 82-90 (2004); U.S. Pat. Nos. 6,686,164 and 6,461,849). For some protein classes such as antibodies, increasing human sequence content (chimeras and/or ‘humanization’) has reduced immunoreactivity, whereas another effective strategy wherein protein solution properties have been improved (e.g. to reduce aggregation propensity) has also led to reduced immune response. Numerous proteins have had antibody epitopes and agretopes removed using iterative site-directed mutagenesis including replacement of hydrophobic and charged residues with polar neutral residues, alanines, or computationally-selected residues to produce less immunoreactive protein variants. In one example, site-directed mutagenesis of streptavidin was used to reduce immunogenicity (Meyer, et al., Protein Sci., 10(3), pp. 491-503 (2001)). In this case, surface “veneering” was used to mutate surface residues capable of forming high energy ionic or hydrophobic interactions to remove such potential interacting sites. Mutants producing high yields of active tetrameric protein were then tested for reduced antibody recognition in mice and humans, and minimized antibody response upon mutant injection in rabbits. In general, substitution of smaller neutral residues for charged, aromatic, or large hydrophobic surface residues reduced the ability to elicit an immune response in rabbits.
Site-directed mutagenesis has been successfully used for point mutagenesis to alleviate immunoreactivity. For example, site-directed rational modification of antigenic determinants was used to downregulate the CD8(+) and CD4(+) T lymphocyte responses (Abrams, et al. Curr. Opin. Immunol., 12(1), pp. 85-91 (2000)). Alternate immunoreactivity reduction routes include the removal of agretopes, the generation of variants less susceptible to antigen-processing cell recognition or binding, or the reduction or removal of MHC binding ability. Different approaches have relied upon humanization (making protein variants with more human sequence content), surface veneering (making protein variants with less immunoreactive surface features, and other similar methods wherein specific mutations are made and then screened for lessened immunoreactivity. For example, the “Immunostealth” method uses a combination of in silico sequence analysis methods and high-throughput in vitro biochemical screening assays to identify HTL epitopes, followed by rational modification to alter their HTL binding capacity, resulting in protein variants non-recognizable by the immune system (Tangri, et al., Curr. Med. Chem., 9(24), pp. 2191-2199 (2002)). In addition, the methods of structure-based protein engineering can be combined with more ‘random’ protein modification methods, such as directed evolution, that can use screening and/or selection to develop more favorable protein variants.
In another approach, the chemical conjugation of a water-soluble polymer, such as polyethylene glycol (PEG), to the protein of interest is a common approach often used to extend the half-lives of proteins in vivo. Generally, polyethylene glycol molecules are connected to the protein via a reactive group found on the protein. Amino groups, such as those on lysine residues or at the N-terminus, are convenient for such attachment. The covalent coupling of activated PEG molecules to the protein of interest (pegylation) has been shown to increase circulation half-times, reduce immunogenicity and antigenicity, and allow retention of bioactivity (Harris, et al., Nat. Rev. Drug Discov., 2(3), pp. 214-221 (2003); Greenwald, et al., Adv Drug Deliv Rev., 55(2), pp. 217-250 (2003); Veronese, et al., Adv Drug Deliv Rev., 54(4), pp. 453-456 (2002); Mehvar, J. Pharm. Pharmaceut. Sci., 3(1), p. 125-136 (2000); Delgado, et al., Critical Reviews in Therapeutic Drug Carrier Systems, 9(3-4), pp. 249-304 (1992)).
Currently, a number of pegylated protein therapeutics have received FDA approval and are being used parenterally to treat a number of diseases such as: hepatitis C and metastatic renal cell carcinoma using PEG-Intron™ (pegylated interferon-alpha2b [Wang, et al., Adv Drug Deliv Rev., 54(4), pp. 547-570 (2002)]) or Pegasys™ (pegylated interferon-alpha2a [Rajender Deliv Rev., 54(4), pp. 571-586 (2002)]); acute lymphoblastic leukemia using Oncaspar™ (Pegaspargase™ or pegylated L-asparaginase [Graham, Adv Drug Deliv Rev., 55(10), pp. 1293-1302 (2003)]); severe combined immunodeficiency (SCID) using Adagen™ (bovine Pegademase™ or pegylated adenosine deaminase [Hershfield, Immunodeficiency, 4(1-4), pp. 93-97 (1993)]); and acromegaly using Somavert™ (Pegvisomant™ or pegylated human growth hormone antagonist [Parkinson, et al., Adv Drug Deliv Rev., 55(10), pp. 1303-1314 (2003)]).
Pegylated Proteins
In addition to the pegylation of native protein, site-specific pegylation of proteins has also been performed. Examples of site-specific pegylation include Cys-pegylated IL-3 (U.S. Pat. No. 5,166,322 and WO 90/12874) and Cys-pegylated IL-2 (U.S. Pat. No. 5,206,344) as well as Lys-pegylated purine nucleoside phosphorylase (Hershfield, et al., Proc. Natl. Acad. Sci. USA, 88, pp. 7185-7189 (1991)), an N-terminal selectively pegylated lysine-deficient mutant TNF-α (Yoshioka, et al., Biochem Biophys Res Commun., 315(4), pp. 808-814 (2004)), an N-terminally site-specific pegylated G-CSF (Kinstler, et al., Pharm. Res., 13(7), pp. 996-1002 (1996)), and gylcosylation site-specific pegylated IL-2 (Goodson, et al., Biotechnology, 8(4), pp. 343-346 (1990)). U.S. Pat. No. 6,451,986 discloses site-specific mutation and pegylation of p75 tumor necrosis factor receptor, and U.S. Pat. No. 5,766,897 discloses site-specific pegylation via an exisiting cysteine residue or introduction of a site-specific cysteine residue (at an N-linked glycosylation site or the position of a residue that is normally solvent-accessible in the naturally-occurring protein). Hermeling, S., et al. discuss the use of site-specific PEG attachment around possible antigenic epitope regions to reduce immunogenicity (Hermeling et al. Pharm Res., 21(6), pp. 897-903 (2004)). Similar approaches to improve protein in vivo lifetimes have been adopted for a Cys-pegylated humanized anti-interleukin-8 antibody (Leong, et al., (2001) ibid.) and an N-terminal aldehyde activated alpha-amine group derivatized on epidermal growth factor (Lee, et al., Pharm. Res., 20(5), pp. 818-825 (2003)). In a related approach, a hyper-glycosylated form of human erythropoietin displayed an improved serum half-life and greater in vivo potency, thereby allowing for less frequent administration to obtain the same biological response (Egrie, et al., Br J Cancer, 84(Suppl 1), pp. 3-10 (2001)); chemical modification of this form of erythropoietin improved in vivo efficacy even more (U.S. Pat. No. 6,586,398). In one example, pegylation plus additional site-directed mutagenesis was necessary in order to engineer an active IL-15 variant (Pettit, et al., J. Biol. Chem., 272(4), pp. 2312-2318 (1997)).
Native Rhodotorula glutinis PAL stabilized with pegylation has been investigated as a therapeutic agent in cancer therapy. However, these agents exhibited residual immunogenicity and protease sensitivity, thereby precluding them from use in human, such as in clinical testing (Wieder, J Biol Chem., 254(24), pp. 12579-12587 (1979)).
The pegylation of PAL to improve L-phenylalanine synthetic capability for industrial applications, and to reduce the immunogenicity of PAL for therapeutic applications has been reported. U.S. Pat. Nos. 4,562,151 and 5,981,239 disclose the use of polyethylene glycol as an agent to improve the activity of PAL for the production of L-phenylalanine and L-phenylalanine analogs, respectively. U.S. patent application Nos. 20020102712 and 20030082238 describe the use of PEG to stabilize, solubilize, and/or reduce the immunogenicity of PAL for phenylketonuria treatment. U.S. Pat. No. 5,766,897 discloses the use of site-specific introduction of cysteine residues in proteins such as PAL for covalent PEG attachment to improve half-life, decrease immunogenicity and antigenicity, and retain substantially the same level of biological activity.
Oral Therapeutics
Parenterally administered protein therapeutics have demonstrated their clinical effectiveness, but alternative routes of administration are also used. For example, there are two “over-the-counter” oral enzyme replacement therapies that are used for dietary digestion remediation. Beano™, alpha-galactosidase from Aspergillis niger (a food grade mold), is used to correct digestive deficiencies associated with deficient carbohydrate processing (and intestinal gas formation) from legume consumption. Additionally, Lactaid™, an orally active form of the lactase enzyme, is used to alleviate problems associated with lactose (milk sugar) intolerance. Both these products demonstrate that orally administered enzymes can function in the gastrointestinal tract and can successfully correct dietary metabolic deficiencies.
Native R. toruloides PAL is very susceptible to protease inactivation (Sarkissian, C. N., et al., (1999) ibid.), requiring either site-directed mutagenesis and/or the introduction of protein surface protective features such as pegylation to produce an orally-effective PAL variant. Additional protease protection can be provided for by using microcapsules (Wang, et al., “Biomater. Artif. Cells Immobilization Biotechnol., 21(5), pp. 637-646 (1993)). Complex microcapsules could be used as an additional measure to protect a therapeutic enzyme from inactivation in both the stomach and the intestine. Semi-permeable microcapsules can be further encapsulated by enteric-soluble materials to protect the microcapsules from gastric juice. When the encapsulated enzyme passes into the intestine, the small molecule L-phenylalanine can rapidly diffuse and equilibrate across the semipermeable membrane, allowing conversion to non-toxic products via the encapsulated enzyme.
U.S. Pat. No. 5,753,487 discloses mutants of R. toruloides PAL wherein one or more amino acids susceptible to proteolytic cleavage are replaced by other amino acids less susceptible to proteolytic cleavage.
Thus, there remains a need for PAL and HAL molecules with optimal kinetic characteristics including potent catalytic activity and greater biological half-life, greater biochemical stability and attenuated immunogenicity.
The present invention is based on the identification and characterization of three-dimensional structure of the crystallized R. toruloides phenylalanine ammonia lyase (PAL). The present invention provides crystallized R. toruloides phenylalanine ammonia-lyase (PAL) and the three-dimensional structure of the crystallized R. toruloides PAL determined to a resolution of 1.6 Å or better. The invention contemplates the preparation of variants, including mutants and analogs, with enhanced properties, such as more potent catalytic activity, greater biochemical stability and, for therapeutic applications, attenuated immunogenicity and greater biological half-life. The present invention thus provides optimal compositions of PAL and biologically active fragments, mutants, variants and analogs thereof, their production and purification, and methods of using such compositions for therapeutic and industrial purposes.
In a first aspect, the present invention provides crystallized R. toruloides phenylalanine ammonia-lyase (PAL) and the three-dimensional structure of the crystallized R. toruloides PAL determined to a resolution of 1.6 Å or better. In a further embodiment, the present invention provides methods for determining the surface-exposed residues of PAL by evaluating the three-dimensional structure of PAL, and the use of the information to design variants and mutants of PAL. The variants and mutants of PAL thus obtained find use as therapeutic agents or in industrial applications.
In a second aspect, the present invention provides compositions of optimized PAL obtained by structure-based molecular engineering approachs and/or chemically-modified (e.g. pegylated) forms of PAL. Specific embodiments contemplate optimal compositions of PAL with enhanced stability, reduced immunogenicity and/or proteolytic sensitivity.
In a third aspect, the invention features novel methods of using PAL compositions for therapeutic and industrial purposes. In one embodiment, the invention contemplates methods of treating disorders caused all or in part by a deficiency in PAH activity by administering a therapeutically effective amount of a pharmaceutical composition comprising PAL to a subject in need of such treatment. The deficiency in PAH activity can be observed, e.g., as activity levels of 50% or less, 25% or less, or 10% or less or 1% or less, compared to normal levels of PAH activity and can manifest as elevated phenylalanine levels, for example, as in hyperphenylalanemia, mild phenylketonuria or classic severe phenylketonuria. In preferred embodiments, the disease is phenylketonuria (PKU).
In specific embodiments, the subject is one who has been diagnosed as having a mutant phenylalanine hydroxylase (PAH). The mutant PAH may comprise a mutation in the catalytic domain of PAH. Exemplary such mutations include but are not limited to mutations F39L, L48S, 165T, R68S, A104D, S110C, D129G, E178G, V190A, P211T, R241C, R261Q, A300S, L308F, A313T, K320N, A373T, V388M E390G, A395P, P407S, and Y414C.
Also contemplated is a method of treating a subject having above normal concentration of plasma phenylalanine (e.g., greater than 180 μM and more preferably, greater than 360 μM) comprising administering to the subject a PAL composition in an amount effective to produce a decrease in the plasma phenylalanine concentration of the subject. The subject will likely have a plasma phenylalanine concentration greater than 180 μM prior to administration of the PAL. More particularly, the subject has a plasma phenylalanine concentration of between 120 μM and 200 μM. In other embodiments, the subject has a plasma phenylalanine concentration of between 200 μM and 600 μM. In still other embodiments, the subject has a plasma phenylalanine concentration of between 600 μM and 1200 μM. Yet another class of subjects to be treated is those that have an unrestricted plasma phenylalanine concentration greater than 1200 μM.
In specific embodiments, the subject is an infant, more particularly, an infant having a plasma phenylalanine concentration greater than 1200 μM. The invention contemplates methods of treating an infant having phenylketonuria, comprising administering a PAL composition to the subject in an amount effective to produce a decrease in the plasma phenylalanine concentration of the infant wherein the infant is between 0 and 3 years of age and the infant has a plasma phenylalanine concentration of between about 360 μM to about 4800 μM. Prior to the administering of PAL, the infant has a phenylalanine concentration of about 1200 μM and the administering of PAL decreases the plasma phenylalanine concentration to about 1000 μM. In other embodiments, prior to the administering of PAL the infant has a phenylalanine concentration of about 800 μM and the administering of PAL decreases the plasma phenylalanine concentration to about 600 μM. In still further embodiments, prior to the administering of PAL the infant has a phenylalanine concentration of about 400 μM and the administering of PAL decreases the plasma phenylalanine concentration to about 300 μM. The therapeutic methods contemplated herein should preferably reduce the plasma phenylalanine concentration of the infant to a range of between about 120 μM to about 360 μM and most preferably to a range of between about 120 μM to about 240 μM.
Also contemplated herein is a method for the treating a pregnant female having hyperphenylalaninemia (HPA) comprising administering to the subject PAL alone or in combination with a protein-restricted diet, wherein administration of PAL alone or in combination with the protein-restricted diet is effective to lower the phenylalanine concentration in the plasma of the subject as compared to the concentration in the absence of the combined administration. In certain embodiments, the subject has an unrestricted plasma phenylalanine concentration of greater than 180 μM but less than 600 μM. In other embodiments, the subject has an unrestricted plasma phenylalanine concentration of greater than 500 μM but less than 1200 μM. In still other embodiments, the subject has an unrestricted plasma phenylalanine concentration of greater than 1200 μM. Pregnant subjects with a plasma phenylalanine concentration greater than 1200 μM are particularly attractive candidates for this type of therapy, as are subject who are females of child-bearing age that are contemplating pregnancy. In those embodiments, in which the subject has a plasma phenylalanine concentration greater than 1200 μM, and the method further comprises administering a protein-restricted diet to the subject.
The invention describes methods of treating classic severe phenylketonuria (PKU) in a subject comprising administering to the subject a PAL or a biologically active fragment, mutant, variant or analog thereof wherein the administration of PAL is effective to lower the phenylalanine concentration in the plasma of the subject as compared to the concentration in the absence of PAL administration. A subject selected for treatment according to the methods of the invention will have an elevated plasma Phe concentration, such a concentration may be greater than 1800 μM in the absence of the therapeutic. Other embodiments contemplate a subject that has a plasma phenylalanine concentration of greater than 1000 μM in the absence of a therapeutic regimen. In preferred embodiments, the combined administration methods of the invention decrease the plasma phenylalanine concentration of the subject to less than 600 μM. More preferably, it is decreased to less than 500 μM. Even more preferably, the combined administration decreases the plasma phenylalanine concentration of the subject in the range from about 120 μM to about 360 μM. Most preferably, the plasma phenylalanine concentration of the subject is reduced in the range from about 120 μM to about 240 μM.
Preferred embodiments include optimizing the dosage to the needs of the organism to be treated, preferably mammals or humans, to effectively ameliorate the disease symptoms. PAL may be administered in a single daily dose, multiple doses on a daily basis, in a single weekly dose or multiple doses on a weekly basis. In some embodiments, the PAL therapy is not continuous, but rather PAL is administered on a daily basis until the plasma phenylalanine concentration of the subject is decreased to less than 360 μM. Preferably, wherein the plasma phenylalanine concentration of the subject is monitored on a daily basis and the PAL is administered when a 10% increase in plasma phenylalanine concentration is observed. In yet other preferred embodiments, doses are delivered once weekly. The invention contemplates doses of at least 0.001 mg/kg, 0.005 mg/kg, 0.01 mg/kg, 0.05 mg/kg, and may range up to 0.1 mg/kg, 0.5 mg/kg, 1.0 mg/kg or higher per week. The preferred dose is 0.001 mg/kg/week.
A variety of parenteral or nonparenteral routes of administration, including oral, transdermal, transmucosal, intrapulmonary (including aerosolized), intramuscular, subcutaneous, or intravenous that deliver equivalent dosages are contemplated. Administration by bolus injection or infusion directly into the joints or CSF is also specifically contemplated, such as intrathecal, intracerebral, intraventricular, via lumbar puncture, or via the cisterna magna. Preferably the doses are delivered subcutaneously or orally.
Other means of increasing PAL activity in the human subjects are also contemplated, including gene therapy. Transfer of a PAL gene is possible through a variety of means known in the art, including viral vectors, homologous recombination, or direct DNA injection. Within the scope of this aspect are embodiments featuring nucleic acid sequences encoding all or a part of PAL or a biologically active mutant or analogs thereof, which may be administered in vivo into cells affected with PAH deficiency.
In another embodiment, PAL may also be administered in combination with a protein restricted diet. The protein-restricted diet administered in the methods herein is one that is a phenylalanine-restricted diet wherein the total phenylalanine intake of the subject is restricted to less than 600 mg per day. In other embodiments, the protein-restricted diet is a phenylalanine-restricted diet wherein the total phenylalanine is restricted to less than 300 mg per day. In still other embodiments, the protein-restricted diet is one, which is supplemented with amino acids, such as tyrosine, valine, isoleucine and leucine. Also contemplated is a composition comprising PAL and a pharmaceutically acceptable carrier, diluent or excipient. The composition may further comprise a medical protein supplement. In other embodiments, the PAL composition is part of an infant formula. In still other embodiments, the protein supplement is phenylalanine free. The protein supplement preferably is fortified with L-tyrosine, L-glutamine, L-carnitine at a concentration of 20 mg/100 g supplement, L-taurine at a concentration of 40 mg/100 g supplement and selenium. It may further comprise the recommended daily doses of minerals, e.g., calcium, phosphorus and magnesium. The supplement further may comprise the recommended daily dose of one or more amino acids selected from the group consisting of L-leucine, L-pro line, L-lysine acetate, L-valine, L-isoleucine, L-arginine, L-alanine, glycine, L-asparagine monohydrate, L-tryptophan, L-serine, L-threonine, L-histidine, L-methionine, L-glutamic acid, and L-aspartic acid. In addition, the supplement may be fortified with the recommended daily dosage of vitamins A, D and E. The supplement preferably comprises a fat content that provides at least 40% of the energy of the supplement. Such a supplement may be provided in the form of a powder supplement or in the form of a protein bar.
The invention contemplates methods of treating various forms of neoplastic growth and cancer, including but not limited to lymphoblastic leukemia, mammary tumors, and melanomas.
The invention contemplates methods of using PAL for the commercial production of phenylalanine from ammonia and t-cinnamate. Phenylalanine is used in aspartame, a sweetener and other food products, including beverages, cereals, cakes, desserts, egg and cheese dishes, fats, oils, fish and other seafoods, meat and meat products, milk and milk products, nuts, sauces and condiments, soups, sugars, jams and spreads, and vegetables.
It is further contemplated that PAL may be used for the production of herbicides and antimicrobial agents including enterocin and erythromycin.
In a fourth aspect, the present invention features a method to produce PAL or a biologically active fragment, mutant, variant or analog thereof in amounts which enable using the enzyme therapeutically. In a broad embodiment, the method comprises the step of transforming a cDNA or DNA encoding for all or a part of a PAL or a biologically active fragment, mutant, variant or analog thereof into a cell suitable for the expression thereof. In preferred embodiments, an expression vector is used to transfer the DNA into a suitable cell or cell line for expression thereof. In one particularly preferred embodiment, the cDNA is transformed into E. coli and recombinant PAL is overexpressed as fusion protein. In a further embodiment, the method of producing PAL comprises the steps of: (a) growing cells transformed with a cDNA encoding all or a biologically active variant, fragment or mutant of PAL in a suitable growth medium to an appropriate density to produce a seed culture, (b) introducing the transformed cells into a bioreactor, (c) supplying a suitable growth medium to the bioreactor, and (d) separating the transfected cells from the media containing the enzyme.
In another embodiment, recombinant PAL or variants thereof are over-expressed as an N-terminal octahistidyl-tagged fusion protein in a vector preferably E coli BL21(DE3)/pLyseS (Invitrogen) with an inducible promoter such as with IPTG (isopropyl-beta-D-thiogalactopyranoside). In a further embodiment, the method of producing PAL comprises the steps of: (1) growing a seed culture for a bioreactor/fermenter from a glycerol stock in shake flasks, (2) introducing such seed culture into a controlled bioreactor in fed-batch mode; (3) growing said culture in glucose-supplemented media, pH (7.8), >20% dissolved oxygen, agitation up to 1200 rpm, 300 C until reaching a cell density of OD600 of 70-100 (˜22-25 hrs); (4) inducing said culture with 0.4 mM IPTG; (5) growing said culture at a reduced temperature of 22 to 260 C until activity change is <0.1 IU/ml (approximately 40-48 hrs and an OD600 typically of 200); and (5) harvesting bacteria by continuous centrifugation. In another embodiment, the cell culture media is typically defined and composed of yeast extract protein, peptone-tryptone, glucose, glycerol, casamino acids, trace salts and phosphate buffering salts.
In a fifth aspect, the present invention features a method to purify PAL or a biologically active fragment, mutant or analog thereof. According to one embodiment, a transformed cell mass is grown and ruptured leaving crude recombinant enzyme. Exogenous materials are normally separated from the crude bulk to prevent fouling of the columns. Chromatographic purification can be conducted using one or several chromatographic resins. Subsequently, the purified protein can be formulated into a buffer designed to provide stable activity over an extended period of time. In another embodiment, the method to purify the PAL comprises the steps of: (a) Lysis of the bacteria containing recombinant PAL; (b) treatment of lysate with heat to inactivate viruses; (c) clarification of this lysate using a second continuous centrifugation step and/or depth filtration (d) passage of clarified lysate through a charcoal filtration step; (e) passage of filtrate in (d) through a final filtration step (as with a Sartorious Sartopore 0.2 μm filter); (f) passage of final filtrate over a hydrophobic interaction chromatography resin, such as a butyl hydrophobic interaction chromatography; (g) passage of eluate in (f) over an anionic chromatography resin, such as a Q ion exchange column; (h) recovery of final product by buffer exchange with tangential flow filtration; and (i) sterilization of the final product. Those skilled in the art readily appreciate that one or more of the chromatography steps may be omitted or substituted, or that the order of the chromatography steps may be changed within the scope of the present invention. Optionally, appropriate sterilizing steps may be performed as desired.
In a sixth aspect, the invention provides methods of using PAL compositions for the diagnosis of diseases, including but not limited to disorders caused all or in part by a deficiency in PAH activity. In one embodiment, PAL is used to measure levels of phenylalanine in blood samples. In a further embodiment, the invention contemplates a diagnostic kit comprising PAL for use in monitoring blood samples of subjects with elevated levels of phenylalanine.
Other features and advantages of the invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, because various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Unless otherwise stated, the following terms used in this application, including the specification and claims, have the definitions given below. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Definition of standard chemistry terms may be found in reference works, including Carey and Sundberg (1992) “Advanced Organic Chemistry 3rd Ed.” Vols. A and B, Plenum Press, New York. The practice of the present invention will employ, unless otherwise indicated, conventional methods of synthetic organic chemistry, mass spectroscopy, preparative and analytical methods of chromatography, protein chemistry, biochemistry, recombinant DNA techniques and pharmacology, within the skill of the art. See, e.g., T. E. Creighton, Proteins: Structures and Molecular Properties (W.H. Freeman and Company, 1993); A. L. Lehninger, Biochemistry (Worth Publishers, Inc., current addition); Sambrook, et al., Molecular Cloning: A Laboratory Manual (2nd Edition, 1989); Methods In Enzymology (S. Colowick and N. Kaplan eds., Academic Press, Inc.); Remington's Pharmaceutical Sciences, 18th Edition (Easton, Pa.: Mack Publishing Company, 1990).
The following amino acid abbreviations are used throughout the text:
The terms “polypeptide” and “protein” refer to a polymer of amino acid residues and are not limited to a minimum length of the product. Thus, peptides, oligopeptides, dimers, multimers, and the like, are included within the definition. Both full-length proteins and fragments thereof are encompassed by the definition. The terms also include postexpression modifications of the polypeptide, for example, glycosylation, acetylation, phosphorylation and the like. Furthermore, for purposes of the present invention, a “polypeptide” refers to a protein which includes modifications, such as deletions, additions and substitutions (generally conservative in nature), to the native sequence, so long as the protein maintains the desired activity. These modifications may be deliberate, as through site-directed mutagenesis, or may be accidental, such as through mutations arising with hosts that produce the proteins or errors due to PCR amplification.
As used herein, an “analogue” or “derivative” is a compound, e.g., a peptide, having more than about 70% sequence but less than 100% sequence similarity with a given compound, e.g., a peptide. Such analogues or derivatives may be comprised of non-naturally occurring amino acid residues, including by way of example and not limitation, homoarginine, ornithine, penicillamine, and norvaline, as well as naturally occurring amino acid residues. Such analogues or derivatives may also be composed of one or a plurality of D-amino acid residues, and may contain non-peptide interlinkages between two or more amino acid residues.
The terms “effective amount” or “pharmaceutically effective amount” refer to a nontoxic but sufficient amount of the agent to provide the desired biological result. That result can be reduction and/or alleviation of the signs, symptoms, or causes of a disease, or any other desired alteration of a biological system. For example, an “effective amount” for therapeutic uses is the amount of the composition comprising an oligonucleotide disclosed herein required to provide a clinically significant decrease in the symptoms of a cardiovascular disease, such as those resulting from a heart attack, for example. An appropriate “effective” amount in any individual case may be determined by one of ordinary skill in the art using routine experimentation.
“Treatment” refers to prophylactic treatment or therapeutic treatment or diagnostic treatment.
A “prophylactic” treatment is a treatment administered to a subject who does not exhibit signs of a disease or exhibits only early signs for the purpose of decreasing the risk of developing pathology. The conjugate compounds of the invention may be given as a prophylactic treatment to reduce the likelihood of developing a pathology or to minimize the severity of the pathology, if developed.
A “therapeutic” treatment is a treatment administered to a subject who exhibits signs or symptoms of pathology for the purpose of diminishing or eliminating those signs or symptoms. The signs or symptoms may be biochemical, cellular, histological, functional, subjective or objective. The conjugate compounds of the invention may be given as a therapeutic treatment or for diagnosis.
“Diagnostic” means identifying the presence or nature of a pathologic condition. Diagnostic methods differ in their specificity and selectivity. While a particular diagnostic method may not provide a definitive diagnosis of a condition, it suffices if the method provides a positive indication that aids in diagnosis.
“Pharmaceutical composition” refers to a composition suitable for pharmaceutical use in subject animal, including humans and mammals. A pharmaceutical composition comprises a pharmacologically effective amount of a PAL polypeptide and also comprises a pharmaceutically acceptable carrier. A pharmaceutical composition encompasses a composition comprising the active ingredient(s), and the inert ingredient(s) that make up the carrier, as well as any product which results, directly or indirectly, from combination, complexation or aggregation of any two or more of the ingredients, or from dissociation of one or more of the ingredients, or from other types of reactions or interactions of one or more of the ingredients. Accordingly, the pharmaceutical compositions of the present invention encompass any composition made by admixing a conjugate compound of the present invention and a pharmaceutically acceptable carrier.
By “pharmaceutically acceptable” or “pharmacologically acceptable” is meant a material which is not biologically or otherwise undesirable, i.e., the material may be administered to an individual without causing any undesirable biological effects or interacting in a deleterious manner with any of the components of the composition in which it is contained.
“Pharmaceutically acceptable carrier” refers to any of the standard pharmaceutical carriers, buffers, and excipients, such as a phosphate buffered saline solution, 5% aqueous solution of dextrose, and emulsions, such as an oil/water or water/oil emulsion, and various types of wetting agents and/or adjuvants. Suitable pharmaceutical carriers and formulations are described in Remington's Pharmaceutical Sciences, 19th Ed. (Mack Publishing Co., Easton, 1995). Preferred pharmaceutical carriers depend upon the intended mode of administration of the active agent. Typical modes of administration include enteral (e.g., oral) or parenteral (e.g., subcutaneous, intramuscular, intravenous or intraperitoneal injection; or topical, transdermal, or transmucosal administration). A “pharmaceutically acceptable salt” is a salt that can be formulated into a compound for pharmaceutical use including, e.g., metal salts (sodium, potassium, magnesium, calcium, etc.) and salts of ammonia or organic amines.
The term “unit dosage form,” as used herein, refers to physically discrete units suitable as unitary dosages for human and animal subjects, each unit containing a predetermined quantity of compounds of the present invention calculated in an amount sufficient to produce the desired effect in association with a pharmaceutically acceptable diluent, carrier or vehicle. The specifications for the novel unit dosage forms of the present invention depend on the particular conjugate employed and the effect to be achieved, and the pharmacodynamics associated with each compound in the host.
By “physiological pH” or a “pH in the physiological range” is meant a pH in the range of approximately 7.2 to 8.0 inclusive, more typically in the range of approximately 7.2 to 7.6 inclusive.
As used herein, the term “subject” encompasses mammals and non-mammals. Examples of mammals include, but are not limited to, any member of the Mammalian class: humans, non-human primates such as chimpanzees, and other apes and monkey species; farm animals such as cattle, horses, sheep, goats, swine; domestic animals such as rabbits, dogs, and cats; laboratory animals including rodents, such as rats, mice and guinea pigs, and the like. Examples of non-mammals include, but are not limited to, birds, fish and the like. The term does not denote a particular age or gender.
A. Structure-Based Protein Engineering
Numerous methods are known for protein engineering using rational optimization based primarily on protein structural information (Brannigan, J. A., et al., (2002) ibid.; 735 Marshall, S. A., et al., “Rational design and engineering of therapeutic proteins”, Drug Discov. Today, 8(5), pp. 212-221 (2003)). Systematic replacement of structural features can lead to improved protein properties and/or a redesign of substrate specificity. Recruitment of function from one member of a gene family into another homologous member can be accomplished by the introduction of a limited number of amino acid substitutions in the immediate substrate binding vicinity. Such improvements in protein function by generating improved protein variants can lead to useful proteins for industrial, agricultural, and therapeutic applications (Bocanegra, et al, Biochemistry, 32(11):2737-2740 (1993); Failla, et al., Fold Des., 1(1):35-42 (1996); Hayes, Proc Natl Acad Sci USA., 99(25):15926-15931 (2002); Voigt, et al., Nat. Struct. Biol., 9(7):553-558 (2002); Malashkevich, et al., Nat Struct Biol., 2(7):548-553 (1995); Wells et al, Proc Natl Acad Sci USA., 84(15):5167-5171 (1987); Wilks et al., Science, 242(4885):1541-1544 (1988)).
B. The Structure of PAL
The three dimensional structure of wild-type unliganded Rhodosporidium toruloides PAL (
The PAL protein is a homotetramer, with each monomer consisting of mainly alpha-helices and subdividible into four domains—a central catalytic domain, an N-terminal domain, and a small C-terminal domain with similarity to the Pseudomonas putida histidine ammonia-lyase structure (HAL, Schwede, et al., Biochemistry, 38(17), pp. 5355-5361 (1999)) plus an additional domain inserted in the C-terminal region that protrudes from the ends of the intact tetramer molecule. The N-terminal first 25 residues are not visible in the structure for all four monomers in the tetramer, and this region is probably disordered. The loop regions between residues 109-123 and 350-353 are disordered for monomer B, with regions 103-123 and 350-353 disordered for monomers A, C, and D in the PAL tetramer. Two other X-ray structures of Rhodosporidium toruloides PAL have been determined using trans-cinnamate and NH4 ion addition during the crystallization process, with resolutions of 2.1 Å (P3221 space group) and 2.7 Å (P21 space group; Calabrese, et al., Biochemistry, 43(36), pp. 11403-11416 (2004)). The lower pH used for crystallization and the lower resolution of these structures led to more inherent disorder in the structures (especially in the N-terminal regions) and the inability to unambiguously assign additional electron density present on the MIO cofactor to an NH2 adduct.
There are a number of related structures (using DALI, Holm, et al., J. Mol. Biol., 233, 123-138 (1993)) in this family of tetrameric enzymes that catalyze the elimination of various groups from carboxylic acids, including the ammonia-lyases (PAL, HAL, and aspartate ammonia-lyase (AAL)), fumarase, and arginosuccinate lyase (Schwede, et al. Biochemistry, 38(17), pp. 5355-5361 (1999)). In addition, the δ-crystallin avian eye lens protein has a similar fold but is a non-enzymatic form of this structural family (Schwede, et al., (1999), ibid.).
The high-resolution three-dimensional protein crystal structure of PAL provided herein can be used in methods using protein engineering to improve the biochemical and biophysical properties of PAL, and to increase the in vivo therapeutic effectiveness of PAL. In addition, the structure provides information regarding which regions of the structure are the most flexible (to remove and generate a more compact and stable form of PAL), which residues are located near the active site (to mutate in order to enhance activity and/or minimize the size of the protein as well as to provide information for structure-based inhibitor design), and which surface locations are close to immunogenic (e.g. linear epitopes identified in mapping studies) and/or proteolytic sensitive sites (from protease mapping studies), allowing for the introduction of site-specific mutants for direct disruption of problem sites or, alternatively, for surface pegylation or other chemical derivatization to protect sensitive sites present in native PAL.
C. Uses of the Structure Coordinates of PAL
The high-resolution three-dimensional crystal structure of PAL provided herein can be used in computerized methods for selecting regions of the protein for mutation, modification, or combined mutation and modification. For example, the commercially available program GETAREA calculates surface-exposure for amino acid residues based upon X-ray crystallographic coordinates.
The high-resolution three-dimensional crystal structure provided herein can further be used in in-silico methods to design ligands for the active site of the enzyme. For example, commercially available software programs for docking and designing structure-based small-molecules can be used to design PAL inhibitors (Billett, et al., Biochim Biophys Acta, 524(1), pp. 219-230 (1978); Janas, et al., Acta Biochim Pol., 32(2), pp. 131-143 (1985); Zon, et al., Phytochemistry, 59(1), pp. 9-21 (2002); Alunni, et al., Arch Biochem Biophys., 412(2), pp. 170-175 (2003))
Structure-Based PAL Engineering
Once a reliable three-dimensional structure or structural model is available for a specific macromolecule, rational design has become a productive method for optimization of specific structure and/or function of said macromolecule (Penning, et al., Chem Rev., 101(10), pp. 3027-3046 (2001)). For example, coenzyme specificity has been re-engineered (Bocanegra, et al., Biochemistry, 32(11), pp. 2737-2740 (1993)), protein stabilities have been improved (Malakauskas, et al., Nat Struct Biol., 5(6), pp. 470-475 (1998); Jiang, et al., Protein Sci., 10(7), pp. 1454-1465 (2001); Luo, et al., Protein Sci., 11(5), pp. 1218-1226 (2002); Filikov, et al., Protein Sci., 11(6), pp. 1452-1461 (2002); O'Fagain, Enz Microb Technol., 33, pp. 137-149 (2003); Cammett, et al., J Mol Biol., 327(1, pp. 285-297 (2003)), substrate specificities have been redesigned (Hedstrom, et al., Science, 255(5049), pp. 1249-1253 (1992); Failla, et al., Fold Des., 1(1), pp. 35-42 (1996); Malashkevich, et al., Nat Struct Biol., 2(7), pp. 548-553 (1995); Wilks, et al., Biochemistry, 31(34), pp. 7802-7806 (1992); Feil, et al., Protein Eng., 10(3), pp. 255-262 (1997); Whittle, et al., J Biol Chem., 276(24), pp. 21500-21505 (2001)), ligand or receptor binding specificities have been altered (Cunningham, et al., Proc Natl Acad Sci USA, 88(8), pp. 3407-3411 (1991); Reddy, et al., Nat Biotechnol., 14(13), pp. 1696-1699 (1996); Doyle, et al., Curr Opin Chem Biol., 4(1), pp. 60-63 (2000)), and biological activities have been re-engineered (Chen, et al., Proc. Natl. Acad. Sci. U.S.A., 90(12), pp. 5618-5622 (1993); Sarkar, et al., Nat Biotechnol., 20, pp. 908-913 (2002); Blatt, et al., J Interferon Cytokine Res., 16(7), pp. 489-499 (1996)).
Structure-based engineering can be used to generate PAL variants including rational mutants such as truncations, deletions, insertions, splice variants, point mutations, substitutions, chimeras, loop re-engineered mutants, loop swapping mutants, surface veneering mutants, as well as stochastically-derived mutants (including directed evolution-derived mutants, alone or in combination with rationally developed mutants). In addition, PAL variants can be made comprising PAL mutants wherein mutations have been introduced for site-specific pegylation and/or other chemical derivatizations. The PAL mutants for use in such methods includes any PAL variant having substantially the same functional activity as wild-type R. toruloides PAL, including variants, fragments, and chemical derivatives of the parent PAL protein.
Directed Evolution Protein Optimization
Directed evolution methods randomly mutate gene(s) of interest to explore more completely larger regions of protein mutational space. Numerous directed evolution methods exist, including error-prone PCR and random insertion and deletion (RID) mutagenesis to introduce diversity throughout a DNA sequence, and more focused or “directed” diversity-generating methods such as site-saturation mutagenesis and other oligonucleotide-based mutagenesis methods (Brannigan, J. A., et al., (2002) ibid.). In addition, DNA sequence recombinational methods have been used to combine advantageous sites of mutation and simultaneously remove deleterious mutations, producing novel DNA sequences (e.g. methods of DNA shuffling, StEP, RACHITT, ITCHY). Finally, structure-based directed evolution techniques have been used to redesign proteins for therapeutic advantage (structure-based combinatortial engineering, SCOPE, and protein design automation, PDA, methods). The SCOPE method is based on a semi-rational protein engineering approach that uses protein structure information coupled with DNA manipulation techniques to design and create multiple crossover protein variant libraries from non-homologous genes (O'Maille, et al., J Mol Biol., 321(4), pp. 677-691 (2002)). In PDA, a computational pre-screening of mutational space allows the inclusion of only mutations compatible with a specific protein fold, thus reducing the number of sequence variants to a size amenable to experimental screening (U.S. Pat. No. 6,403,312; Dahiyat, et al., Proc Natl Acad Sci, USA., 94(19), pp. 10172-10177 (1997); Dahiyat, et al., Protein Sci., 6(6), pp. 1333-1337 (1997); Hayes, et al., Proc Natl Acad Sci USA., 99(25), pp. 15926-15931 (2002)).
A large number of examples exist where the use of directed evolution (with coupling to an effective selection or screening protocol) has led to improved catalytic function and biophysical properties (e.g. reduced immunogenicity, increased stability), starting from an initial enzyme species and mutating that species for altered and/or improved function (Vasserot, et al., Drug Discovery Today, 8(3), pp. 118-126 (2003)). For example, successful mutants have been obtained using directed evolution and other “random” mutagenesis methods on a number of different proteins (Triose-phosphate isomerase, Hermes, et al., Proc Natl Acad Sci USA, 87(2):696-700 (1990); Beta-lactamase, Stemmer, Nature, 370(6488):389-391 (1994), Orencia, et al., Nature Struct Biol, 8:238-242 (2001), Voigt, et al., (2002) ibid; para-nitrobenzyl esterase,) Moore, et al., Nature Biotechnol., 14:458-467 (1996); Galactosidase to fucosidase, Zhang, et al., Proc Natl Acad Sci USA, 94(9):4504-4509 (1997); Aspartate aminotransferase, Yano, et al., Proc Natl Acad Sci USA, 95(10):5511-5515 (1998); Green fluorescent protein, Crameri, et al., Nat Biotechnol, 14(3):315-319 (1996); Horseradish peroxidase, Lin, et al., Biotechnol Prog, 15: 467-471 (1999); Cytochrome P450, Joo, et al., Nature, 399(6737):670-673 (1999); Biphenyl dioxygenase, Kumamaru, et al., Nat Biotechnol, 16(7):663-666 (1998); Arsenate detoxification pathway, Crameri, et al., Nat Biotechnol, 15(5):436-438 (1997); Cephalosporinase, Crameri, et al., Nature, 391(6664):288-291 (1998); various proteins, Shao, et al., Curr Opin Struct Biol, 6(4):513-518 (1996), various proteins, Skandalis, et al., Chem Biol, 4, pp. 889-898 (1997); Subtilisin, Cunningham, et al., Protein Eng., 1(4):319-325 (1987); Nitrilase, DeSantis, et al., J Am Chem Soc., 125(38): 11476-11477 (2003); Alpha-aspartyl dipeptidase, Kong, et al., Biochem Biophys Res Commun., 289(1):137-142 (2001); Aspartate aminotransferase, Rothman, et al., Protein Science, 13(3):763-772 (2004); L-aspartase, Wang, et al., Biochem Biophys Res Commun., 276(1):346-349 (2000); and lactate dehydrogenase, Wilks, et al., Biochemistry 31(34):7802-7806 (1992).
These studies have repeatedly demonstrated the utility of applying “random” mutagenesis techniques to the development of improved enzyme variants with increased stability, activity, and resistance to degradative pathways. Structural analysis of evolved protein clones leads to insight on the molecular changes that are involved with the improved physical and chemical properties that are obtained (Orencia, et al., in Advances in protein chemistry: Evolutionary protein design, F. H. Arnold, Editor, Academic Press: San Diego, pp. 227-259 (2001)). The rewards to be gained with directed evolution techniques are especially evident in light of the repeated occurrence of beneficial mutations that involve non-active site residues, with some sites of mutation located over 15-20 Å from enzyme active site regions having beneficial effects (Oue, et al., J. Biol. Chem., 274(4), pp. 2344-2349 (1999)). Directed evolution and other random mutagenesis techniques, coupled to selection and screening procedures, can be used to develop more proteolytically stable and chemically robust forms of PAL to be used in industrial applications or, alternatively, for enzyme substitution therapy, e.g. for PKU.
D. Mutants of PAL
Previous experiments have described mutants of PAL (Schuster, et al., FEBS Lett., 349(2), pp. 252-254 (1994); Schuster, et al., Proc Natl Acad Sci USA., 92(18), pp. 8433-8437 (1995); Langer, et al., Biochemistry, 36, pp. 10867-10871 (1997); El-Batal, et al., Acta Microbiol Pol., 49(1), pp. 51-61 (2000); Röther, et al., Eur. J. Biochem., 269, pp. 3065-3075 (2002)) and HAL mutants (Taylor, et al., J. Biol. Chem., 269(44), pp. 27473-27477 (1994); Baedeker, et al., J. Biochem., 269(6), pp. 1790-1797 (2002)).
Optimization of PAL Kinetics—Mutants with Enhanced Catalytic Activity
The biologically active sites of wild-type PAL according to the invention may be modified as desired to optimize PAL kinetic characteristics. Km, the concentration of substrate that gives half-maximal activity, is intimately associated with the therapeutic efficacy of PAL in maintaining phe levels within an acceptable range, i.e. 120 uM to 240 uM. Km is the affinity of the enzyme for the substrate. By controlling affinity, one can limit or control the efficacy of any enzyme against substrate at different concentrations. For example, if Km is 1000 uM (Rhodosporidium toruloides), the activity of the enzyme will be reduced to about 12.5% at blood phe levels of 240 uM and to about 3% at blood phe levels of 60 uM. If Km is 240 uM, the activity of the enzyme will be reduced to about 50% at blood phe levels of 240 uM and to about 12% at blood phe levels of 60 uM. If Km is 120 uM, the activity of the enzyme will be reduced to about 70% at blood phe levels of 240 uM and to about 35% at blood phe levels of 60 uM. Optimally, a preferred therapeutic objective would be to have an enzyme with sufficient activity to reduce but also maintain phe within the optimal range of about 120 uM to about 240 uM. An enzyme with a high Km (i.e. 1000 uM) will lose activity rapidly as phe levels drop to within normal range and will also require the impractical administration of highly concentrated or large volumes of doses. On the other hand, an enzyme with a very low Km may rapidly deplete phe levels, which may be fatal for hyperphenylanemias but may be useful in the management of cancer.
In most preferred embodiments, the biologically active modified mutant PAL has a kcat of at least about 4.0 s-1 and preferably greater than 20 s-1. In other preferred embodiments, the biologically active modified PAL has a Km of between about 100 μM to about 1000 μM. In most preferred embodiments, the biologically active modified PAL exhibits enzymatic activity that is from about two-fold to about 1000-fold times greater that that of the wild-type. Such biological active mutants may be formed using methods well known in the art, such as by site-directed mutagenesis.
Specific Protein Variants: Variants Having Reduced Immunogenicity
A number of strategies are currently used to reduce protein imunogenicity. Preferably, modifications that are introduced to minimize the immune response do not destroy the structure, function, or stability of the macromolecule. Effective strategies used include increasing human sequence content (chimeras and/or other ‘humanization’ approaches), improving solution properties, removing antibody epitopes, introducing chemical derivatization (such as pegylation), and/or indetifying and removing MHC agretopes. For an injected therapeutic, in vivo immunoreactivity can be addressed by performing epitope mapping followed by rational mutagenesis to modify and/or otherwise mutate these sites of immunogenicity, alone and in combination with site-specific pegylation (Hershfield, et al., (1991) ibid.; Leong, et al., (2001) ibid.; Lee, et al., Pharm. Res., 20(5), pp. 818-825 (2003)) or other chemical derivatization methods to reduce protein immunoreactivity to an acceptable level.
Modification of antigenic surface protein regions reduces immunogenicity (Chirino, et al., (2004) ibid.). One method of improvement involves the construction of smaller sized proteins that retain catalytic activity (e.g. an absorbance assay is used for activity measurement). A second method of improvement, protein engineering coupled to ELISA screening, can also be used to identify mutants with reduced immunoreactivity. Another method introduces point mutations for additional surface Lys sites for pegylation derivatization, a method shown to reduce immunogencity with the test enzyme purine nucleoside phosphorylase (Hershfield, et al., (1991) ibid.). An alternative pathway uses mutation of residues located in protein epitope regions to remove immunogenic sites (Yeung, et al., Immunol., 172(11), pp. 6658-6665 (2004)). In an approach that is analogous to antibody humanization, homologous loop regions and/or residues from human antibodies are substituted into the corresponding loop regions of a homologous protein.
Removal of protein therapeutic proteolytic processing sites can also provide a reduction in immunogenicity by preventing proteasomal processing, thereby preventing clipping and processing into peptide fragments for antigen presenting cell binding. A similar phenomenon has been observed in the alteration of flanking regions for class II MHC determinants, preventing display to autoreactive T cells (Maverakis, et al., Proc Natl Acad Sci, USA., 100(9), pp. 5342-5347 (2003)).
Epitope Mapping
Protein therapeutic epitopes can be calculated using a number of algorithms or experimentally determined with in vitro or in vivo approaches. Computer programs such as “Peptide Companion” (http://www.5z.com/csps/comer/pcom/manual.html) and “Protean” in the Lasergene program suite from DNAStar (http://www.dnastar.com) are commonly used to estimate surface epitope regions of a protein based on the chemical composition and conformation of a protein. Immunogenic regions in a protein sequence are those regions of highest calculated hydrophilicity, based on a hydrophilicity index, and antigenicity, based on the amphipathicity and other conformational parameters of calculated surface protein regions. Alternatively, agretopes in a protein sequence can be located based on computer-modeled predictions of potential HLA binding (Robinson, et al., Nucleic Acids Res., 31(1), pp. 311-314 (2003); De Groot, et al., Novartis Found. Symp., 254, pp. 57-72 (2003)). In addition, epitopes can be identified using in vitro biochemical (Tangri, et al., (2002) ibid.) and in vitro cell-based methods (Stickler, et al., J Immunother., 23(6), pp. 654-660 (2000); Stickler, et al., J Immunol Methods, 281(1-2), pp. 95-108 (2003)). For protein engineering, the relative reduction in immunogenicity can be monitored using assays similar to the in vitro cell-based assay of Stickler, et al. (Stickler, et al., Toxicol Sci., 77(2), pp. 280-289 (2004)).
Theoretical epitope mapping, using algorithms, has indicated six regions of immunogenicity on the wild-type R. toruloides PAL protein surface (residues 70-88, 226-243, 337-356, 396-413, 569-589, and 619-636) or alternatively seven regions (71-170, 231-270, 331-370, 391-430, 511-550, 571-650, and 671-710) (
Surface Residue Identification and Mutation
The surface-exposed residues in or near the immunogenic regions of PAL can be identified. These locations will be a subset of the total number of solvent-accessible surface locations present in the protein, dependent upon proximity to the surface as well as proximity to regions of immunogenicity/antigenicity. The three-dimensional structure of the protein, determined using X-ray crystallography, NMR, or homology modeling, can be used in commercially available software programs to calculate macromolecule solvent-accessible surface area. The output provided using the program GETAREA 1.1 (Fraczkiewicz, et al., J. Comp. Chem., 19, pp. 319-333 (1998)) gives a reliable estimate of surface accessibility for R. toruloides PAL (Table 7). GETAREA and PARAREA and similar programs calculate solvent-accessible surface area using continuum methods with a parametric approach based on the Gauss-Bonnet theorem. PARAREA finds potential intersection points in the Gauss-Bonnet path using all atom pairs in the neighbor list of each atom, whereas GETAREA more efficiently calculates the solvent-exposed vertices using intersection half-spaces defined by planes of two-sphere intersections.
In native PAL, GETAREA identified twelve surface-exposed Lys residues, distributed throughout the tetrameric PAL protein surface, as well as one partially-exposed surface Cys residue (Cys140). These positions are directly available for pegylation derivatization. Further, the three-dimensional structure of PAL can be used to identify additional surface residues available for site-directed mutagenesis. These additional sites can be mutated using standard protein engineering techniques to generate more favorable PAL mutants with reduced immunogenicity, improved proteolytic resistance, and/or improved stability/activity.
Strategies for mutation of the protein to provide protein mutants with improved properties, such as reduced immunogenicity are known in the art. One popular route mutates every non-alanine residue in an epitope to Ala, and mutate every alanine residue in an epitope to Gly. Other methods remove charged and hydrophobic residues from epitope regions, either by mutation or deletion. Additional mutation strategies introduce site-specific mutations followed by site-specific chemical derivatization.
Truncations can also be used for the production of protein improvements. Bioinformatics analysis of PAL relative to histidine ammonia-lyase (HAL) has suggested truncation mutants (residues 23-716 and 1-564). In addition, analysis of the PAL 3-D structure provides an alternative region for truncation, based on the absence of a C-terminal domain region in the structure of the highly homologous HAL protein. C-terminal domain deletion mutants, including mutants where the corresponding loop region from HAL is fused into the PAL sequence to substitute for the C-terminal domain protruding region of the PAL structure (calculated to have major epitope regions), form smaller, more robust, and predicted less immunogenic variants of PAL.
In another method, protein engineering using rational mutagenesis in combination with directed evolution can be used to obtain mutant forms of PAL. For example, implementation of rational design along with experimental and combinatorial design has improved the activity of compstatin (Morikis, et al., Biochem. Soc. Trans., 32(Pt 1), pp. 28-32 (2004)). The combination of rational mutagenesis and directed evolution has also shown promise (Bornscheuer, et al., Curr. Opin. Chem. Biol., 5(2), pp. 137-143 (2001); Dwyer, et al., Science, 304(5679), pp. 1967-1971 (2004)).
Mutant forms of PAL that display less than optimal enzymatic activity can be evolved for activity using the protein engineering method of directed molecular evolution, wherein a random mutagenesis step is followed by a selection procedure for mutants that are active, producing a new protein mutant pool of only those clones that have activity. For example, if a specific mutant PAL (that we have designed to introduce a surface lysine residue near an epitope-containing region of the structure) is inactive, performing directed evolution on this mutant (mutating the inactive mutant and selecting for transformants with activity) generates a new mutant pool containing this beneficial mutation (the surface lysine site) plus a subset of additional random mutations located throughout the structure that restore activity to each active clone. In addition, the directed evolution technique of molecular breeding that can cross different species of the same protein or similar sequences of different proteins (Crameri, et al., Nature, 391, pp. 288-291 (1998); Minshull, et al., Curr. Opin. Chem. Biol., 3(3), pp. 284-290 (1999)) can substitute the sequence of human histidine ammonia-lyase to replace some of the most immunogenic regions of PAL with a human sequence that won't be recognized by the immune system.
Mutant forms of PAL can be obtained by making hybrid protein variants based on semi-rational approaches thereby allowing for a more directed level of protein design relative to pure directed evolution-based methods, as well as providing for a more random level of mutational manipulation for those regions of a protein structure identified using such biased protein engineering approaches. For example, the PDA method generates computationally pre-screened libraries of protein variants, allowing for more rapid optimization of protein properties over pure random, or non-biased protein engineering methods (U.S. Pat. No. 6,403,312; Dahiyat, Curr Opin Biotechnol., 10(4), pp. 387-390 (1999); Filikov, et al., ibid. (2002); Hayes, et al., (2002) ibid.; Luo, et al., (2002) ibid.). Similarly, the SCOPE method constructs hybrid enzyme variants based on “equivalent” subdomains of structure, allowing the creation of multiple crossover protein variant libraries starting from non-homologous genes (O'Maille, et al., (2002) ibid.). In a similar fashion, the method developed by Voigt, et al., constructs hybrids based upon the application of a computational algorithm that identifies fragments of proteins, or ‘schemas,’ that can be recombined without disrupting the integrity of a protein's three-dimensional structure (Voigt, et al., (2002) ibid.). Computational analysis can also identify conserved core regions of structurally and functionally important positions in a protein fold, based on secondary structural element assignments (Mizuguchi, et al., Bioinformatics, 16(12), pp. 1111-1119 (2000)). Mutant forms of PAL can be obtained following the procedures of any of the art methods.
Hal as an Alternative Enzyme Substitute
The structure of human HAL has been homology modeled based on the structure of P. putida HAL (
Specific Protein Variants: Variants Having Reduced Protease Sensitivity
A number of strategies are currently used to reduce protein protease susceptibility. The modifications introduced to minimize protolytic sensitivity preferably do not destroy the structure, function, or stability of the macromolecule. Effective strategies include providing an enzyme with an active-site stabilizing species such as a competitive inhibitor (Gilbert, et al. (1981) ibid.; U.S. Pat. Nos. 6,584,644; 6,451,986; 6,433,158; 6,461,849), chemically modifying the amino groups in susceptible Lys and/or Arg sites to block trypsin binding sites, mutating chymotrypsin-sensitive Tyr, Phe, and/or Trp residues to smaller neutral amino acids to abolish cleavage susceptibility, ligate or couple PAL to other protective macromolecules (such as Fc antibody domains or the botulinum neurotoxin nontoxic components), and/or introducing Lys or Cys sites near protease susceptible sites for subsequent chemical derivatization with PEG or other chemically protective and stabilizing groups.
Protein engineering was performed on wild-type PAL to construct site-directed mutants to remove the two primary sites of protease sensitivity. Using two different partial proteolytic digests of His-tagged PAL, followed by separation of the two major protein fragments by passage of the protein digest over a nickel chelate column, the primary sites of trypsin and chymotrypsin sensitivity in native PAL were identified based on the N-terminal protein sequences determined for the largest PAL fragments. The primary trypsin site was identified as Arg123, whereas the primary chymotrypsin sensitive site was identified as Tyr110. Six mutants of these protease recognition sites were made (R123H, R123A, R123Q, and Y110H, Y110A, Y110L). All six mutants expressed in levels similar to the wild-type protein and did not show signs of aggregation, but all displayed low specific activity (all units μmol×min−1 mg−1) Y110H 0.084, Y110A 0, Y110L 0, R123A 0.11, R123H 0.074, R123Q 0.033 (versus wild-type 1.32). Testing of protease susceptibility indicated that point mutation provided protection for the three R123 PAL mutants (both the activity and the intact protein size were retained with trypsin exposure) and the three Y110 mutants (low activity negated any observations about residual activity, but SDS-PAGE gel analysis indicated retention of intact protein size upon chymotrypsin incubation). These PAL mutants were then subjected to directed evolution and proteins exhibiting improved activity for these inactive site-directed mutants were selected.
Alternatively, in order to chemically protect the enzyme (e.g. pegylation), a number of surface sites in the proximity of the Tyr110 and Arg123 protease susceptible sites were mutated to lysine to generate additional sites for surface pegylation. Eight lysine mutants of wild-type PAL were constructed and the specific activities of the modified enzymes are shown in
Specific Protein Variants: Variants Having Improved Activity
The mutants R91K, H137K, H598Q and K132R PAL have shown improved activity relative to wild-type R. toruloides PAL. R91K is located in the helix spanning Asp86 to Leu 01, near the surface of the protein (non-“i” scores, see Table 7 output). H137K is located in the helix spanning Asp126 to Leu139, with wild-type His137 forming hydrogen bonds to the amide carbonyls of Ala133 and Leu134 (for ND1) and the NE2 of Gln138 (for NE2); using the program that mutates position 137 to Lys, the side chain moves relative to the position in H137, but hydrogen bonding interactions are still present.
E. Chemically Modified PAL Variants
Macromolecule chemical modification can be performed in a non-specific fashion (leading to mixtures of derivatized species) or in a site-specific fashion (based on wild-type macromolecule reactivity-directed derivatization and/or site-selective modification using a combination of site-directed mutagenesis and chemical modification) or, alternatively, using expressed protein ligation methods (Hofmann, et al., Curr Opin Biotechnol., 13(4), pp. 297-303 (2002)). Preferably, chemical modification is used to reduce immunogenicity. Pegylation is a demonstrated method to reduce immunogenicity of proteins (Bhadra, et al., Pharmazie, 57(1), pp. 5-29 (2002)) but glycosylation and other chemical derivatization procedures, using modification with phosphorylation, amidation, carboxylation, acetylation, methylation, creation of acid-addition salts, amides, esters, and N-acyl derivatives are also possible (Davis, Science, 303, pp. 480-482 (2004)).
Pegylated Proteins
A series of different pegylation reactions on PAL, using a range of PEG chemical reagent to PAL protein ratios, provided PEG-PAL derivatives for each modification method. The optimal degree of pegylation can be determined based upon the residual activity obtained for each derivatized PAL species using the absorbance assay in combination with PAGE and Native gel analysis to determine the extent of PEG derivatization. After initial ranges of optimal modification are determined, comparative kinetic analysis (including Vmax and Km determinations, binding constants of substrates, proteolytic stability, pH dependence of activity, temperature-dependence of activity) and immunoreactivity of optimal PEG-PAL species can be determined by ELISA, immunoprecipitation, and Western blot. Protein engineering can also be used to generate the most favorable PAL mutant for pegylation using the optimal derviatization conditions; by minimizing the size of the PAL protein and only modifying the most antigenic regions of the PAL surface, cost of PEG modification will be reduced while at the same time retaining the maximum amount of enzymatic activity and minimum amount of immunogenicity. Similarly, site-specific pegylation can be used to provide enzyme derivatives.
Other chemical modifications such as phosphorylation or other chemical modification of lys, arg, cys residues can be used to mask immunogenic regions and/or proteolytic sensitive regions. Such chemical modifications include the polymer addition method of Bednarsaki and the Altus Corporation cross-linking method for improving PAL stability, reducing immunogenicity, and improving protease resistance are representative examples. Bednarsaki demonstrated that polymer addition improves protein temperature stability (Wang, et al., J. Am. Chem. Soc., 114(1), pp. 378-380 (1992)), and Altus Corporation has found that glutaraldehyde cross-linking improves enzyme stability.
To discover if the in vivo therapeutic half-life of a protein such as PAL would benefit from pegylation, a variety of different PEG:PAL conjugates were synthesized, characterized in vitro and tested in vivo for L-Phe reduction. In order to both optimize the potential effects of pegylation and to identify the preferred sites of PEG attachment, a design strategy was employed wherein polymer length, conformation, and the degree of PEG attachment were varied.
Methods for preparing the pegylated PAL of the present invention generally comprise the steps of (a) reacting PAL with polyethylene glycol under conditions whereby PAL becomes attached to one or more PEG groups, and (b) obtaining the reaction product(s). Because the specific sites of PAL modification might significantly alter the intrinsic activity of the conjugate, different types and amounts of PEG were explored. The chemistry used for pegylation of PAL was the acylation of the primary amines of PAL using the NHS-ester of methoxy-PEG (O-[(N-Succinimidyloxycarbonyl)-methyl]-O′-methylpolyethylene glycol). Acylation with methoxy-PEG-NHS or methoxy-PEG-SPA results in an amide linkage that eliminates the charge from the original primary amine.
The present methods provide for a substantially homogenous mixture of polymer:protein conjugate. “Substantially homogenous” as used herein means that only polymer:protein conjugate molecules are observed. The polymer:protein conjugate has biological activity and the present “substantially homogenous” pegylated PAL preparations provided herein are those which are homogenous enough to display the advantages of a homogenous preparation, e.g., ease in clinical application in predictability of lot to lot pharmacokinetics.
The polymer molecules contemplated for use in the pegylation approaches described herein may be selected from among water-soluble polymers or a mixture thereof. The water-soluble polymer may be selected from the group consisting of, for example, polyethylene glycol, monomethoxy-polyethylene glycol, dextran, poly-(N-vinyl pyrrolidone), propylene glycol homopolymers, a polypropylene oxide/ethylene oxide co-polymer, polyoxyethylated polyols (e.g., glycerol), dextran, HPMA, Fleximer™, and polyvinyl alcohol. The polymer selected should be water-soluble so that the protein to which it is attached does not precipitate in an aqueous environment, such as a physiological environment. The polymer may be branched or unbranched. Preferably, for therapeutic use of the end-product preparation, the polymer will be pharmaceutically acceptable.
A particularly preferred water-soluble polymer for use herein is polyethylene glycol, abbreviated PEG. As used herein, polyethylene glycol is meant to encompass any of the forms of PEG that have been used to derivatize other proteins, such as mono-(C1-C10) alkoxy- or aryloxy-polyethylene glycol.
The proportion of polyethylene glycol molecules to protein molecules will vary, as will their concentrations in the reaction mixture. In general, the optimum ratio (in terms of efficiency of reaction in that there is no excess unreacted protein or polymer) will be determined by the molecular weight of the polyethylene glycol selected and on the number of available reactive groups (typically ε amino groups) present. As relates to molecular weight, in general, the higher the molecular weight of the polymer used, the fewer number of polymer molecules which may be attached to the protein. Similarly, branching of the polymer should be taken into account when optimizing these parameters. Generally, the higher the molecular weight (or the more branches) the higher the polymer:protein ratio. In the present invention, several different linear PEG polymer lengths were evaluated (5 kDa and 20 kDa). Similarly, conjugates of two-armed branched PEG polymers (10 kDa and 40 kDa) were also tested. In general, for the PEGylation reactions contemplated herein, the preferred average molecular weight is about 2 kDa to about 100 kDa (the term “about” indicating +/−1 kDa). More preferably, the average molecular weight is about 5 kDa to about 40 kDa. The ratio of water-soluble polymer to PAL will generally range from 1:1 for monoPEG-, 2:1 for diPEG etc.
The PAL of the present invention may also include conservative amino acid changes at one or more residues in SEQ ID NO: 1. These changes will have little effect on the biological activity of the analog.
F. PAL and HAL Fusion Proteins
The invention contemplates the preparation and use of fusion proteins comprising a combination of different species of HAL and PAL, including but not limited to bacterial and human HAL, PAL produced by bacterial such as encPAL, yeast (Pichia), and human. A fusion protein refers to a compound comprising PAL or HAL protein or a HAL or PAL polypeptide, or a fragment thereof, attached to another PAL or HAL protein or a HAL or PAL polypeptide, or a fragment thereof. Such fusion proteins may be produced by recombinant genetic engineering methods known to one of ordinary skill in the art. Fusion proteins may be prepared using standard techniques known in the art. Typically, a DNA molecule encoding HAL or PAL or a portion thereof is linked to a DNA molecule encoding the other HAL or PAL proteins or portion thereof. The chimeric DNA construct, along with suitable regulatory elements can be cloned into an expression vector and expressed in a suitable host. The resultant fusion proteins contain HAL or PAL or a portion thereof linked to the other HAL or PAL protein or portion thereof. The fusion protein of the present invention can be produced using host cells expressing a single nucleic acid encoding the entire chimeric protein or more than one nucleic acid sequence, each encoding a domain of the fusion protein and, optionally, an amino acid or amino acids which will serve to link the domains.
G. Selection and Screening Assays
For production and screening of active PAL or HAL variants, initial mutant clone expression can utilize any of the known vector expression systems, such as the His-tag vector expression system, facilitating a high-throughput metal chelate purification step for protein variant isolation. A three-tier screening system can be used to identify favorable protein variants. Initial positive clone identification can use transformation and selection for growth in a phenylalanine auxotrophic E. coli strain. A second round of screening can utilize the OD290 absorbance measurement (Hodgins, D. S., (1968) ibid.) amenable to high-throughput processing. Finally, screening for proteolysis resistance (using incubation in the presence of protease cocktail) or, alternatively, immunogencity reduction (using competitive ELISA measurements), can be used to identify favorable protein variants.
H. Therapeutic Uses and Administration of Optimized PAL Proteins
Various Forms of Hyperphenylalanemia (HPA)
The present invention is directed to the treatment of a variety of HPA patient populations with methods that comprise the use of PAL compositions, either alone or in combination with other therapeutic regimens, for managing HPA and/or PKU. In particular, it is contemplated that PAL compositions may be used to treat that patient population with phenylalanine concentrations that are low enough that dietary intervention is not normally used (i.e., patients with mild HPA), patients with moderate PKU, patients with classic or severe PKU, and any subpopulations thereof. Such patients that are amenable to treatment with PAL compositions to ameliorate the effects of mild HPA, include pregnant women and infants with serum concentrations of less than 200 μM. The various patient populations, and their different therapeutic needs, are discussed in further detail in the present section.
Certain embodiments of the present invention are directed to treating classic severe PKU by administering to the subject a protein-restricted diet in combination with a composition comprising PAL or biologically active variants, mutants, and fragments thereof, wherein the combined administration of the protein-restricted diet and PAL is effective to lower the phenylalanine concentration in the plasma of said subject as compared to said concentration in the absence of said combined administration. In addition, the invention also contemplates treating a pregnant female that has HPA by administering to the female a protein-restricted diet in combination with PAL or a biologically active derivative thereof, such that the combined administration of the protein-restricted diet and PAL is effective to lower the phenylalanine concentration in the plasma of the pregnant woman as compared to such a concentration in the absence of said combined administration. In specific embodiments, therapy is contemplated for patient who manifest Phe levels greater than 420 μM
Other embodiments of the invention entail administering a PAL composition to any individual that has HPA, characterized by a plasma Phe concentration greater than 180 μM prior to the administration of PAL, in an amount effective to produce a decrease in such a plasma Phe concentration of the patient. The methods of the invention will be useful in treating an infant having PKU characterized by an elevated Phe concentrations of between greater than 300 μM with PAL compositions described herein. By “infant” the present application refers to a patient that is between the ages of 0 to about 36 months.
Characteristics of Severe Classical PKU and Methods of Treatment Thereof according to the Present Invention.
Severe PKU manifests in a plasma Phe concentration greater than 1200 μM and may be found to be as high as 4800 μM. Patients that have this disorder must be treated with a Phe-free diet in order to bring their plasma Phe concentrations down to a level that is clinically acceptable (typically, less than 600 μM and preferably less than 300 μM). These patients are only able to tolerate a maximum of between 250-350 mg dietary Phe per day (Spaapen et al., Mol. Genet and Metab. 78: 93-99 (2003)). As such, these patients are started on a Phe-restricted formula diet between 7-10 days after birth and are burdened with this dietary restriction for the remainder their lifespan. Any alleviation of the strict dietary restrictions that these individuals are encumbered with would be beneficial.
The tests used for the diagnosis of individuals with classical Phe are described in further detail below. These tests have revealed that patients with classical severe PKU require a low phenylalanine diet (Lucke et al., Pediatr. Neurol. 28: 228-230 (2003)). Thus, it is contemplated that the methods of the invention will entail determining that the patient is suffering from classical PKU by monitoring the plasma Phe concentration of the individual. The patient is then treated by administering PAL compositions alone or a combined regimen of a low protein diet and PAL such that there is produced at least a 25% decrease in the plasma Phe concentrations of the patient. Preferably, the method will produce a 30% decrease in the plasma Phe concentration. Even more preferably, the method will produce a 40%, 50%, 60%, 70%, 80%, 90% or greater decrease in the plasma Phe concentration of the individual (for example, where a patient with severe classical PKU has a Phe concentration of 4800 μM a 90% decrease in the Phe concentration will produce a plasma Phe concentration of 480 μM, a concentration that is sufficiently low to require little dietary restriction). Of course, it should be understood that the treatment methods of the present invention (whether for treating severe classical PKU or any other HPA described herein), should attempt to lower the plasma Phe concentrations of the patient to levels as close to a range of about 120 μM to about 360 μM±15 μM as possible, and most preferably to an optimal range of about 120 μM to about 240 μM.
In preferred embodiments the plasma Phe concentrations of the classical PKU patient being treated is reduced from any amount of unrestricted plasma Phe concentration that is greater than 1000 μM to any plasma Phe level that is less than 600 μM. Of course, even if the combined treatment with PAL and the protein-restricted diet produces a lesser decrease in plasma Phe concentration, e.g., to a level of between 800 μM to about 1200 μM, this will be viewed as a clinically useful outcome of the therapy because patients that have a plasma Phe concentration in this range can manage the disease by simply restricting the amount of protein in the diet as opposed to eating a Phe-restricted formula, thereby resulting in a marked improvement in the quality of life of the individual, as well as leading to greater patient compliance with the dietary restriction.
Any increase in the amount of dietary Phe levels that can be tolerated by the patient as a result of the treatment will be considered to be a therapeutically effective outcome. For example, it is contemplated that as a result of administering the PAL therapy, the patient will be able to increase his/her intake of dietary Phe from 250-350 mg/day to 350-400 mg/day (i.e., the Phe tolerance phenotype of the patient is altered from that of a classic PKU patient to a moderate PKU patient). Of course, it would be preferable that the therapeutic intervention taught herein would allow the patient to increase his/her intake of dietary Phe from 250-350 mg/day to 400-600 mg/day (i.e., the Phe tolerance phenotype of the patient is altered from that of a classic PKU patient to a mild PKU patient), or even more preferably, to allow the patient to have an intake of greater than 600 mg Phe/day (i.e., normal dietary intake).
Characteristics of BH4-Non Responsive PKU Patients and Methods of Treatment Thereof According to the Present Invention.
A second group of patients that can be treated with the methods of the present invention are those individuals that have been determined to have an elevated plasma Phe concentrations i.e., any concentration that is greater than 200 μM, but have been diagnosed to be non-responsive to BH4 therapy (as determined by the BH4 loading test described below). Such patients may include those individuals that have mild PKU (i.e., plasma Phe concentrations of up to 600 μM), individuals that have moderate PKU (i.e., plasma Phe concentrations of between 600 μM to about 1200 μM), as well as patients that have classic severe PKU (i.e., plasma Phe concentrations that are greater than 1200 μM).
The patients that are non-responsive to BH4 therapy are given PAL in combination with a reduced amount of protein in their diet in order to decrease the plasma Phe concentrations of the patient. The methods of the present invention are such that the administration of PAL produces a greater decrease in the plasma Phe concentrations of the patient as compared to the decrease that is produced with the same dietary protocol administered in the absence of PAL therapy. The dietary restrictions may be a diet that restricts the Phe intake by providing a synthetic medical protein formula that has a diminished amount of Phe or alternatively, the dietary restriction may be one which simply requires that the patient limit his/her overall protein intake but nevertheless allows the patient to eat normal foodstuffs in limited quantities.
The preferred therapeutic outcomes discussed for classical PKU patients are incorporated into the present section by reference. Preferred therapeutic outcomes for patients with moderate PKU (i.e., patients that has an unrestricted plasma Phe concentration of 600 μM/L to 1200M) include at least a 25% decrease in the plasma Phe concentrations of the patient. Preferably, the method will produce a 30% decrease in the plasma Phe concentration. Even more preferably, the method will produce a 40%, 50%, 60%, 70%, 80%, 90% or greater decrease in the plasma Phe concentration of the individual (for example, where a patient with moderate classical PKU has a Phe concentration of 1000 μM, a 90% decrease in the Phe concentration will produce a plasma Phe concentration of 100 μM, a concentration that is sufficiently low to require little or no dietary restriction).
In preferred embodiments, the plasma Phe concentrations of the moderate PKU patient being treated is reduced from any amount of unrestricted plasma Phe concentration that is between 600 μM to 1200 μM to any plasma Phe level that is less than 300 μM. A particularly preferred treatment with PAL (either alone or in combination with a dietary restriction) produces a decrease in plasma Phe concentration, e.g., to a level of between 200 μM to about 400 μM, which will be viewed as a clinically useful outcome of the therapy because patients that have a plasma Phe concentration in this range can manage the disease by simply restricting the amount of protein in the diet as opposed to eating a Phe-restricted formula. Indeed, in many studies, it is taught that such patients may even eat a normal diet.
Any increase in the amount of dietary Phe levels that can be tolerated by the patient as a result of the treatment will be considered to be a therapeutically effective outcome. For example, it is contemplated that as a result of administering the PAL therapy (either alone or in combination with other therapeutic intervention), the patient will be able to increase his/her intake of dietary Phe from 350-400 mg/day to 400-600 mg/day (i.e., the Phe tolerance phenotype of the patient is altered from that of a moderate PKU patient to a mild PKU patient). Of course, it would be preferable that the therapeutic intervention taught herein would allow the patient to increase his/her intake of dietary Phe from 350-400 mg/day to 400 to allow the patient to have an intake of greater than 600 mg Phe/day (i.e., normal dietary intake).
Even if the patient being treated is one who manifests only mild PKU, i.e., has a dietary allowance of 400-600 mg Phe intake/day) will benefit from the PAL-based therapies of the present invention because it is desirable to produce a normalized plasma Phe concentration that is as close to 360 μM±15 μM as possible. For such patients, a preferred therapeutic outcome will include at least a 25% decrease in the plasma Phe concentrations of the patient. Preferably, the method will produce a 30% decrease in the plasma Phe concentration. Even more preferably, the method will produce a 40%, 50%, 60%, or greater decrease in the plasma Phe concentration of the individual (for example, where a patient with mild PKU has a Phe concentration of 600 μM, a 60% decrease in the Phe concentration will produce a plasma Phe concentration of 360 μM, i.e., an acceptable, normal concentration of plasma Phe).
In preferred embodiments, the plasma Phe concentrations of the mild PKU patient being treated is reduced from any amount of non-restricted plasma Phe concentration that is between 400 μM to 600 μM to any plasma Phe level that is less than 100 μM. Of course, even if the treatment with PAL (either alone or in combination with a dietary restriction) produces a lesser decrease in plasma Phe concentration, e.g., to a level of between 200 μM to about 400 μM, this will be viewed as a clinically useful outcome of the therapy.
Any increase the amount of dietary Phe levels that can be tolerated by the patient as a result of the treatment will be considered to be a therapeutically effective outcome. For example, it is contemplated that as a result of administering PAL therapy (either alone or in combination with other therapeutic intervention), the patient will be able to increase his/her intake of dietary Phe from 400-600 mg/day (i.e., the Phe tolerance phenotype of the patient is altered from that of a mild PKU patient to a mild HPA patient) to allow the patient to have an intake of greater than 600 mg Phe/day (i.e., normal dietary intake).
Furthermore, even if the patient is one who only manifests the symptoms of non PKU HPA, i.e., has an elevated plasma Phe concentration of up to 600 μM, but is otherwise allowed to eat a normal protein diet will benefit from PAL therapy of the invention because it has been shown that elevated Phe concentrations have significant effects on the IQ of such individuals. Moreover, as discussed below, PAL therapeutic intervention of subjects with special needs, e.g., pregnant women and infants, is particularly important even if that patient's plasma Phe levels are within the perceived “safe” level of less than 200 μM.
Maternal PKU and Methods of Treatment Thereof According to the Present Invention.
Metabolic control of plasma Phe levels in PKU women planning conception and those who are pregnant is important because of the serious consequences to the fetus exposed to even moderately elevated Phe levels in utero, regardless of the PAH status of the fetus. Therapeutic control of plasma Phe concentration is especially important in the first trimester of pregnancy, as failure to achieve adequate control will result in disorders including microcephaly, mental deficiency and congenital heart disease.
For example, the NIH Consensus Statement (vol 17 #3, October 2000) on Phenylketonuria reported that exposure of a fetus to maternal Phe levels of 3-10 mg/dL produced a 24% incidence of microcephaly, whilst those exposed to greater than 20 mg/dL (i.e., greater than 1200 μM) had a 73% incidence of microcephaly. Likewise congenital heart disease was found in over 10% of children exposed to maternal Phe levels that were greater than 20 mg/dL. Importantly, it has been noted that levels of Phe greater than 6 mg/dL significantly decrease the IQ of the child. Thus, it is imperative to ensure that the plasma Phe concentration of women with all forms of phenylketonuria, even those manifesting the mildest HPA, must be tightly controlled in order to avoid the risk of maternal PKU syndrome. However, the acceptable target levels for the plasma Phe concentrations of PKU women that have been used in U.S. clinics have ranged between 10 mg/dL and 15 mg/dL, which are much higher than the 2-6 mg/dL levels recommended for pregnant women or the 1-4 mg/dL that are used in British and German clinics to diminish the risks of developing maternal PKU syndrome.
Another important consideration for pregnant women is their overall protein intake. During pregnancy, it is important that women eat sufficient protein because it has been suggested that a low protein diet during pregnancy will result in retarded renal development and subsequent reduction in the number of nephrons and potentially leads to hypertension in adulthood. (D'Agostino, N. Engl. J. Med. 348(17): 1723-1724 (2003)). The following table provides exemplary guidelines for the recommended total dietary protein intake for various individuals.
As can be seen from the above exemplary guidelines, in the United States, the recommended protein intake for women of child-bearing age (e.g., less than 51) is from about 44 to 50 g/day, whereas pregnant women require are recommended an intake of about 60 g/day. In Canada and the United Kingdom, the recommended protein intake for pregnant women is in the order of about 70 g/day and 52 g/day. Thus, the need to ensure that the plasma Phe concentration levels of pregnant women are tightly controlled is further complicated by the fact that this group of PKU patient requires more protein than non-pregnant PKU females of comparable age.
In view of the above, it is contemplated that PAL therapies of the present invention will be particularly useful in pregnant women. It is contemplated that a woman suffering from any form of HPA who is pregnant or is contemplating pregnancy will be placed on a course of PAL therapy to ensure that her plasma Phe concentration levels are maintained as close to 180 μM to about 360 μM as possible. Such a course of therapy will preferably allow that woman to increase her level of normal protein intake.
The discussion of levels of plasma Phe concentrations and the degrees to which such Phe concentrations should be decreased discussed herein above in Sections 1A and 1B are incorporated into the present section for pregnant women.
Managing PKU in Infants and Methods of Treatment Thereof According to the Present Invention.
As discussed herein throughout, it has been determined that an elevation in the plasma Phe concentration in infants (ages zero to 3 years old) results in significant drop in IQ of the child. However, as has been discussed elsewhere in the specification, patients that have an elevated plasma Phe concentration of anywhere up to 400 μM do not normally receive any dietary intervention. Thus, infants at the age of zero to 3 years in age suffer from significant deleterious effects from the present therapies. The instant application contemplates treating any infant having an unrestricted plasma Phe concentration that is greater than 360 μM+15 μM with a therapeutic composition that comprises PAL in order to produce a beneficial decrease the plasma Phe concentration of that subject.
In preferred embodiments, the infant is aged between zero and 3 years of age and has an unrestricted plasma Phe concentration of about 1200 μM prior to the administration of PAL and said administration decreases the plasma Phe concentration. Preferably, the plasma Phe concentration is decreased to from greater than 1800 to about 1500 μM, about 1200 μM, about 1100 μM, about 1000 μM, about 900 μM, about 800 μM, about 700 μM, about 600 μM, about 550 μM, about 500 μM, about 450 μM, 400 μM, about 350 μM, about 300 μM, about 275 μM, about 250 μM upon administration. In other embodiments, the infant is aged between zero and 3 years of age and has an unrestricted plasma Phe concentration of greater than 1200 μM and preferably, this plasma Phe concentration is decreased to about 800 μM, or more preferably to about 500 μM or even more preferably to about 360 μM upon administration of PAL, either alone or in combination with diet. Those of skill in the art would understand that the invention contemplates treating infants with unrestricted plasma Phe concentrations of greater than 360 μM with PAL to produce decreases in such plasma Phe concentrations. The discussion of therapeutic reductions of plasma Phe concentrations above are incorporated herein by reference. Further, any decrease over 10% of the initial unrestricted plasma Phe concentration will be considered a therapeutic outcome for the therapeutic regimens for the infants. It should be understood that the PAL therapies may be combined with dietary restrictions to effect the therapeutic decrease in plasma Phe concentrations in such infants.
Table 2 lists a number of disease conditions wherein administration of therapeutically effective amounts of PAL would be beneficial. Parenteral, oral, or other standard routes of administration and dosage can be determined using standard methods.
2. Compositions for Use in the Treatment
The present invention contemplates therapeutic intervention of PKU/HPA. Such intervention is based initially on the use of PAL, which may be used alone or in combination with dietary restrictions. Further PAL and/or dietary restrictions may further be combined with other therapeutic compositions that are designed, for example to combat other manifestations of PKU, such as for example, large neutral amino acids to prevent Phe accumulation in the brain (see Koch et al., Mol. Genet. Metabol. 79: 110-113 (2003)) or tyrosine supplementation. The present section provides a discussion of the compositions that may be used in the treatments contemplated herein. PAL compositions
In general, the present invention contemplates pharmaceutical compositions comprising effective amounts of protein or derivative products of the invention together with pharmaceutically acceptable diluents, stabilizers, preservatives, solubilizers, emulsifiers, adjuvants and/or carriers. Such compositions include diluents of various buffer content (e.g., Tris-HCl, phosphate), pH and ionic strength; additives such as detergents and solubilizing agents (e.g., Polysorbate 20, Polysorbate 80), anti-oxidants (e.g., ascorbic acid, sodium metabisulfite), preservatives (e.g., Thimerosol, benzyl alcohol) and bulking substances (e.g., lactose, mannitol); see, e.g., Remington's Pharmaceutical Sciences, 18th Ed. (1990, Mack Publishing Co., Easton, Pa. 18042) pages 1435-1712. An effective amount of active ingredient is a therapeutically, prophylactically, or diagnostically effective amount, which can be readily determined by a person skilled in the art by taking into consideration such factors as body weight, age, and therapeutic goal.
The PEG:PAL compositions of the present invention may also include a buffering agent to maintain the pH of the solution within a desired range. Preferred agents include sodium acetate, sodium phosphate, and sodium citrate. Mixtures of these buffering agents may also be used. The amount of buffering agent useful in the composition depends largely on the particular buffer used and the pH of the solution. For example, acetate is a more efficient buffer at pH 5 than pH 6 so less acetate may be used in a solution at pH 5 than at pH 6. The preferred pH range for the compositions of the present invention is pH 3.0-7.5.
The compositions of the present invention may further include an isotonicity adjusting agent to render the solution isotonic and more compatible for injection. The most preferred agent is sodium chloride within a concentration range of 0-150 mM.
As used herein, and when contemplating PEG:PAL conjugates, the term “therapeutically effective amount” refers to an amount, which gives a decrease in serum L-phenylalanine that provides benefit to a patient. The amount will vary from one individual to another and will depend upon a number of factors, including the overall physical condition of the patient. The amount of PAL used for therapy gives an acceptable rate of serum L-phenylalanine decrease and maintains this value at a beneficial level (usually at least about 30% and typically in a range of 10% to 50%). A therapeutically effective amount of the present compositions can be readily ascertained by one skilled in the art using publicly available materials and procedures.
The invention provides for administering PEG:PAL conjugates less frequently than native PAL. The dosing frequency will vary depending upon the condition being treated, but in general will be about one time per week. It is understood that the dosing frequencies actually used may vary somewhat from the frequencies disclosed herein due to variations in responses by different individuals to the PEG:PAL conjugates; the term “about” is intended to reflect such variations.
The present invention may thus be used to reduce serum L-phenylalanine levels. Most commonly, serum L-phenylalanine levels are increased due to hyperphenylalaninemia. Among the conditions treatable by the present invention include hyperphenylalaninemia associated with phenylketonuria. Also treatable are conditions that may lead to increased serum L-tyrosine levels such as found in tyrosinemia. In addition, numerous cancer-related conditions, where depletion of serum L-phenylalanine and/or serum L-tyrosine levels would be beneficial, may also be treated with the PEG:PAL conjugates of the invention.
PEG:PAL conjugates prepared in accordance with the present invention are preferably administered by injection intraperitoneally, subcutaneously, or intramuscularly. However, it would be clear to one skilled in the art that other routes of delivery could also be effectively utilized using the compositions of the present invention.
The methods described herein use pharmaceutical compositions comprising the molecules described above, together with one or more pharmaceutically acceptable excipients or vehicles, and optionally other therapeutic and/or prophylactic ingredients. Such excipients include liquids such as water, saline, glycerol, polyethyleneglycol, hyaluronic acid, ethanol, cyclodextrins, modified cyclodextrins (i.e., sulfobutyl ether cyclodextrins) etc. Suitable excipients for non-liquid formulations are also known to those of skill in the art.
Pharmaceutically acceptable salts can be used in the compositions of the present invention and include, for example, mineral acid salts such as hydrochlorides, hydrobromides, phosphates, sulfates, and the like; and the salts of organic acids such as acetates, propionates, malonates, benzoates, and the like. A thorough discussion of pharmaceutically acceptable excipients and salts is available in Remington's Pharmaceutical Sciences, 18th Edition (Easton, Pa.: Mack Publishing Company, 1990).
Additionally, auxiliary substances, such as wetting or emulsifying agents, biological buffering substances, surfactants, and the like, may be present in such vehicles. A biological buffer can be virtually any solution which is pharmacologically acceptable and which provides the formulation with the desired pH, i.e., a pH in the physiologically acceptable range. Examples of buffer solutions include saline, phosphate buffered saline, Tris buffered saline, Hank's buffered saline, and the like.
Depending on the intended mode of administration, the pharmaceutical compositions may be in the form of solid, semi-solid or liquid dosage forms, such as, for example, tablets, suppositories, pills, capsules, powders, liquids, suspensions, creams, ointments, lotions or the like, preferably in unit dosage form suitable for single administration of a precise dosage. The compositions will include an effective amount of the selected drug in combination with a pharmaceutically acceptable carrier and, in addition, may include other pharmaceutical agents, adjuvants, diluents, buffers, etc.
In general, compounds of this invention will be administered as pharmaceutical formulations including those suitable for oral (including buccal and sub-lingual), rectal, nasal, topical, pulmonary, vaginal or parenteral (including intramuscular, intraarterial, intrathecal, subcutaneous and intravenous) administration or in a form suitable for administration by inhalation or insufflation. The preferred manner of administration is intravenous using a convenient daily dosage regimen, which can be adjusted according to the degree of affliction.
For solid compositions, conventional nontoxic solid carriers include, for example, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharin, talc, cellulose, glucose, sucrose, magnesium carbonate, and the like. Liquid pharmaceutically administrable compositions can, for example, be prepared by dissolving, dispersing, etc., an active compound as described herein and optional pharmaceutical adjuvants in an excipient, such as, for example, water, saline, aqueous dextrose, glycerol, ethanol, and the like, to thereby form a solution or suspension. If desired, the pharmaceutical composition to be administered may also contain minor amounts of nontoxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents, tonicifying agents, and the like, for example, sodium acetate, sorbitan monolaurate, triethanolamine sodium acetate, triethanolamine oleate, etc. Actual methods of preparing such dosage forms are known, or will be apparent, to those skilled in this art; for example, see Remington's Pharmaceutical Sciences, referenced above.
For oral administration, the composition will generally take the form of a tablet, capsule, a softgel capsule or may be an aqueous or nonaqueous solution, suspension or syrup. Tablets and capsules are preferred oral administration forms. Tablets and capsules for oral use will generally include one or more commonly used carriers such as lactose and corn starch. Lubricating agents, such as magnesium stearate, are also typically added. When liquid suspensions are used, the active agent may be combined with emulsifying and suspending agents. If desired, flavoring, coloring and/or sweetening agents may be added as well. Other optional components for incorporation into an oral formulation herein include, but are not limited to, preservatives, suspending agents, thickening agents, and the like.
Parenteral formulations can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solubilization or suspension in liquid prior to injection, or as emulsions. Preferably, sterile injectable suspensions are formulated according to techniques known in the art using suitable carriers, dispersing or wetting agents and suspending agents. The sterile injectable formulation may also be a sterile injectable solution or a suspension in a nontoxic parenterally acceptable diluent or solvent. Among the acceptable vehicles and solvents that may be employed are water, Ringer's solution and isotonic sodium chloride solution. In addition, sterile, fixed oils, fatty esters or polyols are conventionally employed as solvents or suspending media. In addition, parenteral administration may involve the use of a slow release or sustained release system such that a constant level of dosage is maintained.
The PEG:PAL compounds identified described above can be administered to a patient at therapeutically effective doses to treat or ameliorate cardiovascular disease. The toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, such as, for example, by determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50/ED50. Compounds exhibiting large therapeutic indices are normally preferred.
The data obtained from the cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage preferably lies within a range of circulating concentrations that include the ED50 with little or minimal toxicity. The dosage can vary within this range depending upon the dosage form employed and the route of administration utilized. The therapeutically effective dose can be determined from cell culture assays, and from animal models.
Dietary Protein
In addition to administering PAL and related analogs to HPA/PKU patients, it is contemplated that the dietary protein of the patients also may be restricted or modified. Those of skill in the art are aware of various commercially available protein formulas for use in the treatment of PKU. Such formulas include MAXIMAID, PHENEX 1, PHENEX 2 (Ross Laboratories, Liverpool, UK), LOFENALAC, PHENYL-FREE (Mead-Johnson), and the like.
Those of skill in the art may use the referenced protein formulas, which are generally free of Phe concentrations. The protein formulas often are supplemented with amino acids that are deficient in PKU patients. Such amino acids include, for example, L-tyrosine, and L-glutamine. It has been suggested that it may be desirable to supplement the diet of PKU patients with valine, isoleucine and leucine (see U.S. Pat. No. 4,252,822). In certain clinical manifestations, the toxic effects of PKU are caused by Phe blocking the brain uptake of other amino acids such as tyrosine and tryptophan. It has been found that supplementing the diet of a PKU patient with excess of such large neutral amino acids blocks Phe uptake into the brain and lowers brain Phe levels. Thus, it is contemplated that for the methods of the present invention, the dietary regimen may further be supplemented with compositions that comprise one or more of these amino acids (Koch et al., Mol. Genet. Metabol. 79: 110-113 (2003)).
Further, as it is known that L-carnitine and taurine, which are normally found in human milk and other foodstuffs of animal origin, also should be supplied in addition to the protein restriction. In certain embodiments, the L-carnitine may be supplied as 20 mg/100 g of protein supplement, and the taurine may be supplied as 40 mg/100 g protein supplement in order to help supply amounts of these factors normally found in human milk and foods of animal origin.
In addition, those of skill in the art are referred to the 2000 National Academy of Sciences-National Research Council Dietary Reference Intakes for a further listing of other components, such as essential vitamins and minerals that should be supplied to the patient to ensure that other supplements are being provided despite the dietary protein restriction.
Referring to the discussion above regarding total protein amounts and desirable plasma Phe concentrations, one of skill in the art will be able to determine the amount of dietary protein restriction that is required and thus adjust the diet of the patient accordingly. Taking for example, a male of about 11-14 years of age, that individual should preferably receive 45 g protein/day. In the event that the individual is one that has severe classic PKU, his unrestricted plasma Phe concentration will likely be greater than 1200 μM, and most, if not all of the dietary protein source for that individual is likely to be from a powdered protein supplement, which preferably lowers his plasma Phe concentrations to less than 600 μM. By administering PAL to that subject, a therapeutic outcome would be one which produces greater decrease in the plasma Phe concentrations of patient or alternatively, the therapeutic outcome is one in which the individual's plasma Phe concentrations is lowered to a similar degree, but that individual is able to tolerate protein from a normal diet rather than from a dietary formula.
Similarly, a male of about 11-14 years of age, is one who has moderate PKU, it may be possible using the methods of the present invention to give him the allotted 45 g protein/day through a normal protein intake rather than a restricted formula. Determining whether the methods of the invention are effective will entail determining the plasma Phe concentrations of the patient on a regular basis to ensure that the plasma Phe concentrations remain below at least 400 μM. Tests for determining such concentrations are described below. Preferably, concentrations of less than or about 360 μM are achieved.
3. Identifying and Monitoring Patient Populations
As discussed herein throughout, it will be necessary in various embodiments of the present invention to determine whether a given patient is responsive to PAL therapy, and to determine the phenylalanine concentrations of the patient both initially to identify the class of PKU patient being treated and during an ongoing therapeutic regimen to monitor the efficacy of the regimen. Exemplary such methods are described herein below.
BH4 Loading Test
The BH4 loading test allows discrimination between patients that have HPA due to a deficit in BH4 or through a deficiency in PAH.
The simplest BH4 loading test is one in which exogenous BH4 is administered and the effects of the administration on lowering of plasma Phe concentrations is determined. Intravenous loading of 2 mg/kg BH4 was initially proposed by Danks et al., (Lancet 1:1236, 1976), as BH4 of greater purity has become available it has become possible to perform the test using an oral administration of BH4 in amounts of about 2.5 mg/kg body weight. Ultimately, a standardized approach was proposed by Niederwieser et al. in which a 7.5 mg/kg single oral dose of BH4 is administered (Eur. J. Pediatr. 138: 441 (1982)), although some laboratories do still use upwards of 20 mg BH4/kg body weight.
In order for the simple BH4 loading test to produce reliable results, the blood Phe levels of the patient need to be higher than 400 μM. Therefore, it is often customary for the patient to be removed from the PKU diet for 2 days prior to performing the loading test. A BH4 test kit is available and distributed by Dr. Schircks Laboratories (Jona, Switzerland). This kit recommends a dosage of 20 mg BH4/kg body weight about 30 minutes after intake of a normal meal.
Determination of Phe Concentrations
There are numerous methods for determining the presence of Phe in blood (Shaw et al., Analytical Methods in Phenylketonuria-Clinical Biochemistry, In Bickett et al. Eds. Phenylketonuria and Some Other Inborn Errors of Amino Acid Metabolism, Stuttgart, Georg Thiem Verlag, 47-56 (1971)). Typically, phenylalanine and tyrosine concentrations are determined from the serum of a patient using a fluorometric assay. This assay relies on the formation of fluorescent substance when phenylalanine is heated with ninhydrin in the presence of leucylalanine (McCaman et al., J. Lab. Clin. Med. 59: 885-890 (1962)).
The most popular method for determining Phe concentrations is the Guthrie test in which discs are punctured from filter paper that has been saturated with a blood sample from the patient. The uniform discs are incubated in a tray of agar that has been seeded with Bacillus subtilis and contains a specific inhibitor of Bacillus subtilis growth. As the phenylalanine transfers from the uniform discs onto the agar, the Phe reverse the inhibition of growth thereby yielding an area of growth that can be correlated to phenylalanine concentration by comparison to similar assays performed using discs containing known amounts of Phe.
Other methods of quantifying Phe concentration include HPLC, mass spectrometry, thin layer chromatography and the like. Such methods can be used to determine the plasma Phe concentration of a patient before the therapy and to monitor the Phe concentration during the therapeutic regimen to determine the efficacy thereof.
It is contemplated that the plasma Phe levels of the patients will be monitored at convenient intervals (e.g., daily, every other day or weekly) throughout the time course of the therapeutic regimen. By monitoring the plasma Phe levels with such regularity, the clinician will be able to assess the efficacy of the treatment and adjust the PAL and/or dietary protein requirements accordingly.
Combination Therapy
Certain methods of the invention involve the combined use of PAL and dietary protein restriction to effect a therapeutic outcome in patients with various forms of HPA. To achieve the appropriate therapeutic outcome in the combination therapies contemplated herein, one would generally administer to the subject the PAL composition and the dietary restriction in a combined amount effective to produce the desired therapeutic outcome (i.e., a lowering of plasma Phe concentration and/or the ability to tolerate greater amounts of Phe/protein intake without producing a concomitant increase in plasma Phe concentrations). This process may involve administering the PAL composition and the dietary protein therapeutic composition at the same time. This may be achieved by administering a single composition or pharmacological protein formulation that includes all of the dietary protein requirements and also includes the PAL within said protein formulation. Alternatively, the dietary protein (supplement or normal protein meal) is taken at about the same time as a pharmacological formulation (tablet, injection or drink) of PAL. PAL also may be formulated into a protein bar or other foodstuff such as brownies, pancakes, cake, suitable for ingestion.
In other alternatives, PAL treatment may precede or follow the dietary protein therapy by intervals ranging from minutes to hours. In embodiments where the protein and the PAL compositions are administered separately, one would generally ensure that a significant period of time did not expire between the time of each delivery, such that PAL will still be able to exert an advantageously effect on the patient. In such instances, it is contemplated that one would administer the PAL within about 2-6 hours (before or after) of the dietary protein intake, with a delay time of only about 1 hour being most preferred. In certain embodiments, it is contemplated that PAL therapy will be a continuous therapy where a daily dose of PAL is administered to the patient indefinitely. In other situations, e.g., in pregnant women having only the milder forms of PKU and HPA, it may be that PAL therapy is only continued for as long as the woman is pregnant and/or breast feeding.
Further, in addition to therapies based solely on the delivery of PAL and dietary protein regulation, the methods of the present invention also contemplate combination therapy with a third composition that specifically targets one or more of the symptoms of HPA. For example, it is known that the deficit in tyrosine caused by HPA results in a deficiency in neurotransmitters dopamine and serotonin. Thus, in the context of the present invention, it is contemplated that PAL and dietary protein based methods could be further combined with administration of L-dopa, carbidopa and 5-hydroxytryptophan neurotransmitters to correct the defects that result from decreased amounts of tyrosine in the diet.
As the administration of phenylase would not generate tyrosine (unlike administration of PAH), such treatment will still result in tyrosine being an essential amino acid for such patients. Therefore dietary supplementation with tyrosine may be desirable for patients receiving phenylase in combination with the BH4 therapy.
I. Production of PAL
Another aspect of the invention is a method of producing PAL. In a preferred embodiment, recombinant PAL is over-expressed as an N-terminal octahistidyl-tagged fusion protein in a vector preferably E coli BL21(DE3)/pLysS (Invitrogen) with an inducible promoter such as with IPTG (isopropyl-beta-D-thiogalactopyranoside). Seed culture for a bioreactor/fermenter can be grown from a glycerol stock in shake flasks. Such seed culture can then be used to spike into a controlled bioreactor in fed-batch mode. Glucose can be supplemented and pH is controlled with base (NH4OH) and agitation is up to 1200 rpm. O2 feed keeps dissolved oxygen to greater than 20%. The cells can be grown at a temperature of 30° C. until reaching and OD600 of 70-100 (˜22-25 hrs) and then induced with 0.4 mM IPTG. The temperature can be reduced to 22 to 26° C. and grown until activity change is <0.1 IU/ml (approximately 40-48 hrs and an OD600 typically of 200). Cell culture media is typically defined and composed of yeast extract protein, peptone-tryptone, glucose, glycerol, casamino acids, trace salts and phosphate buffering salts. The recombinant PAL product is produced intra-cellularly and not secreted. The bacteria can be harvested by continuous centrifugation (Alfa-Laval, Carr, Ceba, or equivalent).
J. Purification of PAL
A further aspect of the present invention features a method to purify PAL or a biologically active fragment, mutant or analog thereof. According to a first embodiment, a transformed cell mass can be grown and ruptured leaving crude recombinant enzyme. Exogenous materials can optionally be separated from the crude bulk to prevent fouling of the columns. Chromatographic purification can be conducted using one or several chromatographic resins. Subsequently, the purified protein can be formulated into a buffer designed to provide stable activity over an extended period of time. In another preferred embodiment, the method to purify the PAL comprises: (a) Lysis of the bacteria containing recombinant PAL using a pressure homogenizer (but potentially by other physical means such as glass bead lysis); (b) Heat treatment (c) Clarification of this lysate using a second continuous centrifugation step and/or depth filtration (as with Cuono Zeta Plus or Maximizer, Pall Filtron, or Millipore Millistak or Opticao filters) (d) passage through a charcoal filtration step (as with Millipore Millistak 40AC); (e) passage through a final filtration step (as with a Sartorious Sartopore 0.2 μm filter); (f) Passage over a butyl hydrophobic interaction chromatography (as in Toyopearl Butyl 650M from Tosoh Biosciences); (g) passage over a Q ion exchange column (as in a Macroprep High Q from BioRad); (h) recovery of final product by buffer exchange with tangential flow filtration (as with a Sartorious Hydrosart or PES 100 kDa membrane). Those skilled in the art readily appreciate that one or more of the chromatography steps may be omitted or substituted, or that the order of the chromatography steps may be changed within the scope of the present invention. Finally, appropriate sterilizing steps may be performed as desired.
Having now generally described the invention, the same may be more readily understood through the following reference to the following examples. The examples are offered for illustrative purposes only, and are not intended to limit the scope of the present invention in any way. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.), but some experimental error and deviation should, of course, be allowed for.
PAL Protein Expression and Purification
Both a full-length R. toruloides PAL DNA clone (pIBX-PAL (Sarkissian, et al., 1999 ibid.), wt-PAL amino acid sequence (shown in
His-tagged PAL was expressed in BL21(DE3) E. coli cells (Novagen) grown in LB medium with 30 μg/ml kanamycin at 37° C. with induction using 1 mM IPTG at an OD600 of 0.8. The temperature was reduced to 23° C. and expression proceeds for 3 hours. Cells were spun down and frozen at −80° C. Cell pellets were resuspended in 100 mM Tris, 90 mM NaCl pH 7.8 with inclusion of an EDTA-free protease inhibitor tablet (Roche Diagnostics GmbH). Solutions were then sonicated for 3 minutes, followed by a centrifugation step at 45,000 rpm for 25 minutes. Lysates were then filtered through a 0.22 μm membrane. Clarified lysate was loaded onto a 7 mL POROS MC 20 column charged with Ni+2. Equilibration/wash buffer contained 25 mM Tris, 100 mM NaCl, 20 mM imidazole, pH 7.8. Elution buffer was the same equilibration/wash buffer but with 500 mM imidazole added. A linear gradient from 0 to 500 mM imidazole was run over the column (20 column volume gradient) and the His-PAL protein begins to elute at approx. 70 mM imidazole. Fractions containing PAL were pooled and ammonium sulfate was added to a concentration of 0.6 M, with stirring at 4° C. for 30 minutes until dissolved, followed by a centrifugation step at 45,000 rpm for 30 minutes and filtering through a 0.22 μm membrane. The protein solution was then run over a 7 mL POROS HP column equilibrated with 25 mM Tris, 0.6 M ammonium sulfate, pH 7.8. PAL does not bind to the column and was collected in the flow through. The PAL fraction was collected and concentrated to 7.5 mg/ml using an Orbital Biosciences Apollo 20-30 kDa molecular weight cut off spin concentrator, with a buffer exchange step to 25 mM Tris, pH 7.8, 90 mM NaCl. Crystallization follows the selenomethionine PAL procedure outlined below. Enzyme purity was determined by SDS-PAGE and enzyme activity was determined using OD290 measurements. Purified PAL samples were tested for in vitro stability and activity.
Alternatively, selenomethionine-expressed PAL was used, since direct MAD (Hendrickson, et al., EMBO J, 9(5), pp. 1665-1672 (1990)) and/or SAD (Brodersen, et al., Acta Crystallogr. D Biol Crystallogr., 56(Pt 4), pp. 431-441 (2000)) crystallographic solutions are possible. For selenomethionine expression, the pIBX-PAL construct was transformed into the E coli methionine-auxotroph B834(DE3) (Novagen), and the cells were grown at 37° C. in minimal medium containing 30 μg/ml kanamycin and 0.76 mM selenomethionine. Cultures were induced at 24° C. for 3 hours by adding 1 mM IPTG when the OD600 reaches 0.6-0.8. Cells were harvested by centrifugation and the cell pellets were frozen at −80° C.
Purification for protein crystallization trials was carried out at 4° C. under helium. Cells from a 9 L culture were lysed in 100 mM Tris, pH 7.8, 10 mM NaCl, 1 mM MgCl2, 0.01% β-mercaptoethanol, EDTA-free protease inhibitor cocktail (Roche Diagnostics GmbH) under vacuum. Solutions were then sonicated for 3 minutes, followed by a centrifugation step at 45,000 rpm for 30 minutes. Lysates were then filtered through a 0.22 μm membrane. The protein solution was then run over a 7 mL POROS HQ column equilibrated with 25 mM Tris, 0.01% β-mercaptoethanol, pH 7.8. PAL was eluted using 25 mM Tris, 1 M NaCl, 0.01% β-mercaptoethanol, pH 7.8 with a linear gradient. The PAL fraction was identified using the activity assay on the elution fractions, and the active samples were collected and ammonium sulfate is added to a concentration of 1.7 M, with stirring at 4° C. for 30 minutes under vacuum, followed by a centrifugation step at 45,000 rpm for 30 minutes and filtering through a 0.22 μm membrane. The protein solution was then run over a 7 mL POROS HP column equilibrated with 25 mM Tris, 1.7 M ammonium sulfate, pH 7.8. Elution used 25 mM Tris, pH 7.8 buffer, with a 20 column volume gradient. The fraction that was active was collected, which is at around 0.8 M ammonium sulfate. The active PAL fraction was then concentrated along with a buffer exchange step to 25 mM Tris, pH 7.8. A DEAE column was then run, using 25 mM Tris, pH 7.8 running buffer and 25 mM Tris, 500 mM NaCl elution buffer using a 20 column volume gradient; the active fraction was collected (the first peak), concentrated, and buffer was exchanged to run a final HQ column (25 mM Tris, pH 7.8 load buffer, 25 mM Tris, 500 mM NaCl, pH 7.8 elution buffer using a 20 column volume gradient) with fractions containing active PAL collected. Active PAL was then concentrated using an Orbital Biosciences Apollo 20-30 kDa molecular weight cut off spin concentrator to 7.5 mg/ml, with buffer exchange to 25 mM Tris pH 7.8, 90 mM NaCl.
Protein Structure Determination of PAL
Active PAL expressed without the His-tag (pIBX-PAL) was produced at 1 mg/L culture yield. Selenomethionine-expressed PAL at a concentration of 5-10 mg/mL, preferably 7.5 mg/mL, in 25 mM Tris pH 7.8, 90 mM NaCl was used in sitting drop crystallization trials at 4° C. Wild type crystals of PAL diffract to 1.6 Å and were obtained using 11-16% MPEG 5K, 80-100 mM MES, pH 6.5. Flash freezing uses a 15% MPD cryoprotectant soak.
For initial evaluation of crystals and cryopreservation strategies, data was collected on an in-house rotating anode FR-D (Rigaku) with R-axis 4 detector and cryo-freezing equipment. Crystals found to exhibit a combination of low mosaicity, reasonable lifetimes, and good diffraction will be transported to a synchrotron radiation source for final data collection. The native PAL processed data was solved by SAD using SHELXD (Sheldrick, et al., Meth Enzymol, 277, pp. 319-343 (1997)) to locate the positions of 52 of the 60 the selenium atoms. The phase was calculated using SHELX and was improved with solvent flattening using DM (Cowtan, Joint CCP4 and ESF-EACBM Newsletter on Protein Crystallography, 31, pp. 34-38 (1994)). The main chain was traced by ARP/wARP (Perrakis, et al., Acta Crystallogr. D Biol. Crystallogr., 57(Pt 10), pp. 1445-1450 (2001)) and the side chains traced using guiSIDE. Model building was carried out with the program 0 (Jones, et al., Acta Crystallogr., A47, pp. 110-119 (1991)). Refinement used the program REFMAC (Murshudov, et al., Acta Cryst., D53, pp. 240-255 (1997)).
The output of crystal structure coordinates, shown in Appendix A, includes residues (e.g. 103-123 and 350-353) that contain high B-values and are very dynamic.
Structural Features of PAL
Using X-ray crystallography, the structure of Rhodosporidium toruloides PAL has been determined (
Each monomer of PAL consists mainly of alpha-helices and is subdividable into four domains—a central catalytic domain, N-terminal domain, and small C-terminal domain with similarity to the histidine ammonia-lyase structure (Schwede, et al., (1999) ibid.) plus an additional domain inserted in the C-terminal region that protrudes from the ends of the intact tetramer molecule, forming an elongated structure with approximate dimensions of 11 {acute over (Å)}×47 {acute over (Å)}×44 {acute over (Å)} (
Domain 1 (D1) includes residues 1-273, which consists of 11 α-helices of various lengths and 7 short β-strands. D1 overlaps well with the N-terminal region of HAL and is the most conserved sequence with HAL (
Domain 2 (D2) is the central domain of both the monomer and tetramer of PAL, contains residues 274-540 and is comprised of almost all α-helical segments. The core of D2 is made up of six nearly parallel α-helices, whose length range varies from 15-38 residues. In the PAL tetramer, the six-helix bundles assemble to form a central core of 24 nearly parallel α-helices. The six α-helical bundles of D2 are connected to each other by loops that range from 10-30 residues in length, which may make this region of the structure very flexible.
Domain 3 (D3) is the major structurally distinct domain between PAL and HAL and is an extra domain in the PAL structure relative to HAL. D3 includes residues 541-655 and consists of a four α-helix bundle. The four α-helices are nearly parallel to each other with only about a 30 degree deviation from co-planarity. One of the α-helices in D3 (residues 541-549) and one α-helix in D2 (residues 505-540) together form a 44 residue long α-helix. D3 has no similar structural architectures when doing a rigid search using DALI (947 Holm, et al., J. Mol. Biol., 233, pp. 123-138 (1993)), however, D3 can be aligned well (with an r.m.s.d. of 1.99 {acute over (Å)}) with the end of the C-terminal region of HAL (residues 453-509) with one twist when doing flexible alignment using the program FATCAT (944 Ye, Y., Bioinformatics, 19(Suppl 2), pp. ii246-ii255 (2003)). D3 is not located in the central interface among the four PAL monomers, but instead is sticking out from the main region of the tetramer with a head-to-head packing arrangement with its D3 tetramer-related counterpart (monomers A-D or monomers B-C).
Domain 4 (D4) is the smallest domain in PAL (residues 656-716), containing a three α-helix bundle and a 20 residue long loop. D4 has a similar arrangement with the end of the C-terminal structure of HAL (residues 453-509). Domain D4 in PAL is located at the periphery of the bundle of 24 α-helices, but is still situated in the main region of the tetramer. Our truncation experiments showed that D4 is important for activity.
The following table summarizes the X-ray crystallography data set of PAL that was used to determine the structure of PAL according to this invention (Table 3).
The three-dimensional structure of residues 114-607 of human HAL (
The active site of PAL was identified based on the combined information from the comparison to the HAL structure, sequence alignments, mechanistic studies and site-directed mutagenesis. PAL has the same active site MIO prosthetic group as HAL that is formed by residues Ala211, Ser212, and Gly213. We define residues in the R. toruloides PAL active site that are within 5 Å of the MIO. The PAL active site consists of residues from three different monomers in a PAL tetramer, including residues from monomer A (A138, A208-A218, A266, A270-A272, A274-A275, A395-A396, A411-A415, A496, A499-A500, and A502-A505), residues from monomer B (B360, B363, B366-B367, and B370-B371), and residues from monomer C(C472). All residues in the R. toruloides PAL active site are from domains D1 and D2. The flexible loop region A106-A124 acts as a cover to the entrance of the active site. Most residues that have been proposed and characterized structurally and biochemically in the HAL active site are found in the PAL active site: Ala211 vs. Ala142, Ser212 vs. Ser143, Gly213 vs. Gly144, Asp214 vs. Asp145, Tyr363 vs. Tyr280, Phe413 vs. Phe329, Arg366 vs. Arg283, Asn270 vs. Asn195, Gly271 vs. Gly196, Leu214 vs. Leu146, Phe116 vs. Phe59, 360 vs. Gln277, the only two different residues between PAL and HAL active site are Gln499 vs. Glu414 and Gln138 vs. His83.
Consistent with the assignment of the active site region, numerous mutations made in these regions are not tolerated (R102K, Q104K, S108K, Y110H, Y110A, Y110L, T114K, R123H, R123A, R123Q, T124P, T124K, and Q131K), however, other mutations of the residues present in active site regions produce similar activity, if not improved activity, variants of PAL (R91K, H137K, R91K+H137K). Pegylation or other chemical derivatization of such variants would lead to PAL conjugates with improved qualities, such as improved immunoprotection and/or improved proteolytic resistance.
Surrounding the PAL active site are five flexible loops: loop 197-218, loop 101-124, loop 392-415 and loop 486-505 from monomer A, as well as loop 360-363 from monomer B. Mutagenesis studies have shown that a number of mutants of Y110 abolish activity, indicating that residue Tyr110 in this loop is important for PAL activity. Our proteolysis study combined with protein sequencing of the cleavage products showed that the most accessible cleavage sites in PAL for trypsin and chymotrypsin are Tyr110 and Arg123 respectively, both are in the 101-124 loop, thus provides further evidence for the flexibility and importance of this loop. Similar to PAL from other species, R. toruloides PAL can be protected from protease inactivation by incubating it with a competitive inhibitor such as tyrosine. Mutants of PAL designed to ‘lock down’ this flexible portion of the active site can lead to variants with less protease susceptibility, especially in light of the observation that flexible loop regions are common sites of protease cleavage (U.S. Pat. No. 6,261,550). In addition, mutation of sites in the proximity of Tyr110 and Arg123 (e.g. Asp95, Lys96, Glu99, Arg102, Thr124, Glu125, Asp126, Glu403, Asn404, Lys405, Val259, Pro262, Val186, Arg359, Val349, Lys350, Val351, Lys352, Gly685, Lys686) to Lys, Cys, or other residues capable of being chemically derivatized can also generate PAL variants with protease resistance.
The program GETAREA 1.1, available on the internet (http://www.scsb.utmb.edu/getarea/area_form.html), was used to determine solvent accessible residues (In/Out ratio designation “o”), residues inside the structure (In/Out ratio designation “i”), and residues partially surface-exposed (In/Out ratio designation missing) based on the PAL crystal structure atomic coordinates (Table 4). With information of this type, residues can be selected for mutation based on their surface accessibility.
In the event that significant changes occur to the 3-dimensional structure (e.g. large truncations) and molecular replacement cannot be used, direct MAD (Hendrickson, W. A., et al., (1990) ibid.) and/or SAD (Brodersen, D. E., et al., (2000) ibid.) phasing using selenomethionine-containing PAL was used. For structures that do not change significantly, such as substrate and/or inhibitor-complexed wild-type PAL as well as PAL mutants, these structures were determined using molecular replacement.
With the high-resolution three-dimensional PAL protein crystal structure, molecular engineering methods were applied to improve the catalytic efficiency, stability, immuno-resistance, and protease resistance to increase the in vivo effectiveness of PAL. With the 1.6 Å resolution structure disclosed above, one of skill in the art can determine the regions of the structure that are the most flexible (to remove and generate a more compact and stable form of PAL), the residues located near the active site (to mutate in order to enhance activity and/or minimize the size of the protein), and the surface locations close to immunogenic (e.g. linear or conformational epitopes identified in mapping studies) and/or proteolytic sensitive sites (from protease mapping studies), thereby allowing for the introduction of site-specific mutants for direct disruption of problem sites or, alternatively, for surface pegylation or other chemical derivatization to protect sensitive sites present in PAL from immunoreaction and/or proteolysis.
Mutagenesis of PAL
The general rationale for mutant generation is based upon four general methods of design. Firstly, truncations, insertions, and point mutations including surface veneering to obstruct or otherwise remove protease and/or immunogenicity sites is used. Secondly, chimeras, including loop re-engineering, loop swapping to graft HAL sequences into the PAL sequence can be used to produce improved PAL variants. Thirdly, point mutants are made to introduce sites for site-specific derivatization. Finally, directed evolution can be used to improve the activity of any mutants made using methods 1-3.
Truncation and Other Mutant Production
Site-directed mutagenesis was performed using the QuikChange kit (Stratagene, U.S. Pat. Nos. 5,789,166 and 6,391,548) and truncations were made with PCR using the appropriate primers designed to generate truncated PAL sequences. Loop spliced mutants were constructed in a two-step PCR process to splice in the appropriate (truncated) loop sequence into the wild-type PAL sequence. All mutations were confirmed with DNA sequencing.
Loop-directed engineering were used for PAL molecular architecture improvement, with surface loops in the PAL structure selected for incorporation of point mutagenesis or alternatively, incorporation of saturation site mutagenesis, along with the possible inclusion of directed evolution methods to fully improve the PAL molecular framework for therapeutic advantage.
Based on the overall 3-D structure of PAL and the mapping results of protease-sensitive sites and major epitope immunogenic sites in PAL, specific point mutants of His-tagged PAL were constructed to remove these sites of protease/immunogenic sensitivity followed by selection for activity, or, alternatively, point mutants were made to introduce specific amino acid residues in these PAL loop regions for site-specific pegylation derivatization (Hershfield, et al., (1991) ibid.; Bhadra, et al., (2002) ibid., Vasserot, et al., (2003) ibid., Sato, Adv. Drug Deliv. Rev., 54(4), pp. 487-504 (2002)).
Single point mutations in the trypsin (Arg123) and chymotrypsin (Tyr110) primary recognition sites that were identified by protein sequence were made: mutations in the trypsin site were Arg123His, Arg123Ala and Arg123Gln, and in the chymotrypsin site Tyr110His, Tyr110Ala and Tyr110Leu. The mutant T124P was made to test if the trypsin target site, Arg123, was protected from proteolysis when the recognition sequence for this protease was modified. All mutants had decreased activity relative to wt-PAL, however, reduced proteolytic susceptibility was evident in numerous samples (reduced proteolysis as determined by SDS-PAGE analysis of PAL variant protease digestions).
Single point mutations in several residues were made to introduce additional lysine sites in the protein that can be pegylated: R91K, R102K, Q104K, S108K, T114K, T124K, Q131K, and H137K (
Additional site-directed mutants of PAL can be constructed to introduce Lys residues in the vicinity of proteolytic and/or immunogenic regions to provide regions for PEG derivatization that will prevent PAL proteolytic and/or immunogenic sensitivity.
The following primers are used for PAL mutagenesis.
Additional mutations based on the computational predicted PAL epitopes using the program Peptide Companion (predictions determined by Bionexus) were made in the R91K mutant form of the protein. The positive mutations (catalytically active and improved immune resistance) were introduced into wt-PAL and R91K-PAL constructs for further expression, activity, pegylation, immunogenicity, protease susceptibility and in vivo studies.
Single point mutations made included:
In the epitope 226-243: H237S, H237Q, H237G, E238Q
In the epitope 337-356: R340K, K352R, E337Q, E346Q, E347Q
In the epitope 396-413: E403Q
In the epitope 569-589: R570K, E575Q, E586Q, D571S
In the epitope 619-630: E631Q
In addition, deletion of residues in PAL epitopes included:
del—61-84, del—237-238, del—348-356, del—396-410, and del—541-655
The following primers are used for R91K-PAL variant mutagenesis.
Mutagenesis Epitopes PAL
Deletions PAL Epitopes
In another method, site saturation mutagenesis is applied to specific loop sequences to mutate these regions of the PAL sequence to remove any unfavorable features found on the PAL surface (Miyazaki, et al., J. Mol. Evol., 49(6), pp. 716-720 (1999); Palzkill, et al., Proteins, 14(1), pp. 29-44 (1992)). Finally, if rational engineering proves difficult to generate an improved PAL mutant, the directed evolution methods of DNA shuffling (Crameri, et al., (1998) ibid.) and molecular breeding (Minshull, et al., (1999) ibid.) can be used on PAL in combination with HAL and/or mutants of PAL to optimize the PAL protein architecture. Directed evolution techniques have been used to improve kinetic and other biophysical features of enzymes, and can be used to alter the pH activity profile for PAL, using alternative pH values for the mutant selection process. In addition, for rationally-designed PAL clones that produce enzymatically poor PAL mutants (such as the R123H, R123A, and R123Q PAL mutants with protease resistance but minimal activity), these mutants can be used as starting points for directed evolution enzymatic activity improvement (as exemplified in (Vasserot, et al., (2003) ibid.)).
Protease mapping studies on native PAL have indicated primary sites of proteolytic sensitivity. These sites cab be removed for the development of an effective oral PKU enzyme substitute. In the first cycle of improvement of the PAL architecture, smaller sized PAL proteins were constructed and screened for retention of activity (using a simple absorbance assay for activity measurement), and in the second cycle of improvement, protein engineering was used to screen for mutants with reduced proteolytic sensitivity. Once the size of the PAL protein is minimized, protease susceptible sites were removed from the PAL framework using a combination of rational and directed evolution methods. The first avenue of modification used site-specific pegylation to mask and remove proteolytically sensitive sites from the surface of PAL. Mutations were made in PAL surface residues at or near the protease sensitive sites (primary sites Tyr110 and Arg123) to add Lys or Cys sites, or to mutate to other residues to abolish such sites. For rationally designed PAL mutants that are inactive, protein engineering using directed evolution with selection in phenylalanine auxotrophic E. coli strains for active mutant proteins was used to produce active mutant forms of PAL, e.g. for further pegylation derivatization.
All directed evolution mutagenesis methods used initial growth and selection in defined minimal media with transformation into an E. coli mutant deficient in PAL activity to identify enzymatically-active mutants. Mutation used mutant PAL clones that display minimal activity (e.g. Y110A, Y101L, or S108K) such that positive selection for new mutants with activity will be the first clone identification step. Either strain JP2250, an E. coli strain that requires tyrosine for growth (Baldwin, et al., Biochem. Biophys., 211(1), pp. 66-75 (1981)), or strain AT2471 (tyrA) which is a mutant auxotrophic for tyrosine (Zhao, et al., Proc. Natl. Acad. Sci. U.S.A., 91(4), pp. 1366-1370 (1994)), were used for positive selection of functional His-tagged PAL clones by inducing and plating transformed cells on M9 minimal media lacking tyrosine and phenylalanine.
Alternatively, the phenylalanine auxotroph studied by Simmonds, et al., were utilized (Simmonds, et al., J. Bacteriol., 83, pp. 256-263 (1962)). Since R. toruloides PAL reacts in a reversible fashion with both L-Phe and tyrosine as substrates, active PAL mutants are selected by growing the transformed and IPTG induced E. coli cells in the presence of the products of the PAL reaction (trans-cinnamic acid, trans-coumaric acid, and ammonium chloride) to select for mutant PALs displaying reverse PAL reaction reactivity. Alternatively, the phenylalanine auxotroph [cited in Gu, et al., Microb Comp Genomics 2(2): 141-158 (1997)] is used for selection.
Analysis of promising clones made with PAL mutagenesis experimentation involved the characterization of purified clones (including Vmax and Km determinations, binding constants of substrates, proteolytic stability, in vitro immunogenicity, pH dependence of activity, temperature-dependence of activity), using the optical absorbance kinetic measurement method for PAL, as well as sequencing to determine the sites of mutation that are present in mutant candidates. Promising PAL clones that pass the activity, immunogenicity, and protease susceptibility requirements are subjected to testing in the murine PKU model system, possibly after pegylation derivatization, dependent on the engineering scheme under consideration. Additionally, mapping of these favorable sites of mutation onto the PAL 3-D structure allows the mechanisms involved with the improved stability to be determined. After initial rounds of directed evolution, the results indicate whether ‘hotspots’ and/or other structure-based functional correlations exist. Further rounds of directed evolution can incorporate site-saturation mutagenesis of functionally important ‘hotspots’ to improve in vivo enzymatic efficiency further.
Mutants obtained by directed evolution are studied using pegylation. If pegylation of mutant PAL proteins does not occur under normal pegylation conditions (varied pH, pegylation reaction time, molar ratio PEG:protein, varying the molecular weights of the PEGs (Hershfield, et al., 1991 ibid.)), further site-directed mutagenesis of surface residues into lysine or cysteine residues is employed to introduce further pegylation sites into the positive clones from the directed evolution experiments.
Activity Assay for PAL variants
Initial selection for active PAL variants uses the optical density activity measurement, the same as native or pegylated PAL samples.
The vector pIBEX-PAL was used to express PAL in E. coli with no tags, and protein was purified using literature method (Sarkissian et al. Proc. Natl. Acad. Sci. USA (1999)) with the following modifications. After homogenization, the PAL lysate was heated at 55° C. for two hours followed by centrifugation. Activated charcoal was added to the filtrated liquid fraction and rocked overnight. The clarified lysate was loaded onto a hydrophobic interaction chromatography resin (Toyopearl Butyl 650M; Tosoh Biosciences, San Diego, Calif.) once the solution was adjusted by adding 1 M Tris, pH 7.8 and ammonium sulfate salt. The product was eluted using a buffer having 25 mM Tris, 120 mM ammonium sulfate, pH 7.8. The PAL eluate solution was diluted with 25 mM Tris, pH 7.8, to a conductivity of 5 mS and loaded onto a Macro Prep High Q column (BioRad, Hercules, Calif.); the product was eluted with a step gradient of 90 mM NaCl. PAL activity measurements were performed using standard reaction conditions with a Cary 50 UV spectrophotometer in the kinetics mode.
PEG:PAL conjugates were produced by coupling either linear 5 kDa or 20 kDa methoxy-PEG-SPA (Nektar Therapeutics) or 10 kDa or 40 kDa branched methoxy-(PEG)2-NHS (Nektar Therapeutics) to PAL. A number of pegylation conditions were initially tested for each PEG reactant, using an established reaction protocol (Hershfield, et al., Proc. Natl. Acad. Sci., USA, 88 (1991), pp. 7185-7189). Reaction conditions were optimized for PAL protein with regards to different buffers, different temperatures for a given reaction, various molar ratios of PAL to PEG, different pH values, and reaction times.
The concentration of PAL in the reaction mixture was 1 mg/ml in 50 mM potassium phosphate buffer, pH 8.5. The amount of PEG to add was calculated based on the number of lysines present in PAL (29), the number of subunits in PAL (4), and the molar ratio excess of PEG chosen (n), as described by:
grams mPEG-SPA or m(PEG)2-NHS=(moles PAL)(# PAL subunits)(# lysines/subunit)(MW mPEG-SPA)(n-fold increase of mPEG-SPA or m(PEG)2-NHS to PAL)
The molar excess of PEG used was 1-32 fold (Table 6).
After the appropriate amounts of PEG and PAL were mixed together, pegylation reactions were incubated, while rocking, at 25° C. for 5 hours up to overnight and then stopped by placing the reactions at 4° C. or −20° C. The degree of modification was controlled by varying the PEG concentration, temperature and time of reaction. Prior to sample characterization, and in order to remove the unreacted excess of PEG, all samples were extensively dialyzed. After the protein modification reaction was completed and in order to remove excess of unreacted PEG, the samples were dialyzed against 1×DPBS, pH 7.4 buffer overnight at 4° C. with stirring using Tube-O-Dialyzer (GenoTechnology). Once protein concentration was determined using the NI protein assay kit (Geno Technology), PAL activity measurements were performed on underivatized and PEG derivatized PAL samples using standard reaction conditions measuring the trans-cinnamic acid production at Abs 290 nm at RT.
This example demonstrates the effects on activity of the degree of substitution and variations of the polymer size and conformation for PEG:PAL conjugates. Using both methoxy-PEG-SPA and methoxy-(PEG)-NHS, a variety of PEG:PAL conjugates were synthesized from 5 kDa or 20 kDa or a combination of 5 kDa+20 kDa linear polymers as well as 10 kDa or 40 kDa branched polymers. Samples of PEG:PAL were characterized with SDS-PAGE and MALDI-TOF-MS analysis for analysis of the extent of derivatization. The resultant preparations ranged in size from about 80 kDa to about 200 kDa, as estimated by SDS-PAGE (
Pegylated PAL samples were analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using 4-10% Bis-Tris gels and 4% and 4-12% Tris-Glycine native gels (NuPage gels from Invitrogen) (
The number of PEG molecules attached to each pegylated PAL conjugate was quantitatively determined using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) using 0.5 M urea or 0.025 M guanidine-HCl to improve subunit dissociation. As shown in Table 8, a number of different pegylated species are formed with PAL. All the lysine residues present in PAL (29 total) are surface exposed and presumably available for derivatization. As published previously, MALDI-TOF MS provides an accurate technique to characterize the number of PEGs that are attached to protein-derivatized species (Lee, et al., Pharm. Res., 1999, 16(6), pp. 813-818; Lee, et al., Pharm. Res., 2003, 20(5), pp. 818-825; Diwan, et al., Int. J. Pharm., 2003, 252(1-2), pp. 111-122; Na, et al., Rapid Commun. Mass Spectrom. 2003, 17, pp. 2241-2244). The relative number of PEG units present in each PAL derivative species can be directly determined from the MALDI-TOF MS spectra; MALDI ionization disrupts the PAL oligomeric associations along with the use of agents such as urea or guanidine-HCl, which help to release the respective PAL subunits from their oligomeric conformation.
In the case of the linear 20 KDa PALPEG molecules, due to the high MW of them, it was not possible to determine the state of the modified protein by either native gel or MALDI-TOF analysis due to the limitation of resolution for high MW molecules with this particular technique. The MALDI-TOF results of the branched 10 KDa series showed that 1 and 2 PEG molecules were attached per PAL monomer for the ratio 1:16 and 1, 2 and 3 for the 1:24 specie.
Western blot analysis was used to characterize in vitro the degree of PAL sample's immunological reactivity for the branched PEG samples using Native gels. The results showed a slight immune protection by the branched PEG compared to the native protein which also correlates with the in vivo results described below. The linear PEG 20 KDa was unable to be tested by this technique due to the high MW of the sample but in other samples using the same type of PEG, the ratio 1:8 of the linear 20 KDa PEG conferred a complete immune protection when it was tested by Immunoprecipitation.
One of the aims in developing an enzyme substitute to use for PKU or tyrosinemia therapy is to have the PEG derivatized form(s) of the enzyme retain catalytic activity. As listed in Table 8, activity measurements on pegylated PAL samples indicated that this was indeed the case, with only very highly pegylated samples losing a small degree of catalytic activity. In most cases of enzyme pegylation, decreases in catalytic activity are realized (Harris, et al., Nat. Rev. Drug Discov. 2(3): 214-221 (2003)), however, a similar improvement in activity has been observed upon pegylation of the enzyme phenylalanine hydroxylase (Gamez, et al., Mol. Ther., 9(1): 124-129 (2004)). Surprisingly, all of these pegylated forms of PAL retained, and in some instances possessed increased catalytic activity versus their non-pegylated forms (Table 7).
Abbreviations:
nt, not tested;
n/a, not applicable (samples unable to run on Native gel)
+: binding;
−: non binding;
+/−: partial binding
aNumber of PEG molecules attached to each PAL monomer using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) using 0.5 M urea or 0.4 M guanidine-HCl to improve subunit dissociation and detection reproducibility.
bTo estimate the number of PEGs attached per monomer of PAL of high molecular weight pegylated species, we used reducing and native 4-12% Bis-Tris gels which were run in MES (2-(N morpholino) ethane sulfonic acid) buffer using MultiMark and HWM native marker in reducing conditions (Amersham Bioscience, Piscataway, NJ).
cWestern blot samples were run on native gels and transferred to nitrocellulose membranes. Anti-serum from PAL treated mice was the positive control, antibody and serum from buffer-treated mice was the negative control. Alkaline phosphatase-conjugated goat anti-mouse IgG (Promega, Madison, WI) was the secondary antibody
dELISA assays of samples, 2-8 μg/mL in pH 8.5 Tris-HCl buffer, were done under standard conditions and scored: positive (+), when the positive control incubation with anti-PAL antibody gave a higher value than the incubation with the negative control serum; negative (−), when there were equivalent absorbance values with either serum
eImmunoprecipitation was performed in TTBS buffer (0.1% Tween in Tris buffered saline); PAL activity was measured before adding the antibody sample. Each sample was incubated with an 8-fold excess of anti-PAL serum and a duplicate negative control reaction using non-immune mouse serum. After incubation, protein G Sepharose 4 (50%,
Pegylated PAL samples were analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using 10% Bis-Tris gels in MOPS (3-(N-morpholino) propane sulfonic acid) buffer. To detect unreacted and potentially immunogenic PAL protein after pegylation, size exclusion chromatography was run using an HPLC (Vision, Applied Biosystems, Foster City, Calif.) on a Superdex 200HR 10/30 column (Amersham Biosciences) equilibrated with 1× Dulbecco's PBS, pH 7.4 (Cellgro) at a flow rate of 0.4 mL/min. In vitro characterization of the linear 20 kDa PEG-PAL series formulations tested in vivo is provided in Table 8.
aProtein concentration was determined using the PAL extinction coefficient (0.5 mg mL−1cm−1) at 280 nm for non-modified protein samples. For polyethylene glycol (PEG) modified (pegylated) PAL, the concentration was calculated using a BSA standard curve and the NI Protein Assay (GenoTechnology, St. Louis, MO).
bOne unit of PAL is defined as that amount of enzyme that produces 1 μmol of trans-cinnamic acid per minute at room temperature.
In this example, different PEG:PAL conjugates with varying degrees of pegylation were evaluated in Enu2/Enu2 mice (PKU model genotype (Sarkissian, et al., Proc Natl Acad Sci USA, 96(5), pp. 2339-2344 (1999); McDonald, et al., Mol. Genet. Metab., 76(4), pp. 256-261 (2002); Sarkissian, et al., Mol. Genet. Metab., 69, pp. 188-194 (2000)) to compare and contrast their L-phenylalanine reduction potential and duration as well as antibody titers (immunogenicity measurement). The three series of compounds tested were: linear 5 kDa PEG:PAL, branched 10 kDa PEG:PAL, and linear 20 kDa PEG:PAL conjugate. Each PEG:PAL conjugate was tested as a single bolus, subcutaneous dose at a dosage of 1 unit. Unmodified PAL was used at a dosage of 1 unit in a single, bolus injection. Injections were performed at days 1, 8, and 22. The in vivo assay results are depicted in
Each PEG:PAL conjugate from the linear and branched polymer series showed significant and comparable prolongation of the L-phenylalanine reduction effect (see
These data demonstrate the unexpected advantage of an increase in L-phenylalanine reduction activity half-life for the PEG:PAL conjugates relative to PAL alone, in that the results demonstrate a clear increase in the magnitude and duration of the response to the PEG:PAL conjugates. In some cases, the linear 5 kDa PEG:PAL conjugate appears to modestly outperform the branched 10 kDa PEG:PAL conjugate, which modestly outperforms the linear 20 kDa PEG:PAL conjugate. Based on an immunogenicity criterion, the 20 kDa PEG:PAL conjugate might be a preferred configuration.
Protein Pegylation
The pegylation of the PAL variants was performed using modifications of literature methods (Hershfield, et al., (1991) ibid.; 304 U.S. Pat. No. 6,057,292; 558 Lu, et al., Biochemistry, 40(44), pp. 13288-13301 (2001); Nektar Therapeutics, 2003 catalog). Activated PEGs included both the linear PEG succinimidyl succinates (mPEG-SPA, MW 5 kDa or MW 20 kDa) and the branched PEG hydrosuccinimides (mPEG2-NHS ester, MW 10 kDa or MW 40 kDa), which are both capped on one end with a methoxy group and available from Nektar Therapeutics; experimental determination of optimal pegylated proteins is normally required (Veronese, et al., Journal of Bioactive and Compatible Polymers, 12: 196-207 (1997)). Optimal pegylation conditions were determined using different ratios of PAL:PEG (taking into account the molar ratio of protein along with the number of lysines per protein monomer), different pHs, different buffers, various temperatures and incubation times. High PAL protein:PEG derivatization ratios are necessary since native PAL has a large number of lysines (29 per monomer) and because unmodified PAL displays immunoreactivity upon repeated injection in mice and since naked (wild-type) PAL is quickly inactivated upon exposure to proteases. Pegylation reactions were stopped by freezing at −20° C., and the samples were analyzed by SDS-PAGE, MALDI-TOF mass spectroscopy, activity assessment, proteolytic sensitivity, and immunoreactivity.
Prior to activity, proteolysis, and immune assessment, and in order to remove excess unreacted PEG, reactions were dialyzed against pH 8.5, 0.05 M potassium phosphate buffer overnight at 4° C. with stirring using Tube-O-Dialyzers (GenoTechnology). After protein concentration was determined using the NI protein assay kit (Geno Technology), PAL activity measurements were performed on underivatized and PEG derivatized PAL samples using standard reaction conditions, as previously described. Following in vitro characterization, in vivo trials were conducted with the most promising pegylated therapeutic candidates using the PKU mouse model.
Characterization
Protein concentration was determined using the PAL extinction coefficient (0.5 mg mL−1 cm−1) at 280 nm for non-modified protein samples and for pegylated protein samples the concentration is calculated using the NI Protein Assay (GenoTechnology) that includes sample processing to remove non-protein contaminants that might interfere with accurate protein concentration determination.
PEG-PAL products were characterized with MALDI-TOF MS to determine the number of PEG molecules attached to each PAL monomer, as well as characterized using activity assessment and SDS-PAGE and native gel analysis, to assure retention of activity, complete derivatization, and no loss of tetrameric PAL formation, respectively. For PAL and PEG-PAL samples, MALDI-TOF mass spectroscopic analysis requires the use of 0.5 M urea or 0.025 M guanidine-HCl to improve subunit dissociation and the reproducibility of species detection.
Activity
PAL activity assay were conducted using a Cary UV spectrophotometer (Cary 50) in the kinetics mode. The activity of PAL with L-phenylalanine substrate was assayed at room temperature (25° C.) by measuring the production of trans-cinnamate monitored by the absorbance increase at 290 nm (Hodgins, D. S., ‘The presence of a carbonyl group at the active site of L-phenylalanine ammonia-lyase”, Biochem. Biophys. Res. Commun., 32, pp. 246-253 (1968)). The molar extinction coefficient of trans-cinnamic acid at 290 nm is 10.2381 liter M−1 cm−1. Reaction mixtures contained 22.5 mM phenylalanine in 100 mM Tris-HCl buffer, pH 8.5. For standard measurements, the final enzyme concentration was 0.0035 mg/mL, but for kinetic studies the enzyme concentration in the assay was adjusted so that the slope at 290 nm per min is in the range of 0.005 to 0.02. Activity data is expressed as specific activity (μmol×min−1 mg−1). One unit of PAL is defined as that amount of enzyme that produces 1 μmol of trans-cinnamic acid per minute at room temperature.
Test of In Vivo Half-Life and Immunogenicity
After biochemical characterization, the most promising PEG-PAL candidates were screened for immunoreactivity against antibodies raised by PKU mice injected with native PAL (non-pegylated) using three different and complimentary techniques (Western blot, ELISA, and immunoprecipitation (IP)).
For Western blot analysis, PAL anti-serum (from mice injected with native PAL) was used in a dilution 1:10,000. As a negative control the serum from buffer treated-mice was also used in the same dilution. The secondary antibody, alkaline phosphatase-conjugated goat anti-mouse IgG (Promega), was diluted to 1:5,000 and color was developed using the AP substrate Western Blue (Promega). The ELISA test was performed using Nunc/Immuno Maxisorp plates (Nalge Nunc International) following standard procedures using 1 mg/mL of PAL in PBS and blocking with PBS, 0.05% Tween-20, 2% BSA. The mouse antisera (from native PAL exposed mice) was diluted 1:10,000 in EB block solution (PBS, 0.05% Tween-20, 2% BSA), and a HRP-goat anti-mouse IgG was used as secondary antibody with TMB used for detection at 450 nm.
Immunoprecipitation was used to test for PAL antibody binding. Protein samples (PAL or pegylated PAL) were incubated in TTBS buffer (Tris buffered saline with 0.1% Tween) and PAL activity was measured before adding the antibody sample. Each sample was incubated with 8-fold excess of positive control anti-PAL serum and a duplicate negative control reaction using non-immune mouse serum. After incubation, protein G Sepharose 4 (50%, v/v) was added in excess, taking into account the mouse IgG binding capacity of the beads, and the samples were incubated again at 4° C. overnight with rotation.
Supernatants were recovered by centrifugation and the PAL activity of each sample was assayed on the supernatants. The bead pellets were not discarded, so that further analysis by Western blot can be performed. To confirm that antibody-bead binding had occurred, Western blot was used to detect the PAL antigen on the beads. Beads that have been recovered by centrifugation after the PAL binding step were washed several times with TTBS and TBS buffers. Following these rinses, SDS-PAGE loading buffer was added to the beads and the samples were heated at 95° C. for 5 minutes. Samples were then analyzed by Western blot using PAL anti-serum. Enzyme variants showing poor antibody binding have corresponding little PAL in the pelleted bead fractions as detected by Western blot and show higher activities remaining in the supernatant as compared to native unmodified PAL which displays high antibody binding.
Promising PAL variants based upon in vitro experimentation include pegylated samples using 1:32 linear 5 kDa PEG, 1:32 branched 10 kDa PEG, 1:8 linear 20 kDa PEG, and 1:16 linear 20 kDa PEG.
Test of Protease Sensitivity
Improved PAL (and PEG-PAL) mutants obtained via protein engineering methods described above that retain activity, screening for protease resistance using incubation with a trypsin/chymotrypsin protease cocktail, followed by monitoring for retention of activity (via OD290 measurement) and reduced protein cleavage (via PAGE gel analysis) allowed for the identification of mutants with appropriate in vitro properties for use in in vivo testing.
Proteolytic stability was assessed using incubation with a protease cocktail that approximates the intestinal environment and contains 2.3 mM trypsin, 3.5 mM chymotrypsin, 3.05 mM carboxypeptidase A, and 3.65 mM carboxypeptidase B. Proteolysis testing involved enzymatic incubations, adding proteases to the PAL solutions to determine the degree of protease sensitivity for the different protein variants being examined (native or mutant protein with or without pegylation or other chemical modification), including time courses of activity retention and stability retention after protease exposure. SDS-PAGE and MALDI-TOF mass spectrometric mapping experiments were used to determine the location of any protease sensitive sites (Kriwacki, et al., (http://abrf.org/JBT/1998/September98/sep98m_r.html) (19980). These mapping results are important to determine primary sites of protease susceptibility (such as the two primary sites already identified), so that all major sensitivity sites can be removed using pegylation protection and/or mutation to remove and/or protect susceptible regions from the PAL architecture.
The various formulations of branched and linear PEG-rPAL and naked rPAL, in 10 mM Na-phosphate, 150 mM NaCl, pH 7.4 and the control buffer, 10 mM Na-phosphate, 150 mM NaCl, pH 7.4, were formulated for injection as shown in Table 10.
Plasma Phe Determination
Animals were bled via the tail vein (approximately 100 μL blood) to collect plasma for Phe determination at 0 hr, 60, 360 and 720 minutes, 24, 48 and 72 hours post dose on days 1, 8 and 22. Plasma was isolated from the blood sample, frozen and transferred on dry ice till analysis (determination of Phe concentration). The data is shown in
Anti-PEG-rPAL/rPAL Antibodies Analysis
Animals were bled via the tail vein (approximately 100 μL blood) to collect serum for PEG-rPAL/rPAL antibody determination at −1 day pre-dose on study days 7, 21 and 36. Collection took place prior to dose administration on applicable days.
The immune in vivo effect of these preparations is shown in
The combined effect of reduced Phe levels along with the lower anti-PAL antibody production that this preparation of PALPEG produces makes the linear PEG 20 KDa the most promising formulation to be used for PKU enzyme replacement therapy using the ratio 1:8 PAL:PEG.
A series of PEG-rPAL derivatives were constructed to determine the effect of varying the proportion of PEG to rPAL on reducing plasma Phe and attenuating the immune response against rPAL. Conjugates consisting of linear 20 kDa PEG and rPAL, at ratios (rPAL:PEG) of: 1:4, 1:8 and 1:16 were formulated in 10 mM Na-phosphate, 150 mM NaCl buffer (pH 7.4). The formulations were injected subcutaneously into ENU-2 mice. Unconjugated rPAL and buffer alone were used as controls (see Table 11).
Plasma Phe Determination
Animals were bled via the tail vein (approximately 100 μL blood) to collect plasma for Phe determination at 0 hr, 60, 360 and 720 minutes, 24, 48 and 72 hours post dose on days 1, 8 and 22. Plasma was isolated from the blood sample, frozen and transferred on dry ice until analysis (determination of Phe concentration). These data, as depicted in
Anti-PEG-rPAL/rPAL Antibodies Analysis
Animals were bled via the tail vein (approximately 100 μL blood) to collect serum for anti-rPAL antibody determination at −1 day pre-dose on study days 7, 21 and 43. Serum collection took place prior to dose administration on applicable days. Conjugation of PEG to rPAL at all ratios tested reduced the anti-rPAL serum antibody titres. The capacity of these derivatives to reduce the immune response against rPAL tended to increase with greater amounts of conjugated PEG (
To determine the effect of increasing the dose of the 1:8 rPAL:PEG conjugate on reducing plasma Phe and attenuating the immune response against rPAL, 1:8 PEG-rPAL was delivered subcutaneously to ENU-2 mice at 3 different doses-0.2, 0.6, 1.25 IU. Each dose, in addition to a native rPAL treatment, was formulated in 10 mM Na-phosphate, 150 mM NaCl buffer (pH 7.4). Buffer alone was also injected as a negative control (see Table 12).
Plasma Phe Determination
Animals were bled via the tail vein (approximately 100 μL blood) to collect plasma for Phe determination at 0 hr, 60, 360 and 720 minutes, 24, 48 and 72 hours post-dose on days 1, 8 and 22. Plasma was isolated, frozen and transferred to dry ice until analysis (determination of Phe concentration). These data, as depicted in
Anti-PEG-rPAL/rPAL Antibodies Analysis
Animals were bled via the tail vein (approximately 100 μL blood) to collect serum for anti-rPAL antibody determination at −1 day pre-dose on study days 7, 21 and 43. Collection took place prior to dose administration on applicable days. Conjugation of PEG to rPAL at all doses tested reduced the anti-rPAL serum antibody titres approximately 10-fold relative to those of native rPAL. There was no significant difference in antibody titre between the 3 doses of conjugated rPAL (
The major binding sites recognized by antibody anti-PAL was determined by scanning an antigen peptide library (peptide scan format 13/11) of PAL (SwissProt-ID:PALY_RHOTO; 716 amino acid residues, resulting in 353 peptides). All of the cysteine residues contained in the synthesized antigen peptides were substituted by serine and all N-termini were acetylated.
Materials and Methods
The materials consisted of primary antibody anti-PAL (format mouse IgG1, 10 μg/mL) and secondary antibody anti-mouse IgG (Sigma A5906, 1.0 μg/mL) labeled with horseradish peroxidase.
Antigen peptides were synthesized on a cellulose membrane in a stepwise manner resulting in a defined arrangement (peptide array) and are covalently bound to the cellulose membrane. Binding assays were performed directly on the peptide array. The peptide array was incubated with a primary (antigen peptide binding) antibody in blocking buffer and then incubated with horseradish peroxidase (HRP)-labeled secondary antibody, which selectively binds the primary antibody. The antigen peptide array was incubated with a blocking buffer for several hours to reduce non-specific binding of the antibody. Alternatively, an HRP-labeled primary antibody in blocking buffer can be used. A short T(Tween-TBS-buffer washing directly after incubation of the antigen peptide array with the secondary antibody or the HRP-labeled primary antibody followed by the first chemiluminescence experiment was made to obtain an initial overview of which antigen peptides do bind the primary antibody. Several buffer washing steps follow (T-TBS- and TBS-buffer) to reduce false-positive binding (unspecific antibody binding to the cellulose membrane itself). After these washing steps the final chemiluminescence analysis is performed. The data were analyzed with an imaging system showing the signal intensity (Boehringer Light units, BLU) as single measurement for each peptide. In order to evaluate non-specific binding of secondary antibodies, incubations have to be performed in the absence of the primary antibody as control incubation. In this case, the secondary antibody showed no binding in the control experiment.
Results
The antibody anti-PAL recognized three major binding sites: peptides nos. 73-74 corresponding to amino acid residues 147-157, peptide nos. 153-154 corresponding to amino acid residues 307-317, and peptide nos. 295-299 corresponding to amino acid residues 597-601 (See
In summary, the antibody recognized three immunodominant regions with major peptide nos. 74, 307 and 296.
The overall immunogenic potential of PAL was assessed and regions (15 to 25 amino acids in length) containing the sequence of PAL with significant potential immunogenicity were identified.
Materials and Methods
Materials included the complete amino acid sequence of PAL (P11544, BIOMARIN™) and EpiMatrix™ System (EpiVax).
The complete amino acid sequence of PAL was parsed into 9-mer analysis frames where each frame overlapped the last 8 amino acids. Each 9-mer frame was evaluated for potential immunogenicity relative to a panel of eight, DRB1*0401 common class II HLA including DRB1*0101, DRB1*0301, DRB1*0401, DRB1*0801, DRB*1*101, DRB1*1301, and DRB1*1501. Each of the analysis frames were blasted against the protein database at Genbank and a report listing of all significant homologies were produced. Each of the analysis frames were blasted against the EpiVax proprietary database of known epitopes and MHC ligands and a report listing of all significant homologies identified was produced. Based on the results of the analysis, the overall immunogenic potential of PAL and regions (15 to 20 amino acids in length) contained within the sequence of PAL with a significant potential for immunogenicity were evaluated.
Results:
The PAL protein is not inherently immunogenic but contains some regions of higher immunogenic potential that could be modified so as to reduce large potential immunogenicity of the protein to the same level as other, safe, non-immunogenic proteins such as albumin, or the constant domain of immunoglobulin.
Overall Immunogenicity Evaluation
Upon analysis of the 708 9-mer frames within the 716 amino acid long sequence against a panel of 8 common Class II alleles, there were 303 potential epitopes identified representing about 5% of the sample. When taking into account the number of potential epitopes and length of the PAL p[protein, the overall immunogenicity score was average. However, when assessing the risk of immunogenicity, it is important to consider not only the overall potential but also regional potential. Potential T cell epitopes are not randomly distributed throughout protein sequences but instead tend to clump together and are referred to as “T cell epitope clusters” or just “cluster”. Clusters range from 9 to 25 amino acids in length and considering their affinity to multiple alleles and across multiple frames, can contain from 4 to 40 binding motifs. Thus a protein with an overall average immunogenicity potential may have enhanced immunogenicity due to one or more clustered regions.
When the PAL protein was scanned for clusters of potential T cell epitopes, nine clusters with significant potential for immunogenicity containing 118 or 39% of the 303 potential epitopes. Another eight clusters less significant potential for immunogenicity contained 51 potential epitopes or 17 percent of the total. The 17 clusters would be considered targets for deimmunizing PAL. Within the 17 target regions, a detailed analysis was conducted highlighting the individual amino acids making the highest aggregate contribution to binding affinity when considering multiple alleles and multiple frames. Such sensitive amino acids would be considered the target of modification when deimmunizing the protein.
When the 9-mer frames contained in the PAL protein were screened against a database of known MHC legends and T cell epitopes, no significant homologies were found. Peptide sequences that are homologous to human sequences may run an increased risk of breaking immune tolerance resulting in unwanted autoimmune reactions. Thus, the 9-mer frames contained in the clustered regions identified in the PAL sequence were blasted against the human sequence protein database in Genbank. There were only a few significant homologies identified.
There were three examples where a 9-mer frame of the PAL protein was an eight of nine match to the human peptide and also was a potential epitope. Frame 109 with peptide VYGITTGFG matched eight of nine to human peptide VYGVTTGFG and was a “hit” on alleles DRB1101 and DRB1*1501. Frame 611 with peptide VLSSTSLSL was an eight of nine match to human peptide VLSSTSLRL and was a “hit” on alleles DRB1*0701 and DRB1*1501. Frame 654 with peptide ALSYLSPRT was an eight of nine match to human peptide ALSYLKPRT and was a “hit” on allele DRB1*1501. No perfect matches were identified. The limited homology found between the sequence of the PAL protein and the human genome does not represent a significant deterrent to the further development of the PAL protein as a human therapeutic agent.
Based on the average amount of predicted immunogenicity for the PAL protein of its size but significant number of high scoring clusters, the protein will be tested in mice before advancing to the clinic If PAL elicits T-cell activity and antibody formation in transgenic mice, the protein will be deimmunized prior to entry into the clinic.
The current PEGylation process for the production of PEG-PAL involves a reaction between 20 kDa linear PEG SPA (PEG-propanoic acid-NHS) at 1.5 mg/ml enzyme concentration and an amount of PEG equal to the molar lysine concentration times a ratio (called the Z-factor). For a Z-factor of 1:8, the final PEG concentration would be 93.5 mg/ml while the enzyme concentration is 1.5 mg/ml. For a Z-factor of 1:16, the final concentration of PEG would be 187 mg/ml while the enzyme concentration remains 1.5 mg/ml enzyme.
The relatively high Z-factors of 1:8 and 1:16 have not been considered economically viable. In addition, the Z-factor of 1:8 using 20 kDa linear PEG SPA (PEG-propanoic acid-NHS) has not conferred sufficient protection to the PEG-PAL molecule against the immune response observed in mice. In fact, by the third injection of PEG-PAL, antibody specific to PEG-PAL titers are greater than 104 compared to controls. An improved PEGylation protocol was considered essential both to improve the economic viability of the final drug substance and to improve its efficacy.
The reasoning for the PEGylation process improvement is as follows. The half-life of 20 kDa linear PEG SPA (PEG-propanoic acid-NHS) in aqueous solution is relatively short, approximately 20 minutes. This loss of activity is essentially an unproductive, competing hydrolysis reaction. Both the hydrolysis and the useful PEGylation reaction are likely proportional to reagent concentrations as typical bimolecular reactions:
(1) PEG-NHS+H2O→PEG (un-reactive, “wasted”), reaction rate=k1[PEG-NHS][H2O]
(2) PEG-NHS+PAL lysines→PEG-PAL, reaction rate=k2[PEG-NHS][lysine]
To reduce the proportion of reaction material wasted in reaction (1) an increase in the concentration of the components in reaction (2), in particular the protein (lysines) is desired. Therefore, the Z-factor should be altered by increasing the protein concentration while keeping the PEG-NHS at a constant (high) level.
Procedure
The final PEG concentration was set at 8 mM (160 mg/ml) because higher concentrations were excessively viscous and difficult to handle and dissolve. Therefore, for a 1:3 Z-factor, the final lysine concentration was 2.67 mM, which gave a protein concentration of 6.85 mg/ml for a PAL molecule with 30 lysines/monomer. The PEGylation procedure was as follows:
1) The protein (PAL) was concentrated to 50-70 mg/ml and buffer-exchanged to 50 mM potassium phosphate, pH 8.5.
2) The amount of dry PEG needed was dissolved in 50 mM potassium phosphate, pH 8.5 and vortexed to dissolve. This step was done rapidly.
3) The protein solution was mixed immediately with the PEG solution to make the final concentrations of PEG and PAL and gently inverted several times.
4) The material was left with very gentle rocking at room temperature for 3 hours.
5) The PEG-PAL was ready to be formulated.
Results
The new PEGylation procedure was used to make PEG-PAL with a Z-factor of 1:3 and was tested in an in vivo mouse model for immunogenicity. The PAL used was the un-mutated wild-type form. Table 13 shows PEGylation results:
The mouse study indicated that the new PEGylation method resulted in a PEG-PAL that was much less immunogenic than that of the original PEGylation method.
A follow-up study was performed using the new PEGylation procedure at lower Z-factors and using the alternate PEG supplier (20 kDa linear ME-200HS (PEG-hexanoic acid-NHS). The characterization results are shown in Table 14. Note that the new PEGylation protocol is referred to as “HC” (High Concentration). The form of PAL used was the R91K mutant.
For the 1:1 “HC” material the PEG concentration was 8 mM (160 mg/ml) and the molar lysine concentration was 8 mM (20.5 mg/ml PAL). For the 1:2 “HC” material the PEG concentration was 8 mM and the molar lysine concentration was 4 mM (10.3 mg/ml PAL). The 1:3 material was made as described in the prior experiment.
SDS PAGE results of the above materials are shown in
Table 15 shows the recoveries from the PEGylation procedures.
The following example provides guidance on the parameters to be used for the clinical evaluation of compositions comprising PAL or biologically active variants, mutants, and fragments thereof (“PAL”) in the therapeutic methods of the present invention. As discussed herein throughout, PAL will be used in the treatment of HPA including HPA, mild phenylketonuria (PKU) and classic PKU. Clinical trials will be conducted which will provide an assessment of oral or subcutaneous doses of PAL for safety, pharmacokinetics, and initial response of both surrogate and defined clinical endpoints. The trial will be conducted for a minimum, but not necessarily limited to, 24 weeks to collect sufficient safety information for 100 evaluable patients. The initial dose for the trials will vary from about 0.001 to about 1.0 mg/kg/week. In the event that this dose does not produce a reduction in excess plasma phenylalanine (Phe) levels in a patient, or produce a significant direct clinical benefit measured as an ability to increase daily oral Phe intake without increases in plasma Phe levels, the dose should be increased as necessary, and maintained for an additional minimal period of, but necessarily limited to, 24 weeks to establish safety and to evaluate further efficacy.
Measurements of safety will include adverse events, allergic reactions, complete clinical chemistry panel (kidney and liver function), urinalysis, and CBC with differential. In addition, other parameters including the reduction in levels of blood Phe levels, neuropsychological and cognitive testing, and global assessments also will be monitored. The present example also contemplates the determination of pharmacokinetic parameters of the drug in the circulation, and general distribution and half-life of PAL in blood. It is anticipated that these measures will help relate dose to clinical response.
Methods
Patients who have elevated levels of plasma Phe will undergo a baseline a medical history and physical exam, neuropsychological and cognitive testing, a standard set of clinical laboratory tests (CBC, Panel 20, CH50, UA), levels of urinary pterins, dihydropteridine reductase (DHPR) levels, and a fasting blood (plasma) panel of serum amino acids. The patient will be followed closely with weekly visits to the clinic. Patients will return to the clinic for a complete evaluation one week after completing the treatment period. Should dose escalation be required, the patients will follow the same schedule outlined above. Safety will be monitored throughout the trial.
Diagnosis and Inclusion/Exclusion Criteria
The patient can be male or female, with a documented diagnosis of HPA or mild PKU confirmed by genetic testing and evidence of elevated Phe levels in blood. The study will include HPA or PKU patients who do not accurately follow dietary control. Female patients of childbearing potential must have a negative pregnancy test (urine β-hCG) just prior to each dosing and must be advised to use a medically accepted method of contraception throughout the study. A patient will be excluded from this study if the patient is pregnant or lactating; has received an investigational drug within 30 days prior to study enrollment; or has a medical condition, serious intercurrent illness, or other extenuating circumstance that may significantly decrease study compliance.
Dietary Intervention
Following the initial randomization and two-week treatment period, all study participants will undergo dietary counseling and will follow a standard Phe-restricted diet complemented with Phe-specific medical foods for a total of four to six weeks. Diets will be managed at home and dietary intake will be recorded in daily logs. Analyses of the intakes of nutrients and medical foods and the percent of Recommended Dietary Intakes (RDI) will be compared among the treatment groups.
PAL Safety
PAL therapy will be determined to be safe if no significant acute or chronic drug reactions occur during the course of the study. The longer-term administration of the drug will be determined to be safe if no significant abnormalities are observed in the clinical examinations, clinical labs, or other appropriate studies.
All printed patents and publications referred to in this application are hereby incorporated herein in their entirety by this reference.
While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Patent Application Nos. 60/610,770 filed on Sep. 17, 2004 and 60/651,950 filed on Feb. 9, 2005, all of which are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60610770 | Sep 2004 | US | |
| 60651950 | Feb 2005 | US |
