Modified ciliary neurotrophic factors

Abstract

Modified ciliary neurotrophic factors and methods for their production and therapeutic use. Also described is a method of screening for novel therapeutic proteins by determining altered electrophoretic binding properties.

Description

BACKGROUND OF THE INVENTION

[0002] The present invention relates to therapeutic CNTF-related polypeptides useful for the treatment of neurological or other diseases or disorders.

[0003] Ciliary neurotrophic factor (CNTF) is a protein that is required for the survival of embryonic chick ciliary ganglion neurons in vitro (Manthorpe et al., 1980, J. Neurochem. 34:69-75). The ciliary ganglion is anatomically located within the orbital cavity, lying between the lateral rectus and the sheath of the optic nerve; it receives parasympathetic nerve fibers from the oculomotor nerve which innervates the ciliary muscle and sphincter pupillae.

[0004] Over the past decade, a number of biological effects have been ascribed to CNTF in addition to its ability to support the survival of ciliary ganglion neurons. CNTF is believed to induce the differentiation of bipotential glial progenitor cells in the perinatal rat optic nerve and brain (Hughes et al., 1988, Nature 335:70-73). Furthermore, it has been observed to promote the survival of embryonic chick dorsal root ganglion sensory neurons (Skaper and Varon, 1986, Brain Res. 389:39-46). In addition, CNTF supports the survival and differentiation of motor neurons, hippocampal neurons and presympathetic spinal cord neurons [Sendtner, et al., 1990, Nature 345: 440-441; Ip, et al. 1991, J. Neurosci. 11:3124-3134; Blottner, et al. 1989, Neurosci. Lett. 105:316-320].

[0005] Recently, CNTF has been cloned and synthesized in bacterial expression systems, as described by Masiakowski, et al., 1991, J. Neurosci. 57:1003-1012 and in International Publication No. WO 91/04316, published on Apr. 4, 1991, which are incorporated by reference in their entirety herein.

[0006] The receptor for CNTF (termed “CNTFRa”) has been cloned, sequenced and expressed [see Davis, et al. (1991) Science 253:59-63]. CNTF and the haemopoetic factor known as leukemia inhibitory factor (LIF) act on neuronal cells via a shared signaling pathway that involves the IL-6 signal transducing component gp130 as well as a second, b-component (know as LIFR b); accordingly, the CNTF/CNTF receptor complex can initiate signal transduction in LIF responsive cells, or other cells which carry the gp130 and LIFRb components [Ip, et al. (1992) Cell 69:1121-1132].

[0007] In addition to human CNTF, the corresponding rat (Stöckli et al., 1989, Nature 342:920-923), and rabbit (Lin et al., 1989, J. Biol. Chem. 265:8942-8947) genes have been cloned and found to encode a protein of 200 amino acids, which share about 80% sequence identity with the human gene. Both the human and rat recombinant proteins have been expressed at exceptionally high levels (up to 70% of total protein) and purified to near homogeneity.

[0008] Despite their structural and functional similarity, recombinant human and rat CNTF differ in several respects. The biological activity of recombinant rat CNTF in supporting survival and neurite outgrowth from embryonic chick ciliary neurons in culture is four times better than that of recombinant human CNTF [Masiakowski et al., (1991), J. Neurochem. 57:1003-1012]. Further, rat CNTF has a higher affinity for the human CNTF receptor than does human CNTF.

[0009] A surprising difference in the physical properties of human and rat CNTF, which are identical in size, is their different mobility on SDS gels. This difference in behaviour suggests the presence of an unusual structural feature in one of the two molecules that persists even in the denatured state (Masiakowski et al., 1991, id.).

[0010] Mutagenesis by genetic engineering has been used extensively in order to elucidate the structural organization of functional domains of recombinant proteins. Several different approaches have been described in the literature for carrying out deletion or substitution mutagenesis. The most successful appear to be alanine scanning mutagenesis [Cunningham and Wells (1989), Science 244: 1081-1085] and homolog-scanning mutagenesis [Cunningham et al., (1989), Science 243:1330-1336]. These approaches helped identify the receptor binding domains of growth hormone and create hybrid proteins with altered binding properties to their cognate receptors.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide novel CTNF-related neurotrophic factors for the treatment of diseases or disorders including, but not limited to, motor neuron diseases and muscle degenerative diseases.

[0012] A further object of the present invention is to provide a method for identifying CNTF-related factors, other than those specifically described herein, that have improved therapeutic properties.

[0013] These and other objects are achieved in accordance with the invention, whereby amino acid substitutions in human CNTF protein enhance its therapeutic properties. In one embodiment, alterations in electrophoretic mobility are used to initially screen potentially useful modified CNTF proteins.

[0014] In a preferred embodiment, the amino acid glutamine in position 63 of human CNTF is replaced with arginine or another amino acid which results in a modified CNTF molecule with improved biological activity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1. Alignment of CNTF protein sequences. A. Human (SEQ ID NO:1), rat (SEQ ID NO:2), rabbit (SEQ ID NO:3), mouse (SEQ ID NO:4), and chicken (SEQ ID NO:5) (Leung, et al., 1992, Neuron 8:1045-1053) sequences. Dots indicate residues found in the human sequence. Panel B. Modified CNTF molecules (186 (SEQ ID NO:6), 187 (SEQ ID NO:7), 188 (SEQ ID NO:8), 189 (SEQ ID NO:9), 192 (SEQ ID NO:10), 218 (SEQ ID NO:11), 219 (SEQ ID NO:12), 222 (SEQ ID NO:13), 223 (SEQ ID NO:14), and 228 (SEQ ID NO:15) showing human CNTF amino acid residues (dots) and rat CNTF (residues shown). The name of the purified recombinant protein corresponding to each sequence is shown on the left.

[0016] FIG. 2. Mobility of human, rat and several modified CNTF molecules on reducing SDS-15% polyacrylamide gels. Purified recombinant proteins were loaded as indicated. Markers of the indicated MW were loaded on lane M.

[0017] FIG. 3. Biological activity of two modified CNTF molecules. A. human CNTF (filled diamonds), rat CNTF (open squares), and RPN219 (filled squares). B. human CNTF (filled diamonds), rat CNTF (open squares), and RPN228 (filled squares). Dose response of dissociated E8 chick ciliary neurons surviving at the indicated protein concentration, as a percentage of the number of neurons surviving in the presence of 2 ng/ml rat CNTF. Each experimental point represents the mean of three determinations.

[0018] FIG. 4. Competitive ligand binding towards A.) SCG neurons and B.) MG87/huCNTFR fibroblasts. Standard deviation from the mean of three determinations is shown by vertical bars.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention relates to a method of treating neurological diseases and disorders in humans or animals. It is based, in part, on the initial finding that recombinant rat CNTF binds more efficiently to the human CNTF receptor than does recombinant human CNTF and the subsequent discovery that amino acid substitutions which cause human CNTF to more closely resemble rat CNTF result in enhanced binding of the modified CNTF to the human CNTF receptor and concomitant enhanced biological activity.

[0020] In a preferred embodiment, alteration of a single amino acid of the human CNTF protein results in a signficant enhancement of the ability of the protein to promote the survival and outgrowth of ciliary ganglion neurons.

[0021] Recombinant human and rat CNTF have the same number of amino acids (199) and similar mass (MW 22,798 and 22,721 respectively, after removal of the N-terminal methionine). Yet, on reducing SDS-PAGE gels, recombinant human CNTF migrates as a protein of MW=27,500, whereas rat CNTF migrates with the expected mobility. In addition, human CNTF has four times lower biological activity towards chick ciliary ganglion (CG) neurons than rat CNTF and the human protein competes for binding to the human or the rat receptor on cell surfaces much less effectively than rat CNTF.

[0022] The above observation led to a directed effort to identify the region on the CNTF molecule responsible for these differences. This method involved the exchange, by genetic engineering methods, of parts of the human CNTF sequence with the corresponding rat CNTF sequence and vice versa. To achieve this, advantage was taken of restriction sites that are common to the two CNTF genes and unique in their corresponding expression vectors. When necessary, such sites were engineered in one or the other of the two genes in areas that encode the same protein sequence. With this approach, expression vectors were obtained for each of the modified proteins shown in FIG. 1. After isolating the individual proteins to at least 60% purity, their properties, as compared to those of human and rat CNTF were determined.

[0023] Because the electrophoretic mobilities of human and rat CNTF differ significantly, the effect of each amino acid substitution was monitored initially by making a determination of the effect of such change on the mobility of the protein. As described herein, electrophoretic mobility data indicated that all of the modified human CNTF molecules that migrated to the same position as rat CNTF had the single amino acid substitution Gln63->Arg (Q63→R).

[0024] Modified human CNTF proteins that demonstrated an electrophoretic mobility similar to that of the rat CNTF molecule were subsequently examined for biological activity and receptor binding.

[0025] CNTF is characterized by its capacity to support the survival of dissociated ciliary neurons of E8 chick embryos. By this criterion, purified recombinant rat CNTF is as active as the native protein from rat, but four times more active than recombinant human CNTF [Masiokowski, et al. (1991), id]. The same assay was utilized to determine the biological activity of the altered molecules prepared as described above. As described herein, all of the modified CNTF molecules that had the Q63->R substitution exhibited an increased ability to support the survival of ciliary ganglion neurons as compared to the parent human CNTF protein. Such results indicated a strong correlation between alteration of the electrophoretic mobility and enhanced biological properties.

[0026] In addition to measuring the biological effect of modifications made to human CNTF, an indication of the potential biological activity of each of the molecules may also be obtained by determining the effect of each modification on the ability of the molecules to bind to the CNTF receptor.

[0027] In one embodiment, the ability of the modified human CNTF proteins to compete with rat CNTF for binding to rat superior cervical ganglia neurons (SCGs) is measured. As described herein, human CNTF is about 90 times less potent in displacing 125I -labelled rat CNTF binding from these cells than unlabelled rat CNTF. Several of the modified human CNTF proteins described herein, however, are more potent than the human CNTF in displacing the rat protein. All of the molecules described herein that had such increased competitive binding ability were molecules that exhibited altered electrophoretic mobility, wherein the molecules migrated in a manner similar to rat CNTF.

[0028] In another embodiment, cells, such as MG87 fibroblasts, are engineered to express the human CNTF receptor a-component and such cells are used to assay the binding capability of the modified protein to the human receptor. Human CNTF is about 12 times less potent than rat CNTF in competing with 125I-labelled rat CNTF for binding to the human CNTF receptor. Several of the modified human CNTF molecules described herein, including all of those with electrophoretic mobility that resemble rat rather than human CNTF, were more potent than human CNTF in competing with binding of 125I-rat CNTF to the cells expressing the human CNTF receptor.

[0029] In another embodiment, an animal model with demonstrated utility in providing an indication of the ability of certain growth and other factors to prevent degeneration of retinal photoreceptors may be used to assess the therapeutic properties of the modified CNTF molecules according to the present invention. As described in Example 4, hCNTF (Gln63→Arg) has a ten-fold higher ability than recombinant human CNTF to prevent degeneration of photoreceptors in a lightinduced damage model of retinal degeneration.

[0030] Thus, according to the invention, certain amino acid substitutions in the human CNTF protein result in modified human CNTF proteins that exhibit enhanced binding to the human CNTF receptor and therefore, would be expected to have enhanced therapeutic properties.

[0031] The modified CNTF molecules useful for practicing the present invention may be prepared by cloning and expression in a prokaryotic or eukaryotic expression system. The recombinant neurotrophin gene may be expressed and purified utilizing any number of methods. The gene encoding the factor may be subcloned into a bacterial expression vector, such as for example, but not by way of limitation, pCP110.

[0032] The recombinant factors may be purified by any technique which allows for the subsequent formation of a stable, biologically active protein. For example, and not by way of limitation, the factors may be recovered from cells either as soluble proteins or as inclusion bodies, from which they may be extracted quantitatively by 8M guanidinium hydrochloride and dialysis. In order to further purify the factors, conventional ion exchange chromatography, hydrophobic interaction chromatography, reverse phase chromatography or gel filtration may be used.

[0033] According to the present invention, modified CNTF molecules produced as described herein, or a hybrid or mutant thereof, may be used to promote differentiation, proliferation or survival in vitro or in vivo of cells that are responsive to CNTF, including cells that express receptors of the CNTF/IL-6/LIF receptor family, or any cells that express the appropriate signal transducing component, as described, for example, in Davis, et al. (1992) Cell 69:1121-1132. Mutants or hybrids may alternatively antagonize cell differentiation or survival.

[0034] The present invention may be used to treat disorders of any cell responsive to CNTF or the CNTF/CNTF receptor complex. In preferred embodiments of the invention, disorders of cells that express members of the CNTF/IL-6/LIF receptor family may be treated according to these methods. Examples of such disorders include but are not limited to those involving the following cells: leukemia cells, hematopoietic stem cells, megakaryocytes and their progenitors, DA1 cells, osteoclasts, osteoblasts, hepatocytes, adipocytes, kidney epithelial cells, embryonic stem cells, renal mesangial cells, T cells, B cells, etc.

[0035] Accordingly, the present invention provides for methods in which a patient suffering from a CNTF-related neurological or differentiation disorder or disease or nerve damage is treated with an effective amount of the modified CNTF, or a hybrid or mutant thereof. The modified CNTF molecules may be utilized to treat disorders or diseases as described for CNTF in International Publication No. WO91/04316 published on Apr. 4, 1991 by Masiakowski, et al. and for CNTF/CNTFR complex as described in International Publication No. WO91/19009 published on Dec. 12, 1991 by Davis, et al. both of which are incorporated by reference in their entirety herein.

[0036] Such diseases or disorders include degenerative diseases, such as retinal degenerations, diseases or disorders involving the spinal cord, cholinergic neurons, hippocampal neurons or diseases or disorders involving motorneurons, such as amyotrophic lateral sclerosis or those of the facial nerve, such as Bell's palsy. Other diseases or disorders that may be treated include peripheral neuropathy, Alzheimer's disease, Parkinson's disease, Huntington's chorea, or muscle atrophy resulting from, for example, denervation, chronic disuse, metabolic stress, and nutritional insufficiency or from a condition such as muscular dystrophy syndrome, congenital myopathy, inflammatory disease of muscle, toxic myopathy, nerve trauma, peripheral neuropathy, drug or toxin-induced damage, or motor neuronopathy.

[0037] The present invention also contemplates diseases or disorders resulting from damage to the nervous system, wherein such damage may be caused by trauma, surgery, infarction, infection and malignancy or by exposure to a toxic agent.

[0038] The present invention also provides for pharmaceutical compositions comprising a modifed CNTF molecule or hybrid or mutant thereof, as described herein, as the sole therapeutic agent or in a complex with the CNTF receptor, in a suitable pharmacologic carrier.

[0039] The active ingredient, which may comprise the modified CNTF, stable modified CNTF/CNTF receptor complex, or a hybrid or mutant thereof, should be formulated in a suitable pharmaceutical carrier for systemic or local administration in vivo by any appropriate route including, but not limited to injection (e.g., intravenous, intraperitoneal, intramuscular, subcutaneous, endoneural, perineural, intraspinal, intraventricular, intravitreal, intrathecal etc.), by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.); or by a sustained release implant, including a cellular or tissue implant.

[0040] Depending upon the mode of administration, the active ingredient may be formulated in a liquid carrier such as saline, incorporated into liposomes, microcapsules, polymer or wax-based and controlled release preparations, or formulated into tablet, pill or capsule forms.

[0041] The concentration of the active ingredient used in the formulation will depend upon the effective dose required and the mode of administration used. The dose used should be sufficient to achieve circulating plasma concentrations of active ingredient that are efficacious. Effective doses may be extrapolated from dose-response curves derived from in vitro or animal model test systems.

[0042] As described herein, applicants have determined that altered electrophoretic mobility provides a reliable method for screening for proteins with enhanced biological activity or ligand binding capability. Accordingly, the method described herein may have general applicability in screening for novel therapeutic proteins. Such a method would involve determining the electrophetic mobility of a wild-type human protein, introducing amino acid substitutions into the wild-type human protein and identifying as potential candidates subtituted proteins that have altered electrophoretic mobility as compared to the electrophoretic mobility of the wild-type protein. Such substitute proteins could be further tested to determine their biological activity and/or binding affinity. Potential amino acid substitutions could be based, for example, on comparable sequences from homologous proteins of non-human species.

[0043] One skilled in the art will recognize that other alterations in the amino acid sequence of CNTF may provide enhanced properties to the molecule. One skilled in the art will also recognize that CNTF homologues from other species, i.e. mouse, rabbit and chicken, may also have enhanced properties in treating human diseases or disorders. Thus, the present invention contemplates a method of identifying novel neurotrophic factors, whereby neurotrophic factors from species other than human are identified and assayed with respect to their ability to bind the human receptor as well as their biological activity in human cell lines and in vivo systems. When neurotrophic factors from animal species are identified which have novel properties, methods known to those in the art, such as those described herein, can be used to interchange portions of the human factor with the animal-derived factor to create novel neurotrophic factors with enhanced therapeutic properties.

EXAMPLES

Example 1

Electrophoretic Mobility of Modified Human CNTF Molecules

[0044] Preparation of Modified CNTF molecules: E. coli K-12 RFJ26 is a strain that overproduces the lactose operon repressor. The expression vectors pRPN33, which carries the human CNTF gene and pRPN110 which carries the rat CNTF gene are nearly identical (Masiakowski, et al. 1991, id.).

[0045] Plasmid pRPN219 was constructed by first digesting pRPN33 with the restriction enzymes Nhe1 plus Hind3 and gel purifying the 4,081 bp fragment. The second, much smaller fragment which codes for part of the human CNTF gene was subsequently replaced with an 167 bp Nhe1-Hind3 fragment that was obtained by PCR amplification from the rat gene using the primers RAT-III-dniH: 5′-ACGGTAAGCTTGGAGGTTCTC-3′ (SEQ ID NO:16); and RAT-Nhe-I-M: 5′-

(SEQ ID NO:17)
TCTATCTGGCTAGCAAGGAAGATTCGTTCAGACCTGACTG-
CTCTTACG-3′.

[0046] Plasmid pRPN228 was constructed in the same manner as pRPN219, except that the 167 bp replacement fragment was amplified using the DNA primers Rat-III-dniH-L-R: 5′-

AAG GTA CGA TAA GCT TGG AGG TTC TCT TGG AGT CGC TCT GCC TCA (SEQ ID NO: 18)
GTC AGC TCA CTC CAA CGA TCA GTG-3′
and Rat-Nhe-I:
5′-TCT ATC TGG CTA GCA AGG AAG-3′. (SEQ ID NO:19)

[0047] Plasmids pRPN186, pRPN187, pRPN188, pRPN189, pRPN192, pRPN218, and pRPN222 were generated by similar means or by direct exchange of DNA fragments using the unique restriction sites shown in FIG. 1. The identity of all plasmids was confirmed by restriction analysis and DNA sequencing.

[0048] Protein Purification: Induction of protein synthesis, selective extraction, solubilization and purification from inclusion bodies were as described for rat and human CNTF (Masiakowski, et al. 1991, id.) except that gel filtration was occasionally used instead or in addition to ion exchange chromatography. Alternatively, proteins were purified from the supernatants of cell lysates by streptomycin and ammonium sulfate fractionation, followed by column chromatography, as described for other proteins (Panayotatos et al., 1989, J. Biol. Chem. 264:15066-15069). All proteins were isolated to at least 60% purity.

[0049] Conditions for enzymatic reactions, DNA electrophoresis and other techniques used in these studies have been described in detail (Panayotatos, N. 1987, Engineering an Efficient Expression System in Plasmids: A practical Approach (Hardy, K. G. ed.) pp 163-176, IRL Press, Oxford, U.K.).

[0050] Results: The mobilities of human, rat and several chimeric CNTF molecules on reducing SDS-polyacrylamide gels are shown in FIG. 2. The chimeric molecules RPN186, RPN189, RPN218 and RPN228 exhibit mobilities comparable to rat CNTF, whereas RPN187, RPN188, RPN192 and RPN222 exhibit mobilities comparable to human CNTF. Cross-reference of these results to the aligned sequences of these proteins in FIG. 1 reveals that all proteins carrying an arginine residue at position 63 (R63) display the mobility of rat CNTF. In the case of RPN228, this single amino acid substitution (Q63->R) is sufficient to confer to human CNTF the normal mobility of rat CNTF.

[0051] FIG. 2 also provides a measure of the purity of the different recombinant proteins. By visual inspection, purity varies from 60% for RPN189 to better than 90% for RPN228.

Example 2

Measurement of Binding Activity of Modified CNTF Molecules

[0052] Preparation of 125I-CNTF. Recombinant rat CNTF (28 mg) in 37 ml 0.2 M sodium borate buffer, pH 8.5 was transfered to a vial containing 4 mCi, (2,000 Ci/mmole; NEN) of 125I and reagent (Bolton and Hunter,1973, Biochem J. 133: 529-539) which had been dried under a gentle stream of nitrogen. Reactions were incubated for 45 min at 0° C. followed by 15 min at room temperature and terminated by the addition of 30 ml of 0.2 M glycine solution. After 15 min, 0.2 ml PBS containing 0.08% gelatin was also added and the mixture was passed through a Superdex-75 column (Pharmacia) to separate the labelled monomeric CNTF from dimeric and other multimeric derivatives. Percentage of incorporation was typically 20%, as determined by thin layer chromatography and the specific activity was typically around 1,000 Ci/mmole. The monomeric 125I-CNTF was stored at 4° C. and used up to one week after preparation. As a test of structural and conformational integrity, 125I-CNTF (approximately 10,000 cpm) was mixed with a 5 mg unlabelled CNTF and analyzed by native gel eletrophoresis. One major band was visible by either Coomassie staining or autoradiography. 125I-CNTF also showed comparable activity to native CNTF in supporting survival of E8 chick ciliary neurons in culture.

[0053] Tissue Culture Techniques: Superior cervical ganglia (SCG) from neonatal rats were treated with trypsin (0.1%), mechanically dissociated and plated on a poly-omithine (30 mg/ml) substratum. Growth medium consisted of Ham's nutrient mixture F12 with 10% heat-inactivated fetal bovine serum (Hyclone), nerve growth factor (NGF) (100 ng/ml), penicillin (50 U/ml) and streptomycin (50 mg/ml). Cultures were maintained at 37° C. in a humidified 95% air/5% CO2 atmosphere. Ganglion non-neuronal cells were eliminated by treatment with araC (10 mM) on days 1 and 3 of culture. Cultures were fed 3 times/week and were routinely used for binding assays within 2 weeks.

[0054] MG87/CNTFR is a fibroblast cell line transfected with the human CNTFa receptor gene (Squinto, et al.,1990, Neuron 5:757-766; Davis et al., 1991, Science 253:59-63).

[0055] Binding Assays: Binding was performed directly on cell monolayers. Cells in culture wells were washed once with assay buffer consisting of phosphate buffered saline (PBS; pH 7.4), 0.1 mM bacitracin, 1 mM PMSF, 1 mg/ml leupeptin, and 1 mg/ml BSA. After incubation with 125I-CNTF for 2 hours at room temperature, cells were quickly washed twice with assay buffer, lysed with PBS containing 1% SDS and counted in a Packard Gamma Counter. Non-specific binding was determined in the presence of 1,000-fold excess of unlabelled CNTF. Specific binding towards MG87/CNTFR was 80-90%. Data were analyzed using the GRAPHPAD program (ISI, Philadelphia, Pa.).

[0056] Results: Competition curves of purified recombinant human, rat and CNTF RPN219 towards 125I-rat CNTF for binding on rat SCG neurons are shown in FIG. 4a. Both rat and human CNTF compete with 125I-rat CNTF for binding to SCG neurons, but human CNTF (IC50=25 nM) is 90 times less potent in displacing 125I-rat CNTF binding than unlabelled rat CNTF (IC50=0.28 nM). In contrast, RPN219 is almost as potent as rat CNTF and clearly more potent than human CNTF (IC50=0.3 nM).

[0057] Similar results were obtained from competition experiments with mouse fibroblasts transfected with a plasmid directing the expression of the human CNTF receptor (FIG. 4b). Both rat, human and RPN228 compete with 125I-rat CNTF for binding to MG87/CNTFR cells. Human CNTF (IC50=30 nM) is 12 times less potent than rat CNTF (IC50=2.8 nM), whereas RPN228 is clearly more potent than the human protein (IC50=5.6 nM).

[0058] Competition binding experiments with the other modified CNTF proteins shown in FIG. 1 also demonstrated that proteins having R63 displayed the biological activity of rat CNTF, whereas proteins having Q63 displayed the binding properties of human CNTF (data not shown). These results indicate that the single amino acid substitution (Q63->R) is sufficient to confer to human CNTF the receptor binding properties characteristic of rat CNTF.

Example 3

Measurement of Biological activity of Modified CNTF Molecules

[0059] Recombinant CNTF was assayed on dissociated cultures of chick ciliary ganglion (CG) neurons as described (Masiakowski et al. 1991, id.), except that surviving cells were stained with MTT (Mosmann, T. 1983; J. Immunol. Methods 65:55-63).

[0060] Results: FIG. 3 shows dose-response curves of dissociated, neuron-enriched cultures of E8 chick embryo ciliary ganglia for purified recombinant human, rat and the modified CNTF proteins RPN219 and RPN228. By this assay, the biological activity of the chimeric proteins is indistinguishable from that of purified recombinant rat CNTF and clearly higher than that of recombinant human CNTF. Comparison of the dose-response curves in FIG. 3 also shows that the maximal levels of surviving neurons obtained with RPN219, RPN228 or rat CNTF are higher than those obtained with human CNTF. These results suggest that RPN219 and RPN228, like rat CNTF, are active towards a larger population of neurons than human CNTF. In parallel experiments, the biological activity of the other modified CNTF proteins shown in FIG. 1 was examined. In every case, modified CNTF proteins carrying the (Q63->R) substitution displayed the biological activity of rat CNTF whereas proteins having Q63 displayed the activity of human CNTF (data not shown).

[0061] Overall, these results indicate that the single amino acid substitution (Q63->R) is sufficient to confer to human CNTF the biological activity of rat CNTF

Example 4

Use of Modified CNTF to Prevent Light Induced Photoreceptor Injury

[0062] Albino rats of either the F344 or Sprague-Dawley strain were used at 2-5 months of age. The rats were maintained in a cyclic light environment (12 hr on: 12 hr off at an in-cage illuminance of less than 25 ft-c) for 9 or more days before being exposed to constant light. The rats were exposed to 1 or 2 weeks of constant light at an illuminance level of 115-200 ft-c (most rats received 125-170 ft-c) provided by two 40 watt General Electric “cool-white” fluorescent bulbs with a white reflector that was suspended 60 cm above the floor of the cage. During light exposure, rats were maintained in transparent polycarbonate cages with stainless steel wire-bar covers.

[0063] Two days before constant light exposure, rats anesthetized with a ketamine-xylazine mixture were injected intravitreally with 1 μl of rat CNTF, human CNTF or modified CNTF [hCNTF (Q63→R)] dissolved in phosphate buffered saline (PBS) at a concentration of 0.1 to 500 ng/μl. The injections were made with the insertion of a 32 gauge needle through the sclera, choroid and retina approximately midway between the ora serrata and equator of the eye. In all cases, the injections were made into the superior hemisphere of the eye.

[0064] Immediately following constant light exposure, the rats were sacrificed by overdose of carbon dioxide followed immediately by vascular perfusion of mixed aldehydes. The eyes were embedded in epoxy resin for sectioning at 1 μm thickness to provide sections of the entire retina along the vertical meridian of the eye. The degree of light-induced retinal degeneration was quantified by assessing the degree of photoreceptor rescue by a 0-4+ pathologist's scale of rescue, 4+ being maximal rescue and almost normal retinal integrity. The degree of photoreceptor rescue in each section, as based on comparison to the control eye in the same rat, was scored by four individuals. This method has the advantage of considering not only the ONL thickness, but also more subtle degenerative changes to the photoreceptor inner and outer segments, as well as spatial degenerative gradients within the eye. Three eyes were examined for each time point to generate a dose response curve.

[0065] Results: The degree of rescue was measured for human, rat and hCNTF (Q63→R). The data indicated that both rat and hCNTF (Q63→R) had ten-fold greater ability to rescue photoreceptors in the light damage model than did recombinant human CNTF.

[0066] It is to be understood that while the invention has been described above in conjunction with preferred specific embodiments, the description and examples are intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims.

Claims

1. A human ciliary neurotrophic factor (CNTF) protein (SEQ ID NO:1) in which glutamine at position 63 (Q63) is substituted by arginine and cysteine at position 17 (C17) is substituted with another amino acid.

2. The protein of claim 1, wherein C17 is substituted by serine or alanine.

3. A human ciliary neurotrophic factor (CNTF) protein (SEQ ID NO:1) in which glutamine at position 63 (Q63) is substituted by another amino acid.

4. The protein of claim 3, wherein Q63 is substituted by alanine, asparagine, histidine, glutamic acid, or lysine.

5. The protein of claim 3, further modified by a substitution of cysteine at position 17 (C17).

6. The protein of claim 3 further modified to reduce immunogenicity.

7. The protein of claim 6, wherein the modification is a truncation of the C-terminus.

8. The protein of claim 7, wherein the truncation is 13 or 15 amino acids.

9. The protein of claim 6, further modified by a substitution of tryptophan at position 64 (W64).

10. The protein of claim 5, further modified by a substitution of tryptophan at position 64 (W64).

11. The protein of claim 5, wherein the substitution at C17 is serine or alanine.

12. The protein of claim 5, further modified to reduce immunogenicity.

13. The protein of claim 12, wherein the modification is a truncation of the C-terminus.

14. The protein of claim 13, wherein the truncation if 13 or 15 amino acids.

15. The protein of claim 12, further modified by a substitution of tryptophan at position 64 (W64).

16. A human ciliary neurotrophic factor (CNTF) protein (SEQ ID NO:1) which is modified by a substitution of glutamine at position 63 (Q63), and a substitution of tryptophan at position 64 (W64).

17. The protein of claim 16, where in the substitution of Q63 is arginine, alanine, asparagine, histidine, glutamic acid, or lysine.

18. The protein of claim 16, where in the substitution of W64 is alanine, phenylalanine, histidine, or glutamine.

19. The protein of claim 16, where in the substitution of Q63 is arginine and the substitution of W64 is alanine.

20. A human ciliary neurotrophic factor (CNTF) protein (SEQ ID NO:1) which is modified by a substitution of glutamine at position 63 (Q63) with alanine, asparagine, histidine, glutamic acid, or lysine, and a substitution of tryptophan at position 64 (W64) with phenylalanine, histidine, or glutamine.

21. The protein of claim 20, further modified to reduce immunogenicity.

22. The protein of claim 21, wherein the modification is a truncation of the C-terminus.

23. The protein of claim 22 wherein the truncation is 13 or 15 amino acids.