Patent Application
20090142391
This invention relates generally to pharmacology and more specifically to the modification of active agents to give them more desirable properties.
RNA interference or RNAi is a promising new approach towards making therapeutics which have more specificity and lower toxicity. RNAi is exquisitely selective for specific targets since it is directed towards gene-specific transcripts. Moreover, unlike anti-sense strategies, RNAi is a catalytic process where the same RNAi can be used many times to effect cleavage of many mRNA molecules. In humans, one molecule of siRNA can cause the cleavage of 60-70 mRNA molecules. For this reason, RNAi has attracted great interest as new method for the treatment of disease caused by the expression of a disease-causing protein. RNAi can be achieved via the use of a range of approaches: chemically synthesized small interfering RNA (siRNA) or endogenous expression of microRNA (miRNA), siRNA, or small hairpin RNA (shRNA). Despite the promise of this technology, there are technical hurdles to overcome: delivery of siRNA to cells is typically not sufficient to allow a therapeutic concentration of siRNA for gene silencing. In addition delivering too much siRNA can activate immune responses in a concentration-dependent manner, and this leads to non-specific gene silencing. Among the current approaches to solving the exogenous, systemic siRNA delivery problem are based on chemically modified siRNA, lipid encapsulation, polymeric carriers, and bioconjugation to biopolymers, but none have emerged as an optimal, general solution for the delivery of siRNA.
An emerging technology for the intracellular delivery and enhanced stability of siRNAs is the use of lipid conjugation. Enhanced lipophilicity is known to increase the membrane permeability of therapeutics and generally enhances the systemic exposure of a drug by increasing the elimination half-life. Additionally, enhancing the binding affinity of siRNA for endogenous human serum albumin by the use of cholesterol-siRNA conjugates, has also been shown to increase the elimination half life of siRNAs from 6 minutes to 95 minutes (Soutschek, J, et al. Nature, vol. 32, pp 173-178) by the introduction of cholesterol to the 3′ end of siRNAs. One disadvantage of the strategy for introducing conjugates to siRNA which enhance albumin binding is the tendency to enhance extra-cellular concentration of siRNA, as opposed to promoting intracellular sequestration. An approach to enhance lipophilicity and enhance intracellular distribution of siRNAs is of therapeutic interest. Moreover, increasing the elimination half life of siRNA is important to reduce the risk of side effects and lower the cost of administration of therapeutic siRNA. Lastly, the introduction of conjugates with independent biological activity such as cholesterol runs the risk that they may have their own side effects. Thus, the use of biologically silent conjugates is of interest to avoid additional side effects.
In an embodiment of this invention, a method for modulating at least one pharmacokinetic property of a drug which degrades mRNA upon administration to a host by an siRNA mechanism is provided. In a further embodiment of this invention, a bifunctional compound comprising an siRNA and a recruiter moiety are provided. The recruiter moiety is lipophilic and enables the siRNA to cross cell membranes and then targets an endogenous, intracellular protein to allow better distribution of the therapeutic into the cell and therefore, higher efficacy. The recruiter moiety is preferably biologically silent and does not have toxic side effects independent of the siRNA at medically relevant dosages.
In a further aspect of the invention, biasing the drug to remain inside cells increases efficacy by a two-fold mechanism: avoiding extracellular RNAse enzymes and avoiding intracellular degradation by enzymes via an association with a non-target intracellular protein which confers protection from intracellular enzymes. The non-target protein must still allow interaction of the siRNA to the RNA-induced silencing complex (RISC) and optimally enhances the binding affinity for RISC, measured directly by the association constant, Ka, or indirectly by IC50 measurements. The intracellular bias is created using ligands for intracellular proteins and ligands which avidly target intracellular proteins. In an additional aspect of the invention, the bifunctional siRNA drug has lower toxicity than the parent compound because a lower dose is required to achieve equivalent efficacy due to enhanced concentration/hour (area under the curve) and lower elimination half life.
In another embodiment of the invention, the recruiter moiety binds to the passenger (antisense) strand of the siRNA, allowing the guide strand to remain in the RISC complex.
In
In
Before describing the present invention in detail, it is to be understood that this invention is not limited to specific solvents, materials, or device structures, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include both singular and plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an active ingredient” includes a plurality of active ingredients as well as a single active ingredient, reference to “a temperature” includes a plurality of temperatures as well as single temperature, and the like.
The term “bifunctional compound” refers to a non-naturally occurring compound that includes a recruiter moiety and a drug moiety, where these two components may be covalently bonded to each other either directly or through a linking group. The term “drug” refers to any active agent that affects any biological process including RNA molecules involved in an RNAi process. Bifunctional compounds may have more than two functionalities.
The term RNAi therapeutic includes any RNA molecule which is used to modulate the level of an mRNA transcript in a cell. Such therapeutics include, but are not limited to, shRNA, miRNA, and siRNA.
The recruiter moiety may be a peptide or protein and may also be an enzyme or nucleic acid or other biomoiety and is covalently attached to the RNAi therapeutic.
By “pharmacologic activity” is meant an activity that modulates or alters a biological process so as to result in a phenotypic change, e.g. cell death, cell proliferation etc.
By “pharmacokinetic property” is meant a parameter that describes the disposition of an active agent in an organism or host. Representative pharmacokinetic properties include: drug half-life, hepatic first-pass metabolism, volume of distribution, degree of blood serum protein, e.g. albumin, binding, etc, degree of tissue targeting, cell type targeting.
By “half-life” is meant the time for one-half of an administered drug to be eliminated through biological processes, e.g. metabolism, excretion, etc.
By “hepatic first-pass metabolism” is meant the propensity of a drug to be metabolized upon first contact with the liver, i.e. during its first pass through the liver.
By “volume of distribution” is meant the distribution and degree of retention of a drug throughout the various compartments of an organism, e.g. intracellular and extracellular spaces, tissues and organs, etc.
The term “efficacy” refers to the effectiveness of a particular active agent for its intended purpose, i.e. the ability of a given active agent to cause its desired pharmacologic effect.
The term “host” refers to any mammal or mammalian cell culture or any bacterial culture.
Where the term cancer is used, it is understood that the invention may be employed on relative chemotherapeutics such as found in other any type of cancer including those cancers found in non-human species or human variants.
Where the term “intracellular” protein is used, this includes any protein that resides predominantly in the intracellular space but may optionally reside as a transmembrane or receptor protein.
The term “biomoiety” refers to a protein, DNA, RNA, ligand, carbohydrate, lipid, or any other component molecule of a prokaryotic or eukaryotic organism.
The term “non-pharmacokinetic properties” may include binding constants, off rate or on rate constants of the RNAi therapeutic moiety and recruiter for their targets. Additional properties may include drug solubility, formulation, and permeability across membranes.
The term “exon skipping” refers to manipulation of pre-mRNA splicing to produce new forms of the mRNA transcript. This technique has therapeutic benefit where the new mRNA transcript produces a protein with enhanced therapeutic benefit or lower toxicity than the “parent” or unmanipulated pre-mRNA moiety. Multiple exons may be removed, as in the simultaneous removal of exons 6 and 8 for the treatment of muscular dystrophy (McClorey, G., et al. Gene Therapy, 13, 1373-1381, 2006). Exon skipping may be seen as a distinct application from gene silencing or modulating the expression of a gene without changing the reading frame or adding or deleting transcribed segments. Exon skipping has been described in Mann, C. J., et al. Proc. Natl. Acad. Sci., 97, 13714-13719 (2000).
Where FK506 is used, variants or analogs of FK506 are included, such as rapamycin, pimecrolimus, or synthetic ligands of FK506 binding proteins (SLFs) such as those disclosed in U.S. Pat. Nos. 5,665,774, 5,622,970, 5,516,797, 5,614,547, and 5,403,833 or described by Holt et al., “Structure-Activity Studies of Synthetic FKBP Ligands as Peptidyl-Prolyl Isomerase Inhibitors,” Bioorganic and Medicinal Chemistry Letters, 4(2):315-320 (1994).
The term “siRNA” may refer to any form of RNA (double stranded RNA, microRNA, or short hairpin RNA) which may be used to silence a gene or create an alternative form of a transcript or protein by a different mechanism such as exon skipping.
In an embodiment of this invention, a method for modulating at least one pharmacokinetic property of an siRNA upon administration to a host is provided. One administers to the host an effective amount of a bifunctional compound of less than about 50000 Daltons comprising the siRNA therapeutic or an active derivative thereof and a recruiter moiety. The recruiter moiety binds to at least one intracellular protein. The bifunctional compound has at least one modulated pharmacokinetic property upon administration to the host as compared to a free drug control that comprises the RNAi therapeutic.
Bifunctional compounds in general have aroused considerable interest in recent years. See, for example, U.S. Pat. Nos. 6,270,957, 6,316,405, 6,372,712, 6,887,842, 6,921,531 and PCT publication WO2007/53792. ConjuChem (Montreal, Canada) scientists have shown that covalent coupling of insulin to human serum albumin can improve the half-life from 8 hours to over 48 hours. Xenoport (Santa Clara, Calif.) has pioneered attachment of receptor ligands to improve drug uptake and distribution. Similarly, siRNA-lipid conjugates have shown therapeutic promise as anti-leukemic drugs. Human trials of methotrexate-albumin conjugates revealed that the modified methotrexate had half-lives of up to two weeks compared with 6 hours for unmodified methotrexate. Other examples include PEGylation of growth factors and attachment of folate groups that “target” anti-cancer drugs. All these strategies use modification of a “parent” drug to provide new binding profiles or enhanced protection from degradation.
More recently, a team attached SLF to ligands for amyloid beta. Amyloid beta oligomers are believed to underlie the neuropathology of Alzheimer's disease. Therefore, methods to decrease amyloid aggregation are of therapeutic interest. Amyloid ligands, such as congo red or curcumin, can be synthetically coupled to FK506 or SLF. The resulting bifunctional compound binds both FKBP and amyloid beta. These molecules are potent inhibitors of amyloid aggregation and they block neurotoxicity in cell culture. Moreover, these ligands penetrate the blood-brain barrier and may assist biodistribution of siRNA to the brain. See Jason E. Gestwicki et al., “Harnessing Chaperones to Generate Small-Molecule Inhibitors of Amyloid β Aggregation,” Science 306:865-69 (2004).
The type of improvements achievable with bifunctional molecules are illustrated in
Bifunctional compounds of the type employed in the present invention are generally described by the formula:
X-L-Z
wherein:
X is a drug moiety, for example an RNAi therapeutic;
L is a bond or linking group; and
Z is a recruiter moiety,
Thus, as may be seen, a bifunctional compound is a non-naturally occurring or synthetic compound that is a conjugate of a drug or derivative thereof and a recruiter moiety, where these two moieties are optionally joined by a linking group.
In bifunctional compounds used in the invention, the recruiter and drug moieties may be different, such that the bifunctional compound may be viewed as a heterodimeric compound produced by the joining of two different moieties. In many embodiments, the recruiter moiety and the drug moiety are chosen such that the corresponding siRNA target and any binding partner of the recruiter moiety, e.g., a recruiter protein to which the recruiter moiety binds, do not naturally associate with each other to produce a biological effect.
The mass of an RNAi therapeutic is typically at least 4000 daltons. As such, the molecular weight of the bifunctional compound is generally at least about 4000 D, usually at least about 6000 D and more usually at least about 10000 D. The molecular weight may be less than about 8000 D, about 12000 D, about 15000 D, or about 20000 D, and may be as great as 30000 D or greater, but usually does not exceed about 50000 D. The preference for small molecules is based in part on the desire to facilitate oral administration of the bifunctional compound. Molecules that are orally administrable tend to be small.
The recruiter moiety modulates a pharmacokinetic property, e.g. half-life, hepatic first-pass metabolism, volume of distribution, degree of albumin binding, and intra- vs. extracellular distribution upon administration to a host as compared to free drug control. By modulated pharmacokinetic property is meant that the bifunctional compound exhibits a change with respect to at least one pharmacokinetic property as compared to a free drug control. For example, a bifunctional compound of the subject invention may exhibit a modulated, e.g. longer, half-life than its corresponding free drug control. Similarly, a bifunctional compound may exhibit a reduced propensity to be eliminated or metabolized upon its first pass through the liver as compared to a free drug control. Likewise, a given bifunctional compound may exhibit a different volume of distribution that its corresponding free drug control, e.g. a higher amount of the bifunctional compound may be found in the intracellular space as compared to a corresponding free drug control. Analogously, a given bifunctional compound may exhibit a modulated degree of albumin binding such that the drug moiety's activity is not as reduced, if at all, upon binding to albumin as compared to its corresponding free drug control. In evaluating whether a given bifunctional compound has at least one modulated pharmacokinetic property, as described above, the pharmacokinetic parameter of interest is typically assessed at a time at least 1 week, usually at least 3 days and more usually at least 1 day following administration, but preferably within about 6 hours and more preferably within about 1 hour following administration.
The linker L, if not simply a bond, may be any of a variety of moieties chosen so that they do not have an adverse effect on the desired operation of the two functionalities of the molecule and also chosen to have an appropriate length and flexibility. The linker may, for example, have the form F1—(CH2)n—F2 where F1 and F2 are suitable functionalities. A linker of this sort comprising an alkylene group of sufficient length may allow, for example, for the free rotation of the drug moiety even when the recruiter moiety is bound. Alternatively, a stiffer linker with less free rotation may be desired. The hydrophobicity or hydrophobicity of the linker is also a relevant consideration.
The drug moiety X may, in certain embodiments of the invention, preferably be an siRNA therapeutic. The drug moiety may also be in the form of short hairpin RNA (shRNA) or micro RNA (miRNA), which modulates the level of a therapeutically important mRNA or protein. The siRNA moiety preferably has a functionality which may readily and controllably be made to react with a linker precursor. The known siRNAs are subject to enzymatic degradation and clearance.
In general, the recruiter moiety Z will be one which is capable of reversible attachment to a common protein, meaning one which is abundant in the body or in particular compartments of the body or particular tissue types. Common proteins include, for example, FK506 binding proteins, cyclophilin, tubulin, actin, heat shock proteins, and albumin. Common proteins are present in concentrations of at least 10 nanomolar, preferably at least 100 nanomolar, more preferably at least 100 micromolar, and even more preferably 1 millimolar in the body or in particular compartments or tissue types. The recruiter moiety should, like the drug, have a moiety which is capable of reacting with suitable linkers.
It is desirable for at least some embodiments of the present invention that the binding of the recruiter moiety Z to a common protein be such as to sterically hinder the activity of common metabolic enzymes such as RNAse enzymes when the bifunctional compound is so bound. Persons of skill in the art will recognize that the effectiveness of this steric hindrance depends, among other factors, on the conformation of the common protein in the vicinity of the recruiter moiety's binding site on the protein, as well as on the size and flexibility of the linker. The choice of a suitable linker and recruiter moiety may be made empirically or it may be made by means of molecular modeling of some sort if an adequate model of the interaction of candidate recruiter moieties with the corresponding common proteins exists. The linker choice is critical since it must balance parameters of length, hydrophobicity, attachment point to the drug target, and attachment point to the ligand.
The attachment point and linker characteristics are preferably selected based on structural information such that the inhibitory potency of the RNAi therapeutic is preserved, giving the desired superior pharmacokinetic characteristics.
Where the recruiter moiety operates by binding a protein, it may be referred to as a “presenter protein ligand” and the protein which it binds to may be referred to as a “presenter protein.”
The recruiter moiety may be, for example, a derivative of FK506 (such as SLF) which has high affinity for the FK506-binding protein (FKBP), as depicted for example in
An inactive form of FK506 may be preferable in many applications to avoid the possibility of side effects due to the possible interaction of the active FK506-FKBP complex with calcineurin. It may be advantageous to use FKBP binding molecules such as synthetic ligands for FKBP (SLFs) described by Holt et al., supra. This class of molecule is lower molecular weight than FK506, and that is generally advantageous for drug delivery and pharmacokinetics. For illustrative purposes, some diagrams will show examples of the use of FK506, though it should be understood that the same strategy can apply to other ligands of peptidyl prolyl isomerases such as the FKBP proteins and that ligands for other presenter proteins may be employed.
The value of FK506 and other FKBP binding moieties as recruiter moieties of the invention is further supported by the following. FK506 (tacrolimus) is an FDA-approved immunosuppressant. It has been determined that FK506 can be readily modified such that it loses all immunomodulatory activity but retains high affinity for FKBP. FKBP is an abundant chaperone that is particularly prevalent (˜μmolar) in red blood cells (rbcs) and lymphocytes. The complex between FK506-FKBP gains affinity for calcineurin and inactivation of calcineurin blocks lymphocyte activation and causes immunosuppression.
This interesting mechanism of action is believed to be a consequence of FK506's chemical structure. FK506 is bifunctional; it has two non-overlapping protein-binding faces. One side binds FKBP, while the other binds calcineurin. This property provides FK506 with remarkable specificity and potency. Moreover, FK506 has a long half-life in non-transplant patients (21 hrs) and excellent pharmacological profile. In part, this is because FK506 is unavailable to metabolic enzymes via its high affinity for FKBP, which favors distribution into protected cellular compartments (72-98% in the blood). It can be expected that suitable bifunctional compounds with an FKBP-binding recruiter moiety will likewise possess some favorable characteristics of inactive FK506, namely, good pharmacokinetics and blood cell distribution, membrane permeability, and long elimination half-life.
In general, the recruiter moiety will have a molecular weight less than about 2000 D, less than about 1800 D, less than about 1500 D, less than about 1100 D, or less than about 900 D or less than 500 daltons.
It is also possible to co administer the common protein to which the recruiter moiety binds with the bifunctional compound in order to modify the pharmacokinetics to a greater degree than would be possible with just the native concentration of the common protein.
In a further embodiment of this invention, a method is provided for synthesizing a bifunctional compound comprising an RNAi therapeutic functionality and the ability to bind to a common protein.
The synthesis of the bifunctional compound starts with a choice of suitable recruiter and drug moieties. It is desirable to identify on each of these moieties a suitable attachment point which will not result in a loss of biological function for either one. This is preferably done based on the existing knowledge of what modifications result or do not result in a biological function. On that basis, it may reliably be conjectured that certain attachment points on the pharmacokinetic and RNAi moieties do not affect biological function. Likewise, in
In a further aspect of the invention, a bifunctional compound comprising a RNAi therapeutic moiety with antiviral activity is formulated, for example in the form of a tablet, capsule, parenteral formulation, to make a pharmaceutical preparation. The pharmaceutical preparation may be employed in a method of treating a patient having cancer against which the RNAi therapeutic moiety is effective. For example, if the RNAi therapeutic moiety is effective against breast cancer, the pharmaceutical preparation may be administered to a patient suffering from breast cancer.
For the preparation of a pharmaceutical formulation containing bifunctional compounds as described in this application, a number of well known techniques may be employed as described for example in Remington: The Science and Practice of Pharmacy, Nineteenth Ed. (Easton, Pa.: Mack Publishing Company, 1995).
In a further embodiment, the invention relates to a method for treating a subject having a disease or at risk of developing a disease caused by the expression of a target gene. In this embodiment, bifunctional molecules comprising siRNA moieties can act as novel therapeutic agents for controlling one or more of cellular proliferative and/or differentiative disorders, disorders associated with bone metabolism, immune disorders, hematopoietic disorders, cardiovascular disorders, liver disorders, viral diseases, or metabolic disorders. The method includes administering a pharmaceutical composition of the invention to the patient (e.g., a human), such that expression of the target gene is silenced. Because of their high efficiency and specificity, the bifunctional molecules of the present invention may specifically target mRNA of target genes of diseased cells and tissues, as described below, at low dosages.
Examples of genes which can be targeted for treatment by the siRNA moiety include, without limitation, an oncogene, a cytokine gene, an idiotype (Id) protein gene, or a prion gene. The targeted gene may result in the expression of molecules that induce angiogenesis, adhesion molecules, or cell surface receptors. The targeted genes may pertain to proteins that are involved in metastasizing and/or invasive processes, or may be genes of proteases, genes of molecules that regulate apoptosis and the cell cycle. One may target, for example, the drug resistance 1 gene, NMDR1.
In the prevention of disease, the target gene may be one which is required for initiation or maintenance of the disease, or which has been identified as being associated with a higher risk of contracting the disease. In the treatment of disease, the siRNA moiety can be brought into contact with the cells or tissue exhibiting the disease. For example, an siRNA moiety substantially identical to all or part of a mutated gene associated with cancer, or one expressed at high levels in tumor cells, may be brought into contact with or introduced into a cancerous cell or tumor gene.
Examples of cellular proliferative and/or differentiative disorders include cancer, e.g., a carcinoma, sarcoma, metastatic disorder or hematopoietic neoplastic disorder, such as a leukemia. A metastatic tumor can arise from a multitude of primary tumor types, including but not limited to those of prostate, colon, lung, breast and liver origin. As used herein, the terms “cancer,” “hyperproliferative,” and “neoplastic” refer to cells having the capacity for autonomous growth, i.e., an abnormal state or condition characterized by rapidly proliferating cell growth. These terms are meant to include all types of cancerous growths or oncogenic processes, metastatic tissues or malignantly transformed cells, tissues, or organs, irrespective of histopathologic type or stage of invasiveness. Proliferative disorders also include hematopoietic neoplastic disorders, including diseases involving hyperplastic/neoplastic cells of hematopoietic origin, e.g., arising from myeloid, lymphoid or erythroid lineages, or precursor cells thereof.
The pharmaceutical compositions of the present invention can also be used to treat a variety of immune disorders, in particular those associated with overexpression or aberrant expression of a gene or expression of a mutant gene. Examples of hematopoietic disorders or diseases include, without limitation, autoimmune diseases (including, for example, diabetes mellitus, arthritis (including rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, psoriatic arthritis), multiple sclerosis, encephalomyelitis, myasthenia gravis, systemic lupus erythematosis, autoimmune thyroiditis, dermatitis (including atopic dermatitis and eczematous dermatitis), psoriasis, Sjogren's syndrome, Crohn's disease, aphthous ulcer, iritis, conjunctivitis, keratoconjunctivitis, ulcerative colitis, asthma, allergic asthma, cutaneous lupus erythematosus, scleroderma, vaginitis, proctitis, drug eruptions, leprosy reversal reactions, erythema nodosum leprosum, autoimmune uveitis, allergic encephalomyelitis, acute necrotizing hemorrhagic encephalopathy, idiopathic bilateral progressive sensorineural hearing, loss, aplastic anemia, pure red cell anemia, idiopathic thrombocytopenia, polychondritis, Wegener's granulomatosis, chronic active hepatitis, Stevens-Johnson syndrome, idiopathic sprue, lichen planus, Graves' disease, sarcoidosis, primary biliary cirrhosis, uveitis posterior, interstitial lung fibrosis, graft-versus-host disease, cases of transplantation, and allergy.
In another embodiment, the invention relates to methods for treating viral diseases, including but not limited to hepatitis C, hepatitis B, herpes simplex virus (HSV), HIV-AIDS, poliovirus, and smallpox virus. Bifunctional molecules containing iRNA therapeutic moieties are prepared as described herein to target expressed sequences of a virus, thus ameliorating viral activity and replication. The bifunctional molecules can be used in the treatment and/or diagnosis of viral infected tissue, both animal and plant. Also, such bifunctional molecules can be used in the treatment of virus-associated carcinoma, such as hepatocellular cancer.
In a further aspect of the invention, the bifunctional compound is prepared conjugated to macromolecular carrier. The macromolecular carrier may be, for example, a liposome which may comprise a polyethylene glycol.
Liposomes in general include vesicles comprising amphiphilic lipids arranged in a spherical layer or bilayers. Liposomes may be unilamellar or multilamellar vesicles. A composition to be delivered is found in the interiors of the vesicles.
A class of liposomes which is useful with nucleic acids is the cationic liposomes, where the lipids are positively charged and are believed to interact with negatively charged DNA molecules to form a stable complex. Certain liposomes that are pH-sensitive or negatively-charged, however, are believed to entrap DNA rather than complex with it. Both cationic and noncationic liposomes have been used to deliver DNA to cells. Information regarding the use of liposomes to deliver nucleic acids is found, for example, in U.S. Published Patent Application No. 2006/62841. Further information regarding the making of liposomes is found, for example, in U.S. Published Patent Application No. 2004/142025.
Liposomes also include sterically stabilized liposomes, which include liposomes comprising one or more specialized lipids that, when incorporated into liposomes, result in enhanced circulation lifetimes relative to liposomes lacking such specialized lipids. Examples of sterically stabilized liposomes are those in which part of the vesicle-forming lipid portion of the liposome comprises one or more glycolipids. The liposome may comprise lipids derivatized with one or more hydrophilic polymers, such as a polyethylene glycol (PEG) moiety. See in this regard, for example, the book Stealth Liposomes (Danilo Lasic & Frank Martin eds., CRC Press 1995).
In a further aspect of the invention, a bifunctional compound is formulated as part of a controlled release formulation in which an additional controlled release mechanism besides the effect of the recruiter moiety is employed to achieve desirable release characteristics. The bifunctional compound is as above, comprising a drug moiety, a linker, and a recruiter moiety.
It is to be understood that while the invention has been described in conjunction with the preferred specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages, and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.
All patents, patent applications, and publications mentioned herein are hereby incorporated by reference in their entireties. However, where a patent, patent application, or publication containing express definitions is incorporated by reference, those express definitions should be understood to apply to the incorporated patent, patent application, or publication in which they are found, and not to the remainder of the text of this application, in particular the claims of this application.
The general method for testing siRNA conjugates is to synthesize the bifunctional compound and test whether the bifunctional version represses apoB protein levels in a cell culture line. ApoB is of clinical interest due to its role in hypercholesterolemia. Initially, genetic databases are searched for candidate siRNAs which are likely to reduce apoB mRNA and protein levels. RT-PCR assays are used to screen lysates of transfected HepG2 liver cells after transfection with the candidate siRNAs. Candidates which reduce the levels of both mRNA transcripts and apoB protein levels are advanced to more detailed screens. These candidates may also be further stabilized against chemical degradation by the use of a phosphorothioate backbone or other modified type of synthetic siRNA. These candidates are then screened in detail for expression in various tissues by an RNA protection assay (RPA). Ideally, dose dependent silencing of apoB expression is observed. Based on the level of expression of apoB vs. amount of siRNAs detected, IC50 values may be calculated. It is desirable to have IC50 values to be less than about 100 nM.
Bifunctional siRNAs are introduced via bolus tail vein injection with volumes of about 200 uL on three consecutive days at an siRNA dosage of about 50 mg/kg. 24 hours after the last injection, apoB mRNA levels are assessed using the Northern blot technique: briefly, radiolabelled probes which are complementary to the antisense strands are used to quantify the siRNA in various tissue lysates harvested from the mice as well as mRNA levels. Tissue lysates are run on a gel which is probed with the relevant RNA to detect transcript levels. As a control, animals injected with saline are used. Tissue samples from the liver and jejenum are of particular interest as these are major sights of apoB expression. Levels of apoB protein expression are assessed via conventional Western blot methods.
Various chemistries may be employed to attach the siRNA to the recruiter moiety. One mode of attachment is to use a thiol group at the 5′ end of one of the strands to attach to a recruiter containing an SH moiety. Briefly, siRNAs designed to target an mRNA of interest using standard bioinformatics processes. Typically, for verification of transfection, an mRNA for luciferase may be used or an mRNA for green fluorescent protein (GFP). A typical siRNA for GFP might target coding region 540-565 (relative to the first nucleotide) and would have the sequences: 5′-rArCrUrArCrCrArGrCrArGrAr-ArCrArCrCrCrCTT-3′ and 5′-rGrGrGrGrUrGrUrUrCrUrGrCrUrGrGrUrArGrUTT-3′. This siRNA may then be modified with a thiol group at the 5′ end on the antisense strand. To conjugate to SLF, a modified version of SLF (Holt, et al. supra) is made containing a thiol. Prior to attachment of SLF, the siRNAs are annealed (30 mM HEPES, 2 mM magnesium acetate, 100 mM potassium acetate, pH=7.4) for 1 minute at 90° C. followed immediately by 60 minutes at 37° C. The annealed siRNAs are then desalted using 1% agarose in 100 mM glucose in a 100 μL Eppendorf pipet tip and 100 μL reaction buffer is added (10 mM HEPES, 1 mM ethylenediamine tetraacetic acid, pH 8.0) to adjust to a final siRNA and SLF concentration of 20 μM. The reaction to conjugate SLF to the passenger strand of siRNA takes place for 1 hour at 41° C. Transfection of cells may then be accomplished by incubation with cells. Typical reaction yields for siRNA-SLF are >80% and are verified using HPLC.
Cell lines are grown according to standard literature methods and are known to one of ordinary skill in the art. Cos-7, C166-GFP, or EOMA-GFP may be used where GFP is green fluorescent protein. The cells are grown in Dulbecco's modified medium (DMEM) supplemented with 10% fetal calf serum (FCS) with added antibiotics. 24 hours after the addition of siRNA and siRNA-SLF, cells are detached from the Petri dish with trypsin and transferred to 24 well plates (300 μL per well). Cells with better transfection efficiencies and better persistence of active siRNA will result in reduced fluorescence of the cell for a longer time period. The siRNAs are added at 25 nM to the transfected cell lines in cell culture media or by transfection with Lipofectamine 2000. Cells containing GFP reporter plasmids are incubated with siRNAs for one week. Gene silencing for cells transfected using siRNA and Lipofectamine and siRNA-SLF and siRNA in buffer is assessed using flow cytometry and Western blot.
For the Western blot, SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) and immunoblotting along with densitometry can be used to assess the relative expression of GFP in control cells (siRNA with and without Lipofectamine) and test cells transfected with siRNA-SLF.
An activated acid derivative of SLF using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxylsuccinimide (NHS) (10 equivalents EDC to 1 equivalent NHS) is prepared to yield a succinimidyl ester derivative of SLF. The reaction takes place in dimethylformamide (DMF) over the course of two hours at room temperature with a yield of over 82%. This SLF succinimidyl ester is then reacted with ethylene diamine in water and (DMF) and the reaction is initiated by dropwise addition of diisopropylethylamine (DIEA, 400 μL of a 5% solution in DMF). After 30 minutes, the reaction mixture is rotary-evaporated to dryness and the typical yield is 92% to give an SLF-amine derivative. This product is purified by reversed phase HPLC in a two-solvent system with solvent A consisting of water with 0.1% acetic acid and solvent B as a 5/2 mix of ethanol and 1-propanol. Next, the SLF-amine is reacted with succinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC) in a 1:20 ratio in 1.5 mL DMF and 5 μL DIEA and stirred for 50 minutes. The solvent is removed and the dry residue is extracted using 2×20 mL water containing 0.1% acetic acid and 6×20 mL water. Residual dissolved chloroform is expelled by bubbling with nitrogen. Excess water is then removed via lyophilization. Purification takes place by reverse phase HPLC using the same solvent system as described above. The reaction scheme is given in
An NHS ester SLF prepared as in Example 5 is conjugated to the sense strand of RNA corresponding to the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene for the purpose of silencing GAPDH. The sense strand is modified as follows where SLF is bound to −5′ GAC UCA UGA CCA CAG UCC A dTdT 3′ and using an unmodified antisense strand as follows: 5′ U GGA CUG UGG UCA UGA GUC dTdT 3′. The RNA is then annealed to form double stranded RNA and administered to a HELA cell culture at a variety of concentrations. GAPDH silencing is then evaluated using a fluorescent indicator to quantitatively detect GAPDH RNA by Quantigene assay (Panomics, Fremont, Calif.). The assay works by binding to GAPDH RNA with oligonucleotides which then bind to a fluorescent indicator. Cell viability is measured using a Cell-Titer Glo Assay (Promega, Madison, Wis.).
Results for cell viability are shown in
The effect on cell viability is more pronounced at 24 hours than at 48 hours. Non-target controls have similar viability to the GAPDH samples.
The modified RNA shows about a 25% lower knockdown than unmodified RNA at both 24 and 48 hours. The effect is more pronounced at 24 hours than at 48 hours. Non-target controls have similar negligible effect on GAPDH expression.
The improved silencing effect achieved by SLF conjugation is further illustrated by an experiment where SLF is attached to the sense RNA coding for the green fluorescent protein (GFP).
The sequences for GFP used were: sense strand: 5′ ArCrUrArCrCrArGrCrArGrArArCrArCrCrCrCTT-3′; antisense strand: 3′-TTUGrArUrGrGrUrCrGrUrCrUrUrGrUrGrGrGrGr-5′ where the sense strand is modified with SLF. In the figure, Amplyx1-GFP indicates SLF modified RNA, GFP is unmodified. Non-target denotes an irrelevant sequence (sense strand: 5′ CGU ACG CGG AAU ACU UCG AdTdT-3′; antisense strand 1 5′ UCG AAG UAU UCC GCG UAC GdTdT-3′). Cells only indicates a control with cells only, and concentrations are in nM as indicated. 50 nM alone means the RNA was added to the cells with no cationic liposome to assist with intracellular delivery. The cell line employed in this experiment was C166-GFP.
This application claims priority to U.S. Provisional Patent Application No. 60/964,748, filed Aug. 14, 2007, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60964748 | Aug 2007 | US |
