Abstract:
The invention relates to compositions and co-crystals each comprising (1S,3aR,6aS)-2-[(2S)-2-[[(2S)-2-Cyclohexyl-2-(pyrazine-2-carbonylamino)acetyl]amino]-3,3-dimethylbutanoyl]-N-[(3S)-1-(cyclopropylamino)-1,2-dioxohexan-3-yl]-3,3a,4,5,6,6a-hexahydro-1H-cyclopenta[c]pyrrole-1-carboxamide having the structure: 
                                 
and the co-crystal former salicylic acid. Also within the scope of this invention are methods of making and using the same.

Description:
CROSS-REFERENCE 
     This application claims the benefits of U.S. Provisional Application Ser. No. 60/777,221, filed on Feb. 27, 2006, which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Infection by hepatitis C virus (“HCV”) is a compelling human medical problem. HCV is recognized as the causative agent for most cases of non-A, non-B hepatitis, with an estimated human prevalence of 3% globally [A. Alberti et al., “Natural History of Hepatitis C,”  J. Hepatology,  31 (Suppl. 1), pp. 17-24 (1999)]. Nearly four million individuals may be infected in the United States alone [M. J. Alter et al., “The Epidemiology of Viral Hepatitis in the United States,  Gastroenterol. Clin. North Am.,  23, pp. 437-455 (1994); M. J. Alter “Hepatitis C Virus Infection in the United States,”  J. Hepatology,  31 (Suppl. 1), pp. 88-91 (1999)]. 
     Upon first exposure to HCV, only about 20% of infected individuals develop acute clinical hepatitis while others appear to resolve the infection spontaneously. In almost 70% of instances, however, the virus establishes a chronic infection that persists for decades [S. Iwarson, “The Natural Course of Chronic Hepatitis,”  FEMS Microbiology Reviews,  14, pp. 201-204 (1994); D. Lavanchy, “Global Surveillance and Control of Hepatitis C,”  J. Viral Hepatitis,  6, pp. 35-47 (1999)]. This usually results in recurrent and progressively worsening liver inflammation, which often leads to more severe disease states such as cirrhosis and hepatocellular carcinoma [M. C. Kew, “Hepatitis C and Hepatocellular Carcinoma”,  FEMS Microbiology Reviews,  14, pp. 211-220 (1994); I. Saito et al., “Hepatitis C Virus Infection is Associated with the Development of Hepatocellular Carcinoma,”  Proc. Natl. Acad. Sci. USA,  87, pp. 6547-6549 (1990)]. Unfortunately, there are no broadly effective treatments for the debilitating progression of chronic HCV. 
     The HCV genome encodes a polyprotein of 3010-3033 amino acids [Q. L. Choo, et al., “Genetic Organization and Diversity of the Hepatitis C Virus.”  Proc. Natl. Acad. Sci. USA,  88, pp. 2451-2455 (1991); N. Kato et al., “Molecular Cloning of the Human Hepatitis C Virus Genome From Japanese Patients with Non-A, Non-B Hepatitis,”  Proc. Natl. Acad. Sci. USA,  87, pp. 9524-9528 (1990); A. Takamizawa et al., “Structure and Organization of the Hepatitis C Virus Genome Isolated From Human Carriers,”  J. Virol.,  65, pp. 1105-1113 (1991)]. The HCV nonstructural (NS) proteins are presumed to provide the essential catalytic machinery for viral replication. The NS proteins are derived by proteolytic cleavage of the polyprotein [R. Bartenschlager et al., “Nonstructural Protein 3 of the Hepatitis C Virus Encodes a Serine-Type Proteinase Required for Cleavage at the NS3/4 and NS4/5 Junctions,” J. Virol.,  67, pp. 3835-3844 (1993); A. Grakoui et al., “Characterization of the Hepatitis C Virus-Encoded Serine Proteinase: Determination of Proteinase-Dependent Polyprotein Cleavage Sites,”  J. Virol.,  67, pp. 2832-2843 (1993); A. Grakoui et al., “Expression and Identification of Hepatitis C Virus Polyprotein Cleavage Products,”  J. Virol.,  67, pp. 1385-1395 (1993); L. Tomei et al., “NS3 is a serine protease required for processing of hepatitis C virus polyprotein”,  J. Virol.,  67, pp. 4017-4026 (1993)]. 
     The HCV NS protein 3 (NS3) is essential for viral replication and infectivity [Kolykhalov,  J. Virology , Volume 74, pp. 2046-2051 2000 “Mutations at the HCV NS3 Serine Protease Catalytic Triad abolish infectivity of HCV RNA in Chimpanzees]. It is known that mutations in the yellow fever virus NS3 protease decrease viral infectivity [Chambers, T. J. et al., “Evidence that the N-terminal Domain of Nonstructural Protein NS3 From Yellow Fever Virus is a Serine Protease Responsible for Site-Specific Cleavages in the Viral Polyprotein”,  Proc. Natl. Acad. Sci. USA,  87, pp. 8898-8902 (1990)]. The first 181 amino acids of NS3 (residues 1027-1207 of the viral polyprotein) have been shown to contain the serine protease domain of NS3 that processes all four downstream sites of the HCV polyprotein [C. Lin et al., “Hepatitis C Virus NS3 Serine Proteinase: Trans-Cleavage Requirements and Processing Kinetics”,  J. Virol.,  68, pp. 8147-8157 (1994)]. 
     The HCV NS3 serine protease and its associated cofactor, NS4A, help process all of the viral enzymes, and is thus considered essential for viral replication. This processing appears to be analogous to that carried out by the human immunodeficiency virus aspartyl protease, which is also involved in viral enzyme processing. HIV protease inhibitors, which inhibit viral protein processing, are potent antiviral agents in man indicating that interrupting this stage of the viral life cycle results in therapeutically active agents. Consequently, HCV NS3 serine protease is also an attractive target for drug discovery. 
     Until recently, the only established therapy for HCV disease was interferon treatment. However, interferons have significant side effects [M. A. Wlaker et al., “Hepatitis C Virus: An Overview of Current Approaches and Progress,”  DDT,  4, pp. 518-29 (1999); D. Moradpour et al., “Current and Evolving Therapies for Hepatitis C,”  Eur. J. Gastroenterol. Hepatol.,  11, pp. 1199-1202 (1999); H. L. A. Janssen et al. “Suicide Associated with Alfa-Interferon Therapy for Chronic Viral Hepatitis,”  J. Hepatol.,  21, pp. 241-243 (1994); P. F. Renault et al., “Side Effects of Alpha Interferon,”  Seminars in Liver Disease,  9, pp. 273-277 (1989)] and induce long term remission in only a fraction (˜25%) of cases [O. Weiland, “Interferon Therapy in Chronic Hepatitis C Virus Infection”,  FEMS Microbiol. Rev.,  14, pp. 279-288 (1994)]. Recent introductions of the pegylated forms of interferon (PEG-INTRON® and PEGASYS®) and the combination therapy of ribavirin and interferon (REBETROL®) have resulted in only modest improvements in remission rates and only partial reductions in side effects. Moreover, the prospects for effective anti-HCV vaccines remain uncertain. 
     Thus, there is a need for more effective anti-HCV therapies. Such inhibitors would have therapeutic potential as protease inhibitors, particularly as serine protease inhibitors, and more particularly as HCV NS3 protease inhibitors. Specifically, such compounds may be useful as antiviral agents, particularly as anti-HCV agents. 
     VX-950, an HCV inhibitor with its structure shown below is such a compound in need. VX-950 is described in PCT Publication Number WO 02/18369, which is incorporated herein by reference in its entirety. 
     
       
                 
         
             
             
         
      
     
     SUMMARY OF THE INVENTION 
     In general, the present invention relates to compositions containing the HCV inhibitor VX-950 and a specific co-crystal former (CCF). Under certain circumstances, VX-950 and the CCF together may form a crystalline composition, i.e., co-crystal. Compared to their free forms, specific VX-950 co-crystals are advantageous as they possess improved dissolution, higher aqueous solubility, and greater solid state physical stability than amorphous VX-950 dispersions. The specific VX-950 co-crystals provide a reduced mass of the dosage form and therefore lower pill burden since the VX-950 co-crystals also exhibit higher bulk densities relative to amorphous forms. Further, VX-950 co-crystals provide manufacturing advantages relative to amorphous forms which require spray drying, melt extrusion, lyophilization, or precipitation. 
     In one aspect, the compositions provided by this invention each contain VX-950 and a CCF compound selected from the group consisting of salicylic acid (SA), 4-amino salicylic acid (4-ASA), and oxalic acid (OA), as a CCF. In one embodiment, VX-950 and the CCF together are in the crystalline form in the composition. 
     In another aspect, this invention provides three VX-950 co-crystals each of which includes VX-950 and a CCF. Specifically, the first co-crystal includes VX-950 and salicylic acid (SA) as the CCF. In some embodiments, when the CCF is SA, the X-ray power diffraction (XRPD) spectrum of the co-crystal exhibits peaks at about 4.43, 7.63, 8.53, 9.63, 12.89, 14.83 and 16.29 2-Theta; and its differential scanning calorimetry (DSC) thermogram shows melting points at about 137° C. and about 223° C. The second co-crystal includes VX-950 and 4-amino salicylic acid (4-ASA) as the CCF. In some embodiments, when the CCF is 4-ASA, the XRPD spectrum of the co-crystal exhibits peaks at about 4.37, 7.57, 8.47, 9.59, 12.81, and 14.75 2-Theta; and its DSC thermogram shows a melting point at about 177° C. The third co-crystal includes VX-950 and oxalic acid (OA) as the CCF. In some embodiments, when the CCF is OA, the XRPD spectrum of this co-crystal exhibits peaks at about 4.65, 6.17, 9.63, 12.65, 14.91, and 28.97 2-Theta. In some embodiments, the ratio of the number of molecules of VX-950 and the CCF in the unit cell are between 0.2 and 5 (e.g., 1). In some embodiments, VX-950 and the CCF are both in the solid state (e.g., crystalline) and are bonded non-covalently (i.e., by hydrogen bond). 
     In another aspect, the invention provides co-crystals of the formula (VX-950) m :(CCF) n , wherein CCF is a co-crystal former selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid; and m and n, independently, are an integer of 1 to 5. In some embodiments, m and n are both 1. 
     In another aspect, the invention provides a co-crystal of VX-950 and a CCF, wherein the CCF is a solid at the room temperature, and VX-950 and the CCF interact by non-covalent bonds. In some embodiments, the CCF is selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid. In certain embodiments, the non-covalent bond interactions between VX-950 and the CCF include hydrogen bonding and van der Waals interactions. 
     In still another aspect, this invention provides a pharmaceutical composition that includes one of the three VX-950 co-crystals described above. In one embodiment, the pharmaceutical composition further includes a diluent, solvent, excipient, or carrier. 
     Still another aspect of this invention provides a method of making a co-crystal of VX-950 and a CCF selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid. The method includes the steps of providing VX-950; providing the co-crystal former salicylic acid, 4-amino salicylic acid, or oxalic acid; grinding, heating, co-subliming, co-melting, or contacting in solution VX-950 with the co-crystal former under crystallization condition so as to form the co-crystal in solid phase; and then optionally isolating the co-crystal formed thereby. In some embodiments, the making a co-crystal of VX-950 and a CCF includes providing VX-950 and the CCF in a molar ratio between about 10 to about 0.1. 
     In yet another aspect, the invention provides a method for modulating a chemical or physical property of interest (such as melting point, solubility, dissolution, hygroscopicity, and bioavailability) of a co-crystal containing VX-950 and a CCF selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid. The method includes the steps of measuring the chemical or physical property of interest for VX-950 and the co-crystal former; determining the mole fraction of the VX-950 and the co-crystal former that will result in the desired modulation of the chemical or physical property of interest; and preparing the co-crystal with the molar fraction as determined. 
     The compositions and co-crystals of this invention can be used for treating diseases implicated by or associated with HCV. Thus, also within the scope of this invention is a method of treating such diseases, which comprising administering to a subject in need thereof a therapeutically effective amount of a co-crystal of this invention or a composition of this invention. 
     The compositions and co-crystals of this invention can also be used as seeds to prepare additional co-crystals containing an active ingredient that can be the same as or different from VX-950, and a CCF that can also be the same as or different from salicylic acid, 4-amino salicylic acid, and oxalic acid. For instance, a small amount of a co-crystal of this invention can be placed into a solution containing the desired active ingredient and the CCF and the mixture is allowed to sit so that additional co-crystal can be formed with and grown out of the existing co-crystal. 
     Additionally, the compositions and co-crystals of this invention can be used as research tools. For instance, crystal structures of the co-crystals can be used for molecular modeling to identify other possible co-crystal formers. They can be used to study the pharmacological properties (such as bioavailability, metabolism, and efficacy). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a thermogravimetric analysis (TGA) spectrum of the co-crystal of VX-950 and SA. 
         FIG. 2  shows a TGA spectrum of the co-crystal of VX-950 and 4-ASA. 
         FIG. 3  shows a DSC thermogram of the co-crystal of VX-950 and SA. 
         FIG. 4  shows a DSC thermogram of the co-crystal of VX-950 and 4-ASA. 
         FIG. 5  shows XRPD spectra of the co-crystal of VX-950 and 4-ASA in water (upper) and 1% HPMC (lower) in 6 hours at room temperature. 
         FIG. 6  shows XRPD spectra of the co-crystal of VX-950 and SA in water in 1 hour (upper), 2 hours (middle), and 6 hours (lower) at room temperature. 
         FIG. 7  shows XRPD spectra of the co-crystal of VX-950 and SA in 1% HPMC in 1 hour (middle), 2 hours (upper), and 6 hours (lower) at the room temperature. 
         FIG. 8  shows an XRPD spectrum of the co-crystal between VX-950 and SA. 
         FIG. 9  shows an XRPD spectrum of the co-crystal of VX-950 and 4-ASA. 
         FIG. 10  shows an XRPD spectrum of the co-crystal of VX-950 and OA. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Methods for preparing and characterizing a co-crystal are well documented in the literature. See, e.g., Trask et al.,  Chem. Commun.,  2004, 890-891; and O. Almarsson and M. J. Zaworotko,  Chem. Commun.,  2004, 1889-1896. These methods in general are also suitable for preparing and characterizing co-crystals of this invention. 
     Examples of preparing co-crystals with an active pharmaceutical ingredients and a CCF include ball-milling, melting in a reaction block, evaporating solvent, slurry conversion, blending, sublimation, or modeling. In the ball-milling method, certain molar ratios of the components of the co-crystal (e.g., a compound of interest, such as VX-950 in this invention, and a CCF) are mixed and milled with balls. Optionally, a solvent such as methyl ethyl ketone can be added to the mixture being ball milled. After milling, the mixture can be dried under vacuum either at the room temperature or in the heated condition, which typically gives a powder product. In the melting method, the components of a co-crystal (e.g., a CCF and VX-950) are mixed, optionally with a solvent such as acetonitrile. The mixture is then placed in a reaction block with the lid closed, and then heated to the endotherm. The resulting mixture is then cooled off and solvent, if used, removed. In the solvent-evaporation method, each component of a co-crystal is first dissolved in a solvent (or a solvent mixture, such as 50/50 toluene and acetonitrile), and the solutions are then mixed together. The mixture is then allowed to sit and solvent to evaporate to dryness, to yield the co-crystal. 
     Examples of characterization methods include thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), solubility analyses, dynamic vapor sorption, infrared off-gas analysis, and suspension stability. TGA can be used to investigate the presence of residual solvents in a co-crystal sample, and to identify the temperature at which decomposition of each co-crystal sample occurs. DSC can be used to look for thermo-transitions occurring in a co-crystal sample as a function of temperature and determine the melting point of each co-crystal sample. XRPD can be used for structural characterization of the co-crystal. Solubility analysis can be performed to reflect the changes in the physical state of each co-crystal sample. And suspension stability analysis can be used to determine the chemical stability of a co-crystal sample in a solvent. 
     An effective amount of co-crystals or compositions of this invention, each including VX-950 and a co-crystal former (CCF) selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid, can be used to treat diseases implicated or associated with the HCV. An effective amount is the amount which is required to confer a therapeutic effect on the treated subject, e.g. a patient. The effective amount of a co-crystal of VX-950 and the CCF is between about 0.1 mg/kg to about 150 mg/kg (e.g., from about 1 mg/kg to about 60 mg/kg). Effective doses will also vary, as recognized by those skilled in the art, dependent on route of administration, excipient usage, and the possibility of co-usage with other therapeutic treatments including use of other therapeutic agents and/or therapy. 
     The co-crystals or pharmaceutical compositions of this invention can be administered to the subject in need thereof (e.g., cells, a tissue, or a patient (including an animal or a human)) by any method that permits the delivery of the compound VX-950, e.g., orally, intravenously, or parenterally. For instance, they can be administered via pills, tablets, capsules, aerosols, suppositories, liquid formulations for ingestion or injection or for use as eye or ear drops, dietary supplements, and topical preparations. 
     The pharmaceutical compositions can include diluents, solvents, excipients and carriers such as water, Ringer&#39;s solution, isotonic saline, 5% glucose, and isotonic sodium chloride solution. In another embodiment, the pharmaceutical composition can further include a solubilizing agent such as cyclodextrin. Additional examples of suitable diluents, solvents, excipients, carriers, and solubilizing agents can be found, e.g., in U.S. Pharmacopeia 23/National Formulary 18, Rockville, Md., U.S. Pharmacopeia Convention, Inc., (1995); Ansel H C, Popovich N G, Allen Jr L V. Pharmaceutical Dosage Forms and Drug Delivery Systems, Baltimore Md., Williams &amp;Wilkins, (1995); Gennaro A R., Remingtons: The Science and Practice of Pharmacy, Easton Pa., Mack Publishing Co., (1995); Wade A, Weller P J. Handbook of Pharmaceutical Excipients, 2nd Ed, Washington D.C., American Pharmaceutical Association, (1994); Baner G S, Rhodes C T. Modern Pharmaceutics, 3rd Ed., New York, Marcel Dekker, Inc., (1995); Ranade V V, Hollinger M A. Drug Delivery Systems. Boca Raton, CRC Press, (1996). 
     The pharmaceutical compositions can also include aqueous solutions of the co-crystal, in an isotonic saline, 5% glucose or other well-known pharmaceutically acceptable excipient(s). Solubilizing agents such as cyclodextrins, or other solubilizing agents well-known to those familiar with the art, can be utilized as pharmaceutical excipients for delivery of the therapeutic compound VX-950. As to route of administration, the co-crystals or pharmaceutical compositions can be administered orally, intranasally, transdermally, intradermally, vaginally, intraaurally, intraocularly, buccally, rectally, transmucosally, or via inhalation, or intravenous administration. The compositions may be delivered intravenously via a balloon catheter. The compositions can be administered to an animal (e.g., a mammal such as a human, non-human primate, horse, dog, cow, pig, sheep, goat, cat, mouse, rat, guinea pig, rabbit, hamster, gerbil, ferret, lizard, reptile, or bird). 
     The co-crystals or pharmaceutical compositions of this invention also can be delivered by implantation (e.g., surgically) such with an implantable device. Examples of implantable devices include, but are not limited to, stents, delivery pumps, vascular filters, and implantable control release compositions. Any implantable device can be used to deliver the compound VX-950 as the active ingredient in the co-crystals or pharmaceutical compositions of this invention, provided that 1) the device, compound VX-950 and any pharmaceutical composition including the compound are biocompatible, and 2) that the device can deliver or release an effective amount of the compound to confer a therapeutic effect on the treated patient. 
     Delivery of therapeutic agents via stents, delivery pumps (e.g., mini-osmotic pumps), and other implantable devices is known in the art. See, e.g., “Recent Developments in Coated Stents” by Hofma et al., published in  Current Interventional Cardiology Reports,  2001, 3: 28-36, the entire contents of which, including references cited therein, are incorporated herein. Other descriptions of implantable devices, such as stents, can be found in U.S. Pat. Nos. 6,569,195 and 6,322,847, and PCT International Publication Numbers WO 04/0044405, WO 04/0018228, WO 03/0229390, WO 03/0228346, WO 03/0225450, WO 03/0216699, and WO 03/0204168, each of which (as well as other publications cited herein) is incorporated herein in its entirety. 
     Described below are examples of preparing and characterizing co-crystals of this invention, which are meant to be only illustrative and not to be limiting in any way. 
     Example 1 
     Preparation by Ball-Milling Method 
     Salicylic Acid (SA): 70 mg of VX-950 and an equal molar equivalent of SA (Sigma Chemicals Co., St. Louis, Mo., USA) as the CCF were mixed with 50 μL of methyl ethyl ketone (“MEK”). The components were milled using a Wig-L-Bug apparatus for 10 minutes. After milling, a batch was dried in a vacuum oven at 75° C. for 2 hours. The resulting material was off-white in color. 
     4-Amino Salicylic Acid (4-ASA): 70 mg of VX-950 and an equal molar equivalent of 4-ASA (15.8 mg) (Sigma Chemicals Co., St. Louis, Mo., USA) as the CCF were mixed with 50 μL of acetonitrile (“ACN”). The components were then milled using a ball-mill apparatus Retsch MM200 (GlenMills Inc, Clifton, N.J.) for 3 hours at the frequency of 15 Hz. The mixture was placed in the milling compartment made of sintered corundum. After milling, the material was moved in 20-mL screw cap scintillation vial (no cap) and dried in the vacuum for 16 hours at the room temperature. After drying, the cap was screwed on. The resulting material was off white-grayish color. 
     Oxalic Acid (OA): 70 mg of VX-950 and an equal molar equivalent of OA (Sigma Chemicals Co., St. Louis, Mo., USA) as the CCF were mixed with 5 μL of less of any of the following solvents (based on 10 mg total solids): ethyl acetate, methyl ethyl ketone, acetonitrile, water or 1,2-dichloroethane. The components were ground together. A co-crystal of VX-950 and OA was obtained after the same procedure as described above. 
     Example 2 
     Preparation by Melting Method 
     100 mg of VX-950 and an equal molar equivalent of a CCF selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid (Sigma Chemicals Co., St. Louis, Mo., USA) were mixed by vortex for 5 minutes. This procedure was performed twice. Once it was performed without a solvent. At the second time, it was performed with 100 μL of acetonitrile, methyl ethyl ketone, and ethyl acetate for 4-amino salicylic acid, salicylic acid, and oxalic acid, respectively. The mixtures were placed in a reaction block (Radley Discovery Technologies, RR 98072) with the lid closed and heated to the endotherm. The mixtures were hold for 30 minutes at the endotherm temperature, and then the resulting mixture was cooled off under ambient conditions with the lid off, and the solvent, when used, removed. 
     Example 3 
     Preparation by Solvent-Evaporation Method 
     VX-950 and a CCF selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid (Sigma Chemicals Co., St. Louis, Mo., USA) were dissolved separately into a solvent mixture of 50% toluene/acetonitrile. Dissolution was aided by rotation and sonication until visual clarity in the solutions was obtained. VX-950 solutions were mixed with CCF solutions in 20-mL screw cap scintillation vials at 0:1, 1:3, 1:1 and 3:1, 1:0 molar ratios in 3 mL final volumes for all. These vials were placed uncapped in a fume hood and solvents allowed to evaporate to dryness over a period of several days, to give a solid material. 
     Example 4 
     Preparing by Modeling Method 
     The modeling also resulted in co-crystals of VX-950 and a CCF selected from the group consisting of salicylic acid, 4-amino salicylic acid, and oxalic acid (Sigma Chemicals Co., St. Louis, Mo., USA). 
     Example 5 
     Thermogravimetric Analysis (TGA) 
     TGA of each sample was performed using a Model Q500 Thermogravimetric Analyzer (TA Instruments, New Castle, Del., USA), which uses its control Thermal Advantage Q Series™ software, Version 2.2.0.248, Thermal Advantage Release 4.2.1 (TA Instruments-Water LLC), with the following components: QAdv.exe version 2.2 build 248.0; RhDII.dII version 2.2 build 248.0; RhBase.dII version 2.2 build 248.0; RhComm.dII version 2.2 build 248.0; TaLicense.dII version 2.2 build 248.0; and TGA.dII version 2.2 build 248.0. In addition, the analysis software used was Universal Analysis 2000 software for Windows 2000/XP, version 4.1 D build 4.1.0.16 (TA Instruments). 
     For all of the experiments, the basic procedure for performing TGA included transferring an aliquot (about 3-8 mg) of a sample into a platinum sample pan (Pan: Part No. 952018.906, TA Instruments). The pan was placed on a loading platform and was then automatically loaded into the Q500 Thermogravimetric Analyzer using the control software. Thermograms were obtained by individually heating the sample at 10° C./minute across a temperature range (generally from the room temperature to 300° C. under flowing dry nitrogen (compressed nitrogen, grade 4.8 (BOC Gases, Murray Hill, N.J., USA), with a sample purge flow rate of 90 L/minute and a balance purge flow rate of 10 L/minute. Thermal transitions (e.g. weight changes) were viewed and analyzed using the analysis software provided with the instrument. 
     As in  FIG. 1 , TGA spectrum of the co-crystal of VX-950 and SA (molar ratio being 1) shows an approximate 2.3% weight loss up to 145° C. and a total of 18% weight loss up to 160° C. This is consistent with the expected loss of salicylic acid for a 1:1 co-crystal. The first weight loss is likely due to the sublimation of salicylic Acid, which begins to sublime at 76° C. 
     As in  FIG. 2 , TGA spectrum of the co-crystal of VX-950 and 4-ASA (molar ratio also being 1) showed an approximate 1.4% weight loss up to 125° C. due to the solvent release and approximate 13% weight loss up to about 250° C. 
     Example 6 
     Differential Scanning Calorimetry (DSC) 
     DSC analysis was performed using an MDSC Q100 Differential Scanning Calorimeter (TA Instruments), which uses its control Thermal Advantage Q Series™ software, version 2.2.0.248, Thermal Advantage Release 4.2.1, with the following components: QAdv.exe version 2.2 build 248.0; RhDII.dII version 2.2 build 248.0; RhBase.dII version 2.2 build 248.0; RhComm.dII version 2.2 build 248.0; TaLicense.dII version 2.2 build 248.0; and DSC.dII version 2.2 build 248.0. In addition, the analysis software used was Universal Analysis 2000 software for Windows 2000/XP, version 4.1 D build 4.1.0.16 (TA Instruments). The instrument was calibrated with indium. 
     For all DSC analysis, an aliquot of a sample (approximately 2 mg) was weighed into an aluminum sample pan (Pan: Part No. 900786.901; and Lid: Part No. 900779.901, TA Instruments). The sample pan was closed by crimping with a single pinhole and then loaded into the Q100 Differential Scanning Calorimeter which was equipped with an autosampler. A thermogram was obtained by individually heating each sample at a rate at 10° C./minute across a temperature range (generally from the room temperature to −300° C.) under flowing dry nitrogen (compressed nitrogen, grade 4.8 (BOC Gases, Murray Hill, N.J., USA), with a sample purge flow rate of 60 L/minute and a balance purge flow rate of 40 L/minute. An empty aluminum pan prepared the same way as the pan with the sample was used a reference. Thermal transitions were viewed and analyzed using the analysis software provided with the instrument. 
     As in  FIG. 3 , DSC thermogram shows the co-crystal of VX-950 and SA first melt at approximately 137° C. The melting points of SA and VX-950 are 159° C. and 247° C., respectively. The second melting transition at 223° C. corresponds roughly to that of the free compound. The lower melting is observed due to the impurity presence, but may include some decomposition. 
     As in  FIG. 4 , DSC thermogram shows the co-crystal of VX-950 and 4-ASA melt at about 177° C. 
     Table 1 below is a summary of DSC screen for potential interaction between VX-950 and a CCF used in this invention. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 CCF 
                 Endo, Tm co-former (° C.) 
                 Endo, Tm possible eutectic (° C.) 
               
               
                   
               
             
             
               
                 4-ASA 
                 134 
                 167 
               
               
                 OA 
                 101 &amp; 192 
                 — 
               
               
                 SA 
                 159 &amp; 176 
                 122 
               
               
                   
               
             
          
         
       
     
     Example 7 
     X-ray Powder Diffraction (XRPD) 
     In XRPD analysis, an instrument from either Bruker or Rigaku was used. 
     a. Bruker 
     The XRPD pattern was obtained at the room temperature in reflection mode by using a Bruker D8 Discover diffractometer that was equipped with a sealed tube source and a Hi-Star area detector (Bruker AXS, Madison, Wis., USA). A copper target X-ray tube (Siemens) was operated at 40 kV and 35 mA. Graphite monochromator and 0.5 mm collimator provided by Bruker were used to produce parallel, monochromatic beam (CuKa, 1=1.5418 Å). The distance between the sample and the detector was approximately 30 cm. The sample was placed on a Si zero-background wafer (The Gem Dugout, State College, Pa.) which was then positioned and centered on XYZ platform. Data were acquired using GADDS software for Windows NT, version 4.1.16 (Bruker AXS, Madison, Wis., USA). Two frames were registered with an exposure time of 120 seconds per frame. The sample was oscillated in both X and Y directions with an amplitude of 1 mm during the exposure. The data were subsequently integrated over the range of 30 to 41° 2-Theta with a step size of 0.020 and merged into one continuous pattern. Corundum plate (NIST standard 1976) was used to calibrate the instrument. 
     b. Rigaku 
     The XRPD pattern was recorded at the room temperature in transmission mode using a rotating anode RUH3R X-ray generator (Rigaku, The Woodlands, Tex., USA) and a Rigaku Raxis IIC detector. Radiation of CuK at 50 kV and 100 mA was used. Focusing mirrors and a Ni filter were used to produce parallel, monochromatic beam (1=1.5418 Å). The sample was held in a 2 mm diameter boron glass capillary (Hampton Research, Aliso Viejo, Calif., USA) and was rotated around the f axis during the experiment. The distance between the sample and the detector was approximately 25 cm. A single frame with an exposure time of 300 seconds was recorded using CrystalClear software, Version 1.3.5 SP2 by Rigaku. The data were subsequently integrated over the range of 30 to 40° 2q with a step size of approximately 0.02°. Silicon powder (NIST standard 640c) was used to calibrate the instrument. 
     As shown in  FIG. 5 , in water and in 1% hydroxypropylmethylcellulose (HPMC) at the room temperature after 6 hours, the co-crystal of VX-950 and 4-ASA showed no sign of conversion to the free form after incubation times of up to 6 hours. At the 24-hour time point, the co-crystal was still intact in the 1% HPMC solution. However, in water the sample had converted back to the free form at the 24 hour time point. 
     By contrast, as shown in  FIG. 6 , the XRPD patterns of the co-crystal of VX-950 and SA, after suspension in water at room temperature, (i) after 1 hour, show a slight conversion from the co-crystal to the free from as indicated by the growth of the peak at 9.1 2-Theta(°), (ii) at the 2-hour time point, show additional conversion, and (iii) at the 6-hour time point, show complete conversion. After suspension in an aqueous solution of 1% HPMC, the same co-crystal shows slight conversion from the co-crystal to the free from at the 1-hour and 2-hour time point, and additional conversion at the 6-hour time point is observed. See  FIG. 7 . 
       FIG. 8 ,  FIG. 9 , and  FIG. 10  are the XRPD spectra of VX-950 co-crystals of SA, 4-ASA, and OA, respectively. Specifically, the co-crystal of VX-950 and SA shows XRPD peaks at 4.43, 7.63, 8.53, 9.63, 12.89, 14.83, and 16.29 2-Theta; the co-crystal of VX-950 and 4-ASA show XRPD peaks at 4.37, 7.57, 8.47, 9.59, 12.81, and 14.75 2-Theta; and the co-crystal of VX-950 and OA shows XRPD peaks at 4.65, 6.17, 8.21, 9.63, 12.65, 14.91, and 28.97 2-Theta. 
     Example 8 
     Solubility Analyses 
     An aliquot of the sample was placed in a tube and then an aqueous medium was added. At set time points, an aliquot of supernatant was withdrawn, filtered through 0.45 PTFE micron filter (Millex, LCR, Millipore) and processed for high performance liquid chromatography (HPLC) analysis (Agilent 1100; Palo Alto, Calif., USA). The system was equipped with an autosampler set at 25° C. For the sample handling, an aliquot of the sample was diluted with acetonitrile at 1 to 1 by v/v ratio. The samples were run isocratically with the detector set at 270 nm. The column was XTerra® Phenyl column 150 mm×4.6 mm, 3.5 μm Particle Size (P/N 186001144) (Waters, Milford, Mass., USA). The mobile phase was potassium phosphate buffer (10 mM, pH=7.0):methanol at 60:40 (v/v) ratio. The run was done at the flow-rate of 1 mL/min and was completed within 15 min. Table 2 below summarized the solubilities of VX-950 and its co-crystal with 4-ASA in simulated intestinal fluid (pH 6.8) at 24-h time point at room temperature (expressed in VX-950 equivalents (VX-950 eluted at 8.8 minutes)). 
     
       
         
               
               
               
               
             
               
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 C., mg/mL 
                 C., mg/mL 
                   
               
               
                 System 
                 Control 
                 Melt 
                 XRPD 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 VX-950 
                 0.025 
                   
                 Amorphous (up to 2 hours at 
               
               
                 alone 
                   
                   
                 room temp.) 
               
               
                   
                 0.0183 
                   
                 Starts crystallizing by about 
               
               
                   
                   
                   
                 4 hours at room temp. 
               
             
          
           
               
                   
                 Not 
                   
                 Crystallizes by 24 hour 
               
               
                   
                 Detected 
                   
                   
               
             
          
           
               
                 VX-950 and 
                   
                 0.148 
                 Crystalline up to 24 hrs. 
               
               
                 4-ASA 
                   
                   
                 No changes 
               
               
                   
               
             
          
         
       
     
     Example 9 
     Suspension Stability 
     The physical stability of the co-crystal upon suspension in aqueous media was evaluated. The co-crystal powder was slurried in (1) unbuffered, deionized water and (2) a 1% (w/w) solution of HPMC (low viscosity grade) at 25° C. at a nominal concentration of approximately 6 mg/ml. Slurries were mixed using a magnetic stir bar and plate. The samples of the solid were isolated by filtration at time intervals of 1, 2, 6 and 24 hours. 
     PXRD patterns of co-crystal of VX-950 and salicylic acid, after suspension in water for 1, 2, and 6 hours, show a slight conversion from the co-crystal to the free form after one hour as indicated by the growth of the peak at 9.1 2-Theta(°). Additional conversion is observed at the 2-hour time point and complete conversion is found at the 6-hour time point. 
     PXRD patterns of co-crystal of VX-950 and salicylic acid, after suspension in an aqueous solution of 1% HPMC at 1, 2, and 6 hours, indicate that the co-crystal underwent slight conversion from the co-crystal to the free from at the one-hour and 2-hour time points. Additional conversion at the 6 hour time point is observed. The HPMC appears to have decreased the conversion rate of the co-crystal to the free form. The slow conversion is also evidenced by the growing peak at 9.1 2-Theta(°). 
     PXRD patterns of co-crystal of VX-950 and 4-amino salicylic acid, after suspension in water and an aqueous solution of 1% HPMC at 6 hours. In both cases, the co-crystal showed no sign of conversion to the free form after incubation times of up to 6 hours. At the 24-hour time point, the co-crystal is still intact in the 1% HPMC solution. However, in water, the sample had converted back to the free form at the 24-hour time point. 
     Other Embodiments 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.