Patent Publication Number: US-2012041067-A1

Title: Methods of Inducing Terminal Differentiation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 12/799,368, filed on Apr. 23, 2010, which is a Divisional of U.S. patent application Ser. No. 11/853,700, filed on Sep. 11, 2007, now U.S. Pat. No. 7,732,490, which is a Continuation of U.S. patent application Ser. No. 10/379,149, filed on Mar. 4, 2003 (abandoned), which claims the benefit of U.S. Provisional Application No. 60/361,759, filed Mar. 4, 2002. The teachings of these applications are incorporated herein by reference in their entirety. 
     REFERENCE TO JOINT RESEARCH AGREEMENT 
     Certain subject matter claimed herein was made under a Joint Research Agreement between Aton Pharma, Inc. and Sloan-Kettering Institute for Cancer Research and its affiliate Memorial Hospital for Cancer and Allied Diseases. 
    
    
     GOVERNMENT INTEREST STATEMENT 
     This invention was made in whole or in part with government support under grant number 1R21CA 096228-01 awarded by the National Cancer Institute. The government may have certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention provides methods of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, and/or inhibiting histone deacetylases (HDAC) administration of pharmaceutical compositions comprising HDAC inhibitors. The oral formulations of the pharmaceutical compositions have favorable pharmacokinetic profiles such as high bioavailability and surprisingly give rise to high blood levels of the active compounds over an extended period of time. 
     BACKGROUND OF THE INVENTION 
     Throughout this application various publications are referenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains. 
     Cancer is a disorder in which a population of cells has become, in varying degrees, unresponsive to the control mechanisms that normally govern proliferation and differentiation. For many years there have been two principal strategies for chemotherapeutic treatment of cancer: a) blocking hormone-dependent tumor cell proliferation by interference with the production or peripheral action of sex hormones; and b) killing cancer cells directly by exposing them to cytotoxic substances, which injure both neoplastic and normal cell populations. 
     Cancer therapy is also being attempted by the induction of terminal differentiation of the neoplastic cells (1). In cell culture models differentiation has been reported by exposure of cells to a variety of stimuli, including: cyclic AMP and retinoic acid (2,3), aclarubicin and other anthracyclines (4). 
     Despite many advances in the field of oncology, the majority of solid tumors remain incurable in the advanced stages. Cytotoxic therapy is used in most cases, however, it often causes significant morbidity to the patient without significant clinical benefit. Less toxic and more specific agents to treat and control advanced malignancies are being explored. 
     There is abundant evidence that neoplastic transformation does not necessarily destroy the potential of cancer cells to differentiate (1,5,6). There are many examples of tumor cells which do not respond to the normal regulators of proliferation and appear to be blocked in the expression of their differentiation program, and yet can be induced to differentiate and cease replicating. A variety of agents, including some relatively simple polar compounds (5,7-9), derivatives of vitamin D and retinoic acid (10-12), steroid hormones (13), growth factors (6,14), proteases (15,16), tumor promoters (17,18), and inhibitors of DNA or RNA synthesis (4,19-24), can induce various transformed cell lines and primary human tumor explants to express more differentiated characteristics. 
     Early studies identified a series of polar compounds that were effective inducers of differentiation in a number of transformed cell lines (8,9). Of these, the most effective inducer was the hybrid polar/apolar compound N,N′-hexamethylene bisacetamide (HMBA) (9). The use of this polar/apolar compound to induce murine erythroleukemia cells (MELC) to undergo erythroid differentiation with suppression of oncogenicity has proved a useful model to study inducer-mediated differentiation of transformed cells (5,7-9). HMBA-induced MELC terminal erythroid differentiation is a multi-step process. Upon addition of HMBA to MELC (745A-DS19) in culture, there is a latent period of 10 to 12 hours before commitment to terminal differentiation is detected. Commitment is defined as the capacity of cells to express terminal differentiation despite removal of inducer (25). Upon continued exposure to HMBA there is progressive recruitment of cells to differentiate. The present inventors have reported that MELC cell lines made resistant to relatively low levels of vincristine become markedly more sensitive to the inducing action of HMBA and can be induced to differentiate with little or no latent period (26). 
     HMBA is capable of inducing phenotypic changes consistent with differentiation in a broad variety of cells lines (5). The characteristics of the drug-induced effect have been most extensively studied in the murine erythroleukemia cell system (MELC) (5,25,27,28). MELC induction of differentiation is both time and concentration dependent. The minimum concentration required to demonstrate an effect in vitro in most strains is 2 to 3 mM; the minimum duration of continuous exposure generally required to induce differentiation in a substantial portion (&gt;20%) of the population without continuing drug exposure is about 36 hours. 
     The primary target of action of HMBA is not known. There is evidence that protein kinase C is involved in the pathway of inducer-mediated differentiation (29). The in vitro studies provided a basis for evaluating the potential of HMBA as a cytodifferentiation agent in the treatment of human cancers (30). Several phase I clinical trials with HMBA have been completed (31-36). Clinical trials have shown that this compound can induce a therapeutic response in patients with cancer (35,36). However, these phase I clinical trials also have demonstrated that the potential efficacy of HMBA is limited, in part, by dose-related toxicity which prevents achieving optimal blood levels and by the need for intravenous administration of large quantities of the agent, over prolonged periods. 
     It has been reported that a number of compounds related to HMBA with polar groups separated by apolar linkages that, on a molar basis, are as active (37) or 100 times more active than HMBA (38). As a class, however, it has been found that the symmetrical dimers such as HMBA and related compounds are not the best cytodifferentiating agents. 
     It has unexpectedly been found that the best compounds comprise two polar end groups separated by a flexible chain of methylene groups, wherein one or both of the polar end groups is a large hydrophobic group. Preferably, the polar end groups are different and only one is a large hydrophobic group. These compounds are unexpectedly a thousand times more active than HMBA and ten times more active than HMBA related compounds. 
     Histone deacetylase inhibitors such as suberoylanilide hydroxamide acid (SAHA), belong to this class of agents that have the ability to induce tumor cell growth arrest, differentiation and/or apoptosis (39). These compounds are targeted towards mechanisms inherent to the ability of a neoplastic cell to become malignant, as they do not appear to have toxicity in doses effective for inhibition of tumor growth in animals (40). There are several lines of evidence that histone acetylation and deacetylation are mechanisms by which transcriptional regulation in a cell is achieved (41). These effects are thought to occur through changes in the structure of chromatin by altering the affinity of histone proteins for coiled DNA in the nucleosome. There are five types of histones that have been identified in nucleosomes (designated H1, H2A, H2B, H3 and H4). Each nucleosome contains two of each histone type within its core, except for H1, which is present singly in the outer portion of the nucleosome structure. It is believed that when the histone proteins are hypoacetylated, there is a greater affinity of the histone to the DNA phosphate backbone This affinity causes DNA to be tightly bound to the histone and renders the DNA inaccessible to transcriptional regulatory elements and machinery. The regulation of acetylated states occurs through the balance of activity between two enzyme complexes, histone acetyl transferase (HAT) and histone deacetylase (HDAC). The hypoacetylated state is thought to inhibit transcription of associated DNA. This hypoacetylated state is catalyzed by large multiprotein complexes that include HDAC enzymes. In particular, HDACs have been shown to catalyze the removal of acetyl groups from the chromatin core histones. 
     The inhibition of HDAC by SAHA is thought occur through direct interaction with the catalytic site of the enzyme as demonstrated by X-ray crystallography studies (42). The result of HDAC inhibition is not believed to have a generalized effect on the genome, but rather, only affects a small subset of the genome (43). Evidence provided by DNA microarrays using malignant cell lines cultured with a HDAC inhibitor shows that there are a finite (1-2%) number of genes whose products are altered. For example, cells treated in culture with HDAC inhibitors show a consistent induction of the cyclin-dependent kinase inhibitor p21 (44). This protein plays an important role in cell cycle arrest. HDAC inhibitors are thought to increase the rate of transcription of p21 by propagating the hyperacetylated state of histones in the region of the p21 gene, thereby making the gene accessible to transcriptional machinery. Genes whose expression is not affected by HDAC inhibitors do not display changes in the acetylation of regional associated histones (45). 
     It has been shown in several instances that the disruption of HAT or HDAC activity is implicated in the development of a malignant phenotype. For instance, in acute promyelocytic leukemia, the oncoprotein produced by the fusion of PML and RAR alpha appears to suppress specific gene transcription through the recruitment of HDACs (46). In this manner, the neoplastic cell is unable to complete differentiation and leads to excess proliferation of the leukemic cell line. 
     U.S. Pat. Nos. 5,369,108, 5,932,616, 5,700,811, 6,087,367 and 6,511,990, issued to some of the present inventors, disclose compounds useful for selectively inducing terminal differentiation of neoplastic cells, which compounds have two polar end groups separated by a flexible chain of methylene groups or a by a rigid phenyl group, wherein one or both of the polar end groups is a large hydrophobic group. Some of the compounds have an additional large hydrophobic group at the same end of the molecule as the first hydrophobic group which further increases differentiation activity about 100 fold in an enzymatic assay and about 50 fold in a cell differentiation assay. Methods of synthesizing the compounds used in the methods and pharmaceutical compositions of this invention are fully described the aforementioned patents, the entire contents of which are incorporated herein by reference. 
     The aforementioned patents do not disclose specific oral formulations of the HDAC inhibitors or specific dosages and dosing schedules of the recited compounds. Importantly, the aforementioned patents do not disclose oral formulations that have favorable pharmacokinetic profiles such as high bioavailability which gives rise to high blood levels of the active compounds over an extended period of time. 
     The class of compounds of the present invention may be useful for selectively inducing terminal differentiation of neoplastic cells and therefore aid in treatment of tumors in patients. Thus there is an urgent need to discover suitable dosages and dosing schedules of these compounds, and to develop formulations, preferably oral formulations, which give rise to steady, therapeutically effective blood levels of the active compounds over an extended period of time. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods of producing a mean plasma concentration of a histone deacetylase (HDAC) inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration, which comprises administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention also provides methods for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, thereby inhibiting proliferation of such cells, and methods for inducing differentiation of tumor cells by producing a mean plasma concentration of a histone deacetylase (HDAC) inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration, by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention further provides methods of producing a mean plasma concentration of at least about 10 nM of suberoylanilide hydroxamic acid (SAHA) in vivo in a subject over a period of at least two hours following administration, which comprises administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention also provides methods for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, thereby inhibiting proliferation of such cells, and methods for inducing differentiation of tumor cells by producing a mean plasma concentration of at least 10 nM of SAHA in vivo in a subject over a period of at least two hours following administration, by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention provides pharmaceutical compositions suitable for oral administration, which comprise a compound useful for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, and/or which is a potent inhibitor of histone deacetylase (HDAC). The pharmaceutical compositions are further comprised of microcrystalline cellulose, croscarmellose sodium and magnesium stearate. The present invention also provides for pharmaceutical compositions for oral administration comprising SAHA, microcrystalline cellulose, croscarmellose sodium and magnesium stearate. The oral bioavailability of the active compounds in the formulations of the present invention is surprisingly high. Moreover, the formulations unexpectedly give rise to high, therapeutically effective blood levels of the active compounds over an extended period of time. The present invention further provides a safe, daily dosing regimen of these formulations, which is easy to follow and to adhere to. 
     As demonstrated herein, it has been surprisingly and unexpectedly found that oral formulations comprising HDAC inhibitors, particularly suberoylanilide hydroxamic acid (SAHA), have very high overall oral bioavailability of the active compound in vivo. Furthermore, the formulations give rise to high blood levels of the active compound, which remain unexpectedly high over an extended period of time, for example, up to 10-12 hours. The oral formulations of the present invention have many advantages, especially when compared to parenteral formulations, since on the one end they provide high, stable and prolonged therapeutically effective blood levels of HDAC inhibitors, and on the other hand are easy to administer to patients by any conventional mode of oral administration. 
     Accordingly, the present invention provides a pharmaceutical composition for oral administration comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. In a preferred embodiment, the concentration of the HDAC inhibitor is effective to inhibit the HDAC for a period of at least 10 hours following administration. 
     In a preferred embodiment, the present invention provides a pharmaceutical composition for oral administration comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of SAHA effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. In a preferred embodiment, the concentration of SAHA is effective to inhibit the HDAC for a period of at least 10 hours following administration. 
     The formulations of the present invention are useful for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells and therefore aid in treatment of tumors in patients. 
     Accordingly, the present invention also provides a method of selectively inducing terminal differentiation of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising the step of orally administering to the subject an effective amount of a pharmaceutical composition comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention also provides a method of selectively inducing cell growth arrest of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising the step of orally administering to the subject an effective amount of a pharmaceutical composition comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention also provides a method of selectively inducing apoptosis of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising the step of orally administering to the subject an effective amount of a pharmaceutical composition comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof; and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention also provides a method of inducing differentiation of tumor cells in a subject having a tumor, comprising the step of orally administering to the subject an effective amount of a pharmaceutical composition comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof; and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention provides a method of inhibiting the activity of a histone deacetylase in a subject, comprising the step of orally administering to the subject an effective amount of a pharmaceutical composition comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention also provides a method of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising the step of administering to the subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof; wherein the composition provides a mean plasma concentration of SAHA effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention also provides a method of inducing differentiation of tumor cells in a subject having a tumor comprising the step of administering to the subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof; wherein the composition provides a mean plasma concentration of SAHA effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     Furthermore, the present invention provides a method of inhibiting the activity of a histone deacetylase in a subject, comprising the step of orally administering to the subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of SAHA effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. 
     In a preferred embodiment, SAHA or any of the HDAC inhibitors are administered to the patient at a total daily dosage of between 25-4000 mg/m 2 . In another preferred embodiment, SAHA or any of the HDAC inhibitors are administered to the patient at a total daily dosage of 200 mg. SAHA or any of the HDAC inhibitors are administered to the patient at a total daily dosage of 400 mg. 
     In one preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor (e.g., SAHA) capable of inhibiting histone deacetylase over a period of at least 2 hours following administration, which is preferably at a concentration of at least about 10 nM. In yet another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 10 nM over a period of at least 10 hours following administration. 
     In one preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor (e.g., SAHA) capable of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, or capable of inducing differentiation of tumor cells in a tumor, wherein the concentration is maintained over a period of at least 2 hours following administration, which is preferably at a concentration of at least about 2.5 In yet another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 2.5 μM over a period of at least 10 hours following administration. 
     The compositions of the present invention may be formulated in any unit dosage form (liquid or solid) suited for oral administration, for example, in the form of a pellet, a tablet, a coated tablet, a capsule, a gelatin capsule, a solution, a suspension, or a dispersion. In a preferred embodiment, the composition is in the form of a gelatin capsule. 
     Any inert excipient that is commonly used as a carrier or diluent may be used in the formulations of the present invention, such as for example, a gum, a starch, a sugar, a cellulosic material, an acrylate, or mixtures thereof. A preferred diluent is microcrystalline cellulose. The compositions may further comprise a disintegrating agent (e.g., sodium croscarmellose) and a lubricant (e.g., magnesium stearate), and in addition may comprise one or more additives selected from a binder, a buffer, a protease inhibitor, a surfactant, a solubilizing agent, a plasticizer, an emulsifier, a stabilizing agent, a viscosity increasing agent, a sweetener, a film forming agent, or any combination thereof. Furthermore, the compositions of the present invention may be in the form of controlled release or immediate release formulations. 
     A wide variety of HDAC inhibitors are suitable for use in the compositions of the present invention. In a preferred embodiment, the HDAC inhibitor is suberoylanilide hydroxamic acid (SAHA). 
     
       
         
         
             
             
         
       
     
     Other non-limiting examples of HDAC inhibitors that are suitable for use in the compositions of the present invention are: 
     Pyroxamide, represented by the structure: 
     
       
         
         
             
             
         
       
     
     A compound represented by the structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 3  and R 4  are independently a substituted or unsubstituted, branched or unbranched alkyl, alkenyl, cycloalkyl, aryl, alkyloxy, aryloxy, arylalkyloxy, or pyridine group, cycloalkyl, aryl, aryloxy, arylalkyloxy, or pyridine group, or R 3  and R 4  bond together to form a piperidine group; R 2  is a hydroxylamino group; and n is an integer from 5 to about 8. 
           
         
       
    
     A compound represented by the structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R is a substituted or unsubstituted phenyl, piperidine, thiazole, 2-pyridine, 3-pyridine or 4-pyridine and n is an integer from about 4 to about 8. 
           
         
       
    
     A compound represented by the structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein A is an amide moiety, R 1  and R 2  are each selected from substituted or unsubstituted aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, pyridineamino, 9-purine-6-amino, thiazoleamino, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; R 4  is hydrogen, a halogen, a phenyl or a cycloalkyl moiety and n is an integer from 3 to 10. 
           
         
       
    
     Furthermore, in accordance with specific embodiments of the present invention, there is provided a pharmaceutical composition for oral administration comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof; microcrystalline cellulose as a carrier or diluent; croscarmellose sodium as a disintegrant; and magnesium stearate as a lubricant; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase in vivo for a period of at least 2 hours following administration. In a preferred embodiment, the HDAC inhibitor is suberoylanilide hydroxamic acid (SAHA). 
     Furthermore, in accordance with specific embodiments of the present invention, there is provided a pharmaceutical composition for oral administration comprising suberoylanilide hydroxamic acid (SAHA) or a pharmaceutically acceptable salt or hydrate thereof; microcrystalline cellulose as a carrier or diluent; croscarmellose sodium as a disintegrant; and magnesium stearate as a lubricant; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase in vivo for a period of at least 2 hours following administration. In another preferred embodiment, the composition comprises 50-70% by weight of SAHA or a pharmaceutically acceptable salt or hydrate thereof; 20-40% by weight microcrystalline cellulose as a carrier or diluent; 5-15% by weight croscarmellose sodium as a disintegrant; and 0.1-5% by weight magnesium stearate as a lubricant. In another preferred embodiment, the composition comprises about 50-200 mg of SAHA. In a particularly preferred embodiment, the composition is in the form of a gelatin capsule. 
     The present invention further provides a safe, daily dosing regimen of these formulations, which is easy to follow and to adhere to. The formulations of the present invention are useful for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells and therefore aid in treatment of tumors in patients. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is a picture of a Western blot (top panel) showing the quantities of acetylated histone-4 (α-ACH4) in the blood plasma of patients following an oral or intravenous (IV) dose of SAHA. IV SAHA was administered at 200 mg infused over two hours. Oral SAHA was administered in a single capsule at 200 mg. The amount of α-ACH4 is shown at the indicated time points. Bottom panel: Coomassie blue stain. 
         FIG. 2  is a picture of a Western blot (top panels) showing the quantities of acetylated histone-4 (α-ACH4) in the blood plasma of patients having a solid tumor, following an oral or intravenous (IV) dose of SAHA. IV and Oral SAHA were administered as in  FIG. 1 . The amount of α-ACH4 is shown at the indicated time points. The experiment is shown in duplicate ( FIG. 2A  and  FIG. 2B ). Bottom panels: Coomassie blue stain. 
         FIG. 3  is a picture of a Western blot (top panels) showing the quantities of acetylated histone-4 (α-ACH4) ( FIG. 3A ) and acetylated histone-3 (α-ACH3) ( FIGS. 3B-E ) in the blood plasma of patients following an oral or intravenous (IV) dose of SAHA, on Day 1 and Day 21. IV and Oral SAHA were administered as in  FIG. 1 . The amount of α-ACH4 or α-ACH3 is shown at the indicated time points. Bottom panels: Coomassie blue stain. 
         FIG. 4  is a picture of a Western blot (top panels) showing the quantities of acetylated histone-3 (α-ACH3) in the blood plasma of patients having a solid tumor, following an oral or intravenous (IV) dose of SAHA. IV and Oral SAHA were administered as in  FIG. 1 . The amount of α-ACH3 is shown at the indicated time points. Bottom panel: Coomassie blue stain. 
         FIG. 5  is a picture of a Western blot (top panels) showing the quantities of acetylated histone-3 (α-ACH3) in the blood plasma of patients following an oral or intravenous (IV) dose of SAHA. IV SAHA was administered at 400 mg infused over two hours. Oral SAHA was administered in a single capsule at 400 mg. The amount of α-ACH4 is shown at the indicated time points. The experiment is shown in triplicate ( FIGS. 5A  and B). Bottom panels: Coomassie blue stain. 
         FIG. 6  is a picture of a Western blot (top panel) showing the quantities of acetylated histone-3 (α-ACH3) in the blood plasma of patients having a solid tumor, following an oral or intravenous (IV) dose of SAHA. IV and Oral SAHA were administered as in  FIG. 5 . The amount of α-ACH3 is shown at the indicated time points. Bottom panel: Coomassie blue stain. 
         FIG. 7  is a picture of a Western blot (top panels) showing the quantities of acetylated histone-3 (α-ACH3) in the blood plasma of patients having a solid tumor following an oral or intravenous (IV) dose of SAHA, on Day 1 and Day 21. IV and Oral SAHA were administered as in  FIG. 4 . The amount of α-ACH4 or α-ACH3 is shown at the indicated time points. The experiment is shown in triplicate ( FIG. 7  A-C). Bottom panels: Coomassie blue stain. 
         FIG. 8  is a picture of a Western blot (top panels) showing the quantities of acetylated histone-3 (α-ACH3) in the blood plasma of patients following an oral or intravenous (IV) dose of SAHA. IV and Oral SAHA were administered as in  FIG. 5 . The amount of α-ACH3 is shown at the indicated time points. Bottom panels: Coomassie blue stain. 
       FIGS.  9 A-C— is a graph showing the mean plasma concentration of SAHA (ng/ml) at the indicated time points following administration.  FIG. 9A : Oral dose (200 mg and 400 mg) under fasting on Day 8.  FIG. 9B : Oral dose with food on Day 9.  FIG. 9C : IV dose on day 1. 
         FIG. 10  shows the apparent half-life of a SAHA 200 mg and 400 mg oral dose, on Days 8, 9 and 22. 
         FIG. 11  shows the AUC (ng/ml/hr) of a SAHA 200 mg and 400 mg oral dose, on Days 8, 9 and 22. 
         FIG. 12  shows the bioavailability of SAHA after a 200 mg and 400 mg oral dose, on Days 8, 9 and 22. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides methods of producing a mean plasma concentration of a histone deacetylase (HDAC) inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration, which comprises administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention also provides methods for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, thereby inhibiting proliferation of such cells, and methods for inducing differentiation of tumor cells by producing a mean plasma concentration of a histone deacetylase (HDAC) inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration, by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention further provides methods of producing a mean plasma concentration of at least about 10 nM of suberoylanilide hydroxamic acid (SAHA) in vivo in a subject over a period of at least two hours following administration, which comprises administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention also provides methods for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, thereby inhibiting proliferation of such cells, and methods for inducing differentiation of tumor cells by producing a mean plasma concentration of at least 10 nM of SAHA in vivo in a subject over a period of at least two hours following administration, by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     The present invention provides pharmaceutical compositions suitable for oral administration, which comprise a compound useful for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, and/or which is a potent inhibitor of histone deacetylase (HDAC). The pharmaceutical compositions are further comprised of microcrystalline cellulose, croscarmellose sodium and magnesium stearate. The present invention also provides for pharmaceutical compositions for oral administration comprising SAHA, microcrystalline cellulose, croscarmellose sodium and magnesium stearate. The oral bioavailability of the active compounds in the formulations of the present invention is surprisingly high. Moreover, the formulations unexpectedly give rise to high, therapeutically effective blood levels of the active compounds over an extended period of time. The present invention further provides a safe, daily dosing regimen of these formulations, which is easy to follow and to adhere to. 
     The oral bioavailability of the active compounds in the formulations of the present invention is surprisingly high. Moreover, the formulations unexpectedly give rise to high, therapeutically effective blood levels of the active compounds over an extended period of time. The present invention further provides a safe, daily dosing regimen of these formulations, which is easy to follow, and which gives rise to a therapeutically effective amount of the recited compounds in vivo. The formulations of the present invention are useful for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, and therefore aid in treatment of tumors in patients. 
     As demonstrated herein, the pharmaceutical compositions provided in the present invention give rise to an initial mean plasma concentration (i.e., the concentration that is obtained immediately after administration of the formulation), which remains unexpectedly high over an extended period of time. As compared with parenteral formulations (such as IV formulations) having the same dosage, in which the active compounds clear almost immediately, the oral compositions retain a high mean plasma concentration of the active compound over an extended period of time, for at least 2 hours, but more typically at least, 10 or 12 hours. Typically, the mean plasma concentration of the oral dosage formulations, does not drop below 50% of the initial mean plasma concentration for a period of time of up to 12 hours or even longer. 
     Up until the findings of the present invention, intravenous administration of the HDAC inhibitors described herein has proven to be the most effective. The intravenous administration of the compound must be performed continuously, i.e., daily, for a prolonged period of time, such as for at least 3 days and preferably more than 5 days. This obviously provides a heavy burden on the patient receiving this treatment. The unexpected and surprising findings of the present invention make it possible to formulate oral dosage forms that give rise to high and steady levels of the active compounds in-vivo, without the need to continuously administer the drugs, by IV infusions, which provides a tremendous advantage for the patient receiving the treatment. 
     Accordingly, the present invention provides a pharmaceutical composition for oral administration comprising a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of the HDAC inhibitor effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. In a preferred embodiment, the concentration of the HDAC inhibitor is effective to inhibit the HDAC for a period of at least 8 hours following administration. In another preferred embodiment, the concentration of the HDAC inhibitor is effective to inhibit the HDAC for a period of at least 10 hours following administration. In another preferred embodiment, the concentration of the HDAC inhibitor is effective to inhibit the HDAC for a period of at least 12 hours following administration. 
     In a preferred embodiment, the present invention provides a pharmaceutical composition for oral administration comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent; wherein the composition provides a mean plasma concentration of SAHA effective to inhibit a histone deacetylase (HDAC) in vivo for a period of at least 2 hours following administration. In a preferred embodiment, the concentration of SAHA is effective to inhibit the HDAC for a period of at least 8 hours following administration. In another preferred embodiment, the concentration of SAHA is effective to inhibit the HDAC for a period of at least 10 hours following administration. In another preferred embodiment, the concentration of SAHA is effective to inhibit the HDAC for a period of at least 12 hours following administration. 
     The formulations of the present invention are useful for selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells and therefore aid in treatment of tumors in patients. 
     Accordingly, the present invention also provides a method of selectively inducing terminal differentiation of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising producing a mean plasma concentration of a HDAC inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of selectively inducing cell growth arrest of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising producing a mean plasma concentration of a HDAC inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of selectively inducing apoptosis of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising producing a mean plasma concentration of a HDAC inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of inducing differentiation of tumor cells in a subject having a tumor, producing a mean plasma concentration of a HDAC inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention provides a method of inhibiting the activity of a histone deacetylase in a subject, comprising producing a mean plasma concentration of a HDAC inhibitor capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising producing a mean plasma concentration of SAHA capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells in a subject and thereby inhibiting proliferation of such cells in the subject, comprising producing a mean plasma concentration of at least 10 nM of SAHA in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of inducing differentiation of tumor cells in a subject having a tumor comprising producing a mean plasma concentration of SAHA capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention also provides a method of inducing differentiation of tumor cells in a subject having a tumor comprising producing a mean plasma concentration of at least 10 nM of SAHA in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention provides a method of inhibiting the activity of a histone deacetylase in a subject, comprising producing a mean plasma concentration of SAHA capable of inhibiting a histone deacetylase in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     Furthermore, the present invention provides a method of inhibiting the activity of a histone deacetylase in a subject, comprising producing a mean plasma concentration of at least 10 nM of SAHA in vivo in a subject over a period of at least two hours following administration by administering to said subject an effective amount of a pharmaceutical composition comprising SAHA or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or diluent. 
     In another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor (e.g., SAHA) capable of inhibiting histone deacetylase over a period of at least 2 hours following administration, which is preferably at a concentration of at least about 10 nM. In another embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 10 nM over a period of at least 8 hours following administration. In yet another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 10 nM over a period of at least 10 hours following administration. In yet another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 10 nM over a period of at least 12 hours following administration. Non-limiting examples of mean plasma concentrations are about 10 nM, 25 nM, 40 nM, 45 nM, 50 nM, 100 nM, 1 μM, 2 μM, 2.5 μM, 5 μM 10 μM, 25, μM, 50 μM, 100 μM and the like. It should be apparent to a person skilled in the art that these doses are in no way limiting the scope of this invention, and that any mean plasma concentration which is capable of inhibiting a histone deacetylase is suitable. 
     In one preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor (e.g., SAHA) capable of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells, or inducing differentiation of tumor cells in a tumor, wherein the concentration is maintained over a period of at least 2 hours following administration, which is preferably at a concentration of at least about 2.5 μM. In another embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 2.5 μM over a period of at least 8 hours following administration. In yet another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 2.5 μM over a period of at least 10 hours following administration. In yet another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor of at least about 2.5 μM over a period of at least 12 hours following administration. Non-limiting examples of mean plasma concentrations are about 10 nM, 25 nM, 40 nM, 45 nM, 50 nM, 100 nM, 1 μM, 2 μM, 2.5 μM, 5 μM 10 μM, 25, μM, 50 μM, 100 μM and the like. It should be apparent to a person skilled in the art that these doses are in no way limiting the scope of this invention, and that any mean plasma concentration which is capable of inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells is suitable. 
     In another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor (e.g., SAHA) effective to induce differentiation of tumor cells in a subject having a tumor, wherein the amount is maintained for a period of at least 2 hours following administration to the subject. In another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor effective to induce differentiation of tumor cells in a subject having a tumor, wherein the amount is maintained for a period of at least 8 hours following administration to the subject. In another preferred embodiment, the composition provides a mean plasma concentration of the HDAC inhibitor effective to induce differentiation of tumor cells in a subject having a tumor, wherein the amount is maintained for a period of at least about 10 hours following administration to the subject. Non-limiting examples of mean plasma concentrations are about 10 nM, 25 nM, 40 nM, 45 nM, 50 nM, 100 nM, 1 μM, 2 μM, 2.5 μM, 5 μM 10 μM, 25, μM, 50 μM, 100 μM and the like. It should be apparent to a person skilled in the art that these doses are in no way limiting the scope of this invention, and that any mean plasma concentration which is capable of inducing differentiation of tumor cells in a tumor is suitable. 
     The methods of the present invention are suitable for practice in vitro and in vivo. If the methods are practiced in vitro, contacting may be effected by incubating the cells with the compound. The concentration of the compound in contact with the cells should be from about 1 about nM to about 25 mM, for example, from about 10 nM to about 1 mM, from about 40 nM to about 0.5 mM. Non-limiting examples of specific doses are 10 nM, 25 nM, 40 nM, 45 nM, 50 nM, 100 nM, 1 μM, 2 μM, 2.5 μM, 5 μM, 10 μM, 25, μM, 50 μM, 100 μM and the like. The concentration depends upon the individual compound and the state of the neoplastic cells. 
     Although the methods of the present invention can be practiced in vitro, it is contemplated that the preferred embodiment for the methods of selectively inducing terminal differentiation, cell growth arrest and/or apoptosis of neoplastic cells will comprise contacting the cells in vivo, i.e., by administering the compounds to a subject harboring neoplastic cells or tumor cells in need of treatment. 
     The methods of the present invention may also comprise initially administering to the subject an antitumor agent so as to render the neoplastic cells in the subject resistant to an antitumor agent and subsequently administering an effective amount of any of the compositions of the present invention, effective to selectively induce terminal differentiation, cell growth arrest and/or apoptosis of such cells. 
     The antitumor agent may be one of numerous chemotherapy agents such as an alkylating agent, an antimetabolite, a hormonal agent, an antibiotic, colchicine, a vinca alkaloid, L-asparaginase, procarbazine, hydroxyurea, mitotane, nitrosoureas or an imidazole carboxamide. Suitable agents are those agents that promote depolarization of tubulin. Preferably the antitumor agent is colchicine or a vinca alkaloid; especially preferred are vinblastine and vincristine. In embodiments where the antitumor agent is vincristine, the cells preferably are treated so that they are resistant to vincristine at a concentration of about 5 mg/ml. The treating of the cells to render them resistant to an antitumor agent may be effected by contacting the cells with the agent for a period of at least 3 to 5 days. The contacting of the resulting cells with any of the compounds above is performed as described previously. In addition to the above chemotherapy agents, the compounds may also be administered together with radiation therapy. 
     The present invention also provides a method of treating a patient having a tumor characterized by proliferation of neoplastic cells which comprises administering to the patient an effective amount of any of the compositions of the present invention above, effective to selectively induce terminal differentiation of such neoplastic cells and thereby inhibit their proliferation. 
     The method of the present invention is intended for the treatment of human patients with tumors. However, it is also likely that the method would be effective in the treatment of tumors in other mammals. The term tumor is intended to include any cancer caused by the proliferation of neoplastic cells, such as lung cancer, acute lymphoid myeloma, Hodgkins lymphoma, non-Hodgkins lymphoma, bladder melanoma, renal carcinoma, breast carcinoma, prostate carcinoma, ovarian carcinoma or colorectal carcinoma. 
     The administration of the pharmaceutical compositions can be carried out in unit dosages which may be administered orally once a day, twice a day, three times a day and the like. Currently preferred embodiments are once-daily administration, twice-daily administration and three-times daily administration. 
     Histone Deacetylases and Histone Deacetylase Inhibitors 
     Histone deacetylases (HDACs), as that term is used herein, are enzymes that catalyze the removal of acetyl groups from lysine residues in the amino terminal tails of the nucleosomal core histones. As such, HDACs together with histone acetyl transferases (HATs) regulate the acetylation status of histones. Histone acetylation affects gene expression and inhibitors of HDACs, such as the hydroxamic acid-based hybrid polar compound suberoylanilide hydroxamic acid (SAHA) induce growth arrest, differentiation and/or apoptosis of transformed cells in vitro and inhibit tumor growth in vivo. HDACs can be divided into three classes based on structural homology. Class I HDACs (HDACs 1, 2, 3 and 8) bear similarity to the yeast RPD3 protein, are located in the nucleus and are found in complexes associated with transcriptional co-repressors. Class II HDACs (HDACs 4, 5, 6, 7 and 9) are similar to the yeast HDA1 protein, and have both nuclear and cytoplasmic subcellular localization. Both Class I and II HDACs are inhibited by hydroxamic acid-based HDAC inhibitors, such as SAHA. Class III HDACs form a structurally distant class of NAD dependent enzymes that are related to the yeast SIR2 proteins and are not inhibited by hydroxamic acid-based HDAC inhibitors. 
     Histone deacetylase inhibitors or HDAC inhibitors, as that term is used herein are compounds that are capable of inhibiting the deacetylation of histones in vivo, in vitro or both. As such, HDAC inhibitors inhibit the activity of at least one histone deacetylase. As a result of inhibiting the deacetylation of at least one histone, an increase in acetylated histone occurs and accumulation of acetylated histone is a suitable biological marker for assessing the activity of HDAC inhibitors. Therefore, procedures that can assay for the accumulation of acetylated histones can be used to determine the HDAC inhibitory activity of compounds of interest. It is understood that compounds that can inhibit histone deacetylase activity can also bind to other substrates and as such can inhibit other biologically active molecules such as enzymes. It is also to be understood that the compounds of the present invention are capable of inhibiting any of the histone deacetylases set forth above, or any other histone deacetylases. 
     For example, in patients receiving HDAC inhibitors, the accumulation of acetylated histones in peripheral mononuclear cells as well as in tissue treated with HDAC inhibitors can be determined against a suitable control. 
     HDAC inhibitory activity of a particular compound can be determined in vitro using, for example, an enzymatic assays which shows inhibition of at least one histone deacetylase. Further, determination of the accumulation of acetylated histones in cells treated with a particular composition can be determinative of the HDAC inhibitory activity of a compound. 
     Assays for the accumulation of acetylated histones are well known in the literature. See, for example, Marks, P. A. et al., J. Natl. Cancer Inst., 92:1210-1215, 2000, Butler, L. M. et al., Cancer Res. 60:5165-5170 (2000), Richon, V. M. et al., Proc. Natl. Acad. Sci., USA, 95:3003-3007, 1998, and Yoshida, M. et al., J. Biol. Chem., 265:17174-17179, 1990. 
     For example, an enzymatic assay to determine the activity of a histone deacetylase inhibitor compound can be conducted as follows. Briefly, the effect of an HDAC inhibitor compound on affinity purified human epitope-tagged (Flag) HDAC1 can be assayed by incubating the enzyme preparation in the absence of substrate on ice for about 20 minutes with the indicated amount of inhibitor compound. Substrate ([ 3 H]acetyl-labelled murine erythroleukemia cell-derived histone) can be added and the sample can be incubated for 20 minutes at 37° C. in a total volume of 30 μL. The reaction can then be stopped and released acetate can be extracted and the amount of radioactivity release determined by scintillation counting. An alternative assay useful for determining the activity of a histone deacetylase inhibitor compound is the “HDAC Fluorescent Activity Assay; Drug Discovery Kit-AK-500” available from BIOMOL® Research Laboratories, Inc., Plymouth Meeting, Pa. 
     In vivo studies can be conducted as follows. Animals, for example, mice, can be injected intraperitoneally with an HDAC inhibitor compound. Selected tissues, for example, brain, spleen, liver etc, can be isolated at predetermined times, post administration. Histones can be isolated from tissues essentially as described by Yoshida et al., J. Biol. Chem. 265:17174-17179, 1990. Equal amounts of histones (about 1 μg) can be electrophoresed on 15% SDS-polyacrylamide gels and can be transferred to Hybond-P filters (available from Amersham). Filters can be blocked with 3% milk and can be probed with a rabbit purified polyclonal anti-acetylated histone H4 antibody (αAc-H4) and anti-acetylated histone H3 antibody (αAc-H3) (Upstate Biotechnology, Inc.). Levels of acetylated histone can be visualized using a horseradish peroxidase-conjugated goat anti-rabbit antibody (1:5000) and the SuperSignal chemiluminescent substrate (Pierce). As a loading control for the histone protein, parallel gels can be run and stained with Coomassie Blue (CB). 
     In addition, hydroxamic acid-based HDAC inhibitors have been shown to up regulate the expression of the p21 WAF1  gene. The p21 WAF1  protein is induced within 2 hours of culture with HDAC inhibitors in a variety of transformed cells using standard methods. The induction of the p21 WAF1  gene is associated with accumulation of acetylated histones in the chromatin region of this gene. Induction of p21 WAF1  can therefore be recognized as involved in the G1 cell cycle arrest caused by HDAC inhibitors in transformed cells. 
     Typically, HDAC inhibitors fall into five general classes: 1) hydroxamic acid derivatives; 2) Short-Chain Fatty Acids (SCFAs); 3) cyclic tetrapeptides; 4) benzamides; and 5) electrophilic ketones. 
     Thus, the present invention includes within its broad scope compositions comprising HDAC inhibitors which are 1) hydroxamic acid derivatives; 2) Short-Chain Fatty Acids (SCFAs); 3) cyclic tetrapeptides; 4) benzamides; 5) electrophilic ketones; and/or any other class of compounds capable of inhibiting histone deacetylases, for use in inhibiting histone deacetylase, inducing terminal differentiation in neoplastic cells, and/or inducing differentiation of tumor cells in a tumor. 
     Examples of such HDAC inhibitors include, but are not limited to: 
     A. Hydroxamic Acid Derivatives such as suberoylanilide hydroxamic acid (SAHA) (Richon et al., Proc. Natl. Acad. Sci. USA 95, 3003-3007 (1998)); m-carboxycinnamic acid bishydroxamide (CBHA) (Richon et al., supra); pyroxamide; trichostatin analogues such as trichostatin A (TSA) and trichostatin C (Koghe et al. 1998. Biochem. Pharmacol. 56: 1359-1364); salicylihydroxamic acid (SBHA) (Andrews et al., International J. Parasitology 30, 761-768 (2000)); suberoyl bishydroxamic acid (SBHA) (U.S. Pat. No. 5,608,108); azelaic bishydroxamic acid (ABHA) (Andrews et al., supra); azelaic-1-hydroxamate-9-anilide (AAHA) (Qiu et al., Mol. Biol. Cell 11, 2069-2083 (2000)); 6-(3-chlorophenylureido) carpoic hydroxamic acid (3C1-UCHA); oxamflatin [(2E)-5-[3-[(phenylsulfonyl) amino]phenyl]-pent-2-en-4-ynohydroxamic acid] (Kim et al. Oncogene, 18: 2461 2470 (1999)); A-161906, Scriptaid (Su et al. 2000 Cancer Research, 60: 3137-3142); PXD-101 (Prolifix); LAQ-824; CHAP; MW2796 (Andrews et al., supra); MW2996 (Andrews et al., supra); or any of the hydroxamic acids disclosed in U.S. Pat. Nos. 5,369,108, 5,932,616, 5,700,811, 6,087,367 and 6,511,990.
 
B. Cyclic Tetrapeptides such as trapoxin A (TPX)-cyclic tetrapeptide (cyclo-(L-phenylalanyl-L-phenylalanyl-D-pipecolinyl-L-2-amino-8-oxo-9,10-epoxy decanoyl)) (Kijima et al., J. Biol. Chem. 268,22429-22435 (1993)); FR901228 (FK 228, depsipeptide) (Nakajima et al., Ex. Cell Res. 241, 126-133 (1998)); FR225497 cyclic tetrapeptide (H. Mori et al., PCT Application WO 00/08048 (17 Feb. 2000)); apicidin cyclic tetrapeptide [cyclo(N—O-methyl-L-tryptophanyl-L-isoleucinyl-D-pipecolinyl-L-2-amino-8-oxodecanoyl)] (Darkin-Rattray et al., Proc. Natl. Acad. Sci. USA 93,1314313147 (1996)); apicidin Ia, apicidin Ib, apicidin Ic, apicidin Ha, and apicidin Hb (P. Dulski et al., PCT Application WO 97/11366); CHAP, HC-toxin cyclic tetrapeptide (Bosch et al., Plant Cell 7, 1941-1950 (1995)); WF27082 cyclic tetrapeptide (PCT Application WO 98/48825); and chlamydocin (Bosch et al., supra).
 
C. Short chain fatty acid (SCFA) derivatives such as: sodium butyrate (Cousens et al., J. Biol. Chem. 254, 1716-1723 (1979)); isovalerate (McBain et al., Biochem. Pharm. 53: 1357-1368 (1997)); valerate (McBain et al., supra); 4-phenylbutyrate (4-PBA) (Lea and Tulsyan, Anticancer Research, 15, 879-873 (1995)); phenylbutyrate (PB) (Wang et al., Cancer Research, 59, 2766-2799 (1999)); propionate (McBain et al., supra); butyramide (Lea and Tulsyan, supra); isobutyramide (Lea and Tulsyan, supra); phenylacetate (Lea and Tulsyan, supra); 3-bromopropionate (Lea and Tulsyan, supra); tributyrin (Guan et al., Cancer Research, 60, 749-755 (2000)); valproic acid and valproate.
 
D. Benzamide derivatives such as CI-994; MS-27-275 [N-(2-aminophenyl)-4-[N-(pyridin-3-ylmethoxycarbonyl) aminomethyl]benzamide] (Saito et al., Proc. Natl. Acad. Sci. USA 96, 4592-4597 (1999)); and 3′-amino derivative of MS-27-275 (Saito et al., supra).
 
E. Electrophilic ketone derivatives such as trifluoromethyl ketones (Frey et al, Bioorganic &amp; Med. Chem. Lett. (2002), 12, 3443-3447; U.S. Pat. No. 6,511,990) and α-keto amides such as N-methyl-α-ketoamides
 
F. Other HDAC Inhibitors such as depudecin (Kwon et al. 1998. PNAS 95: 3356-3361.
 
     Preferred hydroxamic acid based HDAC inhibitors are suberoylanilide hydroxamic acid (SAHA), m-carboxycinnamic acid bishydroxamate (CBHA) and pyroxamide. SAHA has been shown to bind directly in the catalytic pocket of the histone deacetylase enzyme. SAHA induces cell cycle arrest, differentiation and/or apoptosis of transformed cells in culture and inhibits tumor growth in rodents. SAHA is effective at inducing these effects in both solid tumors and hematological cancers. It has been shown that SAHA is effective at inhibiting tumor growth in animals with no toxicity to the animal. The SAHA-induced inhibition of tumor growth is associated with an accumulation of acetylated histones in the tumor. SAHA is effective at inhibiting the development and continued growth of carcinogen-induced (N-methylnitrosourea) mammary tumors in rats. SAHA was administered to the rats in their diet over the 130 days of the study. Thus, SAHA is a nontoxic, orally active antitumor agent whose mechanism of action involves the inhibition of histone deacetylase activity. 
     Preferred HDAC inhibitors are those disclosed in U.S. Pat. Nos. 5,369,108, 5,932,616, 5,700,811, 6,087,367 and 6,511,990, issued to some of the present inventors disclose compounds, the entire contents of which are incorporated herein by reference, non-limiting examples of which are set forth below: 
     Thus, in one embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 1, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein R 1  and R 2  can be the same or different; when R 1  and R 2  are the same, each is a substituted or unsubstituted arylamino, cycloalkylamino, pyridineamino, piperidino, 9-purine-6-amine or thiazoleamino group; when R 1  and R 2  are different R 1 =R 3 —N—R 4 , wherein each of R 3  and R 4  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted, branched or unbranched alkyl, alkenyl, cycloalkyl, aryl alkyloxy, aryloxy, arylalkyloxy or pyridine group, or R 3  and R 4  are bonded together to form a piperidine group, R 2  is a hydroxylamino, hydroxyl, amino, alkylamino, dialkylamino or alkyloxy group and n is an integer from about 4 to about 8. 
     In a particular embodiment of Formula 1, R 1  and R 2  are the same and are a substituted or unsubstituted thiazoleamino group; and n is an integer from about 4 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 2, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of R 3  and R 4  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted, branched or unbranched alkyl, alkenyl, cycloalkyl, arylalkyloxy, aryloxy, arylalkyloxy or pyridine group, or R 3  and R 4  are bonded together to form a piperidine group, R 2  is a hydroxylamino, hydroxyl, amino, alkylamino, dialkylamino or alkyloxy group and n is an integer from about 4 to about 8. 
     In a particular embodiment of formula 2, each of R 3  and R 4  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted, branched or unbranched alkyl, alkenyl, cycloalkyl, aryl, alkyloxy, aryloxy, arylalkyloxy, or pyridine group, or R 3  and R 4  bond together to form a piperidine group; R 2  is a hydroxylamino, hydroxyl, amino, alkylamino, or alkyloxy group; n is an integer from 5 to 7; and R 3 —N—R 4  and R 2  are different. 
     In another particular embodiment of Formula 2, n is 6. In yet another embodiment of Formula II, R 4  is a hydrogen atom, R 3  is a substituted or unsubstituted phenyl and n is 6. In yet another embodiment of Formula II, R 4  is a hydrogen atom, R 3  is a substituted phenyl and n is 6, wherein the phenyl substituent is selected from the group consisting of a methyl, cyano, nitro, trifluoromethyl, amino, aminocarbonyl, methylcyano, chloro, fluoro, bromo, iodo, 2,3-difluoro, 2,4-difluoro, 2,5-difluoro, 3,4-difluoro, 3,5-difluoro, 2,6-difluoro, 1,2,3-trifluoro, 2,3,6-trifluoro, 2,4,6-trifluoro, 3,4,5-trifluoro, 2,3,5,6-tetrafluoro, 2,3,4,5,6-pentafluoro, azido, hexyl, t-butyl, phenyl, carboxyl, hydroxyl, methoxy, phenyloxy, benzyloxy, phenylaminooxy, phenylaminocarbonyl, methoxycarbonyl, methylaminocarbonyl, dimethylamino, dimethylamino carbonyl, or hydroxylaminocarbonyl group. 
     In another embodiment of formula 2, n is 6, R 4  is a hydrogen atom and R 3  is a cyclohexyl group. In another embodiment of formula 2, n is 6, R 4  is a hydrogen atom and R 3  is a methoxy group. In another embodiment of formula 2, n is 6 and R 3  and R 4  bond together to form a piperidine group. In another embodiment of formula 2, n is 6, R 4  is a hydrogen atom and R 3  is a benzyloxy group. In another embodiment of formula 2, R 4  is a hydrogen atom and R 3  is a γ-pyridine group. In another embodiment of formula 2, R 4  is a hydrogen atom and R 3  is a β-pyridine group. In another embodiment of formula 2, R 4  is a hydrogen atom and R 3  is an α-pyridine group. In another embodiment of formula 2, n is 6, and R 3  and R 4  are both methyl groups. In another embodiment of formula II, n is 6, R 4  is a methyl group and R 3  is a phenyl group. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 3, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 5 to about 8. 
     In a preferred embodiment of formula 3, n is 6. In accordance with this embodiment, the present invention provides a pharmaceutical composition comprising SAHA (4), or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. SAHA can be represented by the following structural formula. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 5, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 6 (pyroxamide), or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 7, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 8, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 9, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 10, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein R 3  is hydrogen and R 4  cycloalkyl, aryl, aryloxy, arylalkyloxy, or pyridine group, or R 3  and R 4  bond together to form a piperidine group; R 2  is a hydroxylamino group; and n is an integer from 5 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 11, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein R 3  and R 4  are independently a substituted or unsubstituted, branched or unbranched alkyl, alkenyl, cycloalkyl, aryl, alkyloxy, aryloxy, arylalkyloxy, or pyridine group, cycloalkyl, aryl, aryloxy, arylalkyloxy, or pyridine group, or R 3  and R 4  bond together to form a piperidine group; R 2  is a hydroxylamino group; and n is an integer from 5 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 12, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X and Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino, or aryloxyalkylamino group; R is a hydrogen atom, a hydroxyl, group, a substituted or unsubstituted alkyl, arylalkyloxy, or aryloxy group; and each of m and n are independently the same as or different from each other and are each an integer from about 0 to about 8. 
     In a particular embodiment, the HDAC inhibitor is a compound of Formula XI wherein X, Y and R are each hydroxyl and both m and n are 5. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 13, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X and Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino or aryloxyalkylamino group; each of R 1  and R 2  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted alkyl, aryl, alkyloxy, or aryloxy group; and each of m, n and o are independently the same as or different from each other and are each an integer from about 0 to about 8. 
     In one particular embodiment of formula 13, each of X and Y is a hydroxyl group and each of R 1  and R 2  is a methyl group. In another particular embodiment of formula 13, each of X and Y is a hydroxyl group, each of R 1  and R 2  is a methyl group, each of n and o is 6, and m is 2. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 14, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X and Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino or aryloxyalkylamino group; each of R 1  and R 2  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted alkyl, aryl, alkyloxy, or aryloxy group; and each of m and n are independently the same as or different from each other and are each an integer from about 0 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 15, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X and Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino or aryloxyalkylamino group; and each of m and n are independently the same as or different from each other and are each an integer from about 0 to about 8. 
     In one particular embodiment of formula 1, each of X and Y is a hydroxyl group and each of m and n is 5. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 16, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X and Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino or aryloxyalkylamino group; R 1  and R 2  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted alkyl, arylalkyloxy or aryloxy group; and each of m and n are independently the same as or different from each other and are each an integer from about 0 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 17, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X an Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, or aryloxyalkylamino group; and n is an integer from about 0 to about 8. 
     In one particular embodiment of formula 17, each of X and Y is a hydroxylamino group; R 1  is a methyl group, R 2  is a hydrogen atom; and each of m and n is 2. In another particular embodiment of formula 17, each of X and Y is a hydroxylamino group; R 1  is a carbonylhydroxylamino group, R 2  is a hydrogen atom; and each of m and n is 5. In another particular embodiment of formula 17, each of X and Y is a hydroxylamino group; each of R 1  and R 2  is a fluoro group; and each of m and n is 2. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 18, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of X and Y are independently the same as or different from each other and are a hydroxyl, amino or hydroxylamino group, a substituted or unsubstituted alkyloxy, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkyamino or aryloxyalkylamino group; each of R 1  and R 2  are independently the same as or different from each other and are a hydrogen atom, a hydroxyl group, a substituted or unsubstituted alkyl, aryl, alkyloxy, aryloxy, carbonylhydroxylamino or fluoro group; and each of m and n are independently the same as or different from each other and are each an integer from about 0 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 19, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of R 1  and R 2  are independently the same as or different from each other and are a hydroxyl, alkyloxy, amino, hydroxylamino, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino, or aryloxyalkylamino group. In a particular embodiment, the HDAC inhibitor is a compound of structural Formula X wherein R 1  and R 2  are both hydroxylamino. 
     In one particular embodiment of formula 19, R 1  is a phenylamino group and R 2  is a hydroxylamino group. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 20, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of R 1  and R 2  are independently the same as or different from each other and are a hydroxyl, alkyloxy, amino, hydroxylamino, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino, or aryloxyalkylamino group. In a particular embodiment, the HDAC inhibitor is a compound of structural Formula XI wherein R 1  and R 2  are both hydroxylamino. 
     In one particular embodiment of formula XVIII, R 1  is a hydroxylamino group. In another particular embodiment of formula 21, R 2  is a hydroxylamino group. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 22, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of R 1  and R 2  are independently the same as or different from each other and are a hydroxyl, alkyloxy, amino, hydroxylamino, alkylamino, dialkylamino, arylamino, alkylarylamino, alkyloxyamino, aryloxyamino, alkyloxyalkylamino, or aryloxyalkylamino group. In a particular embodiment, the HDAC inhibitor is a compound of structural Formula XII wherein R 1  and R 2  are both hydroxylamino. 
     In one particular embodiment of formula 23, R 1  is a phenylamino group and R 2  is a hydroxylamino group. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 24, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein R is a phenylamino group substituted with a cyano, methylcyano, nitro, carboxyl, aminocarbonyl, methylaminocarbonyl, dimethylaminocarbonyl, trifluoromethyl, hydroxylaminocarbonyl, N-hydroxylaminocarbonyl, methoxycarbonyl, chloro, fluoro, methyl, methoxy, 2,3-difluoro, 2,4-difluoro, 2,5-difluoro, 2,6-difluoro, 3,5-difluoro, 2,3,6-trifluoro, 2,4,6-trifluoro, 1,2,3-trifluoro, 3,4,5-trifluoro, 2,3,4,5-tetrafluoro, or 2,3,4,5,6-pentafluoro group; and n is an integer from 4 to 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 25 (CBHA), or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 26, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 27, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein R is a substituted or unsubstituted phenyl, piperidine, thiazole, 2-pyridine, 3-pyridine or 4-pyridine and n is an integer from about 4 to about 8. 
     In one particular embodiment of formula 27, R is a substituted phenyl group. In another particular embodiment of formula 27, R is a substituted phenyl group, where the substituent is selected from the group consisting of methyl, cyano, nitro, thio, trifluoromethyl, amino, aminocarbonyl, methylcyano, chloro, fluoro, bromo, iodo, 2,3-difluoro, 2,4-difluoro, 2,5-difluoro, 3,4-difluoro, 3,5-difluoro, 2,6-difluoro, 1,2,3-trifluoro, 2,3,6-trifluoro, 2,4,6-trifluoro, 3,4,5-trifluoro, 2,3,5,6-tetrafluoro, 2,3,4,5,6-pentafluoro, azido, hexyl, t-butyl, phenyl, carboxyl, hydroxyl, methyloxy, phenyloxy, benzyloxy, phenylaminooxy, phenylaminocarbonyl, methyloxycarbonyl, methylaminocarbonyl, dimethylamino, dimethylaminocarbonyl, or hydroxylaminocarbonyl group. 
     In another particular embodiment of formula 27, R is a substituted or unsubstituted 2-pyridine, 3-pyridine or 4-pyridine and n is an integer from about 4 to about 8. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 28, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein R is a substituted or unsubstituted phenyl, pyridine, piperidine or thiazole group and n is an integer from about 4 to about 8 or a pharmaceutically acceptable salt thereof. 
     In a particular embodiment of formula 28, R is a substituted phenyl group. In another particular embodiment of formula 28, R is a substituted phenyl group, where the substituent is selected from the group consisting of methyl, cyano, nitro, thio, trifluoromethyl, amino, aminocarbonyl, methylcyano, chloro, fluoro, bromo, iodo, 2,3-difluoro, 2,4-difluoro, 2,5-difluoro, 3,4-difluoro, 3,5-difluoro, 2,6-difluoro, 1,2,3-trifluoro, 2,3,6-trifluoro, 2,4,6-trifluoro, 3,4,5-trifluoro, 2,3,5,6-tetrafluoro, 2,3,4,5,6-pentafluoro, azido, hexyl, t-butyl, phenyl, carboxyl, hydroxyl, methyloxy, phenyloxy, benzyloxy, phenylaminooxy, phenylaminocarbonyl, methyloxycarbonyl, methylaminocarbonyl, dimethylamino, dimethylaminocarbonyl, or hydroxylaminocarbonyl group. 
     In another particular embodiment of formula 28, R is phenyl and n is 5. In another embodiment, n is 5 and R is 3-chlorophenyl. 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 29, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of R 1  and R 2  is directly attached or through a linker and is substituted or unsubstituted, aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, cycloalkyl, cycloalkylamino, pyridineamino, piperidino, 9-purine-6-amino, thiazoleamino, hydroxyl, branched or unbranched alkyl, alkenyl, alkyloxy, aryloxy, arylalkyloxy, pyridyl, or quinolinyl or isoquinolinyl; n is an integer from about 3 to about 10 and R 3  is a hydroxamic acid, hydroxylamino, hydroxyl, amino, alkylamino or alkyloxy group. The linker can be an amide moiety, e.g., O—, —S—, —NH—, NR 5 , —CH 2 —, —(CH 2 ) m —, —(CH═CH)—, phenylene, cycloalkylene, or any combination thereof, wherein R 5  is a substitute or unsubstituted C 1 -C 5  alkyl. 
     In certain embodiments of formula 29, R 1  is —NH—R 4  wherein R 4  is substituted or unsubstituted, aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, cycloalkyl, cycloalkylamino, pyridineamino, piperidino, 9-purine-6-amino, thiazoleamino, hydroxyl, branched or unbranched alkyl, alkenyl, alkyloxy, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl 
     In another embodiment, the present invention provides a pharmaceutical composition comprising a compound represented by the structure of formula 30, or a pharmaceutically acceptable salt or hydrate thereof, and a pharmaceutically acceptable carrier or excipient. 
     
       
         
         
             
             
         
       
     
     wherein each of R 1  and R 2  is, substituted or unsubstituted, aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, cycloalkyl, cycloalkylamino, pyridineamino, piperidino, 9-purine-6-amino, thiazoleamino, hydroxyl, branched or unbranched alkyl, alkenyl, alkyloxy, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; R 3  is hydroxamic acid, hydroxylamino, hydroxyl, amino, alkylamino or alkyloxy group; R 4  is hydrogen, halogen, phenyl or a cycloalkyl moiety; and A can be the same or different and represents an amide moiety, O—, —S—, —NH—, NR 5 , —CH 2 —, —(CH 2 ) m —, —(CH═CH)—, phenylene, cycloalkylene, or any combination thereof wherein R 5  is a substitute or unsubstituted C 1 -C 5  alkyl; and n and m are each an integer from 3 to 10. 
     In further particular embodiment compounds having a more specific structure within the scope of compounds 29 or 30 are: 
     A compound represented by the structure of formula 31: 
     
       
         
         
             
             
         
       
     
     wherein A is an amide moiety, R 1  and R 2  are each selected from substituted or unsubstituted aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, pyridineamino, 9-purine-6-amino, thiazoleamino, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; and n is an integer from 3 to 10. 
     For example, the compound of formula 30 can have the structure 31 or 32: 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2  and n have the meanings of Formula 30. 
     A compound represented by the structure of formula 33: 
     
       
         
         
             
             
         
       
     
     wherein R 7  is selected from substituted or unsubstituted aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, pyridineamino, 9-purine-6-amino, thiazoleamino, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; n is an integer from 3 to 10 and Y is selected from: 
     
       
         
         
             
             
         
       
     
     A compound represented by the structure of formula 34: 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10, Y is selected from 
     
       
         
         
             
             
         
       
     
     and R 7 ′ is selected from 
     
       
         
         
             
             
         
       
     
     A compound represented by the structure of formula 35: 
     
       
         
         
             
             
         
       
     
     aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, pyridineamino, 9-purine-6-amino, thiazoleamino, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; n is an integer from 3 to 10 and R 7 ′ is selected from 
     
       
         
         
             
             
         
       
     
     A compound represented by the structure of formula 36: 
     
       
         
         
             
             
         
       
     
     wherein A is an amide moiety, R 1  and R 2  are each selected from substituted or unsubstituted aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, pyridineamino, 9-purine-6-amino, thiazoleamino, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; R 4  is hydrogen, a halogen, a phenyl or a cycloalkyl moiety and n is an integer from 3 to 10. 
     For example, the compound of formula 36 can have the structure 37 or 38: 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 4  and n have the meanings of Formula 36. 
     A compound represented by the structure of formula 39: 
     
       
         
         
             
             
         
       
     
     wherein L is a linker selected from the group consisting of an amide moiety, O—, —S—, —NH—, NR 5 , —CH 2 —, —(CH 2 ) m —, —(CH═CH)—, phenylene, cycloalkylene, or any combination thereof wherein R 5  is a substitute or unsubstituted C 1 -C 5  alkyl; and wherein each of R 7  and R 8  are independently a substituted or unsubstituted aryl (e.g., phenyl), arylalkyl (e.g., benzyl), naphthyl, pyridineamino, 9-purine-6-amino, thiazoleamino, aryloxy, arylalkyloxy, pyridyl, quinolinyl or isoquinolinyl; n is an integer from 3 to 10 and m is an integer from 0-10.
 
For example, a compound of Formula 39 can be:
 
     
       
         
         
             
             
         
       
     
     Other HDAC inhibitors suitable for use in the invention include those shown in the following more specific formulas: 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 41, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 42, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 43, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 44, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 45, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 46, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 47, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 48, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 49, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 50, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 51, n=5. 
     
       
         
         
             
             
         
       
     
     wherein n is an integer from 3 to 10 or an enantiomer. In one particular embodiment of formula 52, n=5. 
     Other examples of such compounds and other HDAC inhibitors can be found in U.S. Pat. No. 5,369,108, issued on Nov. 29, 1994, U.S. Pat. No. 5,700,811, issued on Dec. 23, 1997, U.S. Pat. No. 5,773,474, issued on Jun. 30, 1998, U.S. Pat. No. 5,932,616, issued on Aug. 3, 1999 and U.S. Pat. No. 6,511,990, issued Jan. 28, 2003, all to Breslow et al.; U.S. Pat. No. 5,055,608, issued on Oct. 8, 1991, U.S. Pat. No. 5,175,191, issued on Dec. 29, 1992 and U.S. Pat. No. 5,608,108, issued on Mar. 4, 1997, all to Marks et al.; as well as Yoshida, M., et al., Bioassays 17, 423-430 (1995); Saito, A., et al., PNAS USA 96, 4592-4597, (1999); Furamai R. et al., PNAS USA 98 (1), 87-92 (2001); Komatsu, Y., et al., Cancer Res. 61(11), 4459-4466 (2001); Su, G. H., et al., Cancer Res. 60, 3137-3142 (2000); Lee, B. I. et al., Cancer Res. 61(3), 931-934; Suzuki, T., et al., J. Med. Chem. 42(15), 3001-3003 (1999); published PCT Application WO 01/18171 published on Mar. 15, 2001 to Sloan-Kettering Institute for Cancer Research and The Trustees of Columbia University; published PCT Application WO02/246144 to Hoffmann-La Roche; published PCT Application WO02/22577 to Novartis; published PCT Application WO02/30879 to Prolifix; published PCT Applications WO 01/38322 (published May 31, 2001), WO 01/70675 (published on Sep. 27, 2001) and WO 00/71703 (published on Nov. 30, 2000) all to Methylgene, Inc.; published PCT Application WO 00/21979 published on Oct. 8, 1999 to Fujisawa Pharmaceutical Co., Ltd.; published PCT Application WO 98/40080 published on Mar. 11, 1998 to Beacon Laboratories, L.L.C.; and Curtin M. (Current patent status of histone deacetylase inhibitors  Expert Opin. Ther. Patents  (2002) 12(9): 1375-1384 and references cited therein). 
     SAHA or any of the other HDACs can be synthesized according to the methods outlined in the Experimental Details Section, or according to the method set forth in U.S. Pat. Nos. 5,369,108, 5,700,811, 5,932,616 and 6,511,990, the contents of which are incorporated by reference in their entirety, or according to any other method known to a person skilled in the art. 
     This invention, in addition to the above listed compounds, is intended to encompass the use of homologs and analogs of such compounds. In this context, homologs are molecules having substantial structural similarities to the above-described compounds and analogs are molecules having substantial biological similarities regardless of structural similarities. 
     The invention also encompasses pharmaceutical compositions comprising pharmaceutically acceptable salts of the HDAC inhibitors with organic and inorganic acids, for example, acid addition salts which may, for example, be hydrochloric acid, sulphuric acid, methanesulphonic acid, fumaric acid, maleic acid, succinic acid, acetic acid, benzoic: acid, oxalic acid, citric acid, tartaric acid, carbonic acid, phosphoric acid and the like. Pharmaceutically acceptable salts can also be prepared from by treatment with inorganic bases, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, 2-ethylamino ethanol, histidine, procaine, and the like. 
     The invention also encompasses pharmaceutical compositions comprising hydrates of the HDAC inhibitors. The term “hydrate” includes but is not limited to hemihydrate, monohydrate, dihydrate, trihydrate and the like. 
     This invention also encompasses pharmaceutical compositions comprising any solid or liquid physical form of SAHA or any of the other HDAC inhibitors. For example, The HDAC inhibitors can be in a crystalline form, in amorphous form, and have any particle size. The HDAC inhibitor particles may be micronized, or may be agglomerated, particulate granules, powders, oils, oily suspensions or any other form of solid or liquid physical form. 
     Pharmaceutical Compositions 
     The compounds of the invention, and derivatives, fragments, analogs, homologs pharmaceutically acceptable salts or hydrate thereof, can be incorporated into pharmaceutical compositions suitable for oral administration, together with a pharmaceutically acceptable carrier or excipient. Such compositions typically comprise a therapeutically effective amount of any of the compounds above, and a pharmaceutically acceptable carrier. Preferably, the effective amount is an amount effective to selectively induce terminal differentiation of suitable neoplastic cells and less than an amount which causes toxicity in a patient. 
     Any inert excipient that is commonly used as a carrier or diluent may be used in the formulations of the present invention, such as for example, a gum, a starch, a sugar, a cellulosic material, an acrylate, or mixtures thereof. A preferred diluent is microcrystalline cellulose. The compositions may further comprise a disintegrating agent (e.g., croscarmellose sodium) and a lubricant (e.g., magnesium stearate), and in addition may comprise one or more additives selected from a binder, a buffer, a protease inhibitor, a surfactant, a solubilizing agent, a plasticizer, an emulsifier, a stabilizing agent, a viscosity increasing agent, a sweetener, a film forming agent, or any combination thereof. Furthermore, the compositions of the present invention may be in the form of controlled release or immediate release formulations. 
     One embodiment is a pharmaceutical composition for oral administration comprising a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, microcrystalline cellulose, croscarmellose sodium and magnesium stearate. Another embodiment has SAHA as the HDAC inhibitor. Another embodiment comprises 50-70% by weight of a HDAC inhibitor or a pharmaceutically acceptable salt or hydrate thereof, 20-40% by weight microcrystalline cellulose, 5-15% by weight croscarmellose sodium and 0.1-5% by weight magnesium stearate. Another embodiment comprises about 50-200 mg of a HDAC inhibitor. 
     In one embodiment, the pharmaceutical compositions are administered orally, and are thus formulated in a form suitable for oral administration, i.e., as a solid or a liquid preparation. Suitable solid oral formulations include tablets, capsules, pills, granules, pellets and the like. Suitable liquid oral formulations include solutions, suspensions, dispersions, emulsions, oils and the like. In one embodiment of the present invention, the composition is formulated in a capsule. In accordance with this embodiment, the compositions of the present invention comprise in addition to the HDAC inhibitor active compound and the inert carrier or diluent, a hard gelatin capsule. 
     As used herein, “pharmaceutically acceptable carrier” is intended to include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration, such as sterile pyrogen-free water. Suitable carriers are described in the most recent edition of Remington&#39;s Pharmaceutical Sciences, a standard reference text in the field, which is incorporated herein by reference. Preferred examples of such carriers or diluents include, but are not limited to, water, saline, finger&#39;s solutions, dextrose solution, and 5% human serum albumin. Liposomes and non-aqueous vehicles such as fixed oils may also be used. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the compositions is contemplated. Supplementary active compounds can also be incorporated into the compositions. 
     Solid carriers/diluents include, but are not limited to, a gum, a starch (e.g., corn starch, pregelatinized starch), a sugar (e.g., lactose, mannitol, sucrose, dextrose), a cellulosic material (e.g., microcrystalline cellulose), an acrylate (e.g., polymethylacrylate), calcium carbonate, magnesium oxide, talc, or mixtures thereof. 
     For liquid formulations, pharmaceutically acceptable carriers may be aqueous or non-aqueous solutions, suspensions, emulsions or oils. Examples of non-aqueous solvents are propylene glycol, polyethylene glycol, and injectable organic esters such as ethyl oleate. Aqueous carriers include water, alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Examples of oils are those of petroleum, animal, vegetable, or synthetic origin, for example, peanut oil, soybean oil, mineral oil, olive oil, sunflower oil, and fish-liver oil. Solutions or suspensions can also include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid (EDTA); buffers such as acetates, citrates or phosphates, and agents for the adjustment of tonicity such as sodium chloride or dextrose. The pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. 
     In addition, the compositions may further comprise binders (e.g., acacia, cornstarch, gelatin, carbomer, ethyl cellulose, guar gum, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, povidone), disintegrating agents (e.g., cornstarch, potato starch, alginic acid, silicon dioxide, croscarmellose sodium, crospovidone, guar gum, sodium starch glycolate, Primogel), buffers (e.g., tris-HCl., acetate, phosphate) of various pH and ionic strength, additives such as albumin or gelatin to prevent absorption to surfaces, detergents (e.g., Tween 20, Tween 80, Pluronic F68, bile acid salts), protease inhibitors, surfactants (e.g., sodium lauryl sulfate), permeation enhancers, solubilizing agents (e.g., glycerol, polyethylene glycerol), a glidant (e.g., colloidal silicon dioxide), anti-oxidants (e.g., ascorbic acid, sodium metabisulfite, butylated hydroxyanisole), stabilizers (e.g., hydroxypropyl cellulose, hyroxypropylmethyl cellulose), viscosity increasing agents (e.g., carbomer, colloidal silicon dioxide, ethyl cellulose, guar gum), sweeteners (e.g., sucrose, aspartame, citric acid), flavoring agents (e.g., peppermint, methyl salicylate, or orange flavoring), preservatives (e.g., Thimerosal, benzyl alcohol, parabens), lubricants (e.g., stearic acid, magnesium stearate, polyethylene glycol, sodium lauryl sulfate), flow-aids (e.g., colloidal silicon dioxide), plasticizers (e.g., diethyl phthalate, triethyl citrate), emulsifiers (e.g., carbomer, hydroxypropyl cellulose, sodium lauryl sulfate), polymer coatings (e.g., poloxamers or poloxamines), coating and film forming agents (e.g., ethyl cellulose, acrylates, polymethacrylates) and/or adjuvants. 
     In one embodiment, the active compounds are prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation and Nova Pharmaceuticals, Inc. Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) can also be used as pharmaceutically acceptable carriers. These can be prepared according to methods known to those skilled in the art, for example, as described in U.S. Pat. No. 4,522,811. 
     It is especially advantageous to formulate oral compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the subject to be treated; each unit containing a predetermined quantity of active compound calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the dosage unit forms of the invention are dictated by and directly dependent on the unique characteristics of the active compound and the particular therapeutic effect to be achieved, and the limitations inherent in the art of compounding such an active compound for the treatment of individuals. 
     The pharmaceutical compositions can be included in a container, pack, or dispenser together with instructions for administration. 
     The daily administration is then repeated continuously for a period of several days to several years. Oral treatment may continue for between one week and the life of the patient. Preferably the administration takes place for five consecutive days after which time the patient can be evaluated to determine if further administration is required. The administration can be continuous or intermittent, i.e., treatment for a number of consecutive days followed by a rest period. 
     The compounds of the present invention may be administered intravenously on the first day of treatment, with oral administration on the second day and all consecutive days thereafter. 
     The compounds of the present invention may be administered for the purpose of preventing disease progression or stabilizing tumor growth. 
     The preparation of pharmaceutical compositions that contain an active component is well understood in the art, for example, by mixing, granulating, or tablet-forming processes. The active therapeutic ingredient is often mixed with excipients that are pharmaceutically acceptable and compatible with the active ingredient. For oral administration, the active agents are mixed with additives customary for this purpose, such as vehicles, stabilizers, or inert diluents, and converted by customary methods into suitable forms for administration, such as tablets, coated tablets, hard or soft gelatin capsules, aqueous, alcoholic or oily solutions and the like as detailed above. 
     The compounds of the present invention may be administered at orally at a total daily dose of between 25 to 4000 mg/m 2 , for example, about 25 to 1000 mg, 50-1000 mg, 100 mg, 200 mg, 300 mg, 400 mg, 600 mg, 800 mg, 1000 mg and the like. Typically the compound is administered as a single dose when administering up to 400 mg to the patient. For higher total dosages (i.e., greater than 400 mg), the total is split into multiple dosages, for example, twice daily, three times daily or the like, preferably spread out over equal periods of time during the day. For example, two doses, e.g., 500 mg each, can be administered 12 hours apart to achieve a total dosage of 1000 mg in a day. 
     In one currently preferred embodiment, SAHA or any of the HDAC inhibitors are administered to the patient at a total daily dosage of 200 mg. In another currently preferred embodiment, SAHA or any of the HDAC inhibitors are administered to the patient at a total daily dosage of 400 mg. In another currently preferred embodiment, SAHA or any of the HDAC inhibitors are administered to the patient at a total daily dosage of 600 mg. 
     The amount of the compound administered to the patient is less than an amount that would cause toxicity in the patient. In the certain embodiments, the amount of the compound that is administered to the patient is less than the amount that causes a concentration of the compound in the patient&#39;s plasma to equal or exceed the toxic level of the compound. Preferably, the concentration of the compound in the patient&#39;s plasma is maintained at about 10 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 25 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 50 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 100 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 500 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 1000 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 2500 nM. In another embodiment, the concentration of the compound in the patient&#39;s plasma is maintained at about 5000 nM. It has been found with HMBA that administration of the compound in an amount from about 5 gm/m 2 /day to about 30 gm/m 2 /day, particularly about 20 gm/m 2 /day, is effective without producing toxicity in the patient. The optimal amount of the compound that should be administered to the patient in the practice of the present invention will depend on the particular compound used and the type of cancer being treated. 
     In a currently preferred embodiment of the present invention, the pharmaceutical composition comprises a histone deacetylase (HDAC) inhibitor; microcrystalline cellulose as a carrier or diluent; croscarmellose sodium as a disintegrant; and magnesium stearate as a lubricant. In a particularly preferred embodiment, the HDAC inhibitor is suberoylanilide hydroxamic acid (SAHA). 
     The percentage of the active ingredient and various excipients in the formulations may vary. For example, the composition may comprise between 20 and 90%, preferably between 50-70% by weight of the histone deacetylase (HDAC). Furthermore, the composition may comprise between 10 and 70%, preferably between 20-40% by weight microcrystalline cellulose as a carrier or diluent. Furthermore, the composition may comprise between 1 and 30%, preferably 5-15% by weight croscarmellose sodium as a disintegrant. Furthermore, the composition may comprise between 0.1-5% by weight magnesium stearate as a lubricant. In another preferred embodiment, the composition comprises about 50-200 mg of the HDAC inhibitor (e.g., 50 mg, 100 mg and 200 mg for the HDAC inhibitor, for example, SAHA). In a particularly preferred embodiment, the composition is in the form of a gelatin capsule. 
     A currently preferred embodiment of the invention is a solid formulation of SAHA with microcrystalline cellulose, NF (Avicel Ph 101), sodium croscarmellose, NF (AC-Di-Sol) and magnesium stearate, NF, contained in a gelatin capsule. A further preferred embodiment is 200 mg of solid SAHA with 89.5 mg of microcrystalline cellulose, 9 mg of sodium croscarmellose and 1.5 mg of magnesium stearate contained in a gelatin capsule. 
     It should be apparent to a person skilled in the art that the pharmaceutical compositions of the present invention are not only useful for inhibiting the proliferation of neoplastic cells induction and treatment of cancer, and that these compositions are useful in treating a wide range of diseases for which HDAC inhibitors have been found useful. 
     For example, HDAC inhibitors, and in particular SAHA, have been found to be useful in the treatment of a variety of acute and chronic inflammatory diseases, autoimmune diseases, allergic diseases, diseases associated with oxidative stress, and diseases characterized by cellular hyperproliferation. Non-limiting examples are inflammatory conditions of a joint including and rheumatoid arthritis (RA) and psoriatic arthritis; inflammatory bowel diseases such as Crohn&#39;s disease and ulcerative colitis; spondyloarthropathies; scleroderma; psoriasis (including T-cell mediated psoriasis) and inflammatory dermatoses such an dermatitis, eczema, atopic dermatitis, allergic contact dermatitis, urticaria; vasculitis (e.g., necrotizing, cutaneous, and hypersensitivity vasculitis); eosinphilic myositis, eosinophilic fasciitis; cancers with leukocyte infiltration of the skin or organs, ischemic injury, including cerebral ischemia (e.g., brain injury as a result of trauma, epilepsy, hemorrhage or stroke, each of which may lead to neurodegeneration); HIV, heart failure, chronic, acute or malignant liver disease, autoimmune thyroiditis; systemic lupus erythematosus, Sjorgren&#39;s syndrome, lung diseases (e.g., ARDS); acute pancreatitis; amyotrophic lateral sclerosis (ALS); Alzheimer&#39;s disease; cachexia/anorexia; asthma; atherosclerosis; chronic fatigue syndrome, fever; diabetes (e.g., insulin diabetes or juvenile onset diabetes); glomerulonephritis; graft versus host rejection (e.g., in transplantation); hemohorragic shock; hyperalgesia: inflammatory bowel disease; multiple sclerosis; myopathies (e.g., muscle protein metabolism, esp. in sepsis); osteoporosis; Parkinson&#39;s disease; pain; pre-term labor; psoriasis; reperfusion injury; cytokine-induced toxicity (e.g., septic shock, endotoxic shock); side effects from radiation therapy, temporal mandibular joint disease, tumor metastasis; or an inflammatory condition resulting from strain, sprain, cartilage damage, trauma such as burn, orthopedic surgery, infection or other disease processes. Allergic diseases and conditions, include but are not limited to respiratory allergic diseases such as asthma, allergic rhinitis, hypersensitivity lung diseases, hypersensitivity pneumonitis, eosinophilic pneumonias (e.g., Loeffler&#39;s syndrome, chronic eosinophilic pneumonia), delayed-type hypersentitivity, interstitial lung diseases (ILD) (e.g., idiopathic pulmonary fibrosis, or ILD associated with rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, systemic sclerosis, Sjogren&#39;s syndrome, polymyositis or dermatomyositis); systemic anaphylaxis or hypersensitivity responses, drug allergies (e.g., to penicillin, cephalosporins), insect sting allergies, and the like. 
     For example, HDAC inhibitors, and in particular SAHA, have been found to be useful in the treatment of a variety of neurodegenerative diseases, a non-exhaustive list of which is: 
     I. Disorders characterized by progressive dementia in the absence of other prominent neurologic signs, such as Alzheimer&#39;s disease; Senile dementia of the Alzheimer type; and Pick&#39;s disease (lobar atrophy).
 
II. Syndromes combining progressive dementia with other prominent neurologic abnormalities such as A) syndromes appearing mainly in adults (e.g., Huntington&#39;s disease, Multiple system atrophy combining dementia with ataxia and/ormanifestations of Parkinson&#39;s disease, Progressive supranuclear palsy (Steel-Richardson-Olszewski), diffuse Lewy body disease, and corticodentatonigral degeneration); and B) syndromes appearing mainly in children or young adults (e.g., Hallervorden-Spatz disease and progressive familial myoclonic epilepsy).
 
III. Syndromes of gradually developing abnormalities of posture and movement such as paralysis agitans (Parkinson&#39;s disease), striatonigral degeneration, progressive supranuclear palsy, torsion dystonia (torsion spasm; dystonia musculorum deformans), spasmodic torticollis and other dyskinesis, familial tremor, and Gilles de la Tourette syndrome.
 
IV. Syndromes of progressive ataxia such as cerebellar degenerations (e.g., cerebellar cortical degeneration and olivopontocerebellar atrophy (OPCA)); and spinocerebellar degeneration (Friedreich&#39;s atazia and related disorders).
 
V. Syndrome of central autonomic nervous system failure (Shy-Drager syndrome).
 
VI. Syndromes of muscular weakness and wasting without sensory changes (motorneuron disease such as amyotrophic lateral sclerosis, spinal muscular atrophy (e.g., infantile spinal muscular atrophy (Werdnig-Hoffman), juvenile spinal muscular atrophy (Wohlfart-Kugelberg-Welander) and other forms of familial spinal muscular atrophy), primary lateral sclerosis, and hereditary spastic paraplegia.
 
VII. Syndromes combining muscular weakness and wasting with sensory changes (progressive neural muscular atrophy; chronic familial polyneuropathies) such as peroneal muscular atrophy (Charcot-Marie-Tooth), B. Hypertrophic interstitial polyneuropathy (Dejerine-Sottas), and C. Miscellaneous forms of chronic progressive neuropathy.
 
VIII Syndromes of progressive visual loss such as pigmentary degeneration of the retina (retinitis pigmentosa), and hereditary optic atrophy (Leber&#39;s disease).
 
     The invention is illustrated in the examples in the Experimental Details Section which follows. This section is set forth to aid in an understanding of the invention but is not intended to, and should not be construed to limit in any way the invention as set forth in the claims which follow thereafter. 
     EXPERIMENTAL DETAILS SECTION 
     Example 1 
     Synthesis of SAHA 
     SAHA can be synthesized according to the method outlined below, or according to the method set forth in U.S. Pat. No. 5,369,108, the contents of which are incorporated by reference in their entirety, or according to any other method. 
     Synthesis of SAHA 
     Step 1—Synthesis of Suberanilic Acid 
     
       
         
         
             
             
         
       
     
     In a 22 L flask was placed 3,500 g (20.09 moles) of suberic acid, and the acid melted with heat. The temperature was raised to 175° C., and then 2,040 g (21.92 moles) of aniline was added. The temperature was raised to 190° C. and held at that temperature for 20 minutes. The melt was poured into a Nalgene tank that contained 4,017 g of potassium hydroxide dissolved in 50 L of water. The mixture was stirred for 20 minutes following the addition of the melt. The reaction was repeated at the same scale, and the second melt was poured into the same solution of potassium hydroxide. After the mixture was thoroughly stirred, the stirrer was turned off, and the mixture was allowed to settle. The mixture was then filtered through a pad of Celite (4,200 g) (the product was filtered to remove the neutral by-product (from attack by aniline on both ends of suberic acid). The filtrate contained the salt of the product, and also the salt of unreacted suberic acid. The mixture was allowed to settle because the filtration was very slow, taking several days.). The filtrate was acidified using 5 L of concentrated hydrochloric acid; the mixture was stirred for one hour, and then allowed to settle overnight. The product was collected by filtration, and washed on the funnel with deionized water (4×5 L). The wet filter cake was placed in a 72 L flask with 44 L of deionized water, the mixture heated to 50° C., and the solid isolated by a hot filtration (the desired product was contaminated with suberic acid which is has a much greater solubility in hot water. Several hot triturations were done to remove suberic acid. The product was checked by NMR [D 6 DMSO] to monitor the removal of suberic acid). The hot trituration was repeated with 44 L of water at 50° C. The product was again isolated by filtration, and rinsed with 4 L of hot water. It was dried over the weekend in a vacuum oven at 65° C. using a Nash pump as the vacuum source (the Nash pump is a liquid ring pump (water) and pulls a vacuum of about 29 inch of mercury. An intermittent argon purge was used to help carry off water); 4,182.8 g of suberanilic acid was obtained. 
     The product still contained a small amount of suberic acid; therefore the hot trituration was done portionwise at 65° C., using about 300 g of product at a time. Each portion was filtered, and rinsed thoroughly with additional hot water (a total of about 6 L). This was repeated to purify the entire batch. This completely removed suberic acid from the product. The solid product was combined in a flask and stirred with 6 L of methanol/water (1:2), and then isolated by filtration and air dried on the filter over the week end. It was placed in trays and dried in a vacuum oven at 65° C. for 45 hours using the Nash pump and an argon bleed. The final product has a weight of 3,278.4 g (32.7% yield). 
     Step 2—Synthesis of Methyl Suberanilate 
     
       
         
         
             
             
         
       
     
     To a 50 L flask fitted with a mechanical stirrer, and condenser was placed 3,229 g of suberanilic acid from the previous step, 20 L of methanol, and 398.7 g of Dowex 50WX2-400 resin. The mixture was heated to reflux and held at reflux for 18 hours. The mixture was filtered to remove the resin beads, and the filtrate was taken to a residue on a rotary evaporator. 
     The residue from the rotary evaporator was transferred into a 50 L flask fitted with a condenser and mechanical stirrer. To the flask was added 6 L of methanol, and the mixture heated to give a solution. Then 2 L of deionized water was added, and the heat turned off. The stirred mixture was allowed to cool, and then the flask was placed in an ice bath, and the mixture cooled. The solid product was isolated by filtration, and the filter cake was rinsed with 4 L of cold methanol/water (1:1). The product was dried at 45° C. in a vacuum oven using a Nash pump for a total of 64 hours to give 2,850.2 g (84% yield) of methyl suberanilate, CSL Lot #98-794-92-3 1. 
     Step 3—Synthesis of Crude SAHA 
     
       
         
         
             
             
         
       
     
     To a 50 L flask with a mechanical stirrer, thermocouple, and inlet for inert atmosphere was added 1,451.9 g of hydroxylamine hydrochloride, 19 L of anhydrous methanol, and a 3.93 L of a 30% sodium methoxide solution in methanol. The flask was then charged with 2,748.0 g of methyl suberanilate, followed by 1.9 L of a 30% sodium methoxide solution in methanol. The mixture was allowed to stir for 16 hr and 10 minutes. Approximately one half of the reaction mixture was transferred from the reaction flask (flask 1) to a 50 L flask (flask 2) fitted with a mechanical stirrer. Then 27 L of deionized water was added to flask 1 and the mixture was stirrer for 10 minutes. The pH was taken using a pH meter; the pH was 11.56. The pH of the mixture was adjusted to 12.02 by the addition of 100 ml of the 30% sodium methoxide solution in methanol; this gave a clear solution (the reaction mixture at this time contained a small amount of solid. The pH was adjusted to give a clear solution from which the precipitation the product would be precipitated). The reaction mixture in flask 2 was diluted in the same manner; 27 L of deionized water was added, and the pH adjusted by the addition of 100 ml of a 30% sodium methoxide solution to the mixture, to give a pH of 12.01 (clear solution). 
     The reaction mixture in each flask was acidified by the addition of glacial acetic acid to precipitate the product. Flask 1 had a final pH of 8.98, and Flask 2 had a final pH of 8.70. The product from both flasks was isolated by filtration using a Buchner funnel and filter cloth. The filter cake was washed with 15 L of deionized water, and the funnel was covered and the product was partially dried on the funnel under vacuum for 15.5 hr. The product was removed and placed into five glass trays. The trays were placed in a vacuum oven and the product was dried to constant weight. The first drying period was for 22 hours at 60° C. using a Nash pump as the vacuum source with an argon bleed. The trays were removed from the vacuum oven and weighed. The trays were returned to the oven and the product dried for an additional 4 hr and 10 minutes using an oil pump as the vacuum source and with no argon bleed. The material was packaged in double 4-mill polyethylene bags, and placed in a plastic outer container. The final weight after sampling was 2633.4 g (95.6%). 
     Step 4—Recrystallization of Crude SAHA 
     The crude SAHA was recrystallized from methanol/water. A 50 L flask with a mechanical stirrer, thermocouple, condenser, and inlet for inert atmosphere was charged with the crude SAHA to be crystallized (2,525.7 g), followed by 2,625 ml of deionized water and 15,755 ml of methanol. The material was heated to reflux to give a solution. Then 5,250 ml of deionized water was added to the reaction mixture. The heat was turned off, and the mixture was allowed to cool. When the mixture had cooled sufficiently so that the flask could be safely handled (28° C.), the flask was removed from the heating mantle, and placed in a tub for use as a cooling bath. Ice/water was added to the tub to cool the mixture to −5° C. The mixture was held below that temperature for 2 hours. The product was isolated by filtration, and the filter cake washed with 1.5 L of cold methanol/water (2:1). The funnel was covered, and the product was partially dried under vacuum for 1.75 hr. The product was removed from the funnel and placed in 6 glass trays. The trays were placed in a vacuum oven, and the product was dried for 64.75 hr at 60° C. using a Nash pump as the vacuum source, and using an argon bleed. The trays were removed for weighing, and then returned to the oven and dried for an additional 4 hours at 60° C. to give a constant weight. The vacuum source for the second drying period was a oil pump, and no argon bleed was used. The material was packaged in double 4-mill polyethylene bags, and placed in a plastic outer container. The final weight after sampling was 2,540.9 g (92.5%). 
     Example 2 
     Oral Dosing of Suberoylanilide Hydroxamic Acid (SAHA) 
     Background: Treatment with hybrid polar cellular differentiation agents has resulted in the inhibition of growth of human solid tumor derived cell lines and xenografts. The effect is mediated in part by inhibition of histone deacetylase. SAHA is a potent histone deacetylase inhibitor that has been shown to have the ability to induce tumor cell growth arrest, differentiation and apoptosis in the laboratory and in preclinical studies. 
     Objectives: To define a safe daily oral regimen of SAHA that can be used in Phase II studies. In addition, the pharmacokinetic profile of the oral formulation of SAHA was be evaluated. The oral bioavailability of SAHA in humans in the fasting vs. non-fasting state and anti-tumor effects of treatment were also monitored. Additionally, the biological effects of SAHA on normal tissues and tumor cells were assessed and responses with respect to levels of histone acetylation were documented. 
     Patients: Patients with histologically documented advanced stage, primary or metastatic adult solid tumors that are refractory to standard therapy or for which no curative standard therapy exists. Patients must have a Karnofsky Performance Status of ≧0.70%, and adequate hematologic, hepatic and renal function. Patients must be at least four weeks from any prior chemotherapy, radiation therapy or other investigational anticancer drugs. 
     Dosing Schedule: On the first day, patients were first treated with 200 mg of intravenously-administered SAHA. Starting on the second day, patients were treated with daily doses of oral SAHA according to Table 1. Each cohort received a different dose of SAHA. “QD” indicates dosing once a day; “Q12 hours” indicates dosing twice a day. For example, patients in Cohort IV received two 800 mg doses of SAHA per day. Doses were administered to patients daily and continuously. Blood samples were taken on day one and on day 21 of oral treatment. Patients were taken off oral SAHA treatment due to disease progression, tumor regression, unacceptable side effects, or treatment with other therapies. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Oral SAHA Dose Schedule 
               
            
           
           
               
               
               
               
            
               
                 Cohort 
                 Oral Dose (mg) 
                 Number of Days 
                 Daily Dosing Schedule 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 I 
                 200 
                 Continuous 
                 QD 
               
               
                 II 
                 400 
                 Continuous 
                 QD 
               
               
                 III 
                 400 
                 Continuous 
                 Q12 hours 
               
               
                 IV 
                 800 
                 Continuous 
                 Q12 hours 
               
               
                 V 
                 1200 
                 Continuous 
                 Q12 hours 
               
               
                 VI 
                 1600 
                 Continuous 
                 Q12 hours 
               
               
                 VII 
                 2000 
                 Continuous 
                 Q12 hours 
               
               
                   
               
            
           
         
       
     
     Results: Comparison of serum plasma levels shows high bioavailability of SAHA administered orally, both when the patient fasted and when the patient did not fast, compared to SAHA administered intravenously (IV SAHA). “AUC” is an estimate of the bioavailability of SAHA in (ng/ml)min, where 660 ng/ml is equal to 2.5 μM SAHA. The AUC taken together with the half-life (t 1/2 ) shows that the overall bioavailability of oral SAHA is better than that of IV SAHA. C max  is the maximum concentration of SAHA observed after administration. IV SAHA was administered at 200 mg infused over two hours. The oral SAHA was administered in a single capsule at 200 mg. Tables 2 and 3 summarize the results of an HPLC assay (LCMS using a deuterated standard) that quantitates the amount of SAHA in the blood plasma of the patients versus time, using acetylated histone-4 (α-ACH4) as a marker. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Serum Plasma Levels of Oral SAHA - Patient #1 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 IV 
                 Oral (fasting) 
                 Oral (nonfasting) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 C max  (ng/ml) 
                 1329 
                 225 
                 328 
               
               
                   
                 t 1/2  (min) 
                 20 
                 80 
                 64 
               
               
                   
                 AUC (ng/ml)min 
                 153,000 
                 25,000 
                 59,000 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Serum Plasma Levels of Oral SAHA - Patient #2 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 IV 
                 Oral (fasting) 
                 Oral (nonfasting) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 C max  (ng/ml) 
                 1003 
                 362 
                 302 
               
               
                   
                 t 1/2  (min) 
                 21 
                 82 
                 93 
               
               
                   
                 AUC (ng/ml)min 
                 108,130 
                 63,114 
                 59,874 
               
               
                   
                   
               
            
           
         
       
     
       FIGS. 1 to 8  are HPLC slides showing the amount of α-ACH4 in patients in Cohorts I and II, measured at up to 10 hours after receiving the oral dose, compared with the α-ACH4 levels when SAHA was administered intravenously.  FIG. 9  shows the mean plasma concentration of SAHA (ng/ml) at the indicated time points following administration.  FIG. 9A : Oral dose (200 mg and 400 mg) under fasting on Day 8.  FIG. 9B : Oral dose with food on Day 9.  FIG. 9C : IV dose on day 1.  FIG. 10  shows the apparent half-life of a SAHA 200 mg and 400 mg oral dose, on Days 8, 9 and 22.  FIG. 11  shows the AUC (ng/ml/hr) of a SAHA 200 mg and 400 mg oral dose, on Days 8, 9 and 22.  FIG. 12  shows the bioavailability of SAHA after a 200 mg and 400 mg oral dose, on Days 8, 9 and 22. 
     Example 3 
     Oral Dosing of Suberoylanilide Hydroxyamic Acid (SAHA)—Dose Escalation 
     In another experiment, twenty-five patients with solid tumors have been enrolled onto arm A, thirteen patients with Hodgkin&#39;s or non-Hodgkin&#39;s lymphomas have been enrolled onto arm B, and one patient with acute leukemia and one patient with myelodysplastic syndrome have been enrolled onto arm C, as shown in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Dose Escalation Scheme and Number of Patients on Each Dose Level 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                 #Patients Enrolled 
               
               
                   
                 Dose 
                 Dosing 
                 #Days of 
                 Rest 
                 (arm A/arm 
               
               
                 Cohort  
                 (mg/day) 
                 Schedule 
                 Dosing 
                 Period 
                 B/arm C)* 
               
               
                   
               
               
                 I 
                 200 
                 Once a day 
                 Continuous 
                 None 
                 6/0/0 
               
               
                 II 
                 400 
                 Once a day 
                 Continuous 
                 None 
                 5/4/2 
               
               
                 III 
                 400 
                 q 12 hours 
                 Continuous 
                 None 
                 6/3/0 
               
               
                 IV 
                 600 
                 Once a day 
                 Continuous 
                 None 
                 4/3/0 
               
               
                 V 
                 200 
                 q 12 hours 
                 Continuous 
                 None 
                 4/3/0 
               
               
                 VI 
                 300 
                 q 12 hours 
                 Continuous 
                 None 
                 —/—/— 
               
               
                   
                   
                   
                   
                   
                 Sub-totals: 25/13/2 
               
               
                   
                   
                   
                   
                   
                 Total = 40 
               
               
                   
               
               
                 *Arm A = solid tumor, arm B = lymphoma, arm C = leukemia 
               
            
           
         
       
     
     Results: 
     Among eleven patients treated in Cohort II, one patient experienced the DLT of grade 3 diarrhea and grade 3 dehydration during the first treatment cycle. Nine patients were entered into Cohort III. Two patients were inevaluable for the 28-day toxicity assessment because of early study termination due to rapid progression of disease. Of the seven remaining patients, five experienced DLT during the first treatment cycle: diarrhea/dehydration (n=1), fatigue/dehydration (n=1), anorexia (n=1), dehydration (n=1) and anorexia/dehydration (n=1). These five patients recovered in approximately one week after the study drug was held. They were subsequently dose reduced to 400 mg QD which appeared to be well tolerated. The median days on 400 mg BID for all patients in Cohort III was 21 days. Based on these findings the 400 mg q12 hour dosing schedule was judged to have exceeded the maximally tolerated dose. Following protocol amendment, accrual was continued in cohort IV at a dose of 600 mg once a day. Of the seven patients enrolled onto cohort IV, two were inevaluable for the 28-day toxicity assessment because of early study termination due to rapid progression of disease. Three patients experienced DLT during the first treatment cycle: anorexia/dehydration/fatigue (n=1), and diarrhea/dehydration (n=2). The 600 mg dose was therefore judged to have exceeded the maximally tolerated dose and the 400 mg once a day dose was defined as the maximally tolerated dose for once daily oral administration. The protocol was amended to evaluate additional dose levels of the twice a day dosing schedule at 200 mg BID and 300 mg BID administered continuously. 
     The interim pharmacokinetic analysis was based on 18 patients treated on the dose levels of 200 mg QD, 400 mg QD, and 400 mg BID. In general, the mean estimates of C max  and AUC inf  of SAHA administered orally under fasting condition or with food increased proportionally with dose in the 200 mg to 400 mg dose range. Overall, the fraction of AUC inf  due to extrapolation was 1% or less. Mean estimates for apparent half-life were variable across dose groups under fasting condition or with food, ranging from 61 to 114 minutes. The mean estimates of Cmax, varies from 233 ng/ml (0.88 μM) to 570 ng/ml (2.3 μM). The bioavailable fraction of SAHA, calculated from the AUC inf  values after the IV infusion and oral routes, was found to be approximately 0.48. 
     Peripheral blood mononuclear cells were collected pre-therapy, immediately post-infusion and between 2-10 hours after oral ingestion of the SAHA capsules to assess the effect of SAHA on the extent of histone acetylation in a normal host cell. Histones were isolated and probed with anti-acetylated histone (H3) antibody followed by HRP-secondary antibody. Preliminary analysis demonstrated an increase in the accumulation of acetylated histones in peripheral mononuclear cells that could be detected up to 10 hours after ingestion of SAHA capsules at 400 mg per day dose level. 
     Thirteen patients continued treatment for 3-12 months with responding or stable disease: thyroid (n=3), sweat gland (n=1), renal (n=2), larynx (n=1), prostate (n=1), Hodgkin&#39;s lymphoma (n=2), non-Hodgkin&#39;s lymphoma (n=2), and leukemia (n=1). 
     Six patients had tumor shrinkage on CT scans. Three of these six patients meet the criteria of partial response (one patient with metastatic laryngeal cancer and two patients with non-Hodgkin&#39;s lymphomas). These partial responses occurred at the dose levels of 400 mg BID (n=2) and 600 mg QD (n=1). 
     Example 4 
     Intravenous Dosing of SAHA 
     Table 5 shows a dosing schedule for patients receiving SAHA intravenously. Patients begin in Cohort I, receiving 300 mg/m 2  of SAHA for five consecutive days in a week for one week, for a total dose of 1500 mg/m 2 . Patients were then observed for a period of two weeks and continued to Cohort II, then progressed through the Cohorts unless treatment was terminated due to disease progression, tumor regression, unacceptable side effects or the patient received other treatment. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Standard Dose Escalation for Intravenously-Administered SAHA 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Number of 
                 Observation 
                 Total 
               
               
                   
                 Dose 
                 Number of 
                 Consecutive 
                 Period 
                 Dose 
               
               
                 Cohort 
                 (mg/m 2 ) 
                 Days/Week 
                 Weeks 
                 (Weeks) 
                 (mg/m 2 ) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 I 
                 300 
                 5 
                 1 
                 2 
                 1500 
               
               
                 II 
                 300 
                 5 
                 2 
                 2 
                 3000 
               
               
                 III 
                 300 
                 5 
                 3 
                  1* 
                 4500 
               
               
                 IV 
                 600 
                 5 
                 3 
                  1* 
                 9000 
               
               
                 V 
                 800 
                 5 
                 3 
                  1* 
                 13500 
               
               
                 VI 
                 1200 
                 5 
                 3 
                  1* 
                 18000 
               
               
                 VII 
                 1500 
                 5 
                 3 
                  1* 
                 22500 
               
               
                   
               
               
                 *Hematologic patients started at dose level III. 
               
            
           
         
       
     
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the meaning of the invention described. Rather, the scope of the invention is defined by the claims that follow: 
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