Biologically Based Treatment Philip Nivatpumin, Steven D. Gore

Contents

11.1 Introduction . . . 111

11.2 Therapies Targeting Epigenetic Changes 112 11.2.1 DNA Methyltransferase Inhibitors . 112 11.2.2 Histone Deacetylase Inhibitors . . . 113

11.2.3 Combinations of DNA Methyltrans- ferase with Histone Deacetylase Inhibitors . . . 113

11.3 Therapies Targeting Angiogenesis . . . 114

11.3.1 Thalidomide . . . 114

11.3.2 Lenalidomide . . . 114

11.3.3 Bevacizumab . . . 114

11.3.4 SU11248 and PTK787 . . . 115

11.3.5 Arsenic Trioxide . . . 115

11.4 Therapies Targeting Disordered Cytokine Milieu . . . 115

11.4.1 Pentoxifylline . . . 115

11.4.2 SCIO-469 . . . 115

11.4.3 Etanercept and Infliximab . . . 116

11.5 Therapies Targeting the Immune System . . . 116

11.5.1 ATG . . . 116

11.5.2 Cyclosporine . . . 116

11.6 Therapies Targeting Signaling . . . 116

11.6.1 Tipifarnib . . . 116

11.6.2 Lonafarnib . . . 117

11.6.3 Imatinib . . . 117

11.6.4 PKC412 . . . 117

11.7Therapies Targeting Aberrant Differentiation . . . 117

11.7.1 Retinoic Acid . . . . 117

11.7.2 Vitamin D . . . . 118

11.8 Miscellaneous Therapies . . . . 118

11.8.1 TLK199 . . . . 118

11.9 Conclusion . . . . 118

References . . . . 118

11.1 Introduction

With improved insights into the cellular and molecular pathophysiology of myelodysplastic syndrome (MDS), new agents for its treatment have been developed. While these putative `targeted' therapies have been based on testable hypotheses developed from in vitro models, in many instances it has been difficult to validate the mechanism underlying clinical activity. Nevertheless, these studies have led to FDA approval of the first drug for the treatment of MDS. The availability of increasing numbers of active agents is leading to changes in the management of MDS. Patients with MDS must undergo a thorough analysis of prognostic factors, and examina- tion for clinical parameters that may be predictive of re- sponse to specific therapies. Whether these therapies (other then hemopoietic cell transplantation) will alter the natural history of MDS requires further observation.

Biologically Based Treatment

Philip Nivatpumin, Steven D. Gore

11.2 Therapies Targeting Epigenetic Changes 11.2.1 DNA Methyltransferase Inhibitors

The cytosine analogues 5-azacitidine (5AC) and 2'- deoxy-5-azacitidine (decitabine) are both potent inhibi- tors of DNA methyltransferase 1, the enzyme primarily responsible for converting CpG dinucleotides to methyl-CpG dinucleotides in a replicating DNA strand.

This mechanism enables the faithful replication of the CpG methylation pattern in the daughter DNA strand (Jones and Baylin 2002). 5-Azacitidine is converted to 2'-deoxy-5-azacitidine intracellularly; both are then phosphorylated and incorporated into DNA in lieu of cytosine residues. The azacytosine nucleoside is recog- nized by DNA methyltransferase and forms an irreversi- ble adduct. As the DNA undergoes successive cycles of replication, methyltransferase is not available to repro- duce the CpG methylation pattern; thus, with several cell divisions, the DNA is increasingly demethylated. As pro- moter methylation is associated with transcriptional si- lencing of the gene, reversal of gene methylation leads to re-expression of genes, at least in vitro. A similar mech- anism is presumed to occur in response to the adminis- tration of DNA methyltransferase inhibitors in vivo.

Initial development of the DNA methyltransferase inhibitor 5AC for the treatment of MDS was based on the observation that low doses of this nucleoside ana- logue could induce terminal differentiation in in vitro models including mouse erythroleukemia cells (MEL) (Creusot et al. 1982). Initial studies administered 5AC intravenously (Silverman et al. 1993), but due to its ex- tremely short half-life, effective intravenous administra- tion required continuous infusion. Subsequent trials utilized the daily subcutaneous administration of a re- constituted slurry (Silverman 2001; Silverman et al.

2002). Promising Phase II data led to a definitive Phase III trial conducted within the CALGB (Silverman 2001;

Silverman et al. 2002). In this trial, patients with all French-American-British (FAB) classifications, includ- ing low- and high-risk MDS categories, were randomly assigned to treatment with 5AC, 75 mg/m

/day, adminis- tered subcutaneously daily for 7 consecutive days on a 28-day cycle or observation/supportive care. Assigned therapy was to continue for a minimum of four cycles.

Patients whose disease progressed on the observation arm could cross over after 4 months or longer and re- ceive 5AC. This trial showed significant hematologic re- sponses to 5AC, including 21% complete (CR) and par-

tial (PR) remissions, and overall hematologic responses in 60% of patients, compared with 5% in the observa- tion arm (and here apparently related to increasing neu- trophils in the setting of progressive leukemia). Patients assigned to azacitidine experienced a median delay in progression to leukemia of about 8 months.

A companion quality of life assessment study showed that treatment with 5AC was associated with im- provement in several quality of life parameters, includ- ing improved fatigue, dyspnea, physical functioning, positive affect, and psychological distress (Kornblith et al. 2002). However, no survival advantage with azaci- tidine was observed in this trial, possibly due to the al- lowed crossover, such that the majority of patients even- tually received azacitidine. Azacitidine responses were seen in patients with all FAB subtypes, including pa- tients with AML evolved from MDS.

Decitabine has been administered (intravenously) three times daily for 3 days with treatment cycles re- peated every 6 weeks. Response rates were similar to those with 5AC; however, delayed cytopenias appeared to be more pronounced with this schedule of decitabine, particularly in the first cycle of therapy (Wijermans et al. 2000). Cytogenetic remissions occurred in 17% of patients in an intention-to-treat analysis (Lubbert et al. 2001). Results from a randomized trial of decitabine versus observation (similar to the above 5AC trial) in patients with International Prognostic Scoring System (IPSS) intermediate 1, 2 or high-risk MDS have been presented in abstract form. The median number of treatment cycles required to attain remission with deci- tabine was 3±4, and the trial showed hematologic re- sponses in a large proportion of patients and again an increase in the time to disease progression or death (Saba et al. 2004).

A recent dose-finding study of decitabine suggests that schedules of this nucleoside that deliver lower daily doses of drug for longer exposures may increase the re- sponse rate, consistent with the requirement for expo- sure to the azacytosine analogues for several cell divi- sions to effect reversal of DNA methylation (Issa 2003;

Issa et al. 2004).

Like decitabine, azacitidine therapy has been asso- ciated with cytogenetic responses; however, hematolog- ic responses have also been observed in patients who continue to show their original clonal cytogenetic ab- normalities.

These trials suggest that DNA methyltransferase in-

hibitors not only ameliorate cytopenias but also delay

disease progression. Therefore, while supportive care and growth factors may remain reasonable treatment options, DNA methyltransferase inhibitors, by delaying disease progression, may represent attractive alterna- tives for some patients.

Despite their important activity, the relationship be- tween their clinical effects and their molecular proper- ties as DNA methyltransferase inhibitors remains uncer- tain. In earlier studies of decitabine, decreased methyl- ation of the p15

promoter was demonstrated in se- lected patients, apparently along with re-expression of this cyclin-dependent kinase inhibitor as shown by an immunohistochemical technique (Daskalakis et al.

2002). Another study found no relationship between pre-treatment p15 promoter methylation density or change in p15 methylation density and clinical response (Issa et al. 2004). Global and gene-specific DNA methyl- ation has not been systematically analyzed in any study of sufficient size to allow for a meaningfully powered statistical examination of a potential correlation be- tween methylation, reversal of methylation, and clinical response. Similarly, no trials have adequately explored the issue of re-expression of methylated genes and clin- ical response.

Treatment with DNA methyltransferase inhibitors is reasonably well tolerated; however, up to four cycles of therapy are required for most clinical responses to oc- cur. Therapy with DNA methyltransferase inhibitors is often associated with worsening of cytopenias before improvement occurs; thus, a commitment should be made to a minimum of four cycles of therapy with either nucleoside analogue before deeming the treat- ment unsuccessful. The optimal duration of administra- tion of the DNA methyltransferase inhibitors is similarly uncertain. In the randomized trial of 5AC, patients who achieved less than a complete response received on- going therapy with the drug, while patients who achieved a complete response received only two addi- tional cycles of drugs after documentation of response.

In contrast, decitabine trials have in general adminis- tered a maximum of six cycles of drug. This difference in trial design may account for the difference in median response duration (15 months for 5AC, greater than 9 months for decitabine). Determination of the optimal dose schedule and duration of therapy for both drugs will require further trials.

11.2.2 Histone Deacetylase Inhibitors

Initial interest in the use of histone deacetylase inhibi- tors to treat MDS derived from the observation that bu- tyrate could induce differentiation in a variety of mye- loid leukemia models (Leder and Leder 1975; Novo- grodsky et al. 1983; Schroter et al. 1981). Clinical admin- istration of butyrate led to induction of remission in a patient with AML (Novogrodsky et al. 1983), and admin- istration of phenylbutyrate in association with all-trans retinoic acid (ATRA) led to remission in an ATRA-resis- tant relapse of acute promyelocytic leukemia (Warrell et al. 1998). The polar planar compound hexamethylene bisacetamide (HMBA) was associated with limited clin- ical activity in MDS (Andreeff et al. 1992). Second gen- eration compounds based on the activity of HMBA to induce differentiation led to the synthesis of suberoyl- anilide hydroxamic acid (SAHA), another potent HDAC inhibitor (Richon et al. 1996).

Administration of the short chain fatty acid HDAC inhibitor sodium phenylbutyrate (NaPB) as 7-day infu- sions every 14 or 28 days, and as a 21-day infusion re- peated every 28 days (21 days on/7 days off) yielded modest lineage responses in patients with MDS and AML (Gore and Carducci 2000; Gore et al. 1997, 2001, 2002). Sustained plasma concentrations of 0.3±0.5 mM were achieved, comparable to concentrations associated with inhibition of histone deacetylase in vitro. The oral short chain fatty acid, valproic acid, in clinical use as a neuroleptic drug, has similar activity in vitro (Gottli- cher 2004; Gottlicher et al. 2001), and has been shown to have clinical activity in selected patients with MDS and AML (Kuendgen et al. 2004). The more potent and specific HDAC inhibitors SAHA, FK228 (depsipep- tide), MS-275, and LAQ824 have undergone phase I test- ing in MDS; however, clinical outcomes have not been published. The relationship between clinical response to these agents, inhibition of histone deacetylase or other protein deacetylases, and re-expression of si- lenced genes, has not been systematically investigated to date.

11.2.3 Combinations of DNA Methyltransferase and Histone Deacetylase Inhibitors The observation that transcriptional silencing of genes with hypermethylated CpG islands is mediated via re- cruitment of transcriptional corepressor complexes, in-

a 11.2 ´ Therapies Targeting Epigenetic Changes 113

cluding histone deacetylases, led to the in vitro demon- stration that optimal re-expression of such genes re- quired exposure to a DNA methyltransferase inhibitor prior to addition of an HDAC inhibitor (Cameron et al. 1999). This has led to clinical studies investigating the use of HDAC inhibitors in combination with DNA methyltransferase inhibitors for the treatment of MDS and other myeloid malignancies. Trials have been per- formed (or are underway) examining combinations of 5AC and NaPB, MS-275, and SAHA, and decitabine in combination with valproate, SAHA, and FK228. No re- sults have been published to date.

11.3 Therapies Targeting Angiogenesis

Angiogenesis is a complex process that regulates the formation of blood vessels and plays an important role in both normal development and tumorigenesis (Folk- man 1995). Increased microvessel density has been demonstrated in the bone marrow of patients with he- matologic malignancies, including MDS (Alexandrakis et al. 2004, 2005; Padro et al. 2000; Pruneri et al.

1999). While neovascularization has been well docu- mented in bone marrow biopsies from patients with MDS, it is not clear whether this represents a primary pathogenic process or, rather, a response to the disor- dered cytokine milieu in the MDS microenvironment.

In vitro, antagonism of angiogenic factors using anti- bodies that neutralize vascular endothelial growth fac- tor (VEGF) or interfere with its signal transduction leads to increased erythropoiesis from MDS progenitor cells (Bellamy et al. 2001). However, the mechanism un- derlying the effect of the best studied agents on angio- genesis in MDS remains unclear. Nonetheless, signifi- cant activity of these agents has been documented.

11.3.1 Thalidomide

Thalidomide was the first putative anti-angiogenesis agent studied in MDS. Highly active in the treatment of multiple myeloma, the relationship between its activ- ity in myeloma and its anti-angiogenesis activity is un- clear (Anderson 2003; Moehler et al. 2004). Thalido- mide has been studied in four MDS trials. Three trials showed erythroid responses in 29/142 patients treated;

the fourth trial targeted higher doses of thalidomide and responses were observed in only 4/69 patients

(Moreno-Aspitia et al. 2002; Musto 2004; Musto et al.

2002; Raza et al. 2001; Strupp et al. 2002). Thalidomide is poorly tolerated in this patient population due to its neuropathic and sedative effects. Responses are limited to the erythroid series and appear restricted to patients with low-risk MDS. A randomized trial of thalidomide versus placebo has been completed but results have not been released.

11.3.2 Lenalidomide

Lenalidomide is a thalidomide analog with reduced neurotoxicity and increased immunomodulatory activ- ity. In a Phase I/II study of lenalidomide in low-risk MDS, major erythroid responses were observed in 24/

43 patients (List et al. 2005). An especially impressive response rate was observed in patients whose karyotype included deletions at chromosome 5q31.1. Major cytoge- netic responses developed in 10/12 patients with 5q de- letions, including complete cytogenetic responses in 9/10. The molecular mechanism of lenalidomide is un- clear. Confirmatory large Phase II trials of lenalidomide in MDS patients with and without 5q deletions have been completed and await reporting of the data. Should the unique sensitivity of MDS associated with intersti- tial deletions on chromosome 5q be confirmed in the Phase II trials, lenalidomide may represent a powerful tool for probing the molecular pathogenesis of that sub- set of MDS (Giagounidis et al. 2004).

11.3.3 Bevacizumab

Bevacizumab is a monoclonal antibody to VEGF that has been studied in both solid and hematologic malig- nancies. It was recently approved for use in metastatic colorectal cancer after a clinical trial demonstrated im- proved overall survival when given in combination with standard chemotherapy (Hurwitz et al. 2004). In pa- tients with refractory and relapsed AML, a combination of cytarabine, mitoxantrone and bevacizumab was tested (Karp et al. 2004). The overall response rate was 48%, and 33% of patients had complete responses.

Serum VEGF levels were decreased significantly in the

majority of patients in comparison to pretreatment lev-

els.

11.3.4 SU11248 and PTK787

SU11248 is a small molecule receptor tyrosine kinase (RTK) inhibitor that blocks VEGF-mediated cell growth (Glade-Bender et al. 2003). A Phase I trial of SU11248 in 15 patients with refractory or resistant AML showed six responses in ten evaluable patients (Fiedler et al. 2005).

All patients with FLT3 mutations (n=4) had morpholog- ic or partial responses, compared with two of ten evalu- able patients with wild-type FLT3. Another Phase I trial in 29 AML patients showed responses in five of 29 pa- tients (O'Farrell et al. 2003).

PTK787 is another potent orally administered inhib- itor with activity against all VEGF RTKs, PDGFR, c-kit and Flt-1 (Drevs 2003; Thomas et al. 2003). It is cur- rently under evaluation by Cancer and Leukemia Group B (CALGB study 10105).

11.3.5 Arsenic Trioxide

Arsenic trioxide, a potent agent for the treatment of re- lapsed acute promyelocytic leukemia, possesses a vari- ety of molecular activities, including inhibition of an- giogenesis (List et al. 2003; Sekeres 2005). This observa- tion led to several Phase II studies of arsenic trioxide for the treatment of MDS that have not yet been published.

In a trial combining arsenic trioxide with thalidomide in 28 patients with MDS, seven patients responded, in- cluding one complete hematologic and cytogenetic re- sponse and one with regression in spleen size (Raza et al. 2004). Two trilineage responses were seen in patients with inv (3)(q21q26.2).

11.4 Therapies Targeting Disordered Cytokine Milieu

As with angiogenesis, it is not clear whether the disor- dered cytokine milieu in the microenvironment of MDS bone marrows represents a primary pathogenic event or a secondary phenomenon. Nonetheless, the dysregu- lated cytokines (especially increased TNFa and TGFb) can clearly serve as negative regulators of hematopoi- esis, in particular erythropoiesis. Thus, targeting this cytokine dysregulation could be associated with amelio- ration of cytopenias in early stage MDS.

11.4.1 Pentoxifylline

Pentoxifylline (PTX), a xanthine derivative known to in- terfere with the lipid-signaling pathway used by TNFa,aa TGFb F and IL-1b, has been studied in combination with other agents in the treatment of MDS. Raza et al. admin- istered a combination of pentoxifylline, ciprofloxacin and dexamethasone to 25 patients with MDS. Eighteen patients showed some hematologic response, nine of 18 showing an improvement in absolute neutrophil counts only, and nine of 18 showing multi-lineage re- sponses. Raza et al. also administered pentoxifylline, ci- profloxacin and amifostine with and without dexa- methasone to 35 patients with MDS (Raza et al. 2000).

Fifteen patients did not respond until dexamethasone was added, and seven responded before. When exam- ined by lineage, 19 of 22 patients showed improved neu- trophil counts, 11 of 22 demonstrated more than 50% re- duction in blood transfusion requirements, improved Hb levels, or both, and seven of 22 showed improvement in platelet counts. The studies of pentoxifylline have been difficult to assess due to the inclusion of steroids in most combinations; additionally, the response crite- ria used in these studies pre-dated the now-standard IWG criteria (Cheson et al. 2000).

11.4.2 SCIO-469

SCIO-469 is an orally bioavailable inhibitor of p38a mi- togen-activated protein kinase (MAPK). The mamma- lian MAPK cascades are information highways for the transmission of extracellular signals from the cell sur- face to the nucleus. In response to upstream signals, MAPKs phosphorylate their specific substrates at serine or threonine residues. These phosphorylation events can positively or negatively regulate substrates and, thus, the entire signaling cascade. MAPK signaling pathways have numerous roles, including modulation of gene expression, mitosis, proliferation, motility, me- tabolism, and apoptosis (Milella et al. 2003; Wada and Penninger 2004). The p38 MAPK cascade in particular appears to be important for the synthesis and secretion of IL-6, VEGF, and TNFa, important components of the aa bone marrow microenvironment.

SCIO-469 has demonstrated activity in preliminary models of both multiple myeloma and MDS. SCIO-469 treatment augmented cytotoxicity of the proteasome in-

a 11.4 ´ Therapies Targeting Disordered Cytokine Milieu 115

hibitor PS-341 against PS-341-resistant cell lines and pa- tient multiple myeloma cells (Hideshima et al. 2004).

11.4.3 Etanercept and Infliximab

Tumor necrosis factor alpha (TNFa) mRNA and protein levels have been reported to be elevated in both bone marrow and blood plasma samples of patients with MDS, and recent clinical trials have evaluated the effi- cacy of treatment with immunosuppression and anti- TNF therapy (Kitagawa et al. 1997; Maciejewski et al.

1995; Molnar et al. 2000; Rosenfeld and Bedell 2002).

Pilot studies using the soluble TNFa receptor protein have shown its safety in patients with MDS (Deeg et al.

2002; Rosenfeld and Bedell 2002). Deeg et al. (2004) treated 14 transfusion-requiring patients with MDS with the combination of antithymocyte globulin (ATG) and the soluble TNF receptor protein etanercept. Forty-six percent of the patients responded with five patients achieving periods of red blood cell and platelet inde- pendence that exceeded 2 years. These results support the premise that immunosuppression is effective in se- lect patients with MDS.

Infliximab is a chimeric anti-TNFa monoclonal anti- body. It binds both soluble and membrane-bound TNFa.aa Stasi and Amadori (2002) reported one major and one minor erythroid response in two MDS patients treated with infliximab. Other data that have been presented in abstract form show some activity of infliximab in pa- tients with MDS.

11.5 Therapies Targeting the Immune System The incidence of autoimmune disorders is increased in some MDS populations (Saif et al. 2002). Autologous cy- totoxic T-lymphocytes have been observed to exert an inhibitory effect on MDS myelopoiesis in vitro. The clin- ical features of subsets of MDS overlap with aplastic anemia (AA) and large granular lymphocyte (LGL) lym- phoproliferative disorders, two diseases thought to be related to dysregulation of the immune system (Barrett et al. 2000). Clinical studies have shown activity of the immunosuppressives antithymocyte globulin and cy- closporine in the treatment of select groups of MDS pa- tients.

11.5.1 ATG

Single agent ATG has resulted in complete hematologic responses of up to 10±15% of patients with MDS (Killick et al. 2003; Molldrem et al. 2002). Predictors of response to immunosuppressive therapy include younger age, presence of a paroxysmal nocturnal hemoglobinuria (PNH) clone, HLA DR15, hypocellularity and a normal karyotype (Saunthararajah et al. 2002). Response to ATG has been associated with disappearance of T cell clones that demonstrate T cell receptor V beta clonality, and which suppress hematopoiesis ex vivo (Deeg et al.

2004).

11.5.2 Cyclosporine

Cyclosporine, a calcineurin inhibitor that is a potent im- munosuppressive agent used in solid organ and bone marrow transplantation, has been studied in the treat- ment of MDS. Shimamoto et al. (2003) examined the ef- ficacy of cyclosporine A (CsA) in 50 patients with mye- lodysplastic syndrome. Hematological improvement was observed in 30 (60%) patients, all with refractory anemia (RA). There were significantly more responders among patients with good risk karyotype or HLA- DRB1*1501 than among patients with intermediate/poor risk karyotypes or with other HLA-DRB1 types. This supports the notion that certain subsets of MDS have a more ªimmunologicº pathophysiology that is respon- sive to immune suppression.

11.6 Therapies Targeting Signaling 11.6.1 Tipifarnib

Farnesyltransferase (FT) inhibitors have emerged as novel inhibitors of signaling for hematologic malignan- cies (Lancet and Karp 2003). They were originally devel- oped to interfere with the farnesylation of Ras, a gene mutated in a wide array of cancers and in up to 20%

of MDS patients, and have been the focus of intense in- vestigation (Beaupre and Kurzrock 1999; Reuter et al.

2000). Two orally bioavailable compounds, tipifarnib and lonafarnib, are the most advanced to date in terms of clinical testing (Kurzrock et al. 2002).

In an initial Phase I trial in patients with refractory

and relapsed MDS and AML, tipifarnib produced clini-

cal responses in 29% of patients, including two complete remissions (Karp et al. 2001). Interestingly, none of the patients enrolled in the study were found to have Ras mutations. Correlative studies showed inhibition of far- nesyltransferase activity in the bone marrow cells of treated patients. Non-dose-limiting toxicities included nausea, renal insufficiency, polydipsia, paresthesias, and myelosuppression. A Phase II study of tipifarnib in MDS patients reported responses in three of 28 treated patients (Kurzrock et al. 2004). The initial dose of 600 mg orally twice daily was not well tolerated; a lower dose of 300 mg orally twice daily was acceptable.

11.6.2 Lonafarnib

Abstracts presented in recent meetings of the American Society of Hematology have shown promising activity for lonafarnib in the treatment of MDS and AML pa- tients. A Phase III randomized trial is being planned to investigate the clinical benefit and frequency of plate- let response to lonafarnib in patients with chronic mye- lomonocytic leukemia (CMML) or advanced MDS with severe thrombocytopenia.

11.6.3 Imatinib

In a subset of patients with CMML, a reciprocal translo- cation occurs that places the platelet-derived growth factor receptor beta (PDGFRb R ) next to various fusion partners, resulting in constitutive activation of the tyr- osine kinase function of PDGFRb R (Levitzki 2004). Ima- tinib therapy has had promising activity in a subset of patients with a PDGFRb R translocation (Apperley et al.

2002). Four patients with CMML and a PDGFRb R trans- location treated with imatinib 400 mg orally daily sus- tained complete cytogenetic responses.

11.6.4 PKC412

Protein kinase C (PKC) plays an important role in sig- naling pathways that regulate cell structure and gene ex- pression (Newton 2001). Downstream mediators such as MAPKs and phosphatidylinositol 3-kinase are impor- tant for growth and differentiation (Franklin and McCu- brey 2000). PKC412, a potent kinase inhibitor that has activity against PKC and FLT-3, has been studied in he-

matologic and solid malignancies both alone and in conjunction with other agents (George et al. 2004; Mon- nerat et al. 2004; Virchis et al. 2002). It is currently un- der evaluation in myelodysplastic syndromes.

11.7 Therapies Targeting Aberrant Differentiation

With the success of all-trans retinoic acid (ATRA) in treating acute promyelocytic leukemia, there has been increased interest in targeting aberrant differentiation pathways in the treatment of AML and MDS. Retinoic acid derivatives such as ATRA, cis-retinoic acid and vit- amin D have been studied alone and in combination with other agents.

11.7.1 Retinoic Acid

Single agent ATRA has shown limited activity in pa- tients with MDS. Visani et al. (1995) treated ten patients with MDS with oral ATRA for 6 weeks. A rise in hemo- globin concentration >1 g/dl was observed in 3/10 pa- tients, while 5/10 patients showed an increase in granu- locyte counts >0.5 ´ 10

/l without concomitant increase in the percentage of blast cells in the bone marrow. All the effects were transient and maximal responses were obtained by the fourth week of treatment.

13-cis-retinoic acid (13-CRA) has shown mild single agent activity in MDS (Ohno 1994). Koeffler et al. (1988) randomized 68 patients with MDS to receive a single daily dose of either 13-CRA or placebo. Treatment was continued up to 6 months. No significant difference was noted between the two treatment groups in re- sponse to test drug. Clark et al. (1987) evaluated the ef- fect of 13-CRA in 70 patients with MDS and 5% or fewer bone marrow blasts. Among non-sideroblastic patients, 1-year survival was 77% in the treatment arm versus 36% in the control group. Hematologic responses were not characterized with the precision of modern Interna- tional Working Group criteria. More recently, Bourantas et al. (1995) administered 13-CRA to 34 patients with MDS. Partial remission was achieved in four patients, one with RA, two with RA with excess blasts (RAEB) and one with CMML. Questions remain as to the opti- mal dosage, timing and combination of this agent in the treatment of MDS.

a 11.7 ´ Therapies Targeting Aberrant Differentiation 117

Combination of differentiation agents with other agents such as chemotherapy or histone deacetylase in- hibitors has also shown promising results. Ferrero et al.

(2004) tested 13-cis retinoic acid + (OH)2 vitamin D

+ low-dose 6-thioguanine and cytarabine in 26 patients with AML and in four patients with MDS. The response rate was 50%, with 27% complete remissions. Kuendgen et al. (2004) treated 18 patients with MDS and AML with valproic acid (VPA), a histone deacetylase inhibitor. Five patients were treated up front with VPA and ATRA.

There were no responses. Eight patients responded to VPA therapy alone. Four of five patients who relapsed were treated with VPA and ATRA, and two responded.

Erythropoietin has been given in conjunction with ATRA with some clinical responses. In one study, 27 pa- tients with low- or intermediate-risk MDS were enrolled in a 12-week study (Stasi et al. 2002). ATRA was admin- istered orally at doses of 80 mg/m

per day in two di- vided doses for 7 consecutive days every other week. Re- combinant human EPO was given subcutaneously three times a week. Clinically significant erythroid responses with increases in hemoglobin levels of at least 1 g/dl or reduction of transfusion needs were seen in 13 (48%) patients, with four showing improved responses after dose escalation of EPO.

11.7.2 Vitamin D

Vitamin D

analogs can act on the differentiation and maturity of different cell lines in vitro. Vitamin D has been studied in the treatment of both solid and hema- tologic cancers. Mellibovsky et al. (1998) studied the ef- fects of vitamin D analogs in patients with MDS. All the patients were in a low- to intermediate-risk group. In the calcidiol-treated group, one patient responded, three were nonresponders, and one showed progression. In the calcitriol group, ten were responders (two with ma- jor response), and four were non-responders. Side ef- fects were minimal. Studies of vitamin D analogs in conjunction with other agents in the treatment of MDS are underway.

11.8 Miscellaneous Therapies 11.8.1 TLK199

TLK199 is a novel liposomal glutathione derivative that is a peptidomimetic inhibitor of glutathione S-transferase P1-1 (GSTP1-1) (Ruscoe et al. 2001). GSTP1-1 is an abun- dant and ubiquitously expressed protein in normal and malignant mammalian tissues. It is thought to act as a negative growth regulator; inhibition of this pathway might promote cellular proliferation and differentiation.

The results of TLK199 in the treatment of MDS patients have been reported in abstract form. Response rates ap- pear to be in the 20±30% range in low-risk patients.

11.9 Conclusion

The recent FDA approval of azacitidine and the likely fast track review of lenalidomide indicate the emergence of a number of biologically based therapies for MDS.

The market for new therapies is great, given that MDS is primarily a disease of older adults, and demographics in the United States are shifting towards an older pop- ulation. Individually tailored combination therapies tar- geting multiple molecular mechanisms will be the norm in the future. Ideally, orally bioavailable, less toxic therapies will improve the availability and tolerability of treatments for older individuals. Rationally designed clinical studies are critical to sorting through the in- creasing number of agents available for testing. Empha- sis must be placed on verifying the putative `targeted' molecular mechanisms of the novel agents. Understand- ing of the relevant operative mechanisms underlying clinical response will contribute to a better understand- ing of the biology of MDS and will facilitate the rational design of more effective drugs.

References

Alexandrakis MG, Passam FJ, Ganotakis E, Dafnis E, Dambaki C, Konso- las J, Kyriakou DS, Stathopoulos E (2004) Bone marrow microvas- cular density and angiogenic growth factors in multiple myeloma.

Clin Chem Lab Med 42:1122±1126

Alexandrakis MG, Passam FH, Pappa CA, Sfiridaki K, Tsirakis G, Dami- lakis J, Stathopoulos EN, Kyriakou DS (2005) Relation between bone marrow angiogenesis and serum levels of angiogenin in pa- tients with myelodysplastic syndromes. Leuk Res 29:41±46 Anderson KC (2003) The role of immunomodulatory drugs in multiple

myeloma (Review). Semin Hematol 40:23±32

Andreeff M, Stone R, Michaeli J, Young CW, Tong WP, Sogoloff H, Ervin T, Kufe D, Rifkind RA, Marks PA (1992) Hexamethylene bisaceta- mide in myelodysplastic syndrome and acute myelogenous leu- kemia: a phase II clinical trial with a differentiation-inducing agent. Blood 80:2604±2609

Apperley JF, Gardembas M, Melo JV, Russell-Jones R, Bain BJ, Baxter EJ, Chase A, Chessells JM, Colombat M, Dearden CE, Dimitrijevic S, Mahon FX, Marin D, Nikolova Z, Olavarria E, Silberman S, Schultheis B, Cross NC, Goldman JM (2002) Response to imatinib mesylate in patients with chronic myeloproliferative diseases with rearrangements of the platelet-derived growth factor receptor beta. N Engl J Med 347:481±487

Barrett J, Saunthararajah Y, Molldrem J (2000) Myelodysplastic syn- drome and aplastic anemia: distinct entities or diseases linked by a common pathophysiology? (Review). Semin Hematol 37:

15±29

Beaupre DM, Kurzrock R (1999) RAS and leukemia: from basic mecha- nisms to gene-directed therapy (Review). J Clin Oncol 17:1071±

1079

Bellamy WT, Richter L, Sirjani D, Roxas C, Glinsmann-Gibson B, Frutiger Y, Grogan TM, List AF (2001) Vascular endothelial cell growth fac- tor is an autocrine promoter of abnormal localized immature mye- loid precursors and leukemia progenitor formation in myelodys- plastic syndromes. Blood 97:1427±1434

Bourantas KL, Tsiara S, Christou L (1995) Treatment of 34 patients with myelodysplastic syndromes with 13-CIS retinoic acid. Eur J Hae- matol 55:235±239

Cameron EE, Bachman KE, Myohanen S, Herman JG, Baylin SB (1999) Synergy of demethylation and histone deacetylase inhibition in the re-expression of genes silenced in cancer. Nat Genet 21: 103±107 Cheson BD, Bennett JM, Kantarjian H, Pinto A, Schiffer CA, Nimer SD, Læwenberg B, Beran M, de Witte TM, Stone RM, Mittelman M, Sanz GF, Wijermans PW, Gore S, Greenberg PL (2000) Report of an in- ternational working group to standardize response criteria for myelodysplastic syndromes. Blood 96:3671±3674

Clark RE, Jacobs A, Lush CJ, Smith SA (1987) Effect of 13-cis-retinoic acid on survival of patients with myelodysplastic syndrome. Lan- cet 1:763±765

Creusot F, Acs G, Christman JK (1982) Inhibition of DNA methyltrans- ferase and induction of Friend erythroleukemia cell differentiation by 5-azacytidine and 5-aza-2'-deoxycytidine. J Biol Chem 257:2041±2048

Daskalakis M, Nguyen TT, Nguyen C, Guldberg P, Kohler G, Wijermans P, Jones PA, Lubbert M (2002) Demethylation of a hypermethylated P15/INK4B gene in patients with myelodysplastic syndrome by 5- Aza-2'-deoxycytidine (decitabine) treatment. Blood 100:2957±

2964

Deeg HJ, Gotlib J, Beckham C, Dugan K, Holmberg L, Schubert M, Ap- pelbaum F, Greenberg P (2002) Soluble TNF receptor fusion pro- tein (etanercept) for the treatment of myelodysplastic syndrome:

a pilot study. Leukemia 16:162±164

Deeg HJ, Jiang PYZ, Holmberg LA, Scott B, Petersdorf EW, Appelbaum FR (2004) Hematologic responses of patients with MDS to antithy- mocyte globulin plus etanercept correlate with improved flow scores of marrow cells. Leuk Res 28:1177±1180

Drevs J (2003) PTK/ZK (Novartis) (Review). Drugs 6:787±794 Ferrero D, Campa E, Dellacasa C, Campana S, Foli C, Boccadoro M (2004)

Differentiating agents + low-dose chemotherapy in the manage-

ment of old/poor prognosis patients with acute myeloid leukemia or myelodysplastic syndrome. Haematologica 89:619±620 Fiedler W, Serve H, Dohner H, Schwittay M, Ottmann OG, O'Farrell AM,

Bello CL, Allred R, Manning WC, Cherrington JM, Louie SG, Hong W, Brega NM, Massimini G, Scigalla P, Berdel WE, Hossfeld DK (2005) A phase 1 study of SU11248 in the treatment of patients with refractory or resistant acute myeloid leukemia (AML) or not amenable to conventional therapy for the disease. Blood 105:986±993

Folkman J (1995) Angiogenesis in cancer, vascular, rheumatoid and other disease (Review). Nat Med 1:27±31

Franklin RA, McCubrey JA (2000) Kinases: positive and negative regu- lators of apoptosis (Review). Leukemia 14:2019±2034

George P, Bali P, Cohen P, Tao J, Guo F, Sigua C, Vishvanath A, Fiskus W, Scuto A, Annavarapu S, Moscinski L, Bhalla K (2004) Cotreatment with 17-allylamino-demethoxygeldanamycin and FLT-3 kinase in- hibitor PKC412 is highly effective against human acute myeloge- nous leukemia cells with mutant FLT-3. Cancer Res 64:3645±3652 Giagounidis AA, Germing U, Wainscoat JS, Boultwood J, Aul C (2004)

The 5q± syndrome. Hematology 9:271±277

Glade-Bender J, Kandel JJ, Yamashiro DJ (2003) VEGF blocking therapy in the treatment of cancer (Review). Expert Opinion On Biological Therapy 3:263±276

Gore SD, Carducci MA (2000) Modifying histones to tame cancer: clin- ical development of sodium phenylbutyrate and other histone deacetylase inhibitors (Review). Expert Opinion on Investigational Drugs 9:2923±2934

Gore SD, Samid D, Weng LJ (1997) Impact of the putative differentiat- ing agents sodium phenylbutyrate and sodium phenylacetate on proliferation, differentiation, and apoptosis of primary neoplastic myeloid cells. Clin Cancer Res 3:1755±1762

Gore SD, Weng LJ, Zhai S, Figg WD, Donehower RC, Dover GJ, Grever M, Griffin CA, Grochow LB, Rowinsky EK, Zabalena Y, Hawkins AL, Burks K, Miller CB (2001) Impact of the putative differentiating agent sodium phenylbutyrate on myelodysplastic syndromes and acute myeloid leukemia. Clin Cancer Res 7:2330±2339 Gore SD, Weng LJ, Figg WD, Zhai S, Donehower RC, Dover G, Grever

MR, Griffin C, Grochow LB, Hawkins A, Burks K, Zabelena Y, Miller CB (2002) Impact of prolonged infusions of the putative differen- tiating agent sodium phenylbutyrate on myelodysplastic syn- dromes and acute myeloid leukemia. Clin Cancer Res 8:963±970 Gottlicher M (2004) Valproic acid: an old drug newly discovered as in- hibitor of histone deacetylases (Review). Ann Hematol 83[Suppl 1]:S91±S92

Gottlicher M, Minucci S, Zhu P, Kramer OH, Schimpf A, Giavara S, Slee- man JP, Lo CF, Nervi C, Pelicci PG, Heinzel T (2001) Valproic acid defines a novel class of HDAC inhibitors inducing differentiation of transformed cells. EMBO J 20:6969±6978

Hideshima T, Podar K, Chauhan D, Ishitsuka K, Mitsiades C, Tai YT, Ha- masaki M, Raje N, Hideshima H, Schreiner G, Nguyen AN, Navas T, Munshi NC, Richardson PG, Higgins LS, Anderson KC (2004) p38 MAPK inhibition enhances PS-341 (bortezomib)-induced cytotox- icity against multiple myeloma cells. Oncogene 23:8766±8776 Hurwitz H, Fehrenbacher L, Novotny W, Cartwright T, Hainsworth J,

Heim W, Berlin J, Baron A, Griffing S, Holmgren E, Ferrara N, Fyfe G, Rogers B, Ross R, Kabbinavar F (2004) Bevacizumab plus irino- tecan, fluorouracil, and leucovorin for metastatic colorectal can- cer. N Engl J Med 350:2335±2342

a References 119

Issa JP (2003) Decitabine (Review). Curr Opin Oncol 15:446±451 Issa J-P, Garcia-Manero G, Giles FJ, Mannari R, Thomas D, Faderl S, Bayar

E, Lyons J, Rosenfeld CS, Cortes J, Kantarjian HM (2004) Phase 1 study of low-dose prolonged exposure schedules of the hypo- methylating agent 5-aza-2'-deoxycytidine (decitabine) in hemato- poietic malignancies. Blood 103:1635±1640

Jones PA, Baylin SB (2002) The fundamental role of epigenetic events in cancer (Review). Nat Rev Genet 3:415±428

Karp JE, Lancet JE, Kaufmann SH, End DW, Wright JJ, Bol K, Horak I, Tidwell ML, Liesveld J, Kottke TJ, Ange D, Buddharaju L, Gojo I, Highsmith WE, Belly RT, Hohl RJ, Rybak ME, Thibault A, Rosenblatt J (2001) Clinical and biologic activity of the farnesyltransferase in- hibitor R115777 in adults with refractory and relapsed acute leu- kemias: a phase 1 clinical-laboratory correlative trial. Blood 97:3361±3369

Karp JE, Gojo I, Pili R, Gocke CD, Greer J, Guo C, Qian D, Morris L, Tidwell M, Chen H, Zwiebel J (2004) Targeting vascular endothelial growth factor for relapsed and refractory adult acute myelogenous leuke- mias: therapy with sequential 1-beta-d-arabinofuranosylcytosine, mitoxantrone, and bevacizumab. Clin Cancer Res 10:3577±3585 Killick SB, Mufti G, Cavenagh JD, Mijovic A, Peacock JL, Gordon-Smith

EC, Bowen DT, Marsh JC (2003) A pilot study of antithymocyte globulin (ATG) in the treatment of patients with 'low-risk' myelo- dysplasia. Br J Haematol 120:679±684

Kitagawa M, Saito I, Kuwata T, Yoshida S, Yamaguchi S, Takahashi M, Tanizawa T, Kamiyama R, Hirokawa K (1997) Overexpression of tu- mor necrosis factor (TNF)-alpha and interferon (IFN)-gamma by bone marrow cells from patients with myelodysplastic syndromes.

Leukemia 11:2049±2054

Koeffler HP, Heitjan D, Mertelsmann R, Kolitz JE, Schulman P, Itri L, Gun- ter P, Besa E (1988) Randomized study of 13-cis retinoic acid v pla- cebo in the myelodysplastic disorders. Blood 71:703±708 Kornblith AB, Herndon JE, Silverman LR, Demakos EP, Odchimar-Reissig

R, Holland JF, Powell BL, DeCastro C, Ellerton J, Larson RA, Schiffer CA, Holland JC (2002) Impact of azacytidine on the quality of life of patients with myelodysplastic syndrome treated in a random- ized phase III trial: a Cancer and Leukemia Group B study. J Clin Oncol 20:2441±2452

Kuendgen A, Strupp C, Aivado M, Bernhardt A, Hildebrandt B, Haas R, Germing U, Gattermann N (2004) Treatment of myelodysplastic syndromes with valproic acid alone or in combination with all- trans retinoic acid. Blood 104:1266±1269

Kurzrock R, Cortes J, Kantarjian H (2002) Clinical development of far- nesyltransferase inhibitors in leukemias and myelodysplastic syn- drome (Review). Semin Hematol 39:20±24

Kurzrock R, Albitar M, Cortes JE, Estey EH, Faderl SH, Garcia-Manero G, Thomas DA, Giles FJ, Ryback ME, Thibault A, De Porre P, Kantarjian HM (2004) Phase II study of R115777, a farnesyl transferase inhib- itor, in myelodysplastic syndrome. J Clin Oncol 22:1287±1292 Lancet JE, Karp JE (2003) Farnesyltransferase inhibitors in hematologic

malignancies: new horizons in therapy (Review). Blood 102:3880±

3889

Leder A, Leder P (1975) Butyric acid, a potent inducer of erythroid dif- ferentiation in cultured erythroleukemic cells. Cell 5:319±322 Levitzki A (2004) PDGF receptor kinase inhibitors for the treatment of

PDGF driven diseases (Review). Cytokine & Growth Factor Reviews 15:229±235

List A, Beran M, DiPersio J, Slack J, Vey N, Rosenfeld CS, Greenberg P (2003) Opportunities for Trisenox (arsenic trioxide) in the treat- ment of myelodysplastic syndromes. Leukemia 17:1499±1507 List A, Kurtin S, Roe DJ, Buresh A, Mahadevan D, Fuchs D, Rimsza L,

Heaton R, Knight R, Zeldis JB (2005) Efficacy of lenalidomide in myelodysplastic syndromes. N Engl J Med 352:549±557 Lubbert M, Wijermans P, Kunzmann R, Verhoef G, Bosly A, Ravoet C,

Andre M, Ferrant A (2001) Cytogenetic responses in high-risk mye- lodysplastic syndrome following low-dose treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine. Br J Haematol 114:349±357

Maciejewski J, Selleri C, Anderson S, Young NS (1995) Fas antigen ex- pression on CD34

human marrow cells is induced by interferon gamma and tumor necrosis factor alpha and potentiates cyto- kine-mediated hematopoietic suppression in vitro. Blood 85:3183±3190

Mellibovsky L, Diez A, Perez-Vila E, Serrano S, Nacher M, Aubia J, Super- via A, Recker RR (1998) Vitamin D treatment in myelodysplastic syndromes. Br J Haematol 100:516±520

Milella M, Kornblau SM, Andreeff M (2003) The mitogen-activated pro- tein kinase signaling module as a therapeutic target in hemato- logic malignancies (Review). Reviews in Clinical & Experimental Hematology 7:160±190

Moehler TM, Hillengass J, Goldschmidt H, Ho AD (2004) Antiangio- genic therapy in hematologic malignancies (Review). Current Pharmaceutical Design 10:1221±1234

Molldrem JJ, Leifer E, Bahceci E, Saunthararajah Y, Rivera M, Dunbar C, Liu J, Nakamura R, Young NS, Barrett AJ (2002) Antithymocyte globulin for treatment of the bone marrow failure associated with myelodysplastic syndrome [summary for patients in Ann Intern Med 2002 137:I-27]. Ann Intern Med 137:156±163

Molnar L, Berki T, Hussain A, Nemeth P, Losonczy H (2000) Detection of TNFalpha expression in the bone marrow and determination of TNFalpha production of peripheral blood mononuclear cells in myelodysplastic syndrome. Pathol Oncol Res 6:18±23

Monnerat C, Henriksson R, Le Chevalier T, Novello S, Berthaud P, Faivre S, Raymond E (2004) Phase I study of PKC412 (N-benzoyl-stauro- sporine), a novel oral protein kinase C inhibitor, combined with gemcitabine and cisplatin in patients with non-small-cell lung cancer. Ann Oncol 15:316±323

Moreno-Aspitia A, Geyer S, Li C-Y, Tefferi A, Witzig T, Niedrinhaus RD, Yukov AM, Morton R, Fitch T, Addo FE, Dakhil SR, Tschetter L, Co- lon-Otero G (2002) N998B: Multicenter phase II trial of thalidomide (Thal) in adult patients with myelodysplastic syndromes (MDS) [Abstract]. Blood 100:96 a

Musto P (2004) Thalidomide therapy for myelodysplastic syndromes:

current status and future perspectives (Review). Leuk Res 28:

325±332

Musto P, Falcone A, Sanpaolo G, Bisceglia M, Matera R, Carella AM (2002) Thalidomide abolishes transfusion-dependence in selected patients with myelodysplastic syndromes. Haematologica 87:884±

886

Newton AC (2001) Protein kinase C: structural and spatial regulation by phosphorylation, cofactors, and macromolecular interactions (Re- view). Chemical Reviews 101:2353±2364

Novogrodsky A, Dvir A, Ravid A, Shkolnik T, Stenzel KH, Rubin AL, Zai-

zov R (1983) Effect of polar organic compounds on leukemic cells.

Butyrate-induced partial remission of acute myelogenous leuke- mia in a child. Cancer 51:9±14

O'Farrell AM, Foran JM, Fiedler W, Serve H, Paquette RL, Cooper MA, Yuen HA, Louie SG, Kim H, Nicholas S, Heinrich MC, Berdel WE, Bello C, Jacobs M, Scigalla P, Manning WC, Kelsey S, Cherrington JM (2003) An innovative phase I clinical study demonstrates inhi- bition of FLT3 phosphorylation by SU11248 in acute myeloid leu- kemia patients. Clin Cancer Res 9:5465±5476

Ohno R (1994) Differentiation therapy of myelodysplastic syndromes with retinoic acid (Review). Leuk Lymphoma 14:401±409 Padro T, Ruiz S, Bieker R, Burger H, Steins M, Kienast J, Buchner T, Berdel

WE, Mesters RM (2000) Increased angiogenesis in the bone mar- row of patients with acute myeloid leukemia. Blood 95:2637±2644 Pruneri G, Bertolini F, Soligo D, Carboni N, Cortelezzi A, Ferrucci PF, Buf- fa R, Lambertenghi-Deliliers G, Pezzella F (1999) Angiogenesis in myelodysplastic syndromes. Br J Cancer 81:1398±1401 Raza A, Qawi H, Lisak L, Andric T, Dar S, Andrews C, Venugopal P, Gezer

S, Gregory S, Loew J, Robin E, Rifkin S, Hsu WT, Huang RW (2000) Patients with myelodysplastic syndromes benefit from palliative therapy with amifostine, pentoxifylline, and ciprofloxacin with or without dexamethasone. Blood 95:1580±1587

Raza A, Meyer P, Dutt D, Zorat F, Lisak L, Nascimben F, du RM, Kaspar C, Goldberg C, Loew J, Dar S, Gezer S, Venugopal P, Zeldis J (2001) Thalidomide produces transfusion independence in long-stand- ing refractory anemias of patients with myelodysplastic syn- dromes. Blood 98:958±965

Raza A, Buonamici S, Lisak L, Tahir S, Li D, Imran M, Chaudary NI, Pervaiz H, Gallegos JA, Alvi MI, Mumtaz M, Gezer S, Venugopal P, Reddy P, Galili N, Candoni A, Singer J, Nucifora G (2004) Arsenic trioxide and thalidomide combination produces multi-lineage hematological responses in myelodysplastic syndromes patients, particularly in those with high pre-therapy EVI1 expression. Leuk Res 28:791±803 Reuter CW, Morgan MA, Bergmann L (2000) Targeting the Ras signaling pathway: a rational, mechanism-based treatment for hematologic malignancies? (Review). Blood 96:1655±1669

Richon VM, Webb Y, Merger R, Sheppard T, Jursic B, Ngo L, Civoli F, Breslow R, Rifkind RA, Marks PA (1996) Second generation hybrid polar compounds are potent inducers of transformed cell differ- entiation. Proc Natl Acad Sci USA 93:5705±5708

Rosenfeld C, Bedell C (2002) Pilot study of recombinant human soluble tumor necrosis factor receptor (TNFR:Fc) in patients with low risk myelodysplastic syndrome. Leuk Res 26:721±724

Ruscoe JE, Rosario LA, Wang T, Gate L, Arifoglu P, Wolf CR, Henderson CJ, Ronai Z, Tew KD (2001) Pharmacologic or genetic manipula- tion of glutathione S-transferase P1-1 (GSTpi) influences cell pro- liferation pathways. J Pharmacol Exp Ther 298:339±345 Saba H, Rosenfeld C, Issa J-P, DiPersio J, Raza A, Klimek V, Slack J, de

Castro C, Mettinger K, Kantarjian H (2004) First report of the phase III north American trial of decitabine in advanced myelodysplastic syndrome (MDS) [Abstract]. Blood 104:23 a

Saif MW, Hopkins JL, Gore SD (2002) Autoimmune phenomena in pa- tients with myelodysplastic syndromes and chronic myelomono- cytic leukemia (Review). Leuk Lymphoma 43:2083±2092 Saunthararajah Y, Nakamura R, Nam JM, Robyn J, Loberiza F, Macie-

jewski JP, Simonis T, Molldrem J, Young NS, Barrett AJ (2002) HLA-DR15 (DR2) is overrepresented in myelodysplastic syndrome and aplastic anemia and predicts a response to immunosuppres- sion in myelodysplastic syndrome. Blood 100:1570±1574

Schroter H, Gomez-Lira MM, Plank KH, Bode J (1981) The extent of his- tone acetylation induced by butyrate and the turnover of acetyl groups depend on the nature of the cell line. Eur J Biochem 120:21±28

Sekeres MA (2005) Arsenic trioxide as a treatment for myelodysplastic syndrome. Current Hematology Reports 4:59±63

Shimamoto T, Tohyama K, Okamoto T, Uchiyama T, Mori H, Tomonaga M, Asano Y, Niho Y, Teramura M, Mizoguchi H, Omine M, Ohyashiki K (2003) Cyclosporin A therapy for patients with myelodysplastic syndrome: multicenter pilot studies in Japan. Leuk Res 27:783±788 Silverman LR (2001) Targeting hypomethylation of DNA to achieve cel- lular differentiation in myelodysplastic syndromes (MDS) (Review).

Oncologist 6[Suppl 5]:8±14

Silverman LR, Demakos EP, Peterson BL, Kornblith AB, Holland JC, Od- chimar-Reissig R, Stone RM, Nelson D, Powell BL, DeCastro CM, Ellerton J, Larson RA, Schiffer CA, Holland JF (2002) Randomized controlled trial of azacitidine in patients with the myelodysplastic syndrome: a study of the cancer and leukemia group B. J Clin On- col 20:2429±2440

Silverman LR, Holland JF, Weinberg RS, Alter BP, Davis RB, Ellison RR, Demakos EP, Cornell CJJ, Carey RW, Schiffer C (1993) Effects of treatment with 5-azacytidine on the in vivo and in vitro hemato- poiesis in patients with myelodysplastic syndromes. Leukemia 7[Suppl 1]:21±29

Stasi R, Amadori S (2002) Infliximab chimaeric anti-tumour necrosis factor alpha monoclonal antibody treatment for patients with myelodysplastic syndromes. Br J Haematol 116:334±337 Stasi R, Brunetti M, Terzoli E, Amadori S (2002) Sustained response to

recombinant human erythropoietin and intermittent all-trans re- tinoic acid in patients with myelodysplastic syndromes. Blood 99:1578±1584

Strupp C, Germing U, Aivado M, Misgeld E, Haas R, Gattermann N (2002) Thalidomide for the treatment of patients with myelodys- plastic syndromes. Leukemia 16:1±6

Thomas AL, Morgan B, Drevs J, Unger C, Wiedenmann B, Vanhoefer U, Laurent D, Dugan M, Steward WP (2003) Vascular endothelial growth factor receptor tyrosine kinase inhibitors: PTK787/ZK 222584 (Review). Semin Oncol 30:32±38

Virchis A, Ganeshaguru K, Hart S, Jones D, Fletcher L, Wright F, Wick- remasinghe R, Man A, Csermak K, Meyer T, Fabbro D, Champain K, Yap A, Prentice HG, Mehta A (2002) A novel treatment approach for low grade lymphoproliferative disorders using PKC412 (CGP41251), an inhibitor of protein kinase C. Hematol J 3:131±136 Visani G, Tosi P, Manfroi S, Ottaviani E, Finelli C, Cenacchi A, Bendandi M, Tura S (1995) All-trans retinoic acid in the treatment of myelo- dysplastic syndromes. Leuk Lymphoma 19:277±280

Wada T, Penninger JM (2004) Mitogen-activated protein kinases in apoptosis regulation (Review). Oncogene 23:2838±2849 Warrell RPJ, He LZ, Richon V, Calleja E, Pandolfi PP (1998) Therapeutic

targeting of transcription in acute promyelocytic leukemia by use of an inhibitor of histone deacetylase. J Natl Cancer Inst 90:1621±

1625

Wijermans P, Lçbbert M, Verhoef G, Bosly A, Ravoet C, Andre M, Ferrant A (2000) Low-dose 5-aza-2'-deoxycytidine, a DNA hypomethylat- ing agent, for the treatment of high-risk myelodysplastic syn- drome: a multicenter phase II study in elderly patients. J Clin On- col 18:956±962

a References 121