Decitabine with allogeneic peripheral blood stem cell transplantation in the therapy of leukemia relapse following a prior transplant: results of a phase I study

Immune responses to azacytidine in animal models of inflammatory disorders: a systematic review

Inflammatory disorders like diabetes, systemic lupus erythematodes, inflammatory lung diseases, rheumatoid arthritis and multiple sclerosis, but also rejection of transplanted organs and GvHD, form a major burden of disease. Current classes of immune suppressive drugs to treat these disorders are never curative and side effects are common. Therefore there is a need for new drugs with improved and more targeted modes of action. Potential candidates are the DNA methyl transferase inhibitor 5-azacytidine (Aza) and its derivative 5-aza 2′deoxycitidine (DAC). Aza and DAC have been tested in several pre-clinical in vivo studies. In order to obtain an overview of disorders for which Aza and/or DAC can be a potential treatment, and to find out where information is lacking, we systematically reviewed pre-clinical animal studies assessing Aza or DAC as a potential therapy for distinct inflammatory disorders. Also, study quality and risk of bias was systematically assessed. In the 35 identified studies, we show that both Aza and DAC do not only seem to be able to alleviate a number of inflammatory disorders, but also prevent solid organ rejection and GvHD in in vivo pre-clinical animal models. Aza/DAC are known to upregulate FOXP3, a master transcription factor for Treg, in vitro. Seventeen studies described the effect on Treg, of which 16 studies showed an increase in Treg. Increasing Treg therefore seems to be a common mechanism in preventing inflammatory disorders by Aza/DAC. We also found, however, that many essential methodological details were poorly reported leading to an unclear risk of bias. Therefore, reported effects might be an overestimation of the true effect.

Decitabine for relapsed acute lymphoblastic leukemia after allogeneic hematopoietic stem cell transplantation

Relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a main question on treatment failure. Current strategies for management that usually include salvage chemotherapy, donor lymphocytic infusion and second transplantation. Our study assessed the efficacy of decitabine (DAC) for treating patients with acute lymphoblastic leukemia (ALL) who relapsed after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We retrospectively analyzed the outcomes of 12 patients with relapsed ALL after allo-HSCT who received DAC therapy. Nine patients received DAC combined with chemotherapy and donor stem cell infusion, and 3 patients received single- agent DAC. Ten of the 12 patients achieved complete remission (CR), 1 achieved a partial remission (PR), and 1 had no response (NR) after treatment at the latest follow-up (LFU), the median survival was 11.2 months (range, 3.8-34, 7 months). The 1- and 2-year overall survival (OS) rates were 50% (6/12) and 25% (3/12), respectively. Five patients were still alive; 4 had maintained CR and 1 was alive with disease. Patients with Philadelphia chromosome-positive ALL had higher survival rate than patients with Philadelphia chromosome-negative ALL (57.1% vs. 20%). No aggravated flares of graft-versus-host disease (GVHD) were observed during DAC treatment. Therefore, DAC may be a promising therapeutic agent for ALL recurrence after allo-HSCT.

Decitabine

Besides 5-azacytidine (azacitidine, Vidaza®), 5-aza-2'-deoxycytidine (decitabine, Dacogen®) is the most widely used inhibitor of DNA methylation, which triggers demethylation leading to consecutive reactivation of epigenetically silenced tumor suppressor genes in vitro and in vivo. Although antileukemic activity of decitabine is known for almost 40 years, its therapeutic potential in hematologic malignancies has only recently led to its approval in higher-risk MDS patients and as first-line treatment in AML patients>65 years who are not candidates for intensive chemotherapy. Several clinical trials showed promising activity of low-dose decitabine also in CML and hemoglobinopathies, whereas its efficacy in solid tumors is very limited. Clinical responses appear to be exerted both by epigenetic alterations and by induction of cell-cycle arrest and/or apoptosis. Recent and ongoing clinical trials investigate new dosing schedules, routes of administration, and combination of decitabine with other agents, including histone deacetylase inhibitors.

Immune-modulating drugs and hypomethylating agents to prevent or treat relapse after allogeneic stem cell transplantation

Allogeneic stem cell transplantation is a curative treatment option for many hematological diseases, and the numbers of transplantations are steadily increasing worldwide. Major progress has been made in lowering treatment-related mortality by reducing intensity of the conditioning regimen and by improving supportive care (eg, for infectious complications). Accordingly, relapse after allogeneic stem cell transplantation has become the major cause for treatment failure. Major efforts to prevent or treat relapse are focused on cellular- (T cell, natural killer cell), cytokine-, or antibody-based strategies to enhance the graft-versus-tumor effect or circumvent immunoescape. In the more recent years, new classes of agents have shown activity in several hematological malignancies, and besides their immediate antitumor activity, most of them also possess immune-modulatory qualities that may be useful alone or in combination with adoptive immunotherapy after allogeneic stem cell transplantation to enhance graft-versus-tumor effects. Here, we summarize the current knowledge and potential use of 2 of these compounds in preventing or treating relapse after allogeneic stem cell transplantation, namely immune-modulating drugs and hypomethylating agents.

Epigenetic therapy in allogeneic hematopoietic stem cell transplantation

DNA methylation and other epigenetic phenomena appear to be relevant in the pathogenesis of several malignant disorders. DNA methyltransferases add methyl groups to cytosine-phosphate-guanine (CpG) islandsleading to gene promoter silencing. The DNA methyltransferases inhibitors azacitidine and decitabine have anti-tumor activity against a broad range of malignancies, but have been investigated mostly in myelodysplastic syndrome. In addition, these agents have immunomodulatory effects that are under investigation in the allogeneic stem cell transplantation scenario. Both drugs have been used in the perioperative period of allogeneic transplantations with varying degrees of success. It has been hypothesized that low dose azacitidine may increase the graft-versus-leukemia effect and have a role in the maintenance of remission after allogeneic transplantation for myeloid leukemias. It is also intriguing that this favorable effect might occur while mitigating graft-versus-host disease. Here we present a review of the rapidly growing field of epigenetic manipulation using hypomethylating agents in allogeneic transplantation.

DNA methyltransferase inhibitors in acute myeloid leukemia: discovery, design and first therapeutic experiences

INTRODUCTION

DNA methylation is an epigenetic change mediated by DNA methyltranferases (DNMTs), which are promising epigenetic targets for the treatment of acute myeloid leukemia (AML). This is evidenced by the two DNMT inhibitors (azacitidine and decitabine) approved by the Food and Drug Administration of the United States for the treatment of high-risk myelodysplastic syndromes and the first clinical data available in AML.

AREAS COVERED

This paper reviews data from the international literature regarding the design, sites of impact and pharmacodynamic characteristics of DNMT inhibitors, and their first clinical experiences in AML.

EXPERT OPINION

The strongest advances in epigenetic therapy have been in the treatment of AML. There are now an increasing number of DNMT inhibitors. These agents may be potentially administered at different times of leukemia therapy: before or instead of chemotherapy, as maintenance therapy, prior to allogeneic stem cell transplant (SCT) or after relapse following SCT.

Epigenomics in hematopoietic transplantation: novel treatment strategies

Allogeneic hematopoietic stem cell transplantation is a high risk but curative treatment option for leukemia, myelodysplasia and other hematological malignancies. After high dose radio- or chemo-therapy, recipient’s hematopoiesis is replaced by a new immunosystem and residual malignant cells are eliminated by the graft-versus-leukemia reaction. The benefit of this immunological effect is limited by the most frequent complication of hematopoietic stem cell transplantation: graft-versus-host disease. In addition to their well-known anti-tumor activity, epigenetic drugs mediate immunotolerance without reducing alloreactivity or even enhance graft-versus-leukemia effect without inducing graft-versus-host disease by regulating cytokine release, increasing the circulating number of regulatory T cells and interacting with natural killer cells. We focus on the use of epigenetic drugs in the allogeneic transplantation setting in relation to their anti-tumor and immunomodulatory potential.

Relapse after allogeneic stem cell transplantation

Since allogeneic stem cell transplantation (SCT) represents an intensive curative treatment for high-risk malignancies, its failure to prevent relapse leaves few options for successful salvage treatment. While many patients have a high early mortality from relapse, some respond and have sustained remissions, and a minority has a second chance of cure with appropriate therapy. The prognosis for relapsed hematological malignancies after SCT depends on four factors: the time elapsed from SCT to relapse (with relapses occurring within 6 months having the worst prognosis), the disease type (with chronic leukemias and some lymphomas having a second possibility of cure with further treatment), the disease burden and site of relapse (with better treatment success if disease is treated early), and the conditions of the first transplant (with superior outcome for patients where there is an opportunity to increase either the alloimmune effect, the specificity of the antileukemia effect with targeted agents or the intensity of the conditioning in a second transplant). These features direct treatments toward either modified second transplants, chemotherapy, targeted antileukemia therapy, immunotherapy or palliative care.

NCI First International Workshop on The Biology, Prevention and Treatment of Relapse after Allogeneic Hematopoietic Cell Transplantation: report from the committee on prevention of relapse following allogeneic cell transplantation for hematologic malignancies

Prevention of relapse after allogeneic hematopoietic stem cell transplantation is the most likely approach to improve survival of patients treated for hematologic malignancies. Herein we review the limits of currently available transplant therapies and the innovative strategies being developed to overcome resistance to therapy or to fill therapeutic modalities not currently available. These novel strategies include nonimmunologic therapies, such as targeted preparative regimens and posttransplant drug therapy, as well as immunologic interventions, including graft engineering, donor lymphocyte infusions, T cell engineering, vaccination, and dendritic cell-based approaches. Several aspects of the biology of the malignant cells as well as the host have been identified that obviate success of even these newer strategies. To maximize the potential for success, we recommend pursuing research to develop additional targeted therapies to be used in the preparative regimen or as maintenance posttransplant, better characterize the T cell and dendritic cells subsets involved in graft-versus-host disease and the graft-versus-leukemia/tumor effect, identify strategies for timing immunologic or nonimmunologic therapies to eliminate the noncycling cancer stem cell, identify more targets for immunotherapies, develop new vaccines that will not be limited by HLA, and develop methods to identify populations at very high risk for relapse to accelerate clinical development and avoid toxicity in patients not at risk for relapse.

Decitabine

The pyrimidine analogs, 5-azacytidine (azacitidine, Vidaza) and its deoxy derivative, 5-aza-2'-deoxycytidine (decitabine, Dacogen, are the most widely used inhibitors of DNA methylation which trigger demethylation leading to a consecutive reactivation of epigenetically silenced tumor suppressor genes in vitro and in vivo. Although the antileukemic capacity of decitabine has been known for almost 40 years, its therapeutic potential in hematologic malignancies is still under intensive investigation. Multiple clinical trials have shown the promising activity of low-dose decitabine in AML, MDS, CML, and hemoglobinopathies, whereas its efficacy in solid tumors is rather limited.Clinical responses appear to be induced by both epigenetic alterations and the induction of cell-cycle arrest and/or apoptosis. Recent clinical trials have been investigating new dosing schedules, routes of administration, and combination of decitabine with other agents, including histone deacetylase (HDAC) inhibitors.

Decitabine in the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of heterogeneous clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, peripheral blood cytopenias and a propensity to transform into acute myeloid leukemia. There are few treatment options available for patients with MDS. Studies into the molecular biology of MDS have demonstrated abnormal patterns of DNA methylation that lead to silencing of tumor-suppressor genes. Hypomethylating agents are compounds that have the potential to reverse the aberrant DNA methylation and increase the expression of silenced genes, leading to cellular differentiation and/or apoptosis. Decitabine is a cytidine analogue that has activity as a hypomethylating agent and has been evaluated in the therapy of patients with high-risk MDS. Several studies have confirmed the clinical activity of low-dose decitabine in patients with high-risk MDS, leading to responses in approximately 50% of patients, with low treatment-related mortality. Responses have even been seen in patients with high-risk cytogenetic abnormalities, and some studies have demonstrated increased re-expression of genes that were previously silenced by hypermethylation, such as CDKN2B/p15INK4B. There are still some issues concerning the ideal dose and schedule of decitabine for treating patients with MDS. This article focuses on the most recent clinical studies of decitabine for therapy of MDS.

Management of relapse after allo-SCT for AML and the role of second transplantation. Bone Marrow Transplant. 2009;44:769-777. [PMID: 19855439 DOI: 10.1038/bmt.2009.300]

Relapse after allo-SCT for AML carries very poor prognosis. Second allo-SCT, although curative, is not an appropriate treatment option for a large number of relapsing patients (only 2-20% patients receive a second allo-SCT), and efforts to increase the number of patients who may benefit from a second allo-SCT are ongoing. In addition, understanding the varied biological processes that are operative in disease relapse has encouraged the development of novel therapies, and could be beneficial to patients who are currently managed conservatively with supportive care for relapsed disease. Incorporating novel combinations of drugs with immunomodulation, although theoretically attractive, should be tested in the setting of clinical trials. In this review, we discuss the currently available approaches for relapsed AML after allo-SCT.

Efficacy of a 3-day, low-dose treatment with 5-azacytidine followed by donor lymphocyte infusions in older patients with acute myeloid leukemia or chronic myelomonocytic leukemia relapsed after allografting

We have piloted a low-dose schedule of 5-azacytidine followed by donor lymphocyte infusions (DLIs) in patients with relapse of AML or chronic myelomonocytic leukemia (CMMoL) after allografting. Of the 26 patients (median age 62 years, range 28-75) with relapsed AML (n=24) or CMMoL (n=2), 11 (42%) had poor-risk cytogenetics. Twenty-three patients had received fludarabine-based reduced-toxicity conditioning regimens, and three had received conventional myeloablative conditioning. Patients received 5-azacytidine s.c., at a total daily dose of 100 mg, on days 1-3, to be followed by DLI on day 10, with the next course of treatment to be started on day 22. A total of 60 courses of 5-azacytidine were administered, with a median of 2 courses (range: 1-10). In 44 courses, 5-azacytidine was followed by DLI, and thus 19/26 (73%) patients received at least one course of this combined treatment. Clinically relevant neutropenic infections not associated with progressive disease developed in four patients, one of them succumbing to sepsis. Only two patients developed de novo acute GvHD after the combination of 5-azacytidine and DLI. Overall, 66% of the patients benefited from this treatment, with continued CRs achieved in 4 (16%) patients, lasting a median of 525 days (range: 450+ to 820+), and a 50% rate of temporary disease control with stable mixed chimerism (median duration 72 days). The median survival from the start of 5-azacytidine treatment was 136 days (range: 23 to 873+), with an estimated 2-year survival probability of 16%. In conclusion, this non-intensive outpatient regimen of 5-azacytidine followed by DLI is feasible, with a very low aGVHD rate. Objective responses, including continuous complete donor chimerism, occurred also in patients with poor-risk cytogenetics.

Decitabine: a historical review of the development of an epigenetic drug

The development of decitabine from its synthesis in 1964 to the submission of a registration file has been described. Although the unique DNA-demethylating capacity of decitabine is known for a long time, its application is under continuing investigation. The use of decitabine in MDS, AML, CML, stem cell transplant, sickle cell anemia and thalassemia looks promising. The epigenetic dose seems lower than the cytotoxic dose. Whereas most drugs have matured after 40 years, decitabine is only at the beginning of a new development phase in epigenesis.

Inhibitors of DNA methylation: beyond myelodysplastic syndromes

DNA methyltransferase (DNMT) inhibitors, azacitidine (Vidaza, Pharmion, Boulder, CO, USA) and decitabine (Dacogen; SuperGen Inc, Dublin, CA, USA, and MGI Pharma Inc, Bloomington, MN, USA), have had a significant impact on the treatment paradigm of myelodysplastic syndromes (MDSs), previously managed mainly by supportive care and hematopoietic-stem-cell transplantation. The positive clinical experience seen in MDS to date coupled with the persistent challenges faced in the treatment of other hematologic malignancies has served as the impetus for further exploration of the therapeutic value of DNMT inhibitors beyond MDS. In that respect, the majority of data for these agents are in the setting of acute myelogenous leukemia (AML). Experience with these agents in patients with refractory anemia with excess blasts in transformation (reclassified by the World Health Organization as AML) was also reported in the clinical trials submitted to the FDA for approval of azacitidine for MDS. Some use has also been described in chronic myelogenous leukemia and acute lymphocytic leukemia. Further studies are needed to clarify the appropriate dose and the number and duration of cycles in the treatment of leukemias, and to identify ideal candidates for therapy, explore the role of DNMT inhibitors in combination with other agents, especially histone deacetylase inhibitors, delineate differences between the commercially available agents, and establish the long-term safety of these agents. To this end, experience with DNMT inhibitors in hematologic malignancies other than MDS is reviewed in an effort to better understand the therapeutic potential of these agents and to define areas of future exploration in these settings.

Molecularly targeted therapies in myelodysplastic syndromes and acute myeloid leukemias

Although there has been significant progress in acute myeloid leukemia (AML) treatment in younger adults during the last decade, standard induction therapy still fails to induce remission in up to 40% of AML patients. Additionally, relapses are common in 50-70% of patients who achieve a complete remission, and only 20-30% of patients enjoy long-term disease-free survival. The natural history of myelodysplastic syndrome (MDS) is variable, with about half of the patients dying from cytopenic complications, and an additional 20-30% transforming to AML. The advanced age of the majority of MDS patients limits the therapeutic strategies often to supportive care. To address these shortcomings, much effort has been directed toward the development of novel treatment strategies that target the evolution and proliferation of malignant clones. Presented here is an overview of molecularly targeted therapies currently being tested in AML and MDS patients, with a focus on FMS-like tyrosine kinase 3 inhibitors, farnesyltransferase inhibitors, antiangiogenesis agents, DNA hypomethylation agents, and histone deacetylase inhibitors.

Epigenetic drugs: a longstanding story

In this chapter, the development of decitabine from its synthesis in 1964 to the submission of a registration file in 2004 is reviewed. The proper application of the unique properties of decitabine took quite some time to elucidate. In addition, the practical handling in the clinic was not easy as the prolonged myelosuppression of decitabine made it difficult to determine the preferred dose and schedule. Laboratory studies on DNA methylation and cell differentiation showed possible applications in solid and hematologic malignancies. However, despite many attempts, results in solid tumors have been disappointing thus far. After thorough investigation, decitabine achieved therapeutic application in myelodysplastic syndrome (MDS), in particular in patients with a poor prognosis. Further indications may include acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), hematopoietic stem cell transplantation, sickle cell anemia, and thalassemia. Whereas most drugs are already at the end of their life cycle after 40 years, decitabine is only at the beginning. Its application will broaden with the increase in knowledge of epigenetic mechanisms and their relationship to drug therapy.

Decitabine in chronic leukemias

5-Aza-2'-deoxycitidine (decitabine, Dacogen, Bloomington, MN) is a cytosine analogue that promotes hypomethylation of DNA and has documented efficacy in myeloid malignancies. Indeed, promising clinical results have been observed in acute myeloid leukemia (AML) and the myelodysplastic syndromes (MDS). Aberrant methylation has also been found in chronic leukemias, providing a rationale for investigating the use of decitabine in these diseases. There is clear evidence of molecular (hypomethylation) as well as hematologic and cytogenetic responses to decitabine in chronic myelogenous leukemia of all phases, including in patients resistant to imatinib mesylate. Clinical trials of decitabine in chronic lymphocytic leukemia are ongoing. There are many unanswered questions regarding optimizing this treatment for chronic leukemias, but successful proof-of-concept studies for hypomethylating agents move us closer to approaches that may have a significant impact on patient outcomes.

Disease burden may identify patients more likely to benefit from second allogeneic hematopoietic stem cell transplantation to treat relapsed acute myelogenous leukemia

The major cause of failure after allogeneic hematopoietic stem cell transplantation (HSCT) for acute myelogenous leukemia (AML) is disease relapse or progression. We analyzed the outcome of second HSCT for treatment of patients with relapsed, refractory AML/myelodysplastic syndrome (MDS) at our institution. A total of 72 patients were eligible for this analysis. In all, 25 (35%) patients received salvage chemotherapy prior to the second transplant procedure and only two (3%) patients were in complete remission at the time of the second transplant. A total of 20 patients (28%) had low leukemia burden as measured by the absence of peripheral blood blasts and <or=5% blasts in the bone marrow at the time of the second transplant. Although, the overall median survival after the second transplant was 6 months, a subset of patients who had low leukemia burden at the time of the second transplant had a 5-year survival of 25 vs 12% in those with a high leukemia burden. Thus, a second transplant may offer the possibility of long-term disease control in a subset of patients who have a 'low bulk' disease at the time of transplantation.

Future Directions for the Use of Hypomethylating Agents

Epigenetics refers to heritable changes in DNA and chromatin that impact gene expression without a change in DNA sequence. Two major steps involved in epigenetic regulation of gene expression include methylation of the promoter region of the gene and deacetylation of specific lysine residues on promoter-associated histones leading to changes in chromatin structure. Promoter hypermethylation is the most extensively studied epigenetic process. Our expanding knowledge of this process has led to its application in the diagnosis, prognosis, and treatment of various hematologic and neoplastic diseases. Several agents, which reverse promoter methylation or inhibit histone deacetylases, are under development for use alone or in combination for a variety of neoplastic diseases. This review discusses the potential use of methylation reversing agents in the treatment of solid tumors and in benign hematologic disorders along with the rationale for combination therapies using hypomethylating agents.

DNA methylation in haematological malignancies: the role of decitabine

Normal cell development and function is dependent upon controlled gene expression. DNA methylation is an epigenetic modification that can play an important role in the control of gene expression. DNA methylation at cytosine residues in gene promoter CpG sequences is known to inhibit gene transcription. Inappropriate inhibition of the transcription of tumour suppressor genes, genes that inhibit angiogenesis and metastasis and genes involved in DNA repair by uncontrolled methylation, can lead to unregulated growth and proliferation of a cell and carcinogenesis. Promoter hypermethylation affecting the p16 gene, resulting in gene silencing, has been shown to occur in many human solid tumours and a 'hypermethylation profile' in some leukaemias has been defined. The molecular mechanisms by which aberrant DNA methylation takes place during carcinogenesis are still not clear. However, the large number of target genes (involved in tumorigenesis) that are silenced by aberrant methylation suggests that inhibition of this process may have potential as cancer therapy. Decitabine (NSC-127716, Dacogen; SuperGen) is a potent and specific hypomethylating agent and an inhibitor of the DNA methyltransferase activity that mediates DNA methylation. Decitabine has been shown to have a broad range of antineoplastic activity in preclinical studies. This agent has exhibited significant activity in the treatment of patients with myelodysplastic syndrome, chronic myeloid leukaemia and acute myeloid leukaemia, although clinical Phase I and II studies with solid tumours have not been very promising. Phase II and III studies are currently ongoing to evaluate decitabine, both alone and in combination, in various stages of these haematological malignancies.

New agents in acute myeloid leukemia and other myeloid disorders

Over the past several decades, improvements in chemotherapeutic agents and supportive care have resulted in significant progress in treating patients with acute myeloid leukemia (AML). More recently, advances in understanding the biology of AML have resulted in the identification of new therapeutic targets. The success of all-trans-retinoic acid in acute promyelocytic leukemia and of imatinib mesylate in chronic myeloid leukemia have demonstrated that targeted therapy may be more effective and less toxic when well defined targets are available. At the same time, understanding mechanisms of drug resistance and means to overcome them has led to modification of some of the existing cytotoxic agents. Rational design and conduct of clinical trials is necessary to ensure that the full potential of these new agents is realized.

Long-term follow-up of a phase I study of high-dose decitabine, busulfan, and cyclophosphamide plus allogeneic transplantation for the treatment of patients with leukemias

BACKGROUND

Decitabine is a hypomethylating agent that has activity in patients with leukemia. The authors combined decitabine with busulfan and cyclophosphamide as a conditioning regimen prior to allogeneic hematopoietic stem cell transplantation.

METHODS

Patients with high-risk acute myeloid leukemia (AML) (n = 12 patients); chronic myelomonocytic leukemia (CMML) (n = 1 patient); acute lymphocytic leukemia (ALL) (n = 1 patient); or late chronic phase, accelerated, or blastic phase chronic myelogenous leukemia (n = 9 patients) were eligible for the study. The treatment plan was comprised of busulfan, 12 mg/kg orally; cyclophosphamide, 100 mg/kg (n = 4 patients) or 120 mg/kg (n = 19 patients); and decitabine, intravenously at 3 dose levels: 400 mg/m(2) (n = 10 patients), 600 mg/m(2) (n = 8 patients), and 800 mg/m(2) (n = 5 patients). Donors were human leukocyte antigen-identical siblings in all cases, and all but one patient received peripheral blood stem cells. Graft-versus-host disease (GVHD) prophylaxis was tacrolimus based in all but one patient.

RESULTS

The median time to neutrophil and platelet engraftment was 12.5 days and 17.5 days, respectively. Twenty-one patients were engrafted and achieved disease remission. At a median of 3.3 years posttransplantation, 26% of patients (40% of patients with AML) were alive and disease free. The median survival for the group was 17.2 months, and the disease free survival for the group was 8.9 months. Causes of death were disease recurrence (nine patients), chronic GVHD (four patients), infections (three patients), and acute GVHD (one patient). The 100-day mortality rate was 9%. No decitabine dose-limiting toxicity was documented. The treatment-related mortality rate at 3 years was 35%. Responders were treated at all three decitabine dose levels, and no dose-response correlation was observed.

CONCLUSIONS

There was a high response rate with low treatment-related mortality, with 26% of patients alive in remission 3.3 years after transplantation.

Inhibition of HhaI DNA (Cytosine-C5) methyltransferase by oligodeoxyribonucleotides containing 5-aza-2'-deoxycytidine: examination of the intertwined roles of co-factor, target, transition state structure and enzyme conformation

The presence of 5-azacytosine (ZCyt) residues in DNA leads to potent inhibition of DNA (cytosine-C5) methyltranferases (C5-MTases) in vivo and in vitro. Enzymatic methylation of cytosine in mammalian DNA is an epigenetic modification that can alter gene activity and chromosomal stability, influencing both differentiation and tumorigenesis. Thus, it is important to understand the critical mechanistic determinants of ZCyt's inhibitory action. Although several DNA C5-MTases have been reported to undergo essentially irreversible binding to ZCyt in DNA, there is little agreement as to the role of AdoMet and/or methyl transfer in stabilizing enzyme interactions with ZCyt. Our results demonstrate that formation of stable complexes between HhaI methyltransferase (M.HhaI) and oligodeoxyribonucleotides containing ZCyt at the target position for methylation (ZCyt-ODNs) occurs in both the absence and presence of co-factors, AdoMet and AdoHcy. Both binary and ternary complexes survive SDS-PAGE under reducing conditions and take on a compact conformation that increases their electrophoretic mobility in comparison to free M.HhaI. Since methyl transfer can occur only in the presence of AdoMet, these results suggest (1) that the inhibitory capacity of ZCyt in DNA is based on its ability to induce a stable, tightly closed conformation of M.HhaI that prevents DNA and co-factor release and (2) that methylation of ZCyt in DNA is not required for inhibition of M.HhaI.

New drugs in acute myeloid leukemia

The acute myeloid leukemias (AML) are often fatal disorders with a range of clinical, morphologic, cytogenetic, and molecular features and a consequent need for a diverse array of therapies. This need for tailored therapy for subsets of patients with AML is exemplified in those with acute promyelocytic leukemia, the subject of a separate article in this issue (Tallman and Nabhan). Unfortunately, we tend to examine novel agents in patients with very advanced disease, in which prior therapies have inevitably altered the tumor. Of a myriad of possible exciting novel agents, a few, including PS-341, Genasense (Genta, Berkeley Heights, NJ), decitabine, 5-azacytidine, clofarabine, and troxacitabine, are briefly reviewed with an emphasis on their mechanisms of action from a perspective that suggests possible synergistic therapeutic interventions. With the growing appreciation of the pivotal role of angiogenesis in AML, angiogenesis modulators are a good example of a core class of drugs upon which future noncytotoxic combinations may be built. Those agents targeting vascular endothelial growth factor are also briefly reviewed.