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Leukemia stem cells utilize cell adhesion molecules like CXCR4/CXCL12 to home to bone marrow stromal niches where they are maintained in a dormant, protected state. Dociparstat sodium (DSTAT, CX-01) is a low anticoagulant heparin with multiple mechanisms of action, including inhibition of the CXCR4/CXCL12 axis, blocking HMGB1, and binding platelet factor 4 (PF-4). We conducted a pilot study adding DSTAT to azacitidine for patients with AML or MDS unresponsive to or relapsed after prior hypomethylating agent therapy, hypothesizing that DSTAT may improve response rates. Twenty patients were enrolled, with a median of 2 prior lines of therapy and 6 cycles of prior hypomethylating agents. Among fifteen patients evaluable for response, there was 1 complete remission, and 3 marrow complete remissions, for a response rate of 27 % among evaluable patients (20 % overall). Hematologic improvement was observed in 5 additional patients. The median overall survival for all enrolled patients was 205 days (95 % CI 119–302). While cytopenias and infections were common, these were not out of proportion to what would be expected in this population of patients undergoing treatment with azacitidine alone. In summary, this trial demonstrated the feasibility of combining DSTAT with azacitidine, with several responses observed, suggesting this combination warrants further study.

Hypomethylating agent (HMA) failure myelodysplastic syndrome (MDS) patients have poor outcomes and urgent need for novel therapies. Hedgehog pathway signaling upregulation plays a central role in myeloid neoplasm pathogenesis and leukemia stem cell survival. We evaluated the efficacy and safety of the smoothened inhibitor glasdegib in HMA-failure MDS (n = 35, median age 73 years). According to the International Prognostic Scoring System and the MD Anderson Global Risk Model, 54% and 77% had higher risk disease, respectively. Overall response was 6% (n = 2), and best response was marrow complete remission with hematologic improvement in both patients. Median OS and median follow-up were 10.4 and 42.8 months, respectively. Drug response/stable disease (SD) resulted in better OS than treatment failure (20.6 [95% CI, 10.4-] vs 3.9 months [95% CI, 0.7–9.1]; P < .0001). Response/SD was confirmed to be an independent covariate for improved OS (P < .0001). Grade 3 or higher infections occurred in 11% of patients (n = 4); non-hematologic toxicities were rare. Early mortality (< 30 days) occurred in 11% of patients (n = 4). Glasdegib was well tolerated among HMA-failure MDS patients, although single-agent activity was limited. SD or better resulted in notably superior OS. These results support further investigation of glasdegib, potentially in novel drug combinations, in MDS patients.

Phase 1 results from a Phase 1/2 study comprise 18 patients with myelodysplastic syndromes (MDS; n = 9), acute myeloid leukemia (AML; n = 8), and chronic myelomonocytic leukemia (CMML; n = 1) who were either hypomethylating agent naive (n = 10) or relapsed/refractory following prior hypomethylating agent therapy (n = 8) (NCT01926587). Patients received oral rigosertib, an inhibitor of Ras-effector pathways, in 3 successive cohorts (140 mg twice daily, 280 mg twice daily, or 840 mg/day [560 mg morning/280 mg evening]) for 3 weeks of a 4-week cycle. Patients received parenteral azacitidine (75 mg/m2/day × 7 days) during the second week; the cycle repeated every 4 weeks. The combination was well tolerated for a median of 4 (range 1–41) cycles, with 72% of patients experiencing ≥1 serious adverse events. No dose-limiting toxicities were observed. Thus, no maximum tolerated dose was reached. The most frequently reported adverse events were diarrhea (50%), constipation, fatigue, and nausea (each 44%), and pneumonia and back pain (each 33%). Sequential administration demonstrated an overall response rate of 56% in evaluable patients, with responses observed in 7/9 MDS/CMML patients (78%) and 2/7 AML patients (29%). Further clinical studies are warranted to investigate this doublet therapy in patients with myeloid malignancies.

Aim To compare the efficacy and safety between hypomethylating agent (HMA) alone and the combination of HMA and histone deacetylase inhibitor (HDACi) in myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Methods We performed a systematic review and meta-analysis of all available cohort studies regarding the comparison of HMA alone and in combination with HDACi for MDS and AML. Embase and Pubmed databases were searched for relevant studies. The overall hazard ratios for the HMA alone and HDACi combination were extracted. Heterogeneity among the included studies was evaluated by Cochrane’s Q Test and I2 statistics. A random-effect model or a fixed-effect model was applied depending on the heterogeneity. Subgroup analysis was used to evaluate the source of heterogeneity. Results Seven studies comprising 922 patients (458 patients treated with HMA alone and 464 with HMA and HDACi) were included in the analysis. Pooled data showed no significant differences in complete remission (CR) rates, hematologic improvement (HI), overall response rate (ORR), overall survival (OS), and toxicities between HMA alone treatment and HMA with HDACi regimens. Conclusions HDACi and HMA combination does not appear to be more effective and better tolerated than HMA alone. Future randomized controlled trials are needed to confirm its efficacy and safety.

We reviewed the cases of 68 consecutive patients who were diagnosed with myelodysplastic syndrome (MDS, n=61) or acute erythroleukemia (AEL, n=7) according to the World Health Organization (WHO) 2008 criteria and had previously been treated with azacitidine, a hypomethylating agent. Fifteen MDS patients had bone marrow erythroblast frequencies of ≥50%, and 6 out of the 7 AEL patients were reclassified as MDS (refractory anemia with excess blasts [RAEB]-1: 1, RAEB-2: 5) according to the revised WHO 2016 criteria. There was no difference between the overall response ratio (41%), as determined by a hematological improvement in at least one of 3 lineages, of these erythroid rich patients and that of the control group, which comprised 46 MDS patients with bone marrow erythroblast frequencies of

Although the majority of MDS patients fail to achieve clinical improvement to approved therapies, some patients benefit from treatment. Predicting patient response prior to therapy would improve treatment effectiveness, avoid treatment-related adverse events and reduce healthcare costs. Three separate cohorts of MDS patients were used to simulate drug response to lenalidomide alone, hypomethylating agent (HMA) alone, or HMA plus lenalidomide. Utilizing a computational biology program, genomic abnormalities in each patient were used to create an intracellular pathway map that was then used to screen for drug response. In the lenalidomide treated cohort, computer modeling correctly matched clinical responses in 37/46 patients (80%). In the second cohort, 15 HMA patients were modeled and correctly matched to responses in 12 (80%). In the third cohort, computer modeling correctly matched responses in 10/10 patients (100%). This computational biology network approach identified GGH overexpression as a potential resistance factor to HMA treatment and paradoxical activation of beta-catenin (through Csnk1a1 inhibition) as a resistance factor to lenalidomide treatment. We demonstrate that a computational technology is able to map the complexity of the MDS mutanome to simulate and predict drug response. This tool can improve understanding of MDS biology and mechanisms of drug sensitivity and resistance. (C) 2016 The Authors. Published by Elsevier Ltd.

The hypomethylating agent azacitidine can prolong overall survival (OS) in patients with higher risk-myelodysplastic syndromes (HR-MDS) compared to conventional regimens. However, outcomes differ largely between studies, making it challenging to determine the contribution of novel therapies added to azacitidine. Further, a discrepancy is seen between complete (CR) or partial (PR) response rates and OS improvement with azacitidine, making it challenging to rely on earlier endpoints than OS. We conducted a systematic literature search and study-level systematic review of 237 clinical studies to better understand outcomes for HR-MDS patients treated with azacitidine. Pooled marrow CR was 9% (N = 2654; 95% CI: 6-13 %), CR rate was 17 % (N = 6943; 95% CI: 15-20 %), and median OS (mOS) was 18.6 months (N = 2820; 95% CI: 15.3-21.9). A weak correlation to mOS was detected with CR rate (207 patient cohorts, Pearson's r = 0.315; P < 0.0005), and a much stronger correlation with median progression-free survival (mPFS) (r=0.88, P = 3 × 10-14). Six-months progression-free survival rates correlated with 1-year OS rates but were only infrequently reported (N = 41 patient cohorts) therefore not allowing a robust recommendation for a surrogate to the established OS endpoint. Larger patient numbers and patient-level data appear necessary, especially for designing future clinical trials using azacitidine combinations.

The hypomethylating agents (HMA) decitabine and azacitidine are used in acute myeloid leukemia (AML) for induction therapy in select patients. They are given on either inpatient (IP) or outpatient (OP) services and the decision where to administer them is complex but ultimately depends on the risk for neutropenic infections, hyperleukocytosis and other complications. In our study, we investigated 100-day survival differences between IP and OP HMA induction. This study reviewed 68 patients, 29 of whom received HMA as an IP while 39 received it as an OP. Using a logistic regression model, we found that IP induction was associated with a significantly lower odds of survival at 100-days (Odds Ratio 5.90; p=0.005). Given these results, we hypothesize the survival difference was related to the inherent risk associated with being admitted for chemotherapy, whether it be neutropenic fever, hyperleukocytosis or other reasons. We advise physicians who are administering IP HMA to consider its' inherent risk associated with its' administration.

Angiogenesis occurs in response to tissue ischemia and wound healing, and contributes to the pathogenesis of a variety of diseases, such as benign and malignant neoplasia. Several studies have measured bone marrow microvessel density (MVD) in MDS patients and acute myeloid leukemia (AML) patients transformed from MDS, and MVD was higher in MDS patients than controls, but was lower than in AML patients. Vascular endothelial growth factor (VEGF) is expressed in bone marrow blast cells, and an autocrine VEGF signaling mechanism has been established in MDS. Increased bone marrow angiogenesis and VEGF concentrations are adverse prognostic features in all of these patients. In this study, 69 patients were treated in two groups: hypomethylating agents or supportive care with oxymetholone±pyridoxine. We evaluated the MVD and VEGF expression of paraffin-embedded bone marrow samples from patients. We also investigated the relationship between angiogenesis-related biomarkers including MVD, VEGF expression, and clinical factors. The patient median age was 65 years, and the median follow-up duration was 28 months. MVD assessment among subtypes of WHO MDS classification showed that the MVD of RCUD was significantly lower than in other types (p=0.02). However, there was no significant difference in VEGF expression according to the subtype of MDS. Although MVD and VEGF expression did not differ between risk groups based on the IPSS, the low risk group tended to have lower expression of angiogenesis-related biomarkers. MDS patients receiving hypomethylating agents had significantly lower MVD expression in responders than in non-responders (6.13±3.38 vs. 9.89±2.10, respectively, p=0.039). In a consecutive evaluation at the time of diagnosis and 3 months after the initial treatment, the group with a decrease or no change of MVD had a higher response rate compared to that in the group with an increase of MVD (92.9% vs. 58.8%, respectively, p=0.045). Adverse prognostic factors included older age, MDS type other than RCUD, a higher IPSS risk group, and abnormal cytogenetics. Although angiogenesis-related markers did not demonstrate any significant prognostic association with survival, MVD (≥10n/mm2) and a strong expression of VEGF seemed to be associated with lower survival rate. These data suggested that the MVD value might be helpful in predicting responsiveness to treatment, especially in MDS patients treated with hypomethylating agents. Although angiogenesis-related markers including VEGF did not demonstrate a significant association with survival outcomes, we observed that high MVD and strong VEGF expression seemed to be associated with lower survival rate. Therefore, biologic markers related to angiogenesis might have a potential as prognostic factors for MDS patients.

Treatment with hypomethylating agents (HMAs) improves overall survival (OS) in patients who achieve a response of stable disease (SD) or better (complete remission [CR], partial remission [PR], or hematologic improvement [HI]). It is not well established if patients who achieve SD at 4–6 months of therapy should be offered different therapies to optimize their response or continue with the same regimen. Clinical data were obtained from the MDS Clinical Research Consortium database. SD was defined as no evidence of progression and without achievement of any other responses. Of 291 patients treated with AZA or DAC, 55% achieved their best response (BR) at 4–6 months. Among patients with SD at 4–6 months, 29 (20%) achieved a better response at a later treatment time point. Younger patients with lower bone marrow blast percentages, and intermediate risk per IPSS-R were more likely to achieve a better response (CR, PR, or HI) after SD at 4–6 months. Patients with SD who subsequently achieved CR had superior OS compared to patients who remained with SD (28.1 vs. 14.4 months, respectively, p =.04). In conclusion, patients treated with HMAs who achieves CR after a SD status had longer survival with continuous treatment after 6 months.

Intensive treatment for newly diagnosed acute myelogenous leukemia (ND-AML) patients are reserved for "fit" patients. While guidelines recommend evaluation of age, performance status and comorbidities, there is no consensus on the definition of "fitness" or optimal therapy for elderly AML patients. This retrospective study evaluated characteristics and survival outcomes of 274 patients (age ≥60 years) with ND-AML treated with 7 + 3 (cytarabine + an anthracycline) vs. hypomethylating agents (HMAs). Most patients received 7 + 3 (60.2%) vs. HMAs (39.8%) in first-line therapy (1 L T); more HMA patients were ≥75 years old and had more comorbidities. Median progression-free survival (PFS) following 1 L T was longer for patients who received 7 + 3 vs. HMAs (6.7 months [95% confidence interval (CI)]: 4.9, 11.1) vs. 4.1 months (95% CI: 2.8, 4.9, respectively). Median overall survival (OS) following 1 L T was also longer for patients who received 7 + 3 vs. HMAs (14.7 months [95% CI: 11.0, not estimated] vs. 4.3 months [95% CI: 3.2, 5.8], respectively). An age-adjusted Charlson Comorbidity Index score of ≥4 vs. 4 negatively affected PFS and OS irrespective of treatment. Overall, choosing an HMA over 7 + 3 in elderly patients with ND-AML may be influenced by age and comorbidities; patients receiving 7 + 3 had longer survival than those on an HMA.

Myeloproliferative neoplasm (MPN) transformed to acute myeloid leukemia (MPN-AML), MPN in accelerated phase (MPN-AP), and high-risk primary myelofibrosis (PMF) are associated with a poor response to therapy and very short survival. Several reports have suggested clinical activity of hypomethylating agents in these patients. We conducted a retrospective study of 21 patients with MPN-AML, 13 with MPN-AP and 11 with DIPSS-plus high-risk PMF treated with decitabine at our institution over the last 7 years and evaluated their clinical outcomes. Six patients (29%) with MPN-AML responded to decitabine (3 CR, 2 CRi, and 1 PR); median response duration was 7 months. The median overall survival (OS) was significantly higher in those who responded (10.5 vs 4 months). Among patients with MPN-AP, 8 patients (62%) benefited; the median response duration was 6.5 months. The median OS was 11.8 months in responders vs 4.7 months in non-responders. Among patients with DIPSS-plus high-risk PMF, 9 (82%) benefited; the median response duration was 9 months. The median OS was 32 months in responders vs 16.3 months in non-responders. Decitabine is a viable therapeutic option for patients with MPN-AML, MP-AP and high-risk PMF. Prospective clinical studies combining decitabine with other clinically active agents are needed to improve overall outcome.

Hypomethylating agents (HMA), such as 5-azacitidine or decitabine, are currently used to treat patients with myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) until treatment failure. However, the outcomes for patients who discontinue therapy after achieving partial response (PR) or complete remission (CR) but before treatment failure have not been reported. We present a series of 16 patients with higher-risk MDS (n=5; 31%) or AML (n=11; 69%) who achieved PR (n=1) or CR (n=15) and stopped HMA therapy while in response in the context of clinical trials. They received a median of 12 courses (range 1–24) and achieved response after a median of 1 course of therapy (1–4). Loss of response after discontinuation of therapy was rapid, with a median progression-free survival of 4 months (95% CI: 2–6). Median overall survival (OS) from the time of therapy discontinuation was 15 months (95% CI: 6–24). Patients who received 12 cycles of therapy or more had significantly better OS (median: 20 months [95% CI: 12–27]) than those who received fewer than 12 cycles (median: 4 months [95% CI: 1–8]) (p= 0.043). Poor-risk cytogenetics were also associated with lower 1-year OS (33% versus 69%; p= 0.046). According to these results and considering the poor prognosis after HMA failure, HMA interruption should be avoided once a sustained response has been achieved.

In Europe, azacitidine is the only hypomethylating agent approved for the treatment of patients with int-2-/high-risk myelodysplastic syndromes, offering significantly improved survival compared with conventional care. However, not all patients treated with azacitidine respond to treatment, and the vast majority of responders subsequently relapse. Currently, no standard care regimens have been established for patients after failure of azacitidine. Here, we discuss treatment options after loss of response or progression on azacitidine. In addition, we briefly consider optimization of first-line treatment along with potential biomarkers for identifying and monitoring response during treatment with azacitidine.

3q26.2/EVI1 rearrangements resulting in EVI1 overexpression play an important role in leukemogenesis and are associated with treatment resistance and a poorer prognosis in patients with acute myeloid leukemia, myelodysplastic syndrome, chronic myeloid leukemia and BCR-ABL negative myeloproliferative neoplasms. In this study, we aim to explore the clinicopathological features of myelodysplastic/myeloproliferative (MDS/MPN) neoplasms with 3q26.2/EVI1 rearrangements and determine the potential impact of these cytogenetic abnormalities on treatment response and survival. The study group included 12 cases of MDS/MPN with 3q26.2 rearrangements detected by conventional karyotyping. There were 7 men and 5 women with a median age of 67 years (range, 51–79 years) at time of initial MDS/MPN diagnosis. Ten cases were classified as chronic myelomonocytic leukemia (CMML) and 2 were MDS/MPN, unclassifiable. Among CMML cases, 5 (50%) were proliferative type and 5 (50%) were dysplastic type. Based on blast counts, these 10 CMML were: CMML-0 (n = 2), CMML-1 (n = 3), and CMML-2 (n = 5). Eleven (92%) patients had 3q26 rearrangements at the initial diagnosis. Inv(3)(q21q26.2) was most common, identified in 7(58%) patients, followed by t(3;21)(q26.2;q22) in 2 patients and 1 patient each with t(3;3)(q21;q26.2), t(2;3)(p21;q26-27), and t(3;6)(q26.2;q26). Six (50%) patients had 3q26.2 rearrangements as a sole cytogenetic abnormality and 6 (50%) patients had additional cytogenetic abnormalities. Molecular studies revealed DNMT3A mutations in all 3 patients assessed and RAS mutations in 2 of 8 (25%) patients. No mutations in ASXL1 (n = 3), TET2 (n = 3), FLT3 ITD/D835 (n = 10), and CEBPA (n = 7) were detected. Most patients received hypomethylating agent based chemotherapy. The median follow-up was 11.5 months (range, 1.5–24 months) and at time of last follow-up, 11 (92%) died with a median survival of 13.4 months (range, 1.5–24 months). The only patient alive had a relatively short follow-up of 2.4 months and showed disease progression at the last visit. In conclusion, 3q26.2/EVI1 rearrangements are a rare event and usually present at time of initial diagnosis in MDS/MPN. The presence of 3q26.2/EVI1 rearrangements in MDS/MPN is associated with rapid disease progression, poor response to treatment, and a poor prognosis.

The mechanism of clinical action for the FDA approved hypomethylating drugs azacitidine and decitabine remains unresolved and in this context the potential immunomodulatory effect of these agents on leukemic cells is an area of active investigation. Induced expression of methylated Cancer Testis Antigen (CTA) genes has been demonstrated in leukemic cell lines following exposure to hypomethylating drugs in vitro. SGI-110 is a novel hypomethylating dinucleotide with prolonged in vivo exposure and clinical activity in patients with MDS and AML. We demonstrate that this agent, like decitabine, produces robust re-expression of the CTAs NY-ESO-1 and MAGE-A, both in vitro and in leukemia-bearing AML xenografts. Upregulation of these genes in vitro was sufficient to induce cytotoxicity by HLA-compatible CD8+ T-cells specific for NY-ESO-1, a well-recognized and immunogenic CTA. Additionally, exposure to SGI-110 enhances MHC class I and co-stimulatory molecule expression, potentially contributing to recognition of CTAs. SGI-110, like the parent compound decitabine, induces expression of CTAs and might modulate immune recognition of myeloid malignancy.

Relapsed or refractory (R/R) disease remains challenging in acute myeloid leukemia (AML), especially in elderly patients not considered eligible for intensive treatment options. We retrospectively evaluated the safety and efficacy of low-dose melphalan (LD-Mel) in a multicenter analysis in patients over 65 years with R/R AML, who previously had received ≥1 non-curative treatment line. The study included 31 patients (median age 77 years) with 1-4 previous treatment lines. Three patients (9.7%) achieved a complete remission. Two patients (6.5%) achieved a partial remission, nine patients (29.0%) had disease stabilization with reduction of peripheral or bone marrow blast burden, resulting in an overall response rate of 16.1% and 45.2% achieved clinical benefit. Responders showed a significantly longer median overall survival than non-responders (16.3 vs. 2.3 months, p 0.001). Multivariate analysis identified complex karyotype as the only risk factor associated with inferior survival (p 0.001), whereas prior treatment with hypomethylating agents (HMAs) in 25 of 31 patients was associated with superior OS, regardless of prior response to HMAs (p = 0.03). LD-Mel was well tolerated, with mild myelosuppressive side effects. Conclusively, LD-Mel is an effective treatment option in elderly patients with R/R AML, particularly after HMA therapy and in the absence of a complex karyotype.

Treatment of CMML remains a clinical challenge, with no drug demonstrating clear clinical benefit. Even if azacitidine is approved in the treatment of CMML, its role remains disputed. We report a cohort of 76 CMML patients (according to WHO classification) treated with azacitidine in 3 programs (French AZA compassionate program, Cleveland Clinic Foundation and H. Lee Moffitt Cancer Center). 45% had CMML2, and 55% had splenomegaly and/or WBC counts >13 G/L, which are known to be poor prognostic factors in CMML. All patients received AZA for at least one cycle, and the median number of cycles administered was 6. Thirty-three patients (43%) achieved a response according to IWG 2006 criteria, including 13 complete remissions (17%). Median survival was 29 months. Increased bone marrow blast percentage and proliferative features of the disease, including splenomegaly and high WBC counts, were significantly associated with shorter survival. By multivariate analysis, only marrow blasts >10% and palpable splenomegaly had prognostic impact on survival. Although promising, the efficacy of azacitidine in advanced CMML needs to be confirmed in a randomized prospective study.

Abstract 4010 Patients with IPSS intermediate or high risk myelodysplastic syndrome (MDS) have few treatment options once their disease fails to respond to hypomethylating agent therapy. The styryl sulfone mitotic inhibitor ON 01910.Na, inhibits Polo-1 kinase, PI3-kinase and AKT pathways, and the drug has shown promising results in patients (pts) with advanced solid tumors (Jimeno et al, J Clin Onc 26:5504, 2008) and in Phase I/II studies of MDS pts, including those with trisomy 8 (Sloand at al, Proc ASH 2007, #822, Proc ASH 2008, #1651). In an ongoing Phase II clinical trial, we have treated 10 MDS pts unresponsive to at least 4 cycles (range 4–12 cycles) of hypomethylating agent therapy (5 post-azacytidine, 4 post-decitabine, and 1 pt treated with both agents) with ON 01910.Na. The pts had IPSS Intermediate-1 (n=3), Intermediate-2 (n=4) and High (n=3) risk MDS. The study cohort comprised pts with RAEB-1 (4 pts), RAEB-2 (3 pts) and RAEB-T (3 pts), with a median age of 80 years (range 65–86) and 2.3 year median (range 0.4–5.4) prior duration of MDS. Their cytogenetic profile included 5 pts with Good, 4 with Intermediate [t(8,10), t(14,18), +8, and (8+, 19+)], 1 with Poor risk cytogenetics (+8, 5q-, 1p-). At baseline, all pts were red blood cell transfusion-dependent. After the initial 2 pts were treated with 800mg/m2/day × 2day continuous IV infusion (CIVI)/week × 3weeks/month, the subsequent 8 patients received 1800mg/day × 3day CIVI q2weeks/month × 2 months, then monthly. Patients underwent bone marrow sampling and evaluation after every other cycle of treatment. To date, 7 pts have completed at least 2 cycles of therapy, with 2 pts having completed the full treatment course of 7 monthly cycles (median 4.7 for all pts). Responses according to IWG 2006 criteria were: Marrow CR (mCR) (2), Partial response (1), stable disease (SD) with hematologic improvement (HI) (2; 1 HI-E, N, 1 HI-P, N) = 5/10 overall responses (50%). Four pts had SD without HI, 1 pt progressed to AML. mCRs occurred in those with Disclosures: Off Label Use: The drug ON01910.Na is an investigational agent. Felsher:Cell Bioscience: On The Advisory Board. Wilhelm:Onconova Therapeutics Inc: Employment, Equity Ownership. Greenberg:Onconova Therapeutics Inc: Research Funding.

Aberrant DNA methylation of promoter associated CpG islands is a common phenomenon in human leukemias and cooperates with histone code changes in the control of gene expression. 5-Aza-2′-deoxycytidine (DAC) is a hypomethylating agent with significant antileukemia activity in humans. Recently, valproic acid (VPA) has been shown to be a histone deacetylase inhibitor and to have potential antineoplastic activity. In this report, we study the in vitro effects of the combination of DAC and VPA on the leukemic cell lines HL-60 and MOLT4. DAC alone induced growth inhibition and apoptosis at doses of 1 μM, an effect observed with VPA at doses of 1 mM. Each drug alone had the capacity to induce the expression of p57KIP2 and p21CIP1. DAC mediated hypomethylation of p57KIP2 was not required to induce p57KIP2 gene expression, and treatment with DAC resulted in the induction of p21CIP1. VPA induced global histone acetylation, an effect enhanced by the addition of DAC. The combination of DAC and VPA had a synergistic effect in terms of growth inhibition, induction of apoptosis and reactivation of p57KIP2 and p21CIP1. These results suggest that the combination of DAC and VPA could have significant antileukemia activity in vivo.