Final Results of a Phase I/II Study of the Combination of the Hypomethylating Agent 5-aza-2′-Deoxycytidine (DAC) and the Histone Deacetylase Inhibitor Valproic Acid (VPA) in Patients with Leukemia.

The combination of DAC and VPA has synergistic antileukemia activity in vitro. Based on this, we developed a phase I/II study of this combination for patients with leukemia. The dose of DAC was fixed: 15 mg/m2 IV daily x 10. Three dose levels of VPA were studied: 20, 35 and 50 mg/kg orally daily x 10 concomitantly with DAC. The phase I portion of the study followed a classic 3+3 schema. The phase II targeted a response rate of 30%. Patients with relapsed/refractory chronic and acute leukemia with adequate renal, hepatic functions and performance status were eligible. Patients older than 60 years of age with untreated disease were eligible if they were not candidates for higher priority therapies. Fifty four patients have been registered and treated on this study that is now closed to new patient accrual. Median age was 60 years (range 5 to 80). All, but 2 patients with MDS, had AML. Median number of prior therapies was 2 (range 0–5). Thirty patients (56%) had abnormal cytogenetics. No non-hematological VPA dose limiting toxicities were observed during the phase I portion of the study. Therefore the phase II combination consisted of VPA at a dose of 50 mg/kg daily with DAC. Ten patients achieved a CR and 2 a CRP (same criteria as of CR but without complete platelet recovery), for an overall response rate of 22%. The study did not meet any of its planned stopping rules and the maximal number of patients (n=40) was accrued in the phase II portion of the study. Ten out 40 patients (25%) achieved a response in that phase. Two out 12 patients (16%) achieved a response at lower doses of VPA. Five out of 11(45%) previously untreated older patients achieved a CR. The median overall survival (OS) for the whole group was 5.3 months, and it has not been reached for those patients achieving a response. The median duration of response is 8.3 months. Complete cytogenetic responses were observed in 4 out 4 patients with informative karyotypes. A trend toward higher VPA levels was observed in responders (p=0.02). Twelve out 35 (34%) patients receiving VPA at a dose of 50 mg/kg had evidence of histone acetylation compared to 1 out 12 (8%) at lower doses. Histone acetylation was transient. The effects on global methylation were assessed using the LINE assay. Median LINE methylation pretreatment was 44% (range 35.7–57.6%) and it decline to 37.08% (p=0.000) by day 10 to return to baseline by day 28. Methylation of p15, p57, p73, MDR1 and THSB1 was measured pretreatment and serially during therapy. Pretreatment p15 methylation was observed in 36 out 46 patients (78%) with a median value of 18.4% (range 0–80) to decline to 11.7% (range 1.3–67.8), p=0.005, by day 10. Methylation of THSB2 was observed in 19 out 48 patients (39.5%) but it was not affected by the therapy. Methylation of p57KIP2, p73 and MDR1 were rare events in this population. p15 hypomethylation was associated with the the induction of p15 mRNA expression. In summary, the combination of DAC with VPA has significant clinical activity in patients with AML and MDS and effect potentially mediated by the induction of DNA hypomethylation and histone acetylation.