A Phase 1, Open-Label, Dose-Escalation Study to Evaluate the Safety, Pharmacokinetics, and Pharmacodynamics of Oral Azacitidine in Patients with Myelodysplastic Syndromes (MDS) or Acute Myelogenous Leukemia (AML).

Abstract 117

Background: Parenteral azacitidine significantly improves overall survival of subjects with higher-risk MDS and WHO AML (20–30% blasts) compared to conventional care (Fenaux, Lancet Oncol 2009; 10:223). An oral formulation would be a more convenient administration route for patients and allow the evaluation of extended low-dose regimens, which could in turn lead to better treatment efficacy and lower toxicity profiles. The aim of this phase 1 study is to determine the maximum tolerated dose (MTD), dose limiting toxicities (DLTs), safety, pharmacokinetic (PK) and pharmacodynamic (PD) profiles of increasing doses of orally-administered azacitidine in subjects with MDS or AML. Methods: Subjects aged ≥ 18 years with a diagnosis of MDS or AML (not candidates for other therapies) by WHO criteria were enrolled into this multicenter, Phase 1, dose escalation study. Prior treatment with azacitidine or other demethylating agent was permitted. To allow PD/PK analyses of oral vs. subcutaneous (SC) administration, azacitidine was administered SC (75 mg/m2/day x 7 days) in Cycle 1, then orally in Cycle 2 starting at a dose of 120 mg/day x 7 days of every 28-day cycle. A standard “3+3” dose escalation design was used and an expansion cohort at the MTD was planned. Subjects were evaluated for DLT during the first cycle of oral azacitidine therapy. Azacitidine levels in plasma and urine were measured. DNA methylation was assayed using Illumina's Infinium Human Methylation27 BeadArrays. Response was assessed according to International Working Group (IWG) criteria for MDS (2006) and AML (2003). Results: To date, 45 subjects have enrolled into the study. Forty subjects received both SC and oral azacitidine; 5 subjects received SC azacitidine only. Median age is 70 years (range 31–91). Thirty-four subjects had MDS, 9 AML, and 2 CMML. Median pretreatment WBC and platelet counts of MDS subjects were 2.5 × 109/L (range 0.8–39.4) and 55.0 × 109/L (range 4.0–234.0) respectively. For subjects with AML, the median pretreatment WBC and platelet counts were 1.8 × 109/L (range 0.5–3.4) and 42.8 × 109/L (range 10.0–82.0) respectively. Baseline cytogenetics for subjects with MDS were as follows: 12 complex karyotype; 10 diploid; 1 with −7; 1 with t(11q23) and 10 whose karyotype was unknown. Doses of oral azacitidine evaluated were 120, 180, 240, 300, 360, 480 and 600 mg. The MTD of oral azacitidine on a 7-day QD treatment schedule was 480 mg. The DLT was grade 3 or 4 diarrhea in 2 of 3 subjects enrolled in the 600 mg cohort. Other grade 3 or 4 AEs reported include febrile neutropenia (6 subjects), infection (6 subjects), nausea (2 subjects), vomiting (2 subjects), fatigue (2 subjects), and thrombocytopenia (2 subjects). The bioavailability of oral azacitidine ranged from 5% to 35%. The exposure (AUCinf) of oral azacitidine was highly variable compared to SC exposure, ranging from 15% to 74% (except for one subject whose PK exposure following oral therapy was 167% of his SC exposure). Median duration of oral azacitidine was 5+ cycles (range 1–19+) for subjects with MDS and 2.5+ cycles (range 1–6+) for subjects with AML. Responses were evaluated following 6 cycles of oral therapy. To date, 14 subjects have received ≥ 6 cycles of oral azacitidine: 4 (29%) had complete response (CR), 6 (43%) had stable disease (SD), 3 (21%) had disease progression, and 1 subject (7%) was not evaluated. Among subjects with CR or SD, hematologic improvement by disease-specific IWG criteria included erythroid response (n = 5), platelet response (n = 5) and neutrophil response (n = 3). Fourteen subjects are ongoing, but have not completed 6 cycles of oral therapy; 17 subjects discontinued prior to completing 6 cycles. Changes in DNA methylation were observed in the blood of MDS and AML subjects following SC and oral azacitidine treatment, and a set of CpG loci were identified for which these changes were associated with azacitidine AUCinf and/or Cmax.. In addition, approximately 260 hypomethylated loci were common to both SC and oral therapy. Conclusions: Results to date indicate that a 7-day dosing regimen of oral azacitidine is active and well tolerated, with a manageable side effect profile in subjects with MDS or AML. Oral azacitidine exposure was highly variable and lower than that of SC azacitidine. Changes in DNA methylation were observed in the blood of MDS and AML subjects following SC and oral therapy. Evaluation of prolonged and BID treatment schedules is planned.