Evaluation of Oral Azacitidine Using Extended Treatment Schedules: A Phase I Study

Abstract 603

Parenteral azacitidine (AZA) is approved for administration on days 1–7 of a 28-day treatment schedule. Based on the short plasma half-life of AZA, S-phase restricted incorporation into DNA, and rapid re-methylation of DNA, it is possible that chronic daily exposure could enhanced its clinical activity. An oral formulation would be convenient and allow evaluation of lower doses administered on extended schedules. The initial phase I study of oral AZA, administered daily on a 7-day schedule demonstrated that it was bioavailable, safe, and clinically active in patients with MDS and AML (Garcia-Manero G, et al. Blood 2009;114:A117). Here, we report the results of a multicenter phase I exploration of extended oral AZA schedules, including dose-limiting toxicities (DLTs), safety, pharmacokinetic (PK), pharmacodynamic (PD), and preliminary response data. Patients aged ≥ 18 years with MDS, CMML or AML (not candidates for other therapies) were enrolled in the study. Inclusion criteria were a hemoglobin level of ≤ 9.0 g/dL, and/or platelet count of ≤ 50 × 10⁹/L, and/or be RBC transfusion-dependent; prior azanucleoside therapy was not permitted. Patients received oral AZA daily (QD) or twice daily (BID) on 14- or 21-days schedules, with starting at a dose of 300 mg for QD dosing and 200 mg for BID dosing. Patients were enrolled into cohorts of 6 and evaluated for DLTs at the end of Cycle 1. Patients were monitored continuously for adverse events (AEs) and assessed for disease response at the end of every second cycle. During Cycle 1, on the first and last day of treatment, PK parameters were derived from AZA concentrations in the plasma after the first dose of the day. PD samples were collected during the first 2 cycles and DNA methylation changes were evaluated using a LINE-1 assay. To date, 25 patients (median age 68 years [range 44–87]; 14 male and 11 female) with MDS (n = 13), AML (n = 7 de novo and n = 3 transformed), and CMML (n = 2) have received oral AZA on extended treatment schedules. Two DLTs, grade 3 nausea and grade 3 vomiting, occurred in 1 of 6 DLT-evaluable patients treated at 14-days QD (n = 7). No DLTs were observed on the 21-day QD (n = 6) or 14-day BID (n = 6) schedules; safety evaluation for the 21-day BID schedule is ongoing (n = 6). The maximum tolerated dose has not been reached on these schedules; no patient has received > 300 mg per dose. Overall rates of all grades nausea, vomiting, diarrhea, constipation, and abdominal pain with the extended schedules were similar to those observed with the oral 7-day schedule. The rate of febrile neutropenia (all grades) was higher in the 21-day QD cohort. This was observed in 4 patients with baseline ANC < 500 and/or AML diagnosis. Most common grade 3/4 AEs in the QD schedules were febrile neutropenia (14-day, 1/7; 21-day, 4/6), anemia (14-day, 1/7; 21-day, 0/6), thrombocytopenia (14-day, 1/7; 21-day, 1/6), diarrhea (14-day, 0/7; 21-day, 1/6), nausea (14-day, 1/7; 21-day, 0/6), and vomiting (14-day, 1/7; 21-day, 0/6). Extended BID schedules are under evaluation. PK data have been generated for 19 of 25 patients. For the 300 mg 14-day QD, 300 mg 21-day QD, and 200 mg 14-day BID schedules, using mean AUC (first and last day) results, extrapolated cumulative exposures per cycle were ~28%, 42% and 26%, respectively, compared with historical exposure observed following subcutaneous administration. AZA exposure increased with increasing dose, but was not dose-proportional. Clinical responses were observed for MDS/CMML patients on both extended QD schedules, with assessment ongoing for BID schedules (Table). In summary, extended (14- and 21-day) dosing of oral AZA is generally well tolerated, with no AZA accumulation, and promising clinical responses were observed, including complete remission (CR), marrow CR (mCR), and hematologic improvement (HI).