Results of First in Human (FIH) Phase 1 Pharmacokinetic (PK) Guided Dose-Escalation Study of ASTX727, a Combination of the Oral Cytidine Deaminase Inhibitor (CDAi) E7727 with Oral Decitabine in Subjects with Myelodysplastic Syndromes (MDS)

Introduction: Patients with International Prognostic Scoring System (IPSS) intermediate (Int) and high risk (HR) MDS benefit from therapy with hypomethylating agents (HMAs).  Treatment with the HMAs decitabine (DAC) and azacitidine (AZA) requires 5 or 7 daily parenteral doses respectively every month with some patients remaining on treatment for extended periods. An orally administered HMA would provide significant patient convenience, potentially enhance adherence to treatment, and may allow exploring extended treatment schedules with lower doses of DAC. Neither DAC nor AZA is readily bioavailable in oral form due to rapid clearance by cytidine deaminase (CDA) present in the gut and liver.  E7727, a novel CDAi, is orally bioavailable with a large safety margin in preclinical models.  We report here the first Phase 1 results of a PK-guided FIH dose escalation trial of ASTX727 (the combination of oral DAC and E7727).  

Methods: Adult patients with Int or HR MDS or Chronic Myelomonocytic Leukemia (CMML) were enrolled in this dose-escalating trial with a 3+3 design.  In addition to assessing the safety of the combination, the primary PK objective was to achieve a mean AUC of DAC following oral ASTX727 comparable to that achieved by IV DAC at the approved dose of 20 mg/m².  In the first cycle, each patient received an IV DAC dose of 20 mg/m² on Day 1 as an internal comparator followed by oral ASTX727 on Days 2-5 escalated by cohort.  Subsequent cycles were given with oral ASTX727 on Days 1-5 at the same dose of Cycle 1. Cycles were 28 days in length.  Pharmacodynamics (PD) were evaluated by LINE-1 DNA methylation in peripheral blood. A data safety review committee evaluated safety, PK and PD on patients in each completed cohort and determined dosing for each component of ASTX727 at the next cohort.  Only one component at a time was escalated in each cohort and oral doses were not adjusted for weight or body surface area. Responses were assessed using the International Working Group (IWG) criteria for response (Cheson et al, 2006).

Results: The Phase 1 portion of the trial completed dosing of 4 cohorts with 6 subjects each (24 subjects).  The median age was 71 years (range 59-85), 15/24 (63%) were male, and median time from diagnosis was 307 days (range 5-3024).  Prior therapies were administered to 10 patients including five who had received prior HMA.  In cohorts 1-3 ASTX727 was given as a fixed oral DAC dose of 20 mg with escalating doses of oral E7727 at 40, 60, and 100 mg respectively.  In cohort 4, the oral DAC dose was escalated to 40 mg while E7727 was kept at 100 mg. The Day 1 AUC for IV DAC 20 mg/m² over all 4 cohorts had a mean (SD) value of 193(82) ng*hr/mL. After oral ASTX727 on Days 2-5, the mean DAC AUC as % of IV DAC AUC was 17, 19, 32, and 98% on Day 2 and 31, 41, 58 and 148% on Day 5, in cohorts 1-4 respectively (Figure).  DAC AUC variability after oral ASTX727 was acceptable (CV% 35-53 across 4 cohorts). DAC C_max values after oral ASTX727 approached IV (87%) in Cohort 4 on Day 5. Mean % LINE-1 demethylation on cycle 1 Day 8±SE was 6.8%±2.7; 8.6%±2.7; 9.5%±3.3; and 15.3%±3.4 from baseline for cohorts 1-4 respectively.  No Dose Limiting Toxicities (DLTs) or Grade ≥ 3 drug-related non-hematologic AEs were observed in any patient. The most common Grade ≥ 3 AEs regardless of relationship to the drug were thrombocytopenia (37.5%), anemia (33.3%), neutropenia (29.2%) and febrile neutropenia (16.7%). Twenty patients remain on therapy, and at least 5 so far have experienced objective clinical responses (including 1 Complete Response (CR), 1 marrow CR, 1 Partial Response and 2 Hematologic Improvement).   

Conclusions: ASTX727 (the combination of oral DAC and oral CDAi E7727 administered concomitantly) achieved the primary PK objective of reaching (at Day 2) or exceeding (at Day 5) IV DAC 20 mg/m² AUC levels at the doses of 40 mg DAC and 100 mg E7727 with an excellent safety profile.  Day 8 LINE-1 demethylation in Cohort 4 is consistent with that historically reported following DAC 20 mg/m² IV for 5 days. Clinical responses have been observed.  The trial will explore lower doses of oral DAC and will proceed to dose expansion followed by randomized phase 2 portion comparing IV DAC to oral ASTX727 in previously untreated Int or HR MDS and CMML patients.

Figure:

Mean DAC AUC after IV DAC 20 mg/m² (D1) and oral ASTX727 (D2 and D5) for cohorts 1-4