Mitoxantrone, Etoposide, and Cytarabine (MEC) Following Epigenetic Priming with Decitabine in Adults with Relapsed/Refractory Acute Myeloid Leukemia (AML) or High-Risk Myelodysplastic Syndrome (MDS): A Phase 1 Study

Background: Most adults with AML or high-risk MDS will ultimately require salvage therapy. However, the likelihood of achieving a complete remission (CR) with standard salvage regimens is often 15-20% or less. Emerging data suggest that pre-treatment (“priming”) with a hypomethylating agent such as decitabine can sensitize AML cells to chemotherapeutics, prompting a dose-escalation study of MEC preceded by decitabine-priming in relapsed/refractory AML and high-risk MDS.

Methods: This single arm study aimed to estimate the maximum tolerated dose (MTD) of decitabine-primed MEC in adults ≥18 years with relapsed/refractory high-risk MDS (>10% blasts) or AML requiring first or subsequent salvage therapy. Previous treatment with hypomethylating agents or MEC (but not the combination) was acceptable. Trial participation required a treatment-related mortality (TRM) score of <9.2, corresponding to an expected TRM of 4% with standard induction chemotherapy. Patients with post-transplant relapse were eligible if graft-versus host disease was well controlled. Excluded were patients with concomitant illness with expected survival <1 year, and active, uncontrolled infection. Cohorts of 6-12 patients were assigned to 1 of 3 total dose levels of decitabine (20mg/m² for 5, 7, or 10 days) followed by MEC (mitoxantrone 8mg/m²/day x 5 days; etoposide 100 mg/m²/day x 5 days; cytarabine 1 g/m²/day x 5 days) after a break of 5 days. In the case of persistent leukemia, patients were eligible for re-induction provided all non-hematologic toxicities had resolved to grade <2. Patients achieving a CR or CR with incomplete platelet recovery (CRp) could receive 2 additional cycles of decitabine-MEC given at doses identical to those used during induction. Dose-limiting toxicity (DLT) was defined as: 1) any grade 3 non-hematologic toxicity lasting >48 hours that resulted in >7 day delay of the subsequent treatment cycle, with the exception of febrile neutropenia or infection; 2) any grade ≥4 non-hematologic toxicity, with the exception of febrile neutropenia/infection or constitutional symptoms, if recovery to grade ≤2 within 14 days.

Results: 30 patients, median age 55 (range: 19-72) years, with primary refractory disease (n=13), first relapse (n=16), or second relapse (n=1) with median duration of prior CR of 4 (range: 1-19) months were enrolled and received a median of 1 (range: 1-3) cycles of therapy. During dose escalation, 1 DLT occurred at each the 2^nd and 3^rd tested dose level after cycle 1 (septic shock with multi-organ failure in both), identifying a 10-day course of decitabine together with standard dose MEC as the MTD. A total of 12 patients received therapy at the MTD level. 9/30 patients achieved a CR (30%). This CR rate compared favorably relative to a historic control population with patient matching based on duration of prior remission and number of prior salvage therapies (Blood 1996; 88:756), with an observed/expected CR ratio of 1.9. 5 additional patients achieved a CRp, and 1 achieved a CR with incomplete count recovery (CRi) for an overall response rate of 15/30 (50%). Furthermore, 4 patients achieved a morphologic leukemia-free state, 8 had refractory disease, and 3 died before a response was assessed. Of the 15 patients who achieved a remission, 3 remain on study, 9 were taken off protocol to pursue further intensive consolidation therapy including hematopoietic cell transplantation, and 3 have died after a median CR duration of 68 days. In the 15 responders, the median response duration was 68 days (range 0-437), with 6 of these responses ongoing. Overall survival of these 15 patients was longer (median of 211 [range: 59-484] days) than that for patients who failed to achieve remission but lived at least 29 days (i.e. did not experience TRM) (median of 110 [range: 30-303] days). Six patients died within 28 days of treatment initiation for a TRM rate of 20%: 4 from infection, 1 from intracranial hemorrhage, and 1 from unknown cause. Besides grade 3-4 cytopenias, cough, fatigue, nausea and infection/neutropenic fever were the most common adverse events.

Conclusion: Decitabine-primed MEC is feasible, well tolerated, and has anti-leukemic activity in relapsed/refractory AML and high-risk MDS. A phase 2 study based on these findings has been initiated.