Phase 1 Trial of G-CSF, Cladribine, Cytarabine, and Dose-Escalated Mitoxantrone (G-CLAM) in Adults with Relapsed/Refractory Acute Myeloid Leukemia (AML) or High-Risk Myelodysplastic Syndromes (MDS)

Background: Although some adults with AML or high-risk MDS will experience long-term disease-free survival after initiation of curative-intent therapy, most patient will require therapy re-induction therapy either for primary induction failure of disease recurrence after an initial complete remission (CR) was achieved. The outcomes with standard regimens for relapsed/refractory AML are generally poor, with CR rates often not exceeding 15-20%. Data from a large single arm phase 2 study in poor-risk relapsed/refractory AML suggested tolerability and encouraging activity of a combination of G-CSF, cladribine, cytarabine, and mitoxantrone (G-CLAM). Given recent data suggesting benefit of escalated doses of anthracyclines in AML, the goal of our phase 1 study was to determine the maximum tolerated dose (MTD) of mitoxantrone within G-CLAM in adults with relapsed/refractory AML or high-risk MDS and estimate the efficacy of this regimen.

Patients and Methods: Adults ≥18 years of age with relapsed or refractory AML (APL excluded) or high-risk MDS (>10% blasts) were eligible if they had a treatment-related mortality (TRM) score of ≤6.9 (corresponding to a risk of early death with standard induction chemotherapy of ≤3%) and adequate organ function (LVEF ≥45%, creatinine ≤2.0 mg/dL, bilirubin ≤2.5-times upper limit of normal). Excluded were patients with concomitant illness with expected survival <1 year and those with active, uncontrolled infection. Cohorts of 6-12 patients were assigned to 1 of 4 total dose levels of mitoxantrone (12, 14, 16, or 18 mg/m²/day on days 1-3, as compared to 10 mg/m²/day used in standard-dose G-CLAM). Other drug doses were G-CSF 300 or 480 μg/day (for weight <76 kg vs. ≥76 kg; days 0-5), cladribine 5 mg/m²/day (days 1-5), and cytarabine 2 g/m²/day (days 1-5). A second identical course of G-CLAM was given in the case of persistent disease. 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 or infection or constitutional symptoms, if recovery to grade ≤2 within 14 days.

Results: 26 patients (14M, 12F), median age 57 (range: 37-77) years, median TRM score 1.73 (range: 0.29-3.92) with relapsed/refractory AML (n=23), or high-risk MDS (n=3) and cytogenetically favorable (n=2), intermediate (n=13), and adverse (n=11) disease characteristics were enrolled. One DLT occurred at dose level 1 (nausea) and 2 at dose level 4 (encephalitis and cardiogenic shock), establishing G-CLAM with mitoxantrone at 16 mg/m²/day as the MTD in our study. 2 patients (8% [95% exact confidence interval: 1-25%]) died within 28 days of treatment initiation from sepsis and cardiogenic shock, respectively. Overall, 13/26 patients (50% [30-70%]) achieved a CR (n=8) (31% [14-52%]), CRp (n=1) (4% [0-20%]), or CRi (n=4) (15% [4-35%]) with 1-2 cycles of re-induction therapy; one patient each achieved a leukemia-free state and partial remission (in a patient presenting with myeloid sarcomas); nine patients (35% [17-56%]) had persistent disease. We were unable to assess response in 2 patients due to early death (n=1) and refusal for marrow re-assessment (n=1). 7/13 responders (54%) had no evidence of residual disease by flow cytometry at best response. Among responders, median times to an absolute neutrophil count ≥500/µL and a platelet count of 50,000/µL were 33 (range: 17-51) and 31 (range: 18-54) days, respectively. Besides infections and neutropenic fever, nausea, hypoxia (fluid overload/infection-related), and maculopapular rash were the most common grade ≥3 adverse events.

Conclusion G-CLAM with mitoxantrone up to 16 mg/m²/day is feasible, well tolerated, and effective in relapsed/ refractory AML/high-risk MDS. A phase 2 study based on these findings has been initiated.