A Phase 1/2 Study of G-CSF, Cladribine, Cytarabine, and Dose-Escalated Mitoxantrone (G-CLAM) in Adults with Newly Diagnosed Acute Myeloid Leukemia (AML) or High-Risk Myelodysplastic Syndrome (MDS)

Introduction:"7+3" with standard doses of cytarabine and an anthracycline has remained the mainstay of induction chemotherapy for newly diagnosed AML. Since some studies have shown improved outcomes with high-dose cytarabine, cladribine, or escalated doses of anthracyclines, we conducted a phase 1/2 study (NCT02044796) of G-CLAM using escalated doses of mitoxantrone for newly diagnosed AML or high-risk MDS (>10% blasts).

Methods: Patients≥18 years were eligible if they had treatment-related mortality (TRM) scores of ≤6.9 (corresponding to a predicted risk of early death with standard induction chemotherapy of ≤6.9%) and adequate organ function (LVEF ≥45%, creatinine ≤2.0 mg/dL, bilirubin ≤2.5 times upper limit of normal). Excluded were patients with uncontrolled infection or concomitant illness with expected survival <1 year. In phase 1, cohorts of 6-12 patients were assigned to 1 of 4 total dose levels of mitoxantrone (12, 14, 16, or 18 mg/m²/day, days 1-3, compared to 10 mg/m²/day used in standard dose G-CLAM previously established in relapsed/refractory AML). Other drug doses were G-CSF 300 or 480 μg/day (for weight </≥76 kg; days 0-5), cladribine 5 mg/m²/day (days 1-5), and cytarabine 2 g/m²/day (days 1-5). In phase 2, patients were treated at the maximum tolerated dose (MTD) of mitoxantrone. A second identical course of G-CLAM was given if complete remission (CR) was not achieved with cycle 1. Up to 4 cycles of consolidation with G-CLA (mitoxantrone omitted) were allowed if CR or CR with incomplete platelet or blood count recovery (CRp/i) was achieved with 1-2 cycles of induction therapy. Dose-limiting toxicities (DLTs) were: 1) grade 3 non-hematologic toxicity lasting >48 hours that resulted in >7-day delay of the subsequent treatment cycle; 2) grade ≥4 non-hematologic toxicity if recovery to grade ≤2 within 14 days, both excluding febrile neutropenia, infection or constitutional symptoms.

Results: Among 33 patients (median age of 57.3 [range: 26-77], median TRM score 2.31 [0.16-5.90]) treated in phase 1, one DLT occurred at dose levels 3 and 4 (respiratory failure in both cases), establishing G-CLAM with mitoxantrone at 18 mg/m²/day as the MTD. Sixty-two patients, including 6 treated in phase 1, received G-CLAM at MTD. Patient characteristics were as follows: median age 58 (21-81) years, median TRM score 2.85 (0.06-6.73), with AML (n=52) or high-risk MDS (n=10). Cytogenetics were favorable in 6, intermediate in 44, and adverse in 12 (MRC criteria); 11 patients had NPM1 and 6 had FLT3 mutations. Fifty-two patients (83.9%, 95% confidence interval: 72.3-92.0%) achieved a CR (n=48 [77.4%: 65.0-87.1%]), or CRp/i (n=4 [6.5%: 1.8-15.7%]) with 1-2 cycles of therapy. Only 3 patients required 2 cycles to best response. Among the 48 CR patients, 43 (89.6%) were negative for measurable residual disease (MRD^neg) by flow cytometry. Four patients had morphologic leukemia free state, 1 patient with myeloid sarcoma had a partial remission, 4 had resistant disease, and 1 died from indeterminate cause. One patient died within 28 days of treatment initiation (septic shock). Median times to an absolute neutrophil count ≥500/μL and a platelet count of ≥50,000/μL were 26 and 23 days. Besides infections and neutropenic fever, maculopapular rash, and hypoxia (fluid overload/infection-related) were the most common grade ≥3 adverse events. In addition to the phase 1/2 MTD cohort, there were 15 patients treated in an expansion cohort and 3 eligible patients treated off protocol with mitoxantrone at 18 mg/m². For these 80 patients combined treated at MTD, the CR and CR/CRp/i rates were 76.3% and 81.2%. After multivariable adjustment, compared to 300 patients treated with 7+3 on the SWOG S0106 trial, G-CLAM with mitoxantrone 18mg/ m² was associated with an increased probability of CR (odds ratio [OR]= 3.08, p=.02), CR/CRp/i (OR=2.96, p=.03), a trend towards improved MRD^negCR (OR= 3.70, p=.06), and a trend towards improved overall survival ([OS]; hazard ratio=0.34, p=.07). For the entire study cohort, the 6 and 12-month relapse-free survival were 73% (64-83%) and 62% (42-74%) and the 6 and 12-month OS were 89% (82- 96%) and 77% (67-88%).

Conclusions: G-CLAM with mitoxantrone up to 18 mg/m²/day is well tolerated and has potent anti-leukemia activity. This regimen may warrant further randomized comparison with 7+3. We also plan to examine the addition of sorafenib to G-CLAM in newly diagnosed AML patients regardless of FLT3 status.