A Phase II Study Of Tosedostat (TST) In Combination With Either Cytarabine Or Decitabine In Newly Diagnosed Older Patients With Acute Myeloid Leukemia (AML) Or High-Risk Myelodysplastic Syndrome (MDS)

Treatment outcomes for older patients with newly diagnosed AML remain poor. TST is an oral aminopeptidase inhibitor that has anti-neoplastic activity in a variety of malignancies, including AML. Phase I/II monotherapy studies in patients with relapsed AML and MDS have shown TST to have adequate safety and promising efficacy. Pre-clinical AML blast proliferation assays have demonstrated synergy between TST and both cytarabine and hypomethylating agents. For this reason, we performed a randomized, open-label Phase II trial using TST in combination with intermediate-dose cytarabine or decitabine in patients with untreated AML or high-risk MDS (i.e. RAEB-2).

Patients ≥60 years old with untreated AML or high risk MDS were randomized to receive TST 120 mg daily by mouth days 1-21 with 5 days of either cytarabine 1 g/m²/day IV or decitabine 20 mg/m²/day IV delivered every 35 days. Patients received up to three 35-day cycles if they had at least stable disease with an acceptable toxicity profile following the initial course. Patients who did not achieve a complete remission (CR) or CR with incomplete blood count recovery (CRi) after 3 cycles of therapy were taken off study; patients who obtained CR/CRi were eligible to receive up to 2 additional cycles (maximum of 5). The primary objective was to determine the rates of CR and 4 month survival using TST in combination with either cytarabine or decitabine for older patients with untreated AML or high-risk MDS.

A total of 26 patients have been treated, with 14 receiving TST/cytarabine and 12 receiving TST/decitabine. The median age was 69 (range, 60-83), and 22 patients (85%) presented with an ECOG performance status of 1. Nineteen patients (73%) had AML and 7 (27%) had MDS RAEB-2. Nineteen patients (73%) had intermediate-risk and 7 (27%) had adverse-risk disease by European Leukemia Net criteria. Fourteen patients (54%) had secondary AML/MDS or antecedent hematologic disorder. The median duration of treatment was 3 months. The overall CR/CRi rate was 54%, with 10 patients (39%) achieving a CR and 4 patients (15%) achieving a CRi. Five patients required 3 cycles, four patients required 2 cycles and five patients required 1 cycle of therapy to achieve maximal disease response. CR/CRi was attained in 3 patients with adverse cytogenetics and 4 additional patients with FLT3 mutations. Of the 14 patients who achieved a CR/CRi (54%), 7 were treated on each of two study arms. Nine of the 14 patients who achieved a CR/CRi were referred for allogeneic hematopoietic cell transplantation (HCT), 3 patients deferred HCT, and 1 patient died of sepsis in CRi 133 days after starting induction. Ten patients were taken off study after a median of 2 cycles due to lack of response or disease progression. With a median follow-up of 5.7 months (range, 0.5-13.4), 21 patients (81%) lived longer than 4 months. Five (19%) of the 26 patients died within 4 months of starting therapy. Of these five patients, three died of sepsis on subsequent salvage protocols, one with a history of myeloproliferative disorder died of splenic infarct within 15 days of starting therapy and a fifth patient died at age 83 during cycle 2 of unknown cause. Eight patients (31%) were treated completely as outpatients without requiring hospitalization, and 15 patients (58%) were hospitalized at some point during treatment for febrile neutropenia. There were no Grade 3-4 non-hematologic toxicities requiring withdrawal from the study.

These results demonstrate that TST at 120 mg daily in combination with cytarabine or decitabine resulted in a 54% CR/CRi rate in 26 older patients with untreated AML or high-risk MDS. This approach was well tolerated as predominantly outpatient therapy and may warrant further study in a controlled trial.

Wang:Cell Therapeutics, Inc.: Employment. Myint:Cell Therapeutics, Inc: Employment. Singer:Cell Therapeutics, Inc: Employment, Equity Ownership.