A Multicentre Phase II Study of the Aminopeptidase Inhibitor, CHR- 2797, in the Treatment of Elderly and/or Previously Treated patients with Acute Myeloid Leukemia.

Tosedostat (TSD, CHR-2797) is an aminopeptidase inhibitor that selectively depletes amino acid pools in malignant cells, resulting in anti-proliferative, pro-apoptotic and antiangiogenic effects. In a phase I study, treatment with TSD resulted in complete remission in a number of refractory AML patients. The primary objective of this phase II study was to determine whether TSD was a sufficiently effective therapy to warrant pivotal studies.

Methods. This was an open label, single agent, phase II study to assess clinical activity of TSD in elderly and/or previously treated patients with AML/MDS. Patients were treated with once daily oral doses of the maximum acceptable dose (130 mg) of TSD for up to 84 days. Further treatment was allowed if, in the opinion of the investigator, this was considered to be beneficial. Clinical responses were assessed by monthly bone marrow aspirates and weekly hematological assessments.

Results. Of the 41 TSD-treated patients with AML (n=38) or MDS (n=3), who were enrolled between March and October 2007, 27 were male, 14 female, with a mean age of 67 years (range 34–82). The median performance status (ECOG) at baseline was 1 (range 0–2). Twelve (31.6%) AML patients and 2 (66.7%) MDS patients were chemotherapy naïve, and 9 (23.7%) AML patients had either secondary disease or adverse cytogenetics. For 16 (39%) patients, treatment with TSD was a second or later salvage attempt. Thirty two patients (30 AML, 2 MDS-RAEB1 and 2) received ≥28 days treatment, and 21 (51.2%) patients completed the formal 84-day study period (19 AML, 2 MDS). Nine (22%) of the patients (7 AML, 2 MDS) continued treatment with TSD after 84 days, and 6 (15%) patients were on TSD in total for more than 6 months (4 AML, 2 MDS). Ten (26.3%) of the AML patients responded to treatment; amongst these, 2 patients received TSD as 2^nd/3^rd salvage therapy, and a further 2 patients did not show a complete response (CR) after 2 previous induction courses of chemotherapy. Three AML patients achieved a CR (< 5% blasts in bone marrow), of whom 2 were in durable remission (232 days, continuing*; 171 days), and 7 had a partial response (PR, 5–15% blasts) lasting approximately 1–3 months. Two (66.7%) of the MDS patients also responded to treatment with TSD; these patients maintained stable disease for more than 6 months. All responders (CR, PR and SD) were >60 years at the time of the first dose. Median overall survival in AML patients was 130 days (range 8 – 478 days*). The most frequently reported adverse events were: fatigue (61%), thrombocytopenia (49%), pyrexia (39%), peripheral edema (39%) and diarrhea (34%); 9 (22%) patients withdrew due to drug related toxicity. TSD had no effect on hemoglobin or neutrophils.

Conclusions. This study in patients with advanced AML/MDS with adverse prognosis demonstrates the anti-leukemic activity of TSD in elderly AML patients, as measured by CR and decreases in leukemic blasts. In addition, 2 relapsed high risk MDS patients achieved disease stabilization. TSD at 130mg qd is also very well tolerated over a long period of exposure (6–10 months). These results support further pivotal studies with TSD in elderly AML and MDS patients.