Phase 1 study of clofarabine in pediatric patients with relapsed/refractory acute lymphoblastic leukemia in Japan

A phase 1 study was conducted to evaluate the safety, pharmacokinetics (PK), efficacy and pharmacogenetic characteristics of clofarabine in seven Japanese pediatric patients with relapsed/refractory acute lymphoblastic leukemia (ALL). Patients in Cohort 1 received clofarabine 30 mg/m²/day for 5 days, followed by 52 mg/m²/day for 5 days in subsequent cycles. Cohort 2 patients were consistently treated with 52 mg/m²/day for 5 days. No more than six cycles were performed. Every patient had at least one ≥Grade 3 adverse event (AE). AEs (≥Grade 3) related to clofarabine were anaemia, neutropenia, febrile neutropenia, thrombocytopenia, alanine aminotransferase increased, aspartate aminotransferase increased, haemoglobin decreased, and platelet (PLT) count decreased. C_max and AUC of clofarabine increased in a dose-dependent fashion, but its elimination half-life (T_1/2) did not appear to be dependent on dose or duration of treatment. Clofarabine at 52 mg/m²/day shows similarly tolerable safety and PK profiles compared to those in previous studies. No complete remission (CR), CR without PLT recovery, or partial remission was observed. Since clofarabine is already used as a key drug for relapsed/refractory ALL patients in many countries, the efficacy of clofarabine in Japanese pediatric patients should be evaluated in larger study including more patients, such as by post-marketing surveillance.