Background: Clofarabine is a second-generation nucleoside analogue. The aim of the study was the analysis of ex vivo activity of clofarabine and 14 other anticancer drugs in pediatric and adult acute lymphoblastic (ALL) and myeloid (AML) leukemia. Patients and Methods: The ex vivo drug resistance profile was analyzed in 282 patients, including 201 children with ALL de novo, 24 children with relapsed ALL, 25 children with AML de novo and 32 adults with AML. Cellular ex vivo drug resistance was tested by means of the MTT assay. Results: Clofarabine had comparable ex vivo activity against lymphoblasts and myeloblasts, both on initial diagnosis and at relapse, both in children and in adults. Its activity in acute myeloid leukemia was independent of patient age. No significant differences in drug resistance to clofarabine between pediatric age-based subgroups of ALL were detected, while it was observed for most of other drugs. An activity of clofarabine in relapsed pediatric ALL patients was as good as in newly-diagnosed ones. Conclusion: In comparison to childhood acute lymphoblastic leukemia, lack of differences in ex vivo activity gives rationale for use of clofarabine in refractory and relapsed pediatric and adult patients with acute myeloid leukemia
