['Acute myeloid leukemia (AML) remains a major therapeutic challenge in pediatric oncology even with intensified cytarabine (ara-C)-based chemotherapy. Therefore, new therapies are urgently needed to improve treatment outcome of this deadly disease. In this study, we evaluated antileukemic interactions between clofarabine (a second-generation purine nucleoside analog) and valproic acid (VPA, a FDA-approved agent for treating epilepsy in both children and adult and a histone deacetylase inhibitor), in pediatric AML.', 'In vitro clofarabine and VPA cytotoxicities of the pediatric AML cell lines and diagnostic blasts were measured by using MTT assays. The effects of clofarabine and VPA on apoptosis and DNA double strand breaks (DSBs) were determined by flow cytometry analysis and Western blotting, respectively. Active form of Bax was measured by Western blotting post-immunoprecipitation.', 'We demonstrated synergistic antileukemic activities between clofarabine and VPA in both pediatric AML cell lines and diagnostic blasts sensitive to VPA. In contrast, antagonism between the two agents could be detected in AML cells resistant to VPA. Clofarabine and VPA cooperate in inducing DNA DSBs, accompanied by Bax activation and apoptosis in pediatric AML cells.'] Does valproic acid synergistically enhance the cytotoxicity of clofarabine in pediatric acute myeloid leukemia cells?