Co-operation of ABT-199 and gemcitabine in impeding DNA damage repair and inducing cell apoptosis for synergistic therapy of T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is a high-risk subtype of acute lymphoblastic leukemia with limited therapeutic options available. Here, we evaluated the therapeutic potential of the combination of the Bcl-2 antagonist ABT-199 and cytotoxic agent gemcitabine in T-ALL cell lines. Our results showed that the combination of ABT-199 and gemcitabine exhibited synergistic cytotoxicity and induced significant apoptosis in human T-ALL cell lines (Jurkat and Molt4). The augmented apoptosis induced by combination treatment was accompanied by the greater extent of mitochondrial depolarization and enhanced DNA damage. Importantly, single agent induced DNA damage alone but did not inhibit RAD51/BRCA1-mediated repair for DNA double-strand breaks. In contrast, the combination of ABT-199 and gemcitabine disrupted RAD51/BRCA1-dependent DNA repair and remarkably activated caspase-3 and PARP to trigger apoptosis. Moreover, ABT-199 exerted an antagonistic action towards Bcl-2 and Bcl-xL, but to a certain extent moderately increased Mcl-1 level that could be compromised by gemcitabine. In conclusion, our study showed that the combination of ABT-199 and gemcitabine exhibited synergistic cytotoxicity in T-ALL cells by cooperatively targeting DNA damage repair pathway and Bcl-2 family proteins.