Role of poly(ADP-ribose) polymerase activity in imatinib mesylate-induced cell death

Imatinib targets Bcr-Abl, the causative event of chronic myelogenous leukemia (CML), and addresses leukemic cells to growth arrest and cell death. The exact mechanisms responsible for imatinib-induced cell death are still unclear. We investigated the role of poly(ADP-ribose) polymerase ( PARP) activity in imatinib-induced cell death in Bcr-Abl-positive cells. Imatinib leads to a rapid increase of poly( ADP-ribosyl)ation (PAR) preceding loss of integrity of mitochondrial membrane and DNA fragmentation. The effect of imatinib on PAR can be mimicked by inhibition of phosphatidylinositol 3-kinase (PI3-K) implicating a central role of the PI3-K pathway in Bcr-Abl-mediated inhibition of PAR. Importantly, inhibition of PAR in imatinib-treated cells partially prevented cell death to an extent comparable to that observed after caspase inhibition. Simultaneous blockade of both caspases and PAR revealed additive cytoprotective effects indicating that both pathways function in parallel. In conclusion, our results suggest that in addition to the well-documented caspase-dependent pathway, imatinib also induces a PARP-mediated death process.