Description:
Abstract Imatinib resistance is a major problem in treatment of Bcr-Abl positive leukemias, particularly in patients with ALL and advanced CML. One of the major mechanisms of this resistance is overexpression of Bcr-Abl. We investigated the effects of Imatinib deprivation in Bcr-Abl overexpressing Imatinib-resistant ALL cell lines. Removal of Imatinib from culture medium led to a huge induction of Bcr-Abl autophosphorylation and concomitant overstimulation of PI3K-, MAPK-, and JAK/STAT signalling leading to an elevated cell size and cellular protein content. Massive induction of cell death was then observed at later time points (48 hours after Imatinib deprivation) accompanied by loss of outer and inner mitochondrial membrane integrity. Using a protein kinase inhibitor library, we identified inhibitors of glycogen synthase kinase-3 (GSK3) and p38-MAPK as the most potent compounds which completely prevented induction of cell death upon removal of Imatinib whereas the same inhibitors had synergistic effects with Imatinib in Imatinib-sensitive ALL cells. In contrast to GSK3- and p38, inhibition of PI3K had no effect on oncogenic stress upon Imatinib withdrawal in the resistant clones. Importantly, oncogenic stress-induced cell death could not be blocked by the pan-caspase inhibitor z-VAD-fmk whereas the RIP1 inhibitor Necrostatin partially rescued the cells upon Imatinib deprivation. We also detected a posttranslational modification of RIP1 upon Imatinib withdrawal that was completely absent in cells pre-treated with GSK3- or p38 inhibitors indicating a central role of RIP1 for oncogenic stress-induced cell death. In conclusion, we found a massive induction of a necroptosis-like cell death in Bcr-Abl overexpressing ALL cells as a consequence of oncogenic stress upon Imatinib deprivation. GSK3 and p38 turned out to play the most prominent role for oncogenic stress induced cell death. These data implicate that a discontinuous treatment with Imatinib (periods of Imatinib treatment followed by short periods without Imatinib) may prevent the appearance of cell clones with Bcr-Abl overexpression. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4522.