c-IAP1 is Overexpressed in HL-60 Cells Selected for Doxorubicin Resistance: Effects on Etoposide-induced Apoptosis

Background: We previously demonstrated that KN-62, an inhibitor of calcium calmodulin-dependent enzymes, sensitizes human leukemia HL-60 cells resistant to topoisomerase II-targeting drugs. The objective of this study was to determine pathways of apoptosis downstream of DNA damage induced by KN-62 co-treatment with VP-16. Materials and Methods: HL-60/Y/DOX0. 05 cells were treated with VP-16, KN-62, or VP-16 +KN-62. Following treatment, cells were assayed for c-IAP1, c-IAP2 and XIAP protein expression, as well as caspase activation, cytochrome c release and PARP cleavage. Results: Baseline c-IAP1 protein levels were 2-fold higher in HL60 cells selected for resistance to doxorubicin compared to the parent sensitive line. VP-16 and KN-62 co-treatment was associated with caspase activation via the mitochondrial pathway and significant reductions (p=0.002) in c-IAP1 protein expression but not with c-IAP2 or XIAP. Conclusion: These data suggest that KN-62 co-treatment sensitizes doxorubicin-resistant cells to VP-16-induced apoptosis by enhancing caspase activity and reducing c-IAP1 expression.