Enhancement of the caspase-independent apoptotic sensitivity of pancreatic cancer cells by DHMEQ, an NF-κB inhibitor

The effects of the nuclear factor (NF)-κB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), combined with tumor necrosis factor (TNF)-α were evaluated in PK-8 pancreatic cancer cells. NF-κB was activated by TNF-α; however, the administration of DHMEQ abrogated its transcriptional activity. The addition of DHMEQ to TNF-α markedly induced apoptosis in PK-8 cells with down-regulation of anti-apoptotic c-FLIP and survivin. Combined treatment significantly suppressed cell viability in vitro, and the anti-tumor effect of DHMEQ was also significant in vivo. We investigated the apoptosis signaling pathway involved in these cell killing effects. Truncated Bid was produced by activated caspase-8, and the subsequent depolarization of the mitochondrial membrane potential (ΔΨm) peaked at 6 h. Then, the activity of caspase-3 was up-regulated 8-fold. Z-VAD-fmk (a pan-caspase inhibitor) perfectly inhibited the up-regulation of caspase-3 but failed to reverse the cell viability. The above findings indicated that the growth inhibitory effect of combined treatment largely depended on mitochondria-associated caspase-independent apoptosis. The intracellular behavior of apoptosis-inducing factor (AIF) following depolarization of ΔΨm suggested that AIF executed such a caspase-independent apoptosis. Interestingly, caspase-dependent apoptosis appeared within 6 h, whereas the caspase-independent apoptosis lagged. Thus, the addition of DHMEQ to TNF-α was capable of inducing caspase-independent apoptosis in pancreatic cancer cells. Once caspase-independent apoptosis was induced, the apoptosis demonstrated powerful cytotoxicity. Therefore, DHMEQ in combination with TNF-α may be a promising treatment for pancreatic cancer.