An agonistic antibody to human death receptor 4 induces apoptotic cell death in head and neck cancer cells through mitochondrial ROS generation

The proapoptotic death receptor 4 (DR4), along with DR5, is currently regarded as a promising target for development of agonistic anti-cancer agents due to its tumor-selective apoptosis-inducing ability with no significant cytotoxicity to normal cells. In this study, we examine susceptibility of various head and neck cancer (HNC) cells and mechanism of cell death to an anti-DR4 agonistic monoclonal antibody (mAb), AY4. AY4 as a single agent induced caspase-dependent apoptotic cell death of KB and HN9, but not in SNU899 and FaDu cell lines. AY4 treatment resulted in accumulation of intracellular reactive oxygen species (ROS) generated from mitochondria in AY4-sensitive cells. Blockade of ROS production by N-acetyl-l-cysteine (NAC) resulted in protection of AY4-sensitive cells against AY4-induced apoptosis. ROS generation induced by AY4 treatment triggered down-regulation of anti-apoptotic molecules of Bcl-xL and X-linked inhibitor of apoptosis (XIAP) without affecting the expression levels of DR4, Mcl-1, and survivin. AY4 also inhibited growth of pre-established HN9 tumors in a nude mouse xenograft model and did not show noticeable cytotoxicity in a zebrafish model. Our results provide further insight into the mechanism of DR4-mediated cell death and potential use of AY4 mAb as an anti-cancer therapeutic agent in AY4-sensitive HNC types.