65P - Novel HDACi, MHY446, induces apoptosis via regulation of mitochondria-endoplasmic reticulum interaction in HCT116 human colorectal cancer cells

Colorectal cancer (CRC) is one of the leading causes of cancer-related death in the world. Despite considerable research and advancement in CRC diagnosis and therapy, CRC is still clinically challenging and becoming the highest incidence cancer worldwide. There is a need to develop novel therapeutic agents for this malignancy. MHY446, a novel histone deacetylase inhibitor (HDACi), was synthesized on the backbone of hydroxamic acid derivatives that are one of the HDAC inhibitors. We evaluated cytotoxic effects and underlying molecular mechanisms of actions of MHY446 in HCT116 human colorectal cancer cells. MHY446-treated HCT116 cells exhibited cell viability inhibition and an increase in the sub-G1 phase populations and late apoptosis. MHY446-induced apoptosis is accompanied by the activation of caspase-8, -9, and -3; subsequent cleavage of poly(ADP-ribose) polymerase; and alteration in the ratio of Bax/Bcl-2 protein expression level. The presence of Z-VAD-FMK, a pan-caspase inhibitor, significantly attenuated the MHY446-induced apoptosis indicating that apoptotic cell death was caspase-dependent cascading through the activation of both intrinsic and extrinsic signaling pathways. Furthermore, MHY446 caused the loss of mitochondria membrane potential and induced the generation of reactive oxygen species (ROS), evidenced by the scavenging of ROS by N-acetyl-L-cysteine (NAC). Additionally, MHY446 promoted the upregulation of the expression level of endoplasmic reticulum (ER) stress-associated proteins such as BIP, PDI, IRE1α, PERK, p-elF2α, and CHOP. NAC effectively reduced the expression of ER stress-related protein levels, suggesting that ROS acts as an upstream signaling molecule in triggering the ER stress pathway. Taken together, these results demonstrate that MHY446 exerts its anticancer activities through the regulation of ROS-induced ER stress. These results suggest that MHY446 is a promising candidate for the treatment of CRC. The authors. Has not received any funding. All authors have declared no conflicts of interest.