Bongkrekic acid induces selective cytotoxicity in tumor cells, revealed by CCK-8

Bongkrekic acid (BKA) is shown to inhibit adenine nucleotide translocator in the mitochondrial inner membrane, which is bifunctional and facilitates ATP/ADP exchange and permeability transition pore opening in mitochondria. We demonstrate that BKA reduces the viability of tumor cells depending on the cell number in the culture. This reduction was first demonstrated by Cell Counting Kit-8 (CCK-8), which indicates cellular viabilities based on the reduction of a formazan dye by cellular NADH. Reduced viability was not seen in normal cells. The glycolysis inhibitor 2-deoxyglucose enhanced the effect of BKA. BKA is thought to work as a mitochondrial inhibitor; however, its action is different from mitochondrial uncouplers. We further demonstrate that BKA suppresses autophagy induction, directing cells to death in nutrient-depleted conditions. Together these data indicate that BKA is a new type of mitochondrial inhibitor that does not disrupt the mitochondrial membrane and that is thus used together with a glycolysis inhibitor as an anticancer agent.