The apoptotic effect of HA14-1, a Bcl-2-interacting small molecular compound, requires Bax translocation and is enhanced by PK11195.

HA14-1 is a small molecular compound that was identified based on the structure of Bcl-2. HA14-1 interacts with Bcl-2 and inhibits the antiapoptotic effect of Bcl-2. We investigated the mechanism of HA14-1-induced apoptosis and found that HA14-1 induces translocation of Bax from cytosols to the mitochondria. Cells deficient in Bax were much more resistant to HA14-1-induced apoptosis, suggesting that Bax is required for this process. A pan-caspase inhibitor failed to inhibit the apoptotic effect of HA14-1, indicating that this is through a caspase-independent pathway. To eliminate the effect of cytosolic Bax, we incubated cell-free mitochondria with HA14-1 to study its effect on cytochrome c release. HA14-1 was ineffective in causing cytochrome c release from the purified mitochondria. However, the combination of HA14-1 and PK11195, an antagonist of peripheral benzodiazepine receptor of the mitochondria, enhanced the cytochrome c release by HA14-1. The combination of PK11195 and HA14-1 could therefore serve as a potentially useful approach to enhance apoptosis in cancer.