ABT-263, an Inhibitor of Bcl-2 Family Antiapoptotic Proteins, Sensitizes Prometaphase-Arrested HeLa Cells to Apoptosis Induced by Mild Hyperthermia

Aims: We have previously shown that mild hyperthermia (39-42°C) rapidly induces apoptosis in H-HeLa cells arrested in mitosis but not in interphase cells and not in mitotic-arrested cells of other HeLa strains such as HeLa S3. Our goal was to test the idea that this sensitivity to hyperthermia is due to down-regulation of Bcl-2 family antiapoptotic proteins during mitosis. Methodology: HeLa S3 cells were arrested in mitosis with spindle poisons and simultaneously treated with mild hyperthermia (42°C) and ABT-263 (Navitoclax), an inhibitor of Bcl-2 and other anti-apoptotic proteins. Apoptosis was observed microscopically and confirmed by observation of procaspase 3 cleavage using western immunoblotting. Results: Treatment of prometaphase-arrested HeLa S3 cells with mild hyperthermia (42°C) and as little as 200 nM ABT-263 induces apoptosis in the great majority of cells within 2 hr, as judged by blebbing of plasma membranes. The effect is not seen with interphase cells and is blocked by caspase inhibitors z-VAD-fmk and z-DEVD-fmk. Conclusion: Our results show that inhibition of Bcl-2 family antiapoptotic proteins sensitizes prometaphase-arrested HeLa cells, but not interphase cells, to apoptosis induced by mild hyperthermia. An open question is why are prometaphase-arrested cells more susceptible than interphase cells? If the features of mitotic-arrested cells that make them sensitive could be identified and mimicked in interphase cells by appropriate drug treatments, it may be possible to combine systemic chemotherapy with local hyperthermia to provide an effective new treatment for tumors.