Abstract 701: Mitochondrial mass is a critical determinant of cis Pt-induced cell death in ovarian cancer

Platinum compounds are an inherent part of chemotherapy for patients with high grade serous ovarian cancer (HGSC). Platinum based therapeutics, such as cisPt, induce DNA-damage by directly binding to nuclear DNA. Interestingly, cisPt also critically affects mitochondrial DNA. Elucidating the role of mitochondria in cisplatin induced cell death of HGSC cells likely identifies new efficient therapy approaches to overcome resistance. Flow cytometric analysis of cisPt sensitive and resistant HGSC cell lines from the NCI60 panel revealed higher mitochondrial mass and higher levels of mitochondrial ROS (mtROS) in cells that are sensitive to cisPt-induced cell death. In clonal sub-lines derived from OVCAR3 the mitochondrial mass correlates with basal oxygen consumption rate and survival after cisPt exposure. The correlation of mitochondrial mass and sensitivity to cisPt-induced apoptosis is corroborated by data from the human protein atlas (www.proteinatlas.org) that indicates high expression of the mitochondrial transcription factor TFAM and the mitochondrial inner membrane protein TIMM23 as favorable prognostic factors for the survival of ovarian cancer patients. Together, this shows the importance of mitochondrial mass in cellular response to cisPt treatment. Furthermore, exposure to cisPt enhances TFAM expression and increases mitochondrial mass as well as mitochondrial ROS. Incubation with cisPt in the presence of the ROS scavenger glutathione (GSH) or pan-caspase inhibitor zVAD-fmk reduces cisPt induced apoptosis while mitochondrial mass is not affected. However, the oxygen consumption rate in cells exposed to cisPt and GSH shows that increased ROS levels induce mitochondrial dysfunction. In line with a sensitivity-determining role of mitochondrial mass, knock-down of key-regulators of mitochondrial biogenesis, i.e. PGC-1α or TFAM, blocks mitochondrial ROS and protects cells from cisPt-induced apoptosis. Mitochondrial ROS is also reduced in an autoregulatory feedback loop by so-called uncoupling proteins (UCPs). Inhibition of UCP2 by Genipin results in increased induction of mitochondrial ROS by cisPt and consequently results in enhanced apoptosis. A comparable sensitization to cisPt-induced apoptosis and ROS production is evident in cells incubated with the iron chelator VLX600.Mitochondria are a critical element in cell response to cisPt since mitochondrial mass correlates with induction of ROS and apoptosis. We show the relevance of cellular mitochondria