Abstract NT-103: TARGETING OVARIAN TUMORS WITH OXPHOS INHIBITORS

Abstract

Abstract Aerobic glycolysis is an important metabolic adaptation in tumors. However, there is mounting evidence that oxidative phosphorylation (OXPHOS) also contributes to metabolism in cancer cells. Therefore, agents targeting OXPHOS can serve as novel anticancer agents. We will present data on small molecule agents that inhibit the proliferation of ovarian and other cancer cells by inhibiting mitochondrial electron transport. We have focused our attention on citral, plumbagin, curcumin, cinnamaldehyde, piperlongumine, perillaldehyde, nonenal and other naturally occurring agents. All of these molecules share a common molecular epitope, the unsaturated carbonyl that participates in redox reactions. Cancer cells treated with these agents show a marked decrease in oxygen consumption rate and an increase in extracellular acidification. The redox ratio (NADH/FAD) and cellular ATP levels also decrease in response to these small molecule agents. In our search for additional and more potent OXPHOS inhibitors we have discovered that the FDA-approved anti-malarial drug atovaquone is an efficient inhibitor of electron transport in ovarian cancer cells. Chronic administration of atovaquone decreases the growth of ID8 tumors in C57BL/6 mice. Investigation in to the mechanism of action of the unsaturated carbonyl compounds indicates that their initial effect in cancer cells is the immediate and substantial rise in oxygen radicals as a result of OXPHOS inhibition. This increase in reactive oxygen causes extensive oxidative damage leading to DNA strand breaks. Subsequently, we have observed activation of p53-mediated apoptosis. These experiments are suggesting that inhibition of OXPHOS and the subsequent increase in intracellular oxygen radicals can result in the reactivation of the tumor suppressive responses of at least a subset of the p53 mutants. Additionally, our studies also indicate that the oxidative stress occurring as a result of OXPHOS inhibition directly leads to inhibition of ion transport through the Na+/K+-ATPase. As a result of this inhibition, cancer cells are unable to maintain a normal membrane potential. Studies are currently underway to determine if the inability to maintain membrane potential also contributes to apoptotic cancer cell death induced by these unsaturated carbonyl-containing compounds. Oxidative stress caused by these compounds leads to an increase in superoxide dismutase, catalase and glutathione synthesis via the activation of Nrf-2. Inhibition of Nrf-2 results in an increase in the potency of the unsaturated carbonyl compounds. We are therefore examining Nrf-2 increase as a form of chemoresistance mechanism that likely impinges on the anti-cancer activity of the unsaturated carbonyl compounds. These studies are allowing us to develop medicinal chemistry-based approaches to develop novel molecules with increased potency and targetability as OXPHOS inhibitors for the treatment of ovarian cancer. Citation Format: Arvinder Kapur, Amruta Nayak, Mildred Felder, Allegra Cappucini, Spencer Ericksen, Yousef Alharbi, Bikash Pattnaik, Lisa Barroilhet, and Manish S. Patankar. TARGETING OVARIAN TUMORS WITH OXPHOS INHIBITORS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr NT-103.