Abstract 891: Plumbagin and atovaquone inhibit Na+/K+-ATPase through the generation of oxidative stress

Abstract

Abstract Plumbagin and atovaquone are chemotoxic to ovarian, breast and other tumors. Both molecules inhibit oxidative phosphorylation causing a rapid increase in intracellular oxygen radicals and apoptosis. Oxidative stress is also known to inhibit the activity of Na+/K+-ATPase (NKA), the ion channel that maintains the membrane potential. Here, we investigate if the oxidative stress mediated by plumbagin and atovaquone also leads to inhibition of NKA activity. We confirm that plumbagin and atovaquone inhibit proliferation of three human (OVCAR-3, SKOV-3 and TYKNu) and one mouse (ID8) ovarian cancer cell lines. Using SKOV-3 and OVCAR-3 as models for ovarian cancer, we demonstrate that oxygen radical scavenger, N-acetylcysteine (NAC) attenuated the cytotoxicity of plumbagin and atovaquone. Using whole cell patch clamping we demonstrate that plumbagin and atovaquone inhibit outward and inward current flowing through NKA in SKOV-3 and OVCAR-3. Both drugs decrease cellular ATP. Providing exogenous ATP (5 mM) in the pipet solution used during patch clamping did not recover NKA activity in the plumbagin or atovaquone treated SKOV-3 and OVCAR-3 cells. However, pretreatment of the cells with NAC completely abrogated the NKA inhibitory activity of plumbagin and atovaquone. Exposure of the SKOV-3 cells to either of the drugs for 1-2 h resulted in a significant decrease in the expression of NKA. We conclude that oxidative stress caused by plumbagin and atovaquone degrades NKA and hence the membrane potential cannot be optimally maintained. Evaluation of compounds that induce oxidative stress should therefore consider contribution of NKA inhibition to the cytotoxic activity of such agents. Citation Format: Yousef Alharbi, Arvinder Kapur, Mildred Felder, Lisa Barroilhet, Bikash Pattnaik, Manish S. Patankar. Plumbagin and atovaquone inhibit Na+/K+-ATPase through the generation of oxidative stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 891.