Abstract A10: Fatty acid synthesis inhibitor, orlistat, potentiates cisplatin-induced toxicity in ovarian cancer cells

Abstract

Abstract Background: Fatty acid synthase (FAS) is a key enzyme in the synthesis of fatty acids and has been shown to be upregulated in many cancers. Additional studies found that high levels of FAS correlated with worse prognosis and with chemoresistance in ovarian tumors. As such, FAS has become a promising target for antitumor therapies. The aim of this study was to gain mechanistic insights into the cytotoxic effects of fatty acid inhibition with orlistat treatment alone or in combination with cisplatin in the ovarian cancer cell line A2780. Methods: A2780 cells were treated with cisplatin (0.4-12 μM) for 4 hours followed by orlistat (25-100 μM, 24 hr). Cell proliferation was measured via CyQuant assay; cell apoptotic activity was measured by both caspase 3/7 assay and flow cytometry with annexin V and propidium iodide. Fatty acid β-oxidation was then characterized using a Seahorse XF24 Extracellular Flux Analyzer. ATP levels were measured with a luminescent ATP detection kit. Finally, Western blot analyses for capsase 3 and phospho-ATM were performed. Results: Cisplatin treatment (4 and 10 μM) of A2780 cells induced an increase in OXPHOS and steady-state levels of ATP 24 hr after damage. Orlistat (25 and 50 μM, 24 hr) decreased basal oxygen consumption and decreased steady-state ATP levels in cisplatin-treated cells. A2780 cells showed decreased proliferation and increased apoptotic activity (Caspase 3/7 and Annexin V) when treated with cisplatin followed by orlistat, as compared to either drug alone. Using the Chou Talaly method the combination index was found to be 0.73 indicating a synergistic relationship. Cisplatin increased the level of phospho-ATM that was reduced by orlistat. Conclusions: Orlistat in combination with cisplatin treatment of A2780 ovarian tumor cells increased apoptosis compared to either treatment alone. Orlistat caused decreased oxidative phosphorylation and prevented a cisplatin-induced increase in OXPHOS and ATP. The combination of cisplatin and orlistat decreases p-ATM, suggesting decreased activation of the DNA repair pathway after cisplatin treatment. This may represent the mechanism of synergistic action of the combination treatment. Citation Format: Bennett Van Houten, Molly Heft-Neal, Wei Qian, Vera Roginskaya. Fatty acid synthesis inhibitor, orlistat, potentiates cisplatin-induced toxicity in ovarian cancer cells. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A10.