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Abstract 4097: Enhanced synergistic efficacy of simvastatin and metformin on enzalutamide resistant prostate cancer cells

Androgen deprivation therapy (ADT) continues to be the mainstay therapy for advance-stage prostate cancer. Although malignant cells respond to ADT initially, subsequently colonize and re-emerge as castration-resistant prostate cancer (CRPC). Enzalutamide (ENZU), a second-generation AR antagonist exhibits survival advantage in CRPC patients, however, ~30% of patients develop resistance after ENZU treatment, activating AR in these tumors. These ENZU-resistant tumors poorly respond to chemotherapy and other treatment modalities. Therefore, identification of an effective low-cost therapeutic alternative with fewer side effects may lead to increased survival and greatly benefit the quality-of-life of these patients. Activation of aerobic glycolysis and biomass production is implicated, in part, to be responsible for CRPC cells to acquire androgen resistance. Previous studies from our laboratory have demonstrated that synergistic combination of simvastatin (SIM), a drug for the treatment of hypercholesterolemia and metformin (MET), a glucose-lowering drug inhibits CRPC growth, invasiveness and migration with minimal effect on normal prostate epithelial cells (Mol Cancer Ther. 13(10):2288-2302, 2014). Here we examine whether the combination of SIM and MET could be effective in the treatment of ENZU-resistant prostate cancer cells. Human CRPC cells viz. C4-2B and its variant C4-2B-ENZU (C4-2B enzalutamide resistant) and 22Rv1 were used for the experiments. C4-2B-ENZU cells were generated by growing C4-2B cells in 20µM ENZU over 6 months and maintained in 5µM ENZU in the cell culture medium. 22Rv1 cells were inherently resistant to ENZU treatment. Both cells were treated with SIM (4µM) and MET (2mM) individually and in combination, followed by the assessment of cell viability, crystal violet assay, cell cycle analysis, migration, invasion, and expression of various target genes by Western blotting. C4-2B-ENZU and 22Rv1 cells were treated with a combination of SIM and MET at pharmacological dose range (500nM-4µM SIM and 250µM-2mM MET). Combination treatment with 4μM SIM and 2mM MET (SIM+MET) led to significant and synergistic inhibition of cell viability, migration, invasion and cell cycle blockade in both cancer cell lines. The individual treatments of SIM and MET exhibited little or no effect on these cells. Furthermore, SIM+MET combination decreased the expression of AR, AR-V7, p-Akt (Ser473), p-AMPKα1/α2 (Ser-485/491) and simultaneously increased p-AMPKα1 (Thr-172) and AMPKα kinase activity in these cells. We demonstrate, for the first time, that synergistic combination of SIM and MET may be an effective regimen for treatment ENZU-resistant prostate cancer cells. Citation Format: Eswar Shankar, Pingfu Fu, Gregory T. MacLennan, Sanjay Gupta. Enhanced synergistic efficacy of simvastatin and metformin on enzalutamide resistant prostate cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4097.