Abstract 3054: A potent triterpene combination treatment for eliminating castration resistant prostate cancers

Abstract Patients with advanced prostate cancer (PCa) with castration resistance and neuroendocrine phenotype (CRPC) respond poorly to most existing therapies (median survival, <2y). The studies of antitumor activities of the bioactive pentacyclic triterpenes (PTTs), such as Oleanolic Acid (OA) and Ursolic Acid (UA), have been reported in multiple tumor models. Here, we tested the efficacy of OA and UA, individually and in combination, against PCa cells in both in-vitro and in-vivo systems. We found ∼ 50% (p<0.05) reduction in tumor growth and terminal tumor weight in the CRPC line 22Rv1 tumors that were implanted subcutaneously in athymic nude mice following oral gavage at 50 mg/kg with OA and UA alone and in 1:1 combination three times a week. There was no detectable systemic toxicity to the host mice. Further, in-vitro mechanistic investigation of the effect of OA and UA unveiled that at higher concentrations, a 1:1 combination ratio of OA and UA shows synergistic activity against PCa cells (e.g. 22Rv1, PC3, LNCaP, and C4-2), in contrast, this combination showed insignificant toxicity on a non-tumorigenic human prostate epithelial cell line (NHPrE1). To investigate the molecular mechanism of tumor cell-specific cell death, we explored the effect of these PTTs on ROS production, glucose metabolism, extracellular oxygen consumption rate, and ATP production in both 22Rv1 and PC3 cells. The combination treatment of OA and UA significantly increased the ROS level up to 80% (p<0.05) and considerably decreased the mitochondrial Oxygen Consumption Rate (OCR). The levels of intermediates of glycolysis were significantly increased, but tricarboxylic acid (Krebs cycle) metabolites decreased significantly. Immunocytochemical and Immunoblotting analyses of tumor tissues from xenografts showed excessive cytotoxic autophagy as the leading cause of cell death. An increased autophagy-associated membrane-bound LC3B corroborated and higher expression of other markers of autophagy (e.g., Beclin-1, P62/SQSTM1, ATGs, and pULK-1) were seen in cells treated with OA, UA, and their combination. In contrast to increased autophagy markers, markers associated with apoptosis (e.g., cleaved PARP-1, Caspase-3, etc.) were either undetectable or insignificant. Overall, ongoing studies showed that OA and UA in a 1:1 combination induce cancer-cell-specific toxicity mainly via autophagy. This study demonstrated that the triterpenes (OA, UA, and OA+UA) have compelling potential to inhibit CRPC in patients, and because they exhibit little systemic toxicity, yet show significant antitumor activity, they could be used as a neo- or adjuvant therapeutics with current FDA-approved cytotoxic chemotherapy drugs. Citation Format: Kunj Bihari Gupta, Kanza Mamouni, Georgios Kallifatidis, Truett Taylor, Bal. L. Lokeshwar. A potent triterpene combination treatment for eliminating castration resistant prostate cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3054.