DGAT1 Inhibition Enhances Olaparib-Induced Lipotoxic Apoptosis in Metastatic Castration-Resistant Prostate Cancer.

Despite the initial success of poly (ADP-ribose) polymerase (PARP) inhibitors, achieving durable responses and effective treatment outcomes in metastatic castration-resistant prostate cancer (mCRPC) remains challenging. Resistance to the PARP inhibitor Olaparib is primarily mediated by the induction of autophagy, which enhances the availability of free fatty acids (FFA). Cancer cells mitigate the toxic effects of excessive lipid accumulation by sequestering FFA into lipid droplets (LD) through diacylglycerol O-acyltransferase 1 (DGAT1)-mediated lipid storage. We hypothesize that inhibiting DGAT1 disrupts this protective mechanism, induces lipotoxicity, promotes oxidative stress-mediated cell death, and enhances the anti-cancer efficacy of PARP inhibitors. We evaluated the effect of combining a DGAT1 inhibitor (DGAT1i) with Olaparib in aggressive prostate cancer cell lines on lipid metabolism and oxidative stress in vitro. We assessed LD dynamics by immunofluorescence, mitochondrial integrity, FFA accumulation, and oxidative stress. Additionally, targeted protein expression analysis was conducted to examine the expression levels of proteins involved in autophagy, lipogenesis, and apoptosis. DGAT1 inhibition notably potentiated the effects of Olaparib on prostate cancer cell proliferation. Olaparib alone caused an increase in LD formation, whereas the combination treatment reduced them, suggesting a shift in lipid metabolism. Dual treatment of Olaparib and DGAT1 inhibition further promoted FFA accumulation and lipotoxicity. Additionally, the combination elevated intracellular oxidative stress and mitochondrial damage, implying that DGAT1 inhibition accelerates oxidative stress-driven cell death. Flow cytometry and apoptosis array analysis confirmed an increase in programmed cell death in the combination treatment group. Our study proposes a novel therapeutic strategy to enhance Olaparib efficacy and potentially prevent resistance by targeting autophagy-induced LD biogenesis through DGAT1 inhibition. Future studies will focus on elucidating the relationship between Olaparib-induced autophagy, lipogenesis, and DGAT1 inhibition, providing a foundation for clinical trials in patients with mCRPC.