Olaparib, a PARP inhibitor, is a targeted therapy used in treating various cancers, including castration-resistant prostate cancer. Despite its efficacy, resistance to olaparib remains a significant challenge. Understanding the molecular mechanisms underpinning this resistance is crucial for developing more effective treatment strategies. This study focuses on elucidating the role of mitochondrial alterations and the PTEN-induced kinase 1 (PINK1) gene in conferring olaparib resistance in castration-resistant prostate cancer cells. We investigated the transcriptomic and functional differences in mitochondrial activity between olaparib-resistant (2B-OlapR, LN-OlapR) and treatment-naïve prostate cancer cells (C4-2B, LNCaP) in both castration-sensitive and -resistant settings. Through RNA sequencing and gene set enrichment analysis, we identified significant enrichment of mitochondrial activity– and oxidative phosphorylation–related gene sets in olaparib-resistant derived cell lines. Resistant lines exhibited enhanced mitochondrial functionality, including increased basal and maximal respiration rates, as well as elevated ATP production and spare respiratory capacity, compared with parental cells. Subsequent investigations revealed a substantial increase in mitochondrial mass and electron transport chain complex I activity in olaparib-resistant cells. Furthermore, overexpression of the PINK1 gene was observed in resistant cells, which was correlated with resistance to olaparib and poor clinical outcomes in patients with prostate cancer. Inhibition of PINK1 expression significantly reduced mitochondrial function and mass, impaired cell growth, and decreased resistance to olaparib. These findings suggest that PINK1 plays a crucial role in modulating mitochondrial dynamics that confer therapeutic resistance, highlighting its potential as a therapeutic target for overcoming olaparib resistance in prostate cancer. Significance: Olaparib, a PARP inhibitor, is effective against various cancers, including prostate cancer. However, resistance to olaparib poses a significant challenge. This study uncovers that mitochondrial alterations and PINK1 gene overexpression contribute to this resistance in prostate cancer cells. Enhanced mitochondrial functionality and increased PINK1 expression in olaparib-resistant cells underscore the importance of targeting mitochondrial dynamics and PINK1 to develop more effective treatments for overcoming olaparib resistance in prostate cancer.

Enzalutamide resistance remains a significant challenge in the treatment of advanced prostate cancer. Identifying molecular drivers of enzalutamide resistance is crucial for developing effective therapeutic strategies. In this study, we identify insulin-like growth factor–binding protein 3 (IGFBP3) as a key driver of enzalutamide resistance in castration-resistant prostate cancer (CRPC). We demonstrate that IGFBP3 expression is significantly upregulated in enzalutamide-resistant C4-2B MDVR cells compared with parental C4-2B cells. This upregulation was consistently observed across multiple enzalutamide-resistant CRPC models, including LNCaP-derived 42D and 42F cells, as well as long-term enzalutamide-resistant cell lines derived from LNCaP, VCaP, LAPC-4, and CWR-R1 cells. Additionally, enzalutamide treatment directly induced IGFBP3 expression in sensitive cells. Elevated IGFBP3 expression was also observed in CRPC patient samples after enzalutamide treatment and was associated with higher Gleason scores and reduced disease-free survival. Mechanistically, IGFBP3 activates the sphingosine kinase 1 (SphK1)/sphingosine-1-phosphate (S1P) signaling pathway, which promotes cell survival and resistance to enzalutamide. IGFBP3 knockdown decreased SphK1 expression, reduced S1P secretion, and enhanced enzalutamide sensitivity, whereas IGFBP3 overexpression induced SphK1 expression and S1P production, conferring enzalutamide resistance. Inhibition of IGFBP3 via siRNA reduced cell viability, induced apoptosis, and resensitized resistant models to enzalutamide. Similarly, targeting SphK1 with the inhibitor SKI-II suppressed SphK1 activity, reduced S1P production, enhanced enzalutamide sensitivity, and significantly inhibited resistant tumor growth while enhancing enzalutamide sensitivity. Collectively, these findings highlight IGFBP3-mediated SphK1 signaling as a critical mediator of enzalutamide resistance and suggest that targeting the IGFBP3/SphK1/S1P axis represents a promising therapeutic strategy to overcome resistance in advanced prostate cancer.

Background/Objective: The expression of human steroid sulfatase (STS) is upregulated in castration-resistant prostate cancer (CRPC) and is associated with resistance to anti-androgen drugs, such as enzalutamide (Enza) and abiraterone (Abi). Despite the known link between STS overexpression and therapeutic unresponsiveness, the mechanism by which STS confers this phenotype remains incompletely understood. In this study, we sought to understand how STS induces treatment resistance in advanced prostate cancer (PCa) cells by exploring its role in altering mitochondrial activity. Methods: To examine the effects of increased STS expression on mitochondrial respiration and programming, we performed RNA sequencing (RNA-seq) analysis, the Seahorse XF Mito Stress Test, and a mitochondrial Complex I enzyme activity assay in STS-overexpressing cells (C4-2B STS) and in enzalutamide-resistant CPRC cells (C4-2B MDVR). We employed SI-2, the specific chemical inhibitor of STS, on C4-2B STS and C4-2B MDVR cells and evaluated STS activity inhibition on mitochondrial molecular pathways and mitochondrial respiration. Lastly, we examined the effects of dehydroepiandrosterone sulfate (DHEAS) supplementation on C4-2B STS organoids. Results: We present evidence from the transcriptomic profiling of C4-2B STS cells that there are enriched metabolic pathway signatures involved in oxidative phosphorylation, the electron transport chain, and mitochondrial organization. Moreover, upon STS inhibition, signaling in the electron transport chain and mitochondrial organization pathways is markedly attenuated. Findings from the Seahorse XF Mito Stress Test and mitochondrial Complex I enzyme activity assay demonstrate that STS overexpression increases mitochondrial respiration, whereas the inhibition of STS by SI-2 significantly reduces the oxygen consumption rate (OCR) and Complex I enzyme activity in C4-2B STS cells. Similarly, an increased OCR and electron transport chain Complex I enzymatic activity are observed in C4-2B MDVR cells and a decreased OCR upon SI-2 inhibition. Lastly, we show that STS overexpression promotes organoid growth upon DHEAS treatment. Conclusions: Our study demonstrates STS as a key driver of metabolic reprogramming and flexibility in advanced prostate cancer. Disrupting enhanced mitochondrial respiration via STS presents a promising strategy in improving CRPC treatment.