Identification of epigenetic monotherapy candidates in taxane-resistant CRPC.

Background/aim: Taxane resistance remains a significant challenge in the effective treatment of castration-resistant prostate cancer (CRPC). Given the association of epigenetic regulation with chemotherapy resistance and cancer progression, this study aims to identify epigenetic vulnerabilities in two CRPC cell lines (DU145 and 22Rv1) established as resistant to two different taxanes, docetaxel (Dtx) and cabazitaxel (Cbz), using a small-molecule screening approach. Materials and methods: A small-molecule library targeting epigenetic regulators, including histone deacetylases (HDAC), histone methyltransferases, histone demethylases, bromodomain proteins, deoxyribonucleic acid methyltransferases, protein arginine deiminase, and histone acetyltransferase was utilized. Drug screening was performed on parental and taxane-resistant CRPC cell lines. Cell viability was assessed using the sulforhodamine B assay to identify compounds impairing the growth of resistant cells. Selected hits were further evaluated for their impact on colony-forming capacity using clonogenic assays, and cell death was confirmed by Annexin V/PI flow cytometry. Western blotting was used to assess histone modification marks (e.g., H3K27Ac, H3K4me2) and protein targets, including HDAC7 and lysine-specific demethylase 1 (LSD1). In combination studies, resistant cell lines were exposed to fixed-dose taxanes in combination with selected compounds. Combenefit software was used to generate synergy maps. Results: Screening results revealed that taxane-resistant CRPC cells remained susceptible to multiple epigenetic inhibitors rather than a single dominant class. Among the identified compounds, 4-Iodo-SAHA (HDAC inhibitor) and SP2509 (LSD1 inhibitor) emerged as cytotoxic agents, inducing cell death at levels comparable to those of parental cells. Further validation confirmed their efficacy in impairing cell viability and long-term survival in taxane-resistant CRPC cells, as demonstrated by Annexin V/PI flow cytometry. Both compounds induced epigenetic modulations consistent with their targets, reflected by increased histone marks (H3K27Ac for 4-Iodo-SAHA; H3K4me2 for SP2509), and were also associated with depletion of HDAC7 and LSD1, respectively. Combination assays demonstrated that both compounds potentiated Dtx activity and helped overcome resistance in taxane-resistant CRPC models. Conclusion: This study highlights epigenetic vulnerabilities in taxane-resistant CRPC and identifies 4-Iodo-SAHA and SP2509 as promising monotherapy candidates, demonstrating their ability to potentiate Dtx activity and overcome resistance.