Abstract B060: Rewiring the serum response factor interactome to overcome treatment resistance in prostate cancer

Abstract Prostate cancer (PCa) is the most common invasive malignancy among men worldwide. Standard-of-care therapies primarily target the Androgen Receptor (AR) signalling through androgen deprivation therapies (ADT) and AR antagonists such as enzalutamide. Although these therapies initially suppress tumour growth, resistance inevitably develops, creating an urgent need for new therapeutic strategies that bypass direct AR inhibition. The Serum Response Factor (SRF), a transcription factor associated with cancer progression and metastasis, has emerged as a potential AR co-regulator. Previous research in our laboratory identified shared interactors between AR and SRF, including HSP70, HSP90, and components of the PI3K/Akt pathway. This study examines the signalling between AR and SRF and explores whether targeting their shared co-regulators can overcome treatment resistance in advanced PCa. Cell proliferation and viability were measured in a panel of PCa cell lines using MTT assays and live-cell IncuCyte imaging. Pharmacologic inhibitors were used to target SRF (CCG1423, Lestaurtinib), AR (Enzalutamide, EPI7170), HSP70/90 (VER-15508, JG-98, Ganetespib), and the PI3K/Akt pathway (Ipatasertib, Alpelisib). Each compound was tested alone and in combination at sub-cytotoxic concentrations (IC10-IC30) to evaluate synergistic effects. Proteomic analyses were performed following 48-hour treatment with Lestaurtinib to identify molecular changes associated with SRF inhibition. Inhibition of AR, SRF, and their shared interactors reduced PCa cell viability and proliferation, with most inhibitors demonstrating greater potency than enzalutamide, the current standard of care. Multiple drug combinations exhibited synergistic effects, with the most potent interactions observed for Lestaurtinib + Ipatasertib, CCG1423 + EPI7170, EPI7170 + Ipatasertib, and EPI7170 + Lestaurtinib. Proteomic profiling of Lestaurtinib-treated castration resistant 22Rv1 PCa cells revealed a marked downregulation of several proteins implicated in DNA replication, and checkpoint regulation. MCM10 was the most downregulated protein, followed by TGF-β1, which mediates epithelial-mesenchymal transition (EMT) and metastatic potential. Additional downregulated targets include SARG, an androgen-responsive gene, indicating reduced AR activity. Phosphoproteomic analysis are in progress to further define post-translational regulatory effects of combined AR-SRF inhibition. Collectively these findings demonstrate that pharmacologic interference of the AR-SRF signalling axis and its shared cofactors exerts synergistic antiproliferative effects and reprograms critical oncogenic pathways in PCa cells. The substantial downregulation of proteins governing DNA replication, checkpoint control suggests that targeting SRF and its interactome represents a promising strategy for restoring therapeutic sensitivity in ADT-resistant PCa. Ongoing phosphoproteomic analyses will provide deeper insight into resistance mechanisms and may uncover additional therapeutic targets suitable for clinical translation. Citation Format: Kim Zitzmann, Jay Campbell, Kieran Wynne, Maria Prencipe. Rewiring the serum response factor interactome to overcome treatment resistance in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr B060.