Abstract 304: Profiling the acute effects of androgen receptor inhibition in hormone-sensitive prostate cancer

Abstract Introduction: Metastatic prostate cancer (mPC) is driven by androgen signaling. Standard treatment involves androgen-deprivation therapy (ADT) and androgen receptor (AR) inhibitors (e.g. enzalutamide), but resistance eventually arises, leading to metastatic castration-resistant prostate cancer (mCRPC). This study investigated the acute effects of AR inhibition in hormone-sensitive mPC to identify therapeutic targets to prevent resistance. Methods: We analyzed RNAseq before and after 3 or 6 months of AR inhibition from two neoadjuvant enzalutamide clinical trials in PC (NCT03297385, n=39; NCT02430480, n=37) using Hallmark pathways, and with a focus on senescence and senescence associated secretory phenotype (SASP) signatures. In vitro, we treated human (LNCaP, VCaP, LAPC4) and murine (Myc-CaP, Ptenpc-/-Lkb1pc-/-) mPC cells with enzalutamide and we assessed proliferation (CCK8, BrdU), viability (AnnexinV/PI), cell cycle distribution, SAβGAL activity, cyclin-dependent kinase (CDK) inhibitors, and RNAseq. We derived an RNA hormonal therapy-induced senescence (HTIS) signature from LNCaP cells treated with enzalutamide for 2 days vs 2 weeks or 6 weeks. ssGSEA analysis assigned a senescence score to patient samples for clinical outcome correlations. In vivo, HTIS was validated in LNCaP and mPC patient-derived xenografts (PDX) models using SAβGAL activity, Ki67 (proliferation), p16/p21, and RNAseq. Results: Upon enzalutamide, GSEA analysis of patient samples (NCT03297385, NCT02430480) revealed downregulated Hallmark gene sets linked to proliferation/AR signaling, and upregulated pathways related to protein secretion, inflammation, TNFα-NFκB, and IL6-JAK-STAT3 signaling. Senescence and SASP signatures were enriched in post-enzalutamide biopsies. In vitro, AR inhibition in LNCaP, VCaP, LAPC4, Myc-CaP and Ptenpc-/-Lkb1pc-/- induced G0/G1 proliferation arrest without affecting cell viability, alongside senescence features such as increased SAβGAL activity, and upregulation of p16/p21 and SASP genes. HTIS signature from LNCaP cells, which incorporated downregulated genes linked to proliferation and upregulated genes linked to inflammation was validated in vivo, where castration or enzalutamide in LNCaP xenografts and PDXs tumors resulted in decreased proliferation (Ki67), increased SAβGAL activity, upregulation of p16 or p21, and enrichment for senescence and SASP signatures. Last, patients from the NCT03297385 dataset with high HTIS signature scores showed greater correlation with other senescence signatures and lower rates of biochemical relapse (high = 28% (7/25); mid = 42.9% (3/7); low = 85.7% (6/7)). Conclusions: We demonstrate that AR inhibition induces a senescent phenotype in hormone-naïve prostate cancer models, including PDXs. RNAseq of patient biopsies suggest this adaptive phenotype is present also in patients and has prognostic implications. Citation Format: Julian Brandariz, Lara de Llobet Cucalon, Daniel Aguilar, Andrei Salca, Victor Esquefa, Youhao Chen, Gisela Mir, Anna Oliveira, Irene Casanova-Salas, Alba Escriche, Manuel Jara Espejo, José Alberto López-Domínguez, Victoria Cid, Marco Piva, Maria Abad, Francisco Martínez-Jiménez, Raquel Perez-Lopez, Manuel Serrano, Arkaitz Carracedo, Nicolas Herranz, Joaquin Mateo. Profiling the acute effects of androgen receptor inhibition in hormone-sensitive prostate cancer [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 304.