A reciprocal signaling crosstalk between the AR and BCl2-AKT pathways induces castration resistance in castration sensitive prostate cancer

Introduction: A leading contributor to the significant mortality burden of prostate cancer (PC) is the resistance to androgen deprivation therapy (ADT). Although most PCs are initially sensitive to ADT, the duration of response is variable, and relapse invariably occurs in the transition to metastatic castration-resistant prostate cancer (mCRPC), the lethal form of the disease. Therefore, it is essential to discover and validate early resistance mechanisms that initially protect castration sensitive prostate cancer (CSPC) cells from ADT and to develop novel combination therapies that can block or delay the ADT-induced shift from CSPC to mCRPC. Overexpression of the hallmark antiapoptotic gene B-cell lymphoma 2 (BCL2) is a potential mechanism of resistance to ADT. Methods: To discover the molecular drivers of castration resistance, we analyzed the tumor transcriptomic profile of a cohort of localized PC patients (N=58) treated with neoadjuvant-intensive ADT (NCT00924469; Taplin et al, 2014, Sowalsky et al, 2018). Experimentally, we treated CSPC cells and genetically engineered mice (GEM) prostate tumors with ADT and analyzed the signaling pathways, which were enriched post-ADT treatment compared untreated samples. Results: We discovered ~10-fold increased mRNA expression of BCL2 (p<0.001) in ADT-treated localized PC patients compared to untreated (standard of care surgery) patients in NCT00924469 samples. Our experimental study showed that treatment with AR inhibitors strongly augments BCL2 expression in human CSPC cell lines and GEM PC model, indicating possible direct negative regulation of BCL2 by the AR-signaling pathway. Mechanistically, our preliminary data reveal a striking induction of cell metabolism pathways (fatty acid and xenobiotic metabolism), including activation of PI3K/AKT signaling in BCL2-overexpressing CSPC cells. We used siRNA-mediated BCL2 knockdown in LNCaP cells and showed that loss of BCL2 strongly suppressed ADT-induced AKT- phosphorylation. We also showed increased Bcl2 mRNA expression in PTEN-knockout mice-derived prostate organoids compared to the wild-type control. Furthermore, we observed that AKT kinase -inhibitor MK2206 strongly inhibits enzalutamide-induced BCL2 expression in LNCaP cells. Conclusion: Together our data indicate a non-canonical role of BCL2 in activating PI3K/AKT signaling in prostate cancer. For the first time, we demonstrate the crucial importance of AR-BCL2-AKT signaling pathway crosstalk in CSPC biology and reveal this complex signaling crosstalk may act as a key driver of CSPC transformation to lethal CRPC. Citation Format: Goutam Chakraborty, Rahim Hirani, Subhiksha Nandakumar, Nabila Zaman, Teja Muralidhar Kalidindi, Sai Harisha Rajanala, Gwo-Shu M. Lee, Konrad H. Stopsack, Naga Vara Kishore Pillarsetty, Lorelei A. Mucci, Daniel C. Danila, Philip W. Kantoff. A reciprocal signaling crosstalk between the AR and BCl2-AKT pathways induces castration resistance in castration sensitive prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A002.