Abstract 1337: Androgen receptor mediates radioresistance through autophagy and DNA repair in AR-positive prostate cancer

Abstract Background: Androgen receptor (AR) is a critical therapeutic target in prostate cancer (PC) and androgen blockade is known to act synergistically with radiotherapy (RT), however, the mechanisms through which AR modulates RT response is complex and remains poorly elucidated. Aims and Methods: We compared the radiation responses in LNCaP (AR-positive), PC3 (AR-negative), and HEK293T (non-malignant) cells by analyzing DSB induction, cell cycle arrest, and apoptosis. Mechanistic studies, including AR silencing and inhibition, were validated through RNA sequencing and IHC analysis of cell lines and irradiated patient-derived prostate tumors. Results: At 24-hours post-RT, the apoptotic rate increased by 6-fold in HEK293T and PC3 cells versus LNCaP cells. Cell viability at 48-hours post-RT was decreased to less than 10% in HEK293T, remaining at ∼60% in LNCaP cells. Moreover, over 70% of LNCaP cells were arrested in the G1 phase post-RT, accompanied by rapid p53 activation and p21 induction within 3-hours. AR silencing significantly increased radiosensitivity and reduced cell proliferation in LNCaP but did not alter the expression of p53 downstream genes, eg. BAX and p21. Interestingly, AR silencing reduced the phosphorylation of DNA-PKcs, a critical mediator of non-homologous end joining (NHEJ) repair, suggesting that AR facilitates NHEJ. This was further supported by the comet assay results showing that LNCaP repaired RT-induced DSBs more efficiently than PC3 cells. Moreover, AR regulates autophagy post-RT as AR silencing decreased autophagy-related gene (ATG) expression, and macroautophagy was augmented in LNCaP cells post-RT through LC3-II expression and autophagic vacuole formation. Bulk transcriptome analysis revealed significant upregulation of 11 ATGs, including ULK1 and ATG2, at 24-hours post-RT. Moreover, IHC analysis of patient-derived PC ex vivo irradiated tumors consistently showed that RT-induced autophagy supports the survival of AR-positive PC cells. Discussion and Conclusion: Our results demonstrate that AR plays an essential role in mediating radioresistance in AR-positive PC by enhancing both autophagy and DNA repair, with ongoing spatial transcriptome analysis to further explore these mechanisms in patient-derived tumors. Citation Format: Ken-ichi Kudo, Qianhua Feng, Maria Chosco, Leslie Wenning, Ziyi Huang, Jonathan Anzules, Jeshwanth Mohan, Nathan Lin, Zhao V. Wang, June-Wha Rhee, Yun Li. Androgen receptor mediates radioresistance through autophagy and DNA repair in AR-positive 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 1337.