Abstract 529: Interplay of circadian cryptochrome 1 (CRY1) and DNA repair in prostate cancer (PCa).

Abstract Background: Disruptions in circadian rhythm are linked to prostate cancer (PCa). Previous studies indicate that the core circadian clock factor cryptochrome 1 (CRY1) is pro-tumorigenic and associated with poor clinical outcomes in PCa. Beyond its transcriptional co-regulatory function, CRY1 was recently identified as a modulator of DNA damage repair (DDR) in advanced PCa. Molecular and pharmacological suppression of CRY1 impairs PCa cell growth, induces G2/M arrest, and disrupts homologous recombination (HR)-mediated DNA repair. However, the mechanistic role of CRY1 in disease progression from hormone therapy sensitive (HTS) to castration resistant prostate cancer (CRPC) remains incompletely defined. Methods: We employed doxycycline-inducible CRY1 knockdown models of both HTS, using LNCaP cell line, and CRPC, using C4-2 cell line, along with pharmacological strategies to recapitulate physiologically relevant CRY1 modulation. Transcriptomic profiling, DDR-focused CRISPR knockout (KO) screening, and downstream functional assays were used to define CRY1-dependent transcriptional and repair programs across disease stages. This allows for the identification of potential novel targeted therapies as well as predicts patient response to DDR targeted therapy. Results: Transcriptomic analyses revealed distinct CRY1-regulated gene networks in HTS versus CRPC models. In HTS, CRY1 activity was associated with pathways including base excision repair, mismatch repair, and G2/M checkpoint regulation, while in CRPC, CRY1 was specifically linked to HR-mediated DNA repair. DDR-targeted CRISPR screening further demonstrated that CRY1 promotes tumorigenesis via nucleotide excision repair in HTS and shifts to HR reliance in CRPC, suggesting stage-specific rewiring of repair pathway choice driven by CRY1. These findings identify a novel mechanism of DDR regulation across PCa progression. Conclusions: In sum, our study reveals that CRY1 supports PCa progression via distinct DDR mechanisms in HTS and CRPC. Thus, targeting CRY1, alonge or in combination with DDR inhibitors, offers a promising therapeutic strategy tailored to disease stage in PCa. Citation Format: Arwa Fallatah, Stefan DiFazio, Lakshmi Ravindranath, Orly Richter, Christopher McNair, Ayesha Shafi. Interplay of circadian cryptochrome 1 (CRY1) and DNA repair in prostate cancer (PCa) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 529.