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Background Resistance to poly (ADP-ribose) polymerase inhibitors (PARPi) poses a major challenge to therapeutic efficacy in castration-resistant prostate cancer (CRPC). Although circular RNAs (circRNAs) have emerged as critical regulators in cancer biology, their involvement in PARPi resistance remains largely uncharacterized. Objective This study aims to elucidate the molecular mechanism by which hsa_circ_0038737 modulates PARPi resistance in CRPC through post-transcriptional regulatory pathways. Methods We employed a comprehensive set of in vitro and in vivo approaches, including qRT-PCR, RNA sequencing, RNA-protein pull-down, RNA immunoprecipitation, functional assays, and xenograft/organoid models, to investigate the biological function and mechanistic role of hsa_circ_0038737 in CRPC progression and therapeutic response. Results We identified hsa_circ_0038737 as a nuclear-enriched circRNA significantly upregulated in CRPC, with expression levels correlating with poor prognosis and aggressive clinical features. Mechanistically, hsa_circ_0038737 interacts with RNA-binding protein (RBP) IGF2BP3, enhancing the stability of DNPH1 mRNA, a nucleotide sanitizer critical for DNA repair. The circRNA-RBP-mRNA regulatory axis promotes PARPi resistance by facilitating DNA damage repair capacity. Moreover, we revealed that reverse-complementary Alu elements mediate circRNA biogenesis, with HNRNPDL facilitating this process. Pharmacologic inhibition of DNPH1 effectively restored PARPi sensitivity both in vitro and in vivo. Conclusion Our findings reveal a novel hsa_circ_0038737/IGF2BP3/DNPH1 axis driving PARPi resistance in CRPC, offering promising potential biomarkers and therapeutic targets to overcome resistance and improve treatment outcomes in advanced prostate cancer. Keywords: Castration-resistant prostate cancer (CRPC), Circular RNA (circRNA), PARP inhibitor, IGF2BP3, DNPH1 stabilization

Background Resistance to poly (ADP-ribose) polymerase inhibitors (PARPi) poses a major challenge to therapeutic efficacy in castration-resistant prostate cancer (CRPC). Although circular RNAs (circRNAs) have emerged as critical regulators in cancer biology, their involvement in PARPi resistance remains largely uncharacterized. Objective This study aims to elucidate the molecular mechanism by which hsa_circ_0038737 modulates PARPi resistance in CRPC through post-transcriptional regulatory pathways. Methods We employed a comprehensive set of in vitro and in vivo approaches, including qRT-PCR, RNA sequencing, RNA-protein pull-down, RNA immunoprecipitation, functional assays, and xenograft/organoid models, to investigate the biological function and mechanistic role of hsa_circ_0038737 in CRPC progression and therapeutic response. Results We identified hsa_circ_0038737 as a nuclear-enriched circRNA significantly upregulated in CRPC, with expression levels correlating with poor prognosis and aggressive clinical features. Mechanistically, hsa_circ_0038737 interacts with RNA-binding protein (RBP) IGF2BP3, enhancing the stability of DNPH1 mRNA, a nucleotide sanitizer critical for DNA repair. The circRNA-RBP-mRNA regulatory axis promotes PARPi resistance by facilitating DNA damage repair capacity. Moreover, we revealed that reverse-complementary Alu elements mediate circRNA biogenesis, with HNRNPDL facilitating this process. Pharmacologic inhibition of DNPH1 effectively restored PARPi sensitivity both in vitro and in vivo. Conclusion Our findings reveal a novel hsa_circ_0038737/IGF2BP3/DNPH1 axis driving PARPi resistance in CRPC, offering promising potential biomarkers and therapeutic targets to overcome resistance and improve treatment outcomes in advanced prostate cancer.