circRNA signatures associated with BRCA mutation status in ovarian cancer and a RASSF8-derived candidate biomarker.

Abstract

e17548 Background: Clinically actionable variants (CAVs) in BRCA1 and BRCA2 determine eligibility for targeted therapy in high grade serous ovarian cancer (HGSOC). However, RNA based biomarkers indicating BRCA status remain limited. Circular RNAs (circRNAs) are non coding RNAs with regulatory roles in gene expression. Their stability and detectability in human biofluids make circRNAs attractive liquid biopsy candidates. This study examined whether circRNA expression varies by BRCA background and assessed translational potential. Methods: This was a translational biomarker study examining circRNA expression across distinct BRCA backgrounds in high grade serous ovarian cancer. Three HGSOC cell lines representing BRCA1 mutant, BRCA2 mutant, and BRCA wildtype backgrounds were analysed. The primary endpoint was identification of circRNAs differentially expressed according to BRCA status. circRNA profiling was performed using the Arraystar circRNA microarray platform. Differential expression was assessed using normalised signal intensity, a fold change threshold ≥2, and associated statistical outputs, with adjustment for multiple testing. Candidate circRNAs were prioritised based on fold change, reproducibility, and annotation quality. Selected circRNAs were validated using divergent primers and quantitative PCR across the HGSOC panel, a chemotherapy resistant model, and clinical tumour samples stratified by BRCA status. Results: Heatmaps and volcano plots showed circRNA profiles were driven mainly by cell line specific patterns. However, at the individual transcript level, distinct circRNAs demonstrated BRCA associated differences. Five circRNAs were prioritised for validation. Three circRNAs (hsa_circ_400223, hsa_circ_008026, and hsa_circ_003300) were upregulated in both BRCA1 and BRCA2 mutant models compared with wildtype. hsa_circ_100059 was predominantly expressed in the BRCA1 mutant cell line, while hsa_circ_025636 was highly expressed in the BRCA2 mutant cell line. In clinical samples, hsa_circ_025636, a RASSF8 derived circRNA, showed higher expression in a subset of BRCA mutant cases relative to wildtype (p<0.05). Conclusions: This study provides evidence that circRNAs may serve as biomarkers of BRCA status in HGSOC. While global circRNA profiles were not defined by BRCA genotype, specific circRNAs demonstrated BRCA associated expression. The RASSF8 derived circRNA hsa_circ_025636 is a promising candidate and warrants evaluation in larger cohorts alongside functional studies.