Abstract 5170: Novel dSTRIDE-HR assays can accurately assess DNA repair defects in human cancers and distinguish HR status of tumors

Abstract Accurate patient stratification is crucial for the successful application of targeted anti-cancer therapeutic approaches. It has been shown that PARP inhibitors are synthetic lethal with defective homologous recombination (HR) repair, with genes such as BRCA1 and BRCA2 identified as conferring therapy resistance or sensitivity, depending on their mutational status. Moreover, there is evidence of patient benefit of carboplatin-based therapy in HR deficient (HRD) tumors. With a growing emphasis on HRD in cancer treatment, efforts have been made to define the HRD phenotype. Nonetheless, the current approaches employed in the clinic, such as Next Generation Sequencing (NGS), HRD score or RAD51 assays have significant limitations and their interpretation can be unclear. To answer the need for a functional HR-specific biomarker, we have recently developed and introduced two new assays, called collectively dSTRIDE-HR. The assays are based on the STRIDE platform technology that enables direct and sensitive detection of single- or double-strand DNA breaks in situ in fixed cells. Novel dSTRIDE-HR explicitly detect double-strand DNA breaks localized in close proximity to RPA (dSTRIDE-RPA) or RAD51 (dSTRIDE-RAD51) proteins. The assays have been shown to be reliable reporters of HR activation in cellular models after exogenous DNA damage induction, yet their potential to predict HR status in an in vivo setting has not been tested so far. To assess the suitability of the dSTRIDE-HR assays for determining the HR status of patients’ tumor cells, we applied these assays in FFPE sections from biopsies derived from breast cancer patients with a different mutational status of BRCA1 and BRCA2 genes. The assays showed low dSTRIDE-RPA and dSTRIDE-RAD51 readouts in BRCA1/2 mutated tumors in comparison to wild type tumors, as well as a great concordance of readouts within a given genetic background. Additionally, the cell cycle analysis proved nearly twofold increase in foci numbers of dSTRIDE-RPA and dSTRIDE-RAD51 in G2/S phase. Our study unveils a potential of dSTRIDE-HR assays to become predictive biomarkers reporting on the status of HR repair in breast tumors, although more patient samples need to be tested to confirm initial findings. Citation Format: Monika Jarosz, Zsombor Prucsi, Franek Sierpowski, Karolina Stepien, Sophie Ostrowska-Paton, Szymon Koman, Nadeem Riaz, Simon Powell, Fresia Pareja, Edaise da Silva, Magdalena Kordon-Kiszala, Kamil Solarczyk. Novel dSTRIDE-HR assays can accurately assess DNA repair defects in human cancers and distinguish HR status of tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5170.