Automated Scoring to Assess RAD51-Mediated Homologous Recombination in Ovarian Patient-Derived Tumor Organoids

Poly(ADP-ribose) polymerase inhibitors (PARPi) have been shown to improve progression-free survival, particularly in homologous recombination-deficient ovarian cancers. Identifying patients eligible for PARPi is currently based on next-generation sequencing, but the persistence of genomic scars in tumors after restoration of homologous recombination (HR) or epigenetic changes can be a limitation. Functional assays could thus be used to improve this profiling and faithfully identify homologous recombination-deficient tumors. The repair capacity (RECAP) test assesses the formation of RAD51 foci in proliferating cells after irradiation and can be used on tumors as well as on patient-derived tumor organoids (PDTO). However, RAD51 foci scoring is often performed manually without standardization. The purpose of this translational study was to develop an automated tool for scoring RAD51-mediated HR based on whole slide imaging of ovarian PDTO. To that end, we quantified Cyclin A2 and RAD51 immunofluorescence on 9 PDTO models derived from 8 ovarian cancer patients, and next, we compared the RECAP test results to genome instability score and to the patient clinical response. We therefore developed a standardized and automatized quantitative histoimaging tool allowing a comparative RAD51 foci evaluation and thus to define the HR status in PDTO. Our RECAP-based classification was correlated to the genome instability score, offering a new opportunity for standardization of HR assessment in PDTO. This new automated tool to score HR status, which remains to be validated on a large cohort of patients, may thus be used as a complement to next-generation sequencing-based tests in order to improve the identification of the number of patients eligible for PARPi.