Automated scoring to assess RAD51-mediated homologous recombination in ovarian patient-derived tumor organoids.

Abstract

PARP inhibitors (PARPi) have been shown to improve progression-free survival, particularly in homologous recombination deficient (HRD) ovarian cancers. Identifying patients eligible to PARPi is currently based on next-generation sequencing (NGS), but the persistence of genomic scars in tumors after restoration of HR or epigenetic changes can be a limitation. Functional assays could thus be used to improve this profiling and faithfully identify HRD tumors. The 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 compared RECAP test results to genome instability score (GIScar) and to the patient clinical response. We therefore developed a standardized and automatized quantitative histo-imaging tool allowing a comparative RAD51 foci evaluation and thus to define the HR status in PDTO. Our RECAP-based classification was correlated to the GIScar score, offering a new opportunity for standardization of HR assessment in PDTO. This new automated tool to score HR status, that remains to be validated on a large cohort of patients, may thus be used as a complement to NGS-based tests in order to improve the identification of the number of patients eligible to PARPi.