Development of a functional assay to test for homologous recombination in ovarian cancer

Background: PARP inhibitors selectively target homologous recombination (HR) defective cells and show good clinical activity in hereditary breast and ovarian cancer associated with BRCAl12 mutations. A high proportion (up to 50%) of sporadic epithelial ovarian cancers (EOC) could be deficient in HR due to genetic or epigenetic inactivation of BR CA 112 or other HR genes. Therefore there is a potential for extending the use of P ARP inhibitors to these patients if HR status can be identified. Aims: To develop a functional assay of HR status that correlates with sensitivity to the PARP inhibitor AG014699. Methods: Primary cultures were derived from ascitic fluid from patients with EOCs. HR status was investigated by yH2AX and RAD51 focus formation by immunofluorescence. Cytotoxicity to the PARP inhibitor AG014699 was tested by SRB and cell survival assay. Clinical outcome and platinum sensitivity was correlated prospectively with predicted HR status. Results: The success rate of generating primary cultures (n=75) was> 90%. 48 EOCs were evaluated for HR status and cytotoxicity; HR deficiency (HRD) was predicted in 25/48(52%) cultures showing no increase in RAD51 foci. Cytotoxicity was observed in 23/25 HR deficient (PPV-93%) but none of 23 HR competent (NPV-I00%) cultures. 35 patients completed clinical follow up; compared to HR competent patients (n=18), the HR deficient group (n=17) were predominantly serous (p=0.041), sensitive to platinum (58.8% vs. 29.4%) with lower tumour progression rates at 6 months (5.9% vs. 27.8%) and lower death rates at 12 months (17.6% vs. 44.4%). Conclusion: HR status can be determined in primary cancer samples by RAD51 focus formation. 50% EOCs appear to have HR defects. HRD as predicted by the RAD51 assay correlates with ex vivo PARP inhibitor sensitivity, clinical platinum sensitivity and improved survival outcome.EThOS - Electronic Theses Online ServiceGBUnited Kingdo