Abstract A54: Generation and characterization of a novel panel of platinum-resistant HGSOC models

Background: High-grade serous ovarian cancer (HGSOC) is the most common ovarian cancer subtype. Although it is initially responsive to platinum-containing chemotherapy, the emergence of chemoresistant cells is inevitable. Most women with HGSOC die of platinum-resistant cancer, and the five-year survival for ovarian cancer has changed little in recent decades. There is therefore a need to develop chemotherapy-resistant preclinical models to discover novel therapies for women with these resistant cancers. Methods: Established chemo-sensitive HGSOC cell lines Ovcar4, COV318 and OVSAHO were passaged in vitro with increasing doses of either cisplatin or carboplatin. Doses of carboplatin and cisplatin were incremented by 0.1μM when cells reached confluence. Resistance was assessed by clonogenic assay. To reflect the extent of chemoresistance commonly found in patient tumor samples, dose escalation was stopped once a 5-10 fold difference in IC50 was achieved in resistant compared to sensitive parental cells. Cells were then grown in parallel in the presence or absence of chemotherapy drug to determine whether resistance was maintained. Resistant cell lines were characterized based on molecular markers, cell growth, migration, and spheroid formation. Cells were lentivirally transfected with fluorescent proteins and Firefly luciferase. Intraperitoneal tumor growth was assessed in female CD1 nude mice. Survival was compared and tumors were sectioned and analyzed using H&E staining and IHC for p53, PAX8, and Ki67 expression. Results: All six platinum-resistant cell lines achieved a 5-10 fold increase in resistance based on IC50 values. Maintenance of resistance when drug was withdrawn varied between different cell lines. In vitro proliferation, migration, and spheroid formation varied between matched sensitive and resistant cells. The carboplatin-resistant cells, Ov4Carbo and OVSAHOCarbo, proliferated more rapidly compared to the parental cells from which they were derived (Ovcar4 and OVSAHO) and compared to their cisplatin-resistant counterparts (Ov4Cis and OVSAHOCis). Carboplatin-resistant Ovcar4 cells (Ov4Carbo) also formed spheroids more effectively and displayed greater in vitro migration than Ovcar4 and Ov4Cis. We have tested Ovcar4, Ov4Carbo, and Ov4Cis in vivo and found that all formed tumors in the peritoneum of nude mice. Sequential bioluminescent readings correlated with survival. In keeping with our in vitro findings, these three cells lines exhibited dif