Comparative selection strategies for development of platinum-drug resistant ovarian cancer cell lines

Abstract

The development of a drug-resistant cell line in vitro can take from 3 to 18 months. However, little is published on the methodology of this development process. Clinically relevant drug-resistant cell lines are developed by mimicking the conditions cancer patients experience during chemotherapy Doses of drug administered are low, and a pulsed treatment strategy is often used where the cells recover in drug-free media. It is common to have difficulty developing stable clinically relevant drug-resistant cell lines. A comparative selection strategy of multiple cell lines or multiple chemotherapeutic agents mitigates this risk and gives insight into which agents or which clinical phenotypes develops resistance easily. Cell models were chosen to represent different phenotypes of clinical ovarian cancer BRCA1/2 Wildtype (UPN-251, CAOV3), BRCA Mutated (UWB1.289) and BRCA1 Methylated (OVCAR8). Pulsed selection with drug was used to develop resistance to carboplatin and taxol as these drugs are delivered by an I.V bolus. A continuous selection strategy was used to develop resistance to parp inhibitors olaparib and talazoparib as patients take these drugs orally every day. Continuous treatment with parp inhibitors led to stably drug resistant models in all cell lines treated (CAOV3, UWB1.289 and OVCAR8). Resistance to carboplatin was detected in the daughter sublines after 1 - 3 rounds of drug treatment, which was continued to complete 7– 8 rounds, equating to 5-6 months of drug treatment. Alternating the treatment of carboplatin and taxol slowed the development of stable drug resistance compared to treating with single agent (UPN-251 and OVCAR8). The BRCA1 methylated cell line (OVCAR8) was harder to develop into a carboplatin resistant cell line than the other models. In one strategy OVCAR8 models were abandoned as unstably resistant after 7 treatment cycles over 6 months. In a new treatment strategy OVCAR8 developed carboplatin resistance after an extended treatment period 13 cycles over 11 months. BRCA1 methylated patients may therefore benefit from treatment with carboplatin in part due to the slower onset of carboplatin resistance