Evaluating carboplatin and PARP inhibitor combination efficacy using high-grade serous carcinoma spheroids and organoids.

PARP inhibitors (PARPis) are new targeted agents that exploit homologous recombination DNA repair deficiencies (HRDs), which are present in 50% of high-grade serous carcinoma (HGSC) cases. Currently, olaparib is approved as maintenance therapy for BRCA1/2-mutated HGSC, and niraparib is approved for platinum-sensitive recurrent disease. However, research is currently expanding their potential as front-line agents or in combination with carboplatin, a standard HGSC chemotherapeutic. Immortalized ovarian cancer (iOvCa) cell lines, developed from HGSC patient ascites, were treated with carboplatin, olaparib and niraparib to determine their sensitivity. Immunofluorescence analysis of RAD51 was conducted for HRD testing of all the cell lines. The cell lines were cultured as three-dimensional organoids and spheroids to mimic tumor growth and metastasis, respectively, and then treated to assess the effects of different drug combinations. The half-maximal inhibitory concentrations of olaparib and niraparib varied across our iOvCa cell lines, with iOvCa195 BRCA1-mutant line exhibiting the expected high sensitivity to both PARPis. Direct combination of carboplatin with olaparib or niraparib enhanced cell killing, yet achieved cell viability levels to those of carboplatin alone. In sequential experiments, carboplatin followed by either PARPi or vice versa showed no significant difference in cell viability to carboplatin alone, except in iOvCa195 organoids when treated with a PARPi first. Overall, first-line carboplatin treatment remains ideal, yet there may be select utility for PARPi prior to chemotherapy. Using patient-derived tumor models such as spheroids and organoids may provide insights for on-going and future clinical trials to enhance therapeutic outcomes for HGSC patients.