Exposure to escalating olaparib does not induce acquired resistance to PARPi and to other chemotherapeutic compounds in ovarian cancer cell lines

Abstract

Poly (ADP-ribose) polymerase (PARP)-inhibitors (PARPi) such as olaparib and niraparib are currently used as a treatment option for BRCA -deficient tumors and also show efficacy in platinum-sensitive tumors. However, resistance to PARPi occurs in numerous patients and in particular acquired PARPi resistance presents a major obstacle in the treatment of these tumors. In the present study, it was investigated whether stepwise exposure of ovarian cancer cells to escalating concentrations of olaparib produced subcells with acquired resistance to PARPi and/or acquired cross-resistance to platinum compounds, paclitaxel, and doxorubicin. To this aim, the sensitivity of fourteen ovarian cancer cell lines, including nine with TP53 -mutations and five carrying BRCA -mutations, to olaparib and niraparib was determined and a subset of seven cell lines was selected to investigate the potential of olaparib to produce resistance. It was identified that escalating olaparib did neither produce subcells with acquired PARPi-resistance nor did it produce acquired cross-resistance to platinum compounds, doxorubicin, and paclitaxel. This finding was independent of the cells' TP53 and BRCA mutation status. CRISPR- Cas9 mediated deletion of PARP1 did not affect sensitivity to PARPi, platinum compounds, doxorubicin, and paclitaxel. In addition, olaparib sensitivity correlated with niraparib sensitivity, but BRCA -mutated cells were not more sensitive to PARPi. Moreover, PARPi sensitivity associated with cross-sensitivity not only to platinum compounds but also to anthracylines, paclitaxel, and inhibitors of histone deacetylases. These in vitro data indicated that olaparib exposure is unlikely to produce an acquired resistance phenotype and that PARPi-sensitive ovarian cancer cells are also cross-sensitive to non-platinum and even to compounds not directly interacting with the DNA.

Establishment and Molecular Characterization of an In Vitro Model for PARPi-Resistant Ovarian Cancer

“…Our model is principally in line with previous studies in experimental models of ovarian cancer, reporting on the emergence of an acquired phenotype of PARPi resistance after long-term PARPi exposure [17,[19][20][21]. Still, one previous study reported that olaparib exposure is unlikely to produce an acquired resistance phenotype [22]. This could be due to a completely different schedule of olaparib exposure in this study, with several cycles of 48 h treatment followed by drug-free recovery after each cycle.…”

“…Therefore, critical assessment is highly important when comparing and interpreting results of these models. While in the majority of reports, PARPi-resistant cells have successfully been established by long-term PARPi exposure, one study reported that olaparib exposure is unlikely to produce an acquired resistance phenotype [22], indicating that in vitro models of PARPi resistance are neither interchangeable nor generalizable.…”

Overlapping gene dependencies for PARP inhibitors and carboplatin response identified by functional CRISPR-Cas9 screening in ovarian cancer

“…Delivery of drugs at passage 1 was performed with different PARPi (olaparib, niraparib and talazoparib) and carboplatin using a concentration causing approximately 10% growth inhibition (IC 10 ) [ 36 ] for additional five passages. Dropout values represent the fold-change of the percentage of EGFP + or mOrange + cells at each passage, relative to passage 0 (3 days after transduction) and was used as a readout of effects on cell fitness or drug sensitivity conferred by the CRISPR- Cas9 mediated gene mutations.…”