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Targeting Wnt Signaling To Overcome PARP Inhibitor Resistance

Epithelial ovarian cancer (EOC) has one of the highest deaths to incidence ratios. High grade serous ovarian carcinoma (HGSOC) is the most common and deadliest EOC histotype because of the lack of secondary therapeutic options following debulking surgery and platinum/taxane-based chemotherapies. For recurrent chemosensitive HGSOC, poly(ADP)-ribose polymerase inhibitors (PARPi; olaparib, rucaparib, or niraparib) represent an emerging treatment strategy. While PARPi are most effective in homologous recombination DNA repair-deficient (HRD) HGSOCs, more recent studies have observed a significant clinical benefit in non-HRD HGSOCs. However, all HGSOC patients are likely to acquire resistance to PARPi. Therefore, there is an urgent clinical need to better understand PARPi resistance, and to introduce novel combinatorial therapies to overcome PARPi resistance and extend HGSOC disease-free intervals. Utilizing a two BRCA2-mutated and one BRCA-wildtype HGSOC cell lines that are olaparib sensitive, we established resistant cells. Transcriptome analysis of the matched olaparib-sensitive versus resistant cells did not detect BRCA2 reversion mutations, but revealed activation of Wnt/TCF signaling pathway, as TCF transcriptional activity was significantly increased in PARPi-resistant cells. In parallel, forced activation of Wnt signaling in PARPi-sensitive cells via WNT3A stimulation reduced response to PARPi. In a recurrent-HGSOC PARPi insensitive patient-derived xenograft model there was an increase in a Wnt/TCF transcriptional target. PARPi resistant cells were sensitive to inhibition of Wnt signaling using the FDA-approved compound, pyrvinium pamoate, which has been shown to inhibit Wnt signaling. We observed that combining pyrvinium pamoate with olaparib resulted in a significant decrease in tumor burden and number of tumor nodules. This study demonstrates that Wnt signaling can mediate PARPi resistance in HGSOC and provides a clinical rationale for combining PARPi and Wnt inhibitors.