DNA Methyltransferase Inhibition Prevents Platinum-Induced Ovarian Cancer Stem Cell Enrichment

Platinum-based therapy is the standard first-line treatment for high-grade serous ovarian cancer (HGSC). However, most patients develop resistance and recurrence despite an initial response to therapy. Ovarian cancer stem cells (OCSC) are enriched in recurrent tumors and contribute to platinum resistance. These tumors also show promoter DNA hypermethylation, and DNA methyltransferase inhibitors (DNMTi) have been shown to restore sensitivity in platinum-resistant ovarian cancer cells. In this study, we demonstrated that combining DNMTi treamtent with platinum prevented the platinum-induced enrichment of OCSCs and identified nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription 3 (STAT3) signaling pathways as potential regulators of platinum-induced OCSC enrichment. STAT3 was active at baseline in ovarian cancer cells, and platinum treatment alone activated NF-κB while maintaining STAT3 activity. Platinum combined with DNMTi treatment decreased STAT3 activation, while still inducing NF-κB activation. Knockdown experiments demonstrated that the presence of both NF-κB and STAT3 was necessary for platinum-induced OCSC enrichment. Analysis of STAT3 and NF-κB subunit p65 CUT&RUN data showed increased binding in introns and intergenic regions in response to platinum. Additionally, DNMTi treatment enriched NF-κB binding at endogenous retroviruses, which correlated with changes in expression of nearby genes when DNMTi treatment was combined with platinum. We conclude that combining DNMTis with platinum modulates STAT3 and NF-κB activation and genomic binding, potentially influencing target gene expression and preventing platinum-induced enrichment of OCSCs.

OCSCs promote relapse and chemoresistance in HGSC. We show that combining standard platinum-based therapy with DNMTi treatment prevents platinum-induced enrichment of OCSCs. Our findings support the use of DNMTis in combination with platinum as a strategy to reduce OCSC enrichment and platinum resistance in ovarian cancer.