Targeting Ovarian Cancer Stem Cells by Dual Inhibition of HOTAIR and DNA Methylation

Abstract

Ovarian cancer is a chemoresponsive tumor with very high initial response rates to standard therapy consisting of platinum/paclitaxel. However, most women eventually develop recurrence, which rapidly evolves into chemo-resistant disease. Persistence of ovarian cancer stem cells (OCSC) at the end of therapy has been shown to contribute to resistant tumors. In this study, we demonstrate that the long non-coding RNA HOTAIR is overexpressed in HGSOC cell lines. Furthermore, HOTAIR expression was upregulated in OCSC compared to non-CSC, ectopic overexpression of HOTAIR enriched the ALDH+ cell population and HOTAIR overexpression increased spheroid formation and colony forming ability. Targeting HOTAIR using peptide nucleic acid-PNA3®, which acts by disrupting the interaction between HOTAIR and EZH2, in combination with a DNMT inhibitor inhibited OCSC spheroid formation and decreased the percentage of ALDH+ cells. Disrupting HOTAIR-EZH2 with PNA3® in combination with the DNMTi on the ability of OCSC to initiate tumors in vivo as xenografts was examined. HGSOC OVCAR3 cells were treated with PNA3® in vitro and then implanted in nude mice. Tumor growth, initiation and stem cell frequency were inhibited. Collectively, these results demonstrate that blocking HOTAIR-EZH2 interaction combined with inhibiting DNA methylation is a potential approach to eradicate OCSCs and block disease recurrence.