Abstract 2580: Targeting chromatin in ovarian cancer stem cells

Abstract

Abstract The dynamic organization of chromatin, governed by epigenetic modifiers, critically regulates cell plasticity and determines cell fate in both normal and malignant stem cells. We hypothesized that chromatin architecture plays a role in regulating transcriptional heterogeneity in ovarian cancer stem cells (OCSCs) to maintain stemness and chemoresistance. PWS microscopy showed that ALDH+ OCSCs derived displayed higher nuclear fractal dimension D signals (P<0.05) than ALDH- non-OCSCs, indicating that chromatin in OCSCs possesses higher packing compared to non-OCSCs. Cut & TAG Sequencing showed that of the 3606-histone repressive H3K27m3 enriched regions (P<0.05, fold change >2), 3208 were detected in OCSCs while 398 peaks were present in non-OCSCs, consistent with findings supporting high D features in OCSCs. The active mark H3K4me3 was enriched at the promoter of stemness-associated genes, including SOX2, ALDH1A3, and FZD7 in OCSCs; and the repressive histone mark H3K27me3 was enriched at the promoter of the epithelial cell marker CDH1 in OCSCs. These results support that the chromatin of OCSCs contains open genomic regions, corresponding to stemness-associated genes and repressed regions associated with genes related to differentiation. RNA sequencing indicated that the coefficient of variance (COV) reflecting transcriptional heterogeneity in OCSCs was higher than in non-OCSCs at baseline. In response to platinum, genes with low baseline expression in OCSCs were most upregulated, supporting increased transcriptional heterogeneity in response to chemotherapy. Inhibitors of epigenetic modifiers (DNMTi, EZH2i, and Dot1Li) induced chromatin re-organization in OCSCs and promoted OCSCs transition toward differentiation, supporting that stemness-associated chromatin structure is targetable. We demonstrated that a Dot1L inhibitor (Dot1Li) targeted OCSCs by decreasing chromatin packing D, resulting in decreased transcriptional heterogeneity. In conclusion, OCSCs harbor highly packed chromatin, contributing to chemoresistance and cell plasticity. Epigenetic modifiers (such as Dot1Li) inhibit stemness by regulating chromatin organization and transcriptional malleability. Citation Format: Yinu Wang, Jane Frederick, Yaqi Zhang, Elizabeth Thomas Bartom, Greta Bauer, Edward Tanner, Vadim Backman, Daniela Matei. Targeting chromatin in ovarian cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2580.