Functional effect of DOT1L pharmacological inhibition in ERa-positive Ovarian Cancer cells

Estrogen Receptor alpha (ERa), a nuclear receptor with transcriptional activity, is a master regulator of estrogen signaling, widely known as therapeutic target in hormone-responsive breast cancer (BC). Moreover, ERa is highly expressed in approximately 80% of High Grade Serous Ovarian Cancer (HGSOC), the most common epithelial ovarian carcinoma. Despite some promising clinical trials evaluating endocrine therapy in this type of tumor, the role of ERa is still unknown. Epigenetic changes, such as DNA methylation, are emerging as key contributing factors to carcinogenesis. Disruptor of telomeric silencing-1-like (DOT1L), the only known histone methyl transferase capable to produce H3K79 mono, di and tri-methylation, modulates ERa actions in hormone-responsive BC. Considering this evidence, ERa-DOT1L association was confirmed in ERa-positive OC cells, PEO1 and PEO4, by Co-IP. DOT1L pharmacological inhibition by EPZ004777 (EPZ) revealed the involvement of this epigenetic enzyme in cell proliferation, cell cycle progression and apoptosis. Transcriptome profiling after ICI (a Selective Estrogen Receptor Degrader) and EPZ treatment, in both cell lines, has underlined a deep impact of both compounds on ERa-modulated genes, including the down-regulation of ERa itself. On the other hand, functional analysis showed that commonly affected transcripts are involved in different cellular processes, such as cancer cell survival, chemoresistance and cell cycle progression. Moreover, ChIP-qPCR performed on ERa promoter highlighted ERa and DOT1L co-localization, both in PEO1 and in PEO4 cells, which was reduced after EPZ treatment, suggesting a role of this complex on receptor transcriptional activity. In addition, drug combination studies performed with EPZ and ICI showed an additive effect in cell growth inhibition. Taken together, these results suggest DOT1L as a potential therapeutic target in the treatment of OC.