Epigenetic reprogramming towards mesenchymal-epithelial transition in ovarian cancer-associated mesenchymal stem cells drives metastasis

Ovarian cancer develops early intra-peritoneal metastasis establishing a supportive tumor microenvironment (TME) through reprogramming normal mesenchymal stem cells into carcinoma-associated mesenchymal stem cells (CA-MSCs). CA-MSCs are the stromal stem cell of the TME, supporting cancer growth, increasing desmoplasia, angiogenesis and chemotherapy resistance. We demonstrate epigenetic reprogramming drives CA-MSC formation via enhancer-enriched DNA hypermethylation, altered chromatin accessibility and differential histone modifications inducing a partial mesenchymal to epithelial transition (MET) increasing adhesion to tumor cells. Direct CA-MSC:tumor cell interactions, confirmed in patient ascites, facilitate ovarian cancer metastasis through co-migration. WT1, a developmental mediator of MET, and EZH2, mediate CA-MSC epigenetic reprogramming. WT1 overexpression induces CA-MSC conversion while WT1 knock-down, along with EZH2 inhibition, blocks CA-MSC formation. EZH2 inhibition subsequently decreases intra-abdominal metastasis. SignificanceThis work presents a new paradigm of stromal reprogramming involving a partial mesenchymal to epithelial transition. Rather than a classic tumor cell epithelial to mesenchymal transition, metastasis relies on epigenetic rewiring of a CA-MSC allowing enhanced tumor cell binding and co-migration with tumor cells to form metastasis. Indeed, CA-MSCs in complex with tumor cells are abundant in patient ascites. Reversion of CA-MSCs to normal MSCs is observed in patients achieving complete response with neoadjuvant therapy. Identification of WT1 and EZH2 as mediators of the epigenetic reprogramming of CA-MSCs present potential targets to block the formation of CA-MSCs thus disrupting the TME and limiting ovarian cancer metastasis.