Epigenetic and oncogenic inhibitors cooperatively drive differentiation and kill KRAS-mutant colorectal cancers [LOVO sgTLE4]

Current treatments for KRAS-mutant colorectal cancers (CRCs) are often limited by cellular plasticity and rewiring responses. Here we describe a promising therapeutic strategy that simultaneously targets epigenetic and oncogenic signals. Specifically, we show that inhibitors of the histone methyltransferase, EZH2, synergize with various RAS pathway inhibitors and promote dramatic tumor regression in vivo. Together these agents cooperatively suppress WNT-driven transcription and drive CRCs into a more differentiated cell state by inducing the Groucho/TLE corepressor, TLE4, along with a network of WNT pathway inhibitors and intestinal differentiation proteins. However, these agents also induce the pro-apoptotic protein BMF, which subsequently kills these more differentiated cells. Accordingly, cell death can be prevented by activating ß-catenin, blocking differentiation, or by ablating BMF expression. Collectively, these studies reveal a new therapeutic approach for treating KRAS-mutant CRCs and illustrate a critical convergence of EZH2 and RAS on oncogenic WNT signals, intestinal differentiation, and apoptosis. Overall design: Colorectal cancer cell line, LOVO, were transduced with lentivirus to ectopically express an empty vector or a constitutively active form of B-catenin, and then treated with vehicle, tazemetostat (EZH2i), and/or trametinib (MEKi). Cells were pretreated with DMSO or EZH2i (tazemetostat at 5uM) for 5 days, and then seeded into 6cm plates of 300,000 to 350,000 cells per plate. The following day, cells were treated with DMSO, MEKi (50nM trametinib), with and without EZH2i. Cells were collected 16-24 hours after combined treatment before onset of cell death.