Loss of Kmt2c/d promotes gastric cancer and confers vulnerability to mTORC1 and PD1 inhibition

Based on the observation that loss-of-function mutations of KMT2C and KMT2D (KMT2C/D) are enriched and co-occur in gastric adenocarcinoma, we developed genetically engineered mouse model (GEMM) to conditionally knock out Kmt2c and Kmt2d in gastric epithelial cells. We observed that Kmt2c/d loss led to nuclear dysplasia, cellular crowding, and expansion of cells with mixed gastric lineage markers. When combined with Pten deletion, Kmt2c/d loss drove rapid development of muscle-invasive gastric adenocarcinoma as early as 3 weeks post Cre-mediated gene deletion. The adenocarcinoma exhibited decreased expression of gastric lineage markers and increased expression of intestinal differentiation markers, phenocopying human intestinal type gastric adenocarcinoma. Bioinformatic integration of single cell RNA-seq of our GEMMs and human gastric cancer datasets shows co-clustering of normal and of cancerous gastric epithelial cells. Kmt2c/d knockout in gastric epithelium reduced protein synthesis but upregulated transcription of ribosomal proteins, rendering the cells to be hypersensitive to mTORC1 inhibitors. Additionally, Kmt2c/d knockout increased MHC-I molecule expression and enhanced antigen presentation. Combination of mTORC1 inhibition and anti-PD1 immunotherapy markedly suppressed tumor growth in immune-competent mice. Together, these findings reveal the role of Kmt2c/d loss in gastric cancer initiation and suggest the potential therapeutic strategies for KMT2C/D-deficient gastric cancer.