Stroma-oriented tumor microenvironment facilitates intraosseous ameloblastoma tumor growth.

Ameloblastoma (AM) is a locally aggressive odontogenic epithelial tumor with poorly understood intraosseous pathogenesis. Here, we established an orthotopic intraosseous mouse model using AM epithelial cells in combination with AM-derived mesenchymal stromal cells (AMMSCs) or their secretome. AMMSC-derived extracellular vesicle-enriched secretome enhances stemness, epithelial-mesenchymal transition (EMT) phenotypes, and tumorigenic ability of AM epithelial cells. A unique signature of microRNAs in AMMSC-derived secretome is functionally associated with the upregulation of EMT-regulatory transcription factors in tumor epithelial cells. Single-nucleus assay for transposase-accessible chromatin (ATAC) and RNA sequencing revealed dynamic EMT states in primary human AM-derived epithelial cells treated with paired AMMSC-derived secretome. This study suggests that AMMSCs and their secretome drive orthotopic AM tumor development by promoting tumor epithelial cell proliferation, EMT, and vascular formation in the tumor microenvironment. This stromal-oriented orthotopic model provides a clinically relevant platform for dissecting tumor-stroma crosstalk and identifying therapeutic vulnerabilities in AM.