Sonic hedgehog medulloblastoma cells in co-culture with cerebellar organoids converge towards in vivo malignant cell states.

Background: In the malignant brain tumor sonic hedgehog medulloblastoma (SHH-MB) the properties of cancer cells are influenced by their microenvironment, but the nature of those effects and the phenotypic consequences for the tumor are poorly understood. The aim of this study was to identify the phenotypic properties of SHH-MB cells that were driven by the nonmalignant tumor microenvironment. Methods: Human induced pluripotent cells (iPSC) were differentiated to cerebellar organoids to simulate the nonmaliganant tumor microenvironment. Tumor spheroids were generated from 2 distinct, long-established SHH-MB cell lines which were co-cultured with cerebellar organoids. We profiled the cellular transcriptomes of malignant and nonmalignant cells by performing droplet-based single-cell RNA sequencing (scRNA-seq). The transcriptional profiles of tumor cells in co-culture were compared with those of malignant cell monocultures and with public SHH-MB datasets of patient tumors and patient-derived orthotopic xenograft (PDX) mouse models. Results: SHH-MB cell lines in organoid co-culture adopted patient tumor-associated phenotypes and showed increased heterogeneity compared to monocultures. Subpopulations of co-cultured SHH-MB cells activated a key marker of differentiating granule cells, Conclusions: For SHH-MB cell lines in co-culture, there was a convergence of malignant cell states towards patterns of heterogeneity in patient tumors and PDX models implying these states were non-cell autonomously induced by the microenvironment. Therefore, we have generated an advanced, novel in vitro model of SHH-MB with potential translational applications.