Background

In the malignant brain tumour 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 tumour are poorly understood. The aim of this study was to identify phenotypic properties of SHH-MB cells that were driven by the non-malignant tumour microenvironment.

Methods

Human induced pluripotent cells (iPSC) were differentiated to cerebellar organoids to simulate the non-malignant tumour microenvironment. Tumour spheroids were generated from two distinct, long-established SHH-MB cell lines which were co-cultured with cerebellar organoids. We profiled the cellular transcriptomes of malignant and non-malignant cells by performing droplet-based single-cell RNA-sequencing (scRNA-seq). The transcriptional profiles of tumour cells in co-culture were compared with those of malignant cells cultured in isolation and with public SHH-MB datasets of patient tumours and patient-derived xenograft (PDX) models.

Results

SHH-MB cell lines in organoid co-culture adopted patient tumour-associated phenotypes and showed increased heterogeneity compared to monocultures. Sub-populations of co-cultured SHH-MB cells activated a key marker of differentiating granule cells, NEUROD1 that was not observed in tumour monocultures. Other sub-populations expressed transcriptional determinants consistent with a cancer stem cell (CSC)-like state that resembled cell states identified in vivo .

Conclusion

For SHH-MB cell lines in co-culture, there was a convergence of malignant cell states towards patterns of heterogeneity in patient tumours 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.