ID #569 Regional dynamics of tumor initiation in neural stem cells upon oncogenic germline mutations/tumor predisposition syndromes

Abstract

Tumor predisposition syndromes (TPS) contribute to more than 10% of pediatric brain tumors. TPS-associated brain tumors occur in multiple brain regions, with disease severity often linked to tumor location. Thus, one must consider the importance of the microenvironment in cancer initiation.

We hypothesize, that distinct microenvironments harbor different vulnerable time points/stem cell identities that undergo oncogenic transformation in a brain region-specific manner. Our experimental model is based on TPS patient-derived iPSCs and brain region-specific organoid cultures to model tumor development in vitro. Our highly reproducible hindbrain and forebrain organoid protocols efficiently induce regional patterning. We focus on the two ultra-rare and highly aggressive TPS termed Constitutional Mismatch Repair Deficiency (CMMRD) and Rhabdoid Tumor Predisposition Syndrome (RTPS) to not only understand critical time windows of oncogenic transformation and the region-derived cues contributing to tumor initiation, but also to dissect TPS-specific mechanisms affecting neural stem cell behavior during development.

Within 2 months of culture, we have identified tumor-like lesions in both, forebrain and hindbrain CMMRD-derived organoids. These organoids show a disruption of germinal zone morphology and development of tumor-like lesions, characterized by loss of the apical adherence junction belt, a differentiation block and the formation of hyperproliferative zones. In order to link region-specific physiological outcomes to the (epi)genetic and transcriptomic landscapes, we have performed TSO500 panel sequencing, methylation profiling with nanopore sequencing and snRNAseq. We have uncovered distinct signatures between control and TPS-derived organoids, additional pathological mutations and particular gene expression patterns correlating with oncogenic programs.

Our platform offers an unparalleled opportunity to establish a highly relevant translational model for affected patients. Overall, our research seeks to improve the diagnostic and therapeutic options for brain tumor patients by extracting novel biomarkers with predictive value for the clinics.