Bsld-02 elucidating leptomeningeal microenvironment cues that promote metastasis and chemotherapy resistance in high-risk medulloblastoma

Abstract Medulloblastoma is a molecularly heterogenous brain tumor of the cerebellum and is a leading cause of pediatric cancer mortality due to its propensity for leptomeningeal metastasis. Leptomeningeal metastasis occurs in over 20-30% of patients despite age- and risk- adapted chemoradiation therapy. The mechanisms responsible for medulloblastoma metastasis and therapy resistance remain incompletely understood. The leptomeninges represent a fundamentally distinct microenvironment from the primary cerebellar tumor. We hypothesized that unique signaling inputs from the cellular and extracellular milieu of the leptomeninges drive distinct medulloblastoma biology that leads to resistance to current standard of care therapy. We tested this hypothesis using Group 3-MYC amplified (Grp3-MA) cell lines given their high metastatic potential. Primary tumors grow within a glycosaminoglycan (hyaluronan) rich matrix while leptomeningeal metastases grow in a laminar fashion attached to leptomeningeal (pial) cells that were enriched for laminins, collagens, and fibronectin. Analogously, Grp3-MA cells grow in suspension at steady state, but subpopulations readily adhere to a leptomeningeal membrane mimetic in vitro. This attachment required integrin beta 1 (ITGB1) and promoted chemotherapy resistance. We additionally have created a novel co-culture model wherein medulloblastoma cells grow as adherent clusters on a layer of primary leptomeningeal cells in an ITGB1 dependent manner. We are using this co-culture platform to perform single cell RNA sequencing and ligand receptor analysis to understand how cell-cell communication between leptomeningeal cells and medulloblastoma cells promotes tumor cell growth. Collectively, our studies demonstrate that cues from the leptomeningeal microenvironment alter medulloblastoma cell behavior and are attractive targets for developing novel therapies against metastasis.