270 Inducing Neural Maturation and Increasing Survival in SHH Medulloblastoma Using EZH2 Inhibition in a Mouse Model

INTRODUCTION: Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Genetically, MB can be divided into four subgroups of which the SHH subtype histologically shows nodular architecture. Within this nodular architecture, there are islands of mature cells, with more abundant neuropil and a low proliferation rate, scattered among sheets of primitive cells. METHODS: We performed laser capture microdissection followed by whole transcriptome analysis, spatial transcriptomics using Digital Spatial Profiling, whole genome DNA methylation and ChIP-Seq analysis of mature and primitive areas from 8 medulloblastomas. We developed a genetically-engineered mouse model of SHH MB showing spontaneous maturation and lack of maturation with a conditional EZH2 genetic ablation or EZH2 overactivation respectively. Finally, we developed a fucoidan-based nanoparticle drug delivery across the blood brain barrier (BBB) for targeted molecular inhibition. RESULTS: Using whole transcriptome and DNA methylation analysis, we identified ∼120 differentially expressed genes between primitive and mature regions with enrichment for genes regulated by H3K4me3 and H3K27me3. ChIP-Seq analysis showed striking differences in H3K27me3 enrichment between primitive and mature medulloblastoma cells including at the EZH2 locus. Medulloblastoma specific EZH2 genetic ablation resulted in diffuse tumor cell differentiation and prolonged survival in mice (n = 10 per group, log-rank p = 0.01). Conversely, conditional EZH2 (Y641F) activation prevented medulloblastoma differentiation. A fucoidan-based nanoparticle successfully delivered the EZH2 inhibitor (EPZ-6438) across the murine BBB to achieve significant extension of mouse survival (median 70 days compared to 21 days in control mice; *p = 0.01, Mantel-Cox). CONCLUSIONS: Spontaneous maturation of medulloblastoma cells can be induced by inhibition of EZH2. Fucoidan-based nanoparticle delivery systems allows tumor specific targeted delivery across the BBB extending survival in mice.