PATH-89. The single cell landscape of NF1-associated gliomas pre- and post-treatment and comparison to their sporadic counterparts

BACKGROUND Gliomas arising in the setting of neurofibromatosis type 1 (NF1) are heterogeneous, occurring from childhood through adulthood, can be either histologically low-grade or high-grade, and follow an indolent or aggressive clinical course. Our prior studies showed that NF1-associated gliomas predominantly segregate into three molecular types: pilocytic astrocytoma (PA), high-grade astrocytoma with piloid features (HGAP), and IDH-wildtype glioblastoma (GBM). The cellular composition and gene expression signatures that define these syndromic gliomas and distinguish them from their sporadic counterparts has yet to be elucidated. METHODS We performed single nucleus RNA-sequencing on 12 gliomas arising in the setting of NF1 belonging to the different molecular subtypes and occurring at different anatomic sites, as well as paired initial pre-treatment and recurrent post-treatment tumor samples. These syndromic gliomas were also compared to a cohort of matched sporadic counterparts. RESULTS Transcriptomic signatures were overall highly similar for NF1-associated pilocytic astrocytomas arising in the optic pathway, cerebral hemispheres, and cerebellum, indicating a similar cell of origin and cellular state of these gliomas despite the different anatomic sites. In contrast, NF1-associated high-grade glioma cells including both HGAP and GBM had many recurrent differentially expressed genes/pathways compared to NF1-associated pilocytic astrocytomas, including significantly higher expression levels of the G-protein signaling regulator RGS6. Compared to their paired initial pre-treatment tumors, recurrent post-treatment NF1-associated high-grade glioma cells had upregulation of many neurogenesis and synaptogenesis genes and downregulation of glial differentiation genes (e.g. GFAP, ANK2), suggesting potential mechanisms underlying treatment resistance. CONCLUSION Our study defines the single cell transcriptomic landscape of NF1-associated gliomas, identifies the unique cellular composition of these syndromic tumors in comparison to their sporadic counterparts, and provides mechanistic insight into therapeutic resistance pathways in NF1-associated high-grade gliomas.