DIPG-28. IDENTIFICATION AND TARGETING OF METABOLIC VULNERABILITIES IN COMBINATION WITH PDGFRA-INHIBITION IN DIFFUSE MIDLINE GLIOMA

Diffuse midline gliomas (DMG) are driven by self-renewing, stem-like glioma cells stalled in an oligodendrocyte precursor cell (OPC)-like state that are characterized by high expression of PDGFRA. This lineage overexpression of PDGFRA, together with commonly found genomic amplifications and mutations in PDGFRA, has been shown to cooperate with H3-K27M mutations in tumor development. Therefore, targeting PDGFRA has long been proposed as a potential treatment strategy for DMG. Our previous work revealed that Avapritinib, a small molecule inhibitor of PDGFRA, is highly effective in DMG cells in vitro and in vivo. Following these preclinical findings, nine DMG patients were treated with Avapritinib for the first time. While 50% of all treated patients experienced a strong clinical response from Avapritinib, tumor progression and treatment escape were eventually observed in most patients. Here, we investigated which mechanisms DMG cells use to escape Avapritinib treatment and explored how these resistance mechanisms can be therapeutically exploited. Transcriptional analysis of a DMG cell line previously identified as Avapritinib-resistant revealed an upregulation of genes associated with fatty acid metabolism and oxidative phosphorylation (OXPHOS) following treatment with Avapritinib. Functional assays confirmed elevated OXPHOS in Avapritinib-resistant cells with significant (i) increase in mitochondrial energy transduction, (ii) increase in palmitate- (a product of fatty acid metabolism) driven oxygen consumption rate and (iii) greater incorporation of palmitate-derived carbons into the tricarboxylic acid cycle. These metabolic changes could be genetically reproduced in the same cell line after CRISPR-Cas9-mediated knockout of PDGFRA. To determine which therapies could target the dependency of Avapritinib-resistant cells on OXPHOS and fatty acid metabolism, we performed a metabolic drug screening and identified two metabolic drugs to have synergistic cytotoxic effects with Avapritinib. Together, we revealed distinct metabolic changes in Avapritinib-resistant DMG cells and showed that targeting these metabolic vulnerabilities might further increase the clinical benefit of Avapritinib.