DMG-38. Effective targeting of EGFR-driven diffuse midline glioma with X117195, a novel brain-penetrant EGFR-targeting tyrosine kinase inhibitor (TKI)

Diffuse midline gliomas (DMGs) are lethal pediatric high-grade brain tumors with a prognosis of less than two years from diagnosis. A subgroup of DMGs harbor alterations in epidermal growth factor receptor (EGFR), including wildtype amplification (WT) and mutations in the extracellular domain (exon 7, e.g. A289T) or kinase domain (exon 20, e.g. 767delins). EGFR-targeting TKIs have shown limited efficacy against brain tumors but have not been developed to address the unique biology and EGFR alterations specific to H3K27M-DMG. Further, EGFR alterations are being validated as a biomarker of resistance to ONC201 suggesting that targeting EGFR may have broad utility for H3K27M-DMG. To this end, we established multiple human and murine models of H3K27M-DMG tumor cells with isogenic EGFR alterations (WT/A289T/767delins) and systematically evaluated the efficacy of the novel TKI X117195 (Blueprint Medicines). X117195 was uniquely effective in nanomolar concentrations against H3K27M-DMG cells that express these EGFR alterations. Notably, the IC50 value of < 0.2 µM against 767delins distinguished X117195. In cell-free kinase inhibition assays X117195 reduced EGFR WT and T790M activity by 50% at ∼1 nM. We applied high-throughput kinase-activity mapping (HT-KAM) to detect the catalytic activity of > 900 kinase-substrate nodes in EGFR-driven H3K27M-DMG cells. X117195 induced significant modulation of key oncogenic pathways in EGFR-767delins cells, including decreased MAPK family activity. In vivo testing demonstrated that daily 50 mg/kg X117195 treatment resulted in tumor eradication of isogenic EGFR-mutant (A289T/767delins) human H3K27M-DMG flank xenograft models within four weeks without any signs of toxicity. Immunohistochemical analysis showed that X117195 treatment decreased pERK and increased H3K27me3 in flank tumors. Pharmacokinetic analysis of 50 mg/kg X117195 resulted in peak brain concentrations of ∼2 µM. Further assessment of the efficacy of X117195 against intracranial H3K27M-DMG is ongoing. Collectively, these preclinical studies highlight the potential of X117195 as a novel, targeted TKI therapeutic for EGFR-driven H3K27M-DMGs.