TBIO-16. NOTCH1 PATHWAY AS TARGET FOR DRUG INTERVENTION FOR HISTONE 3 G34R MUTATED pHGG

There have been no significant improvements in the treatments for childhood High-Grade Glioma (pHGG) and Diffuse Intrinsic Pontine Glioblastoma (DIPG), which continue to have a very poor prognosis. These cancers harbor mutations affecting histone 3 (H3) proteins; 80% of DIPGs with histone H3 K27M somatic mutations whilst 30% of pHGGs exhibit H3.3 G34R or G34V mutations. We have generated and validated a histone 3.3 G34R mutant-specific antibody and investigated the downstream effects of H3.3 G34R mutations in pHGG. In order to identify the genes that may be deregulated by G34R mutant histone expression, we have performed chromatin immunoprecipitation (ChIP) assays with our H3.3 G34R and wild type H3 antibodies, using pHGG H3 G34R mutant and wild-type cell lines. Initial analyses of ChIP data have implicated deregulation of cell-signaling pathways including Notch1, Hedgehog, PPAR-1, PLC-beta and Androgen, in H3 G34R mutated pHGG. We are currently determining the effects of altered expression of Notch1 pathway components on tumorigenesis of H3 G34R mutated pHGG, through gene and protein expression and inhibition assays. Specifically we find that the Notch1 pathway component HES1 shows increased expression in G34R mutant cells compared to controls, directing our evaluation of the utility of gamma-secretase inhibitors as potential therapeutics. These analyses may underpin development of novel treatment strategies for H3 mutated pHGG.