Figure 7.

PIK3R1 mutations predict sensitivity in pediatric HGG and DMG samples to MEK inhibition. A, Trametinib AUC (left) and log₂[IC₅₀] (right) values for noncancerous brain samples versus pediatric HGG and DMG samples without bona fide alterations in RAS–MAPK signaling. Horizontal lines represent median values. B, GSEA of MSigDB GO:BP gene sets on the genes positively correlated with trametinib sensitivity (NES < 0). Dot size indicates NES and dots above the dotted line (FDR q value > 0.01) are not significant. Biological processes associated with RAS–MAPK and PI3K signaling are highlighted in red and orange, respectively. C, Activation status of RAS–MAPK and PI3K signaling pathways in trametinib-sensitive DMG samples zcc372 and zcc135 harboring a PIK3R1 mutation. DMG sample zcc135 harbors an additional activating mutation in PIK3CA and both DMG samples zcc372 and zcc135 harbor gain of AKT3. RAS–MAPK and PI3K pathway activation was established after 40-minute treatment with DMSO (= baseline levels) or 50 nmol/L trametinib by Western blot analysis of phosphorylated and total levels of ERK1/2 and AKT and S6K, respectively. Trametinib-sensitive DMG sample zcc116 harboring a BRAF V600E mutation and trametinib-insensitive DMG sample zcc92 without bona fide alterations in RAS–MAPK or PI3K signaling have been included as controls. β-Actin was used as loading control. The color of the crosses indicates the sensitivity of the sample to trametinib. Red, sensitive; blue, insensitive. D, Lollipop diagram of the PIK3R1 mutations in brain tumors in our cohort (indicated in black) that are associated with trametinib sensitivity. nSH2 domain mutations associated with neomorphic-activated RAS–MAPK signaling and increased sensitivity to MEK inhibition are indicated in gray. Genome coordinates are in hg19.