Combined inhibition of SHP2 overcomes adaptive resistance to type 1 BRAF inhibitors in BRAF V600E-driven high-grade glioma.

BACKGROUND: BRAF-mutant gliomas can be targeted therapeutically using BRAF-selective inhibitors, yet responses are often transient due to adaptive resistance through reactivation of RAS-ERK signaling. Here, we evaluate the role of SHP2, a central regulator of RAS activity, and SHP2 inhibitors in overcoming resistance to BRAF inhibitors in glioma. METHODS: RNAseq and protein expression in human tissue samples and glioma cell lines were used to identify resistance mechanisms. BRAF p.V600E glioma cell lines were tested to evaluate the impact of combined SHP2 and BRAF inhibition on ERK pathway activity, cell growth/death, and tumor forming ability. In vivo studies utilized heterotopic and orthotopic cell lines and patient-derived xenografts (PDX). RESULTS: We observed frequent ERK pathway reactivation in human glioma specimens following BRAF inhibitors, most commonly through EGFR and PDGFRβ activation. In glioma models, we observed that knockdown of SHP2 prevented adaptive upregulation of ERK activity in response to BRAF or MEK inhibitors. Combined small molecule inhibition with SHP2 and BRAF/MEK inhibitors increased the depth and durability of ERK suppression, inhibited growth, and killed tumor cells. RNA sequencing analysis revealed profound suppression of ERK transcriptional output with combined therapy and decreased EGFR reactivation. In cell lines with treatment-emergent resistance, combined SHP2 and BRAF inhibition overcame resistance to monotherapy. In vivo experiments confirmed enhanced tumor growth inhibition with combined therapy. CONCLUSIONS: Our findings demonstrate the critical role of RAS-ERK signaling reactivation in driving resistance to BRAF inhibition in glioma and demonstrate the potential utility of adding SHP2 inhibitors to overcome resistance.