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

BRAF -mutant gliomas can be therapeutically targeted with BRAF mutant-selective inhibitors, yet responses are often transient due to short-term adaptive or long-term treatment-emergent resistance. We hypothesized that vertical inhibition of multiple signaling nodes could improve the durability of BRAF inhibition and prevent or overcome adaptive resistance. Using human tissue samples, we identified frequent RAS pathway reactivation in gliomas resistant to BRAF inhibitors, suggesting a common escape mechanism. Using patient-derived cell lines, we observed that upregulation of RAS activity was an adaptive response to BRAFi and that knockdown of SHP2, a central regulator of RAS activity, resulted in enhanced sensitivity to BRAF or MEK inhibition. Moreover, combined small molecule inhibition with SHP2 and BRAF or MEK inhibitors increased the depth and durability of ERK pathway inhibition, as well as prevented paradoxical upregulation of RAS activity. RNA sequencing analysis revealed deeper suppression of ERK transcriptional output with combined therapy, along with decreased reactivation of EGFR. Combined SHP2/BRAF small molecule inhibitors prevented growth and induced cell death in some cell line models. In cell lines with treatment-emergent resistance, moreover, combined SHP2 and BRAF inhibition overcame resistance to BRAF inhibitor monotherapy. In vivo orthotopic and patient-derived xenograft models confirmed enhanced tumor growth inhibition with combined therapy. Together, our findings demonstrate the critical role of RAS/ERK signaling reactivation in driving resistance to BRAF inhibition in glioma, and demonstrate the potential utility for adding SHP2 inhibitors to overcome resistance in BRAF V600E mutant glioma.