Lalwani, K. | Search bioRxiv

bioRxiv2024

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. SignificanceThe addition of a SHP2i to BRAFi in BRAF-V600E glioma cells prevents tumor growth and can overcome resistance to BRAFi in preclinical models in vitro and in vivo.

cancer biology↗

bioRxiv2023

MEK inhibition enhances the antitumor effect of radiation therapy in NF1-deficient glioblastoma

Individuals with neurofibromatosis type 1 (NF-1), an autosomal dominant neurogenetic and tumor predisposition syndrome, are susceptible to developing low-grade glioma (LGG) and, less commonly, high-grade glioma (HGG). These gliomas exhibit loss of the neurofibromin gene (NF1), and 10-15% of sporadic HGG have somatic NF1 alterations. Loss of NF1 leads to hyperactive RAS signaling, creating opportunity given the established efficacy of MEK inhibitors (MEKi) in plexiform neurofibromas and some individuals with LGG. We observed that NF1-deficient glioblastoma neurospheres were sensitive to the combination of a MEKi (mirdametinib) with irradiation, as evidenced by synergistic inhibition of cell growth, colony formation, and increased cell death. In contrast, NF1-intact neurospheres were not sensitive to the combination, despite complete ERK pathway inhibition. No neurosphere lines exhibited enhanced sensitivity to temozolomide combined with mirdametinib. Mirdametinib decreased transcription of homologous recombination genes and RAD51 foci, associated with DNA damage repair, in sensitive models. Heterotopic xenograft models displayed synergistic growth inhibition to mirdametinib combined with irradiation in NF1-deficient glioma xenografts, but not those with intact NF1. In sensitive models, benefits were observed at least three weeks beyond the completion of treatment, including sustained phospho-ERK inhibition on immunoblot and decreased Ki-67 expression. These observations demonstrate synergistic activity between mirdametinib and irradiation in NF1-deficient glioma models and may have clinical implications for patients with gliomas that harbor germline or somatic NF1 alterations.

cancer biology↗