Abstract C141: Targeting SHP2-dependent adaptive resistance to BRAF and MEK inhibition in gliomas
Authors: Ayanlaja Abiola Abdulrahman , Lalwani Kriti , Ioannou Maria , Pratilas Christine , Schreck Karisa 
Published: December 2023

Abstract
Introduction: BRAF-mutant gliomas, common in children, are sensitive to MEK and/or BRAF inhibitors. However, responses are incomplete and can be short-lived, due to poorly understood mechanisms of resistance that are likely to involve kinome re-programming, treatment-emergent resistance mutations, and adaptive resistance, by which upstream signaling components become activated due to release of negative feedback. Based on the critical role of SHP2 upstream of RAS pathway, we postulated that the combination of SHP2i and BRAFi/MEKi would maintain superior ERK pathway inhibition in gliomas. Here, we demonstrate that combined SHP2i+BRAFi can be efficacious in BRAFV600E mutant gliomas, potentially without the toxicity posed by SHP2i+MEKi in human participants.
Methods: Using a panel of BRAFV600E mutant and wild-type glioma cell lines, we examined cell growth with Incucyte live-cell imaging, RAS activity with pull-down assay, and immunoblots of ERK signaling activity in response to MEKi (Trametinib), BRAFi (Dabrafenib), and/or SHP2i (TNO155). NSG immune-deficient mice were implanted subcutaneously with human-derived glioma lines and patient-derived xenografts (PDXs), then treated via oral gavage for ≤28 days while recording tumor volume and weight.
Results: In BRAFV600E glioma cells, we observed ERK reactivation and increased RAS activity in response to BRAFi or MEKi. SHP2 knockdown using PTPN11 pooled siRNA partially inhibited cell growth, while the addition of BRAFi/MEKi enhanced growth inhibition compared with either intervention alone. BRAFV600E cells showed insensitivity to small molecule SHP2i monotherapy, but augmented growth inhibition upon the combination with either BRAFi or MEKi due to prolonged ERK pathway suppression. BRAF wt glioma cell lines exhibit sensitivity to TNO155 monotherapy, and combination with MEKi demonstrates sustained pERK suppression in NF1-mut and NF1 wt cell lines. Additionally, we evaluated the effect of combined BRAFi+SHP2i in heterotopic xenografts using human-derived glioma lines and PDXs. In both models, tumor growth was significantly slower in the combined treatment group than either monotherapy. Moreover, mice tolerated the combination well with no weight loss or lethargy.
Conclusion. Combined MEKi and SHP2i attenuate RAS reactivation in response to MEKi and demonstrates additive effects in glioma cell lines that are resistant to MEKi monotherapy. Moreover, SHP2i in combination with BRAFi in BRAFV600E mutant glioma cells synergistically attenuated tumor growth in vitro and shows superior preclinical activity to BRAFi or SHP2i alone in BRAFV600E models of gliomas.
Citation Format: Abiola Abdulrahman Ayanlaja, Kriti Lalwani, Maria Ioannou, Christine Pratilas, Karisa Schreck. Targeting SHP2-dependent adaptive resistance to BRAF and MEK inhibition in gliomas [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C141.