Dasatinib resensitizes BRAF/MEK inhibitor efficacy in patient-derived xenografts from patients with progression on BRAF/MEK inhibitor treatment

Although BRAF/MEK inhibitor (BRAFi/MEKi) therapy initially shows high efficacy in patients with BRAFV600E/K cutaneous melanoma, resistance develops in over 75% of cases. We tested robustness of the umbrella trial strategy in this population by analyzing relationships between genomic status of a gene and associated downstream consequences at the protein level, which reveal poor relationships between mutations, copy number amplification, protein expression and activation. An in vivo compound repurposing screen using 11 clinically relevant agents from an NCI-portfolio with pan-RTK, non-RTK and/or PI3K-mTOR specificity identified dasatinib as most capable of restoring sensitivity to BRAFi/MEKi in patient-derived xenograft (PDX) models originating from tumors that had progressed on BRAFi +/- MEKi. High baseline expression of BRAFi/MEKi resistance-associated proteins (e.g., AXL, YAP, HSP70, phospho-AKT) was predictive of response to BRAFi/MEKi plus dasatinib combination therapy. These findings suggest that adding dasatinib may help overcome resistance and restore anti-tumor activity in patients with BRAFi/MEKi-refractory cutaneous melanoma.