...we assessed the antitumor efficacy of VS-4718 in Merlin-negative MDA-MB-231 and Merlin-positive MDA-MB-468 human triple negative breast cancer xenograft models. In vitro, MDA-MB-231 cells were >60 fold more sensitive to VS-4718 than MDA-MB-468 cells (Fig. 1B, C). In vivo, in the MDA-MB-231 xenograft model, mice dosed orally twice daily with VS-4718 at 25 mg/kg had significantly smaller tumors (p=0.006) than mice receiving vehicle control after 29 days of treatment. Moreover, tumor regression was observed in mice treated with 100 mg/kg VS-4718 (p< 0.0001; Fig. 1D) with corresponding significant reduction of tumor FAK (pY397) autophosphorylation (p=0.03)...we conclude that Merlin-negative cancer cells are especially sensitive to the FAK inhibitor VS-4718 in vitro and in vivo.