Structure-based discovery of cellular-active allosteric inhibitors of FAK

In order to develop potent and selective focal adhesion kinase (FAK) inhibitors, synthetic studies on pyrazolo4,3-c]2,1]benzothiazines targeted for the FAK allosteric site were carried out. Based on the X-ray structural analysis of the co-crystal of the lead compound, 8-(4-ethylphenyl)-5-methyl-1,5-dihydropyrazolo4,3-c]2,1]benzothiazine 4,4-dioxide 1 with FAK, we designed and prepared 1,5-dimethyl-1,5-dihydropyrazolo4,3-c]2,1]benzothiazin derivatives which selectively inhibited kinase activity of FAK without affecting seven other kinases. The optimized compound, N-(4-tert-butylbenzyl)-1,5-dimethyl-1,5-dihydropyrazolo4,3-c]2,1]benzothiazin-8-amine 4,4-dioxide 30 possessed significant FAK kinase inhibitory activities both in cell-free (IC₅₀ = 0.64 μM) and in cellular assays (IC₅₀ = 7.1 μM). These results clearly demonstrated a potential of FAK allosteric inhibitors as antitumor agents.