Kinase inhibitors. Kinase inhibitors are classified by their binding modes. Type I and II inhibitors occupy mainly the front cleft and form hydrogen bonds with the hinge region: Type I and I 1 /2 inhibitors bind to the active and inactive DFG-in conformation, respectively, whereas type II inhibitors stabilize the inactive DFG-out conformation. Allosteric inhibitors bind only next to the ATP binding site (type III) or outside of the catalytic cleft (type IV). Type V inhibitors are bivalent, i.e. binding different regions simultaneously. While type I-V inhibitors bind reversibly, covalent inhibitors are classified as type VI.