kinase inhibitor

Cells use enzymes called kinases as on-off switches: a kinase flips a target protein 'on' by attaching a phosphate group, and many of these switches drive growth and division. In some cancers a switch is jammed permanently on. A kinase inhibitor is a wedge that blocks the switch, halting the runaway 'grow' signal.

Mechanistically, kinases transfer the gamma-phosphate of ATP onto their substrates. Most kinase inhibitors are small molecules that occupy the ATP-binding pocket, forming hydrogen bonds to the conserved 'hinge' region just as the adenine of ATP would. Because that pocket is shared across hundreds of kinases, achieving selectivity is a central design challenge.

Inhibitors are often grouped by how they bind. Type I binders fit the active (DFG-in) conformation; Type II binders such as imatinib reach into an adjacent pocket exposed only in the inactive (DFG-out) state, which can improve selectivity; allosteric and covalent inhibitors offer further strategies. Many are tyrosine kinase inhibitors used in targeted cancer therapy.

An honest caveat: tumors frequently evolve resistance mutations in the kinase that weaken drug binding, so later-generation inhibitors are repeatedly designed to overcome them, an ongoing arms race.