Structure-based approaches to improve selectivity:: CDK2-GSK3β binding site analysis

An evaluation and comparison of two different approaches, GRID/CPCA and GRIND/CPCA (CPCA = consensus principal component analysis; GRIND = GRid-INdependent Descriptors), suitable for visualizing the structural differences between related proteins is presented. Ten crystal structures of CDK2/cyclin A and GSK3 beta solved in-house with different inhibitors were compared with the aim of highlighting regions that could be potential sites for gaining selectivity for CDK2 versus GSK3 beta. The analyses pointed out remarkable differences in the backs of the CDK2-GSK3 beta ATP binding pockets that guided the optimization toward a selective benzodipyrazole CDK2 inhibitor. The gain in selectivity can be associated with the two main differences in the ATP pocket between the enzymes. Phe80 of CDK2, the so-called gatekeeper residue often exploited for the design of kinase selective ligands, is replaced by a leucine in GSK3 beta, and Ala144 is replaced by a cysteine. As a consequence of these mutations, CDK2 has a less elongated and less flat buried region at the back of the ATP pocket.