Potent, Selective, and Drug-Like G Protein-Coupled Receptor Kinase 5 and 6 Inhibitors: Design, Synthesis, and X-Ray Structural Studies.

Herein, the design, synthesis, and evaluation of small molecules, drug-like G protein-coupled receptor kinase 5 (GRK5) inhibitors are reported. GRK5 has become an important drug development target against heart failure and cancer. GRK6, a close homolog of GRK5, is considered as a possible therapeutic target for multiple myeloma. A series of drug-like GRK5 inhibitors that form noncovalent interactions in the GRK5 active site are designed. In the design of these molecules, pyrroloindoline basic scaffold of sunitinib, an FDA-approved drug, is utilized and various N-heterocyclic carboxamides in the active site are incorporated. Several inhibitors exhibit low nanomolar GRK5 inhibitory activity and high selectivity over GRK2. Several compounds also display very potent activity and selectivity for GRK6. A high-resolution X-ray crystal structure of one of these small molecule inhibitors in complex with GRK5 is determined. The structure provides important molecular insights regarding ligand-binding site interactions, GRK5 inhibition, and selectivity against GRK2.