Inhibitors of p21-Activated Kinases (PAKs)

The p21-activated kinase (PAK) family of serine/threonine protein kinases plays important roles in cytoskeletal organization, cellular morphogenesis, and survival, and members of this family have been implicated in many diseases including cancer, infectious diseases, and neurological disorders. Owing to their large and flexible ATP binding cleft, PAKs, particularly group I PAKs (PAK1, -2, and -3), are difficult to drug; hence, few PAK inhibitors with satisfactory kinase selectivity and druglike properties have been reported to date. Examples are a recently discovered group II PAK (PAK4, -5, -6) selective inhibitor series based on a benzimidazole core, a group I PAK selective series based on a pyrido[2,3-d]pyrimidine-7-one core, and an allosteric dibenzodiazepine PAK1 inhibitor series. Only one compound, an aminopyrazole based pan-PAK inhibitor, entered clinical trials but did not progress beyond phase I trials. Clinical proof of concept for pan-group I, pan-group II, or PAK isoform selective inhibition has yet to be demonstrated.