Discovery, Optimization, and in Vivo Evaluation of Benzimidazole Derivatives AM-8508 and AM-9635 as Potent and Selective PI3Kδ Inhibitors.

Lead optimization efforts resulted in the discovery of two potent, selective, and orally bioavailable PI3K delta inhibitors, 1 (AM-8508) and 2 (AM-9635), with good pharmacokinetic properties. The compounds inhibit B cell receptor (BCR)-mediated AKT phosphorylation (pAKT) in PI3K delta-dependent in vitro cell based assays. These compounds which share a benzimidazole bicycle are effective when administered in vivo at unbound concentrations consistent with their in vitro cell potency as a consequence of improved unbound drug concentration with lower unbound clearance. Furthermore, the compounds demonstrated efficacy in a Keyhole Limpet Hemocyanin (KLH) study in rats, where the blockade of PI3K delta activity by inbibitors 1 and 2 led to effective inhibition of antigen-specific IgG and IgM formation after immunization with KLH.