In vitro activity: IPA-3 is a non ATP-competitive, allosteric inhibitor of p21-activated kinase 1 (Pak1). PIR3.5 is the control compound of IPA-3. IPA-3 prevents Cdc42-stimulated Pak1 autophosphorylation on Thr423. IPA-3 also prevents sphingosine-dependent Pak1 autophosphorylation. IPA-3 does not target exposed cysteine residues on Pak1. The disulfide bond of IPA-3 is critical for inhibition of Pak1 and in vitro reduction by the reducing agent dithiothreitol (DTT) abolishes Pak1 inhibition by IPA-3. IPA-3 inhibits activation of Pak1 by diverse activators, but does not inhibit preactivated Pak1. IPA-3 inhibits PDGF-stimulated Pak activation in mouse embryonic fibroblasts. IPA-3 inhibits Pak1 activation in part by binding covalently to the regulatory domain of Pak1. IPA-3 binds Pak1 covalently in a time- and temperature-dependent manner. IPA-3 prevents binding of the Pak1 activator Cdc42. IPA-3 binds directly to the Pak1 autoregulatory domain. IPA-3 reversibly inhibits PMA-induced membrane ruffling in cells.

Kinase Assay: IPA-3 is a highly selective and non-ATP-competitive inhibitor that targets the autoregulatory mechanism of group I Paks. IPA-3 is screened out as an inhibitor of Pak1 by measuring ATP hydrolysis.

Cell Assay: In the in vitro assays, IPA-3 inhibits Pak1 autophosphorylation stimulated by Cdc42 or sphingosine. It shows an IC50 value of 2.5μM in the kinase assay. This inhibition of Pak1 is reported to be noncompetitive with ATP. Besides that, IPA-3 is found to remarkably inhibit the kinase activity of other group I Pak members, Pak2 and 3 at concentration of 10μM. Furthermore, 30μM IPA-3 can prevent both basal and PDGF-stimulated Pak activities in mouse embryonic fibroblasts

Chem Biol. 2008 Apr;15(4):322-31; Mol Cancer Ther. 2009 Sep;8(9):2559-65.