G-5555 is a potent inhibitor of p21-activated kinase 1 (PAK1) (Kis: 3.7 nM and 11 nM for PAK1 and PAK2, respectively).

PAK1:3.7 nM (ki), PAK2:11 nM (ki)

G-5555 shows high selectivity for the group I PAKs and it also shows excellent kinase selectivity and inhibits only eight out of the 235 kinases tested other than PAK1 with inhibition >70%: PAK2, PAK3, KHS1, Lck, MST3, MST4, SIK2, and YSK1. The IC50s of G-5555 against SIK2, PAK2, KHS1, MST4, YSK1, MST3, and Lck are 9, 11, 10, 20, 34, 43, 52 nM, respectively. There is a negligible activity for G-5555 against the hERG channel with IC50 more than 10 μM in a patch-clamp assay[1]. G-5555 potently inhibits PAK2 (Ki: 11 nM). G-5555 has obviously greater growth inhibitory activity in cell lines that are PAK-amplified compared to non-amplified lines, in an array of 23 breast cancer cell lines[2].

G-5555 has low blood clearance and an acceptable half-life. Good oral exposure (AUC = 30 μM?h) and high oral bioavailability (F = 80%) are achieved[1]. G-5555 inhibits phosphorylation of the PAK1/2 downstream substrate mitogen-activated protein kinase 1 (MEK1) S298, in an H292 non-small cell lunger cancer (NSCLC) xenograft study in mice. When administered at an oral dose of 25 mg/kg b.i.d., imparts 60% tumor growth inhibition in this model13 and a PAK1 amplified breast cancer xenograft model, MDAMB-175. [2]