G-5555 is an inhibitor of p21-activated kinase 1 (PAK1; Ki = 3.7 nM), a non-receptor serine/threonine kinase involved in tumorigenesis. It is selective for PAK1 over the majority of targets in a panel of 235 kinases but does inhibit PAK2, PAK3, KHS1, LCK, MST3, MST4, SIK2, and YSK1 by greater than 70% with IC50 values ranging from 9 to 52 nM. G-5555 inhibits phosphorylation of MEK, a downstream target of PAK1, in EBC1 cells (IC50 = 69 nM). G-5555 (10, 20, and 30 mg/kg) dose-dependently reduces phosphorylation of MEK in tumors from an H292 non-small cell lung cancer (NSCLC) mouse xenograft model. G-5555 inhibits hERG channels less than 50% at a concentration of 10 μM, indicating the potential for a low risk of QT interval prolongation and potentially fatal arrhythmias.
