PAK4-IN-5 (Compound 12i) is a PAK4 inhibitor (IC 50 : 7.68 nM for PAK4 , 1872.01 nM for PAK1 ). PAK4-IN-5 binds to PAK4 stably via multiple interactions. PAK4-IN-5 inhibits the proliferation and the migratory potential of MDA-MB-231 cells by inhibiting the phosphorylation of PAK4 and LIMK1. PAK4-IN-5 arrests cell cycle in the G0/G1 phase, induces apoptosis and ROS production. LD 50 : >500 mg/kg for mice (p.o.).