CK-636 is an Arp2/3 complex inhibitor with IC50 of 4 μM, 24 μM and 32 μM for inhibition of actin polymerization induced by human, fission yeast and bovine Arp2/3 complex, respectively. CK-636 binds between Arp2 and Arp3, where it appears to block movement of Arp2 and Arp3 into their active conformation. CK-636 inhibits actin polymerization mediated by Arp2/3 complex in live cells, and reduces the formation of actin filament comet tails by Listeria in infected SKOV3 cells. CK-636 inhibits lamellipodia formation at the leading edges of migrating T cells, and causes reduced velocity. In addition, a substantial fraction of CK-636-treated T cells on zigzag patterns with an acute turning angle are trapped near the interfaces formed by the turning points of zigzag patterns.