ZCL 278 is a cell-permeable inhibitor of Cdc42, a Rho family GTPase. It binds into the surface groove on Cdc42 (K_d = 6.4-11.4 µM), blocking interaction with intersectin (ITSN), a guanine nucleotide exchange factor (GEF). It inhibits Cdc42-mediated microspike formation and neuronal…