The present invention relates to molecules which function as selective modulators (i.e., inhibitors and agonists, preferably inhibitors) of the Ras-homologous (Rho) family of small GTPases, in particular, Cdc42 GTPase and their use to treat diseases, for example cancers, including metastatic cancer, where Cdc42 GTPase is overexpressed or hyperactivated, genetic and acquired diseases where activation of Cdc42 GTPase plays a pivotal role (e.g., neurodegenerative diseases), rheumatoid arthritis, atherosclerosis, diabetes type I, autosomal polycystic kidney diease, cystic kidney disease, precystic kidney disease and microbial infections. Additionally, compounds according to the present invention may be used to inhibit rejection (graft host response) in transplant patients (pursuant to transplantation), to promote immunosuppression, anti-inflammatory response and to mobilize stem cell (migration) in patients in need, among others.