Next, we characterized the improved EHop-016 derivative, MBQ-167, as a dual Rac1 and Cdc42 inhibitor with IC50 values of 103 and 78 nmol/L, respectively, in metastatic breast cancer cells. MBQ-167 inhibits PAK/LIM kinase/Cofilin signaling, lamellipodia extension, metastatic cancer cell polarity, migration, stem cell–like mammosphere formation, cell-cycle progression, and viability and induces apoptosis in metastatic cancer cells. This evidence concerns the gene RAC1 and breast cancer.