Characterization of Novel Derivatives of MBQ-167, an Inhibitor of the GTP-binding Proteins Rac/Cdc42

Rac and Cdc42, are homologous GTPases that regulate cell migration, invasion, and cell-cycle progression; thus, representing key targets for metastasis therapy. We previously reported on the efficacy of MBQ-167, which blocks both Rac1 and Cdc42 in breast cancer cells and mouse models of metastasis. To identify compounds with increased activity, a panel of MBQ-167 derivatives was synthesized, maintaining its 9-ethyl-3-(1H1,2,3-triazol-1-yl)-9H-carbazole core. Similar to MBQ-167, MBQ-168 and EHop-097 inhibit activation of Rac and Rac1B splice variant and breast cancer cell viability, and induce apoptosis. MBQ-167 and MBQ-168 inhibit Rac and Cdc42 by interfering with guanine nucleotide binding, and MBQ168 is a more effective inhibitor of P21-activated kinase (1-3) activation. EHop-097 acts via a different mechanism by inhibiting the interaction of the guanine nucleotide exchange factor Vav with Rac. MBQ-168 and EHop097 inhibit metastatic breast cancer cell migration, and MBQ-168 promotes loss of cancer cell polarity to result in disorganization of the actin cytoskeleton and detachment from the substratum. In lung cancer cells, MBQ-168 ismore effective than MBQ-167 or EHop-097 at reducing ruffle formation in response to EGF. Comparable with MBQ-167, MBQ-168 significantly inhibits HER2-positive tumor growth and metastasis to lung, liver, and spleen. Both MBQ-167 and MBQ-168 inhibit the cytochrome P450 (CYP) enzymes 3A4, 2C9, and 2C19. However, MBQ-168 is approximately 10x less potent than MBQ-167 at inhibiting CYP3A4, thus demonstrating its utility in relevant combination therapies. In conclusion, the MBQ-167 derivatives MBQ-168 and EHop-097 are additional promising antimetastatic cancer compounds with similar and distinct mechanisms.Significance: Targeting the related GTPases Rac and Cdc42 that regu-late cancer metastasis is a viable strategy to impede metastasis of solid cancers. Herein, we describe new Rac and Cdc42 inhibitors with unique mechanisms and varying potency in different cancer cell lines. The MBQ-167 derivatives MBQ-168 and EHop-097 show promise as potential antimetastatic cancer agents.