Targeting Cdc42 with the anticancer compound MBQ-167 inhibits cell polarity and growth in the budding yeast S. cerevisiae

Abstract

The Rho GTPase Cdc42 is highly conserved in structure and function. Mechanical or chemical cues in the microenvironment stimulate the localized activation of Cdc42 to rearrange the actin cytoskeleton and establish cell polarity. A role for Cdc42 in cell polarization was first discovered in the budding yeast Saccharomyces cerevisiae, and subsequently shown to also regulate directional motility in animal cells. Accordingly, in cancer Cdc42 promotes migration, invasion, and spread of tumor cells. Therefore, we targeted Cdc42 as a therapeutic strategy to treat metastatic breast cancer and designed the small molecule MBQ-167 as a potent inhibitor against Cdc42 and the homolog Rac. MBQ-167 inhibited cancer cell proliferation and migration in-vitro, and tumor growth and spread in-vivo in a mouse xenograft model of metastatic breast cancer. Since haploid budding yeast express a single Cdc42 gene, and do not express Rac, we used this well characterized model of polarization to define the contribution of Cdc42 inhibition to the effects of MBQ-167 in eukaryotic cells. Growth, budding pattern, and Cdc42 activity was determined in wildtype yeast or cells expressing a conditional knockdown of Cdc42 in response to vehicle or MBQ-167 treatment. As expected, growth and budding polarity were reduced by knocking-down Cdc42, with a parallel effect observed with MBQ-167. Cdc42 activity assays confirmed that MBQ-167 inhibits Cdc42 activation in yeast, and thus, bud polarity. Hence, we have validated MBQ-167 as a Cdc42 inhibitor in another biological context and present a method to screen Cdc42 inhibitors with potential as anti-metastatic cancer drugs.

Efficacy of Rac and Cdc42 Inhibitor MBQ-167 in Triple-negative Breast Cancer

“…MBQ-167 treatment of TNBC, HER2 (þ) breast, gastric, pancreatic, and ovarian cancer and neuroblastoma, as well as yeast cells that are dependent on Cdc42 for cell polarity, result in a loss of cell viability and polarity and detachment from the substrate (12,16). This phenotype is demonstrated in Fig.…”

Focus on Cdc42 in Breast Cancer: New Insights, Target Therapy Development and Non-Coding RNAs

“…In recent years, MBQ-167 has been designed to form H bonds with the Asn39 side-chain of Cdc42 and Rac and Asn39 replacement leads to loss of GEF binding [146]. Surprisingly, MBQ-167 inhibits Cdc42 activation with an IC 50 of 78 nmol/L, which make it one of the most effective Cdc42 inhibitors at present [151,152]. MBQ-167 has been shown to inhibit a large proportion of Cdc42 downstream effectors, like PAK and LIMK.…”

“…MBQ-167 can inhibit nearly all Cdc42-induced tumor processes in breast cancer, including cell polarity, cell cycle progression, apoptosis and metastasis [152]. However, MBQ-167 only inhibits Cdc42 activity in breast cancer cells that undergo EMT, rather than non-cancer cells or cancer cells without EMT [151].…”

Physiologically-Based Pharmacokinetic/Pharmacodynamic Model of MBQ-167 to Predict Tumor Growth Inhibition in Mice

“…MBQ-167 dually inhibits the activation of both GTPases, with half-maximal inhibitory concentrations ( IC 50 ) of 0.1 μM and 0.08 μM for Rac and Cdc42, respectively. Preclinical studies have shown that MBQ-167 inhibits breast cancer cell migration, viability, tumor growth, and metastasis in vivo without apparent toxicity [ 18 , 24 ]. Currently, this compound is being developed for clinical applications as a potential anti-metastatic therapeutic.…”