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

Abstract

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer, with a high predisposition for locally invasive and metastatic cancer. With the objective to reduce cancer metastasis, we developed small molecule inhibitors to target the drivers of metastasis, the Rho GTPases Rac and Cdc42. Of these, MBQ-167 inhibits both Rac and Cdc42 with IC50s of 103 and 78 nmol/L, respectively; and consequently, inhibits p21-activated kinase (PAK) signaling, metastatic cancer cell proliferation, migration, and mammosphere growth; induces cell-cycle arrest and apoptosis; and decreases HER2-type mammary fatpad tumor growth and metastasis (Humphries-Bickley and colleagues, 2017). Herein, we used nuclear magnetic resonance to show that MBQ-167 directly interacts with Rac1 to displace specific amino acids, and consequently inhibits Rac.GTP loading and viability in TNBC cell lines. Phosphokinome arrays in the MDA-MB-231 human TNBC cells show that phosphorylation status of kinases independent of the Rac/Cdc42/PAK pathway are not significantly changed following 200 nmol/L MBQ-167 treatment. Western blotting shows that initial increases in phospho-c-Jun and phospho-CREB in response to MBQ-167 are not sustained with prolonged exposure, as also confirmed by a decrease in their transcriptional targets. MBQ-167 inhibits tumor growth, and spontaneous and experimental metastasis in immunocompromised (human TNBC) and immunocompetent (mouse TNBC) models. Moreover, per oral administration of MBQ-167 at 100 mg/kg body weight is not toxic to immunocompetent BALB/c mice and has a half-life of 4.6 hours in plasma. These results highlight the specificity, potency, and bioavailability of MBQ-167, and support its clinical potential as a TNBC therapeutic.

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

“…2A and B ). MBQ-167 induces detachment of metastatic cancer cells from the substrate to ultimately undergo anoikis, as was reported for MDA-MB-231, GFP-HER2-BM, and MDA-MB-468 cells ( 24 ). Thus, MDA-MB-231 cells were treated with MBQ-167, MBQ-168, or Ehop-097 for 12 hours at 250 nmol/L, and the actin cytoskeleton was stained with rhodamine phalloidin to identify changes in F-actin, which are required for cell migration.…”

“…Consequently, MBQ-167 inhibits HER-2–positive (HER2 + ) tumor growth and metastasis to all organs by approximately 90% in immunocompromised mice ( 23 ). Moreover, in TNBC, MBQ-167 inhibits tumor growth, and spontaneous and experimental metastasis in immunocompromised and immunocompetent mouse models ( 24 ). In mice, MBQ-167 exhibits 35% bioavailability with half-lives of approximately 2.5 hours in plasma and approximately 8 hours in tumor tissue ( 25 ).…”

Rac1 as a Target to Treat Dysfunctions and Cancer of the Bladder

“…The latter compound has been shown to inhibit Rac1/2/3 in MDA-MB-231 triple-negative breast cancer cells (IC 50 = 103 nM) in addition to inhibiting the other GTPase Cdc42 (cell division control protein 42) (IC 50 = 78 nM) [ 134 ]. It is a potent anticancer agent, at least at the preclinical level, currently positioned to treat triple-negative breast cancer [ 135 , 136 ]. However, the scope of tumors addressable with such a pan-Rac inhibitor is large and includes breast, colon, liver, lung, and other tumor types [ 132 ].…”

Structure-based design of CDC42 effector interaction inhibitors for the treatment of cancer

“…RAC1 also plays an important role in the cardiovascular system, and some CDC42/RAC1 inhibitors targeting RAC1 results in cardiotoxicity ( Sawada et al, 2008 , 2010 ; Tan et al, 2008 ). While newer inhibitors such as MBQ-167 can block the interaction of CDC42 and RAC1 with GEFs that activate them without inducing cardiotoxicity ( Cruz-Collazo et al, 2021 ), these small molecules cannot target the CDC42 family GTPase RHOJ, which differs in its N-terminal sequence and is activated by a different mechanism ( Ackermann et al, 2016 ; Florke et al, 2020 ). New structure-based, protein-protein interaction targeting strategies are needed to develop selective drug-like inhibitors that target all members of the CDC42 family, particularly given the important role of RHOJ in tumor angiogenesis.…”