The Rho GTPases Rac (Ras-related C3 botulinum toxin substrate) and Cdc42 (cell division control protein 42 homolog) regulate cell functions governing cancer malignancy, including cell polarity, migration, and cell cycle progression. Accordingly, our recently developed Rac inhibitor EHop-016 (IC50, 1,100 nM) inhibits cancer cell migration and viability, and reduces tumor growth, metastasis, and angiogenesis in vivo. Herein, we describe MBQ-167, which inhibits Rac and Cdc42 with IC50s of 103 nM and 78 nM respectively, in metastatic breast cancer cells. Consequently, MBQ-167 significantly decreases Rac and Cdc42 downstream effector p21-activated kinase (PAK) signaling and the activity of signal transducer and activator of transcription (STAT3), without affecting Rho, MAPK, or Akt activities. MBQ-167 also inhibits breast cancer cell migration, viability, and mammosphere formation. Moreover, MBQ-167 affects cancer cells that have undergone epithelial to mesenchymal transition by a loss of cell polarity, and inhibition of cell surface actin-based extensions, to ultimately result in detachment from the substratum. Prolonged incubation (120 h) in MBQ-167 decreases metastatic cancer cell viability with a GI50 of ~130 nM, without affecting non-cancer mammary epithelial cells. The loss in cancer cell viability is due to MBQ-167-mediated G2/M cell cycle arrest and subsequent apoptosis, especially of the detached cells. In vivo, MBQ-167 inhibits mammary tumor growth and metastasis in immunocompromised mice by ~90%. In conclusion, MBQ-167 is 10X more potent than other currently available Rac/Cdc42 inhibitors, and has potential to be developed as an anticancer drug, as well as a dual inhibitory probe for the study of Rac and Cdc42.

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.

Introduction:Transforming growth factor β (TGFβ) promotes cell survival by endorsing DNA damage repair and mediates an immunosuppressive tumor microenvironment. Thus, TGFβ activation in response to radiation therapy is potentially targetable because it opposes therapeutic control. Strategies to assess this potential in the clinic are needed. Methods & Materials:We evaluated positron emission tomography (PET) to image 89 Zrfresolimumab, a humanized TGFβ neutralizing monoclonal antibody, as means to detect TGFβ

Background Even though targeted therapies are available for cancers expressing oncogenic epidermal growth receptor (EGFR) and (or) human EGFR2 (HER2), acquired or intrinsic resistance often confounds therapy success. Common mechanisms of therapy resistance involve activating receptor point mutations and (or) upregulation of signaling downstream of EGFR/HER2 to Akt and (or) mitogen activated protein kinase (MAPK) pathways. However, additional pathways of resistance may exist thus, confounding successful therapy. Methods To determine novel mechanisms of EGFR/HER2 therapy resistance in breast cancer, gefitinib or lapatinib resistant variants were created from SKBR3 breast cancer cells. Syngenic therapy sensitive and resistant SKBR3 variants were characterized for mechanisms of resistance by mammosphere assays, viability assays, and western blotting for total and phospho proteins. Results Gefitinib and lapatinib treatments reduced mammosphere formation in the sensitive cells, but not in the therapy resistant variants, indicating enhanced mesenchymal and cancer stem cell-like characteristics in therapy resistant cells. The therapy resistant variants did not show significant changes in known therapy resistant pathways of AKT and MAPK activities downstream of EGFR/HER2. However, these cells exhibited elevated expression and activation of the small GTPase Rac, which is a pivotal intermediate of GFR signaling in EMT and metastasis. Therefore, the potential of the Rac inhibitors EHop-016 and MBQ-167 to overcome therapy resistance was tested, and found to inhibit viability and induce apoptosis of therapy resistant cells. Conclusions Rac inhibition may represent a viable strategy for treatment of EGFR/HER2 targeted therapy resistant breast cancer.

Background: Equol, a daidzein metabolite, is a potent regulator of the cancer-promoting effects of dietary daidzein. Results: Silencing of eIF4G or c-Myc demonstrated that the equol-mediated c-Myc up-regulation is central to the pro-cancer effects of equol. Conclusion: Equol may promote cancer via c-Myc. Significance: Caution must be exercised regarding soyfood consumption for patients with ER (Ϫ) breast cancer.