Abstract P5-08-09: Characterization of the Rac/Cdc42 inhibitor MBQ-168 as an anti-cancer compound
Authors: Medina Julia , Matos Tatiana , Velazquez Luis , Rivera Michael , Cruz-Collazo Ailed , Hernandez Eliud , Vlaar Cornelis , Dharmawardhane Suranganie 
Published: March 2022

Abstract
Metastasis continues to be the primary cause of cancer-related death in women with breast cancer, needing targeted therapies to inhibit this process. Therefore, we developed inhibitors targeting the homologous Rho GTPases Rac1 and Cdc42, which direct the actin cytoskeletal changes required for cell migration/invasion; and thus, metastasis. We characterized the potent inhibitor, MBQ-167 that blocks both Rac1 and Cdc42 at IC50s 103 nM and 78 nM, respectively, in human HER2 (+) and triple-negative breast cancer (TNBC) cells. Consequently, MBQ-167 inhibits tumor growth and metastasis by ~90% in pre-clinical mouse models of breast cancer (Humphries-Bickley, et al., 2017). To improve the activity and solubility of MBQ-167, we synthesized a panel of derivatives, maintaining the 9-ethyl-3-(1H-1,2,3-triazol-1-yl)-9H-carbazole as the core for each derivative. Of the derivatives tested, MBQ-168 demonstrated improved solubility and comparable efficacy. Similar to MBQ-167, MBQ-168 induced actin cytoskeletal disintegration, cell rounding, and detachment to ultimately undergo anoikis. In 120hrs, MBQ-168 significantly inhibited the viability of MDA-MB-231 at a GI50 of 228nM and HER2+ MDA-MB-435 cells with a GI50 of 137 nM, without affecting the viability of Human Mammary Epithelial Cells (HMEC). In apoptosis assays, MBQ-168 treatment, at 500nM for 48 hrs, demonstrated a similar response to MBQ-167 by &gt;4-fold increase in Caspase 3/7 activity in HER2 (+), and MDA-MB-231 and MDA-MB-468 TNBC cells. In wound healing assays, MBQ-168 also responded similar to MBQ-167 by a ~80% inhibition of breast cancer cell migration at 250nM and 500nM for 24hrs. Moreover, as quantified from Rac1.GTP pulldown assays, following 250nM treatment for 24hrs, MBQ-168 inhibited Rac1 activation in the attached cell population by ~70%, and in the detached cell population by ~100%, demonstrating a potent inhibition of Rac1 activation. In a preliminary study for relative efficacy in mice, MBQ-168 significantly reduced HER2+ MDA-MB-435 mammary tumor growth (~90%) at 5mg/kg BW via IP administration. In conclusion, MBQ-168 is an effective Rac inhibitor that reduces breast cancer cell viability, induces apoptosis, and inhibits breast cancer cell migration, actin cytoskeletal extensions, and Rac1 activation to result in a drastic reduction in mammary tumor growth in mice. We predict that the increased solubility of MBQ-168 will make it more bioavailable than MBQ-167. Thus, we have demonstrated that small structural modifications of MBQ-167 can affect the cytotoxic activity of carbazole derivatives with potential as anti-cancer drugs, and as tools to block Rac/Cdc42 activities in biological systems.
Citation Format: Julia Medina, Tatiana Matos, Luis Velazquez, Michael Rivera, Ailed Cruz-Collazo, Eliud Hernandez, Cornelis Vlaar, Suranganie Dharmawardhane. Characterization of the Rac/Cdc42 inhibitor MBQ-168 as an anti-cancer compound [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-08-09.