Abstract 623: Investigating potential off-target effects of the dual Rac and Cdc42 inhibitor MBQ-167

Metastasis is a major cause of death in epithelial cancers, largely because of a lack of effective treatments. The metastatic inhibitor MBQ-167 was developed to target the Rho GTPases Rac and Cdc42, which promote cell cycle progression, proliferation, survival, migration/invasion, and thus, metastasis. Our published data show that MBQ-167 inhibits the activation of Rac and Cdc42 with ~100 nM IC50, and subsequently inhibits their effector p21-activated kinase (PAK) activation by autophosphorylation. In metastatic cancer cells, MBQ-167 induces a loss of cell polarity, followed by detachment from the substrate, and subsequent apoptosis (anoikis). The objective herein was to determine the potential off-target effects of MBQ-167. Therefore, the effect of MBQ-167 on the triple negative breast cancer kinome was investigated using a Human Phospho-Kinase Array for 45 phospho proteins. MDA-MB-231 cells treated with MBQ-167 for 24 h at 200 nM demonstrated no difference in phosphorylation of off-target kinases. However, phospho (p)-CREB and p-c-Jun transcription factor levels increased by ~3-fold in the cells that remained attached following MBQ-167 treatment. This was confirmed by Western blot for p-CREB and p-c-Jun as well as their transcriptional targets (Cyclin D1, survivin, ZEB1). However, a time-course analysis via Western blot revealed that this increase in CREB and c-Jun activity is transient. Western blotting of the attached and detached cell populations of MDA-MB-231 cells following MBQ-167 treatment for 24, 48, or 96 h demonstrated decreased c-Jun/p-c-jun, and CREB and Jun targets in the detached cell population. Moreover, the detached cells demonstrated additional decreases in phospho forms of ERK1/2, Akt, mTOR, beta catenin and STAT3, which have all been implicated in Rac/PAK signaling; as well as reduced expression of the anti-apoptotic proteins Bcl2, BCL-XL, and MCl-1. Therefore, we posit that the initial upregulation of transcription factors in response to MBQ-167 is a transient reaction to its strong Rac/Cdc42/PAK inhibition. Prolonged treatment with MBQ-167 causes a massive deregulation of cancer drivers and pro-survival proteins to ultimately result in anoikis. We attempted to create a MBQ-167 resistant cell population by treating MDA-MB-231 cells with ascending concentrations of MBQ-167 over time, but were unable to recover any live cells. Therefore, we conclude that MBQ-167 is a direct and specific inhibitor of Rac and Cdc42 and that potential off-target effects of MBQ-167 are only temporary, where 100% of the metastatic cancer cells treated with MBQ-167 ultimately undergo apoptosis. Collectively, our data on the mechanism of action of MBQ-167 and its efficacy in vitro and in vivo in mouse models of metastatic cancer demonstrate that MBQ-167 is a viable anti-metastatic cancer inhibitor for further development as an experimental therapeutic.

Citation Format: Hector M. Picon, Maria Del Mar Maldonado, Surangani F. Dharmawardhane Flanagan. Investigating potential off-target effects of the dual Rac and Cdc42 inhibitor MBQ-167 [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 623.

Abstract B094: The dual Rac/Cdc42 inhibitor MBQ-167 and derivatives as anticancer compounds

Metastatic disease lacks effective treatments, and remains the primary cause of mortality from epithelial cancers. The Rho family GTPases Rac and Cdc42 and their downstream effector p21-activated kinase (PAK) are pivotal regulators of metastatic cancer cell migration and invasion; thus, overexpression of Rac/Cdc42/PAK has been correlated with reduced patient survival in breast, gastric, and lung cancer. Our studies on the efficacy and pharmacokinetics of the Rac inhibitor EHop-016 (US patents # 8,884,006 B2; 9,278,956B1) validated the development of Rac and Cdc42 inhibitors as anti-metastatic cancer therapeutics. To improve the pharmacologic utility of EHop-016, structural derivatives were screened for enhanced efficacy and bioavailability. We recently identified a dual Rac and Cdc42 inhibitor, MetaBloq(MBQ)-167, which inhibits Rac and Cdc42 activation with IC50s of 103 nM for Rac inhibition and 78 nM for Cdc42 inhibition. Moreover, MBQ-167 is specific to cancer cells that have undergone epithelial-to-mesenchymal transition (EMT), but not epithelial cancer cells or noncancer cells. In metastatic cancer cells, MBQ-167 induces a unique phenotype of loss in cell polarity, cell surface actin extensions, and cell-substrate attachments to undergo anoikis (apoptosis due to inadequate cell-matrix interactions). In vivo, MBQ-167 inhibits HER2 type mammary tumor growth and metastasis in immunocompromised mice by ~90-100% (Humphries-Bickley et al., Mol Cancer Ther 2017; patent applications US 15/499532, PCT/US17/29921). In this study, we have further tested the pharmacokinetics and utility of MBQ-167 in additional models of cancer and screened MBQ-167 derivatives for their utility as Rac/Cdc42 inhibitors. Similar to the results with HER2 type breast cancer, in severe combined immunodeficiency (SCID) mice with mammary fat pad tumors from the triple-negative MDA-MB-231 human breast cancer cell line, the effect of MBQ-167 saturated at 1 mg/kg BW with a 80% reduction in tumor growth and a 100% reduction in metastasis. In gastric cancer, MBQ-167 reduced the viability of metastatic NCI-N87 gastric cancer cells, induced anoikis without affecting the AGS nonmetastatic gastric cancer cells, and inhibited tumor growth in SCID mice. We have screened a range of MBQ-167 derivatives for cell viability and the “anoikis” phenotype and isolated 4 compounds that reduced breast cancer cell viability with GI50s in the nM range. From this screen, MBQ-14 acts similar to MBQ-167, and thus is considered to be a viable inhibitor for further investigation. We have developed a quantitative method for identifying MBQ-167 and MBQ-14 from mouse plasma using ultra-performance convergence chromatography (UPC2)/MS/MS, and find that MBQ-167 is bioavailable in mouse plasma with a half-life of ~4h following oral or intraperitoneal administration. Overall our data demonstrate the utility of further developing MBQ-167 and derivatives as anti-metastatic cancer therapeutics.

Citation Format: Linette Castillo-PIchardo, Maria Del Mar Maldonado, Jean Ruiz-Calderon, Jose F. Rodriguez-Orengo, Eliud Hernandez, Cornelis Vlaar, Surangani F. Dharmawardhane Flanagan. The dual Rac/Cdc42 inhibitor MBQ-167 and derivatives as anticancer compounds [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B094.

Abstract A155: The Rac and PAK inhibitor EHop-016 inhibits mammary tumor growth and metastasis in a nude mouse model

The Rho GTPase Rac is a central regulator of cancer cell migration/invasion that has been implicated with cancer metastasis. Therefore, we designed and developed small molecule compounds that specifically target Rac in metastatic cancer cells. We recently reported the characterization of EHop-016 as a Rac inhibitor in metastatic cancer cells, where EHop-016 was shown to inhibit Rac activity with an IC50 of 1 μM. At higher concentrations (>10 μM) EHop-016 reduced cell viability and inhibited the related Rho GTPase Cdc42, but not Rho. EHop-016 decreased the activation of Rac by the oncogenic guanine nucleotide exchange factor Vav, the activity of the Rac effector p21-activated kinase (PAK), and the extension of actin cytoskeletal structures and migration of metastatic cancer cells. Next, we determined the efficacy of EHop-016 in vivo, using a mouse model of experimental metastasis. Green fluorescent protein (GFP) tagged MDA-MB-435 human metastatic cancer cells were inoculated at the mammary fat pad of nude mice and treated with 0, 5, 10, 25, or 40 mg/kg body weight (BW) EHop-016 3X a week for ∼8 weeks. Mammary tumor growth and metastases in lungs, spleens, kidneys, livers, hearts, and femurs were quantified by fluorescence image analysis. At concentrations >10 mg/kg BW, EHop-016 significantly inhibited mammary tumor growth and metastasis to distant organs. EHop-016 had no effect on mouse weight or their gross phenotype, indicating that EHop-016 did not exert toxic effects in athymic nude mice. This data demonstrate that EHop-016 and derivatives hold promise for further development as targeted anti-cancer therapeutics.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A155.

Citation Format: Linette Castillo-Pichardo, Tessa Humphries-Bickley, Eliud Hernandez, Columba de la Parra, Luis Cubano, Cornelis Vlaar, Surangani F. Dharmawardhane Flanagan. The Rac and PAK inhibitor EHop-016 inhibits mammary tumor growth and metastasis in a nude mouse model. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A155.