Efficacy and delivery strategies of the dual Rac/Cdc42 inhibitor MBQ-167 in HER2 overexpressing breast cancer

Trastuzumab and trastuzumab-based treatments are the standard of care for breast cancer patients who overexpress the human epidermal growth factor receptor 2 (HER2). However, patients often develop resistance to trastuzumab via signaling from alternative growth factor receptors that converge to activate guanine nucleotide exchange factors (GEFs) that in turn activate the Rho GTPases Rac and Cdc42. Since Rac and Cdc42 have been implicated in high tumor grade and therapy resistance, inhibiting the activity of Rac and Cdc42 is a rational strategy to overcome HER2-targeted therapy resistance. Therefore, our group developed MBQ-167, a dual Rac/Cdc42 inhibitor with IC50s of 103 nM and 78 nM for Rac and Cdc42, respectively, which is highly effective in reducing cell and tumor growth and metastasis in breast cancer cell and mouse models. Herein, we created a trastuzumab resistant variant of the SKBR3 HER2 positive breast cancer cell line and show that Rac activation is a central mechanism in trastuzumab resistance. Next, we tested the potential of targeting MBQ-167 to HER2 overexpressing trastuzumab-resistant cell lines in vitro, and show that MBQ-167, but not trastuzumab, reduces cell viability and induces apoptosis. When MBQ-167 was targeted to mammary fatpad tumors established from HER2 overexpressing cells via immunoliposomes functionalized with trastuzumab, MBQ-167 and MBQ-167-loaded liposomes show equal efficacy in reducing the viability of trastuzumab-resistant cells, inhibiting tumor growth in mouse xenografts, and reducing metastasis to lungs and liver. This study demonstrates the efficacy of MBQ-167 as an alternative therapeutic in HER2 overexpressing cancers, delivered either in free form or in liposomes.

Synthesis of Novel Heterocyclic Ferrocenyl Chalcones and Their Biological Evaluation

Breast cancer is currently the most commonly diagnosed cancer, with 287,850 new cases estimated for 2022 as reported by the American Cancer Society. Therefore, finding an effective treatment for this disease is imperative. Chalcones are α,β-unsaturated systems found in nature. These compounds have shown a wide array of biological activities, making them popular synthetic targets. Chalcones consist of two aromatic substituents connected by an enone bridge; this arrangement allows for a large number of derivatives. Given the biological relevance of these compounds, novel ferrocene-heterocycle-containing chalcones were synthesized and characterized based on a hybrid drug design approach. These heterocycles included thiophene, pyrimidine, thiazolyl, and indole groups. Fourteen novel heterocyclic ferrocenyl chalcones were synthesized and characterized. Herein, we also report their cytotoxicity against triple-negative breast cancer cell lines MDA-MB-231 and 4T1 and the noncancer lung cell line MRC-5. System 3 ferrocenyl chalcones displayed superior anticancer properties compared to their system 1 analogues. System 3 chalcones bearing five-membered heterocyclic substituents (thiophene, pyrazole, pyrrole, and pyrimidine) were the most active toward the MDA-MB-231 cancer cell line with IC50 values from 6.59 to 12.51 μM. Cytotoxicity of the evaluated compounds in the 4T1 cell line exhibited IC50 values from 13.23 to 213.7 μM. System 3 pyrazole chalcone had consistent toxicity toward both cell lines (IC50 ∼ 13 μM) as well as promising selectivity relative to the noncancer MRC-5 control. Antioxidant activity was also evaluated, where, contrary to anticancer capabilities, system 1 ferrocenyl chalcones were superior to their system 3 analogues. Antioxidant activity comparable to that of ascorbic acid was observed for thiophene-bearing ferrocenyl chalcone with EC50 = 31 μM.

Rac and Cdc42 inhibitors reduce macrophage function in breast cancer preclinical models

Background

Metastatic disease lacks effective treatments and remains the primary cause of mortality from epithelial cancers, especially breast cancer. The metastatic cascade involves cancer cell migration and invasion and modulation of the tumor microenvironment (TME). A viable anti-metastasis strategy is to simultaneously target the migration of cancer cells and the tumor-infiltrating immunosuppressive inflammatory cells such as activated macrophages, neutrophils, and myeloid-derived suppressor cells (MDSC). The Rho GTPases Rac and Cdc42 are ideal molecular targets that regulate both cancer cell and immune cell migration, as well as their crosstalk signaling at the TME. Therefore, we tested the hypothesis that Rac and Cdc42 inhibitors target immunosuppressive immune cells, in addition to cancer cells. Our published data demonstrate that the Vav/Rac inhibitor EHop-016 and the Rac/Cdc42 guanine nucleotide association inhibitor MBQ-167 reduce mammary tumor growth and prevent breast cancer metastasis from pre-clinical mouse models without toxic effects.

Methods

The potential of Rac/Cdc42 inhibitors EHop-016 and MBQ-167 to target macrophages was tested in human and mouse macrophage cell lines via activity assays, MTT assays, wound healing, ELISA assays, and phagocytosis assays. Immunofluorescence, immunohistochemistry, and flow cytometry were used to identify myeloid cell subsets from tumors and spleens of mice following EHop-016 or MBQ-167 treatment.

Results

EHop-016 and MBQ-167 inhibited Rac and Cdc42 activation, actin cytoskeletal extensions, migration, and phagocytosis without affecting macrophage cell viability. Rac/Cdc42 inhibitors also reduced tumor- infiltrating macrophages and neutrophils in tumors of mice treated with EHop-016, and macrophages and MDSCs from spleens and tumors of mice with breast cancer, including activated macrophages and monocytes, following MBQ-167 treatment. Mice with breast tumors treated with EHop-016 significantly decreased the proinflammatory cytokine Interleukin-6 (IL-6) from plasma and the TME. This was confirmed from splenocytes treated with lipopolysaccharide (LPS) where EHop-016 or MBQ-167 reduced IL-6 secretion in response to LPS.

Conclusion

Rac/Cdc42 inhibition induces an antitumor environment via inhibition of both metastatic cancer cells and immunosuppressive myeloid cells in the TME.

Abstract 2617: Rac and Cdc42 inhibition on macrophage function in the pancreatic tumor microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal forms of cancer. To date, there are few therapies that are efficient against this disease, and patients often develop therapy resistance. The homologous Rho GTPases, Rac and Cdc42, are overexpressed in pancreatic cancer and correlated with poor prognosis. Rho GTPases regulate cell migration/invasion, cell morphology/polarity, and cell survival/viability. Rac and Cdc42 are essential Rho GTPases in oncogenic transformation and invasiveness and govern invasion in both cancer cells and tumor-associated macrophages (TAMs). TAMs are immunosuppressive cells that exacerbate cancer progression via inflammatory responses and crosstalk signaling with malignant cancer cells to promote invasion and immunesuppression. Our laboratory has developed a dual Rac/Cdc42 inhibitor, MBQ-167 (IC50 100nM), as an anticancer agent that recently received IND approval from the US FDA due to its safety and efficacy in breast cancer models. The hypothesis tested in this study is that MBQ-167 will simultaneously target the migration and activity of pancreatic cancer cells and immunosuppressive cells in the tumor microenvironment (TME). To evaluate this, we performed pulldown assays for Rac and Cdc42 activation, MTT cell viability assays, wound-healing assays for cell migration, and phagocytosis assays using human and rat macrophage and human pancreatic cancer cell lines. Results show that MBQ-167 is not toxic to macrophages even at concentrations as high as 10uM. MBQ-167 inhibited Rac1activation by 75% and Cdc42 activation by 40% in THP-1 human macrophages at 500nM. MBQ-167 reduced macrophage migration by 67% at 150nM, and decreased pancreatic cancer cell migration by 60% at 250nM. In addition, MBQ-167 reduced macrophage phagocytosis by 56% at 500nM. This study demonstrates the utility of Rac/Cdc42 inhibition to reduce pancreatic cancer progression in the TME.

Citation Format: Anamaris Torres-Sánchez, Michael Rivera-Robles, Stephanie Dorta-Estremera, Suranganie Dharmawardhane. Rac and Cdc42 inhibition on macrophage function in the pancreatic tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2617.

Abstract 2622: Targeting Rac/Cdc42 GTPases to overcome HER2-targeted therapy resistance

Breast cancer is the most common cancer in women. Breast cancer is categorized by the overexpression (or lack thereof) of estrogen receptors (ER+/-), progesterone receptors (PR+/-) or human epidermal growth factor 2 receptors (HER2+/-). Specifically, HER2+ breast cancer is one of the most aggressive subtypes, comprising ~20% of all cases. Overexpression of the HER2 receptor leads to active downstream signaling that results in cell proliferation and metastasis. Clinically, this problem has been tackled by targeting the HER2 receptor with antibodies (e.g., Trastuzumab, Pertuzumab) and (or) tyrosine kinase inhibitors (TKIs; e.g., Lapatinib). However, patients may present with intrinsic or acquired resistance to these therapies. Molecular mechanisms of resistance to HER2 targeted therapy include activating mutations, alterations in downstream effectors, and compensation from other growth factor receptors. The active signaling sequelae from such mechanisms converge on the activation of guanine nucleotide exchange factors (GEFs) that regulate the GTPases Rac and Cdc42. These GTPases are critical for cell migration/invasion and have been correlated with poor prognosis in breast cancer patients. Therefore, targeting the activation of Rac/Cdc42 is a rational strategy to overcome HER2-targeted therapy resistance. Previously, we characterized the dual Rac/Cdc42 inhibitor MBQ-167 with IC50s of 103nM and 78nM for Rac and Cdc42, respectively. Our objective is to test MBQ-167 as an alternative to overcome HER2-targeted therapy resistance. To test the hypothesis that MBQ-167 will overcome HER2 therapy resistance, metastatic trastuzumab resistant HER2 overexpressing cells were treated with vehicle or individual or combined Trastuzumab and MBQ-167. Rac activity was determined by pulldown assays for active (GTP-bound) Rac, and viability was tested by MTT assays. Additionally, we measured apoptosis via caspase 3/7 activity and western blotted for the active signaling sequelae downstream of Rac. MBQ-167 reduced Rac activity and downstream signaling, as well as cell viability with a GI50 of 78nM after 72 hours, while caspase activity was increased after 24 hours of treatment. The results presented herein show the utility of the Rac/Cdc42 inhibitor MBQ-167 in overcoming HER2-targeted therapy resistance.

Citation Format: Miciely Cristal Aponte Reyes, Luis E. Velazquez Vega, Suranganie Dharmawardhane. Targeting Rac/Cdc42 GTPases to overcome HER2-targeted therapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2622.

Abstract 1998: Characterization of immunoliposomes for HER2-targeted delivery of the dual Rac/Cdc42 inhibitor MBQ-167

Breast cancer is the second leading cause of mortality among women in the US. Among the various subtypes, human epidermal growth factor receptor 2 (HER2) positive breast cancer shows a very aggressive and invasive phenotype. This subtype is characterized by the overexpression of HER2 receptor on the cell surface that upon ligand binding and dimerization, leads to overactive cell signaling that promotes cell proliferation and metastasis. Even though therapies have been developed to treat this type of breast cancer by targeting HER2 and preventing dimerization (eg. Trastuzumab), patients can present with acquired or intrinsic therapy resistance. One of the mechanisms of resistance is the compensation of intracellular signaling from other receptors. This signaling converges on guanine nucleotide exchange factors (GEFs) that activate Rac and Cdc42 by exchanging GDP for GTP, thus activating downstream effectors that modulate the actin cytoskeleton to promote cell migration and invasion. Therefore, targeting Rac and Cdc42 activation selectively in HER2 positive breast cancer is a promising strategy for overcoming HER2-targeted therapy resistance. Previously, we characterized the dual Rac/Cdc42 inhibitor MBQ-167 that inhibits Rac and Cdc42 activity with IC50s of 103nM and 78nM, respectively. However, there is a need to develop selective delivery systems that transport MBQ-167 directly into HER2-positive breast cancer cells. Our objective is to deliver MBQ-167 selectively into HER2-positive cells using liposomes coated with Trastuzumab, a clinically used monoclonal antibody that targets HER2. We conjugated Trastuzumab to a lipid linker (DSPE-PEG-Maleimide) by reacting Trastuzumab with 2-iminothiolane (Traut’s reagent) under nitrogenated (low oxygen) conditions and then mixing with the lipid linker overnight. This reaction was characterized by measuring the thiol groups formed after the reaction with Traut’s reagent and after mixing with the lipid, followed by mixing the Trastuzumab-lipid conjugate with liposomes containing MBQ-167. To quantify the amount of MBQ-167 in the liposomes, we determined the excitation/emission parameters of the molecule and measured the concentration of MBQ-167 by fluorescence. We found an increase in thiol groups after the reaction with Traut’s reagent, which decreased after mixing with the lipids, suggesting the formation of the DSPE-PEG-Trastuzumab conjugate. Additionally, we determined the excitation/emission parameters (320nm/430nm), quantified a lower limit of detection (LLOD) at 0.1mM, and calculated an encapsulation efficiency of 97% (530μM). Future studies include testing our formulation in vitro and in vivo in HER2+ breast cancer models.

Citation Format: Luis E. Velazquez, Suranganie Dharmawardhane. Characterization of immunoliposomes for HER2-targeted delivery of the dual Rac/Cdc42 inhibitor MBQ-167 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1998.

Abstract B011: Rac and Cdc42 inhibition in the tumor microenvironment as a strategy to prevent metastasis

Metastatic disease lacks effective treatments and remains the primary cause of mortality from epithelial cancers, especially breast cancer. The metastatic cascade involves cancer cell migration and invasion, modulation of the tumor microenvironment (TME), plasticity, and ability to colonize secondary tissues. Therefore, a viable anti-metastasis strategy needs to simultaneously target the migration of cancer cells and the tumor-infiltrating immunosuppressive inflammatory cells such as activated macrophages, neutrophils, and myeloid-derived suppressor cells (MDSC). The Rho GTPases Rac and Cdc42 are ideal molecular targets that regulate both cancer cell and immune cell migration, as well as their crosstalk signaling at the TME. Therefore, the purpose of this study was to test the hypothesis that Rac and Cdc42 inhibitors target both migratory cancer cells and immunosuppressive cells in the TME. Our published data demonstrate that the Vav/Rac inhibitor EHop-016 and the Rac/Cdc42 guanine nucleotide association inhibitor MBQ-167 reduce mammary tumor growth and prevent breast cancer metastasis from pre-clinical mouse models without toxic effects. Since the targets of these inhibitors may also affect immune cell behavior, we first tested their potential to target Rac/Cdc42 function in human and rat macrophage cell lines and show that EHop-016 and MBQ-167 inhibit Rac activation (at 5X higher concentration than the IC50 in breast cancer cells), actin cytoskeletal extensions, and migration, without affecting cell viability. EHop-016 and MBQ-167 significantly decrease the proinflammatory cytokine Interleukin-6 (Il-6) from plasma and the TME. Next, we tested the in vivo effect of MBQ-167 on immune cells from breast cancer mouse models. Tumors from immunodeficient mice bearing mammary tumors that were treated with vehicle or 50mg/kg MBQ-167 5x a week for 5 weeks, were analyzed by flow cytometry to quantify different immune cell types. MBQ-167 treated mice demonstrated elevated CD11+F4/80+CD86+ M1 macrophages and reduced MDSCs in mammary tumors. In the immunocompetent 4T-1 breast cancer model, spleens contained a lower frequency of macrophages and neutrophils, accompanied by an increase in activated cytotoxic CD69+, CD8+T cells. Moreover, when metastasis to the lungs was reduced by ~90% following MBQ-167 treatment, granzyme B+ CD8+ T cells were elevated in the lung extracts, without affecting the immunosuppressive CD4+ regulatory T cell counts. In vitro, we also demonstrated that increasing doses of MBQ-167 induced T cell activation and interferon-gamma secretion, a cytokine known to have antitumor properties. Taken together, Rac/Cdc42 inhibitors induce anti-metastatic cancer effects via inhibition of both metastatic cancer cells and immunosuppressive myeloid cells, while promoting the activation of cytotoxic T cells, in the tumor and the metastasis microenvironment. Therefore, MBQ-167 promises to be an effective antimetastatic cancer therapeutic that is poised to enter Phase I clinical trials.

Citation Format: Stephanie Dorta-Estremera, Anamaris Torres, Michael Rivera-Robles, Ailed Cruz-Collazo, Luis Borrero-Garcia, Suranganie Dharmawardhane. Rac and Cdc42 inhibition in the tumor microenvironment as a strategy to prevent metastasis [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B011.

Characterization of Novel Derivatives of MBQ-167, an inhibitor of the GTP-binding proteins Rac/Cdc42

Rac and Cdc42, are homologous GTPases that regulate cell migration, invasion, and cell cycle progression; thus, representing key targets for metastasis therapy. We previously reported on the efficacy of MBQ-167, which blocks both Rac1 and Cdc42 in breast cancer cells and mouse models of metastasis. To identify compounds with increased activity, a panel of MBQ-167 derivatives was synthesized, maintaining its 9-ethyl-3-(1H-1,2,3-triazol-1-yl)-9H-carbazole core. Similar to MBQ-167, MBQ-168 and EHop-097, inhibit activation of Rac and Rac1B splice variant and breast cancer cell viability, and induce apoptosis. MBQ-167 and MBQ-168 inhibit Rac and Cdc42 by interfering with guanine nucleotide binding, and MBQ-168 is a more effective inhibitor of PAK (1,2,3) activation. EHop-097 acts via a different mechanism by inhibiting the interaction of the guanine nucleotide exchange factor (GEF) Vav with Rac. MBQ-168 and EHop-097 inhibit metastatic breast cancer cell migration, and MBQ-168 promotes loss of cancer cell polarity to result in disorganization of the actin cytoskeleton and detachment from the substratum. In lung cancer cells, MBQ-168 is more effective than MBQ-167 or EHop-097 at reducing ruffle formation in response to EGF. Comparable to MBQ-167, MBQ-168 significantly inhibits HER2+ tumor growth and metastasis to lung, liver, and spleen. Both MBQ-167 and MBQ-168 inhibit the cytochrome P450 (CYP) enzymes 3A4, 2C9, and 2C19. However, MBQ-168 is ~10X less potent than MBQ-167 at inhibiting CYP3A4, thus demonstrating its utility in relevant combination therapies. In conclusion, the MBQ-167 derivatives MBQ-168 and EHop-097 are additional promising anti metastatic cancer compounds with similar and distinct mechanisms.

Abstract 4065: Efficacy of the Rac/Cdc42 inhibitor MBQ-167 in combination therapy with Paclitaxel

Triple negative breast cancer (TNBC) represents a challenge because of its aggressiveness and resistance to standard chemotherapy. Since TNBC lacks targeted therapy options, the frontline therapy is Paclitaxel, which targets actively dividing cells inducing subsequent apoptosis. Since dormant cells or metastatic cancer cells are not targeted by Paclitaxel, more targeted treatment options are needed. MBQ-167, a small molecule developed by us to target the metastasis drivers Rac and Cdc42, is highly effective in reducing tumor growth and metastasis in mouse models of TNBC (Cruz-Collazo et al., 2021, Molecular Cancer Therapeutics). The purpose of this study is to test the hypothesis that MBQ-167 is a viable candidate for combined therapy with Paclitaxel in TNBC. Therefore, we tested the efficacy of MBQ-167 in combination with Paclitaxel in MDA-MB-231 human TNBC cells via MTT viability assays and caspase 3/7 apoptosis, using effective concentrations of MBQ-167 and/or Paclitaxel for 24, 48, 96 & 120 hrs. We found that individual MBQ-167 or the combination therapy was more effective at 48-120 hrs at reducing cell viability by ~80% compared to ~60% by Paclitaxel treatment alone and significatively increasing apoptosis. Next, we tested individual or combined MBQ-167 (5 mg/kg 5X a week) and Paclitaxel (10 mg/kg 1X a week) on SCID mice bearing MDA-MB-231 tumors, via intraperitoneal administration. We report a significant reduction in tumor growth and lung metastasis in response to combined MBQ-167 and Paclitaxel compared to either treatment alone. A more aggressive syngeneic model of 4T-1 mouse breast cancer cells in BALB/c immunocompetent model was used to determine the direct effect of MBQ-167 and Paclitaxel on metastasis. When 4T-1 tumors were surgically removed and MBQ-167, Paclitaxel, or the combination administered for 17 days, the combination treatment, but not individual compounds, significantly reduced lung metastases by ~80%. In conclusion, this study validates the clinical testing of MBQ-167 in combination with Paclitaxel as a potential therapeutic for TNBC.

Citation Format: Ailed M. Cruz-Collazo, Olga Katsara, Elizabeth Salvo, Jean Ruiz, Robert Schneider, Suranganie Dharmawardhane. Efficacy of the Rac/Cdc42 inhibitor MBQ-167 in combination therapy with Paclitaxel [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4065.

Abstract 347: Comparative activity of MBQ-167 metabolites in metastatic breast cancer

Metastasis continues to be the most difficult phase for cancer treatment due to few targeted therapy options. Therefore, we focus on targeting the Rho GTPases Rac1 and Cdc42, key drivers of the primary steps of metastasis: cell migration and invasion. We developed MBQ-167 as a small molecule dual inhibitor for Rac1 and Cdc42 activation with IC50s of 103 and 78 nM, respectively. In metastatic human breast cancer cells, MBQ-167 inhibits the Rac/Cdc42 downstream effector p21-activated kinase (PAK)/LIM kinase/Cofilin signaling, lamellipodia extension, and thus, cell polarity, and migration. In addition, in metastatic breast cancer cells, MBQ-167 inhibits cell proliferation and cell cycle progression to ultimately induce apoptosis via anoikis. MBQ-167 inhibits tumor growth and metastasis in experimental and spontaneous HER-positive and Triple negative breast cancer (TNBC) mouse models. MBQ-167 has 35% bioavailability and is not toxic in rodent or canine models up to 1000 mg/kg. Therefore, we are further developing MBQ-167 as a lead anti metastatic cancer compound. The objective in this study is to elucidate potential activity of MBQ-167 metabolites. Prior work has identified MBQ-167 metabolites via LC MS/MS from a mammalian liver microsome (rats and human) assay. Four of the MBQ-167 metabolites with the highest MS peak area, were analyzed in metastatic breast cancer cell lines, for cell viability via MTT assays and apoptosis via caspase 3/7 assays. We report that the metabolites M6, M7, M8, and M9 did not inhibit cell viability or induce apoptosis at 250 or 500 nM in HER2-type MDA-MB-435, and TNBC MDA-MB-231 and MDA-MB-468 breast cancer cell lines, compared to MBQ-167. We next analyzed whether these metabolites could inhibit the activation of Rac and Cdc42 by analyzing the phosphorylation status of its downstream effector p-21 activated kinase isoforms 1/2/3 (PAK1/2/3). When MBQ-167 and metabolites at 250nM were incubated for 24h in HER2-type MDA-MB-435 metastatic cancer cells, and the lysates western blotted with antibodies to total PAK1/2/3 or phospho-Pak1/2/3, we found a decrease in the phosphorylation levels of PAK in response to MBQ-167 and metabolite M6. However, since the peak area of M6 in the microsome assay is only 6% compared to MBQ-167, we conclude that MBQ-167 is the major active compound with anti-metastatic cancer properties.

Citation Format: Julia I. Medina, Eliud Hernández, Cornelis Vlaar, Suranganie Dharmawardhane. Comparative activity of MBQ-167 metabolites in metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 347.

Abstract 2973: Rac inhibitors for cancer therapy

Among all cancers worldwide, breast cancer is the first cause of death in women. One of the most aggressive subtypes of breast cancer is the triple negative form, which account for the 10-15% of breast cancer cases. Due to its complex heterogeneity triple negative breast cancer available treatments are limited, being chemotherapy in the first line of use. Despite advances in the search for new treatments, there is still a lack of effective therapies, being the metastatic disease the principal cause of breast cancer mortality. Therefore, it is critical to develop a new and effective strategies to inhibit metastasis. The Rho GTPase Rac has been identified as a promising target for anti-metastatic cancer therapy as it has been shown to play key roles in metastatic cancer cells dynamics as: cellular adhesion, migration, proliferation, survival and invasion. To this extent, in an effort to find a compound with increased Rac inhibitory capacity our group developed Ehop-016 derivatives HV-107 and HV-118. Previously we have reported HV-107 and HV-118 to affect cell viability promoting a G2-M cell cycle arrest with a sub-G1 population indicative of cell death in MDA-MB-231. Also, an increase of caspases activity validating apoptosis as a mechanism of cell death was shown. In addition, a decrease in tumor growth and metastasis by ~35 to 40% in an in vivo study using HV-118 at 1 mg/kg body weightwas also reported. Currently, through pulldown assays we have showed HV-107 and HV-118 to inhibit Rac activity at~500-2000 nM and 10 nM respectively in MDA-MB-231 and MDA-MB-468 breast cancer cells. Using trypan blue excision assay HV-107(>500 nM) and HV-118(>50 nM) were shown to affect cell viability promoting a G2-M cell cycle arrest in MDA-MB-468. We also demonstrated HV-107 and HV-118 to inhibit the direct downstream effector of Rac, PAK at >500 nM(HV-107) and >50 nM(HV-118) in MDA-MB-231 cells. In addition, HV-107 was also shown to increase Rho activity at concentrations significantly higher than the effective for Rac inhibition. Rho activity up-regulation has been reported to negatively affect migration of cancerous cells. Finally, we tested HV-107 in a mouse model of metastatic breast cancer. A decrease of ~ 40% in liver metastasis was shown for mice treated with 5 mg/kg BW HV-107. Taken together, our results indicate HV-107 and HV-118 are approximately 4-100 times more efficient than the parent compound Ehop-016 and have potential as anti-breast cancer metastasis therapeutics.

This study is supported by NIH Grant 1SC1GM122691, and PRINBRE P20GM103475 from NIGMS of the NIH to GVC

Citation Format: Grace Enid Velez Crespo, Eliud Hernandez, Suranganie Dharmawardhane, Cornelis Vlaar, Linnette Castillo, Lilia Kucheryavykh. Rac inhibitors for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2973.

Abstract P5-08-09: Characterization of the Rac/Cdc42 inhibitor MBQ-168 as an anti-cancer compound

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 >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.

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

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.

Soy and Frequent Dairy Consumption with Subsequent Equol Production Reveals Decreased Gut Health in a Cohort of Healthy Puerto Rican Women

The U.S. Hispanic female population has one of the highest breast cancer (BC) incidence and mortality rates, while BC is the leading cause of cancer death in Puerto Rican women. Certain foods may predispose to carcinogenesis. Our previous studies indicate that consuming combined soy isoflavones (genistein, daidzein, and glycitein) promotes tumor metastasis possibly through increased protein synthesis activated by equol, a secondary dietary metabolite. Equol is a bacterial metabolite produced in about 20-60% of the population that harbor and exhibit specific gut microbiota capable of producing it from daidzein. The aim of the current study was to investigate the prevalence of equol production in Puerto Rican women and identify the equol producing microbiota in this understudied population. Herein, we conducted a cross-sectional characterization of equol production in a clinically based sample of eighty healthy 25-50 year old Puerto Rican women. Urine samples were collected and evaluated by GCMS for the presence of soy isoflavones and metabolites to determine the ratio of equol producers to equol non-producers. Furthermore, fecal samples were collected for gut microbiota characterization on a subset of women using next generation sequencing (NGS). We report that 25% of the participants were classified as equol producers. Importantly, the gut microbiota from equol non-producers demonstrated a higher diversity. Our results suggest that healthy women with soy and high dairy consumption with subsequent equol production may result in gut dysbiosis by having reduced quantities (diversity) of healthy bacterial biomarkers, which might be associated to increased diseased outcomes (e.g., cancer, and other diseases).

Rac inhibition as a novel therapeutic strategy for EGFR/HER2 targeted therapy resistant breast cancer

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08366-7.

Rho Family GTPases in Cancer

This Special Issue containing seminal contributions from international experts highlights the current understanding of Rho GTPases in cancer, with an emphasis on recognizing their central importance as critical targets for cancer therapy and for chemosensitization of current therapeutic strategies [...].

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

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.

Abstract 4018: Interaction site elucidation of the Rac1/Cdc42 inhibitor, MBQ-167

Metastasis continues to be the primary cause of cancer-related death. Therefore, we focus on designing small molecules inhibitors to block metastasis. The Rho GTPase family members Rac1, and Cdc42 are critical regulators of cancer cell migration and invasion, and thus, metastasis. Rac1 is activated by Guanine Nucleotide Exchange Factors (GEFs), which promote the exchange of GDP to GTP. In most cancers, the homologous Rac1 and Cdc42 are hyperactivated due to the overexpression of GEFs. Therefore, we designed inhibitors to block the activation and interaction of Rac1 and Cdc42 with their GEFs. Our lead compound MBQ-167, is a dual inhibitor of Rac1 and Cdc42 with IC50s of 103 nM and 78 nM, respectively. MBQ-167 inhibited the viability and migration of metastatic cancer cells without affecting non-metastatic or non-cancer cells. Moreover, MBQ-167 reduced mammary tumor growth and metastasis of HER2 positive and triple-negative breast cancer cells in immunocompromised mice by ~ 90%. To further elucidate the mechanism of action of MBQ-167, we tested the hypothesis that MBQ-167 blocks the interaction of specific Rac1/Cdc42 GEFs by interaction with particular amino acid residues in the switch I and II homologous regions of Rac1 and Cdc42 proteins. Therefore, to achieve the objective of elucidating the interaction site of MBQ-167 on Rac1 and Cdc42, we used in silico analysis and Nuclear Magnetic Resonance (NMR) of MBQ-167 with Rac1 in a GDP bound state. These results were biochemically validated by pulldown assays using a G15A nucleotide-free mutant predicted to interact tightly with Rac1/Cdc42 GEFs. In silico, using Autodock Tools, MBQ-167 was docked to the GEF binding domain of Rac1 and Cdc42 with low binding energy, indicating a tight interaction. For the NMR structural analyses, Rac1 was isotopically labeled with 15N and titrated with several concentrations of MBQ-167, at ratios of 1:1, 1:2, 1:3, and 1:4. We were able to detect chemical shift perturbations in key residues in the switch I and II regions that interact with Rac1/Cdc42 GEFs and regulate the activity. Moreover, these perturbations were more intense with increasing amounts of MBQ-167, confirming the specificity of the interaction. Therefore, our data signify the direct interaction of MBQ-167 with Rac1, thus validating the role of MBQ-167 as a specific Rac1/Cdc42 inhibitor.

Citation Format: Julia I. Medina, Marvin Bayro, Eliud Hernandez, Cornelis Vlaar, Ricardo Gonzalez, Suranganie Dharmawardhane. Interaction site elucidation of the Rac1/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 4018.

Abstract 3020: Tumor pharmacokinetics of the metastatic cancer inhibitor MBQ-167 in mice

The Rho GTPases Rac and Cdc42 are potential targets against metastatic disease. Our group characterized the small molecule MBQ-167 as an effective dual Rac/Cdc42 inhibitor that reduces HER2 positive and triple negative tumor growth and metastasis in mice by ~90%. To continue validating this drug for FDA approval, we recently elucidated the plasma pharmacokinetics and the tissue distribution of MBQ-167 in mice (Maldonado et al., 2019). However, further studies are needed to characterize the tumor pharmacokinetics of MBQ-167 to determine drug exposure, time-to-peak, and the length of time that MBQ-167 remains in tumors after administration. The purpose of this study was to determine the tumor pharmacokinetics of MBQ-167 in a single dose input scheme (10 mg/kg BW) following intraperitoneal (IP) administration. Thirty-five female BALB/c mice (5 mice/group) were injected with 2.5 × 105 4T1 murine metastatic breast cancer cells at the mammary fat pad. After tumor establishment, a single dose of MBQ-167 (10 mg/kg BW) was administered via IP. Tumors were collected at 0.5, 1, 3, 6, 9,12, and 24 hours following drug administration. We used a validated bioanalytical method using supercritical fluid chromatography coupled with tandem mass spectrometry (SFC-MS/MS) to quantify MBQ-167 in tumors. Pharmacokinetic parameters were obtained by non-compartmental analysis using WinNolin® software. Pharmacokinetic analysis revealed that MBQ-167 has an elimination half-life (t1/2) of 8.64 hours in tumors, which is much longer than its half-life in plasma (2.17 hours), indicating preferential absorption and retention of this lipophilic small molecule in tumor tissues. The area under the curve (AUC0-t) was 4.39 %ID⋅hr/g with a maximum concentration (Cmax) of 1268.9 ng/g in tumors. Moreover, the time-to-peak concentration in tumors was 0.5 hours. Hence, this study supports the continued development of MBQ-167 as a potential anti-cancer therapeutic.

Citation Format: Maria Del Mar Maldonado, Ailed M. Cruz-Collazo, Luis D. Borrero-García, Gabriela T. Rosado-González, Jean F. Ruiz-Calderon, Jorge Duconge, Suranganie Dharmawardhane. Tumor pharmacokinetics of the metastatic cancer inhibitor MBQ-167 in mice [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 3020.

Targeting Rac and Cdc42 GEFs in Metastatic Cancer

The Rho family GTPases Rho, Rac, and Cdc42 have emerged as key players in cancer metastasis, due to their essential roles in regulating cell division and actin cytoskeletal rearrangements; and thus, cell growth, migration/invasion, polarity, and adhesion. This review will focus on the close homologs Rac and Cdc42, which have been established as drivers of metastasis and therapy resistance in multiple cancer types. Rac and Cdc42 are often dysregulated in cancer due to hyperactivation by guanine nucleotide exchange factors (GEFs), belonging to both the diffuse B-cell lymphoma (Dbl) and dedicator of cytokinesis (DOCK) families. Rac/Cdc42 GEFs are activated by a myriad of oncogenic cell surface receptors, such as growth factor receptors, G-protein coupled receptors, cytokine receptors, and integrins; consequently, a number of Rac/Cdc42 GEFs have been implicated in metastatic cancer. Hence, inhibiting GEF-mediated Rac/Cdc42 activation represents a promising strategy for targeted metastatic cancer therapy. Herein, we focus on the role of oncogenic Rac/Cdc42 GEFs and discuss the recent advancements in the development of Rac and Cdc42 GEF-interacting inhibitors as targeted therapy for metastatic cancer, as well as their potential for overcoming cancer therapy resistance.

Simalikalactone D, a Potential Anticancer Compound from Simarouba tulae, an Endemic Plant of Puerto Rico

Species of the genus Simarouba have been studied because of their antimalarial and antileukemic activities. A group of oxygenated terpenes called quassinoids have been isolated from species of the Simarouba genus, and are responsible for its therapeutic properties. We hypothesized that Simarouba tulae, an endemic plant from Puerto Rico, is a natural source rich in quassinoid compounds with anticancer activity. The leaves were processed and extracted with solvents of different polarities. The extracts were screened for their antiproliferative activity, and it was shown that the chloroform extract was the most active extract. This extract was purified using different chromatographic techniques to afford the quassinoid simalikalactone D (SKD). This compound was further characterized using NMR and X-ray diffraction analysis. A reassessment of original structural assignments for SKD is proposed. SKD showed high cytotoxicity activity, with an IC₅₀ of 55, 58, and 65 nM in A2780CP20 (ovarian), MDA-MB-435 (breast), and MDA-MB-231 (breast) cell lines, respectively. Exposure to SKD led to 15% inhibition of the migration of MDA-MB-231 cells.

Pharmacokinetics of the Rac/Cdc42 Inhibitor MBQ-167 in Mice by Supercritical Fluid Chromatography-Tandem Mass Spectrometry

The Rho GTPases Rac and Cdc42 are potential targets against metastatic diseases. We characterized the small molecule MBQ-167 as an effective dual Rac/Cdc42 inhibitor that reduces HER2-type tumor growth and metastasis in mice by ∼90%. This study reports the pharmacokinetics and tissue distribution of MBQ-167 following intraperitoneal and oral single-dose administrations. We first developed and validated a bioanalytical method for the quantitation of MBQ-167 in mouse plasma and tissues by supercritical fluid chromatography coupled with electrospray ionization tandem mass spectrometry. MBQ-167 was rapidly distributed into the kidneys after intraperitoneal dosing, whereas oral administration resulted in higher distribution to lungs. The elimination half-lives were 2.17 and 2.6 h for the intraperitoneal and oral dosing, respectively. The relative bioavailability of MBQ-167 after oral administration was 35%. This investigation presents the first analysis of the pharmacokinetics of MBQ-167 and supports further preclinical evaluation of this drug as a potential anticancer therapeutic.

Protective effects of eicosapentaenoic acid in adipocyte-breast cancer cell cross talk

Breast cancer is the leading cause of death in women among all cancer types. Obesity is one of the factors that promote progression of breast cancer, especially in post-menopausal women. Increasingly, adipose tissue is recognized for its active role in the tumor microenvironment. We hypothesized that adipocytes conditioned medium can impact breast cancer progression by increasing inflammatory cytokines production by cancer cells, and subsequently increasing their motility. By contrast, eicosapentaenoic acid (EPA), an anti-inflammatory n-3 polyunsaturated fatty acid, reduces adipocyte-secreted inflammatory factors, leading to reduced cancer cell motility. To test these hypotheses, we investigated the direct effects of EPA on MCF-7 and MDA-MB-231 breast cancer cells and the effects of conditioned medium from 3 T3-L1 or human mesenchymal stem cells (HMSC)-derived adipocytes treated with or without EPA supplementation on breast cancer cells. We observed that conditioned medium from HMSC-derived adipocytes significantly increased mRNA transcription levels of cancer-associated genes such as FASN, STAT3 and cIAP2, while EPA-treated HMSC-derived adipocytes significantly reduced mRNA levels of these genes. However, direct EPA treatment significantly reduced mRNA content of these tumor-associated markers (FASN, STAT3, cIAP-2) only in MDA-MB-231 cells not in MCF-7 cells. Conditioned medium from EPA-treated 3 T3-L1 adipocytes further decreased inflammation, cell motility and glycolysis in cancer cells. Our data confirms that adipocytes play a significant role in promoting breast cancer progression and demonstrates that EPA-treated adipocytes reduced the negative impact of adipocyte-secreted factors on breast cancer cell inflammation and migration.

Synthesis, Anti-Cancer and Anti-Migratory Evaluation of 3,6-Dibromocarbazole and 5-Bromoindole Derivatives

In this study, a new series of N-alkyl-3,6-dibromocarbazole and N-alkyl-5-bromoindole derivatives have been synthesized and evaluated in vitro as anti-cancer and anti-migration agents. Cytotoxic and anti-migratory effects of these compounds were evaluated in MCF-7 and MDA-MB-231 breast cancer cell lines and an insight on the structure-activity relationship was developed. Preliminary investigations of their anti-cancer activity demonstrated that several compounds have moderate antiproliferative effects on cancer cell lines with GI50 values in the range of 4.7-32.2 µM. Moreover, carbazole derivatives 10, 14, 15, 23, and 24 inhibit migration activity of metastatic cell line MDA-MB-231 in the range of 18-20%. The effect of compounds 10, 14, and 15 in extension of invadopodia and filopodia was evaluated by fluorescence microscopy and results demonstrated a reduction in actin-based cell extensions by compounds 10 and 15.

Abstract 4390: Dietary soy isoflavone equol promotes breast cancer progression via regulation of protein synthesis initiation

We previously reported that dietary daidzein, a soy isoflavone, increased breast cancer progression in a nude mouse model of breast cancer metastasis. Further studies indicated that equol, a metabolite of the soy isoflavone daidzein is responsible for the cancer promoting effects of soy isoflavones in breast cancer cells in vitro. We reported that equol increases the expression of the eukaryotic protein synthesis initiation factor eIF4G1, and the transcription factor c-Myc. Increased eIF4G in response to equol resulted in the non-canonical protein synthesis of pro-cancer molecules such as Cyclin D, Bcl-XL, p120, matrix metalloproteinases, etc., as confirmed by ribosome profiling and eIF4G1 knockdown studies. This study tested the hypothesis that equol promoted breast cancer progression via eIF4G1 upregulation. Immunocompromised nude mice were used to establish mammary fatpad tumors from human metastatic breast cancer cells expressing eIF4G1 knockdowns via a Tetracycline-inducible promoter. Oral gavage of 50 mg/kg BW Doxycycline 3X a week for 4 weeks was enough to knockdown eIF4G1 expression by ~80%. Therefore, one week following tumor establishment, the mice were treated with vehicle (90% corn oil, 10% ethanol), equol, Doxycycline or, equol and Doxycycline. Data show that as expected, equol treatment increased tumor growth relative to vehicle treatment. Moreover, eIF4G1 knockdown abolished the effect of equol on tumor growth. Interestingly, the effect of eIF4G1 knockdown on mammary tumor growth was not evident until 55 days of doxycycline treatment. Therefore, we tested the cell and tumor lysates for potential expression of the eIF4G1 isoform Dap5 when eIF4G1 is knocked out. Dap5 protein was expressed in eIF4G1 knockdown cells and was increased by equol treatment, indicating that Dap5 may compensate for eIF4G1 knockdown by inducing alternative cap-mediated protein synthesis. In conclusion, the cancer promoting effect of equol is abolished in breast tumors where eIF4G1 expression was stably knocked down, thus, validating our hypothesis that equol increases breast cancer progression via upregulation of eIF4G1 dependent protein synthesis initiation.

Citation Format: Ailed M. Cruz-Collazo, Columba De la Parra, Robert Schneider, Suranganie Dharmawardhane. Dietary soy isoflavone equol promotes breast cancer progression via regulation of protein synthesis initiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4390.

Abstract 1997: The Rac inhibitors HV-107 and HV-118 as potential therapeutics for metastatic breast cancer

Breast cancer is the first cause of death in women globally. Metastatic breast cancer is stimated to affect more than a quarter of million of women in the US. Due to the lack of effective treatment, metastasis remains the main cause of breast cancer mortality. Therefore, it is imperative to develop novel effective strategies against metastasis. A promising target for anti-metastatic therapy is the Rho GTPase Rac because it plays a key role in metastatic cancer progression by regulating cellular processes such as adhesion, migration, proliferation and survival. Our group developed Ehop-016, a small molecule that inhibits Rac in metastatic breast cancer cells with an IC50=1µM and significantly reduces tumor growth, angiogenesis, and metastasis in a mouse model of metastatic breast cancer. However, its relative bioavailability is moderate and should be improved. Therefore, to find a compound with increased potency and bioavailability, we tested several Ehop-016 derivatives. Using Rac pulldown assays we show that HV-107 and HV-118 inhibit Rac activation by 60% in MDA-MB-231 and MDA-MB-435 metastatic breast cancer cells at 100 and 250nM, respectively. MTT assays show HV-107 (at ≥500nM) and HV-118 (at ≥50nM) significantly inhibit metastatic breast cancer cell viability, while showing minimal toxicity towards non-cancerous cells. Cell cycle analysis by flow cytometry demonstrates a G2-M arrest and a prominent sub-G1 population, indicative of cell death, in metastatic breast cancer cells treated with HV-107 (1000 nM) and HV-118 (100 nM). To evaluate apoptosis as a potential cell death mechanism, we measured caspase 3 activity. Our results show HV-107 and HV-118 significantly induce caspase 3 activity by approximately 1.6-fold at 1000 and 100nM, respectively in metastatic breast cancer cells. Therefore, these Rac inhibitors affect cell viability by inhibiting cell cycle progression and inducing apoptosis. Finally, we tested HV-118 (at 1mg/kg BW) in a mouse model of metastatic breast cancer and found a 30% reduction in tumor growth and a 90% inhibition in metastasis. Taken together, our results indicate HV-107 and HV-118 have potential as anti-breast cancer metastasis therapeutics. This study was supported by awards from the Susan Komen for the Cure, NIH/NIMHHD U54MD008149, and the Puerto Rico Science and Technology Trust to SD; NIH/NCRR R25GM061838 to UPR MSC; NIH/NIMHHD RCMI 8G12MD007583RCMI, Title V PPOHA 031M10505 and Title V Cooperative P031S130068 from U.S. Department of Education to UCC; and and PRINBRE (NIH/NIGMS P20GM103475-13) Sub-Award to LCP.

Citation Format: Grace E. Velez, Cornelis Vlaar, Eliud Hernandez, Anibal Valentin, Linette Castillo-Pichardo, Suranganie Dharmawardhane. The Rac inhibitors HV-107 and HV-118 as potential therapeutics for metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1997.

Abstract 2185: Efficacy of Rac/Cdc42 inhibitors in multiple cancer models

The RhoGTPases Rac and Cdc42 are excellent therapeutic targets for inhibiting metastasis because these homologous proteins regulate numerous cellular functions that promote tumorigenesis, angiogenesis, invasion and therefore, metastasis. Also, Rac1, Cdc42, and their effector p21-activated kinase (PAK) are overexpressed in multiple cancer types, including breast, gastric, and pancreatic, and are associated with higher mortality rates. Furthermore, Rac and Cdc42 are activated through the signaling of oncogenic cell surface receptors such as EGFR and HER2, therefore hyperactivating their signaling pathways. Our laboratory has developed two small molecules targeting Rac and Cdc42, Ehop-016 and MBQ-167, that inhibit Rac1 and Cdc42 with IC50s in the low micro- and nano-molar concentrations, respectively (Montalvo-Ortiz et al. 2012, J Biol Chem; Humphries-Bickley et al. 2017, Mol Cancer Therap), making them the most potent Rac/Cdc42 inhibitors developed to date. We hypothesize that targeting Rac1, 3, and Cdc42 is a rational strategy to inhibit aggressive TNBC, pancreatic and gastric cancer. To test this hypothesis, we treated the TNBC cell lines MDA-MB-231, MDA-MB-468 and 4T1 (murine breast cancer), gastric cancer cells NCI-N87, and pancreatic cancer cells MIA-PaCa-2 with 4uM and 500nM of Ehop-016 and MBQ-167 respectively, and measured cell viability. Both TNBC cell lines and the pancreatic cancer cell line exhibited a drastic reduction in cell viability (&gt60%) after 48hrs of treatment Ehop-016 or MBQ-167. Additionally, experimental and spontaneous metastasis assays were performed with TNBC and gastric cancer xenografts in immunocompromised and immunocompetent mice. Treatment with 1 mg/kg BW MBQ-167 3X week resulted in reduced tumor growth by 60-90% in TNBC and gastric cancer models, and metastasis inhibition by ~90% in the MDA-MB-231 model. In the syngeneic experimental metastasis study with 4T1, both Ehop-016 and MBQ-167 reduced lung metastasis in comparison to the vehicle treated group. Moreover, these compounds were not toxic to both immunocompromised and immunocompetent mice, as observed by no significant changes in weight and liver enzymes. Therefore, both Ehop-016 and MBQ-167 are promising targeted therapeutics against cancers that overexpress Rac, Cdc42, and PAK.

Citation Format: Jean F. Ruiz Calderon, Linette Castillo-Pichardo, Irmaris Lopez-Lopez, Suranganie Dharmawardhane. Efficacy of Rac/Cdc42 inhibitors in multiple cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2185.

Abstract P6-21-14: Targeting Rac/Cdc42 in human epidermal growth factor receptor 2 (HER2)-positive breast cancer

Breast cancer metastasis, when cancer cells move and establish tumors in distant organs, confounds treatment options. Therefore, there is an unmet need for targeted therapeutics to address metastasis, especially in the intractable HER2 positive (+) breast cancer type. HER2 (+) breast cancer is treated with the monoclonal HER2 antibody trastuzumab and the HER2/EGFR targeting small molecule lapatinib. However, ˜20% of early stage breast cancer patients and ˜70% of patients with metastatic disease are resistant to trastuzumab. Trastuzumab-resistant breast cancers circumvent HER2 inhibition via bypass signaling, which includes the PI3-K/Akt/mTOR pathway. HER2/EGFR and PI-3K/Akt signaling activate the Rho GTPases Rac and Cdc42, and overexpression of Rac or its downstream effector p21-activated kinase (PAK) significantly diminishes response to anti HER2 therapy and patient survival. Therefore, targeting Rac and Cdc42, pivotal regulators of cancer cell migration/invasion, and thus, metastasis, is a viable option to overcome HER2/EGFR therapy resistance. First, we designed and developed the Rac inhibitor Ehop-016 (US patents 8,884,006 B2, 9,278,956B1), which inhibits Rac activation with an IC50 of 1 μM and reduces breast cancer growth and metastasis in mouse models of trastuzumab resistant HER2 (+) breast cancer. A more potent dual Rac and Cdc42 inhibitor, MBQ-167 (US Patent 9,981,980 B2), inhibits Rac and Cdc42 activation with IC50s of 103 nM and 78 nM, respectively. In vivo, MBQ-167 inhibits trastuzumab resistant HER2 (+) mammary tumor growth and metastasis by ˜90-100% (Humphries-Bickley et al. 2017, Mol Cancer Therap). Therefore, Rac/Cdc42 inhibition blocks cell proliferation, cell cycle progression, migration, and induces apoptosis to ultimately impede tumor growth and metastasis in trastuzumab resistant HER2 (+) breast cancer models. To further investigate the role of Rac/Cdc42 inhibitors in overcoming HER2 therapy resistance, we developed a lapatinib resistant variant of the SKBR3 HER2 (+) breast cancer cell line and found that Rac was overexpressed and over activated in the therapy resistant variant compared to the parental cells. Accordingly, the Rac/Cdc42 inhibitors overcame lapatinib resistance by decreasing cell viability and inducing apoptosis in parental and SKBR3 therapy resistant variants. Pharmacokinetic analysis in mouse plasma demonstrated that the bioavailability of EHop-016 and MBQ-167 is ˜30% with a half-life of 3-4 h. Therefore, to increase the bioavailability of Rac/Cdc42 inhibitors and to facilitate sensitization of trastuzumab therapy, we designed and developed novel nanoliposomal formulations containing Rac/Cdc42 inhibitors with trastuzumab on the outer surface to target HER2 (+) breast cancer cells. This data demonstrates the utility of developing Rac/Cdc42 inhibitors as mono or combined therapy with current targeted therapeutics for HER2 (+) breast cancer.

Citation Format: Rivera-Robles MJ, Medina-Vlazquez JI, Borrero-Garcia LD, Velazquez-Vega LE, Maldonado MdM, Ruiz-Calderon J, Castillo-Pichardo L, Vivas-Mejia P, Dharmawardhane S. Targeting Rac/Cdc42 in human epidermal growth factor receptor 2 (HER2)-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-21-14.

Abstract 4185: The novel Rac inhibitor HV-107 as a potential therapeutic for metastatic breast cancer

Breast cancer is the first cause of death in women globally. Metastatic breast cancer, which occurs when cancer cells migrate from the primary tumor and establish in distant organs, is estimated to affect more than a quarter of a million of women in the US. Regrettably, metastatic breast cancer still lacks effective treatment and remains the principal cause of breast cancer mortality. Therefore, it is imperative to develop new and more effective strategies to inhibit metastasis. A promising target for anti-metastatic cancer therapy is the Rho GTPase Rac because it plays a key role in the regulation of cellular adhesion, migration, proliferation and survival; processes which promote tumorigenesis and metastasis. Recently, our group developed Ehop-016, a small molecule that inhibits Rac in metastatic breast cancer cells with an IC50 of 1µM and reduces the activity of its downstream effector p21-activated kinase (PAK). Ehop-016 also inhibits tumor growth, angiogenesis, and metastasis in a mouse model of metastatic breast cancer. However, its relative bioavailability is moderate and should be further improved. Therefore, in an effort to find a compound with greater inhibitory capacity and bioavailability, we tested several Ehop-016 derivatives for their activity against Rac and their toxicity towards metastatic breast cancer cells. Using Rac pulldown assays we show that HV-107 at 250nM inhibits Rac activation by 55% in MDA-MB-231 and MDA-MB-435 metastatic breast cancer cells. The effects of HV-107 on cell viability were tested by MTT assays and our results indicate HV-107 at ≥500nM significantly inhibits metastatic breast cancer cell viability, while showing minimal toxicity towards non-cancerous mammary epithelial cells. We also measured caspase 3 activity, in order to evaluate apoptosis as a potential mechanism of HV-107-induced cell death. Our results show HV-107 at 1000nM causes a significant 1.5 fold increase in caspase 3 activity in MDA-MB-231 cells, indicating HV-107 affects cell viability by inducing apoptosis. Finally, we tested HV-107 in a mouse model of metastatic breast cancer and found a 25% reduction in tumor growth in mice treated with 5mg/kg BW HV-107. Taken together, our results suggest HV-107 is approximately four times more efficient than the parent compound Ehop-016 and has potential as anti-breast cancer metastasis therapeutic.

This study was supported by awards from the Susan Komen for the Cure, NIH/NIMHHD U54MD008149, and the Puerto Rico Science and Technology Trust to SD; NIH/NCRR R25GM061838 to UPR MSC; NIH/NIMHHD RCMI 8G12MD007583RCMI, Title V PPOHA 031M10505 and Title V Cooperative P031S130068 from U.S. Department of Education to UCC; and PRINBRE (NIH/NIGMS P20GM103475-13) Sub-Award to LCP.

Citation Format: Grace E. Velez Crespo, Eliud Hernández, Cornelis Vlaar, Suranganie Dharmawardhane, Linette Castillo-Pichardo. The novel Rac inhibitor HV-107 as a potential therapeutic for metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4185.

Abstract 1905: New targeted therapeutics for gastric cancer

Gastric cancer is a health disparity with 2.3 times higher incidence rates in Hispanics than in Non-Hispanic Whites (NHWs). Very few studies have been conducted to characterize this health disparity in Hispanics; however, studies from East Asian patients, where gastric cancer is also a health disparity, have revealed that p21-activated kinases (PAKs 1,2 and 4) are biomarkers for gastric cancer. Even though inhibition of PAKs impedes gastric cancer progression, current PAK inhibitors have failed to successfully complete clinical trials. Thus, we hypothesize that the inhibition of upstream effectors of PAK, the Rho GTPases Rac and Cdc42 is a rational treatment for gastric cancers with high PAK expression. The purpose of this study is to correlate Rac/Cdc42 and PAK expression and activation with Hispanic gastric cancer malignancy, and to test the efficacy of our recently developed Rac/Cdc42 inhibitor MBQ-167 (Humphries-Bickley, et al., Mol Cancer Therap. 2017, 16:805-818). In a related Aim, to identify new targets and biomarkers for Hispanic gastric cancer, gastric cancer tissues and normal gastric mucosa from biopsies and/or surgery were collected from Puerto Rican patients for expression profiling with customized qRT-PCR arrays for mRNA and Agilent arrays for non-coding RNAs (ncRNAs), and western blotting. Western blotting of gastric cancer cell lines revealed that NCI-N87 metastatic gastric cancer cells express more PAK isoforms and phospho (active)-PAK compared to the AGS non-metastatic gastric cancer cells; accordingly, MBQ-167 reduces the viability of NCI-N87 cells without affecting AGS cells. Therefore, to test the efficacy of Rac/Cdc42 inhibition in gastric cancer, immunocompromised mice with subcutaneous tumors from GFP-NCI-N87 cells were treated 3X week with vehicle or 1mg/kg BW of MBQ-167. Tumor growth calculated by image J analysis of fluorescent digital images. A drastic reduction in NCI-N87 tumor growth was observed in the MBQ-167 treated mice with a 61% inhibition in tumor size compared to the controls, and a tumor growth delay of >90% after the second doubling time. Gene expression profiling revealed that 13 genes were overexpressed (>1.5 fold change) in Puerto Rican gastric cancer tissue in comparison to the normal gastric mucosa, including Rac1, PAK1, STAT3, KDR (VEGFR2), CXCR4, IGF1, VEGFA, and IL-6, all of which are associated with Rac/Cdc42/Pak signaling. Differential profiling using a custom-made Agilent array for ncRNAs demonstrated upregulation of a number of pro-cancer microRNAs (miRNAs) such as miR-106b and downregulation of tumor suppressors such as let-7a and miR-145, as well as upregulation of the long ncRNA CCAT2, which we have shown to be important for colon cancer malignancy. Taken together, our data show that Hispanic gastric cancers have known and novel biomarkers, and MBQ-167 is a viable targeted therapeutic option for gastric cancers with elevated Rac/Cdc42/PAK signaling.

Citation Format: Jean F. Ruiz Calderon, Marcia Cruz-Correa, George A. Calin, Linette Castillo-Pichardo, Suranganie Dharmawardhane. New targeted therapeutics for gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1905.

Abstract 4923: Pharmacokinetics of the metastatic cancer inhibitor MBQ-167 in mice

Metastasis is the principal cause of death for most cancer patients; however, effective treatment options are limited. The Rho GTPases Rac and Cdc42 are critical regulators of cancer cell migration and invasion; processes required for metastatic progression. Hence, targeting of these pivotal regulators is a rational approach for novel metastasis focused therapy design. We previously characterized the small molecule MBQ-167 as a novel Rac/Cdc42 inhibitor that inhibits mammary tumor growth and metastasis in immunocompromised mice by ~90%, which is ten times more potent than other currently available Rac inhibitors (Humphries-Bickley, et al., 2017). However, further studies are needed to determine the pharmacokinetic (PK) parameters of MBQ-167 in rodents to understand the mechanisms of drug distribution and elimination of this compound. The purpose of this study was to determine the pharmacokinetics and bioavailability of MBQ-167 in a single dose input scheme (10 mg/kg BW) following intraperitoneal (IP) and oral gavage (PO) administration. The drug was administered to BALB/c mice (4 mice/group) and plasma was collected at 0.5, 1, 3, 6, 9, and 12 hours after IP or PO administration. We developed and validated a bioanalytical method using supercritical fluid chromatography (SFC) coupled with electrospray ionization tandem mass spectrometry (MS/MS) for the detection of MBQ-167 in plasma. SFC-MS/MS was selected because it uses supercritical carbon dioxide (SCO2) as the mobile phase and offers advantages such as high sensitivity, increased resolution, and rapid analysis times. Pharmacokinetic parameters were obtained by mono-compartmental and bi-compartmental analysis for IP and PO dosing respectively using WinNolin® software, Version 7.0. Preliminary pharmacokinetic analysis revealed that the area under the curve (AUC0-∞) was 749 ng·hr/mL and 255 ng·hr/mL for IP and PO dosing respectively. The elimination half-life (t1/2) was 2.4 hours for IP dosing and the mean residence time (MRT) was 3.4 hours and 2.3 hours for the IP and PO dosing respectively. The maximum plasma drug concentration (Cmax) was 220 ng/mL after IP administration, compared to 127 ng/mL following PO administration. Furthermore, the time-to-peak for both administration routes was 30 minutes. The relative bioavailability of MBQ-167 after oral gavage administration was 34%. This study presents the first analysis of the pharmacokinetics of the Rac/Cdc42 inhibitor MBQ-167 in mice and it supports the continued development of this drug as a potential anti-cancer therapeutic.

Citation Format: Maria del Mar Maldonado, Linette Castillo-Pichardo, Joseph Bloom, Jorge Duconge, Jose F. Rodriguez-Orengo, Eliud Hernandez-O'Farrill, Cornelis Vlaar, Suranganie Dharmawardhane. Pharmacokinetics of the metastatic cancer inhibitor MBQ-167 in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4923.

Abstract 1824: Mechanisms of resistance to anti-EGFR/HER2 therapy in breast cancer

Therapy resistance to epidermal growth factor receptor family (EGFR and HER2) targeted therapies has been an obstacle for treatment success in breast cancer. Therefore, our goal is to investigate the mechanisms of resistance to these therapeutics and look for alternative ways to overcome such resistance. We previously created and characterized syngeneic gefitinib and lapatinib (EGFR and HER2 therapeutics) therapy resistant variants of the therapy sensitive SKBR3 human breast cancer cell line. We found that key mechanisms of resistance involved downregulation of miR-200a and upregulation of miR-221/222 families, which are known to regulate epithelial to mesenchymal transition (EMT). To validate the role of miR-221/222 in therapy resistance, western blots were performed for the miR-221/222 target Trichorhinophalangeal syndrome type I (TRPS1) protein. Downregulation of TRPS1 is known to promote EMT and metastasis. As expected, our results showed a downregulation of TRPS1 in the therapy resistant cells compare to the therapy sensitive cells. Since miR-200a was significantly downregulated in the therapy resistant cells, we ectopically expressed miR-200a in the EGFR therapy resistant SKBR3 cells using a lentiviral vector. MiR-200a expressing cells were selected by puromycin resistance. Preliminary data showed a decrease in the fold resistance of cells resistant to lapatinib transfected with lentiviral vector overexpressing miR-200a. These results suggest that overexpression of miR-200a in lapatinib resistant cells can be used to overcome therapy resistance in breast cancer.

Citation Format: Luis Daniel Borrero-García, Brian Vidal, Suranganie Dharmawardhane. Mechanisms of resistance to anti-EGFR/HER2 therapy in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1824.

Targeting Rac and Cdc42 GTPases in Cancer

Rac and Cdc42 are small GTPases that have been linked to multiple human cancers and are implicated in epithelial to mesenchymal transition, cell-cycle progression, migration/invasion, tumor growth, angiogenesis, and oncogenic transformation. With the exception of the P29S driver mutation in melanoma, Rac and Cdc42 are not generally mutated in cancer, but are overexpressed (gene amplification and mRNA upregulation) or hyperactivated. Rac and Cdc42 are hyperactivated via signaling through oncogenic cell surface receptors, such as growth factor receptors, which converge on the guanine nucleotide exchange factors that regulate their GDP/GTP exchange. Hence, targeting Rac and Cdc42 represents a promising strategy for precise cancer therapy, as well as for inhibition of bypass signaling that promotes resistance to cell surface receptor-targeted therapies. Therefore, an understanding of the regulatory mechanisms of these pivotal signaling intermediates is key for the development of effective inhibitors. In this review, we focus on the role of Rac and Cdc42 in cancer and summarize the regulatory mechanisms, inhibitory efficacy, and the anticancer potential of Rac- and Cdc42-targeting agents. Cancer Res; 78(12); 3101-11. ©2018 AACR.

Abstract A44: Establishment of patient-derived Hispanic gastric cancer xenografts to test targeted therapeutics

Gastric cancer is a health disparity with 2.3 times higher incidence rates in Hispanics than in non-Hispanic Whites (NHWs). Very few studies have been conducted to characterize this health disparity in Hispanics; however, studies from East Asian patients, in whom gastric cancer is also a health disparity, have revealed that p21-activated kinases (PAKs 1,2 and 4), which are known to regulate cancer metastasis, are biomarkers for gastric cancer. Even though inhibition of PAKs impedes gastric cancer progression, current PAK inhibitors have failed to successfully complete clinical trials. Thus, we hypothesize that the inhibition of upstream effectors of PAK, the Rho GTPases Rac and Cdc42, is a rational treatment for gastric cancers with high PAK expression. The purpose of this study is to identify the Rac/Cdc42/PAK pathway as novel biomarkers for Hispanic gastric cancer and to test targeted therapeutics in patient-derived gastric cancer xenografts (PDGCXs). To achieve this aim, gastric cancer tissues and normal gastric mucosa from biopsies and/or surgery are being collected for expression profiling with customized qRT-PCR arrays for mRNA and Agilent arrays for noncoding RNAs (ncRNAs), and Western blotting. Using immunodeficient mice, xenografts have been established from the NCI-N87 gastric cancer cell line (from ATCC) and a tumor from a 58-year-old Hispanic (Puerto Rican) female (San Juan Oncology Hospital). As demonstrated by Western blotting, compared to the AGS nonmetastatic gastric cancer cell line, the NCI-N87 metastatic gastric cancer cells express more PAK isoforms and phospho (active)-PAK. We have also shown that our recently developed Rac/Cdc42 inhibitor MBQ-167 reduces the viability of the NCI-N87 cell line (Humphries-Bickley et al., Mol Cancer Therap 2017;16:805-18). Therefore, we are currently testing the effect of MBQ-167 in SCID mice with NCI-N87 xenografts. Gene expression profiling of the gastric cancer tissue from the Hispanic patient revealed that 13 genes were overexpressed (>1.5-fold change) in gastric cancer tissue in comparison to the normal gastric mucosa, including Rac1, PAK1, STAT3, KDR (VEGFR2), CXCR4, IGF1, VEGFA, and IL-6, all of which are associated with Rac/Cdc42/Pak signaling. Differential profiling using a custom-made Agilent array for ncRNAs demonstrated upregulation of a number of procancer microRNAs (miRNAs) such as miR-106b and downregulation of tumor suppressors such as let-7a and miR-145, as well as upregulation of the long ncRNA CCAT2, which we have shown to be important for colon cancer malignancy. Overall, our data show that a number of unique and established biomarkers are present in Hispanic gastric cancer, including elevated Rac/Cdc42/PAK signaling. Therefore, treatment with drugs targeting the Rac/Cdc42/PAK pathway represents a novel therapeutic option for such gastric cancers. In conclusion, modeling gastric cancer in PDGCXs is expected to enable the testing and design of targeted and individualized treatments for Puerto Rican patients.

Citation Format: Jean F. Ruiz-Calderon, Marcia Cruz-Correa, George A. Calin, Suranganie Dharmawardhane. Establishment of patient-derived Hispanic gastric cancer xenografts to test targeted therapeutics [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A44.

Characterization of a Dual Rac/Cdc42 Inhibitor MBQ-167 in Metastatic Cancer

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 nmol/L) 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 IC₅₀ values of 103 and 78 nmol/L, 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 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 hours) in MBQ-167 decreases metastatic cancer cell viability with a GI₅₀ of approximately 130 nmol/L, without affecting noncancer 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 approximately 90%. In conclusion, MBQ-167 is 10× more potent than other currently available Rac/Cdc42 inhibitors and has the potential to be developed as an anticancer drug, as well as a dual inhibitory probe for the study of Rac and Cdc42. Mol Cancer Ther; 16(5); 805-18. ©2017 AACR.

Protective properties of n-3 fatty acids and implications in obesity-associated breast cancer

Obesity is well documented as a risk factor for developing breast cancer, especially in postmenopausal women. Adipose tissue in the breast under obese conditions induces inflammation by increasing macrophage infiltration and pro-inflammatory cytokines that in turn up-regulates genes and signaling pathways, resulting in increased inflammation, cell proliferation and tumor growth in the breast. Due to their potent anti-inflammatory effects, n-3 polyunsaturated fatty acids (n-3 PUFA) are a promising and safe dietary intervention in reducing breast cancer risk. Here, we briefly review current status of breast cancer and its relationship with obesity. We then review in depth, current research and knowledge on the role of n-3 PUFA in reducing/preventing breast cancer cell growth in vitro, in vivo and in human studies, and how n-3 PUFA may modulate signaling pathways mitigating their effects on breast cancer development.

Abstract 181: Discovery of novel targeted therapeutics for metastatic breast cancer

Metastatic disease is the primary cause of breast cancer mortality, due to the lack of effective therapy. The Rho GTPase Rac is integral for the promotion of cancer cell migration/invasion, proliferation, and survival. Since metastatic breast cancers often overexpress or exhibit high Rac activity, inhibition of Rac is a viable strategy against metastatic cancer. Recently, we characterized EHop-016, a small molecule that inhibits Rac activity of metastatic breast cancer cells with an IC50 of 1 µM. EHop-016 is 10-100 times more active than previously available Rac inhibitors, and is the first compound shown to inhibit the activation of Rac by the oncogenic GEF Vav. EHop-016 inhibits the activity of the Rac downstream effector p21 activated kinase (PAK), lamellipodia extension, and cell migration of metastatic breast cancer cells. We also reported that EHop-016 at ≥ 25 mg/kg Body Weight (BW) significantly reduced tumor growth, metastasis, and angiogenesis in a mouse model. However, our recent pharmacokinetic study of EHop-016 in a mouse model demonstrated that the bioavailability of Ehop-016 needs to be improved for further pharmacological development. Therefore our hypothesis is that improvement of the EHop-016 structure will provide probes with increased potency against Rac and, therefore, increased bioavailability. Herein we have tested several Ehop-016 derivatives for their effects on breast cancer cell viability and Rac activation. Using MTT assays we found that the Ehop-016 derivatives, HV-107 and HV-118, significantly inhibit the viability of metastatic breast cancer cell lines MDA-MB-231 and MDA-MB-435. The effects of HV-107 and HV-118 on the inhibition of Rac activation were tested by ELISA-based Rac activity assays and pulldown assays. Results show that at 250nM, HV-107 inhibits Rac activation by 55%, whereas HV-118 has a similar effect at 100nM in MDA-MB-231 and MDA-MB-435 cells. Taken together, our findings suggest HV-107 and HV-118 as promising Ehop-016 derivatives with potential as anti-metastatic agents, which should be further characterized.

This study was supported by awards from the Susan Komen for the Cure, NIH/NIMHHD U54MD008149, and the Puerto Rico Science and Technology Trust to SD; NIH/NCRR R25GM061838 to UPR MSC; NIH/NIMHHD RCMI 8G12MD007583RCMI, Title V PPOHA 031M10505 and Title V Cooperative P031S130068 from U.S. Department of Education to UCC; and PRINBRE (NIH/NIGMS P20GM103475-13) Pilot Project to LCP.

Citation Format: Cristina Del Valle, Eliud Hernández, Cornelis P. Vlaar, Luis A. Cubano, Suranganie Dharmawardhane, Linette Castillo-Pichardo. Discovery of novel targeted therapeutics for metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 181. doi:10.1158/1538-7445.AM2017-181

Anti-Breast Cancer Potential of Quercetin via the Akt/AMPK/Mammalian Target of Rapamycin (mTOR) Signaling Cascade

The Akt/adenosine monophosphate protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway has emerged as a critical signaling nexus for regulating cellular metabolism, energy homeostasis, and cell growth. Thus, dysregulation of this pathway contributes to the development of metabolic disorders such as obesity, type 2diabetes, and cancer. We previously reported that a combination of grape polyphenols (resveratrol, quercetin and catechin: RQC), at equimolar concentrations, reduces breast cancer (BC) growth and metastasis in nude mice, and inhibits Akt and mTOR activities and activates AMPK, an endogenous inhibitor of mTOR, in metastatic BC cells. The objective of the present study was to determine the contribution of individual polyphenols to the effect of combined RQC on mTOR signaling. Metastatic BC cells were treated with RQC individually or in combination, at various concentrations, and the activities (phosphorylation) of AMPK, Akt, and the mTOR downstream effectors, p70S6 kinase (p70S6K) and 4E binding protein (4EBP1), were determined by Western blot. Results show that quercetin was the most effective compound for Akt/mTOR inhibition. Treatment with quercetin at 15μM had a similar effect as the RQC combination in the inhibition of BC cell proliferation, apoptosis, and migration. However, cell cycle analysis showed that the RQC treatment arrested BC cells in the G1 phase, while quercetin arrested the cell cycle in G2/M. In vivo experiments, using SCID mice with implanted tumors from metastatic BC cells, demonstrated that administration of quercetin at 15mg/kg body weight resulted in a ~70% reduction in tumor growth. In conclusion, quercetin appears to be a viable grape polyphenol for future development as an anti BC therapeutic.

Abstract B29: Anti-breast cancer effects of the Vav/Rac inhibitor Ehop-016 in the tumor microenvironment

Metastatic breast cancer still lacks effective treatment, and remains the primary cause of mortality. Therefore, new effective strategies to inhibit breast cancer metastasis are needed. The Rho family GTPase Rac is an ideal target for anti-metastatic cancer therapy, because Rac is a key molecular switch that can promote cancer cell migration/invasion and survival. Previously, we reported the design and development of EHop-016, a small molecule compound, which inhibits Rac activation by the oncogene Vav in metastatic cancer cells with an IC50 of 1 microM. Consequently, EHop-016 inhibits the activity of the Rac downstream effector p21-activated kinase (PAK) and cell migration in metastatic breast cancer cells; and significantly reduces tumor growth, metastasis, and angiogenesis in a mouse model of metastatic breast cancer. The reduced tumor angiogenesis in response to EHop-016 treatment may be attributed to the inhibition of the Vav/Rac activity of endothelial cells, as shown by the ability of EHop-016 to inhibit the Rac activation and capillary tube formation of endothelial cells, in vitro. Recent studies have also shown a pivotal role for tumor associated stromal cells in signaling to the cancer cells to leave the primary tumor to initiate metastasis. Because Ehop-016 acts as a specific inhibitor of the Vav/Rac interaction, we hypothesize that EHop-016 inhibits the Vav/Rac signaling in not only cancer cells, but also in fibroblasts and leukocytes. To determine whether EHop-016 treatment affects the tumor microenvironment (TME), athymic nude mice bearing mammary fatpad tumors were treated with vehicle or 30 mg/kg BW EHop-016 by IP, 3X a week, for 52 days. Immunofluorescence microscopy of mammary tumor tissue sections demonstrated a statistically significant 40% decrease in Ki-67 expression, a 60% decrease in capillary tubes as quantified by CD-31 staining, and a 33% decrease in F4/80 positive macrophages in the tumors from mice following EHop-016 treatment, compared to those treated with vehicle. To investigate the effect of EHop-016 on the cytokine milieu, plasma recovered from the mice in this study were subjected to a cytokine array for common inflammatory mediators. EHop-016 treatment demonstrated a statistically significant decrease in mouse plasma levels of the major inflammatory mediator interleukin-6 (IL-6) that has been implicated with cancer progression in the TME, as well as a trend in reduced monocyte chemoattractant protein and tumor necrosis factor alpha. A PCR array analysis of the mammary tumors from this study also demonstrated a decrease in IL-6 levels in tumor tissue. Reduced macrophages and IL-6 signaling in the TME, in response to EHop-016 treatment, is expected to decrease the cytokine-mediated malignant signaling cross talk between cancer cells and stromal cells. Therefore, inhibition of Vav/Rac signaling in the TME may additionally enhance the anti-metastatic effects of EHop-016.

This study was supported by National Institute on Minority Health and Health Disparities of the National Institutes of Health (NIMHHD/NIH) U54MD008149 and the Puerto Rico Science and Technology Trust to SD; Title V PPOHA P031M10505 and Title V Cooperative P031S130068 from U.S. Department of Education, and RCMI 8G12MD007583 to UCC; and UPR RCM NIH/NIMHHD grants 5U54CA096297 andR25GM061838 to THB.

Citation Format: Linette Castillo-Pichardo, Cristina Del Valle, Jessica Morales, Valance Washington, Krizia Rohena-Rivera, Magaly Martinez, Luis Cubano, Suranganie Dharmawardhane. Anti-breast cancer effects of the Vav/Rac inhibitor Ehop-016 in the tumor microenvironment. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B29.

Soy Isoflavone Genistein-Mediated Downregulation of miR-155 Contributes to the Anticancer Effects of Genistein

We previously reported that dietary genistein inhibits mammary tumor growth and metastasis of the highly metastatic MDA-MB-435 cancer cells in immunocompromised mice. The purpose herein was to characterize the role of the novel oncogenic microRNA (miRNA) miR-155 in the anticancer effects of genistein in metastatic breast cancer. The effect of genistein was determined on breast cancer cell viability, apoptosis, and expression of miR-155 and its targets. At low physiologically relevant concentrations, genistein inhibits cell viability and induces apoptosis in metastatic MDA-MB-435 and Hs578t breast cancer cells, without affecting the viability of nonmetastatic MCF-7 breast cancer cells. In parallel with reduced cell viability, miR-155 is downregulated, whereas proapoptotic and anticell proliferative miR-155 targets FOXO3, PTEN, casein kinase, and p27 are upregulated in MDA-MB-435 and Hs578t cells in response to genistein treatment. However, miR-155 levels remain unchanged in response to genistein in the MCF-7 cells. Ectopic expression of miR-155 in MDA-MB-435 and Hs578t cells decreases the effects of genistein on cell viability and abrogates the effects of genistein on apoptosis and expression of proapoptotic genes. Therefore, genistein-mediated downregulation of miR-155 contributes to the anticancer effects of genistein in metastatic breast cancer.

Abstract A141: A novel inhibitor of malignant signaling in metastatic breast cancer

The Rho GTPase Rac is a pivotal regulator of cancer cell migration and invasion; processes required for metastatic progression. We previously characterized the small molecule EHop-016 as a novel Rac inhibitor in metastatic breast cancer cells and recently reported that EHop-016 was effective at reducing tumor growth, metastasis, and angiogenesis in nude mice at 25 mg/kg bodyweight (BW) (Castillo-Pichardo, et al. 2014). We also determined the pharmacokinetics and bioavailability of EHop-016, and reported that EHop-016 is rapidly cleared from mouse plasma with a half-life of ∼5 hrs and ∼30% bioavailability (Humphries-Bickley, et al., 2015). To improve the bioavailability and efficacy of EHop-016, we synthesized and screened a number of derivatives, from which EHop-016A was identified as a potent Rac inhibitor at nM concentrations. Moreover, as determined from immunofluorescence and brightfield microscopy of several breast cancer cell lines, EHop-016A has a dramatic effect on cell morphology by inducing a loss of cell polarity, and inhibiting cell surface actin-based extensions and focal adhesions, to ultimately result in the detachment of cells from the extracellular matrix (ECM). In addition, EHop-016A reduces breast cancer cell migration in a transwell assay. EHop-016A also decreases mammosphere formation, indicating an inhibitory effect on breast cancer stem cell-like properties. The effect of EHop-016A on metastatic cancer cell viability was determined via MTT assays. EHop-016A decreases cell viability with a GI50 of 150 nM and 110 nM in MDA-MB-435 and MDA-MB-231 human metastatic cancer cell lines respectively. Western blotting demonstrated that EHop-016A decreases anti-apoptotic proteins BCL-2 and BCL-xL without affecting their gene expression, as quantified by qPCR. Consequently, EHop-016A increases pro-apoptotic caspase 3/7 activity. These results indicate that the EHop-016A induced cell rounding and detachment from the substratum results in anoikis (apoptosis due to dissolution of integrin-mediated cell to ECM attachments). Therefore, this new small molecule compound has potential as an inhibitor of metastatic breast cancer progression, and warrants further investigation as an anticancer agent.

Citation Format: Tessa Humphries-Bickley, Linette Castillo-Pichardo, Luis Borrero-Garcia, Ingrid Forestier-Roman, Luis Cubano, Eliud Hernandez-O'Farrill, Cornelis Vlaar, Suranganie Dharmawardhane. A novel inhibitor of malignant signaling in metastatic breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A141.