Abstract B29: Anti-breast cancer effects of the Vav/Rac inhibitor Ehop-016 in the tumor microenvironment (2016)

Abstract 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.