Abstract 2197: Characterization of immunoliposomes as delivery vehicles for the Rac inhibitor Ehop-016 in HER2 type breast cancer

Field: Pharmacology, Toxicology and Pharmaceutics (Life Sciences)

Abstract Due to the critical need for improved therapeutics against advanced Stage IV breast cancer, we developed and pre-clinically validated the small molecule Ehop-016 as a potential anti-metastatic drug. Ehop-016 is a small molecule inhibitor of the interaction Rac with the guanine nucleotide exchange factor (GEF) Vav2, which consequently decreases invasive actin structures and cellular migration. In a human epidermal growth factor receptor 2 (HER2) type breast cancer model in nude mice, Ehop-016 inhibits mammary tumor growth, angiogenesis, and metastasis. Moreover, Ehop-016 reduces HER2++ cancer cell viability and migration, individually or in combination with anti HER2 or EGFR directed therapeutics. By inhibiting the key signaling intermediate Rac, Ehop-016 has the potential to block signaling downstream of HER2 and EGFRs, as well as signaling via the myriad of receptors that activate Rac, and inhibit cancer progression. Our new results demonstrate that Ehop-016 inhibits both cancer cells and leukocytes in the tumor microenvironment, as well as cytokine levels (IL-6) in mouse plasma. Even though these characteristics are desirable in anticancer agents, systemic therapy with Ehop-016 may adversely affect normal immune system function. Therefore, a strategy was developed for the targeted delivery of Ehop-016 into mammary tumors, using nanoliposomes containing the current breast cancer therapeutic, Trastuzumab, a monoclonal antibody directed at the HER2. We tested various nanoliposome formulations as targeted delivery systems for Ehop-016. First, the encapsulation efficiency of Ehop-016 loaded liposomes was tested using different drug loading methods. To obtain HER2 targeted liposomes, we prepared Trastuzumab-lipid conjugates and incorporated them into the Ehop-016 containing liposomes. The binding, internalization and selectivity of our HER2 targeted delivery system was verified in human metastatic breast cancer cell lines, by using fluorescence microscopy to assess the co-staining of the lipid bilayer and Trastuzumab. In order to evaluate the effectiveness and selectivity of the immunoliposomes in delivering Ehop-016 and inhibiting Rac activity, pull-down assays were performed to detect active Rac-GTP in cells treated with Ehop-016 alone or Trastuzumab-conjugated liposomes with Ehop-016. Results show that the Trastuzumab-conjugated liposomes are more selective at binding to HER2+ breast cancer cells and inhibiting Rac, than treatment with Ehop-016 alone. In summary, our novel delivery system containing Ehop-016 and Trastuzumab has been shown to be effective in breast cancer cells, and needs to be validated in animal models of metastatic breast cancer. The development of this targeted delivery system has implications, not only in the field of breast cancer therapeutics, but may be adapted for the treatment of other diseases, and used to overcome the side effects of current treatments. Citation Format: Michael J. Rivera-Robles, Pablo E. Vivas-Mejia, Linette Castillo-Pichardo, Cornelis Vlaar, Eliud Hernández, Suranganie Dharmawardhane. Characterization of immunoliposomes as delivery vehicles for the Rac inhibitor Ehop-016 in HER2 type 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 2197. doi:10.1158/1538-7445.AM2017-2197