Abstract 1866: EphA2 siRNA-loaded lipid nanoparticles decrease tumor burden in breast cancer liver metastases models by modulating the tumor microenvironment

Abstract Breast cancer is the leading cause of cancer-related mortality in women, with distant metastasis being the primary reason. The liver is the third most frequent site of breast cancer distant metastasis. Unlike primary tumors and metastatic lesions in other organs, breast cancer liver metastasis (BCLM) growth relies heavily on the organ vasculature, leading to lesions that are hypovascularized. This prevents systemically administered agents from efficiently reaching the cancer cells in these lesions, causing transport-related resistance to therapy. Macrophages are the most abundant immune cell type in the cancer tumor microenvironment (TME), playing important roles in tissue remodeling, homeostasis, angiogenesis, progression, and response to therapy. These phagocytic cells remain in close proximity to BCLM and have been clinically utilized for imaging with nanomaterials. Transport barriers can be overcome using macrophages as carriers for nanotherapeutics, leading to efficient therapy for BCLM. siRNA therapeutics are nucleic acid-based macromolecules that hold promise for tumor therapy. Challenges related to siRNA delivery and clinical translation include poor stability and limited transport across biological barriers, which necessitate using nanoparticles as carriers. Ephrin type-A receptor 2 (EphA2) tyrosine kinase regulates important tumor-driving processes and is overexpressed in breast cancer. In the present study, we designed, characterized and evaluated the effect of siRNA EphA2 loaded lipid nanoparticles (siEphA2-LNP) in combination with albumin bound paclitaxel (nAb-PTX) on macrophage phenotype, transport and anti-cancer efficacy in in vitro and in vivo BCLM models. The siEphA2-LNP and nAb-PTX treated macrophages shifted the TME towards the pro-inflammatory, anti-tumorigenic milieu by polarizing the macrophages from the M2 to M1 phenotype. This resulted in increased apoptosis and decreased proliferation in MCF7 and MDA-MB-231 human breast cancer cells in treated groups as compared to controls. Studies in the 3D in vitro model that mimics clinically observed hypovascularized BCLM surrounded by macrophages, suggested that a balance between M1 and M2 macrophage phenotypes in the TME is required to optimize nanotherapeutic efficiency. In vivo studies in a syngeneic model of primary triple negative breast cancer and experimental BCLM showed decreased tumor volume when treated with siEphA2-LNP. Additionally, there was an increase in CD163 (M2 marker), F4/80 (pan-macrophage) and Ki67 (apoptosis) in the lesions. These findings were further utilized to computationally simulate BCLM therapeutic response to siEphA2-LNP and evaluate clinically relevant dosing strategies. Altogether, this study shows that EphA2 siRNA-loaded lipid nanoparticles can decrease BCLM tumor burden by modulating the tumor microenvironment. Citation Format: Anjana Tiwari,Eric Chau,Jenna Carr,LaMargaret Temukisa Johnson,Dylan Goodin,Hermann Frieboes,Biana Godin.. EphA2 siRNA-loaded lipid nanoparticles decrease tumor burden in breast cancer liver metastases models by modulating the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1866.