(H-284) Utilizing Macrophages to Transport Drug Nanoparticles in Breast Cancer Liver Metastasis

Introduction:: Breast cancer is the most frequent malignancy in women worldwide. Liver is one of the most common locations for breast tumor dissemination and breast cancer liver metastases (BCLM) account for the highest mortality rate in patients. Unlike primary tumors and metastatic lesions in other organs, BCLM growth relies heavily on the liver vasculature, leading to lesions that are hypo-perfused. Consequently, most BCLM clinically appear as hypoattenuating spots. This lack of perfusion prevents systemically administered agents from reaching the tumor core, thus causing physiological, transport-related resistance to therapy. The liver is an organ enriched in macrophages, which play important roles by affecting tumor growth, angiogenesis, metastasis and chemoresistance. These phagocytic cells are localized in proximity to BCLM and have been clinically utilized for imaging with nanomaterials. Macrophages influence the local immune response by releasing factors that aid tumor progression (M2 phenotype) or its inhibition (M1 macrophages). Our previous studies have shown that drug transport barriers in BCLM can be overcome using macrophages as carriers for nanotherapeutics, leading to an efficient therapy for hypovascularized lesions in the liver. When drug is retained in the cellular milieu in the proximity of the tumor lesion, sufficiently high local concentrations of therapeutics can be obtained to kill the tumor cells. The prerequisite for this therapy is the ability of BCLM to attract macrophages from surrounding liver tissue.


Materials and Methods:: We utilized 2D and 3D co-cultures to study the recruitment of macrophages by a variety of human breast cancer cells, including, MCF7 (ER+, PR+/-, HER2-), T-47D (ER+, PR+/-, HER2-), MDA-MB-231 (triple negative breast cancer, TNBC), SUM-159 (TNBC) for the purpose. Human macrophages were derived from buffy coats from healthy donors and prelabelled for co-culture experiments. We determined the macrophage infiltration using a) confocal (static) and Incucyte (kinetic) microscope imaging, b) transwell cell migration assay for cell number, c) immunofluorescence, d) directionality/path length. We have also assessed the efficacy of Eph2 siRNA and albumin bound paclitaxel nanoparticles in the presence and absence of macrophages and their activated subsets (M1/M2) by WST-1 assay.


Results, Conclusions, and Discussions:: TNBC cell lines (MDA-MB-231 and SUM-159) were more prominent in recruiting macrophages, which can be clinically correlated to TNBC aggressive nature associated clinically with reduced overall and relapse-free survival. EphA2 siRNA and paclitaxel LNP pretreated macrophages (M0) inhibited growth of BC spheroids in dose and time- dependent manner. These findings were further utilized to mathematically model and experimentally evaluate BCLM therapeutic response to nanocarriers loaded with high molecular weight (HMW) therapeutics, showing that macrophages play an important role in the efficacy of nanotherapeutics in hypovascularized tumors.
Our study provides a rationale for utilizing macrophages as a depot for nanotherapeutics in BCLM microenvironment. This technique could be utilized to design improved nanocarriers for the therapy of BCLM and other hypo-perfused tumors. These findings are being evaluated in mice with BCLM in vivo.


Acknowledgements (Optional): : The authors acknowledge generous support from the Department of Defense/US Army Medical Research Grant W81XWH2110012.


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