Abstract B16: Lymphatics in triple-negative breast cancer: Contribution to chemotherapeutic efficacy in vitro and in vivo
Authors: Harris Alexandra H. , Munson Jennifer M. 
Published: October 2016

Abstract
Background: Triple-negative breast cancer (TNBC) accounts for approximately 15% of breast cancers and is associated with a poorer prognosis and higher rate of distant recurrence compared to receptor positive breast cancer. Due to an absence of effective targeted therapies, cytotoxic chemotherapy remains the standard of care for TNBC patients. However, the aggressive nature of these tumors makes preventing progression to metastatic disease a priority in therapeutic strategy. Inhibition of lymphatic activation represents an attractive approach to reduce peritumoral lymphatic vessel recruitment and attenuate cancer cell invasion to lymph nodes and subsequent metastasis to distant sites. However, little is currently known regarding the role of lymphatics in TNBC and how common therapeutic strategies can influence lymphatic reactivity. We hypothesized that inhibiting lymphatic activation in combination with standard of care chemotherapy will enhance therapeutic response in TNBC.
Methods: Our lab has developed a novel 3D tissue-engineered tri-culture system that recapitulates the tumor-lymphatic interface within the breast tumor microenvironment. It consists of a porous tissue culture insert on which we seed human lymphatic endothelial cells (LECs) to form a monolayer on the underside. Atop the insert, we place Collagen I gel with human mammary fibroblasts and human breast cancer cells labeled with fluorescent Cell Tracker dye. After gelation, flow is applied via a pressure head and the system equilibrates overnight (16-18h). Drugs are applied via flow and then flushed from the system with basal media. After 48h from first application, gels are removed, dissociated, and analyzed via flow cytometry for death [Live/Dead and apoptosis (Caspase 3/7)], while the inserts are analyzed via microscopy for invaded cancer cells. Animal experiments were performed according to guidelines set forth by the UVA Animal Care and Use Committee. Twenty female Balb/c mice were implanted with 250,000 4T1 cells and treated with either anti-VEGFR3 antibody or IgG control and docetaxel (n=5 per group) or saline control once tumors were palpable. Tumors were dissected and dissociated once they reached 150 mm3, and analyzed via flow cytometry for stromal cell populations. Lungs were analyzed for metastases by cryosectioning and H&E staining.
Results: We used our in vitro system to screen the common chemotherapeutics docetaxel, doxorubicin, 5-FU, and carboplatin across three common TNBC cell lines MDAMB231, HCC1806, and HCC38. We found that the presence of LECs significantly increases TNBC cell survival and invasiveness, shifting EC50s for cell death 10-1000 fold (EC50 shift nonlinear regression, p&lt;0.05 for +/- LECs) and doubling to tripling invasion of cancer cells (analysis by two-way ANOVA, p&lt;0.05). This poor response to therapy can be attenuated by treatment with the VEGFR3 inhibitor MAZ51. In vivo, we have seen that adjuvant anti- VEGFR3 therapy can reduce lymphatic endothelial cell populations in the tumor stroma with and without docetaxel chemotherapy when analyzed by flow cytometry (n=4 per group, p&lt;0.05). Additionally, combination-treated mice showed reduced metastasis to the lung.
Conclusion: Together, these data could indicate the effectiveness of anti-VEGFR3 therapy as an addition to chemotherapy to reduce metastatic progression of TNBC by limiting tumor-induced and therapy-induced lymphangiogenesis. Studies are ongoing to optimize and understand the ability of this adjuvant therapeutic strategy to increase therapeutic efficacy in TNBC.
Citation Format: Alexandra H. Harris, Jennifer M. Munson. Lymphatics in triple-negative breast cancer: Contribution to chemotherapeutic efficacy in vitro and in vivo. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr B16.