Supplementary Methods; Figure S1: Immunoblot and immunofluorescence analysis of MET and HGF in TNBC and fibroblast cell lines. Figure S2: Met inhibition has minimal effect on ERK5 signaling in human TNBC cells. Figure S3: XL184 and U0126 significantly reduce volume and outgrowths of MDA-MB-231 structures. Figure S4: Minimal growth recovery is observed after XL184 removal Figure S5: MET inhibition in C3H-SCID mice.
ARTICLE ABSTRACT
Purpose: Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype that is associated with poor clinical outcome. There is a vital need for effective targeted therapeutics for TNBC patients, yet treatment strategies are challenged by the significant intertumoral heterogeneity within the TNBC subtype and its surrounding microenvironment. Receptor tyrosine kinases (RTK) are highly expressed in several TNBC subtypes and are promising therapeutic targets. In this study, we targeted the MET receptor, which is highly expressed across several TNBC subtypes.Experimental Design: Using the small-molecule inhibitor cabozantinib (XL184), we examined the efficacy of MET inhibition in preclinical models that recapitulate human TNBC and its microenvironment. To analyze the dynamic interactions between TNBC cells and fibroblasts over time, we utilized a 3D model referred to as MAME (Mammary Architecture and Microenvironment Engineering) with quantitative image analysis. To investigate cabozantinib inhibition in vivo, we used a novel xenograft model that expresses human HGF and supports paracrine MET signaling.Results: XL184 treatment of MAME cultures of MDA-MB-231 and HCC70 cells (± HGF-expressing fibroblasts) was cytotoxic and significantly reduced multicellular invasive outgrowths, even in cultures with HGF-expressing fibroblasts. Treatment with XL184 had no significant effects on METneg breast cancer cell growth. In vivo assays demonstrated that cabozantinib treatment significantly inhibited TNBC growth and metastasis.Conclusions: Using preclinical TNBC models that recapitulate the breast tumor microenvironment, we demonstrate that cabozantinib inhibition is an effective therapeutic strategy in several TNBC subtypes. Clin Cancer Res; 22(4); 923–34. ©2015 AACR.
