Angiogenesis, Metastasis, and the Cellular Microenvironment Cancer-Associated Fibroblasts Induce Matrix Metalloproteinase–Mediated Cetuximab Resistance in Head and Neck Squamous Cell Carcinoma

A growing body of evidence suggests that components of the tumor microenvironment, including cancer-associated fibroblasts (CAF), may modulate the treatment sensitivity of tumor cells. Here, we investigated the possible influence of CAFs on the sensitivity of head and neck squamous cell carcinoma (HNSCC) cell lines to cetuximab, an antagonistic epidermal growth factor receptor (EGFR) antibody. Cetuximab treatment caused a reduction in the proliferation rate of HNSCC cell lines, whereas the growth of HNSCC-derived CAF cultures was unaffected. When tumor cells were cocultured with CAFs in a transwell system, the cetuximab-induced growth inhibition was reduced, and a complete protection from growth inhibition was observed in one of the tumor cell lines investigated. Media that had been conditioned by CAFs offered protection from cetuximab treatment in a concentration-dependentmanner, suggesting that the resistance to treatmentwasmediated byCAF-derived soluble factors. The coculture of HNSCC cell lines with CAFs resulted in an elevated expression of matrix metallopro-teinase-1 (MMP-1) in both the tumor cells and CAFs. Moreover, the CAF-induced resistance was partly abolished by the presence of anMMP inhibitor. However, CAFs treated with siRNA targetingMMP-1 still protected tumor cells from cetuximab treatment, suggesting that several MMPs may cooperate to facilitate resistance or that the protective effect is mediated by anothermember of theMMP family. These results identify a novel CAF-dependent modulation of cetuximab sensitivity and suggest that inhibiting MMPs may improve the effects of EGFR-targeted therapy. Mol Cancer Res; 10(9); 1158–68. 2012 AACR