Abstract 524: Stromal fibroblasts diminish the growth-inhibitory effect of the epidermal growth factor receptor antagonist cetuximab in head and neck squamous cell carcinoma cell cultures

Abstract

Abstract There is a growing body of evidence that components of the tumor microenvironment, including stromal fibroblasts, may modulate the treatment sensitivity of tumor cells. Thus, we aimed to investigate the possible influence of stromal fibroblasts on the cetuximab sensitivity of head and neck squamous cell carcinoma (HNSCC) cells. Stromal fibroblasts isolated from 7 HNSCC patients were co-cultured with HNSCC cells in a transwell system. Mono- and co-cultures were exposed to the epidermal growth factor receptor (EGFR) antagonist cetuximab (30 nM) and cell proliferation was determined by crystal violet staining. The level of EGFR, Akt, Erk (p42/p44 MAPK), and Met activation was assessed by western blot analysis. Cetuximab elicited an anti-proliferative response in tumor cell monocultures while the growth rate of stromal fibroblasts remained unchanged. When tumor cells were co-cultured with fibroblasts or grown in media conditioned from fibroblast cultures the anti-proliferative effect of cetuximab was diminished. Furthermore, stromal fibroblasts desensitized tumor cells to treatment with gefitinib, an EGFR tyrosine kinase inhibitor, excluding the possibility that fibroblast-derived factors confer resistance by interfering with the EGFR-cetuximab interaction. Results from experiments using size-fractionated conditioned media suggest that at least two soluble factors, 50-100 kDa and greater than 100 kDa in size, confer treatment resistance. In cetuximab-treated cultures, phosphorylation of EGFR and Erk was reduced, while the level of Akt phosphorylation remained unchanged. The cetuximab resistance observed in co-cultures could not be explained by changes in either EGFR or Erk phosphorylation. However, there was a higher level of activation of the hepatocyte growth factor (HGF) receptor Met in co-cultures, and when recombinant HGF was added to tumor cell monocultures the response to cetuximab was reduced. These results identify a previously unrecognized fibroblast-dependent modulation of cetuximab sensitivity, and also suggest fibroblast-derived HGF as one of the mediators of this paracrine cross-talk. The results also suggest targeting of fibroblast-derived factors, possibly including HGF, as a novel strategy to improve the therapeutic effects of cetuximab. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 524. doi:10.1158/1538-7445.AM2011-524