Abstract 705: Crosstalk with stromal fibroblasts contributes to EGFR inhibitor resistance in colorectal cancer cells

Abstract

Abstract The mechanism for resistance to EGFR targeted therapies in colorectal cancer (CRC) with intact KRAS is still unknown. Host stromal cells contribute to tumorigenicity; however their effect on the sensitivity to EGFR targeted therapies has still to be determined. We hypothesized that crosstalk between stromal fibroblasts and CRC cancer cells contributes to cetuximab resistance via activation of the HGF/MET axis. Primary CRC associated fibroblasts (CAFs) were isolated and expanded from five surgical specimens. Fibroblasts were enriched by magnetic activated cell sorting (MACS®) and activated fibroblast lineage was confirmed by alpha smooth muscle actin (SMA) immunofluorescence. Supernatant HGF content and cellular mRNA expression levels in primary CRC CAFs, an embryonic lung fibroblast cell line (MRC-5), and a normal colon fibroblast cell line (CCD18) were determined by ELISA and quantitative RT-PCR. The effect of fibroblasts or HGF (75ng/ml) on the CRC cell lines LIM1215 and DiFi treated with cetuximab (5nM) for 72 hours was determined by co-culture using Transwells and WST-1 cell proliferation assays. Alterations in proliferation were compared by ANOVA. Mean fibroblast HGF secretion (8.3 ng/ml) and relative mRNA expression (2.0) could be augmented by co-culture with conditioned media (CM) from the CRC cell LIM1215 (14.1 ng/ml and 4.1, respectively) (Table). Further, co-culture of CRC cells with HGF, CCD18 cells, or primary CAFs reversed cetuximab-induced growth inhibition. LIM1215 proliferation was inhibited by cetuximab (55.3 ± 14.4%) which could be reversed by co-culture with either HGF (93.1 ± 10.2%) or CCD18 cells (107.2 ± 10.8%) (p<0.01 for both). Stromal-tumor interactions may play an important role in CRC resistance to cetuximab via the HGF/MET axis. Inhibition of both EGFR and MET may be necessary to realize the full potential of EGFR targeted therapies in CRC.Supernatant HGF levels and relative mRNA expression in fibroblasts treated with LIM1215 CM LIM1215 (Control)MRC5CCD18CAF3CAF4CAF5CAF6HGF (ng/ml) Ctrl<0.11.217.310.97.24.08.9LIM1215-CM<0.10.840.015.08.45.015.5 HGF mRNA Ctrl00.81.82.63.01.6 LIM1215-CM01.07.65.44.91.8 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 705.