Background: Overexpression of epidermal growth factor receptor 1 (EGFR1) plays a central role in malignant transformation and tumor progression. EGFR1 inhibition by specific antibodies or tyrosine-kinase inhibitors yielded therapeutic effects in colon and lung cancer. Aim of this study was to evaluate the effect of EGFR1 inhibition alone or in combination with chemotherapy on human gastric cancer cell lines in vitro and in an orthotopic nude mouse model. Methods: In vitro: 3 human gastric cancer cell lines (poorly differentiated MKN-45 and AGS; well differentiated NCI-N87) were exposed to increasing concentrations of the chemotherapeutics Carboplatin (0 - 3000 µg/ml), Irinotecan (0 - 1000 µg/ml), Docetaxel (0 - 300 µg/ml), or to the EGFR1-antibody Cetuximab (0 - 100 µg/ml) and the EGFR-tyrosine-kinase inhibitor Erlotinib (0 - 10 µM). Cell proliferation was assessed after 24 hours by MTT-assay. In vivo: 1 cmm fragments from subcutaneous MKN-45 donor tumors were orthotopically implanted into the gastric corpus of 48 nude mice. Animals were randomized in control and 3 treatment groups: the application of Carboplatin (20 mg/kg, weekly ip.), Cetuximab (1 mg, weekly ip.) or the combination of both substances started 4 weeks after tumor induction and was continued for 14 weeks or until death. Primary tumor volume, local infiltration and metastatic spread (dissemination score) were determined at autopsy. H&E stained sections of all organs were analyzed to assess micrometastasis. Results: In vitro: Carboplatin was most effective among the evaluated chemotherapeutics and significantly reduced proliferation of gastric cancer cells in a dose dependent manner (MKN-45: - 81 %; AGS: - 57 %; NCI-N87: - 67 %). High concentrations of the EGFR1 inhibitors Cetuximab and Erlotinib only reduced proliferation of MKN-45 cells (- 16 % and - 17 %, respectively). In vivo: table. Conclusion: The evaluated chemotherapeutics reduce proliferation of human gastric cancer cell lines in vitro, but not in vivo: Carboplatin as the most potent drug did not exert an effect, at least in a therapeutic setting, which started 4 weeks after tumor induction. Activating K-Ras mutations downstream of the EGFR may be a possible explanation for lacking effects of the EGFR-inhibitors.
In vivo results (MKN-45 tumors):

Therapy	Tumor volume (cmm)	Dissemination Score (points)
Control	656 ± 220	5.8 ± 1.4
Carboplatin	608 ± 139	4.0 ± 0.9
Cetuximab	700 ± 139	5.6 ± 1.2
Combination	783 ± 227	7.5 ± 1.5