Hypoxia is recognized as an important factor contributing to cancer development and drug resistance. Cetuximab, a chimeric monoclonal antibody to EGFR, is known to inhibit HIF-1α expression levels and to enhance the cytotoxicity of chemotherapeutic agents. We demonstrated that hypoxia induced drug resistance in gastric cancer cells. Cetuximab enhanced oxaliplatin-induced cytotoxicity and apoptosis in normoxia and caused a reversal of drug resistance in hypoxia. Normoxic and hypoxic gastric cancer cells were treated with cetuximab, oxaliplatin or the combination and assessed for cell growth, proliferation, and apoptosis. Combination treatment resulted in a marked inhibition of HIF-1α expression levels in hypoxic cells and caused a significant reduction in the expression of activated phosphorylated AKT, ERK1/2, p-BAD and VEGF in both normoxia and hypoxia with greater levels of inhibition in hypoxia. In summary, cetuximab inhibits HIF-1α expression via the MAPK/ERK and PI3K/AKT signaling pathways and functions to overcome drug resistance induced by hypoxia. Cetuximab-oxaliplatin combination therapy may therefore emerge as an attractive treatment strategy for advanced gastric cancer.

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