Synergistic inhibitory effect of cetuximab and tectochrysin on human colon cancer cell growth via inhibition of EGFR signal.

The purpose of this study was to evaluate the enhancing potency of tectochrysin, a flavonoid isolated from Alpinia oxyphylla Miquel by combining cetuximab, an anti-EGFR monoclonal antibody, on human colon cancer cell growth through further inhibition of EGFR pathway. HCT116 and SW480 colon cancer cells were treated with cetuximab (30 μg/mL, 1/10 of IC50), tectochrysin (5 μg/mL, 1/3 of IC50), or the combination of both agents. The growth inhibitory effect was examined using the MTT assay while apoptotic cell death was performed using TUNEL staining assays. The DNA binding activity of NF-kappa B and AP-1 was investigated by electrophoretic mobility shift assay. Protein expression was determined by Western blot. Cell proliferation was significantly inhibited by the combination of cetuximab and tectochrysin than treatment with cetuximab or tectochrysin alone (combination index: 0.572 and 0.533, respectively). Combination treatment of cells with cetuximab and tectochrysin significantly reduced the expressions of p-EGFR and COX-2 in both cell lines. Combination treatment also significantly inhibited activities of NF-kB and AP-1 compared to the single agent treatment. Our results indicate that combined therapy with lower concentration of cetuximab and tectochrysin could significantly enhance the cancer cell growth inhibitory effect through the inhibition of EGFR signaling.