Synergistic inhibition of head and neck tumor growth by green tea (-)-epigallocatechin-3-gallate and EGFR tyrosine kinase inhibitor

One of the mechanisms of the antitumor activity of green tea (-)-epigallocatechin-3-gallate (EGCG) is associated with its effect on epidermal growth factor receptor (EGFR)-mediated signaling transduction pathways. We investigated whether combining EGCG with the EGFR-tyrosine kinase inhibitor (EGFR-TKI) erlotinib may augment erlotinib-induced cell growth inhibition of squamous cell carcinoma of the head and neck (SCCHN) in a mouse xenograft model. In vitro studies with 5 head and neck cancer cell lines revealed that synergistic cell growth inhibition by the combination of EGCG and erlotinib was associated with significantly greater inhibition of pEGFR and pAKT, increased activation of caspases 9, 3 and PARP compared to the inhibition induced by EGCG or erlotinib alone. Erlotinib inhibited phosphorylation of EGFR, stabilizing EGFR at the plasma membrane, whereas EGCG induced EGFR internalization and ubiquitin-degradation, ultimately undermining EGFR signaling. The efficacy of the combination treatment was investigated with nude mice (n = 25) orally gavaged with vehicle control, EGCG, erlotinib or the combination at the same doses for 7 days, followed by subcutaneous injection with Tu212 cells. Animals were continuously administered the agents 5 days weekly for 7 weeks. The combined treatment resulted in significantly greater inhibition of tumor growth and delayed tumor progression as a result of increased apoptosis, decreased cell proliferation and reduced pEGFR and pAKT compared to the single agent treatment groups. Our results suggest a synergistic antitumor effect of a combined treatment with EGCG and erlotinib, and provide a promising regimen for future chemoprevention and treatment of SCCHN. (C) 2008 Wiley-Liss, Inc.