Effects of Epigallocatechin-3-gallate on Growth, Epidermal Growth Factor Receptor Signaling Pathways, Gene Expression, and Chemosensitivity in Human Head and Neck Squamous Cell Carcinoma Cell Lines

Abstract

The antitumor effects of the green tea compound epigallocatechin-3-gallate (EGCG) have not been studied in detail previously in head and neck squamous cell carcinoma (HNSCC) cells. Overexpression of the epidermal growth factor receptor (EGFR) occurs frequently in HNSCC, which is an adverse prognostic factor. Therefore, we examined in detail the molecular effects of EGCG on two human HNSCC cell lines, YCU-N861 and YCU-H891, focusing on the EGFR signaling pathway. The 70% lethal dose (IC₇₀) of EGCG for both cell lines was 10 μg/ml. Treatment with EGCG increased the proportion of cells in the G₁ phase of the cell cycle and induced apoptosis. In cells treated with EGCG, there was a decrease in the cyclin D1 protein, an increase in the p21^Cip1 and p27^Kip1 proteins, and a reduction in the hyperphosphorylated form of pRB, changes that may account for the arrest in G₁. EGCG also caused a decrease in the Bcl-2 and Bcl-X_L proteins, an increase in the Bax protein, and activation of caspase 9, suggesting that EGCG induces apoptosis via a mitochondrial pathway. Treatment with EGCG inhibited phosphorylation of the EGFR, signal transducer and activator of transcription3 (Stat3), and extracellular regulated kinase (ERK) proteins and also inhibited basal and transforming growth factor-α-stimulated c-fos and cyclin D1 promoter activity. EGCG at 0.1 μg/ml (a concentration found in serum after oral administration) markedly enhanced the growth-inhibitory effects of 5-fluorouracil. Taken together, these findings provide insights into molecular mechanisms of growth inhibition by EGCG and suggest that this naturally occurring compound may be useful, when used alone or in combination with other agents, in the chemoprevention and/or treatment of HNSCC.