Cancer prevention by tea: animal studies, molecular mechanisms and human relevance

Abstract

Extracts of tea, especially green tea, and tea polyphenols have been shown to inhibit the formation and development of tumours at different organ sites in animal models. There is considerable evidence that tea polyphenols, in particular (-)-epigallocatechin-3-gallate, inhibit enzyme activities and signal transduction pathways, resulting in the suppression of cell proliferation and enhancement of apoptosis, as well as the inhibition of cell invasion,angiogenesis and metastasis. Here, we review these biological activities and existing data relating tea consumption to human cancer risk in an attempt to understand the potential use of tea for cancer prevention.

Figure 1. Possible targets for the cancer preventive activity of (−)-epigallocatechin -3-gallate (EGCG)

Some of these are direct targets through binding; others are affected indirectly. The reported effective concentrations, in IC₅₀, K_i. (inhibition constant) or K_d (dissociation constant) are shown in μM. All these are from studies in vitro. When two values are given, the first value is from cell-free systems and the second value is from studies in cell lines. 67LR, 67 kDa laminin receptor; CDK, cyclin-dependent kinase; DNMT, DNA methyltransferase; EGFR, epidermal growth factor receptor receptor; GRP78, glucose-regulated protein 78kDa; HGFR, hepatocyte growth factor receptor; IGF1R, insulin-like growth factor 1 receptor; MMP, matrix metalloproteinase; ROS, reactive oxygen species; VEGFA, vascular endothelial growth factor A.