Cancer Preventive Activities of Tea Catechins

Abstract

Catechins are widely occurring in our diet and beverages. The cancer-preventive activities of catechins have been extensively studied. Of these, (-)-epigallocatechin-3-gallate (EGCG), the principal catechin in green tea, has received the most attention. The inhibitory activities of tea catechins against carcinogenesis and cancer cell growth have been demonstrated in a large number of laboratory studies. Many mechanisms for modulating cancer signaling and metabolic pathways have been proposed based on numerous studies in cell lines with EGCG, the most active tea catechin. Nevertheless, it is not known whether many of these mechanisms indeed contribute to the anti-cancer activities in animals and in humans. Human studies have provided some results for the cancer preventive activities of tea catechins; however, the activities are not strong. This article reviews the cancer preventive activities and mechanisms of action of tea catechins involving their redox activities, biochemical properties and binding to key enzymes or signal transduction proteins. These mechanisms lead to suppression of cell proliferation, increased apoptosis and inhibition of angiogenesis. The relevance of the proposed mechanisms for cancer prevention are assessed in the light of the situation in vivo. The potential and possible problems in the application of tea and tea-derived products for cancer prevention are discussed.

Keywords: EGCG; animal models; cancer signaling; cell lines; tea catechins.

Figure 1

Structures of (−)-epigallocatechin-3-gallate (EGCG), (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epicatechin (EC).

Figure 2

Possible targets for the cancer preventive activity of EGCG (A) and subsequent cellular events (B). Some of these are direct binding targets; 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 (modified from [3]).