Induction of apoptosis in human leukemia cells by black tea and its polyphenol theaflavin Trina Kundu a , Subhabrata Dey b , Madhumita Roy a , M. Siddiqi c , R.K. Bhattacharya a, * a Department of Environmental Carcinogenesis and Toxicology, Chittaranjan National Cancer Institute, 37 S.P. Mukherjee Road, Kolkata 700 026, India b HPLC Unit, CRIF, Chittaranjan National Cancer Institute, 37 S.P. Mukherjee Road, Kolkata 700 026, India c Bose Institute, Centenary Building, P-1/12, CIT Scheme VIIM, Kolkata 700 054, India Received 14 September 2004; received in revised form 18 December 2004; accepted 20 December 2004 Abstract Treatment of human leukemic cell lines HL-60 and K-562 with extracts of green and black tea and their polyphenols epigallocatechin gallate and theaflavins, respectively, showed a dose dependent inhibition of growth as a result of cytotoxicity and suppression of cell proliferation. Based on the IC 50 values obtained from cytotoxicity data it was clearly evident that black tea was as efficient as green tea. Analysis of polyphenol contents of tea extracts revealed that not only epigallocatechin gallate, which is a predominant polyphenol of green tea, but also theaflavin that is abundantly present in black tea affords significant chemotherapeutic action by imparting cytotoxicity to human leukemic cells. Electrophoretic analysis of fragmented DNA from treated cells displayed characteristic ladder pattern. Flow cytometric analysis revealed the dose dependent increase in sub-G 1 peak. These criteria confirmed that cytotoxic activity of green and black tea was due to induction of apoptosis. Such induction was found to be mediated through activation of caspases 3 and 8, particularly caspase 3 and by altering apoptosis related genes as evident by down-regulation of Bcl-2 and up-regulation of Bax proteins. q 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Apoptosis; Leukemia cells; Black tea; Theaflavin 1. Introduction Program cell death (apoptosis) is an important process in the development and tissue homeostasis. This phenomenon occurs in cells injured by certain levels of toxic agents. This is a crucial process for eliminating cancer cells. Therefore, induction of apoptosis is a key mechanism by which anticancer therapy works. In recent years, attention has been paid to food components with potential cancer inhibiting effect. Identification of effective chemopreventive diets or dietary supplements for human use is of much interest. Polyphenols present in food have been demonstrated to decrease various types of experimental carcinogenesis. Tea and its polyphenols, 0304-3835/$ - see front matter q 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.canlet.2004.12.035 Cancer Letters 230 (2005) 111–121 www.elsevier.com/locate/canlet * Corresponding author. Tel.: C91 33 476 5101; fax: C91 33 475 7606. E-mail addresses: mitacnci@yahoo.co.in (M. Roy), rathin_b2001@yahoo.co.in (R.K. Bhattacharya).