Synergistic enhancement of anticancer effects on numerous human cancer cell lines treated with the combination of EGCG, other green tea catechins, and anticancer compounds

In 2008, we reported that 10 Japanese-size cups of green tea daily, supplemented with tablets of green tea extract (GTE), reduced the recurrence of colorectal adenoma by 51.6 % in patients after polypectomy. Based on these results, we paid special attention to Japanese cancer patients, who consume green tea every day and are administered anticancer drugs. This encouraged us to study whether the combination of green tea catechins and anticancer drugs has the potential to enhance the efficacy of the drugs. The combination of GTE and NSAIDs synergistically inhibited tumor development in rodents through the activation of the GADD153-DR5-TRAIL apoptotic pathway. Since then, this study was further extended by various investigators to the combinations of EGCG and other green tea catechins with anticancer compounds, the latter of which include NSAIDs, phytochemicals, and anticancer drugs. In order to demonstrate whether diversity of the combinations would generally induce synergistic anticancer effects on numerous human cancer cell lines, we studied the results of 42 in vitro combination experiments and the synergistic inhibition of tumor volume of 13 combination experiments using xenograft mouse models, which were previously reported by other investigators. The various combinations of EGCG and anticancer compounds induced similar synergistic anticancer effects for both in vitro and in vivo experiments, and showed an average reduction in tumor volume by 70.3 %. Considering the evidence showing that treatment with EGCG inhibited self-renewal of cancer stem cells, the combination shows a great advantage. Green tea is a cancer preventive for humans, showing a new trend of green tea catechins as synergists with anticancer compounds.