In order to study the biological activities of tea preparations and purified tea polyphenols, their growth inhibitory effects were investigated using four human cancer cell lines. Growth inhibition was measured by [3H]thymidine incorporation after 48 h of treatment. The green tea catechins (-)-epigallocatechin-3-gallate (EGCG) and (-)-epigallocatechin (EGC) displayed strong growth inhibitory effects against lung tumor cell lines H661 and H1299, with estimated IC50 values of 22 microM, but were less effective against lung cancer cell line H441 and colon cancer cell line HT-29 with IC50 values 2- to 3-fold higher. (-)-Epicatechin-3-gallate, had lower activities, and (-)-epicatechin was even less effective. Preparations of green tea polyphenols and theaflavins had higher activities than extracts of green tea and decaffeinated green tea. The results suggest that the growth inhibitory activity of tea extracts is caused by the activities of different tea polyphenols. Exposure of H661 cells to 30 microM EGCG, EGC or theaflavins for 24 h led to the induction of apoptosis as determined by an annexin V apoptosis assay, showing apoptosis indices of 23, 26 and 8%, respectively; with 100 microM of these compounds, the apoptosis indices were 82, 76 and 78%, respectively. Incubation of H661 cells with EGCG also induced a dose-dependent formation of H2O2. Addition of H2O2 to H661 cells caused apoptosis in a manner similar to that caused by EGCG. The EGCG-induced apoptosis in H661 cells was completely inhibited by exogenously added catalase (50 units/ml). These results suggest that tea polyphenol-induced production of H2O2 may mediate apoptosis and that this may contribute to the growth inhibitory activities of tea polyphenols in vitro.

Many plant polyphenolic compounds have been shown to have cancer-preventing activities in laboratory studies. For example, tea and tea preparations have been shown to inhibit tumorigenesis in a variety of animal models of carcinogenesis, involving organ sites such as the skin, lungs, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, and prostate. In some of these models, inhibitory activity was demonstrated when tea was administered during the initiation, promotion, or progression stage of carcinogenesis. The cancer-preventing activities of these and other polyphenols, such as curcumin, genistein, and quercetin, are reviewed. In studies in vitro, many of these compounds have been shown to affect signal transduction pathways, leading to inhibition of cell growth and transformation, enhanced apoptosis, reduced invasive behavior, and slowed angiogenesis. However, the concentrations used in cell culture studies were much higher than those found in vivo. If we propose mechanisms for cancer prevention on the basis of cell line experiments, then these activities must be demonstrated in vivo. The bioavailability, ie, tissue and cellular concentrations, of dietary polyphenols is a determining factor in their cancer-preventing activity in vivo. For example, compounds such as curcumin are effective when applied topically to the skin or administered orally to affect the colon but are not effective in internal organs such as the lungs. More in-depth studies on bioavailability should facilitate correlation of mechanisms determined in vitro with in vivo situations, increase our understanding of dose-response relationships, and facilitate extrapolation of results from animal studies to human situations.

SKH-1 hairless mice were irradiated with ultraviolet B (UVB) twice weekly for 20 weeks. These tumor-free mice, which had a high risk of developing skin tumors during the next several months, were then treated topically with caffeine (6.2 mol) or (؊)-epigallocatechin gallate (EGCG; 6.5 mol) once a day 5 days a week for 18 weeks in the absence of further treatment with UVB. Topical applications of caffeine to these mice decreased the number of nonmalignant and malignant skin tumors per mouse by 44% and 72%, respectively. Topical applications of EGCG decreased the number of nonmalignant and malignant tumors per mouse by 55% and 66%, respectively. Immunohistochemical analysis showed that topical applications of caffeine or EGCG increased apoptosis as measured by the number of caspase 3-positive cells in nonmalignant skin tumors by 87% or 72%, respectively, and in squamous cell carcinomas by 92% or 56%, respectively, but there was no effect on apoptosis in nontumor areas of the epidermis. Topical applications of caffeine or EGCG had a small inhibitory effect on proliferation in nonmalignant tumors as measured by BrdUrd labeling (16 -22%), and there was also a similar, but nonsignificant, inhibitory effect on proliferation in malignant tumors. The results suggest a need for further studies to determine whether topical applications of caffeine or EGCG can inhibit sunlight-induced skin cancer in humans.tea constituents ͉ programmed cell death ͉ caspase 3 S kin cancer is a major cancer in the United States, and its incidence is expected to increase substantially because of increased recreational exposure to sunlight and depletion of the ozone layer (1, 2). The identification and use of protective agents should have an important impact on the formation of these cancers. Although the use of sunscreens is an approach that has decreased the risk of skin cancers (3, 4), there is also a need to identify additional approaches for skin cancer prevention in individuals previously exposed to high-dose levels of sunlight (high-risk individuals). Treatment of SKH-1 hairless mice with ultraviolet B (UVB) (30 mJ͞cm 2 ) twice a week for 20 weeks resulted in mice without tumors but with epidermal hyperplasia and a high risk of developing skin tumors during the next several months in the absence of further UVB treatment (initiated high-risk mice) (5). This animal model resembles humans who are heavily exposed to sunlight early in life and then have reduced exposure later in life. We have used UVB-pretreated high-risk mice for evaluating the effects of potential chemopreventive agents on skin tumor formation in the absence of further exposure to UVB. Oral administration of green tea, black tea, or caffeine to UVBpretreated high-risk mice inhibited tumorigenesis, but the decaffeinated teas had little or no activity, and reconstitution of the decaffeinated teas with caffeine restored biological activity (5). These observations indicate that caffeine is a major cancer chemopreventive constituent in tea. Potential antitumor mechanisms include...

Recent advancements in single-cell RNA sequencing (scRNA-seq) have facilitated the classification of thousands of cells through transcriptome profiling, wherein accurate cell type identification is critical for mechanistic studies. In most current analysis protocols, cell type-based cluster annotation is manually performed and heavily relies on prior knowledge, resulting in poor replicability of cell type annotation. This study aimed to introduce a single-cell Cluster-based Automatic Annotation Toolkit for Cellular Heterogeneity (scCATCH, https://github.com/ZJUFanLab/scCATCH). Using three benchmark datasets, the feasibility of evidence-based scoring and tissue-specific cellular annotation strategies were demonstrated by high concordance among cell types, and scCATCH outperformed Seurat, a popular method for marker genes identification, and cell-based annotation methods. Furthermore, scCATCH accurately annotated 67%-100% (average, 83%) clusters in six published scRNA-seq datasets originating from various tissues. The present results show that scCATCH accurately revealed cell identities with high reproducibility, thus potentially providing insights into mechanisms underlying disease pathogenesis and progression.

The present study was designed to investigate the effects of two main constituents of green tea, (À)-epigallocatechin-3-gallate (EGCG) and caffeine, on intestinal tumorigenesis in Apc min/+ mice, a recognized mouse model for human intestinal cancer, and to elucidate possible mechanisms involved in the inhibitory action of the active constituent. We found that p.o. administration of EGCG at doses of 0.08% or 0.16% in drinking fluid significantly decreased small intestinal tumor formation by 37% or 47%, respectively, whereas caffeine at a dose of 0.044% in drinking fluid had no inhibitory activity against intestinal tumorigenesis. In another experiment, small intestinal tumorigenesis was inhibited in a dose-dependent manner by p.o. administration of EGCG in a dose range of 0.02% to 0.32%. P.o. administration of EGCG resulted in increased levels of E-cadherin and decreased levels of nuclear B-catenin, c-Myc, phospho-Akt, and phospho-extracellular signal-regulated kinase 1/2 (ERK1/ 2) in small intestinal tumors. Treatment of HT29 human colon cancer cells with EGCG (12.5 or 20 Mmol/L at different times) also increased protein levels of E-cadherin by 27% to 58%, induced the translocation of B-catenin from nucleus to cytoplasm and plasma membrane, and decreased c-Myc and cyclin D1 (20 Mmol/L EGCG for 24 hours). These results indicate that EGCG effectively inhibited intestinal tumorigenesis in Apc min/+ mice, possibly through the attenuation of the carcinogenic events, which include aberrant nuclear B-catenin and activated Akt and ERK signaling. (Cancer Res 2005; 65(22): 10623-31)