MECHANISMS OF GROWTH-INHIBITION OF HUMAN LUNG-CANCER CELL-LINE, PC-9,BY TEA POLYPHENOLS

(-)-Epigallocatechin gallate (EGCG), the main constituent of green tea , and green tea extract show growth inhibition of various cancer cell lines, such as lung, mammary, and stomach. We studied how tea polyphen ols induce growth inhibition of cancer cells. Since green tea extract contains various tea polyphenols, such as EGCG, (-)-epigallocatechin ( EGC), (-)-epicatechin gallate (EGG), and (-)-epicatechin (EC), the inh ibitory potential of each tea polyphenol on the growth of a human lung cancer cell line, PC-9 cells, was first examined. EGC and ECG inhibit ed the growth of PC-9 cells as potently as did EGCG, but EC did not sh ow significant growth inhibition. The mechanism of growth inhibition b y EGCG was studied in relation to cell cycle regulation. Flow cytometr ic analysis revealed that treatment with 50 mu M and 100 mu M EGCG inc reased the percentages of cells in the G(2)-M phase from 13.8% to 15.6 % and 24.1%, respectively. The DNA histogram after treatment with 100 mu M EGCG was similar to that after treatment with genistein, suggesti ng that EGCG induces G(2)-M arrest in PC-9 cells. Moreover, we found b y microautoradiography that [H-3]EGCG was incorporated into the cytoso l, as well as the nuclei. These results provide new insights into the mechanisms of action of EGCG and green tea extract as cancer-preventiv e agents in humans.