Considering the problems involved in prevention of human lung cancer, growth inhibition of human lung cancer cell line A549 was studied with emphasis on two parameters: green tea polyphenols, such as (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG); and heterogeneous nuclear ribonucleoprotein B1 (hnRNP B1), a new biomarker of human lung cancer which is highly expressed in the very early stages of human lung cancer. The inhibitory potencies of green tea polyphenols were compared with those of genistein as a control. EGCG or ECG and genistein as a control dose-dependently inhibited the growth of A549 cells, which strongly elevated hnRNP B1 protein, and increased G2/M phase cells associated with induction of apoptotic cells. The results were confirmed by previous evidence with human lung cancer cell line PC-9. Some larger differences in mechanisms of action between green tea polyphenols and genistein were presented. Treatment of A549 cells with EGCG, ECG or genistein significantly inhibited the expression levels of hnRNP B1 mRNA and the elevated levels of hnRNP B1 protein, both of which are constitutively elevated in cancer cells. Furthermore, both EGCG and genistein inhibited the promoter activity of hnRNP A2/B1 gene expression, with IC50 values 29 μM for EGCG and 66 μM for genistein, suggesting the interaction of EGCG or genistein with the transcriptional complex. Looking at our results here, and those of previously reported epidemiological studies with green tea, we discuss the steadily accumulating evidence that clinical trials with green tea extract would be an efficient means of lung cancer prevention.

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