Screening of natural products with anti-tumor activity as telomerase inhibitor is a new subject in the field of tumor therapy. Using telomerase PCR ELISA, telomere DNA hybridization and flow cytometry analysis, the effects of verbascoside, a phenylpropanoid glucoside extracted from Pedicularis striata Pall, on telomerase activity, telomere length and cell cycle of human gastric carcinoma cells MKN45 was examined in vitro . After being treated with a 50 % inhibition concentration of verbascoside (17.8 μg/ml), telomerase activity in the cells was significantly inhibited but not in the cellular supernatant, the average telomere length became remarkably short, and the sub-G0 /G1 peak and G2/M arrest were also displayed when compared to the control cells. These results suggest that verbascoside mediated-cell differentiation and apoptosis may be affected by telomere-telomerase-cell cycle dependent modulation. Thus, the antitumor mechanism of verbascoside is demonstrated once more by its inhibiting effect on telomerase activity in tumor cells, and the telomerase assay may provide a valuable screening method for antitumor activity of natural products. Abbreviations PCR:polymerase chain reaction ELISA:enzyme-linked immunosorbent assay DDW:disinfected distillation water TRAP:telomere repeat amplification protocol PPG:phenylpropanoid glycoside RT:room temperature OD:optical density tel IC 50 :50 % inhibition of the telomerase activity TRF:telomeric restriction fragments FCM:flow cytometry NC:nitrocellulose
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Zhang et al. (2002) studied this question.