Hamamelitannin from Witch Hazel (Hamamelis virginiana) Displays Specific Cytotoxic Activity against Colon Cancer Cells

Hamamelis virginiana (witch hazel) bark is a rich source of condensed and hydrolyzable tannins reported to exert a protective action against colon cancer. The present study characterizes different witch hazel tannins as selective cytotoxic agents against colon cancer. To cover the structural diversity of the tannins that occur in H. virginiana bark, the hydrolyzable tannins, hamamelitannin and pentagalloylglucose, together with a proanthocyanidin-rich fraction (F800H4) were selected for the study. Treatment with these compounds reduced tumor viability and induced apoptosis, necrosis, and S-phase arrest in the cell cycle of HT29 cells, with hamamelitannin being the most efficient. Owing to polyphenol-mediated H2O2 formation in the incubation media, the antiproliferative effect was determined in the presence and absence of catalase to rule out any such interference. The presence of catalase significantly changed the IC50 only for F800H4. Furthermore, at concentrations that inhibit the growth of HT29 cells b...