Essiac® (ES) and Flor-Essence® (FE) are two herbal teas widely taken by North American cancer patients during chemo- and radiation therapy. In vitro studies on the antiproliferative and differentiation inducing activities of these teas were performed. ES and FE showed negligible antiproliferative activity on Jurkat leukemia cells. Both herbal teas inhibited 50% (IC50) of MCF7 breast cancer cell growth at 1/10 dilution. The IC50 was about 1/40 and 1/10 dilution of FE and ES respectively for MDA-MB-468 human breast cancer cells. The IC50 for HL60 cells was at 1/10 dilution of FE and less than 1/10 dilution of ES. ES at 1/10 dilution induced expression of non-specific esterase in 16% of HL60 cells, compared to about 5% in FE treated cells and untreated controls. ES treatment of HL60 cells induced 47-67% nitroblue tetrazolium positive staining cells compared to 24.6±3.1% in cells treated with 1/10 dilution of FE. Flow cytometry analysis showed that both ES and FE treatment between 1/10 and 1/100 dilutions only slightly affected the cell cycle progression of MCF7, MDA-MB-468, Jurkat and HL60 cells. Our data show that both ES and FE herbal teas demonstrated antiproliferative and differentiation inducting properties in vitro only at high concentrations. Further research is needed to elucidate the in vivo activities.

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