Positive Health Online

Abstract

GUTHRIE and colleagues, Deaprtment of Biochemistry, The University of Western Ontario, London, Canada studied the inhibition of proliferation of oestrogen receptor-negative human breast cancer cells with various forms and mixtures of vitamin E, in combination with tamoxifen.

Background

Methodology

and RESULTS: Tocotrienols are a form of vitamin E with an unsaturated isoprenoid side chain rather than the saturated side-chain of tocopherols. The tocotrienol-rich fraction (TRF) from palm oil contains alpha-tocopherol and a mixture of alpha-, gamma- and delta- tocotrienols which have, in previously published research by the authors, demonstrated inhibition of proliferation of oestrogen receptor-negative MDA-MG-435 human breast cancer cells in 50% inhibitory concentrations (IC50) of 180, 90, 30 and 90 microg/ml for TRF, alpha-, gamma- and delta-tocotrienols respectively, with alpha-tocopherol showing no effect even up to 500 microg/ml. Tocotrienols also inhibited oestrogen receptor-positive MCF-7 human breast cancer cells with IC50s of 4, 125, 6, 2 and 2 microg/ml respectively. Tamoxifen, the widely used synthetic antioestrogen inhibited the growth MCF-7 cells with an IC50 of 0.04 microg/ml. In experiments with 1:1 combinations of TRF, alpha-tocopherol and individual tocotrienols with tamoxifen in MDA-MB-435 cells, all combinations were found to be synergistic, whereas in MCF-7 cells, only 1:1 combinations of gamma- or delta-tocotrienol with tamoxifen demonstrated a synergistic inhibitory effect upon cell proliferation and growth. The inhibition by tocotrienols was not overcome by addition of excess oestradiol.

Results

Conclusion

These results suggest that tocotrienols are effective inhibitors of oestrogen receptor-negative and -positive cells and that combinations with tamoxifen may be considered as a potential improvement to breast cancer therapy.

References

Guthrie N et al. Inhibition of proliferation of estrogen receptor-negative MDA-MB-435 and -positive MCF-7 human breast cancer cells by palm oil tocotrienols and tamoxifen, alone and in combination. J Nutr 127(3): 544S-548S. Mar 1997.