EFFECT OF TOCOTRIENOLS ON THE GROWTH OF A HUMAN BREAST-CANCER CELL-LINE IN CULTURE

The tocotrienol-rich fraction (TRF) of palm oil consists of tocotrieno ls and some alpha-tocopherol (alpha-T). Tocotrienols are a form of vit amin E having an unsaturated sidechain, rather than the saturated side -chain of the more common tocopherols. Because palm oil has been shown not to promote chemically-induced mammary carcinogenesis, we tested e ffects of TRF and alpha-T on the proliferation, growth, and plating ef ficiency (PE) of MDA-MB-435 estrogen-receptor-negative human breast ca ncer cells. TRF inhibited the proliferation of these cells with a conc entration required to inhibit cell proliferation by 50% of 180 mu g/mL , whereas alpha-T had no effect at concentrations up to 1000 mu g/mL a s measured by incorporation of [H-3]thymidine, The effects of TRF and alpha-T also were tested in longer-term growth experiments, using conc entrations of 180 and 500 mu g/mL. We found that TRF inhibited the gro wth of these eel Is by 50%, whereas alpha-T did not, Their effect on t he ability of these cells to form colonies also was studied, and it wa s found that TRF inhibited PE, whereas alpha-T had no effect. These re sults suggest that the inhibition is due to the presence of tocotrieno ls in TRF rather than alpha-T.