Background: Tocotrienols, a subgroup of the vitamin E family, have demonstrated antioxidant and anticancer properties. Differential growth responses among different types of tocotrienols have been observed in breast cancer cells; however, specific bioactivity of each individual tocotrienol remains to be elucidated.
Materials and methods: In this study, the effects of gamma-tocotrienol were examined with regard to its ability to suppress cell proliferation via modulation of cell cycle regulatory protein expression, and also from the perspective of control of cellular oxidoreductive status through regulation of detoxification enzymes, e.g., quinone reductase NQO2, using estrogen receptor-positive MCF-7 human breast cancer cells.
Results: It was shown that treatment by gamma-tocotrienol suppressed MCF-7 cell proliferation in a dose- and time-dependent manner. Growth suppression by gamma-tocotrienol was accompanied by changes in the levels of cell cycle regulatory proteins, notably, Rb/E2F complex, cyclin D1/cdk4 and cyclin B1/cdk1, as exemplified by loss of cyclin D1, inhibition of specific Rb phosphorylation (pRb-p at Thr821), and by the time- and dose-dependent increase in the expression of NQO2.
Conclusion: By exerting control on expression of specific cell cycle regulatory proteins in concomitance with suppression of cell proliferation, as well as the induction of NQO2, gamma-tocotrienol offers promise as an added chemopreventive and/or chemotherapeutic agent against breast cancer carcinogenesis.