Synergistic antiproliferative effects of γ-tocotrienol and statin treatment on mammary tumor cells

Statins are potent inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCoA) reductase and display anticancer activity, but their clinical use is limited by their high-dose toxicity. Similarly, gamma-tocotrienol, an isoform of vitamin E, also reduces HMGCoA reductase activity and displays potent anticancer activity. Studies were conducted to determine if combined low dose treatment of gamma-tocotrienol with individual statins resulted in a synergistic antiproliferative effect on neoplastic mouse +SA mammary epithelial cells. Treatment with 3-4 mu M gamma-tocotrienol or 2-8 mu M simvastatin, lovastatin or mevastatin alone resulted in a significant decrease, whereas treatment with 10-100 mu M pravastatin had no effect on +SA cell growth. However, combined treatment of subeffective doses (0.25 or 10 mu M) of individual statins with 0.25-2.0 mu M gamma-tocotrienol resulted in a dose-responsive synergistic inhibition in +SA cell proliferation. Additional studies showed that treatment with subeffective doses of individual statins or gamma-tocotrienol alone had no effect, whereas combined treatment of these compounds resulted in a relatively large decrease in intracellular levels of phosphorylated (activated) MAPK, JNK, p38, and Akt. These findings strongly suggest that combined low dose treatment of gamma-tocotrienol with individual statins may have potential value in the treatment of breast cancer without causing myotoxicity that is associated with high dose statin treatment.