Palm tocotrienols cause cleavage of poly-(ADP)-ribose polymerase enzyme and down-regulation of cyclooxygenase-2 protein level in human breast cancer cells

Breast cancer is a leading cause of cancer-related deaths in women globally. The anti-cancer effects of various forms of vitamin E from palm oil [tocotrienol-rich fraction (TRF): natural form of vitamin E complex in palm oil, tocotrienol-enriched fraction (TEF), and major vitamin E homologues in palm oil: α-tocopherol (αToc) and tocotrienols (T3) (α, δ or γ)] were tested on two human breast cancer cell lines [MDA-MB-231 (triple negative) and MCF-7 (oestrogen-dependent)]. Chronic inflammation plays a key role in tumourigenesis. Both cell lines used express high levels of poly-(ADP)-ribose polymerase-1 (PARP-1) and cyclooxygenase-2 (COX-2), which are key mediators of inflammation. Tocotrienols exerted marked anti-proliferative by promoting apoptosis in both MDA-MB-231 and MCF-7 cells. In addition, T3 also induced time-dependent inactivation of PARP-1 as well as inhibited expression of COX-2 in both MDA-MB-231 and MCF-7 cells. The rate of T3 uptake was found to be comparable to the anti-proliferative and apoptotic activities observed. In conclusion, T3 induced marked anti-proliferative (p<0.05) and pro-apoptotic (p<0.05) effects, which were most likely associated with PARP-1 inactivation and COX-2 down-regulation in these human breast cancer cells.