Anticancer activity and mitochondrial mechanism of the vitamin E form delta-tocotrienol (delta-T3) was investigated in HER-2/neu-overexpressing human SKBR3 and murine TUBO breast cancer cells. delta-T3 was confirmed to possess high cytotoxic and apoptotic activity in SKBR3 cells as compared with all natural forms of vitamin E and several synthetic forms that included novel derivatives with the same backbone of delta-T3 such as delta-tocotrienyl-succinyl amide (delta-T3AS) and the redox-active analogue delta-tocotrienyl amine (delta-T3NH2). As observed in the case of alpha-TOS, a prototypical anticancer drug derived from alpha-tocopherol, succinylation of delta-T3 enhanced citotoxicity and apoptotic activity of the vitamer. delta-T3 induced apoptosis of SKBR3 cells was associated with mitochondrial destabilization, energy failure, and unbalanced activity of stress/survival MAPKs, namely p38 and ERK1/2 pathways. An increased generation of ROS followed to such a series of early events. Enhanced activity of delta-T3 in this human carcinoma cell line was characterized by the sustained uptake and oxidative transformation to the quinone derivative delta-T3Q, thereby suggesting redox effects in SKBR3 mitochondria by this vitamer. Viability and uptake data show a different pattern of responses in TUBO cells with higher response to synthetic derivatives of delta-T3 than in SKBR3 cells. In conclusion, synthetic derivatives of delta-T3 with enhanced apoptotic activity in breast carcinoma cells are investigated for the first time in this study also describing mechanistic aspects of mitochondrial effects of delta-T3. Further investigation in preclinical models of HER2/neu-high breast adenocarcinoma is underway to identify other and more effective forms of VE in this type of cancer.
