Triple-negative breast cancers (TNBCs) lack the estrogen receptor, progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). Therefore, hormone or targeted therapies are not effective in the treatment of TNBC and thus the development of novel therapeutic strategies is crucial. Methotrexate (MTX), a folate antagonist, has been used in the treatment of various types of cancer; however, the anticancer effects of MTX treatment on breast cancer have thus far been ineffective. Vitamin E variants and derivatives have been applied for cancer therapy. Previous studies have indicated that vitamin E variants and derivatives exert distinct anticancer effects on different types of cancer. However, whether MTX plus vitamin E variants or its derivatives can inhibit TNBC remains unclear. The aim of the present study was to examine the anticancer effects and mechanisms of action of MTX in combination with vitamin E variants (α-tocopherol) and derivatives (α-tocopherol succinate) on TNBC. In the present study, MTT assay and western blot analysis were used to determine the cell survival rates and protein levels. The results demonstrated that combination treatment with MTX and α-tocopherol suppressed TNBC cell proliferation. In addition, various concentrations of MTX exerted distinct cytotoxic effects on α-tocopherol succinate-treated cells. Furthermore, high-dose MTX enhanced α-tocopherol succinate-induced anticancer activity; however, low-dose MTX inhibited α-tocopherol succinate-induced anticancer activity. The present study also demonstrated that caspase-3 activation and poly(adenosine diphosphate-ribose) polymerase cleavage were observed in the α-tocopherol succinate/MTX-treated cells. In conclusion, the findings of the present study demonstrated that high-dose MTX enhanced anticancer activity in α-TOS-treated TNBC, while low-dose MTX reduced anticancer activity in α-TOS-treated TNBC.

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