Inhibitory Effects of γ- and δ-Tocopherols on Estrogen-Stimulated Breast Cancer In Vitro and In Vivo

Abstract

Estrogens have been implicated as complete carcinogens for breast and other tissues through mechanisms involving increased cell proliferation, oxidative stress and DNA damage. Because of their potent antioxidant activity and other effects, tocopherols have been shown to exert anti-tumor activities in various cancers. However, limited information is available on the effect of different forms of tocopherols in estrogen-mediated breast cancer. To address this, we examined the effects of α-, γ- and δ-tocopherols as well as a natural γ-tocopherol rich mixture of tocopherols, γ-TmT, on estrogen-stimulated MCF-7 cells in vitro and in vivo. For the in vivo studies, MCF-7 cells were injected into the mammary fat pad of immunodeficient mice previously implanted with estrogen pellets. Mice were then administered diets containing 0.2% α-, γ-, δ-tocopherol or γ-TmT for 5 weeks. Treatment with α-, γ-, δ-tocopherols and γ-TmT reduced tumor volumes by 29% (p<0.05), 45% (p<0.05), 41% (p<0.05) and 58% (p<0.01), as well as tumor weights by 20%, 37% (p<0.05), 39% (p<0.05) and 52% (p<0.05), respectively. γ- and δ-Tocopherols and γ-TmT inhibited the expression of cell proliferation-related genes such as cyclin D1 and c-Myc, and estrogen-related genes such as TFF/pS2, cathepsin D and progesterone receptor in estrogen-stimulated MCF-7 cells in vitro. Further, γ- and δ-tocopherols decreased the levels of estrogen-induced oxidative stress and nitrosative stress markers, 8-hydroxy-2’-deoxyguanosine and nitrotyrosine, as well as the DNA damage marker, γ-H2AX. Our results suggest that γ- and δ-tocopherols and the γ-tocopherol rich mixture are effective natural agents for the prevention and treatment of estrogen-mediated breast cancer.

Vitamin E and cancer prevention: Studies with different forms of tocopherols and tocotrienols

“…Dietary administration of δ‐T and γ‐T, but not α‐T, was shown to inhibit tumorigenesis in ER‐positive breast cancer, while did not provide protective effects against ER‐negative and HER‐2 positive breast cancer, suggesting that the chemopreventive effects are due to estrogen‐mediated and ER‐dependent mechanisms 97 . δ‐T and γ‐T have been shown to inhibit estrogen‐stimulated breast cancer tumor growth 101 . In a breast cancer model, mice with MCF‐7 xenograft tumors implanted with estrogen, treatment with γ‐T, δ‐T, or γ‐TmT (2 g/kg diet) significantly reduced tumor volume and tumor weight, and inhibited cell proliferation‐related genes such as cyclin D1 and c‐Myc as well as estrogen‐related genes TFF/pS2, cathepsin D, and progesterone receptor 101 .…”

“…δ‐T and γ‐T have been shown to inhibit estrogen‐stimulated breast cancer tumor growth 101 . In a breast cancer model, mice with MCF‐7 xenograft tumors implanted with estrogen, treatment with γ‐T, δ‐T, or γ‐TmT (2 g/kg diet) significantly reduced tumor volume and tumor weight, and inhibited cell proliferation‐related genes such as cyclin D1 and c‐Myc as well as estrogen‐related genes TFF/pS2, cathepsin D, and progesterone receptor 101 . Furthermore, decreased the levels of estrogen‐induced oxidative stress and nitrosative stress markers, 8‐oxo‐dG, and nitrotyrosine, as well as the DNA damage marker, phosphorylated histone 2A variant X (γ‐H2AX), were evident 101 .…”

“…In a breast cancer model, mice with MCF‐7 xenograft tumors implanted with estrogen, treatment with γ‐T, δ‐T, or γ‐TmT (2 g/kg diet) significantly reduced tumor volume and tumor weight, and inhibited cell proliferation‐related genes such as cyclin D1 and c‐Myc as well as estrogen‐related genes TFF/pS2, cathepsin D, and progesterone receptor 101 . Furthermore, decreased the levels of estrogen‐induced oxidative stress and nitrosative stress markers, 8‐oxo‐dG, and nitrotyrosine, as well as the DNA damage marker, phosphorylated histone 2A variant X (γ‐H2AX), were evident 101 . The differences in chemopreventive efficacy of α‐T, δ‐T, γ‐T, and γ‐TmT (2 g/kg diet) were further evaluated in female August‐Copenhagen Irish (ACI) rats receiving estrogen implants in an experiment of 30 weeks.…”

“…164 However, in our studies in animal models with tocopherols at 2 or 3 g/kg diet did not produce any observable toxic effect. 93,94,97,[98][99][100][101][102]107,108,110,111 In our unpublished phase 0 study, a commercial γ-T-rich mixture of tocopherols (790 mg) were given daily to prostate cancer patients 2 weeks before surgery (as described in Section 2), estimated blood loss was not significantly different from the placebo group and no adverse events were observed (Yang et al, unpublished results).…”

Differential Gene Regulation and Tumor-Inhibitory Activities of Alpha-, Delta-, and Gamma-Tocopherols in Estrogen-Mediated Mammary Carcinogenesis

“…We have previously reported that δ-T, γ-T and γ-TmT suppress N -methyl- N -nitrosourea induced mammary tumor growth in Sprague Dawley rats (9,10). Recently, the tumor inhibitory effects of δ-T, γ-T and γ-TmT in MCF-7 xenografts supplemented with estrogen have been demonstrated (26). August-Copenhagen Irish (ACI) rats exhibit 80-100% tumor incidence upon prolonged exposure to estrogen (27), providing a physiologically relevant model for long-term cancer prevention studies.…”