ABSTRACT
Breast cancer is the second most frequent cancer affecting women worldwide after lung cancer. The toxicity factor associated with synthetic drugs has turned the attention toward natural compounds as the primary focus of interest as anticancer agents. Vitamin E derivatives consisting of the well-established tocopherols and their analogs namely tocotrienols have been extensively studied due to their remarkable biological properties. While tocopherols have failed to offer protection, tocotrienols, in particular, α-, δ-, and γ-tocotrienols alone and in combination have demonstrated anticancer properties. The discovery of the antiangiogenic, antiproliferative, and apoptotic effects of tocotrienols, as well as their role as an inducer of immunological functions, not only reveals a new horizon as a potent antitumor agent but also reinforces the notion that tocotrienols are indeed more than antioxidants. On the basis of a transcriptomic platform, we have recently demonstrated a novel mechanism for tocotrienol activity that involves estrogen receptor (ER) signaling. In silico simulations and in vitro binding analyses indicate a high affinity of specific forms of tocotrienols for ERß, but not for ERα. Moreover, we have demonstrated that specific tocotrienols increase ERß translocation into the nucleus which, in turn, activates the expression of estrogen-responsive genes (MIC-1, EGR-1 and Cathepsin D) in breast cancer cells only expressing ERß cells (MDA-MB-231) and in cells expressing both ER isoforms (MCF-7). The binding of specific tocotrienol forms to ERß is associated with the alteration of cell morphology, caspase-3 activation, DNA fragmentation, and apoptosis. Furthermore, a recently concluded clinical trial seems to suggest that tocotrienols in combination with tamoxifen may have the potential to extend breast cancer-specific survival.
ABSTRACT
BACKGROUND: Tocotrienols belong to the vitamin E family and have multiple anticancer effects, such as antiproliferative, antioxidant, pro-apoptosis and antimetastatic. This study aimed to identify the genes that are regulated in human breast cancer cells following exposure to various isomers of vitamin E as these may be potential targets for the treatment of breast cancer. MATERIALS AND METHODS: Gene expression profiling was performed with MCF-7 cells at inhibitory conditions of IC(50) using Illumina's Sentrix Array Human-6 BeadChips. The expression levels of selected differentially expressed genes were verified by quantitative real-time-PCR (qRT-PCR). RESULTS: The treatment with tocotrienol-rich palm oil fraction (TRF), α-tocopherol and isomers of tocotrienols (α, γ, and δ) altered the expression of several genes that code for proteins involved in the regulation of immune response, tumour growth and metastatic suppression, apoptotic signalling, transcription, protein biosynthesis regulation and many others. CONCLUSION: Treatment of human MCF-7 cells with tocotrienol isomers causes the down-regulation of the API5 gene and up-regulation of the MIG6 gene and the differential expression of other genes reported to play a key role in breast cancer biology.
Subject(s)
Adaptor Proteins, Signal Transducing/genetics , Antineoplastic Agents/pharmacology , Apoptosis Regulatory Proteins/genetics , Breast Neoplasms/genetics , Gene Expression Regulation, Neoplastic/drug effects , Nuclear Proteins/genetics , Tocotrienols/pharmacology , Tumor Suppressor Proteins/genetics , Apoptosis Regulatory Proteins/antagonists & inhibitors , Cell Line, Tumor , Down-Regulation , Female , Humans , Nuclear Proteins/antagonists & inhibitors , Up-Regulation , alpha-Tocopherol/pharmacologyABSTRACT
INTRODUCTION: Basic research has indicated that tocotrienols have potent antiproliferative and proapoptotic effects that would be expected to reduce the effect of breast cancer. METHODS: We conducted a double-blinded, placebo-controlled pilot trial to test the effectiveness of adjuvant tocotrienol therapy in combination with tamoxifen for five years in women with early breast cancer. Two-hundred-forty women, aged between 40-60 years, with either tumor node metastases (TNM) Stage I or II breast cancer and estrogen receptor (ER) positive tumors were non-randomly assigned to two groups. The intervention group received tocotrienol rich fraction (TRF) plus tamoxifen whilst the control group received placebo plus tamoxifen, for five years. RESULTS: During the five years of study, 8 patients died due to breast cancer while 36 patients developed local or systemic recurrence. Five-year breast cancer specific survival was 98.3% (95% confidence interval (CI): 95.9% to 100%) in the intervention group and 95%, (95% CI: 91.1% to 98.9%) in the control group, while 5-years disease free survival was 86.7% (95% CI: 80.6% to 92.8%) and 83.3% (95% CI: 76.6% to 90.0%), respectively. Risk of mortality due to breast cancer was 60% (HR: 0.40; 95% CI: 0.08 to 2.05) lower in the intervention group versus the controls following adjustment for age, ethnicity, stage and lymph node status but this was not statistically significant. Adjuvant TRF therapy was not associated with breast cancer recurrence (HR: 0.84; 95% CI: 0.43-1.65). CONCLUSIONS: From the current study, there seems to be no association between adjuvant tocotrienol therapy and breast cancer specific survival in women with early breast cancer. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01157026.