INTRODUCTION
Breast cancer is the most common female cancer globally, representing nearly a quarter (25%) of all cancers. Organic carcinogens covalently bind DNA formingstable and depurinating adducts. The compound 4-hydroxyestradiol and estradiol-3, 4-quinone (E1(E2)-3,4-Q)) produces significantly higher levels of depurinating adduct and smaller stable adduct (1). These estrogen-DNA adducts are quickly lost by the cleavage of the glycosyl bond from DNA and create apurinic sites that can cause cancer (2,3). Mounting evidences demonstrate that a few E2 metabolites (i.e. CE-3, 4-Q) interact with DNA and form 4-OHE1(E2)−1-N3Ade and 4-OHE1(E2)-1-N7Gua that causes DNA mutation  and potential cellular transformation (4,5).
The use of human breast epithelial cell lines such as MCF-10F, an immortalized, non-transformed estrogen receptor (ER)-α-negative cell line has identified the initiation of cancer by estrogen-DNA adducts. Results indicate that beside the alteration of E2-ER signaling, genotoxic effects via estrogen metabolite are partly responsible for the malignant transition . These findings support the hypothesis that the availability of the active estrogen is a critical determinant in the treatment of some breast cancer.
A large percentage of breast cancers are sensitive to estrogen and have a good response to endocrine therapy based on selective ER modulators (SERM) i.e. tamoxifen (7) and fulvestrant (8). Reduction in estrogen synthesis by aromatase-inhibitors of is also a vital strategy (9). Beyond these strategies, estrogen metabolizing enzymes are given less priority for research. SULT1E1, a phase II metabolizing enzyme that is located in the cytoplasm and responsible for sulfonation of estrogen (10). SULT1E1 polymorphisms are shown to be a risk factor for breast and endometrial cancers, (11) suggesting that its modulation might be an attractive strategy in the prevention, management and or treatment of breast cancer. In contrary, the steroid sulfatases (STs) converts water soluble sulfated-estrogen to insoluble estrogen in the target tissues. Roughly, it sketches that activation of SULT1E1 and inhibition of STS might work in favor of breast cancer treatment.
The induction of SULT1E1 along with anti-breast cancer action of TM208 and tamoxifen (ER antagonist) may bring better treatment outcomes in hormone ER+ breast cancers. Estrogen is differentially metabolized in healthy ovarian surface epithelium (OSE) and in epithelial ovarian cancer (EOC) cells. Total mRNA assay by qRT-PCR revealed significantly higher SULT1E1 mRNA expression in OSE than in EOC. Inflammatory cytokines further augmented the local production of E2 by stimulating STS and suppressing SULT1E1 (12). It was concluded that the local estrogen metabolism may be a target for EOC treatment. SULT1E1 is transcriptionaly regulated under oxidative stress, and is also a target of NRF2. Oxidative stress responses augment Nrf-2 and HIF-1a in breast cancer cell. Hypoxia Inducing Factor (HIF) target genes in every step of the metastatic process. Digoxin which blocks HIF action eventually decreases primary tumor growth, vascularization and invasive metastasis in animal models of breast cancer (13,14). Degeneration of extracellular matrix is implicated as the metastatic growth factor and MMPs are highly expressed in advanced breast cancer. A high expression of MMP-2 and MMP-9 was found in >75% of breast cancer patients (15). So, it is suggested that the restriction in HIF1α and MMP activities may have therapeutic prospects against breast cancer.
In our earlier study, we explored that the pre-tumorigenic condition induced by ethylnitrosourea (ENU) and E2 showed impairment of SULT1E1 expression and E2 regulations via oxidant-stress signaling (16). Thus, induction and activation of SULT1E1 might become cancer prevention and treatment startegy. An earlier study demonstrated that dialylsulfide (DAS) treatment caused the nuclear accumulation of constitutive androstane receptor (CAR) resulting in a significant increase of SULT1E1 mRNA and protein in the liver of female mice. DAS effectively reduces lipid peroxidation, recovering cell viability, attenuating DNA strand breaks in cultured breast cancer MCF-10A cells (17). Despite of significant SULT1E1 induction by DAS, the endogenous E2 level was unaltered and no increase in estrone sulfate level was noticed. Contrarily, the clearance of exogenously administrated E2 was accelerated in DAS treated mice (18). This suggests that under variable oxidative stress condition, SULT1E1 transits between gain and loss of enzyme activity Our previous report suggests that oxidative stress induced SULT1E1 modifications may be similar in human breast cancer tissue and experimental animal model (16). Further study demonstrates that transcriptional regulation of stress, promotes Nrf-2 and proinflammatory marker NFkβ through E2 mediated signaling. These signallings are also associated with breast cancer initiation and severity. So, a reducing environment is required to keep SULT1E1 active which may keep E2 levels under control, SULT1A1 also sulfoconjuagtes E2 but at higher concentration and definitely contributes to control the E2 pool. Chalcone posses oxidative stress relieving property and and act as antioxidant in different diseases (19). Hence, we opted for Chalcone in this study to induce cellular reducing environment to keep SULT1E1 active together with Dialylsulfide that induces mRNA/protein expression of SULT1E1. Our present study may have some therapeutic implications in breast cancers.