Addressing the soy and breast cancer relationship: review, commentary, and workshop proceedings

The impact of soyfood intake on breast cancer risk has been investigated extensively. Much of this focus can be attributed to the soybean being a dietary source that is uniquely rich in isoflavones. The chemical structure of isoflavones is similar to that of estrogen, and isoflavones bind to both estrogen receptors (ER alpha and ER beta) (although they preferentially bind to and activate ER beta) and exert estrogen-like effects under some experimental conditions. Isoflavones also possess nonhormonal properties that are associated with the inhibition of cancer cell growth. Thus, there are several possible mechanisms by which soy may reduce the risk of breast cancer. However, the role of isoflavones in breast cancer has become controversial because, in contrast to the possible beneficial effects, some data from in vitro and animal studies suggest that isoflavones, especially genistein, the aglycone of the main soybean isoflavone genistin, may stimulate the growth of estrogen-sensitive tumors. Limited human data directly address the tumor-promoting effects of isoflavones and soy. Because the use of soyfoods and isoflavone supplements is increasing, it is important from a public health perspective to understand the impact of these products on breast cancer risk in women at high risk of the disease and on the survival of breast cancer patients. To this end, a workshop was held in November 2005 to review the existing literature and to make research recommendations. This paper summarizes the workshop findings and recommendations. The primary research recommendation is that the impact of isoflavones on breast tissue needs to be evaluated at the cellular level in women at high risk for breast cancer.     

Inhibitory effects of Bifidobacterium-fermented soy milk on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced rat mammary carcinogenesis, with a partial contribution of its component isoflavones

High consumption of soybean and soybean-related products is hypothesized to contribute to protection against breast cancer. Soybean is a rich source of genistein, a putative cancer chemopreventive agent. Fermented soy milk (FSM), which is made of soy milk fermented with the Bifidobacterium breve strain Yakult, contains larger amounts of the isoflavone aglycones genistein and daidzein than unfermented soy milk. In the present study, we examined the effects of FSM and its component isoflavone mixture (genistein:daidzein 4:1) on 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP)-induced mammary carcinogenesis in rats. Starting at 7 weeks of age, female Sprague-Dawley rats were given PhIP at a dose of 85 mg/kg body wt by intragastric administration four times a week for 2 weeks. They were fed control high fat basal diet or experimental high fat diet containing 10% FSM or 0.02 or 0.04% isoflavone mixture during and after carcinogen exposure. The incidences (percentage of rats with tumors) of mammary gland tumors were 71% in the control diet group, 51% in the FSM group and 68 and 61% in the groups treated with isoflavone mixture at 0.02 and 0.04%, respectively. Mammary tumor multiplicities (number of tumors per rat) were 1.2 +/- 0.2 for 10% FSM, 2.2 +/- 0.4 for 0.02% isoflavone mixture and 1.5 +/- 0.3 for 0.04% isoflavone mixture, being clearly smaller than the control diet value (2.6 +/- 0.5). Furthermore, feeding of FSM and the isoflavone mixture at both doses reduced the sizes of mammary tumors. Since the amounts of isoflavones in 10% FSM are approximately equivalent to those in the 0.02% isoflavone mixture, the chemopreventive activity of FSM could be partly attributable to the presence of isoflavones such as genistein and daidzein.     

Dietary genistein results in larger MNU-induced, estrogen-dependent mammary tumors following ovariectomy of Sprague-Dawley rats

Due to the estrogenic properties of soy-derived isoflavones, many postmenopausal women are using these compounds as a natural alternative to hormone replacement therapy (HRT). How isoflavones impact breast cancer in postmenopausal women is important, because a majority of breast cancer cases occur in this age group. Chemical induction of mammary tumors in female rats has been used to determine that exposure of the mammary gland to soy isoflavones prior to tumor induction is protective against tumor formation. Here we investigate the effect of dietary genistein on mammary tumors that have already formed. The study was designed to determine the action of dietary genistein in a low endogenous estrogen environment as is observed in postmenopausal women. Animals were ovariectomized (OVX) after mammary tumor development and were then placed into one of three treatment groups: positive-control (OVX+ estradiol implant), genistein (OVX+ 750 p.p.m. genistein) and negative-control (OVX alone). Tumors were distinguished as malignant or benign by histopathological examination and were further characterized as either estrogen-dependent or estrogen-independent using immunohistochemistry to identify the presence of both estrogen receptor (ER) alpha and the progesterone receptor (PR). Genistein at 750 p.p.m. increased the weight of estrogen-dependent adenocarcinomas in ovariectomized rats compared with the negative-control animals. Genistein treatment also resulted in a higher percentage of proliferative cells in tumors and increased uterine weights when compared with negative-control animals. Collectively, these effects are probably due to the estrogenic activity of genistein. Plasma genistein concentrations in animals fed the isoflavone-containing diet were at physiological levels relevant to human exposure. Estradiol concentrations in ovariectomized animals not receiving an estradiol supplement were similar to those observed in postmenopausal women. The data suggest that in an endogenous estrogen environment similar to that of a postmenopausal woman, dietary genistein can stimulate the growth of a mammary carcinogen MNU-induced estrogen-dependent mammary tumors.     

Soybean products and reduction of breast cancer risk: a case-control study in Japan

Components of the Japanese diet, which might contribute to the relatively low breast cancer incidence rates in Japan, have not been clarified in detail. Since soybean products are widely consumed in Japan, a case-control study taking account of the menopausal status was conducted using data from the hospital-based epidemiologic research program at Aichi Cancer Center (HERPACC). In total, 167 breast cancer cases were included and 854 women confirmed as free of cancer were recruited as the control group. Odds ratios (OR) and 95% confidence intervals (95% CI) were determined by multiple logistic regression analysis. There were reductions in risk of breast cancer associated with high intake of soybean products among premenopausal women. Compared with women in the lowest tertile, the adjusted ORs for top tertile intake of tofu (soybean curd) was 0.49 (95% CI, 0.25-0.95). A significant decrease in premenopausal breast cancer risk was also observed for increasing consumption of isoflavones (OR=0.44; 95% CI, 0.22-0.89 for highest vs lowest tertile; P for trend=0.02). The present study found a statistically inverse association between tofu or isoflavone intake and risk of breast cancer in Japanese premenopausal women, while no statistically significant association was evident with the risk among postmenopausal women.     

Effects of soybean isoflavones on cell growth and apoptosis of the human prostatic cancer cell line LNCaP

BACKGROUND: Epidemiological studies have suggested that soybean isoflavones are associated with a lower risk of prostate cancer. However, the mechanisms of prostate cancer prevention by soybean isoflavones have yet to be fully clarified. METHODS: Two soybean isoflavones (genistein and daidzein) and their glucosides (genistin and daidzin) were tested for their effects on cell growth and apoptosis of the LNCaP human prostatic cancer cell line. RESULTS: Among these isoflavones, genistein was found to inhibit the growth of LNCaP most effectively, with an IC50 value of 40 microM. The inhibition of cell growth by genistein was accompanied by the suppression of DNA synthesis and the induction of apoptosis. Expression of prostate-specific antigen (PSA) in LNCaP was also significantly reduced by the treatment with genistein. CONCLUSIONS: The results suggest that genistein might primarily influence human prostate cancer development by reducing tumor growth.      

Regulation of stromal versican expression by breast cancer cells and importance to relapse-free survival in patients with node-negative primary breast cancer.

PURPOSE: Determination of meaningful prognostic indicesremains a high priority for women diagnosed with node-negative primary breast cancer. Currently, 30% of these women relapse, and there is no reliable means of predicting this group of patients. This study investigates whether the level of expression of versican, an anticell adhesive proteoglycan, in the peritumoral stromal tissue of women with node-negative, primary breast cancer predicts relapse-free survival. This study also examines whether breast cancer cells regulate the secretion of versican by mammary fibroblasts. EXPERIMENTAL DESIGN: Immunoreactive versican was measured in breast cancer tissue sections of 58 node-negative patients by video image analysis. Primary isolates of mammary fibroblasts were cultured in medium conditioned by the breast cancer cell lines ZR-75-1, MCF-7, BT-20, and MB231. Changes in versican secretion were measured by immunoblotting and enhanced chemiluminescence. RESULTS: Cox analyses indicated that peritumoral versican level was the sole predictor of relapse-free survival. The relapse rate in patients with low versican levels was lower than in patients with high versican levels (Kaplan-Meier: 83% relapse free at 5 years for versican mean integrated absorbance <14 versus 33% for > or = 14, P = 0.0006). Accumulation of versican in medium of mammary fibroblasts was increased after culture in conditioned medium from breast cancer cell lines. CONCLUSIONS: Relapse in women with node-negative breast cancer is related to the level of versican deposited in peritumoral stroma by mammary fibroblasts. Versican secretion appears to be regulated by breast cancer cell mediators. Neoplastic remodeling of extracellular matrix through increased versican deposition may facilitate local invasion and metastasis.     

Trichostatin A is a histone deacetylase inhibitor with potent antitumor activity against breast cancer in vivo.

PURPOSE: Trichostatin A (TSA), an antifungal antibiotic with cytostatic and differentiating properties in mammalian cell culture, is a potent and specific inhibitor of histone deacetylase (HDAC) activity. The purpose of this study was to evaluate the antiproliferative and HDAC inhibitory activity of TSA in vitro in human breast cancer cell lines and to assess its antitumor efficacy and toxicity in vivo in a carcinogen-induced rat mammary cancer model. EXPERIMENTAL DESIGN AND RESULTS: TSA inhibited proliferation of eight breast carcinoma cell lines with mean +/- SD IC(50) of 124.4 +/- 120.4 nM (range, 26.4-308.1 nM). HDAC inhibitory activity of TSA was similar in all cell lines with mean +/- SD IC(50) of 2.4 +/- 0.5 nM (range, 1.5-2.9 nM), and TSA treatment resulted in pronounced histone H4 hyperacetylation. In randomized controlled efficacy studies using the N-methyl-N-nitrosourea carcinogen-induced rat mammary carcinoma model, TSA had pronounced antitumor activity in vivo when administered to 16 animals at a dose of 500 microg/kg by s.c. injection daily for 4 weeks compared with 14 control animals. Furthermore, TSA did not cause any measurable toxicity in doses of up to 5 mg/kg by s.c. injection. Forty-one tumors from 26 animals were examined by histology. Six tumors from 3 rats treated with TSA and 14 tumors from 9 control animals were adenocarcinomas. In contrast, 19 tumors from 12 TSA-treated rats had a benign phenotype, either fibroadenoma or tubular adenoma, suggesting that the antitumor activity of TSA may be attributable to induction of differentiation. Two control rats each had tumors with benign histology. CONCLUSIONS: The present studies confirm the potent dose-dependent antitumor activity of TSA against breast cancer in vitro and in vivo, strongly supporting HDAC as a molecular target for anticancer therapy in breast cancer.     

Effects of human recombinant alpha 2 arg-interferon and gamma-interferon on human breast cancer cell lines: dissociation of antiproliferative activity and induction of HLA-DR antigen expression

Human recombinant gamma-interferon (rhu-IFN-gamma) and human recombinant alpha-interferon (rhu-IFN-alpha 2 arg) with a chemical purity of over 95% were compared for their antiproliferative and HLA-DR-inducing activity in five human breast cancer cell lines (BT 20, ZR 75.1, MCF 7, 734B, Hs578T). Cytostatic effects on tumor cells were evaluated in monolayer cultures. HLA-DR antigen expression was examined by an indirect immunofluorescence technique using two different anti-HLA-DR monoclonal antibodies (anti-HLA-DR, VID-1) against framework determinants. rhu-IFN-gamma and rhu-IFN-alpha 2 arg differed in their antiproliferative efficiency in terms of both dose dependency and the spectrum of sensitive target cells. Combinations of rhu-IFN-gamma and rhu-IFN-alpha 2 always resulted in higher cytostatic effects. HLA-DR expression was exclusively inducible by rhu-IFN-gamma and did not correspond to its antiproliferative activity. Furthermore, HLA-DR expression did not depend on proliferation but did require intact RNA and protein syntheses as shown by inhibition with cycloheximide and actinomycin D. HLA-DR antigen expression in mammary cancer lines was dependent on time, dose, and the continued presence of rhu-IFN-gamma. Thus, our data suggest that in particular combinations type I and type II interferons might be useful in the treatment of breast cancer because they provide effective cytostatic and cell membrane-modulating properties.     

Anticancer SAR models for MCF-7 and MDA-MB-231 breast cell lines

The National Cancer Institute's Developmental Therapeutics Program (DTP) maintains the screening results obtained in 60 standardized cancer cell lines for ~43,000 compounds. Here the application of the categorical structure-activity relationship (cat-SAR) program for the identification of the structural attributes of identified compounds that display differential cytostatic or cytotoxic activity to one breast cancer cell line and not another is reported. The goal of this approach is to separate features associated with antiproliferative activity towards many cell lines from those that affect only a specific cell type. To assess this approach, SAR models were developed for cytostatic and cytotoxic activity against the human breast cancer cell lines MCF-7 and MDAMB-231 and three differential activity models for compounds that were potent cytostatic and cytotoxic agents in MCF-7 cells, but relatively inactive against MDA-MB-231 cells. The MCF-7 and MDA-MB-231 models comprised the most potent 200 active and least potent 200 inactive compounds found in the DTP database and the differential activity models comprised 200 compounds potent in one cell line and not the other and 200 compounds equally potent between the cell lines. Leave-one-out validations of the individual MCF-7 and MDA-MB-231 models returned values between 83 and 85% concordance, with values obtained between 66 and 76% concordance for the differential activity models. The cat-SAR approach identified the chemical attributes associated with cytostatic and cytotoxic activity for the MCF-7 and MDA-MB-231 breast cancer cell lines included in the DTP and furthermore, were able to differentiate the selective activity of compounds between the two breast cancer lines. Thus it is conceivable that such cell line-specific mechanisms could be exploited for the discovery of highly specific anti-breast cancer agents and could also potentially facilitate the development of SAR models with sufficient resolution and clarity to identify chemical moieties associated with antiproliferative activity towards selective individual cancer types while being innocuous to other cell types.     

Characterization of mammary cancer stem cells in the MMTV-PyMT mouse model

Breast cancer stem cells, the root of tumor growth, present challenges to investigate: Primary human breast cancer cells are difficult to establish in culture and inconsistently yield tumors after transplantation into immune-deficient recipient mice. Furthermore, there is limited characterization of mammary cancer stem cells in mice, the ideal model for the study of breast cancer. We herein describe a pre-clinical breast cancer stem cell model, based on the properties of cancer stem cells, derived from transgenic MMTV-PyMT mice. Using a defined set of cell surface markers to identify cancer stem cells by flow cytometry, at least four cell populations were recovered from primary mammary cancers. Only two of the four populations, one epithelial and one mesenchymal, were able to survive and proliferate in vitro. The epithelial population exhibited tumor initiation potential with as few as 10 cells injected into syngeneic immune-competent recipients. Tumors initiated from injected cell lines recapitulated the morphological and physiological components of the primary tumor. To highlight the stemness potential of the putative cancer stem cells, B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) expression was knocked down via shRNA targeting Bmi-1. Without Bmi-1 expression, putative cancer stem cells could no longer initiate tumors, but tumor initiation was rescued with the introduction of a Bmi-1 overexpression vector in the Bmi-1 knockdown cells. In conclusion, our data show that primary mammary cancers from MMTV-PyMT mice contain putative cancer stem cells that survive in culture and can be used to create a model for study of mammary cancer stem cells.     

Induction of thymidine phosphorylase expression and enhancement of efficacy of capecitabine or 5'-deoxy-5-fluorouridine by cyclophosphamide in mammary tumor models.

Thymidine phosphorylase (dThdPase) is an essential enzyme for the activation of the oral cytostatic drugs capecitabine (N(4)-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine, Xeloda(trade mark)) and its intermediate metabolite doxifluridine [5'-deoxy-5-fluorouridine (5'-dFUrd, Furtulon((R)))] to 5-fluorouracil (5-FUra) in tumors. In a previous study, we found that several cytostatics were able to up-regulate tumor levels of dThdPase in a human colon cancer xenograft model. In the present study, we confirmed that the administration of cytostatics used for breast cancer treatment, such as taxanes and cyclophosphamide (CPA), up-regulated the tumor level of dThdPase in mammary tumor models as well. Because the dThdPase up-regulation was observed even when CPA was given orally, we investigated further the usefulness of combination therapy with the 2 oral drugs, 5'-dFUrd/capecitabine and CPA in mammary tumor models. Daily oral administration of CPA up-regulated human dThdPase levels in the tumor tissue of mice bearing a human mammary tumor xenograft, MX-1, whereas in the small intestine and liver, it did not affect levels of pyrimidine nucleoside phosphorylases (PyNPase) including dThdPase and uridine phosphorylase. The preferential up-regulation of PyNPase activity in the tumor by CPA administration was also confirmed in mice bearing a syngeneic murine mammary adenocarcinoma, A755. In both models, combination therapy of 5'-dFUrd/capecitabine with CPA showed synergistic antitumor activity, without significant potentiation of toxicity. In contrast, treatment with CPA and either 5-FUra or UFT (a mixture of tegafur and uracil) in combination showed only additive activity. Our results suggest that CPA and capecitabine/5'-dFUrd, both available for oral administration, would be good partners, and that clinical trials with this drug combination against breast cancer are warranted.     

豆制品摄入与乳腺癌发生风险的系统评价

目的 评价豆制品摄入与乳腺癌发生风险的相关性.方法 检索CNKI、VIP、CBM、PubMed、EMBase、the Cochrane library数据库(1990-2010年),收集国内外发表的关于豆制品摄入与乳腺癌发生风险的病例对照研究资料,筛选符合纳入标准的研究,运用RevMan 5.0软件对相关数据进行Meta分析,采用漏斗图分析发表偏倚.结果 根据标准筛选出15篇文献其中13篇为英文,2篇中文,病例数7530,总人数32319,以进食豆制品的量分为常食组与偶食组,豆制品摄入与乳腺癌发生风险的Meta分析结果显示:OR=0.80,95%CI=(0.69,0.92),(P<0.05).结论 豆制品是乳腺癌发生的保护性因素,经常食用豆制品的妇女发生乳腺癌的风险降低.     

Epidemiological Evidences on Dietary Flavonoids and Breast Cancer Risk: A Narrative Review

Epidemiological studies on associations between intake of flavonoids and breast cancer risk are highly needed to assess the actual effects of flavonoids in humans. Experimental investigations in vitro conditions cannot detect and model the real action of these phytochemicals due to the limitations to consider absorption and metabolic biotransformation as well as several complex interactions. Therefore, the data about association findings between intake of flavonoids and breast cancer risk are compiled and analyzed in the current review by evaluating both the results obtained using food composition databases as well as different biomarkers. Although several case-control studies demonstrate some reduction in breast cancer risk related to high consumption of flavones and flavonols, large-scale prospective cohort studies with follow-up times of many years do not confirm these findings. Intake of isoflavones can be associated with a decrease in breast tumorigenesis only in Asian countries where the consumption of soy foods is high but not among Western women with significantly lower ingestion amounts, suggesting the presence of so-called threshold level of effect. Besides doses, the timing of exposure to isoflavones seems also to be a significant factor as childhood and prepubertal age can be critical periods. Although women may need to consume high amounts of isoflavones typical to Asian diets to gain beneficial effects and protection against mammary carcinogenesis, it is still too early to give any specific recommendations to prevent breast tumors by diet rich in certain flavonoids.     

乳腺癌组织中端粒酶活性的定量检测及其与临床病理的关系

背景与目的:端粒酶是一种在细胞永生化及癌症发生过程中起重要作用的核蛋白酶。最近关于乳腺癌中端粒酶活性与预后因素间的关系,因研究方法的差异而呈现出不一致的报道。本研究旨在建立一种可行的银染端粒酶定量检测法,以探讨乳腺癌中端粒酶活性与临床病理学预后因素间的关系。方法:运用银染端粒重复序列扩增法(SS-TRAP)检测了52例新鲜乳腺癌及其癌旁组织,32例乳腺良性病变和14例正常乳腺组织中端粒酶的活性表达,对结果予以定量并结合临床资料进行分析。结果:乳腺癌、癌旁组织、良性病变及正常乳腺组织中端粒酶阳性率分别为90.38%(47/52)、28.85%(15/52)、31.25%(10/32)、0(0/14)。端粒酶分别为36.91±15.35、8.27±4.37、14.10±5.28、0(TPG单位),单因素方差分析结果显示,乳腺癌组端粒酶活性水平明显高于其他3组(P值均<0.01)。Logistic回归分析结果表明,乳腺癌中端粒酶的表达与病理类型、分化程度明显相关(P=0.003及0.004),即随着肿瘤的进展,端粒酶活性亦增加。其中,浸润性非特殊癌端粒酶活性水平明显高于浸润性特殊癌(P<0.05);中、低分化癌端粒酶活性均高于高分化癌(P<0.05),中、低分化癌间无显著性差异(P>0.05)。端粒酶活性表达在患者病程、年龄、绝经状况间均无显著性差异(P>0.05)。结论:与经典TRAP