Dietary lariciresinol attenuates mammary tumor growth and reduces blood vessel density in human MCF-7 breast cancer xenografts and carcinogen-induced mammary tumors in rats

Lariciresinol is a dietary lignan that accounts for a significant portion of the total phytoestrogen intake from Western foods. Recent epidemiological studies suggest that high dietary intake of lignans and lariciresinol is associated with reduced breast cancer risk. However, no causal relationship between lariciresinol intake and breast cancer development has been established. In this study, we investigated for the first time the effects and possible mechanisms of action of lariciresinol on hormone responsive mammary cancer in vivo in dimethylbenz[a]anthracene induced mammary cancer in rats, and in human MCF-7 breast cancer xenografts in athymic mice. For tumor bearing rats, lariciresinol (3 or 15 mg/kg of body weight) or vehicle was administered p.o. daily for 9 weeks. For E2-maintained ovariectomized athymic mice bearing orthotopic MCF-7 tumors, control diet (AIN-93G) or lariciresinol containing diet (AIN-93G supplemented with 20 or 100 mg of lariciresinol/kg of diet) was administered for 5 weeks. In both models, lariciresinol administration inhibited the tumor growth and tumor angiogenesis. In MCF-7 cells, enterolactone significantly inhibited the E2-stimulated VEGF secretion. Moreover, in MCF-7 xenografts, lariciresinol administration enhanced tumor cell apoptosis and increased estrogen receptor beta expression. Lariciresinol and its further metabolites secoisolariciresinol, enterodiol and enterolactone were found in serum of both rats and athymic mice confirming a similar lignan metabolism pattern as in humans. These findings indicate conceivable importance of dietary lignan lariciresinol in inhibition of breast cancer development.     

Dietary lignan intakes and risk of pre- and postmenopausal breast cancer

Lignans are plant compounds metabolized in the mammalian gut to produce the phytoestrogens enterolactone and enterodiol. Because estrogens have been linked to breast cancer etiology, lignans could affect breast cancer risk through modulation of endogenous estrogen metabolism or competitive inhibition with estrogen receptors. We examined breast cancer risk and dietary lignan intake in a population-based case-control study of 1,122 women with primary, incident, histologically confirmed breast cancer and 2,036 controls frequency matched to cases on age and county of residence as part of the Western New York Exposures and Breast Cancer (WEB) Study. Diet was assessed with a self-administered 104-item food frequency questionnaire and other relevant data were collected by detailed in-person interviews. Lignans were expressed as the sum of the dietary precursors secoisolariciresinol and matairesinol. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by unconditional logistic regression, adjusting for age, total energy and other breast cancer risk factors. Premenopausal women in the highest quartile of dietary lignan intake had reduced breast cancer risk (OR = 0.66; 95% CI = 0.44-0.98). No association was observed between lignan intakes and postmenopausal breast cancer. Our results suggest that dietary lignans may be important in the etiology of breast cancer, particularly among premenopausal women.     

Plasma insulin-like growth factor I levels in rats are reduced by dietary supplementation of flaxseed or its lignan secoisolariciresinol diglycoside

Flaxseed and its lignan secoisolariciresinol diglycoside (SDG) inhibit mammary tumor development in rats. Increased plasma insulin-like growth factor I (IGF-I) concentrations are associated with increased breast cancer risk. Therefore, the effect of flaxseed (5%) or SDG (1.5 mg/day) supplementation on plasma IGF-I levels was examined in rats treated with or without N-methyl-N-nitrosourea (MNU). In MNU-free rats, flaxseed and SDG reduced plasma IGF-I levels, which were inversely related to urinary lignan excretion. Only flaxseed significantly reduced plasma IGF-I concentrations in MNU-treated rats. The anticancer effect of flaxseed and SDG may be related, in part, to reductions in plasma IGF-I.     

Lignans and breast cancer risk in pre- and post-menopausal women: meta-analyses of observational studies

Phyto-oestrogens are plant compounds structurally similar to oestradiol, which have been proposed to have protective effects against breast cancer. The main class of phyto-oestrogens in the Western diet is lignans. Literature reports on the effect of lignans in breast cancer risk have been conflicting. We performed three separate meta-analyses to examine the relationships between (i) plant lignan intake, (ii) enterolignan exposure and (iii) blood enterolactone levels and breast cancer risk. Medline, BIOSIS and EMBASE databases were searched for publications up to 30 September 2008, and 23 studies were included in the random effects meta-analyses. Overall, there was little association between high plant lignan intake and breast cancer risk (11 studies, combined odds ratio (OR): 0.93, 95% confidence interval (95% CI): 0.83–1.03, P=0.15), but this association was subjected to marked heterogeneity (I²=44%). Restricting the analysis to post-menopausal women, high levels of plant lignan intake were associated with reduced breast cancer risk (7 studies, combined OR: 0.85, 95% CI: 0.78, 0.93, P<0.001) and heterogeneity was markedly reduced (I²=0%). High enterolignan exposure was also associated with breast cancer (5 studies, combined OR: 0.73, 95% CI: 0.57, 0.92, P=0.009) but, again, there was marked heterogeneity (I²=63%). No association was found with blood enterolactone levels (combined OR: 0.82, 95% CI: 0.59–1.14, P=0.24). In conclusion, plant lignans may be associated with a small reduction in post-menopausal breast cancer risk, but further studies are required to confirm these results.     

Dietary phytoestrogen intake and premenopausal breast cancer risk in a German case-control study

A diet high in isoflavonoids (soy) is associated with lower breast cancer risk in Asian populations. Due to the low soy intake, dietary lignans may be the more important phytoestrogen class in Western populations. We used a population-based case-control study of breast cancer by age 50 in southern Germany to evaluate the association between dietary intake of different phytoestrogens and premenopausal breast cancer risk. Dietary information was collected from 278 premenopausal cases and 666 age-matched controls, using a validated FFQ. Using multivariate logistic regression, the highest vs. lowest intake quartiles of daidzein and genistein yielded significantly reduced ORs (95% CI) for breast cancer risk of 0.62 (0.40-0.95) and 0.47 (0.29-0.74), respectively. The protective effects of daidzein and genistein were found only for hormone receptor-positive tumors. High intake of other isoflavonoids, e.g., formononetin and biochanin A, as well as the sum of isoflavonoids were not associated with a decrease in risk. Breast cancer risk significantly decreased with a high intake of the plant lignan matairesinol (OR = 0.58, 95% CI 0.37-0.94) but not secoisolariciresinol or the sum of plant lignans. However, both estimated mammalian lignans, enterodiol and enterolactone, were inversely associated with breast cancer risk, with ORs (95% CI) of 0.61 (0.39-0.98) and 0.57 (0.35-0.92), respectively. No effect was found for total phytoestrogen intake. Our results suggest an important role of dietary intake of daidzein and genistein, despite low levels, as well as of matairesinol and mammalian lignans to reduce premenopausal breast cancer risk in this study population.     

Dietary lignan intakes and risk of breast cancer by tumor estrogen receptor status

We examined the association of dietary lignan intake with estrogen receptor negative (ER−) and ER positive (ER+) breast cancer risk in a breast cancer case–control study. Among premenopausal women only, there was a reduced risk of ER− breast cancer for those in the highest compared to the lowest quartile of lignan intake suggesting that the observed negative association of lignans with breast cancer may be limited to ER− tumors.     

Flaxseed attenuates the tumor growth stimulating effect of soy protein in ovariectomized athymic mice with MCF-7 human breast cancer xenografts

In several epidemiological studies, a phytoestrogen-rich diet containing lignans and isoflavones is associated with reduced breast cancer risk, but experimental findings are controversial. In postmenopausal mammary cancer xenograft model, flaxseed (FS), a rich source of plant lignans, reduced breast cancer growth, while soy protein (SP), a rich source of isoflavones, enhanced it. The intake of phytoestrogens is increasing particularly among postmenopausal women, emphasizing the importance of elucidating their interactive effects on breast cancer. Our study determined the effect of FS and SP diets, alone and in combination, on the established human breast cancer MCF-7 tumor growth in ovariectomized athymic nude mice. Tumor bearing mice were divided into 4 groups and fed for 25 weeks either the basal diet (BD), or BD supplemented with 10% FS, 20% SP or 10% FS and 20% SP. After estrogen deprivation, FS regressed the tumor size similar to that of control. SP initially regressed the tumors but starting at week 13, the tumors regressed significantly less than in control and 43% of the tumors were regrowing until the end of the experiment and were significantly larger in size than in control. The combination of SP with FS reduced the tumor growth similar to that of control, as suggested also by the reduced tumor cell proliferation index. In conclusion, dietary FS did not stimulate the growth of estrogen responsive MCF-7 cancers in ovariectomized mice, while long-term consumption of SP did. Furthermore, FS reduced the tumor growth stimulating effect of SP to the same level as control, suggesting tumor growth attenuating effect of FS.     

Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer.

PURPOSE: Flaxseed, the richest source of mammalian lignan precursors, has previously been shown to reduce the growth of tumors in rats. This study examined, in a randomized double-blind placebo-controlled clinical trial, the effects of dietary flaxseed on tumor biological markers and urinary lignan excretion in postmenopausal patients with newly diagnosed breast cancer. EXPERIMENTAL DESIGN: Patients were randomized to daily intake of either a 25 g flaxseed-containing muffin (n = 19) or a control (placebo) muffin (n = 13). At the time of diagnosis and again at definitive surgery, tumor tissue was analyzed for the rate of tumor cell proliferation (Ki-67 labeling index, primary end point), apoptosis, c-erbB2 expression, and estrogen and progesterone receptor levels. Twenty-four-hour urine samples were analyzed for lignans, and 3-day diet records were evaluated for macronutrient and caloric intake. Mean treatment times were 39 and 32 days in the placebo and flaxseed groups, respectively. RESULTS: Reductions in Ki-67 labeling index (34.2%; P = 0.001) and in c-erbB2 expression (71.0%; P = 0.003) and an increase in apoptosis (30.7%; P = 0.007) were observed in the flaxseed, but not in the placebo group. No significant differences in caloric and macronutrient intake were seen between groups and between pre- and posttreatment periods. A significant increase in mean urinary lignan excretion was observed in the flaxseed group (1,300%; P < 0.01) compared with placebo controls. The total intake of flaxseed was correlated with changes in c-erbB2 score (r = -0.373; P = 0.036) and apoptotic index (r = 0.495; P < 0.004). CONCLUSION: Dietary flaxseed has the potential to reduce tumor growth in patients with breast cancer.     

Plasma enterolignans are associated with lower colorectal adenoma risk.

Lignans are biphenolic compounds that occur in foods of plant origin such as whole grains, seeds, fruits and vegetables, and beverages, such as coffee and tea. Plant lignans are converted by intestinal bacteria into the enterolignans, enterodiol and enterolactone. Enterolignans possess several biological activities, whereby they may influence carcinogenesis. We studied the associations between plasma enterolignans and the risk of colorectal adenomas in a Dutch case-control study. Colorectal adenomas are considered to be precursors of colorectal cancer. Cases (n = 532) with at least one histologically confirmed colorectal adenoma and controls (n = 503) with no history of any type of adenoma were included. Plasma enterodiol and enterolactone concentrations were measured by liquid chromatography with tandem mass spectrometry. Associations were stronger for incident than for prevalent cases. When only incident cases (n = 262) were included, high compared to low plasma concentrations of enterodiol were associated with a reduction in colorectal adenoma risk after adjustment for confounding variables. Enterodiol odds ratios (95% confidence intervals) were 1.00, 0.69 (0.42-1.13), 0.60 (0.37-0.99), and 0.53 (0.32-0.88) with a significant trend (P = 0.01) through the quartiles. Although enterolactone plasma concentrations were 10-fold higher, enterolactone's reduction in risk was not statistically significant (P for trend = 0.09). Use of oral antibiotic therapy could decrease the plasma concentrations of enterolactone. Exclusion of antibiotic users resulted in similar odds ratios for both enterolignans, but the association for enterolactone became somewhat stronger (P = 0.05 versus P = 0.09). We observed a substantial reduction in colorectal adenoma risk among subjects with high plasma concentrations of enterolignans, in particular, enterodiol. These findings could be important in the prevention of colorectal adenomas.     

Flaxseed inhibits metastasis and decreases extracellular vascular endothelial growth factor in human breast cancer xenografts

Angiogenesis is important in tumor growth, progression and metastatic dissemination. Vascular endothelial growth factor (VEGF) is one key factor in promotion of breast cancer angiogenesis. VEGFs are bioactive in the extracellular space where they become available to the endothelial cells. Phytoestrogens such as lignans have been shown to alter breast cancer incidence and be cancer-protective in rats. We show that supplementation of 10% flaxseed, the richest source of mammalian lignans, to nude mice with established human breast tumors reduced tumor growth and metastasis. Moreover, flaxseed decreased extracellular levels of VEGF, which may be one mechanistic explanation to the decreased tumor growth and metastasis.     

Differential sensitivity of human gastric cancer ATPase and normal gastric mucosa ATPase to the synthetic mammalian lignan analogue 2,3-dibenzylbutane-1,4-diol (hattalin)

Plasma membrane-associated adenosine triphosphatase (ATPase) samples partially purified from the tumor dissections of 15 gastric cancer patients were examined for sensitivity to the synthetic lignan, 2,3-dibenzylbutane-1,4-diol (hattalin), and ouabain in the presence of Mg2+, Na+, and K+. Hattalin was the strongest Na+, K(+)-ATPase inhibitor among the lignans previously examined. The enzyme from normal gastric tissue of the same patient was used as control. The specific activity of ATPase from cancer tissue (C-ATPase) was inhibited by more than 50% by 2.0 mM hattalin, whereas only 33.1% of the specific activity of ATPase from normal gastric mucosa (N-ATPase) was inhibited by 2.0 mM hattalin. There was statistical significance of lignan sensitivity between C- and N-ATPase (p less than 0.02). Ouabain also inhibited C-ATPase in preference to N-ATPase, though not significantly. Hattalin inhibited both C- and N-ATPase more strongly than did ouabain (p less than 0.05). Moreover, the lignan inhibited both C- and N-ATPase in the absence of Na+ and K+. From these data, it is evident that the sensitivity of plasma membrane-associated to lignan increased by gastric canceration. The target ATPase of hattalin is likely to be one other than sodium- and potassium-dependent, ouabain-sensitive ATPase.     

Plasma enterolactone and genistein and the risk of premenopausal breast cancer.

BACKGROUND: The scientific debate on the role of dietary phytoestrogens for prevention of breast cancer is still ongoing. We previously reported an inverse association between dietary phytoestrogen intake and premenopausal breast cancer risk and now examine the relationship with plasma phytoestrogen concentrations. METHODS: We measured enterolactone (mammalian lignan) and genistein (isoflavone) concentrations in plasma samples of 220 premenopausal cases and 237 age-matched controls from a population-based case-control study in Germany. RESULTS: Median plasma enterolactone concentrations in cases and controls were 6.3 and 9.7 nmol/l, respectively, and median genistein concentrations were 4.5 and 3.7 nmol/l, respectively. Premenopausal breast cancer risk decreased with increasing plasma enterolactone concentrations. Adjusted odds ratios (95% confidence intervals) were 0.42 (0.20-0.90) and 0.38 (0.17-0.85) (P for trend 0.007) for women in the third and fourth quartile of plasma enterolactone compared to those in the lowest quartile. There was no significant association between plasma genistein concentration and premenopausal breast cancer risk. CONCLUSION: Using biomarkers of phytoestrogen intake, we confirmed the strong inverse association between enterolactone and premenopausal breast cancer risk as found with dietary intake estimates. This result gives support to the potential role of mammalian lignans for breast cancer prevention among premenopausal women in Western populations.     

Urinary excretion of phytoestrogens and risk of breast cancer among Chinese women in Shanghai.

Although the majority of ecological and experimental studies have suggested a potential role of phytoestrogens in breast cancer prevention, findings from epidemiological studies have been inconsistent. Part of the inconsistencies may be attributable to the difficulty in measuring intake levels of phytoestrogens. Overnight urine samples from 250 incident breast cancer cases and their individually matched controls were analyzed for urinary excretion rates of isoflavonoids, mammalian lignans, and citrus flavonoids. The study subjects were a subset of the participants in the Shanghai Breast Cancer Study, a large population-based case-control study conducted in Shanghai from 1996-1998. To minimize potential influence of treatment on the exposure of interest, urine samples from breast cancer cases were collected before cancer therapy. Urinary excretion of total isoflavonoids and mammalian lignans was substantially lower in breast cancer cases than in controls. The median excretion rate of total isoflavonoids was 13.97 nmol/mg creatinine in cases and 23.09 in controls (P = 0.01), and the median excretion rate of total lignans was 1.77 in cases and 4.16 in controls (P < 0.01). The risk of breast cancer was reduced with increasing excretion of total isoflavonoids (P for trend, 0.04) and total lignans (P for trend, <0.01), with adjusted odds ratios of 0.62 (95% confidence interval, 0.39-0.99) and 0.40 (95% confidence interval, 0.24-0.64) observed for the highest versus the lowest tertile of total isoflavonoid and lignan excretion, respectively. The adjusted odds ratio was 0.28 (95% confidence interval, 0.15-0.50) for women who had a high excretion rate of both total lignans and isoflavonoids compared with those with a low excretion of both groups of phytoestrogens. No association was observed with citrus flavonoids. The results from this study suggest that high intake of certain phytoestrogens may reduce the risk of breast cancer.     

五味子对乳腺癌细胞抑制作用的体外研究

目的:评估中药五味子抗癌有效成分木酚素及其代谢产物对雌激素受体阳性以及阴性的乳腺癌细胞株的体外作用,并评价五味子对于乳腺癌的体外杀伤作用。方法:利用ATP 生物荧光药物敏感性检测技术(ATP-TCA),检测五味子木酚素对50例乳腺癌的体外杀伤作用,并检测不同浓度五味子木酚素及其代谢物（END、ENL）对于ER（＋）的MCF-7、T47D和ER（－）的MDA-MB-231、MDA-MB-435细胞株的杀伤作用。评价五味子的体外作用有效率及其与雌激素受体表型是否相关。结果:五味子对乳腺癌患者的乳腺癌细胞具有明显的体外杀伤作用,体外有效率为34.0%(17/50);五味子木酚素以浓度依赖的方式,显著降低乳腺癌细胞株MCF-7、T47D、MDA-MB-435、MDA-MB-231的存活率,且该抑制作用和细胞雌激素受体的关系并不明显（P＞0.05）,五味子木酚素在较低浓度（0.1-30μmol/L）下对雌激素受体阳性乳腺癌细胞株MCF-7、T47D表现出促进增殖的作用,当浓度提高至100μmol/L后,五味子木酚素对MCF-7、T47D增殖表现出显著的抑制作用,并呈剂量-效应关系。木酚素的低浓度促进乳腺癌细胞增殖作用在雌激素受体阴性乳腺癌细胞株MDA-MB-435、MDA-MB-231中并不明显,当浓度提高至100μmol/L后,五味子木酚素对MDA-MB-435、MDA-MB-231增殖表现出显著的抑制作用,并呈剂量-效应关系。ENL、END(3-1000μmol/L)在体外对乳腺癌细胞株存在显著抑制作用（P＜0.05）,并有剂量依赖效应,未发现其与细胞雌激素受体表型有关联（P＞0.05）。木酚素在较低浓度区间（0.1-30μmol/L）促进ER(＋)细胞株的增殖,但对ER(－)细胞株作用不显著。结论:五味子对乳腺癌细胞系以及乳腺癌患者细胞均具有较强的杀伤作用,值得进一步临床研究和应用。     

Phytoestrogen and cancer prevention

Phytoestrogens are defined to be plant chemicals that modify estrogenic effects in the body by binding to the estrogen receptors in mammals. Isoflavones, coumestane, lignan, and prenylflavones are examples of these, with isoflavones from soy foods and lignans from rye being a major dietary contribution. Mechanisms of cancer prevention by these phytoestrogens are reviewed, and human epidemiological studies, especially for breast and prostate cancers, are summarized and the results discussed.     

Phytoestrogen intake from foods,during adolescence and adulthood,and risk of breast cancer by estrogen and progesterone receptor tumor subgroup among Ontario women

Phytoestrogen intake may reduce breast cancer risk and limited evidence suggests this association may hold for hormone receptor‐positive tumors only. The study aims were to assess whether the association between phytoestrogen intake during adolescence and adulthood and breast cancer risk varies by estrogen and progesterone receptor (ERPR) tumor subgroup. Cases were identified from the Ontario Cancer Registry (2002–2003), and ERPR status was ascertained from pathology reports for 81% of cases (n = 2,438). Controls were identified through random digit dialing of Ontario households (n = 3,370). Published phytoestrogen food values were applied to food frequency questionnaire responses to assess isoflavone, lignan and total phytoestrogen intake, during adolescence and adulthood. Polytomous multivariate logistic regression was used to estimate adjusted odds ratios (ORs) for association between phytoestrogen intake and breast cancer risk by hormone receptor ERPR tumor subgroups. Among premenopausal women, few associations were observed for adolescent or adult phytoestrogen intake across all tumor subgroups. Among postmenopausal women, adolescent phytoestrogen intake (isoflavone, lignan and total) was associated with reduced risk across all hormone receptor subgroups; however, statistical significance was most consistent within the ER+PR+ subgroup. For example, ER+PR+ postmenopausal breast cancer risk was associated with adolescent phytoestrogen intake (highest vs. lowest: OR = 0.79; 95% confidence interval: 0.65–0.96). Among all women and postmenopausal women, ORs for high adult lignan intake were all below 1.0 within each tumor subgroup, suggesting reduced breast cancer risk, although none reached statistical significance. In conclusion, adolescent phytoestrogen intake was associated with reduced postmenopausal breast cancer, particularly for ER+PR+ tumor subgroup.     

The inhibitory effect of flaxseed on the growth and metastasis of estrogen receptor negative human breast cancer xenograftsis attributed to both its lignan and oil components

Our previous studies have shown that dietary flaxseed (FS) can reduce the growth and metastasis of human estrogen receptor negative (ER-) breast cancer in nude mice. The aims of our study were to determine (i) whether the tumor inhibitory effect of FS was due to its oil (FO), lignan secoisolariciresinol diglycoside (SDG), or both components, and (ii) whether the effect on tumor growth was related to increased lipid peroxidation. Athymic nude mice were orthotopically injected with ER- breast cancer cells (MDA-MB-435) and 8 weeks later were fed either the basal diet (BD) or BD supplemented with 10% FS, SDG, FO, or combined SDG and FO (SDG + FO) for 6 weeks. The SDG and FO levels were equivalent to the amounts in the 10% FS. Compared to the BD group, the tumor growth rate was significantly lower (p < 0.05) in the FS, FO, and SDG + FO groups, in concordance with decreased cell proliferation and increased apoptosis; however, these did not significantly relate to the lipid peroxidation, indexed as malonaldehyde (MDA), in the primary tumors. Lung metastasis incidence was reduced (16-70%) by all treatments, significantly in the FS and SDG + FO groups. The distant lymph node metastasis was significantly decreased (52%) only in the FO group. Although the total metastasis incidence was lowered (42%) significantly only in the SDG + FO group, all treatment groups did not differ significantly. In conclusion, FS reduced the growth and metastasis of established ER- human breast cancer in part due to its lignan and FO components, and not to lipid peroxidation.     

Do phytoestrogens reduce the risk of breast cancer and breast cancer recurrence? What clinicians need to know

Oestrogen is an important determinant of breast cancer risk. Oestrogen-mimicking plant compounds called phytoestrogens can bind to oestrogen receptors and exert weak oestrogenic effects. Despite this activity, epidemiological studies suggest that the incidence of breast cancer is lower in countries where the intake of phytoestrogens is high, implying that these compounds may reduce breast cancer risk, and possibly have an impact on survival. Isoflavones and lignans are the most common phytoestrogens in the diet. In this article, we present findings from human observational and intervention studies related to both isoflavone and lignan exposure and breast cancer risk and survival. In addition, the clinical implications of these findings are examined in the light of a growing dietary supplement market. An increasing number of breast cancer patients seek to take supplements together with their standard treatment in the hope that these will either prevent recurrence or treat their menopausal symptoms. Observational studies suggest a protective effect of isoflavones on breast cancer risk and the case may be similar for increasing lignan consumption although evidence so far is inconsistent. In contrast, short-term intervention studies suggest a possible stimulatory effect on breast tissue raising concerns of possible adverse effects in breast cancer patients. However, owing to the dearth of human studies investigating effects on breast cancer recurrence and survival the role of phytoestrogens remains unclear. So far, not enough clear evidence exists on which to base guidelines for clinical use, although raising patient awareness of the uncertain effect of phytoestrogens is recommended.     

Overexpression of KAI1 suppresses in vitro invasiveness and in vivo metastasis in breast cancer cells.

KAI1 is a metastasis suppressor gene for human prostate cancer and is also involved in the progression of a variety of other human cancers. Previously, we have demonstrated that KAI1 expression was down-regulated in metastatic breast cancer cell lines as well as in highly aggressive breast cancer specimens. To determine whether KAI1 expression is responsible for the metastasis suppression in breast cancer, we transfected the human KAI1 cDNA into two highly malignant breast cancer cell lines, LCC6 and MDA-MB-231, which both have low levels of endogenous KAI1 expression. Parental, vector-only transfectants and KAI1 transfectant clones were injected into the mammary fat pads and tail veins, respectively, of athymic nude mice and assessed for both spontaneous and experimental lung metastasis. High KAI1 expression significantly suppressed the metastatic potential of KAI1-transfected LCC6 cells. Metastasis suppression correlated with the reduced rate of tumor growth and a decreased clonogenicity in soft agar. Furthermore, KAI1 expression significantly suppressed the in vitro cell invasion in KAI1-transfected MDA-MB-231 cells. Our results suggested that KAI1 may function as a negative regulator of breast cancer metastasis.     

Prolactin binding to R3230AC mammary carcinoma and liver in hormone-treated and diabetic rats.

Specific 125I-labeled prolactin binding was measured in membrane particles prepared from R3230AC mammary carcinoma and liver of tumor-bearing Fischer rats after either prolactin, estrogen, or lergotrile mesylate treatment, or after the induction of diabetes by streptozotocin. Hormone binding to tumors was decreased by treatment with prolactin (0.5 or 1 mg/day) or estradiol valerate (7.5 mg/kg/week). In contrast, prolactin treatment did not affect prolactin binding to liver membrane particles, but estradiol valerate treatment resulted in a four-fold increase in prolactin binding to this tissue. Lergotrile mesylate, which lowers plasma prolactin levels, did not affect tumor growth or prolactin binding to either tumor or liver. Prolactin binding to both tumor and liver was significantly reduced in diabetic rats, suggesting that insulin may play an important role in controlling tissue sensitivity to prolactin. Specific binding of 125I-labeled prolactin to enzymatically dissociated cells from R3230AC tumors was demonstrated in vitro. The binding capacity of the cells was found to be of the same order of magnitude as the binding capacity in membrane preparations when appropriate corrections were applied for yields of cells and membranes. R3230AC tumor, which is responsive to prolactin appears therefore to be a useful model system for further study aimed at elucidation of growth and metabolic response to the hormone prolactin in breast cancer.