Effects of Tamoxifen on Endometrial Carcinogenesis in Mice

Two experiments were conducted to determine the effect of tamoxifen (TAM) in mouse endometrium in comparison with that of 17β-estradiol (E₂). In a medium-term assay, TAM as well as E₂ treatment semi-dose-dependently increased the levels of fos/jun mRNA and their oncoproteins (Fos/Jun). The long-term effect of TAM on mouse endometrial carcinogenesis was also examined in the following model. A total of 150 female ICR mice, 12–13 weeks of age, were used. Of these, 125 mice received an injection of N-methyl-N-nitrosourea (MNU) solution (1 mg/100 g body weight) into their left uterine tube and saline into the right. One week later, they were divided into four groups: groups 1 (35 mice) and 2 (30 mice) were given 25 ppm and 5 ppm E₂-containing diet, respectively, while group 3 (30 mice) was fed 5 ppm TAM-containing diet. Group 5 (30 mice) was fed basal diet alone. The remaining 25 mice (group 4) received 5 ppm TAM-containing diet alone. At the termination of the experiment (30 weeks), endometrial carcinomas were confirmed to be present in the groups exposed to MNU. TAM increased the incidence of preneoplastic lesions of the endometrium, while E₂ enhanced the occurrence of the carcinoma. No carcinomas were found in the group given TAM alone. In the ovaries, corpora lutea were lacking in most of the mice exposed to TAM, suggesting that the animals were not cycling. Such findings indicate that TAM has an enhancing effect on endometrial carcinogenesis in mice, probably via a mechanism involving overexpression of Fos/Jun proteins.     

Inhibitory Effects of Medroxyprogesterone Acetate on Mouse Endometrial Carcinogenesis

The present study was undertaken to examine the effects of cyclic administration of low-dose progestogen on endometrial carcinogenesis in mice. A total of 115 female ICR mice, 10 weeks of age, were divided into four experimental and control groups. Mice in groups 1–3 received laparotomy and were injected with N-methyl-N-nitrosourea (MNU) solution at a dose of 1 mg/100 g body weight to the left uterine tube and with normal saline to the right uterine tube. From one week after the MNU exposure, groups 1 and 2 were given 5 ppm 17β-estradiol (E₂)-containing diet throughout the experiment. Mice in group 1 received 5 s.c. injections of medroxyprogesterone acetate (MPA) (2 mg/ mouse) at intervals of 4 weeks from week 7. Group 3 was treated with MNU/normal saline alone. Group 4 consisted of mice treated with MPA alone. At the termination of the experiment (week 30), all animals were killed and autopsied for pathological examinations. It was found that adenocarcinomas and preneoplastic lesions developed in the bilateral uterine corpora in mice of groups 1–3. MPA treatment significantly decreased the weight of the uterine corpus (P< 0.05) and the incidences of endometrial adenocarcinoma and atypical or adenomatous (P< 0.001) but not cystic glandular hyperplasias in the MNU/E₂-treated groups. Additionally, MPA treatment tended to decrease the proliferating cell nuclear antigen-labeling index in endometrial glandular cells. These data indicate that MPA, even at low dose, has an inhibitory effect on mouse endometrial carcinogenesis induced by MNU and E₂.     

Rapid Induction of Endometrial Carcinoma in ICR Mice Treated with N-Methyl-N-nitrosourea and 17β-Estradiol

The present study was undertaken to develop an animal model for endometrial neoplasms. A total of 107 female ICR mice, 10 weeks of age, were used and treated as follows: Group 1 (31 mice) was given intravaginal instillation of N-methyl-N-nitrosourea (MNU) solution (1 mg/100 g body wt.) once a week for three weeks and then fed diet containing 5 ppm 17/β-estradiol (E₂) for 20 weeks, starting one week after the last exposure to MNU, Group 2 (30 mice) was given MNU alone. Group 3 (31 mice) was given E₂ diet alone. Group 4 (15 mice) was fed the basal diet alone and served as the untreated control. At the termination of the experiment (week 23), all surviving mice were killed. Histopathological examination revealed that adenocarcinomas in the uterine corpus developed in mice of Groups 1-3, with a high incidence of endometrial hyperplasia. The incidence of endometrial carcinomas in Group 1 (15/31, 48%) was significantly higher than in Group 2 (2/29, 7%, P < 0.001) or Group 3 (7/31, 23%, P > 0.01). In the uterine cervix, small numbers of squamous cell carcinomas and pre-neoplastic lesions (dysplasias and hyperplasias) were also present in mice of Groups 13. In Groups 1 and 3, an increased E₂/progesterone (P) ratio was observed. Thus, the results indicated that this medium-term model for endometrial neoplasms is useful for studying the pathogenesis of endometrial cancer and that an increased E₂/P ratio is an important factor for the development of endometrial adenocarcinoma.     

Inhibitory effects of toremifene on N-methyl-N-nitrosourea and estradiol-17beta-induced endometrial carcinogenesis in mice.

Short- and long-term experiments were designed to determine the effects of toremifene (TOR) on estrogen-related endometrial carcinogenesis in mice. In the short-term experiment, a single low dose of TOR (0.2 mg / 30 g body weight) decreased expression of c-fos, interleukin (IL)-1alpha, estrogen receptor (ER)-alpha mRNAs and corresponding proteins induced by estradiol-17beta (E(2)), in the uteri of the ovariectomized mice. Expression of ER-beta mRNA was increased by the TOR treatment, compared with the control. In the long-term experiment, 106 female ICR mice were given N-methyl-N-nitrosourea (MNU) into their uterine corpora. The animals were divided into four groups as follows: group 1, E(2) diet (5 ppm) plus TOR (0.2 mg / 30 g body weight, subcutaneously, every four weeks); group 2, E(2) diet alone; group 3, basal diet plus TOR. Group 4 served as the control. TOR treatment decreased the incidence of MNU and E(2)-induced endometrial adenocarcinoma and atypical hyperplasia at the termination of the experiment (30 weeks after the start). These results suggest that TOR exerts preventive effects against estrogen-related endometrial carcinogenesis in mice, through the suppression of c-fos as well as IL-1alpha expression induced by E(2). Such suppressive effects of TOR may be related to the decreased ER-alpha and increased ER-beta expressions.     

Preventive Effects of Isoflavones, Genistein and Daidzein, on Estradiol-17β-related Endometrial Carcinogenesis in Mice

The effects of isoflavones (genistein and daidzein) on endometrial carcinogenesis in mice were investigated in two experiments. In the short-term experiment (2 weeks), single subcutaneous (s.c.) administration of genistein [1 mg/30 g body weight (b.w.)] significantly decreased the levels of estradiol-l7β (E2) (5 ppm in diet)-induced expression of c-jun, interleukin-lα (IL-lα) and tumor necrosis factor-a (TNF-a) mRNAs in the uteri of ovariectomized mice (P<0.005, P<0.05 and P<0.01, respectively). Daidzein significantly inhibited E2-induced expression of c-fos and IL-lα (P<0.01, P<0.01 respectively). In the long-term experiment (30 weeks), 140 female ICR mice were given N-methyl-N-nitrosourea-containing solution (1 mg/100 g b.w.) and normal saline (as controls) into their left and right uterine corpora, respectively. They were divided into six groups; group 1 was given E2 (in diet) alone. Group 2 was given E2 and genistein (1 mg/30 g b.w., s.c., every four weeks). Group 3 was exposed to E2 and daidzein (1 mg/30 g b.w., s.c., every four weeks). Groups 4 and 5 respectively received genistein and daidzein, and were kept on the basal diet. Group 6 was kept on the basal diet and served as a control. At the termination of the experiment, incidences of endometrial adenocarcinoma and atypical endometrial hyperplasia of the group given E2 and genistein or daidzein were significantly lower than of the group with E2 alone (P<0.01 and P<0.05, respectively). It is suggested that both genistein and daidzein have an inhibitory effect on estrogen-related endometrial carcinogenesis in mice, possibly by suppressing expression of estrogen-induced estrogen-related genes c-fos and c-jun, and internal cytokines IL-lα and TNF-α through a cytokine and estrogen receptor-mediated pathway.     

Binding Sites of Droloxifene in the Cytosol of 7,12-Dimethylbenz[α]anthracene-induced Rat Mammary Tumor Cells

The binding sites, other than the estrogen receptor (ER), of the antiestrogens droloxifene (DROL, (E)-α-[ p [2-(dimethylamino)ethoxy]-phenyl]-α'-ethyl-3-stilbenol) and tamoxifen (TAM), and estradiol-17β (E₂) in the cytosol of 7,12-dimethylbenz[α]anthracene-induced rat mammary ER-positive tumor cells were studied using a high-performance liquid chromatography (HPLC) gel filtration assay. The cytosol was incubated with ³H-labeled drug with or without unlabeled drug, and separated by HPLC gel filtration. ³H-E₂ produced two major peaks of radioactivity at fractions No. 40 and No. 70. The peak at fraction No. 70 was identified as the ER in an ER-enzyme-immuno assay. This peak was dose-dependently inhibited by unlabeled DROL or TAM, DROL being a more potent inhibitor than TAM. The peak at fraction No. 40 was also inhibited by co-incubation with unlabeled DROL or TAM. ³H-DROL or ³H-TAM provided only one peak at fraction No. 43. This peak was thought to be an antiestrogen binding site (AEBS), because it was inhibited by unlabeled antiestrogen hut not by E₂. The results suggest that the antiestrogens DROL and TAM have a higher affinity for the AEBS than for the ER in the absence of E₂, while in the presence of E₂ both have an affinity for the ER and inhibit E₂ binding to the ER.     

Maintenance of Androgen-, Glucocorticoid- or Estrogen-responsive Growth in Shionogi Carcinoma 115 Subline Sustained in Castrated Mice with High Dose of Estrogen for 30 Generations (3 Years)

Shionogi carcinoma 115 (SC115), an androgen-dependent mouse mammary tumor, rapidly loses its androgen responsiveness after androgen withdrawal. The growth of this tumor can also be stimulated by high doses of estrogen or glucocorticoid. In the present study, the maintenance of hormone-responsive growth of SC115 tumors with a high dose of estrogen was examined in castrated male mice using an SCI 15 subline obtained by serial transplantations of SCI 15 tumors in estrogen-treated castrated mice for 3 years (30 generations) (subline E₂). Seed tumors from both SC115 and subline E₂ could rapidly grow in castrated mice given daily injections of testosterone propionate (TP), 17β-estradiol (E₂), or dexamethasone (Dex) (100 μg/mouse/day) but not in those given vehicle alone. Although SCI 15 and subline-E₂ tumors grown with TP or Dex showed temporary regression after steroid withdrawal, the tumors grown with E₂ did not show such temporary regression. The TP-, E₂-, or Dex-induced growth of subline-E₂ tumors was almost the same as that of the original SCI 15 tumors. However, responsiveness to androgen, estrogen or glucocorticoid of both tumors disappeared within one passage in steroid-depleted castrated mice. The present findings demonstrate that the loss of responsiveness to androgen as well as to high doses of estrogen or glucocorticoid of SCI 15 tumors can be prevented in castrated mice not only with androgen but also with high doses of estrogen.     

Tumorigenic Conversion of a Rat Urothelial Cell Line by Human Polymorphonuclear Leukocytes Activated by Lipopolysaccharide

Chronic inflammation is a significant risk factor for the development of urinary bladder cancer. We have shown that inflammation induced by killed Escherichia coli and also by its lipopolysaccharide (LPS) strikingly enhances N-methyl-N-nitrosourea (MNU)-initiated rat bladder carcinogenesis. Aspirates from the bladder lumen contained a large quantity of hydrogen peroxide (H₂O₂) and several cytokines. In this study, we tested the hypothesis that reactive oxygen intermediates (ROI) released from activated polymorphonuclear leukocytes (PMN) are involved in inflammation-associated bladder carcinogenesis. Using an immortalized nontumorigenic rat urothelial cell line, MYP3, we examined the effect of LPS-activated PMN on malignant transformation. MYP3 cells pretreated with or without MNU were exposed daily to LPS-activated PMN for one week and were then tested for growth in soft agar. In contrast to no colony formation by the parental cells, a varying number of colonies developed from cells treated with LPS-activated PMN. Although combined treatment with MNU and PMN was most effective ( P < 0.01), cells treated with LPS-activated PMN alone also formed a small number of colonies. Addition of catalase, which decomposes H₂O₂, and/or an antioxidant, α-tocopherol, reduced the number of colonies induced by LPS-activated PMN (P<0.05). Cells derived from colonies were tumorigenic in athymic nude mice. However, tumorigenicity in mice was greater with cells treated with both MNU and PMN than with cells treated with PMN alone. Our results suggest that ROI released from LPS-activated PMN may be one of the mechanisms involved in the carcinogenesis associated with active urinary tract infection.     

Combined effects of prostaglandin E receptor subtype EP1 and subtype EP4 antagonists on intestinal tumorigenesis in adenomatous polyposis coli gene knockout mice

Previous studies have shown that prostaglandin E₂ (PGE₂) is involved in intestinal carcinogenesis through its binding to the PGE₂ receptor subtypes EP₁ and EP₄ and activation of downstream pathways. ONO-8711 and ONO-AE2–227, prostaglandin E receptor subtype EP₁- and EP₄-selective antagonists, respectively, are known to suppress formation of intestinal polyps in adenomatous polyposis coli gene-deficient mice. The present study was designed to investigate the combined effects of EP₁ and EP₄ antagonists on spontaneous polyp formation in APC1309 mice in order to determine the contribution of each receptor to intestinal tumorigenesis. APC1309 mice were treated with 400 ppm of ONO-8711 alone, 400 ppm of ONO-AE2–227 alone or both in combination in the diet for 6 weeks. The mean area of polyps found in the intestine, calculated as the longer diameter × the shorter diameter ×π, was reduced by 12%, 43% (P<0.01) and 56% (P<0.01) of the mean control value (8.8 mm²) in the ONO-8711 alone, ONO-AE2–227 alone and combination treatment groups, respectively, suggesting clear additive effects of the combination. The same additive tendency for suppression was also observed with respect to the numbers of polyps in the intestine. Polyp size reduction was more remarkable with the EP₄ antagonist, while the number reduction was more pronounced with the EP₁ antagonist. Our results indicate that EP₁ and EP₄ may have separate intrinsic roles and, to some extent, contribute to polyp formation independently. Thus, combination treatment has potential for the chemoprevention of colon carcinogenesis.     

Effects of Sex Steroids and Growth Factors on Invasive Activity and 5'-Deoxy-5-fluorouridine Sensitivity in Ovarian Adenocarcinoma OMC-3 Cells

Effects of sex steroids (estradiol-17β, E₂; progesterone, Prog) and growth factors (epidermal growth factor, EGF; transforming growth factor-α, TGF-α) on invasive activity and 5'-deoxy-5-fluorouridine (5'-dFUrd) sensitivity of ovarian adenocarcinoma OMC-3 cells were investigated. Tumor cell migration along a gradient of substratum-bound fibronectin and invasion into reconstituted basement membrane were inhibited by 10 μ M Prog, but stimulated by 0.1–10 n M EGF and TGF-α in a concentration-dependent manner. E₂ did not have any effect on tumor cell migration or invasion. The zymography of tumor conditioned medium showed that the treatment of OMC-3 cells with EGF and TGF-α resulted in increases of type IV collagenase, stromelysin and urokinase-type plasminogen activator (uPA). EGF and TGF-α up-regulated thymidine phosphorylase (dThdPase) expression of tumor cells and consequently enhanced the antiproliferative action of 5'-dFUrd, which is converted to 5-fluorouracil by dThdPase. E₂ and Prog did not have significant effects on the expression of proteolytic enzymes and dThdPase, or on the 5'-dFUrd sensitivity of tumor cells. The inhibitory effect of Prog on tumor cell invasion may depend on its inhibitory action on the motility of tumor cells. These results suggest that EGF and TGF-α simultaneously up-regulate the potential of ovarian adenocarcinoma cells to invade extracellular matrices and their dThdPase expression, both of which are associated with the specific action of 5'-dFUrd selectively to kill tumor cells with high invasive and metastatic potential.     

Effects of Hormones on Tumor Growth and Immunoreactive Insulin–like Growth Factor–1 of Estrogen Receptor–positive Human Breast Cancer (MCF-7) Transplanted in Nude Mice

The effects of estrogens and tamoxifen were analyzed on estrogen receptor–positive human breast cancer (MCF–7) transplanted into athymic nude mice. It was found that (1) the tumor growth and the proportion of ³H–thymidine –labeled cells were significantly increased in the 17β– estradiol dipropionate (E₂) group, but significantly decreased In the tamoxifen (TAM) group with respect to the control group, and (2) the tumor content of insulin–like growth factor–1 (IGF–1) and the rate of IGF–1–positive cells were significantly lower in the E₂ group, but significantly higher in the TAM group than in the control group. It was concluded that the tumor content of IGF–1 and the proportion of IGF–I–positive cells were inversely correlated to the tumor growth and the ³H–thymidine labeling index in vivo ,     

Interrelationship between Estradiol and Tamoxifen Responses for Clinical Breast Carcinoma Cells Cultured on Contact-sensitive Plates

An in vitro assay system for predicting the estradiol (E₂) sensitivity of clinical cancer cells was applied to 54 patients with breast carcinoma to compare the responses to E₂ and tamoxifen (TAM) with the estrogen receptor (ER) status. We found that 18 of the 35 cases in the ER-positive group and 6 of the 19 cases in the ER-negative group were stimulated by E₂. It is suggested that ER status alone can not predict the response of cultured cells to E₂ in clinical breast cancer. Cell growth of 11/35 (31%) of the ER-positive cases and that of 8/19 (42%) of the ER-negative cases was inhibited by E₂. Since the cases inhibited by E₂ could not be distinguished by ER status alone, an assay system based on a quantitative proliferative response was considered necessary. There were 20 (83%) cases of inhibition by TAM among the 24 stimulated by E₂. Only 18/35 (51%) of the ER-positive group exhibited growth inhibition by TAM. In our (CSP) assay, 20 (83%) of the 24 cases stimulated by E₂ were inhibited by TAM, 10 (91%) of the 11 E₂-insensitive cases were insensitive to TAM and 13 (68%) of the 19 cases inhibited by E₂ were stimulated by TAM. In short, TAM response and E₂ response tended to be inversely related (43/54=80%, P <0.01). Furthermore, the E₂-response rate showed a good correlation with the TAM-response rate (R₂= 0.825). These results indicate the feasibility of predicting individual tumor responses to either E₂ or TAM by using CSPs.     

Clinicopathological Characteristics of Estrogen Receptor-(3-positive Human Breast Cancers

Recent studies have identified the presence of estrogen receptor (ER)-β in addition to ER-α in human breast cancers, but the Clinicopathological characteristics of ER-β-positive tumors remain to be established. In this study, we have conducted an immunohistochemical analysis of ER-α and ER-β expression in human breast cancers. In addition, we investigated the correlation of ER-α and ER-β expression with progesterone receptor (PR) status, determined by enzyme immunoassay, and with various Clinicopathological factors. Of 79 tumors, 49 (62%) were positive for ER-α and 24 (30%) were positive for ER-β, and there was no significant association between ER-α and ER-β expression. ER-α-positive tumors were significantly more likely to be PR-positive than were ER-α-negative tumors (P<0.0001), but there was no significant association between ER-β expression and PR status. However, the PR values of ER-α-positive and ER-β -positive tumors (65±17 fmol/mg protein, mean±SE) were marginally significantly lower than those of ER-α-positive and ER-β -negative tumors (340±109) (P=0.08). ER-β positivity was significantly associated with small tumor size (<2 cm) and high histological grade (P<0.05), and this association was also observed when only ER-α-positive tumors were considered. These results suggest that determination of ER-β status might be clinically useful for further defining the characteristics of ER-α-positive tumors     

Shimotsu-to is the agent in Juzen-taiho-to responsible for the prevention of endometrial carcinogenesis in mice

We have found that Juzen-taiho-to has a preventive effect on endometrial carcinogenesis in mice (Carcinogenesis 22 (2001) 587). In the present study, the constituents of Juzen-taiho-to responsible for this effect were explored using a short-term experiment. Thirty female ICR mice were divided into five groups: Group 1 was given a diet containing 0.2% of Juzen-taiho-to and 5ppm estradiol-17beta (E(2)); Group 2 was given a diet containing Shimotsu-to (0.07%) and E(2) (5ppm); Group 3 received Shikunshi-to (0.08%) and E(2) (5ppm) in the diet; Group 4 was given 5ppm E(2) in the diet; and Group 5 served as a control. Exposure of Juzen-taiho-to or Shimotsu-to decreased E(2)-stimulated expression of estrogen-related gene c-fos mRNA (P<0.05), and the cytokines interleukin-1alpha mRNA and tumor necrosis factor alpha mRNA P<0.01). A similar trend was not found upon treatment with Shikunshi-to. These findings suggest that Shimotsu-to is responsible for the inhibitory effects of Juzen-taiho-to on the estrogen-related endometrial carcinogenesis in mice.     

Strain Difference in Regulation of Pituitary Tumor Transforming Gene (PTTG) in Estrogen–induced Pituitary Tumorigenesis in Rats

Recently a novel oncogene, PTTG (pituitary tumor transforming gene) was isolated from a rat pituitary tumor cell line whose expression is apparently correlated with pituitary tumorigenesis. In the rat, estradiol (E₂) is known to induce anterior pituitary hyperplasia. The effects of E₂, however, vary greatly among rat strains. Therefore we examined the expression of PTTG and its regulation by E₂ in F344, Wistar, Brown–Norway and Donryu rats. Four–week–old females were ovariecto–mized and a pellet containing 10 mg of E₂ was given s.c. Total RNA was isolated from the pituitary gland and PTTG mRNA was measured with a competitive RT–PCR technique. The F344 strain was the most susceptible to E₂ induction of pituitary tumorigenesis, followed by Wistar and Brown–Norway, while no increase in pituitary weight was noted in Donryu rats. PTTG mRNA in the gland was induced by E₂ within 48–72 h in F344 and Wistar, but not in Brown–Norway or Donryu strains. These data suggest that PTTG expression may at least in part be responsible for strain differences in E₂–induced pituitary tumorigenesis     

Hypoxia Reduces Hormone Responsiveness of Human Breast Cancer Cells

Resistance to hormonal therapy frequently occurs following successful treatment in breast cancer. The mechanism responsible for this acquired resistance is still unknown. It has been suggested that a hypoxic tumor microenvironment promotes malignant progression of cancer, i.e., hypoxia may promote estrogen-independent growth (a more malignant phenotype) of breast cancer. To clarify this hypothesis, the effects of hypoxia on the growth responses to hormonal agents and the expression levels of estrogen receptor (ER)-α and progesterone receptor (PgR) were investigated in two human breast cancer cell lines, ML-20 and KPL-1. The expression level of ER-α was significantly decreased by hypoxia (1% O₂) in a tune-dependent manner in both cell lines. Hypoxia also significantly reduced the growth-promoting effect of estradiol (E2) and the growth-inhibitory effects of an antiestrogen, ICI 182 780, and a progestin, medroxyprogesterone acetate, in both cell lines. In addition, hypoxia markedly suppressed the induction of PgR mRNA and protein by E2 in both cell lines. To clarify further the effect of hypoxia on ER-α expression, the expression levels of hypoxia-inducible factor-la (HIF-lα), a marker of hypoxia and ER-α were immunohistochemically examined in 36 breast cancer specimens. ER-α expression (both its proportion and intensity) was significantly lower in nuclear HIF-lα-positive tumors than in negative tumors. These findings indicate that hypoxia down-regulates ER-α expression as well as ER-α function in breast cancer cells. These processes may lead to an acquired resistance to hormonal therapy in breast cancer     

Isoliquiritigenin, a flavonoid from licorice, reduces prostaglandin E2 and nitric oxide, causes apoptosis, and suppresses aberrant crypt foci development

Isoliquiritigenin (ILTG), a flavonoid group compound, exists in some foodstuffs and herbal medicines such as licorice ( Glycyrrhiza uralensis Fisher). Previously, we showed that ILTG can suppress azoxymethane (AOM)-induced colon carcinogenesis in ddY mice. In the present report, we present evidence that ILTG markedly decreases both prostaglandin E₂ (PGE₂) and nitric oxide (NO) production in RAW264.7 mouse macrophage cells. The decrease of PGE₂ was dependent on cyclooxygenase-2 (COX-2) expression and the decrease of NO appeared due to a decrease in inducible nitric oxide synthase (iNOS) protein expression. In mouse and human colon carcinoma cells, ILTG treatment suppressed cell growth and caused apoptosis. Furthermore, in vivo administration of ILTG inhibited the induction of preneoplastic aberrant crypt foci (ACF) in the male F344 rat colon. Our results suggest that ILTG is a promising chemopreventive agent against colon carcinogenesis.     

Preventive effects of isoflavones, genistein and daidzein, on estradiol-17beta-related endometrial carcinogenesis in mice.

The effects of isoflavones (genistein and daidzein) on endometrial carcinogenesis in mice were investigated in two experiments. In the short-term experiment (2 weeks), single subcutaneous (s.c.) administration of genistein [1 mg / 30 g body weight (b.w.)] significantly decreased the levels of estradiol-17beta (E(2)) (5 ppm in diet)-induced expression of c-jun, interleukin-1alpha (IL-1alpha) and tumor necrosis factor-alpha (TNF-alpha) mRNAs in the uteri of ovariectomized mice (P < 0.005, P < 0.05 and P < 0.01, respectively). Daidzein significantly inhibited E(2)-induced expression of c-fos and IL-1alpha (P < 0.01, P < 0.01 respectively). In the long-term experiment (30 weeks), 140 female ICR mice were given N-methyl-N-nitrosourea-containing solution (1 mg / 100 g b.w.) and normal saline (as controls) into their left and right uterine corpora, respectively. They were divided into six groups; group 1 was given E(2) (in diet) alone. Group 2 was given E(2) and genistein (1 mg / 30 g b.w., s.c., every four weeks). Group 3 was exposed to E(2) and daidzein (1 mg / 30 g b.w., s.c., every four weeks). Groups 4 and 5 respectively received genistein and daidzein, and were kept on the basal diet. Group 6 was kept on the basal diet and served as a control. At the termination of the experiment, incidences of endometrial adenocarcinoma and atypical endometrial hyperplasia of the group given E(2) and genistein or daidzein were significantly lower than of the group with E(2) alone (P < 0.01 and P < 0.05, respectively). It is suggested that both genistein and daidzein have an inhibitory effect on estrogen-related endometrial carcinogenesis in mice, possibly by suppressing expression of estrogen-induced estrogen-related genes c-fos and c-jun, and internal cytokines IL-1alpha and TNF-alpha through a cytokine and estrogen receptor-mediated pathway.