Sex hormones and neoplasia: liver tumors in rodents

Urogenital carcinogenesis in female CD1 mice induced by in utero arsenic exposure is exacerbated by postnatal diethylstilbestrol treatment

Transplacental inorganic arsenic carcinogenicity, together with postnatal exposure to diethylstilbestrol or tamoxifen, was studied. Pregnant CD1 mice received 85 ppm arsenic in the drinking water from gestation days 8 to 18 and were allowed to give birth. Groups (n = 35) of female offspring were injected s.c. on postpartum days 1 through 5 with diethylstilbestrol (2 microg/pup/d) or tamoxifen (10 microg/pup/d) and observed for 90 weeks. Arsenic alone induced some urogenital system tumors, including mostly benign tumors of the ovary and uterus, and adrenal adenoma. Diethylstilbestrol alone induced some tumors (primarily cervical) but when given after in utero arsenic, it greatly enhanced urogenital tumor incidence, multiplicity, and progression. For instance, compared with the incidence of urogenital malignancies in the control (0%), arsenic alone (9%), and diethylstilbestrol alone (21%) groups, arsenic plus diethylstilbestrol acted synergistically, inducing a 48% incidence of malignant urogenital tumors. Of the urogenital tumors induced by arsenic plus diethylstilbestrol, 80% were malignant, and 55% were multiple site. Arsenic plus diethylstilbestrol increased ovarian, uterine, and vaginal tumors, and urinary bladder proliferative lesions, including three transitional cell carcinomas. Tamoxifen alone did not increase urogenital tumors or affect arsenic-induced neoplasia but did increase arsenic-induced uroepithelial proliferative lesions. Uterine and bladder carcinoma induced by arsenic plus diethylstilbestrol greatly overexpressed estrogen receptor-alpha (ER-alpha) and pS2, an estrogen-regulated gene. In neonatal uteri, prenatal arsenic increased ER-alpha expression and enhanced estrogen-related gene expression induced by postnatal diethylstilbestrol. Thus, arsenic acts with estrogens to enhance production of female mouse urogenital cancers.

Genotoxicity of hormonal steroids

Hormonal steroids have a widespread use in medicine and their side effects are continuously debated. The possible genotoxic activity of steroids has been the subject of many investigations. The natural estrogens estradiol, estrone and estriol are generally negative in the ICH core battery of tests, but several positive results have been obtained when using additional endpoints of genotoxicity. The genotoxic activity of the 4-hydroxy metabolites of estradiol and estrone is well established. The synthetic steroidal estrogens have a comparable profile of negative and positive test results. Cyproterone acetate and some of its analogues have a special position within the group of progestins. Their genotoxic potential has been established. Other progestins are generally negative in the routine tests. Anti-glucocorticoids, anti-progestins, corticosteroids, androgens, anabolics and anti-androgens appear to be devoid of genotoxic activities. The genotoxic potential of estradiol, estrone and cyproterone acetate with its analogues may play no role under normal physiological and therapeutic conditions. The metabolic conditions that are needed for the formation of DNA-reactive metabolites and oxygen radicals may not be present in humans. Epidemiological cancer data seem to support this view. The importance of thresholds in the dose-effect-relationship of genotoxicity data and their use in risk assessment is discussed.

Estrogen signaling in livers of male mice with hepatocellular carcinoma induced by exposure to arsenic in utero

BACKGROUND

Exposure of pregnant mice to inorganic arsenic induces a spectrum of tumors, including hepatocellular carcinoma (HCC), in their adult offspring similar to that induced by exposing adult mice to estrogenic compounds. To investigate whether arsenic exposure in utero causes altered estrogen signaling, we examined expression of estrogen receptor-alpha (ER-alpha), cyclin D1 (an estrogen-responsive hepatic oncogene), and several cytochrome P450 genes (with sexually dimorphic liver expression patterns) in livers from adult male mice with in utero arsenic-induced HCC.

METHODS

Quantitative real-time reverse transcription-polymerase chain reaction was used to evaluate gene expression in livers of adult male mice that had (i.e., exposed mice; n = 8) or had not (i.e., control mice; n = 5) been exposed to arsenic in utero. DNA methylation status of portions of the ER-alpha and cyclin D1 gene promoters in liver tissue was measured using methylation-specific polymerase chain reaction. Statistical tests were two-sided.

RESULTS

ER-alpha mRNA levels were 3.1-fold (95% confidence interval [CI] = 2.0-fold to 4.3-fold) higher in livers of exposed mice than in those of control mice, and cyclin D1 levels were 3.0-fold (95% CI = 1.7-fold to 4.3-fold) higher. Exposed mice showed a feminized expression pattern of several cytochrome P450 genes, expressing the female-dominant CYP2A4 (P =.017 versus control) and CYP2B9 (P<.001) genes at 8.7 and 10.5 times, respectively, the level in control mice and expressing the male-dominant CYP7B1 at approximately one-fourth the level in control mice(P =.0012). Exposed mice exhibited reduced (by approximately 90%) methylation of the ER-alpha gene promoter in liver DNA as compared with control mice; the cyclin D1 gene promoter was not methylated in either exposed or control mice.

CONCLUSION

Altered estrogen signaling may play a role in induction of HCC by arsenic exposure in utero. Specifically, overexpression of ER-alpha, potentially through promoter region hypomethylation, in livers of such mice may be linked to the hepatocarcinogenicity of arsenic.

Effects of husbandry practices, gender, and normal physiological variation on growth and reproduction of Japanese medaka, Oryzias latipes

Japanese medaka, Oryzias latipes, are currently used in a variety of research applications for toxicological and carcinogenesis research, yet the impact of certain husbandry factors on study outcome has received limited attention. In this study, we demonstrated significant effects of stocking density (SD), dietary restriction (DR) and photoperiod on somatic growth in medaka. Higher stocking densities significantly inhibited somatic and hepatic growth in females, while having no similar effects on males. Daily egg production declined in a step-wise manner in groups of fish stocked at densities ranging from 0.38 to 2.6 fish per l. Significantly slower somatic growth was observed in fish fed on a mildly restrictive dietary protocol compared with those fish fed to excess. Further significant declines were observed in somatic growth of fish fed at a rate comparable to that used in research studies (3-4% body weight (BW) per day). Fish reared at an 8-h light:16-h dark (8L/16D) photoperiod were significantly smaller than cohorts reared at a 16-h light:8-h dark (16L/8D) photoperiod and female sexual maturity was delayed in the short photoperiod cohort. In normal female medaka, a high degree of individual variation was observed in daily egg production, as well as diurnal fluctuations in ovarian weight, gonadosomatic index (GSI) and hepatosomatic index (HSI). These results indicate some husbandry factors affect growth, sexual maturation and egg production in medaka and should be taken into consideration in studies evaluating endpoints that may be impacted by growth and reproductive performance, i.e. carcinogenesis and endocrine disruption studies. The high degree of individual variation among normal females and daily fluctuations in organ weights should also be considered in study design.

Induction of proliferative lesions of the uterus, testes, and liver in swiss mice given repeated injections of sodium arsenate: possible estrogenic mode of action

Inorganic arsenic (As) is a human carcinogen but has not been unequivocally proven carcinogenic in rodents. For instance, one older study indicates that repeated iv injections of sodium arsenate might induce lymphomas in Swiss mice (58% incidence) (Osswald and Goerttler, Verh. Dtsch. Ges. Pathol. 55, 289-293, 1971), but it was considered inadequate for critical evaluation of carcinogenic potential largely because of issues in experimental design. Therefore, we studied repeated iv sodium arsenate injection and neoplastic response in male and female Swiss mice. Groups (n = 25) of mice received sodium arsenate (0.5 mg/kg, iv) or saline (control) once/week for 20 weeks and were observed for a total of 96 weeks when the study ended. Differences in survival and body weights were unremarkable. In females, arsenate induced marked increases in the incidence and severity of cystic hyperplasia of the uterus compared against controls. Arsenate also was associated with a rare adenocarcinoma of the uterus. Hyperplastic uterine epithelium from arsenate-exposed animals showed strong positive immunostaining for the proliferating cell nuclear antigen (PCNA). There was also an upregulation of estrogen receptor (ER) immunoreactive protein in the early lesions of uterine luminal and glandular hyperplasia, although a progressive decrease in its expression was seen in the severe hyperplastic or neoplastic epithelium. In common with the preneoplastic and neoplastic gynecological lesions in humans, the levels of immunoreactive inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine-containing proteins were greater in the uterine hyperplastic epidermis and their intensity was positively correlated with the severity of the lesions. Arsenate-induced uterine hyperplastic lesions also showed a strong upregulation of cyclin D1, an estrogen-associated gene product essential for progression through the G1 phase of the cell cycle. In other tissues, arsenate increased testicular interstitial cell hyperplasia incidence and severity over control but without affecting the incidence of tubular degeneration. Arsenate also induced increases in hepatic proliferative lesions (HPL; foci of alteration + neoplasia), but only in females. Significant skin changes (incidence of hyperkeratotic lesions) and renal lesions (severity of nephropathy) also occurred in arsenate-treated females. Thus, repeated arsenate exposure, though not outright tumorigenic in the present study, was associated with proliferative, preneoplastic lesions of the uterus, testes, and liver. Estrogen treatment has been associated with proliferative lesions and tumors of the uterus, female liver, and testes in other studies, supporting a hypothesis that arsenate might somehow act through an estrogenic mode of action.

Chemicals with carcinogenic activity in the rodent liver; mechanistic evaluation of human risk

A wide variety of chemicals, both naturally occurring and synthetic, have exhibited carcinogenic activity in rodent liver. Some are clearly DNA reactive whereas others produce only epigenetic effects. Hepatocarcinogens are categorized according to these properties and the characteristics of examples of both types are reviewed. DNA-reactive rodent hepatocarcinogens represent human cancer risk even at non-toxic exposures, whereas epigenetic agents pose either no risk because their effects are specific to rodents, or a risk only at high exposures at which they produce the same cellular effects in humans that are the basis for their carcinogenic activity in rodents.

Comparison of toremifene and tamoxifen in post-menopausal patients with advanced breast cancer: a randomized double-blind, the 'nordic' phase III study

The study was planned to compare, in a prospective double-blind randomized trial, the efficacy and safety of toremifene (TOR) and tamoxifen (TAM) in post-menopausal patients with advanced breast cancer who have not had prior systemic therapy for advanced disease. Four hundred and fifteen post-menopausal patients with oestrogen receptor (ER)-positive or ER-unknown advanced breast cancer were randomly assigned to receive daily either 60 mg TOR or 40 mg TAM. The patients were stratified to measurable and non-measurable but evaluable groups. They were assessed for response to therapy, time to progression (TTP), time to treatment failure (TTF), response duration, overall survival and drug toxicity. Two hundred and fourteen patients were randomized into TOR and 201 into TAM treatment. The response rate (complete + partial) was 31.3% for TOR and 37.3% for TAM (P = 0.215). The 95% confidence interval (CI) for the 6% difference was -15.1% to 3.1%. The median TTP was 7.3 months for TOR and 10.2 months for TAM (P = 0.047). The 95% CI for the hazard ratio of 0.80 was 0.64-1.00. A percentage of the TOR patients (9.8%) and the TAM patients (18.9%) discontinued the treatment prematurely (P = 0.011) for various reasons. Consequently, the median TTF of 6.3 vs 8.5 months did not differ significantly (P = 0.271). The hazard ratio was 0.89 and the subsequent 95% CI 0.73-1.09. The median overall survival was 33.0 months for TOR and 38.7 months for TAM (P = 0.645). The hazard ratio was 0.94 with 95% CI of 0.73-1.22. The transient difference in TTP may be related to an imbalance in ER content of the tumours. When only patients with ER-positive tumours were considered (n = 238), no difference between two treatments was seen (P = 0.578). TAM was associated with an overall slightly higher frequency of adverse drug reactions than TOR (44.3 vs 39.3%) and a higher discontinuation rate due to these events (3.5% vs 0.9%). Treatment-emerged moderate dizziness (P = 0.026) and cataracts (P = 0.026) were more frequent among TAM than among TOR patients. In conclusion, TOR (60 mg day(-1)) and TAM (40 mg day(-1)) are equally effective and safe in the treatment of advanced post-menopausal ER-positive or ER-unknown breast cancer.

Hepatocellular carcinoma in long-term oral contraceptive use

Hepatocellular carcinoma (HCC) is one of the most common malignancies in certain parts of the world, particularly in Africa and Asia, but it is less commonly encountered in the United States. It is closely associated with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, and almost always develops in a cirrhotic liver. In non-cirrhotic livers, HCC is found in about 20% of asymptomatic carriers of HBV and rarely in patients taking androgenic-anabolic or oral contraceptive (OC) steroids. We report four patients, who developed HCC after prolonged use of OC steroids. Whether OC steroids act as mutagen or co-carcinogen in hepatocarcinogenesis is not clear. To exclude latent HCV and HBV infections which may occur in the absence of their serological markers, we employed polymerase chain reaction for the detection of HBV and HCV sequences in the tumor and non-tumorous liver tissue. Viral sequences of HBV and HCV were undetectable in all four cases. These findings suggest OC use as the only known risk factor in these cases and, therefore, strengthen its possible role in hepatocarcinogenesis.

Correlation between serum prolactin levels and hepatocellular tumorigenesis induced by 3'-methyl-4-dimethylaminoazobenzene in mice

Ovariectomy at 1 month of age promotes development of hepatocellular adenomatous nodules in female C57BL/6 x DS-F1 mice treated neonatally with 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB). Implantation of oestradiol-17 beta (E2) pellets at 1 month of age suppresses nodule development. Since E2 increases serum levels of prolactin, high serum levels of prolactin in mice that have received implants of E2 pellets may play a role in the suppression of hepatocellular tumorigenesis. Therefore, to investigate the role of prolactin in hepatocellular tumorigenesis, we examined development of adenomatous nodules in female mice that had been treated neonatally with 3'-Me-DAB and had undergone ovariectomy at 1 month of age, under various serum levels of prolactin. Treatment of these mice with perphenazine (dopamine antagonist) from 6 months of age or transplantation of pituitary glands under the renal capsule at 6 months of age markedly increased serum levels of prolactin and significantly suppressed the incidence of adenomatous nodules at 12 months of age. Implantation of E2 pellets at 1 month of age increased serum levels of prolactin to a greater extent and further decreased the incidence of adenomatous nodules. Treatment of mice that had received implants of E2 pellets at 1 month of age with bromocriptine (dopamine agonist) from 6 months of age decreased serum levels of prolactin, and was accompanied by an increase in the incidence of nodules. The present results showed that an increase in serum levels of prolactin was accompanied by a decrease in incidence of liver tumours induced by 3'-Me-DAB in mice, suggesting a suppressive effect of prolactin on liver tumorigenesis in mice. Thus, it is possible that the suppressive effect of oestrogen on liver tumorigenesis in mice is mediated, at least in part, by prolactin.

Suppression by oestrogen of hepatocellular tumourigenesis induced in mice by 3'-methyl-4-dimethylaminoazobenzene

Treatment of female C57BL/6 x DS-F1 mice with 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) neonatally resulted in the development of adenomatous nodules and glucose-6-phosphatase (G-6-Pase) deficient foci at 8 and 6 months of age, respectively. Ovariectomy of these mice at 1 month of age hastened the development and increased the incidences of these lesions. Subcutaneous implantation of estradiol-17 beta (E2) with ovariectomy at 1 month of age markedly decreased the incidences of adenomatous nodules and G-6-Pase deficient foci at 10 or 12 months of age, but subcutaneous implantation of progesterone did not reduce their incidences. Subcutaneous implantation of E2 into ovariectomised mice at 6 months of age resulted in significant decreases in the incidences of adenomatous nodules and G-6-Pase deficient foci at 10 months of age, but implantation of E2 into the spleen of ovariectomised mice of the same age had no effect on their incidences. The present results suggest that E2 suppresses the development of adenomatous nodules and G-6-Pase deficient foci induced in the mouse liver by 3'-Me-DAB by actions on tissues other than the liver.

Diethylstilbestrol liver carcinogenicity and modification of DNA in rats

Administration of diethylstilbestrol to female Sprague-Dawley rats at 10 mg/kg body weight daily by gavage for 1 year induced liver adenomas and carcinomas and pituitary adenomas. Using the 32P-postlabeling assay for DNA alterations, at 24 h after administration of a single dose of 100 mg/kg, modified bases were found.

Promoting effect of ovariectomy on hepatocellular tumorigenesis induced in mice by 3'-methyl-4-dimethylaminoazobenzene

The treatment of female C57BL/6 x DS-F1 mice with 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) at 10, 12, 14, 16 and 18 days of age resulted in the development of hepatocellular adenomatous nodules after 10 months of age. Ovariectomy in these mice at 1 month of age hastened the development of adenomatous nodules, which then first appeared at 8 months of age. The incidence of adenomatous nodules in females ovariectomized at the age of 1 month was much higher than that in intact females of the same age. These results showed that the ovaries exerted a suppressive effect on the development of adenomatous nodules. To determine the time from which the ovaries exert this suppressive effect, females were ovariectomized at 4, 6, 8, and 10 months of age, and the incidences of adenomatous nodules were compared at 10 and 12 months of age. Delayed ovariectomy after 8 months of age did decrease the incidence of adenomatous nodules at 10 and 12 months of age, but ovariectomy after 4 and 6 months of age did not. When the incidence of adenomatous nodules in females ovariectomized at 10 months of age was examined over the subsequent 6 months, it became significantly higher after 14 months of age compared with that in intact females. The results show that the ovariectomy has the promoting effect on the development of adenomatous nodules in the liver induced by 3'-Me-DAB after 6 months of age.

32P-postlabeling analysis of DNA adducts in rats during estrogen-induced hepatocarcinogenesis and effect of tamoxifen on DNA adduct level

DNA adduct formation in the liver, pancreas, kidneys and uterus in ethynylestradiol (EE)-induced carcinogenesis and the effect of tamoxifen (TAM) on DNA adduct formation were evaluated in female Wistar JCL rats using the 32P-postlabeling method. Hyperplastic nodules were noted in the liver of all rats 4 months after the first oral administration of 0.075 mg of EE, and hepatocellular carcinoma was detected in 8.1% of rats treated with EE for 12 months. DNA adducts increased in the liver for 4 months, reaching a level of 7.3 adducts/10(7) nucleotides and decreasing thereafter. Formation of DNA adducts was also noted in the pancreas and kidney, but the adduct levels were lower than those in the liver. TAM inhibited estrogen receptors (ER) in liver tissues and completely suppressed the development of hyperplastic nodules or hepatocellular carcinoma but did not affect DNA adduct formation in the liver. In this model, therefore, EE is considered to cause mutations of hepatocytes due to DNA adduct formation without mediation by ER and to induce initiated cells to develop into hepatocellular carcinoma in the presence of ER-mediated hormonal activities.

Depot-medroxyprogesterone acetate (DMPA) and risk of liver cancer. The WHO Collaborative Study of Neoplasia and Steroid Contraceptives

A hospital-based case-control study was conducted to assess the possible relationship between use of depot-medroxyprogesterone acetate (DMPA), an injectable progestational contraceptive, and the development of liver cancer in 2 developing countries where hepatitis B is endemic. Information about prior DMPA use and potential confounders was ascertained during personal interviews with 71 cases and 530 controls from 3 hospitals in Thailand and 1 hospital in Kenya. No significant association between liver cancer and DMPA use was observed in Kenya (RR = 1.64, 95% Cl = 0.4-0.6) or Thailand (RR = 0.33, 95% Cl = 0.1-1.0). No consistent changes in risk were observed with duration of use, time since last use, or time since first use. No significant associations were observed between DMPA use and risks of either hepatocellular carcinoma or cholangiocarcinoma. These findings suggest that risk of liver cancer in areas where hepatitis B is endemic is not appreciably altered by the use of DMPA.

Biology of female sex hormone action in relation to contraceptive agents and neoplasia

This article will present an overview of estrogen and progestin action at a cellular level, with emphasis on points that are relevant to neoplasia. In breast, endometrium and ovary, these two classes of hormone are clearly implicated in carcinogenesis, but their involvement with cancers of the liver, cervix and other tissues is more problematic. In the latter situations, I will highlight the major points to be considered if the hormones are involved without wishing to judge whether there actually is a causal involvement.

Sex hormones and neoplasia: genotoxic effects in short term assays

The mechanism of the tumorigenic effects of sex hormones in the liver and in other organs is still unclear. Clues towards an understanding of this action of sex hormones can be gained from short-term assays suitable for revealing adverse effects at different molecular levels relevant to the process of neoplastic transformation. The available data on the effects of sex hormones indicating gene mutations, unscheduled DNA synthesis, sister chromatid exchange, chromosomal anomalies, induction of aneuploidy and cell transformation are reviewed. Although the data base is scant, in particular for androgens and progestins and in systems other than the mutational assays, it can be concluded that sex hormones, in general, fail to induce gene mutations. On the other hand, recent evidence shows that diethylstilbestrol and steroidal estrogens are capable of inducing neoplastic transformation in vitro. In this context, the induction of aneuploidy is discussed as non-mutational but genotoxic effect of estrogens responsible for the neoplastic transformation. Morphological transformation and scoring for chromosomal anomalies can provide useful endpoints for further evaluation of sex hormones with suspected carcinogenic properties.