17beta-oestradiol and Enovid mammary tumorigenesis in C3H/HeJ female mice: counteraction by concurrent 2-bromo-alpha-ergocryptine

Oral contraceptive use as a risk factor for premenopausal breast cancer: a meta-analysis

OBJECTIVE

To perform a meta-analysis of case-control studies that addressed whether prior oral contraceptive (OC) use is associated with premenopausal breast cancer.

METHODS

We searched the MEDLINE and PubMed databases and bibliography reviews to identify case-control studies of OCs and premenopausal breast cancer published in or after 1980. Search terms used included breast neoplasms, oral contraceptives, contraceptive agents, and case-control studies. Studies reported in all languages were included. Thirty-four studies were identified that met inclusion criteria. Two reviewers extracted data from original research articles or additional data provided by study authors. We used the DerSimonian-Laird method to compute pooled odds ratios (ORs) and confidence intervals (CIs) and the Mantel-Haenszel test to assess association between OC use and cancer.

RESULTS

Use of OCs was associated with an increased risk of premenopausal breast cancer in general (OR, 1.19; 95% CI, 1.09-1.29) and across various patterns of OC use. Among studies that provided data on nulliparous and parous women separately, OC use was associated with breast cancer risk in both parous (OR, 1.29; 95% CI, 1.20-1.40) and nulliparous (OR, 1.24; 95% CI, 0.92-1.67) women. Longer duration of use did not substantially alter risk in nulliparous women (OR, 1.29; 95% CI, 0.85-1.96). Among parous women, the association was stronger when OCs were used before first full-term pregnancy (FFTP) (OR, 1.44; 95% CI, 1.28-1.62) than after FFTP (OR, 1.15; 95% CI, 1.06-1.26). The association between OC use and breast cancer risk was greatest for parous women who used OCs 4 or more years before FFTP (OR, 1.52; 95% CI, 1.26-1.82).

CONCLUSION

Use of OCs is associated with an increased risk of premenopausal breast cancer, especially with use before FFTP in parous women.

Repeated exposure of C3H/HeJ mice to ultra-wideband electromagnetic pulses: lack of effects on mammary tumors

It has been suggested that chronic, low-level exposure to radiofrequency (RF) radiation may promote the formation of tumors. Previous studies, however, showed that low-level, long-term exposure of mammary tumor-prone mice to 435 MHz or 2450 MHz RF radiation did not affect the incidence of mammary tumors. In this study, we investigated the effects of exposure to a unique type of electromagnetic energy: pulses composed of an ultra-wideband (UWB) of frequencies, including those in the RF range. One hundred C3H/HeJ mice were exposed to UWB pulses (rise time 176 ps, fall time 3.5 ns, pulse width 1.9 ns, peak E-field 40 kV/m, repetition rate 1 kHz). Each animal was exposed for 2 min once a week for 12 weeks. One hundred mice were used as sham controls. There were no significant differences between groups with respect to incidence of palpated mammary tumors, latency to tumor onset, rate of tumor growth, or animal survival. Histopathological evaluations revealed no significant differences between the two groups in numbers of neoplasms in all tissues studied (lymphoreticular tissue, thymus, respiratory, digestive and urinary tracts, reproductive, mammary and endocrine systems, and skin). Our major finding was the lack of effects of UWB-pulse exposure on promotion of mammary tumors in a well-established animal model of mammary cancer.

Role of prolactin in chloro-S-triazine rat mammary tumorigenesis

Chloro-S-triazine herbicides [cyanazine (CZ), atrazine (AZ), simazine (SZ)] increase mammary tumors in Crl:CD BR rats but not in F-344 rats or in mice. A nongenotoxic mechanism was investigated since the chloro-S-triazines are negative in short-term tests for genotoxicity. An in vivo battery was used to assess the chloro-S-triazines for estrogenic activity or for their ability to increase prolactin (PRL) levels, both of which play important roles in enhancing mammary gland tumorigenesis in rodents. Ovariectomized (OVX) female rats were treated with AZ, CZ, SZ, or three CZ metabolites for 4 days via intraperitoneal injection. The pattern of responses between the chloro-S-triazines and four controls (estradiol, estriol, haloperidol, reserpine) was compared. For the 6 end-points examined, the responses from rats treated with AZ, CZ, SZ, and the metabolites of CZ most closely matched the responses from the reserpine-treated rats (a PRL rather than estrogenic mechanism). In addition, AZ, CZ, and SZ were tested in several other in vitro models (estrogen/biogenic amine receptor competition assays and a yeast-expressed human estrogen receptor transcription assay) as well as an in vivo 24 h time-course experiment to characterize the CZ-induced increases in PRL levels. AZ, CZ, and SZ are not estrogen receptor (ER) activating compounds based on yeast transactivation and receptor competition data. CZ and AZ demonstrated marginal competition (at mM levels) to the D and alpha2 adrenergic receptors. Ligands to the D2 receptor, but not the alpha2 adrenergic receptor, are known to induce mammary tumors. CZ was also found to produce elevated PRL levels in a time-course similar to that seen with reserpine and haloperidol. Overall, the pattern of responses obtained with the chloro-S-triazines most closely matched the responses observed for reserpine. Taken together, these data suggest chloro-S-triazine-induced mammary tumors in rats are mediated through a PRL mechanism, which is thought to be of low relevance to humans.

Detection of dopaminergic modulators in a tier I screening battery for identifying endocrine-active compounds (EACs)

Apomorphine (APO; D(2) receptor agonist), haloperidol (HAL; D(2) receptor antagonist), and reserpine (RES; a dopamine depletor that acts to lower brain dopamine levels by depleting central nervous system monoamines via disrupting storage vesicle function) have been examined in a Tier I screening battery, which has been designed to detect endocrine-active compounds (EACs). The Tier I battery incorporates two short-term in vivo tests (a 5-day ovariectomized female battery and a 15-day intact male battery using Sprague-Dawley rats) and an in vitro yeast transactivation system (YTS). In addition, two blood collection procedures were evaluated for their utility in detecting HAL-induced increases in serum prolactin (PRL) levels (i.e., the stress associated with each procedure). In the in vivo female battery, both HAL and RES increased serum PRL concentrations as expected, although the increase caused by RES was marginal. Increases in serum PRL levels are enhanced when daily dosages are administered via multiple-daily dosing of the test compound, which results in higher sustained blood levels of the test compounds. APO failed to decrease serum PRL concentrations in the female battery. In the in vivo male battery, HAL increased serum PRL concentrations as expected. However, APO and RES failed to affect serum PRL concentrations. The blood collection comparison experiment demonstrated that possible confounding of the data can occur with serum PRL concentrations when animals are exposed to stress. Basal levels of PRL were approximately fourfold higher in animals that were bled via the tail vein procedure when compared to PRL levels from animals that were bled under CO(2) anesthesia at euthanization. As a result of the higher basal PRL levels, the HAL-induced increase in serum PRL concentrations was completely attenuated in the tail-vein bled animals (1.3-fold). In contrast, HAL produced a fivefold increase in serum PRL in animals where blood was collected under CO(2) anesthesia at euthanization. Hence, collection of blood from animals under CO(2) anesthesia at euthanization is an acceptable approach for detection of compounds that increase PRL. In summary, HAL-like compounds would be identified in the Tier I male and female battery primarily via increased serum PRL concentrations. RES-like compounds would be identified in the Tier I male battery via decreased gonadotropins and steroids and possibly in the Tier I female battery by a minimal increase in serum PRL concentrations. Compounds that produce a marginal increase in serum PRL when administered using single daily dosing can also be confirmed in an in vivo female battery with multiple dosing because this regimen increases the magnitude of the PRL increase. APO, a D(2) receptor agonist, was not detected in the in vivo male or female batteries, but in both instances the top dosage produced minimal decreases in body weight (99 to 96% of control). Hence, the proposed Tier I battery needs to be further evaluated with higher dosages of APO and other D(2) receptor agonists to determine whether it is capable of detecting such agents.

Is estradiol a genotoxic mutagenic carcinogen?

The natural hormone 17 beta-estradiol (E2) induces tumors in various organs of rats, mice, and hamsters. In humans, slightly elevated circulating estrogen levels caused either by increased endogenous hormone production or by therapeutic doses of estrogen medications increase breast or uterine cancer risk. Several epigenetic mechanisms of tumor induction by this hormone have been proposed based on its lack of mutagenic activity in bacterial and mammalian cell test systems. More recent evidence supports a dual role of estrogen in carcinogenesis as a hormone stimulating cell proliferation and as a procarcinogen inducing genetic damage. Tumors may be initiated by metabolic conversion of E2 to 4-hydroxyestradiol catalyzed by a specific 4-hydroxylase (CYP1B1) and by further activation of this catechol to reactive semiquinone/quinone intermediates. Several types of direct and indirect free radical-mediated DNA damage are induced by E2, 4-hydroxyestradiol, or its corresponding quinone in cell-free systems, in cells in culture, and/or in vivo. E2 also induces various chromosomal and genetic lesions including aneuploidy, chromosomal aberrations, gene amplification, and microsatellite instability in cells in culture and/or in vivo and gene mutations in several cell test systems. These data suggest that E2 is a weak carcinogen and weak mutagen capable of inducing genetic lesions with low frequency. Tumors may develop by hormone receptor-mediated proliferation of such damaged cells.

Animal toxicity studies performed for risk assessment of the once-a-month injectable contraceptive Mesigyna

Results from toxicity studies performed for risk assessment of the combined injectable hormonal preparation Mesigyna are reviewed. Both components of Mesigyna, i.e., estradiol valerate (E2Val) and norethisterone enanthate (NET-EN), have been thoroughly investigated as individual compounds and some limited toxicity data have been obtained for the combination. Most findings which were gathered in these studies from different animal species occurred in the gonads, accessory genital and endocrine organs and can be related to the known species-specific pharmacological activity of a typical estrogen or progestin, respectively. No additional or unexpected information which might indicate a possible estrogen/progestin interaction was gained from the administration of the combined preparation to animals. Based on the results from toxicity testing, there were no objections to the long-term therapeutic use of Mesigyna for hormonal contraception. The predictive value of the effects (including the tumorigenicity) observed in the common laboratory animals with regard to human safety is critically discussed, taking the vast amount of previous experience with hormonal contraceptives into consideration. The conclusion is drawn that there is no animal model for safety assessment of sex steroids that adequately represents the human situation. Quantitative extrapolations from animal toxicity findings to humans, therefore, are not possible. Especially, the value of long-term studies and of toxicity studies on estrogen/progestin combinations is put into question. Like endocrine pharmacology studies, the toxicity studies with these steroid hormones are useful for the characterization of the possible endocrine pharmacological profile only.

High dose levels are not necessary in rodent studies to detect human carcinogens

Guidelines for the conduct of rodent carcinogenicity studies stipulate that when the test substance is administered via the diet, its concentration need not exceed 5% of the diet. Since it is now apparent that human carcinogens are amongst the most potent of rodent carcinogens, it should be possible to detect accurately potential human carcinogens by using only relatively low dose levels in rodent studies. Our analysis of the potency of human carcinogens in rodent studies leads to the conclusion that, even after applying a safety factor of 10, there is no purpose in using dose levels higher than 500 mg/kg body weight or 1% in the diet.

Comparative aspects of contraceptive steroids: effects observed in rats

Current regulatory guidelines for testing contraceptive drugs in long-term rodent studies have established dosages based on multiples of the proposed human usage level. These multiples in rodents are 1-2, 10, and 50. The estrogen/progestogen ratio for most human contraceptive drugs ranges from 1/5 to 1/80. One of the biological endpoints in arriving at the human estrogen/progestogen ratio is the development of an endometrial decidualization response. The ratio necessary to achieve a similar uterine response in the rat is 1:10,000 to 1:20,000. Thus, dosages in the rodent, when based only on a multiple of the proposed human usage level, result in a highly estrogenic combination with estrogen being completely dominant. Continuously elevated estrogen in the rat is toxic to dopaminergic neurons in the hypothalamus which secrete prolactin inhibiting factor (PIF). Hyperplasia of pituitary lactotrophs occurs from both the direct stimulatory effect of estrogen and the uninhibited secretory activity of lactotrophs related to depressed PIF secretions. Prolactinomas result. Increased levels of prolactin lead to mammary gland stimulation and tumor development. Dosage levels for future rodent studies of contraceptive drugs should be based on pharmacokinetics, endocrine profiles, and biological endpoints rather than on multiples of the human usage level.

Effects of perinatal exposure to a synthetic estrogen and progestin on mammary tumorigenesis in mice

The effects of perinatal exposure to synthetic estrogens and progestins on mammary tumorigenesis were studied in female C3H/HeN/MTV + mice. Mice were treated neonatally with 0.001 microgram/day diethylstilbestrol (DES), with 15 micrograms/day 17 alpha-hydroxyprogesterone caproate (HPC), or with oil on days 1-5 of life (birth = day 1). As adults, neonatally hormone-treated mice received long-term treatment with a synthetic estrogen and progestin combination or vehicle. Animals were palpated weekly for mammary gland tumors. The effect of treatment on the probability of tumor development was examined. Neonatal treatment with a low dose of DES increased the probability of mammary-gland tumor formation, whereas neonatal treatment with HPC had a slightly protective effect on tumorigenesis. Subsequent treatment of adult mice with synthetic steroids did not affect mammary gland tumorigenesis in neonatally DES-treated or oil-treated animals. There was a significant interaction between the effect of neonatal HPC treatment and subsequent steroid treatment on mammary tumorigenesis but examination of the data indicated that this interaction was due to the protective effect of HPC in the absence of subsequent exposure to synthetic steroids and the probability of tumor appearance in mice treated with both HPC and synthetic steroids as adults did not differ from that of neonatally oil-treated controls.

Inhibition of mammary tumorigenesis in GR mice with 2-bromo-alpha-ergocryptine

A high incidence of mammary tumors is found in multiparous GR mice during the 2nd and 3rd pregnancies and in nulliparous GR mice treated with estrone/progesterone. The purpose of this study was to determine if prolactin is a contributing hormone in the genesis of these neoplasms. In one series of experiments, 238 15-week-old nulliparous GR mice were treated with estrone (drinking water, 0.5 mg/liter) plus progesterone (30 mg progesterone pellet with cholesterol, implanted SC once monthly) for a period of 13 weeks. Half of these mice were injected SC once daily with 100 micrograms of the prolactin-suppressing drug 2-bromo-alpha-ergocryptine (CB-154) for the duration of hormone treatment, and the other half were injected SC once daily with 0.9% NaCl solution (controls). In another series of experiments, 87 pregnant GR mice were divided into two groups and injected SC once daily from day 7 to 21 of pregnancy with 0.9% NaCl solution (controls) or CB-154 (100 micrograms/mouse). In the first series, the numbers of mice with mammary tumors and total number of mammary tumors were: controls, 58/119 (49%) and 73; CB-154 treatment, 34/119 (29%) and 37, respectively. In the second series, the numbers were: controls, 39/44 (89%) and 73; CB-154 treatment, 24/43 (56%) and 43, respectively. In both studies, CB-154 treatment significantly (p less than 0.05-0.005) reduced the percentage of mice with mammary tumors and total number of mammary tumors. These results provide evidence that prolactin is a contributing hormone in the genesis of estrone/progesterone and pregnancy-induced mammary tumors in female GR mice.

Neuroendocrine effects of neuropsychotropic drugs and their possible influence on toxic reactions in animals and man -- the role of the dopamine-prolactin system

As an example for the importance of the neuroendocrine system in the toxicological evaluation of neuropsychotropic drugs, the influence of functional dopaminergic agonists and antagonists on the secretion of prolactin is studied. In rats, all functional dopamine antagonists (reserpine alone or combined with alpha-methyl-p-tyrosine or benserazide, haloperidol, spiroperidol, sulpiride) increased serum PRL levels. Dopaminergic agonists (apomorphine, piribedil, d-amphetamine, L-DOPA, and the ergot derivatives bromocriptine and lisuride) all caused a decrease of serum prolactin levels. The same effect could be observed also after treatment with other ergot derivatives such as d-LSD, methergoline, methysergide and ergotamine. Also in this case, the prolactin-lowering effect seems to be related to dopaminergic activity. This was suggested by the inhibitory effect of pretreatment with the dopamine antagonist spiroperidol or with sulpiride on the prolactin-lowering effect of lisuride. In dogs, thyrotropin releasing hormone (TRH) increased and lisuride decreased serum prolactin levels determined with a new radioimmunoassay. As an example for the situation in humans, the effects of the dopamine antagonist sulpiride and of the dopamine agonist bromocriptine were described. The prolactin levels were higher in the presence of estrogens. The relevance of these neuroendocrine effects of neuropsychotropic drugs on physiological systmes in animals and man is discussed.