Sex hormone-induced mammary carcinogenesis in female Noble rats: detection of differentially expressed genes

Rat Models of Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) breast cancer (BC) is the most common type of breast cancer among women worldwide, accounting for 70-80% of all invasive cases. Patients with HR+ BC are commonly treated with endocrine therapy, but intrinsic or acquired resistance is a frequent problem, making HR+ BC a focal point of intense research. Despite this, the malignancy still lacks adequate in vitro and in vivo models for the study of its initiation and progression as well as response and resistance to endocrine therapy. No mouse models that fully mimic the human disease are available, however rat mammary tumor models pose a promising alternative to overcome this limitation. Compared to mice, rats are more similar to humans in terms of mammary gland architecture, ductal origin of neoplastic lesions and hormone dependency status. Moreover, rats can develop spontaneous or induced mammary tumors that resemble human HR+ BC. To date, six different types of rat models of HR+ BC have been established. These include the spontaneous, carcinogen-induced, transplantation, hormone-induced, radiation-induced and genetically engineered rat mammary tumor models. Each model has distinct advantages, disadvantages and utility for studying HR+ BC. This review provides a comprehensive overview of all published models to date.

Doping and Urologic Tumors

Several substances such as growth hormone (GH), erythropoietin (Epo), and anabolic steroids (AS) are improperly utilized to increase the performance of athletes. Evaluating the potential cancer risk associated with doping agents is difficult since these drugs are often used at very high doses and in combination with other licit or illicit drugs.

The GH, via its mediator, the insulin-like growth factor 1 (IGF-1), is involved in the development and progression of cancer. Animal studies suggested that high levels of GH/IGF-1 increase progression of androgen-independent prostate cancer. Clinical data regarding prostate cancer are mostly based on epidemiological studies or indirect data such as IGF-1 high levels in patients with prostate cancer. Even if experimental studies showed a correlation between Epo and cancer, no clinical data are currently available on cancer development related to Epo as a doping agent. Androgens are involved in prostate carcinogenesis modulating genes that regulate cell proliferation, apoptosis and angiogenesis. Most information on AS is anecdotal (case reports on prostate, kidney and testicular cancers). Prospective epidemiologic studies failed to support the hypothesis that circulating androgens are positively associated with prostate cancer risk.

Currently, clinical and epidemiological studies supporting association between doping and urological neoplasias are not available. Nowadays, exposure to doping agents starts more prematurely with a consequent longer exposition period; drugs are often used at very high doses and in combination with other licit or illicit drugs. Due to all these elements it is impossible to predict all the side effects, including cancer; more detailed studies are therefore necessary.

Estradiol enhances sociosexual behavior and can have proliferative effects in ovariectomized rats

Although estradiol (E(2)) may have some beneficial effects as a treatment for menopause symptoms, E(2) also has trophic effects that can increase vulnerability to some cancers, such as breast cancer. In the present study, a model to investigate the concomitant behavioral and proliferative effects of E(2) was developed. First, the effects of different duration of chronic E(2) exposure (2 vs 6 months), or no such exposure, on proliferation (tumor incidence and weight, uterine weight) in adult, ovariectomized (OVX) rats was determined. Second, the effects of different dosages of E(2) (0.03 or 0.09 mg/kg) compared to vehicle only on sexual behavior, and measures of proliferation of adult OVX rats treated with a chemical carcinogen (DMBA; 1.25, 12.50, or 25.00 mg), or inert vehicle, were investigated. Vehicle or E(2) was administered subcutaneously (SC) to OVX rats once per week for 14 weeks. Six months of continuous E(2) exposure increased tumor incidence, tumor weight, and uterine weight, compared to 2 months of E(2) or no E(2) exposure. Rats administered DMBA had increased incidence, number, and size of tumors compared to vehicle treatment, and this effect appeared to be augmented by E(2). Compared to vehicle, E(2) increased lordosis and uterine weight. Thus, E(2) may have the unfavorable effect of increasing proliferation when administered in chronic situations. Studies investigating the action of E(2) for these effects are ongoing.

Effects of two estradiol regimens on anxiety and depressive behaviors and trophic effects in peripheral tissues in a rodent model

BACKGROUND

With aging and menopause, which are associated with decreases in ovarian steroids such as 17beta-estradiol (E(2)), women might experience negative psychological symptoms, including anxiety and depression. Some women use E(2)-based therapies to alleviate these symptoms, but E(2) has been associated with trophic effects that might increase vulnerability to some steroid-sensitive cancers, such as breast cancer, in both premenopausal and postmenopausal women.

OBJECTIVE

This study investigated the relationships between the possible beneficial effects of E(2) on anxiety and depressive behaviors concurrent with trophic effects using an animal model of E(2) decline and replacement.

METHODS

Dose-dependent effects of E(2) on affective, sexual, and motor behavior of young adult rats were studied. Ovariectomized (OVX) rats were administered the chemical carcinogen 7,12-dimethylbenz(a) anthracene (DMBA) 1.25 mg or inactive vehicle (vegetable oil; control) by gavage. E(2) (0.03 or 0.09 mg/kg) or vehicle was administered subcutaneously 44 to 48 hours before assessments of anxiety (light-dark transition), depression (forced swim test), sexual (lordosis), and motor (activity monitor) behaviors. Fourteen weeks after carcinogen exposure, E(2) concentrations in plasma and brain regions (cortex, hippocampus, and hypothalamus) were determined. Incidences and numbers of tumors and uterine weight were analyzed.

RESULTS

Administration of E(2) (0.09 mg/kg) was associated with significant increases in antianxiety-like behavior in the light-dark transition task, antidepressant-like behavior in the forced swim test, and physiologic circulating and central E(2) concentrations compared with E(2) (0.03 mg/kg) and vehicle. Compared with vehicle, E(2) (0.9 > 0.3 mg/kg) was associated with significant increases in lordosis and uterine weight. Administration of DMBA was associated with significant increases in the incidences and numbers of tumors; this effect was augmented by E(2)administration.

CONCLUSIONS

Based on the findings in this rat model, the hypothesis that E(2) may be effective in reducing anxiety and depressive behaviors and enhance sexual behavior in OVX rats, concurrent with trophic effects in the periphery, was supported. Moderate physiologic levels of E(2) might have beneficial effects on affective and sexual behaviors in female rodents, but regimens including E(2) might increase tumorigenic capacity.

Growth hormone and insulin-like growth factor-I in the transition from normal mammary development to preneoplastic mammary lesions

Adult female mammary development starts at puberty and is controlled by tightly regulated cross-talk between a group of hormones and growth factors. Although estrogen is the initial driving force and is joined by luteal phase progesterone, both of these hormones require GH-induced IGF-I in the mammary gland in order to act. The same group of hormones, when experimentally perturbed, can lead to development of hyperplastic lesions and increase the chances, or be precursors, of mammary carcinoma. For example, systemic administration of GH or IGF-I causes mammary hyperplasia, and overproduction of IGF-I in transgenic animals can cause the development of usual or atypical hyperplasias and sometimes carcinoma. Although studies have clearly demonstrated the transforming potential of both GH and IGF-I receptor in cell culture and in animals, debate remains as to whether their main role is actually instructive or permissive in progression to cancer in vivo. Genetic imprinting has been shown to occur in precursor lesions as early as atypical hyperplasia in women. Thus, the concept of progression from normal development to cancer through precursor lesions sensitive to hormones and growth factors discussed above is gaining support in humans as well as in animal models. Indeed, elevation of estrogen receptor, GH, IGF-I, and IGF-I receptor during progression suggests a role for these pathways in this process. New agents targeting the GH/IGF-I axis may provide a novel means to block formation and progression of precursor lesions to overt carcinoma. A novel somatostatin analog has recently been shown to prevent mammary development in rats via targeted IGF-I action inhibition at the mammary gland. Similarly, pegvisomant, a GH antagonist, and other IGF-I antagonists such as IGF binding proteins 1 and 5 also block mammary gland development. It is, therefore, possible that inhibition of IGF-I action, or perhaps GH, in the mammary gland may eventually play a role in breast cancer chemoprevention by preventing actions of both estrogen and progesterone, especially in women at extremely high risk for developing breast cancer such as BRCA gene 1 or 2 mutations.

Estradiol and medroxyprogesterone acetate regulated genes in T47D breast cancer cells

Many mammary tumors express estrogen receptors (ER) and progesterone receptors (PR), and there is increasing evidence that progestins influence gene expression of breast tumor cells. To analyse the impact of progestins on breast cancer cells, we compared (a) the expression of two cytokines, involved in tumor progression, and searched (b) for differentially regulated genes by a microarray, containing 2400 genes, on T47D breast cancer cells cultured for 6 days with 17beta-estradiol (E2) or E2+medroxyprogesterone acetate (E2+MPA). Lower amounts of PDGF and TNFalpha were found in culture supernatants of E2+MPA treated T47D cells. MPA addition induced a 2.8-3.5-fold increase of the mRNA expression of (a) tristetraprolin, which is involved in the posttranscriptional regulation of cytokine biosynthesis, and (b) zinc-alpha2-glycoprotein and Na, K-ATPase alpha1-subunit, which both resemble differentiation markers of breast epithelium. In contrast, the mRNA expression of lipocalin 2, which promotes matrixmetalloproteinase-9 activity, was decreased five-fold in E2+MPA treated cells. Our data show that the expression of genes from various functional gene families is regulated differentially by E2 and E2+MPA treatment in T47D cells. This suggests that exogenous progestins applied for therapy and endogenous changes of the progesterone levels during the menstrual cycle both influence breast cancer pathophysiology.