Autochthonous prostate adenocarcinomas in Lobund-Wistar rats: a model system

Predicting Dose-Dependent Carcinogenicity of Chemical Mixtures Using a Novel Hybrid Neural Network Framework and Mathematical Approach

This study addresses the challenge of assessing the carcinogenic potential of hazardous chemical mixtures, such as per- and polyfluorinated substances (PFASs), which are known to contribute significantly to cancer development. Here, we propose a novel framework called HNN_MixCancer that utilizes a hybrid neural network (HNN) integrated into a machine-learning framework. This framework incorporates a mathematical model to simulate chemical mixtures, enabling the creation of classification models for binary (carcinogenic or noncarcinogenic) and multiclass classification (categorical carcinogenicity) and regression (carcinogenic potency). Through extensive experimentation, we demonstrate that our HNN model outperforms other methodologies, including random forest, bootstrap aggregating, adaptive boosting, support vector regressor, gradient boosting, kernel ridge, decision tree with AdaBoost, and KNeighbors, achieving a superior accuracy of 92.7% in binary classification. To address the limited availability of experimental data and enrich the training data, we generate an assumption-based virtual library of chemical mixtures using a known carcinogenic and noncarcinogenic single chemical for all the classification models. Remarkably, in this case, all methods achieve accuracies exceeding 98% for binary classification. In external validation tests, our HNN method achieves the highest accuracy of 80.5%. Furthermore, in multiclass classification, the HNN demonstrates an overall accuracy of 96.3%, outperforming RF, Bagging, and AdaBoost, which achieved 91.4%, 91.7%, and 80.2%, respectively. In regression models, HNN, RF, SVR, GB, KR, DT with AdaBoost, and KN achieved average R² values of 0.96, 0.90, 0.77, 0.94, 0.96, 0.96, and 0.97, respectively, showcasing their effectiveness in predicting the concentration at which a chemical mixture becomes carcinogenic. Our method exhibits exceptional predictive power in prioritizing carcinogenic chemical mixtures, even when relying on assumption-based mixtures. This capability is particularly valuable for toxicology studies that lack experimental data on the carcinogenicity and toxicity of chemical mixtures. To our knowledge, this study introduces the first method for predicting the carcinogenic potential of chemical mixtures. The HNN_MixCancer framework offers a novel alternative for dose-dependent carcinogen prediction. Ongoing efforts involve implementing the HNN method to predict mixture toxicity and expanding the application of HNN_MixCancer to include multiple mixtures such as PFAS mixtures and co-occurring chemicals.

Hormone receptor expression in aging mammary tissue and carcinoma from a rodent model after xenoestrogen disruption

AIMS

Hormone receptors are the main markers applied for prognosis of breast cancer subtypes. Among modulators, exogenous chemical agents known as endocrine disruptors interact with certain receptors, triggering molecular pathways or increasing their expression. Bisphenol A (BPA), a xenoestrogen, interacts with several hormone receptors. Thus, our aim was to characterize the hormone receptor status in the mammary gland (MG) of aged female Mongolian gerbils exposed to BPA in pregnancy and lactation.

METHODS

We evaluated the expression of receptors for estrogens (ERα and ERβ), progesterone (PR), prolactin (PRL-R), HER2/ErbB2, and androgen (AR) in normal and hyperplastic mammary tissue and in carcinomas developed after BPA exposure.

KEY FINDINGS

BPA-exposed MG presented increased ERα, whereas ERβ, PR, and PRL-R showed lower expression. AR and HER2/ErbB2 showed similar expression in normal and hyperplastic tissue from control, vehicle, and BPA groups. Both receptors were found in cytoplasm and nucleus in BPA-induced carcinoma. We demonstrate the presence of EZH2 expression, an epigenetic and epithelial-mesenchymal transition (EMT) marker, with a high H-score in BPA-exposed MG, which was associated with poor prognosis of cancer. Co-localization of ERα and EZH2 was present in normal and carcinoma features, corroborating the installation of ERα-positive mammary cancer associated with the EMT process. Enhanced EZH2 in BPA-exposed mammary tissue could decrease ERβ expression and promote tumorigenesis progress through HER2/ErbB2.

SIGNIFICANCE

The present study proposes the Mongolian gerbil as an experimental model for mammary carcinogenesis studies, based on BPA disruption that triggers a phenotype of increased ERα/HER2 positivity and depletion of ERβ/PR expression.

Gnotobiotics and the Microbiome

This chapter provides an overview of germfree (GF), gnotobiotic (GN), and defined flora (DF) laboratory rats, relating their history, traditional and modern derivation procedures, the anatomy and physiology, and their use in the study of mammalian host–microbiome relationships. Extensive literature on the nutrition and physiology of GF rats and the expanding library of immunological reagents have increased the research utility of GF, GN, or DF rats. Such rats have been extensively used in metabolic experiments as nucleus seed stocks for the production of disease-free animals and as tools for infectious disease studies, among others. The chapter also presents research applications of GF rats that are particularly suitable for testing candidate viral carcinogens since they are uniquely free of all known viruses, for pathology studies in the distinguishing of primary mediation lesions from those associated with infections, and the study of the biological effects of radiation.

Colorectal carcinogenesis: Insights into the cell death and signal transduction pathways: A review

Colorectal carcinogenesis (CRC) imposes a major health burden in developing countries. It is the third major cause of cancer deaths. Despite several treatment strategies, novel drugs are warranted to reduce the severity of this disease. Adenomatous polyps in the colon are the major culprits in CRC and found in 45% of cancers, especially in patients 60 years of age. Inflammatory polyps are currently gaining attention in CRC, and a growing body of evidence denotes the role of inflammation in CRC. Several experimental models are being employed to investigate CRC in animals, which include the APC^min/+ mouse model, Azoxymethane, Dimethyl hydrazine, and a combination of Dextran sodium sulphate and dimethyl hydrazine. During CRC progression, several signal transduction pathways are activated. Among the major signal transduction pathways are p53, Transforming growth factor beta, Wnt/β-catenin, Delta Notch, Hippo signalling, nuclear factor erythroid 2-related factor 2 and Kelch-like ECH-associated protein 1 pathways. These signalling pathways collaborate with cell death mechanisms, which include apoptosis, necroptosis and autophagy, to determine cell fate. Extensive research has been carried out in our laboratory to investigate these signal transduction and cell death mechanistic pathways in CRC. This review summarizes CRC pathogenesis and the related cell death and signal transduction pathways.

Chemoprevention of Prostate Carcinogenesis by DFMO and/or Finasteride Treatment in Male Wistar Rats

In the present study the chemopreventive activities of DFMO, the irreversible inhibitor of ornithine decarboxylase, and finasteride, the inhibitor of prostatic 5a-reductase, against the development of chemically induced prostate adenocarcinoma by methylnitrosourea/testosterone propionate in male Wistar rats were investigated. According to histological examination, oral administration of DFMO and finasteride, either alone or combined, for two months to MNU/TP-inoculated rats reduced the tumor incidence to 11.11%, 10% and 10%, respectively, compared to tumored controls (64.3%). DFMO and/or finasteride treatment resulted in significant reductions in the wet weight of the prostate gland and seminal vesicles and its ratio relative to the total body weight, as well as the levels of prostate total protein, DNA, RNA and DNA/RNA ratio, compared to tumored controls. However, the effect of the combined treatment was of no statistical significance compared to single DFMO or finasteride treatment, as demonstrated by the non-significant differences between the mean values of most of the studied parameters. The tumor chemopreventive activity and the prostate growth inhibitory effect of DFMO and finasteride were due to suppression of prostate polyamine synthesis. ANOVA test revealed that the relative weight of the prostate as well as blood and tissue polyamine levels could be used as significant endpoint biomarkers for DFMO and finasteride as cancer chemopreventive agents.

Testosterone treatment is a potent tumor promoter for the rat prostate

Testosterone is increasingly prescribed to middle aged and older men, but the safety of this treatment has been called into question, and the possible risk of prostate cancer is unknown. We treated Wistar Cpb: WU rats chronically via slow-release Silastic implants with doses of testosterone that increased circulating levels in a dose-related fashion with or without a preceding single injection of the carcinogen N-nitroso-N-methylurea (MNU). Without MNU, testosterone induced prostate carcinomas in 10%-18% of rats, and after MNU injection, testosterone treatment caused prostate cancer in 50%-71% of rats with a very steep dose response, producing a 50% prostatic tumor incidence even at a testosterone dose that did not elevate circulating testosterone levels. Prostate cancers did not occur in rats given MNU or no treatment, whereas testosterone alone induced a low incidence of prostate cancer and increased the number rats bearing tumors at other sites, particularly malignant tumors. Thus, testosterone was shown to be a weak complete carcinogen and a strong tumor promoter for the rat prostate in this study. These findings have potential significant public health implications for the use of testosterone therapy in men.

Animal models of colorectal cancer

Colorectal cancer is a heterogeneous disease that afflicts a large number of people in the USA. The use of animal models has the potential to increase our understanding of carcinogenesis, tumor biology, and the impact of specific molecular events on colon biology. In addition, animal models with features of specific human colorectal cancers can be used to test strategies for cancer prevention and treatment. In this review, we provide an overview of the mechanisms driving human cancer, we discuss the approaches one can take to model colon cancer in animals, and we describe a number of specific animal models that have been developed for the study of colon cancer. We believe that there are many valuable animal models to study various aspects of human colorectal cancer. However, opportunities for improving upon these models exist.

A new proposed rodent model of chemically induced prostate carcinogenesis: distinct time-course prostate cancer progression in the dorsolateral and ventral lobes

BACKGROUND

Characterization of novel rodent models for prostate cancer studies requires evaluation of either spontaneous and carcinogen-induced tumors as well as tumor incidence in different prostatic lobes. We propose a new short-term rodent model of chemically induced prostate carcinogenesis in which prostate cancer progression occurs differentially in the dorsolateral and ventral lobes.

METHODS

Adult gerbils were treated with MNU alone or associated with testosterone for 3 or 6 months of treatment. Tumor incidence, latency, localization, and immunohistochemistry (AR, PCNA, smooth muscle α-actin, p63, MGMT, and E-cadherin) were studied in both lobes.

RESULTS

Comparisons between both lobes revealed that lesions developed first in the DL while the VL presented longer tumor latency. However, after 6 months, there was a dramatic increase in tumor multiplicity in the VL, mainly in MNU-treated groups. Lesions clearly progressed from a premalignant to a malignant phenotype over time and tumor latency was decreased by MNU + testosterone administration. Three-dimensional reconstruction of the prostatic complex showed that the DL developed tumors exclusively in the periurethral area and showed intense AR, PCNA, and MGMT immunostaining. Moreover, VL lesions emerged throughout the entire lobe. MNU-induced lesions presented markers indicative of an aggressive phenotype: lack of basal cells, rupture of the smooth muscle cell layer, loss of E-cadherin, and high MGMT staining.

CONCLUSIONS

There are distinct pathways involved in tumor progression in gerbil prostate lobes. This animal provides a good model for prostate cancer since it allows the investigation of advanced steps of carcinogenesis with shorter latency periods in both lobes.

Transgenic models for prostate cancer research

The ability to introduce novel or specifically altered genes into the germ line of mice and directly perturb gene expression in a specific tissue can facilitate characterization of the molecular mechanisms governing transformation of differentiating tissue within the context of an intact developing animal. Transgenics provide a powerful and remarkably flexible system that can be used to study the cooperation between proto-oncogenes, tumor suppressor genes, and other epigenetic factors in the development of cancer.

A perspective on the role of estrogen in hormone-induced prostate carcinogenesis

Androgens are thought to cause prostate cancer, but the precise mechanisms by which they do so are unclear. Data, mostly from animal studies, suggest that for androgens to cause prostate cancer they must be aromatized to estrogen and act in concert with these estrogen metabolites. Androgen-receptor mediated activity of androgens and estrogen receptor-mediated effects of estrogen metabolites are likely to be necessary, but estrogen genotoxicity appears to be a probable critical factor as well. Only when all these mechanisms are active, may prostate carcinogenesis result. Convincing proof-of-concept studies are needed to definitively test this concept which, if proven, may lead to clinically feasible chemoprevention approaches interfering with these mechanisms.

Hormones and prostate carcinogenesis: Androgens and estrogens

Prostate cancer is the leading non-skin malignancy detected in US males and the second cause of death due to male cancer in the US. Androgenic hormones are generally believed to be causatively associated with prostate carcinogenesis, but human evidence, mostly epidemiological, for this is minimal. Circulating hormone levels are not associated with the risk of prostate cancer and neither are polymorphisms in various genes encoding the androgen metabolizing enzymes or androgen receptors. Evidence in support of the involvement of androgens in prostate cancer development is derived from clinical trials with 5α-reductase inhibitors, which reduced the risk by approximately 25%. Animal studies using rat models, however, provide clear evidence that testosterone can induce prostate cancer and can act as a strong tumor promoter in concert with genotoxic carcinogens. One such genotoxic factor may be 17β-estradiol, which is generated from testosterone by the aromatase enzyme. Estradiol can be converted to catecholestrogens, which through redox cycling, generate reactive metabolites that can adduct the DNA and potentially lead to mutations. Animal studies and limited human evidence suggest that estrogens can be involved in prostate carcinogenesis by such a genotoxic mechanism. However, how androgens exert their tumor-promoting effect is not clear. It is likely that hormonal and non-hormonal factors as well as genetic and non-genetic (environmental) factors interact in a highly complex and poorly understood manner to determine the risk of prostate cancer.

The effects of aging on the molecular and cellular composition of the prostate microenvironment

Background

Advancing age is associated with substantial increases in the incidence rates of common diseases affecting the prostate gland including benign prostatic hyperplasia (BPH) and prostate carcinoma. The prostate is comprised of a functional secretory epithelium, a basal epithelium, and a supporting stroma comprised of structural elements, and a spectrum of cell types that includes smooth muscle cells, fibroblasts, and inflammatory cells. As reciprocal interactions between epithelium and stromal constituents are essential for normal organogenesis and serve to maintain normal functions, discordance within the stroma could permit or promote disease processes. In this study we sought to identify aging-associated alterations in the mouse prostate microenvironment that could influence pathology.

Methodology/Principal Findings

We quantitated transcript levels in microdissected glandular-adjacent stroma from young (age 4 months) and old (age 20–24 months) C57BL/6 mice, and identified a significant change in the expression of 1259 genes (p<0.05). These included increases in transcripts encoding proteins associated with inflammation (e.g., Ccl8, Ccl12), genotoxic/oxidative stress (e.g., Apod, Serpinb5) and other paracrine-acting effects (e.g., Cyr61). The expression of several collagen genes (e.g., Col1a1 and Col3a1) exhibited age-associated declines. By histology, immunofluorescence, and electron microscopy we determined that the collagen matrix is abundant and disorganized, smooth muscle cell orientation is disordered, and inflammatory infiltrates are significantly increased, and are comprised of macrophages, T cells and, to a lesser extent, B cells.

Conclusion/Significance

These findings demonstrate that during normal aging the prostate stroma exhibits phenotypic and molecular characteristics plausibly contributing to the striking age associated pathologies affecting the prostate.

The effect of dietary supplementation with limonene or myo-inositol on the induction of neoplasia and matrix metalloproteinase and plasminogen activator activities in accessory sex organs of male Lobund-Wistar rats

Prostate cancer, the most prevalent non-cutaneous cancer in men, is associated with increased age. This suggests that dietary chemopreventive measures could be effective in delaying the onset or decreasing the severity of the disease. We utilized the Lobund-Wistar rat nitrosomethylurea induced, testosterone promoted (NMU-T) model of male sex accessory gland cancer to test the potential chemopreventive effects of myo-inositol and limonene on tumor incidence and associated protease activities. Tumors were found to arise in the seminal vesicles and dorsal and anterior prostate lobes. There were also some tumors that appeared to arise in both the seminal vesicles and anterior prostate, and in some cases the tissue of origin was not clear. The distribution of tumors as to site of origin in limonene or myo-inositol treated animals did not vary from that of the starch fed control animals, and the number of animals presenting with metastases did not vary significantly between treatment groups. There was a statistically significant delay in onset of tumors in myo-inositol, but not limonene fed rats, at 10 months post-induction of carcinogenesis; however, at 12 and 15 months this was not significant. The ventral prostate and seminal vesicles expressed pro-MMP-2 and plasminogen activator (PA) activities. Based on sensitivity to amiloride, the PA activities were predominately urokinase (uPA) in the ventral prostate and a mixture of tissue-type activator (tPA) and uPA in the seminal vesicles of non-treated rats. Sex accessory gland tumors, and metastases, expressed increased levels PA and pro- and active forms of MMP-2 and -9. The PA activities of the tumors were a mixture of uPA and tPA. There was no difference in the levels of these protease activities based on the tissue of tumor origin, nor in tumor vs metastasis. These studies indicate that MMP and PA activities play a role in sex accessory gland tumor biology and that dietary supplementation with myo-inositol can delay but not ultimately prevent the development of such tumors.

Age-related histopathological lesions in the Mongolian gerbil ventral prostate as a good model for studies of spontaneous hormone-related disorders

The Meriones unguiculatus (Mongolian) gerbil has demonstrated significant prostatic responses to hormonal treatments, and to drugs against human prostatic hyperplasia. Spontaneous neoplasia develops in the older animals. Thirty gerbils (age 18 months) were divided into non-affected and prostatic lesion bearers and the prostate lesions were evaluated morphologically, immunohistochemically and quantitatively. The most frequent changes were in epithelial sites and, namely prostatic intraepithelial neoplasias, microinvasive carcinomas and adenocarcinomas. In the stromal compartment, cellular hyperplasia, when verified, was always associated with the sites of anomalous epithelium. Additionally, larger deposition of collagen fibrils, generating stromal fibrosis, was found in all the old gerbils analysed. The quantitative analysis showed that prostatic tissue proportions differed in altered areas, being specific for each lesion type. Isolated nuclear and nucleolar parameters were not effective in diagnosing the malign potential of lesions. However, the cellular proliferation and death indexes indicated larger cellular turnover in invasive lesions such as carcinomas. With these analyses, it could be verified that old gerbils present high propensity to develop spontaneous prostate changes and this may aid in a better understanding of the biological behaviour of human prostate cancer.

Experimental rodent models of prostatitis: limitations and potential

Prostatitis is a polyetiological inflammation of the prostate gland in men characterized by pelvic pain, irritative voiding symptoms, and sexual dysfunction. Histologically prostatitis is characterized by poly- and mononuclear cell infiltrates (neutrophils, lymphocytes, macrophages and plasma cells) in the stromal connective tissue around the acini or ducts. Prostatitis is an important worldwide health problem in men. The pathogenesis and diagnostic criteria for the condition are obscure, with the result that the development of management programs for this condition has been hindered. Animal model(s) might be useful in elucidating mechanisms involved in the molecular pathogenesis of chronic nonbacterial prostatitis and chronic pelvic pain syndrome. Given that prostatitis might have a multifactorial etiology, several animal models with unique features may prove helpful. This review examines a number of experimental rodent models of prostatitis and evaluates their advantages and limitations.

Dietary gamma-linolenate attenuates tumor growth in a rodent model of prostatic adenocarcinoma via suppression of elevated generation of PGE(2) and 5S-HETE

Prostate cancer poses considerable threat to the aging male population as it has become a leading cause of cancer death to this group. Due to the complexity of this age-related disease, the mechanism(s) and factors resulting in prostate cancer remain unclear. Reports showing an increase risk in prostatic cancer with increasing dietary fat are contrasted by other studies suggesting the beneficial effects of certain polyunsaturated fatty acid (PUFA) in the modulation of tumor development. The n-6 PUFA, gamma-linolenic acid (GLA), has been shown to suppress tumor growth in vitro. Therefore, using the Lobund-Wistar (L-W) rat model of prostate cancer, we tested the hypothesis whether dietary supplementation of GLA could suppress tumor growth and development in vivo. Prostatic adenocarcinomas were induced in two groups of L-W rats, the experimental group (N-nitroso-N-methylurea, NMU/testosterone propionate, TP) and the GLA group (NMU/TP/GLA fed) undergoing similar treatment but fed a purified diet supplemented with GLA. Our findings revealed a decrease in prostate growth in the NMU/TP/GLA-fed group as determined by weight, tissue size, DNA content and prostate-specific antigen (tumor marker of prostate cancer). Comparison between the two groups showed a significant increase in 5S-hydroxyeicosatetraenoic acid and prostaglandin E(2) in the NMU/TP group. These increases paralleled the increased protein expression and activity of cyclooxygenase-2 as well as increased activity of 5-lipoxygenase. Taken together, the findings showed that intake of GLA-enriched diet does reduce prostatic cancer development in L-W rats and could serve as a non-toxic adjunct in management of human prostatic cancer.

Prevention of de novo prostate cancer by immunization with tumor-derived vaccines

Since advanced prostate cancer is difficult to treat, we have chosen a very different approach: the development of vaccines to prevent initial de novo tumor formation. To test the hypothesis that prostate cancer can be prevented by vaccination, Lobund-Wistar (LW) rats were vaccinated subcutaneously with complete Freund's adjuvant (CFA) plus glutaraldehyde-fixed (GFT) whole cell or potassium thiocyanate extract (PTE) preparations derived from in vivo tumors, or with media and CFA (media-vaccinated). Rats were vaccinated each month substituting incomplete Freund's adjuvant for CFA, from age 3 to 12 months, and methylnitrosourea (30 mg/kg) was administered intravenously at 4 months of age. Groups of 30 GFT cell-vaccinated rats showed a 90% reduction, and PTE-vaccinated rats, a 50% reduction in the occurrence of de novo prostate tumors compared with media-vaccinated controls. When splenocytes from vaccinated rats were incubated with tumor cells prior to subcutaneous implantation, PTE-vaccinated rats showed a 80% reduction, and GFT cell-vaccinated rats showed a 40% reduction in the occurrence of tumors, demonstrating a role for the spleen in the protective response. The inflammatory responses in tumors from GFT cell-vaccinated rats and PTE-vaccinated rats were distinguished by an influx of eosinophils compared with the responses in tumors from media-vaccinated rats. These results demonstrate the possibility that prostate cancer can be prevented by immunization with vaccines based on whole tumor-derived vaccines.

Estrogen enhancement of androgen-responsive gene expression in hormone-induced hyperplasia in the ventral prostate of F344 rats

It has been postulated that, in addition to the crucial role of androgens, estrogens may be involved in development of prostate hyperplasia and cancer. In rats, combined administration of estrogen and androgen synergistically increases ventral prostate weight, and continued treatment results in the development of glandular hyperplasia. Prostate adenocarcinoma can be induced by chemical carcinogens in rats, and estrogen given together with an androgen generally shortens the latent period or increases the incidence and/or multiplicity of carcinomas. However, the mechanisms responsible for these synergistic effects of estrogen and androgen are poorly understood. In the present study, we examined the combined effects of 17beta-estradiol (E2) and testosterone (T) on gene expression in an early stage of prostate hyperplasia in an F344 rat model. ERalpha expression, which has been suggested to contribute to development of prostatic hyperplasia, was increased by the combined treatment with T and E2, while it was suppressed by T alone. Expression levels of two androgen-responsive genes, probasin and kallikrein S3, were increased in the ventral prostate of rats treated with T plus E2 for 4 weeks in a dose-dependent manner, while short-term treatment did not alter the expression. These results suggested that enhancing effects of E2 on transcription of androgen-responsive genes, as well as an increased level of ERalpha may play roles in the synergistic effects of E2 on T-induced prostate hyperplasia.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Refractory hypothalamic alpha-mSH satiety and AGRP feeding systems in rats bearing MCA sarcomas

In pre-anorectic tumor-bearing (TB: methylcholanthrene-induced sarcoma) rats, injection of alpha-melanocyte stimulating hormone (alpha-MSH) into the perifornical hypothalamus (PFH) had no significant effect on food intake at a dose (5 microg) that reduced feeding in non-TB control rats. Following the development of anorexia, injection of alpha-MSH MC3/MC4 receptor antagonists, SHU9119 (1 microg) or 4 microg agouti-related protein (AGRP), stimulated feeding in non-TB rats, while having no significant effect in TB rats. Concentrations of alpha-MSH were not altered significantly in ventromedial, dorsomedial or lateral hypothalamic areas of TB rats, and proopiomelanocortin (POMC) messenger RNA was not changed in TB rats in these hypothalamic areas. Determination of cytokines by ELISA in non-operated TB and non-TB rats revealed elevated IL-2 in plasma and hypothalamus as well as increased TNF-alpha in the hypothalamus of anorectic TB rats. IL-1B was not detectable in plasma and was not altered significantly in hypothalamus of TB rats. These results suggest that the POMC alpha-MSH satiety system is refractory in TB rats, even prior to the onset of anorexia. This change in MC3/MC4 receptor response does not appear to be secondary to alterations of endogenous alpha-MSH in TB rats. Cytokine involvement in the altered response to MC3/MC4 receptor stimulation and blockade is a possibility, since TNF-alpha and IL-2 were increased in hypothalamus of anorectic TB rats. Therefore, these results suggest major alterations in POMC neuropeptide systems in TB rats as anorexia progresses. Although these changes do not appear to have occurred due to grossly-altered concentrations of alpha-MSH, elevated cytokine activity in the hypothalamus may be an important factor. Due to the complex multi-factorial nature of feeding control, additional factors are likely to be involved in cancer anorexia.

Expressed sequence tag profiling identifies developmental and anatomic partitioning of gene expression in the mouse prostate

BACKGROUND

The prostate gland is an organ with highly specialized functional attributes that serves to enhance the fertility of mammalian species. Much of the information pertaining to normal and pathological conditions affecting the prostate has been obtained through extensive developmental, biochemical and genetic analyses of rodent species. Although important insights can be obtained through detailed anatomical and histological assessments of mouse and rat models, further mechanistic explanations are greatly aided through studies of gene and protein expression.

RESULTS

In this article we characterize the repertoire of genes expressed in the normal developing mouse prostate through the analysis of 50,562 expressed sequence tags derived from 14 mouse prostate cDNA libraries. Sequence assemblies and annotations identified 15,009 unique transcriptional units of which more than 600 represent high quality assemblies without corresponding annotations in public gene expression databases. Quantitative analyses demonstrate distinct anatomical and developmental partitioning of prostate gene expression. This finding may assist in the interpretation of comparative studies between human and mouse and guide the development of new transgenic murine disease models. The identification of several novel genes is reported, including a new member of the beta-defensin gene family with prostate-restricted expression.

CONCLUSIONS

These findings suggest a potential role for the prostate as a defensive barrier for entry of pathogens into the genitourinary tract and, further, serve to emphasize the utility of the continued evaluation of transcriptomes from a diverse repertoire of tissues and cell types.

5 alpha-reductase-catalyzed conversion of testosterone to dihydrotestosterone is increased in prostatic adenocarcinoma cells: suppression by 15-lipoxygenase metabolites of gamma-linolenic and eicosapentaenoic acids

Although the androgens, testosterone (T) and its highly active metabolite dihydrotestosterone (DHT) play a role in the development and progression of prostate cancer, the mechanism(s) are unclear. Furthermore, 5 alpha-reductase which catalyze the conversion of T to DHT, has been a target of manipulation in the treatment of prostatic cancer, hence synthetic 5 alpha-reductase activity inhibitors have shown therapeutic promise. To demonstrate that nutrients derived from dietary sources can exert similar therapeutic promise, this study was designed using benign hyperplastic cells (BHC) and malignant tumorigenic cells (MTC) derived from Lobund-Wistar (L-W) rat model of prostatic adenocarcinoma to test the effects of gamma-linolenic acid (GLA), eicosapentaenoic acid (EPA) and their 15-lipoxygenase metabolites on cellular 5 alpha-reductase activity. Our data revealed: (i) that incubation of MTC with [3H]-T resulted in marked conversion to [3H]-DHT when compared to similar incubation with BHC; (ii) that DHT-enhanced activity of 5 alpha-reductase was inhibited 80% by 15S-hydroxyeicosatrienoic acid, the 15-lipoxygenase metabolite of GLA, when compared to 55% by 15S-hydroxyeicosapentaenoic acid, the 15-lipoxygenase metabolite of EPA; and (iii) that their precursor fatty acids, respectively, exerted moderate inhibition. Taken together, the study underscores the biological importance of 15-lipoxygenase metabolites of polyunsaturated fatty acids (PUFAs) in androgen metabolism.

Joint effects of smoking and body mass index on prostate cancer risk

Between 1979 and 1985, a population-based case-control study of cancer at multiple sites was carried out in Montréal. A total of 399 cases with histologically confirmed prostate cancer and 476 population controls, 45-70 years of age, gave face-to-face interviews and provided adequate smoking histories. We analyzed the effects of smoking cigarettes only and of smoking cigars, or pipes, or both, with or without cigarettes, on the risk of prostate cancer. Overall, the associations between smoking cigarettes and prostate cancer were weak and compatible with no effect; the associations with cigar and pipe smoking were stronger. Among men with high body mass index, however, we found appreciable associations between cigarette smoking and prostate cancer risk. A history of ever smoking daily was associated with an odds ratio of 2.31 (95% confidence interval = 1.09-4.89). Risk increased with the amount smoked per day and with the duration of smoking. Taken together, the findings of increased risk associated with cigar and pipe smoking and the findings of increased risk associated with cigarette smoking among obese men suggest that tobacco smoking may be a risk factor for prostate cancer.

Growth factors and epithelial-stromal interactions in prostate cancer development

Epithelial-stromal interactions are important not only in growth, development, and functional cytodifferentiation of the prostate but also in derangements of prostate gland such as BPH and prostate carcinoma. This chapter explores the roles of epithelium and stroma during this delicate process and highlights the role and mutual influence of each on the other. It also examines the importance of ECM in mediating the effects of androgens and drawn attention to estrogen and genetic factors in the process. During this process of epithelial-stromal interaction, growth factors play a central role in mediating the interactions. This chapter focuses on the role of several growth factors including epidermal growth factor, fibroblast growth factor, transforming growth factor alpha, transforming growth factor beta, insulin-like growth factor-1, vascular endothelial growth factor, nerve growth factor, platelet-derived growth factor, and hepatocyte growth factor. This chapter emphasizes the importance of epithelial-stromal interactions in tumorigenesis and highlights the switch of paracrine to autocrine mode during the process of carcinogenesis.

Experimental prostate carcinogenesis - rodent models

A number of rodent models of prostate carcinoma development have been established to study mechanisms and modifying potential. All except for transgenic mouse models need long experimental periods for generation of a high yield of cancers. Spontaneous prostate tumor models, while not practical in terms of time and tumor incidences, allow the natural course of multistep neoplasia to be followed without a need for chemical exposure. Carcinogens, especially in combination with testosterone, can induce prostate carcinomas in rats, but none are prostate-specific, so that tumor development in other organs is a complicating factor. Induction of invasive prostate carcinomas in the rat frequently requires long-term administration of a pharmacological dose of testosterone with or without application of a chemical carcinogen. While there are several transgenic mouse models, each also has strong and weak points, and it is therefore necessary to select the best model for the purpose of any experimental study.

Prevention of prostate-related cancers in Lobund-Wistar rats

BACKGROUND

Since prostate cancer (PC) development involves a combination of genetic predisposition and promotional mechanisms, especially the metabolic conversion of testosterone to 5alpha dihydrotestosterone (DHT) by 5alpha reductase, how do mechanisms in man relate to prostate-seminal vesicle (P-SV) tumor development in Lobund-Wistar (L-W) rats? The disease in man and in L-W rats shares developmental mechanisms and characteristics to the extent that prevention of P-SV tumors in L-W rats could be predictive of similar results in man. The epidemiology of PC in man and P-SV tumors in L-W rats indicates that both are hormone-related diseases based on genetic predisposition, high production of androgens (which are activated to DHT by 5alpha reductase), and early development of androgen-dependent and metastasizing late androgen-independent stages of adenocarcinomas, all after long latency periods.

METHODS

L-W rats at risk of developing spontaneous or induced P-SV tumors were subjected to putative antitumor agents or procedures. These included dietary restriction, testosterone ablation, soybean-derived isoflavones, antiangiogenic linomide, tamoxifen, and a vitamin D analogue.

RESULTS

L-W rats subjected to 1) early onset of dietary restriction manifested suppression of spontaneous and induced development of P-SV tumors; 2) testosterone-ablation by nonesterified DHT (NE-DHT) suppressed early onset of induced P-SV tumors and to a lesser extent late onset of spontaneous tumors; 3) diets containing soy protein isolate (high isoflavones) manifested marginal suppressive effects against induced P-SV tumors, but in 12-month-old rats, the development of spontaneous tumors was reduced in incidence; 4) early administrations of antiangiogenic linomide suppressed development of induced P-SV tumors and of transplanted prostate adenocarcinoma III (PA-III) tumors, but linomide had little antitumor effect against large advanced stage tumors; and 5) tamoxifen and vitamin D analogue suppressed development of P-SV tumors. Results in conditions 1-3 were negative when tested against PA-III tumors.

CONCLUSIONS

Developing stages of P-SV tumors were prevented in L-W rats with autochthonous spontaneous and induced tumors, but most of the agents tested were of no therapeutic benefit against advanced-stage and transplanted PA-III tumors. However, early administrations of antiangiogenic linomide suppressed early growth of induced and transplanted PA-III tumors.

Adoptive immunotherapy prevents prostate cancer in a transgenic animal model

Cancer-related mortality can be decreased by prevention, early detection and improved therapies. Although animal models should be used to evaluate the success of cancer therapies, their usefulness is controversial. Many cancer therapies that have cured tumors in mice have not met with similar success when attempted in humans. Current animal models rely mainly on inoculating cell lines into animals, a method that does not reproduce the natural development of the tumor, both for the kinetics of induction and the anatomical site concerned. In this study, we have used an SV40 T-antigen-transgenic mouse model of prostate cancer in which the tumor spontaneously develops orthotopically with a disease progression that closely resembles the progression of human prostate cancer. We have used this model to test the suitability of adoptive cellular immunotherapy. Transfer of naive cells obtained from a T-antigen-negative congenic animal had significant but partial effects: it prevented development of malignant tumors, leaving just minor foci of residual tumor and/or hyperplasia. Adoptive transfer of memory lymphocytes specific for T-antigen, which is a prostatic self antigen in this model, prevented tumor development and progression without affecting the morphology and function of involved tissues. Treated animals were able to breed, and their survival was greatly increased. These results strongly suggest that adoptive immunotherapy should be successful in treating early stages of human prostate cancer.

Dihydrotestosterone prevents spontaneous adenocarcinomas in the prostate-seminal vesicle in aging L-W rats

BACKGROUND

Gene-regulated mechanisms govern tumor development, but the actual development of tumors can be suppressed or promoted by epigenetic factors. Lobund-Wistar (L-W) rats are genetically predisposed to development of spontaneous and induced metastasizing moderately differentiated adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. In L-W rats with one slow-release subcutaneous implant of dihydrotestosterone (DHT) (5alpha-Androstan-17beta-ol-3-one), the development of induced P-SV tumors 14 months later was significantly suppressed, with involution of testes, aspermia, and absence of detectable serum testosterone. The tumor-suppressive effect of DHT was confirmed. Spontaneous P-SV tumors developed in 57 of 220 control L-W rats (26%) at an average age 20 months.

METHODS

At age 12 months, 70 L-W rats were administered an implant of 40 mg of DHT, and 75 untreated rats served as controls. All rats that developed palpable P-SV tumors were autopsied, and surviving rats were autopsied at age 24 months.

RESULTS

At age 24 months, 9 of 70 DHT-treated rats (12.8%) and 20 of 75 DHT-free control rats (26.6%) had developed P-SV tumors spontaneously at average age 20.5 and 20 months, respectively.

CONCLUSIONS

Slow-release implants of DHT administered to L-W rats at age 12 months reduced by 50% the development of spontaneous P-SV tumors by age 24 months.

Brain cytokine mRNAs in anorectic rats bearing prostate adenocarcinoma tumor cells

Cancer is consistently associated with anorexia. The Lobund-Wistar rat model of prostate cancer exhibits clinical manifestations (including anorexia) that resemble many aspects of the human disease. Cytokines are proposed to be involved in cancer-associated anorexia. Here we investigated mRNA profiles of feeding-modulatory cytokines and neuropeptides in specific brain regions of anorectic Lobund-Wistar rats bearing prostate adenocarcinoma tumor cells. Interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), tumor necrosis factor-alpha, transforming growth factor-beta1, glycoprotein 130 (IL-6 receptor signal transducer), proopiomelanocortin (POMC, opioid peptide precursor), and neuropeptide Y (NPY) mRNAs were analyzed with sensitive and specific RNase protection assays. The same brain region sample was assayed for all components. The data show that early anorexia in tumor-bearing rats was associated with an upregulation of IL-1beta mRNA in the brain regions examined (cerebellum, cortex, and hypothalamus). IL-1 receptor antagonist (IL-1Ra) mRNA and IL-1 receptor type I mRNA levels were also significantly increased in the cortex and hypothalamus. All other cytokine components, POMC, or NPY mRNA levels were not significantly different between tumor-bearing and pair-fed (control) rats. IL-1beta mRNA and IL-1Ra mRNA were also significantly upregulated in the spleen of tumor-bearing rats. These data suggest that 1) IL-1beta mRNA upregulation in the brain may be relevant to the anorexia exhibited by the tumor-bearing Lobund-Wistar rat and 2) in vivo characterization of cytokine components in discrete brain regions during cancer is necessary to understand underlying molecular mechanisms responsible for cancer-associated neurological manifestations.

Effects of linomide on advanced prostate-seminal vesicle cancers in Lobund-Wistar rats

BACKGROUND

Angiogenesis and antiangiogenesis, as applied to oncology, are phenomena in which (1) tumors acquire a new blood vascular system from the host that is needed for their growth progression and metastasis; and (2) factors are produced that interfere with neovascularization, thereby inhibiting growth and metastasis of the tumor. Linomide, a chemical antiangiogenesis agent, inhibited the growth of transplanted tumors in mice and rats and inhibited the early development of metastasizing tumors induced in the prostate-seminal vesicle (P-SV) complex of genetically susceptible Lobund-Wistar (L-W) rats.

METHODS

L-W rats with small induced P-SV tumors were treated with a recommended dosage of linomide (100 mg/kg BW/day) by the intraperitoneal and oral routes. The rats were monitored for the next 1-2 months, and the primary and metastatic tumors were compared with related data in drug-free tumor-bearing control rats.

RESULTS

P-SV tumors in linomide-treated and untreated control rats continued to grow, except that in the former (1) the tumors were marginally smaller, (2) the centers of the primary P-SV tumors had failed to grow, (3) the peripheral areas of the tumors contained actively proliferating tumor cells, and (4) metastatic P-SV tumors in the lungs were disrupted with focal areas of necrosis, but areas of intact tumor cells survived. Spread of tumor cells into the peritoneal cavity was not inhibited. Rats on orally administered linomide lived significantly longer than rats inoculated by the intraperitoneal route and untreated control rats. The dosage of linomide used showed evidence of toxicity.

CONCLUSIONS

Although primary and metastatic P-SV tumors were damaged in L-W rats treated with linomide, this antiangiogenic drug was of minimal therapeutic benefit to rats in which a palpable P-SV tumor had developed before onset of treatments.

Neuroendocrine cells in the prostate of the rat, guinea pig, cat, and dog

BACKGROUND

The neuroendocrine (NE) cells in the human prostate gland probably have a local regulatory role in both prostatic growth and differentiation as well as in the exocrine secretory process. Moreover, NE cells may be involved in the pathogenesis of both prostatic cancer and hyperplasia. To enhance the knowledge of the physiological and pathophysiological role of NE cells in the prostate gland, we wanted to establish an experimental animal model.

METHODS

All lobes of the prostatic complex of rats with different serum levels of testosterone, as well as the prostate of the guinea pig, cat, and dog, were studied. Prostatic tissue fixed in different fixatives was studied with regard to NE cells by using cytochemical and immunohistochemical staining techniques, as well as Northern blotting and reverse transcriptase polymerase chain reaction (RT-PCR) for detection of rat chromogranin A (CgA) mRNA.

RESULTS

The present study indicates the absence of NE cells in the rat prostatic complex. No expression of CgA RNA was detectable either by Northern blotting or by RT-PCR. Only a few argyrophil cells in the prostatic complex of guinea pig were detected in tissue fixed in Bouin's solution.

CONCLUSIONS

Rat, guinea pig, cat, and dog are not suitable animals in physiological studies of NE cells in the prostate gland.

Fine structural studies of induced tumors arising within the prostatic complex of Lobund-Wistar rats

BACKGROUND

Morris Pollard, Phyllis Luckert, and colleagues have reported the occurrence of spontaneously arising tumors of the prostatic complex in aged Lobund-Wistar (L-W) rats, and have also shown that the genesis of such tumors may be accelerated by means of intravenous administration of methylnitrosourea, followed by androgen supplementation.

METHODS

Light and electron microscopic investigations of the tumors arising under this regime were conducted, with the objective of documenting morphological changes attending the transformation process; 10 tumor samples were used for the electron microscopic studies.

RESULTS

All tumors studied were adenocarcinomas arising within the prostatic complex of induced animals. These tumors varied in size, degree of differentiation, and invasiveness. Foci of prostatic intraepithelial neoplasia were noted in light microscopic studies as well. Consistent fine structural features exhibited by cells of the induced adenocarcinomas included a large nuclear to cytoplasmic ratio; large irregular nuclei with heavily marginated chromatin; conspicuous nucleoli; abundant ribosomes and polysomes and a paucity of rough endoplasmic reticulum; and numerous cytoplasmic vesicles and lipid inclusions. Numerous, short microvilli extended from the cell surface into a copious surrounding extracellular matrix.

CONCLUSIONS

Thus, these tumors shared many of the fine structural features characteristic of the Dunning (rat) and human prostatic adenocarcinomas.

Influence of isoflavones in soy protein isolates on development of induced prostate-related cancers in L-W rats

Lobund-Wistar (L-W) rats are inherently susceptible to spontaneous and induced metastasizing adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. L-W rats were fed soy protein isolates containing high isoflavones (genistein and daidzein) or low isoflavones to determine their effects on development of induced P-SV tumors in two stages of the tumorigenic process. In rats fed the high-isoflavone-supplemented soy diet before initiation by methylnitrosourea (MNU), the incidence of induced prostate-related cancer was reduced and the disease-free period was prolonged by 27% compared with rats fed the same diet but low in isoflavones. Rats fed the same diets, started after MNU, manifested suggestive but less consistent results than those noted above. The incidence rates were of marginal significance, suggesting that the high intensity of the active induced disease may not represent the character of the slower-growing spontaneous (natural) disease. The delay of disease onset is of clinical significance.

High incidence and histogenesis of seminal vesicle adenocarcinoma and lower incidence of prostate carcinomas in the Lobund-Wistar prostate cancer rat model using N-nitrosomethylurea and testosterone

The origin of chemically induced male accessory sex gland tumors was studied in Lobund-Wistar rats. Rats were treated at the age of 3 months with a single intravenous injection of 30 mg N-nitrosomethylurea (NMU)/kg body weight and given subcutaneous silastic implants filled with 40 mg testosterone propionate. Previous reports described a high incidence of prostate carcinomas in these rats with this treatment protocol. Additional animal groups included untreated controls, rats that received only an injection of 30 mg NMU/kg, and rats that were subjected to ablation of the seminal vesicle lobes prior to the treatment with NMU and testosterone. Three to 14 rats per group were sacrificed 4 to 10 months after NMU treatment and all remaining rats after 12 months. Twenty-four additional rats died or became moribund during the study. All rats were necropsied and the dorsolateral and ventral prostate and seminal vesicles with coagulating gland (anterior prostate) were examined histologically according to a standardized protocol. Lesions detected included atypical hyperplasia in all glands (resembling prostate intraepithelial neoplasia of human beings), adenomas in seminal vesicles only, and early carcinomas and adenocarcinomas in seminal vesicles and coagulating gland. Early carcinomas of the seminal vesicle, microscopically small and with invasion of the lamina propria and/or tunica muscularis, were detected as rapidly as 4 months after treatment. The vast majority (> 95%) of the grossly visible nodules/masses originated from the seminal vesicles. Testosterone treatment enhanced occurrence and increased the incidence of all lesions, particularly of seminal vesicle adenocarcinomas, from 30% (7/23) to 64% (21/33). Coagulating gland tumors were found in 21% (7/33) of the rats. Ablation of the seminal vesicle lobes reduced the incidence of seminal vesicle adenocarcinomas to 11% (3/29), and these tumors arose from tissues remaining within the parenchyma of the seminal vesicle/prostate complex after ablation. Thus, NMU-induced and testosterone-promoted male sex gland tumors of the Lobund-Wistar rat arise almost exclusively in the seminal vesicles and coagulating gland (anterior prostate), are highly invasive in seminal vesicles before attaining a grossly visible size, and progress rapidly within 4 months, spreading to adjacent tissues and other organs.

Studies of rhodamine-123: effect on rat prostate cancer and human prostate cancer cells in vitro

The effect of the lipophilic, cationic dye, Rhodamine-123 (Rh-123), on prostate cancer in rats, and on three tumor cell lines in vitro is reported here. The general toxicity of Rh-123 in mice has been found to be minimal. Lobund-Wistar (L-W) rats with the autochthonous prostate cancer of Pollard were treated for six doses with Rh-123 at a dose of 15 mg/kg subcutaneously every other day. Microscopic examination of the tumors revealed cellular and acinar destruction. The effectiveness of Rh-123 as a cytotoxic agent was tested by clonogenic and viability assays in vitro with three human prostate cancer cell lines. Severe (60-95%) growth inhibition was observed following Rh-123 exposure for 2-5 days at doses as low as 1.6 micrograms/ml in all three prostate cancer cell lines.

Prostate and mammary adenocarcinoma in transgenic mice carrying a rat C3(1) simian virus 40 large tumor antigen fusion gene

A transgenic mouse model for prostate and mammary cancer has been developed in mice containing a recombinant gene expressing the simian virus 40 early-region transforming sequences under the regulatory control of the rat prostatic steroid binding protein [C3(1)] gene. Male transgenic mice develop prostatic hyperplasia in early life that progresses to adenoma or adenocarcinoma in most animals surviving to longer than 7 months of age. Prostate cancer metastases to lung have been observed. Female animals from the same founder lines generally develop mammary hyperplasia by 3 months of age with subsequent development of mammary adenocarcinoma by 6 months of age in 100% of the animals. The development of tumors correlates with the expression of the transgene as determined by Northern blot and immunohistochemical analyses. The results of these experiments demonstrate that the C3(1) regulatory region used in these experiments is useful for targeting expression to the prostate and mammary gland. To our knowledge, this experimental system is the first reported transgenic mouse model for prostate cancer. These transgenic animals offer the opportunity to study hormone response elements in vivo and the multistage progression from normal tissue to carcinoma in the prostate and mammary glands.

Activation of dormant cancer cells in the prostates and seminal vesicles of Lobund-Wistar rats

Lobund-Wistar (L-W) rats are unique in their susceptibility to spontaneous and induced metastasizing adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. Tumors were induced in 70-100% of rats by a combination of i.v. inoculated methylnitrosourea (MNU) followed by a series of subcutaneous slow-release implants of testosterone propionate (TP). Adenocarcinoma cells initiated by MNU in 3-month-old L-W rats were activated significantly by implants of the promoter, TP, after intervening periods of 3, 6 and 12 months following their exposures to MNU. The longer the time between MNU and TP, the shorter the subsequent latent period. Control rats inoculated with MNU (without TP) did not develop tumors during the observation period of 12 months, and their dormant tumor cells were activated by a single implant of TP, thereby eliciting P-SV tumors.

Prostatic dysplasia associated with increased expression of c-myc in neonatally estrogenized mice

Neonatal estrogenization of the mouse with diethylstilbestrol (DES; 2 micrograms./pup/day for days 1 to 3) or 17 beta-estradiol (200 micrograms./pup/day for days 1 to 3) resulted in epithelial dysplasia in the posterior periurethral region of the prostate at the age of 1 year. The dysplastic lesions ranged from mild to severe and, in addition to emergence of nuclear anaplasia, the architectural pattern of the glands was disturbed. Prenatal estrogenization (100 micrograms./kg. of maternal body weight on days 13 and 15 of gestation) only resulted in mild epithelial hyperplasia and occasional dysplasia in the ventral lobe of the prostate, but not in the posterior periurethral region. When neonatally estrogenized mice were allowed to grow until the age of 18 months, the degree and extent of the dysplasia of the posterior periurethral region was increased, but no frank invasion or metastases could be demonstrated. Combined estrogen and androgen treatment of neonatally estrogenized mice for 3 months (between 9 and 12 months of age) augmented nuclear dysplasia, but no invasive growth was seen in this group, either. Mild epithelial dysplasia was found in the dorsolateral lobes and coagulating glands of similarly treated control animals. A relation between the activation of certain proto-oncogenes and the development of several cancers has been shown in humans and experimental animals. In the present study, Northern blot analysis of total RNAs showed that the levels of c-myc mRNA were increased in the ventral and dorsolateral lobes, coagulating glands and prostatic urethra of neoDES mice at the age of 9 months. However, it remains to be determined whether the increase in c-myc expression is involved in the development of hyperplastic and dysplastic changes in the prostate of neoDES mice.

Early manifestations of induced prostate tumors in Lobund-Wistar rats

Lobund-Wistar (L-W) rats are susceptible to spontaneous and induced metastasizing prostate cancer. In the search for the initial site of tumor development in the induced disease, rats at risk were examined periodically to acquire this information. In the course of 12 months after the onset of the induction of prostate cancer in L-W rats, 14 of 40 rats (35%) developed visible tumors in the anterior and in the dorso-lateral lobes of the gland. The prostate tumors appeared at 7 months and thereafter. Two of the tumor-bearing rats had developed, in addition, a visible neoplasm in the seminal vesicle. None of the rats with small early tumors had developed visible metastatic tumors, which were manifested in rats with large tumors.

The Lobund-Wistar rat model of prostate cancer

Two models of preventable metastasizing autochthonous prostate adenocarcinoma (PA) have been described in Lobund-Wistar (L-W) rats: spontaneous PAs that develop at a mean age of 26 months; and induced PAs that develop at a mean time of 10.5 months. Both are similar in many respects to the counterpart disease in man. PAs develop spontaneously, and by induction through a combination of N-methyl-N-nitrosourea (MNU)/testosterone treatments. Our investigations with L-W rats show that PA is manifested spontaneously in 26% of aged L-W rats, and by induction in approximately 90% of younger rats. It is characterized by metastatic adenocarcinoma initiated in, and expanding from, the dorso-lateral and anterior lobes, and occasionally in the seminal vesicles. It is regulated by genetic, hormonal, and age-related mechanisms. Spontaneous PAs are prevented by life-long moderate (25%) diet restriction and, in rats at risk of developing induced PA, by early treatments with estradiol, with dihydrotestosterone, with a retinoid, and by castration. While the "premalignant" stages of induced tumorigenesis are susceptible to intervention, the overtly malignant stage resists therapeutic trials with the same agents and procedures. The transition from dependency to autonomy has not yet been defined.

Animal prostate carcinoma models: limited potential for vertebral metastasis

Several methods for induction of rat prostate carcinomas are now available. The induced adenocarcinomas, which develop normally in the lateral and/or dorsal prostate, are invasive and can form distant metastases. Metastatic sites include the abdominal cavity, liver, lung, and/or lymph nodes but, as yet, bone metastasis of prostate cancers in experimental animals has not been reported, despite its being very common in man. Anatomical and hemodynamic differences seem to be account for this lack of bone metastasis.

The inhibitory effect of 4-hydroxyphenyl retinamide (4-HPR) on metastasis of prostate adenocarcinoma-III cells in Lobund-Wistar rats

Tumor cells of transplanted prostate adenocarcinoma-III (PA-III) spread with very high frequency from the extravascular implant site through ipsilateral lymphatic channels to the lungs in which they produce visible focal tumors. The latter enlarge, coalesce and eventually kill the host. This system was used to demonstrate the effect of a retinoid on metastasis. Lobund-Wistar (L-W) rats were administered 1 mmol 4-HPR/kg diet L-485, and control rats received the same diet without 4-HPR. After an interval, all rats were inoculated subcutaneously with PA-III cells. When examined at autopsy, all rats had developed an anticipated tumor at the implant site. However, the numbers of focal PA-III tumors in the lungs were significantly reduced among the 4-HPR-treated rats compared to the control rats (P = 0.002).