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

Hormone-Refractory Prostate Cancer in the Lobund-Wistar Rat

Research on cancer prevention and therapy must focus on the refractory disease, the fatal end-stage of cancer that develops in patients with organ-related solid tumors. Refractory cancers develop spontaneously in advanced-stage tumors or in relapsed cases after failed therapy. Because neither prevention nor therapy is currently feasible, refractory cancer is a major impediment to survival. There is a great need for an animal model of prostate cancer (PC), one that develops cancer from initial premalignant to the terminal refractory stages. We describe here a model of hormone-refractory prostate cancer (HRPC) that develops spontaneously through two stages by endogenous mechanisms in the Lobund-Wistar (LW) rat. The early premalignant, testosterone (T)-dependent stage is promoted by high levels of endogenous T, and up to age 12 months is reversible by T deprivation; without this intervention, the tumorigenic process progresses to the refractory stage, which is highly aggressive and does not respond to T deprivation or to a wide range of therapies. Initial refractory tumors are palpable at approximately 18 months of age. As they continue to grow, the tumors express characteristics seen in refractory cancers in humans (i.e., hypoxia, expression of hypoxia-inducible factors, and metastasis). Chemically induced HRPCs in LW rats manifest the same two developmental stages, but with shorter latency periods. A transplantable, metastasizing cell line (PAID) was derived from a germfree LW rat with advanced-stage cancer. Both spontaneous and chemically induced autochthonous HRPC model systems serve as outstanding models for studies on the prevention and therapy of refractory cancer.

Three-Dimensional Study of the Terminal Portion in Sprague-Dawley Rat Ejaculatory Ducts

In mammals, a pair of ejaculatory ducts exists in the urethra at the seminal colliculus. The detailed anatomical structures of the distal end of the ejaculatory ducts of Sprague-Dawley rats were investigated by the computer-assisted three-dimensional reconstruction analysis using light-microscopic serial sections. A three-dimensional reconstruction revealed that in adult rats, the ejaculatory sinus pair consists of two parts: the cranial section - a compartment region composed of a fusion of the ampullary gland duct and the seminal vesicle duct, and the caudal section - a grooved region composed of a long slitlike ejaculatory ostium that extends into the urethra on both sides of the seminal colliculus. But the sphincter structure was not observed. The long axis of the compartment region was approximately 58 μm in length, and that of the groove region was approximately 495 μm. Although many epithelial glands ducts were distributed throughout the ejaculatory sinuses, the prostate and coagulation gland ducts did not open in these sinuses. The urethra was composed of transitional epithelium, while the ejaculatory sinuses were composed of single to stratified cuboidal epithelium. The ejaculatory ducts continued to the ejaculatory ostium in male adult Sprague-Dawley rat were composed of the seminal vesicle ducts received the ampullary gland ducts.

Three-dimensional reconstruction of deferent ducts papillae in urogenital duct system of the male rat

BACKGROUND

The rodent ejaculatory ducts penetrate the male accessory sex gland complex and open into the urethra, anatomically similar to humans. Although the deferent ducts papillae in rodents have been described at the distal end of deferent ducts, they are absent in humans, and their detailed morphology has been unclear.

METHODS

The detailed anatomical structures of the distal end of the deferent ducts of rats were investigated by the computer assisted three-dimensional reconstruction analysis using serial sections of the male accessory sex gland complexes in rats.

RESULTS

The present study revealed that a pair of deferent ducts enters the ventral side of the male accessory sex gland complex, runs caudally parallel to the urethra, and then exits at about midsection of the dorso-lateral lobe of prostate. They are composed of mammilliform papillae, called the deferent duct papillae, which dorso-laterally protrude into the duct lumen from intra-ventral portion of the main duct of ampullary gland. The internal surface of the deferent ducts papillae is composed of ciliated columnar epithelium continuous from the deferent ducts, while their external surface is composed of the columnar secretory epithelium of the ampullary glands. Sphincter muscles were not observed in the deferent ducts papillae, while their lamina propria were occupied by many arterial or venous capillaries.

CONCLUSIONS

The deferent ducts of rat terminated at the deferent ducts papillae that located at the main duct of ampullary glands that drained into the urethra. The deferent ducts papillae might be controlled by the expansion/contraction of well-developed papillary mucosal capillary vessels.

Insulin-Like growth factor 1 related pathways and high-fat diet promotion of transgenic adenocarcinoma mouse prostate (TRAMP) cancer progression

INTRODUCTION

We aimed to investigate the role of IGF-1 related pathway in high-fat diet (HFD) promotion of TRAMP mouse PCa progression.

METHODS

TRAMP mice were randomly divided into two groups: HFD group and normal diet group. TRAMP mice of both groups were sacrificed and sampled on the 20th, 24th and 28th week respectively. Serum levels of insulin, IGF-1 and IGF-2 were tested by ELISA. Prostate tissue of TRAMP mice was used for both HE staining and immunohistochemical staining of IGF-1 related pathway proteins, including IGF-1Rα, IGF -1Rβ, IGFBPs and AKT.

RESULTS

The mortality of TRAMP mice from HFD group was significantly higher than that of normal diet group (23.81% and 7.14%, p=.035). The tumor incidence of HFD TRAMP mice at 20(th) week was significantly higher than normal diet group (78.57% and 35.71%, p=.022). Serum IGF-1 level of HFD TRAMP mice was significantly higher than that of normal diet TRAMP mice. Serum IGF-1 level tended to increase with HFD TRAMP mice's age. HFD TRAMP mice had higher positive staining rate of IGF-1Rα, IGF-1Rβ, IGFBP3 and Akt than normal diet TRAMP mice.

CONCLUSIONS

IGF-1 related pathway played an important role in high-fat diet promotion of TRAMP mouse PCa development and progression.

Proinflammatory cytokines in prostate cancer development and progression promoted by high-fat diet

Background. We aimed to examine whether proinflammatory cytokines participated in prostate cancer (PCa) development and progression promoted by high-fat diet (HFD). Methods. TRAMP (transgenic adenocarcinoma mouse prostate) mice were randomly divided into two groups: normal diet group and HFD group. Mortality rate and tumor formation rate were examined. TRAMP mice were sacrificed and sampled on the 20th, 24th, and 28th week, respectively. Levels of proinflammatory cytokines, including IL-1α, IL-1β, IL-6, and TNF-α, were tested by FlowCytomix. Prostate tissue of TRAMP mice was used for histology study. Results. A total of 13 deaths of TRAMP mice were observed, among which 3 (8.33%) were from the normal diet group and 10 (27.78%) from the HFD group. The mortality rate of TRAMP mice from HFD group was significantly higher than that of normal diet group (P = 0.032). Tumor formation rate at 20th week of age of HFD group was significantly higher than that of normal diet group (P = 0.045). Proinflammatory cytokines levels, including IL-1α, IL-1β, IL-6, and TNF-α, were significantly higher in HFD TRAMP mice. Conclusions. HFD could promote TRAMP mouse PCa development and progression with elevated proinflammatory cytokines levels. Proinflammatory cytokines could contribute to PCa development and progression promoted by HFD.

Will metformin postpone high-fat diet promotion of TRAMP mouse prostate cancer development and progression?

PURPOSE

We aimed to examine the effect of high-fat diet (HFD) on prostate cancer (PCa) development and progression and to investigate whether metformin would postpone PCa development and progression promoted by HFD.

METHODS

TRAMP mice were randomly divided into three groups: normal diet group, HFD group and metformin-HFD (Met-HFD) group. Mortality rate and tumor formation rate were examined. TRAMP mice were sacrificed and sampled on the 20th, 24(th), and 28th week, respectively. Serum levels of insulin and IGF-1 were tested by ELISA. Prostate tissue of TRAMP mice was used for HE staining.

RESULTS

A total of 17 deaths of TRAMP mice were observed, including 3 (10 %) from the normal diet group, 10 (33.33 %) from the HFD group, and 4 (13.33 %) from Met-HFD group. The mortality rate of TRAMP mice from HFD group was significantly higher than that of normal diet group (P = 0.028), and metformin could moderately decrease the mortality rate by 60.01 % (P = 0.067). Tumor formation rates were not significantly different among the three groups. Levels of glucose, insulin, and IGF-1 tended to increase with TRAMP mice's age in HFD group. TRAMP mice from HFD group had higher serum insulin and IGF-1 levels. A moderate decrease in IGF-1 was also seen in Met-HFD group.

CONCLUSIONS

HFD could promote TRAMP mouse PCa development and progression and metformin had moderate effect of reducing PCa mortality rate with a decrease in serum IGF-1 level.

Effects of dietary high fat on prostate intraepithelial neoplasia in TRAMP mice

Increased fat intake is known to be a major cause of prostate cancer. In this study, we investigated the effect of dietary high fat on prostate intraepithelial neoplasia using transgenic adenocarcinoma mouse prostate (TRAMP) mice. Six-week-old male TRAMP mice were fed AIN93G (control group, 4.0 kcal/kg, n=6) and AIN93G-HFD (experimental group, 4.8 kcal/kg, n=7) for 10 weeks. Prostate histopathology, urogenital tract (UGT) weight, epididymal white adipose tissue weight, argyrophilic nucleolar organizer regions (AgNORs) counts, and serum leptin levels were examined. AIN93G-HFD fed group showed progressed neoplastic lesions in the prostate (P<0.05) compared to AIN93G fed group. AIN93G-HFD intake resulted in a increase in the weight of UGT (P<0.05) and epididymal white adipose tissue. The number of Ag-NOR positive dots significantly increased in each prostate lobe and final serum leptin levels in AIN93G-HFD fed group were about twice those of AIN93G fed group (P<0.05). Dietary high fat was related to the prostate cancer progression in the early stage of TRAMP mice and increased serum leptin levels, suggesting that the regulation of dietary components could delay the progression of prostate cancer.

Proliferative and nonproliferative lesions of the rat and mouse male reproductive system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and differential diagnosis for classifying microscopic lesions observed in the male reproductive system of laboratory rats and mice, with color microphotographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available for society members electronically on the Internet (http://goreni.org). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for lesions of the male reproductive system in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

The effect of green tea on oxidative damage and tumour formation in Lobund-Wistar rats

A number of epidemiological studies suggest that the consumption of green tea reduces the incidence of prostate cancer. As the major catechins present in green tea are potent antioxidants, we hypothesized that genetic and cellular damage induced by oxygen free radicals could be significantly reduced by potent antioxidants in green tea, thus reducing the cumulative genetic and cellular damage with age, and slowing or preventing tumour formation. Long-term administration of a decaffeinated green tea extract to Lobund-Wistar rats for periods up to 26 months almost halved the incidence of primary tumours in the genitourinary tract when compared with an age-matched cohort receiving just water. We observed no inhibition of DNA adduct formation or lipid peroxidation in animals consuming green tea compared with animals consuming deionized water. The decrease in tumour formation was associated with an increase in 8-hydroxy-2'deoxyguanosine and 4-hydroxynonenal content (markers of DNA adduct formation and lipid peroxidation, respectively) in the epithelium of the ventral prostate in aging animals. In addition, there was an increase in 8-hydroxy-2'deoxyguanosine expression, but no change in 4-hydroxynonenal expression in the seminal vesicles of older animals. An age-associated increase in expression of the antioxidant enzymes manganese superoxide dismutase and catalase in the epithelium of the ventral prostate of aging animals was observed. Furthermore, there was also an increase in manganese superoxide dismutase expression, but no change in catalase expression in the seminal vesicles of older animals. These data demonstrate that consumption of green tea decreases the incidence of genitourinary tract tumours in the Lobund-Wistar rat, but has no effect on age-associated DNA adduct formation and lipid peroxidation in the ventral prostate and seminal vesicles of the aging rat.

Null effect of dietary restriction on prostate carcinogenesis in the Wistar-Unilever rat

Chronic dietary restriction inhibits carcinogenesis in several sites in laboratory animals. To determine the effects of dietary restriction on prostate carcinogenesis, prostate cancers were induced in male Wistar-Unilever rats by a sequential regimen of cyproterone acetate (50 mg/day; 21 days); testosterone propionate (100 mg/kg/day; 3 days); N-methyl-N-nitrosourea [MNU; 30 mg/kg; single dose]; and testosterone (subcutaneous implants of 2 pellets containing 40 mg each). Dietary restriction (0% [ad libitum control], 15%, or 30%) was initiated 2 wk post-MNU, and continued until study termination at 12 mo. Dietary restriction induced a rapid suppression of body weight gain but conferred no protection against prostate carcinogenesis. 74% of carcinogen-treated ad libitum controls developed accessory sex gland cancers, versus cancer incidences of 64% and 72% in groups restricted by 15% and 30%, respectively. Similarly, 44% of dietary controls developed cancers limited to the dorsolateral/prostate, versus incidences of 45% and 53% in groups restricted by 15% and 30%. The results of the present study do not support the hypothesis that prostate carcinogenesis can be prevented by reducing caloric intake. Reducing mean body weight by up to 25% through chronic dietary restriction has no effect on the induction of prostate cancers in the Wistar-Unilever rat model.

Increased phospho-AKT is associated with loss of the androgen receptor during the progression of N-methyl-N-nitrosourea-induced prostate carcinogenesis in rats

BACKGROUND

Characterization of molecular events during N-methyl-N-nitrosourea (MNU)-induced rat prostate carcinogenesis enhances the utility of this model for the preclinical assessment of preventive strategies. Androgen independence is typical of advanced human prostate cancer and may occur through multiple mechanisms including the loss of androgen receptor (AR) expression and the activation of alternative signaling pathways.

METHODS

We examined the interrelationships between AR and p-AKT expression by immunohistochemical staining during MNU-androgen-induced prostate carcinogenesis in male Wistar-Unilever rats. Histone nuclear staining and image analysis was employed to assess parallel changes in chromatin and nuclear structure.

RESULTS

The percentage of AR positive nuclei decreased (P < 0.01) as carcinogenesis progressed: hyperplasia (92%), atypical hyperplasia (92%), well-differentiated adenocarcinoma (57%), moderately-differentiated adenocarcinoma (19%), and poorly-differentiated adenocarcinoma (10%). Conversely, p-AKT staining increased significantly during carcinogenesis. Sparse staining was observed in normal tissues (0.2% of epithelial area) and hyperplastic lesions (0.1%), while expression increased significantly (P < 0.001) in atypical hyperplasia (7.6%), well-differentiated adenocarcinoma (16.7%), moderately-differentiated adenocarcinoma (19.6%), and poorly-differentiated adenocarcinoma (17.4%). In parallel, nuclear morphometry revealed increased nuclear size, greater irregularity, and lower DNA compactness as cancers became more poorly differentiated.

CONCLUSIONS

In the MNU model, the progressive evolution of dominant tumor cell populations showing an increase in p-AKT in parallel with a decline in AR staining suggests that activation of AKT signaling may be one of several mechanisms contributing to androgen insensitivity during prostate cancer progression. Our observations mimic findings suggested by human studies and support the relevance of the MNU model in preclinical studies of preventive strategies.

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.

Prostate-seminal vesicle cancers induced in noble rats

Susceptibility of Noble strain rats to induced cancers in the accessory sex glands was determined. Following an IV inoculation of methylnitrosourea plus three successive SC implants of testosterone propionate, early stage adenocarcinomas were observed in the seminal vesicles and anterior prostates, but not in the dorsolateral nor in the ventral lobes.

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.

Androgen receptor expression in primary prostate cancers of Lobund-Wistar rats and in tumor-derived cell lines

Prostate tumors were induced in Lobund-Wistar rats by treatment with N-methyl-N-nitrosourea (MNU) and testosterone propionate (TP). Androgen receptor (AR) expression was confirmed in 16 (100%) of the primary prostate cancers, with strong uniform staining in well-differentiated tumors and more variable AR immunoreactivity in poorly differentiated tumors. Epithelial cell lines were established from nine of the tumors. At early passages, four of the tumor cell lines tested were strongly immunoreactive for AR; however, only two of the cell lines, E2(A) and F2, have remained AR-positive. These cell lines specifically bind 5H-DHT at 40 and 19 fmol/mg protein, respectively, and express a 110 kDa AR immunoreactive protein. Proliferation in in vitro culture of both E2(A) and F2 cells was increased in the presence of 5alpha-dihydrotestosterone (DHT). The antiandrogen, hydroxyflutamide was able to prevent the DHT-induced growth of E2(A) but not F2 cells. Furthermore, hydroxyflutamide alone increased proliferation of F2 cells, suggesting that the androgen signalling pathway in this cell line may be abnormal. Tumorigenicity of the AR-expressing and nonexpressing cell lines was confirmed by xenograft formation following subcutaneous inoculation into intact male nude mice. In summary, carcinogen-induced prostate tumors of Lobund-Wistar rats express AR and two of nine cell lines derived from the tumors express AR. Further evaluation of AR structure in primary prostate tumors forming spontaneously or following MNU and TP induction will determine whether, as in human prostate cancers, disease progression in Lobund-Wistar rats is associated with mutations in the AR gene.

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.