Prostate Pathology of Genetically Engineered Mice: Definitions and Classification. The Consensus Report from the Bar Harbor Meeting of the Mouse Models of Human Cancer Consortium Prostate Pathology Committee

Dynamics of expression of growth differentiation factor 15 in normal and PIN development in the mouse

Growth differentiation factor (GDF15) is a distant member of the transforming growth factor-beta superfamily, a diverse group of structurally related proteins that exert multiple effects on cell fate such as on cell growth and differentiation but little is known about GDF15 in these processes. Previously we observed the mature GDF15 to be associated with human prostate carcinogenesis hence prompting us to study GDF15 further. Here we report gdf15 expression both at the RNA and protein levels, in normal prostatic tissues of wild type (wt) and prostatic intraepithelial neoplasia (PIN) of transgenic (Tg) 12T-7s model mice during embryonic, postnatal, and adult prostate formation up to 15 weeks after birth. Dynamic changes in expression, at both the mRNA and protein level, correlated with cell proliferation and differentiation during distinct phases of normal mouse prostate development and alterations in the dynamics of gdf15 expression correlated with the changes in development resulting in PIN formation. Most notably mature gdf15 protein was significantly elevated during hyperplasia and PIN development. Changes in the protein levels did not always correlate well with the mRNA levels. This was more prominent during PIN than during normal prostate development suggesting that this may also be an indicator of disturbed regulation of gdf15 in PIN. We propose that gdf15 is a growth factor with dual function either promoting proliferation or growth arrest and differentiation due most likely to differences in cellular differentiation. Because of the differentiation defect in PIN its epithelium no longer responds to gdf15 by cellular growth arrest as does the normal epithelium and gdf may even stimulate proliferation. The data supports our hypothesis that GDF15 plays a role in the early stages of human prostate cancer.

Phytosterol Pygeum africanum regulates prostate cancer in vitro and in vivo

BACKGROUND

Prostate cancer is an important public health problem. It is an excellent candidate disease for chemoprevention because prostate cancer is typically slow growing and is usually diagnosed in elderly males. Pygeum africanum (Prunus africana or Rosaceae) is an African prune (plum) tree found in tropical Africa. An extract from the bark of Pygeum africanum has been used in Europe as a prevention and treatment of prostate disorders including benign prostatic hypertrophy (BPH). More recently in the USA, the phytotherapeutic preparations of Pygeum africanum and Saw palmetto have been marketed for prostate health including prostate cancer prevention and treatment.

METHODS

The anti-cancer potential of Pygeum africanum has been tested both in vitro (PC-3 and LNCaP cells) and in vivo (TRAMP mouse model).

RESULTS

In tissue culture, ethanolic extracts (30%) of Pygeum africanum inhibited the growth of PC-3 and LNCaP cells; induced apoptosis and altered cell kinetics; down regulated ERalpha and PKC-alpha protein, and demonstrated good binding ability to both mouse uterine estrogen receptors and LNCaP human androgen receptors. TRAMP mice fed Pygeum africanum showed a significant reduction (P = 0.034) in prostate cancer incidence (35%) compared to casein fed mice (62.5%).

CONCLUSION

Pygeum africanum, which is widely used in Europe and USA for treatment of BPH, has a significant role in regulation of prostate cancer both in vitro and in vivo and therefore may be a useful supplement for people at high risk for developing prostate cancer.

Bub1 up-regulation and hyperphosphorylation promote malignant transformation in SV40 tag-induced transgenic mouse models

Rodents do not naturally develop prostate cancer. Currently, most widely used genetically engineered mouse prostate cancer models use SV40 T/tag oncogene. To understand the mechanism underlying prostate cancer development in transgenic and knock-in SV40 Tag mouse models, we did cDNA microarray analyses, comparing gene expression profiles of prostate cancer tissues from early-, late-, and advance-stage androgen-independent prostate cancers. Of the 67 genes that were up-regulated by > or = 10-fold, 40 are known to be required for chromosome stability. In particular, the spindle checkpoint component Bub1 was persistently up-regulated from early to advanced androgen-independent prostate cancer lesions. Significantly, Bub1, which is required for accurate chromosome segregation during mitosis, has recently been reported to bind SV40 Tag. Consistent with a spindle checkpoint defect, flow cytometry experiments indicate that advanced androgen-independent prostate cancer tumors exhibit aneuploidy, along with up-regulation of levels of both Bub1 mRNA and Bub1 protein or hyperphosphorylation. Importantly, up-regulation and hyperphosphorylation of Bub1 were also observed in established human prostate cancer cell lines and in clinical studies. Furthermore, analysis of human prostate cancer lines showed impaired spindle checkpoint function and endoreduplication following exposure to spindle toxins. Small interfering RNA-mediated repression of Bub1 in the human prostate cancer line PC-3 restrained cell proliferation, an effect mimicked by inhibition of mitogen-activated protein kinase, an upstream activator of Bub1. Thus, by perturbing Bub1 function, our observations suggest a new mechanism whereby the SV40 Tag oncoprotein promotes chromosomal instability and aneuploidy in transgenic mouse prostate cancer models. Whereas the exact details of this mechanism remain unclear, our novel findings raise the possibility of exploiting Bub1 as a new therapeutic target in the treatment of prostate cancer, the most common cancer in adult men in North America.

Precancer in mice: animal models used to understand, prevent, and treat human precancers

We present a status report from the NCI Mouse Models of Human Cancers Consortium (MMHCC) Precancers Workshop held November 8 and 9, 2004. An expert panel, the Mouse Models Group (MMG) evaluated the status of mouse models of precancer emphasizing genetically engineered mouse models, especially of lining epithelium and their utilitarian value to human carcinogenesis. An outline of the background for the panel's considerations is provided with examples of past and current precancerous lesions in mice. The experimental use of oncogenic viruses and chemical carcinogens in mice led to operational definitions of initiation, promotion, and preneoplasia Preneoplastic and precancerous lesions are found in these models. In this precancer concept, most preneoplastic lesions are considered as potentially precancerous or at least an earlier stage in cancer development than typical pre-invasive epithelial lesions, which are often seen in these mouse models. Genetically engineered mice, used to test the oncogenicity of individual genes, develop precancers that are initiated by defined molecular and histopathologic changes. The mouse can be used to isolate and study precancers in detail, thereby providing a level of biological understanding not readily available in clinical disease. These studies suggest that genetically engineered mice are very useful preclinical models for chemoprevention and therapy.

Lobe Identity in the Mongolian Gerbil Prostatic Complex: A New Rodent Model for Prostate Study

Knowledge of structural and physiological differences among the prostatic lobes (PL) is the basis for development of experimental studies in traditional laboratory rodents. Although Mongolian gerbil reproductive organs have been increasingly investigated, its prostate structure is far from being properly known, and investigations of this organ focused on the ventral lobe (VL). Thus, the present study provides a thorough morphological description of prostatic complex in the male adult gerbil on the basis of topographic, histological, and ultrastructural analysis and ductal branching. Like other rodents, four pairs of PL were observed. However, in contrast to the rat and mouse, the VL is the least voluminous component and the dorsolateral lobe (DLL) is the most prominent and spatially isolated from remaining PL. The occurrence of a dorsal lobe (DL), hidden between bladder and insertion of seminal vesicles, has not been mentioned in previous reports with Mongolian gerbil. Collagenase digestion followed by microdissection revealed that, except for DL, which has a tubular-acinar organization, all PL exhibit tubular organization and variable ductal branching. Distinct histological and ultrastructural features such as secretory epithelium, aspect of luminal secretion and stromal organization are reported for each PL and are confirmed by morphometric and stereological methods. Histological sections showed at least three intralobar segments in VL and DL. Ultrastructural analysis evidenced that, although luminal epithelial cells of PL share typical features of exocrine secretory cells, there are striking lobe phenotypical variations. Both merocrine and apocrine pathways are observed in variable rates in all PL, with the predominance of the former in the DLL and the latter in the CG. The morphological observations presented herein point to distinct structural identities for each PL, which probably reflects specific functional compromise of seminal fluid secretion. These data also point to the gerbil as a good model for investigations concerning the regulation of prostate development and homeostasis, mainly with regard to the dorsal and dorsolateral PL.

Expression profiling of the mouse prostate after castration and hormone replacement: implication of H-cadherin in prostate tumorigenesis

Mice have been used extensively for studying normal prostate development and for generation of transgenic or knock-out prostate cancer animal models. To understand systematically and thoroughly the androgen responsive program in the mouse prostate, we carried out microarray analysis to profile gene expression changes during prostate involution and re-growth triggered by castration and subsequent hormone replacement. Genes with significant changes in these two processes were identified and gene ontology analyses revealed that they were mainly involved in response mechanisms, cell adhesion, metabolism, protein metabolism, and cell-cycle progression. The changes observed during prostate involution were largely reversed during re-growth. Sixty-four genes, including Nkx3.1 and probasin, and 65 other genes, including insulin-like growth factor binding protein 3 and H-cadherin (H-Cad), were further identified respectively as androgen-responsive genes and genes inversely correlated with androgen, based on their down- or up-regulation following castration and up- or down-regulation following androgen replacement. Potential androgen-responsive elements were found in the 5' upstream promoter region of 47 of those 65 genes, suggesting a potential suppression mechanism by androgen receptor. Of these, the role of H-Cad in tumorigenesis was further evaluated. Reduction of H-Cad transcript level was found in the majority of human prostate cancer cell lines and prostatic adenocarcinoma samples examined. Furthermore, induced H-Cad expression in DU145 cells, and knock-down of H-Cad expression in BPH1 cells inhibited and facilitated tumorigenicity, respectively. Taken together, our study provides a molecular understanding of the mouse prostate involution and re-growth processes and identifies a set of genes that are inversely correlated with androgen and may be potentially suppressive for tumorigenesis.

Inflammation and atrophy precede prostatic neoplasia in a PhIP-induced rat model

2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) has been implicated as a major mutagenic heterocyclic amine in the human diet and is carcinogenic in the rat prostate. To validate PhIP-induced rat prostatic neoplasia as a model of human prostate cancer progression, we sought to study the earliest histologic and morphologic changes in the prostate and to follow progressive changes over time. We fed sixty-seven 5-week-old male Fischer F344 rats with PhIP (400 ppm) or control diets for 20 weeks, and then sacrificed animals for histomorphologic examination at the ages of 25, 45, and 65 weeks. Animals treated with PhIP showed significantly more inflammation (P = .002, > .001, and .016 for 25, 45, and 65 weeks, respectively) and atrophy (P = .003, > .001, and .006 for 25, 45, and 65 weeks, respectively) in their prostate glands relative to controls. Prostatic intraepithelial neoplasia (PIN) occurred only in PhIP-treated rats. PIN lesions arose in areas of glandular atrophy, most often in the ventral prostate. Atypical cells in areas of atrophy show loss of glutathione S-transferase pi immunostaining preceding the development of PIN. None of the animals in this study developed invasive carcinomas, differing from those in previous reports. Overall, these findings suggest that the pathogenesis of prostatic neoplasia in the PhIP-treated rat prostate proceeds from inflammation to postinflammatory proliferative atrophy to PIN.

Conditional expression of human 15-lipoxygenase-1 in mouse prostate induces prostatic intraepithelial neoplasia: the FLiMP mouse model

The incidence and mortality of prostate cancer (PCa) vary greatly in different geographic regions, for which lifestyle factors, such as dietary fat intake, have been implicated. Human 15-lipoxygenase-1 (h15-LO-1), which metabolizes polyunsaturated fatty acids, is a highly regulated, tissue-specific, lipid-peroxidating enzyme that functions in physiological membrane remodeling and in the pathogenesis of atherosclerosis, inflammation, and carcinogenesis. We have shown that aberrant overexpression of 15-LO-1 occurs in human PCa, particularly high-grade PCa, and in high-grade prostatic intraepithelial neoplasia (HGPIN), and that the murine orthologue is increased in SV40-based genetically engineered mouse (GEM) models of PCa, such as LADY and TRansgenic Adenocarcinoma of Mouse Prostate. To further define the role of 15-LO-1 in prostate carcinogenesis, we established a novel GEM model with targeted overexpression of h15-LO-1 in the prostate [human fifteen lipoxygenase-1 in mouse prostate (FLiMP)]. We used a Cre- mediated and a loxP-mediated recombination strategy to target h15-LO-1 specifically to the prostate of C57BL/6 mice. Wild-type (wt), FLiMP+/-, and FLiMP+/+ mice aged 7 to 21, 24 to 28, and 35 weeks were characterized by histopathology, immunohistochemistry (IHC), and DNA/RNA and enzyme analyses. Compared to wt mice, h15-LO-1 enzyme activity was increased similarly in both homozygous FLiMP+/+ and hemizygous FLiMP+/- prostates. Dorsolateral and ventral prostates of FLiMP mice showed focal and progressive epithelial hyperplasia with nuclear atypia, indicative of the definition of mouse prostatic intraepithelial neoplasia (mPIN) according to the National Cancer Institute. These foci showed increased proliferation by Ki-67 IHC. No progression to invasive PCa was noted up to 35 weeks. By IHC, h15-LO-1 expression was limited to luminal epithelial cells, with increased expression in mPIN foci (similar to human HGPIN). In summary, targeted overexpression of h15-LO-1 (a gene overexpressed in human PCa and HGPIN) to mouse prostate is sufficient to promote epithelial proliferation and mPIN development. These results support 15-LO-1 as having a role in prostate tumor initiation and as an early target for dietary or other prevention strategies. The FLiMP mouse model should also be useful in crosses with other GEM models to further define the combinations of molecular alterations necessary for PCa progression.

Developmental exposure to estradiol and bisphenol A increases susceptibility to prostate carcinogenesis and epigenetically regulates phosphodiesterase type 4 variant 4

Early developmental perturbations have been linked to adult-onset prostate pathology, including excessive exposure to estrogenic compounds; however, the molecular basis for this imprinting event is not known. An important and controversial health concern is whether low-dose exposures to hormonally active environmental estrogens, such as bisphenol A, can promote human diseases, including prostate cancer. Here, we show that transient developmental exposure of rats to low, environmentally relevant doses of bisphenol A or estradiol increases prostate gland susceptibility to adult-onset precancerous lesions and hormonal carcinogenesis. We found permanent alterations in the DNA methylation patterns of multiple cell signaling genes, suggesting an epigenetic basis for estrogen imprinting. For phosphodiesterase type 4 variant 4 (PDE4D4), an enzyme responsible for cyclic AMP breakdown, a specific methylation cluster was identified in the 5'-flanking CpG island that was gradually hypermethylated with aging in normal prostates, resulting in loss of gene expression. Early and prolonged hypomethylation at this site following neonatal estradiol or bisphenol A exposure resulted in continued, elevated PDE4D4 expression. Cell line studies confirmed that site-specific methylation is involved in transcriptional silencing of the PDE4D4 gene and showed hypomethylation of this gene in prostate cancer cells. Importantly, the PDE4D4 alterations in the estrogen-exposed prostates were distinguishable before histopathologic changes of the gland, making PDE4D4 a candidate molecular marker for prostate cancer risk assessment as a result of endocrine disruptors. In total, these findings indicate that low-dose exposures to ubiquitous environmental estrogens affect the prostate epigenome during development and, in so doing, promote prostate disease with aging.

Orthotopic expression of human 15-lipoxygenase (LO)-1 in the dorsolateral prostate of normal wild-type C57BL/6 mouse causes PIN-like lesions

The lipid-peroxidating enzyme, 15-lipoxygenase (LO)-1 and its metabolite, 13-S-hydroxyoctadecadienoic acid (13-S-HODE), likely contribute to prostate tumorigenesis. Thus, this study evaluated adenovirus-mediated overexpression of 15-LO-1 on normal mouse prostate. Adenovirus expressing either human 15-LO-1 tagged with green fluorescent protein (GFP) or GFP alone was orthotopically injected into the dorsolateral prostates of C57BL/6 mice, three times over the course of 60 days. On day 90, pathological changes in prostate tissue were assessed by hematoxylin and eosin (H&E) staining. Expression of the proliferation marker Ki-67 was evaluated by immunohistochemistry and expression of angiogenesis markers were analyzed by an antibody array. Based on the latter study, immunoprecipitation analysis was used to measure the effect of 13-S-HODE, with or without conditioned media, on fibroblast growth factor-a and b (FGF-a and FGF-b) expression in human PrEC (normal prostate epithelial), PrSMC (normal prostate smooth muscle) and PrSC (normal prostate stromal) lines. Expression of viral 15-LO-1-GFP, but not GFP alone, resulted in the development of a prostate intraepithelial neoplasia (PIN)-like phenotype with increased expression of Ki-67. Aberrant 15-LO-1 expression also induced the angiogenic markers FGF-a and FGF-b. Human PrEC, PrSMC and PrSC lines demonstrated an increase in FGF-b expression upon stimulation with 13-S-HODE, which was further increased by the addition of conditioned media from the epithelial or smooth muscle cells. Using adenoviral mediated 15-LO-1 gene delivery, this study suggests that aberrant 15-LO-1 overexpression in normal prostate can trigger events leading to prostate epithelial and stromal cell proliferation. Thus, our findings demonstrate the effectiveness of this viral system for 15-LO-1 expression studies in tissues.

The deficiency of Akt1 is sufficient to suppress tumor development in Pten+/- mice

The tumor suppressor PTEN is frequently inactivated in human cancers. A major downstream effector of PTEN is Akt, which is hyperactivated via PTEN inactivation. It is not known, however, whether diminished Akt activity is sufficient to inhibit tumorigenesis initiated by Pten deficiency. Here we showed that the deficiency of Akt1 is sufficient to dramatically inhibit tumor development in Pten+/- mice. Akt1 deficiency had a profound effect on endometrium and prostate neoplasia, two types of human cancer, in which PTEN is frequently mutated, and also affected thyroid and adrenal medulla tumors and intestinal polyps. Even haplodeficiency of Akt1 was sufficient to markedly attenuate the development of high-grade prostate intraepithelial neoplasia (PIN) and endometrial carcinoma. These results have significant implications for cancer therapy.

Expression and role of Foxa proteins in prostate cancer

The molecular mechanism(s) for prostate cancer progression to androgen independence are poorly understood. We have recently shown that Foxa1 and Foxa2 proteins are differentially expressed in epithelial cells during murine prostate development, growth, and adult function. Currently, the role of Foxa proteins in prostate cancer development and progression is unknown. Foxa protein expression was investigated in the LPB-Tag LADY mouse prostate cancer models, in human prostate cancer specimens, and various prostate cancer cell lines using Western blot and immunostaining analysis. In vitro transient transfection, studies were performed to investigate Foxa/prostate-specific gene regulation. Foxa1 was strongly expressed in areas of prostatic intraepithelial neoplasia (PIN) in both the androgen dependent 12T-7f and in the metastatic, androgen independent 12T-10 LADY models. Prominent Foxa1 and Foxa2 expression was observed in 12T-10 invasive undifferentiated neuroendocrine carcinomas, in the hormone independent and metastasizing 12T-10 derived, NE-10 allograft tumors, and in all metastatic lesions isolated from 12T-10 mice. Foxa1 protein expression was always observed in human prostate carcinomas, regardless of Gleason grade score, while Foxa2 was only detected in neuroendocrine small cell carcinomas and in some high Gleason score adenocarcinomas. Foxa proteins were also differentially expressed in three prostate cancer cell lines. Importantly, in vitro functional assays demonstrated that Foxa2 could activate androgen-dependent prostate-specific genes in an androgen receptor and ligand-independent manner. These results suggest that Foxa proteins are important in prostate carcinogenesis. In particular, Foxa2 may be involved in progression of prostate cancer to androgen independence. As such, Foxa proteins may represent novel targets for therapeutic intervention.

Histopathological characteristics of a novel knock-in mouse prostate cancer model

Prostate cancer is relatively unique to man. There is no naturally occurring prostate cancer in the mouse. Pre-clinical studies involve the establishment of a genetically engineered mouse prostate cancer model with features close to those of the human situation. A new knock-in mouse adenocarcinoma prostate (KIMAP) model was established, which showed close-to-human kinetics of tumor development. In order to determine if the similar kinetics is associated with heterogeneous tumor architecture similar to the human situation, we utilized a new mouse histological grading system (Gleason analogous grading system) similar to the Gleason human grading system and flow cytometry DNA analysis to measure and compare the adenocarcinoma of the KIMAP model with human prostate cancer. Sixty KIMAP prostate cancer samples from 60 mice were measured and compared with human prostate cancer. Flow cytometry DNA analysis was performed on malignant prostate tissues obtained from KIMAP models. Mice with prostate cancer from KIMAP models showed a 53.3% compound histological score rate, which was close to the human clinical average (50%) and showed a significant correlation with age (P = 0.001). Flow cytometry analyses demonstrated that most KIMAP tumor tissues were diploid, analogous to the human situation. The similarities of the KIMAP mouse model with tumors of the human prostate suggest the use of this experimental model to complement studies of human prostate cancer.

Selenoprotein deficiency accelerates prostate carcinogenesis in a transgenic model

Considerable animal and human data have indicated that selenium is effective in reducing the incidence of several different types of cancer, including that of the prostate. However, the mechanism by which selenium inhibits carcinogenesis remains unknown. One possibility is that dietary selenium influences the levels of selenium-containing proteins, or selenoproteins. Selenoproteins contain selenium in the form of selenocysteine and perform a variety of cellular functions, including antioxidant defense. To determine whether the levels of selenoproteins can influence carcinogenesis independent of selenium intake, a unique mouse model was developed by breeding two transgenic animals: mice with reduced selenoprotein levels because of the expression of an altered selenocysteine-tRNA (i6A-) and mice that develop prostate cancer because of the targeted expression of the SV40 large T and small t oncogenes to that organ [C3(1)/Tag]. The resulting bigenic animals (i6A-/Tag) and control WT/Tag mice were assessed for the presence, degree, and progression of prostatic epithelial hyperplasia and nuclear atypia. The selenoprotein-deficient mice exhibited accelerated development of lesions associated with prostate cancer progression, implicating selenoproteins in cancer risk and development and raising the possibility that selenium prevents cancer by modulating the levels of these selenoproteins.

In vivo magnetic resonance volumetric and spectroscopic analysis of mouse prostate cancer models

BACKGROUND

Mouse prostate cancer modeling presents unique obstacles to the study of spontaneous tumor initiation and progression due to the anatomical location of the tissue.

RESULTS

High resolution (130 microm(x) x 130 microm(y) x 300 microm(z)), three-dimensional MRI allowed for the visualization, segmentation, and volumetric measurement of the prostate from normal and genetically engineered animals, in vivo. Additionally, MRS performed on the prostate epithelia of probasin-ErbB-2Delta x Pten(+/-) mice identified changes in the relative concentrations of the metabolites choline and citrate, which was not observed in TRAMP mice.

METHODS

T1-weighted MRI was performed on normal, TRAMP, probasin-ErbB-2/Her2/Neu (probasin-ErbB-2Delta), and probasin-ErbB-2Delta in the context of decreased Pten activity (probasin-ErbB-2Delta x Pten(+/-)) mice. Volume-localized single-voxel proton magnetic resonance spectroscopy (SVS (1)H MRS) was also performed.

CONCLUSIONS

The data presented supports the use of combined MRI and MRS for the measurement of biochemical and morphometric alterations in mouse models of prostate cancer.

Characterization of an antibody that can detect the Kai1/CD82 murine metastasis suppressor

BACKGROUND

Kai1, also known as CD82, is a member of the tetraspanin family (TM4SF). The human homolog, KAI1, is an activation antigen of T-cells and is a metastasis suppressor for prostate and other cancers. Little is known about the mouse protein because of the lack of antibody reagents.

METHODS

Peptide immunized rabbits were used to generate polyclonal antibody to Kai1. The antibody was analyzed using immunoblotting, flow cytometry, and immunohistochemistry.

RESULTS

This antibody specifically recognizes murine Kai1 protein, crossreacts with rat Kai1 but not with human KAI1. The normal tissue distribution of this protein in mice is shown to be similar to that of the human homolog. Interestingly, mouse prostatic epithelium showed differential expression within the lobes.

CONCLUSION

This antibody, the first described that can specifically detect murine Kai1/CD82, should be very useful in addressing the mechanism of action of Kai1 in metastatic suppression.

Insulin-like growth factor (IGF) binding protein-3 attenuates prostate tumor growth by IGF-dependent and IGF-independent mechanisms

IGF binding protein (IGFBP)-3 inhibits cell growth and promotes apoptosis by sequestering free IGFs. In addition IGFBP-3 has IGF-independent, proapoptotic, antiproliferative effects on prostate cancer cells in vitro. Expression of the large T-antigen (Tag) under the long probasin promoter (LPB) in LPB-Tag mice results in prostate tumorigenesis. To investigate the IGF-dependent and IGF-independent effects of IGFBP-3 on prostate tumor growth, we crossed LPB-Tag mice with cytomegalovirus (CMVBP-3) and phosphoglycerate kinase (PGKBP-3) mice that overexpress IGFBP-3 under the cytomegalovirus promoter and the phosphoglycerate kinase promoter, respectively, and also I56G/L80G/L81G-mutant IGFBP-3 (PGKmBP-3) mice that express I56G/L80G/L81G-IGFBP-3, a mutant, that does not bind IGF-I but retains IGF-independent proapoptotic effects in vitro. Prostate tumor size and the steady-state level of p53 were attenuated in LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice, compared with LPB-Tag/wild-type (Wt) mice. A more marked effect was observed in LPB-Tag/CMVBP-3, compared with LPB-Tag/PGKBP-3, reflecting increased levels of transgene expression in CMVBP-3 prostate tissue. No attenuation of tumor growth was observed in LPB-Tag/PGKmBP-3 mice during the early tumor development, indicating that the inhibitory effects of IGFBP-3 were most likely IGF dependent during the initiation of tumorigenesis. At 15 wk of age, epidermal growth factor receptor expression was increased in LPB-Tag/Wt and LPB-Tag/PGKmBP-3 tissue, compared with LPB-Tag/PGKBP-3. IGF receptor was increased in all transgenic mice, but pAkt expression, a marker of downstream IGF-I action, was increased only in LPB-Tag/Wt and LPB-Tag/PGKmBP-3. After 15 wk of age, a marked reduction in tumor growth was apparent in LPB-Tag/PGKmBP-3 mice, indicating that the IGF-independent effects of IGFBP-3 may be important in inhibiting tumor progression.

ADAM12 is highly expressed in carcinoma-associated stroma and is required for mouse prostate tumor progression

The interaction between stromal cells and tumor cells is emerging as a critical aspect of tumor progression. Yet there is a paucity of molecular markers for cells participating in such interactions, and only few genes are known to play a critical role in this process. Here, we describe the identification of ADAM12 (a disintegrin and metalloprotease 12) as a novel marker for a subpopulation of stromal cells that are adjacent to epithelial tumor cells in three mouse carcinoma models (models for prostate, breast and colon cancer). Moreover, we show that ADAM12 is essential for tumor development and progression in the W10 mouse model for prostate cancer. These results suggest that ADAM12 might be a useful marker for stromal cells in mouse tumors that are likely to participate in stromal/tumor cell crosstalk, and that ADAM12 is a potential target for design of drugs that prevent carcinoma growth.

Establishment of a serum tumor marker for preclinical trials of mouse prostate cancer models

Current prostate cancer research in both basic and preclinical trial studies employ genetically engineered mouse models. However, unlike in human prostate cancer patients, rodents have no counterpart of prostatic-specific antigen (PSA) for monitoring prostate cancer initiation and progression. In this study, we established a mouse serum tumor marker from a mouse homologue of human prostate secretory protein of 94 amino acids (PSP94). Immunohistochemistry studies on different histologic grades from both transgenic and knock-in mouse prostate cancer models showed the down-regulation of tissue PSP94 expression (P < 0.001), the same as for PSA and PSP94 in humans. The presence of mouse serum PSP94 was shown by affinity column and immunoprecipitation purification using a polyclonal mouse PSP94 antibody. A competitive ELISA protocol was established to quantify serum PSP94 levels with a sensitivity of 1 ng/mL. Quantified serum levels of mouse PSP94 ranged from 49.84 ng/mL in wild-type mice to 113.86, 400.45, and 930.90 ng/mL in mouse prostatic intraepithelial neoplasia with microinvasion, well differentiated, moderately differentiated, and poorly differentiated prostate cancer genetically engineered prostate cancer mice, respectively (P < 0.01, n = 68). This increase in serum PSP94 is also well correlated with age and tumor weight. Through longitudinal monitoring of serum PSP94 levels of castrated mice (androgen ablation therapy), we found a correlation between responsiveness/refractory prostate tissues and serum PSP94 levels. The utility of mouse serum PSP94 as a marker in hormone therapy was further confirmed by three-dimensional ultrasound imaging. The establishment of the first rodent prostate cancer serum biomarker will greatly facilitate both basic and preclinical research on human prostate cancer.

Increased levels of the FoxM1 transcription factor accelerate development and progression of prostate carcinomas in both TRAMP and LADY transgenic mice

The proliferation-specific Forkhead Box M1 (FoxM1 or FoxM1b) transcription factor is overexpressed in a number of aggressive human carcinomas. Mouse hepatocytes deficient in FoxM1 fail to proliferate and are highly resistant to developing carcinogen-induced liver tumors. We previously developed a transgenic (TG) mouse line in which the ubiquitous Rosa26 promoter was used to drive expression of the human FoxM1b cDNA transgene in all mouse cell types. To investigate the role of FoxM1b in prostate cancer progression, we bred Rosa26-FoxM1b mice with both TRAMP and LADY TG mouse models of prostate cancer. We show that increased expression of FoxM1b accelerated development, proliferation, and growth of prostatic tumors in both TRAMP and LADY double TG mice. Furthermore, development of prostate carcinomas in TRAMP/Rosa26-FoxM1b double TG mice required high levels of FoxM1 protein to overcome sustained expression of the alternative reading frame tumor suppressor, a potent inhibitor of FoxM1 transcriptional activity. Depletion of FoxM1 levels in prostate cancer cell lines PC-3, LNCaP, or DU-145 by small interfering RNA transfection caused significant reduction in proliferation and anchorage-independent growth on soft agar. This phenotype was associated with increased nuclear levels of the cyclin-dependent kinase inhibitor protein p27(Kip1) and diminished expression of S-phase promoting cyclin A2 and M-phase promoting cyclin B1 proteins. Finally, we show that elevated levels of FoxM1 protein correlate with high proliferation rates in human prostate adenocarcinomas. Our results suggest that the FoxM1 transcription factor regulates development and proliferation of prostate tumors, and that FoxM1 is a novel target for prostate cancer treatment.

Adenocarcina of the mouse prostate growth inhibition by celecoxib: downregulation of transcription factors involved in COX-2 inhibition

BACKGROUND

Epidemiological studies have shown a decreased risk of prostate cancer among men who regularly take aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs). In this study, we examined a dose-dependent effect of a cyclooxygenase-2 (COX-2) inhibitor, celecoxib against transgenic adenocarcinoma of the mouse prostate.

METHODS

Efficacy of four different doses in parts per million of celecoxib, such as 200 ppm, 400 ppm, 600 ppm, and 1,000 ppm representing very low, moderate, and high doses, respectively were tested against adenocarcinoma of the mouse prostate using a transgenic adenocarcinoma of the mouse prostate (TRAMP) model assay.

RESULTS

Dietary supplement of celecoxib at doses of 400 ppm, 600 ppm, and 1,000 ppm are most effective against mPIN (mouse prostatic intraepithelial neoplasia) and adenocarcinoma of the prostate. Tumor growth inhibition by celecoxib was associated with increased rate of apoptosis. At 1,000 ppm, a complete inhibition of the PIN lesions was extended to limit the growth of adenocarcinoma (from 85% to 15%) and metastasis of the mouse prostate. The chemopreventive effect was significant (P<0.01) at 400 ppm, 600 ppm, and 1,000 ppm doses compared to that at the lowest dose of 200 ppm and control. A dose-dependent effect on tumor growth inhibition was associated with reduced expression of NF-kappaBp65 and COX-2.

CONCLUSIONS

Dietary supplementation of celecoxib at different doses provides evidence for the suppression of prostate adenocarcinoma tumor growth in a dose-dependent manner. Suppression of adenocarcinoma by celecoxib further limits the growth of metastatic prostate cancer.

Selective evolution of stromal mesenchyme with p53 loss in response to epithelial tumorigenesis

Our understanding of cancer has largely come from the analysis of aberrations within the tumor cell population. Yet it is increasingly clear that the tumor microenvironment can significantly influence tumorigenesis. For example, the mesenchyme can support the growth of tumorigenic epithelium. However, whether fibroblasts are subject to genetic/epigenetic changes as a result of selective pressures conferred by oncogenic stress in the epithelium has not been experimentally assessed. Recent analyses of some human carcinomas have shown tumor-suppressor gene mutations within the stroma, suggesting that the interplay among multiple cell types can select for aberrations nonautonomously during tumor progression. We demonstrate that this indeed occurs in a mouse model of prostate cancer where epithelial cell cycle disruption via cell-specific inhibition of pRb function induces a paracrine p53 response that suppresses fibroblast proliferation in associated stroma. This interaction imposes strong selective pressure yielding a highly proliferative mesenchyme that has undergone p53 loss.

Notch signaling is required for normal prostatic epithelial cell proliferation and differentiation

Notch pathway is crucial for stem/progenitor cell maintenance, growth and differentiation in a variety of tissues. Using a transgenic cell ablation approach, we found in our previous study that cells expressing Notch1 are crucial for prostate early development and re-growth. Here, we further define the role of Notch signaling in regulating prostatic epithelial cell growth and differentiation using biochemical and genetic approaches in ex vivo or in vivo systems. Treatment of developing prostate grown in culture with inhibitors of gamma-secretase/presenilin, which is required for Notch cleavage and activation, caused a robust increase in proliferation of epithelial cells co-expressing cytokeratin 8 and 14, lack of luminal/basal layer segregation and dramatically reduced branching morphogenesis. Using conditional Notch1 gene deletion mouse models, we found that inactivation of Notch1 signaling resulted in profound prostatic alterations, including increased tufting, bridging and enhanced epithelial proliferation. Cells within these lesions co-expressed both luminal and basal cell markers, a feature of prostatic epithelial cells in predifferentiation developmental stages. Microarray analysis revealed that the gene expression in a number of genetic networks was altered following Notch1 gene deletion in prostate. Furthermore, expression of Notch1 and its effector Hey-1 gene in human prostate adenocarcinomas were found significantly down-regulated compared to normal control tissues. Taken together, these data suggest that Notch signaling is critical for normal cell proliferation and differentiation in the prostate, and deregulation of this pathway may facilitate prostatic tumorigenesis.

Prostate tumor growth and recurrence can be modulated by the omega-6:omega-3 ratio in diet: athymic mouse xenograft model simulating radical prostatectomy

Evidence indicates that a diet rich in omega (omega)-6 polyunsaturated fatty acids (PUFAs) [e.g., linoleic acid (LA)] increases prostate cancer (PCa) risk, whereas a diet rich in omega-3 decreases risk. Precisely how these PUFAs affect disease development remains unclear. So we examined the roles that PUFAs play in PCa, and we determined if increased omega-3 consumption can impede tumor growth. We previously demonstrated an increased expression of an omega-6 LA-metabolizing enzyme, 15-lipoxygenase-1 (15-LO-1, ALOX15), in prostate tumor tissue compared with normal adjacent prostate tissue, and that elevated 15-LO-1 activity in PCa cells has a protumorigenic effect. A PCa cell line, Los Angeles Prostate Cancer-4 (LAPC-4), expresses prostate-specific antigen (PSA) as well an active 15-LO-1 enzyme. Therefore, to study whether or not the protumorigenic role of 15-LO-1 and dietary omega-6 LA can be modulated by altering omega-3 levels through diet, we surgically removed tumors caused by LAPC-4 cells (mouse model to simulate radical prostatectomy). Mice were then randomly divided into three different diet groups-namely, high omega-6 LA, high omega-3 stearidonic acid (SDA), and no fat-and examined the effects of omega-6 and omega-3 fatty acids in diet on LAPC-4 tumor recurrence by monitoring for PSA. Mice in these diet groups were monitored for food consumption, body weight, and serum PSA indicative of the presence of LAPC-4 cells. Fatty acid methyl esters from erythrocyte membranes were examined for omega-6 and omega-3 levels to reflect long-term dietary intake. Our results provide evidence that prostate tumors can be modulated by the manipulation of omega-6:omega-3 ratios through diet and that the omega-3 fatty acid SDA [precursor of eicosapentaenoic acid (EPA)] promotes apoptosis and decreases proliferation in cancer cells, causing decreased PSA doubling time, compared to omega-6 LA fatty acid, likely by competing with the enzymes of LA and AA pathways, namely, 15-LO-1 and cyclooxygenases (COXs). Thus, EPA and DHA (major components of fish oil) could potentially be promising dietary intervention agents in PCa prevention aimed at 15-LO-1 and COX-2 as molecular targets. These observations also provide clues as to its mechanisms of action.

Angiogenesis with pericyte abnormalities in a transgenic model of prostate carcinoma

BACKGROUND

Previous studies of the TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model vasculature suggest that, as tumors develop, vessels invade the glandular epithelium. However, changes in the vasculature are difficult to study in conventional thin tissue sections. The authors used a new approach to characterize morphologic and architectural changes of blood vessels and pericytes during tumor development in TRAMP mice.

METHODS

Eighty-micron cryostat sections of normal prostate and three histopathologic stages of TRAMP tumor sections, classified by epithelial cell E-cadherin immunoreactivity, were immunostained with vascular endothelial cell and pericyte receptor antibodies and evaluated by confocal microscopy.

RESULTS

In the normal mouse prostate, capillaries were most abundant in the fibromuscular tunica between the epithelium and smooth muscle of the ductules. In the prostatic intraepithelial neoplasia (PIN) stage, vessels accompanied epithelial cell protrusions into the ductule lumen but remained in the connective tissue at the basal side of the epithelium. Well differentiated tissues had extensive angiogenesis with five times the normal mean vascularity outside ductules. Vessels were of variable diameter, were associated with an increased number of pericytes, and some had endothelial sprouts. Angiogenic blood vessels from poorly differentiated adenocarcinomas were tortuous, variable in caliber, and lacked the normal hierarchy. Pericytes on these vessels had an abnormal phenotype manifested by alpha-smooth muscle actin expression and loose association with endothelial cells. Angiogenesis and loss of vascular hierarchy were also found in human prostate carcinoma.

CONCLUSIONS

Vascular abnormalities, which begin at the PIN stage and intensify in well differentiated and poorly differentiated tumors, may be useful readouts for early detection and treatment assessment in prostate carcinoma.

Application of Gleason analogous grading system and flow cytometry DNA analysis in a novel knock-in mouse prostate cancer model

OBJECTIVE

A new knock-in mouse adenocarcinoma prostate model (KIMAP) was established, which showed a close to human kinetics of tumour development. This study used a new mouse histological grading system similar to the human Gleason grading system and flow cytometry DNA analysis to measure and compare the new KIMAP model with human CaP and transgenic mouse adenocarcinoma prostate (TGMAP) model.

METHODS

According to heterogeneity of the clinical standard for prostate cancer diagnosis, a close to human mouse standard for histological grading and scoring system, Gleason analogous grading system, was established in this study. Sixty KIMAP and 48 TGMAP prostate cancer samples were measured and compared with human CaP. Flow cytometry DNA analysis was performed on malignant prostate tissues obtained from both TGMAP and KIMAP models.

RESULTS

Mice with CaP from KIMAP (n = 60) and TGMAP (n = 48) models showed a different distribution of histological scores (p = 0.000). KIMAP mice showed higher percentage (53.3%) of compound histological score rate than TGMAP (25%), but closer to the human clinical average (50%), which showed significant correlation with age (p = 0.001), while TGMAP mice showed unbalanced and random score distribution in all age groups. Flow cytometry analyses showed that most tumour tissues in KIMAP were diploid, analogous to the human condition, while all the TGMAP mice showed aneuploid tumours.

CONCLUSIONS

Results of this study further show that KIMAP, a new generation of murine prostate cancer model, could be used as a supplementary model in addition to the currently widely used transgenic models.

Critical function for ADAM9 in mouse prostate cancer

ADAM9 is a membrane-anchored metalloprotease that is markedly up-regulated in several human carcinomas. Here, we show that ADAM9 is similarly up-regulated in mouse models for prostate, breast, and intestinal carcinoma. To assess whether ADAM9 is critical for the pathogenesis of prostate carcinoma, one of the most common cancers in men, we evaluated how loss of ADAM9 affects tumorigenesis in W(10) mice, a mouse model for this disease. In the absence of ADAM9, most tumors in 50-week-old W(10) mice were well differentiated, whereas littermate controls expressing wild-type ADAM9 had predominantly poorly differentiated, and in some cases significantly larger, tumors. Moreover, gain-of-function experiments in which ADAM9 was overexpressed in mouse prostate epithelium resulted in significant abnormalities, including epithelial hyperplasia at 4 to 6 months of age, and prostatic intraepithelial neoplasia after 1 year. A potential underlying mechanism for the role of ADAM9 in prostate cancer emerged from cell-based assays: ADAM9 can cleave and release epidermal growth factor and FGFR2iiib from cells, both of which have pivotal functions in the pathogenesis of this disease. Taken together, these results suggest that ADAM9 contributes to the pathogenesis of prostate cancer and potentially also other carcinomas, raising the possibility that ADAM9 might be a good target for antitumor drugs.

Disruption of growth hormone signaling retards early stages of prostate carcinogenesis in the C3(1)/T antigen mouse

Recent epidemiological studies suggest that elevated serum titers of IGF-I, which are, to a large degree, regulated by GH, are associated with an increase in prostate cancer risk. The purpose of the current study was to develop the first animal models to directly test the hypothesis that a normal, functional GH/IGF-I axis is required for prostate cancer progression. The GH receptor (GHR) gene-disrupted mouse (Ghr(-/-)), which has less than 10% of the plasma IGF-I found in GHR wild-type mice, was crossed with the C3(1)/T antigen (Tag) mouse, which develops prostatic intraepithelial neoplasia driven by the large Tag that progress to invasive prostate carcinoma in a manner similar to the process observed in humans. Progeny of this cross were genotyped and Tag/Ghr(+/+) and Tag/Ghr(-/-) mice were killed at 9 months of age. Seven of eight Tag/Ghr(+/+) mice harbored prostatic intraepithelial neoplasia lesions of various grades. In contrast, only one of the eight Tag/Ghr(-/-) mice exhibited atypia (P < 0.01, Fischer's exact test). Disruption of the GHR gene altered neither prostate androgen receptor expression nor serum testosterone titers. Expression of the Tag oncogene was similar in the prostates of the two mouse strains. Immunohistochemistry revealed a significant decrease in prostate epithelial cell proliferation and an increase in basal apoptotic indices. These results indicate that disruption of GH signaling significantly inhibits prostate carcinogenesis.

Challenges in prostate cancer research: animal models for nutritional studies of chemoprevention and disease progression

Prostate cancer is the second leading cause of cancer-related death in the United States. The American Cancer Society estimates that there will be over 232,000 new cases of prostate cancer in 2005. Evidence suggests that diet can act as a chemopreventive agent to reduce the incidence of prostate cancer as well as to reduce the mortality of the disease. Epidemiologic studies suggest that diets rich in specific vitamins, grains, fruits, and vegetables may be associated with lower cancer rates than high-fat diets, yet the molecular bases for these positive nutritional actions are largely unknown. The interactions of diet in combination with genetic determinants of disease progression are unclear because prostate cancer is also a disease resulting from abnormal gene expression. Hence, the biology of normal prostate development and the mechanisms underlying the initiation, progression, and metastatic spread of prostate cancer must be understood at the molecular level to develop effective nutritional prevention and intervention strategies to control and treat this malignant disease. However, progress toward understanding the biology of prostate cancer and the development of new therapies has been hampered by the lack of in vivo model systems that adequately capitulate the spectrum of benign, latent, aggressive, and metastatic forms of the human disease. In this review we discuss the diverse animal models of prostate cancer available and their applicability for nutritional studies of cancer prevention.

Heterogeneous Tumor Evolution Initiated by Loss of pRb Function in a Preclinical Prostate Cancer Model

Because each change in the evolution of a cancer is predicated on the effects of previous events, a full understanding of selective changes and their effect on tumor progression can only be understood in the context of appropriate initiating events. Here, we define the effect of pRb function inactivation in prostate epithelium on both the initiation of prostate cancer and the establishment of selective pressures that lead to diminished Pten function and tumor evolution. Using genetically engineered mice, we show that inactivation of the pRb family proteins (Rb/p107/p130) induces epithelial proliferation and apoptosis and is sufficient to produce prostatic intraepithelial neoplasia (PIN) lesions. Over time, adenocarcinomas develop in all mice with no evidence of neuroendocrine tumors. Apoptosis is dependent on Pten function and not p53, unlike other epithelial cell types tested previously. Consequently, Pten hemizygosity reduces apoptosis by 50%, accelerating progression to adenocarcinomas with heterogeneous composition. Heterogeneity is associated with concurrent Pten haploinsufficiency and focal selective progression to complete Pten loss, which yields distinct tumor properties. Given that this analysis models the apparent timing of highly penetrant events in human prostate cancer, observed effects may recapitulate the natural evolution of prostate cancer development.

beta1A integrin expression is required for type 1 insulin-like growth factor receptor mitogenic and transforming activities and localization to focal contacts

The cells' ability to proliferate in response to growth factor stimulation is significantly altered during cancer progression. To investigate the mechanisms underlying these alterations in prostate cancer, the role and expression of beta1A integrin and type 1 insulin-like growth factor receptor (IGF-IR), known to contribute to cell proliferation and transformation, were analyzed. Using small interfering RNA oligonucleotides to down-regulate beta1A, we show that beta1A expression is required for IGF-IR-mediated prostate cancer cell proliferation and anchorage-independent growth. In vivo, using age-matched transgenic adenocarcinoma of mouse prostate (TRAMP) mice at different stages of prostate cancer [prostatic intraepithelial neoplasia, PIN; well-differentiated adenocarcinoma, WD; and poorly differentiated adenocarcinoma, PD], the expression of beta1A and of IGF-IR was studied. beta1A and IGF-IR expression levels were concurrently up-regulated in high PIN and WD, whereas their expression did not correlate in late-stage PD. In contrast to the up-regulated expression of beta1A, the levels of beta1C, a beta1 cytoplasmic variant that inhibits cell proliferation, were down-regulated in all stages of prostate cancer. A similar expression pattern was observed for a beta1C downstream effector, Grb2-associated binder-1 (Gab1) which is known to inhibit IGF-IR phosphorylation. To analyze in vitro the mechanistic implications of beta1A, beta1C, and Gab1 deregulation in prostate cancer, we investigated whether expression of either beta1 variant in beta1-null cells affected IGF-IR localization. We found that IGF-IR and beta1A were colocalized in highly specialized integrin signaling compartments, designated focal contacts. However, in the presence of beta1C, IGF-IR remained diffuse on the cell surface and did not localize to focal contacts. The findings that beta1 integrins and IGF-IR are concurrently deregulated and that expression of beta1 integrins is necessary to achieve appropriate IGF-IR intracellular distribution point to the important role that the cross-talk between these receptors may have during prostate cancer progression and will be helpful in formulating new therapeutic strategies.

Current models of human prostate contractility

1. The human prostate is a compact gland contributing to seminal fluid. With increasing age, most humans will develop benign prostatic hyperplasia, a condition of prostatic enlargement and contractility that leads to occlusion of the urethra. Over many years, investigators have used a variety of animal and cell culture models to elucidate some of the contractile and proliferative mechanisms that may be associated with the development of this condition. 2. This review briefly assesses the current state of knowledge of the mechanisms underlying human prostatic contractility and compares it with that of animal and cell culture models. It is not intended as a comprehensive methodological review, nor is it intended to indicate our preferences for either model. Our aim is to correlate findings from animal and cell culture models with the current understanding of human prostate contractility. 3. We hope that the present review will increase awareness of the suitability of the current models in developing our understanding of benign prostatic hyperplasia.

Tumor-suppression function of transcription factor USF2 in prostate carcinogenesis

Although the transcription factor USF2 has been implicated in the regulation of cellular growth and proliferation, it is unknown whether alterations in USF2 contribute to tumorigenesis and tumor development. We examined the role of USF2 in prostate tumorigenesis. Western blot analysis revealed markedly decreased USF2 levels in three androgen-independent prostate cancer cell lines, PC-3, DU145, and M12, as compared to nontumorigenic prostate epithelial cells or the androgen-dependent cell line, LNCaP. Ectopic expression of USF2 in PC-3 cells did not affect the cell proliferation rate of PC-3 cells on plastic surfaces. However, it dramatically decreased anchorage-independent growth of PC-3 cells in soft agar (90-98% inhibition) and the invasion capability (80% inhibition) of PC-3 cells in matrix gel assay. Importantly, expression of USF2 in PC-3 cells inhibited the tumorigenicity of PC-3 cells in an in vivo nude mice xenograft model (80-90% inhibition). These results suggest that USF2 has tumor-suppression function. Consistent with its function in tumor suppression, we found that the USF2 protein is present in normal prostate epithelial cells but absent in 18 of 42 (43%) human prostate cancer tissues (P = 0.015). To further examine the functional role of USF2 in vivo, we generated mice with genetic deletion of USF2 gene. We found that USF2-null mice displayed marked prostate hyperplasia at a young age, suggesting that USF2 is involved in the normal growth and differentiation of prostate. Together, these studies demonstrate that USF2 has tumor-suppressor function and plays a role in prostate carcinogenesis.

Use of tissue recombination to predict phenotypes of transgenic mouse models of prostate carcinoma

Transgenic mouse models of cancer represent a powerful approach for exploring disease processes and testing potential therapeutic interventions. Currently, it is difficult to predict if a specific genetic manipulation will result in a desirable phenotype. The present study tests the idea that tissue recombinants recapitulate the pathologic features of the neoplastic prostate seen in transgenic mice, and would thus be suitable predictive models for new mouse design. The large probasin-large T-antigen (LPB-Tag) transgenic lines 12T-7f and 12T-10 were used as a basis for this study. Tissue recombinants of bladder epithelium (BlE) and urogenital sinus mesenchyme (UGM) were implanted under the renal capsule of athymic mice. Recombinants composed of BlE from 12T-10 LPB-Tag and wild-type (wt) UGM faithfully recapitulated the histopathologic and temporal features of intact transgenic mice of this line. Tissue recombinants using BlE from 12T-7f mice and wt UGM developed epithelial proliferation with atypia that lacked the associated hypercellular stroma seen in the intact 12T-7f line. Recombinants using 12T-7f UGM demonstrated that the hypercellular stroma results from stromal cell expression of the SV40 large T antigen. Corresponding to the recombinant phenotypes, stromal Tag immunostaining was observed in prostate tissues from intact 12T-7f but not 12T-10 mice. Similar stromal expression of Tag was also noted in the hypercellular TRAMP prostatic stroma. Further analysis revealed a previously unreported pattern of SV40T expression in the LADY and TRAMP models including ductus deferens and seminal vesicle stroma as well as region and cell type-specific patterns in the epididymis. The present study demonstrates the utility of using tissue recombination to explore organ-specific phenotypes. Recombination strategies should enable quick and cost-effective screening for likely phenotypes in transgenic animals. This comparison of tissue recombination to existing models shows that this approach can elicit new information on well-characterized models.

The use of genetically engineered mouse models of prostate cancer for nutrition and cancer chemoprevention research

The ability to modify the expression of specific genes in the mouse through genetic engineering technologies allows for the generation of previously unavailable models for prostate cancer prevention research. Although animal models have existed for some time for the study of prostate cancer prevention (primarily in the rat), it is uncertain if the mechanisms that drive prostate carcinogenesis in these models are relevant to those in human prostate cancer. Cell culture studies are of limited usefulness because the conditions are inherently artificial. Factors such as relevant physiologic concentrations and metabolism of putative chemoprevention compounds are difficult to model in an in vitro system. These studies also preclude the types of interactions known to occur between multiple cell types in vivo. In addition, all prostate cancer cell lines are already highly progressed and are not representative of the type of cells to which most preventive strategies would be targeted. Due to the advent of genetically engineered mouse (GEM) models, we now have models of prostate cancer that are dependent on molecular mechanisms already implicated in human prostate carcinogenesis. With these models we can perform a variety of experiments that could previously only be done in cell culture or in prostate cancer cell line xenografts. The currently available GEM models of prostate cancer have been extensively reviewed therefore, this review will focus on the types of models available and their usefulness for various types of preclinical studies relevant to prostate cancer prevention.

Expression signature of the mouse prostate

Genetically engineered mice are being used increasingly for delineating the molecular mechanisms of prostate cancer development. Epithelium-stroma interactions play a critical role in prostate development and tumorigenesis. To better understand gene expression patterns in the normal sexually mature mouse prostate, epithelium and stroma were laser-capture microdissected from ventral, dorsolateral, and anterior prostate lobes. Genome-wide expression was measured by DNA microarrays. Our analysis indicated that the gene expression pattern in the mouse dorsolateral lobe was closest to that of the human prostate peripheral zone, supporting the hypothesis that these prostate compartments are functionally equivalent. Stroma from a given lobe had closer gene expression patterns with stroma from other lobes than epithelium from the same lobe. Stroma appeared to have higher expression complexity than epithelium. Specifically, stromal cells had higher expression levels of genes implicated in cell adhesion, muscle development, and contraction, in structural constituents of cytoskeleton and actin binding, and in components such as sarcomere and extracellular matrix collagen. Among the genes that were enriched in the epithelium were secretory proteins, including seminal vesicle protein secretion 2 and 5. Surprisingly, prostate stroma expressed many osteogenic molecules, as confirmed by immunohistochemistry. A "bone-like" environment in the prostate may predispose prostate cells for survival in the bone. Chemokine Cxcl12 but not its receptor, Cxcr4, was expressed in normal prostate. In prostate tumors, interestingly, Cxcl12 was up-regulated in epithelial cells with a concomitant expression of Cxcr4. Expression of both the receptor and ligand may provide an autocrine mechanism for tumor cell migration and invasion.

A novel knock-in prostate cancer model demonstrates biology similar to that of human prostate cancer and suitable for preclinical studies

Preclinical studies of prostate cancer (CaP) have employed a genetically engineered mouse model, since there is no naturally occurring CaP in rodents. We have previously reported a new knock-in mouse adenocarcinoma prostate (KIMAP) model. In this study, we demonstrate that the new model possesses a tumor architecture of heterogeneity and multifocality similar to that of human CaP, by utilizing a new compound scoring system to compare with the PSP94 (approved gene symbol Msmb) gene-directed transgenic mouse CaP model (TGMAP). KIMAP mice showed a balanced distribution of tumor extent, which penetrated the prostate gland. Comparative studies on cDNA microarrays demonstrated that KIMAP tumors were upregulated with higher contents of immunoresponse genes, whereas PSP-TGMAP tumors had neuroendocrine (NE) differentiation. The majority of KIMAP mice did not progress to NE CaP, which was observed only at a very late stage and a low frequency. Several tumor marker genes characteristic of human CaP were uniquely identified in KIMAP tumors, including hepsin, maspin, Nkx3.1, CD10 and PSP94 (similar to PSA), etc. The differences between these two CaP models are attributed to the introduction of a single endogenous knock-in mutation. Due to the similarities between human CaP tumors and the PSP-KIMAP tumors, this preclinical model may supplement the current transgenic models to study CaP more accurately.

Evidence for downregulation of calcium signaling proteins in advanced mouse adenocarcinoma

BACKGROUND

Prostate cancer (PCa) is the leading cancer related death in America. Gleason grading is currently the predominant method for prediction, with only few biomarkers available. More biomarkers, especially as they relate to cancer progression are desirable.

METHODS

The abundance of several important proteins in prostate tissue was compared between wild-type mouse dorsal prostate and well-differentiated transgenic adenocarcinoma mouse prostate (TRAMP) mouse dorsal prostates, and between wild-type mouse dorsal prostate and poorly-differentiated TRAMP mouse tumor tissue. 2DIGE method in conjunction with MALDI-ToF and Western blots was used to determine differential expression.

RESULTS

In TRAMP dorsal prostates with well-differentiated adenocarcinoma, there were few significant changes in the protein abundances compared to wild-type dorsal prostates, with the exception of increases in proliferating cell nuclear antigen (PCNA) and beta tubulin, two proteins implicated in cell proliferation, and a more than 2-fold increase in Hsp60, a protein involved in the suppression of apoptosis. In the poorly-differentiated tumors, the changes in protein abundance were substantial. While some of those changes could be related to the disappearance of stromal tissue or the appearance of epithelial tissue, other changes in protein abundance were more significant to the cancer development itself. Most notable was the overall decrease in calcium homeostasis proteins with a 10-fold decrease in calreticulin and Hsp70 and a 40-fold decrease in creatine kinase bb in the cancerous tissue.

CONCLUSIONS

Proteomics of TRAMP mice provide an excellent method to observe changes in protein abundance, revealing changes in pathways during cancer progression.

Genetically engineered murine models of prostate cancer: insights into mechanisms of tumorigenesis and potential utility

There has been substantial progress made recently in the effort to model human prostate cancer in mice. Several mutant mice have been generated which mimic various aspects of the human disease, including the development of preneoplastic lesions, invasive carcinoma, and metastases. These mouse reagents provide the research community with valuable new tools for dissecting the mechanisms of tumorigenesis, as well as for testing new targeted therapies. This review will summarize some of these models and their utility, as well as propose future challenges for developing improved models.

Survey of genetically engineered mouse models for prostate cancer: analyzing the molecular basis of prostate cancer development, progression, and metastasis

Genetically engineered mouse models have been generated to study the molecular basis of prostate cancer (PCa) development, progression, and metastasis. Selection of a prostate-specific promoter, such as the probasin (PB) and prostate specific antigen (PSA) promoters, is critical for generating sufficient levels of transgene expression to elicit a phenotypic response. To date, target genes have included growth factors, cell cycle regulators, pro- and anti-apoptotic proteins, steroid hormone and growth factor receptors, oncogenes, tumor suppressors, and homeobox genes. The experimental approaches used to generate these mouse models include overexpression of the transgene, knock-out/knock-in of transgene expression and conditional regulation of expression using Cre/lox technology. This review summarizes the promoters, which have been utilized to create genetically engineered mouse models for PCa. Furthermore, the effects of gene disruption on promoting low- and high-grade intraepithelial neoplasia (LGPIN and HGPIN, respectively), locally invasive carcinoma and metastatic lesions will be discussed. To date, the PB-Cre4 x PTENloxp/loxp model appears to be the only model that represents the entire continuum of prostate adenocarcinoma development, tumor progression, and metastasis, although models that develop prostatic neuroendocrine (NE) cancer can be generated by disrupting one genetic event. Indeed, analysis of bigenic mouse models indicates that two genetic events are generally required for progression from HGPIN to locally invasive adenocarcinoma and that two to five genetic events can promote metastasis to distant sites. Studying the effects of genetic perturbation on PCa biology will increase our understanding of the disease process and potentially provide targets for developing novel therapeutic approaches.

Regression of mouse prostatic intraepithelial neoplasia by nonsteroidal anti-inflammatory drugs in the transgenic adenocarcinoma mouse prostate model

PURPOSE

Epidemiologic studies have revealed a decreased risk of colon cancer among people who have regularly taken cyclooxygenase (COX)-2 inhibitors such as aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs). Whereas the selective COX-2 inhibitor celecoxib and exisulind, a metabolic product of sulindac, have gained increasing attention as efficacious chemopreventive agents against colon and prostate cancer, not much is known about the underlying molecular targets and mechanisms. Moreover, the side effects of NSAIDs are a major obstacle for large-scale application to the prevention of cancer in humans; for example, in the United States in 1998, there were 16,550 deaths from NSAID-induced gastrointestinal complications. The toxicity associated with these compounds is raising concerns, and more needs to be known about their mode of action and molecular targets.

EXPERIMENTAL DESIGN

We used the transgenic mouse prostate (TRAMP) model, which exhibits similarities with human prostate cancer, including epithelial origin, progression from the PIN stage to adenocarcinoma, and metastasis by a transgene that is hormonally regulated by androgens. In addition to histologically analyzing the PIN lesions of the dorsolateral prostate from TRAMP mice, we delineated the molecular targets and mechanisms of celecoxib and exisulind against mouse PIN lesions. We performed Western blot analysis of the total protein lysate from the tissues of mouse PIN lesions to measure the level of expression of androgen receptor, vascular endothelial growth factor, nuclear factor-kappaB p65, BclII, AKT (total and phosphorylated Ser473), p53, cyclin-dependent kinase inhibitor p21WAF1/CIP1, p27, BAX, and caspase-3 to demonstrate the COX-2-independent mechanism involved in the inhibition of PIN lesions of the dorsolateral prostate by both celecoxib and exisulind.

RESULTS

We found for the first time that (a) both celecoxib and exisulind as dietary supplements induce strong inhibitory effects against prostate cancer at doses of 800 and 500 ppm, respectively, after 16 weeks; (b) the histologic analysis of the dorsolateral prostate after 2 weeks of treatment indicated a reduction of PIN lesions from 75% to 19% with celecoxib and to 16% with exisulind; (c) more importantly, those few PINs and adenocarcinomas in the groups treated with celecoxib or exisulind showed more apoptotic cells, lower levels of proliferating cell nuclear antigen, and a lower number of mitotic cells. To understand the molecular mechanisms involved in the inhibition of PIN lesions, first, we examined the expression of molecular targets involved in angiogenesis and inflammatory processes. It was clearly evident from Western blot analysis of the total protein lysate derived from the dorsolateral prostate tissues with PIN lesions that expression of androgen receptor, vascular endothelial growth factor, nuclear factor-kappaB p65, and BclII is down-regulated more effectively by celecoxib. Down-regulation of AKT protein (total and phosphorylated at Ser473) signaling by celecoxib clearly indicates an inhibition of the survival gene and the pathological process that could otherwise lead to adenocarcinoma.

CONCLUSIONS

Overall, the findings from this study clearly show the effectiveness of celecoxib and exisulind in reducing the PIN lesions by modulating a cascade of molecular targets involved in COX-2-dependent and -independent mechanisms. Whereas these agents are already in clinical trial or in use as chemopreventive agents, findings from this study demonstrate the difference in their mode of action, thus helping us to understand the side effects.

Serum Antibodies to Huntingtin Interacting Protein-1: A New Blood Test for Prostate Cancer

Huntingtin-interacting protein 1 (HIP1) is frequently overexpressed in prostate cancer. HIP1 is a clathrin-binding protein involved in growth factor receptor trafficking that transforms fibroblasts by prolonging the half-life of growth factor receptors. In addition to human cancers, HIP1 is also overexpressed in prostate tumors from the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse model. Here we provide evidence that HIP1 plays an important role in mouse tumor development, as tumor formation in the TRAMP mice was impaired in the Hip1null/null background. In addition, we report that autoantibodies to HIP1 developed in the sera of TRAMP mice with prostate cancer as well as in the sera from human prostate cancer patients. This led to the development of an anti-HIP1 serum test in humans that had a similar sensitivity and specificity to the anti-alpha-methylacyl CoA racemase (AMACR) and prostate-specific antigen tests for prostate cancer and when combined with the anti-AMACR test yielded a specificity of 97%. These data suggest that HIP1 plays a functional role in tumorigenesis and that a positive HIP1 autoantibody test may be an important serum marker of prostate cancer.

Culture of mouse prostatic epithelial cells from genetically engineered mice

BACKGROUND

The lack of appropriate prostate cancer models is a major problem for prostate cancer research. Progress has been made towards the development of better in vivo rodent genetic models for prostatic disease. However, an in vitro model is often preferred for the elucidation of cellular mechanisms involved in the disease.

METHODS

We microdissected the four prostatic lobes from young male mice, harvested the epithelial components, and grew epithelial cells from these tissues. We maintained the growth of these cells in long-term and three-dimensional culture.

RESULTS

We have reproducibly harvested and cultured for extended passages mouse prostatic epithelial cells (MPECs) from a variety of mouse genetic strains. These cells express luminal and basal epithelial markers as well as the androgen receptor. Additionally, MPECs form classic branching structures in a three-dimensional collagen matrix.

CONCLUSIONS

We have developed a novel culture system to harvest and grow MPECs in long-term culture. These cells will serve as a useful in vitro complement to studies using mouse genetic models for prostatic disease.

The Sca-1 cell surface marker enriches for a prostate-regenerating cell subpopulation that can initiate prostate tumorigenesis

Sca-1 (stem cell antigen-1) enriches for murine prostate cells capable of regenerating tubular structures containing basal and luminal cell lineages in a dissociated cell prostate regeneration system. Sca-1(+) fractions are enriched for cells at the G(0) stage of the cell cycle, and Sca-1(+) cells cluster in the proximal region of prostatic tubules where replication-quiescent cells have been localized. Castration-induced enrichment for androgen-independent cells results in a concomitant enrichment for Sca-1(+) cells. Genetic perturbations of PTEN/AKT signaling in prostate-regenerating cells leads to the initiation of tumorigenesis, and cancer progression is associated with a dramatic increase in Sca-1(+) cells. Sca-1-enriched prostate-regenerating cells possess multiple stem/progenitor cell properties and can serve as targets for cancer initiation.

Characterization of a lymph node within the mouse prostate: Detailed analysis using whole mount histology

BACKGROUND

Due to the prevalence of prostate disease, there is a growing interest in the immunobiology of the prostate and its contribution to such pathologies. Further study is needed to fully characterize immune responses within the prostate.

METHODS

Mouse ventral prostates were removed and analyzed using conventional immunohistochemistry, or by a novel whole mount technique, which allows the visualization of complete structures within the prostate.

RESULTS

A lymphoid structure was detected within the base of the mouse ventral prostate. Whole mount and cryostat sections revealed an organized arrangement of lymphocytes, along with dendritic cells interspersed throughout the node. It possessed a rich network of lymph node specific high endothelial venules (HEVs) and adjoining lymphatics containing immune cells.

CONCLUSIONS

Our results demonstrate the presence of a lymphoid structure within the base of the mouse ventral prostate possessing traits characteristic of an organized peripheral lymph node.

Lack of significant modifying effect of arctiin on prostate carcinogenesis in probasin/SV40 T antigen transgenic rats

Arctiin, a plant lignan that can be extracted from the Arctium lappa (burdock) seeds, is a possible environmental endocrine disruptor compounds and have been shown to influence sex hormone metabolism as well as protein synthesis, steroid biosynthesis. Modifying effects of arctiin on prostate carcinogenesis in probasin/SV 40 T antigen (Tag) transgenic (TG) rats were examined. A total of 64 male TG rats, 6 weeks old, were randomly divided to three experimental groups (soybean free Oriental MF diet with 0.1, 0.02, or 0.004% arctiin) and a control group (soybean free Oriental MF diet). Animals were killed at the end of week 18. Histopathological evaluation of prostate revealed that all the rats in any group developed adenocarcinoma in dorsolateral lobe of prostate, except two rats in 0.1% arctiin treated and one rat in 0.002% arctiin treated groups without prostate adenocarcinoma development. However, there were no definite treatment-related changes with statistical significance in all parameters for prostate carcinomas measured in this experiment. These results indicated that arctiin might not exert significant modifying effect on prostate carcinogenesis in SV 40 Tag TG rats at least under the present experiment.

INCREASED EXPRESSION OF MUC18 CORRELATES WITH THE METASTATIC PROGRESSION OF MOUSE PROSTATE ADENOCARCINOMA IN THE TRAMP MODEL

PURPOSE

The transgenic adenocarcinoma mouse prostate (TRAMP) model is a paradigm that closely mimics the progression of clinical prostate cancer. We have previously reported that MUC18, a cell adhesion molecule in the Ig gene superfamily, is a marker as well as an important mediator for the metastatic potential of human prostate cancer cells. In this study we investigated the possible correlation of increased MUC18 expression with the malignant progression of prostate cancer in the TRAMP model.

MATERIALS AND METHODS

We used immunohistochemistry, Western blot and reverse transcriptase-polymerase chain reaction analyses to determine MUC18 expression in the prostate gland of 178 to 282-day-old TRAMP positive males with a prostate tumor size of 0.4 to 12.7 gm. Eight normal prostates, 10 prostates with high grade prostatic intraepithelial neoplasia (PIN), 24 prostates with primary prostate cancer, 10 metastatic lesions from 50 pure C57BL/6 TRAMP mice (Wu colony) and 2 normal prostates, 2 prostates with high grade PIN, 6 prostates with primary prostate cancer and 4 metastatic lesions from 10 [C57BL/6 TRAMP x FVB] F1 mice (NMG colony) were used.

RESULTS

We found that mouse MUC18 was expressed in all (100%) high grade PIN, adenocarcinomas and metastatic lesions. All mice bearing primary prostate tumors had prostate cancer metastatic to the peri-aortic lymph nodes and some had it to other organs (liver, lung, kidney, testes, seminal vesicles and abdominal cavity). In contrast, prostates from 10 nontransgenic littermates did not have detectable MUC18 expression.

CONCLUSIONS

MUC18 expression is up-regulated in the TRAMP model and it correlates with the malignant progression of mouse prostate adenocarcinoma in this transgenic model. This further strengthens the hypothesis that MUC18 has an important role in increasing the metastatic potential of prostate cancer cells.

Overexpression of 12/15-lipoxygenase, an ortholog of human 15-lipoxygenase-1, in the prostate tumors of TRAMP mice

Changes in the expression and activity of lipid-metabolizing enzymes, including the linoleic acid (LA)-metabolizing enzyme 15-lipoxygenase-1 (15-LO-1), may play a role in the development and progression of human prostate carcinoma (PCa). We reported that human 15-LO-1 (designated as leukocyte type 12-LO or 12/15-LO in mouse) is expressed in human prostate and increased in PCa, particularly high-grade PCa. Genetically engineered mouse (GEM) models of PCa could facilitate the study of this gene and its regulation and function in PCa progression. In this study, we examine the protein expression and enzyme activity levels of 12/15-LO associated with PCa progression in the TRansgenic Adenocarcinoma of Mouse Prostate (TRAMP) model of PCa. This GEM model develops prostatic intraepithelial neoplasia (PIN), followed by invasive gland-forming PCa and invasive and metastatic less differentiated PCa, with neuroendocrine (NE) differentiation (NE Ca). In the wild-type and TRAMP prostates, the most prominent LA metabolite was 13-hydroxyoctadecadienoic acid (13-HODE). Lesser amounts of 12-hydroxyeicosatetraenoic acid and 15-hydroxyeicosatetraenoic acid (HETE) were made from arachidonic acid (AA). In TRAMP prostates, 12/15-LO activity was increased compared to wild type at 20, 29, 39, and 49 weeks, as assessed by LA conversion to 13-HODE, and by AA conversion to 12/15-HETE, respectively. Immunostaining demonstrated that the increased capacity to generate 13-HODE was paralleled by an increase in neoplastic epithelial expression of 12/15-LO in PIN and invasive carcinomas. In conclusion, although there is a basal 12/15-LO activity in the wild-type mouse prostate, there is a marked increase in the expression of 12/15-LO with TRAMP PCa progression, paralleling our previously reported increased expression of the ortholog 15-LO-1 in high-grade human PCa. Thus, 12/15-LO and LA metabolism in the TRAMP model shares similarities to human PCa, and may allow to confirm a role for LA metabolism and other biologic functions of 15-LO-1 in human PCa. In addition, the TRAMP model will serve as a tool for testing the suitability of 12/15-LO-and ultimately human 15-LO--as a therapeutic target during PCa progression.

The Immunogenicity of Dendritic Cell-Based Vaccines Is Not Hampered by Doxorubicin and Melphalan Administration

Immunization of cancer patients is most effective in tumor-free conditions or in the presence of minimal residual disease. In the attempt to develop new strategies able to control tumor recurrence while allowing the development of protective immunity, we have investigated the immunogenic potential of two distinct vaccine formulations when provided alone or upon single and repeated treatment with chemotherapeutics drugs. Vaccine-induced T cell responses were first investigated by tracing Ag-specific T cell responses in mice bearing detectable frequencies of Ag-specific TCR transgenic CD4 and CD8 T cells. These studies indicated that immunization with peptide-pulsed dendritic cells and soluble Ag plus adjuvant elicited a comparable expansion and differentiation of CD4 and CD8 effector cells in the peripheral lymphoid tissues when provided alone or shortly after Doxorubicin or Melphalan administration. We also analyzed the potency of the combined vaccination in transgenic adenocarcinoma mouse prostate mice, which develop spontaneous prostate cancer. Dendritic cell-based vaccination elicited potent tumor-specific cytotoxic responses in mice bearing prostate intraepithelial neoplasia both in the absence and in the presence of Doxorubicin. Together our results indicate that Doxorubicin- or Melphalan-based chemotherapy and Ag-specific vaccination can be combined for adjuvant treatments of cancer patients.