Characterization of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) as a model to study effects of castration therapy

Suppression of prostate cancer and amelioration of the immunosuppressive tumor microenvironment through selective immunoproteasome inhibition

New treatment options to battle hormone-refractory prostate carcinoma (PC) are a pressing medical need. Chronic inflammation has been implicated in PC etiology. The pro-inflammatory cytokines IL-6, IL-23 and IL-17 are key mediators to promote growth of PC. Here, we evaluate the potential of immunoproteasome inhibition for anti-inflammatory and direct anti-tumorigenic therapy of PC. The anti-tumor effect of immunoproteasome inhibitor ONX 0914 was tested in mouse and human PC cells and the in vivo therapeutic efficacy of immunoproteasome inhibition was analyzed in transgenic adenocarcinoma of the mouse prostate (TRAMP) mice in preventive and therapeutic settings and in castration-resistant (CR)PC after castration. Inhibition of the immunoproteasome subunit LMP7 induced apoptotic cell death in PC cell lines. In TRAMP mice, ONX 0914-treatment resulted in significant inhibition of PC growth with a decreased frequency of malignant prostatic lesions and inhibition of metastasis formation. The number of immunosuppressive myeloid cells in PC was greatly reduced in response to ONX 0914. Thus, immunoproteasome inhibition shows remarkable efficacy against PC progression in vivo and impedes tumor recurrence in CRPC-TRAMP mice by blocking the immunosuppressive inflammatory response in the tumor microenvironment. In conclusion, we show that the immunoproteasome is a promising drug target for the treatment of PC.

Dietary tomato inhibits angiogenesis in TRAMP prostate cancer but is not protective with a Western-style diet in this pilot study

Prostate cancer (PCa) remains the second most diagnosed cancer worldwide. Higher body weight is associated with chronic inflammation, increased angiogenesis, and treatment-resistant tumor phenotypes. Dietary tomato reduces PCa risk, which may be due to tomato inhibition of angiogenesis and disruption of androgen signaling. This pilot study investigated the interplay between tomato powder (TP), incorporated into control (CON) and obesogenic (OB) diets, and PCa tumor growth and blood perfusion over time in a transgenic model of PCa (TRAMP). Ultrasound microvessel imaging (UMI) results showed good agreement with gold-standard immunohistochemistry quantification of endothelial cell density, indicating that this technique can be applied to non-invasively monitor tumor blood perfusion in vivo. Greater body weight was positively associated with tumor growth. We also found that TP significantly inhibited prostate tumor angiogenesis but that this inhibition differentially affected measured outcomes depending on CON or OB diets. TP led to reduced tumor growth, intratumoral inflammation, and intratumoral androgen-regulated gene expression (srd5a1, srd5a2) when incorporated with the CON diet but greater tumor growth and intratumoral gene expression when incorporated with the OB diet. Results from this study show that protective benefits from dietary tomato are lost, or may become deleterious, when combined with a Western-style diet.

GPR30 knockdown weakens the capacity of CAF in promoting prostate cancer cell invasion via reducing macrophage infiltration and M2 polarization

Cancer-associated fibroblasts (CAFs) can promote the development and metastasis of prostate cancer partly by mediating tumor-associated inflammation. An increasing amount of studies have focused on the functional interactions between CAFs and immune cells in the tumor microenvironment (TME). We previously reported that G protein-coupled receptor 30 (GPR30) was highly expressed in prostate CAFs and plays a crucial role in prostate stromal cell activation. However, the effect and underlying mechanism of GPR30 expression in prostate CAFs affecting the interaction between CAFs and tumor-associated macrophages (TAMs) need further elucidation. Here, we found that, compared with CAF-shControl, CAF-shGPR30 inhibited macrophage migration through transwell migration assays, which should be attributed to the decreased expression of C-X-C motif chemokine ligand 12 (CXCL12). In addition, macrophages treated with a culture medium of CAF-shGPR30 exhibited attenuated M2 polarization with downregulated M2-like markers expression. Moreover, macrophages stimulated with a culture medium of CAF-shGPR30 were less efficient in promoting activation of fibroblast cells and invasion of PCa cells. Finally, cocultured CAF-shGPR30 and macrophages suppressed PCa cell invasion compared to cocultured CAF-shControl and macrophages by decreasing interleukin-6 (IL-6) secretion, and this effect could be abrogated with rescue expression of IL-6. Our results pinpoint the function of GPR30 in prostate CAFs on regulating the CAF-TAM interaction in the TME and provide new insights into PCa therapies via regulating TME.

P21 and P27 promote tumorigenesis and progression via cell cycle acceleration in seminal vesicles of TRAMP mice

Transgenic adenocarcinoma mouse prostate (TRAMP) model is established to mimic human prostate cancer progression, where seminal vesicle lesions often occur and has been described as phyllodes-like epithelial-stromal tumors. However, the molecular mechanism regulating tumorigenesis and progression in seminal vesicles of TRAMP mice remains largely unknown. In this study, C57BL/6 TRAMP mice were found to have a significantly shorter lifespan than wild-type (WT) mice and all of the seminal vesicles were markedly increased in size and weight with age from 24 weeks exhibiting a clearly papillary-phyllode pattern, though no obvious difference was observed in multiple organs including heart, liver, spleen, lungs, kidneys, testicles and bone between TRAMP and WT mice, and less than 10% of TRAMP mice developed prostate tumors. Western blotting showed Cyclin (CCN) B1 and CCND1 were remarkably overexpressed in seminal vesicle tumors of TRAMP mice at 24 weeks of age and increased with age till the end of trial, which was confirmed by Immunohistochemistry (IHC). P21 and P27 were also significantly augmented, whereas P53 and phosphorylated P53 (p-P53) were constantly expressed in normal controls and P53 did not appear to be mutated. Not only cyclin-dependent kinase (CDK) 1 and phosphorylated forkhead box protein (FOX) O1 but also CDK4, CDK6 and phosphorylated retinoblastoma-associated protein (RB) had similar increase trends, so did epidermal growth factor receptor (EGFR), AKT serine/threonine kinase (AKT), and their respective phosphorylation levels. Signal transducer and activator of transcription (STAT) 3, p-STAT3, enhancer of zeste homolog 2 (EZH2) and EZH2 mediated trimethylation of histone H3 lysine 27 (H3K27me3) were considerably elevated, too. Taken together, this finding suggests P21 and P27 promote carcinogenesis and development in seminal vesicles of TRAMP mice via accelerating cell cycle progression, in which oncogenic transformation of P21 and P27 might be through regulation of EGFR-AKT signaling.

The impact of finasteride and dutasteride treatments on proliferation, apoptosis, androgen receptor, 5α-reductase 1 and 5α-reductase 2 in TRAMP mouse prostates

BACKGROUND

Previously, we studied the effect of finasteride- or dutasteride-containing diets in male C57BL/6 TRAMP x FVB mice. Pre (6 weeks of age) and post (12 weeks of age) groups received finasteride or dutasteride to determine the efficacy of these pharmaceuticals on prostate cancer (PCa) development in male C57BL/6 TRAMP x FVB mice. Post-Dutasteride treatment was more effective than Pre-Dutasteride treatment, and dutasteride treatments were more effective than finasteride treatments in decreasing prostatic intraepithelial neoplasia (PIN) progression and PCa development. Finasteride and Pre-Dutasteride treatments significantly decreased high-grade PIN incidence, but increased poorly differentiated PCa incidence. In this study, molecular changes in prostates of these mice were characterized in an effort to elucidate the discordant response in Pre-Dutasteride and finasteride groups, and determine why Post-Dutasteride treatment was more effective.

METHOD/PRINCIPAL FINDINGS

Ki-67 (proliferation marker) and androgen receptor (AR) protein, apoptotic DNA fragmentation (TUNEL assay), 5α-reductase 1 (5αR1) and 5α-reductase 2 (5αR2) mRNA were quantified in male TRAMP mice prostate tissues with genitourinary weight < 1 and > 1 gram. Overall, proliferation and AR were decreased and apoptosis was increased in most tumors versus prostate epithelium and hyperplasia. Proliferation and AR were increased notably in hyperplasia versus prostate epithelium and tumor. There were no clear trends or differences in 5α-reductase 1 and 5α-reductase 2 levels between large and small tumors. The discordant response in Pre-Finasteride and Pre-Dutasteride groups may be due to upregulated 5αR1 levels in large versus small tumors. It is not clear what the mechanism is for the different response in the Post-Finasteride group. Post-Dutasteride treatment was more effective than Pre-Dutasteride treatment in decreasing 5αR1 in large tumors. Therefore, this may be why this treatment was more effective in decreasing PIN progression and PCa development.

CONCLUSION

The effect of finasteride and dutasteride on these biomarkers did not clearly elucidate their mechanism of action, but tumor 5αR1 levels were significantly positively correlated with adjusted prostate severe lesion score.

Nintedanib antiangiogenic inhibitor effectiveness in delaying adenocarcinoma progression in Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP)

Background

In recent times, anti-cancer treatments have focused on Fibroblast Growth Factor (FGF) and Vascular-Endothelial Growth Factor (VEGF) pathway inhibitors so as to target tumor angiogenesis and cellular proliferation. One such drug is Nintedanib; the present study evaluated the effectiveness of Nintedanib treatment against in vitro proliferation of human prostate cancer (PCa) cell lines, and growth and progression of different grades of PCa lesions in pre-clinical PCa transgenic adenocarcinoma for the mouse prostate (TRAMP) model.

Methods

Both androgen-independent (LNCaP) and androgen-dependent (PC3) PCa cell lines were treated with a range of Nintedanib doses for 72 h, and effect on cell growth and expression of angiogenesis associated VEGF receptors was analyzed. In pre-clinical efficacy evaluation, male TRAMP mice starting at 8 and 12 weeks of age were orally-fed with vehicle control (10% Tween 20) or Nintedanib (10 mg/Kg/day in vehicle control) for 4 weeks, and sacrificed immediately after 4 weeks of drug treatment or sacrificed 6–10 weeks after stopping drug treatments. At the end of treatment schedule, mice were sacrificed and ventral lobe of prostate was excised along with essential metabolic organ liver, and subjected to histopathological and extensive molecular evaluations.

Results

The total cell number decreased by 56–80% in LNCaP and 45–93% in PC3 cells after 72 h of Nintedanib treatment at 2.5–25 μM concentrations. In pre-clinical TRAMP studies, Nintedanib led to a delay in tumor progression in all treatment groups; the effect was more pronounced when treatment was given at the beginning of the glandular lesion development and continued till study end. A decreased microvessel density and VEGF immunolocalization was observed, besides decreased expression of Androgen Receptor (AR), VEGFR-1 and FGFR-3 in some of the treated groups. No changes were observed in the histological liver analysis.

Conclusions

Nintedanib treatment was able to significantly decrease the growth of PCa cell lines and also delay growth and progression of PCa lesions to higher grades of malignancy (without inducing any hepatotoxic effects) in TRAMP mice. Furthermore, it was observed that Nintedanib intervention is more effective when administered during the early stages of neoplastic development, although the drug is capable of reducing cell proliferation even after treatment interruption.

5α-reductase 1 mRNA levels are positively correlated with TRAMP mouse prostate most severe lesion scores

BACKGROUND

The contribution of 5α-reductase 1 and 5α-reductase 2 to prostate cancer development and progression is not clearly understood. TRAMP mice are a common prostate cancer model, in which 5α-reductase 1 and 5α-reductase 2 expression levels, along with prostate lesions scores, have not been investigated at different time points to further understand prostate carcinogenesis.

METHOD/PRINCIPAL FINDINGS

To this end, 8-, 12-, 16-, and 20-week-old male C57BL/6TRAMP x FVB mice prostate most severe and most common lesion scores, 5α-reductase 1 and 5α-reductase 2 in situ hybridization expression, and Ki-67, androgen receptor, and apoptosis immunohistochemistry levels were measured. Levels of these markers were quantified in prostate epithelium, hyperplasia, and tumors sections. Mice developed low- to high-grade prostatic intraepithelial neoplasia at 8 weeks as the most severe and most common lesions, and moderate- and high-grade prostatic intraepithelial neoplasia at 12 and 16 weeks as the most severe lesion in all lobes. Moderately differentiated adenocarcinoma was observed at 20 weeks in all lobes. Poorly differentiated carcinoma was not observed in any lobe until 12-weeks-old. 5α-reductase 1 and 5α-reductase 2 were not significantly decreased in tumors compared to prostate epithelium and hyperplasia in all groups, while proliferation, apoptosis, and androgen receptor were either notably or significantly decreased in tumors compared with prostate epithelium and hyperplasia in most or all groups. Prostate 5αR1 levels were positively correlated with adjusted prostate most severe lesion scores.

CONCLUSION

Downregulation of androgen receptor and 5α-reductase 2, along with upregulation of 5α-reductase 1 in tumors may promote prostatic intraepithelial neoplasia and prostate cancer development in TRAMP mice.

Preclinical evaluation of investigational radiopharmaceutical RISAD-P intended for use as a diagnostic and molecular radiotherapy agent for prostate cancer

BACKGROUND

The androgen receptor (AR) plays a dominant role in the pathogenesis of prostate cancer. 5-Radioiodo-3'-O-(17β-succinyl-5α-androstan-3-one)-2'-deoxyuridin-5'-yl phosphate (RISAD-P) is an AR-targeting reagent developed for noninvasive assessment of AR and proliferative status of the AR-expressing tumors, and for molecular radiotherapy with Auger electron-emitting radionuclides. In this study, the preclinical toxicity and targeting potential of RISAD-P was evaluated.

METHODS

Effects of nonradioactive ISAD-P and RISAD-P labeled with (123) I, (124) I, and (125) I were evaluated in male mice. Expanded-acute single dose toxicity studies, hematologic toxicity, liver and kidney function, pharmacokinetics, biodistribution, and imaging studies were conducted. Imaging and pilot therapy studies were conducted in transgenic mice.

RESULTS

RISAD-P is not toxic at doses projected for clinical use. Its tissue distribution compares favorably with the distribution reported for (18) F-dihydrotestosterone derivatives. RISAD-P has excellent prostate cancer targeting properties. One hour after (125) IRISAD-P administration, nearly 10% of the injected dose is associated with prostate tumor. The tumor clearance is biphasic and plateaus between 24 and 48 hr post-injection. The estimated radiation doses calculated for 1 g tumor using the MIRD convention are well within the therapeutic range with values of 170, 250, 1,240 Gy × MBq(-1)  × g(-1) for (125) I-, (123) I-, and (124) I-labeled RISAD-P, respectively. The transient uptake of radioactivity is observed in the genitourinary tract and stomach. Without the potassium iodide blockade, thyroid uptake is also observed.

CONCLUSIONS

Biodistribution, toxicity, and radiation dosimetry studies suggest that RISAD-P holds characteristics of a promising candidate for imaging of AR expression and tumor proliferation, as well as molecular radiotherapy for metastatic or locally, regionally advanced prostate cancer.

The stroma-a key regulator in prostate function and malignancy

Prostate cancer is a very common and highly unpredictable form of cancer. Whereas many prostate cancers are slow growing and could be left without treatment, others are very aggressive. Additionally, today there is no curative treatment for prostate cancer patients with local or distant metastasis. Identification of new, improved prognostic and diagnostic biomarkers for prostate cancer and the finding of better treatment strategies for metastatic prostate cancer is therefore highly warranted. Interactions between epithelium and stroma are known to be important already during prostate development and this interplay is critical also in development, progression of primary tumors and growth of metastases. It is therefore reasonable to expect that future biomarkers and therapeutic targets can be identified in the prostate tumor and metastasis stroma and this possibility should be further explored.

S100A9 interaction with TLR4 promotes tumor growth

By breeding TRAMP mice with S100A9 knock-out (S100A9^−/−) animals and scoring the appearance of palpable tumors we observed a delayed tumor growth in animals devoid of S100A9 expression. CD11b⁺ S100A9 expressing cells were not observed in normal prostate tissue from control C57BL/6 mice but were readily detected in TRAMP prostate tumors. Also, S100A9 expression was observed in association with CD68⁺ macrophages in biopsies from human prostate tumors. Delayed growth of TRAMP tumors was also observed in mice lacking the S100A9 ligand TLR4. In the EL-4 lymphoma model tumor growth inhibition was observed in S100A9^−/− and TLR4^−/−, but not in RAGE^−/− animals lacking an alternative S100A9 receptor. When expression of immune-regulating genes was analyzed using RT-PCR the only common change observed in mice lacking S100A9 and TLR4 was a down-regulation of TGFβ expression in splenic CD11b⁺ cells. Lastly, treatment of mice with a small molecule (ABR-215050) that inhibits S100A9 binding to TLR4 inhibited EL4 tumor growth. Thus, S100A9 and TLR4 appear to be involved in promoting tumor growth in two different tumor models and pharmacological inhibition of S100A9-TLR4 interactions is a novel and promising target for anti-tumor therapies.

Lobe-specific lineages of carcinogenesis in the transgenic adenocarcinoma of mouse prostate and their responses to chemopreventive selenium

BACKGROUND

The transgenic adenocarcinoma of mouse prostate (TRAMP) model is by far the most practical transgenic model for preclinical prostate cancer chemoprevention studies. It is critical to characterize the prostate lobe-specificity of lesion lineages to consolidate the advantages of this model and minimize its limitations for chemoprevention studies.

METHODS

We dissected dorsolateral (DLP), ventral (VP), and anterior prostate (AP) lobes, and macroscopic tumors from 90 male C57BL/6J TRAMP mice at 22-24 weeks of age (WOA) and analyzed lesions by histological, biochemical and proteomic approaches. To determine whether methylseleninic acid (MSeA) led to a deletion of initiated cells, we gave oral MSeA to TRAMP mice from 5 to 23 WOA or from 5 to 15 WOA and analyzed lesions at 23 WOA.

RESULTS

All tumors (n = 18) were T-antigen(+), synaptophysin (SYP)(+), androgen-receptor(-), and E-cadherin(-) poorly differentiated neuroendocrine carcinomas (NE-Ca). They were traceable most frequently to VP (66.7%) and rarely to DLP (11.1%) and AP (5.6%) with an estimated life-time incidence of 1 out of 3 mice. In DLP, epithelial lesions ranged from mild-to-severe atypical hyperplasia, with T-antigen(+), SYP(-), androgen-receptor(+), and E-cadherin(+). Proteomic profiling revealed many molecular differences between VP and DLP. In MSeA experiment, 6 out of 19 (31.5%) mice developed NE-Ca in the control group, only 2 in each MSeA group of 17-18 mice (11.1-11.8%) bore a detectable NE-Ca.

CONCLUSION

The C57BL/6J TRAMP mouse represents at least two lineages of prostate carcinogenesis. Chemoprevention studies should incorporate this knowledge for efficacy assessment and molecular target validations.

Targeting castration-induced tumour hypoxia enhances the acute effects of castration therapy in a rat prostate cancer model

What's known on the subject? and What does the study add? Castration therapy has rather modest effects on cell death in tumours but can be enhanced by other treatments targeting tumour stroma and vasculature. This study shows that the prostate becomes hypoxic following castration and that targeting hypoxic cells during castration therapy potently enhances the effects of castration.

OBJECTIVE

To explore the effects of castration therapy, the standard treatment for advanced prostate cancer, in relation to tumour hypoxia and to elicit its importance for the short- and long-term therapeutic response.

MATERIAL AND METHODS

We used the androgen-sensitive rat Dunning H prostate tumour model that transiently responds to castration treatment followed by a subsequent relapse, much like the scenario in human patients. Tumour tissues were analysed using stereological methods in intact, 1 and 7 days after castration therapy.

RESULTS

Hypoxia was transiently up-regulated after castration therapy and correlated with the induction of tumour cell apoptosis. When castration therapy was combined with tirapazamine (TPZ), a drug that targets hypoxic cells and the vasculature, the effects on tumour cell apoptosis and tumour volume were enhanced in comparison to either castration or TPZ alone.

CONCLUSION

The present study suggests that castration-induced tumour hypoxia is a novel target for therapy.

Indoleamine 2,3-dioxygenase (IDO) activity influence tumor growth in the TRAMP prostate cancer model

BACKGROUND

Indoleamine 2,3-dioxygenase (IDO) activity has been shown to be expressed in local lymph nodes and induce immune suppression of tumor immunity. Here we analyze the effect of IDO expression on prostate tumor growth using the transgenic adenocarcinoma of mouse prostate (TRAMP) animal model.

METHODS

Mice deficient in IDO expression were crossed to TRAMP mice and the time to the appearance of palpable tumors were measured. Immune histology was used to analyze the IDO expressing cells in tumors and in local lymph nodes. The levels of the substrate for IDO (tryptophane) and its product (kynurenine) was measured by HPLC.

RESULTS

We found that systemic IDO activity, determined as the kynurenine/tryptophan ratio in serum, correlated with the presence of palpable tumor. Immunohistological analysis showed increased numbers of IDO expressing cells in local lymph nodes. In tumors, IDO expression could be detected in the tumor stroma by both CD31+ and CD31(-) cells. Essentially no CD45+, IDO expressing cells could be detected in the tumors. The influence of IDO activity on tumor progression was analyzed by back-crossing TRAMP mice with IDO(-/-) animals and J-chain negative (J(-/-)) mice that have perturbed IDO activity. In both crosses a delayed tumor incidence was observed.

CONCLUSION

Our results argue for a role for IDO mediated immune suppression in the early stages of prostate cancer progression. However, since the intra-tumor IDO expression in J(-/-) mice was indistinguishable from that of C57BL/6 animals the IDO expression in the tumor tissue appears to be irrelevant for TRAMP tumor incidence.

Genistein and resveratrol, alone and in combination, suppress prostate cancer in SV-40 tag rats

BACKGROUND

Chemoprevention utilizing dietary agents is an effective means to slow the development of prostate cancer. We evaluated the potential additive and synergistic effects of genistein and resveratrol for suppressing prostate cancer in the Simian Virus-40 T-antigen (SV-40 Tag) targeted probasin promoter rat model, a transgenic model of spontaneously developing prostate cancer.

METHODS

Rats were fed genistein or resveratrol (250 mg/kg AIN-76A diet) alone and in combination, and a low-dose combination (83 mg genistein + 83 mg resveratrol/kg diet). Histopathology and mechanisms of action studies were conducted at 30 and 12 weeks of age, respectively.

RESULTS

Genistein, resveratrol, and the high-dose combination treatments suppressed prostate cancer. The low-dose combination did not elicit protection against prostate cancer and was most likely below the effective dose for causing significant histopathological changes. Total genistein and resveratrol concentrations in the blood reached 2,160 and 211 nM, respectively in rats exposed to the single treatments. Polyphenol treatments decreased cell proliferation and insulin-like growth factor-1 (IGF-1) protein expression in the prostate. In addition, genistein as a single agent induced apoptosis and decreased steroid receptor coactivator-3 (SRC-3) in the ventral prostate (VP).

CONCLUSIONS

Genistein and resveratrol, alone and in combination, suppress prostate cancer development in the SV-40 Tag model. Regulation of SRC-3 and growth factor signaling proteins are consistent with these nutritional polyphenols reducing cell proliferation and increasing apoptosis in the prostate.

The prostatic environment suppresses growth of androgen-independent prostate cancer xenografts: an effect influenced by testosterone

BACKGROUND

Interactions between prostate cancer cells and their surrounding stroma play an important role in the growth and maintenance of prostate tumors. To elucidate this further, we investigated how growth of androgen-dependent (AD) LNCaP and androgen-independent (AI) LNCaP-19 prostate tumors was affected by different microenvironments and androgen levels.

METHODS

Tumor cells were implanted subcutaneously and orthotopically in intact and castrated immunodeficient mice. Orthotopic tumor growth was followed by magnetic resonance imaging (MRI). Gene expression in the tumors was evaluated by means of microarray analysis and microvessel density (MVD) was analyzed using immunohistochemistry.

RESULTS

The results showed that LNCaP-19 tumors grew more rapidly at the subcutaneous site than in the prostate, where tumors were obviously inhibited. Castration of the mice did not affect ectopic tumors but did result in increased tumor growth in the prostatic environment. This effect was reversed by testosterone treatment. In contrast to LNCaP-19, the LNCaP cells grew rapidly in the prostate and castration reduced tumor development. Gene expression analysis of LNCaP-19 tumors revealed an upregulation of genes, inhibiting tumor growth (including ADAMTS1, RGS2 and protocadherin 20) and a downregulation of genes, promoting cell adhesion and metastasis (including N-cadherin and NRCAM) in the slow-growing orthotopic tumors from intact mice.

CONCLUSIONS

The results show that the prostatic environment has a varying impact on AD and AI tumor xenografts. Data indicate that the androgen-stimulated prostatic environment limits growth of orthotopic AI tumors through induction of genes that inhibit tumor growth and suppression of genes that promote cell adhesion and metastasis.

Interspecies comparison of prostate cancer gene-expression profiles reveals genes associated with aggressive tumors

Prostate cancer (PC) is a heterogeneous disease whose aggressive phenotype is the second leading cause of cancer-related death in men. The identification of key molecules and pathways that play a pivotal role in PC progression towards an aggressive form is crucial. A major effort towards this end has been taken by global analyses of gene expression profiles. However, the large body of data did not provide a definitive idea about the genes which are associated with the aggressive growth of PC. In order to identify such genes, we performed an interspecies comparison between several human data sets and high quality microarray data that we generated from the transgenic adenocarcinoma of mouse prostate (TRAMP) strain. The TRAMP PC mimics the histological and pathological appearance as well as the aggressive phenotype of human PC (huPC). Analysis of the microarray data, derived from microdissected TRAMP specimens removed at different stages of the disease yielded genetic signatures delineating the TRAMP PC development and progression. Comparison of the TRAMP data with a set of genes representing the core expression signature of huPC yielded a limited set genes. Some of these genes are known predictors of poor prognosis in huPC. Interestingly, the modulation of genes responsible for the invasive phenotype of huPC occurs in TRAMP already during the transition to prostate intraepithelial neoplasia (PIN) and onwards to localized tumors. We therefore suggest that critical oncogenic events leading to an aggressive phenotype of huPC can be studied in the PIN stage of TRAMP.

Early and delayed castrations confer a similar survival advantage in TRAMP mice

The most appropriate time to introduce androgen deprivation therapy for prostate cancer remains controversial. Our aim was to evaluate the effects of early versus delayed surgical castration on prostate cancer progression and survival in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model. TRAMP mice were randomly divided into three groups: the early castration group (on which castration was performed at the age of 4 weeks), the delayed castration group (on which castration was performed when abdominal tumours could be palpated), and the sham-castrated group. Mice were monitored daily throughout their lives until cancer-related death or the development of an obviously moribund appearance, at which time the individual mouse was killed. Androgen receptor expression in prostate tumours was also evaluated. The results shows that the average lifespan in early castration, delayed castration and sham-castrated groups were 54.1 weeks, 59.9 weeks and 39.1 weeks, respectively. Both early castration and delayed castration conferred a statistically significant survival advantage when compared with the sham-castrated group (P<0.001). However, the difference in lifespan between the early castration group and the delayed castration group was not statistically significant (P=0.85). The increase in lifespan in the TRAMP mice that received either early or delayed castration correlated with lower G/B value (genitourinary tract weight/body weight) at death than the sham-castrated mice. In conclusion, early and delayed castrations in TRAMP mice prolonged survival to a similar extent. This finding may provide a guide for clinical practice in prostate cancer therapy.

Characterization of SV-40 Tag rats as a model to study prostate cancer

Background

Prostate cancer is the second most frequently diagnosed cancer in men. Animal models that closely mimic clinical disease in humans are invaluable tools in the fight against prostate cancer. Recently, a Simian Virus-40 T-antigen (SV-40 Tag) targeted probasin promoter rat model was developed. This model, however, has not been extensively characterized; hence we have investigated the ontogeny of prostate cancer and determined the role of sex steroid receptor and insulin-like growth factor-1 (IGF-1) signaling proteins in the novel SV-40 Tag rat.

Methods

The SV-40 Tag rat was histopathologically characterized for time to tumor development, incidence and multiplicity and in the ventral, dorsal, lateral and anterior lobes of the prostate. Immunoassay techniques were employed to measure cell proliferation, apoptosis, and sex steroid receptor and growth factor signaling-related proteins. Steroid hormone concentrations were measured via coated well enzyme linked immunosorbent assay (ELISA) kits.

Results

Prostatic intraepithelial neoplasia (PIN) and well-differentiated prostate cancer developed as early as 2 and 10 weeks of age, respectively in the ventral prostate (VP) followed by in the dorsolateral (DLP). At 8 weeks of age, testosterone and dihydrotestosterone (DHT) concentrations in SV-40 Tag rats were increased when compared to non-transgenic rats. High cell proliferation and apoptotic indices were found in VP and DLP of transgenic rats. Furthermore, we observed increased protein expression of androgen receptor, IGF-1, IGF-1 receptor, and extracellular signal-regulated kinases in the prostates of SV-40 Tag rats.

Conclusion

The rapid development of PIN and prostate cancer in conjunction with the large prostate size makes the SV-40 Tag rat a useful model for studying prostate cancer. This study provides evidence of the role of sex steroid and growth factor proteins in prostate cancer development and defines appropriate windows of opportunity for preclinical trials and aids in the rational design of chemoprevention, intervention, regression, and therapeutic studies using prostate cancer rodent models.

Gene expression profile of mouse prostate tumors reveals dysregulations in major biological processes and identifies potential murine targets for preclinical development of human prostate cancer therapy

BACKGROUND

Translation of preclinical studies into effective human cancer therapy is hampered by the lack of defined molecular expression patterns in mouse models that correspond to the human counterpart. We sought to generate an open source TRAMP mouse microarray dataset and to use this array to identify differentially expressed genes from human prostate cancer (PCa) that have concordant expression in TRAMP tumors, and thereby represent lead targets for preclinical therapy development.

METHODS

We performed microarrays on total RNA extracted and amplified from eight TRAMP tumors and nine normal prostates. A subset of differentially expressed genes was validated by QRT-PCR. Differentially expressed TRAMP genes were analyzed for concordant expression in publicly available human prostate array datasets and a subset of resulting genes was analyzed by QRT-PCR.

RESULTS

Cross-referencing differentially expressed TRAMP genes to public human prostate array datasets revealed 66 genes with concordant expression in mouse and human PCa; 56 between metastases and normal and 10 between primary tumor and normal tissues. Of these 10 genes, two, Sox4 and Tubb2a, were validated by QRT-PCR. Our analysis also revealed various dysregulations in major biologic pathways in the TRAMP prostates.

CONCLUSIONS

We report a TRAMP microarray dataset of which a gene subset was validated by QRT-PCR with expression patterns consistent with previous gene-specific TRAMP studies. Concordance analysis between TRAMP and human PCa associated genes supports the utility of the model and suggests several novel molecular targets for preclinical therapy.

Axin2 expression identifies progenitor cells in the murine prostate

BACKGROUND

We previously reported that prostatic stem/progenitor cells are concentrated in the proximal region of prostatic ducts and express stem cell antigen 1 (Sca-1). As Wnt signaling is important for the maintenance of stem cells, we determined whether Sca-1 expressing cells also express Axin2, as Axin2 expression is highly suggestive of active Wnt signaling.

METHODS

Axin2 promoter reporter mice were used for whole mount and fluorescence activated cell sorting (FACS) analysis to determine its expression in the prostate. Axin2 expressing cells were also examined for the co-expression of Sca-1. We also used a chemical activator of Wnt signaling, BIO, to determine the effects of Wnt signaling on the growth of primary prostate cells in vitro.

RESULTS

We show that Axin2 expression is present in all lobes and is regulated by androgens with the highest Axin2 expression in the lateral and dorsal prostate. Furthermore, a fraction of Axin2 expressing cells co-express Sca-1, suggesting that some progenitor cells have active Wnt signaling. Lastly, we demonstrate that activation of the Wnt pathway may result in increased growth, consistent with a role for Wnt signaling in maintenance and/or expansion of the progenitor cell population.

CONCLUSION

Axin2 expressing cells that co-express Sca-1 are present in all prostate lobes suggesting that progenitor cells reside within the Wnt active population. An understanding of the basic biology of signaling pathways mediating growth in the prostate may lead to rational therapies to treat benign prostatic hyperplasia and prostate cancer.

Vasculature-targeted tumor necrosis factor-alpha increases the therapeutic index of doxorubicin against prostate cancer

BACKGROUND

Poor penetration and uneven distribution of doxorubicin in tumors limits the efficacy of this drug in patients with prostate cancer (PC). Aim of the study was to investigate whether pre-treatment with NGR-TNF, a tumor necrosis factor-alpha derivative able to target tumor vessels and alter vessel permeability, increases the penetration and the efficacy of doxorubicin in pre-clinical models of PC.

METHODS

Wild type C57BL/6 mice bearing androgen-independent TRAMP-C1 PC and transgenic adenocarcinoma of the mouse prostate (TRAMP) mice, which spontaneously develop PC and metastasis, were treated with repeated cycles of doxorubicin, administered either alone or following NGR-TNF. Tumor growth and drug uptake by cancer cells was evaluated.

RESULTS

Doxorubicin as a single agent blocked the growth of TRAMP-C1 cells in vitro but not in vivo. Pre-treatment of mice bearing subcutaneous TRAMP-C1 tumors with NGR-TNF favored doxorubicin penetration into the tumor mass, and in both TRAMP-C1 and TRAMP models significantly delayed tumor growth without increasing drug-related toxicity.

CONCLUSIONS

Pre-treatment with NGR-TNF significantly expanded the therapeutic index of doxorubicin in mouse models of hormone-dependent and -independent PC.

Effects of castration on the development of prostate adenocarcinoma from its precursor HGPIN and on the occurrence of androgen-independent, poorly differentiated carcinoma in TRAMP mice

Androgen ablation is thought to exert selective pressure for the development of androgen-independent forms of prostate cancer. This study was set up to investigate the effects of surgical castration on the development of prostate adenocarcinoma (ADC) from its precursor (high-grade prostate intraepithelial neoplasia (HGPIN)) and on the occurrence of androgen-independent, poorly differentiated carcinoma (PDC) in (C57Bl/6 transgenic adenocarcinoma of mouse prostate) TRAMP mice. It was found that castration cures HGPIN and ADC and prevents their further occurrence and growth, but has no effect on PDC. This indicates that in this model, PDC is not the progression of ADC favoured by androgen ablation and that its initiating cells are different from those of HGPIN and ADC.

Deletion of PSCA increases metastasis of TRAMP-induced prostate tumors without altering primary tumor formation

BACKGROUND

Prostate stem cell antigen (PSCA) is expressed in normal epithelium of various tissues, in embryos and adult animals. PSCA expression is upregulated in up to 70% of prostate tumors and metastases, and a subset of bladder and pancreatic cancers. However, its function is unknown. We studied the effect of targeted gene deletion of PSCA on normal organ development and prostate carcinogenesis.

METHODS

PSCA +/+, PSCA +/-, and PSCA -/- mice were bred and aged to 22 months. A cohort of animals was treated with gamma-irradiation at 2 and 6 months of age. PSCA knockout mice were crossed to TRAMP mice and TRAMP+ PSCA +/+, TRAMP+ PSCA +/-, and TRAMP+ PSCA -/- mice and offspring aged to 10 months of age. Tissues were analyzed by RT-PCR, histology, and immunohistochemistry for markers of proliferation, apoptosis, angiogenesis, and tumor progression.

RESULTS

PSCA knockout animals were viable, fertile and indistinguishable from wild-type littermates. Spontaneous or radiation-induced primary epithelial tumor formation was also similar in wild-type and PSCA knockout mice. We observed an increased frequency of metastasis in TRAMP+ PSCA heterozygous and knockout mice, compared to TRAMP+ wild-type mice. Metastases were largely negative for PSCA and androgen receptor. Cleaved-caspase 3 and CD31 staining was similar in all genotypes. Aurora-A and Aurora-B kinases were detected in the cytoplasm of PSCA heterozygous and knockout tumors, suggesting aberrant kinase function.

CONCLUSION

These data suggest that PSCA may play a role in limiting tumor progression in certain contexts, and deletion of PSCA may promote tumor migration and metastasis.

Origin of androgen-insensitive poorly differentiated tumors in the transgenic adenocarcinoma of mouse prostate model

Following castration, the transgenic adenocarcinoma of mouse prostate (TRAMP) model demonstrates rapid development of SV40-Tag-driven poorly differentiated tumors that express neuroendocrine cell markers. The cell population dynamics within the prostates of castrated TRAMP mice were characterized by analyzing the incorporation of 5-bromodeoxyuridine (BrdUrd) and the expression of SV40-Tag, synaptophysin, and androgen receptor (AR). Fourteen days postcastration, the remaining epithelial cells and adenocarcinoma cells were nonproliferative and lacked detectable SV40-Tag or synaptophysin expression. In contrast, morphologically distinct intraglandular foci were identified which expressed SV40-Tag, synaptophysin, and Ki67, but that lacked AR expression. These proliferative SV40-Tag and synaptophysin-expressing intraglandular foci were associated with the rare BrdUrd-retaining cells. These foci expanded rapidly in the postcastration prostate environment, in contrast to the AR- and SV40-Tag-expressing adenocarcinoma cells that lost SV40-Tag expression and underwent apoptosis after castration. Intraglandular foci of synaptophysin-expressing cells were also observed in the prostates of intact TRAMP mice at a comparable frequency; however, they did not progress to rapidly expanding tumors until much later in the life of the mice. This suggests that the foci of neuroendocrine-like cells that express SV40-Tag and synaptophysin, but lack AR, arise independent of androgen-deprivation and represent the source of the poorly differentiated tumors that are the lethal phenotype in the TRAMP model.

Loss of Nkx3.1 expression in the transgenic adenocarcinoma of mouse prostate model

BACKGROUND

The transgenic adenocarcinoma of mouse prostate (TRAMP) model has been extensively characterized at the histological and molecular levels, and has been shown to mimic significant features of human prostate cancer. However, the status of Nkx3.1 expression in the TRAMP model has not been elucidated.

METHODS

Immunohistochemical analyses were performed using dorsal, lateral, and ventral prostate (VP) lobes from ages 6 to 30 weeks. Quantitative RT-PCR analyses were performed to determine relative mRNA expression.

RESULTS

Heterogeneous loss of Nkx3.1 was observed in hyperplastic lesions of the ventral, dorsal, and lateral lobes. At 6 weeks of age, the ventral lobe displayed profound loss of Nkx3.1. Diminished Nkx3.1 protein was observed in well- to moderately-differentiated cancer lesions of all lobes. Poorly differentiated (PD) tumors stained negatively for Nkx3.1. Quantitative RT-PCR analyses revealed the presence of Nkx3.1 mRNA in each lobe at all ages, albeit reduced to variable levels.

CONCLUSIONS

These data suggest that disease progression in the TRAMP model may be driven by loss of function of Nkx3.1, in addition to p53 and Rb. Lobe-specific disease progression in the TRAMP model correlates with the reduction of Nkx3.1 protein. Regulation of Nkx3.1 expression during tumorigenesis appears to occur by post-transcriptional and post-translational mechanisms.

A stroma targeted therapy enhances castration effects in a transplantable rat prostate cancer model

BACKGROUND

Castration results in a major involution of the normal prostate gland. This process is initiated by effects in the prostate stroma and vasculature. Castration-induced regression of androgen sensitive prostate tumors is however less prominent and hypothetically this could be related to a limited stromal/vascular response. We therefore used animal tumor models to explore the importance of stroma and vascular effects, and if castration effects could be enhanced by a simultaneous therapy targeting the tumor stroma.

METHODS

Using rats with Dunning PAP and H tumors, stereological methods, immunohistochemistry, and Western blotting, we studied the tumor response 7 and 28 days after castration and after the addition of stroma targeted therapies.

RESULTS

In the normal ventral prostate (VP) nuclear androgen receptors (AR) were rapidly downregulated after castration. In contrast, the Dunning tumors downregulated the AR in the cancerous epithelium, but not in the surrounding stroma. Vascular regulators such as the angiopoietins, tie 2, and PDGF-Rbeta were not decreased in the stroma after castration, as observed in the VP, creating an environment that prevents vascular involution. When a tumor stroma targeted therapy inhibiting the tie 2 receptor and the PDGF-Rbeta simultaneously was added to castration it resulted in a decreased vascular density, increased tumor cell apoptosis and decreased tumor growth compared to castration alone.

CONCLUSIONS

The stroma in highly differentiated androgen sensitive Dunning tumors is apparently androgen insensitive. If this unresponsive stroma is targeted the effects of castration can be enhanced.

Rye bran diet increases epithelial cell apoptosis and decreases epithelial cell volume in TRAMP (transgenic adenocarcinoma of the mouse prostate) tumors

A rye bran diet has been suggested to retard prostate cancer growth and increase tumor cell apoptosis in animal models and in men with prostate cancer. Transgenic mice designed to develop prostate cancer (transgenic adenocarcinoma of the mouse prostate, TRAMP) were therefore treated with a rye bran diet. TRAMP mice were fed a rye bran (n = 13) or a control diet (n = 15) from 4 to 24 wk of age. Tumor histology, cell proliferation, and apoptosis were accessed using stereological and immunohistochemical techniques. In the dorsolateral prostate lobe in TRAMP mice, epithelial cell apoptosis was increased by 31%, and the volume fraction of epithelial cells was reduced by 20% (P < 0.05) in the rye bran-treated group compared with the control diet group. There were, however, no significant changes detected in lobe weights or tumor grade. In conclusion, a rye bran diet increases epithelial apoptosis and reduces the epithelial cell fraction in TRAMP tumors.

The Magnitude of Early Castration-Induced Primary Tumour Regression in Prostate Cancer Does Not Predict Clinical Outcome

INTRODUCTION

This study was designed to test whether early castration-induced short-term cellular changes in primary prostate tumours could predict clinical outcome in advanced disease.

PATIENTS AND METHODS

Biopsies from 83 patients obtained before and within two weeks after surgical castration were investigated. Tumour epithelial cell apoptosis, proliferation, and prostate specific antigen (PSA) levels were quantified using immunohistochemistry, laser capture micro-dissection, and real time RT-PCR. Cellular effects were related to changes in serum PSA levels and clinical outcome.

RESULTS

Decreased proliferation and PSA mRNA levels, and increased apoptosis were observed in most tumours. These early cellular responses were not correlated to each other and did not predict serum PSA response or cancer-specific survival. A nadir PSA level below 1 ng/ml predicted a longer cancer-specific survival after castration therapy.

CONCLUSION

Castration therapy causes primary tumour regression in most patients with advanced prostate cancer, but these primary tumour effects are not predictive for systemic disease control. Studies of early changes in metastases during hormonal therapy will probably give more predictive information for clinical outcome than further studies in primary tumours.

Breast cancer resistance protein-mediated efflux of androgen in putative benign and malignant prostate stem cells

Malignantly transformed stem cells represent a potential common nidus for the primary cancer and the recurrent cancer that arises after treatment failure. Putative prostate stem cells and prostate tumor stem cells in benign and malignant human prostate tissue, in primary human prostate xenografts, and in the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse model of prostate cancer, are defined by expression of breast cancer resistance protein (BCRP), a marker of pluripotent hematopoietic, muscle, and neural stem cells, and by an absence of androgen receptor (AR) protein. Inhibition of BCRP-mediated efflux of dihydrotestosterone by novobiocin or fumitremorgin C in a rat prostate progenitor cell line that expresses BCRP and AR mRNAs, but minimal AR protein, results in stabilization and nuclear translocation of AR protein, providing a mechanism for lack of AR protein in BCRP-expressing stem cells. In both benign and malignant human prostate tissue, the rare epithelial cells that express BCRP and lack AR protein are localized in the basal cell compartment, survive androgen deprivation, and maintain proliferative potential in the hypoxic, androgen-deprived prostate. Putative prostate tumor stem cells that express BCRP but not AR protein in TRAMP are the source of a BCRP-negative and AR-negative, Foxa2- and SV40Tag-expressing, transit amplifying compartment that progresses to the poorly differentiated carcinomas that arise rapidly after castration. Therefore, BCRP expression isolates prostate stem/tumor stem cells from the prostate tissue microenvironment through constitutive efflux of androgen, protecting the putative tumor stem cells from androgen deprivation, hypoxia, or adjuvant chemotherapy, and providing the nidus for recurrent prostate cancer.