Enforced expression of FGF-7 promotes epithelial hyperplasia whereas a dominant negative FGFR2iiib promotes the emergence of neuroendocrine phenotype in prostate glands of transgenic mice

Vascularized fascial flap for reconstruction of combined oral mucosa-mandibular defects: The multi-modal biological assessment

OBJECTIVE

The reconstruction of composite defects in the oral and maxillofacial region using vascularized fascial flaps, such as the fibular, iliac, and temporal fascial flaps, has gained increasing attention among surgeons. However, there remains uncertainty regarding the suitability of fascial flaps as transplants, as well as their healing processes and outcomes, due to their non-mucosal nature. This study aims to comprehensively assess the biological aspects of vascularized fascial flaps at clinical, histological, and genetic levels, with the goal of providing essential biological references for their clinical application.

STUDY DESIGN

This study enrolled three patients who underwent reconstruction of combined oral mucosa-mandibular defects using fibular vascularized fascial flaps between 2020 and 2023. Data regarding changes in the appearance of the fascial flaps, bulk-RNA sequencing, and histological slices of initial fascia, initial gingiva, and transformed fascia were collected and analyzed.

RESULTS

Within three months, the fascial flaps exhibited rapid epithelial coverage and displayed distinct characteristics resembling mucosa. High-throughput RNA sequencing analyses and histological slices revealed that the transformed fascia exhibited tissue structures similar to mucosa and demonstrated unique advantages in promoting blood vessel formation and reducing scarring through the high-level expression of relevant genes.

CONCLUSION

These findings emphasize the potential and feasibility of utilizing vascularized fascial flaps for oral mucosa reconstruction, establishing their unique advantage as transplant materials, and providing significant biological information and references for their selection and clinical application.

Prostate cancer cell heterogeneity and plasticity: Insights from studies of genetically-engineered mouse models

Although prostate adenocarcinoma lacks distinguishable histopathological subtypes, prostate cancer displays significant inter- and intratumor heterogeneity at the molecular level and with respect to disease prognosis and treatment response. In principle, understanding the basis for prostate cancer heterogeneity can help distinguish aggressive from indolent disease, and help overcome castration-resistance in advanced prostate cancer. In this review, we will discuss recent advances in understanding the cell types of origin, putative cancer stem cells, and tumor plasticity in prostate cancer, focusing on insights from studies of genetically engineered mouse models (GEMMs). We will also outline future directions for investigating tumor heterogeneity using mouse models of prostate cancer.

2b or Not 2b: How Opposing FGF Receptor Splice Variants Are Blocking Progress in Precision Oncology

More than ten thousand peer-reviewed studies have assessed the role of fibroblast growth factors (FGFs) and their receptors (FGFRs) in cancer, but few patients have yet benefited from drugs targeting this molecular family. Strategizing how best to use FGFR-targeted drugs is complicated by multiple variables, including RNA splicing events that alter the affinity of ligands for FGFRs and hence change the outcomes of stromal-epithelial interactions. The effects of splicing are most relevant to FGFR2; expression of the FGFR2b splice isoform can restore apoptotic sensitivity to cancer cells, whereas switching to FGFR2c may drive tumor progression by triggering epithelial-mesenchymal transition. The differentiating and regulatory actions of wild-type FGFR2b contrast with the proliferative actions of FGFR1 and FGFR3, and may be converted to mitogenicity either by splice switching or by silencing of tumor suppressor genes such as CDH1 or PTEN. Exclusive use of small-molecule pan-FGFR inhibitors may thus cause nonselective blockade of FGFR2 isoforms with opposing actions, undermining the rationale of FGFR2 drug targeting. This splice-dependent ability of FGFR2 to switch between tumor-suppressing and -driving functions highlights an unmet oncologic need for isoform-specific drug targeting, e.g., by antibody inhibition of ligand-FGFR2c binding, as well as for more nuanced molecular pathology prediction of FGFR2 actions in different stromal-tumor contexts.

The FGF/FGFR system in the physiopathology of the prostate gland

Fibroblast growth factors (FGFs) are a family of proteins possessing paracrine, autocrine, or endocrine functions in a variety of biological processes, including embryonic development, angiogenesis, tissue homeostasis, wound repair, and cancer. Canonical FGFs bind and activate tyrosine kinase FGF receptors (FGFRs), triggering intracellular signaling cascades that mediate their biological activity. Experimental evidence indicates that FGFs play a complex role in the physiopathology of the prostate gland that ranges from essential functions during embryonic development to modulation of neoplastic transformation. The use of ligand- and receptor-deleted mouse models has highlighted the requirement for FGF signaling in the normal development of the prostate gland. In adult prostate, the maintenance of a functional FGF/FGFR signaling axis is critical for organ homeostasis and function, as its disruption leads to prostate hyperplasia and may contribute to cancer progression and metastatic dissemination. Dissection of the molecular landscape modulated by the FGF family will facilitate ongoing translational efforts directed toward prostate cancer therapy.

Neuroendocrine cells of prostate cancer: biologic functions and molecular mechanisms

Prostate cancer (PCa) is a major health risk for older men worldwide. Existing systemic therapies mostly target androgen receptor (AR). Although treatments are initially effective, the disease always recurs. A potential mechanism for the treatment failure is that PCa contains, in addition to the AR-positive luminal type tumor cells, a small component of neuroendocrine (NE) cells. The function of NE cells in PCa remains poorly understood, and one important characteristic of these cells is their lack of expression of AR and resistance to hormonal therapy. In addition, many patients develop the more aggressive small-cell neuroendocrine carcinoma (SCNC) after hormonal therapy. Although this clinical phenomenon of disease transformation from adenocarcinoma to SCNC is well established, the cell of origin for SCNC remains unclear. Recently, loss of function of Rb and TP53 and amplification and overexpression of MYCN and Aurora A kinase have been identified as important biomarkers and potential disease drivers. In this article, we systematically review the histology of normal prostate and prostate cancer including the main histologic types: adenocarcinoma and SCNC. We also review the findings from many studies using cellular and animal models as well as human specimens that attempt to understand the molecular mechanisms of treatment failure, disease progression, and tumor transformation from adenocarcinoma to SCNC.

Intrinsic FGFR2 and Ectopic FGFR1 Signaling in the Prostate and Prostate Cancer

Advanced castrate-resistant prostate cancer (CRPC) is a poorly prognostic disease currently lacking effective cure. Understanding the molecular mechanism that underlies the initiation and progression of CRPC will provide new strategies for treating this deadly disease. One candidate target is the fibroblast growth factor (FGF) signaling axis. Loss of the intrinsic FGF7/FGF10-type 2 FGF receptor (FGFR2) pathway and gain of the ectopic type 1 FGF receptor (FGFR1) pathway are associated with the progression to malignancy in prostate cancer (PCa) and many other epithelial originating lesions. Although FGFR1 and FGFR2 share similar amino acid sequences and structural domains, the two transmembrane tyrosine kinases elicit distinctive, even sometime opposite signals in cells. Recent studies have revealed that the ectopic FGFR1 signaling pathway contributes to PCa progression via multiple mechanisms, including promoting tumor angiogenesis, reprogramming cancer cell metabolism, and potentiating inflammation in the tumor microenvironment. Thus, suppression of FGFR1 signaling can be an effective novel strategy to treat CRPC.

The host microenvironment influences prostate cancer invasion, systemic spread, bone colonization, and osteoblastic metastasis

Prostate cancer (PCa) is the second leading cause of cancer death in men worldwide. Most PCa deaths are due to osteoblastic bone metastases. What triggers PCa metastasis to the bone and what causes osteoblastic lesions remain unanswered. A major contributor to PCa metastasis is the host microenvironment. Here, we address how the primary tumor microenvironment influences PCa metastasis via integrins, extracellular proteases, and transient epithelia-mesenchymal transition (EMT) to promote PCa progression, invasion, and metastasis. We discuss how the bone-microenvironment influences metastasis; where chemotactic cytokines favor bone homing, adhesion molecules promote colonization, and bone-derived signals induce osteoblastic lesions. Animal models that fully recapitulate human PCa progression from primary tumor to bone metastasis are needed to understand the PCa pathophysiology that leads to bone metastasis. Better delineation of the specific processes involved in PCa bone metastasize is needed to prevent or treat metastatic PCa. Therapeutic regimens that focus on the tumor microenvironment could add to the PCa pharmacopeia.

Activation of FGF2-FGFR signaling in the castrated mouse prostate stimulates the proliferation of basal epithelial cells

The prostate gland is unique in that it undergoes rapid regression following castration but regenerates completely once androgens are replaced. Residual ductal components play an important role in the regeneration of a fully functional prostate. In this study, to examine how androgen status affects prostate structure and components, we conducted histopathological studies of the involuted and regenerated mouse dorsolateral prostate (DLP). In the castrated mouse DLP, the number of luminal epithelial cells decreased in a time-dependent manner. On Day 14 postandrogen replacement, the number of luminal epithelial cells was completely restored to the baseline level. In contrast, the number of basal epithelial cells gradually increased in the castrated mouse prostate. The Ki67-labeling index of prostate basal epithelial cells was significantly increased after castration. The number of basal epithelial cells decreased to baseline after androgen replacement. After castration, mRNA expression levels of specific growth factors, such as Fgf2, Fgf7, Hgf, Tgfa, and Tgfb, were relatively abundant in whole mouse DLPs. In organ culture experiments, basal epithelial proliferation was recapitulated in the absence of dihydrotestosterone (DHT). The proliferation of basal epithelial cells in the absence of DHT was suppressed by treatment with an FGF receptor inhibitor (PD173074). Moreover, FGF2 treatment directly stimulated the proliferation of basal epithelial cells. Taken together, these data indicated that the FGF2-FGF receptor signal cascade in the prostate gland may be one of the pathways stimulating the proliferation of basal epithelial cells in the absence of androgens.

Current mouse and cell models in prostate cancer research

Mouse models of prostate cancer (PCa) are critical for understanding the biology of PCa initiation, progression, and treatment modalities. Here, we summarize recent advances in PCa mouse models that led to new insights into specific gene functions in PCa. For example, the study of transgenic mice with TMPRSS2/ERG, an androgen-regulated fusion protein, revealed its role in developing PCa precursor lesions, prostate intraepithelial neoplasia; however, it is not sufficient for PCa development. Double deficiency of Pten and Smad4 leads to a high incidence of metastatic PCa. Targeted deletion of Pten in castration-resistant Nkx3-1-expressing cells results in rapid carcinoma formation after androgen-mediated regeneration, indicating that progenitor cells with luminal characteristics can play a role in initiation of PCa. Transgenic mice with activated oncogenes, growth factors, and steroid hormone receptors or inactivated tumor suppressors continue to provide insights into disease progression from initiation to metastasis. Further development of new PCa models with spatial and temporal regulation of candidate gene expression will probably enhance our understanding of the complex events that lead to PCa initiation and progression, thereby invoking novel strategies to combat this common disease in men.

Genetically engineered mouse models of prostate cancer

Despite major improvement in treatment of early stage localised prostate cancer, the distinction between indolent tumors and those that will become aggressive, as well as the lack of efficient therapies of advanced prostate cancer, remain major health problems. Genetically engineered mice (GEM) have been extensively used to investigate the molecular and cellular mechanisms underlying prostate tumor initiation and progression, and to evaluate new therapies. Moreover, the recent development of conditional somatic mutagenesis in the mouse prostate offers the possibility to generate new models that more faithfully reproduce the human disease, and thus should contribute to improve diagnosis and treatments. The strengths and weaknesses of various models will be discussed, as well as future opportunities.

Regional distribution of neuroendocrine cells in the urogenital duct system of the male rat

BACKGROUND

Neuroendocrine (NE) cells are frequently present in the human prostate and urethra, whereas they are lacking in the other urogenital organs. This study was undertaken as there are only few detailed studies available on the distribution, form and function of NE cells and the structure of excretory ducts of the accessory sex organs in the male rat.

METHODS

Systematic gross anatomical dissections were combined with immunohistochemical and electron microscopic studies of the excretory ducts of the urogenital glands in male rats, with particular focus on the distribution and ultrastructure of the NE cells.

RESULTS

The topography and structure of the excretory ducts of the different glands were characterized in detail and analyzed for the distribution of NE cells. These are present (in falling frequencies) in the ducts of seminal vesicles and ventral and lateral prostate and are rare in ducts of coagulating gland, dorsal prostate, urethral epithelium, and excretory ducts of the (bulbo) urethral glands. They are absent in the respective glands proper, the deferent duct and ejaculatory ampulla. Approximately 40% of the NE cells of the ventral prostate ducts are of the "open" type, whereas these are less frequent (14%) in the seminal vesicle ducts, where the "closed" type prevails.

CONCLUSIONS

NE cells are present in unequal quantities in the excretory ducts of the accessory sex glands, but they are absent in the glands proper and the deferent ducts. This distribution pattern points to a strictly localized function and differentiation potency of NE precursor cells.

Molecular genetics of prostate cancer: new prospects for old challenges

Despite much recent progress, prostate cancer continues to represent a major cause of cancer-related mortality and morbidity in men. Since early studies on the role of the androgen receptor that led to the advent of androgen deprivation therapy in the 1940s, there has long been intensive interest in the basic mechanisms underlying prostate cancer initiation and progression, as well as the potential to target these processes for therapeutic intervention. Here, we present an overview of major themes in prostate cancer research, focusing on current knowledge of principal events in cancer initiation and progression. We discuss recent advances, including new insights into the mechanisms of castration resistance, identification of stem cells and tumor-initiating cells, and development of mouse models for preclinical evaluation of novel therapuetics. Overall, we highlight the tremendous research progress made in recent years, and underscore the challenges that lie ahead.

Effect of transforming growth factor α overexpression on urogenital organ development in mouse

Transforming growth factor-α (TGFα) promotes cell proliferation by binding to the epidermal growth factor receptor (EGFR). TGFα and EGFR overexpression have been reported in various human cancers. However, whether TGFα induces cancer by itself is unknown in urogenital organs. To investigate whether TGFα overexpression induces carcinogenesis in urogenital organs, we analyzed the phenotypes of urogenital organs in male TGFα transgenic (TG) mice of the CD1 strain. Urogenital organs including the kidney, bladder, prostate, seminal vesicles, testes, and epididymis were isolated from 4- to 48-week-old TGFα TG and wild-type (WT) CD1 mice. Prostates were separated into anterior prostate (AP), dorsolateral prostate (DLP), and ventral prostate (VP). Neither tumor formation nor epithelial hyperplasia was observed in the TGFα TG mouse urogenital organs that we have investigated. Histopathologically, in prostate, we found an increased number of p63-positive basal epithelial cells in the TGFα TG mice AP and DLP. There was no morphological change in the stromal component, such as hypercellular stroma or fibrosis. However, bladder weight was greater in TGFα TG mice than that in WT mice, and distended bladders were observed macroscopically in 19 of 20 TGFα TG mice over 20 weeks of age. Ki67 labeling index was increased significantly in the TGFα TG mouse urethral epithelium, whereas neither epithelial hyperplasia nor hypertrophy was observed. In conclusion, our results suggest that TGFα overexpression in mouse urogenital organs alone may not be responsible for tumor formation and epithelial hyperplasia, but is involved in bladder outlet obstruction.

Modeling prostate cancer: a perspective on transgenic mouse models

Despite considerable success in treatment of early stage localized prostate cancer (PC), acute inadequacy of late stage PC treatment and its inherent heterogeneity poses a formidable challenge. Clearly, an improved understanding of PC genesis and progression along with the development of new targeted therapies are warranted. Animal models, especially, transgenic immunocompetent mouse models, have proven to be the best ally in this respect. A series of models have been developed by modulation of expression of genes implicated in cancer-genesis and progression; mainly, modulation of expression of oncogenes, steroid hormone receptors, growth factors and their receptors, cell cycle and apoptosis regulators, and tumor suppressor genes have been used. Such models have contributed significantly to our understanding of the molecular and pathological aspects of PC initiation and progression. In particular, the transgenic mouse models based on multiple genetic alterations can more accurately address the inherent complexity of PC, not only in revealing the mechanisms of tumorigenesis and progression but also for clinically relevant evaluation of new therapies. Further, with advances in conditional knockout technologies, otherwise embryonically lethal gene changes can be incorporated leading to the development of new generation transgenics, thus adding significantly to our existing knowledge base. Different models and their relevance to PC research are discussed.

Role of stromal tenascin-C in mouse prostatic development and epithelial cell differentiation

Deregulation of epithelial-stromal interactions is considered to play a critical role in the initiation and promotion of benign prostatic hyperplasia (BPH) and prostate carcinoma (PCa). Expression of tenascin-C (TN-C), an extracellular matrix (ECM) glycoprotein, is reportedly higher in BPH and PCa as compared with normal prostate. Remodeling of the ECM alters the homeostatic balance between epithelium and stroma, resulting in physiological changes in cellular functions. To investigate the role of TN-C in prostatic development and differentiation, we evaluated the morphological phenotype of TN-C knockout (KO) mouse prostate (ventral: VP, dorsolateral: DLP, and anterior: AP) and examined tissue recombinants composed of adult mouse DLP epithelium and fetal TN-C KO urogenital sinus mesenchyme (UGM). Histological analysis showed epithelial cell clusters protruding into the ductal lumens in TN-C KO AP and DLP. Interestingly, binucleated cells appeared in epithelium of TN-C KO DLP at 8 weeks. Simultaneously, androgen receptor (AR)-positive cells were decreased in TN-C KO epithelia. Similar to the TN-C KO phenotype, protruded epithelial clusters, binucleated cells, and AR-negative nuclei were induced in DLP epithelium by recombining with TN-C KO UGM. Our results suggest that stromal TN-C might be involved in maintaining epithelial cytodifferentiation, morphogenesis, and androgen receptor expression of normal prostate glands in adult mice.

Protease-activated receptor-1 upregulates fibroblast growth factor 7 in stroma of benign prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is characterized by abnormal epithelial and stromal proliferation causing urinary obstruction. Prostate growth is regulated by a variety of growth factors secreted from the stroma, including fibroblast growth factor 7 (FGF-7), a potent epithelial-specific growth factor which is increased in hyperplastic prostate. However, the mediator(s) of FGF-7 over-expression is unclear. Protease-activated receptor-1 (PAR-1) is a G-protein coupled receptor known to induce multiple biological processes, but its effect on BPH pathogenesis is mostly unknown. The aim of this study was to investigate the role of PAR-1 as a mediator of BPH development.

METHODS

PAR-1 expression was investigated in BPH and normal prostate tissues by immunohistochemistry. Prostate stromal cells were isolated from BPH specimens, cultured and immunohistochemically characterized. Cultured stromal cells were stimulated with PAR-1 agonists, and extracellular-signal regulated kinase (ERK1/2) activation and cell proliferation were examined. PAR-1 mediated FGF-7 production by cultured stromal cells was assessed by RT-PCR and immunoassays, and verified by small interfering RNA (siRNA).

RESULTS

PAR-1 expression was increased in BPH stroma. In stromal cells isolated from BPH tissues, PAR-1 agonists activated ERK1/2 in a time- and concentration-dependent manner and with resultant enhanced cell proliferation. Pertussis toxin-sensitive G protein/(betagamma-subunits)-phosphatidylinositol 3-kinase and protein kinase C pathways were involved in ERK1/2 phosphorylation. PAR-1 activation strikingly induced FGF-7 production from cultured stromal cells mediated predominantly via ERK1/2 signaling pathway, and PAR-1 siRNA decreased the elicited FGF-7 upregulation.

CONCLUSIONS

The expression and function of PAR-1 in BPH stroma indicate PAR-1 may play important roles in BPH pathogenesis.

Advances in mouse models of prostate cancer

Advances in science and technology have allowed us to manipulate the mouse genome and analyse the effect of specific genetic alterations on the development of prostate cancer in vivo. We can now analyse the molecular basis of initiation, invasion and progression to metastatic disease. The current mouse models utilise knockout, knock-in or conditional regulation of expression using Cre-loxP technology. Genes that have been targeted include homeobox genes, tumour suppressors and oncogenes, growth factors (and their receptors), steroid hormones and cell-cycle regulators, as well as pro- and anti-apoptotic proteins. Bigenic models indicate that that two 'hits' are required for progression from intra-epithelial neoplasia (PIN) to invasion carcinoma, and two to five hits are needed for metastasis. Here, we discuss the numerous models that mimic various aspects of the disease process, such as PIN, locally invasive adenocarcinoma and metastatic disease. Currently the PB-Cre4 x PTEN(loxP/loxP) mouse is the only model that spans the entire continuum from initiation to local invasion and metastasis. Such mouse models increase our understanding of the disease process and provide targets for novel therapeutic approaches. Hopefully, the transgenic models will become inducible and ultimately allow both temporal and spatial gene inactivation. Compound mutational models will also develop further, with double and triple knock-in or knockout systems adding to our knowledge of the interaction between different signalling cascades.

Enhanced paracrine FGF10 expression promotes formation of multifocal prostate adenocarcinoma and an increase in epithelial androgen receptor

Enhanced mesenchymal expression of FGF10 led to the formation of multifocal PIN or prostate cancer. Inhibition of epithelial FGFR1 signaling using DN FGFR1 led to reversal of the cancer phenotype. A subset of the FGF10-induced carcinoma was serially transplantable. Paracrine FGF10 led to an increase in epithelial androgen receptor and synergized with cell-autonomous activated AKT. Our observations indicate that stromal FGF10 expression may facilitate the multifocal histology observed in prostate adenocarcinoma and suggest the FGF10/FGFR1 axis as a potential therapeutic target in treating hormone-sensitive or refractory prostate cancer. We also show that transient exposure to a paracrine growth factor may be sufficient for the initiation of oncogenic transformation.

Development-related expression of KGF and FGF-10 mRNA in the canine prostate gland

Keratinocyte growth factor (KGF) and fibroblast growth factor 10 (FGF-10) are stromal-derived growth factors that interact with their epithelial FGFR2 receptors to mediate stromal--epithelial cell interaction within the prostate gland. This study was conducted to compare the development-related mRNA expression of KGF, FGF-10 and their receptor FGFR2 in immature and mature canine prostate glands. In addition, their expression levels were correlated with the differentiation of stromal cells using vimentin as a mesenchymal cell marker. Quantitative mRNA expression was assessed by real-time polymerase chain reaction (PCR) and the results were expressed as relative mRNA expression of the target gene, which was normalized to the GAPDH reference gene. mRNA analysis revealed a differential expression of KGF, FGF-10 and FGFR2 receptor by the prostate glands of immature and mature dogs. The results showed a 7.3- and 9-fold decrease in mRNA expression of KGF and FGF-10 by mature and immature prostate glands respectively. However, there was no significant change in FGFR2 receptor mRNA expression by mature or immature prostate glands. This downregulation of KGF and FGF-10 expression was associated with a 15-fold decrease in vimentin expression. These results indicate that KGF and FGF-10 expression varied according to the differentiation status of stromal cells and might reflect differential developmental requirements of immature and mature canine prostate glands.

Estrogens and aspects of prostate disease

Estrogens have long been associated with the processes involved in prostate carcinogenesis, particularly in cancer suppression. However, the synergistic influence of low concentrations of estrogens, together with androgens, in promoting aberrant growth of the gland has also been recognized. As new insights into the complex molecular events implicated in growth regulation of the prostate are revealed, the role of the estrogens has become clearer. The present review considers this role in relation to the pathogenesis of prostate cancer and the potential cancer-repressive influence of the dietary estrogens.

The impact of cell adhesion changes on proliferation and survival during prostate cancer development and progression

In the normal prostate epithelium, androgen receptor (AR) negative basal epithelial cells adhere to the substratum, while AR expressing secretory cells lose substratum adhesion. In contrast, prostate cancer cells both express AR and adhere to a tumor basement membrane. In this review, we describe the differential expression of integrins, growth factor receptors (GFRs), and AR in normal and cancerous epithelium. In addition, we discuss how signals from integrins, GFRs, and AR are integrated to regulate the proliferation and survival of normal and malignant prostate epithelial cells. While cell adhesion is likely of great importance when considering therapeutic approaches for treatment of metastatic prostate cancer, no data on integrin expression are available from tissues of prostate cancer metastasis. However, several drug targets that are upregulated after androgen ablative therapy regulate cell adhesion and thus novel targeted therapies indirectly interfere with cell adhesion mechanisms in prostate cancer cells.

Keratinocyte growth factor expression and activity in cancer: implications for use in patients with solid tumors

Keratinocyte growth factor (KGF) is a locally acting epithelial mitogen that is produced by cells of mesenchymal origin and has an important role in protecting and repairing epithelial tissues. Use of recombinant human KGF (palifermin) in patients with hematologic malignancies reduces the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. These results suggest that KGF may be useful in the treatment of patients with other kinds of tumors, including those of epithelial origin. However, its application in this context raises issues that were not pertinent to its use in hematologic cancer because epithelial tumor cells, unlike blood cells, often express the KGF receptor (FGFR2b). Thus, it is important to examine whether KGF could promote the growth of epithelial tumors or protect such tumor cells from the effects of chemotherapy agents. Analyses of KGF and FGFR2b expression in tumor specimens and of KGF activity on transformed cells in vitro and in vivo do not indicate a definitive role for KGF in tumorigenesis. On the contrary, restoring FGFR2b expression to certain malignant cells can induce cell differentiation or apoptosis. However, other observations suggest that, in specific situations, KGF may contribute to epithelial tumorigenesis. Thus, further studies are warranted to examine the nature and extent of KGF involvement in these settings. In addition, clinical trials in patients with solid tumors are underway to assess the potential benefits of using KGF to protect normal tissue from the adverse effects of chemoradiotherapy and its possible impact on clinical outcome.

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.

BMP7 inhibits branching morphogenesis in the prostate gland and interferes with Notch signaling

The mouse prostate gland develops by branching morphogenesis from the urogenital epithelium and mesenchyme. Androgens and developmental factors, including FGF10 and SHH, promote prostate growth (Berman, D.M., Desai, N., Wang, X., Karhadkar, S.S., Reynon, M., Abate-Shen, C., Beachy, P.A., Shen, M.M., 2004. Roles for Hedgehog signaling in androgen production and prostate ductal morphogenesis. Dev. Biol. 267, 387-398; Donjacour, A.A., Thomson, A.A., Cunha, G.R., 2003. FGF-10 plays an essential role in the growth of the fetal prostate. Dev. Biol. 261, 39-54), while BMP4 signaling from the mesenchyme has been shown to suppresses prostate branching (Lamm, M.L., Podlasek, C.A., Barnett, D.H., Lee, J., Clemens, J.Q., Hebner, C.M., Bushman, W., 2001. Mesenchymal factor bone morphogenetic protein 4 restricts ductal budding and branching morphogenesis in the developing prostate. Dev. Biol. 232, 301-314). Here, we show that Bone Morphogenetic Protein 7 (BMP7) restricts branching of the prostate epithelium. BMP7 is expressed in the periurethral urogenital mesenchyme prior to formation of the prostate buds and, subsequently, in the prostate epithelium. We show that BMP7(lacZ/lacZ) null prostates show a two-fold increase in prostate branching, while recombinant BMP7 inhibits prostate morphogenesis in organ culture in a concentration-dependent manner. We further explore the mechanisms by which the developmental signals may be interpreted in the urogenital epithelium to regulate branching morphogenesis. We show that Notch1 activity is associated with the formation of the prostate buds, and that Notch1 signaling is derepressed in BMP7 null urogenital epithelium. Based on our studies, we propose a model that BMP7 inhibits branching morphogenesis in the prostate and limits the number of domains with high Notch1/Hes1 activity.

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.

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.

Mutation of the androgen receptor causes oncogenic transformation of the prostate

Recent evidence demonstrates that the androgen receptor (AR) continues to influence prostate cancer growth despite medical therapies that reduce circulating androgen ligands to castrate levels and/or block ligand binding. Whereas the mutation, amplification, overexpression of AR, or cross-talk between AR and other growth factor pathways may explain the failure of androgen ablation therapies in some cases, there is little evidence supporting a causal role between AR and prostate cancer. In this study, we functionally and directly address the role whereby AR contributes to spontaneous cancer progression by generating transgenic mice expressing (i) AR-WT to recapitulate increased AR levels and ligand sensitivity, (ii) AR-T857A to represent a promiscuous AR ligand response, and (iii) AR-E231G to model altered AR function. Whereas transgenes encoding either AR-WT or AR-T857A did not cause prostate cancer when expressed at equivalent levels, expression of AR-E231G, which carries a mutation in the most highly conserved signature motif of the NH2-terminal domain that also influences interactions with cellular coregulators, caused rapid development of prostatic intraepithelial neoplasia that progressed to invasive and metastatic disease in 100% of mice examined. Taken together, our data now demonstrate the oncogenic potential of steroid receptors and implicate altered AR function and receptor coregulator interaction as critical determinants of prostate cancer initiation, invasion, and metastasis.

Keratinocyte growth factor/fibroblast growth factor 7, a homeostatic factor with therapeutic potential for epithelial protection and repair

Keratinocyte growth factor (KGF) is a paracrine-acting, epithelial mitogen produced by cells of mesenchymal origin. It is a member of the fibroblast growth factor (FGF) family, and acts exclusively through a subset of FGF receptor isoforms (FGFR2b) expressed predominantly by epithelial cells. The upregulation of KGF after epithelial injury suggested it had an important role in tissue repair. This hypothesis was reinforced by evidence that intestinal damage was worse and healing impaired in KGF null mice. Preclinical data from several animal models demonstrated that recombinant human KGF could enhance the regenerative capacity of epithelial tissues and protect them from a variety of toxic exposures. These beneficial effects are attributed to multiple mechanisms that collectively act to strengthen the integrity of the epithelial barrier, and include the stimulation of cell proliferation, migration, differentiation, survival, DNA repair, and induction of enzymes involved in the detoxification of reactive oxygen species. KGF is currently being evaluated in clinical trials to test its ability to ameliorate severe oral mucositis (OM) that results from cancer chemoradiotherapy. In a phase 3 trial involving patients who were treated with myeloablative chemoradiotherapy before autologous peripheral blood progenitor cell transplantation for hematologic malignancies, KGF significantly reduced both the incidence and duration of severe OM. Similar investigations are underway in patients being treated for solid tumors. On the basis of its success in ameliorating chemoradiotherapy-induced OM in humans and tissue damage in a variety of animal models, additional clinical applications of KGF are worthy of investigation.

Retinoic acid slows progression and promotes apoptosis of spontaneous prostate cancer

BACKGROUND

All-trans retinoic acid (ATRA) promotes terminal differentiation in epithelial cells and anti-angiogenesis and thus, may have beneficial effects in an intervention therapy for prostate cancer.

METHODS

We used the autochthonous spontaneous transgenic adenocarcinoma of the mouse prostate (TRAMP) model system to test the ability of ATRA to prevent initiation and progression of prostate cancer in a pre-clinical setting.

RESULTS

Initial studies demonstrated that exposure of TRAMP-derived C2N prostate tumor cells to ATRA in vitro decreased total viable cell numbers with a concomitant decrease in the fraction of cells in S phase. When TRAMP mice were treated in vivo with ATRA for either 6 or 8 weeks at low, medium, or high dose, mice on average presented with lower grade and more differentiated tumors. However, ATRA therapy conferred no significant protection on incidence of tumors or frequency of metastasis at any dose. Nevertheless, we were able to observe a significant decrease in the expression of synaptophysin, a marker of neuroendocrine differentiation, in tumors of mice receiving the highest dose of ATRA. As well, expression of the cell cycle inhibitor p21 was found to be elevated only in well-differentiated tumors of mice, treated with ATRA while expression of p27, was found to be elevated only in the poorly differentiated tumors.

CONCLUSIONS

Collectively, our in vitro and in vivo data demonstrates that ATRA was able to slow prostate tumor cell proliferation, induce apoptosis, and block the emergence of the neuroendocrine phenotype. Furthermore, our study suggests the differential regulation of p21 and p27 as a molecular mechanism whereby ATRA intervention therapy can inhibit the natural history of spontaneous prostate cancer.

Steroid hormones, polypeptide growth factors, hormone refractory prostate cancer, and the neuroendocrine phenotype

The growth, development, and differentiation of the prostate gland is largely dependent on the action of androgens and peptide growth factors that act differentially at the level of the mesenchymal and epithelial compartments. It is our premise that to understand the emergence of metastatic and hormone refractory prostate cancer we need to investigate: (1) how androgen action at the level of the mesenchyme induces the production of peptide growth factors that in turn can facilitate the growth and development of the epithelial compartment; (2) how androgen action at the level of the epithelium induces and maintains cellular differentiation, function, and replicative senescence; and (3) how transformation of the prostate gland can corrupt androgen and growth factor signaling homeostasis. To this end, we focus our discussion on how deregulation of the growth factor signaling axis can cooperate with deregulation of the androgen signaling axis to facilitate transformation, metastasis, and the emergence of the hormone refractory and neuroendocrine phenotypes associated with progressive androgen-independent prostate cancer. Finally, we suggest a working hypothesis to explain why hormone ablation therapy works to control early disease but fails to control, and may even facilitate, advanced prostate cancer.

Chronic activity of ectopic type 1 fibroblast growth factor receptor tyrosine kinase in prostate epithelium results in hyperplasia accompanied by intraepithelial neoplasia

BACKGROUND

Ectopic expression of fibroblast growth factor receptor 1 (FGFR1) tyrosine kinase in epithelial cells is associated with progression of prostate cancer. Ectopic expression by transfection of FGFR1 in premalignant epithelial cells from nonmalignant Dunning tumors accelerated time-dependent progression of epithelial cells to malignancy. This study was designed to test the effect of chronic androgen-dependent ectopic activity of FGFR1 in the normal adult mouse epithelium by gene targeting.

MATERIALS AND METHODS

Constitutively active FGFR1 (caFGFR1) was targeted to prostate epithelial cells using the androgen-dependent probasin (PB) promoter. Prostate tissues of three strains were characterized over a period of 2 years by HE staining, immunohistochemical analyses for cytokeratin and alpha-actin, and rate of androgen-induced regeneration after castration.

RESULTS

Relative to wildtype littermates, transgenic mice showed increased overall size, hyperplasia in epithelial, and, to a lesser extent, stromal compartments and nuclear atypia in epithelial cells of the prostate with increasing age. Androgen-induced regeneration after castration was enhanced at day 3 by two-fold in mice expressing ectopic caFGFR1.

CONCLUSIONS

The ectopic presence and chronic activation of FGFR1 in mouse prostate epithelial cells induces progressive prostate intraepithelial neoplasia. These results confirm results suggested by the transplantable Dunning tumor and cell culture models that, in contrast to homeostasis-promoting resident FGFR2, chronic ectopic FGFR1 kinase activity in the epithelium disrupts homeostasis between stroma and epithelium. Although insufficient alone, it may cooperate with other oncogenic changes to promote epithelial cells down the path to malignancy.

Role of the stromal microenvironment in carcinogenesis of the prostate

The topic of this review is the role of stromal-epithelial interactions in normal and malignant prostatic growth. Because cell-cell interactions and androgens play such key roles in the prostate, the goal of this review will be to apply endocrinologic and developmental concepts to the understanding of normal and malignant prostatic growth. Prostatic development is induced by androgens, which act via androgen receptors. Androgens elicit prostatic epithelial growth during fetal and prepubertal periods, and in adulthood androgens act via reciprocal homeostatic stromal-epithelial interactions to maintain functional differentiation and growth quiescence. During carcinogenesis, these reciprocal homeostatic stromal-epithelial interactions are disrupted. In this review, 2 models of prostatic carcinogenesis will be reviewed, both of which emphasize the role of the stromal microenvironment in the carcinogenic process. Hormonal carcinogenesis of the prostate can be elicited by treatment of rats and mice with testosterone plus estradiol (T+E2). Using an immortalized but nontumorigenic human prostatic epithelial cell line (BPH-1), tissue recombinant studies were employed to explore the cellular mechanisms of prostatic carcinogenesis. Accordingly, human BPH-1 prostatic epithelial cells were combined with rat UGM, and the resultant UGM+BPH-1 recombinants were grown in adult male nude mouse hosts. In untreated mouse hosts, UGM+BPH-1 recombinants produced solid branched epithelial cords and ductal structures exhibiting benign growth. In T+E2-treated hosts, UGM+BPH-1 recombinants formed invasive carcinomas. Since BPH-1 cells lack androgen and estrogen receptors, whereas rat UGM expresses both of these receptors, it is proposed that hormonal carcinogenesis is elicited by T+E2 via paracrine mechanisms mediated by the stromal microenvironment. During prostatic carcinogenesis in rats and humans, the periepithelial stroma undergoes progressive loss in smooth muscle with the appearance of carcinoma-associated fibroblasts (CAFs). This abnormal stroma was shown to promote carcinogenesis in genetically abnormal but nontumorigenic epithelial cells. CAF+BPH-1 tissue recombinants grown in male hosts formed carcinomas, whereas benign growth and orderly tissue architecture developed in recombinants composed of normal prostatic stroma+BPH-1. Malignant transformation triggered by CAF was associated with additional genetic alterations and changes in gene expression in the BPH-1 cells. Thus, the stromal microenvironment is a critical determinant of benign versus malignant growth.

Prostate Development and Carcinogenesis

The process involved in the development and carcinogenesis of the prostate gland is complex. During early prostate development, the androgenic hormone from embryonic testicles is required for ductal formation, growth, and branching morphogenesis of the prostate gland. From this early stage, interactions between the epithelium and mesenchyme become firmly established through paracrine influence (i.e., growth factors) from mesenchyme (stroma), in response to testosterone, acting on epithelium to stimulate its proliferation, morphogenetic differentiation, and function. In return, the epithelium also exerts its paracrine effects on mesenchyme by regulating the differentiation and specific organizational pattern of its stromal smooth muscle. In a normal adult prostate, the maintenance of normal glandular structure and function is dependent not only on the constant presence of testosterone, but also on a normal intact and stable stroma. This chapter will concentrate first on factors involved in the normal development of the prostate gland and then on the aberrant changes in the homeostatic balance arising either from within (i.e., mutations) or outside (i.e., changes in hormonal balance) that result in derangements of the prostate gland. Finally, environmental and genetic factors that lead to prostate carcinogenesis including activation of oncogenes and mutations of tumor suppressor genes are also discussed.