Simultaneous haploinsufficiency of Pten and Trp53 tumor suppressor genes accelerates tumorigenesis in a mouse model of prostate cancer

Loss of ING3 in the Prostate Leads to Activation of DNA Damage Repair Markers

BACKGROUND/OBJECTIVES

The inhibitor of growth family member 3 (ING3) acts as an epigenetic reader through physical interactions with histone-modifying enzymes and subsequent chromatin remodelling processes. It is involved in various cellular functions, such as cell cycle control, cell growth, and apoptosis. Although ING3 was assigned tumour suppressor candidate status in some types of cancers, including prostate cancer, some studies suggest it acts to promote growth. To address these contradictory reports regarding its role in the initiation and progression of prostate cancer, we specifically addressed the question of whether ablation of ING3 in the mouse prostate is sufficient to initiate malignant transformation of the prostate and support its (candidate) tumour suppressor status.

METHODS

To generate the prostate-specific Ing3 knockout mouse, paternal inheritance of the PB-Cre4 transgene was used, while for the generation of a global knockout control, a female mouse harbouring the PB-Cre4 transgene was utilized. To determine the recombination efficiency of the Cre-LoxP system in the prostate at the Ing3 locus, a duplex probe-based digital PCR assay capable of counting undisrupted Ing3 copies was designed. The impact of DNA recombination on the protein level was investigated by immunohistochemical staining of prostate tissue samples.

RESULTS

In the prostate-specific knockout, digital PCR analysis revealed mosaic gene deletion. We found recombination efficiencies in the anterior, dorsolateral, and ventral prostate lobes ranging from approximately 15 to 30%. ING3 staining in the prostate was faint with no detectable differences in signal intensity between the knockout specimen and wild-type controls. This low ING3 expression in the prostate is consistent with observations of X-gal staining of an Ing3-LacZ reporter allele. Immunohistochemistry showed increased expression of DNA-damage-associated markers γH2AX and 53BP1. However, no gross anatomical abnormalities or prostate intraepithelial neoplasia (PIN) lesions in the prostate of tissue-specific knockout animals compared to wild-type controls were observed.

CONCLUSIONS

Altogether, our data provide evidence that disruption of ING3 expression in prostate cells does not lead to malignant transformation and challenges the idea that ING3 acts primarily in a tumour-suppressive manner. Furthermore, this work supports the crucial role of ING3 in maintaining genomic stability, and we confirmed the embryonic lethal phenotype of homozygous Ing3 null mice that is rescued by ectopic expression of ING3.

Network pharmacology and transcriptomics reveal androgen receptor as a potential protein target for 6PPD-quinone

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone, or 6PPD-Q) has received increasing attention as an emerging hotspot contaminant. The occurrence of 6PPD-Q in dust and fine atmospheric particles indicates substantial human exposure to this toxicant but the hazards of 6PPD-Q to human health is unknown. We used in silico approaches to identify potential human protein targets of 6PPD-Q and conducted preliminary validation through an in vitro cell proliferation assay and an in vivo transcriptomic analysis of prostate tissues from 6PPD-Q-treated mice. Receptor-based reverse screening and network pharmacology identified four hub targets of 6PPD-Q that were closely related to prostate carcinogenesis. Among these four targets, 6PPD-Q exhibited a strong binding tendency to androgen receptor (AR) with a binding free energy of -23.04 kcal/mol. A support vector machine (SVM) model for predicting chemicals with AR agonism or AR-inactivity was established with good prediction performance (mean prediction accuracy: 0.92). SVM prediction and AR-mediated cell-based assays, with a known AR agonist and a proposed AR inactive agent as positive and negative controls, confirmed that 6PPD-Q displayed AR agonism. Upregulation of Ar mRNA expression (FC = 1.29, p = 0.0404) and its related prostate cancer pathway was observed in the prostate of mice exposed to environmentally realistic concentrations of 6PPD-Q, suggesting a potential role in promoting prostate carcinogenesis. These findings provide evidence that 6PPD-Q agonized AR to exert downstream gene transactivation and imply its prostate cancer risks to humans.

Immunological facets of prostate cancer and the potential of immune checkpoint inhibition in disease management

Prostate cancer (PCa) is the most common non-cutaneous cancer in men and a major cause of cancer-related deaths. Whereas localized PCa can be cured by surgery and radiotherapy, metastatic disease can be treated, but is not curable. Inhibition of androgen signaling remains the main therapeutic intervention for treatment of metastatic PCa, in addition to chemotherapy, radionuclide therapy and emerging targeted therapies. Although initial responses are favorable, resistance to these therapies invariably arise with development of castration resistant PCa (CRPC) and lethal phenotypes. Recent findings have implicated the crosstalk between PCa cells and the tumor microenvironment (TME) as a key factor for disease progression and metastasis, and the immune system is becoming an increasingly attractive target for therapy. Given the striking success of immune checkpoint inhibitors (ICIs) in various cancer types, preclinical and clinical studies have begun to explore their potential in PCa. It has become clear that the PCa TME is largely immunosuppressive, and ICI therapy does not have efficacy for PCa. Intense effort is therefore being made in the field to understand the mechanisms of suppression and to turn the immunosuppressive TME into an immune active one that would enable ICI efficacy. Herein we examine this recent body of knowledge and how the mutational landscape of PCa integrates with an immunosuppressive TME to circumvent ICI-mediated T-cell activity and tumor killing. We then review the emerging potential success of combinatorial ICI approaches, utility of careful patient selection, and potential novel strategies to improve the efficacy of ICI for PCa therapy.

Alterations of the AKT Pathway in Sporadic Human Tumors, Inherited Susceptibility to Cancer, and Overgrowth Syndromes

The AKT kinases are critical signaling molecules that regulate cellular physiology upon the activation of tyrosine kinase receptors and phosphatidylinositol 3-kinases (PI3K). AKT kinases govern many cellular processes considered hallmarks of cancer, including cell proliferation and survival, cell size, tumor invasion, metastasis, and angiogenesis. AKT signaling is regulated by multiple tumor suppressors and oncogenic proteins whose loss or activation, respectively, leads to dysregulation of this pathway, thereby contributing to oncogenesis. Herein, we review the enormous body of literature documenting how the AKT pathway becomes hyperactivated in sporadic human tumors and various hereditary cancer syndromes. We also discuss the role of activating mutations of AKT pathway genes in various chimeric overgrowth disorders, including Proteus syndrome, hypoglycemia with hypertrophy, CLOVES and SOLAMEN syndromes, and hemimegalencephaly.

In Vivo Models for Prostate Cancer Research

In 2022, prostate cancer (PCa) is estimated to be the most commonly diagnosed cancer in men in the United States-almost 270,000 American men are estimated to be diagnosed with PCa in 2022. This review compares and contrasts in vivo models of PCa with regards to the altered genes, signaling pathways, and stages of tumor progression associated with each model. The main type of model included in this review are genetically engineered mouse models, which include conditional and constitutive knockout model. 2D cell lines, 3D organoids and spheroids, xenografts and allografts, and patient derived models are also included. The major applications, advantages and disadvantages, and ease of use and cost are unique to each type of model, but they all make it easier to translate the tumor progression that is seen in the mouse prostate to the human prostate. Although both human and mouse prostates are androgen-dependent, the fact that the native, genetically unaltered prostate in mice cannot give rise to carcinoma is an especially critical component of PCa models. Thanks to the similarities between the mouse and human genome, our knowledge of PCa has been expanded, and will continue to do so, through models of PCa.

Progress in gene therapy treatments for prostate cancer

Prostate cancer is one of the predominant cancers affecting men and has been widely reported. In the past, various therapies and drugs have been proposed to treat prostate cancer. Among these treatments, gene therapy has been considered to be an optimal and widely applicable treatment. Furthermore, due to the increased specificity of gene sequence complementation, the targeted delivery of complementary gene sequences may represent a useful treatment in certain instances. Various gene therapies, including tumor-suppressor gene therapy, suicide gene therapy, immunomodulation gene therapy and anti-oncogene therapies, have been established to treat a wide range of diseases, such as cardiac disease, cystic fibrosis, HIV/AIDS, diabetes, hemophilia, and cancers. To this end, several gene therapy clinical trials at various phases are underway. This overview describes the developments and progress in gene therapy, with a special focus being placed on prostate cancer.

Double heterozygosity for TP53 and BRCA1 mutations: clinical implications in populations with founder mutations

PURPOSE

The co-occurrence or double heterozygosity of pathogenic/likely pathogenic sequence variants (P/LPSVs) in major cancer susceptibility genes has rarely been reported. Such co-occurrence raises the issues of accurate genetic counseling, preferred recommended surveillance scheme, and the use of preimplantation genetic diagnosis (PGD).

METHODS

A clinical report of an Ashkenazi Jewish (AJ) family with co occurrence of two PSVs in BRCA1 and TP53 and a literature search.

RESULTS

In an AJ family with a substantial history of cancer limited to the maternal side, two siblings co-harbored TP53 (c.733C>A; p.G245S) and the predominant 5266dup BRCA1 mutation, originating from the mother and the father, respectively. PGD is ongoing. Four families were thus far reported as double heterozygotes for both BRCA1/BRCA2 and TP53. Based on the limited available data, it seems that the phenotype in double PSV heterozygotes is not more severe than in single PSV carrier in either gene.

CONCLUSIONS

This family highlights the need to genotype both parents, especially in populations with founder mutations, when a BRCA1 mutation is detected in an offspring, regardless of family history. The combination of mutations in these two genes presents a challenge for PGD since both genes are located on chromosome 17.

Loss of Ceacam1 promotes prostate cancer progression in Pten haploinsufficient male mice

OBJECTIVE

PTEN haploinsufficiency plays an important role in prostate cancer development in men. However, monoallelic deletion of Pten gene failed to induce high prostate intraepithelial neoplasia (PIN) until Pten+/- mice aged or fed a high-calorie diet. Because CEACAM1, a cell adhesion molecule with a potential tumor suppression activity, is induced in Pten+/- prostates, the study aimed at examining whether the rise of CEACAM1 limited neoplastic progression in Pten+/- prostates.

METHODS

Pten+/- were crossbred with Cc1-/- mice harboring a null deletion of Ceacam1 gene to produce Pten+/-/Cc1-/- double mutants. Prostates from 7-month old male mice were analyzed histologically and biochemically for PIN progression.

RESULTS

Deleting Ceacam1 in Pten+/- mice caused an early development of high-grade PIN in parallel to hyperactivation of PI3 kinase/Akt and Ras/MAP kinase pathways, with an increase in cell proliferation, epithelial-to-mesenchymal transition, angiogenesis and inflammation relative to Pten+/- and Cc1-/- individual mutants. It also caused a remarkable increase in lipogenesis in prostate despite maintaining insulin sensitivity. Concomitant Ceacam1 deletion with Pten+/- activated the IL-6/STAT3 signaling pathways to suppress Irf-8 transcription that in turn, led to a decrease in the expression level of promyelocytic leukemia gene, a well characterized tumor suppressor in prostate.

CONCLUSIONS

Ceacam1 deletion accelerated high-grade prostate intraepithelial neoplasia in Pten haploinsufficient mice while preserving insulin sensitivity. This demonstrated that the combined loss of Ceacam1 and Pten advanced prostate cancer by increasing lipogenesis and modifying the STAT3-dependent inflammatory microenvironment of prostate.

Silencing of PTEN inhibits the oxidative stress damage and hippocampal cell apoptosis induced by Sevoflurane through activating MEK1/ERK signaling pathway in infant rats

Phosphatase and tensin homolog (PTEN) is a suppressive player in tumor but its concrete role in oxidative stress (OS) damage and cell apoptosis remains much exploration. Thus, this study is conducted to explore the participation of PTEN and its mechanisms in OS damage and cell apoptosis in hippocampal cells.Infant rats were grouped into normal, Sevo, Sevo + si-negative control (NC), Sevo + si-PTEN and Sevo + si-PTEN + PD (MEK1/ERK signaling pathway inhibitor) groups. Infant hippocampal cells were grouped into blank, Sevo, Sevo + si-NC, Sevo + si-PTEN and Sevo + si-PTEN + PD groups. The expressions of PTEN and MEK1/ERK signaling pathway-related proteins were determined. OS-related indices in hippocampal tissues and cells were detected. Cell apoptosis was detected by flow cytometry.Sevoflurane up-regulated PTEN expression and silencing of PTEN activates MEK1/ERK signaling pathway in hippocampal tissues and cells of infant rats. Silencing of PTEN alleviated hippocampal tissue pathological status and inhibited sevoflurane-induced cell apoptosis in hippocampal tissues of infant rats. Silencing of PTEN alleviated OS damage in hippocampal tissues of infant rats. Silencing of PTEN inhibited sevoflurane-induced apoptosis after OS damage in hippocampal cells of infant rats. Silencing of PTEN reduced sevoflurane-induced OS damage in hippocampal cells of infant rats.Our study demonstrates that PTEN silencing inhibits the OS damage and cell apoptosis in hippocampal cells induced by Sevoflurane through activating MEK1/ERK signaling pathway in infant rats.

COMMD3:BMI1 Fusion and COMMD3 Protein Regulate C-MYC Transcription: Novel Therapeutic Target for Metastatic Prostate Cancer

Gene rearrangement is reported to be associated to the aggressive phenotype and poor prognosis in prostate cancer. We identified a gene fusion between a transcription repressor (BMI1) and transcriptional factor (COMMD3) in human prostate cancer. We show that COMMD3:BMI1 fusion expression is significantly increased in prostate cancer disease in an order: normal tissue < primary < metastatic tumors (Mets). Although elevated TMPRSS-ERG/ETV fusion is reported in prostate cancer, we identified a subtype of Mets exhibiting low TMPRSS:ETV and high COMMD3:BMI1 We delineated the mechanism and function of COMMD3 and COMMD3:BMI1 in prostate cancer. We show that COMMD3 level is elevated in prostate cancer cell models, PDX models (adenocarcinoma, NECaP), and Mets. The analysis of TCGA/NIH/GEO clinical data showed a positive correlation between increased COMMD3 expression to the disease recurrence and poor survival in prostate cancer. We show that COMMD3 drives proliferation of normal cells and promotes migration/invasiveness of neoplastic cells. We show that COMMD3:BMI1 and COMMD3 regulate C-MYC transcription and C-MYC downstream pathway. The ChIP analysis showed that COMMD3 protein is recruited at the promoter of C-MYC gene. On the basis of these data, we investigated the relevance of COMMD3:BMI1 and COMMD3 as therapeutic targets using in vitro and xenograft mouse models. We show that siRNA-mediated targeting of COMMD3:BMI1 and COMMD3 significantly decreases (i) C-MYC expression in BRD/BET inhibitor-resistant cells, (ii) proliferation/invasion in vitro, and (iii) growth of prostate cancer cell tumors in mice. The IHC analysis of tumors confirmed the targeting of COMMD3-regulated molecular pathway under in vivo conditions. We conclude that COMMD3:BMI1 and COMMD3 are potential progression biomarkers and therapeutic targets of metastatic prostate cancer.

Genetically Engineered Mouse Models of Prostate Cancer in the Postgenomic Era

Recent genomic sequencing analyses have unveiled the spectrum of genomic alterations that occur in primary and advanced prostate cancer, raising the question of whether the corresponding genes are functionally relevant for prostate tumorigenesis, and whether such functions are associated with particular disease stages. In this review, we describe genetically engineered mouse models (GEMMs) of prostate cancer, focusing on those that model genomic alterations known to occur in human prostate cancer. We consider whether the phenotypes of GEMMs based on gain or loss of function of the relevant genes provide reliable counterparts to study the predicted consequences of the corresponding genomic alterations as occur in human prostate cancer, and we discuss exceptions in which the GEMMs do not fully emulate the expected phenotypes. Last, we highlight future directions for the generation of new GEMMs of prostate cancer and consider how we can use GEMMs most effectively to decipher the biological and molecular mechanisms of disease progression, as well as to tackle clinically relevant questions.

Clinical implications of PTEN loss in prostate cancer

Genomic aberrations of the PTEN tumour suppressor gene are among the most common in prostate cancer. Inactivation of PTEN by deletion or mutation is identified in ∼20% of primary prostate tumour samples at radical prostatectomy and in as many as 50% of castration-resistant tumours. Loss of phosphatase and tensin homologue (PTEN) function leads to activation of the PI3K-AKT (phosphoinositide 3-kinase-RAC-alpha serine/threonine-protein kinase) pathway and is strongly associated with adverse oncological outcomes, making PTEN a potentially useful genomic marker to distinguish indolent from aggressive disease in patients with clinically localized tumours. At the other end of the disease spectrum, therapeutic compounds targeting nodes in the PI3K-AKT-mTOR (mechanistic target of rapamycin) signalling pathway are being tested in clinical trials for patients with metastatic castration-resistant prostate cancer. Knowledge of PTEN status might be helpful to identify patients who are more likely to benefit from these therapies. To enable the use of PTEN status as a prognostic and predictive biomarker, analytically validated assays have been developed for reliable and reproducible detection of PTEN loss in tumour tissue and in blood liquid biopsies. The use of clinical-grade assays in tumour tissue has shown a robust correlation between loss of PTEN and its protein as well as a strong association between PTEN loss and adverse pathological features and oncological outcomes. In advanced disease, assessing PTEN status in liquid biopsies shows promise in predicting response to targeted therapy. Finally, studies have shown that PTEN might have additional functions that are independent of the PI3K-AKT pathway, including those affecting tumour growth through modulation of the immune response and tumour microenvironment.

Efficient Generation of Somatic Cell Nuclear Transfer-Competent Porcine Cells with Mutated Alleles at Multiple Target Loci by Using CRISPR/Cas9 Combined with Targeted Toxin-Based Selection System

The recent advancement in genome editing such a CRISPR/Cas9 system has enabled isolation of cells with knocked multiple alleles through a one-step transfection. Somatic cell nuclear transfer (SCNT) has been frequently employed as one of the efficient tools for the production of genetically modified (GM) animals. To use GM cells as SCNT donor, efficient isolation of transfectants with mutations at multiple target loci is often required. The methods for the isolation of such GM cells largely rely on the use of drug selection-based approach using selectable genes; however, it is often difficult to isolate cells with mutations at multiple target loci. In this study, we used a novel approach for the efficient isolation of porcine cells with at least two target loci mutations by one-step introduction of CRISPR/Cas9-related components. A single guide (sg) RNA targeted to GGTA1 gene, involved in the synthesis of cell-surface α-Gal epitope (known as xenogenic antigen), is always a prerequisite. When the transfected cells were reacted with toxin-labeled BS-I-B₄ isolectin for 2 h at 37 °C to eliminate α-Gal epitope-expressing cells, the surviving clones lacked α-Gal epitope expression and were highly expected to exhibit induced mutations at another target loci. Analysis of these α-Gal epitope-negative surviving cells demonstrated a 100% occurrence of genome editing at target loci. SCNT using these cells as donors resulted in the production of cloned blastocysts with the genotype similar to that of the donor cells used. Thus, this novel system will be useful for SCNT-mediated acquisition of GM cloned piglets, in which multiple target loci may be mutated.

Combined Loss of EAF2 and p53 Induces Prostate Carcinogenesis in Male Mice

Mutations in the p53 tumor suppressor are frequent in patients with castration-resistant prostate cancer but less so in patients with localized disease, and patients who have Li-Fraumeni with germline p53 mutations do not have an increased incidence of prostate cancer, suggesting that additional molecular and/or genetic changes are required for p53 to promote prostate carcinogenesis. ELL-associated factor 2 (EAF2) is a tumor suppressor that is frequently downregulated in advanced prostate cancer. Previous studies have suggested that p53 binds to EAF2, providing a potential mechanism for their functional interactions. In this study, we tested whether p53 and EAF2 could functionally interact in prostate cancer cells and whether concurrent inactivation of p53 and EAF2 could promote prostate carcinogenesis in a murine knockout model. Endogenous p53 coprecipitated with EAF2 in prostate cancer cells, and deletion mutagenesis indicated that this interaction was mediated through the C terminus of EAF2 and the DNA binding domain of p53. Concurrent knockdown of p53 and EAF2 induced an increase in proliferation and migration in cultured prostate cancer cells, and conventional p53 and EAF2 knockout mice developed prostate cancer. In human prostate cancer specimens, concurrent p53 nuclear staining and EAF2 downregulation was associated with high Gleason score. These findings suggest that EAF2 and p53 functionally interact in prostate tumor suppression and that simultaneous inactivation of EAF2 and p53 can drive prostate carcinogenesis.

Transdifferentiation as a Mechanism of Treatment Resistance in a Mouse Model of Castration-Resistant Prostate Cancer

Current treatments for castration-resistant prostate cancer (CRPC) that target androgen receptor (AR) signaling improve patient survival, yet ultimately fail. Here, we provide novel insights into treatment response for the antiandrogen abiraterone by analyses of a genetically engineered mouse (GEM) model with combined inactivation of Trp53 and Pten, which are frequently comutated in human CRPC. These NPp53 mice fail to respond to abiraterone and display accelerated progression to tumors resembling treatment-related CRPC with neuroendocrine differentiation (CRPC-NE) in humans. Cross-species computational analyses identify master regulators of adverse response that are conserved with human CRPC-NE, including the neural differentiation factor SOX11, which promotes neuroendocrine differentiation in cells derived from NPp53 tumors. Furthermore, abiraterone-treated NPp53 prostate tumors contain regions of focal and/or overt neuroendocrine differentiation, distinguished by their proliferative potential. Notably, lineage tracing in vivo provides definitive and quantitative evidence that focal and overt neuroendocrine regions arise by transdifferentiation of luminal adenocarcinoma cells. These findings underscore principal roles for TP53 and PTEN inactivation in abiraterone resistance and progression from adenocarcinoma to CRPC-NE by transdifferentiation.Significance: Understanding adverse treatment response and identifying patients likely to fail treatment represent fundamental clinical challenges. By integrating analyses of GEM models and human clinical data, we provide direct genetic evidence for transdifferentiation as a mechanism of drug resistance as well as for stratifying patients for treatment with antiandrogens. Cancer Discov; 7(7); 736-49. ©2017 AACR.See related commentary by Sinha and Nelson, p. 673This article is highlighted in the In This Issue feature, p. 653.

E3 ubiquitin ligase isolated by differential display regulates cervical cancer growth in vitro and in vivo via microRNA-143

Cervical cancer is one of the most common gynecological cancers worldwide. Aberrant expression of E3 ubiquitin ligase isolated by differential display (EDD) has been detected in various types of tumor and has been demonstrated to have an important role in carcinogenesis, tumor growth and drug resistance. However, the role of EDD in cervical cancer and its underlying molecular mechanisms remains unknown. The present study aimed to investigate the role of EDD in the tumorigenicity of cervical cancer. EDD expression levels were measured using reverse transcription-quantitative polymerase chain reaction and western blotting in SiHa, HeLa, CaSki, c-41 and c-33A cervical cancer cell lines and cervical cancer tissue specimens. A functional study was performed using cell proliferation, colony formation, cell apoptosis assays in vitro and tumor growth assays in vivo with EDD either overexpressed or silenced. In the present study, EDD expression levels were significantly upregulated in cervical cancer cell lines and tissue samples. EDD knockdown significantly inhibited colony formation, cell proliferation and tumor growth and accelerated cell apoptosis in the cervical cancer cell lines and tissue samples. Furthermore, microRNA (miR)-143 expression levels were low in cervical cancer tissue samples and were negatively correlated with EDD expression. miR-143 silencing eliminated the effect of EDD on cell proliferation, colony formation and cell apoptosis in the cervical cancer cells, which suggested that miR-143 is critical for EDD-mediated regulation of cervical cancer cell growth. The results of the present study indicated that EDD may promote cervical cancer growth in vivo and in vitro by targeting miR-143. In conclusion, EDD may have an oncogenic role in cervical cancer and may serve as a potential therapeutic target for the treatment of patients with cervical cancer.

Mouse Models in Prostate Cancer Translational Research: From Xenograft to PDX

Despite the advancement of clinical and preclinical research on PCa, which resulted in the last five years in a decrement of disease incidence by 3-4%, it remains the most frequent cancer in men and the second for mortality rate. Based on this evidence we present a brief dissertation on numerous preclinical models, comparing their advantages and disadvantages; among this we report the PDX mouse models that show greater fidelity to the disease, in terms of histopathologic features of implanted tumor, gene and miRNA expression, and metastatic pattern, well describing all tumor progression stages; this characteristic encourages the translation of preclinical results. These models become particularly useful in meeting the need of new treatments identification that eradicate PCa bone metastases growing, clarifying pathway of angiogenesis, identifying castration-resistant stem-like cells, and studying the antiandrogen therapies. Also of considerable interest are the studies of 3D cell cultures derived from PDX, which have the ability to maintain PDX cell viability with continued native androgen receptor expression, also showing a differential sensitivity to drugs. 3D PDX PCa may represent a diagnostic platform for the rapid assessment of drugs and push personalized medicine. Today the development of preclinical models in vitro and in vivo is necessary in order to obtain increasingly reliable answers before reaching phase III of the drug discovery.

Drug discovery in prostate cancer mouse models

INTRODUCTION

The mouse is an important, though imperfect, organism with which to model human disease and to discover and test novel drugs in a preclinical setting. Many experimental strategies have been used to discover new biological and molecular targets in the mouse, with the hopes of translating these discoveries into novel drugs to treat prostate cancer in humans. Modeling prostate cancer in the mouse, however, has been challenging, and often drugs that work in mice have failed in human trials.

AREAS COVERED

The authors discuss the similarities and differences between mice and men; the types of mouse models that exist to model prostate cancer; practical questions one must ask when using a mouse as a model; and potential reasons that drugs do not often translate to humans. They also discuss the current value in using mouse models for drug discovery to treat prostate cancer and what needs are still unmet in field.

EXPERT OPINION

With proper planning and following practical guidelines by the researcher, the mouse is a powerful experimental tool. The field lacks genetically engineered metastatic models, and xenograft models do not allow for the study of the immune system during the metastatic process. There remain several important limitations to discovering and testing novel drugs in mice for eventual human use, but these can often be overcome. Overall, mouse modeling is an essential part of prostate cancer research and drug discovery. Emerging technologies and better and ever-increasing forms of communication are moving the field in a hopeful direction.

Genetically engineered mouse models to study prostate cancer

Genetically engineered mouse models have become fundamental tools in the basic and translational research of prostate cancer. There is a plethora of models available to dissect the genetic alterations and aberrant signaling events associated with human prostate cancer and, furthermore, to investigate new and "personalized" therapies to treat the disease. In this chapter, we discuss some of the models recently and currently used to study prostate cancer in vivo, and some considerations when selecting an appropriate model to investigate particular aspects of the disease. We describe the methods required to isolate prostate tumors and conduct basic characterization of the tumor to determine tumor load and histopathology. We also discuss important aspects to be considered when processing samples for further analysis.

The PI3K/AKT/mTOR interactive pathway

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of the rapamycin (mTOR) signalling pathway is hyperactivated or altered in many cancer types and regulates a broad range of cellular processes including survival, proliferation, growth, metabolism, angiogenesis and metastasis.

Loss of survivin in the prostate epithelium impedes carcinogenesis in a mouse model of prostate adenocarcinoma

The inhibitor of apoptosis protein survivin is expressed in most cancers. Using the conditional PTEN deletion mouse model, we previously reported that survivin levels increase with prostate tumor growth. Here we evaluated the functional role of survivin in prostate tumor growth. First, we demonstrated that mice lacking the survivin gene in prostate epithelium were fertile and had normal prostate growth and development. We then serially, from about 10-56 weeks of age, evaluated histopathologic changes in the prostate of mice with PTEN deletion combined with survivin mono- or bi-allelic gene deletion. While within this time period most of the animals with wild-type or monoallelic survivin deletion developed adenocarcinomas, the most severe lesions in the biallelic survivin deleted mice were high-grade prostatic intra-epithelial neoplasia with distinct histopathology. Many atypical cells contained large hypertrophic cytoplasm and desmoplastic reaction in the prostatic intra-epithelial neoplasia lesions of this group was minimal until the late ages. A reduced proliferation index as well as apoptotic and senescent cells were detected in the lesions of mice with compound PTEN/survivin deficiency throughout the time points examined. Survivin deletion was also associated with reduced tumor expression of another inhibitor of apoptosis member, the X-linked inhibitor of apoptosis. Our findings suggest that survivin participates in the progression of prostatic intraepithelial neoplasia to adenocarcinoma, and that survivin interference at the prostatic intraepithelial neoplasia stages may be a potential therapeutic strategy to halt or delay further progression.

Androgen receptor (AR) differential roles in hormone-related tumors including prostate, bladder, kidney, lung, breast and liver

The androgen receptor (AR) is expressed in many cell types and the androgen/AR signaling has been found to have important roles in modulating tumorigenesis and metastasis in several cancers including prostate, bladder, kidney, lung, breast and liver. However, whether AR has differential roles in the individual cells within these tumors that contain a variety of cell types remains unclear. Generation of AR knockout (ARKO) mouse models with deletion of AR in selective cells within tumors indeed have uncovered many unique AR roles in the individual cell types during cancer development and progression. This review will discuss the results obtained from various ARKO mice and different human cell lines with special attention to the cell type- and tissue-specific ARKO models. The understanding of various results showing the AR indeed has distinct and contrasting roles in each cell type within many hormone-related tumors (as stimulator in bladder, kidney and lung metastases vs as suppressor in prostate and liver metastases) may eventually help us to develop better therapeutic approaches by targeting the AR or its downstream signaling in individual cell types to better battle these hormone-related tumors in different stages.

Diverse mechanisms of AKT pathway activation in human malignancy

AKT/PKB (Protein Kinase B) are central proteins mediating signals from receptor tyrosine kinases and phosphatidylinositol 3-kinase. AKT kinases are involved in a number of important cellular processes including cell proliferation and survival, cell size in response to nutrient availability, tumor invasion/metastasis, and angiogenesis.Various components of the AKT signaling pathway are encoded by tumor suppressor genes and oncogenes whose loss or activation, respectively, plays an important role in tumorigenesis. The growing body of evidence connecting deregulated AKT signaling with sporadic human cancers and inherited cancer predisposition syndromes is discussed. We also highlight new findings regarding the involvement of activating mutations of AKT1, AKT2, and AKT3 in somatic overgrowth disorders: Proteus syndrome, hypoglycemia with hypertrophy, and hemimegalencephaly, respectively. In addition, we review recent literature documenting the various ways the AKT signaling pathway is activated in human cancers and consequences for molecularly targeted therapies.

Doxycycline regulated induction of AKT in murine prostate drives proliferation independently of p27 cyclin dependent kinase inhibitor downregulation

The PI3 kinase/AKT pathway has been shown to increase degradation of the p27 cyclin dependent kinase inhibitor through phosphorylation of consensus AKT sites on p27 and SKP2, and AKT driven proliferation may be checked by feedback mechanisms that increase p27 expression and induce senescence. However, these AKT sites are not conserved in mouse, and it has not been clear whether AKT negatively regulates murine p27. Transgenic mice with a probasin promoter controlled prostate specific reverse tetracycline transactivator (ARR2Pb-rtTA) were generated and used to achieve doxycycline inducible expression of a tetracycline operon regulated constitutively active myristoylated AKT1 transgene (tetO-myrAKT). Doxycycline induction of myrAKT occurred within 1 day and rapidly induced proliferation (within 4 days) and the development of prostatic intraepithelial neoplasia (PIN) lesions in ventral prostate, which did not progress to prostate cancer. Cells in these lesions expressed high levels of p27, had increased proliferation, and there was apoptosis of centrally located cells. Doxycycline withdrawal resulted in apoptosis of cells throughout the lesions and rapid clearing of hyperplastic glands, confirming in vivo the critical antiapoptotic functions of AKT. Significantly, analyses of prostates immediately after initiating doxycycline treatment further showed that p27 expression was rapidly increased, coincident with the induction of myrAKT and prior to the development of hyperplasia and PIN. These findings establish in vivo that murine p27 is not negatively regulated by AKT and indicate that proliferation in PI3 kinase/AKT pathway driven mouse models is mediated by p27 independent mechanisms that may be distinct from those in human. Further studies using prostate specific doxycycline regulated transgene expression may be useful to assess the acute effects of inducing additional transgenes in adult murine prostate epithelium, and to assess the requirements for continued transgene expression in transgene induced tumors.

Genomic deletion of PTEN is associated with tumor progression and early PSA recurrence in ERG fusion-positive and fusion-negative prostate cancer

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene is often altered in prostate cancer. To determine the prevalence and clinical significance of the different mechanisms of PTEN inactivation, we analyzed PTEN deletions in TMAs containing 4699 hormone-naïve and 57 hormone-refractory prostate cancers using fluorescence in situ hybridization analysis. PTEN mutations and methylation were analyzed in subsets of 149 and 34 tumors, respectively. PTEN deletions were present in 20.2% (458/2266) of prostate cancers, including 8.1% heterozygous and 12.1% homozygous deletions, and were linked to advanced tumor stage (P < 0.0001), high Gleason grade (P < 0.0001), presence of lymph node metastasis (P = 0.0002), hormone-refractory disease (P < 0.0001), presence of ERG gene fusion (P < 0.0001), and nuclear p53 accumulation (P < 0.0001). PTEN deletions were also associated with early prostate-specific antigen recurrence in univariate (P < 0.0001) and multivariate (P = 0.0158) analyses. The prognostic impact of PTEN deletion was seen in both ERG fusion-positive and ERG fusion-negative tumors. PTEN mutations were found in 4 (12.9%) of 31 cancers with heterozygous PTEN deletions but in only 1 (2%) of 59 cancers without PTEN deletion (P = 0.027). Aberrant PTEN promoter methylation was not detected in 34 tumors. The results of this study demonstrate that biallelic PTEN inactivation, by either homozygous deletion or deletion of one allele and mutation of the other, occurs in most PTEN-defective cancers and characterizes a particularly aggressive subset of metastatic and hormone-refractory prostate cancers.

Androgen hormone action in prostatic carcinogenesis: stromal androgen receptors mediate prostate cancer progression, malignant transformation and metastasis

It has been postulated that prostatic carcinogenesis is androgen dependent and that androgens mediate their effects primarily through epithelial cells; however, definitive proof of androgen hormone action in prostate cancer (PRCA) progression is lacking. Here we demonstrate through genetic loss of function experiments that PRCA progression is androgen dependent and that androgen dependency occurs via prostatic stromal androgen receptors (AR) but not epithelial AR. Utilizing tissue recombination models of prostatic carcinogenesis, loss of AR function was evaluated by surgical castration or genetic deletion. Loss of AR function prevented prostatic carcinogenesis, malignant transformation and metastasis. Tissue-specific evaluation of androgen hormone action demonstrated that epithelial AR was not necessary for PRCA progression, whereas stromal AR was essential for PRCA progression, malignant transformation and metastasis. Stromal AR was not necessary for prostatic maintenance, suggesting that the lack of cancer progression due to stromal AR deletion was not related to altered prostatic homeostasis. Gene expression analysis identified numerous androgen-regulated stromal factors. Four candidate stromal AR-regulated genes were secreted growth factors: fibroblast growth factors-2, -7, -10 and hepatocyte growth factor which were significantly affected by androgens and anti-androgens in stromal cells grown in vitro. These data support the concept that androgens are necessary for PRCA progression and that the androgen-regulated stromal microenvironment is essential to carcinogenesis, malignant transformation and metastasis and may serve as a potential target in the prevention of PRCA.

Mechanisms of increased risk of tumorigenesis in Atm and Brca1 double heterozygosity

BACKGROUND

Both epidemiological and experimental studies suggest that heterozygosity for a single gene is linked with tumorigenesis and heterozygosity for two genes increases the risk of tumor incidence. Our previous work has demonstrated that Atm/Brca1 double heterozygosity leads to higher cell transformation rate than single heterozygosity. However, the underlying mechanisms have not been fully understood yet. In the present study, a series of pathways were investigated to clarify the possible mechanisms of increased risk of tumorigenesis in Atm and Brca1 heterozygosity.

METHODS

Wild type cells, Atm or Brca1 single heterozygous cells, and Atm/Brca1 double heterozygous cells were used to investigate DNA damage and repair, cell cycle, micronuclei, and cell transformation after photon irradiation.

RESULTS

Remarkable high transformation frequency was confirmed in Atm/Brca1 double heterozygous cells compared to wild type cells. It was observed that delayed DNA damage recognition, disturbed cell cycle checkpoint, incomplete DNA repair, and increased genomic instability were involved in the biological networks. Haploinsufficiency of either ATM or BRCA1 negatively impacts these pathways.

CONCLUSIONS

The quantity of critical proteins such as ATM and BRCA1 plays an important role in determination of the fate of cells exposed to ionizing radiation and double heterozygosity increases the risk of tumorigenesis. These findings also benefit understanding of the individual susceptibility to tumor initiation.

Animal models relevant to human prostate carcinogenesis underlining the critical implication of prostatic stem/progenitor cells

Recent development of animal models relevant to human prostate cancer (PC) etiopathogenesis has provided important information on the specific functions provided by key gene products altered during disease initiation and progression to locally invasive, metastatic and hormone-refractory stages. Especially, the characterization of transgenic mouse models has indicated that the inactivation of distinct tumor suppressor proteins such as phosphatase tensin homolog deleted on chromosome 10 (PTEN), Nkx3.1, p27(KIP1), p53 and retinoblastoma (pRb) may cooperate for the malignant transformation of prostatic stem/progenitor cells into PC stem/progenitor cells and tumor development and metastases. Moreover, the sustained activation of diverse oncogenic signaling elements, including epidermal growth factor receptor (EGFR), sonic hedgehog, Wnt/β-catenin, c-Myc, Akt and nuclear factor-kappaB (NF-κB) also may contribute to the acquisition of more aggressive and hormone-refractory phenotypes by PC stem/progenitor cells and their progenies during disease progression. Importantly, it has also been shown that an enrichment of PC stem/progenitor cells expressing stem cell-like markers may occur after androgen deprivation therapy and docetaxel treatment in the transgenic mouse models of PC suggesting the critical implication of these immature PC cells in treatment resistance, tumor re-growth and disease recurrence. Of clinical interest, the molecular targeting of distinct gene products altered in PC cells by using different dietary compounds has also been shown to counteract PC initiation and progression in animal models supporting their potential use as chemopreventive or chemotherapeutic agents for eradicating the total tumor cell mass, improving current anti-hormonal and chemotherapies and preventing disease relapse.

Frequent gene products and molecular pathways altered in prostate cancer- and metastasis-initiating cells and their progenies and novel promising multitargeted therapies

Recent gene expression profiling analyses and gain- and loss-of-function studies performed with distinct prostate cancer (PC) cell models indicated that the alterations in specific gene products and molecular pathways often occur in PC stem/progenitor cells and their progenies during prostate carcinogenesis and metastases at distant sites, including bones. Particularly, the sustained activation of epidermal growth factor receptor (EGFR), hedgehog, Wnt/β-catenin, Notch, hyaluronan (HA)/CD44 and stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) during the epithelial-mesenchymal transition (EMT) process may provide critical functions for PC progression to locally invasive, metastatic and androgen-independent disease states and treatment resistance. Moreover, an enhanced glycolytic metabolism in PC stem/progenitor cells and their progenies concomitant with the changes in their local microenvironment, including the induction of tumor hypoxia and release of diverse soluble factors by tumor myofibroblasts, also may promote the tumor growth, angiogenesis and metastases. More particularly, these molecular transforming events may cooperate to upregulate Akt, nuclear factor (NF)-κB, hypoxia-inducible factors (HIFs) and stemness gene products such as Oct3/4, Sox2, Nanog and Bmi-1 in PC cells that contribute to their acquisition of high self-renewal, tumorigenic and invasive capacities and survival advantages during PC progression. Consequently, the molecular targeting of these deregulated gene products in the PC- and metastasis-initiating cells and their progenies represent new promising therapeutic strategies of great clinical interest for eradicating the total PC cell mass and improving current antihormonal treatments and docetaxel-based chemotherapies, thereby preventing disease relapse and the death of PC patients.

Mouse models of prostate cancer

The development and optimization of high-throughput screening methods has identified a multitude of genetic changes associated with human disease. The use of immunodeficient and genetically engineered mouse models that mimic the human disease has been crucial in validating the importance of these genetic pathways in prostate cancer. These models provide a platform for finding novel therapies to treat human patients afflicted with prostate cancer as well as those who have debilitating bone metastases. In this paper, we focus on the historical development and phenotypic descriptions of mouse models used to study prostate cancer. We also comment on how closely each model recapitulates human prostate cancer.

eIF4E phosphorylation promotes tumorigenesis and is associated with prostate cancer progression

Translational regulation plays a critical role in the control of cell growth and proliferation. A key player in translational control is eIF4E, the mRNA 5' cap-binding protein. Aberrant expression of eIF4E promotes tumorigenesis and has been implicated in cancer development and progression. The activity of eIF4E is dysregulated in cancer. Regulation of eIF4E is partly achieved through phosphorylation. However, the physiological significance of eIF4E phosphorylation in mammals is not clear. Here, we show that knock-in mice expressing a nonphosphorylatable form of eIF4E are resistant to tumorigenesis in a prostate cancer model. By using a genome-wide analysis of translated mRNAs, we show that the phosphorylation of eIF4E is required for translational up-regulation of several proteins implicated in tumorigenesis. Accordingly, increased phospho-eIF4E levels correlate with disease progression in patients with prostate cancer. Our findings establish eIF4E phosphorylation as a critical event in tumorigenesis. These findings raise the possibility that chemical compounds that prevent the phosphorylation of eIF4E could act as anticancer drugs.