Novel human prostate epithelial cell culture models for the study of carcinogenesis and of normal stem cells and cancer stem cells

Cultures derived from pancreatic cancer xenografts with long-term gemcitabine treatment produce chemoresistant secondary xenografts: Establishment of isogenic gemcitabine-sensitive and -resistant models

In attempts to establish sophisticated models to reproduce the process of acquired drug resistance, we transformed normal human pancreatic ductal epithelial cells by introducing genes for multiple cellular factors. We also created isogenic gemcitabine-sensitive and -resistant models by short- and long-term gemcitabine treatment, respectively. These models demonstrated differences in drug resistance in vivo, but not in vitro. Gemcitabine treatment also induced squamous transdifferentiation in xenografts in mice. The transcription factor p63 was identified as a possible resistance-determining factor but was unlikely to be solely responsible for the resistance to gemcitabine. This system would prove useful to discover novel molecular targets to overcome chemotherapy resistance, by allowing the evaluation of molecules of interest in xenograft models after in vitro genetic ablation.

Difference in the malignancy between RAS and GLI1-transformed astrocytes is associated with frequency of p27KIP1-positive cells in xenograft tissues

We demonstrate that the introduction of GLI1 is sufficient for immortalized human astrocytes to be transformed whereas FOXM1 fails to induce malignant transformation, suggesting differences between GLI1 and FOXM1 in terms of transforming ability despite both transcription factors being overexpressed in malignant gliomas. Moreover, in investigations of mechanisms underlying relatively less-malignant features of GLI1-transformed astrocytes, we found that p27KIP1-positive cells were frequently observed in xenografts derived from GLI1-transformed astrocytes compared to those from RAS-transformed cells. As shRNA-mediated knockdown of p27KIP1 accelerates tumor progression of GLI1-transformed astrocytes, downregulation of p27KIP1 contributes to malignant features of transformed astrocytes. We propose that the models using immortalized/transformed astrocytes are useful to identify the minimal and most crucial set of changes required for glioma formation.

KRAS-retroviral fusion transcripts and gene amplification in arsenic-transformed, human prostate CAsE-PE cancer cells

CAsE-PE cells are an arsenic-transformed, human prostate epithelial line containing oncogenic mutations in KRAS compared to immortalized, normal KRAS parent cells, RWPE-1. We previously reported increased copy number of mutated KRAS in CAsE-PE cells, suggesting gene amplification. Here, KRAS flanking genomic and transcriptomic regions were sequenced in CAsE-PE cells for insight into KRAS amplification. Comparison of DNA-Seq and RNA-Seq showed increased reads from background aligning to all KRAS exons in CAsE-PE cells, while a uniform DNA-Seq read distribution occurred in RWPE-1 cells with normal transcript expression. We searched for KRAS fusions in DNA and RNA sequencing data finding a portion of reads aligning to KRAS and viral sequence. After generation of cDNA from total RNA, short and long KRAS probes were generated to hybridize cDNA and KRAS enriched fragments were PacBio sequenced. More KRAS reads were captured from CAsE-PE cDNA versus RWPE-1 by each probe set. Only CAsE-PE cDNA showed KRAS viral fusion transcripts, primarily mapping to LTR and endogenous retrovirus sequences on either 5'- or 3'-ends of KRAS. Most KRAS viral fusion transcripts contained 4 to 6 exons but some PacBio sequences were in unusual orientations, suggesting viral insertions within the gene body. Additionally, conditioned media was extracted for potential retroviral particles. RNA-Seq of culture media isolates identified KRAS retroviral fusion transcripts in CAsE-PE media only. Truncated KRAS transcripts suggested multiple retroviral integration sites occurred within the KRAS gene producing KRAS retroviral fusions of various lengths. Findings suggest activation of endogenous retroviruses in arsenic carcinogenesis should be explored.

Assessing the Advantages, Limitations and Potential of Human Primary Prostate Epithelial Cells as a Pre-clinical Model for Prostate Cancer Research

Choosing an appropriate cell model(s) is the first decision to be made before starting a new project or programme of study. Here, we address the rationale that can be behind this decision and we summarize the current cell models that are used to study prostate cancer. Researchers face the challenge of choosing a model that recapitulates the complexity and heterogeneity of prostate cancer. The use of primary prostate epithelial cells cultured from patient tissue is discussed, and the necessity for close clinical-academic collaboration in order to do this is highlighted. Finally, a novel quantitative phase imaging technique is described, along with the potential for cell characterization to not only include gene expression and protein markers but also morphological features, cell behaviour and kinetic activity.

Arsenite malignantly transforms human prostate epithelial cells in vitro by gene amplification of mutated KRAS

Inorganic arsenic is an environmental human carcinogen of several organs including the urinary tract. RWPE-1 cells are immortalized, non-tumorigenic, human prostate epithelia that become malignantly transformed into the CAsE-PE line after continuous in vitro exposure to 5μM arsenite over a period of months. For insight into in vitro arsenite transformation, we performed RNA-seq for differential gene expression and targeted sequencing of KRAS. We report >7,000 differentially expressed transcripts in CAsE-PE cells compared to RWPE-1 cells at >2-fold change, q<0.05 by RNA-seq. Notably, KRAS expression was highly elevated in CAsE-PE cells, with pathway analysis supporting increased cell proliferation, cell motility, survival and cancer pathways. Targeted DNA sequencing of KRAS revealed a mutant specific allelic imbalance, ‘MASI’, frequently found in primary clinical tumors. We found high expression of a mutated KRAS transcript carrying oncogenic mutations at codons 12 and 59 and many silent mutations, accompanied by lower expression of a wild-type allele. Parallel cultures of RWPE-1 cells retained a wild-type KRAS genotype. Copy number analysis and sequencing showed amplification of the mutant KRAS allele. KRAS is expressed as two splice variants, KRAS4a and KRAS4b, where variant 4b is more prevalent in normal cells compared to greater levels of variant 4a seen in tumor cells. 454 Roche sequencing measured KRAS variants in each cell type. We found KRAS4a as the predominant transcript variant in CAsE-PE cells compared to KRAS4b, the variant expressed primarily in RWPE-1 cells and in normal prostate, early passage, primary epithelial cells. Overall, gene expression data were consistent with KRAS-driven proliferation pathways found in spontaneous tumors and malignantly transformed cell lines. Arsenite is recognized as an important environmental carcinogen, but it is not a direct mutagen. Further investigations into this in vitro transformation model will focus on genomic events that cause arsenite-mediated mutation and overexpression of KRAS in CAsE-PE cells.

Structure-activity relationship and pharmacokinetic studies of 3-O-substitutedflavonols as anti-prostate cancer agents

Thirty-eight 3-O-substituted-3',4'-dimethoxyflavonols and twenty-five 3-O-substituted-3',4',7-trimethoxyflavonols have been synthesized for systematic investigation on the structure-activity relationships of 3-O-substituted-3',4'-dimethoxyflavonols in three human prostate cancer cell models. Our findings indicate that incorporation of an appropriate amino group to 3-OH of 3',4'-dimethoxyflavonol and 3',4',7-trimethoxyflavonol through a 3- to 5-carbon linker can substantially improve the in vitro antiproliferative potency in three human prostate cancer cell models, but not in two non-neoplastic human epithelial cell models (MCF 10A and PWR-1E). 1-Methylpiperazine, pyrrolidine, and dibutylamine are optimal terminal amine groups that, in combination with a 3- to 5-carbon linker, are notably beneficial to the anti-proliferative potency of 3-O-substituted-3',4'-dimethoxyflavonols. It is worth noting that 3-O-(4-methylpiperazin-1-yl)propyl-3',4',7-trimethoxyflavonol (76) induces PC-3 cell death in a completely different way from 3-O-pyrrolidinopentyl-3',4',7-trimethoxyflavonol (81) even though they belong to 3-O-substituted-3',4',7-trimethoxyflavonols and exhibit similar potency in inhibiting PC-3 cell proliferation, suggesting that the mechanism of action for each specific 3-O-substitutedflavonol varies with different amino moiety. 3-O-(N,N-Dibutylamino)propyl-3',4'-dimethoxyflavonol (42) emerged as the most promising derivative due to its substantially improved potency in cell models, superior bioavailability in rats, and good selectivity of inhibiting prostate cancer cell proliferation over non-neoplastic human epithelial cell proliferation.

[Progress in prostate cancer study: 3D cell culture enables the ex vivo reproduction of tumor characteristics]

Despite new therapeutics options, Prostate Cancer (PCa) remains a public health challenge because of its high incidence and mortality. Limits in PCa research come from the lack of in vitro and in vivo models that mimic the human disease. Currently, 2D in vitro tissue culture models of PCa are widely used but they present numerous limits. They do not reproduce cellular morphology, tissue architecture, inter-patients and intratumor heterogeneity. Furthermore, they lack two key components of PCa tumors, the tumoral microenvironment and the cancer stem cells. In vivo murine models of PCa cannot be representative of all the genetic alterations known in prostate tumors and they hardly reproduce the pathophysiology of human metastatic progression. Consequently, the physiology of these in vitro and in vivo models do not well represent patients tumors. 3D cell cultures overcome many of these limits by sharing morphologic characteristics with in vivo tumors as well as reproducibility of in vitro models. 3D models of PCa include spheroids derived from tumor cell lines, and organoids, derived from patient. In 3D cell cultures, cell fitness is maintained, the physiological cells-cells and cell-matrix interactions are restored and an extracellular matrix surrounds the cells. Organoids, generated from PCa primary tumors or metastases, allow studies on cancer stem cells and their microenvironment. Moreover, organoids retain genetic integrity of PCa tumors. PCa organoid model is an innovative tool that offers great perspectives of therapeutic screening. In the future, organoids generated from patients' biopsies may also lead to personalized medicine.

3-O-Substituted-3',4',5'-trimethoxyflavonols: Synthesis and cell-based evaluation as anti-prostate cancer agents

Twenty-two 3-O-substituted-3',4',5'-trimethoxyflavonols have been designed and synthesized for their anti-proliferative activity towards three human prostate cancer cell lines. Our results indicate that most of them are significantly more potent than the parent 3',4',5'-trimethoxyflavonol in inhibiting the cell proliferation in PC-3 and LNCaP prostate cancer cell models. 3-O-Substituted-3',4',5'-trimethoxyflavonols have generally higher potency towards PC-3 and LNCaP cell lines than the DU145 cell line. Incorporation of an ethyl group to 3-OH of 3',4',5'-trimethoxyflavonol leads to 3-O-ethyl-3',4',5'-trimethoxyflavonol as the optimal derivative with up to 36-fold enhanced potency as compared with the corresponding lead compound 3',4',5'-trimethoxyflavonol, but with reversed PC-3 cell apoptotic response. Introduction of a dipentylaminopropyl group to 3-OH increases not only the antiproliferative potency but also the ability in activating PC-3 cell apoptosis. Our findings imply that modification on 3-OH of trimethoxyflavonol can further enhance its in vitro anti-proliferative potency and PC-3 cell apoptosis induction.

Protein profile of basal prostate epithelial progenitor cells--stage-specific embryonal antigen 4 expressing cells have enhanced regenerative potential in vivo

The long‐term propagation of basal prostate progenitor cells ex vivo has been very difficult in the past. The development of novel methods to expand prostate progenitor cells in vitro allows determining their cell surface phenotype in greater detail. Mouse (Lin⁻Sca‐1⁺CD49f⁺ Trop2^high‐phenotype) and human (Lin⁻CD49f⁺TROP2^high) basal prostate progenitor cells were expanded in vitro. Human and mouse cells were screened using 242 anti‐human or 176 antimouse monoclonal antibodies recognizing the cell surface protein profile. Quantitative expression was evaluated at the single‐cell level using flow cytometry. Differentially expressed cell surface proteins were evaluated in conjunction with the known CD49f⁺/TROP2^high phenotype of basal prostate progenitor cells and characterized by in vivo sandwich‐transplantation experiments using nude mice. The phenotype of basal prostate progenitor cells was determined as CD9⁺/CD24⁺/CD29⁺/CD44⁺/CD47⁺/CD49f⁺/CD104⁺/CD147⁺/CD326⁺/Trop2^high of mouse as well as human origin. Our analysis revealed several proteins, such as CD13, Syndecan‐1 and stage‐specific embryonal antigens (SSEAs), as being differentially expressed on murine and human CD49f⁺TROP2⁺ basal prostate progenitor cells. Transplantation experiments suggest that CD49f⁺TROP2^highSSEA‐4^high human prostate basal progenitor cells to be more potent to regenerate prostate tubules in vivo as compared with CD49f⁺TROP2^high or CD49f⁺TROP2^highSSEA‐4^low cells. Determination of the cell surface protein profile of functionally defined murine and human basal prostate progenitor cells reveals differentially expressed proteins that may change the potency and regenerative function of epithelial progenitor cells within the prostate. SSEA‐4 is a candidate cell surface marker that putatively enables a more accurate identification of the basal PESC lineage.

Defined conditions for the isolation and expansion of basal prostate progenitor cells of mouse and human origin

Methods to isolate and culture primary prostate epithelial stem/progenitor cells (PESCs) have proven difficult and ineffective. Here, we present a method to grow and expand both murine and human basal PESCs long term in serum- and feeder-free conditions. The method enriches for adherent mouse basal PESCs with a Lin⁻SCA-1⁺CD49f⁺TROP2^high phenotype. Progesterone and sodium selenite are additionally required for the growth of human Lin⁻CD49f⁺TROP2^high PESCs. The gene-expression profiles of expanded basal PESCs show similarities to ESCs, and NF-kB function is critical for epithelial differentiation of sphere-cultured PESCs. When transplanted in combination with urogenital sinus mesenchyme, expanded mouse and human PESCs generate ectopic prostatic tubules, demonstrating their stem cell activity in vivo. This novel method will facilitate the molecular, genomic, and functional characterization of normal and pathologic prostate glands of mouse and human origin.

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Basal prostate epithelial stem/progenitor cells (PESCs) are expanded in vitro

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Expanded PESCs can differentiate into glandular structures in vitro and in vivo

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A surface-marker screen identifies marker candidates for prostate basal stem cells

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Gene-expression analysis shows a role of NF-kB signaling in PESC differentiation

In vitro model systems to study androgen receptor signaling in prostate cancer

Prostate cancer (PCa) is one of the most common causes of male cancer-related death in Western nations. The cellular response to androgens is mediated via the androgen receptor (AR), a ligand-inducible transcription factor whose dysregulation plays a key role during PCa development and progression following androgen deprivation therapy, the current mainstay systemic treatment for advanced PCa. Thus, a better understanding of AR signaling and new strategies to abrogate AR activity are essential for improved therapeutic intervention. Consequently, a large number of experimental cell culture models have been established to facilitate in vitro investigations into the role of AR signaling in PCa development and progression. These different model systems mimic distinct stages of this heterogeneous disease and exhibit differences with respect to AR expression/status and androgen responsiveness. Technological advances have facilitated the development of in vitro systems that more closely reflect the physiological setting, for example via the use of three-dimensional coculture to study the interaction of prostate epithelial cells with the stroma, endothelium, immune system and tissue matrix environment. This review provides an overview of the most commonly used in vitro cell models currently available to study AR signaling with particular focus on their use in addressing key questions relating to the development and progression of PCa. It is hoped that the continued development of in vitro models will provide more biologically relevant platforms for mechanistic studies, drug discovery and design ensuring a more rapid transfer of knowledge from the laboratory to the clinic.

Cancer stem cells and their role in metastasis

Cancer stem cells (CSCs), which comprise a small fraction of cancer cells, are believed to constitute the origin of most human tumors. Considerable effort has been focused on identifying CSCs in multiple tumor types and identifying genetic signatures that distinguish CSCs from normal tissue stem cells. Many studies also suggest that CSCs serve as the basis of metastases. Yet, experimental evidence that CSCs are the basis of disseminated metastases has lagged behind the conceptual construct of CSCs. Recent work, however, has demonstrated that CSCs may directly or indirectly contribute to the generation of metastasis. Moreover, CSC heterogeneity may be largely responsible for the considerable complexity and organ specificity of metastases. In this review, we discuss the role of CSCs in metastasis and their potential as therapeutic targets.