Establishment and serial passage of cell cultures derived from LuCaP xenografts

Tumor promoting effect of spheroids in an orthotopic prostate cancer mouse model

In this study, we aimed to establish a technique for intraprostatic implantation of prostate cancer (PCa) spheroids and to identify the impact of three-dimensional organization of PCa cells on tumor progression and metastasis in a representative in vivo model. 40,000 LNCaP cells were implanted into the prostate of immunodeficient SCID mice either as single cells (n = 8) or as preformed 3D spheroids (n = 8). For a follow up of 20 weeks, tumor growth was monitored by serum PSA and high-resolution 3D ultrasonography. Eventually, animals were sacrificed and autopsied. The organ dissects were analyzed for the presence of metastases by histology (H&E) and immunohistochemistry (AMACR, AR, Ki-67, CK5, CK8, E-Cadherin, Vimentin). Solid intraprostatic tumors developed in 50% of mice after spheroid implantation and in 50% of mice after implantation of a single cells. Primary tumors of LNCaP spheroids evolved earlier, exhibiting a shorter tumor doubling time whilst developing larger tumor volumes, which was reflected by a higher immunohistochemical expression of Ki-67 and AR, too. Spheroid tumors established lung and lymph node metastases in 75% of mice, in contrast to 50% of mice after single cell implantation. Our technique enables a variety of studies regarding the influence of the tumor microenvironment on PCa progression.

Bone mimetic environments support engineering, propagation, and analysis of therapeutic response of patient-derived cells, ex vivo and in vivo

Bone metastases are the most common milestone in the lethal progression of prostate cancer and prominent in a substantial portion of renal malignancies. Interactions between cancer and bone host cells have emerged as drivers of both disease progression and therapeutic resistance. To best understand these central host-epithelial cell interactions, biologically relevant preclinical models are required. To achieve this goal, we here established and characterized tissue-engineered bone mimetic environments (BME) capable of supporting the growth of patient-derived xenograft (PDX) cells, ex vivo and in vivo. The BME consisted of a polycaprolactone (PCL) scaffold colonized by human mesenchymal stem cells (hMSCs) differentiated into osteoblasts. PDX-derived cells were isolated from bone metastatic prostate or renal tumors, engineered to express GFP or luciferase and seeded onto the BMEs. BMEs supported the growth and therapy response of PDX-derived cells, ex vivo. Additionally, BMEs survived after in vivo implantation and further sustained the growth of PDX-derived cells, their serial transplant, and their application to study the response to treatment. Taken together, this demonstrates the utility of BMEs in combination with patient-derived cells, both ex vivo and in vivo. STATEMENT OF SIGNIFICANCE: Our tissue-engineered BME supported the growth of patient-derived cells and proved useful to monitor the therapy response, both ex vivo and in vivo. This approach has the potential to enable co-clinical strategies to monitor bone metastatic tumor progression and therapy response, including identification and prioritization of new targets for patient treatment.

Prostate cancer research: tools, cell types, and molecular targets

Multiple cancer cell types are found in prostate tumors. They are either luminal-like adenocarcinoma or less luminal-like and more stem-like non-adenocarcinoma and small cell carcinoma. These types are lineage related through differentiation. Loss of cancer differentiation from luminal-like to stem-like is mediated by the activation of stem cell transcription factors (scTF) such as LIN28A, NANOG, POU5F1 and SOX2. scTF expression leads to down-regulation of β2-microglobulin (B2M). Thus, cancer cells can change from the scT F ˜ B 2 M hi phenotype of differentiated to that of scT F ˙ B 2 M lo of dedifferentiated in the disease course. In development, epithelial cell differentiation is induced by stromal signaling and cell contact. One of the stromal factors specific to prostate encodes proenkephalin (PENK). PENK can down-regulate scTF and up-regulate B2M in stem-like small cell carcinoma LuCaP 145.1 cells indicative of exit from the stem state and differentiation. In fact, prostate cancer cells can be made to undergo dedifferentiation or reprogramming by scTF transfection and then to differentiate by PENK transfection. Therapies need to be designed for treating the different cancer cell types. Extracellular anterior gradient 2 (eAGR2) is an adenocarcinoma antigen associated with cancer differentiation that can be targeted by antibodies to lyse tumor cells with immune system components. eAGR2 is specific to cancer as normal cells express only the intracellular form (iAGR2). For AGR2-negative stem-like cancer cells, factors like PENK that can target scTF could be effective in differentiation therapy.

Introduction of Androgen Receptor Targeting shRNA Inhibits Tumor Growth in Patient-Derived Prostate Cancer Xenografts

Patient-derived xenograft (PDX) models have been established as important preclinical cancer models, overcoming some of the limitations associated with the use of cancer cell lines. The utility of prostate cancer PDX models has been limited by an inability to genetically manipulate them in vivo and difficulties sustaining PDX-derived cancer cells in culture. Viable, short-term propagation of PDX models would allow in vitro transfection with traceable reporters or manipulation of gene expression relevant to different studies within the prostate cancer field. Here, we report an organoid culture system that supports the growth of prostate cancer PDX cells in vitro and permits genetic manipulation, substantially increasing the scope to use PDXs to study the pathobiology of prostate cancer and define potential therapeutic targets. We have established a short-term PDX-derived in vitro cell culture system which enables genetic manipulation of prostate cancer PDXs LuCaP35 and BM18. Genetically manipulated cells could be re-established as viable xenografts when re-implanted subcutaneously in immunocompromised mice and were able to be serially passaged. Tumor growth of the androgen-dependent LuCaP35 PDX was significantly inhibited following depletion of the androgen receptor (AR) in vivo. Taken together, this system provides a method to generate novel preclinical models to assess the impact of controlled genetic perturbations and allows for targeting specific genes of interest in the complex biological setting of solid tumors.

Experimental in vitro, ex vivo and in vivo models in prostate cancer research

Androgen deprivation therapy has a central role in the treatment of advanced prostate cancer, often causing initial tumour remission before increasing independence from signal transduction mechanisms of the androgen receptor and then eventual disease progression. Novel treatment approaches are urgently needed, but only a fraction of promising drug candidates from the laboratory will eventually reach clinical approval, highlighting the demand for critical assessment of current preclinical models. Such models include standard, genetically modified and patient-derived cell lines, spheroid and organoid culture models, scaffold and hydrogel cultures, tissue slices, tumour xenograft models, patient-derived xenograft and circulating tumour cell eXplant models as well as transgenic and knockout mouse models. These models need to account for inter-patient and intra-patient heterogeneity, the acquisition of primary or secondary resistance, the interaction of tumour cells with their microenvironment, which make crucial contributions to tumour progression and resistance, as well as the effects of the 3D tissue network on drug penetration, bioavailability and efficacy.

Geometric tumor embolic budding characterizes inflammatory breast cancer

PURPOSE

Inflammatory breast cancer (IBC) is characterized by numerous tumor emboli especially within dermal lymphatics. The explanation remains a mystery.

METHODS

This study combines experimental studies with two different IBC xenografts with image algorithmic studies utilizing human tissue microarrays (TMAs) of IBC vs non-IBC cases to support a novel hypothesis to explain IBC's sina qua non signature of florid lymphovascular emboli.

RESULTS

In the human TMAs, compared to tumor features like nuclear grade (size), mitosis and Ki-67 immunoreactivity which show that IBC is only modestly more proliferative with larger nuclei than non-IBC, what really sets IBC apart is the markedly greater number of tumor emboli and distinctly smaller emboli whose numbers indicate geometric or exponential differences between IBC and non-IBC. In the experimental xenograft studies, Mary-X gives rise to tight spheroids in vitro which exhibit dynamic budding into smaller daughter spheroids whereas Karen-X exhibits only loose non-budding aggregates. Furthermore Mary-X emboli also bud dramatically into smaller daughter emboli in vivo. The mechanism that regulates this involves the generation of E-cad/NTF1, a calpain-mediated cleavage 100 kDa product of 120 kDa full length membrane E-cadherin. Inhibiting this calpain-mediated cleavage of E-cadherin by blocking either the calpain site of cleavage (SC) or the site of binding (SB) with specific decapeptides that both penetrate the cell membrane and mimic either the cleavage site or the binding site on E-cadherin, inhibits the generation of E-cad/NTF1 in a dose-dependent manner, reduces spheroid compactness and decreases budding.

CONCLUSION

Since E-cad/NFT1 retains the p120ctn binding site but loses the α-and β-catenin sites, promoting its 360° distribution around the cell's membrane, the vacilating levels of this molecule trigger budding of both the spheroids as well as the emboli. Recurrent and geometric budding of parental emboli into daughter emboli then would account for the plethora of emboli seen in IBC.

SU086, an inhibitor of HSP90, impairs glycolysis and represents a treatment strategy for advanced prostate cancer

Among men, prostate cancer is the second leading cause of cancer-associated mortality, with advanced disease remaining a major clinical challenge. We describe a small molecule, SU086, as a therapeutic strategy for advanced prostate cancer. We demonstrate that SU086 inhibits the growth of prostate cancer cells in vitro, cell-line and patient-derived xenografts in vivo, and ex vivo prostate cancer patient specimens. Furthermore, SU086 in combination with standard of care second-generation anti-androgen therapies displays increased impairment of prostate cancer cell and tumor growth in vitro and in vivo. Cellular thermal shift assay reveals that SU086 binds to heat shock protein 90 (HSP90) and leads to a decrease in HSP90 levels. Proteomic profiling demonstrates that SU086 binds to and decreases HSP90. Metabolomic profiling reveals that SU086 leads to perturbation of glycolysis. Our study identifies SU086 as a treatment for advanced prostate cancer as a single agent or when combined with second-generation anti-androgens.

Primary Tumor Resection Decelerates Disease Progression in an Orthotopic Mouse Model of Metastatic Prostate Cancer

Radical prostatectomy in oligometastatic prostate cancer is a matter of intense debate. Besides avoiding local complications, it is hypothesized that primary tumor resection may result in better oncological outcomes. The aim of our study was to analyze the effect of primary tumor resection on disease progression in an orthotopic prostate cancer mouse model. First, the optimal time point for primary tumor resection, when metastases have already occurred, but the primary tumor is still resectable, was determined as 8 weeks after inoculation of 5 × 10⁵ LuCaP136 cells. In a second in vivo experiment, 64 mice with metastatic prostate cancer were randomized into two groups, primary tumor resection or sham operation, and disease progression was followed up for 10 weeks. The technique of orthotopic primary tumor resection was successfully established. Compared with the sham operation group, mice with primary tumor resection showed a significantly longer survival (p < 0.001), a significantly slower PSA increase (p < 0.01), and a lower number of lung metastases (p = 0.073). In conclusion, primary tumor resection resulted in slower disease progression and longer survival in an orthotopic mouse model of metastatic prostate cancer. In future studies, this model will be used to unravel the molecular mechanisms of primary tumor/metastasis interaction in prostate cancer.

Overcoming biological barriers to improve solid tumor immunotherapy

Cancer immunotherapy has been at the forefront of therapeutic interventions for many different tumor types over the last decade. While the discovery of immunotherapeutics continues to occur at an accelerated rate, their translation is often hindered by a lack of strategies to deliver them specifically into solid tumors. Accordingly, significant scientific efforts have been dedicated to understanding the underlying mechanisms that govern their delivery into tumors and the subsequent immune modulation. In this review, we aim to summarize the efforts focused on overcoming tumor-associated biological barriers and enhancing the potency of immunotherapy. We summarize the current understanding of biological barriers that limit the entry of intravascularly administered immunotherapies into the tumors, in vitro techniques developed to investigate the underlying transport processes, and delivery strategies developed to overcome the barriers. Overall, we aim to provide the reader with a framework that guides the rational development of technologies for improved solid tumor immunotherapy.

3D Cell Culture Systems: Tumor Application, Advantages, and Disadvantages

The traditional two-dimensional (2D) in vitro cell culture system (on a flat support) has long been used in cancer research. However, this system cannot be fully translated into clinical trials to ideally represent physiological conditions. This culture cannot mimic the natural tumor microenvironment due to the lack of cellular communication (cell-cell) and interaction (cell-cell and cell-matrix). To overcome these limitations, three-dimensional (3D) culture systems are increasingly developed in research and have become essential for tumor research, tissue engineering, and basic biology research. 3D culture has received much attention in the field of biomedicine due to its ability to mimic tissue structure and function. The 3D matrix presents a highly dynamic framework where its components are deposited, degraded, or modified to delineate functions and provide a platform where cells attach to perform their specific functions, including adhesion, proliferation, communication, and apoptosis. So far, various types of models belong to this culture: either the culture based on natural or synthetic adherent matrices used to design 3D scaffolds as biomaterials to form a 3D matrix or based on non-adherent and/or matrix-free matrices to form the spheroids. In this review, we first summarize a comparison between 2D and 3D cultures. Then, we focus on the different components of the natural extracellular matrix that can be used as supports in 3D culture. Then we detail different types of natural supports such as matrigel, hydrogels, hard supports, and different synthetic strategies of 3D matrices such as lyophilization, electrospiding, stereolithography, microfluid by citing the advantages and disadvantages of each of them. Finally, we summarize the different methods of generating normal and tumor spheroids, citing their respective advantages and disadvantages in order to obtain an ideal 3D model (matrix) that retains the following characteristics: better biocompatibility, good mechanical properties corresponding to the tumor tissue, degradability, controllable microstructure and chemical components like the tumor tissue, favorable nutrient exchange and easy separation of the cells from the matrix.

High-Throughput Imaging Assay for Drug Screening of 3D Prostate Cancer Organoids

New treatments are required for advanced prostate cancer; however, there are fewer preclinical models of prostate cancer than other common tumor types to test candidate therapeutics. One opportunity to increase the scope of preclinical studies is to grow tissue from patient-derived xenografts (PDXs) as organoid cultures. Here we report a scalable pipeline for automated seeding, treatment and an analysis of the drug responses of prostate cancer organoids. We established organoid cultures from 5 PDXs with diverse phenotypes of prostate cancer, including castrate-sensitive and castrate-resistant disease, as well as adenocarcinoma and neuroendocrine pathology. We robotically embedded organoids in Matrigel in 384-well plates and monitored growth via brightfield microscopy before treatment with poly ADP-ribose polymerase inhibitors or a compound library. Independent readouts including metabolic activity and live-cell imaging–based features provided robust measures of organoid growth and complementary ways of assessing drug efficacy. Single organoid analyses enabled in-depth assessment of morphological differences between patients and within organoid populations and revealed that larger organoids had more striking changes in morphology and composition after drug treatment. By increasing the scale and scope of organoid experiments, this automated assay complements other patient-derived models and will expedite preclinical testing of new treatments for prostate cancer.

3D Tumor Spheroid Models for In Vitro Therapeutic Screening of Nanoparticles

The anticancer activity of compounds and nanoparticles is most often determined in the cell monolayer. However, three-dimensional (3D) systems, such as tumor spheroids, are more representing the natural tumor microenvironment. They have been shown to have higher invasiveness and resistance to cytotoxic agents and radiotherapy compared to cells growing in 2D monolayer. Furthermore, to improve the prediction of clinical efficacy of drugs, in the past decades, even more sophisticated systems, such as multicellular 3D cultures, closely representing natural tumor microenvironment have been developed. Those cultures are formed from either cell lines or patient-derived tumor cells. Such models are very attractive and could improve the selection of tested materials for clinical trials avoiding unnecessary expensive tests in vivo. The microenvironment in tumor spheroids is different, and those differences or the interaction between several cell populations may contribute to different tumor response to the treatment. Also, different types of nanoparticles may have different behavior in 3D models, depending on their nature, physicochemical properties, the presence of targeting ligands on the surface, etc. Therefore, it is very important to understand in which cases which type of tumor spheroid is more suitable for testing specific types of nanoparticles, which conditions should be used, and which analytical method should be applied.

Cancer-associated fibroblasts stimulate primary tumor growth and metastatic spread in an orthotopic prostate cancer xenograft model

The unique microenvironment of the prostate plays a crucial role in the development and progression of prostate cancer (PCa). We examined the effects of cancer-associated fibroblasts (CAFs) on PCa progression using patient-derived fibroblast primary cultures in a representative orthotopic xenograft model. Primary cultures of CAFs, non-cancer-associated fibroblasts (NCAFs) and benign prostate hyperplasia-associated fibroblasts (BPHFs) were generated from patient-derived tissue specimens. These fibroblasts were coinjected together with cancer cells (LuCaP136 spheroids or LNCaP cells) in orthotopic PCa xenografts to investigate their effects on local and systemic tumor progression. Primary tumor growth as well as metastatic spread to lymph nodes and lungs were significantly stimulated by CAF coinjection in LuCaP136 xenografts. When NCAFs or BPHFs were coinjected, tumor progression was similar to injection of tumor cells alone. In LNCaP xenografts, all three fibroblast types significantly stimulated primary tumor progression compared to injection of LNCaP cells alone. CAF coinjection further increased the frequency of lymph node and lung metastases. This is the first study using an orthotopic spheroid culture xenograft model to demonstrate a stimulatory effect of patient-derived CAFs on PCa progression. The established experimental setup will provide a valuable tool to further unravel the interacting mechanisms between PCa cells and their microenvironment.

Challenges, applications and future directions of precision medicine in prostate cancer - the role of organoids and patient-derived xenografts

OBJECTIVE

To provide a clinically relevant outline of various current precision medicine principles and available evidence on the application and potential for a precision medicine approach in prostate cancer.

METHODS

Narrative review of the current literature in the field.

CONCLUSION

Precision medicine is the concept of individualising patient management based on specific tumour characteristics and biology, rather than traditional histological subtypes. The overall aim is to personalise management to individual patients, to provide the right cancer treatment, to the right patient, at the right time. While the approach aims to improve clinical outcomes, decrease morbidity and improve survival in men with advanced prostate cancer, its clinical application is in its infancy. It does however show great promise in this and other cancers, and will continue to be an area of active research and clinical investigation.

Integrated cancer tissue engineering models for precision medicine

Tumors are not merely cancerous cells that undergo mindless proliferation. Rather, they are highly organized and interconnected organ systems. Tumor cells reside in complex microenvironments in which they are subjected to a variety of physical and chemical stimuli that influence cell behavior and ultimately the progression and maintenance of the tumor. As cancer bioengineers, it is our responsibility to create physiologic models that enable accurate understanding of the multi-dimensional structure, organization, and complex relationships in diverse tumor microenvironments. Such models can greatly expedite clinical discovery and translation by closely replicating the physiological conditions while maintaining high tunability and control of extrinsic factors. In this review, we discuss the current models that target key aspects of the tumor microenvironment and their role in cancer progression. In order to address sources of experimental variation and model limitations, we also make recommendations for methods to improve overall physiologic reproducibility, experimental repeatability, and rigor within the field. Improvements can be made through an enhanced emphasis on mathematical modeling, standardized in vitro model characterization, transparent reporting of methodologies, and designing experiments with physiological metrics. Taken together these considerations will enhance the relevance of in vitro tumor models, biological understanding, and accelerate treatment exploration ultimately leading to improved clinical outcomes. Moreover, the development of robust, user-friendly models that integrate important stimuli will allow for the in-depth study of tumors as they undergo progression from non-transformed primary cells to metastatic disease and facilitate translation to a wide variety of biological and clinical studies.

A novel mouse model of human prostate cancer to study intraprostatic tumor growth and the development of lymph node metastases

BACKGROUND

In this study, we aimed to establish a versatile in vivo model of prostate cancer, which adequately mimics intraprostatic tumor growth, and the natural routes of metastatic spread. In addition, we analyzed the capability of high-resolution ultrasonography (hrUS), in vivo micro-CT (μCT), and 9.4T MRI to monitor tumor growth and the development of lymph node metastases.

METHODS

A total of 5 × 10⁵ VCaP cells or 5 × 10⁵ cells of LuCaP136- or LuCaP147 spheroids were injected into the prostate of male CB17-SCID mice (n = 8 for each cell type). During 12 weeks of follow-up, orthotopic tumor growth, and metastatic spread were monitored by repetitive serum-PSA measurements and imaging studies including hrUS, μCT, and 9.4T MRI. At autopsy, primary tumors and metastases were harvested and examined by histology and immunohistochemistry (CK5, CK8, AMACR, AR, Ki67, ERG, and PSA). From imaging results and PSA-measurements, tumor volume doubling time, tumor-specific growth rate, and PSA-density were calculated.

RESULTS

All 24 mice developed orthotopic tumors. The tumor growth could be reliably monitored by a combination of hrUS, μCT, MRI, and serum-PSA measurements. In most animals, lymph node metastases could be detected after 12 weeks, which could also be well visualized by hrUS, and MRI. Immunohistochemistry showed positive signals for CK8, AMACR, and AR in all xenograft types. CK5 was negative in VCaP- and focally positive in LuCaP136- and LuCaP147-xenografts. ERG was positive in VCaP- and negative in LuCaP136- and LuCaP147-xenografts. Tumor volume doubling times and tumor-specific growth rates were 21.2 days and 3.9 %/day for VCaP-, 27.6 days and 3.1 %/day for LuCaP136- and 16.2 days and 4.5 %/day for LuCaP147-xenografts, respectively. PSA-densities were 433.9 ng/mL per milliliter tumor for VCaP-, 6.5 ng/mL per milliliter tumor for LuCaP136-, and 11.2 ng/mL per milliliter tumor for LuCaP147-xenografts.

CONCLUSIONS

By using different monolayer and 3D spheroid cell cultures in an orthotopic xenograft model, we established an innovative, versatile in vivo model of prostate cancer, which enables the study of both intraprostatic tumor growth as well as metastatic spread to regional lymph nodes. HrUS and MRI are feasible tools to monitor tumor growth and the development of lymph node metastases while these cannot be visualized by μCT.

Androgen Receptor Variant AR-V9 Is Coexpressed with AR-V7 in Prostate Cancer Metastases and Predicts Abiraterone Resistance

Purpose: Androgen receptor (AR) variant AR-V7 is a ligand-independent transcription factor that promotes prostate cancer resistance to AR-targeted therapies. Accordingly, efforts are under way to develop strategies for monitoring and inhibiting AR-V7 in castration-resistant prostate cancer (CRPC). The purpose of this study was to understand whether other AR variants may be coexpressed with AR-V7 and promote resistance to AR-targeted therapies.Experimental Design: We utilized complementary short- and long-read sequencing of intact AR mRNA isoforms to characterize AR expression in CRPC models. Coexpression of AR-V7 and AR-V9 mRNA in CRPC metastases and circulating tumor cells was assessed by RNA-seq and RT-PCR, respectively. Expression of AR-V9 protein in CRPC models was evaluated with polyclonal antisera. Multivariate analysis was performed to test whether AR variant mRNA expression in metastatic tissues was associated with a 12-week progression-free survival endpoint in a prospective clinical trial of 78 CRPC-stage patients initiating therapy with the androgen synthesis inhibitor, abiraterone acetate.Results: AR-V9 was frequently coexpressed with AR-V7. Both AR variant species were found to share a common 3' terminal cryptic exon, which rendered AR-V9 susceptible to experimental manipulations that were previously thought to target AR-V7 uniquely. AR-V9 promoted ligand-independent growth of prostate cancer cells. High AR-V9 mRNA expression in CRPC metastases was predictive of primary resistance to abiraterone acetate (HR = 4.0; 95% confidence interval, 1.31-12.2; P = 0.02).Conclusions: AR-V9 may be an important component of therapeutic resistance in CRPC. Clin Cancer Res; 23(16); 4704-15. ©2017 AACR.

The recurrent architecture of tumour initiation, progression and drug sensitivity

Recent studies across multiple tumour types are starting to reveal a recurrent regulatory architecture in which genomic alterations cluster upstream of functional master regulator (MR) proteins, the aberrant activity of which is both necessary and sufficient to maintain tumour cell state. These proteins form small, hyperconnected and autoregulated modules (termed tumour checkpoints) that are increasingly emerging as optimal biomarkers and therapeutic targets. Crucially, as their activity is mostly dysregulated in a post-translational manner, rather than by mutations in their corresponding genes or by differential expression, the identification of MR proteins by conventional methods is challenging. In this Opinion article, we discuss novel methods for the systematic analysis of MR proteins and of the modular regulatory architecture they implement, including their use as a valuable reductionist framework to study the genetic heterogeneity of human disease and to drive key translational applications.

Liquid-based three-dimensional tumor models for cancer research and drug discovery

Tumors are three-dimensional tissues where close contacts between cancer cells, intercellular interactions between cancer and stromal cells, adhesion of cancer cells to the extracellular matrix, and signaling of soluble factors modulate functions of cancer cells and their response to therapeutics. Three-dimensional cultures of cancer cells overcome limitations of traditionally used monolayer cultures and recreate essential characteristics of tumors such as spatial gradients of oxygen, growth factors, and metabolites and presence of necrotic, hypoxic, quiescent, and proliferative cells. As such, three-dimensional tumor models provide a valuable tool for cancer research and oncology drug discovery. Here, we describe different tumor models and primarily focus on a model known as tumor spheroid. We summarize different technologies of spheroid formation, and discuss the use of spheroids to address the influence of stromal fibroblasts and immune cells on cancer cells in tumor microenvironment, study cancer stem cells, and facilitate compound screening in the drug discovery process. We review major techniques for quantification of cellular responses to drugs and discuss challenges ahead to enable broad utility of tumor spheroids in research laboratories, integrate spheroid models into drug development and discovery pipeline, and use primary tumor cells for drug screening studies to realize personalized cancer treatment.

Spheroid culture of LuCaP 136 patient-derived xenograft enables versatile preclinical models of prostate cancer

LuCaP serially transplantable patient-derived xenografts (PDXs) are valuable preclinical models of locally advanced or metastatic prostate cancer. Using spheroid culture methodology, we recently established cell lines from several LuCaP PDXs. Here, we characterized in depth the features of xenografts derived from LuCaP 136 spheroid cultures and found faithful retention of the phenotype of the original PDX. In vitro culture enabled luciferase transfection into LuCaP 136 spheroids, facilitating in vivo imaging. We showed that LuCaP 136 spheroids formed intratibial, orthotopic, and subcutaneous tumors when re-introduced into mice. Intratibial tumors responded to castration and were highly osteosclerotic. LuCaP 136 is a realistic in vitro-in vivo preclinical model of a subtype of bone metastatic prostate cancer.

Conversion of Prostate Adenocarcinoma to Small Cell Carcinoma-Like by Reprogramming

The lineage relationship between prostate adenocarcinoma and small cell carcinoma was studied by using the LuCaP family of xenografts established from primary neoplasm to metastasis. Expression of four stem cell transcription factor (TF) genes, LIN28A, NANOG, POU5F1, SOX2, were analyzed in the LuCaP lines. These genes, when force expressed in differentiated cells, can reprogram the recipients into stem-like induced pluripotent stem (iPS) cells. Most LuCaP lines expressed POU5F1, while LuCaP 145.1, representative of small cell carcinoma, expressed all four. Through transcriptome database query, many small cell carcinoma genes were also found in stem cells. To test the hypothesis that prostate cancer progression from "differentiated" adenocarcinoma to "undifferentiated" small cell carcinoma could involve re-expression of stem cell genes, the four TF genes were transduced via lentiviral vectors into five adenocarcinoma LuCaP lines-70CR, 73CR, 86.2, 92, 105CR-as done in iPS cell reprogramming. The resultant cells from these five transductions displayed a morphology of small size and dark appearing unlike the parentals. Transcriptome analysis of LuCaP 70CR* ("*" to denote transfected progeny) revealed a unique gene expression close to that of LuCaP 145.1. In a prostate principal components analysis space based on cell-type transcriptomes, the different LuCaP transcriptome datapoints were aligned to suggest a possible ordered sequence of expression changes from the differentiated luminal-like adenocarcinoma cell types to the less differentiated, more stem-like small cell carcinoma types, and LuCaP 70CR*. Prostate cancer progression can thus be molecularly characterized by loss of differentiation with re-expression of stem cell genes. J. Cell. Physiol. 231: 2040-2047, 2016. © 2016 Wiley Periodicals, Inc.

Spherical cancer models in tumor biology

Three-dimensional (3D) in vitro models have been used in cancer research as an intermediate model between in vitro cancer cell line cultures and in vivo tumor. Spherical cancer models represent major 3D in vitro models that have been described over the past 4 decades. These models have gained popularity in cancer stem cell research using tumorospheres. Thus, it is crucial to define and clarify the different spherical cancer models thus far described. Here, we focus on in vitro multicellular spheres used in cancer research. All these spherelike structures are characterized by their well-rounded shape, the presence of cancer cells, and their capacity to be maintained as free-floating cultures. We propose a rational classification of the four most commonly used spherical cancer models in cancer research based on culture methods for obtaining them and on subsequent differences in sphere biology: the multicellular tumor spheroid model, first described in the early 70s and obtained by culture of cancer cell lines under nonadherent conditions; tumorospheres, a model of cancer stem cell expansion established in a serum-free medium supplemented with growth factors; tissue-derived tumor spheres and organotypic multicellular spheroids, obtained by tumor tissue mechanical dissociation and cutting. In addition, we describe their applications to and interest in cancer research; in particular, we describe their contribution to chemoresistance, radioresistance, tumorigenicity, and invasion and migration studies. Although these models share a common 3D conformation, each displays its own intrinsic properties. Therefore, the most relevant spherical cancer model must be carefully selected, as a function of the study aim and cancer type.

Establishment of primary patient-derived xenografts of palliative TURP specimens to study castrate-resistant prostate cancer

BACKGROUND

Fresh patient specimens of castrate-resistant prostate cancer (CRPC) are invaluable for studying tumor heterogeneity and responses to current treatments. They can be used for primary patient-derived xenografts (PDXs) or serially transplantable PDXs, but only a small proportion of samples grow successfully. To improve the efficiency and quality of PDXs, we investigated the factors that determine the initial engraftment of patient tissues derived from TURP specimens.

METHODS

Fresh tissue was collected from castrate patients who required a TURP for urinary symptoms. Tissue was grafted under the renal capsule of immune-compromised mice for up to 14 weeks. The abundance of cancer in ungrafted and grafted specimens was compared using histopathology. Mice were castrated or implanted with testosterone pellets to determine the androgen-responsiveness of CRPC PDXs from TURP tissue.

RESULTS

Primary PDXs were successfully established from 7 of 10 patients that underwent grafting. Of the 112 grafts generated from these 10 patients, 21% contained cancer at harvest. Grafts were most successful when the original patient specimens contained high amounts of viable cancer, defined as samples with (i) at least 50% cancer cells, (ii) no physical damage, and (iii) detectable Ki67 expression. PDX grafts survived in castrated hosts and proliferated in response to testosterone, confirming that they were castrate resistant but androgen-responsive.

CONCLUSIONS

Primary PDXs of CRPC can be established from TURP specimens with modest success. The take rate can be increased if the original tissues contain sufficient numbers of actively proliferating cancer cells. Selecting specimens with abundant viable cancer will maximize the rate of engraftment and increase the efficiency of establishing PDXs that can be serially transplanted.

Reprogramming of prostate cancer cells--technical challenges

Prostate cancer progression is characterized by tumor dedifferentiation. Cancer cells of less differentiated tumors have a gene expression/transcriptome more similar to that of stem cells. In dedifferentiation, cancer cells may follow a specific program of gene expression changes to a stem-like state. In order to treat cancer effectively, the stem-like cancer cells and cancer differentiation pathway need to be identified and studied. Due to the very low abundance of stem-like cancer cells, their isolation from fresh human tumors is technically challenging. Induced pluripotent stem cell technology can reprogram differentiated cells into stem-like, and this may be a tool to generate sufficient stem-like cancer cells.

Cellular Adhesion Promotes Prostate Cancer Cells Escape from Dormancy

Dissemination of prostate cancer (PCa) cells to the bone marrow is an early event in the disease process. In some patients, disseminated tumor cells (DTC) proliferate to form active metastases after a prolonged period of undetectable disease known as tumor dormancy. Identifying mechanisms of PCa dormancy and reactivation remain a challenge partly due to the lack of in vitro models. Here, we characterized in vitro PCa dormancy-reactivation by inducing cells from three patient-derived xenograft (PDX) lines to proliferate through tumor cell contact with each other and with bone marrow stroma. Proliferating PCa cells demonstrated tumor cell-cell contact and integrin clustering by immunofluorescence. Global gene expression analyses on proliferating cells cultured on bone marrow stroma revealed a downregulation of TGFB2 in all of the three proliferating PCa PDX lines when compared to their non-proliferating counterparts. Furthermore, constitutive activation of myosin light chain kinase (MLCK), a downstream effector of integrin-beta1 and TGF-beta2, in non-proliferating cells promoted cell proliferation. This cell proliferation was associated with an upregulation of CDK6 and a downregulation of E2F4. Taken together, our data provide the first clinically relevant in vitro model to support cellular adhesion and downregulation of TGFB2 as a potential mechanism by which PCa cells may escape from dormancy. Targeting the TGF-beta2-associated mechanism could provide novel opportunities to prevent lethal PCa metastasis.

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.

Spheroid culture of LuCaP 147 as an authentic preclinical model of prostate cancer subtype with SPOP mutation and hypermutator phenotype

LuCaP serially transplantable xenografts are valuable preclinical models of locally advanced or metastatic prostate cancer. For the first time, we recently succeeded in establishing and serially passaging spheroid cultures of several LuCaP xenografts. Here, we characterized in depth the molecular and cellular phenotype of LuCaP 147 cultures and found faithful retention of the characteristics of the original xenograft, including immunophenotype, genetic fidelity, gene expression profile and responsiveness to androgen. Furthermore, we demonstrated capabilities for high-throughput drug screening and that anti-cancer agents induced cell cycle arrest and apoptosis in spheroid cultures. Finally, we showed that cells formed tumors when re-introduced into mice, providing an authentic in vitro-in vivo preclinical model of a subtype of prostate cancer with a hypermutator phenotype and an SPOP mutation.