Pluripotent stem cell models of early mammalian development

Pluripotent stem cells derived from the early mammalian embryo offer a convenient model system for studying cell fate decisions in embryogenesis. The last 10 years have seen a boom in the popularity of two-dimensional micropatterns and three-dimensional stem cell culture systems as a way to recreate the architecture and interactions of particular cell populations during development. These methods enable the controlled exploration of cellular organization and patterning during development, using cell lines instead of embryos. They have established a new class of in vitro model system for pre-implantation and peri-implantation embryogenesis, ranging from models of the blastocyst stage, through gastrulation and toward early organogenesis. This review aims to set these systems in context and to highlight the strengths and suitability of each approach in modelling early mammalian development.     

Pluripotent Stem Cells Models for Huntington＇s Disease： Prospects and Challenges

Pluripotent cellular models have shown great promise in the study of a number of neurological disorders.Several advantages of using a stem cell model include the potential for cells to derive disease relevant neuronal cell types,providing a system for researchers to monitor disease progression during neurogenesis,along with serving as a platform for drug discovery.A number of stem cell derived models have been employed to establish in vitro research models of Huntington’s disease that can be used to investigate cellular pathology and screen for drug and cell-based therapies.Although some progress has been made,there are a number of challenges and limitations that must be overcome before the true potential of this research strategy is achieved.In this article we review current stem cell models that have been reported,as well as discuss the issues that impair these studies.We also highlight the prospective application of Huntington’s disease stem cell models in the development of novel therapeutic strategies and advancement of personalized medicine.     

Human embryonic stem cell technologies and drug discovery

Development of new drugs is costly and takes huge resources into consideration. The big pharmaceutical companies are currently facing increasing developmental costs and a lower success‐rate of bringing new compounds to the market. Therefore, it is now of outmost importance that the drug‐hunting companies minimize late attritions due to sub‐optimal pharmacokinetic properties or unexpected toxicity when entering the clinical programs. To achieve this, a strong need to test new candidate drugs in assays of high human relevance in vitro as early as possible has been identified. The traditionally used cell systems are however remarkably limited in this sense, and new improved technologies are of greatest importance. The human embryonic stem cells (hESC) is one of the most powerful cell types known. They have not only the possibility to divide indefinitely; these cells can also differentiate into all mature cell types of the human body. This makes them potentially very valuable for pharmaceutical development, spanning from use as tools in early target studies, DMPK or safety assessment, as screening models to find new chemical entities modulating adult stem cell fate, or as the direct use in cell therapies. This review illustrates the use of hESC in the drug discovery process, today, as well as in a future perspective. This will specifically be exemplified with the most important cell type for pharmaceutical development—the hepatocyte. We discuss how hESC‐derived hepatocyte‐like cells could improve this process, and how these cells should be cultured if optimized functionality and usefulness should be achieved. J. Cell. Physiol. 219: 513–519, 2009. © 2009 Wiley‐Liss, Inc.     

Impact of drug discovery on stem cell biology

Despite the rapid technical progress in pharmaceutical industry in the past decade, it is still a great challenge to find new drugs and the situation seems more and more serious. However, the history of pharmaceutical industry clearly indicated that the significance of drug discovery went far beyond providing new drugs. For instance, drugs or candidates could be used as selective probes to reveal novel cellular mechanisms, which is a fundamental tenet of chemical biology. More interestingly, accumulating evidence indicates that drugs and candidates can find important use in stem cell biology. Not only approved drugs but also undeveloped pharmacological agents could serve as efficient agents to regulate stem cell fate. Moreover, the target and activity knowledge accumulated during the drug discovery process will help select the stem cell fate modulators in a rational manner. As the progress in stem cell biology will bring positive influence to drug discovery, it can be expected that the current drug discovery efforts will finally bear great fruits in the future.     

Large animal models for cardiac stem cell therapies

Cardiovascular disease is the leading cause of death in developed countries and is one of the leading causes of disease burden in developing countries. Therapies have markedly increased survival in several categories of patients, nonetheless mortality still remains high. For this reason high hopes are associated with recent developments in stem cell biology and regenerative medicine that promise to replace damaged or lost cardiac muscle with healthy tissue, and thus to dramatically improve the quality of life and survival in patients with various cardiomyopathies.Much of our insight into the molecular and cellular basis of cardiovascular biology comes from small animal models, particularly mice. However, significant differences exist with regard to several cardiac characteristics when mice are compared with humans. For this reason, large animal models like dog, sheep and pig have a well established role in cardiac research. A distinct characteristic of cardiac stem cells is that they can either be endogenous or derive from outside the heart itself; they can originate as the natural course of their differentiation programme (e.g., embryonic stem cells) or can be the result of specific inductive conditions (e.g., mesenchymal stem cells). In this review we will summarize the current knowledge on the kind of heart-related stem cells currently available in large animal species and their relevance to human studies as pre-clinical models.     

Cardiomyocyte differentiation of pluripotent stem cells and their use as cardiac disease models

More than 10 years after their first isolation, human embryonic stem cells are finally 'coming of age' in research and biotechnology applications as protocols for their differentiation and undifferentiated expansion in culture become robust and scalable, and validated commercial reagents become available. Production of human cardiomyocytes is now feasible on a daily basis for many laboratories with tissue culture expertise. An additional recent surge of interest resulting from the first production of human iPSCs (induced pluripotent stem cells) from somatic cells of patients now makes these technologies of even greater importance since it is likely that (genetic) cardiac disease phenotypes can be captured in the cardiac derivatives of these cells. Although cell therapy based on replacing cardiomyocytes lost or dysfunctional owing to cardiac disease are probably as far away as ever, biotechnology and pharmaceutical applications in safety pharmacology and drug discovery will probably impact this clinical area in the very near future. In the present paper, we review the cutting edge of this exciting area of translational research.     

Human biomarker discovery and predictive models for disease progression for idiopathic pneumonia syndrome following allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (SCT) is the only curative therapy for many malignant and nonmalignant conditions. Idiopathic pneumonia syndrome (IPS) is a frequently fatal complication that limits successful outcomes. Preclinical models suggest that IPS represents an immune mediated attack on the lung involving elements of both the adaptive and the innate immune system. However, the etiology of IPS in humans is less well understood. To explore the disease pathway and uncover potential biomarkers of disease, we performed two separate label-free, proteomics experiments defining the plasma protein profiles of allogeneic SCT patients with IPS. Samples obtained from SCT recipients without complications served as controls. The initial discovery study, intended to explore the disease pathway in humans, identified a set of 81 IPS-associated proteins. These data revealed similarities between the known IPS pathways in mice and the condition in humans, in particular in the acute phase response. In addition, pattern recognition pathways were judged to be significant as a function of development of IPS, and from this pathway we chose the lipopolysaccaharide-binding protein (LBP) protein as a candidate molecular diagnostic for IPS, and verified its increase as a function of disease using an ELISA assay. In a separately designed study, we identified protein-based classifiers that could predict, at day 0 of SCT, patients who: 1) progress to IPS and 2) respond to cytokine neutralization therapy. Using cross-validation strategies, we built highly predictive classifier models of both disease progression and therapeutic response. In sum, data generated in this report confirm previous clinical and experimental findings, provide new insights into the pathophysiology of IPS, identify potential molecular classifiers of the condition, and uncover a set of markers potentially of interest for patient stratification as a basis for individualized therapy.     

Advances in the development of chordoma models for drug discovery and precision medicine

Chordomas are malignant bone tumors that arise from remnants of the notochord. These tumors are generally slow-growing, locally aggressive, and invasive. Chordomas are typically resistant to conventional chemo- and radiotherapy. The clinical management of this disease is very challenging, usually, treatment is surgical resection, which may be combined with radiotherapy. Although chordomas have undergone histologic and genetic analysis, the molecular mechanisms that drive their pathogenesis and resistance are still largely unknown. For many years this could be attributed to the lack of accurate and reliable in vitro and in vivo tumor models. Yet, over the past decade, many efforts have been made to prioritize the generation of useful chordoma cell lines, and tumor models that have shed more light on this malignancy and have made efficacious drug discovery a greater possibility. This review summarizes and discusses recent enhancements and improvements made to generate useful chordoma models and their applications in drug discovery and precision medicine.     

Bioprocessing of embryonic stem cells for drug discovery

Embryonic stem cells provide a potential resource for research and drug screening. To make such a resource feasible, it is necessary to generate cells of sufficient quality and quantity. The challenge is to expand cell numbers while maintaining the fidelity of phenotype and to control and direct differentiation to produce the cell type of interest in a format that is suitable for drug screening. At present, large-scale culturing of human ES cell lines is problematic and provides substantial challenges. This article provides an overview of current bioprocessing techniques that could be used to generate cells for drug discovery applications. This will generate further technical expertise that can be applied in the production of cells for potential therapeutic applications.     

Prospects for pluripotent stem cell‐derived cardiomyocytes in cardiac cell therapy and as disease models

The derivation of embryonic stem cells (hESC) from human embryos a decade ago started a new era in perspectives for cell therapy as well as understanding human development and disease. More recently, reprogramming of somatic cells to an embryonic stem cell‐like state (induced pluripotent stem cells, iPS) presented a new milestone in this area, making it possible to derive all cells types from any patients bearing specific genetic mutations. With the development of efficient differentiation protocols we are now able to use the derivatives of pluripotent stem cells to study mechanisms of disease and as human models for drug and toxicology testing. In addition derivatives of pluripotent stem cells are now close to be used in clinical practice although for the heart, specific additional challenges have been identified that preclude short‐term application in cell therapy. Here we review techniques presently used to induce differentiation of pluripotent stem cells into cardiomyocytes and the potential these cells have as disease models and for therapy. J. Cell. Biochem. 107: 592–599, 2009. © 2009 Wiley‐Liss, Inc.     

Pluripotent human stem cells for the treatment of retinal disease

Despite advancements made in our understanding of ocular biology, therapeutic options for many debilitating retinal diseases remain limited. Stem cell-based therapies are a potential avenue for treatment of retinal disease, and this mini-review will focus on current research in this area. Cellular therapies to replace retinal pigmented epithelium (RPE) and/or photoreceptors to treat age-related macular degeneration (AMD), Stargardt's macular dystrophy, and retinitis pigmentosa are currently being developed. Over the past decade, significant advancements have been made using different types of human stem cells with varying capacities to differentiate into these target retinal cell types. We review and evaluate pluripotent stem cells, both human embryonic stem cells and human induced pluripotent stem cells, as well as protocols for differentiation of ocular cells, and culture and transplant techniques that might be used to deliver cells to patients.     

Molecular imaging strategies for drug discovery and development

Recent advances in non-invasive molecular imaging provide exciting opportunities for discovery, validation and development of novel therapeutics. As the arsenal of detection devices and strategies, injectable probes, genetically encoded reporters and animal models rapidly expands, molecular imaging is becoming indispensable for drug discovery and development. Not only do such strategies reduce the time, cost and workload associated with conventional destructive end-point assays, but they also enable spatial and temporal monitoring of in vivo gene expression, signaling pathways, biochemical reactions and targets as they relate to the pharmacokinetics and pharmacodynamics of novel drugs.     

Constructing and deconstructing stem cell models of neurological disease

Among the disciplines of medicine, the study of neurological disorders is particularly challenging. The fundamental inaccessibility of the human neural types affected by disease prevents their isolation for in?vitro studies of degenerative mechanisms or for drug screening efforts. However, the ability to reprogram readily accessible tissue from patients into pluripotent stem (iPS) cells may now provide a general solution to this shortage of human neurons. Gradually improving methods for directing the differentiation of patient-specific stem cells has enabled the production of several neural cell types affected by disease. Furthermore, initial studies with stem cell lines derived from individuals with pediatric, monogenic disorders have validated the stem cell approach to disease modeling, allowing relevant neural phenotypes to be observed and studied. Whether iPS cell-derived neurons will always faithfully recapitulate the same degenerative processes observed in patients and serve as platforms for drug discovery relevant to common late-onset diseases remains to be determined.     

Biocatalysis in drug discovery and development

Enzyme catalysis, enabled by advances in protein engineering and directed evolution, is beginning to transform chemical synthesis in the pharmaceutical industry. This review presents recent examples of the creative use of biocatalysis to enable drug discovery and development. We illustrate how increased access to novel biotransformations and the rise of cascade biocatalysis allowed fundamentally new syntheses of novel medicines, representing progress toward more sustainable pharmaceutical manufacturing. Finally, we describe the opportunities and challenges the industry must address to ensure the reduction to practice of biotechnological innovations to develop new therapies in a faster, more economical, and environmentally benign way.     

Pluripotent stem cell heterogeneity and the evolving role of proteomic technologies in stem cell biology

Stem cells represent obvious choices for regenerative medicine and are invaluable for studies of human development and drug testing. The proteomic landscape of pluripotent stem cells (PSCs), in particular, is not yet clearly defined; consequently, this field of research would greatly benefit from concerted efforts designed to better characterize these cells. In this concise review, we provide an overview of stem cell potency, highlight the types and practical implications of heterogeneity in PSCs and provide a detailed analysis of the current view of the pluripotent proteome in a unique resource for this rapidly evolving field. Our goal in this review is to provide specific insights into the current status of the known proteome of both mouse and human PSCs. This has been accomplished by integrating published data into a unified PSC proteome to facilitate the identification of proteins, which may be informative for the stem cell state as well as to reveal areas where our current view is limited. These analyses provide insight into the challenges faced in the proteomic analysis of PSCs and reveal one area--the cell surface subproteome--that would especially benefit from enhanced research efforts.