The application of human embryonic stem cell technologies to drug discovery

The possible use of stem cells in regenerative medicine: dream or reality?

Stem cells are one of the most fascinating areas in regenerative medicine today. They play a crucial role in the development and regeneration of human life and are defined as cells that continuously reproduce themselves while maintaining the ability to differentiate into various cell types. Stem cells are found at all developmental stages, from embryonic stem cells that differentiate into all cell types found in the human body to adult stem cells that are responsible for tissue regeneration. The general opinion postulates that clinical therapies based on the properties of stem cells may have the potential to change the treatment of degenerative diseases or important traumatic injuries in the "near" future. We here briefly review the literature in particularly for the liver, heart, kidney, cartilage, and bone regeneration.

High-throughput cellular microarray platforms: applications in drug discovery, toxicology and stem cell research

Cellular microarrays are powerful experimental tools for high-throughput screening of large numbers of test samples. Miniaturization increases assay throughput while reducing reagent consumption and the number of cells required, making these systems attractive for a wide range of assays in drug discovery, toxicology, stem cell research and potentially therapy. Here, we provide an overview of the emerging technologies that can be used to generate cellular microarrays, and we highlight recent significant advances in the field. This emerging and multidisciplinary approach offers new opportunities for the design and control of stem cells in tissue engineering and cellular therapies and promises to expedite drug discovery in the biotechnology and pharmaceutical industries.

Gene expression profiling of functional murine embryonic stem cell-derived cardiomyocytes and comparison with adult heart: profiling of murine ESC-derived cardiomyocytes

Although embryonic stem cell (ESC)-derived cardiomyocytes may be a powerful tool in drug discovery, their potential has not yet been fully explored. Nor has a detailed comparison with adult heart tissue been performed. We have developed a method for efficient production of cardiomyocyte-rich embryoid bodies (EBs) from murine ESCs. Analysis of global gene expression profiles showed that EBs on day 7 and/or 21 of differentiation (d7CMs and d21CMs, respectively) were similar to adult heart tissue for genes categorized as regulators of muscle contraction or voltage-gated ion channel activity, although d21CMs were more mature than d7CMs for contractile components related to morphological structures. Calcium and sodium channel blockers altered Ca2+ transients, and isoproterenol, a beta-adrenergic compound, increased the rate of beating in d7CMs and d21CMs. Our gene analytic system therefore enabled us to identify genes that are expressed in the physiological pathways associated with ion channels and structural components in d7CMs and d21CMs. We conclude that EBs might be of use for the basic screening of drugs that might affect contractile function through ion channels.

Human embryonic stem cell-derived motor neurons are sensitive to the toxic effect of glial cells carrying an ALS-causing mutation

It has been proposed that human embryonic stem cells could be used to provide an inexhaustible supply of differentiated cell types for the study of disease processes. Although methods for differentiating embryonic stem cells into specific cell types have become increasingly sophisticated, the utility of the resulting cells for modeling disease has not been determined. We have asked whether specific neuronal subtypes produced from human embryonic stem cells can be used to investigate the mechanisms leading to neural degeneration in amyotrophic lateral sclerosis (ALS). We show that human spinal motor neurons, but not interneurons, are selectively sensitive to the toxic effect of glial cells carrying an ALS-causing mutation in the SOD1 gene. Our findings demonstrate the relevance of these non-cell-autonomous effects to human motor neurons and more broadly demonstrate the utility of human embryonic stem cells for studying disease and identifying potential therapeutics.

An historical overview of drug discovery

Drug Discovery in modern times straddles three main periods. The first notable period can be traced to the nineteenth century where the basis of drug discovery relied on the serendipity of the medicinal chemists. The second period commenced around the early twentieth century when new drug structures were found, which contributed for a new era of antibiotics discovery. Based on these known structures, and with the development of powerful new techniques such as molecular modelling, combinatorial chemistry, and automated high-throughput screening, rapid advances occurred in drug discovery towards the end of the century. The period also was revolutionized by the emergence of recombinant DNA technology, where it became possible to develop potential drugs target candidates. With all the expansion of new technologies and the onset of the "Omics" revolution in the twenty-first century, the third period has kick-started with an increase in biopharmaceutical drugs approved by FDA/EMEA for therapeutic use.

[Human embryonic stem cells within the context of international research activity]

Research involving pluripotent human embryonic stem cells (hESCs) is a rapidly growing field of science. Since hESCs originate from early human embryos, alternative methods for producing pluripotent cells have been developed. This article introduces some of those strategies and, in addition, covers international efforts to establish consistent international standards for cultivation, characterization and preservation of hESCs. Furthermore, global trends to form networks in the field of stem cell research as well as endeavors to harmonize ethical standards for hESC research are presented. Finally, potential applications of hESCs in the field of pharmacology/toxicology are discussed as well as recent results of animal studies using hESCs.

Investigations into the liver effects of ximelagatran using high content screening of primary human hepatocyte cultures

BACKGROUND

Ximelagatran, the first oral agent in the new class of direct thrombin inhibitors, was withdrawn from the market due to increased rates of liver enzyme elevations in long-term treatments. Despite intensive pre clinical investigations the cellular mechanisms behind the observed hepatic effects remain unknown.

OBJECTIVE

The aim of this study was to assess drug-induced cytotoxicity in primary human hepatocyte cultures by ximelagatran and other reference pharmaceutical agents with known in vivo hepatotoxic profiles.

METHODS

Drugs cause liver injury by many distinct mechanisms that result in abnormal cellular functioning and different patterns of injury. To address many potential toxic mechanisms in a human-relevant model, freshly isolated human hepatocytes were used in automated imaging assays. Ximelagatran was used as a test compound to study biochemical and morphological changes in human hepatocytes. In addition, 11 control, reference and comparator compounds with known liver-toxic potential in humans were used. The response to these compounds was assessed across five different hepatocyte donor preparations.

RESULTS

Cytotoxicity induced by a number of compounds was quantitatively monitored using an automated imaging technique. A variety of morphological changes in hepatocyte cytoskeleton and mitochondrial function could be identified at sublethal doses of test compounds. Doses of ximelagatran up to 500 microM did not cause a cytotoxic response in the majority of preparations and no subcytotoxic response was observed at doses below 125 microM.

CONCLUSIONS

The experiments described here demonstrate that primary human hepatocytes may be used in a medium-throughput format for screening using imaging-based assays for the identification of cellular responses. Overall, it is concluded that ximelagatran did not cause a significant decrease in cell viability when incubated for 24 h at considerably higher concentrations than are found in plasma following therapeutic dosing.

Molecular signature of cardiomyocyte clusters derived from human embryonic stem cells

Human embryonic stem cells (hESCs) can differentiate in vitro into spontaneously contracting cardiomyocytes (CMs). These cells may prove extremely useful for various applications in basic research, drug discovery, and regenerative medicine. To fully use the potential of the cells, they need to be extensively characterized, and the regulatory mechanisms that control hESC differentiation toward the cardiac lineage need to be better defined. In this study, we used microarrays to analyze, for the first time, the global gene expression profile of isolated hESC-derived CM clusters. By comparing the clusters with undifferentiated hESCs and using stringent selection criteria, we identified 530 upregulated and 40 downregulated genes in the contracting clusters. To further characterize the family of upregulated genes in the hESC-derived CM clusters, the genes were classified according to their Gene Ontology annotation. The results indicate that the hESC-derived CM clusters display high similarities, on a molecular level, to human heart tissue. Moreover, using the family of upregulated genes, we created protein interaction maps that revealed topological characteristics. We also searched for cellular pathways among the upregulated genes in the hESC-derived CM clusters and identified eight significantly upregulated pathways. Real-time quantitative polymerase chain reaction and immunohistochemical analysis confirmed the expression of a subset of the genes identified by the microarrays. Taken together, the results presented here provide a molecular signature of hESC-derived CM clusters and further our understanding of the biological processes that are active in these cells.