Embryonic stem cells: a novel source of dendritic cells for clinical applications

As arbitrators of the immune response, dendritic cells (DC) are uniquely placed to negotiate the balance between the opposing forces of tolerance and immunity, making them attractive candidates for clinical applications. Accordingly, DC have been used successfully in the treatment of cancer, enhancing immune responses to tumour-associated antigens (TAA) in experimental animal models and phase I clinical trials. A novel source of DC that has recently been described is the embryonic stem (ES) cell whose differentiation in vitro may be directed along multiple lineage pathways. Such pluripotency offers unparalleled opportunities for the treatment of chronic and degenerative disease states by the replacement of affected tissues, a vision which has inspired the emerging field of regenerative medicine. By sharing the genotype of therapeutic cell types, such as cardiomyocytes and dopaminergic neurons derived from the same ES cell line, so-called esDC may offer prospects for reprogramming the immune system to tolerate the grafted tissues. Here, we describe how the unique properties of esDC and the ES cells from which they derive, make them eminently suited to clinical applications, overcoming many of the issues that currently limit the effectiveness of DC-based immune intervention.     

Drug delivery strategies for therapeutic angiogenesis and antiangiogenesis

INTRODUCTION: Angiogenesis is essential to human biology and of great clinical significance. Excessive or reduced angiogenesis can result in, or exacerbate, several disease states, including tumor formation, exudative age-related macular degeneration (AMD) and ischemia. Innovative drug delivery systems can increase the effectiveness of therapies used to treat angiogenesis-related diseases. AREAS COVERED: This paper reviews the basic biology of angiogenesis, including current knowledge about its disruption in diseases, with the focus on cancer and AMD. Anti- and proangiogenic drugs available for clinical use or in development are also discussed, as well as experimental drug delivery systems that can potentially improve these therapies to enhance or reduce angiogenesis in a more controlled manner. EXPERT OPINION: Laboratory and clinical results have shown pro- or antiangiogenic drug delivery strategies to be effective in drastically slowing disease progression. Further research in this area will increase the efficacy, specificity and duration of these therapies. Future directions with composite drug delivery systems may make possible targeting of multiple factors for synergistic effects.     

Drug delivery strategies for therapeutic angiogenesis and antiangiogenesis

Introduction: Angiogenesis is essential to human biology and of great clinical significance. Excessive or reduced angiogenesis can result in, or exacerbate, several disease states, including tumor formation, exudative age-related macular degeneration (AMD) and ischemia. Innovative drug delivery systems can increase the effectiveness of therapies used to treat angiogenesis-related diseases.

Areas covered: This paper reviews the basic biology of angiogenesis, including current knowledge about its disruption in diseases, with the focus on cancer and AMD. Anti- and proangiogenic drugs available for clinical use or in development are also discussed, as well as experimental drug delivery systems that can potentially improve these therapies to enhance or reduce angiogenesis in a more controlled manner.

Expert opinion: Laboratory and clinical results have shown pro- or antiangiogenic drug delivery strategies to be effective in drastically slowing disease progression. Further research in this area will increase the efficacy, specificity and duration of these therapies. Future directions with composite drug delivery systems may make possible targeting of multiple factors for synergistic effects.     

Embryonic stem cells: meeting the needs for cell therapy

Cell therapy in diverse organs has bloomed for degenerative diseases over the past decade, following a previous period of development in which haematopoietic stem cells grafts in oncology were its most prominent clinical application. One main limitation that has, however, been encountered on the path for transforming pioneering successes into real therapeutics, that would be applicable to a clinically relevant number of patients, is the difficulty in accessing "therapeutic" cells, such as foetal neurons in neurodegenerative diseases, adult pancreatic beta cells in diabetes or else myoblasts in heart failure and myopathy. The future of cell therapy definitely belongs to cell banks, from which physicians would simply have to draw according to their needs. However, besides haematopoietic stem cells, for which such infrastructures begin to exist for clinical purposes (in particular from cord blood), cell banks are still up to now essentially a scientific concept. This review focuses on the possibility for human ES cells to meet both the requirements of cell banking and the needs for substitutive cell therapy.     

Embryonic stem cells: a great hope for a new era of medicine

Current stem-cell research has the potential to lead to new approaches for the treatment of cardiovascular, neurodegenerative and musculoskeletal diseases, as well as diabetes and cancer. Stem-cell-based approaches could be employed in cell-replacement therapy or in drug treatments that encourage adult stem cells to migrate and activate at a site of injury or disease. For such therapeutic approaches to be successful, a greater understanding of the signaling pathways that determine the diverse developmental fates of these cells is needed. From a drug-discovery perspective, efforts are being deployed in developing cell-based assays to screen for small molecules that can modulate stem-cell fate. Such compounds will provide new insights into stem-cell biology, and may ultimately contribute to effective disease treatments.     

Embryonic stem cells as a source of models for drug discovery

Embryonic stem cells (ESCs) will become a source of models for a wide range of adult differentiated cells, providing that reliable protocols for directed differentiation can be established. Stem-cell technology has the potential to revolutionize drug discovery, making models available for primary screens, secondary pharmacology, safety pharmacology, metabolic profiling and toxicity evaluation. Models of differentiated cells that are derived from mouse ESCs are already in use in drug discovery, and are beginning to find uses in high-throughput screens. Before analogous human models can be obtained in adequate numbers, reliable methods for the expansion of human ESC cultures will be needed. For applications in drug discovery, involving either species, protocols for directed differentiation will need to be robust and affordable. Here, we explore current challenges and future opportunities in relation to the use of stem-cell technology in drug discovery, and address the use of both mouse and human models.     

Neural stem cells: a pharmacological tool for brain diseases?

Stem cells are believed to provide a tool by which new cells and tissues can be made and by which damaged ones can be replaced or repaired. Over the past few years, the existence of a subset of stem cells has been documented in the fetal brain, therefore named neural stem cells (NSCs). To this regard, the more recent demonstration that similar cells are present in the adult mammalian brain and retain the capability to produce new neurons, has undermined the dogma that neurons are only generated during the fetal life and has stimulated investigations into the regulation and role of adult neurogenesis. Here, we will review the recent advancements on the biology of brain stem cells and discuss the mechanisms and drugs regulating adult neurogenesis, aiming at better estimating the possible future applications of NSCs for brain repair.     

Embryonic stem cells: a perfect marriage between gene regulation and regenerative medicine

The mechanism of mammalian gene regulation is highly complex, involving multiple layers of feedback control loops and dynamic chromatin remodeling. The current approach used to dissect the genetic circuitry of mammalian gene regulation utilizes somatic cells and protein fusion as a means to modulate protein interactions. This approach has several limitations that include (i) genome inaccessibility, (ii) high background interferences and, (iii) limited cellular phenotypes. Previously, the two broad fields of research "control of gene expression" and "stem cell biology" had been pursued separately by cell biologists; this review outlines evidence suggesting that integration of these two fields would provide a comprehensive platform for interdisciplinary research seeking to address mechanistic questions concerning gene regulation-that could have enormous implication for the development of therapeutic applications.     

Integrin alpha v beta 3 as a therapeutic target for blocking tumor-induced angiogenesis

The integrin receptor alphavbeta3 has been shown to play a critical role in several distinct processes, such as angiogenesis, osteoclast-mediated bone resorption and tumor metastasis. Its expression is upregulated in newly synthesized blood vessels produced in response to a variety of tumors and purified angiogenic factors. Studies show that alphavbeta3 is a critical target downstream from perhaps all angiogcnic factors. Proof-of-principle that alphavbeta3 antagonists such as monoclonal antibodies and small molecules block angiogenesis and tumor growth has been obtained in several animal models. Many endogenous inhibitors of angiogenesis such as angiostatin, endostatin and tumstatin seem to work through the alphavbeta3 receptor further emphasizing the critical role of this receptor in angiogenesis. In addition, the alphavbeta3 receptor has been clearly implicated in several pathological processes such as rheumatoid arthritis, osteoporosis, and metastasis of prostate cancer to bone. Thus alphavbeta3 may prove to be an important target for pharmacological intervention in more than one clinical setting.     

Embryonic stem cells and the next generation of developmental toxicity testing

Introduction: The advent of stem cell technology has seen the establishment of embryonic stem cells (ESCs) as molecular model systems and screening tools. Although ESCs are nowadays widely used in research, regulatory implementation for developmental toxicity testing is pending.

Areas Covered: This review evaluates the performance of current ESC, including human (h)ESC testing systems, trying to elucidate their potential for developmental toxicity testing. It shall discuss defining parameters and mechanisms, their relevance and contemplate what can realistically be expected. Crucially this includes the question of how to ascertain the quality of currently employed cell lines and tests based thereon. Finally, the use of hESCs will raise ethical concerns which should be addressed early on.

Expert Opinion: While the suitability of (h)ESCs as tools for research and development goes undisputed, any routine use for developmental toxicity testing currently still seems premature. The reasons for this comprise inherent biological deficiencies as well as cell line quality and system validation. Overcoming these issues will require collaboration of scientists, test developers and regulators. Also, validation needs to be made worthwhile for academia. Finally we have to continuously rethink existing strategies, making room for improved testing and innovative approaches.     

Embryonic stem cell-derived hematopoietic stem cells: challenges in development, differentiation, and immunogenicity

Embryonic stem cells (ESC) can potentially be manipulated in vitro to differentiate into cells and tissues of all three germ layers. This pluripotent feature is being exploited to use ESC-derived tissues as therapies for degenerative diseases and replacement of damaged organs. Although their potential is great, the promise of ESC-derived therapies will be unfulfilled unless several challenges are overcome. For example, inefficient production of ESC-derived tissues before transplantation, inability of ESC-derived tissues to integrate well into the adult microenvironments due to developmental stage incompatibility, or active immune rejection of the ESC-derived graft are all potential challenges to successful ESC-derived therapies. One way to induce immunological tolerance to allogeneic tissues is via the establishment of mixed hematopoietic chimerism in which the host and donor cells are educated to recognize each other as "self". Proof of principle that in vitro cultured ESC-derived hematopoietic progenitors can be transplanted and induce immunological tolerance to allogeneic tissues exists in mouse models. In this review, we discuss the challenges to in vitro development of a bona fide ESC-derived hematopoietic stem cell and their differentiation fate in vivo, and provide suggestions to predict the immunogenicity of specific ESC-derived hematopoietic populations before transplantation that could be used to prevent their rejection after transplantation into an adult host.     

Stem cells and small molecule screening: haploid embryonic stem cells as a new tool

Stem cells can both self-renew and differentiate into various cell types under certain conditions, which makes them a good model for development and disease studies. Recently, chemical approaches have been widely applied in stem cell biology by promoting stem cell self-renewal, proliferation, differentiation and somatic cell reprogramming using specific small molecules. Conversely, stem cells and their derivatives also provide an efficient and robust platform for small molecule and drug screening. Here, we review the current research and applications of small molecules that modulate stem cell self-renewal and differentiation and improve reprogramming, as well as the applications that use stem cells as a tool for small molecule screening. Moreover, we introduce the recent advance in haploid embryonic stem cells research. Haploid embryonic stem cells maintain haploidy and stable growth over extensive passages, possess the ability to differentiate into all three germ layers in vitro and in vivo, and contribute to the germlines of chimeras when injected into blastocysts. Androgenetic haploid stem cells can also be used in place of sperm to produce fertile progeny after intracytoplasmic injection into mature oocytes. Such characteristics demonstrate that haploid stem cells are a new approach for genetic studies at both the cellular and animal levels and that they are a valuable platform for future small molecule screening.     

Embryonic stem cells: understanding their history, cell biology and signalling

Embryonic stem cells offer enormous potential as a source of a variety of differentiated cells for cell therapy, drug discovery and toxicology screening. With the creation of human embryonic stem cell lines we now have a resource with the potential to differentiate into every tissue of the body. To fully harness this resource it is necessary to understand their biology. Here we give a background to their history, describe interesting elements of their cell biology and introduce the underlying signalling mechanisms that control their ability to self-renew and differentiate.     

Induced pluripotent stem cells: a new tool to confront the challenge of neuropsychiatric disorders

Studies in the area of human brain development are critical as research on neurological and psychiatric disorders has advanced, revealing the origins of pathophysiology to be in the earliest developmental stages. Only with a more precise understanding of the genes and environments that influence the brain in these early stages can we address questions about the pathology, diagnosis, prevention and treatment of neuropsychiatric disorders of developmental origin, like autism, schizophrenia, and Tourette syndrome. A new approach for studying early developmental events is the use of induced pluripotent stem cells (iPSCs). These are cells with wide potential, similar to that of embryonic stem cells, derived from mature somatic cells. We review the protocols used to create iPSCs, including the most efficient and reliable reprogramming strategies available to date for generating iPSCs. In addition, we discuss how this new tool can be applied to neuropsychiatric research. The use of iPSCs can advance our understanding of how genes and gene products are dynamically involved in the formation of unique features of the human brain, and how aberrant genetic variation may interfere with its typical formation. The iPSC technology, if properly applied, can also address basic questions about neural differentiation such as how stem cells can be guided into general and specific neurodevelopmental pathways. Current work in neuropsychiatry with iPSCs derived from patients has focused on disorders with specific genetics deficits and those with less-defined origins; it has revealed previously unknown aspects of pathology and potential pharmacological interventions. These exciting advances based on the use of iPSCs hold promise for improving early diagnosis and, possibly, treatment of psychiatric disorders. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.     

Differential role of epigenetic modulators in malignant and normal stem cells: a novel tool in preclinical in vitro toxicology and clinical therapy

Adult stem cells are primitive cells that undergo asymmetric division, thereby giving rise to one clonogenic, self-renewing cell and one cell able to undergo multipotent differentiation. Disturbance of this controlled process by epigenetic alterations, including imbalance of histone acetylation/histone deacetylation and DNA methylation/demethylation, may result in uncontrolled growth, formation of self-renewing malignant stem cells and eventually cancer. In view of this notion, several epigenetic modulators, in particular those with histone deacetylase inhibiting activity, are currently being tested in phase I and II clinical trials for their promising chemotherapeutic properties in cancer therapy. As chromatin modulation is also involved in regulation of differentiation, normal development, embryonic and adult stem cell functions and maintenance of their plasticity during embryonic organogenesis, the question can be raised whether predestined cell fate can be modified through epigenetic interference. And if so, could this strategy enforce adult stem cells to differentiate into different types of functional cells? In particular, functional hepatocytes seem important for preclinical toxicity screening of candidate drugs. This paper reviews the potential use and relevance of epigenetic modifiers, including inhibitors of histone deacetylases and DNA methyltransferases (1) to change cell fate and ‘trans’differentiate normal adult stem cells into hepatocyte-like cells and (2) to cure disorders, caused by uncontrolled growth of malignant stem cells.     

Intrapleural delivery of mesenchymal stem cells: a novel potential treatment for pleural diseases

Aim:

To develop a method to deliver mesenchymal stem cells (MSCs) into the pleural cavity for the treatment of pleural diseases.

Methods:

MSCs were isolated from rat bone marrow of rats and labeled with 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) or green fluorescent protein (GFP) using a lentiviral vector. Eighteen Sprague-Dawley (SD) rats were inoculated intrapleurally with 1×10⁶ MSCs-DAPI. The distribution of the fluorescent cells was observed using fluorescent microscopy for the following 30 d. Another 12 rats inoculated intrapleurally with 1×10⁶ MSCs-GFP were observed for 14 d.

Results:

The isolated cells were typical MSC phenotypes and could differentiate into adipocytes, osteoblasts, and chondroblasts in vitro. Microscopic analysis revealed that the labeled cells adhered to the surface of the pleural cavity. The highest number of the labeled cells was found to be adhered to all specimens from the mediastinal pleura, but no labeled cells were detected in the lung parenchyma or other tissues/organs, such as the liver, kidney, spleen, and mesenterium. Incidentally, stomas were found in the mediastinal pleura. The recovered MSCs-GFP from the pleural cavity retained their ability to adhere and proliferate.

Conclusion:

We have established a novel method for intrapleural delivery of MSCs. The distribution of intrapleurally delivered MSCs was found to be limited to the pleurae and the pleural cavity, thereby providing us with a new approach to further investigation of the therapeutic roles of MSCs in pleural diseases.     

PI-88: a novel inhibitor of angiogenesis

Growth factors that stimulate angiogenesis are vital in tumor development and maintenance. Inhibitors of angiogenesis are emerging as key elements in anticancer treatments, and now antibodies and small molecule kinase inhibitors are approved in the treatment of a variety of solid tumors. These have shown modest but statistically significant benefit in colon, breast and lung cancers. PI-88 has a novel mechanism of action compared to the drugs on the market today. By inhibiting heparanase, PI-88 blocks angiogenesis on several different cellular and biological levels. Promising results from Phase I/II trials are being seen with PI-88 in a variety of tumor types including melanoma and hepatocellular carcinoma. However, the development of antibody-induced thrombocytopenia has limited its use in some patients.     

PI-88: a novel inhibitor of angiogenesis

Growth factors that stimulate angiogenesis are vital in tumor development and maintenance. Inhibitors of angiogenesis are emerging as key elements in anticancer treatments, and now antibodies and small molecule kinase inhibitors are approved in the treatment of a variety of solid tumors. These have shown modest but statistically significant benefit in colon, breast and lung cancers. PI-88 has a novel mechanism of action compared to the drugs on the market today. By inhibiting heparanase, PI-88 blocks angiogenesis on several different cellular and biological levels. Promising results from Phase I/II trials are being seen with PI-88 in a variety of tumor types including melanoma and hepatocellular carcinoma. However, the development of antibody-induced thrombocytopenia has limited its use in some patients.     

Stem cells as a novel tool for drug screening and treatment of degenerative diseases

Degenerative diseases similarly as acute tissue injuries lead to massive cell loss and may cause organ failure of vital organs (e.g., heart, central nervous system). Therefore, they belong to a group of disorders that may significantly benefit from stem cells (SCs)-based therapies. Several stem and progenitor cell populations have already been described as valuable tools for developing therapeutic strategies in regenerative medicine. In particular, pluripotent stem cells (PSCs), including adult-tissue-derived PSCs, neonatal-tissue-derived SCs, embryonic stem cells (ESCs), and recently described induced pluripotent stem cells (iPSCs), are the focus of particular attention because of their capacity to differentiate into all the cell lineages. Although PSCs are predominantly envisioned to be applied for organ regeneration, they may be also successfully employed in drug screening and disease modeling. In particular, adult PSCs and iPSCs derived from patient tissues may not only be a source of cells for autologous therapies but also for individual customized in vitro drug testing and studies on the molecular mechanisms of disease. In this review, we will focus on the potential applications of SCs, especially PSCs i) in regenerative medicine therapies, ii) in studying mechanisms of disease, as well as iii) in drug screening and toxicology tests that are crucial in new drug development. In particular, we will discuss the application of SCs in developing new therapeutic approaches to treat degenerative diseases of the neural system and heart. The advantage of adult PSCs in all the above-mentioned settings is that they can be directly harvested from patient tissues and used not only as a safe non-immunogenic source of cells for therapy but also as tools for personalized drug screening and pharmacological therapies.