Developing Genome-Edited Stem Cells for Therapy of Patients: Assessing Efficacy and Toxicology
Lecturer: Matthew H. Porteus, Stanford University, Stanford, CA.
Genome editing provides a mechanism to precisely alter the DNA sequence of a cell. The most efficient mechanism to achieve genome editing is to induce a site-specific DNA double-strand break at the genomic target site to be modified, thereby activating the cell’s own repair machinery. The CRISPR-Cas9-gRNA system has accelerated the field of genome editing because of its ease of use, its high on-target activity, and its high specificity compared to other nuclease platforms. If a donor template is provided along with the nuclease, the cell will use that donor template to repair the break by homologous recombination and precise sequence changes can be introduced into the target gene. We have focused our efforts on developing a clinically compatible method of engineering human primary blood cells, including hematopoietic stem cells, by homologous recombination. Using this system, we now achieve gene editing by homologous recombination frequencies of 40–80% in CD34+ hematopoietic stem and progenitor cells and 20–50% in primary human T cells. I will discuss our translation of this process to the clinic for genetic diseases of the blood and immune system, including sickle cell disease, and our ability to use homologous recombination to engineer complex phenotypes in primary human T cells. As genome-edited primary human cells are a novel therapeutic, a careful assessment of the safety and toxicology of such products is critical. Traditional methods of evaluating such toxicology using the paradigms of small molecules or biologics may not be appropriate for this different class of therapeutics. Genetically engineered cell based therapeutics have a different PK/PD profile, for example, that needs to be considered. I will discuss some of the approaches we have taken to evaluate safety and toxicology in our genome-edited cell based products.
Adverse Outcome Pathways Are the Future for Regulatory Toxicology
Chairpersons: Ron Hines, US EPA, Research Triangle Park, NC; and Heather Wallace, University of Aberdeen, Aberdeen, United Kingdom.
SOT Debater: Daniel Villeneuve, US EPA, Duluth, MN.
EUROTOX Debater: Brigitte Landesmann, European Commission Joint Research Centre Institute for Health and Consumer Protection, Ispra, Italy.
Each year, the SOT Annual Meeting includes a debate in which leading toxicologists advocate opposing sides of an issue of significant toxicological importance. The debate continues a tradition that originated in the early 1990s. This year, the debaters will address the proposition "Adverse Outcome Pathways Are the Future for Regulatory Toxicology."
Following the recommendations of the 1997 National Academy of Sciences Report Toxicity Testing in the 21st Century, A Vision and Strategy, there has been considerable effort in identifying and characterizing toxicity pathways, i.e., biological pathways with which environmental stressors interact, resulting in an adverse outcome. The toxicity pathway concept was expanded from a focus on individual, human toxicity to adverse impacts on populations and ecosystems with the landmark paper by Ankley et al. (Environ Toxicol Chem 29:730-40, 2010) in which the term adverse outcome pathway (AOP) was coined and defined as "a [chemically agnostic] conceptual construct that portrays existing knowledge concerning the linkage between a direct molecular initiating event and an adverse outcome at a biological level of organization relevant to risk assessment." Since that time, there have been numerous workshops and studies expanding and refining the AOP framework such that it now encompasses signaling networks and represents a framework for organizing and presenting data gathered using multiple approaches. In a joint effort between the US Environmental Protection Agency (US EPA) and the Organisation for Economic Co-operation and Development (OECD), an AOP knowledge base is being developed. Although the AOP framework has seen widespread acceptance within the environmental sciences, the use of the framework as a risk assessment and decision-making tool is less apparent. The debaters will discuss the state of AOP science and whether the AOP concept is simply a research tool or truly represents a framework that will serve as the basis for most future regulatory decision making.
Regardless of framework differences and personal convictions, each scientific debate delegate will present relevant evidence and compelling scientific arguments to persuade and appeal to the audience in order to obtain the approval or refusal of the motion. In addition to being a featured session at this meeting, this debate will again take place (with the debaters taking the reverse positions) in Brussels, Belgium, during the 54th Congress of the European Societies of Toxicology (2018 EUROTOX Annual Congress), September 2–5, 2018.
A Conversation with Linda S. Birnbaum, Mark S. Johnson, and Edward J. Perkins
Chairperson: Leigh Ann Burns Naas, Gilead Sciences, Inc., Foster City, CA.
Lecturers: Linda S. Birnbaum, NIEHS, Research Triangle Park, NC; Mark S. Johnson, US Army Public Health Center, Aberdeen Proving Ground, MD; and Edward J. Perkins, US Army Engineer Research and Development Center, Vicksburg, MS.
This important session will provide an informal venue for meeting attendees to have a candid and open discussion with three key leaders of federal organizations with missions to protect and improve public health: Linda S. Birnbaum, PhD, director, National Institute of Environmental Health Sciences (NIEHS), and Mark S. Johnson, PhD, DABT, ATS, and Edward J. Perkins, PhD, two directors from the US Department of Defense (US DoD). The entire session will be devoted to a question-and-answer format concerning scientific directions and priorities for NIEHS and the US DoD (e.g., DTRA, DARPA, SERDP, and ESTCP) including funding priorities and outlooks and training opportunities. Dr. Birnbaum has served as the director of the National Institute of Environmental Health Sciences and the National Toxicology Program since 2009. Dr. Johnson is the director of toxicology at the US Army Public Health Center and the chair of the Tri-Service Toxicology Consortium. Dr. Perkins is a senior scientist in environmental networks and toxicology at the US Army Engineer Research and Development Center.
Circadian Clocks: Setting the Tempo of Our Life
Lecturer: Michael Hastings, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom.
Circadian (approximately one day) rhythms dominate our lives, most obviously via the sleep/wake cycle. Driven by internal clocks, they adapt us to the world by preparing tissues to perform appropriate, but very different, functions in anticipated day and anticipated night. The suprachiasmatic nucleus (SCN) of the hypothalamus is the principal circadian clock of the mammalian brain. It is entrained to solar time by direct retinal innervation, and in turn, it co-ordinates innumerable cellular clocks distributed in all major organs across the body. At a cellular level, circadian timekeeping in SCN and other cells pivots around self-sustaining transcriptional/translational feedback loops (TTFLs) in which the positive regulators CLOCK and BMAL1 drive expression of the negative regulators PERIOD (PER) and CRYPTOCHROME (CRY) via E-box DNA regulatory sequences. Delayed negative feedback by PER and CRY at E-boxes, followed by degradation of PER and CRY, establishes a spontaneous oscillation with a period of approximately 24 hours. This mechanism orchestrates local cell type-specific circadian transcriptomes, synchronized by SCN-dependent behavioral, neuroendocrine, and autonomic cues. These programs in turn sustain the coherent 24-hour cycles of local gene expression that underpin circadian behavior, metabolism, and physiology. This presentation will review recent advances in understanding of the molecular genetic basis of the cell-autonomous clock mechanism of the SCN. It will then consider how circuit-level cellular interactions establish the SCN as a powerful self-sustained clock. Finally, it will consider how the SCN directs circadian behavior and physiology. Where appropriate, it will illustrate how developments in real-time imaging of neuronal function and genetic code expansion have been useful in elucidating the clock’s inner mechanism. The overarching message from the circadian neurobiology field is that our bodies are extremely sophisticated 24-hour machines, an observation with significant implications for health and disease.
Environmental Neurodevelopmental Risk
Chairpersons: Leigh Ann Burns Naas, Gilead Sciences, Inc., Foster City, CA; and Jun Kanno, Japan Organization of Occupational Health and Safety, Kanagawa, Japan.
The Society of Toxicology (SOT) and the Japanese Society of Toxicology (JSOT) are delighted to jointly sponsor a symposium on a topic of mutual interest: environmental neurodevelopmental risk. Each Society has selected from among its membership true leaders in the field to provide their perspectives on recent advances in this area. Understanding critical organ system developmental windows is crucial for determining potentially unique susceptibility to chemical exposure. In 2000, a workshop aimed at identifying how chemical exposure timing during the pre-conception, prenatal, and postnatal period affects outcomes did much to bring to light the concern for potential health risk to these life stages with respect to multiple organ systems, including the central nervous system. In the intervening years, substantial research efforts and regulatory discussion has occurred to identify agents which may impact these systems in a negative way in additional critical developmental phases. Notably, with respect to the developing brain, a significant and controversial debate has arisen across the public domain regarding the notable rise in neurodevelopmental disorders (e.g., attention deficit hyperactivity disorder (ADHD), autism/autism spectrum, learning disabilities, etc.) observed in children over the past 10+ years. While some of the increase (typically cited as a 10-20% rise over the past decade) can be attributed to changes in diagnostic criteria and reporting methodologies, there is still up to 40% of this increase which does not have an identifiable cause. The etiology of neurodevelopmental disorders is clearly a complex and multifactorial one. Genetics may play a role, but alone do not account for the rise in incidence. It is clear that many chemicals can interfere with brain development, some at very low systemic exposures. When this exposure occurs during specific critical developmental windows, the potential for lasting and/or heritable (epigenetic) effects exists. This symposium will explore evidence that exposure to a variety of environmental chemicals at different stages of neurological development may play unique roles in neurodevelopmental risk and will discuss possible paths forward to help curb the rise in this effect in future generations.
Adverse Effects of Neonicotinoids on Mammalian Brain Development: Possible Risk Factors for Neurodevelopmental Disorders Like Autism or ADHD?
Lecturer: Yoichiro Kuroda, Environmental Neuroscience Information Center, Tokyo, Japan.
Junko Kimura-Kuroda, Tokyo Metropolitan Institute of Medical Science, is a co-author of this research.
In the United States, Republic of Korea, and Japan, incidence of neurodevelopmental disorders, such as autism and attention deficit hyperactivity disorder (ADHD), has increased in recent decades. The cause of increase is obviously not genetic, but environmental. Genetic background (more than 800 autism-related genes have been reported) concerning synaptogenesis for higher functions in such impaired children’s brain contributes vulnerability of the disorders. Many environmental chemicals trigger the developmental disorders. Epidemiologic and animal studies demonstrate associations between exposure to organophosphate pesticides and neurodevelopmental disorders, such as decreased cognitive function and behavioral problems. Perinatal exposures of various environmental chemicals (pesticides, PCBs, methylmercury, etc.) disrupt gene expression for synaptogenesis spatiotemporally. Neonicotinoids are used worldwide as pesticides, and with similar chemical structures to nicotine, neonicotinoids also share agonist activity at nicotinic acetylcholine receptors (nAChRs). Because of the importance of nAChRs for mammalian brain development, adverse effects of neonicotinoid exposure in fetus and children are concerning. Previously, we showed that nicotine and two neonicotinoids, acetamiprid and imidacloprid, exert similar excitatory effects on rat cerebellar neurons. Furthermore, we reported these neonicotinoids disrupt expression of synaptogenesis-related genes in rat developing cerebellar cultures, by whole genome microarray. Other reports demonstrate that maternal exposure of neonicotinoids induced behavioral problems in her pups’ mice. Neonicotinoids disrupt human α4β2 and α7 nAChRs responses against the endogenous ligand acetylcholine. These data suggest neonicotinoids are possible causal factors of neurodevelopmental disorders.
Impact of Prenatal Exposure to Phenols and Phthalates on Early Cognitive Development
Lecturer: Susan Schantz, University of Illinois at Urbana-Champaign, Urbana, IL.
The potential for exposure to endocrine-disrupting chemicals (EDCs), including phthalates, bisphenol A (BPA), and recent replacements for these chemicals, to affect neurodevelopment is of growing concern. Exposure to these chemicals occurs through a wide range of consumer products and is ubiquitous among pregnant women. Prenatal exposure to phthalates and BPA has been associated with adverse neurodevelopmental outcomes during childhood. However, few, if any, studies have assessed the effects of these chemicals or their replacements on cognitive development during infancy. In an effort to characterize more specific aspects of cognition and obtain results earlier in life than most previous studies, our research group is using innovative measures that are early indicators of later cognitive function. This work builds on research in developmental psychology demonstrating that infant looking behaviors can be used to obtain reliable, stable, and valid measures of basic cognitive processes, including working memory, information processing speed, and visual attention. Infant looking behaviors also can be used to measure face processing, which is critical for proper social interactions. The Illinois Kids Development Study (I-KIDS) is a prospective pregnancy cohort currently under recruitment at the University of Illinois. I-KIDS has gathered a wealth of information on prenatal exposures and maternal health, diet, demographic and lifestyle variables, in addition to measuring cognitive outcomes in infants. This talk will describe our approach, which uses infrared eye-tracking to record the infant’s looking behavior during the presentation of stimuli and videos on a large-screen high-definition TV. In addition to assessing the impact of prenatal exposures to EDCs, we also will assess whether other maternal risk factors, such as obesity or prenatal stress, interact with chemical exposure to increase risk. Initial results suggesting that both higher maternal prenatal stress and higher maternal prenatal EDC exposure can negatively impact cognitive outcomes in infants will be presented.
Neurobehavioral Toxicity at Adult Period Induced by Neonicotinoid Pesticides Exposure at Juvenile Period of Male Mice.
Lecturer: Satoshi Kitajima, National Institute of Health Sciences, Tokyo, Japan.
Kentaro Tanemura, Tohoku University, is a co-author of this research.
Central nervous system is formed under the genetic information and fine-tuned by the proper neural signals at each developmental phase. The proper neuronal activities are used for the formulation and the maturation of the neural networks, and normal brain functions are established. In this context, the brain dysfunction or morphological defect associated with the behavioral abnormality in the adult phase can be caused by the exogenous disturbance, including chemicals, of neural signals during early periods of brain development.
Under current regulation of chemicals, adult experimental animals are exposed, and the methods to monitor neuronal endpoints are largely limited to those related to peripheral nervous system. Adverse effects on behavioral endpoints are known to be difficult to monitor in such studies. Theoretically, as mentioned above, late neurobehavioral effect induced by early exposure should be addressed by postnatal or perinatal exposure studies. We have developed a screening system to identify delayed neurobehavioral toxicity induced by early exposure to chemicals with quantitative indicators generated by a battery of five tests (i.e., open field test, light-dark transition test, elevated plus maze test, fear conditioned learning test, and prepulse inhibition test). Male C57BL/6 mice were subject to the test battery at the age of 12 weeks (w). Chemical exposure was performed, orally, at 2 w (juvenile exposure, oral gavage) or, for comparison, at 11 w (adult exposure, oral gavage). Here, we report a case study on acetamiprid, a neonicotinoid insecticide. The impairment of learning and memory associated with anxiety-related behavioral anomaly at 12 w were induced by the single oral administration of acetamiprid at 2 w. Immunohistochemical analysis on the brains of 12 w mice revealed reduction in neurogenesis activities in hippocampus. “Percellome” gene expression analysis on the hippocampus of 12 w mice revealed alteration of gamma-Aminobutyric acid (GABA) signaling and CREB signaling as a result of juvenile exposure. These findings are considered to link to the behavioral impairments. More details will be presented.
Developmental Exposure to Fine Particle Air Pollution and Neurodevelopmental Disorders.
Lecturer: Deborah Cory-Slechta, University of Rochester Medical Center, Rochester, NY.
Air pollution (a mixture of particles, metals, organic contaminants, and gases) is a worldwide public health problem. Particulate matter (PM) sizes range from coarse (2.5–10 μm) to fine (<2.5 μm) to ultrafine (UFP, <100 nm or 0.1 μm). The UFP component of air pollution is considered most reactive as it provides the greatest surface area for adsorption of toxic organic and metal contaminants. Impacts of air pollution on the brain are increasingly being reported in epidemiological studies. Exposures during the period of early brain development, a period encompassing a highly orchestrated and synchronized trajectory of events, may represent a period of particular vulnerability to such effects and contribute to various neurodevelopmental disorders, likely via inflammatory mechanisms. In a mouse model of gestational exposure to concentrated ambient fine and ultrafine particles, both male and female offspring demonstrated ventriculomegaly, a clinical indicator of poor prognosis for development and cognition. In addition, early and excessive myelination was found which correlated with increased brain iron concentrations in females. Subsequent analyses revealed an accelerated maturation of the oligodendrocyte precursor cells for myelination. Exposures to concentrated ambient UFP during the early postnatal period, considered equivalent to human third trimester associated with rapid neuro- and gliogenesis, produced effects that were more extensive and of greater magnitude in males that included persistent ventriculomegaly, reductions in myelination and size of the corpus callosum, microglial activation, and increases in glutamate. Behavioral changes included impulsivity and learning impairments. Male susceptibility to postnatal exposures may reflect an earlier colonization of brain with activated microglia requisite to neuro- and gliogenesis. Collectively, these findings support a potential role for air pollution in neurodevelopmental disorders. Notably, while neurodevelopmental disorders each have some unique features, they also show extensive overlap in characteristics and are typically heterogeneous in expression. Air pollution, if a risk factor for autism spectrum disorder, could likewise contribute to heterogeneity, given the extensive differences in such exposures in different geographical areas, even within relatively localized areas and in timing of such exposures.
Born in the southern part of Sweden in 1918, Bo Holmstedt was an internationally renowned toxicologist. He was known for his outstanding research contributions and his engagement in education and was a leading figure in the toxicology community. In his memory, EUROTOX established the Bo Holmstedt Memorial Lecture. This merit award recognizes scientific excellence in the area of toxicological sciences and is presented to an outstanding European toxicologist at the EUROTOX Annual Congress. For the first time, the SOT Scientific Program Committee is pleased to present a lecture exchange of eminent scientists between SOT and EUROTOX. As part of the exchange, Vera Rogiers, Vrije Universiteit Brussel, (2017 Bo Holmstedt Memorial Lecture awardee) will be presenting at the SOT Annual Meeting, and the 2018 SOT Merit Award recipient Robert J. Kavlock, US Environmental Protection Agency (US EPA), will present at the EUROTOX Annual Congress in Belgium in September 2018.
Human Skin Stem Cell-Derived Hepatic Cells and Their Potential Applications in Toxicology
Lecturer: Vera Rogiers, Vrije Universiteit Brussel, Brussels, Belgium.
Human skin-derived precursor cells (hSKP) are somatic, immune-privileged stem cells that reside in the dermis throughout life and harbour a high self-renewal and multipotent capacity. More specifically, it could be shown that besides their ectodermal and mesodermal differentiation potential, they can be directed towards the hepatic lineage. Indeed, upon sequential exposure in vitro to hepatogenic growth factors and cytokines, hSKP are able to generate hepatic progenitor-like cells (hSKP-HPC). As such, they represent a convenient human cell source with a normal genotype (patented protocol EP1824965 B1). They express not only hepatic progenitor cell markers, but also some typical features of adult hepatocytes, such as albumin production. They also express a number of key biotransformation enzymes, including CYP1B1, FMO1, GSTA4, and GSTM3, and influx and efflux drug transporters, such as ABCC4, ABCA1, and SLC2A5. These properties give the cells a unique position among the actually existing in vitro models, which makes them suitable for pharmaceutical, toxicological, and clinical applications. The predictive capacity of the hSKP-HPC for identifying hepatotoxic compounds was evaluated. Using a toxicogenomics approach, it was found that hSKP-HPC can predict hepatotoxicity equivalent to primary human hepatocytes. They even more closely reflect clinical samples from acute liver failure (ALF) and fatty liver patients in response to hepatotoxic compounds than primary human hepatocytes. The ability of hSKP-HPC to deliver in vitro prediction of hepatotoxicity for ALF (acetaminophen), phospholipidosis (amiodarone), and hepatic steatosis (sodium valproate) is especially relevant for drug discovery programs, where drug-induced liver injury (DILI) contributes to high attrition rates. Furthermore, hSKP-HPC’s sensitivity to hepatic steatosis underlies its relevance as a disease model for non-alcoholic fatty liver disease (NAFLD), which affects 20% of the adult population and which may evolve into severe, life-threatening non-alcoholic steatohepatitis (NASH). Current preclinical investigations rely on animal or human in vitro models that do not accurately reflect clinical NAFLD. We have demonstrated that exposure to steatogenic compounds, including insulin, induces triglyceride accumulation in hSKP-HPC, a central feature of clinical NAFLD. Moreover, it could be shown that the key molecular mechanisms that underlie this effect can be modeled and modulated in hSKP-HPC, providing a valuable disease model for screening of novel anti-NAFLD molecules. Finally, hSKP themselves are key candidates for autologous and allogeneic cell-based therapy for the treatment of liver disease, given their immune privileged state. In a transgenic murine model of liver deficiency (uPA+/+/SCID), injected hSKP cells successfully engrafted survived and repopulated the hepatic liver tissue and contributed to the increase in liver mass. Also, after oral administration of dianabol, an anabolic steroid, the in vitro-generated hSKP-derived hepatocytes produced human-specific metabolites, detectable in the urine of the chimeric mice. This clearly demonstrates the in vivo biotransformation capacity of the hSKP-derived hepatocytes. Further developments are underway, among which the development of a hSKP-based NASH model suitable for toxicological screening and drug discovery.