Use of tracheal organ cultures in toxicity testing.
Fragments of tracheal epithelium alone or in continuity with connective tissues, can be maintained in culture medium and used for short term or long term studies of toxicity of a variety of chemicals. Large numbers of uniform cultures are prepared with the aid of a slicing device or by application of simple method for dissecting sheets of epithelium free from underlying cartilage. The cultures may be placed in an exposure chamber-incubator mounted on a microscope stage and monitored continually for ciliostasis and exfoliation of cells. Morphology is further studied by fixation of selected specimens and preparation for light microscopy and electron microscopy. Synthetic functions are evaluated by autoradiographic measurement of incorporation of radioactive precursors into macromolecules and other dynamic features are indirectly assessed by histochemical and histoenzymatic methods. Short-term studies using these several techniques have shown that ciliostasis does not correlate with cell injury in all instances, and a long-term study has demonstrated dose dependence of a cytotoxic agent when duration of culture viability is measured. The method lends itself to a broad range of investigations in which dose, period of exposure, and role of cofactors must be independently and quantitatively assessed. (+info)
Chemical hormesis: its historical foundations as a biological hypothesis.
Despite the long history of hormesis-related experimental research, no systematic effort to describe its early history has been undertaken. The present paper attempts to reconstruct and assess the early history of such research and to evaluate how advances in related scientific fields affected the course of hormesis-related research. The purpose of this paper is not only to satisfy this gap in current knowledge but also to provide a foundation for the assessment of how the concept of hormetic dose-response relationships may have affected the nature of the bioassay, especially with respect to hazard assessment practices within a modern risk assessment framework. (+info)
The ToxChip, a DNA microarray chip, allows the monitoring of the expression levels of thousands of different genes at a time, thereby condensing months of painstaking laboratory tasks into a day's work. For toxicology researchers in particular, this tool is important because it promises a more effective way to identify environmental hazards and their effects on DNA. The ToxChip, developed by NIEHS scientists J. Carl Barrett, Cynthia Afshari, and Emile F. Nuwaysir, could transform the way toxicologists approach environmental problems. (+info)
Preclinical development strategies for novel gene therapeutic products.
With over 220 investigational new drug applications currently active, gene therapy represents one of the fastest growing areas in biotherapeutic research. Initially conceived for replacing defective genes in diseases such as cystic fibrosis or inborn errors of metabolism with genes encoding the normal, or wild-type, gene product, gene therapy has expanded into other novel applications such as treatment of cancer or cardiovascular disease, where the risk:benefit profiles may be more acceptable in relation to the severity of the disease. Different types of vectors, including modified retroviruses, adenoviruses, adenovirus-associated viruses, and herpesviruses and plasmid DNA, are used to transfer foreign genetic material into patients' cells or tissues. Developing a toxicology program to determine the safety of these agents, therefore, requires a modified approach that encompasses the pharmacology and toxicity of both the gene product itself and the vector system used for delivery in the context of the application for the clinical trial. In general, the issues involved in designing and developing appropriate preclinical testing to determine the safety of these products are similar to those encountered for other recombinant molecules, including protein biotherapeutics. Limitations to some of the typical toxicology studies conducted for a traditional drug development program may exist for these agents, and nontraditional approaches may be required to demonstrate their safety. Many factors may affect the safety and clinical activity of these agents, including the route, frequency, and duration of exposure and the type of vector employed. Other safety considerations include quantitation of the duration and degree of expression of the vector in target and other tissues, the effects of gene expression on organ pathology and/or histology, evaluation of trafficking of gene-transduced cells or vector after injection, and interactions of the host immune system with the transduced cell population. Because of the unique concerns regarding each of these therapies, the Center for Biologics Evaluation and Research encourages sponsors to obtain toxicity data whenever possible while evaluating the pharmacologic activity of the vector in a species or animal model relevant to their clinical indication. Sponsors are encouraged to discuss preclinical study design and results with the Center during product development to facilitate early identification of safety concerns prior to entry of these novel agents into the clinical setting and to ensure an uninterrupted course of development while addressing issues required for licensure. (+info)
Regulatory decision strategy for entry of a novel biological therapeutic with a clinically unmonitorable toxicity into clinical trials: pre-IND meetings and a case example.
The following material was derived from a synthesis of case histories taken from investigational new drug (IND) applications and drug sponsors' experiences, utilizing fictionalized data to avoid any resemblance to any proprietary information; any such resemblance is accidental. These examples are used as an instructional scenario to illustrate appropriate handling of a difficult toxicology issue. In this scenario, a drug caused a toxicity in animals that was detected only by histopathologic analysis; if it were to develop in patients, no conventional clinical methods could be identified to monitor for it. It is not unusual for a firm to cancel clinical development plans for a lead drug candidate that causes such a toxicity, especially if such a drug is intended for use as a chronic therapeutic in a population of patients with a chronic disease. This case synthesis was inspired by a Food and Drug Administration (FDA) agreement to allow such a product to proceed into clinical trials after substantive pre-IND discussions and agreement on well-considered toxicology program designs. The scientists most closely involved in the strategy development included the sponsor's toxicologist, veterinary toxicologic pathologist, and pharmacokineticist, as well as the FDA's reviewing pharmacologist. The basis of this decision was thorough toxicity characterization (1-month studies in 2 species); correlating toxicities with a particular cumulative area under the curve (AUC) in both species; identification of the most sensitive species (the species that showed the lower AUC correlating with toxicity); allometric assessment of clearance of the drug in 3 nonhuman species; construction of a model of human kinetics (based on extrapolation from animal kinetics); and finally, estimation of clinical safety factors (ratios of the human estimated cumulative AUC at the proposed clinical doses, over the animal cumulative AUC that correlated with the no adverse effect levels). Industry and FDA scientists negotiated a joint assessment of risk and benefit in patients, resulting in the FDA permitting such a compound to enter into clinical trials for a serious autoimmune disease. Such constructive, early communication starts with the pre-IND meeting, and the conduct and planning for this meeting can be very important in establishing smooth scientific and regulatory groundwork for the future of a drug under IND investigation. (+info)
The pathologist and toxicologist in pharmaceutical product discovery.
Significant change is occurring in the drug discovery paradigm; many companies are utilizing dedicated groups from the toxicology/ pathology disciplines to support early stage activities. The goal is to improve the efficiency of the discovery process for selecting a successful clinical candidate. Toxicity can be predicted by leveraging molecular techniques via rapid high-throughput, low-resource in vitro and in vivo test systems. Several important activities help create a platform to support rapid development of a new molecular entity. The proceedings of this symposium provide excellent examples of these applied concepts in pharmaceutical research and development. Leading biopharmaceutical companies recognize that a competitive advantage can be maintained via rapid characterization of animal models, the cellular identification of therapeutic targets, and improved sensitivity of efficacy assessment. The participation of the molecular pathologist in this quest is evolving rapidly, as evidenced by the growing number of pathologists that interact with drug discovery organizations. (+info)
Revolution through genomics in investigative and discovery toxicology.
The remarkable technologic and methodologic advances spurred on by the Human Genome Project are being applied throughout the life sciences. In the field of toxicology, high-resolution assays now make it possible to discover virtually all the differences in gene expression brought on by exposure to a particular xenobiotic. There are 2 principal approaches used to build a catalog of changes in gene expression: hybridization microarrays and gel-based methods, such as differential display and AFLP-based mRNA finger-printing. The power of such approaches is exemplified by the identification of more than 300 genes that differ in expression level by at least 2-fold in response to the nongenotoxic rodent liver carcinogen phenobarbital. (+info)
Optimal design for a study of butadiene toxicokinetics in humans.
The derivation of the optimal design for an upcoming toxicokinetic study of butadiene in humans is presented. The specific goal of the planned study is to obtain a precise estimate of butadiene metabolic clearance for each study subject, together with a good characterization of its population variance. We used a two-compartment toxicokinetic model, imbedded in a hierarchical population model of variability, in conjunction with a preliminary set of butadiene kinetic data in humans, as a basis for design optimization. Optimization was performed using Monte Carlo simulations. Candidate designs differed in the number and timing of exhaled air samples to be collected. Simulations indicated that only 10 air samples should be necessary to obtain a coefficient of variation of 15% for the estimated clearance rate, if the timing of those samples is properly chosen. Optimal sampling times were found to closely bracket the end of exposure. This efficient design will allow the recruitment of more subjects in the study, in particular to match prescribed levels of accuracy in the estimate of the population variance of the butadiene metabolic rate constant. The techniques presented here have general applicability to the design of human and animal toxicology studies. (+info)