Jeffrey C. Bemis, Ph.D. - US grants

DESCRIPTION (provided by applicant): Human exposure to radiation, whether by accidental or intentional use, has the potential to impact large populations and severely tax the facilities and resources mandated to respond to such incidents. The current state of clinical management of radiation exposure is lacking in its ability to rapidly and reliably provide relevant human dose estimation. Such information is critical for clinicians to make informed decisions regarding the treatment of patients potentially exposed to hazardous levels of radiation. Thus numerous agencies have placed a high priority on the development of novel radiation biodosimetry methods for use in triage situations. This proposal describes the further evaluation of a novel HemAtotoxicity Response Matrix (HARM) that will provide a multiparametric assessment of radiation-induced damage to the hematopoietic system that can be used to estimate dose. The assay is based on the interrogation of whole blood cell populations for alterations in the number of cells present and the health status of these cells. This is accomplished by using a flow cytometer to count cells and measure alterations in mitochondrial membrane potential (MMP) as an indicator of apoptosis. Preliminary experiments demonstrate that the HARM assay is rapid, minimally invasive, inexpensive and has the potential to discriminate clinically relevant radiation doses. The experiments described in this proposal will provide more definitive proof-of-principle data regarding the ability of the assay to meet the requirements of a functional human radiation biodosimeter. Thus, portability studies will determine the ability of the HARM assay to be adopted by other laboratories and the assay's compatibility with mobile flow cytometry instrumentation. The requirement for increased throughput capabilities will be examined via application of automated sample processing technologies and high throughput sample analysis instrumentation to the current method. The intention is to produce a multiparametric assay with high information content that will significantly improve our current ability to determine human exposure to clinically relevant radiation doses. Future studies will investigate the production of highly portable, dedicated instrumentation for field use, a more extensive examination of higher-species responses to irradiation and potential confounding factors such as non-homogenous exposure, combined injury or pre-existing drug effects. By producing methodologies that will improve our ability to characterize the extent and amount of human exposure following a radiological incident, we can more efficiently manage these crisis situations. PUBLIC HEALTH RELEVANCE: In the aftermath of a large-scale human radiation exposure incident, methods that can rapidly estimate an individual's radiation exposure will help clinicians make better decisions regarding allocation of resources to those that require it. This proposal seeks to extend the assessment a novel methodology that can estimate exposure by monitoring the effects of radiation on circulating blood cells. Such technologies will ultimately enhance our nation's ability to manage these hazardous scenarios.

DESCRIPTION (provided by applicant): Large-scale disaster situations put considerable demands on existing medical infrastructure, as well as local governing and safety agencies. When the additional factor of ionizing radiation and exposure of humans is part of the emergency, the lack of effective assessment tools and management strategies can easily become overwhelming. As part of efforts to devise methods and technologies that will address this critical need, this proposal is designed to develop and evaluate two radiation- sensitive endpoints that can be obtained from a small volume blood sample. The goal is to create an analytical platform that could be integrated into mobile response units that can quickly survey the thousands of subjects expected in certain emergency triage situations. The key to delivering useful dose/exposure estimation with a sufficiently rapid turnaround is the combination of cell enrichment via immunomagnetic technologies with high throughput analytical platforms that employ multi-well plates, e.g. 384 or 1536 well. An ultra-high throughput method that enumerates circulating lymphocytes will serve as an initial screen that can rapidly survey and flag subjects for further analysis. Using the same blood sample, the confirmatory assay will employ flow cytometric assessment of micronucleated reticulocytes as a marker of radiation-induced chromosome damage. This two-stage approach will enable the first screen to quickly dismiss the majority of individuals that have received minimal-to-no exposure and the subsequent assay will focus on definitive identification of subjects that will require further medical care. By quickly and efficiently sending the worried-well home, more effective allocation of resources and care can be directed where it is ultimately needed. Such an approach is critical to ensuring an immediate and sufficient response to large-scale emergencies such as those presented by exposure of human populations to ionizing radiation.

DESCRIPTION (provided by applicant): Despite the extensive work being performed to understand cancer and carcinogenic properties of chemicals and other agents, there are still gaps in our ability to efficiently identify carcinogens, and elucidate their mode(s) of action. The current state of assays designed to examine mutation and carcinogenic mechanisms are especially limited by their high costs and low throughput capacities. This laboratory has developed a gene mutation assay that is based on the endogenous Pig-a gene. The Pig-a gene product is essential for the biosynthesis of glycosyl phosphatidylinositol (GPI) anchors. Mutations giving rise to nonfunctional GPI anchors prevent certain proteins from being expressed on the cell surface, and this represents a phenotype that can be measured by flow cytometry. The work proposed herein will extend our development efforts by creating a suite of assays that represent a platform for studying a key mode of carcinogenic action, mutation. By devising Pig-a based methods that examine cells in culture, laboratory rodents, and human subjects, a truly comprehensive bridging biomarker will be realized. The bridging capabilities and high throughput nature of the proposed mutation assessment tools will contribute significantly to important areas of research that include academic, regulatory, and industrial settings.

DESCRIPTION (provided by applicant): It is well recognized that current batteries of genetic toxicology assays exhibit relatively high sensitivity, meaning they effectively identify genotoxic carcinogens. However, a critical deficiency with current approaches exists-namely, the specificity of the in vitro mammalian cell genotoxicity tests is low, as they yield a high incidenc of positive results that do not have in vivo relevance (so-called misleading or irrelevant positives). This high incidence of irrelevant in vitro positive results leads to extensive and costy additional testing, often with whole animal models, or else abandonment of potentially valuable products. We will address this major problem with current in vitro mammalian cell genetic toxicity assays by developing commercial kits that enable an automated testing strategy that exhibits both high sensitivity and specificity. This system will categorize positive results according to the predominant mode of genotoxic activity, and importantly, will reliably identify irrelevant mode(s) of action that are likely to be nonoperational in vivo. A secondary objective of the proposed work is the development of methods for characterizing clastogens. That is, we will develop tools that elucidate whether clastogenic activity is the result of DNA-reactivity, or whether it is mediated by an indirect mechanism.

? DESCRIPTION (provided by applicant): Assessment of chemicals' potential to cause chromosomal damage is an established and important part of preclinical genotoxicity safety testing for many consumer products, industrial chemicals, and all pharmaceutical agents. Currently the mammalian erythrocyte micronucleus test is the most commonly employed assay for in vivo assessment of chromosomal damage, but this assay reports specifically on genotoxicity that occurs in the bone marrow. In order to obtain a more comprehensive understanding of potential genotoxicity, testing guidance's recommend evaluation of a second tissue. The liver, the site of metabolism and in many cases activation of genotoxicants, is usually regarded as the preferred second tissue. Even so, there is a lack of efficient and effective tools for studying liver genotoxicity. The Comet assay and transgenic rodent mutation models can be employed to study the liver, but these assays suffer from methodological and cost issues that limit their utility. Another important consideration is that these assays are not highly amenable to integration with on-going toxicology studies, meaning additional animals are required for the liver genotoxicity assessment. One alternative approach is to examine liver hepatocytes for the formation of micronuclei, an established indicator of chromosomal damage. However existing methods for examining liver micronuclei are still emerging and currently based on a multi-step sample processing scheme followed by manual scoring by microscopy. This approach is subjective and labor- intensive, and results in too few cells being scored for reliable enumeration of micronucleated hepatocytes, a situation that diminishes the ability of the test to detect weakly genotoxic agents. We will overcome these deficiencies by combining simple, rapid tissue processing and staining with high-speed flow cytometric analysis to greatly improve the execution of liver micronucleus scoring. Furthermore, we will multiplex several cytotoxicity measurements into the liver micronucleus assay, thereby providing information that we predict will be important for interpreting the genotoxicity results. The methodology will be reduced to practice in the form of commercially available kits, and will contribute to the reduction and refinement of animal testing, as it will make it feasible to integrate a liver genotoxicity assay ito ongoing toxicology studies. Overall, this project will meet a critical need in the practice of genetic toxicology by improving chemical safety assessments in several meaningful ways.

Project Summary It is well recognized that current batteries of genetic toxicology assays exhibit two critical deficiencies. First, the throughput capacity of in vitro mammalian cell genotoxicity tests is low, and does not meet current needs. Second, conventional assays provide simplistic binary calls, genotoxic or non-genotoxic. In this scheme there is little or no consideration for potency, and virtually no information is provided about molecular targets and mechanisms. These deficiencies in hazard characterization prevent genotoxicity data from optimally contributing to modern risk assessments, where this information is essential. We will address these major problems with current in vitro mammalian cell genetic toxicity assays by developing methods and associated commercial assay kits that dramatically enhance throughput capacity, and delineate genotoxicants' primary molecular targets, while simultaneously providing information about potency. Once biomarkers and a family of multiplexed assays have been developed for these purposes, an interlaboratory trial will be performed with prototype assay kits to assess the transferability of the methods.

Project Summary This project will validate two high throughput human blood-based DNA damage assays and develop them into commercial kits. The assays monitor types of damage associated with important human diseases. Whereas the PIG-A assay reports on gene mutation, the micronucleated reticulocyte (MN-RET) assay is responsive to chromosomal breaks and/or losses. The biomarkers are applicable to both humans and laboratory animals and will fulfill two important needs: extension of findings in laboratory animal models to direct studies in humans, and performance of well-controlled mechanistic laboratory studies to understand observations first made in humans. The assays utilize immunomagnetic separation prior to flow cytometry to dramatically enrich the relevant cell populations and thereby enhance assay precision and sensitivity. By providing simple-to-use kits with thoroughly documented reproducibility and inter-laboratory transferability, and validating the biomarkers for specific uses, researchers will have available tools with unprecedented efficiencies for comprehensively studying those factors that contribute to inter-individual differences in human DNA damage. Applications include the study of drug treatments, host and/or life-style factors that contribute to inter-individual differences in DNA damage and repair, exaggerated sensitivities to anti- neoplastic therapies, and population-based epidemiology studies of environmental exposures, including occupational exposures. The project benefits from a strong multidisciplinary team of internationally recognized scientists with a proven track record of successfully converting research advances into reliable commercial assay kits.