Use of genetic toxicology information for risk assessment

Genotoxicity induced by nerol, an essential oil present in citric plants using human peripheral blood mononuclear cells (PBMC) and HepG2/C3A cells as a model

Nerol (cis-3,7-dimethyl-2,6-octadien-1-ol) is a monoterpene widely used in cosmetic products, household detergents and cleaners, as well as a flavoring in several food products. Despite the high level of human exposure to nerol, an absence of studies regarding potential genetic toxicity in human cells exists. The aim of this investigation was to examine the cytotoxic and genotoxic potential of this monoterpene on human peripheral blood mononuclear cells as well as hepatic metabolizing HepG2/C3A human cell line. Cytotoxicity was assessed using trypan blue staining and MTT assay while genotoxicity was determined utilizing the comet and micronucleus test. Cytotoxicity tests showed cell viability greater than 70% for concentrations between 2.5 and 500 µg/ml. Both cell types exhibited significant DNA damage and chromosomal mutations after medium and high concentration incubation with nerol indicating that the safety of use of this monoterpene in various formulations to which humans are exposed needs to be monitored and requires more comprehensive investigations.

The promise of toxicogenomics for genetic toxicology: past, present and future

Toxicogenomics, the application of genomics to toxicology, was described as 'a new era' for toxicology. Standard toxicity tests typically involve a number of short-term bioassays that are costly, time consuming, require large numbers of animals and generally focus on a single end point. Toxicogenomics was heralded as a way to improve the efficiency of toxicity testing by assessing gene regulation across the genome, allowing rapid classification of compounds based on characteristic expression profiles. Gene expression microarrays could measure and characterise genome-wide gene expression changes in a single study and while transcriptomic profiles that can discriminate between genotoxic and non-genotoxic carcinogens have been identified, challenges with the approach limited its application. As such, toxicogenomics did not transform the field of genetic toxicology in the way it was predicted. More recently, next generation sequencing (NGS) technologies have revolutionised genomics owing to the fact that hundreds of billions of base pairs can be sequenced simultaneously cheaper and quicker than traditional Sanger methods. In relation to genetic toxicology, and thousands of cancer genomes have been sequenced with single-base substitution mutational signatures identified, and mutation signatures have been identified following treatment of cells with known or suspected environmental carcinogens. RNAseq has been applied to detect transcriptional changes following treatment with genotoxins; modified RNAseq protocols have been developed to identify adducts in the genome and Duplex sequencing is an example of a technique that has recently been developed to accurately detect mutation. Machine learning, including MutationSeq and SomaticSeq, has also been applied to somatic mutation detection and improvements in automation and/or the application of machine learning algorithms may allow high-throughput mutation sequencing in the future. This review will discuss the initial promise of transcriptomics for genetic toxicology, and how the development of NGS technologies and new machine learning algorithms may finally realise that promise.

Human health risks by potentially toxic metals in drinking water along the Hattar Industrial Estate, Pakistan

This study aimed to investigate the contamination of drinking water sources with potentially toxic metals (PTMs) together with some hydrochemical characteristics in the highly populated industrial zone of Pakistan. For this purpose, drinking (n = 40) and surface (n = 20) water samples were collected and analyzed for PTM using graphite furnace atomic absorption spectrophotometer (GFAAS, PerkinElmer-700, USA). The metals, including cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), and zinc (Zn), showed significantly (p = 0.05) higher concentrations than their respective limits set by the World Health Organization (WHO 2011) in drinking water. The chronic daily intake (CDI) and human hazard quotient (HQ) were also evaluated. The highest daily intake through drinking water consumption was found for Ni (4.3 μg/kg/day), while lowest for Cd (0.25 μg/kg/day). The highest hazard quotient values were found for Cd (0.33) and Ni (0.29) that could be attributed to industrial wastewater discharge. Higher CDI and HQ values of Ni and Cd may cause chronic human health problems. According to the Chadha Piper diagram, the hydrochemical facies distribution indicated that water trend in the study area followed an order such as follows: Ca-Mg-Cl < Na-Cl < Ca-HCO₃ < Na-HCO₃. Statistical analysis using one-way ANOVA, correlation analysis, and principal component analysis (PCA) revealed that the elevated levels of PTM were attributed to industrial wastewater discharge. This study provides baseline information for policy makers and the effective management of water in populated industrialized zone.

Carcinogenic potential of sanguinarine, a phytochemical used in 'therapeutic' black salve and mouthwash

Black salves are escharotic skin cancer therapies in clinical use since the mid 19th century. Sanguinaria canadensis, a major ingredient of black salve formulations, contains a number of bioactive phytochemicals including the alkaloid sanguinarine. Despite its prolonged history of clinical use, conflicting experimental results have prevented the carcinogenic potential of sanguinarine from being definitively determined. Sanguinarine has a molecular structure similar to known polyaromatic hydrocarbon carcinogens and is a DNA intercalator. Sanguinarine also generates oxidative and endoplasmic reticulum stress resulting in the unfolded protein response and the formation of 8-hydroxyguanine genetic lesions. Sanguinarine has been the subject of contradictory in vitro and in vivo genotoxicity and murine carcinogenesis test results that have delayed its carcinogenic classification. Despite this, epidemiological studies have linked mouthwash that contains sanguinarine with the development of oral leukoplakia. Sanguinarine is also proposed as an aetiological agent in gallbladder carcinoma. This literature review investigates the carcinogenic potential of sanguinarine. Reasons for contradictory genotoxicity and carcinogenesis results are explored, knowledge gaps identified and a strategy for determining the carcinogenic potential of sanguinarine especialy relating to black salve are discussed. As patients continue to apply black salve, especially to skin regions suffering from field cancerization and skin malignancies, an understanding of the genotoxic and carcinogenic potential of sanguinarine is of urgent clinical relevance.

Statement on the validity of the conclusions of a mouse carcinogenicity study on sucralose (E 955) performed by the Ramazzini Institute

The Panel on Food Additives and Nutrient Sources added to Food (ANS) was requested from the European Commission to provide a statement on the validity of the conclusions of a mouse study on the carcinogenic potential of sucralose (E 955) performed by the Ramazzini Institute (Soffritti et al., 2016). Sucralose (E 955) is authorised as a food additive in the EU in accordance with Annex II to Regulation (EC) No 1333/2008 on food additives. According to Commission Regulation (EU) No 257/2010, the full re-evaluation of sucralose shall be completed by December 2020. Taking into consideration the publication from Soffritti et al. (2016), the technical report and additional information provided by the Ramazzini Institute and other information available for sucralose (E 955), the Panel noted: (i) the design of the bioassay that considers exposure from gestation up to natural death of animals implies an increase in background pathology that results in the possibility of misclassifications and a difficult interpretation of data, especially in the absence of both an appropriate concurrent control group and a recent historical database; (ii) the lack of a dose-response relationship between the exposure to sucralose and incidence of lymphomas and leukaemias (combined); (iii) the lack of a mode of action and failure to meet all the Bradford-Hill considerations for a cause-effect relationship between intake of sucralose and the development of tumours in male mice only; (iv) a comprehensive database was available for sucralose and no carcinogenic effect was reported in adequate studies in rats and mice. Moreover, there was no reliable evidence of in vivo genotoxicity. Therefore, the Panel concluded that the available data did not support the conclusions of the authors (Soffritti et al., 2016) that sucralose induced haematopoietic neoplasias in male Swiss mice.

Challenges in risk assessment of multiple mycotoxins in food

Most fungi are able to produce several mycotoxins simultaneously and, consequently, to contaminate a wide variety of foodstuffs. Therefore, the risk of human co-exposure to multiple mycotoxins is real, raising a growing concern about their potential impact on human health. Besides, government and industry regulations are usually based on individual toxicities, and do not take into account the complex dynamics associated with interactions between co-occurring groups of mycotoxins. The present work assembles, for the first time, the challenges posed by the likelihood of human co-exposure to these toxins and the possibility of interactive effects occurring after absorption, towards knowledge generation to support a more accurate human risk assessment. Regarding hazard assessment, a physiologically-based framework is proposed in order to infer the health effects from exposure to multiple mycotoxins in food, including knowledge on the bioaccessibility, toxicokinetics and toxicodynamics of single and combined toxins. The prioritisation of the most relevant mixtures to be tested under experimental conditions that attempt to mimic human exposure and the use of adequate mathematical approaches to evaluate interactions, particularly concerning the combined genotoxicity, were identified as the main challenges for hazard assessment. Regarding exposure assessment, the need of harmonised food consumption data, availability of multianalyte methods for mycotoxin quantification, management of left-censored data, use of probabilistic models and multibiomarker approaches are highlighted, in order to develop a more precise and realistic exposure assessment. To conclude, further studies on hazard and exposure assessment of multiple mycotoxins, using harmonised methodologies, are crucial towards an improvement of data quality and a more reliable and robust risk characterisation, which is central for risk management and, consequently, to prevent mycotoxins-associated adverse effects. A deep understanding of the nature of interactions between multiple mycotoxins will contribute to draw real conclusions on the health impact of human exposure to mycotoxin mixtures.

[Genotoxicity risk assessment and oocytes: basis of genetic toxicology and application in reproductive science]

The aim of genotoxicity tests in germ cells is to assess the impact of exposure to environmental mutagens that may represent a risk for the fertility or for the offspring of exposed subject. The comet assay on mature mouse oocytes is a simple, reproductive and rapid test to study primary DNA damage in oocytes. This test is used to complete toxicology assays applied in first line to somatic cells, and could find many applications in reproductive toxicology to study impact of environmental factors on female germ cells. We describe a practical application of comet assay in reproductive biology to assess the genotoxicity of cryoprotectants used at high concentrations in oocyte vitrification protocols. This test allowed us to demonstrate that dimethylsulfoxide and ethylene glycol are non-genotoxic for the mouse oocytes and led us to hypothesize a genotoxic effect of 1,2-propanediol (PrOH) at high concentrations after having observed induction of significant DNA damage on CHO cell line and on mouse oocytes.

Follow-up actions from positive results of in vitro genetic toxicity testing

Appropriate follow-up actions and decisions are needed when evaluating and interpreting clear positive results obtained in the in vitro assays used in the initial genotoxicity screening battery (i.e., the battery of tests generally required by regulatory authorities) to assist in overall risk-based decision making concerning the potential effects of human exposure to the agent under test. Over the past few years, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) Project Committee on the Relevance and Follow-up of Positive Results in In Vitro Genetic Toxicity (IVGT) Testing developed a decision process flow chart to be applied in case of clear positive results in vitro. It provides for a variety of different possibilities and allows flexibility in choosing follow-up action(s), depending on the results obtained in the initial battery of assays and available information. The intent of the Review Subgroup was not to provide a prescriptive testing strategy, but rather to reinforce the concept of weighing the totality of the evidence. The Review Subgroup of the IVGT committee highlighted the importance of properly analyzing the existing data, and considering potential confounding factors (e.g., possible interactions with the test systems, presence of impurities, irrelevant metabolism), and chemical modes of action when analyzing and interpreting positive results in the in vitro genotoxicity assays and determining appropriate follow-up testing. The Review Subgroup also examined the characteristics, strengths, and limitations of each of the existing in vitro and in vivo genotoxicity assays to determine their usefulness in any follow-up testing.

An evaluation of the mode of action framework for mutagenic carcinogens case study II: chromium (VI)

In response to the 2005 revised U.S Environmental Protection Agency's (EPA) Cancer Guidelines, a strategy is being developed to include all mutagenicity and other genotoxicity data with additional information to determine whether the initiating step in carcinogenesis is through a mutagenic mode of action (MOA). This information is necessary to decide if age-dependent adjustment factors (ADAFs) should be applied to the risk assessment. Chromium (VI) [Cr (VI)], a carcinogen in animals and humans via inhalation, was reassessed by the National Toxicology Program (NTP) in 2-year drinking water studies in rodents. From these data, NTP concluded that the results with Cr (VI) showed clear evidence of carcinogenicity in male and female mice and rats. Cr (VI) is also mutagenic, in numerous in vitro assays, in animals (mice and rats) and in humans. Accordingly, Cr (VI) was processed through the MOA framework; postulated key steps in tumor formation were interaction of DNA with Cr (VI) and reduction to Cr (III), mutagenesis, cell proliferation, and tumor formation. Within the timeframe and tumorigenic dose range for early events, genetic changes in mice (single/double-stranded DNA breaks) commence within 24 hr. Mechanistic evidence was also found for oxidative damage and DNA adduct formation contributing to the tumor response. The weight of evidence supports the plausibility that Cr (VI) may act through a mutagenic MOA. Therefore, the Cancer Guidelines recommend a linear extrapolation for the oral risk assessment. Cr (VI) also induces germ cell mutagenicity and causes DNA deletions in developing embryos; thus, it is recommended that the ADAFs be applied.

Mutagenicity testing for chemical risk assessment: update of the WHO/IPCS Harmonized Scheme

Since the publication of the International Programme on Chemical Safety (IPCS) Harmonized Scheme for Mutagenicity Testing, there have been a number of publications addressing test strategies for mutagenicity. Safety assessments of substances with regard to genotoxicity are generally based on a combination of tests to assess effects on three major end points of genetic damage associated with human disease: gene mutation, clastogenicity and aneuploidy. It is now clear from the results of international collaborative studies and the large databases that are currently available for the assays evaluated that no single assay can detect all genotoxic substances. The World Health Organization therefore decided to update the IPCS Harmonized Scheme for Mutagenicity Testing as part of the IPCS project on the Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals. The approach presented in this paper focuses on the identification of mutagens and genotoxic carcinogens. Selection of appropriate in vitro and in vivo tests as well as a strategy for germ cell testing are described.

Characterization and interlaboratory comparison of a gene expression signature for differentiating genotoxic mechanisms

The genotoxicity testing battery is highly sensitive for detection of chemical carcinogens. However, it features a low specificity and provides only limited mechanistic information required for risk assessment of positive findings. This is especially important in case of positive findings in the in vitro chromosome damage assays, because chromosome damage may be also induced secondarily to cell death. An increasing body of evidence indicates that toxicogenomic analysis of cellular stress responses provides an insight into mechanisms of action of genotoxicants. To evaluate the utility of such a toxicogenomic analysis we evaluated gene expression profiles of TK6 cells treated with four model genotoxic agents using a targeted high density real-time PCR approach in a multilaboratory project coordinated by the Health and Environmental Sciences Institute Committee on the Application of Genomics in Mechanism-based Risk Assessment. We show that this gene profiling technology produced reproducible data across laboratories allowing us to conclude that expression analysis of a relevant gene set is capable of distinguishing compounds that cause DNA adducts or double strand breaks from those that interfere with mitotic spindle function or that cause chromosome damage as a consequence of cytotoxicity. Furthermore, our data suggest that the gene expression profiles at early time points are most likely to provide information relevant to mechanisms of genotoxic damage and that larger gene expression arrays will likely provide richer information for differentiating molecular mechanisms of action of genotoxicants. Although more compounds need to be tested to identify a robust molecular signature, this study confirms the potential of toxicogenomic analysis for investigation of genotoxic mechanisms.

Improving prediction of chemical carcinogenicity by considering multiple mechanisms and applying toxicogenomic approaches

While scientific knowledge of the potential health significance of chemical exposures has grown, experimental methods for predicting the carcinogenicity of environmental agents have not been substantially updated in the last two decades. Current methodologies focus first on identifying genotoxicants under the premise that agents capable of directly damaging DNA are most likely to be carcinogenic to humans. Emphasis on the distinction between genotoxic and non-genotoxic carcinogens is also motivated by assumed implications for the dose-response curve; it is purported that genotoxicants would lack a threshold in the low dose region, in contrast to non-genotoxic agents. However, for the vast majority of carcinogens, little if any empirical data exist to clarify the nature of the cancer dose-response relationship at low doses in the exposed human population. Recent advances in scientific understanding of cancer biology-and increased appreciation of the multiple impacts of carcinogens on this disease process-support the view that environmental chemicals can act through multiple toxicity pathways, modes and/or mechanisms of action to induce cancer and other adverse health outcomes. Moreover, the relationship between dose and a particular outcome in an individual could take multiple forms depending on genetic background, target tissue, internal dose and other factors besides mechanisms or modes of action; inter-individual variability and susceptibility in response are, in turn, key determinants of the population dose-response curve. New bioanalytical approaches (e.g., transcriptomics, proteomics, and metabolomics) applied in human, animal and in vitro studies could better characterize a wider array of hazard traits and improve the ability to predict the potential carcinogenicity of chemicals.

Use of the alkaline comet assay for the detection of transplacental genotoxins in newborn mice

Several lines of evidence show that in utero exposure to different toxicants has greater consequences than their exposure during adult life. This may be due to involvement of critical developmental stages, physiological immaturity and the long later-life span over which disease may initiate, develop and progress. The in vivo alkaline comet (single-cell gel electrophoresis) assay has been favoured by the scientific community for the evaluation of genotoxins. The objective of this study was to demonstrate the suitability of alkaline comet assay in detecting transplacental genotoxins using newborn mice. Here, we report the successful use of the comet assay in detecting multi-organ genotoxicity of known transplacental genotoxins in newborn mice. Three well known transplacental genotoxic agents, cyclophosphamide (CP), mitomycin-C (MMC) and zidovudine (AZT) were tested in pregnant Swiss mice. These compounds were administered in the late gestational period (16-20th days of pregnancy) and the comet assay was performed with lymphocytes, bone marrow, liver and kidney cells of newborn mice. Significant DNA damage was observed in all the tissues with tested transplacental genotoxins. The results of the comet assay were confirmed by the micronucleus (MN) assay of the peripheral blood of newborn mice. The results of this study provide sufficient evidence that the comet assay can be applied successfully for the detection of transplacental genotoxins in newborn mice.

An evaluation of the mode of action framework for mutagenic carcinogens case study: Cyclophosphamide

In response to the 2005 revised US Environmental Protection Agency (EPA) Cancer Guidelines, a Risk Assessment Forum's Technical Panel has devised a strategy in which genetic toxicology data combined with other information are assessed to determine whether a carcinogen operates through a mutagenic mode of action (MOA). This information is necessary for EPA to decide whether age-dependent adjustment factors (ADAFs) should be applied to the cancer risk assessment. A decision tree has been developed as a part of this approach and outlines the critical steps for analyzing a compound for carcinogenicity through a mutagenic MOA (e.g., data analysis, determination of mutagenicity in animals and in humans). Agents, showing mutagenicity in animals and humans, proceed through the Agency's framework analysis for MOAs. Cyclophosphamide (CP), an antineoplastic agent, which is carcinogenic in animals and humans and mutagenic in vitro and in vivo, was selected as a case study to illustrate how the framework analysis would be applied to prove that a carcinogen operates through a mutagenic MOA. Consistent positive results have been seen for mutagenic activity in numerous in vitro assays, in animals (mice, rats, and hamsters) and in humans. Accordingly, CP was processed through the framework analysis and key steps leading to tumor formation were identified as follows: metabolism of the parent compound to alkylating metabolites, DNA damage followed by induction of multiple adverse genetic events, cell proliferation, and bladder tumors. Genetic changes in rats (sister chromatid exchanges at 0.62 mg/kg) can commence within 30 min and in cancer patients, chromosome aberrations at 35 mg/kg are seen by 1 hr, well within the timeframe and tumorigenic dose range for early events. Supporting evidence is also found for cell proliferation, indicating that mutagenicity, associated with cytotoxicity, leads to a proliferative response, which occurs early (48 hr) in the process of tumor induction. Overall, the weight of evidence evaluation supports CP acting through a mutagenic MOA. In addition, no data were found that an alternative MOA might be operative. Therefore, the cancer guidelines recommend a linear extrapolation for the risk assessment. Additionally, data exist showing that CP induces mutagenicity in fetal blood and in the peripheral blood of pediatric patients; thus, the ADAFs would be applied.

Genetic toxicity assessment: employing the best science for human safety evaluation Part VII: Why not start with a single test: a transformational alternative to genotoxicity hazard and risk assessment

A transformational alternative for genotoxicity hazard and risk assessment is proposed to the current standard regulatory test battery. In principle, the proposed approach consists of a single in vitro test system with high genomic sequence homology to humans that addresses the relevant principal genetic lesions assessed in the current test battery. The single test system also possesses higher throughput attributes to permit the screening of large numbers of compounds and allow for an initial differentiation of genotoxic mechanisms (i.e., direct vs. indirect mechanisms) by how the hazard end point is measured. To differentiate compounds showing positive results, toxicogenomic analysis can be conducted to evaluate genotoxic mechanisms and further support risk assessment. Lastly, the results from the single test system can be followed up with a complementary in vivo assessment to establish mechanistic relevance at potential target tissues. Here, we propose the in vitro (yeast) DNA deletion (DEL) recombination assay as a single test alternative to the current genotoxicity test battery with a mechanistic follow up toxicogenomic analysis of genotoxic stress response as one approach that requires broader evaluation and validation. In this assay, intrachromosomal recombination events between a repeated DNA sequence lead to DNA deletions, which have been shown to be inducible by a variety of carcinogens including those both negative and positive in the standard Salmonella Ames assay. It is hoped that the general framework outlined along with this specific example will provoke broader interest to propose other potential test systems.

Application of toxicogenomics to genetic toxicology risk assessment

Based on the assumption that compounds having similar toxic modes of action induce specific gene expression changes, the toxicity of unknown compounds can be predicted after comparison of their molecular fingerprints with those obtained with compounds of known toxicity. These predictive models will therefore rely on the characterization of marker genes. Toxicogenomics (TGX) also provides mechanistic insight into the mode of toxicity, and can therefore be used as an adjunct to the standard battery of genotoxicity tests. Promising results, highlighting the ability of TGX to differentiate genotoxic from non-genotoxic carcinogens, as well as DNA-reactive from non-DNA reactive genotoxins, have been reported. Additional data suggested the possibility of ranking genotoxins according to the nature of their interactions with DNA. This new approach could contribute to the improvement of risk assessment. TGX could be applied as a follow-up testing strategy in case of positive in vitro genotoxicity findings, and could contribute to improve our ability to identify the molecular mechanism of action and to possibly better assess dose-response curves. TGX has been found to be less sensitive than the standard genotoxicity end-points, probably because it measures the whole cell population response, when compared with standard tests designed to detect rare events in a small number of cells. Further validation will be needed (1) to better link the profiles obtained with TGX to the established genotoxicity end-points, (2) to improve the gene annotation tools, and (3) to standardise study design and data analysis and to better evaluate the impact of variability between platforms and bioinformatics approaches.

Relevance and follow-up of positive results in in vitro genetic toxicity assays: an ILSI-HESI initiative

In vitro genotoxicity assays are often used to screen and predict whether chemicals might represent mutagenic and carcinogenic risks for humans. Recent discussions have focused on the high rate of positive results in in vitro tests, especially in those assays performed in mammalian cells that are not confirmed in vivo. Currently, there is no general consensus in the scientific community on the interpretation of the significance of positive results from the in vitro genotoxicity assays. To address this issue, the Health and Environmental Sciences Institute (HESI), held an international workshop in June 2006 to discuss the relevance and follow-up of positive results in in vitro genetic toxicity assays. The goals of the meeting were to examine ways to advance the scientific basis for the interpretation of positive findings in in vitro assays, to facilitate the development of follow-up testing strategies and to define criteria for determining the relevance to human health. The workshop identified specific needs in two general categories, i.e., improved testing and improved data interpretation and risk assessment. Recommendations to improve testing included: (1) re-examine the maximum level of cytotoxicity currently required for in vitro tests; (2) re-examine the upper limit concentration for in vitro mammalian studies; (3) develop improved testing strategies using current in vitro assays; (4) define criteria to guide selection of the appropriate follow-up in vivo studies; (5) develop new and more predictive in vitro and in vivo tests. Recommendations for improving interpretation and assessment included: (1) examine the suitability of applying the threshold of toxicological concern concepts to genotoxicity data; (2) develop a structured weight of evidence approach for assessing genotoxic/carcinogenic hazard; and (3) re-examine in vitro and in vivo correlations qualitatively and quantitatively. Conclusions from the workshop highlighted a willingness of scientists from various sectors to change and improve the current paradigm and move from a hazard identification approach to a "realistic" risk-based approach that incorporates information on mechanism of action, kinetics, and human exposure..

The pathogen reduction treatment of platelets with S-59 HCl (Amotosalen) plus ultraviolet A light: genotoxicity profile and hazard assessment

Despite restrictive donor criteria and screening procedures, infections resulting from the transfusion of bacterially contaminated platelet products continue to occur. Pathogen reduction technologies targeting nucleic acids have been developed. However, concerns about the safety of these procedures exist; the main concern being the possible mutagenic and carcinogenic effects of the pathogen-inactivated preparation in the recipient. This report reviews the genotoxicity profile of the S-59 (Amotosalen) plus long wavelength ultraviolet light (UVA) pathogen reduction technology, and assesses the mutagenic and carcinogenic hazards in recipients of treated platelets. S-59, a synthetic heterocyclic psoralen, non-covalently intercalates into the nucleic acids of pathogens and forms crosslinks when UVA photoactivated. Before clinical use, the levels of residual S-59 and free photoproducts are greatly reduced using a 'compound adsorption device' (CAD). In vitro, S-59 is mutagenic in Salmonella typhimurium and mouse lymphoma L5178Y TK(+/-) cells, and is clastogenic in CHO cells. There is reduced activity (Salmonella, CHO cells) or no activity (mouse lymphoma cells) with metabolic activation (S9 mix). When tested up to toxic dose levels, S-59 was negative in the mouse bone marrow micronucleus assay and the rat hepatocyte unscheduled DNA synthesis (UDS) test. Based on comparative studies conducted with S-59 plus UVA-treated platelets (up to 25 times without CAD), any genotoxic effects can be attributed to residual S-59. Considering (1) the known genotoxic mechanism of action for S-59, (2) the negative in vivo studies for S-59 at multiples >40,000x over clinical peak plasma levels, and (3) the fact that the positive in vitro genotoxicity effects for the end product seem due to residual S-59, any mutagenic hazard to a recipient of S-59 plus UVA-treated platelets is negligible and there is no concern about a carcinogenic potential as a consequence of a mutagenic activity. This conclusion is supported by a negative p53(+/-) mouse carcinogenicity study.

Follow-up testing of rodent carcinogens not positive in the standard genotoxicity testing battery: IWGT workgroup report

At the Plymouth Third International Workshop on Genotoxicity Testing in June 2002, a new expert group started a working process to provide guidance on a common strategy for genotoxicity testing beyond the current standard battery. The group identified amongst others "Follow-up testing of tumorigenic agents not positive in the standard genotoxicity test battery" as one subject for further consideration [L. Müller, D. Blakey, K.L. Dearfield, S. Galloway, P. Guzzie, M. Hayashi, P. Kasper, D. Kirkland, J.T. MacGregor, J.M. Parry, L. Schechtman, A. Smith, N. Tanaka, D. Tweats, H. Yamasaki, Strategy for genotoxicity testing and stratification of genotoxicity test results-report on initial activities of the IWGT Expert Group, Mutat. Res. 540 (2003) 177-181]. A workgroup devoted to this topic was formed and met on September 9-10, 2005, in San Francisco. This workgroup was devoted to the discussion of when it would be appropriate to conduct additional genetic toxicology studies, as well as what type of studies, if the initial standard battery of tests was negative, but tumor formation was observed in the rodent carcinogenicity assessment. The important role of the standard genetic toxicology testing to determine the mode of action (MOA) for carcinogenesis (genotoxic versus non-genotoxic) was discussed, but the limitations of the standard testing were also reviewed. The workgroup also acknowledged that the entire toxicological profile (e.g. structure-activity relationships, the nature of the tumor finding and metabolic profiles) of a compound needed to be taken into consideration before the conduct of any additional testing. As part of the meeting, case studies were discussed to understand the practical application of additional testing as well as to form a decision tree. Finally, suitable additional genetic toxicology assays to help determine the carcinogenic MOA or establish a weight of evidence (WOE) argument were discussed and formulated into a decision tree.

Strategy for genotoxicity testing: Hazard identification and risk assessment in relation to in vitro testing

This report summarizes the proceedings of the September 9-10, 2005 meeting of the Expert Working Group on Hazard Identification and Risk Assessment in Relation to In Vitro Testing, part of an initiative on genetic toxicology. The objective of the Working Group was to develop recommendations for interpretation of results from tests commonly included in regulatory genetic toxicology test batteries, and to propose an appropriate strategy for follow-up testing when positive in vitro results were obtained in these assays. The Group noted the high frequency of positive in vitro findings in the genotoxicity test batteries with agents found not to be carcinogenic and thought not to pose a carcinogenic health hazard to humans. The Group agreed that a set of consensus principles for appropriate interpretation and follow-up testing when initial in vitro tests are positive was needed. Current differences in emphasis and policy among different regulatory agencies were recognized as a basis of this need. Using a consensus process among a balanced group of recognized international authorities from industry, government, and academia, it was agreed that a strategy based on these principles should include guidance on: (1) interpretation of initial results in the "core" test battery; (2) criteria for determining when follow-up testing is needed; (3) criteria for selecting appropriate follow-up tests; (4) definition of when the evidence is sufficient to define the mode of action and the relevance to human exposure; and (5) definition of approaches to evaluate the degree of health risk under conditions of exposure of the species of concern (generally the human). A framework for addressing these issues was discussed, and a general "decision tree" was developed that included criteria for assessing the need for further testing, selecting appropriate follow-up tests, and determining a sufficient weight of evidence to attribute a level of risk and stop testing. The discussion included case studies based on actual test results that illustrated common situations encountered, and consensus opinions were developed based on group analysis of these cases. The Working Group defined circumstances in which the pattern and magnitude of positive results was such that there was very low or no concern (e.g., non-reproducible or marginal responses), and no further testing would be needed. This included a discussion of the importance of the use of historical control data. The criteria for determining when follow-up testing is needed included factors, such as evidence of reproducibility, level of cytotoxicity at which an increased DNA damage or mutation frequency is observed, relationship of results to the historical control range of values, and total weight of evidence across assays. When the initial battery is negative, further testing might be required based on information from the published literature, structure activity considerations, or the potential for significant human metabolites not generated in the test systems. Additional testing might also be needed retrospectively when increase in tumors or evidence of pre-neoplastic change is seen. When follow-up testing is needed, it should be based on knowledge about the mode of action, based on reports in the literature or learned from the nature of the responses observed in the initial tests. The initial findings, and available information about the biochemical and pharmacological nature of the agent, are generally sufficient to conclude that the responses observed are consistent with certain molecular mechanisms and inconsistent with others. Follow-up tests should be sensitive to the types of genetic damage known to be capable of inducing the response observed initially. It was recognized that genotoxic events might arise from processes other than direct reactivity with DNA, that these mechanisms may have a non-linear, or threshold, dose-response relationship, and that in such cases it may be possible to determine an exposure level below which there is negligible concern about an effect due to human exposures. When a test result is clearly positive, consideration of relevance to human health includes whether other assays for the same endpoint support the results observed, whether the mode or mechanism of action is relevant to the human, and - most importantly - whether the effect observed is likely to occur in vivo at concentrations expected as a result of human exposure. Although general principles were agreed upon, time did not permit the development of recommendations for the selection of specific tests beyond those commonly employed in initial test batteries.

Comparison of the mutagenic potential of 17 physical and chemical agents analyzed by the flow cytometry mutation assay

Several methods to assess genotoxicity of physical and chemical agents have been developed, most of which depend on growing colonies in selective medium. We recently published a new method for detecting mutations in the CD59 gene in a Chinese hamster ovary cell line that contains a single copy of human chromosome 11 (CHO A(L)). The assay is based on detecting the surface expression of CD59 with monoclonal antibodies using flow cytometry. The capabilities of this flow cytometry mutation assay (FCMA) to detect mutations from a wide variety of genotoxic agents are described here. There was a 400-fold separation between CD59- and CD59+ populations based on fluorescence intensity. Small numbers of negative cells mixed in with positive cells were detected in a highly linear fashion. Mutation dose response curves over a dose range yielding 80% to 20% survival are shown for ethyl methane sulfonate (EMS), mitomycin C (MMC) and lead acetate. EMS and lead acetate exhibited a threshold in response while MMC had a linear dose response over the full dose range. The mutant fraction was measured over time periods ranging up to 35 days following treatment. The mutant fraction peaked at different times ranging from 6 to 12 days after treatment. An additional 14 chemical and physical agents including point mutagens, heavy metals, ionizing and UV radiation, and DNA intercalators and cross linkers, were analyzed for mutagenic potential after doses giving 80% to 20% survival. The results presented here demonstrate the sensitivity and broad-ranging capability of the FCMA to detect mutations induced by a variety of genotoxic agents.

The cannabinoid CB1 receptor antagonist rimonabant (SR141716) inhibits human breast cancer cell proliferation through a lipid raft-mediated mechanism

The endocannabinoid system has been shown to modulate key cell-signaling pathways involved in cancer cell growth. In this study, we show that cannabinoid receptor type 1 (CB1) antagonist Rimonabant (SR141716) inhibited human breast cancer cell proliferation, being more effective in highly invasive metastatic MDA-MB-231 cells than in less-invasive T47D and MCF-7 cells. The SR141716 antiproliferative effect was not accompanied by apoptosis or necrosis and was characterized by a G1/S-phase cell cycle arrest, decreased expression of cyclin D and E, and increased levels of cyclin-dependent kinase inhibitor p27KIP1. We have also shown that SR141716 exerted a significant antiproliferative action, in vivo, by reducing the volume of xenograft tumors induced by MDA-MB-231 injection in mice. On the other hand, at the concentration range in which we observed the antiproliferative effect in tumor cells, we did not observe evidence of any genotoxic effect on normal cells. Our data also indicate that the SR141716 antiproliferative effect requires lipid raft/caveolae integrity to occur. Indeed, we found that CB1 receptor (CB1R) is completely displaced from lipid rafts in SR141716-treated MDA-MB-231 cells, and cholesterol depletion by methyl-beta-cyclodextrin strongly prevented SR141716-mediated antiproliferative effect. Taken together, our results suggest that SR141716 inhibits human breast cancer cell growth via a CB1R lipid raft/caveolae-mediated mechanism.

Comparative overview of current international strategies and guidelines for genetic toxicology testing for regulatory purposes

National and international regulatory agencies historically have used genotoxicity information as part of a weight-of-evidence approach to evaluate potential human carcinogenicity. Additionally, some agencies consider heritable mutation a regulatory endpoint. Furthermore, genotoxicity has the potential to contribute to other adverse health conditions. This article provides a comparative overview of the testing strategies used by regulatory agencies throughout the world. Despite minor variations in details, the genotoxicity test schemes for most regulatory entities generally comprise three tests: a bacterial gene mutation assay, an in vitro mammalian cell assay for gene mutation and/or chromosome aberrations, and often an in vivo assay for chromosomal effects. In some cases, fewer than these three tests are required. In other cases, when exposure data, structure-activity considerations, or other factors warrant, even chemicals negative in the three baseline tests may be subject to additional testing. If genotoxicity is identified by the baseline screening tests, assessment of the ability of the chemical to interact with DNA in the gonad may be required. This may apply regardless of whether or not a cancer bioassay has been triggered. Mutagens positive in second stage gonadal assay(s) may be tested in third stage in vivo rodent tests to provide data for a quantitative risk assessment. In all testing, theutilization of internationally-recognized protocols, where they exist, is advisable, although not in all instances required. When testing for regulatory purposes, it is advisable to verify the testing program with the specific regulatory body or bodies responsible forregulatory oversight before beginning testing.

An analysis of genetic toxicity, reproductive and developmental toxicity, and carcinogenicity data: II. Identification of genotoxicants, reprotoxicants, and carcinogens using in silico methods

This study examined a novel method to identify carcinogens that employed expanded data sets composed of in silico data pooled with actual experimental genetic toxicity (genetox) and reproductive and developmental toxicity (reprotox) data. We constructed 21 modules using the MC4PC program including 13 of 14 (11 genetox and 3 reprotox) tests that we found correlated with results of rodent carcinogenicity bioassays (rcbioassays) [Matthews, E.J., Kruhlak, N.L., Cimino, M.C., Benz, R.D., Contrera, J.F., 2005b. An analysis of genetic toxicity, reproductive and developmental toxicity, and carcinogenicity data: I. Identification of carcinogens using surrogate endpoints. Regul. Toxicol. Pharmacol.]. Each of the 21 modules was evaluated by cross-validation experiments and those with high specificity (SP) and positive predictivity (PPV) were used to predict activities of the 1442 chemicals tested for carcinogenicity for which actual genetox or reprotox data were missing. The expanded data sets had approximately 70% in silico data pooled with approximately 30% experimental data. Based upon SP and PPV, the expanded data sets showed good correlation with carcinogenicity testing results and had correlation indicator (CI, the average of SP and PPV) values of 75.5-88.7%. Conversely, expanded data sets for 9 non-correlated test endpoints were shown not to correlate with carcinogenicity results (CI values <75%). Results also showed that when Salmonella mutagenic carcinogens were removed from the 12 correlated, expanded data sets, only 7 endpoints showed added value by detecting significantly more additional carcinogens than non-carcinogens.