Re-evaluation of chromosomal aberration induction on nine mouse lymphoma assay "unique positive' NTP carcinogens

RIFM fragrance ingredient safety assessment, 3-phenylpropyl acetate, CAS Registry Number 122-72-5

Therefore, the phenethyl formate MOE for the fertility endpoint can be calculated by dividing the phenethyl alcohol NOAEL in mg/kg/day by the total systemic exposure to phenethyl formate, 1000/0.00062 or 1612903.

RIFM fragrance ingredient safety assessment, phenylethyl anthranilate, CAS Registry Number 133-18-6

The existing information supports the use of this material as described in this safety assessment. Phenylethyl anthranilate was evaluated for genotoxicity, repeated dose toxicity, developmental and reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, and environmental safety. Data from phenylethyl anthranilate and the read-across analog cinnamyl anthranilate (CAS # 87-29-6) show that phenylethyl anthranilate is not expected to be genotoxic. The skin sensitization endpoint was completed using the DST for non-reactive materials (900 μg/cm²); exposure is below the DST. The reproductive and local respiratory toxicity endpoints were evaluated using the TTC for a Cramer Class II material, and the exposure to phenylethyl anthranilate is below the TTC (0.009 mg/kg/day and 0.47 mg/day, respectively). Data on read-across analogs phenethyl alcohol (CAS # 60-12-8) and anthranilic acid (CAS # 118-92-3) provide a calculated MOE >100 for the repeated dose and developmental toxicity endpoints. The phototoxicity/photoallergenicity endpoints were evaluated based on UV spectra; phenylethyl anthranilate is not expected to be phototoxic/photoallergenic. The environmental endpoints were evaluated; phenylethyl anthranilate was found not to be PBT as per the IFRA Environmental Standards, and its risk quotients, based on its current volume of use in Europe and North America (i.e., PEC/PNEC), are <1.

In silico prediction of chromosome damage: comparison of three (Q)SAR models

Two major endpoints for genotoxicity tests are gene mutation and chromosome damage (CD), which includes clastogenicity and aneugenicity detected by chromosomal aberration (CA) test or micronucleus (MN) test. Many in silico prediction systems for bacterial mutagenicity (i.e. Ames test results) have been developed and marketed. They show good performance for prediction of Ames mutagenicity. On the other hand, it seems that in silico prediction of CD does not progress as much as Ames prediction. Reasons for this include different mechanisms and detection methods, many false positives and conflicting test results. However, some (quantitative) structure-activity relationship ((Q)SAR) models (e.g. Derek Nexus [Derek], ADMEWorks [AWorks] and CASE Ultra [MCase]) can predict CA test results. Therefore, performances of the three (Q)SAR models were compared using the expanded Carcinogenicity Genotoxicity eXperience (CGX) dataset for understanding current situations and future development. The constructed dataset contained 440 chemicals (325 carcinogens and 115 non-carcinogens). Sensitivity, specificity, accuracy or applicability of each model were 56.0, 86.9, 68.6 or 89.1% in Derek, 67.7, 61.5, 65.2 or 99.3% in AWorks, and 91.0, 64.9, 80.5 or 97.7% in MCase, respectively. The performances (sensitivity and accuracy) of MCase were higher than those of Derek or AWorks. Analysis of predictivity of (Q)SAR models of certain chemical classes revealed no remarkable differences among the models. The tendency of positive prediction by (Q)SAR models was observed in alkylating agents, aromatic amines or amides, aromatic nitro compounds, epoxides, halides and N-nitro or N-nitroso compounds. In an additional investigation, high sensitivity but low specificity was noted in in vivo MN prediction by MCase. Refinement of test data to be used for in silico system (e.g. consideration of cytotoxicity or re-evaluation of conflicting test results) will be needed to improve performance of CD prediction.

The influence of exogenous metabolism on the specificity of in vitro mammalian genotoxicity tests

A two-part study was designed to determine whether the inclusion of the rodent liver 'S9' exogenous metabolic activating system contributes to the generation of misleading positive results by the regulator-required in vitro mammalian genotoxicity tests. The mono-oxygenase enzymes in S9 produce direct-acting DNA-reactive electrophiles, and are included in in vitro genotoxicity tests to enhance the detection of substances which only become genotoxic following metabolism. However, as the S9 system lacks 'detoxifying' phase 2 factors it was hypothesised that increased chemical metabolism per se may lead to an increase in irrelevant S9 test outcomes in safety assessment. To test this, 89 compounds with positive or negative carcinogenicity data were identified, which produced negative Ames test data (+/- S9), and only produced positive in vitro mammalian test data in the presence of S9. This allowed a determination of whether or not misleading predictions of carcinogenicity by the in vitro mammalian tests were more or less prevalent in the presence of S9. A subset of these compounds was then tested with and without S9 in the GADD45a-GFP genotoxicity test, in order to determine whether misleading in vitro mammalian positive results were generally more prevalent with S9, or reflected particular tests' liabilities. This study suggests that the use of S9 metabolic activation in in vitro genotoxicity tests does not increase the prevalence of misleading positive results in in vitro mammalian genotoxicity assays, at least amongst Ames negative compounds.

A toxicological and dermatological assessment of aryl alkyl alcohol simple acid ester derivatives when used as fragrance ingredients

The aryl alkyl alcohol simple acid ester derivatives (AAASAE) group of fragrance ingredients was critically evaluated for safety following a complete literature search of the pertinent data. For high end users, calculated maximum skin exposures vary widely from 0.01% to 4.17%. AAASAE exhibit a common route of primary metabolism by carboxylesterases resulting in the formation of the simple acid and an aryl alkyl alcohol. They have low acute toxicity. No significant toxicity was observed in repeat-dose toxicity tests. There was no evidence of carcinogenicity of benzyl alcohol when it was administered in the feed; gavage studies resulted in pancreatic carcinogenesis due to the corn oil vehicle. The AAASAE are not mutagenic in bacterial systems or in vitro in mammalian cells, and have little to no in vivo genotoxicity. Reproductive and developmental toxicity data show no indication of adverse effects on reproductive function and NOELs for maternal and developmental toxicity are far in excess of current exposure levels. The AAASAE are generally not irritating or sensitizing at the current levels of exposure. The Panel is of the opinion that there are no safety concerns regarding the AAASAE at the current levels of use and exposure.

ECVAM retrospective validation of in vitro micronucleus test (MNT)

In the past decade several studies comparing the in vitro chromosome aberration test (CAT) and the in vitro micronucleus test (MNT) were performed. A high correlation was observed in each of the studies (>85%); however, no formal validation for the micronucleus in vitro assay had been carried out. Therefore, a working group was established by the European Centre for the Validation of Alternative Methods (ECVAM) to perform a retrospective validation of the existing data, in order to evaluate the validity of the in vitro MNT on the basis of the modular validation approach. The primary focus of this retrospective validation was on the evaluation of the potential of the in vitro MNT as alternative to the standard in vitro CAT. The working group evaluated, in a first step, the available published data and came to the conclusion that two studies [German ring trial, von der Hude, W., Kalweit, S., Engelhardt, G. et al. (2000) In-vitro micronucleus assay with Chinese hamster V79 cells: results of a collaborative study with 26 chemicals. Mutat. Res., 468, 137–163, and SFTG International Collaborative Study, Lorge, E., Thybaud, V., Aardema, M., Oliver, J., Wataka, A., Lorenzon, G. and Marzin, D. (2006) SFTG International Collaborative Study on in-vitro micronucleus test I. General conditions and overall conclusions of the study. Mutat. Res., 607, 13–36] met the criteria for a retrospective validation according to the criteria previously defined by the working group. These two studies were evaluated in depth (including the reanalysis of raw data) and provided the information required for assessing the reliability (reproducibility) of the test. For the assessment of the concordance between the in vitro MNT and the in vitro CAT, additional published data were considered. Based on this retrospective validation, the ECVAM Validation Management Team concluded that the in vitro MNT is reliable and relevant and can therefore be used as an alternative method to the in vitro CAT. Following peer review, these conclusions were formally endorsed by the ECVAM Scientific Advisory Committee.

Cytogenetic effects of 1,1-dichloroethane in mice bone marrow cells

The major concern for the halogenated compounds is their widespread distribution, in addition to occupational exposures. Several chlorinated alkanes and alkenes were found to induce toxic effects. In this study, we investigated the genotoxic potential of 1,1-dichloroethane in the bone marrow cells obtained from Swiss-Webster mice, using chromosomal aberrations (CA), mitotic index (MI), and micronuclei (MN) formation as toxicological endpoints. Five groups of three male mice each, weighing an average of 24 +/- 2 g, were injected intraperitoneally, once with doses of 100, 200, 300, 400, 500 mg/kg body weight (BW) of 1,1-dichloroethane dissolved in ethanol. A control group was also made of three animals injected with ethanol (1%) without the chemical. All animals were sacrificed 24 hours after the treatment. Chromosome and micronuclei preparations were obtained from bone marrow cells following standard protocols. Chromatid and chromosome aberrations were investigated in 100 metaphase cells per animal and percent micronuclei frequencies were investigated in 1,000 metaphase cells per animal. 1,1-dichloroethane exposures significantly increased the number of chromosomal aberrations and the frequency of micronucleated cells in the bone marrow cells of Swiss-Webster mice. Percent chromosomal aberrations of 2.67 +/- 0.577, 7.66 +/- 2.89, 8.33 +/- 2.08, 14.67 +/- 2.51, 20.3 +/- 3.21, 28 +/- 3.61; mitotic index of 9.4%, 7.9%, 6.2%, 4.3%, 3.0%, 2.6% and micronuclei frequencies of 3.33 +/- 0.7, 7.33 +/- 0.9, 8.00 +/- 1.0, 11.67 +/- 1.2, 15.33 +/- 0.7, 18.00 +/- 1.7 were recorded for the control, 100, 200, 300, 400, and 500 mg/kg BW respectively; indicating a gradual increase in number of chromosomal aberrations and micronuclei formation, with increasing dose of 1,1,-dichloroethane. Our results indicate that 1,1-dichloroethane has a genotoxic potential as measured by the bone marrow CA and MN tests in Swiss-Webster mice.

Evaluation of the ability of a battery of three in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens I. Sensitivity, specificity and relative predictivity

The performance of a battery of three of the most commonly used in vitro genotoxicity tests--Ames+mouse lymphoma assay (MLA)+in vitro micronucleus (MN) or chromosomal aberrations (CA) test--has been evaluated for its ability to discriminate rodent carcinogens and non-carcinogens, from a large database of over 700 chemicals compiled from the CPDB ("Gold"), NTP, IARC and other publications. We re-evaluated many (113 MLA and 30 CA) previously published genotoxicity results in order to categorise the performance of these assays using the response categories we established. The sensitivity of the three-test battery was high. Of the 553 carcinogens for which there were valid genotoxicity data, 93% of the rodent carcinogens evaluated in at least one assay gave positive results in at least one of the three tests. Combinations of two and three test systems had greater sensitivity than individual tests resulting in sensitivities of around 90% or more, depending on test combination. Only 19 carcinogens (out of 206 tested in all three tests, considering CA and MN as alternatives) gave consistently negative results in a full three-test battery. Most were either carcinogenic via a non-genotoxic mechanism (liver enzyme inducers, peroxisome proliferators, hormonal carcinogens) considered not necessarily relevant for humans, or were extremely weak (presumed) genotoxic carcinogens (e.g. N-nitrosodiphenylamine). Two carcinogens (5-chloro-o-toluidine, 1,1,2,2-tetrachloroethane) may have a genotoxic element to their carcinogenicity and may have been expected to produce positive results somewhere in the battery. We identified 183 chemicals that were non-carcinogenic after testing in both male and female rats and mice. There were genotoxicity data on 177 of these. The specificity of the Ames test was reasonable (73.9%), but all mammalian cell tests had very low specificity (i.e. below 45%), and this declined to extremely low levels in combinations of two and three test systems. When all three tests were performed, 75-95% of non-carcinogens gave positive (i.e. false positive) results in at least one test in the battery. The extremely low specificity highlights the importance of understanding the mechanism by which genotoxicity may be induced (whether it is relevant for the whole animal or human) and using weight of evidence approaches to assess the carcinogenic risk from a positive genotoxicity signal. It also highlights deficiencies in the current prediction from and understanding of such in vitro results for the in vivo situation. It may even signal the need for either a reassessment of the conditions and criteria for positive results (cytotoxicity, solubility, etc.) or the development and use of a completely new set of in vitro tests (e.g. mutation in transgenic cell lines, systems with inherent metabolic activity avoiding the use of S9, measurement of genetic changes in more cancer-relevant genes or hotspots of genes, etc.). It was very difficult to assess the performance of the in vitro MN test, particularly in combination with other assays, because the published database for this assay is relatively small at this time. The specificity values for the in vitro MN assay may improve if data from a larger proportion of the known non-carcinogens becomes available, and a larger published database of results with the MN assay is urgently needed if this test is to be appreciated for regulatory use. However, specificity levels of <50% will still be unacceptable. Despite these issues, by adopting a relative predictivity (RP) measure (ratio of real:false results), it was possible to establish that positive results in all three tests indicate the chemical is greater than three times more likely to be a rodent carcinogen than a non-carcinogen. Likewise, negative results in all three tests indicate the chemical is greater than two times more likely to be a rodent non-carcinogen than a carcinogen. This RP measure is considered a useful tool for industry to assess the likelihood of a chemical possessing carcinogenic potential from batteries of positive or negative results.

The FEMA GRAS assessment of benzyl derivatives used as flavor ingredients

This publication is the eighth in a series of safety evaluations performed by the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA). In 1993, the panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavoring substances under conditions of intended use. Elements that are fundamental to the safety evaluation of flavor ingredients include exposure, structural analogy, metabolism, pharmacokinetics and toxicology. Flavor ingredients are evaluated individually and in the context of the available scientific information on the group of structurally related substances. Scientific data relevant to the safety evaluation of the use of benzyl derivatives as flavoring ingredients is evaluated. The group of benzyl derivatives was reaffirmed as GRAS (GRASr) based, in part, on their self-limiting properties as flavoring substances in food; their rapid absorption, metabolic detoxication, and excretion in humans and other animals, their low level of flavor use, the wide margins of safety between the conservative estimates of intake and the no-observed-adverse effect levels determined from subchronic and chronic studies and the lack of significant genotoxic and mutagenic potential. This evidence of safety is supported by the fact that the intake of benzyl derivatives as natural components of traditional foods is greater than their intake as intentionally added flavoring substances.

Carcinogenicity of bromodichloromethane administered in drinking water to Male F344/N Rats and B6C3F1 mice

A life-time exposure study was conducted to assess the carcinogenicity of bromodichloromethane (BDCM) administered in the drinking water to male F344/N rats and B6C3F(1) mice. In mouse, the calculated mean daily BDCM concentrations (measured concentrations corrected for on-cage loss of chemical) were 0.06, 0.28 and 0.49 g/l. Time-weighted water consumption of 135, 97, and 89 ml/kg/day resulted in mean daily doses of 8.1, 27.2, and 43.4 mg BDCM/kg/day. No changes in feed consumption, final body weight, or survival were observed. Kidney weights were significantly depressed at 27.2 and 43.4 mg BDCM/kg/day. There was no increase in neoplasia in the liver, kidney, spleen, testis, bladder, sections along the alimentary tract, excised lesions, or at any other organ site. In rat, the corrected mean daily BDCM concentrations were 0.06, 0.33, and 0.62 g/l. Time-weighted water consumption of 65, 63, and 59 ml/kg/day yielded 3.9, 20.6 and 36.3 mg BDCM/kg/day. No alterations in feed consumption, body weight gain, and survival were seen. Kidney weight was significantly depressed in the 36.3-mg/kg/day treatment group. There was a significantly enhanced prevalence and multiplicity of hepatocellular adenomas at 3.9 mg BDCM/kg/day (15.5% and 0.16/animal vs. 2.2% and 0.02/animal for the control). Hepatocellular carcinomas increased from 2.2% and 0.02/animal for the control and 3.9 mg BDCM/kg/day to 8.3% and 0.10/animal at 20.6 mg BDCM/kg/day. The combined neoplasms were enhanced at 3.9 and 20.6 mg BDCM/kg/day. Liver neoplasia was depressed to the control value at 36.3 mg BDCM/kg. The prevalence of basophilic and clear cell, but not eosinophilic cells, altered foci of cells declined with increasing dose. BDCM did not increase cancer in the large bowel, renal tubules, or in any of the other tissues examined. Renal tubular hyperplasia was observed at 36.3 mg BDCM/kg (15.8% vs. 8.7% for the control group). Under the conditions of the study, BDCM in the drinking water was not carcinogenic in the male B6C3F(1) mouse, but was carcinogenic in the male F344/N rat based on an increased hepatocellular neoplasia.

Role of inflammation in chemical-induced lung cancer

Chemical-induced carcinogenesis has been in the focus of toxicological research for many decades. However, the mechanisms leading to tumor formation are only understood with certain substances. The intake of potential carcinogens by inhalation is a major route of exposure. Chemical-induced lung tumors are the final manifestation of a multistep pathway, resulting in an imbalance between cell proliferation and cell death by apoptosis. The impact of certain confounding factors e.g. extent of inflammatory response, type of genotoxic event, antagonizing principles and genetic background are discussed in this article. Finally, methods to assess the inflammatory potential of chemicals are referred to.

ICH-harmonised guidances on genotoxicity testing of pharmaceuticals: evolution, reasoning and impact

The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) has convened an expert working group which consisted of the authors of this paper and their respective committees, consulting groups and task forces. Two ICH guidances regarding genotoxicity testing have been issued: S2A, 'Guidance on Specific Aspects of Regulatory Genotoxicity Tests' and S2B, 'Genotoxicity: A Standard Battery for Genotoxicity Testing of Pharmaceuticals.' Together, these guidance documents now form the regulatory backbone for genotoxicity testing and assessment of pharmaceuticals in the European Union, Japan, and the USA. These guidances do not constitute a revolutionary new approach to genotoxicity testing and assessment, instead they are an evolution from preexisting regional guidelines, guidances and technical approaches. Both guidances describe a number of specific criteria as well as a general test philosophy in genotoxicity testing. Although these guidances were previously released within the participating regions in their respective regulatory communiqués, to ensure their wider distribution and better understanding, the texts of the guidances are reproduced here in their entirety (see Appendix A) and the background for the recommendations are described. The establishment of a standard battery for genotoxicity testing of pharmaceuticals was one of the most important issues of the harmonisation effort. This battery currently consists of: (i) a test for gene mutation in bacteria, (ii) an in vitro test with cytogenetic evaluation of chromosomal damage with mammalian cells or an in vitro mouse lymphoma tk assay, (iii) an in vivo test for chromosomal damage using rodent hematopoietic cells. A major change in testing philosophy is the acceptance of the interchangeability of testing for chromosomal aberrations in mammalian cells and the mouse lymphoma tk assay. This agreement was reached on the basis of the extensive review of databases and newly generated experimental data which are in part described in this publication. The authors are fully aware of the fact that some of the recommendations given in these ICH guidances are transient in nature and that the dynamic qualities and ongoing evolution of genetic toxicology makes necessary a continuous maintenance process that would serve to update the guidance as necessary.