Identifying chemical carcinogens and assessing potential risk in short-term bioassays using transgenic mouse models

Non-sugar sweeteners and cancer: Toxicological and epidemiological evidence

Several toxicological and epidemiological studies were published during the last five decades on non-sugar sweeteners (NSS) and cancer. Despite the large amount of research, the issue still continues to be of interest. In this review, we provided a comprehensive quantitative review of the toxicological and epidemiological evidence on the possible relation between NSS and cancer. The toxicological section includes the evaluation of genotoxicity and carcinogenicity data for acesulfame K, advantame, aspartame, cyclamates, saccharin, steviol glycosides and sucralose. The epidemiological section includes the results of a systematic search of cohort and case-control studies. The majority of the 22 cohort studies and 46 case-control studies showed no associations. Some risks for bladder, pancreas and hematopoietic cancers found in a few studies were not confirmed in other studies. Based on the review of both the experimental data on genotoxicity or carcinogenicity of the specific NSS evaluated, and the epidemiological studies it can be concluded that there is no evidence of cancer risk associated to NSS consumption.

Short-term carcinogenicity study of N-methyl-N-nitrosourea in FVB-Trp53 heterozygous mice

Carcinogenicity tests predict the tumorigenic potential of various substances in the human body by studying tumor induction in experimental animals. There is a need for studies that explore the use of FVB/N-Trp53em2Hwl/Korl (FVB-Trp53+/-) mice, created by TALEN-mediated gene targeting in Korea, in carcinogenicity tests. This study was performed to determine whether FVB-Trp53+/- mice are a suitable model for short-term carcinogenicity studies. To compare the carcinogenicity at different concentrations, 25, 50, and 75 mg/kg of N-methyl-N-nitrosourea (MNU), a known carcinogen, were administered intraperitoneally to FVB-Trp53+/- and wild-type male mice. After 26 weeks, the survival rate was significantly reduced in FVB-Trp53+/- mice compared to the wild-type mice in the 50 and 75 mg/kg groups. The incidence of thymic malignant lymphoma (TML) in the 50 and 75 mg/kg groups was 54.2 and 59.1% in FVB-Trp53+/- male mice, respectively. TML metastasized to the lungs, spleen, lymph nodes, liver, kidney, and heart in FVB-Trp53+/- male mice. Furthermore, the incidence of primary lung tumors, such as adenomas and adenocarcinomas, was 65.4, 62.5, and 45.4% in the FVB-Trp53+/- mice of the 25, 50, and 75 mg/kg groups, respectively. The main tumor types in FVB-Trp53+/- mice were TML and primary lung tumors, regardless of the dose of MNU administered. These results suggest that systemic tumors may result from malfunctions in the p53 gene and pathway, which is an important factor in the pathogenesis of human cancers. Therefore, FVB-Trp53 heterozygous mice are suitable for short-term carcinogenicity tests using positive carcinogens, and that the best result using MNU, a positive carcinogen, might have a single dose of 50 mg/kg.

Lack of potential carcinogenicity for acesulfame potassium - Systematic evaluation and integration of mechanistic data into the totality of the evidence

The safety of low- and no-calorie sweeteners remains a topic of general interest. Substantial evidence exists demonstrating a lack of carcinogenicity of the no-calorie sweetener acesulfame potassium (Ace K). The objective of this evaluation was to conduct a systematic assessment of available mechanistic data using a framework that quantitatively integrates proposed key characteristics of carcinogens (KCCs) into the totality of the evidence. Over 800 KCC-relevant endpoints from a variety of in vitro and in vivo assays were assessed for quality, relevance, and activity, and integrated to determine the overall strength of the evidence for plausibility that Ace K acts through the KCC. Overall, there was a lack of activity across the KCCs (overall integrated score <0 and no "strong" categorization for evidence of activity) in which data were identified. Together with the absence of treatment-related tumor effects in rodent bioassays, these results support the conclusion that Ace K is unlikely to induce a carcinogenic response. This assessment employed a weight of the evidence analysis that includes the consideration of factors such as reliability, strength of the model system, activity, and dose in a complex and heterogeneous dataset, and the ultimate integration of multiple data streams in the cancer hazard evaluation.

Safety Assessment of Diethanolamine and Its Salts as Used in Cosmetics

The Cosmetic Ingredient Review (CIR) Expert Panel assessed the safety of diethanolamine and its salts as used in cosmetics. Diethanolamine functions as a pH adjuster; the 16 salts included in this rereview reportedly function as surfactants, emulsifying agents, viscosity increasing agents, hair or skin conditioning agents, foam boosters, or antistatic agents. The Panel reviewed available animal and clinical data, as well as information from previous CIR reports. Since data were not available for each individual ingredient, and since the salts dissociate freely in water, the Panel extrapolated from previous reports to support safety. The Panel concluded that diethanolamine and its salts are safe for use when formulated to be nonirritating. These ingredients should not be used in cosmetic products in which N-nitroso compounds can be formed.

Survival rates of homozygotic Tp53 knockout rats as a tool for preclinical assessment of cancer prevention and treatment

Background

The gene that encodes tumor protein p53, Tp53, is mutated or silenced in most human cancers and is recognized as one of the most important cancer drivers. Homozygotic Tp53 knockout mice, which develop lethal cancers early in their lives, are already used in cancer prevention studies, and now Tp53 knockout rats have also been generated. This study assessed feasibility of using homozygous Tp53 knockout rats to evaluate the possible outcome of cancer chemoprevention.

Methods

A small colony of Tp53 knockout rats with a Wistar strain genetic background was initiated and maintained in the animal house at our institution. Tp53 heterozygotic females were bred with Tp53 homozygous knockout males to obtain a surplus of knockout homozygotes. To evaluate the reproducibility of their lifespan, 4 groups of Tp53 homozygous knockout male rats born during consecutive quarters of the year were kept behind a sanitary barrier in a controlled environment until they reached a moribund state. Their individual lifespan data were used to construct quarterly survival curves.

Results

The four consecutive quarterly survival curves were highly reproducible. They were combined into a single “master” curve for use as a reference in intervention studies. The average lifespan of untreated male Tp53 homozygous knockout rats was normally distributed, with a median of 133 days. Sample size vs. effect calculations revealed that confirming a 20% and 30% increase in the lifespan would respectively require a sample size of 18 and 9 animals (when assessed using the t-test with a power of 80% and alpha set at 0.05). As an example, the Tp53 homozygous knockout rat model was used to test the chemopreventive properties of carnosine, a dipeptide with suspected anticancer properties possibly involving modulation of the mTOR pathway. The result was negative.

Conclusion

Further evaluation of the Tp53 homozygous knockout male rat colony is required before it can be confirmed as a viable tool for assessing new methods of cancer prevention or treatment.

Stem cell proliferation patterns as an alternative for in vivo prediction and discrimination of carcinogenic compounds

One of the major challenges in the development of alternative carcinogenicity assays is the prediction of non-genotoxic carcinogens. The variety of non-genotoxic cancer pathways complicates the search for reliable parameters expressing their carcinogenicity. As non-genotoxic and genotoxic carcinogens have different cancer risks, the objective of this study was to develop a concept for an in vivo test, based on flatworm stem cell dynamics, to detect and classify carcinogenic compounds. Our methodology entails an exposure to carcinogenic compounds during the animal's regeneration process, which revealed differences in proliferative responses between non-genotoxic and genotoxic carcinogens during the initial stages of the regeneration process. A proof of concept was obtained after an extensive study of proliferation dynamics of a genotoxic and a non-genotoxic compound. A pilot validation with a limited set of compounds showed that the proposed concept not only enabled a simple prediction of genotoxic and non-genotoxic carcinogens, but also had the power to discriminate between both. We further optimized this discrimination by combining stem cell proliferation responses with a phenotypic screening and by using specific knockdowns. In the future, more compounds will be tested to further validate and prove this concept.

Evaluation of the Carcinogenic Potential of Clofibrate in the Neonatal Mouse

This study was conducted in support of the International Life Sciences Institute (ILSI) alternative carcinogenicity models initiative to evaluate the carcinogenic potential of clofibrate, a nongenotoxic peroxisome proliferator-activated receptor (PPAR) α agonist, following oral administration to neonatal mice. Male and female neonatal CD-1 mice were dosed with clofibrate at doses of 100, 250, and 500 mg/kg or with the positive control, diethyl-nitrosamine (DEN), at 2 mg/kg by oral gavage on days 9 and 16 post birth and observed for approximately 1 year for the development of tumors. Plasma levels of clofibric acid after the second administration increased with dose, but were not dose proportional. Clofibrate administered by gavage on litter days 9 and 16 to neonatal mice at doses of 100, 250, or 500 mg/kg did not produce a carcinogenic effect. The positive control DEN did produce tumors in the liver and lung (single and multiple adenomas and carcinomas) and harderian gland (adenoma) of both sexes. Non-neoplastic lesions related to DEN treatment were confined to myocardial degeneration/fibrosis and testicular interstitial hyperplasia in males, and to glomerulonephrosis and gastritis in both sexes.

Studies Evaluating the Utility of N-Methyl-N-Nitrosourea as a Positive Control in Carcinogenicity Studies in the p53+/– Mouse

Studies conducted under the auspices of International Life Sciences Institute (ILSI) have suggested that an alternative mouse carcinogenicity study may be substituted for the traditional 2-year mouse bioassay typically conducted to support the development of drug candidates. The purpose of this study was to characterize the carcinogenic potential of N-methyl- N-nitrosourea (MNU), a DNA alkylating agent, in p53+ /– knockout mice to determine its suitability as a positive control agent in an alternative carcinogenicity model. p53+ /– knockout mice were administered a single oral dose of 90 mg/kg and maintained for up to 13 weeks prior to evaluation of neoplasms. Treatment was generally well tolerated; however, 4 of 30 mice died between the days of 75 and 92 due to neoplasms. MNU-related macroscopic observations included enlargement of the thymus, spleen, mandibular and mesenteric lymph nodes; and pale liver, heart, kidney, and bone marrow, which correlated with the diagnosis of lymphoma of the hematopoietic system, noted in the thymus of all affected animals and in the spleen, liver, lungs, and kidneys of some animals. Other treatment-related single neoplasms included a squamous-cell carcinoma in the nonglandular stomach and leiomyosarcoma in the glandular stomach. Non-neoplastic proliferative lesions included acanthosis and hyperkeratosis in the nonglandular stomach, focal papillary hyperplasia of the nonglandular stomach, glandular hyperplasia of the stomach, and adenomatous hyperplasia of the duodenum or ileum. The increased incidence of neoplastic and proliferative changes in MNU-treated mice suggests MNU could serve as a positive control in alternative carcinogenicity studies conducted in p53+ /– knockout mice.

Evaluation of the Carcinogenic Potential of Clofibrate in the p53+/− Mouse

This study was conducted as part of International Life Sciences Institute (ILSI) program to evaluate the carcinogenic potential of clofibrate, a nongenotoxic, peroxisome proliferator-activated receptor (PPAR) α agonist, following oral administration to p53+ /− heterozygous mice for a minimum of 26 weeks. p-Cresidine, a urinary bladder carcinogen, was given orally at 400 mg/kg/day as a positive control. Initial clofibrate doses were 50, 250, and 400 mg/kg/day for males and 50, 200, and 500 mg/kg/day for females. Due to unexpected mortality during the first week of dosing, clofibrate doses were lowered to 25, 75, and 100 mg/kg/day for males and 25, 75, and 125 mg/kg/day for females. Clinical signs and mortality were greater in p53+ /− than wild-type (WT) mice. With the exception of liver weights, no marked differences in any other parameters either between the sexes or between WT and p53+ /− mice were noted. Moderate increases in liver weights noted in WT males given 100 mg/kg/day clofibrate were not associated with any microscopic changes. No neoplastic response was observed in p53+ /−mice after 6 months of exposure to clofibrate at doses up to 100 mg/kg/day for males and 125 mg/kg/day for females. Transitional-cell hyperplasia and carcinoma of the urinary bladder were noted in both sexes given p-cresidine, demonstrating that the p53+ /− mouse responded to a known mouse carcinogen as expected. Clofibrate produced non-neoplastic findings in the adrenals, pancreas, and prostate, whereas p-cresidine affected the kidney, liver, pancreas, and spleen.

Evaluation of the Xpa-Deficient Transgenic Mouse Model for Short-Term Carcinogenicity Testing: 9-Month Studies with Haloperidol, Reserpine, Phenacetin, and D-Mannitol

As part of the international evaluation program coordinated by ILSI/HESI, the potential of DNA repair deficient Xpa- /- mice and the double knockout Xpa- /- .p53+ /- mice for short term carcinogenicity assays was evaluated. For comparison also wild-type C57BL/6 mice (WT) were included in these studies. Four test compounds were administered to groups of 15 male and 15 female Xpa- /- mice, Xpa- /- .p53+ /- mice and WT mice for 39 weeks. The model compounds investigated were haloperidol, reserpine (nongenotoxic rodent carcinogens, putative human noncarcinogens), phenacetin (genotoxic rodent carcinogen, suspected human carcinogen), and D-mannitol (noncarcinogen in rodents and humans). The test compounds were administered as admixture to rodent diet at levels up to 25 mg/kg diet for haloperidol, 7.5 mg/kg diet for reserpine, 0.75% for phenacetin, and 10% for D-mannitol. These levels included the maximum tolerable dose (MTD). Survival was not affected with any of the test compounds. Haloperidol, reserpine and D-mannitol were negative in the carcinogenicity assay with Xpa- /- and Xpa- /- .p53+ /- mice, showing low and comparable tumor incidences in controls and high-dose animals. The results obtained with phenacetin may be designated equivocal in Xpa- /- .p53+ /- mice, based on the occurrence of a single rare tumor in the target organ (kidney) accompanied by a low incidence of hyperplastic renal lesions and a high incidence of karyomegaly. These results are in agreement with the currently known carcinogenic potential of the 4 test compounds in humans.

Review of Research Trends and Methods in Nano Environmental, Health, and Safety Risk Analysis

Despite the many touted benefits of nanomaterials, concerns remain about their possible environmental, health, and safety (EHS) risks in terms of their toxicity, long-term accumulation effects, or dose-response relationships. The published studies on EHS risks of nanomaterials have increased significantly over the past decade and half, with most focused on nanotoxicology. Researchers are still learning about health consequences of nanomaterials and how to make environmentally responsible decisions regarding their production. This article characterizes the scientific literature on nano-EHS risk analysis to map the state-of-the-art developments in this field and chart guidance for the future directions. First, an analysis of keyword co-occurrence networks is investigated for nano-EHS literature published in the past decade to identify the intellectual turning points and research trends in nanorisk analysis studies. The exposure groups targeted in emerging nano-EHS studies are also assessed. System engineering methods for risk, safety, uncertainty, and system reliability analysis are reviewed, followed by detailed descriptions where applications of these methods are utilized to analyze nanomaterial EHS risks. Finally, the trends, methods, future directions, and opportunities of system engineering methods in nano-EHS research are discussed. The analysis of nano-EHS literature presented in this article provides important insights on risk assessment and risk management tools associated with nanotechnology, nanomanufacturing, and nano-enabled products.

Prediction of Rodent Carcinogenesis: An Evaluation of Prechronic Liver Lesions as Forecasters of Liver Tumors in NTP Carcinogenicity Studies

The National Toxicology Program (NTP) developed the chronic 2-year bioassay as a mechanism for predicting the carcinogenic potential of chemicals in humans. The cost and duration of these studies has limited their use to small numbers of selected chemicals. Many different short-term methods aimed at increasing predictive accuracy and the number of chemicals evaluated have been developed in attempts to successfully correlate their results with evidence of carcinogenicity (or lack of carcinogenicity). Using NTP studies, the effectiveness of correlating prechronic liver lesions with liver cancer encompassing multiple studies using mice (83 compounds) and rats (87 compounds) was assessed. These lesions include hepatocellular necrosis, hepatocellular hypertrophy, hepatocellular cytomegaly, bile duct hyperplasia, and hepatocellular degeneration, along with increased liver weight. Our results indicate that pooling 3 of these prechronic data points (hepatocellular necrosis, hepatocellular hypertrophy, and hepatocellular cytomegaly) can be very predictive of carcinogenicity in the 2-year study ( p < 0 .05). The inclusion of increased liver weight as an endpoint in the pool of data points increases the number of rodent liver carcinogens that are successfully predicted ( p < 0 .05), but also results in the prediction of increased numbers of noncarcinogenic chemicals as carcinogens. The use of multiple prechronic study endpoints provides supplementary information that enhances the predictivity of identifying chemicals with carcinogenic potential.

Possible Application of Human c-Ha-ras Proto-Oncogene Transgenic Rats in a Medium-Term Bioassay Model for Carcinogens

With the aim of developing a medium-term assay for screening of environmental carcinogens, we exposed mammary carcinogen sensitive human c-Ha-ras proto-oncogene transgenic (Hras128) rats to various carcinogens, including compounds that do not normally induce mammary tumors. Seven-week-old Hras128 rats and wild-type littermates received administrations of 3-methylcholanthrene (3-MC), benzo[a]pyrene (B[a]P), anthracene, pyrene, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), dimethylarsinic acid (DMA), diethylnitrosamine (DEN) or azoxymethane (AOM) and were sacrificed at week 12 (females) (at week 10 for the 3-MC group) or week 20 (males). Female Hras128 rats receiving NNK, DEN, or DMA showed a significant increase in mammary tumor incidence and/or multiplicity compared to the respective values with olive oil or deionized distilled water (DDW) vehicles. In male Hras128 rats, a significant increase in mammary tumors was also observed in groups administered 3-MC, B[a]P, anthracene, IQ, and NNK. Mutations of transgenes were observed in codons 12 and/or 61 in the induced tumors by PCR-RFLP except in the DEN group in female and in the MeIQx group in male Hras128 rats. Thus various carcinogens, not necessarily limited to those normally targeting the breast, were found to induce mammary carcinomas in Hras128 rats, especially in females, pointing to potential use for medium-term screening.

Twenty-six-week oral carcinogenicity study of 3-monochloropropane-1,2-diol in CB6F1-rasH2 transgenic mice

The carcinogenic potential of 3-monochloro-1,2-propanediol (3-MCPD) was evaluated in a short-term carcinogenicity testing study using CB6F1 rasH2-Tg (rasH2-Tg) mice. 3-MCPD is found in many foods and food ingredients as a result of storage or processing and is regarded as a carcinogen since it is known to induce Leydig cell and kidney tumors in rats. Male and female rasH2-Tg mice were administered 3-MCPD once daily by oral gavage at doses of 0, 10, 20, and 40 mg/kg body weight (bw) per day for 26 weeks. As a positive control, N-methyl-N-nitrosourea (MNU) was administered as a single intraperitoneal injection (75 mg/kg). In 3-MCPD-treated mice, there was no increase in the incidence of neoplastic lesions compared to the incidence in vehicle control mice. However, 3-MCPD treatment resulted in an increased incidence of tubular basophilia in the kidneys and germ cell degeneration in the testes, with degenerative germ cell debris in the epididymides of males at 20 and 40 mg/kg bw per day. In 3-MCPD-treated females, vacuolation of the brain and spinal cord was observed at 40 mg/kg bw per day; however, only one incidence of vacuolation was observed in males. Forestomach and cutaneous papilloma and/or carcinoma and lymphoma were observed in most rasH2 mice receiving MNU treatment. We concluded that 3-MCPD did not show carcinogenic potential in the present study using rasH2-Tg mice. The findings of this study suggest that the carcinogenic potential of 3-MCPD is species specific.

An FDA overview of rodent carcinogenicity studies of angiotensin II AT-1 receptor blockers: pulmonary adenomas and carcinomas

Sipahi et al. (2010) performed a meta-analysis of 5 clinical trials (n=68,402) of 3 Angiotensin II (AngII) receptor subtype AT-1 blockers (ARBs) in cardiovascular disease. It revealed excess new lung cancer diagnoses in the cohorts treated with an ARB and background therapy (0.9% vs. 0.7% in non-ARB control; RR: 1.25; CI: 1.05-1.49; p=0.01). The FDA responded with a larger meta-analysis of 31 clinical trials (n=155,816) of ARBs that found no evidence of any excess of site-specific cancer (lung, breast, prostate), solid/skin cancer or cancer death (FDA safety communication, 3 June 2011). The FDA then re-visited the 19 rodent carcinogenicity assays of 9 ARBs, starting with those for Losartan in 1994, for any evidence of dosage-related lung tumorigenicity in this class. Assays were performed in 5 strains of rats and 5 strains of wild-type and transgenic mice per protocols and dosages sanctioned by FDA's executive carcinogenicity assessment committee (eCAC). Duration was lifetime except for 26-week assays of azilsartan and olmesartan in transgenic Tg rasH2 mice, and an assay of olmesartan in p53(+/-) transgenic mice. The dosages provided exposures approximating, and in most cases up to 20-300times greater than, that in patients. Depending on strain, up to 35% of untreated mice spontaneously developed lung tumors. Regression analysis of placebo-corrected mouse lung tumor incidence collapsed across strains, gender, and ARBs vs. multiples of human exposure revealed no excess lung neoplasia. The R(2) of <0.001 reflected the virtually identical number of treated cohorts with more tumors than its control cohort vs. those with less. Regardless of strain, both control and medicated rats were essentially devoid of lung tumors in the lifetime trials. Accordingly, there was neither promotion of background lung tumors in the mouse, nor initiation of de novo lung tumors in the rat. The negative lung findings in the mouse Tg rasH2 strain are also noteworthy given that, historically, the most prevalent spontaneous tumors in 26week trials in that model are lung adenomas and carcinomas. The negative results of the 19, mostly lifetime, assays for cancer viewed en masse add to the results of the meta-analysis of the shorter clinical trials of ARBs that were benign regardless of statistical method used (random vs. fixed effect), comparator arm (with or without ACE-inhibitors) and major co-factors (smoking or cancer history).

The use of genetically modified mice in cancer risk assessment: challenges and limitations

The use of genetically modified (GM) mice to assess carcinogenicity is playing an increasingly important role in the safety evaluation of chemicals. While progress has been made in developing and evaluating mouse models such as the Trp53⁺/⁻, Tg.AC and the rasH2, the suitability of these models as replacements for the conventional rodent cancer bioassay and for assessing human health risks remains uncertain. The objective of this research was to evaluate the use of accelerated cancer bioassays with GM mice for assessing the potential health risks associated with exposure to carcinogenic agents. We compared the published results from the GM bioassays to those obtained in the National Toxicology Program's conventional chronic mouse bioassay for their potential use in risk assessment. Our analysis indicates that the GM models are less efficient in detecting carcinogenic agents but more consistent in identifying non-carcinogenic agents. We identified several issues of concern related to the design of the accelerated bioassays (e.g., sample size, study duration, genetic stability and reproducibility) as well as pathway-dependency of effects, and different carcinogenic mechanisms operable in GM and non-GM mice. The use of the GM models for dose-response assessment is particularly problematic as these models are, at times, much more or less sensitive than the conventional rodent cancer bioassays. Thus, the existing GM mouse models may be useful for hazard identification, but will be of limited use for dose-response assessment. Hence, caution should be exercised when using GM mouse models to assess the carcinogenic risks of chemicals.

Comparative time course profiles of phthalate stereoisomers in mice

More efficient models are needed to assess potential carcinogenicity hazard of environmental chemicals based on early events in tumorigenesis. Here, we investigated time course profiles for key events in an established cancer mode of action. Using a case study approach, we evaluated two reference phthalates, di(2-ethylhexyl) phthalate (DEHP) and its stereoisomer di-n-octyl phthalate (DNOP), across the span of a two-year carcinogenicity bioassay. Male B6C3F1 mice received diets with no phthalate added (control), DEHP at 0.12, 0.60, or 1.20%, or DNOP at 0.10, 0.50, or 1.00% (n = 80-83/group) for up to 104 weeks with six interim evaluations starting at week 4. Mean phthalate doses were 139, 845, and 3147 mg/kg/day for DEHP and 113, 755, and 1281 mg/kg/day for DNOP groups, respectively. Incidence and number of hepatocellular tumors (adenoma and/or carcinoma) were greater at ≥ 60 weeks for all DEHP groups with time and dose trends, whereas DNOP had no significant effects. Key events supported a peroxisome proliferator-activated receptor alpha (PPARα) mode of action for DEHP, with secondary cytotoxicity at the high dose, whereas DNOP induced modest increases in PPARα activity without proliferative or cytotoxic effects. Threshold estimates for later tumorigenic effects were identified at week 4 for relative liver weight (+24%) and PPARα activity (+79%) relative to the control group. Benchmark doses (BMDs) for these measures at week 4 clearly distinguished DEHP and DNOP and showed strong concordance with values at later time points and tumorigenic BMDs. Other target sites included testis and kidney, which showed degenerative changes at higher doses of DEHP but not DNOP. Our results highlight marked differences in the chronic toxicity profiles of structurally similar phthalates and demonstrate quantitative relationships between early bioindicators and later tumor outcomes.

Reassessing the two-year rodent carcinogenicity bioassay: a review of the applicability to human risk and current perspectives

The 2-year rodent carcinogenicity test has been the regulatory standard for the prediction of human outcomes for exposure to industrial and agro-chemicals, food additives, pharmaceuticals and environmental pollutants for over 50 years. The extensive experience and data accumulated over that time has spurred a vigorous debate and assessment, particularly over the last 10 years, of the usefulness of this test in terms of cost and time for the information obtained. With renewed interest in the United States and globally, plus new regulations in the European Union, to reduce, refine and replace sentinel animals, this review offers the recommendation that reliance on information obtained from detailed shorter-term, 6 months rodent studies, combined with genotoxicity and chemical mode of action can realize effective prediction of human carcinogenicity instead of the classical two year rodent bioassay. The aim of carcinogenicity studies should not be on the length of time, and by obligation, number of animals expended but on the combined systemic pathophysiologic influence of a suspected chemical in determining disease. This perspective is in coordination with progressive regulatory standards and goals globally to utilize effectively resources of animal usage, time and cost for the goal of human disease predictability.

Toxicology and carcinogenesis study of senna in C3B6.129F1-Trp53 tm1Brd N12 haploinsufficient mice

Senna is a pod or leaf of Senna alexandrina P. Mill and is used as a stimulant laxative. In the large intestine, bacterial enzymes reduce sennosides to rhein-9-anthrone, the active form for the laxative effect. To determine the potential toxic effects of senna, a 5-week dose range finding study in the C57BL/6N mouse and a 40-week toxicology and carcinogenesis study in the C3B6.129F1-Trp53 (tm1Brd) N12 haploinsufficient (p53(+/-)) mouse were conducted. In the 5-week study, C57BL/6N mice were exposed to up to 10,000 ppm senna in feed. Increased incidences of epithelial hyperplasia of the cecum and colon were observed in males and females exposed to 5,000 or 10,000 ppm senna. These intestinal lesions were not considered to be of sufficient severity to cause mortality and, thus, in the p53(+/-) mouse 40-week study, the high dose of 10,000 ppm was selected. Significant increases in the incidences of epithelial hyperplasia of the colon and cecum were observed at 10,000 ppm in p53(+/-) males and females, and the incidence of hyperplasia of the colon was significantly increased at 3,000 ppm in females. In conclusion, the large intestine was the major target of senna-induced toxicity in both wild-type and the p53(+/-) mouse model. There was no neoplastic change when senna was administered to p53(+/-) mouse.

Safety Assessment of Triethanolamine and Triethanolamine-Containing Ingredients as Used in Cosmetics

The Cosmetic Ingredient Review Expert Panel assessed the safety of triethanolamine (TEA) and 31 related TEA-containing ingredients as used in cosmetics. The TEA is reported to function as a surfactant or pH adjuster; the related TEA-containing ingredients included in this safety assessment are reported to function as surfactants and hair- or skin-conditioning agents. The exception is TEA-sorbate, which is reported to function as a preservative. The Panel reviewed the available animal and clinical data. Although data were not available for all the ingredients, the panel relied on the information available for TEA in conjunction with previous safety assessments of components of TEA-containing ingredients. These data could be extrapolated to support the safety of all included ingredients. The panel concluded that TEA and related TEA-containing ingredients named in this report are safe as used when formulated to be nonirritating. These ingredients should not be used in cosmetic products in which N-nitroso compounds can be formed.

Current Status of Short-Term Tests for Evaluation of Genotoxicity, Mutagenicity, and Carcinogenicity of Environmental Chemicals and NCEs

The advent of the industrial revolution has seen a significant increase in the number of new chemical entities (NCEs) released in the environment. It becomes imperative to check the toxic potential of NCEs to nontarget species before they are released for commercial purposes because some of these may exert genotoxicity, mutagenicity, or carcinogenicity. Exposure to such compounds produces chemical changes in DNA, which are generally repaired by the DNA repair enzymes. However, DNA damage and its fixation may occur in the form of gene mutations, chromosomal damage, and numerical chromosomal changes and recombination. This may affect the incidence of heritable mutations in man and may be transferred to the progeny or lead to the development of cancer. Hence, adequate tests on NCEs have to be undertaken for the risk assessment and hazard prediction. Compounds that are positive in tests that detect such damages have the potential to be human mutagens/carcinogens. Only long-term animal bioassays, involving lifetime studies on animals, were used earlier to classify substances as mutagens/carcinogens. These tests were cumbersome and time consuming and required a lot of facilities and personnel. Short-term tests, therefore, were brought into practice. A "battery" of three to four of these short-term tests has been proposed now by a number of regulatory authorities for the classification of compounds as mutagenic or carcinogenic. This review deals with the current status of these short-term tests.

Reduction in the Number of Animals and the Evaluation Period for the Positive Control Group in Tg.rasH2 Short-Term Carcinogenicity Studies

The lack of a clear guidance on the adequate number of animals used for positive controls in the short-term (26-weeks) transgenic mouse carcinogenicity studies has resulted in the use of high number of animals. In our earlier Tg.rasH2 studies, 25 mice/sex were used in the urethane-positive control dose groups that were sacrificed by 18 weeks. Based on a robust response, several of our protocols for Tg.rasH2 studies with 15 mice/sex and terminal sacrifice at 17 ± 1 weeks were submitted and accepted by the Carcinogenicity Assessment Committee of the US Food and Drug Administration since we demonstrated close to 100% response for the development of lung and splenic tumors (target organs) in 500 mice/sex. These 500 mice/sex included 17 groups of 25 mice/sex and 5 groups of 15 mice/sex.  The objective of this investigation was to determine whether the number of animals can be further reduced along with the shortened duration of exposure to urethane. Accordingly, 10 Tg.rasH2 mice/sex/group were administered a total of 3 intraperitoneal (IP) injections of urethane (1000 mg/kg per day) on study days 1, 3, and 5, and the presence of tumors in the lungs and spleen was evaluated after 8, 10, 12, 14, or 16 weeks. Our results demonstrate that 100% of the mice at 8 weeks had developed lung tumors, whereas close to 100% of the mice at 14 weeks had developed splenic tumors. Based on the development of lung tumors alone in 100% of the mice, we recommend that 10 mice/sex are sufficient and that these mice can also be sacrificed as early as 10 ± 1 weeks following the administration of urethane.

Strategies for the optimisation of in vivo experiments in accordance with the 3Rs philosophy

There are a large number of chemicals in current use for which adequate toxicity data are not available. Whilst there are clear ethical and legal obligations to obtain data from sources other than in vivo experiments wherever possible, in certain cases in vivo assays may be deemed necessary. In such circumstances, it is essential to ensure that the maximum amount of high quality data is obtained from the minimum number of animals, using the most humane procedures, in accordance with the philosophy of reduction, refinement and replacement (3Rs). The aim of this report is to provide a strategy for anyone involved in animal experimentation, for either toxicological or pharmacological purposes, as to how in vivo experiments may be optimised. The impact of generic and endpoint specific sources of variability has been highlighted in a proof-of-principle analysis considering the variation in protocols for assays for four human health endpoints (skin sensitisation, reproductive/developmental toxicity, mutagenicity and carcinogenicity). Other factors such as operator training, experimental/statistical design, use of lower species and use of combined assays are also discussed. Recommendations for optimisation of in vivo assays, in terms of the 3Rs philosophy, applied to performing tests, harvesting data and appropriate reporting are summarised as a checklist of issues to be addressed prior to undertaking such assays.

Power, expertise and the limits of representative democracy: genetics as scientific progress or political legitimation in carcinogenic risk assessment of pharmaceuticals?

In modern 'representative' democratic states, the legitimacy of governments' actions rests on their publicly declared commitment to protect the interests of their citizens. Regarding the pharmaceutical sector in most democracies, new drug products are developed and marketed by a capitalist industry, whose member firms, via shareholders, have commercial interests in expanding product sales. In those democracies, states have established government agencies to regulate the pharmaceutical industry on behalf of citizens. State legislatures, such as the US Congress and European Parliaments, have charged government drug regulatory agencies with the legal responsibility to protect public health. Yet, this paper argues that government drug regulatory agencies in the EU, Japan, and USA have permitted the pharmaceutical industry to reshape the regulatory guidance for carcinogenic risk assessment of pharmaceuticals in ways that are not techno-scientifically defensible as bases for improved, or even equivalent, protection of public health, compared with the previous techno-regulatory standards. By adopting the industry's agenda of streamlining carcinogenicity testing in order to accelerate drug development and regulatory review, it is contended that these regulatory agencies have allowed the techno-regulatory standards for carcinogenic risk assessment to be loosened in ways that are presented as scientific progress resulting from new genetics, but for which there is little evidence of progress in public health protection.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

When NRF2 talks, who's listening?

Activation of the KEAP1-NRF2 signaling pathway is an adaptive response to environmental and endogenous stresses and serves to render animals resistant to chemical carcinogenesis and other forms of toxicity, whereas disruption of the pathway exacerbates these outcomes. This pathway, which can be activated by sulfhydryl-reactive, small-molecule pharmacologic agents, regulates the inducible expression of an extended battery of cytoprotective genes, often by direct binding of the transcription factor to antioxidant response elements in the promoter regions of target genes. However, it is becoming evident that some of the protective effects may be mediated indirectly through cross talk with additional pathways affecting cell survival and other aspects of cell fate. These interactions provide a multi-tiered, integrated response to chemical stresses. This review highlights recent observations on the molecular interactions and their functional consequences between NRF2 and the arylhydrocarbon receptor (AhR), NF-κB, p53, and Notch1 signaling pathways.

An Industry Perspective on the Utility of Short-Term Carcinogenicity Testing in Transgenic Mice in Pharmaceutical Development

International guidelines allow for use of a short-term cancer bioassay (twenty-six weeks) in transgenic mice as a substitute for one of the two required long-term rodent bioassays in the preclinical safety evaluation of pharmaceuticals. The two models that have gained the widest acceptance by sponsors and regulatory authorities are the CB6F1-RasH2 mouse hemizygous for a human H-ras transgene and the B6.129N5-Trp53 mouse heterozygous for a p53 null allele. The p53+/- model is of particular value for compounds with residual concern that genotoxic activity may contribute to tumorigenesis. The rasH2 model is an appropriate alternative without regard to evidence of genotoxic potential. Since results from a short-term bioassay can be obtained relatively early in drug development, there is the potential for more timely assessment of cancer risk for individuals in long-term clinical trials. Use of these models in preclinical safety evaluation also significantly reduces animal use, time, and manpower. Preliminary findings indicate that prediction of two-year rat bioassay outcomes based on data from chronic rat toxicity studies, together with early assessment of carcinogenic potential in short-term transgenic models, may have the potential to increase the timeliness and efficiency of strategies for the identification of human carcinogenic hazards.

Integrated decision-tree testing strategies for mutagenicity and carcinogenicity with respect to the requirements of the EU REACH legislation

Liverpool John Moores University and FRAME recently conducted a research project sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with the REACH system. This paper focuses on the prospects for using alternative methods (both in vitro and in silico) for mutagenicity (genotoxicity) and carcinogenicity testing--two toxicity endpoints, which, together with reproductive toxicity, are of pivotal importance for the REACH system. The manuscript critically discusses well-established testing approaches, and in particular, the requirement for short-term in vivo tests for confirming positive mutagenicity, and the need for the rodent bioassay for detecting non-genotoxic carcinogens. Recently-proposed testing strategies focusing on non-animal approaches are also considered, and our own testing scheme is presented and supported with background information. This scheme makes maximum use of pre-existing data, computer (in silico) and in vitro methods, with weight-of-evidence assessments at each major stage. The need for the improvement of in vitro methods, to reduce the generation of false-positive results, is also discussed. Lastly, ways in which reduction and refinement measures can be used are also considered, and some recommendations are made for future research to facilitate the implementation of the proposed testing scheme.

Evaluation of dichloroacetic acid for carcinogenicity in genetically modified Tg.AC hemizygous and p53 haploinsufficient mice

There has been considerable interest in the use of genetically modified mice for detecting potential environmental carcinogens. For this reason, the National Toxicology Program has been evaluating Tg.AC hemizygous and p53 haploinsufficient mice as models to detect potential carcinogens. It was reasoned that these mouse models might also prove more effective than standard rodent models in evaluating the numerous disinfection byproducts that are found in low concentrations in drinking water. Dichloroacetic acid (DCA) is one of the most frequently found disinfection byproducts and DCA has been consistently shown to cause hepatocellular tumors in rats and mice in standard rodent studies. Tg.AC hemizygous and p53 haploinsufficient mice were exposed in the drinking water to DCA for up to 41 weeks. In a second study Tg.AC mice were subjected to dermal DCA exposure for up to 39 weeks. Increased incidences and severity of cytoplasmic vacuolization of hepatocytes were seen in the p53 mice, but there was no evidence of carcinogenic activity at exposures of up to 2000 mg/l in the drinking water. Increased incidences and severity of cytoplasmic vacuolization of hepatocytes were seen in the drinking water study with Tg.AC mice and a modest non-dose-related increase in pulmonary adenomas was observed in males exposed to 1000 mg/l in the drinking water. Dermal exposure up to 500 mg/kg for 39 weeks resulted in increased dermal papillomas at the site of application in Tg.AC mice. No significant increase in papillomas under the same study conditions was seen in the 26-week study. For DCA under these study conditions, the p53 and Tg.AC mice appear less sensitive to hepatocarcinogenesis than standard rodent models. These results suggest caution for the use of Tg.AC and p53 mice to screen unknown chemicals in drinking water for potential carcinogenicity.

Aspartame: a safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies

Aspartame is a methyl ester of a dipeptide used as a synthetic nonnutritive sweetener in over 90 countries worldwide in over 6000 products. The purpose of this investigation was to review the scientific literature on the absorption and metabolism, the current consumption levels worldwide, the toxicology, and recent epidemiological studies on aspartame. Current use levels of aspartame, even by high users in special subgroups, remains well below the U.S. Food and Drug Administration and European Food Safety Authority established acceptable daily intake levels of 50 and 40 mg/kg bw/day, respectively. Consumption of large doses of aspartame in a single bolus dose will have an effect on some biochemical parameters, including plasma amino acid levels and brain neurotransmitter levels. The rise in plasma levels of phenylalanine and aspartic acid following administration of aspartame at doses less than or equal to 50 mg/kg bw do not exceed those observed postprandially. Acute, subacute and chronic toxicity studies with aspartame, and its decomposition products, conducted in mice, rats, hamsters and dogs have consistently found no adverse effect of aspartame with doses up to at least 4000 mg/kg bw/day. Critical review of all carcinogenicity studies conducted on aspartame found no credible evidence that aspartame is carcinogenic. The data from the extensive investigations into the possibility of neurotoxic effects of aspartame, in general, do not support the hypothesis that aspartame in the human diet will affect nervous system function, learning or behavior. Epidemiological studies on aspartame include several case-control studies and one well-conducted prospective epidemiological study with a large cohort, in which the consumption of aspartame was measured. The studies provide no evidence to support an association between aspartame and cancer in any tissue. The weight of existing evidence is that aspartame is safe at current levels of consumption as a nonnutritive sweetener.

LF, Lopes C. Chemical carcinogenesis

The use of chemical compounds benefits society in a number of ways. Pesticides, for instance, enable foodstuffs to be produced in sufficient quantities to satisfy the needs of millions of people, a condition that has led to an increase in levels of life expectancy. Yet, at times, these benefits are offset by certain disadvantages, notably the toxic side effects of the chemical compounds used. Exposure to these compounds can have varying effects, ranging from instant death to a gradual process of chemical carcinogenesis. There are three stages involved in chemical carcinogenesis. These are defined as initiation, promotion and progression. Each of these stages is characterised by morphological and biochemical modifications and result from genetic and/or epigenetic alterations. These genetic modifications include: mutations in genes that control cell proliferation, cell death and DNA repair - i.e. mutations in proto-oncogenes and tumour suppressing genes. The epigenetic factors, also considered as being non-genetic in character, can also contribute to carcinogenesis via epigenetic mechanisms which silence gene expression. The control of responses to carcinogenesis through the application of several chemical, biochemical and biological techniques facilitates the identification of those basic mechanisms involved in neoplasic development. Experimental assays with laboratory animals, epidemiological studies and quick tests enable the identification of carcinogenic compounds, the dissection of many aspects of carcinogenesis, and the establishment of effective strategies to prevent the cancer which results from exposure to chemicals.

Proposed integrated decision-tree testing strategies for mutagenicity and carcinogenicity in relation to the EU REACH legislation

Liverpool John Moores University and FRAME recently conducted a research project sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with the REACH system. This paper focuses on the prospects for using alternative methods (both in vitro and in silico) for mutagenicity (genotoxicity) and carcinogenicity testing - two toxicity endpoints, which, together with reproductive toxicity, are of pivotal importance for the REACH system. The manuscript critically discusses well-established testing approaches, and in particular, the requirement for short-term in vivo tests for confirming positive mutagenicity, and the need for the rodent bioassay for detecting non-genotoxic carcinogens. Recently-proposed testing strategies focusing on non-animal approaches are also considered, and our own testing scheme is presented and supported with background information. This scheme makes maximum use of pre-existing data, computer (in silico) and in vitro methods, with weight-of-evidence assessments at each major stage. The need for the improvement of in vitro methods, to reduce the generation of false-positive results, is also discussed. Lastly, ways in which reduction and refinement measures can be used are also considered, and some recommendations are made for future research to facilitate the implementation of the proposed testing scheme.

Prediction of rodent carcinogenic potential of naturally occurring chemicals in the human diet using high-throughput QSAR predictive modeling

Consistent with the U.S. Food and Drug Administration (FDA) Critical Path Initiative, predictive toxicology software programs employing quantitative structure-activity relationship (QSAR) models are currently under evaluation for regulatory risk assessment and scientific decision support for highly sensitive endpoints such as carcinogenicity, mutagenicity and reproductive toxicity. At the FDA's Center for Food Safety and Applied Nutrition's Office of Food Additive Safety and the Center for Drug Evaluation and Research's Informatics and Computational Safety Analysis Staff (ICSAS), the use of computational SAR tools for both qualitative and quantitative risk assessment applications are being developed and evaluated. One tool of current interest is MDL-QSAR predictive discriminant analysis modeling of rodent carcinogenicity, which has been previously evaluated for pharmaceutical applications by the FDA ICSAS. The study described in this paper aims to evaluate the utility of this software to estimate the carcinogenic potential of small, organic, naturally occurring chemicals found in the human diet. In addition, a group of 19 known synthetic dietary constituents that were positive in rodent carcinogenicity studies served as a control group. In the test group of naturally occurring chemicals, 101 were found to be suitable for predictive modeling using this software's discriminant analysis modeling approach. Predictions performed on these compounds were compared to published experimental evidence of each compound's carcinogenic potential. Experimental evidence included relevant toxicological studies such as rodent cancer bioassays, rodent anti-carcinogenicity studies, genotoxic studies, and the presence of chemical structural alerts. Statistical indices of predictive performance were calculated to assess the utility of the predictive modeling method. Results revealed good predictive performance using this software's rodent carcinogenicity module of over 1200 chemicals, comprised primarily of pharmaceutical, industrial and some natural products developed under an FDA-MDL cooperative research and development agreement (CRADA). The predictive performance for this group of dietary natural products and the control group was 97% sensitivity and 80% concordance. Specificity was marginal at 53%. This study finds that the in silico QSAR analysis employing this software's rodent carcinogenicity database is capable of identifying the rodent carcinogenic potential of naturally occurring organic molecules found in the human diet with a high degree of sensitivity. It is the first study to demonstrate successful QSAR predictive modeling of naturally occurring carcinogens found in the human diet using an external validation test. Further test validation of this software and expansion of the training data set for dietary chemicals will help to support the future use of such QSAR methods for screening and prioritizing the risk of dietary chemicals when actual animal data are inadequate, equivocal, or absent.

Frequency of Hprt mutant lymphocytes and micronucleated erythrocytes in p53-haplodeficient mice treated perinatally with AZT and AZT in combination with 3TC

Azidothymidine (AZT) is a nucleoside reverse transcriptase inhibitor (NRTI) that is used for reducing mother-to-child transmission of human immunodeficiency virus I. Combinations of AZT and 3'-thiacytidine (3TC) are even more effective than AZT alone. AZT, however, is a mutagen and carcinogen in rodent models and 3TC can increase the genotoxicity of AZT. Since p53 plays a key role in human and mouse tumorigenesis, p53-haplodeficient mice are currently being evaluated as a model for assessing the carcinogenicity of perinatal exposure to NRTIs. In the present study, male C57BL/6 p53(+/+) and p53(-/-) mice were mated with C3H p53(+/+) females; the pregnant females were treated on gestation day 12 through parturition with 40, 80, and 160 mg/kg of AZT or a combination of 160 mg/kg AZT and 100 mg/kg 3TC (AZT-3TC); the p53(+/+) and p53(+/-) offspring were treated daily after birth through postnatal day (PND) 28. The frequencies of micronucleated reticulocytes (MN-RETs) and micronucleated normochromatic erythrocytes (MN-NCEs) were determined on PND1, PND10, and PND28; the frequency of Hprt mutant lymphocytes was measured on PND28. The frequencies of MN-RETs and MN-NCEs were increased in treated animals at all time points; there were no differences in the responses of p53(+/+) and p53(+/-) animals treated with identical doses of NRTIs. After correction for clonal expansion, both AZT and AZT-3TC treatments induced small but significant increases in the frequency of Hprt mutant lymphocytes in p53(+/-) mice, but not in p53(+/+) mice. The data indicate that p53 haplodeficiency affects the genotoxicity of NRTIs; thus, p53(+/-) mice may be a sensitive model for evaluating the carcinogenicity of perinatal exposure to NRTIs.

Biological, cellular, and molecular characteristics of an inducible transgenic skin tumor model: a review

The genetically initiated Tg.AC transgenic mouse carries a transgene consisting of an oncogenic v-Ha-ras coding region flanked 5' by a mouse zeta-globin promoter and 3' by an SV-40 polyadenylation sequence. Located on chromosome 11, the transgene is transcriptionally silent until activated by chemical carcinogens, UV light, or full-thickness wounding. Expression of the transgene is an early event that drives cellular proliferation resulting in clonal expansion and tumor formation, the unique characteristics now associated with the Tg.AC mouse. This ras-dependent phenotype has resulted in the widespread interest and use of the Tg.AC mouse in experimental skin carcinogenesis and as an alternative carcinogenesis assay. This review examines the general biology of the tumorigenic responses observed in Tg.AC mice, the genetic interactions of the ras transgene, and explores the cellular and molecular regulation of zeta-globin promoted transgene expression. As a prototype alternative model to the current long-term rodent bioassays, the Tg.AC has generated a healthy discussion on the future of transgenic bioassays, and opened the doors for subsequent models for toxicity testing. The further exploration and elucidation of the molecular controls of transgene expression will enhance the usefulness of this mouse and enable a better understanding of the Tg.AC's discriminate response to chemical carcinogens.

Evaluation of the carcinogenic potential of clofibrate in the FVB/Tg.AC mouse after dermal application--part II

This study was conducted as part of the International Life Sciences Institute (ILSI) Alternatives to Carcinogenicity Testing program and evaluated the carcinogenic potential of clofibrate, a nongenotoxic, peroxisome proliferator-activated receptor (PPAR) alpha agonist following dermal application to transgenic Tg.AC and nontransgenic FVB mice for a minimum of 26 weeks. Clofibrate doses of 12, 28, or 36 mg/200 microl/day were used. Positive controls for papilloma formation were benzene (174.8 mg/200 microl), and 12-o-tetradecanoylphorbol-13-acetate (TPA [0.00250 mg/200 microl]). Clofibrate was tolerated at doses up to 36 mg/200 microl. In Tg.AC mice, clofibrate produced a dose-related increase in the incidence of mice with cutaneous papillomas; and dose-related decreases in mean time to first tumor, mean multiplicity of tumors per mouse, and mean weeks to maximal yield, as well as numerous nonneoplastic microscopic lesions in the liver, kidney, spleen, and skin. Benzene and TPA induced both neoplastic and/or non-neoplastic proliferative lesions in Tg.AC mice. Clofibrate did not increase the incidence or multiplicity of papillomas, or any other tumors in FVB mice. These data show that the Tg.AC dermal model has increased sensitivity in detecting skin papillomas caused by the nongenotoxic rodent carcinogen, clofibrate, compared to wild type FVB mice, at systemic exposures that are 3x higher than the systemic exposure observed in humans taking clofibrate (AUC = 1100 microg.h/ml) at the recommended maximum therapeutic dose of 500 mg. In addition, this study supports the proposed concept that Tg.AC model may detect compounds with nongenotoxic carcinogenic potential in a shorter timeframe than conventional mouse carcinogenicity bioassays.

Evaluation of the carcinogenic potential of clofibrate in the FVB/Tg.AC mouse after oral administration--part I

This study was conducted as part of the International Life Sciences Institute (ILSI) program to evaluate the carcinogenic potential of clofibrate, a nongenotoxic, peroxisome proliferator-activated receptor (PPAR) alpha agonist following oral administration to Tg.AC (transgenic) and wild-type FVB (nontransgenic) mice for a minimum for 6 months. Clofibrate was well tolerated at doses up to 500 (males) and 650 (females) mg/kg/day. Oral administration of clofibrate to Tg.AC or FVB (wild-type) male and female mice for 6 months did not result in the increased formation of neoplastic lesions. Epithelial hyperplasia in the urinary bladder (Tg.AC and FVB) and prostate gland (Tg.AC only), and interstitial-cell hyperplasia in the testes (Tg.AC) were noted at 500 mg/kg/day. Non-neoplastic nonproliferative findings included hepatic hypertrophy and hematopoietic changes (myeloid hyperplasia, myelodysplasia, lymphoid depletion, and erythropoiesis) in Tg.AC and FVB mice of both sexes; reproductive (cystic degeneration and dilatation, hypospermia, spermatocele, dilated inspissated protein) and urogenital (tubular-cell hypertrophy, degenerative/regenerative nephropathy, necrosis/fibrosis) changes in Tg.AC and FVB male mice; congestion in the lung in male Tg.AC mice; gall bladder dilatation in female Tg.AC mice; and adrenal (intracellular lipofuscinosis and atrophy) and heart (eosinophillic myofibers) findings in Tg.AC mice of both sexes and in female FVB mice. The results of this study indicate that the clofibrate is not carcinogenic when administered to Tg.AC mice by oral gavage for 6 months at doses up to 500 (males) and 650 (females) mg/kg/day, which did produce liver hypertrophy.

Evaluation of the carcinogenic potential of clofibrate in the rasH2 mouse

The purpose of the study was to support of the International Life Sciences Institute (ILSI) alternative carcinogenicity models initiative to evaluate the carcinogenic potential of the nongenotoxic carcinogen, clofibrate, a peroxisome proliferator-activated receptor (PPAR) alpha agonist, following oral administration to rasH2 mice. Peroxisome proliferators are one of the most widely studied of the nongenotoxic carcinogens and have diverse industrial and therapeutic uses (Gonzalez et al. J. Nat. Cancer Inst. 90: 1702-1709, 1998); however, the nongenotoxic mechanism of carcinogenicity is currently unknown. Male mice were administered doses of clofibrate at 50, 100, or 200 mg/kg/day and female mice were administered doses of 50, 150, or 250 mg/kg/day by oral gavage at 10 ml/kg for 27 weeks. In addition, rasH2 male and female mice were treated with N-nitroso-N-methylurea (NMU). Nontransgenic male and female mice were treated with 200 and 250 mg/kg/day, respectively, of clofibrate. The NMU-treated mice were given a single intraperitoneal dose of 75 mg/kg, which was followed by a 90-day observation period; all others were sacrificed after 6 months of daily dosing. Hepatocellular neoplasms were observed in clofibrate-treated rasH2 male mice after 6 months of treatment but not in nontransgenic males or females. Clofibrate treatment (250 mg/kg/day) of female rasH2 mice was associated with a slight increase in the incidence of various neoplasms (harderian gland, lungs, skin, spleen, tail, thymus, and uterus) compared with untreated transgenic mice and with similarly treated nontransgenic mice. Non-neoplastic changes were found in the liver of transgenic and nontransgenic mice of both sexes and in the kidneys of male mice. NMU produced findings are consistent with previous studies. The data suggest that the rasH2 mice are a good model for testing epigenetic carcinogens in a shorter timeframe than conventional mouse carcinogenicity bioassays.

The utility of genetically altered mouse models for nutrition and cancer chemoprevention research

The development of effective cancer preventive interventions is being enhanced by the use of relevant animal models to confirm, refine, and extend potential leads from clinical and epidemiologic studies. In particular, genetically altered mice, with specific cancer-related genes modulated, are providing powerful tools for studying carcinogenesis, as well as important conduits for translating basic research findings from the laboratory bench to the bedside. This review explores the utility of genetically altered mice for developing cancer preventive strategies that can offset increased cancer susceptibility resulting from specific genetic lesions. Examples will focus on preventing cancer by dietary interventions, particularly obesity prevention/energy balance modulation, as well as chemoprevention, in mice with alterations in genes such as the p53 or Apc tumor suppressors, components of the ErbB pathway, and other pathways frequently altered in human cancer.

Absence of acute apoptotic response to genotoxic carcinogens in p53-deficient mice is associated with increased susceptibility to azoxymethane-induced colon tumours

Acute apoptotic response to genotoxic carcinogens (AARGC) might be important for controlling the consequences of mutational load in the colon. It has been shown to occur in parallel with activation of DNA repair mechanisms. Inadequate AARGC might allow development of mutated clones with the potential to progress to cancer. In this study, we tested if p53 levels were important for AARGC in the colon and whether defective AARGC was associated with increased risk for colorectal oncogenesis. Apoptosis was measured in colonic epithelium of mice from each p53 genotype (p53-/-, p53+/-, wild-type) without and 8 hr following a single injection of azoxymethane (AOM). To determine risk for carcinogen-induced colorectal cancer (CRC), groups of mice from each p53 genotype received 3 weekly injections of AOM and colons were examined for tumour 20 weeks later. Rates of spontaneous apoptosis in colon were not affected by p53 level. However, AARGC was absent in p53-/- mice and reduced by 50% in p53+/- mice (both p < 0.01) compared to wild-type mice. AOM induced tumours in 30% of wild-type mice (average multiplicity 1.0 tumours/mouse) compared to 72% of p53+/- mice (2.0 tumours/mouse, p < 0.01) and 100% of p53-/- mice (2.8 tumours/mouse, p < 0.01). Without AOM, significantly fewer mice in all groups had tumours. Rates of apoptosis in tumours were independent of p53 status. p53 dysfunction puts intestinal epithelia at increased risk of genotoxin-induced oncogenesis due to impairment of apoptotic response mechanisms. p53 levels do not appear, however, to be important for spontaneous apoptosis in normal epithelium or apoptosis in tumours. Subsequent studies are now warranted to test the converse, namely, that enhanced apoptotic response to carcinogen reduces risk for colorectal oncogenesis.

Nucleotide excision repair- and p53-deficient mouse models in cancer research

Cancer is caused by the loss of controlled cell growth due to mutational (in)activation of critical genes known to be involved in cell cycle regulation. Three main mechanisms are known to be involved in the prevention of cells from becoming cancerous; DNA repair and cell cycle control, important to remove DNA damage before it will be fixed into mutations and apoptosis, resulting in the elimination of cells containing severe DNA damage. Several human syndromes are known to have (partially) deficiencies in these pathways, and are therefore highly cancer prone. Examples are xeroderma pigmentosum (XP) caused by an inborn defect in the nucleotide excision repair (NER) pathway and the Li-Fraumeni syndrome, which is the result of a germ line mutation in the p53 gene. XP patients develop skin cancer on sun exposed areas at a relatively early age, whereas Li-Fraumeni patients spontaneously develop a wide variety of early onset tumors, including sarcomas, leukemia's and mammary gland carcinomas. Several mouse models have been generated to mimic these human syndromes, providing us information about the role of these particular gene defects in the tumorigenesis process. In this review, spontaneous phenotypes of mice deficient for nucleotide excision repair and/or the p53 gene will be described, together with their responses upon exposure to either chemical carcinogens or radiation. Furthermore, possible applications of these and newly generated mouse models for cancer will be given.

Genetically engineered animals in drug discovery and development: a maturing resource for toxicologic research

Genetically engineered mice that either over-express a foreign gene (transgenic) or in which the activity of a specific gene has been removed ("knock-out") or replaced ("knock-in") will be used increasingly to investigate molecular mechanisms of disease, to evaluate innovative therapeutic targets, and to screen novel agents for efficacy and/or toxicity. Recent innovations of relevance to toxicologic researchers include the construction of genetically engineered mice with (1) multiple engineered genes, (2) mutations that can be induced at specific sites and times throughout life, and (3) the substitution of human genes for their mouse counterparts ("humanized" mice) to allow in vivo investigation of xenobiotic toxicity. Contemporary applications of genetically engineered mice in toxicology include basic mechanistic research exploiting newly engineered mouse lines as well as applied screening for genotoxicity and carcinogenicity using commercially available animals. Many caveats must be considered when interpreting genetically engineered mice-derived toxicity data, the chief of which will be the extent to which the model's phenotype has been fully characterized, the type and incidence of background lesions for the given mouse strain and engineered gene, and the possibility of misinterpreting the presence or absence of a phenotype due to compensatory physiologic processes that mask the outcome produced by the engineering event. Toxicity data acquired using genetically engineered mice currently supplements and in time likely will supplant those gathered using the present "gold standard" bioassays, as genetically engineered mice typically develop more lesions after a shorter latency period than do age- and strain-matched, wild-type mice.