Genotoxicity and carcinogenicity studies of bronchodilators and antiasthma drugs.

This survey is a compendium of genotoxicity and carcinogenicity information of bronchodilators and antiasthma drugs. Data from 46 marketed drugs were collected. Of these 46 drugs, 25 (54.3%) did not have retrievable genotoxicity or carcinogenicity data. The remaining 21 (45.7%) had at least one genotoxicity or carcinogenicity test result. Of these 21 drugs, 10 had at least one positive finding: three tested positive in at least one genotoxicity assay, eight in at least one carcinogenicity assay, and one of them gave positive results in both genotoxicity assay and carcinogenicity assay. Concerning the predictivity of genetic toxicology findings for the result(s) of long-term carcinogenesis assays, 15 drugs had both genotoxicity and carcinogenicity data: seven of them (46.6%) were neither genotoxic nor carcinogenic, 6 (40.0%) were carcinogenic in at least one sex of mice or rats but tested negative in genotoxicity assays, 1 (6.7%) tested positive in genotoxicity assay but was non-carcinogenic, and 1 (6.7%) gave positive responses in both genotoxicity and carcinogenicity assay. Only 11 (23.9%) of the 46 drugs considered had all data required by current guidelines for testing of pharmaceuticals, but a large fraction of them were developed and marketed prior to the present regulatory climate.

Clues to detect tumor necrosis factor receptor-associated periodic syndrome (TRAPS) among patients with idiopathic recurrent acute pericarditis: results of a multicentre study.

BACKGROUND: The potential clinical expression of tumor necrosis factor receptor-associated periodic syndrome (TRAPS), in the form of idiopathic recurrent acute pericarditis (IRAP) has not been explored in the medical literature. The aim of this study was to evaluate the incidence of TRAPS mutations in patients with recurrent pericarditis and identify possible clues to TRAPS diagnosis. METHODS: Therefore, 131 consecutive Caucasian IRAP patients were investigated for mutations of the TRAPS gene and prospectively evaluated. RESULTS: Out of 131 patients, 8 (6.1%) carried a mutation in the TNFRSF1A gene. Compared with those without genetic mutations, patients with TRAPS mutations had more frequently a positive family history for pericarditis and periodic fever syndromes (p < 0.001), a higher mean number of recurrences after the first year (p < 0.001), on colchicine treatment (p < 0.001), and a higher need of immunosuppressive therapies (p < 0.001). CONCLUSION: TRAPS is a cause of recurrent pericarditis in 6% of unselected cases with recurrent pericarditis. A positive family history for pericarditis or periodic fever syndromes, a poor response to colchicine, recurrences after the first year from the index attack or on colchicine treatment, as well as the need of immunosuppressive agents are clues of the possible presence of TNFRSF1A gene mutations in patients with recurrent pericarditis.

Studies on genotoxicity and carcinogenicity of antibacterial, antiviral, antimalarial and antifungal drugs.

This review provides a compendium of retrievable results of genotoxicity and animal carcinogenicity studies performed of antibacterial, antiviral, antimalarial and antifungal drugs of long-term or intermittent frequent use. Of the 48 drugs considered, 9 (18.75%) do not have retrievable data, whereas the other 39 (81.25%) have at least one genotoxicity or carcinogenicity tests result. Of these 39 drugs, 24 tested positive in at least one genotoxicity assay and 19 in at least one carcinogenicity assay; 14 of them gave a positive response in both at least one genotoxicity assay and at least one carcinogenicity assay. Concerning the predictivity of genetic toxicology findings for the results of long-term carcinogenesis assays, of 23 drugs with both genotoxicity and carcinogenicity data: 2 (8.7%) were neither genotoxic nor carcinogenic, 2 (8.7%) tested positive in at least one genotoxicity assay but were non-carcinogenic, 4 (17.4%) tested negative in genotoxicity assays but were carcinogenic, and 15 (65.2%) gave a positive response in at least one genotoxicity assay and in at least one carcinogenicity assay. Only 18 (37.5%) of the 48 drugs examined had all data required by present guidelines for testing of pharmaceuticals, but a fraction of them (49%) were developed and marketed prior to the present regulatory climate. In the absence of compelling indications, the prescription of the 19 drugs that are animal carcinogens should be avoided.

Arylamine drugs: genotoxic-carcinogenic activity of NO-derivatives.

This review provides information on arylamine drugs which have been tested for the formation of N-nitroso compounds (NOC) by reacting with nitrite, and on the genotoxic-carcinogenic effects of their nitrosation products. In an extensive search we have found that 109 arylamine drugs were examined for their ability to react with nitrite, and 105 of them (96.3 %) were found to form NOC or in some cases other reactive species. Moreover, 78 arylamine drugs were examined in short-term genotoxicity tests and/or in long-term carcinogenicity assays, either in combination with nitrite or using their nitrosation product; 67 of them (85.9 %) have been found to give at least one positive response. Only a small fraction, the 19.1 % of theoretically nitrosatable arylamine drugs, has been examined for the possible formation of genotoxic-carcinogenic NOC, guidelines for genotoxicity testing of pharmaceuticals do not indicate the need of appropriate tests, and patients are not informed that the drug-nitrite interaction and the consequent risk can be reduced to a large extent by consuming the nitrosatable drug with ascorbic acid.

Update of carcinogenicity studies in animals and humans of 535 marketed pharmaceuticals.

This survey is a compendium of information retrieved on carcinogenicity in animals and humans of 535 marketed pharmaceuticals whose expected clinical use is continuous for at least 6 months or intermittent over an extended period of time. Of the 535 drugs, 530 have the result of at least one carcinogenicity assay in animals, and 279 (52.1%) of them gave a positive response in at least one assay. Only 186 drugs (34.8%) have retrievable information on carcinogenicity in humans, and 104 of them gave to a variable extent evidence of a potential carcinogenic activity. Concerning the correlation between results obtained in animals and epidemiological findings, 58 drugs gave at least one positive result in carcinogenicity assays performed in animals and to a variable extent displayed evidence of carcinogenicity in humans, but 97 drugs tested positive in animals and were noncarcinogenic in humans or vice versa. Our findings, which are in agreement with previous studies, indicate that the evaluation of the benefit/carcinogenic risk ratio should be always made in prescribing a drug.

Genotoxicity and carcinogenicity studies of antihistamines.

This review provides a compendium of the results of genotoxicity and carcinogenicity assays performed on marketed antihistamines. Of the 70 drugs examined, 29 (41.4%) have at least one genotoxicity and/or carcinogenicity test result: 12 tested positive in at least one genotoxicity assay, six in at least one carcinogenicity assay, and four gave a positive response in both at least one genotoxicity assay and at least one carcinogenicity assay. Of 19 drugs with both genotoxicity and carcinogenicity data, eight were neither genotoxic nor carcinogenic, two were carcinogenic in at least one sex of mice or rats but tested negative in genotoxicity assays, five tested positive in at least one genotoxicity assay but were non-carcinogenic, and four gave a positive response in at least one genotoxicity assay and in at least one carcinogenicity assay. Only 12 (17.1%) of the 70 drugs examined have all data required by present guidelines for testing of pharmaceuticals, but it should be considered that a large fraction of them were developed and marketed prior the present regulatory climate.

Genotoxic and carcinogenic effects of gastrointestinal drugs.

This review provides a compendium of retrievable results of genotoxicity and carcinogenicity assays performed on marketed gastrointestinal drugs. Of the 71 drugs considered, 38 (53.5%) do not have retrievable data, whereas the other 33 (46.5%) have at least one genotoxicity or carcinogenicity test result. Of these 33 drugs, 15 tested positive in at least one genotoxicity assay and 13 in at least one carcinogenicity assay; 8 of them gave a positive response in both at least one genotoxicity assay and at least one carcinogenicity assay. Concerning the predictivity of genetic toxicology findings for the result(s) of long-term carcinogenesis assays, of 21 drugs with both genotoxicity and carcinogenicity data: 6 (28.6%) are neither genotoxic nor carcinogenic, 2 (9.5%) tested positive in at least one genotoxicity assay but were non-carcinogenic, 5 (23.8%) tested negative in genotoxicity assays but were carcinogenic and 8 (38.1%) gave a positive response in at least one genotoxicity assay and in at least one carcinogenicity assay. Only 12 (16.9%) of the 71 drugs examined have all data required by present guidelines for testing of pharmaceuticals, but a large fraction of them were developed and marketed prior the present regulatory climate.

Genotoxicity and carcinogenicity testing of pharmaceuticals: correlations between induction of DNA lesions and carcinogenic activity.

This survey is a compendium of the results of DNA lesions assays (DNA adducts, DNA strand breaks, DNA repair synthesis) and of the results of carcinogenicity assays of 146 pharmaceuticals. Of these drugs, 55 (37.7%) tested negative in both DNA lesions assay(s) and in carcinogenicity assay(s); 65 (44.5%) tested negative in DNA lesions assay(s), but gave a positive response in at least one carcinogenicity assay; 6 (4.1%) tested positive in at least one DNA lesions assay, but negative in carcinogenicity assay(s); 20 (13.7%) tested positive in at least one DNA lesions assay and in at least one carcinogenicity assay. Concerning the predictivity of DNA lesions assays findings for the results of long-term carcinogenesis assays performed in mice, rats or other species, concordance was found to exist for the 46.2% of pharmaceuticals in the case of DNA adducts, for 63.1% in the case of DNA strand breaks, and for 47.3% in the case of DNA repair synthesis (UDS).

Genotoxicity and carcinogenicity studies of analgesics, anti-inflammatory drugs and antipyretics.

This survey is a compendium of genotoxicity and carcinogenicity information of analgesics, anti-inflammatory drugs and antipyretics. Data from 120 drugs were collected; 109 of them are still in the market. Of these 120 drugs, 58 (48.3%) do not have retrievable genotoxicity or carcinogenicity data. The remaining 62 (51.7%) have at least one genotoxicity or carcinogenicity test result. Of these 62 drugs, 31 have at least one positive finding: 26 tested positive in at least one genotoxicity assay, 13 in at least one carcinogenicity assay, and 8 gave a positive result in both at least one genotoxicity assay and at least one carcinogenicity assay. In terms of correlation between results of the various genotoxicity assays and absence of carcinogenic activity in mice and/or rats or in other species, 12 of 23 non-carcinogenic drugs tested positive in at least one of the various genotoxicity assay systems. Concerning the predictivity of genetic toxicology findings for the result(s) of long-term carcinogenesis assays, 35 drugs have both genotoxicity and carcinogenicity data: 11 of them (31.4%) were neither genotoxic nor carcinogenic, 4 (11.4%) were carcinogenic in at least one sex of mice or rats but tested negative in genotoxicity assays, 12 (34.3%) tested positive in at least one genotoxicity assay but were non-carcinogenic, and 8 (22,9%) gave a positive response in at least one genotoxicity assay and in at least one carcinogenicity assay. Only 22 (18.3%) of the 120 drugs considered have all data required by current guidelines for testing of pharmaceuticals, but a large fraction of them were developed and marketed prior the present regulatory climate.

Genotoxic and carcinogenic effects of antipsychotics and antidepressants.

This review provides a compendium of the results of genotoxicity and carcinogenicity assays performed on marketed antipsychotics and antidepressants. Of the 104 drugs examined, 47 (45.2%) do not have retrievable data. The remaining 57 (54.8%) have at least one and often more than one genotoxicity and/or carcinogenicity test result. Of these 57 drugs, 33 (57.9%) have at least one positive finding: 24 tested positive in at least one genotoxicity assay, 14 in at least one carcinogenicity assay, and 5 gave a positive response in both. Concerning the predictivity of genetic toxicology findings for the result(s) of long-term carcinogenesis assays, 25 drugs have both genotoxicity and carcinogenicity data: 8 of them (32.0%) were neither genotoxic nor carcinogenic, 8 (32.0%) were carcinogenic in at least one sex of mice or rats but tested negative in genotoxicity assays, 4 (16.0%) tested positive in at least one genotoxicity assay but were non-carcinogenic, and 5 (20.0%) gave a positive response in at least one genotoxicity assay and in at least one carcinogenicity assay. Only 16 (15.4%) of the 104 drugs examined have all data required by present guidelines for testing of pharmaceuticals, but it should be considered that a large fraction of them were developed and marketed prior to the present regulatory climate.

Update on genotoxicity and carcinogenicity testing of 472 marketed pharmaceuticals.

This survey is a compendium of genotoxicity and carcinogenicity information of 838 marketed drugs, whose expected clinical use is continuous for at least 6 months or intermittent over an extended period of time. Of these 838 drugs, 366 (43.7%) do not have retrievable genotoxicity or carcinogenicity data. The remaining 472 (56.3%) have at least one genotoxicity or carcinogenicity test result. Of the 449 drugs with at least one genotoxicity test result, 183 (40.8%) have at least one positive finding. Of the 338 drugs with at least one carcinogenicity test result, 160 (47.3%) have at least one positive result. Concerning the predictivity of genetic toxicology findings for long-term carcinogenesis assays, of the 315 drugs which have both genotoxicity and carcinogenicity data 116 (36.8%) are neither genotoxic nor carcinogenic, 50 (15.9%) are non-carcinogens which test positive in at least one genotoxicity assay, 75 (23.8%) are carcinogenic in at least one sex of mice or rats but test negative in genotoxicity assays, and 74 (23.5%) are both genotoxic and carcinogenic. Only 208 (24.8%) of the 838 drugs considered have all data required by current guidelines for testing of pharmaceuticals. However, it should be noted that a large fraction of the drugs considered were developed and marketed prior to the present regulatory climate. Although the laws do not require re-testing based on revised standards, in the absence of epidemiological studies excluding a carcinogenic risk to humans, a re-evalutation would be appropriate.

Genotoxicity and carcinogenicity studies of benzodiazepines.

This survey is a compendium of genotoxicity and carcinogenicity information of benzodiazepines and benzodiazepine analogues. Data from 51 drugs were collected; 41 of them are still in the market. Of the 51 drugs, 12 (23.5%) do not have retrievable genotoxicity or carcinogenicity data. The remaining 39 (76.5%) have at least one genotoxicity or carcinogenicity test result. Of these 39, 12 (30.8%) have at least one positive finding: 9 tested positive in at least one genotoxicity assay, 8 in at least one carcinogenicity assay, and 5 gave a positive result in both at least one genotoxicity assay and at least one carcinogenicity assay. In terms of correlation between results of the various genotoxicity assays and absence of carcinogenic activity in mice and/or rats or in other species, none of the 11 non-carcinogenic drugs tested positive in one of the various genotoxicity assay systems. Concerning the predictivity of genetic toxicology findings for the result(s) of long-term carcinogenesis assays, 18 drugs had both genotoxicity and carcinogenicity data; of these 11 (61.1%) were neither genotoxic nor carcinogenic, 2 (11.1%) were carcinogenic in at least one sex of mice or rats but tested negative in genotoxicity assays, and 5 (27.8%) gave a positive response in at least one genotoxicity assay and in at least one carcinogenicity assay. Only 8 (19.5%) of the 41 marketed benzodiazepines and benzodiazepine analogues had all data required by current guidelines for testing of pharmaceuticals.

Formation of DNA-damaging N-nitroso compounds from the interaction of calcium-channel blockers with nitrite.

A large number of drugs have been shown to react with nitrite to give genotoxic-carcinogenic N-nitroso compounds (NOC). However, the majority of drugs remain to be examined in this respect, among which calcium-channel blockers, all theoretically nitrosatable and widely used in the therapy of hypertension and other cardiovascular diseases. In this preliminary investigation, seven calcium-channel blockers have been examined either for their in vitro nitrosation according to the procedure recommended by the WHO, or for occurrence of liver DNA fragmentation, as detected by the Comet assay, in rats given by gavage 1/2 LD50 of the drug and 80 mg/kg of sodium nitrite. After 6h incubation the yields of NOC formed in vitro from nicardipine, nifedipine, nimodipine and nitrendipine ranged from 37 to 45% of the theoretical one, whereas the yields of NOC formed from diltiazem, gallopamil and verapamil ranged from 2 to 5%. In vivo, as compared with the effect of the same dose of the drug alone, a significant increase of both tail length and tail moment, indicative of an increased frequency of DNA single-strand breaks and alkali-labile sites, was produced in rat liver DNA by the administration with nitrite of gallopamil, nifedipine, nimodipine and nitrendipine, the ratio [tail length of drug+NaNO(2)/tail length of drug alone] being 3.2 for nimodipine, 3.1 for gallopamil 2.2 for nifedipine, and 2.1 for nitrendipine. Even if present, the increase in the degree of DNA fragmentation did not reach the statistical significance in rats given with nitrite nicardipine, diltiazem and verapamil. Further studies should be performed to investigate the formation of NOC in conditions simulating those occurring in the stomach of humans treated with a therapeutic dose, and to quantitate their genotoxic potency.

Strategy for genotoxicity testing--metabolic considerations.

The report from the 2002 International Workshop on Genotoxicity Tests (IWGT) Strategy Expert Group emphasized metabolic considerations as an important area to address in developing a common strategy for genotoxicity testing. A working group convened at the 2005 4th IWGT to discuss this area further and propose practical strategy recommendations. To propose a strategy, the working group reviewed: (1) the current status and deficiencies, including examples of carcinogens "missed" in genotoxicity testing, established shortcomings of the standard in vitro induced S9 activation system and drug metabolite case examples; (2) the current status of possible remedies, including alternative S9 sources, other external metabolism systems or genetically engineered test systems; (3) any existing positions or guidance. The working group established consensus principles to guide strategy development. Thus, a human metabolite of interest should be represented in genotoxicity and carcinogenicity testing, including evaluation of alternative genotoxicity in vitro metabolic activation or test systems, and the selection of a carcinogenicity test species showing appropriate biotransformation. Appropriate action triggers need to be defined based on the extent of human exposure, considering any structural knowledge of the metabolite, and when genotoxicity is observed upon in vitro testing in the presence of metabolic activation. These triggers also need to be considered in defining the timing of human pharmaceutical ADME assessments. The working group proposed two strategies to consider; a more proactive approach, which emphasizes early metabolism predictions to drive appropriate hazard assessment; and a retroactive approach to manage safety risks of a unique or "major" metabolite once identified and quantitated from human clinical ADME studies. In both strategies, the assessment of the genotoxic potential of a metabolite could include the use of an alternative or optimized in vitro metabolic activation system, or direct testing of an isolated or synthesized metabolite. The working group also identified specific areas where more data or experiences need to be gained to reach consensus. These included defining a discrete exposure action trigger for safety assessment and when direct testing of a metabolite of interest is warranted versus the use of an alternative in vitro activation system, a universal recommendation for the timing of human ADME studies for drug candidates and the positioning of metabolite structural knowledge (through in silico systems, literature, expert analysis) in supporting metabolite safety qualification. Lastly, the working group outlined future considerations for refining the initially proposed strategies. These included the need for further evaluation of the current in vitro genotoxicity testing protocols that can potentially perturb or reduce the level of metabolic activity (potential alterations in metabolism associated with both the use of some solvents to solubilize test chemicals and testing to the guidance limit dose), and proposing broader evaluations of alternative metabolic activation sources or engineered test systems to further challenge the suitability of (or replace) the current induced liver S9 activation source.

Genotoxic and carcinogenic risk to humans of drug-nitrite interaction products.

The large majority of N-nitroso compounds (NOC) have been found to produce genotoxic effects and to cause tumor development in laboratory animals; four NOC have been classified by the International Agency for Research on Cancer (IARC) as probably and another 15 as possibly carcinogenic to humans. A considerable fraction of drugs are theoretically nitrosatable due to the presence of amine, amide or other groups which by reacting with nitrite in the gastric environment, or even in other sites, can give rise to the formation of NOC, and in some cases other reactive species. This review provides a synthesis of information on the chemistry of NOC formation, the carcinogenic activity of NOC in animals and humans and the inhibitors of nitrosation reactions. It contains information on the drugs which have been tested for the formation of NOC by reaction with nitrite and the genotoxic-carcinogenic effects of their nitrosation products. In an extensive search we have found that 182 drugs, representing a wide variety of chemical structures and therapeutic activities, were examined in various experimental conditions for their ability to react with nitrite, and 173 (95%) of them were found to form NOC or other reactive species. Moreover, 136 drugs were examined in short-term genotoxicity tests and/or in long-term carcinogenesis assays, either in combination with nitrite or using their nitrosation product, in order to establish whether they produce genotoxic and carcinogenic effects; 112 (82.4%) of them have been found to give at least one positive response. The problem of endogenous drug nitrosation is largely unrecognized. Only a small fraction of theoretically nitrosatable drugs have been examined for the possible formation of genotoxic-carcinogenic NOC, guidelines for genotoxicity testing of pharmaceuticals do not indicate the need of performing the appropriate tests, and patients are not informed that the drug-nitrite interaction and the consequent risk can be reduced to a large extent by consuming the nitrosatable drug with ascorbic acid.

DNA fragmentation and DNA repair synthesis induced in rat and human thyroid cells by chemicals carcinogenic to the rat thyroid.

Five chemicals that are known to induce in rats thyroid follicular-cell adenomas and carcinomas were assayed for their ability to induce DNA damage and DNA repair synthesis in primary cultures of human thyroid cells. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the same Comet assay, were obtained after a 20-h exposure to the following subtoxic concentrations of the five test compounds: methimazole from 2.5 to 10mM; nitrobenzene, potassium bromate, N,N'-diethylthiourea and ethylenethiourea from 1.25 to 5mM. Under the same experimental conditions, DNA repair synthesis, as evaluated by quantitative autoradiography, was present in potassium bromate-exposed thyroid cells from all the three donors and in those from two of three donors with either nitrobenzene or ethylenethiourea, but did not match the criteria for a positive response in thyroid cells from any of the donors with methimazole and N,N'-diethylthiourea. Consistently with their ability to induce thyroid tumors, all the five test compounds, administered p.o. in rats in a single dose corresponding to 1/2 LD50, induced a statistically significant degree of DNA fragmentation in the thyroid. These findings suggest that the five test compounds might be carcinogenic to thyroid in humans.

Correlation between induction of DNA fragmentation in lung cells from rats and humans and carcinogenic activity.

Six chemicals, known to induce lung tumors in rats, were examined for their ability to induce DNA fragmentation in primary cultures of rat and human lung cells, and in the lung of intact rats. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the single-cell gel electrophoresis (Comet) assay, were obtained in primary lung cells from male rats with the following, minimally toxic, concentrations of the six test compounds: N-nitrosodimethylamine (NDMA; 2.5-10 mM), hydrazine (HZ; 0.5-4 mM), cadmium sulfate (CD; 31.2 and 62.5 µM), 4,4'-methylene bis (2-chloroaniline) (MOCA; 31.2-125 µM), isobutyl nitrite (IBN; 7.8-31.2 µM) and tetranitromethane (TNM; 1.9-15.6 µM). Similar degrees of DNA fragmentation were obtained in primary human lung cells; however, due to inter-donor differences, the minimum effective concentrations were in some donors lower and in others higher than in rats, and IBN induced DNA damage only in one of three donors. The DNA-damaging potency of HZ was higher in rats than in humans, and the opposite was true for MOCA. In agreement with these findings, statistically significant increases in the average frequency of DNA breaks were obtained in the lung of rats given a single oral dose (1/2 LD50) of the six test compounds. These findings give evidence that genotoxic lung carcinogens may be identified by use of the DNA fragmentation/Comet assay on rat lung cells as targets cells, and show that the six compounds tested produce in primary cultures of lung cells from human donors DNA-damaging effects substantially similar to those observed in rats.

Genotoxicity and carcinogenicity studies of antihypertensive agents.

This survey is a compendium of genotoxicity and carcinogenicity information of antihypertensive drugs. Data from 164 marketed drugs were collected. Of the 164 drugs, 65 (39.6%) had no retrievable genotoxicity or carcinogenicity data; this group was comprised largely of drugs marketed in a limited number of countries. The remaining 99 (60.4%) had at least one genotoxicity or carcinogenicity test result. Of these 99, 48 (48.5%) had at least one positive finding: 32 tested positive in at least one genotoxicity assay, 26 in at least one carcinogenicity assay, and 10 gave a positive result in both at least one genotoxicity assay and at least one carcinogenicity assay. In terms of correlation between results of the various genotoxicity assays and absence of carcinogenic activity in both mice and rats 2 of 44 non-carcinogenic drugs tested positive in the in vitro bacterial mutagenesis assay, 2 of 9 tested positive in the mouse lymphoma assay, none of 14 tested positive for gene mutation at the hprt locus, 5 of 25 tested positive in in vitro cytogenetic assays, none of 31 in in vivo cytogenetic assays, and none of 14 in inducing DNA damage and/or repair in in vitro and/or in vivo assays. Concerning the predictivity of genetic toxicology findings for long-term carcinogenesis assays, 75 drugs had both genotoxicity and carcinogenicity data; of these 37 (49.3%) were neither genotoxic nor carcinogenic, 14 (18.7%) were non-carcinogens which tested positive in at least one genotoxicity assay, 14 (18.7%) were carcinogenic in at least one sex of mice or rats but tested negative in genotoxicity assays, and 10 (13.3%) were both genotoxic and carcinogenic. Only 42 of the 164 marketed antihypertensives (25.6%) had all data required by the guidelines for testing of pharmaceuticals.

DNA fragmentation and DNA repair synthesis induced in rat and human thyroid cells by four rat thyroid carcinogens.

Four chemicals that are known to induce in rats thyroid follicular-cell adenomas and carcinomas were assayed for their ability to induce DNA damage and DNA repair synthesis in primary cultures of human thyroid cells. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measures by the Comet assay, were obtained after a 20-h exposure to the following subtoxic concentrations of the four test compounds: 2,4-diaminoanisole (DAA) from 0.10 to 1.0 mM, 4,4'-methylene-bis(N,N-dimethyl)benzenamine (MDB) from 0.32 to 1.8 mM, propylthiouracil (PTU) from 1.8 to 5.6 mM, and 4,4'-thiodianiline (THA) from 0.032 to 0.18 mM. Under the same experimental conditions, DNA repair synthesis, as evaluated by quantitative autoradiography, was present in thyreocytes exposed to DAA but absent after treatment with MDB, PTU, and THA. Consistent with their thyroid-specific carcinogenic activity, all the four chemicals, administered p.o. in rats in a single dose corresponding to 1/2 LD50, induced a statistically significant degree of DNA fragmentation in the thyroid, whereas any substantial evidence of DNA lesions was absent in liver, kidney, and lung, which, with the exception of liver tumors caused by THA, are not targets of the carcinogenic activity of the four test compounds. These findings indicate that the DNA damage observed in thyroid cells was consistent with the carcinogenicity of the four test compounds, and suggest that DAA, MDB, PTU, and THA might be carcinogenic to thyroid in humans.