Carcinogenicity and mutagenicity testing, then and now.

Cancer is a dread disease worldwide. Mortality of individuals suffering from cancer is high, despite the current improved methods of precocious detection, surgery and therapy. Prevention of cancer is the recognized goal of many activities in cancer research. This aim was recognized early to involve the bioassay of environmental chemicals or mixtures. The first such study involved application of coal tar to the ear of rabbits, and later on to the skin of mice. Subsequently, laboratory rats were introduced, and hamsters were utilized as a substitute for the unwieldy tests in rabbits. Investigators also became concerned with the mechanisms of carcinogenesis, and more definitive approaches to carcinogen bioassay in laboratory animals, as possible indicators of cancer risk in humans. These tests were expensive and lengthy, and did not serve the important purpose of accurately measuring risk of cancer to humans. Once it was realized that DNA and the genetic apparatus might be a key target, rapid bioassays in bacterial and mammalian cell systems were introduced successfully. Thus, batteries of tests are now available to detect effectively human cancer risks, and provide novel approaches to determine the underlying mechanisms, as a sound basis for cancer prevention.     

Mutagenicity,carcinogenicity, and teratogenicity of acrylonitrile

Acrylonitrile (AN) is an important intermediary for the synthesis of a variety of organic products, such as artificial fibres, household articles and resins. Although acute effects are the primary concern for an exposure to AN, potential genotoxic, carcinogenic and teratogenic risks of AN have to be taken seriously in view of the large number of workers employed in such industries and the world-wide population using products containing and possibly liberating AN. An understanding of the effect of acrylonitrile must be based on a characterization of its metabolism as well as of the resulting products and their genotoxic properties. Tests for mutagenicity in bacteria have in general been positive, those in plants and on unscheduled DNA synthesis doubtful, and those on chromosome aberrations in vivo negative. Wherever positive results had been obtained, metabolic activation of AN appeared to be a prerequisite. The extent to which such mutagenic effects are significant in man depends, however, also on the conditions of exposure. It appears from the limited data that the ultimate mutagenic factor(s), such as 2-cyanoethylene oxide, may have little opportunity to act under conditions where people are exposed because it is formed only in small amounts and is rapidly degraded. The carcinogenic action of AN has been evaluated by various agencies and ranged from `reasonably be anticipated to be a human carcinogen' to `cannot be excluded', the most recent evaluation being `possibly carcinogenic to humans'. Animal data that confirm the carcinogenic potential of AN have certain limitations with respect to the choice of species, type of tumors and length of follow up. Epidemiological studies which sometimes, but not always, yielded positive results, encounter the usual difficulties of confounding factors in chemical industries. Exposure of workers to AN should continue to be carefully monitored, but AN would not have to be considered a cancer risk to the population provided limitations on releases from consumer products and guidelines on AN in water and air are enforced. AN is teratogenic in laboratory animals (rat, hamster) at high doses when foetal/embryonic (and maternal) toxicity already is manifest. Pregnant workers should not be exposed to AN. In view of the small concentrations generally encountered outside plants, women not professionally exposed would appear not to be at risk of teratogenic effects due to AN. Future research should concentrate on the elucidation of the different degradation pathways in man and on epidemiological studies in workers including pregnant women, assessing also, if possible, individual exposure by bio-monitoring.     

Mutagenicity, carcinogenicity and teratogenicity of aluminium

Aluminium and its salts, which are extensively used in the household and in industry, do not constitute a carcinogenic, mutagenic or teratogenic hazard, except, perhaps, in cases of extremely high exposure. The large majority of the experiments performed to assess the carcinogenicity of aluminium in laboratory animals gave negative results or even suggested some antitumor activity. Moreover, epidemiological studies have not provided clear evidence of a carcinogenic hazard of aluminium to man, and short-term tests made in vitro and in vivo to demonstrate mutagenic activity of A1 were negative except for some experiments in plants. The embryotoxic properties suggested by the studies on birds and mammals could result from the influence of A1 on phosphate and calcium metabolism or from interference with the polymerization of microtubules.     

Mutagenicity, carcinogenicity and teratogenicity of beryllium

The carcinogenicity of a number of beryllium compounds has been confirmed in experiments on laboratory animals and this metal has to be treated as a possible carcinogenic threat to man. These carcinogenic properties are associated with mutagenic activity as shown by the results of short-term tests performed in vitro with beryllium chloride and beryllium sulfate. These soluble beryllium compounds can produce some infidelity of in vitro synthesis, forward gene mutations in microorganisms and in mammalian cells. They are also able to induce cell transformation. In addition to the positive results obtained in several short-term assays beryllium compounds have been found to bind to nucleoproteins, to inhibit certain enzymes needed for DNA synthesis, to bind nucleic acids to cell membranes and to inhibit microtubule polymerization. The teratogenicity of beryllium salts is relatively unknown and needs additional investigation.     

Mutagenicity, carcinogenicity and teratogenicity of zinc

Zinc is a common element in the human environment and constitutes an important trace element intervening in many biological processes. Toxicity of zinc is low; zinc deficiency represents, however, a hazard for human health. Zinc is not mutagenic and has little, if any, clastogenic properties. Zinc can induce tumours but only following local application, and does not represent a carcinogenic risk to man. It is still uncertain whether zinc can cause malignant transformation but zinc is needed for cellular proliferation of existing tumours and tumour growth is retarded by zinc deficiency. Zinc is not teratogenic; it can, in fact, avert teratogenicity of other agents. Conversely, zinc deficiency may be harmful to the developing organism.     

Mutagenicity, carcinogenicity, and teratogenicity of acrylonitrile.

Acrylonitrile (AN) is an important intermediary for the synthesis of a variety of organic products, such as artificial fibres, household articles and resins. Although acute effects are the primary concern for an exposure to AN, potential genotoxic, carcinogenic and teratogenic risks of AN have to be taken seriously in view of the large number of workers employed in such industries and the world-wide population using products containing and possibly liberating AN. An understanding of the effect of acrylonitrile must be based on a characterization of its metabolism as well as of the resulting products and their genotoxic properties. Tests for mutagenicity in bacteria have in general been positive, those in plants and on unscheduled DNA synthesis doubtful, and those on chromosome aberrations in vivo negative. Wherever positive results had been obtained, metabolic activation of AN appeared to be a prerequisite. The extent to which such mutagenic effects are significant in man depends, however, also on the conditions of exposure. It appears from the limited data that the ultimate mutagenic factor(s), such as 2-cyanoethylene oxide, may have little opportunity to act under conditions where people are exposed because it is formed only in small amounts and is rapidly degraded. The carcinogenic action of AN has been evaluated by various agencies and ranged from 'reasonably be anticipated to be a human carcinogen' to 'cannot be excluded', the most recent evaluation being 'possibly carcinogenic to humans'. Animal data that confirm the carcinogenic potential of AN have certain limitations with respect to the choice of species, type of tumors and length of follow up. Epidemiological studies which sometimes, but not always, yielded positive results, encounter the usual difficulties of confounding factors in chemical industries. Exposure of workers to AN should continue to be carefully monitored, but AN would not have to be considered a cancer risk to the population provided limitations on releases from consumer products and guidelines on AN in water and air are enforced. AN is teratogenic in laboratory animals (rat, hamster) at high doses when foetal/embryonic (and maternal) toxicity already is manifest. Pregnant workers should not be exposed to AN. In view of the small concentrations generally encountered outside plants, women not professionally exposed would appear not to be at risk of teratogenic effects due to AN. Future research should concentrate on the elucidation of the different degradation pathways in man and on epidemiological studies in workers including pregnant women, assessing also, if possible, individual exposure by bio-monitoring.     

Mutagenicity,carcinogenicity and teratogenicity of vanadium compounds

The mutagenic, carcinogenic and teratogenic effects of vanadium and its compounds are reviewed. It is concluded that vanadium is not clastogenic and only weakly mutagenic; it has marked mitogenic activity affecting the distribution of chromosomes during mitosis and possibly causing aneuploidy. The few positive data on effects of vanadium during development leave it open whether direct effects on the embryo or fetus or physiological disturbances in the mother are responsible. No data exist indicating that vanadium is carcinogenic in animals or man, but since it interferes with mitosis and chromosome distribution, the possibility that vanadium might be carcinogenic under certain conditions cannot be dismissed offhand.     

Combined chemotherapy and teratogenicity

BACKGROUND: The concomitant occurrence of breast cancer and pregnancy is relatively uncommon. We report the case of a patient with syndactyly, cleft hands, and absence of distal finger phalanges associated with maternal exposure to chemotherapeutic agents during the first trimester of pregnancy. These associations have not been previously described. CASE: The patient was born by normal delivery after 38 weeks of pregnancy. His mother became pregnant while receiving chemotherapy (cyclophosphamide, 5-fluorouracil, and adriamycin) for breast cancer, and the fetus was exposed to these drugs from conception to the 16th week of pregnancy. At birth, anomalies were observed, including a high-arched palate, microcephaly, a flat nasal bridge, bilateral syndactyly in the first and second fingers with a hand cleft between the second and third fingers and hypoplasia of the fifth fingers, and dystrophic nail of the fourth finger of the left hand. The patient's growth and development were deficient. CONCLUSIONS: The malformations associated with in utero exposure to these chemotherapeutic agents are highly variable, but growth deficiency and anomalies of the craniofacial region and limbs are the most common. The pattern of malformations in children who were congenitally exposed to chemotherapeutic agents appears to be directly related to the age at and duration of exposure, rather than to the specific drug itself. Effective contraception is essential for the safe use of a potential teratogen in nonpregnant women of reproductive age.     

Mutagenicity, carcinogenicity and teratogenicity of cobalt metal and cobalt compounds

Cobalt metal and cobalt compounds are extensively used for the production of high-temperature alloys, diamond tools, cemented carbides and hard metals, for the production of various salts used in electroplating and as catalysts, drying agents in paints, additives in animal feeds and pigments. Cobalt oxides are used not only in the enameling industry and for pigments, but also in catalytic applications. There is no indication that cobalt metal and cobalt compounds constitute a health risk for the general population. Allergic reactions (asthma, contact dermatitis) can be induced by certain cobalt compounds. Interstitial fibrosis has also been observed in workers exposed to high concentrations of dust containing cobalt, tungsten, iron, etc., mainly in the cemented carbides and the diamond-polishing industries. Several experiments have demonstrated that single or repeated injections of cobalt metal powder or some forms of cobalt salt and cobalt oxide may give rise to injection site sarcoma in rats and in rabbits but the human health significance of such data is questionable. Intratracheal administration of a high dose of one type of cobalt oxide induces lung tumors in rats but not in hamsters. In the latter long-term inhalation of cobalt oxide (10 mg/m3) did not increase the incidence of lung cancer. The human data are too limited to assess the potential carcinogenic risk for workers. Co2+ interacts with protein and nucleic acid synthesis and displays only weak mutagenic activity in microorganisms. Some cobalt salts have been reported to enhance morphological transformation of Syrian hamster embryo cells. Cobalt chloride displays some limited mutagenic activity in yeast and some cobalt compounds are able to produce numerical and structural chromosome aberrations in plant cells. Cobalt and its salts appear to be devoid of mutagenic and clastogenic activity in mammalian cells. Cobaltous acetate and cobaltous chloride have not been found to be teratogenic in hamsters and rats respectively.     

Mutagenicity and teratogenicity of mercury compounds

Agriculture, consumption of fossil fuels and, to a lesser extent, industry, are the main sources of pollution by mercury which is discharged into the environment as metallic mercury, as inorganic mercury compounds, or as organic compounds. Once in the environment, mercury compounds are capable of a variety of transformations.Some professional or accidental mercury poisonings have been reported in human populations, but they can easily be minimized by appropriate preventive measures.Production of C-mitosis in plant material is the most noticeable genetic effect of mercury compounds.No positive report that mercury could be carcinogenic in man has appeared up to now and animal experiments have also provided negative results. Although placenta may represent a certain barrier to mercury, embryotoxicity and teratogenicity of organic mercury compounds have been observed in numerous systems such as fish, birds and mammals.     

Carcinogenicity and metabolic activation of hexestrol

The carcinogenic activity of the synthetic estrogen hexestrol was measured in male Syrian hamsters. Between 90% and 100% of the animals treated with hexestrol or with 3',3",5',5"-tetradeuteriohexestrol, implanted subcutaneously as 25-mg pellets, were found with renal carcinoma after 6-7 months. In vitro hexestrol metabolism, mediated by phenobarbital-induced rat liver microsomes, led to the formation of 3'-hydroxyhexestrol. This metabolite was identified by comparison with authentic reference material synthesized by oxidation of hexestrol with Fremy's salt. Diethylstilbestrol could not be detected as a metabolite. In urine of male Syrian hamsters, 3'-hydroxyhexestrol, 3'-methoxyhexestrol, 1-hydroxyhexestrol, and other hydroxylated and/or methoxylated hexestrol metabolites were identified. Again, diethylstilbestrol was not detectable as a hexestrol metabolite in vivo. The reactivity of 3'-hydroxyhexestrol was then studied to determine if this catechol estrogen played a role in hexestrol carcinogenicity. Horseradish peroxidase catalyzed the oxidation of 3'-hydroxyhexestrol to 3',4'-hexestrol quinone. This oxidation reaction could also be carried out non-enzymatically using silver oxide or silver carbonate on celite as oxidants. The quinone was unstable (t1/2 in methylene chloride: 53 min). It reacted with sulfur-containing compounds such as mercaptoethanol by Michael addition to form 3'-(2-hydroxyethylthio)-5'-hydroxyhexestrol. 3',4'-Hexestrol quinone reacted with simple amines such as ethylamine to form N-ethyl-aminohexestrol. The chemical reactions described above were carried out to test the reactivity of identified or suspected metabolic intermediates of hexestrol. It was concluded that carcinogenicity of hexestrol was not based on its conversion to diethylstilbestrol. Rather, catechol estrogen formation may be necessary for the carcinogenic action of hexestrol in analogy to events observed earlier with estradiol.     

Relative teratogenicity of nitrofen analogs in mice: unchlorinated, monochlorinated, and dichlorinated-phenyl ethers

To determine the role of number and position of chlorine substituents on the developmental toxicity of diphenyl ether analogs of nitrofen, we have evaluated one unchlorinated, three monochlorinated, and five dichlorinated-phenyl 4'-nitrophenyl ethers with respect to effects on liver weight and on maintenance of pregnancy in females, and with respect to postnatal survival and the occurrence of small or absent Harderian glands in offspring. None of the diphenyl ethers evaluated in these experiments was as active as nitrofen with respect to any parameter evaluated. Both the position and the number of chlorine substituents affected toxicity, but no simple relationship between number or position of chlorine substituents and either maternal or fetal endpoints was established.     

Mutascreen, an automated bacterial mutagenicity assay

Mutascreen^® is an automated instrument for bacterial mutagenicity testing. The biological principles of the Mutascreen assay are the same as those of the bacterial reverse-mutation assays, like the Ames test, but several operational principles are different. The Mutascreen assay takes place in wells containing only 400 μl of liquid medium. Also, the dispensing of the liquid medium, the bacterial tester strains, the metabolic activation system (S9), and the test solutions is all performed by a computer-controlled robot according to the user's preprogrammed instructions. The turbidity in up to 200 wells is monitored intermittently over a 24-h period by a vertical-pathway photometer, thereby avoiding measurement problems caused by sedimentation. The data for the resulting growth curves is stored for analysis. The auxotrophic growth pattern is altered characteristically by test solutions that are toxic or contain endogenous growth factor(s), while prototrophic growth is observed earlier in the 24-h period when revertants have been induced by the test solution. To compare the Mutascreen assay with the conventional plate assay, 36 chemicals including known carcinogens and noncarcinogens were tested. Both assays identified the same chemicals as mutagens and gave quantitatively similar results, thus testifying to the potential usefulness of automated bacterial mutagenicity testing.     

Rodent tumor profiles, Salmonella mutagenicity and risk assessment

The tumorigenesis profiles of 116 chemicals, which proved to induce cancer in the NCI/NTP experimentation, were studied by multivariate data analysis methods. Three main patterns of tumor induction were evident. One chemical (benzene) was not classifiable in any of the 3 clusters of chemicals. The carcinogen classes based on patterns of tumor induction did not reflect a repartition between Ames-positive and Ames-negative chemicals. Therefore any classification of carcinogens as either 'primary' (genotoxic, hence assumed to pose a greater risk) or 'secondary' (presumably carcinogenic via non-genotoxic mechanisms) would seem to be a subject for research and speculation, and, for the present, an unsuitable basis for risk assessment.