Long-term Carcinogenicity Tests Research Articles

Genotoxicity study of 2-methoxyethanol and benzalkonium chloride through Comet assay using 3D cultured HepG2 cells.

Though the key data in identifying carcinogenicity is experience in human, long-term carcinogenicity tests using experimental animals are more realistic. Because carcinogenicity tests require much time and cost, performing the test is minimized through pre-screening. Recently, as bioethics has been strengthened, it is required to minimize animal testing in screening tests as well as carcinogenicity tests. The replacement of the micronucleus assay in experimental animal is the beginning, and the ultimate goal is to replace the carcinogenicity test using experimental animals. The micronucleus assay and the comet assay in 3D culture system of human-derived cells is considered as the most applicable practical measures at this stage. This study was conducted to provide more diverse information in the evaluation of carcinogenicity by establishing the comet test method in a three-dimensional cell culture system. In this study, HepG2 cells were cultured for 4 days in hang-in drop method, and then cultured for 7 days on a low adhesion plate to prepare spheroids. The methods were confirmed by d-mannitol (negative control), ethylmethane sulfonate (positive control), and cyclophosphamide (positive control for metabolite). 2-methoxyethanol and benzalkonium chloride were selected as test substances. Though 2-methoxyethanol is positive in in vivo comet assay and in vitro mammalian chromosome aberration test, it is considered negative in the comprehensive genotoxicity evaluation based on negative in bacterial reverse mutation assay, in vitro mammalian cell gene mutation test and mammalian chromosome aberration test. Benzalkonium chloride has been questioned on carcinogenicity because it is a disinfectant ingredient that has become a social issue in Korea. As a result of the Comet assay for 2-methoxyethanol and benzalkonium chloride in the cultured HepG2 cell line, 2-methoxyethanol was evaluated as positive in the metabolic activation system, but benzalkonium chloride was evaluated as negative in both the presence and absence of the metabolic activation system. Therefore, in order to clarify the carcinogenic potential of 2-methoxyethanol, it is judged that additional studies based on mechanistic studies are needed.

Early detection of urinary bladder carcinogens in rats by immunohistochemistry for γ-H2AX: a review from analyses of 100 chemicals.

In safety evaluations of chemicals, there is an urgent need to develop short-term methods to replace long-term carcinogenicity tests. We have reported that immunohistochemistry for γ-H2AX, a well-established biomarker of DNA damage, can detect bladder carcinogens at an early stage using histopathological specimens from 28-day repeated-dose oral toxicity studies in rats. Given the markedly low level of γ-H2AX formation in the bladder urothelium of untreated rats, an increase in γ-H2AX-positive cells following chemical exposure can be relatively easy to identify. Among the 100 compounds examined to date, bladder carcinogens can be detected with high sensitivity (33/39; 84.6%) and specificity (58/61; 95.1%). As expected, γ-H2AX formation levels tended to be high following exposure to genotoxic bladder carcinogens, whereas nongenotoxic bladder carcinogens also increased the number of γ-H2AX-positive cells, probably through secondary DNA damage associated with sustained proliferative stimulation. γ-H2AX formation in the bladder urothelium reflects species differences in susceptibility to bladder carcinogenesis between rats and mice and shows a clear dose-dependency associated with the intensity of tumor development as well as high reproducibility. Some of the bladder carcinogens that showed false-negative results in the evaluation of γ-H2AX alone could be detected by combined evaluation with immunostaining for bladder stem cell markers, including aldehyde dehydrogenase 1A1. This method may be useful for the early detection of bladder carcinogens, as it can be performed by simple addition of conventional immunostaining using formalin-fixed paraffin-embedded tissues from 28-day repeated-dose toxicity studies in rodents, which are commonly used in safety evaluations of chemical substances.

Science, politics, and health in the brave new world of pharmaceutical carcinogenic risk assessment: Technical progress or cycle of regulatory capture?

The carcinogenicity (cancer-inducing potential) of pharmaceuticals is an important risk factor for health when considering whether thousands of patients on drug trials or millions/billions of consumers in the marketplace should be exposed to a new drug. Drawing on fieldwork involving over 50 interviews and documentary research spanning 2002–2010 in Europe and the US, and on regulatory capture theory, this article investigates how the techno-regulatory standards for carcinogenicity testing of pharmaceuticals have altered since 1998. It focuses on the replacement of long-term carcinogenicity tests in rodents (especially mice) with shorter-term tests involving genetically-engineered mice (GEM). Based on evidence regarding financial/organizational control, methodological design, and interpretation of the validation and application of these new GEM tests, it is argued that regulatory agencies permitted the drug industry to shape such validation and application in ways that prioritized commercial interests over the need to protect public health. Boundary-work enabling industry scientists to define some standards of public-health policy facilitated such capture. However, as the scientific credibility of GEM tests as tools to protect public health by screening out carcinogens became inescapably problematic, a regulatory resurgence, impelled by reputational concerns, exercised more control over industry’s construction and use of the tests, The extensive problems with GEM tests as public-health protective regulatory science raises the spectre that alterations to pharmaceutical carcinogenicity-testing standards since the 1990s may have been boundary-work in which the political project of decreasing the chance that companies’ products are defined as carcinogenic has masqueraded as techno-science.

Concordance between Results of Medium-term Liver Carcinogenesis Bioassays and Long-term Findings for Carcinogenic 2-Nitropropane and Non-carcinogenic1-Nitropropane in F344 Rats.

This study was conducted to determine the concordance of results for a pair of structural isomers, 2-nitropropane (2-NP) and 1-nitropropane (1-NP), using the rat medium-term liver carcinogenesis bioassay (Ito test) and previously published long-term carcinogenicity tests. Male F344 rats were given a single intraperitoneal injection of DEN (200 mg/kg b.w.) to initiate hepatocarcinogenesis. After 2 weeks, they received per os 0, 0.8, 4 or 20 mg/kg/day of 2-NP or 1-NP six times a week and were subjected to two-thirds partial hepatectomy at week 3. Non-initiated groups receiving 0 or 20 mg/kg/day were also included. The animals were sacrificed for quantitative analysis of GST-P-positive foci at week 8. With the highest dose of 2-NP, significantly increased numbers and areas of GST-P-positive foci were demonstrated as compared with the respective control but were not noted with 1-NP. In the non-DEN-initiated groups, many small GST-P-positive foci of less than 0.2 mm in diameter were also induced in the rats treated with 2-NP at 20 mg/kg/day but were lacking with 1-NP. These results strongly support that 2-NP is a complete hepatocarcinogen with a potent initiation activity, whereas 1-NP is not.

Occupational cancer and social inequities

Absent from five relevant papers on Environmental Inequities (Eur J Public Health, Jan 2010) was any mention or discussion of occupational health and safety among the lower economic status workforce. These papers oriented more towards the negative impacts that social inequities have on environmental health and the influence of waste management policies, ambient air quality and residential location. The late Lorenzo Tomatis championed blue-collar workers and their struggling plight in unhealthy, unsafe and discriminatory occupational conditions, and especially being exposed chronically to known mutagens and carcinogens.1–3 This led from his equal campaign struggle for primary prevention of cancer,3–5 culminating in his establishing in the 1960s/early 1970s the Monographs Programme, International Agency for Research on Cancer,3–5 now in Volume 100 (http://monographs.iarc.fr/). Our collective battle to eliminate or minimize the impact that social injustice has on occupational cancers and other work-related diseases continues as fewer and fewer efforts are devoted to either poverty and cancer1–3 or primary prevention of cancer.3–5 For the latter, identifying likely carcinogens using animal surrogates receives lesser funding and diminished attention beginning in the 1990s onwards than in earlier decades of 1950–80s. Much of this decline likely centers on the glamorous rush to replace carcinogenesis bioassays with molecular biology and mechanistic research discerning carcinogenesis processes, hoping for eventual molecular or genomic intervention. This is unfortunate as ‘New developments in molecular biology do not invalidate ipso facto all that has been done before. While the new insights about certain aspects of the carcinogenesis process and the new techniques that have been developed in parallel demand that new approaches be explored and developed, there is little justification for downgrading long-term carcinogenicity tests, which provide proven, efficient warning about possible hazards to humans.’4 Not only do occupational cancers continue to show up in older or retired workers, but also myriad exposure circumstances of younger workers to potential carcinogens are multiple and enormous as more chemicals, mixtures of chemicals and product formulations remain or newly enter commerce. Often overlooked are chemicals, mostly untested; and sources the general public is exposed to adds significantly to the burden of those exposed to higher levels in the workplace: personal care products, shampoo, lotions, toothpastes, cleaning products, laundry and washing soaps, synthetics, pharmaceuticals, fluoride and chlorine in water, herbicides/pesticides/fungicides and other chemicals in food, hormones/steroids/antibiotics in food animals, pesticides and other chemicals for yard or inside homes, air fresheners in cars and homes, dry cleaning chemicals, drugs, alcohol and so on (from ‘The Hundred Year Lie’ by Randall Fitzgerald, 2006). Newer innovations like nanotechnology represent another burgeoning yet untested human health threat having worldwide distribution with little or minimal toxicologic evaluation for potential hazards. And much of these new hazards again fall disproportionately onto the lower social classes of workers or residents living near manufacturing plants and unsanitary conditions. Older industries like asbestos and chemicals or pesticides are often exported to developing nations, previously banned in developed countries; another debilitating source of social inequities and invisible punishment.1 These profit-minded practices need better and more protective health and safety export regulations and legislation. Conflict of Interest Statement: None declared.

A medium‐term rat liver bioassay for rapid in vivo detection of carcinogenic potential of chemicals

A reliable medium-term bioassay system for rapid detection of carcinogenic potential of chemicals in the human environment has been developed. The 8-week-protocol consists of 2 stages; male F344 rats are given a single intraperitoneal injection of diethylnitrosamine (200 mg/kg) for initiation of liver carcinogenesis, followed by a 6-week test chemical treatment starting 2 weeks thereafter. Test chemicals are usually given in the diet or the drinking water and in the 2nd week of test chemical treatment, all rats are subjected to two-thirds partial hepatectomy in order to induce regenerative cell replication. The end-point marker is the glutathione S-transferase placental form (GST-P)-positive hepatic focus, the numbers and sizes of which are analyzed using an image-analyzer and expressed as values per unit liver section (1 cm2). When the yield of GST-P-positive foci is significantly enhanced (P<0.05) over the control value, a chemical is judged to possess carcinogenic or promotion potential for the liver. Among 313 chemicals already tested in this system in our laboratory, 30/31 (97%) mutagenic hepatocarcinogens and 29/33 (88%) non-mutagenic hepatocarcinogens gave positive results. Ten out of 43 (23%) agents known to be carcinogenic in organs other than the liver were also positive. It is particularly important that only one of 48 non-carcinogens gave a very weak positive result, so that the system has a very low false-positivity rate. It is now well documented that the assay system is highly effective for detecting hepatocarcinogens, bridging the gap between traditional long-term carcinogenicity tests and short-term screening assays. At the Fourth International Conference on Harmonization, our medium-term liver bioassay based on an initiation and promotion protocol was recommended in the guidelines as an acceptable alternative to the long-term rodent carcinogenicity test.

Early detection of carcinogenic substances and modifiers in rats.

Over the past 20 years, we have been developing in vivo medium-term bioassay systems in rats for detecting carcinogenic and modifying effects of test compounds. The systems are based on the two-step hypothesis of carcinogenesis. In a liver model, male F344 rats are initially given a single dose of diethylnitrosamine (DEN, 200 mg/kg, i.p.) and starting 2 weeks later are treated with test compounds for 6 weeks and then killed, all rats being subjected to two-thirds partial hepatectomy at week 3. Carcinogenic potential is scored by comparing the numbers and areas per cm(2) of induced glutathione S-transferase placental form (GST-P) positive foci in the livers of groups of about 15 rats with those of corresponding control groups given DEN alone. A positive response is defined as a significant increase in the quantitative values of GST-P-positive foci, such a negative response as no change or a decrease. The results obtained have been compared with reported Salmonella/microsome and long-term carcinogenicity test findings for the same compounds. Of the liver carcinogens, 30 out of 31 (97%) mutagenic and 29 out of 33 (88%) non-mutagenic compounds gave positive results. Carcinogens other than hepatocarcinogens gave a lower proportion of positive results (9 out of 42, 21%). This bioassay also provides information concerning inhibitory potential. The practical utility and benefits of a multi-organ medium-term experimental protocol for early detection of carcinogenic agents and modifiers acting at sites other than the liver are also discussed.

Medium-term bioassays as alternative carcinogenicity test.

A medium-term liver bioassay system for rapid detection of carcinogenic agents using male F344 rats has been developed, in order to bridge the gap between long-term carcinogenicity tests and short-term screening assays. The system is fundamentally based on the two-stage hypothesis of carcinogenesis: initiation with diethylnitrosamine (200 mg/kg bw, i.p.) is followed by test chemical administration during the second, in combination with 2/3 partial hepatectomy. It requires only 8 weeks for animal experimental treatment and a further few weeks for quantitative analysis of immunohistochemically-demonstrated glutathione S-transferase placental form positive hepatic foci. A total of 291 chemicals/substances have already been analyzed in this laboratory and the efficacy of the system for hepatocarcinogens has thereby been well established. This bioassay is particularly useful for dose-response and chemical mixture studies, usually requiring large-scale experiments and also for evaluation of chemopreventive agents. Another bioassay, a medium-term multiorgan bioassay system, using 5 different chemical carcinogens, diethylnitrosamine (DEN), N-methylnitrosourea (MNU), N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), 1,2-dimethylhydrazine (DMH) and 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN), has also been established for rapid detection of not only hepatocarcinogens, but also other organ-target carcinogens. Rats were initially treated with a single i.p. administration of 100 mg/kg DEN, 4 i.p. administrations of 20 mg/kg MNU, 4 s.c. doses of 40 mg/kg DMH for 2 weeks and then 0.1% DHPN for 2 weeks. Test chemicals are administered after the carcinogens exposure. Animals were sacrificed at the end of week 36, and major organs were examined histologically. Carcinogenic activities of test chemicals were compared between the test chemical treated group and carcinogen exposures group (control group). It is increasingly becoming regarded that these bioassays are useful methods and are appropriate alternative tests systems for carcinogenicity risk assessment. Therefore, 'the International Conference on Harmonization (ICH) of Technical Requirements for the Registration of Pharmaceuticals for Human Use' has proposed that these two bioassays can be used as "additional tests for carcinogenic activity in vivo."

Medium-term Rat Liver Bioassay for Rapid Detection of Hepatocarcinogenic Substances.

We have developed a medium-term liver bioassay system for rapid detection of carcinogenic agents using male F344 rats to bridge the gap between long-term carcinogenicity tests and short-term screening assays. The system is fundamen-tally based on the two-stage hypothesis with regard to tumor production, employing initiation by diethylnitrosamine (200mg/kg, ip) in the first stage and test chemical administration during the second, in combination with 2/3 partial hepatectomy. It requires only 8 weeks for animal experimentation and a further few weeks for quantitative analysis of immunohistochemically-demonstrated glutathione S-transferase placental form positive hepatic foci. A total of 277 chemicals/substances have already been analyzed in our laboratory and the efficacy of the system for hepatocarcinogens has thereby been well established. This bioassay is increasingly becoming regarded as an appropriate alternative test system for carcinogenicity risk assessment. It is particularly useful for studies which require many experimental groups and for evaluation of chemopreventive agents.

Medium-term liver and multi-organ carcinogenesis bioassays for carcinogens and chemopreventive agents

To bridge the gap between long-term carcinogenicity tests and short-term screening assays such as the Ames test, several types of medium-term bioassay for rapid detection of carcinogenic agents have been developed using male F344 rats. The liver model, in which diethylnitrosamine initiation and acceleration of carcinogenesis by partial hepatectomy are essential components, requires only 8 weeks of animal experimentation and a few weeks for quantitative analysis of hepatic preneoplastic lesions. Using the model, a total of 250 chemicals have been analyzed and the efficacy of the system for hapatocarcinogens has thereby been well established. Other models are so-called multi-organ bioassays for detection of carcinogenic agents in multiple organs within relatively short periods. Among these, the DMBDD bioassay with 5 known carcinogens as initiators has been found to be most applicable and has now been introduced for practical use. Data from these bioassays and several single organ carcinogenesis systems have demonstrated that carcinogenic and modifying effects of individual exogenous agents may markedly differ from organ to organ. Therefore, research into chemoprevention should be based on a whole body level analysis. The present medium-term systems are very useful for this purpose.

Initiation-promotion model for assessment of carcinogenicity: medium-term liver bioassay in rats for rapid detection of carcinogenic agents.

To bridge the gap between long-term carcinogenicity tests and short-term screening assays, a medium-term liver bioassay system for rapid detection of carcinogenic agents using male F344 rats has been developed. The system is fundamentally based on the two-stage hypothesis of carcinogenesis: initiation with diethylnitrosamine (200 mg/kg, ip) is followed by test chemical administration during the second stage in combination with 2/3 partial hepatectomy. It requires only 8 weeks for the animal treatment and a further few weeks for quantitative analysis of immunohistochemically-demonstrated glutathione S-transferase placental form positive hepatic foci. A total of 277 chemicals have already been analyzed in this laboratory and the efficacy of the system for hepatocarcinogens has thereby been well established. This bioassay is particularly useful for dose-response and chemical mixture studies usually requiring large-scale experiments and also for evaluation of chemopreventive agents. Furthermore, medium-term multi-organ bioassay system, using 5 different chemical carcinogens (DEN, MNU, BBN, DMH and DHPN) has also been established for rapid detection of not only hepatocarcinogens, but also other carcinogens.

The effects of adult belt laws and other factors on restraint use for children under age 11 : J. Russell, M. Kresnow, R. Brackbill, Accident Analysis and Prevention, vol. 26, no. 3, pp. 287–295

Different types of additives are added to food products to achieve desired characteristics like taste, preservation, and sweetening. The International Conferences on Harmonization, Organization for Economic Cooperation and Development, European Food Safety Authority, and the U.S. Food and Drug Administration issue guidelines for the rules and regulation of safe use and also publish lists of approved food additives. The food additives are specially screened for cytotoxicity, genotoxicity, mutagenicity, and hepatotoxicity by various methods. The food additive safety studies are carried out by cytogenetic evaluation in which gene mutation assay, long-term carcinogenicity tests, reproductive and developmental toxicology tests, hyperactivity, anxiety, and depression activity tests are performed. The limitations of these studies are inappropriate in vivo follow-up assay and specificity of subjects. Furthermore, the main challenge is that there are no uniform guidelines on the status of these agents across the various regions or worldwide.

Medium-term rat liver bioassay for rapid detection of carcinogens and modifiers of hepatocarcinogenesis.

For rapid detection of carcinogenic agents, a medium-term liver bioassay has been established in our laboratory using preneoplastic glutathione S-transferase placental form (GST-P) positive foci in the rat liver as endpoint marker lesions. A total of 237 compounds have so far been tested in this system and the results compared with reported Salmonella/microsome and long-term carcinogenicity test findings. The positive rate was found to be extremely high, 97% (28 of 29 compounds) for genotoxic hepatocarcinogens; and satisfactory, 86% (23 of 27 chemicals) for nongenotoxic ones. The positive rate for carcinogens targeting organs other than the liver, however, is relatively low (24%). Malathion and vinclozolin proved positive, although both have been reported to be noncarcinogenic in rats and mice. Those chemicals which exerted positive results in this system might be hepatopromoting agents even if hepatocarcinogenicity has not been established. Five of the six false-negative hepatocarcinogens could be categorized as peroxisome proliferators. In addition, a number of inhibitory agents for GST-P-positive foci development have been detected and many are categorized as antioxidants. The validity of this system as a tool for rapid detection of carcinogenic and chemopreventive agents is discussed.

Medium-term bioassay system for detection of carcinogens and modifiers of hepatocarcinogenesis utilizing the GST-P positive liver cell focus as an endpoint marker.

We have developed a medium-term bioassay system of 8 weeks duration utilizing male Fischer 344 (F344) rats for detection of liver carcinogens and modifiers of hepatocarcinogenesis. The system consists of a single intraperitoneal injection of diethylnitrosamine (DEN, 200 mg/kg), 6-weeks-administration of test chemical beginning 2 weeks after the DEN injection, and 2/3 partial hepatectomy (PH) performed at week 3. Carcinogenic potency of test chemicals is predicted based on the results of quantitative analyses of immunohistochemically-demonstrated glutathione S-transferase placental form (GST-P) positive liver cell foci. At present, a total of 140 chemicals have been tested using this system, and the findings show a good correlation with reported carcinogenic activities in long-term tests. Furthermore, the reliability of the system has been extensively examined: the results from the medium-term bioassay were compared with those from long-term experiments using the same doses of selected chemicals; the data from presently-used 2-dimensional analysis were compared with calculated values utilizing mathematical formulae for three-dimensional analysis: conformity of phenotypic expression of enzymes in preneoplastic lesions was examined in relation to their growth activity. In conclusion, although the results with non-hepatocarcinogens were less than satisfactory, the present experimental protocol, which requires far fewer animals and shorter duration than a long-term carcinogenicity test, appears of advantage for rapid screening of the large number of environmental chemicals which may possess hazard potential for induction of liver cancer in man.

Enhancing effect of various hepatocarcinogens on induction of preneoplastic glutathione S-transferase placental form positive foci in rats—an approach for a new medium-term bioassay system

A large series of assays of the hepatocarcinogenic potential of 112 different compounds were carried out using a rapid bioassay system developed in this laboratory based on the two-step concept of hepatocarcinogenesis. Rats were initially given a single dose (200 mg/kg) of diethylnitrosamine (DEN) i.p. and starting 2 weeks later were treated with test compounds for 6 weeks and then killed, all rats being subjected to two-thirds partial hepatectomy (PH) at week 3. Carcinogenic potential was scored by comparing the number and area per cm2 of induced glutathione S-transferase placental form-positive (GST-P+) foci in the liver with those of the corresponding control group given DEN alone. Positive was scored for a significant increase in the value of GST-P+ foci, negative for no change or a decrease. Results were compared to reported Salmonella/microsome and long-term carcinogenicity test findings. Of the liver carcinogens, 10 out of 11 (90.9%) mutagenic, and 11 out of 13 (84.6%) non-mutagenic compounds gave positive results (mean, 87.5%). Carcinogens other than the hepatocarcinogens gave less positive results (two out of 17, 11.8%). None of the compounds reported as non-carcinogenic demonstrated positivity suggesting that the assay system does not suffer from the disadvantage of false-positive results. The protocol system also provided information concerning the inhibitory potential of compounds such as anti-oxidants. It is concluded that the present experimental protocol which requires far fewer animals and shorter duration than a long-term carcinogenicity test has practical applications for the rapid and economical screening of environmental hepatocarcinogens and their inhibitory agents.

An efficient primary prevention of cancer requires an integrated approach: Mühlbock memorial lecture

In addition to a wide gradation of levels of exposure to man-made, naturally occurring and endogenous chemicals, to viruses and to radiation, there is a gradation of genetic susceptibility for resistance to the mutagenic and other damaging effects of noxious environmental and endogenous agents. This interplay between environmental and host factors is probably not limited to the early stage of carcinogenesis but extends over the later stages of promotion and progression. The risk of cancer in humans is thus increased by a wide spectrum of factors, which ranges from exposure to an identified agent, such as environmental chemicals or a virus, to culturally determined behaviour, such as age at first pregnancy. We are able today to intervene in some of these factors, while others affect risk by as yet undetermined pathways. Only progress in the understanding of the mechanisms by which these factors act can lead to specific means of cancer prevention. New developments in molecular biology do not invalidate ipso facto all that has been done before. While the new insights about certain aspects of the carcinogenesis process and the new techniques that have been developed in parallel demand that new approaches be explored and developed, there is little justification for downgrading long-term carcinogenicity tests, which provide proven, efficient warning about possible hazards to humans. Support for the maintenance of a programme for testing of environmental chemicals does not mean, however, that one can expect that all or even most of the agents that are carcinogenic to humans will be identified by traditional long-term testing in rodents. Basic and applied research, studies on the mechanisms of carcinogenesis and research on aetiology and prevention are neither opposite nor separate areas of scientific activity. They must be, and indeed are, closely interrelated. The understanding of certain stages of the carcinogenesis process is progressing side by side with the development of much more precise methods than ever existed before for monitoring low doses of exposure at the individual level. While this will be of very considerable help in the conduct of epidemiological investigations, it is clear that the efficacy of primary prevention will increase with, and indeed depend on, understanding of the mechanisms by which a factor or a series of factors contribute to the malignant transformation of cells and/or to their progression to clinical cancer. It would be a grave error for scientists to see basic and applied research as separate or competitive. Scientists should also try not to give in to the tendency to favour the development of projects that fall in line with the preferred orientations of granting agencies and contract makers. This can result in mechanisms by which the obtaining of funds becomes a conditioning and limiting factor in the choice and design of research projects.

Response of experimental animals to human carcinogens: an analysis based upon the IARC Monographs programme.

Only the results of epidemiological studies can be used to establish a causal relationship between an exposure to an agent and human cancer; however, such studies often cannot be carried out due to limitations of population or latent period or to the presence of mixed exposures. It is essential, therefore, that the validity be established of extrapolating to humans the results obtained from long-term carcinogenicity tests in animals. The responses of experimental animals to known and suspected human carcinogens, as evaluated in the IARC Monographs series, were analysed as an indication of the sensitivity of animal tests for predicting human carcinogens. Although the response was high - 84% - it would have been even higher had all the compounds been adequately tested experimentally. An additional finding was that for many exposures causally related to human cancer, there is a target organ in common between humans and at least one animal species, despite many inherent physiological differences. These findings show clearly the importance of experimental carcinogenicity studies in the primary prevention of cancer.

Zeolithe A—A phosphate substitute for detergents: Toxicological investigation

Tests on Zeolithe A, a sodium aluminium silicate developed as a substitute for phosphates in detergents, were designed to investigate the safety of exposure to the material, or to detergents containing it, either under industrial conditions encountered during manufacturing processes or as a consequence of domestic use. The test programme included oral studies (acute, subchronic and long-term carcinogenicity tests and absorption measurements), and dermal, ocular and inhalation studies on the silicate alone and on appropriate detergent formulations, as well as studies of possible silicogenic activity and metal-complexing potential and measurements of dust generation and particle-size distribution. These studies did not produce any evidence to suggest that levels of domestic and industrial exposure resulting from the projected use of Zeolithe A in detergents would present any hazard to health. Zeolithe A did not induce silicotic tissue reactions and when incorporated into detergent formulations did not increase the liberation of fine dusts.

Long-term carcinogenicity tests of orally administered zinc and tin

Long-term carcinogenicity tests of orally administered zinc and tin