Complete Carcinogen Research Articles

The effect of complete carcinogens on intercellular transfer of lucifer yellow in fibroblast culture

The effect on permeability of gap junctions of complete powerful carcinogens, 3-methylcholanthrene (MC), 7,12-dimethylbenz(a)anthracene (DMBA), ethyl methanesulfonate (EMS), and weak carcinogens, benz(a)anthracene (BA), benzo(e)pyrene (B(e)P) as well as the aryl-hydroxylase inhibitor 7,8-benzoflavone (7,8-BF) has been studied with the use of a dye-coupling technique and transformed Djungarian hamster DM15 fibroblasts. MC, EMS and 7,8-BF were found to exert a strong inhibitory effect on cell-to-cell dye transfer. BA and DMBA had the uncoupling activity only in 2 out of 4 experiments. B(e)P was not shown to affect LY transfer between DM15 cells. The uncoupling effect of MC, 7,8-BF and EMS (only when EMS used at the concentration of 600 micrograms/ml but not 1000 micrograms/ml) appeared reversible. The causes of failure to detect DMBA and B(e)P effects on gap junctions are discussed.

Generation of reactive oxygen by tumor promoters and complete carcinogens in rat liver

Generation of reactive oxygen by tumor promoters and complete carcinogens in rat liver

Induction of protein kinase C activity by ultraviolet radiation

Exposure to ultraviolet (UV) radiation has been well correlated with skin cancer incidence. Long wave UV radiation (320-400 nm, UVA) is a major component of natural sunlight and cosmetic tanning 'salon' light, and has been shown not only to damage DNA and to act as a complete carcinogen, but also to promote ultraviolet B (280-320 nm, UVB) carcinogenesis. The mechanism by which the latter occurs is unknown, but it is believed to be related to the inflammation and irritation which results from UV exposure. In order to examine the possibility that UVA stimulates the same signalling pathway as do the phorbol esters, a class of much more thoroughly characterized skin tumor promoters, we exposed cells in culture to UVA radiation and measured cellular responses related to protein kinase C (PKC) activation. The data presented here demonstrate that a low, physiologic dose of UVA inhibits epidermal growth factor binding and increases PKC activity in cultured mammalian fibroblasts. The increase in cytosolic activity is not completely translocated to the membrane, and can be partially suppressed by puromycin and cycloheximide but not by actinomycin D. These observations are the first evidence to suggest that a protein which has been strongly linked to chemical tumor promotion may also be a critical mediator for UV-induced promotion. The response of cells to UVA is also unique, in that it does not cause a 12-O-tetradecanoyl phorbol-13-acetate-like rapid redistribution of PKC activity followed by down regulation.

Comparative tumorigenicity of picene and dibenz[a,h]anthracene in the mouse

The carcinogenic activity of the two polycyclic aromatic hydrocarbons (PAHs), picene (benzo[a]chrysene) and dibenz[a,h]anthracene (DBA), was determined in NMRI mice by five different experimental protocols in order to find out if picene is a carcinogen as predicted by recent quantum mechanical calculations in contrast to earlier observations which could not confirm any carcinogenic activity of picene. Single s.c. treatment of adult mice with picene or DBA (308 nmol/animal, each) led to the formation of fibrosarcomas in 63.3% of treated animals regardless of the PAH used. Chronic epicutaneous application of both PAHs (total dose 1.36 mumol) to the back of mice resulted in the development of papillomas with a tumor rate of 22% in the case of picene and of 32% in the case of DBA. When newborn mice were s.c. treated once on day 2 of their life with each of the two PAHs (400 nmol/animal), 27.8% of treated animals developed lung adenomas after 40 weeks in the case of picene compared to 92.1% in the case of DBA. Histopathological examination of the tumors in the three experimental models revealed no difference in the type of tumor between picene and DBA. Epicutaneous application of both PAHs (600 nmol/animal) followed by chronic treatment with 12-O-tetradecanoyl-phorbol-13-acetate for 24 weeks led to the formation of papillomas in 93% of animals treated with DBA while picene showed no tumorigenic activity at all. Initiation of tumorigenesis in the two-stage tumor model with 7,12-dimethylbenz[a]anthracene (1 mumol/animal) and chronic treatment with picene (total dose 4.8 mumol) for 24 weeks was equally ineffective in producing tumors in NMRI mice. This rare biological property of picene, which is a complete carcinogen, yet at most a very weak tumor initiator, is explained in terms of its inefficient biotransformation to mutagenic and carcinogenic metabolites as compared to the strong tumor initiator DBA.

Ultraviolet radiation--induced malignant melanoma in Monodelphis domestica.

Several lines of evidence support the hypothesis that ultraviolet radiation (UVR) is involved in the etiology of cutaneous melanoma in humans. However, progress in understanding the mechanisms involved in induction of melanotic tumors by UVR has been hindered by lack of a suitable animal model. During the course of multiple exposures (3 times/wk for 70 wk) of the South American opossum, Monodelphis domestica, to UVR, we first observed the appearance of areas of dermal melanocytic hyperplasia (MH) on the exposed skin. Post-UVR exposure to photoreactivating light (320-500 nm) suppressed the occurrence of MH. We also observed at 100 weeks from first exposure that 10 of 46 surviving animals had developed melanotic tumors which arose, presumably, from areas of MH. Tumors on three of the 10 animals have been classified as malignant melanomas based on metastasis to lymph nodes. We conclude from these results that UVR can act as a complete carcinogen for melanoma induction and, based on the photoreactivation of MH induction, that DNA damage is involved in melanoma formation.

Comparative carcinogenicity of the PAHs as a basis for acceptable exposure levels (AELs) in drinking water

The carcinogenicity of various polynuclear aromatic hydrocarbons (PAHs) has generally been demonstrated by their ability to act as complete carcinogens in the development of cancers in rodent skin tests. In order to develop proposed acceptable concentration levels for various PAHs in drinking water, we reviewed the studies that formed the basis for determining that these specific PAHs were carcinogenic in animals. We found that the relative potency of these PAHs varied over a range of many orders of magnitude. For example, the carcinogenic strength of benz aanthracene (BaA) is found to be about 1/2000th that of benzo apyrene (BaP). We have used the calculated carcinogenic potency of the various PAHs relative to that of BaP as a means for proposing specific acceptable concentration levels in drinking water for each of the specific PAHs. BaP is the only carcinogenic PAH for which EPA has published an acceptable concentration level based on carcinogenicity. Based on the level EPA set for BaP (0.028 μg/liter), this methodology has provided for the specific PAHs a determination of proposed acceptable concentration levels quantitatively based on the same data that were used to qualitatively determine them to be animal carcinogens. We have proposed acceptable concentration levels for the variinogenic PAHs in drinking water that range from 0.03 μg/liter for BaP to 6.5 μg/liter for BaA. We recommend that acceptable concentration levels for the various PAHs be based on their relative carcinogenic potencies rather than the EPA method of using the potency of only one specific PAH, BaP, to serve as the exposure level determinant for all PAHs. We further suggest that this methodology may be applicable to other classes of carcinogenic compounds. We have also found useful for the determination of acceptable concentration levels for the noncarcinogenic PAHs an analogous methodology based on the relative toxicities of the noncarcinogenic PAHs.

Human Melanocytic Neoplasms and Their Etiologic Relationship with Sunlight

Two hypotheses have been presented. The first states that melanomas commonly evolve from normal melanocytes by a tumor progression pathway from a banal nevus to a nevus with dysplasia, to a micro-invasive, and then to a evolved, tumorigenic, primary melanoma which has competence for metastasis. It is important to note that not all melanomas follow this complete pathway. As Foulds noted long ago, tumors may bypass any of the stages of tumor progression. Thus, many melanomas do not, apparently, arise in nevi, and melanomas may evolve fully formed as pure tumorigenic nodules. However, from the biological point of view, study of the benign potential precursors (nevi and, especially, dysplastic nevi as well as microinvasive melanomas) may well reveal mechanisms of progression that are applicable to all melanomas, and perhaps to other solid tumors as well. From a clinical viewpoint, follow-up and education of patients at increased risk for melanoma, and early diagnosis of melanomas in their curable, microinvasive stages may result in a reduction of mortality from the disease, even without influencing its overall incidence. The melanomas that occur on plantar and palmar (acral) skin appear to progress through a microinvasive stage similar to that of other cutaneous melanomas. However, the significance of precursor and marker lesions (if any exist) in acral melanoma remains to be elucidated by clinicopathologic and epidemiologic studies. The possibility of etiologic agents other than UV light, such as chemical carcinogens and/or viruses, should be investigated in these cases. The second hypothesis presented here, that UV light is etiologic for the common cutaneous melanoma of white populations, has support from clinical, epidemiologic, and biologic observations. From a biologic viewpoint, ultraviolet light has all of the properties that might enable it to act as a complete carcinogen, and to enhance tumor progression in melanocytic potential-precursor lesions. Clinically, it seems appropriate to encourage patients (and members of the general population, as well) to adopt sensible attitudes to sun exposure. By such means, it is possible that some melanomas might be prevented, or that the rate and incidence of progression to more-advanced stages might be inhibited.

Oxidation of DNA Bases by Tumor Promoter-Activated Processes

Evidence has accumulated showing that active oxygen species participate in at least one stage of tumor promotion. Tumor promoters can induce various types of cells to undergo processes that result in formation of active oxygen species. They stimulate polymorphonuclear leukocytes (PMNs) to undergo an oxidative burst that is characterized by rapid formation of .O2- and H2O2. We find that in vitro formation of H2O2 by tumor promoter-activated PMNs correlates with their in vivo first-stage promoting activity. Moreover, two thymidine derivatives are formed in DNA coincubated with tumor promoter-stimulated PMNs: 5-hydroxymethyl-2'-deoxyuridine (HMdU) and thymidine glycol (dTG). The amounts of HMdU and dTG formed correlate with the first-stage tumor-promoting potencies of the agents used for PMN stimulation and with the amount of H2O2 generated. We find that HMdU is also formed in the DNA of HeLa cells coincubated with 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated PMNs, with the amount of HMdU being proportional to that of TPA used. Even in the absence of PMNs, HMdU is increasingly formed in cellular DNA with increased TPA concentration, although at much lower levels than in the presence of PMNs. When rat liver microsomes are incubated with benzo[a]pyrene (BaP), a complete carcinogen, H2O2 is also generated. Production of H2O2 increases linearly with increasing concentrations of BaP. Furthermore, HMdU is formed in DNA exposed to BaP-treated microsomes, and its formation is inhibited by catalase. These results suggest that carcinogen-induced processes generating H2O2 are associated with the first-stage promoting activity of complete carcinogens.

Oxidation of DNA bases by tumor promoter-activated processes.

Evidence has accumulated showing that active oxygen species participate in at least one stage of tumor promotion. Tumor promoters can induce various types of cells to undergo processes that result in formation of active oxygen species. They stimulate polymorphonuclear leukocytes (PMNs) to undergo an oxidative burst that is characterized by rapid formation of .O2- and H2O2. We find that in vitro formation of H2O2 by tumor promoter-activated PMNs correlates with their in vivo first-stage promoting activity. Moreover, two thymidine derivatives are formed in DNA coincubated with tumor promoter-stimulated PMNs: 5-hydroxymethyl-2'-deoxyuridine (HMdU) and thymidine glycol (dTG). The amounts of HMdU and dTG formed correlate with the first-stage tumor-promoting potencies of the agents used for PMN stimulation and with the amount of H2O2 generated. We find that HMdU is also formed in the DNA of HeLa cells coincubated with 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated PMNs, with the amount of HMdU being proportional to that of TPA used. Even in the absence of PMNs, HMdU is increasingly formed in cellular DNA with increased TPA concentration, although at much lower levels than in the presence of PMNs. When rat liver microsomes are incubated with benzo[a]pyrene (BaP), a complete carcinogen, H2O2 is also generated. Production of H2O2 increases linearly with increasing concentrations of BaP. Furthermore, HMdU is formed in DNA exposed to BaP-treated microsomes, and its formation is inhibited by catalase. These results suggest that carcinogen-induced processes generating H2O2 are associated with the first-stage promoting activity of complete carcinogens.

Multiple mechanisms for the carcinogenic effects of asbestos and other mineral fibers.

Asbestos and other mineral fibers are carcinogenic to humans and animals but differ from many carcinogens in that they do not induce gene mutations. An understanding of these interesting human carcinogens, therefore, is an important problem in cancer research. Asbestos and other fibers induce predominantly two types of cancers: mesotheliomas and bronchogenic carcinomas. Fiber size is an important factor in the carcinogenic activity of these substances as has been shown for mesothelioma induction. For bronchogenic carcinomas, but not for mesotheliomas, a synergistic effect of asbestos exposure and cigarette smoke has been observed in humans. The mechanisms by which fibers alone versus fibers in concert with other carcinogens induce cancers are probably distinct. In addition to fiber dimensions, fiber durability and surface properties of fibers are important properties affecting carcinogenicity. Evidence exists that asbestos is a complete carcinogen, an initiator and a promoter. Multiple mechanisms must be operative to explain the diverse effects of mineral fibers. Although asbestos is inactive as a gene mutagen, there is now clear evidence that it induces chromosomal mutations (aneuploidy and aberrations) in a wide variety of mammalian cells including mesothelial cells. Asbestos also induces transformation of cells in culture including mesothelial cells and fibroblasts. A mechanism for cell transformation, which is dependent on fiber dimension, has been proposed. The fibers are phagocytized by the cells and accumulate in the perinuclear region of the cells. When the cell undergoes mitosis, the physical presence of the fibers interferes with chromosome segregation and results in anaphase abnormalities. The transformed cells show aneuploidy and other chromosome abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Human Melanocytic Neoplasms and Their Etiologic Relationship with Sunlight.

Two hypotheses have been presented. The first states that melanomas commonly evolve from normal melanocytes by a tumor progression pathway from a banal nevus to a nevus with dysplasia, to a micro-invasive, and then to a fully evolved, tumorigenic, primary melanoma which has competence for metastasis. It is important to note that not all melanomas follow this complete pathway. As Foulds noted long ago, tumors may bypass any of the stages of tumor progression. Thus, many melanomas do not, apparently, arise in nevi, and melanomas may evolve "fully formed" as pure tumorigenic nodules. However, from the biological point of view, study of the benign potential precursors (nevi and, especially, dysplastic nevi as well as microinvasive melanomas) may well reveal mechanisms of progression that are applicable to all melanomas, and perhaps to other solid tumors as well. From a clinical viewpoint, follow-up and education of patients at increased risk for melanoma, and early diagnosis of melanomas in their curable, microinvasive stages may result in a reduction of mortality from the disease, even without influencing its overall incidence. The melanomas that occur on plantar and palmar (acral) skin appear to progress through a microinvasive stage similar to that of other cutaneous melanomas. However, the significance of precursor and marker lesions (if any exist) in acral melanoma remains to be elucidated by clinicopathologic and epidemiologic studies. The possibility of etiologic agents other than UV light, such as chemical carcinogens and/or viruses, should be investigated in these cases. The second hypothesis presented here, that UV light is etiologic for the common cutaneous melanoma of white populations, has support from clinical, epidemiologic, and biologic observations. From a biologic viewpoint, ultraviolet light has all of the properties that might enable it to act as a complete carcinogen, and to enhance tumor progression in melanocytic "potential-precursor" lesions. Clinically, it seems appropriate to encourage patients (and members of the general population, as well) to adopt sensible attitudes to sun exposure. By such means, it is possible that some melanomas might be prevented, or that the rate and incidence of progression to more-advanced stages might be inhibited.

The effect of inducers of mixed-function oxidases on hepatic microsome-mediated aflatoxin B 1 transformation in [formula omitted] cells

The potent hepatotoxin and hepatocarcinogen aflatoxin B 1 (AFB 1) is metabolized by different forms of cytochrome P450 associated with the hepatic mixed-function oxidase system. C3H 10T 1 2 (10 T 1 2 ) cells, which have limited inherent capacity to metabolize AFB 1, were treated with AFB 1 in the presence of hepatic microsomes isolated from chemically treated rats to investigate the effects of the induction of specific cytochromes P450 on AFB 1-mediated toxicity and transformation. Relative to uninduced microsomes, phenobarbital (PB) treatment induced AFB 1-DNA binding (essentially representing the formation of AFB 1-8,9-oxide bound to DNA) 3.2-fold, while pretreatment with Aroclor 1254, 3-methylcholanthrene (3-MC), or 5,6-benzoflavone (β-NF) preferentially induced aflatoxin M 1 (AFM 1) formation from 2- to 5-fold. 10 T 1 2 cells were exposed to a multiple treatment regimen with 4 μ m AFB 1 and hepatic microsomes from uninduced, PB-, Aroclor 1254-, 3-MC-, or β-NF-treated rats; respective cumulative toxicities of approximately 90, 95, 70, 60, and 40% control (no microsomes) values resulted. An enhanced AFB 1 transformation response correlated with the increasing toxicities observed for the different treatments, with uninduced or PB-induced microsomes yielding approximately four foci/dish, while treatments with Aroclor 1254-, 3-MC-, or β-NF-induced microsomes resulted in only one to two foci/dish. These results demonstrate that AFB 1 is a complete carcinogen in the 10 T 1 2 system when repetitive incubations are used in conjunction with an appropriate hepatic microsomal activation system. These data also correlate the induction of AFB 1-4-hydroxylase with a decrease in AFB 1-mediated toxicity and transformation of 10 T 1 2 cells, and support the hypothesis that the Phase I metabolic conversion of AFB 1 to AFM 1 in the liver represents an effective detoxication pathway per se.

Sodium o-phenylphenate (OPP-Na) promotes skin carcinogenesis in CD-1 female mice initiated with 7, 12-dethylbenz[a]anthracene

Sodium o-phenylphenate (OPP-Na) was applied at a dose level of 5.0 mg/animal dermally to the fur-clipped dorsal area of female CD-1 mice twice weekly for 47 weeks after applications of 10 micrograms of 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator twice weekly for 5 weeks. A total of 25 skin tumors (21 papillomas and four carcinomas) developed in 15 out of 20 mice (75%). The incidence and yield of skin tumors in this DMBA/OPP-Na group were significantly higher than in the DMBA/acetone-treated group where only six tumors (five papillomas and one carcinoma) were observed in five out of 20 mice (25%). Only one papilloma developed in OPP-Na/12-o-tetradecanoylphorbol 13-acetate (TPA) treated animals (initiation testing group), and no tumors were observed in mice receiving OPP-Na/acetone. OPP-Na elevated 5-bromodeoxyuridine(BrdU) incorporation in basal cells of mouse epidermis dose-relatedly and the thickness of the skin in the treated group was also increased to approximately 2- or 3-fold that of controls. In addition, high dose application (20 mg/mouse) caused ulceration. O-Phenylphenol (OPP) administration was associated with extensive corrosive effects. The data suggest that OPP-Na is an ulcerogenic agent which induces epidermal proliferation and which can act as a promoter, but not as an initiator or a complete carcinogen, in two-stage mouse skin carcinogenesis.

Analysis of 2,3,7,8-TCDD tumor promotion activity and its relationship to cancer

2,3,7,8-tetrachlorodibenzo- p-dioxin (hereafter referred to as TCDD) has a high estimated cancer potency in animals which has been reasoned to imply that TCDD might be carcinogenic to man. The animal cancer data show that TCDD can act in a solitary manner causing tumors without the participation of other known factors. However, there exists animal cancer data indicating that TCDD can act as a tumor promoting compound. This analysis examines which type of carcinogen and which mechanism best characterizes TCDD cancer activity. It is suggested that TCDD acts by a hormonal mechanism to cause cancer in a solitary manner, at low doses, in two species, and in a number of different organs, including rare sites. These observations in toto characterize TCDD as a complete carcinogen, which by definition encompasses both initiation and promotion carcinogenic activities.

N-nitrosocimetidine as an initiator of murine skin tumors with associated H-ras oncogene activation.

N-Nitrosocimetidine (NCM) is a derivative of the drug cimetidine, a methylguanidine derivative used in the treatment of peptic ulcer, and is known to be inactive as a complete mouse skin carcinogen, even when given in repeated high doses for a long period. In the current experiment, NCM was tested for its ability to initiate skin tumors on Sencar mice. It was applied at doses of 1 or 0.3 mg, 5 times/week for 6 weeks, followed by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), 1 microgram, 2 times/week for 50 weeks. Controls received acetone. The higher NCM dose had significant effects on TPA-promotable tumors, resulting in shortened time to first tumor, increased incidence of all tumors (2-fold) and of malignant tumors (4-fold), and greater tumor growth rate (2-fold), compared with the acetone/TPA-treated mice. The mice given the lower NCM dose did not exhibit increased tumor incidence, but their tumors had a significantly higher growth rate (3-fold) than those of the TPA controls. NCM without TPA treatment caused no tumors. Thus, NCM is a definitive, though weak initiator of TPA-promotable tumors. Nine tumors from the NCM-treatment groups were analyzed for activated oncogenes by the NIH 3T3 cell transfection assay. Five were positive and four of these were found by selective oligonucleotide hybridization analysis to have an A to T transversion in the second position of codon 61 of the H-ras oncogene. One of two tumors from the acetone/TPA group also contained transforming DNA and demonstrated this mutation. None of the tumors had a G----A transition mutation at the second position of codon 12 of this oncogene. Tumor initiation by NCM may then be associated with the same oncogene mutation reported for mouse skin tumors initiated by other types of carcinogens, although occurrence of the mutated oncogene in TPA controls precludes a definitive conclusion.

Evaluation of chlordecone in a two-stage model of hepatocarcinogenesis: a significant sex difference in the hepatocellular carcinoma incidence

Chlordecone (Kepone) has been extensively studied for its toxicity in male production workers who were exposed to large quantities of this organochlorine pesticide. Concern that these workers might be at an increased risk of developing liver cancer prompted us to test chlordecone in a two-stage rat model of hepatocarcinogenesis. Chlordecone acted largely as a liver tumor promoter rather than as a complete hepatic carcinogen in both male and female Sprague-Dawley rats. Dose-response experiments showed that the hepatocarcinogenic effects of long-term chlordecone administration became undetectable at concentrations in non-initiated rat liver in the same range as those measured in human biopsies taken from exposed workers who exhibited no liver effects. Although the toxicity of chlordecone in women has never been studied, we found a dramatic sex difference in the incidence of malignant liver tumors caused by chlordecone promotion in rats. Frank hepatocellular carcinomas were observed in up to 63% of female rats whose livers were previously 'initiated' with a subcarcinogenic dose of diethylnitrosamine given 24 h after partial hepatectomy, and then 'promoted' by 27 weeks of chlordecone administration. In contrast, none of comparably treated males had malignant liver tumors, even after 44 weeks of 'promotion' with chlordecone. Females in the diethylnitrosamine-initiated/chlordecone-promotion groups also contained gamma-glutamyltranspeptidase-positive 'preneoplastic' hepatocellular foci that were more abundant and larger than those observed in comparably-treated males. Moreover, because similar levels of chlordecone were measured in the livers of both sexes at the end of the experimental period, the development of hepatocellular carcinomas in the diethylnitrosamine-initiated female rats appeared to be due to their increased sensitivity to the promotion treatment.

Structure and carcinogenicity of dibenzo(c,g)carbazole derivatives.

The carcinogenicity of several groups of carcinogens is evoked with particular reference to Dibenzo(c,g)carbazole derivatives. The activity of these derivatives is discussed with respect to their species and organ specificity. The enzymatic equipment is decisive as to whether the compounds formed can react with DNA or are simply detoxified and eliminated. All these carcinogens are complete carcinogens, i.e. they have the property of both initiation and promotion.

Tumor initiation and promotion effects of petroleum streams in mouse skin

A furnace oil, a dewaxed heavy paraffinic distillate, and a solvent-extracted lubricant base oil induced skin tumors in 9 43 , 26 48 , and 1 47 male C3H mice, respectively, during lifetime skin-painting bioassays. An initiation/promotion (I/P) bioassay was conducted to assess the I/P potential of these materials. During a 28-week initiation bioassay, groups of 30 male CD-1 mice were first treated dermally once daily for 5 days with 25 or 50 μl of test materials or 50 μl of acetone, rested for 2 weeks, then treated twice per week for 25 weeks with 50 μl (0.1 mg/ml) phorbol-12-myristate-13-acetate (PMA). Only groups treated with the heavy paraffinic distillate had a significantly higher incidence of papillomas relative to the acetone control group. During a 28-week promotion bioassay, groups of 30 male CD-1 mice were treated once with 50 μl of either DMBA (1.0 mg/ml) or acetone, rested for 2 weeks, and then treated twice per week with test material for the remaining 25 weeks. The furnace oil and dewaxed heavy paraffinic distillate showed significantly higher incidences of carcinomas and papillomas in DMBA-initiated mice relative to their acetone-initiated controls. Together these bioassay data suggest that only the dewaxed heavy paraffinic distillate is a complete carcinogen, having both initiating and promoting activity; furnace oil is a promoter only, while the solvent-extracted lubricating oil is noncarcinogenic. Overall, the I/P bioassay correlated well with the results of the lifetime skin-painting bioassay.

Rat liver foci and in vitro assays to detect initiating and promoting effects of chlorinated ethanes and ethylenes.

Nine chlorinated aliphatics (CAs) were examined in a rat liver foci assay for tumor initiating and promoting activities. In this model, young adult male Osborne Mendel rats were first subjected to a partial hepatectomy, the test chemical was then administered at the maximum tolerated dose in the initiation or promotion phase in conjunction with diethylnitrosamine (DEN; 30 mg/kg b.w.) or phenobarbital (PB; 0.05 percent, w/w, in the diet), and gamma glutamyltranspeptidase (GGT) was used as a putative preneoplastic indicator. When administered in the promotion protocol after initiation with DEN, 1,1-dichloroethane, 1,1,2-trichloroethane (1,1,2-TCE), 1,1,2,2-tetrachloroethane (1,1,2,2-TTCE), tetrachloroethylene (TTCY), and hexachloroethane induced significant increases in GGT+-foci above control levels. 1,1,2,2-TTCE, TTCY, and 1,1,2-TCE also induced significant increases in GGT+-foci when administered in the promotion protocol without DEN initiation. Two variants of GGT+-foci were observed: the classical type associated with PB promotion, and the other, which was more diffuse, less intensely stained, resembling foci undergoing redifferentiation and associated with CAs. A number of CAs were also genotoxic in short-term in vitro tests. Taken together, the studies suggest that CAs may be complete carcinogens in vivo with weak initiating activity and stronger promoting activity.

The study of multi-stage carcinogenesis in retinoblastoma and familial polyposis coli patient-derived skin fibroblast cell culture systems

Carcinogenesis is considered to be a multi-step process comprising ‘initiation’, ‘promotion’ and ‘conversion’ events. Skin fibroblasts from patients with hereditary retinoblastoma (RB) and familial polyposis coli (FPC) were chosen for study since their predisposition to the tumour may be due to an inherited ‘initiation’ event which is present in every cell. Experiments involving skin fibroblasts from FPC patients showed certain of these cells to grow in semi-solid medium following treatment with the complete carcinogen N-methyl- N′-nitrosoguanidine (MNNG) and the tumourpromoter 12- O-tetradecanoypphorbol-13-acetate (TPA) alone. When tested prior to the commencement of the experiments the FPC patient cell populations had shown no strong predisposition to malignant transformation as assessed by increased saturation densities, reduced serum requirements, altered migration patterns in collagen gels, anchorage-independent growth and tumourigenicity in nude mice. Following carcinogen or promoter treatment, apart from exhibiting low-level frequencies of anchorage-independent growth, the cells appeared no more transformed than they were before. Parallel cytogenetic studies showed TPA to increase both tetraploidy and the chromosome-aberration frequency during the course of these transformation studies. However, the FPC cell clones induced by TPA to grow in semi-solid medium were, at best, considered to be only partially transformed when their properties were compared with those of tumour-derived cell lines.