RESUMO
In a Government/Industry/Academic partnership to evaluate alternative approaches to carcinogenicity testing, 21 pharmaceutical agents representing a variety of chemical and pharmacological classes and possessing known human and or rodent carcinogenic potential were selected for study in several rodent models. The studies from this partnership project, coordinated by the International Life Sciences Institute, provide additional data to better understand the models' limitations and sensitivity in identifying carcinogens. The results of these alternative model studies were reviewed by members of Assay Working Groups (AWG) composed of scientists from government and industry with expertise in toxicology, genetics, statistics, and pathology. The Tg.AC genetically manipulated mouse was one of the models selected for this project based on previous studies indicating that Tg.AC mice seem to respond to topical application of either mutagenic or nonmutagenic carcinogens with papilloma formation at the site of application. This communication describes the results and AWG interpretations of studies conducted on 14 chemicals administered by the topical and oral (gavage and/or diet) routes to Tg.AC genetically manipulated mice. Cyclosporin A, an immunosuppresant human carcinogen, ethinyl estradiol and diethylstilbestrol (human hormone carcinogens) and clofibrate, an hepatocarcinogenic peroxisome proliferator in rodents, were considered clearly positive in the topical studies. In the oral studies, ethinyl estradiol and diethylstilbestrol were negative, cyclosporin was considered equivocal, and results were not available for the clofibrate study. Of the 3 genotoxic human carcinogens (phenacetin, melphalan, and cyclophosphamide), phenacetin was negative by both the topical and oral routes. Melphalan and cyclophosphamide are, respectively, direct and indirect DNA alkylating agents and topical administration of both caused equivocal responses. With the exception of clofibrate, Tg.AC mice did not exhibit tumor responses to the rodent carcinogens that were putative human noncarcinogens, (di(2-ethylhexyl) phthalate, methapyraline HCl, phenobarbital Na, reserpine, sulfamethoxazole or WY-14643, or the nongenotoxic, noncarcinogen, sulfisoxazole) regardless of route of administration. Based on the observed responses in these studies, it was concluded by the AWG that the Tg.AC model was not overly sensitive and possesses utility as an adjunct to the battery of toxicity studies used to establish human carcinogenic risk.
Assuntos
Testes de Carcinogenicidade/métodos , Carcinógenos/toxicidade , Genes ras , Papiloma/induzido quimicamente , Neoplasias Cutâneas/induzido quimicamente , Alternativas aos Testes com Animais , Animais , Modelos Animais de Doenças , Feminino , Genótipo , Masculino , Camundongos , Camundongos Transgênicos , Papiloma/genética , Papiloma/patologia , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Neoplasias Cutâneas/genética , Neoplasias Cutâneas/patologiaRESUMO
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by accumulation of amyloid plaques and neurofibrillary tangles in the brain. The major components of plaque, beta-amyloid peptides (Abetas), are produced from amyloid precursor protein (APP) by the activity of beta- and gamma-secretases. beta-secretase activity cleaves APP to define the N-terminus of the Abeta1-x peptides and, therefore, has been a long- sought therapeutic target for treatment of AD. The gene encoding a beta-secretase for beta-site APP cleaving enzyme (BACE) was identified recently. However, it was not known whether BACE was the primary beta-secretase in mammalian brain nor whether inhibition of beta-secretase might have effects in mammals that would preclude its utility as a therapeutic target. In the work described herein, we generated two lines of BACE knockout mice and characterized them for pathology, beta-secretase activity and Abeta production. These mice appeared to develop normally and showed no consistent phenotypic differences from their wild-type littermates, including overall normal tissue morphology and brain histochemistry, normal blood and urine chemistries, normal blood-cell composition, and no overt behavioral and neuromuscular effects. Brain and primary cortical cultures from BACE knockout mice showed no detectable beta-secretase activity, and primary cortical cultures from BACE knockout mice produced much less Abeta from APP. The findings that BACE is the primary beta-secretase activity in brain and that loss of beta-secretase activity produces no profound phenotypic defects with a concomitant reduction in beta-amyloid peptide clearly indicate that BACE is an excellent therapeutic target for treatment of AD.
Assuntos
Doença de Alzheimer/enzimologia , Peptídeos beta-Amiloides/biossíntese , Precursor de Proteína beta-Amiloide/metabolismo , Ácido Aspártico Endopeptidases/metabolismo , Encéfalo/enzimologia , Doença de Alzheimer/tratamento farmacológico , Secretases da Proteína Precursora do Amiloide , Animais , Ácido Aspártico Endopeptidases/antagonistas & inibidores , Encéfalo/metabolismo , Linhagem Celular , Células Cultivadas , Técnicas de Cultura , Endopeptidases , Inibidores Enzimáticos/uso terapêutico , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos CBA , Camundongos KnockoutRESUMO
The importance of toxicokinetics in the drug development has been identified in the last decade. The main objectives of toxicokinetics in general are to define the drug bioavailability, dose proportionality, gender differences, and species differences in pharmacokinetics and metabolism, from which the target organ toxicity can be predicted and the safety doses in the first human clinical trial can be established. Toxicokinetic studies may also serve as a tool for the toxicologic pathologist in understanding models used for predicting and assessing drug-related toxic response. Toxicokinetics/toxicodynamics are critical to investigating the toxicological mechanism and understanding the comparative toxicity between animals and humans. This report presents an overview of the application of toxicokinetics and its impact in the drug development of PNU-101017, a drug candidate for the treatment of anxioety. Serial specifically designed toxicokinetic studies identified a steep dose-response relationship between the clinical signs and PNU-101017 serum or CSF concentrations, characterized the centrally mediated respiratory depression as the toxicity leading to the lethality, and demonstrated marked species differences in the sensitivity to the toxic effects. These findings lead to a termination of PNU-101017 development due to the safety concern in humans.
Assuntos
Ansiolíticos/farmacocinética , Ansiolíticos/toxicidade , Agonistas GABAérgicos/farmacocinética , Agonistas GABAérgicos/toxicidade , Quinolinas/farmacocinética , Quinolinas/toxicidade , Animais , Ligação Proteica , Distribuição TecidualRESUMO
Delavirdine mesylate (U-90152T) is a highly specific nonnucleoside HIV-1 reverse transcriptase inhibitor currently under development for the treatment of AIDS. The excretion, disposition, brain penetration, and metabolism of delavirdine were investigated in CD-1 mice after oral administration of [14C]delavirdine mesylate at single doses of 10 and/or 250 mg/kg and multiple doses of 200 mg/kg/day. Studies were conducted with 14C-carboxamide and 2-14C-pyridine labels, as well as 13C3-labeled drug to facilitate metabolite identification. Excretion was dose dependent with 57-70% of the radioactivity eliminated in feces and 25-36% in urine. Pharmacokinetic analyses of delavirdine and its N-desisopropyl metabolite (desalkyl delavirdine) in plasma showed that delavirdine was absorbed and metabolized rapidly, that it constituted a minor component in circulation, that its pharmacokinetics were nonlinear, and that its metabolism to desalkyl delavirdine was capacity limited or inhibitable. Delavirdine did not significantly cross the blood-brain barrier; however, its N-isopropylpyridinepiperazine metabolite arising from amide bond cleavage-was present in brain at levels 2- to 3-fold higher than in plasma. The metabolism of delavirdine in the mouse was extensive and involved amide bond cleavage, N-desalkylation, hydroxylation at the C-6' position of the pyridine ring, and pyridine ring-cleavage as determined by MS and/or 1H and 13C NMR spectroscopies. N-desalkylation and amide bond cleavage were the primary metabolic pathways at low drug doses and, as the biotransformation of delavirdine to desalkyl delavirdine reached saturation or inhibition, amide bond cleavage became the predominant pathway at higher doses and after multiple doses.
Assuntos
Fármacos Anti-HIV/farmacocinética , HIV-1/enzimologia , Indóis/farmacocinética , Piperazinas/farmacocinética , Inibidores da Transcriptase Reversa/farmacocinética , Animais , Biotransformação , Cromatografia Líquida de Alta Pressão , Delavirdina , Fezes/química , Feminino , Hidrólise , Espectroscopia de Ressonância Magnética , Masculino , Espectrometria de Massas , Camundongos , Espectrofotometria Ultravioleta , Distribuição TecidualRESUMO
Quinolone antibiotics are extensively utilized in antimicrobial chemotherapy. However, quinolone treatment in developing adolescents of several animal species is associated with acute arthropathy of the weight-bearing joints. Although arthropathy has rarely been observed following quinolone therapy in man, the toxicity observed in immature animals has resulted in restricted use of these drugs in children and pregnant women. Therefore, identification of novel quinolone antibiotics which do not cause arthropathy is highly desirable. This task would be facilitated by a bioassay of cartilage toxicity which utilizes small quantities of test material and has greater sensitivity than current toxicity assays. This study evaluated the utility of neonatal mice as a potential bioassay of quinolone-induced joint toxicity. Seven-day-old CF-1 mice (8-10/dose group) were treated subcutaneously with either pipemidic acid (50, 400, or 3150 mg/kg/day) for 7 or 14 days or ciprofloxacin (50 or 200 mg/kg/day) for 5, 7, or 14 days. Lameness was observed only after high-dose pipemidic acid treatment for 2-7 days. Histopathological assessment of the principal weight-bearing joints (knee, elbow, and multiple articulations in the fore- and hind-feet) revealed a lesion characterized by chondrocyte loss, matrix degeneration, and erosion of the articular cartilage in mice treated with pipemidic acid at 400 or 3150 mg/kg/day for 7 days or ciprofloxacin at 200 mg/kg/day for 5 days. Mice treated for 14 days with 400 mg/kg/day pipemidic acid demonstrated a lower incidence of lesions than mice treated for 7 days, suggesting the potential for reversibility during ongoing treatment. The results suggest that neonatal mice are sensitive to quinolone-induced arthropathy, but less so than previously reported for adolescent dogs. It is concluded that the neonatal mouse may be an appropriate screening system for identifying novel quinolones devoid of cartilage toxicity; however, follow-up studies with select compounds in a more sensitive species, such as the dog, are encouraged.
Assuntos
Animais Recém-Nascidos/fisiologia , Anti-Infecciosos/toxicidade , Cartilagem Articular/patologia , Ciprofloxacina/toxicidade , Artropatias/induzido quimicamente , Ácido Pipemídico/toxicidade , Quinolonas/toxicidade , Animais , Peso Corporal/efeitos dos fármacos , Feminino , Pé/patologia , Artropatias/patologia , Camundongos , GravidezRESUMO
The non-benzodiazepine anxiolytic, panadiplon, was discontinued from clinical development due to evidence of hepatic toxicity in human volunteers that was not predicted by rat or monkey preclinical development studies. The present study was conducted to examine potential toxicity in the rabbit. Three groups of female rabbits were administered vehicle, 10 mg/kg per day or 20 mg/kg per day of panadiplon by oral gavage for 14 days. Animals in the 20 mg/kg group lost weight, and 6/10 developed a profound lethargy. Hepatic toxicity was observed in treated animals, evidenced by dose- and time-related increases in serum transaminase activities, gross hepatic lesions and multifocal centrilobular necrosis. Hepatic microvesicular steatosis was evident in treated animals; lipid analysis revealed a 123% increase in hepatic triglyceride. A time-dependent increase in serum triglyceride levels was observed in the high-dose group beginning on day 4. Hepatic glycogen was reduced, and histochemical examination revealed the reduction to be heterogeneous across the lobule with some areas showing a complete absence of glycogen. One rabbit in each drug-treated group showed mild hypoglycemia at day 12, and 4/10 rabbits in the high-dose group showed hyperglycemia at days 12-14. We conclude that panadiplon produced a microvesicular steatosis and hepatic toxicity in the rabbit. The observed toxicity resembled a Reye's syndrome-like toxicity produced by a variety of mitochondrial fatty acid oxidation inhibitors.
Assuntos
Ansiolíticos/toxicidade , Fígado Gorduroso/induzido quimicamente , Oxidiazóis/toxicidade , Quinoxalinas/toxicidade , Animais , DNA/metabolismo , Fígado Gorduroso/sangue , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Feminino , Glicogênio Hepático/metabolismo , Proteínas/metabolismo , Coelhos , Estatística como AssuntoRESUMO
The in vivo genotoxic effects of the antitumor antibiotic, (+)-CC-1065, and its unnatural enantiomer, (-)-CC-1065, were investigated in two mouse models. These two compounds alkylate AT-rich regions of double stranded DNA with distinct sequence selectivities. (+)-CC-1065 dose-dependently increased the chromosomal aberration frequency in bone marrow cells of CD-1 mice from 1.2 +/- 0.8% in vehicle control animals to 5.0 +/- 1.2%, 11.4 +/- 3.9%, and 20.6 +/- 2.3% 24 hours following single intravenous doses of 2, 4, and 8 micrograms/kg, respectively. (-)-CC-1065 was significantly less potent with a maximal response at 8 micrograms/kg approximately one-third of that observed for (+)-CC-1065. (+)-CC-1065 induced a significant (P < or = 0.05), three-fold increase in the number of lung tumors/mouse in strain A/J mice from 0.27 +/- 0.15 for vehicle control animals to 0.83 +/- 0.15 24 weeks following a single intravenous dose of 8 micrograms/kg. This effect was paralleled by corresponding threefold increases in the percentage of mice with tumors and the percentage of mice with multiple tumors, compared to vehicle controls. (-)-CC-1065 at 8 micrograms/kg induced 0.67 +/- 0.15 tumors/mouse and resulted in slightly smaller increases in the tumor incidence and multiple tumor incidence, compared to (+)-CC-1065. The above results demonstrate that single intravenous doses of (+)- CC-1065 and (-)-CC-1065 which cause chromosomal damage in CD-1 mice also induce an increased incidence of lung tumors in A/J mice.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Antibióticos Antineoplásicos/toxicidade , Indóis , Leucomicinas/toxicidade , Neoplasias Pulmonares/induzido quimicamente , Mutagênicos/toxicidade , Animais , Medula Óssea/efeitos dos fármacos , Medula Óssea/ultraestrutura , Testes de Carcinogenicidade , Aberrações Cromossômicas , Duocarmicinas , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/ultraestrutura , Camundongos , Camundongos Endogâmicos A , EstereoisomerismoRESUMO
Bropirimine is a biological response modifier (BRM) with potential antineoplastic and antiviral indications. Recent results have documented the negative findings in the Ames Salmonella assay, the in vitro UDS assay and the mouse lymphoma TK+/- assay as well as positive findings in the in vitro cytogenetic assay in CHO cells. Extensive mechanistic studies failed to establish the reason for positive findings in the in vitro cytogenetic assays. The data reported here cast doubt on the relevance of the in vitro cytogenetic results and suggest limited in vivo genotoxic potential. At doses as high as 150 mg/kg (i.p.) and 6.73 g/kg (p.o.), no evidence of chromosome aberration induction was observed in rat bone marrow cytogenetic assays. Consistent with these data, plasma and bone marrow tissue levels in similarly treated animals were well below those required for activity in the in vitro chromosome aberration assays. Positive results were obtained in the mouse micronucleus assay. However, the significance of these findings may be explained by markedly different pathways of metabolism in that species as compared to the rat. Hence, the findings in the mouse are of questionable relevance to human risk assessment. Exposure of humans to bropirimine, under therapeutically acceptable regimens is unlikely to constitute a genotoxic health hazard.
Assuntos
Antineoplásicos/toxicidade , Aberrações Cromossômicas , Citosina/análogos & derivados , Testes para Micronúcleos , Mutagênicos , Animais , Medula Óssea/efeitos dos fármacos , Células da Medula Óssea , Cromatografia Líquida de Alta Pressão , Ciclofosfamida/farmacologia , Citosina/sangue , Citosina/toxicidade , Citosina/urina , Feminino , Fígado/citologia , Fígado/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos , Testes de Mutagenicidade , Ratos , Ratos EndogâmicosRESUMO
The number, size, and histological pattern of lung tumors collected 6 months after being induced in C3HeB/FeJ mice by ethylnitrosourea (ENU) treatment on one of days 13-19 of gestation, or days 5, 15, or 35 after birth, or as 9-month-old adults was investigated. The number of lung tumors induced increased when treatment occurred between days 13-16 and then decreased when treatment occurred on days 17-19 of gestation. There was a marked increase in lung tumor numbers induced on day 5 after birth, which decreased to much lower levels on days 15 and 35 after birth and in the treated adult mice. The size of lung tumors was greater in males than females in all groups and decreased as the age at the time of ENU treatment increased. A greater proportion (60-65%) of papillary tumors were induced following treatment on days 13-16 whereas, with one exception, alveolar lining tumors were the predominant histological type when treatment occurred after day 16. When treatment occurred on day 5 after birth, papillary tumors were once again the predominant type (66%) induced. The changes in tumor numbers induced and in the histological type of tumor induced occur at periods when major shifts in the histological development of the lung occur. The results indicate that the histological type of tumor induced by ENU treatment is developmentally regulated and suggests that alveolar lining and papillary tumors behave as two separate populations of tumors.
Assuntos
Neoplasias Pulmonares/patologia , Pulmão/crescimento & desenvolvimento , Animais , Etilnitrosoureia , Feminino , Pulmão/embriologia , Neoplasias Pulmonares/induzido quimicamente , Neoplasias Pulmonares/embriologia , Masculino , Camundongos , Camundongos Endogâmicos C3H , Gravidez , Efeitos Tardios da Exposição Pré-NatalRESUMO
Bropirimine is an immunomodulator with experimental antiviral and antitumor activities. This pyrimidinone has been found to be embryolethal at doses (200 and 400 mg/kg) that produce only transient maternal toxicity, when administered to pregnant Upj:TUC(SD)spf rats on specific days of gestation. Serum analyses carried out in previous studies have shown marked decreases in progesterone levels in the 24 hr following bropirimine administration. In the present study, each of four groups of 5 bred rats and four groups of 10 bred rats was given bropirimine (gastric intubation) on Day 10 of gestation. Also, on Day 10 of gestation, progesterone (0.25, 0.50, or 1.00 mg/rat) was administered (im) twice (12-hr interval) a day to three of the groups of 5 dams each that had received bropirimine. In addition, three of the groups of 10 dams each received progesterone (0.25, 0.50, or 1.00 mg/rat) twice a day on Days 10-19 of gestation. Another group of 5 dams received progesterone only (0.50 mg/rat, b.i.d.) on Day 10 while a group of 10 dams received this same dose of progesterone on Days 10-19 of gestation. The groups containing 5 dams each were killed 24 hr postdosing while the groups containing 10 dams each were killed on Day 20 of gestation. The uteri were removed from the dams and examined. Administration of bropirimine alone resulted in the death of 100% of the embryos, at both the 24-hr and the Gestation Day 20 terminations. Exogenous administration of progesterone protected against bropirimine-mediated embryolethality; however, maternal effects were not alleviated. Thus, it appears likely that the embryolethality of bropirimine is the result of interruption of progesterone release from, or synthesis by, the corpora lutea, rather than direct toxicity toward the embryo, or lethal defects during organogenesis (terata).
Assuntos
Adjuvantes Imunológicos/toxicidade , Antineoplásicos/toxicidade , Citosina/análogos & derivados , Embrião de Mamíferos/efeitos dos fármacos , Progesterona/farmacologia , Animais , Peso Corporal/efeitos dos fármacos , Citosina/toxicidade , Feminino , Reabsorção do Feto/induzido quimicamente , Ovário/efeitos dos fármacos , Progesterona/sangue , Ratos , Ratos EndogâmicosRESUMO
The aim of this study was to determine the mechanism by which bropirimine exerts its developmental toxicity. This drug is an immunomodulator and interferon inducer with antiviral and antitumor activities in experimental models. Timed-pregnant Upj:TUC(SD)spf (Sprague-Dawley) rats were given a single oral (gastric intubation) dose of bropirimine at 200 or 400 mg/kg (doses as high as 100 mg/kg/day have been employed in human cancer trials) on days 5, 6, 7, 8, 9, 10, 11, or 12 of gestation and in a second experiment on day 12, 13, 14, 15, 16, 17, 18, or 19 of gestation. The dams were killed 24 hours after dosing and their uterine contents examined. In a third experiment, bropirimine (400 mg/kg) was administered on day 4 of gestation and the uteri of different groups were examined on day 8, 9, 10, 11, or 12 of gestation. Serum progesterone levels were measured at sacrifice. In the first two experiments a battery of hematologic/clinical chemistry assays also were performed. In all three experiments, bropirimine-related maternal toxicity was observed; such toxicity was characterized by significant decreases in weight gain, relative to the concurrent vehicle controls, as well as significant differences in several blood parameters including platelets, white blood cells, alanine aminotransferase, and aspartate transaminase. In the first experiment, bropirimine treatment on day 11, but not day 12, resulted in significant decreases in the mean number of live embryos per litter. In the second experiment, significant decreases in the number of live fetuses per litter occurred 24 hours after dosing on day 18 (200 and 400 mg/kg groups) or day 19 (400 mg/kg group). Decreases in serum progesterone appeared to correlate well with the embryolethal effects seen after treatment between days 6 and 11 of gestation, but not with the fetal lethality seen when treatment was given on day 17 or 18. The decreases in serum progesterone levels found most likely were the result of a luteolytic effect, although it is unknown if bropirimine has a direct or indirect effect on the corpora lutea. In the third experiment, bropirimine treatment on day 4 of gestation resulted in only slight preimplantational losses, but significant decreases were found in mean number of live embryos per litter after day 9. Uterine decidual necrosis has been observed in the first experiment where bropirimine was given on day 11; however, treatment on day 4 resulted in an apparent decrease in decidual development but not necrosis.
Assuntos
Citosina/análogos & derivados , Desenvolvimento Embrionário e Fetal/efeitos dos fármacos , Troca Materno-Fetal , Teratogênicos , Doenças Uterinas/patologia , Animais , Citosina/toxicidade , Feminino , Idade Gestacional , Necrose , Gravidez , Progesterona/sangue , Ratos , Ratos Endogâmicos , Doenças Uterinas/induzido quimicamenteRESUMO
Pregnant C3HeB/FeJ mice were treated with ethylnitrosourea (ENU) on one of gestation Days 10, 13, or 15 to determine if ENU treatment at different stages of gestation would result in morphological or quantitative differences in liver tumors induced in the offspring. Liver tumors were counted and measured 6 mo after treatment with ENU. Foci of cellular alteration were identified histologically and counted. Liver tumor number and foci of cellular alteration increased as a function of increasing dose and age at the time of ENU treatment. An inverse relationship between age at the time of treatment and the size of liver tumors was found. The mean tumor volume of male mice exposed on Day 10 of gestation was 123-fold larger than for spontaneous tumors observed in controls. The differences between mean liver tumor volume in mice which had been exposed to ENU on Days 10, 13, or 15 of gestation appeared to be associated with the exponential growth of the fetus during this period of gestation. Unique, large, multinodular foci of cellular alteration were found in mice treated on Day 10 of gestation. The relationship between the stage of gestation and the size of chemically induced liver tumors in these mice is similar to previous observations with transplacentally induced lung tumors in C3HeB/FeJ mice. This indicates that developmentally regulated cell proliferation occurring at the time of carcinogen exposure may affect the subsequent extent of tumor development in both the liver and lung. Therefore, cells transformed during early development may result in tumors that pose a greater biological hazard than those transformed in later development.
Assuntos
Etilnitrosoureia , Neoplasias Hepáticas/induzido quimicamente , Fígado/embriologia , Animais , Feminino , Idade Gestacional , Fígado/citologia , Neoplasias Hepáticas/patologia , Troca Materno-Fetal , Camundongos , Camundongos Endogâmicos C3H , GravidezRESUMO
Pregnant C3HeB/FeJ mice were treated with ethylnitrosourea (ENU) on one of gestation Days 10, 13, or 15 to determine if ENU treatment at different stages of gestation would result in qualitative or quantitative differences in lung tumors induced in the offspring. Lung tumors were counted and measured 6 mo after treatment with ENU. Offspring of mice treated with ENU on Day 10 of gestation had a small increase in lung tumors while those treated on gestation Day 13 or 15 had significantly more tumors than controls and 6- to 8-fold more tumors than the treated mothers. An inverse relationship between age at the time of treatment and lung tumor size was found. The mean lung tumor volume of mice exposed on Day 10 of gestation was 167-fold larger than that of mice exposed to ENU as adults. The difference between mean lung tumor volume in mice which had been exposed to ENU on Day 10, 13, or 15 of gestation appeared to be associated with the exponential growth of the fetus during this period of gestation. Lung tumors induced on Days 10 and 13 of gestation were irregular in contour and were multinodular. Sixty-five to 85% of the lung tumors in offspring treated during gestation versus 20% in mice treated as adults had a papillary morphology. These differences in tumor size and morphology indicate that cells transformed during early development may pose a greater biological hazard than cells transformed in older animals.
Assuntos
Feto/efeitos dos fármacos , Neoplasias Pulmonares/patologia , Animais , Peso Corporal , Etilnitrosoureia , Feminino , Feto/patologia , Idade Gestacional , Pulmão/patologia , Neoplasias Pulmonares/induzido quimicamente , Masculino , Camundongos , GravidezRESUMO
We have confirmed previous results which suggest that transplacental exposure of fetal mice to carcinogens does not cause an increase in tumor incidence as they mature unless treatment occurs after midorganogenesis. In C3HeB/FeJ mice we found a negligible increase in tumor incidence and multiplicity following transplacental exposure to the direct-acting carcinogen ethylnitrosourea (ENU) on gestation day 10, but significant increases in lung and liver tumor incidence following exposure on days 13 or 15 or in adults. To explore the possibility that this observed difference is due to differences in the biodistribution of the carcinogen or its interaction with cellular macromolecules, the level of covalent binding between ENU and fetal and maternal DNA following an i.p. injection of a dose of 50 mg/kg of tritium-labeled ENU was measured 30 min after its injection into pregnant females on days 10, 13, and 15 of gestation. The DNA from fetal and maternal lung, liver, and brain was isolated and the amount of covalent binding estimated from the dpm/mg DNA recovered. Samples of DNA were hydrolyzed and chromatographed to determine that the bound tritium was associated with ENU-DNA adducts and not as a product of DNA synthesis. The level of binding of ENU to fetal DNA was equivalent at all gestation days studied but was significantly less than maternal tissues. Binding to the DNA of maternal liver was 4-fold greater than to fetal DNA while maternal lung and brain DNA were bound at intermediate levels. We conclude that the lack of carcinogenic response to ENU documented here, in fetal mice exposed early in gestation (day 10), is not due to differences in ENU binding to fetal DNA during development.
Assuntos
Dano ao DNA , Etilnitrosoureia , Neoplasias Experimentais/induzido quimicamente , Adenoma/induzido quimicamente , Animais , DNA/efeitos dos fármacos , Etilnitrosoureia/metabolismo , Feminino , Idade Gestacional , Neoplasias Hepáticas/induzido quimicamente , Neoplasias Pulmonares/induzido quimicamente , Masculino , Troca Materno-Fetal , Camundongos , Gravidez , Distribuição TecidualRESUMO
This study was undertaken to compare the ability of a series of compounds from different chemical classes to induce lung tumors in strain A/J mice after either ip or po administration. 3-Methylcholanthrene, benzo(a)pyrene, urethan, diethylnitrosamine, ethylnitrosourea, and dimethylhydrazine induced a significant (p less than 0.05; t test) increase in the lung tumor response when given both ip and po. 2,4-Dinitrotoluene, 2,6-dinitrotoluene, and a 2:1 mixture of 2,4-dinitrotoluene and 2,6-dinitrotoluene were inactive by both routes of administration and at all dose levels. The lung tumor response to all doses of 3-methylcholanthrene and benzo(a)pyrene, the highest dose of diethylnitrosamine, and the middle doses of both ethylnitrosourea and dimethylhydrazine varied as a function of the route of administration. This finding was most evident for the polycyclic hydrocarbons, e.g., the average number of lung tumors per mouse in animals that received the middle dose of 3-methylcholanthrene or the highest dose of benzo(a)pyrene by the ip route exceeded that by the po route by factors of 12 and 13, respectively. Tissue distribution and elimination studies were conducted in an effort to determine the basis for the observed difference in lung tumor response to 3-methylcholanthrene after ip or po administration. The data indicated that 3-methylcholanthrene persists for longer periods in the animals when given ip, thus potentially providing an extended carcinogenic stimulus. Extrapulmonary lesions observed at a higher than normal frequency at necropsy included peritoneal sarcomas (in 3-methylcholanthrene-treated mice), and both squamous cell carcinomas of the forestomach and abnormal lesions of the liver (in diethylnitrosamine-treated mice).