RESUMEN
The increase in carcinogenicity of polycyclic aromatic compounds following bay-region methyl group substitution involves a steric component: increasing the size of the alkyl substituent decreases the carcinogenic activity of the compound. To determine whether there is also an electronic component to this effect, we synthesized a bay-region 11-trifluoromethyl analogue of 15,16-dihydrocyclopenta[alpha]phenanthren-17-one which is sterically similar but electronically very different from the 11-methyl derivative. This trifluoromethyl derivative bound to DNA in cultures of the human mammary carcinoma cell line MCF-7 to a much lower extent than the methyl-substituted compound. The trifluoromethyl derivative did not form detectable levels of DNA adducts in the epidermis of Sencar mice and was inactive as an initiator after promotion with 12-O-tetradecanoylphorbol-13-acetate for 20 weeks. In contrast, the 11-methyl derivative formed > 3 pmol adducts/mg DNA and initiated eight papillomas per mouse. These data indicate that both the steric configuration and the electronic nature of a bay-region substituent are important in determining the overall effect of the substituent on the biological activity of the molecule.
Asunto(s)
Carcinógenos/metabolismo , Carcinógenos/toxicidad , Aductos de ADN/metabolismo , ADN/metabolismo , Gonanos/metabolismo , Gonanos/toxicidad , Neoplasias Cutáneas/inducido químicamente , Animales , Neoplasias de la Mama , Línea Celular , Epidermis/efectos de los fármacos , Epidermis/metabolismo , Epidermis/patología , Femenino , Humanos , Metilación , Ratones , Ratones Endogámicos SENCAR , Neoplasias Cutáneas/metabolismo , Neoplasias Cutáneas/patología , Relación Estructura-Actividad , Acetato de Tetradecanoilforbol/toxicidad , Factores de Tiempo , Células Tumorales CultivadasRESUMEN
The present study was undertaken in order to rationalise the apparent biological inactivity of 15,16-dihydro-6-methylcyclopenta[a]phenanthren-17- one (4) when other methyl isomers of 15,16-dihydrocyclopenta[a]phenanthren- -17-one, e.g. the 11-methyl derivative (2), display appreciable tumorigenicity. In vitro metabolism of the 6-methyl-ketone-17-one (4) demonstrated that its principal metabolite was the 3,4-dihydro-3,4-diol (3,4-dihydroxy-6-methyl-3,4,15,16- tetrahydrocyclopenta[a]phenanthren-17-one) (5) which, in the case of the active 11-methyl derivative, is the proximate genotoxin. Thus the inactivity of this 6-methyl-17-ketone cannot be ascribed to lack of formation of the 3,4-dihydro-3,4-diol, the precursor of the 3,4-diol-1,2-epoxides (the ultimate mutagens in this series). However, the 6-methyl-3,4-dihydro-3,4-diol exists in a pseudo-diaxial rather than a pseudo-diequatorial conformation characteristic of the 3,4-dihydro-3,4-diols of the other members of the series. It is therefore suggested that a diequatorial conformation in the dihydrodiol is essential to the metabolic activation of the cyclopenta[a]phenanthren-17-ones.
Asunto(s)
Gonanos/metabolismo , Gonanos/toxicidad , Mutágenos/metabolismo , Mutágenos/toxicidad , Animales , Biotransformación , Técnicas In Vitro , Masculino , Microsomas Hepáticos/metabolismo , Conformación Molecular , Ratas , Ratas Wistar , Relación Estructura-ActividadRESUMEN
A series of four 11-alkoxy cyclopenta[a]phenanthren-17-ones, ranging from the methoxy to the butoxy derivative, has been synthesised in order to investigate the effect of the size of the 11-substituent on the mutagenicity and ability of these compounds to induce hepatic CYP1 activity in rats. The latter was monitored by using as diagnostic probes methoxy and ethoxy-resorufin, and immunologically in Western blots employing anti-CYP1A1 antibodies. All four members of the series induced both CYP1A1 and CYP1A2 activities and apoprotein levels, but the methoxy- and ethoxy-CPP-17-ones were clearly the most potent. Of the four isomers, only 11-methoxy-CPP-17-one displaced 3H-TCDD from the cytosolic Ah receptor. Similarly only 11-methoxy-CPP-17-one elicited a positive mutagenic response in the Ames test in the presence of an Aroclor 1254-induced activation system. The relevance of these findings to the carcinogenicity of these compounds in the mouse skin painting model is discussed.
Asunto(s)
Sistema Enzimático del Citocromo P-450/efectos de los fármacos , Gonanos/toxicidad , Hígado/metabolismo , Mutágenos/toxicidad , Fenantrenos/toxicidad , Compuestos Policíclicos/metabolismo , Animales , Citocromo P-450 CYP1A2 , Sistema Enzimático del Citocromo P-450/inmunología , Sistema Enzimático del Citocromo P-450/metabolismo , Hígado/efectos de los fármacos , Hígado/enzimología , Masculino , Pruebas de Mutagenicidad , Oxidorreductasas/efectos de los fármacos , Oxidorreductasas/metabolismo , Ratas , Ratas Wistar , Salmonella/efectos de los fármacos , Salmonella/genética , Relación Estructura-ActividadRESUMEN
A strongly electronegative, bay-region analogue of the potent carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one, namely 15,16-dihydro-11-trifluoromethylcyclopenta[a]phenanthren-17-one, is mutagenic to Salmonella typhimurium TA100. Also it is metabolized at the 1,2- and 3,4-positions in the A-ring as well as C-15 in the D-ring to give 3,4-dihydroxy-3,4,15,16-tetrahydro-11-trifluoromethyl- cyclopenta[a]phenanthren-17-one as the only mutagenic metabolite. In these respects its behaviour is closely similar to that of the 11-methyl compound, suggesting that the electronic nature of the bay-region substituent is rather less critical than its spatial configuration in influencing metabolism to genotoxic intermediates. It remains to be seen, however, whether the trifluoromethyl compound is also a carcinogen.
Asunto(s)
Carcinógenos/farmacocinética , Gonanos/farmacocinética , Mutágenos/farmacocinética , Animales , Biotransformación , Carcinógenos/toxicidad , Gonanos/toxicidad , Espectrometría de Masas , Microsomas Hepáticos/metabolismo , Pruebas de Mutagenicidad , Mutágenos/toxicidad , Ratas , Espectrofotometría UltravioletaRESUMEN
The in vitro metabolism and activation to mutagens of 15,16-dihydrocyclopenta[a]phenanthren-17-one (CPP-17-one) were investigated using hepatic preparations from rats pretreated with prototype inducers of the cytochrome P-450-dependent mixed-function oxidases. Aroclor 1254-induced microsomes were the most effective metabolisers of this compound, the major metabolites being oxidation products of the bay region A ring. To a lesser extent hydroxylation of the non-aromatic D ring occurred, the products being the 15- and 16-hydroxyderivatives. Oxidation of the A ring was also achieved with microsomes from benzo[a]pyrene-treated rats but not with those from rats treated with clofibrate, phenobarbitone, isoniazid, dexamethasone and CPP-17-one itself, where the metabolites were primarily the oxidation products of the D ring. When CPP-17-one was used as a promutagen in the Ames test, only microsomes from Aroclor 1254-treated rats could elicit a positive mutagenic response. When 3,4-dihydrodihydroxy-CPP-17-one, the precursor of the ultimate mutagen, was used as the promutagen, a positive response was observed with microsomes from Aroclor 1254- and benzo[a]pyrene-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Sistema Enzimático del Citocromo P-450/metabolismo , Gonanos/metabolismo , Microsomas Hepáticos/metabolismo , Animales , Arocloros/farmacología , Biotransformación/efectos de los fármacos , Carcinógenos/toxicidad , Gonanos/toxicidad , Hidroxilación , Técnicas In Vitro , Masculino , Microsomas Hepáticos/efectos de los fármacos , Pruebas de Mutagenicidad , Ratas , Ratas WistarRESUMEN
The most potent carcinogen of the cyclopenta[a]phenanthrene series, 15, 16-dihydro-11-methylcyclopenta[a]phenanthren-17-one and its non-carcinogenic, unmethylated parent compound, were compared for their abilities to induce micronuclei in epidermal keratinocytes after application onto the dorsal skin of Skh/HR-1 hairless mice. Although both substances were shown to be mutagenic in vitro, only the 11-methyl derivative has been proven to initiate cancer in TO and Sencar mouse strains. In the present study, only the 11-methyl derivative was active as a cancer initiator in Skh/HR-1 mice. For studying micronucleus induction, a preliminary experiment was conducted to establish doses of both chemicals that allowed cell survival. Subsequently, micronucleus induction in epidermal keratinocytes was shown to agree with the cancer-initiating potential of the two compounds. Only the carcinogenic derivative induced a statistically significant increase in micronuclei, over the range 10-100 nmol. This is considerably lower than the dose of approximately 1600 nmol commonly used to initiate skin cancer in mice, but is comparable to the active dose range for skin micronucleus induction by benzo[a]pyrene, a chemical of equivalent carcinogenic potency.
Asunto(s)
Gonanos/toxicidad , Papiloma/inducido químicamente , Neoplasias Cutáneas/inducido químicamente , Animales , Queratinocitos/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos , Ratones Desnudos , Pruebas de MicronúcleosRESUMEN
Pleural implant experiments using Sprague-Dawley rats have shown that those injected with the carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenenthren-17-one (11-methyl-17-ketone) intraperitoneally followed by silica fibres intrapleurally develop mesotheliomas. These tumours were histologically similar to those induced by crocidolite alone. The intraperitoneal injection of 11-methyl-17-ketone also induced leukaemia.
Asunto(s)
Mesotelioma/inducido químicamente , Dióxido de Silicio/toxicidad , Adenoma/inducido químicamente , Animales , Carcinógenos/toxicidad , Gonanos/toxicidad , Inyecciones , Inyecciones Intraperitoneales , Leucemia Mieloide/inducido químicamente , Neoplasias Pulmonares/inducido químicamente , Masculino , Papiloma/inducido químicamente , Pleura , Ratas , Ratas EndogámicasRESUMEN
Two newly synthesized cyclopenta[a]phenanthrenes, namely the 1-methyl (VIII) and 7,11-dimethyl (VII) derivatives of the parent ketone 15,16-dihydrocyclopenta[a]phenanthren-17-one (I), have been tested for their capacity to produce skin tumors in mice. The former (VIII) is essentially inactive, whereas the latter (VII) is very potent in both repeated application and two-stage tests. X-ray crystallographic structure analyses have been carried out on seven derivatives of (I), namely its 11-methyl (II), 11,12-dimethyl (III), 11-methoxy (V), 11-ethyl (VI) and 7,11-dimethyl (VII) analogues (carcinogens), the 1-methyl derivative (VIII), and 11,12,15,16-tetrahydro-11-methyl-17-oxocyclopenta[a]phenanthrene (IV) (both non-carcinogens). The detailed molecular structures resulting from these studies have shown the effects of steric interactions and substitutions on the bay-region geometry. The methyl group on C(11) causes distortions of the molecule in the bay region. Out-of-plane distortions in the bay regions of the 11-methyl derivatives (II, III, VII) are greater than for the 11-methoxy or the 11-ethyl derivatives (V, VI). Molecules (except for III and IV) are packed in the crystals with interactions that include C = O...H interactions; this packing is in layers that are nearly parallel to each other. A hydrogen atom of the 11-methyl group appears, from computer modeling, to interact sterically with the hydrogen atom of the bay-region expoxide group in the activated diol-epoxide; this steric interaction may force one conformer of the diol-epoxide to be the predominant form, thereby accounting for the importance of a bay-region methyl group. Further computer modeling has been used to analyze possible modes of interaction of the diol-epoxides of cyclopenta[a]phenanthrenes with DNA.
Asunto(s)
Carcinógenos , Gonanos/toxicidad , Neoplasias Cutáneas/inducido químicamente , Animales , Femenino , Masculino , Ratones , Modelos Moleculares , Conformación Molecular , Relación Estructura-Actividad , Difracción de Rayos XRESUMEN
The proposal that an unobstructed bay region is a prerequisite for tumorigenic activity in cyclopenta[a]phenanthrene-17-ones is not supported by the observation of the tumorigenicity of 15,16-dihydro-1,11-methanocyclopenta[a]phenanthrene-17-one towards the skin of T.O. mice. The title compound is oxidised in vitro by a mixed function oxidase to produce, inter alia, a trans-3,4-dihydrodiol, postulated as the proximate tumorigen. Unequivocal identification of a second metabolite as a trans-1,2-dihydrodiol derivative demonstrates the potential for enzymatic oxidation within the obstructed bay region and supports the proposal that the ultimate tumorigen is a trans-3,4-dihydrodiol-anti-1,2-oxide. This is further substantiated by the chromatographic behaviour of the major hydrocarbon-nucleoside adduct derived from mouse skin treated with the parent compound in vivo. The structures of certain others of the metabolites produced in vitro are also considered.
Asunto(s)
Carcinógenos/metabolismo , Gonanos/metabolismo , Neoplasias Cutáneas/inducido químicamente , Animales , ADN/metabolismo , Femenino , Gonanos/toxicidad , Técnicas In Vitro , Espectroscopía de Resonancia Magnética , Masculino , Espectrometría de Masas , Ratones , Mutágenos , Relación Estructura-ActividadRESUMEN
Comparative X-ray crystallographic structure analyses have been carried out on seven cyclopenta[a]phenanthrenes, namely 15,16-dihydocyclopenta[a]phenanthren-17-one and its 2-, 6- and 12-methyl homologues (non-carcinogens) and the 7-and 11-methyl and 1,11-methano derivatives (carcinogens). All-valence-electron molecular-orbital calculations by the CNDO/2 method, using the crystallographic parameters, have also been executed. Charge distribution and the energies of the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) have been calculated. With one exception all the molecules show only small deviations from planarity, the exception being the strongly carcinogenic 11-methyl-17-ketone in which the bay-region methyl group causes out-of-plane deformation of the benzo rings of 12.5 degrees. Among the other six compounds the two carcinogens are readily differentiated by high angle strain induced by a 7-methyl group or a 1,11-methano bridge. As expected, the HOMO's of these molecules to some extent reflect their ease of chemical oxidation at the 6,7-double bond; biological oxidation is less easy to correlate probably due to spatial restrictions at the active site within the mono-oxygenase.
Asunto(s)
Carcinógenos , Gonanos , Gonanos/toxicidad , Modelos Moleculares , Conformación Molecular , Relación Estructura-Actividad , Difracción de Rayos XRESUMEN
The incidence of skin tumors has been studied in three strains of mice, namely, TO, C57BL, and DBA/2, after treatment with the carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one. After either a single dose followed by croton oil promotion or a continual dose of the carcinogen, tumors were observed in the TO and C57BL strains, with the TO mice having the shorter mean latent period. The DBA/2 mice, however, appeared to be resistant to tumor formation by either treatment. To understand the mechanism of resistance, several criteria have been investigated. Metabolism of the carcinogen was assessed in terms of the total DNA adduct formation and the pattern of individual adducts after separation by high-pressure liquid chromatography, and no major differences between the three strains was found. Similarly, the rates of disappearance of the individual adducts when measured over 14 days posttreatment were not strain specific. Persistent binding of the carcinogen after 2 months was found in all three strains and could be reduced markedly if croton oil was administered throughout this period. The ability of the phorbol esters to cause biochemical changes in both sensitive and resistant strains was indicated by the induction of ornithine decarboxylase in each of the three strains after treatment with either croton oil or its active component, 12-O-tetradecanoylphorbol-13-acetate.
Asunto(s)
Carcinógenos/toxicidad , ADN/metabolismo , Gonanos/toxicidad , Neoplasias Cutáneas/inducido químicamente , Animales , Carcinógenos/metabolismo , Cocarcinogénesis , Gonanos/metabolismo , Ratones , Ratones Endogámicos/metabolismo , Neoplasias Experimentales/inducido químicamente , Ornitina Descarboxilasa/metabolismo , Ésteres del Forbol/farmacología , Piel/metabolismo , Especificidad de la Especie , Factores de TiempoRESUMEN
An experiment is described to investigate whether coadministration of a promoting agent would enhance the carcinogenicity of a repeatedly administered complete carcinogen. Topical application of the strong carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one (I) in toluene containing 1% v/v croton oil is about five times more effective than applications in toluene alone, as judged from the respective mean latent periods. A similar effect is also apparent for benzo[a]pyrene.
Asunto(s)
Carcinógenos/farmacología , Cocarcinogénesis , Animales , Aceite de Crotón/toxicidad , Contaminantes Ambientales/toxicidad , Femenino , Gonanos/toxicidad , Masculino , RatonesRESUMEN
Direct comparison of skin-tumour induction by 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one (I) and by benzo[a]pyrene on mouse skin, both by repeated application or by initiation with a single dose followed by promotion with croton oil, demonstrated that these two carcinogens have similar potency. After repeated application of (I) the mean latent period for skin-tumour induction was linearly related to the logarithm of the dose over a 10-fold dose range. Under these conditions, application of the aryl-hydrocarbon-hydroxylase inhibitor 7,8-benzoflavone together with (I) inhibited tumour induction by about 40%. By contrast, in the 2-stage experiment, little effect on tumour incidence or latent period was observed when this inhibitor was applied with the single initiating dose of (I). Co-administration of the epoxide-hydratase inhibitor 1,1,1-trichloropropene oxide caused enhancement by shortening the latent period. After s.c. injection of (I) into mice, a similar number of tumours was induced on skin remote from the site of injection by promotion with corton oil begun either one week or 6 months after initiation. Gastric instillation of (I) into female rats induced mammary adenocarcinomas.