15-16-dihydro-11-methylcyclopenta(a)phenanthren-17-one and Skin-Neoplasms

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.

Topics: Animals; Breast Neoplasms; Carcinogens; Cell Line; DNA; DNA Adducts; Epidermis; Female; Gonanes; Humans; Methylation; Mice; Mice, Inbred SENCAR; Skin Neoplasms; Structure-Activity Relationship; Tetradecanoylphorbol Acetate; Time Factors; Tumor Cells, Cultured

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.

Topics: Animals; Gonanes; Keratinocytes; Male; Mice; Mice, Inbred Strains; Mice, Nude; Micronucleus Tests; Papilloma; Skin Neoplasms

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.

Topics: Animals; Carcinogens; Cocarcinogenesis; DNA; Gonanes; Mice; Mice, Inbred Strains; Neoplasms, Experimental; Ornithine Decarboxylase; Phorbol Esters; Skin; Skin Neoplasms; Species Specificity; Time Factors

Eight main metabolites of the parent carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthrene-17-one (I) were assayed for their ability to initiate skin tumours in T.O. mice after topical application in two-stage experiments with croton oil used as the promoter. All were less active than 1 with the exception of the trans-3,4-dihydro-3,4-diol which was more than ten times as active. This diol is therefore confirmed as the proximate carcinogen, a conclusion reached previously on different evidence.

Topics: Animals; Carcinogens; Gonanes; Mice; Neoplasms, Experimental; Skin Neoplasms

Microsomal metabolites of the carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one (Structure I) were separated by high-pressure liquid chromatography, and their structures were established on the basis of their ultraviolet and mass spectra, together with considerations of their general chemical properties. This was assisted by comparisons with metabolites formed in the same way from the synthetic 15-hydroxy (Structure III), 16-hydroxy (Structure II), and 11-hydroxymethyl (Structure IV) derivatives, which themselves occur as metabolites of Structural I. Products derived from attack at the two benzo-ring double bonds occurred, but no K-region products were found. Only metabolites having a non-bay region 3,4-dihydrodiol system were mutagenic and bound to DNA after in vitro microsomal activation, and it was concluded that the 3,4-dihydro-3,4-diol (Metabolite e) was the main form and that the 3,4-diols of the monools (Structure II to IV) were minor proximate forms of this carcinogen. In a two-stage experiment, the synthetic 16-ol (Structure II) was shown to be almost as carcinogenic as was Structure I itself in mice; the 15-ol (Structure III) and 11-hydroxymethyl derivative (Structure IV) were much less active. The same order was also observed in the mutagenicity of these compounds in the Ames test.

Topics: Animals; Biotransformation; Carcinogens; Female; Gonanes; Male; Microsomes, Liver; Mutagenicity Tests; Mutagens; Neoplasms, Experimental; Rats; Skin Neoplasms; Spectrophotometry, Ultraviolet; Structure-Activity Relationship

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.

Topics: Animals; Benzopyrenes; Dose-Response Relationship, Drug; Female; Gonanes; Male; Mammary Neoplasms, Experimental; Mice; Rats; Skin Neoplasms