Biomedical subjects

J DiGiovanni

Publications and source records attributed to J DiGiovanni.

At least 91 records · Page 5Linked to original sources

PubMed1990

Distribution of covalent DNA adducts in mouse epidermal subpopulations after topical application of benzo(a)pyrene and 7,12-dimethylbenz(a)anthracene.

The distribution of benzo(a)pyrene [B(a)P] and 7,12-dimethylbenz(a)anthracene (DMBA):DNA adducts was examined in five different subpopulations of SENCAR mouse epidermal cells separated based on buoyant density in continuous gradients of 61.5% Percoll. Three fractions consisted of primarily basal cells (Fractions 3 to 5), while two less dense fractions (Fractions 1 and 2) consisted of primarily differentiating keratinocytes. The levels of B(a)P and DMBA:DNA adducts were examined at 1 h, 6 h, 24 h, 72 h (except DMBA), and 28 days after a single topical application of an initiating dose. Among the basal cell subpopulations, the level of covalent B(a)P:DNA adducts in Fraction 5 cells was significantly higher (P less than 0.05) than Fractions 3 and 4 at every time point examined. On the other hand, B(a)P:DNA adduct levels in Fraction 5 were only significantly higher than Fraction 2 at 6 h and 72 h and not significantly different from Fraction 1 at any time point. With DMBA, no significant differences were initially observed in the levels of covalent DNA adducts among the various Percoll fractions at 1 h and 6 h after treatment. However, at 24 h and at 28 days. Fraction 5 cells had significantly higher (P less than 0.05) levels of covalent DMBA:DNA adducts than Fractions 1 to 4. To explore whether the observed differences in DNA adduct levels were due to differences in metabolic activation, we examined the levels of covalent adducts among epidermal subpopulations after topical application of (+/-)-anti-benzo(a)pyrene-7,8-diol-9,10-epoxide (anti-BPDE). Interestingly, 3 h after treatment with anti-BPDE, significantly higher (P less than 0.05) levels of binding were found in Fraction 5 compared with Fractions 1 to 4. High-pressure liquid chromatographic analyses of B(a)P and DMBA:DNA adducts 6 h and 24 h after treatment did not show any significant differences in adduct profiles among the various subpopulations. These results demonstrate the presence and persistence of hydrocarbon:DNA adducts in all epidermal subpopulations isolated on continuous Percoll gradients for at least 28 days after treatment. Furthermore, of the three basal cell subpopulations, the most dense cells (Fraction 5) developed the highest DNA adduct levels within 24 h and retained these higher levels over 28 days. Finally, differences in DNA adduct levels among epidermal subpopulations do not appear to result from different metabolic capabilities of the cells. The potential significance of these results is discussed in terms of the process of skin tumor initiation.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1990

Partial characterization of epidermal protein kinase C in mice sensitive or resistant to phorbol ester.

The present study has characterized several aspects of the mouse epidermal protein kinase C (PKC) system and compared phorbol ester-sensitive and -resistant mice. Protein immunoblots of partially purified epidermal PKC preparations from SENCAR and C57BL/6 mice indicated the presence of the gamma-, beta-, and alpha-isozymes of PKC in both strains. Hydroxylapatite chromatography profiles of epidermal PKC isozymes from SENCAR and C57BL/6 mice revealed three major peaks of PKC activity eluting in fractions similar to those observed in chromatograms of brain tissue and corresponding to PKC-gamma, -beta, and -alpha. Further analyses of hydroxylapatite chromatography fractions revealed that PKC-gamma and -beta were present in approximately similar proportions and were much more abundant than PKC-alpha. This distribution of epidermal PKC isozymes was similar in both strains. After a single topical application of 3.4 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) to SENCAR mouse epidermis, total PKC activity in the cytosol fraction decreased rapidly to about 50% of control within 15 min and was accompanied by an increase (approximately 150% of control) of PKC activity in the membrane fraction. At 4 h, PKC activities were significantly lower than the control levels and remained downregulated through 96 h with a maximal decrease (to approximately 25-30% of the control) in both cytosol and membrane fractions at h. PKC activity returned to control levels by 168 h. Ca++/phospholipid-independent kinase activity was the same as control levels at 15 min, 1 h, and 4 h after TPA treatment but was elevated above control levels at 24 h, 48 h, and 96 h, and by 168 h returned essentially to control levels. No differences were found in the magnitude or kinetics of TPA-induced translocation and downregulation of total PKC or appearance of Ca++/phospholipid-independent kinase activity between SENCAR, DBA/2, and C57BL/6 mice. Scatchard analyses using a two binding site model revealed that the apparent Kd and Bmax values for binding of PDBu to epidermal cytosol and membrane fractions were similar between SSln, SENCAR, DBA/2, and C57BL/6 mice. The present results demonstrate for the first time that mouse epidermis contains significant amounts of the three major PKC isozymes that are present in brain, especially PKC-gamma. In addition, topical application of a promoting dose of TPA did not lead to complete loss of PKC activity in either the membrane or cytosol fractions of mouse epidermis. In conclusion, no differences were observed between phorbol ester-sensitive and -resistant mice in any aspect of epidermal PKC examined.

Animals↗

PubMed1990

Comparison of lung injury induced in 4 strains of mice by butylated hydroxytoluene.

Butylated hydroxytoluene (BHT) is a phenolic antioxidant which induces lung injury in all strains of mice which have been tested, but not in any other species. The mortality of mice treated with BHT is also highly strain-dependent, with LD50s ranging from 138 to 1739 mg/kg. Despite this wide range of toxic doses, the relationship between lung damage and dose has not been well studied. The data presented here demonstrate that BALB/c, ICR and C57BL/6NHsd mice, with LD50s of 1739, 1243 and 917 respectively, exhibit similar time courses of repair (as assessed by the incorporation of radiolabelled thymidine into DNA) and pulmonary fibrosis (as assessed by lung hydroxyproline content) when given a single 400 mg/kg dose of BHT. SSIn mice, with an LD50 of approximately 350 mg/kg, also exhibited a similar time course of repair when given a single dose of 300 mg/kg BHT, although fibrosis did not develop in these animals. These data indicate that all strains of mice develop similar levels of lung injury at equivalent doses and that the extent of lung damage produced in mice does not correlate with the lethal dose.

Animals↗

PubMed1990

Epidermal ornithine decarboxylase induction and mouse skin tumor promotion by quinones.

The generation of reactive oxygen species and the subsequent development of a pro-oxidant state, such as occurs during the redox cycling of quinones, has been suggested to play a role in the tumor promotion. Moreover, we have recently shown that the relative tumor promoting activity of a series of structurally related anthrones correlated with their ability to undergo base-catalyzed oxidation. We therefore analyzed dose-response relationships for skin tumor promoting activity and the ability to induce epidermal ornithine decarboxylase (ODC) with a series of structurally related quinones. Single topical applications of 1,4-naphthoquinone and its 5-hydroxy analog (juglone) produced dose-dependent increases in epidermal ODC activity in the dose range 880-3520 nmol/mouse. These two quinones also promoted papilloma formation in female SENCAR mice initiated with 25 nmol 7,12-dimethylbenz[a]anthracene at doses capable of inducing epidermal ODC. The tumor promoting response with juglone (1760 nmol) was dependent upon the frequency of application, with the highest tumor response obtained with a three times per week application regimen. In contrast, neither 1,8-dihydroxy-9,10-anthraquinone nor 1,4-benzoquinone, at doses up to 1760 nmol/mouse, had any effect on epidermal ODC, nor did they possess tumor promoting activity after 31 weeks of promotion. Interestingly, 3-methyl-1,4-naphthoquinone (meadione), a relatively good redox cycling quinone, at a dose of 3520 nmol had only very weak ODC inducing activity and after 31 weeks of promotion (1760 nmol) did not produce a significant papilloma response in SENCAR mice. Thus, there was a good correlation between the ability of structurally related quinones to induce epidermal ODC and their ability to behave as tumor promoters. In contrast, a relationship between quinone redox cycling and tumor promotion was not readily apparent. Finally, under optimal promoting conditions, juglone was very effective at supporting the conversion of papillomas to carcinomas (carcinoma/papilloma ratio of 0.35). In addition, histological examination of all tumors produced during promotion with juglone revealed the presence of both kerathoacanthomas and sebaceous squamous cell carcinomas. These latter tumors, not found in the anthrone group, may be indicative of a potentially unique site and/or mechanism of action for this class of compounds.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1990

Inhibition of the binding of 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene to DNA in mouse skin epidermis by 1-ethynylpyrene.

The effects of 1-ethynylpyrene (EP), 1-vinylpyrene (VP) and 2-ethynlnaphthalene (EN) on the covalent binding of 7,12-dimethylbenz[a]anthracene (DMBA) and of benzo[a]-pyrene (B[a]P) to the epidermal DNA in mouse skin were investigated. When applied topically, 5 min before an initiating dose of 10 nmol DMBA or of 200 nmol B[a]P, EP was an effective inhibitor of the formation of the covalent complexes of these procarcinogenic polycyclic aromatic hydrocarbons (PAHs) with the epidermal DNA. VP, applied under the same conditions, was a significantly less effective inhibitor of the binding of DMBA to DNA and showed even weaker inhibition of the binding of B[a]P. EN was ineffective as an inhibitor of the binding of either DMBA or B[a]P. These results establish that both the pyrene nucleus and the ethynyl substituent of EP contribute to the effective inhibition of the binding of DMBA and B[a]P to the epidermal DNA of mouse skin. No significant changes in the ratios of the anti- to the syndiol epoxide-DNA adducts of DMBA or of B[a]P were produced by doses of EP that produced inhibitions of the binding to DNA. At doses of VP that inhibited covalent binding of both DMBA and B[a]P, no changes in DMBA-DNA adduct distributions were observed but changes in the relative proportions of several B[a]P-DNA adducts were noted. These data are discussed in terms of the potential of aryl acetylenes to act as suicide inhibitors (mechanism-based inactivators) of cytochrome P450-dependent monooxygenase isozymes.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1990

Differential mechanism for the inhibition of epidermal growth factor binding to its receptor on mouse keratinocytes by anthrones and phorbol esters.

1,8-Dihydroxy-3-methyl-9-anthrone (chrysarobin), a potent anthrone tumor promoter, reduced [125I] epidermal growth factor (EGF) binding to its receptor in primary epidermal cells from SENCAR mice maintained in low Ca2+ containing medium. The time course for this effect with chrysarobin was different from that of 12-O-tetradecanoylphorbol-13-acetate (TPA). Maximum inhibition of [125I]EGF binding was observed at 18 h versus 1 h respectively. Scatchard analyses revealed that the inhibition by chrysarobin was due to a decrease in the number of both high- and low-affinity classes of EGF receptors. In contrast, TPA caused a rapid inhibition of EGF binding, primarily due to a loss of high-affinity receptors. The mechanism by which chrysarobin inhibited the binding of EGF to its receptor involved neither direct activation nor membrane translocation of epidermal protein kinase C, whereas the rapid decrease in EGF binding induced by TPA was consistent with its ability to activate protein kinase C. Structure-activity relationships for EGF binding inhibition by anthrones revealed that inhibition was inversely proportional to chain length at the C10-position, which correlated closely with oxidation rate and skin tumor-promoting activity. alpha-Tocopherol was able to block partially the effect of chrysarobin but not TPA on EGF binding. These results suggest that oxidation at position C10 is at least partially responsible for the inhibition of EGF binding induced by chrysarobin. Furthermore, these studies support the hypothesis that changes in EGF receptor binding and/or function may play a role in skin tumor promotion by diverse classes of promoting agents.

Animals↗

PubMed1989

Effect of extracellular calcium concentration on the metabolism of polycyclic aromatic hydrocarbons by cultured mouse keratinocytes.

Cultures of adult mouse epidermal keratinocytes (MEKs) were utilized to determine whether the metabolism and metabolic activation of polycyclic aromatic hydrocarbons varied as a function of extracellular calcium (Ca2+) concentration. MEKs grown in low Ca2+-containing medium (0.05-0.10 mM) maintain basal cell morphology and proliferate while increasing the Ca2+ concentration in the medium to 1.2-1.4 mM signals the cells to undergo terminal differentiation. Relative to cultures of undifferentiated MEKs (low Ca2+), cultures of differentiated MEKs that had been switched to high Ca2+ medium 48 h prior to treatment with benzo(a)-pyrene [B(a)P] and 7,12-dimethylbenz(a)anthracene (DMBA) exhibited more rapid overall metabolism of both hydrocarbons. The greatest differences in the metabolism of B(a)P and DMBA between the two types of cultures occurred after a 3-6-h lag period. In addition, the levels of DNA-adducts formed from B(a)P and DMBA after a 24-h exposure to the hydrocarbon were 4- and 3-fold higher respectively, in cultures of differentiated MEKs (high Ca2+). Higher levels of mutagenesis and cytotoxicity were also observed in cocultures of Chinese hamster lung V-79 cells and MEKs that had been switched to high Ca2+-containing medium. In cocultures treated with the hydrocarbons at the time of Ca2+ shift, several hours elapsed before differences in mutagenesis were apparent between high and low Ca2+-containing cultures. This lag period was eliminated if the MEKs were switched to high Ca2+ medium 24 h prior to exposure to DMBA. Based on the present data, we propose that the expression and inducibility of certain enzyme activities involved in the metabolism of B(a)P and DMBA by cultured MEKs is regulated by the extracellular Ca2+ concentration and possibly the Ca2+-induced differentiation of MEKs.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1989

Further characterization of skin tumor promotion and progression by mezerein in SENCAR mice.

This study evaluated the skin tumor-promoting activity of mezerein in SENCAR mice. The effect of initiation dose of 7,12-dimethylbenz(a)anthracene (DMBA) on tumor promotion by mezerein was examined. Excellent dose-response relationships were observed for initiation with DMBA at 0.2-20 micrograms per mouse with mezerein as a complete promoter. None of the mezerein-only promotion groups had papilloma responses similar to those of the corresponding groups receiving two-stage promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA) followed by mezerein, even when a 40-micrograms initiating dose of DMBA was used. The effect delaying promotion with mezerein for 10 weeks was also examined in mice initiated with either 0.2, 2, 20, or 40 micrograms of DMBA per mouse. The 10-week delay led to a slight increase in the number of papillomas per mouse in some but not all treatment groups. Again, none of the delayed-mezerein-treatment groups had papilloma responses similar to those of the corresponding two-stage promotion (TPA-mezerein) groups at any corresponding initiating dose of DMBA. Finally, the progression of papillomas to carcinomas during promotion with mezerein was examined in groups of mice initiated with either 2 or 20 micrograms of DMBA. Higher ratios of carcinomas to papillomas were observed in mice promoted with mezerein than in mice receiving TPA promotion or two-stage promotion (TPA-mezerein). However, the presence of two to four times more papillomas in some mezerein-treated groups did not lead to greater numbers of carcinomas than in the groups with fewer papillomas. The data do not support the idea that spontaneous stage I promotion can be induced by delaying mezerein treatment for 10 weeks. Furthermore, the data suggest that the higher ratio of carcinomas to papillomas observed with mezerein promotion may be a function of the lower tumor burdens obtained after promotion with this compound rather than a specific property of the chemical.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1989

Histologic alterations produced by chrysarobin (1,8-dihydroxy-3-methyl-9-anthrone) in SENCAR mouse skin: relationship to skin tumor promoting activity.

Histologic changes induced in SENCAR skin following a single treatment with chrysarobin (1,8-dihydroxy-3-methyl-9-anthrone) exhibited differences in time course from that observed with 12-O-tetradecanoylphorbol-13-acetate (TPA). Although not significantly different, maximum elevations in epidermal thickness, total number of nucleated epidermal cells, and dark basal keratinocytes (DCs) induced by 220 nmol chrysarobin occurred at 96 h after treatment, while those induced by 3.4 nmol TPA occurred at 48 h. Both compounds elicited comparable inflammatory responses. Twice-weekly applications of chrysarobin for 2.5 weeks induced a moderate hyperplasia, increase in total nucleated epidermal cells, and increased DCs at 48 and 96 h after the last treatment, with a higher value for these parameters occurring at 48 h. Interestingly, the magnitude of these changes was similar to that observed after a single application. In contrast, twice-weekly applications of TPA induced a dramatic, potentiated induction of epidermal hyperplasia and DCs. Once-weekly applications of chrysarobin led to a potentiated induction of both hyperplasia and DCs compared to the twice-weekly treatment regimen and also more effectively promoted epidermal papillomas in previously initiated SENCAR mice. Skin sections from mice treated with chrysarobin displayed overt signs of epidermal toxicity including altered basal cell morphology and a decreased number of basal cells per 125 micron of basement membrane. Hyperplasia induced by multiple but not single treatments with chrysarobin and TPA correlated quantitatively with their papilloma promoting activity. In addition, the data suggest that epidermal toxicity may play a role in tumor promotion by anthrones.

Administration, Cutaneous↗

PubMed1989

Genetic background and development of skin tumors.

Inbred mouse strains that differing widely in their susceptibility to multistage skin carcinogenesis provide useful models for studying the genetic factors involved and advancing our understanding of the biochemical and molecular events associated with this process. The process of skin tumor initiation appears to be somewhat similar in various strains of mice, and most data in the literature suggest that differences in response to skin tumor promoters are a major determinant in controlling susceptibility to multistage skin carcinogenesis. A model system has been developed for examining the genetics of susceptibility to skin tumor promotion. The susceptibility to phorbol ester skin tumor promotion in crosses between DBA/2 and C57BL/6 mice is inherited as an incomplete dominant trait, and neither X-chromosome nor cytoplasmic genetic determinants appear to play a major role in determining susceptibility in these two inbred strains. In addition, two or more genetic loci contribute to the higher sensitivity of DBA/2 mice than C57BL/6 mice to TPA-induced skin tumor promotion. Further studies to characterize these genes will contribute greatly to our understanding of the mechanisms of phorbol ester skin tumor promotion. In addition, much work should now be directed at understanding the cellular, biochemical, and molecular mechanisms for differential responsiveness not only to phorbol esters but also to other classes of tumor promoters.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1989

Metabolism of polycyclic aromatic hydrocarbons and phorbol esters by mouse skin: relevance to mechanism of action and trans-species/strain carcinogenesis.

Mouse epidermal cells are a useful model system for studying chemical carcinogenesis in epithelial tissues. The available data suggest that some aspects of the metabolic activation and covalent binding of PAH carcinogens are similar in mouse and in human epidermis, whereas notable differences include conjugation pathways and wide interindividual differences, especially in adduct formation. Further work is necessary to determine the role of these differences in susceptibility to PAH carcinogenesis. Clearly, future in vitro assay systems for species extrapolation of epidermal carcinogenesis data must take into account the differentiation state of the cells, among other factors. We showed that the differentiation state of keratinocytes may profoundly influence the metabolic activation of PAHs. Also needed are in vivo assay systems in which quantitative data such as specific DNA adduct levels can be related to the biologic end point of cellular transformation. Several systems were discussed that may fulfill this need. With regard to skin tumor promoters, much less is known about the role of metabolism in mediating species and strain differences in responsiveness. The data available for phorbol esters indicate that differences in the metabolic inactivation of TPA cannot explain the marked species differences in sensitivity to this class of promoters. Much less is known about other chemical classes of promoters, which also require further investigation.

Animals↗

PubMed1988

Tumor progression in Sencar mouse skin as a function of initiator dose and promoter dose, duration, and type.

The influence of initiator dose and promoter dose, duration, and type on the progression of papillomas to carcinomas was examined in Sencar mice. A good dose-response relationship for promotion of papilloma formation by 12-O-tetradecanoylphorbol-13-acetate (TPA) [following initiation with 6.5 micrograms of 7,12-dimethylbenz(a)anthracene (DMBA)] was observed in the range of 0.125 to 2.0 micrograms/mouse. A maximal papilloma response was induced with 2 micrograms/mouse (24 papillomas/mouse). When adjusted for mortality, the carcinoma incidence after 60 wk of promotion was essentially the same (approximately 80%) for doses above 0.5 micrograms/mouse. In a related experiment, mice were given an initiation dose of either 2 or 20 micrograms of DMBA followed by applications of 2 micrograms of TPA for 3, 5, 7, or 60 wk. Papilloma formation was proportional to length of treatment, with a maximum of 29 papillomas/mouse (20-micrograms initiating dose of DMBA) and 10 papillomas/mouse (2-micrograms initiating dose of DMBA) occurring between 10 and 15 wk of promotion. In this experiment, the carcinoma incidence was clearly proportional to the duration of promoter treatment at the low initiation dose of DMBA. The carcinoma incidence, on the other hand, was similar (approximately 70%) in groups of mice given an initiation dose of 20 micrograms of DMBA and promotion treatment for greater than or equal to 5 wk. Thus, the initiator dose had a dramatic effect on the outcome of these experiments. Additional experiments were performed to compare tumor progression with the anthrone promoter, chrysarobin. At optimal promoting doses, chrysarobin treatment produced a maximum number of papillomas that was approximately 1/3 that produced by TPA (6.4 versus 17.0 papillomas per mouse, respectively). However, the carcinoma response was very similar in these two treatment groups, confirming previous work from this laboratory. In addition, chrysarobin treatment following 10 wk of TPA promotion did not enhance the progression of preexisting papillomas to carcinomas. The data presented in this paper are consistent with a model in which several types or stages of papillomas are initially produced during two-stage carcinogenesis in mouse skin with different probabilities of progressing to carcinomas. However, the data indicate that optimal doses of promoter and initiator exist and can influence interpretation of tumor progression studies in mouse skin.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1988

Alterations in epidermal polyamine levels and DNA synthesis following topical treatment with chrysarobin in SENCAR mice.

A single topical application of chrysarobin (220 nmol) to SENCAR mouse skin produced alterations in epidermal polyamine levels distinctly different from that following a single topical treatment with 3.4 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA). Putrescine and spermidine levels were elevated prior to the induction of epidermal ornithine decarboxylase. In this regard, putrescine levels were elevated at 6 and 24 h after a single application of chrysarobin. In addition, putrescine levels were elevated with a second major peak at 64 h after chrysarobin which coincided with elevated epidermal ornithine decarboxylase activity. Spermidine levels were substantially elevated from 24 to 96 h (peak at 60 h) after a single treatment. TPA treatment produced peak elevations in epidermal putrescine levels at 6 h and epidermal spermidine levels at 24 h after a single treatment. Epidermal spermine levels were dramatically depressed following treatment with chrysarobin (peak depression of approximately 60% below control at 24 h), but only slightly altered following treatment with TPA. The time courses for changes in epidermal DNA synthesis in mouse skin following single treatments with 3.4 nmol of TPA or 220 nmol of chrysarobin also showed considerable differences. TPA treatment produced several waves of DNA synthesis at approximately 18 and 48 h after treatment, while chrysarobin produced a single broad peak at 72 h after treatment. Treatment with chrysarobin was also associated with an initial, dramatic inhibition in epidermal DNA synthesis (to 23% of the control value) which was much more extensive than that elicited by TPA. Inhibition of epidermal DNA synthesis following treatment with chrysarobin was observed within a few hours after treatment and remained depressed until approximately 36 h after treatment. Following treatment with both chrysarobin and TPA, higher levels of epidermal DNA synthesis correlated closely with higher molar ratios of spermidine/spermine, indicating a strong relationship between epidermal spermidine levels and epidermal cell proliferation induced by both promoters. The data suggest that TPA and chrysarobin bring about initial changes in epidermal polyamines by distinct mechanisms; however, both compounds ultimately lead to a dramatic stimulation of epidermal DNA synthesis. These data further support our working hypothesis that anthrones promote skin tumors by an initial mechanism different from that of the phorbol esters.

Administration, Topical↗

PubMed1988

Biologically active dihydrodiol metabolites of polycyclic aromatic hydrocarbons structurally related to the potent carcinogenic hydrocarbon 7,12-dimethylbenz[a]anthracene.

Syntheses of the trans-dihydrodiol derivatives implicated as the proximate carcinogenic metabolites of the polycyclic hydrocarbons cholanthrene, 6-methylcholanthrene, benz[a]anthracene, and 7- and 12-methylbenz[a]anthracene are described. These compounds are useful models for research to determine the molecular basis of the strong enhancement of carcinogenicity consequent upon methyl substitution in nonbenzo bay molecular sites and meso regions of polycyclic hydrocarbons. Synthesis of the bay region anti-diol epoxide derivative of cholanthrene, its putative ultimate carcinogenic metabolite, is also described. Tumorigenicity assays indicate that the 9,10-dihydrodiol derivatives of cholanthrene and its 3- and 6-methyl derivatives are all potent tumor initiators on mouse skin. The most active member of the series is the dihydrodiol derivative of 6-methylcholanthrene, which contains a bay region methyl group. The ability of the dihydrodiols 3a-c and the trans-3,4-dihydrodiol of 7,12-dimethylbenz[a]anthracene (3d) to induce chromosomal aberrations in rat bone marrow cells was also examined. The observed order of activity was 3d greater than 3c greater than 3b greater than 3a. These findings are consistent with the hypothesis that the diol epoxide metabolites of these dihydrodiols are the active carcinogenic forms of the parent hydrocarbons.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1988

Synthesis of the tumorigenic 3,4-dihydrodiol metabolites of dibenz[a,j]anthracene and 7,14-dimethyldibenz[a,j]anthracene.

Syntheses are described of the trans-3,4-dihydrodiol derivatives (2a and 2b) of dibenz[a,j]anthracene and 7,14-dimethyldibenz[a,j]anthracene (1a and 1b), implicated as their proximate carcinogenic metabolites. Conversion of 2a to the bay region anti-diol epoxide derivative 3a, its putative ultimate carcinogenic metabolite, is also reported. The related diol epoxide derivative of 2b could not be prepared due to its chemical instability. Tumorigenicity assays confirm that 1b and 2b are potent carcinogens on mouse skin, while 1a and 2a are only relatively weakly active. The diol epoxide 3a exhibited significantly higher tumorigenicity than its dihydrodiol precursor 2a. These findings are consistent with the hypothesis that the bay region diol epoxide metabolites are the active carcinogenic forms of these hydrocarbons. They also support the generalization that methyl substitution in bay regions enhances the carcinogenic activity of polycyclic aromatic hydrocarbons.

Animals↗

PubMed1988

Presence of a functionally altered ornithine decarboxylase activity in chrysarobin-promoted mouse epidermal papillomas.

Recent work from this laboratory has demonstrated the presence of a structurally and functionally different ornithine decarboxylase (ODC) in mouse epidermal tumors induced by a two-stage protocol involving initiation with 7,12-dimethylbenzanthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). In this report, the enzymatic properties of ODC present in DMBA-initiated chrysarobin-promoted papillomas are compared to the enzyme induced by chrysarobin in normal epidermis. Analyses of 13 individual tumor extracts indicated each had an elevated level of ODC activity compared to uninduced normal epidermis. Addition of GTP to the enzyme assay caused a marked stimulation of ODC activity in nine of 13 tumor extracts but had no effect on chrysarobin-induced epidermal ODC. Enzyme kinetic analyses indicated that GTP lowered the atypically high apparent Km values for L-ornithine of the papilloma enzyme to values typical of epidermal ODC. The K 1/2 for GTP activation of papilloma ODC was approximately 7 x 10(-9) M. When a series of nucleotides was tested, only GTP, the non-hydrolysable analog GTP gamma S, dGTP and GDP were capable of significant activation at 1 microM, while other derivatives including GMP, ATP and CTP were less effective. The ability of the tumor enzyme to bind GTP was confirmed by the results of GTP-agarose chromatography, in which the papilloma enzyme (but not chrysarobin-induced epidermal ODC) bound to this affinity column and could be eluted by GTP. While some differences were observed in the properties of ODC from chrysarobin-promoted versus TPA-promoted papillomas, the major conclusion of this study is that both agents cause the appearance of a functionally altered ODC in the majority of papillomas produced by a two-step protocol.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1988

Tumor-initiating activity of the bay-region dihydrodiols and diol-epoxides of dibenz[a,j]anthracene and cholanthrene on mouse skin.

The tumor-initiating activity of dibenz[a,j]anthracene, (+/-)dibenz[a,j]anthracene-trans-3,4-diol and (+/-)dibenz[a,j]-anthracene-anti-3,4-diol-1,2-epoxide in mouse skin was examined and compared to that of cholanthrene, (+/-) cholanthrene-trans-9,10-diol and (+/-)cholanthrene-anti-9,10-diol-7,8-epoxide. The tumor-initiating activity of these compounds dissolved in acetone or in tetrahydrofuran (THF) was also compared. In acetone, dibenz[a,j]anthracene was a weak tumor initiator with maximal tumor yields of 1.27 and 3.00 per mouse at 400 and 800 nmol doses, respectively. At the 400 nmol dose, the diol of this compound was slightly more active than the parent compound while the tumorigenic activity of the diol-epoxide was significantly higher. The diol-epoxide was almost three times more active than the parent compound as a tumor-initiator. Cholanthrene was a moderate tumor-initiator with maximal tumor yields of 6.90 and 8.86 tumors per mouse at 200 and 600 nmol doses, respectively, after 20 weeks of promotion. At comparable doses, (+/-)cholanthrene-trans-9,10-diol was approximately 50% as potent as cholanthrene as a tumor initiator whereas the diol-epoxide was only minimally active. Replacing the acetone with THF as solvent vehicle increased the tumor-initiating activity of cholanthrene-diol-epoxide; however, the parent compound still retained higher tumor-initiating activity than its bay-region diol-epoxide. The low tumorigenic activity of cholanthrene-diol-epoxide is thought to reflect the high chemical reactivity and low stability of this derivative, which may prevent it from penetrating to epidermal targets. In contrast, the bay-region diol-epoxide derivative of dibenz[a,j]anthracene appears to be stable enough to exert greater biologic activity when applied to mouse skin.

Animals↗

PubMed1988

sn-1,2-didecanoylglycerol effectively induces epidermal ornithine decarboxylase but only weak hyperplasia in mouse skin.

The abilities of sn-1,2-didecanoylglycerol (sn-1,2-DDG) to induce epidermal ornithine decarboxylase (ODC) activity and epidermal hyperplasia were tested using SENCAR, DBA/2 and C57BL/6 mice. Following a single application of 5000 nmol of sn-1,2-DDG, ODC activity reached a maximum at 4 h after treatment with a peak activity of 6.03 nmol CO2/mg protein/60 min in C57BL/6, 1.50 in SENCAR and 0.73 in DBA/2, respectively. The time course and magnitude for induction of ODC activity after multiple treatments was very similar to that after a single application in these three mouse lines. Interestingly, the induced ODC activity in C57BL/6 was always higher than that in SENCAR and DBA/2 mouse epidermis regardless of the treatment protocol. Induction of hyperplasia and dark basal keratinocytes (DCs) and changes in the labeling index (LI) of basal keratinocytes in DBA/2 and C57BL/6 mice following treatment with sn-1,2-DDG were investigated. Multiple treatments (twice weekly for 2 weeks) of 5000 nmol sn-1,2-DDG did not induce substantial increases in epidermal thickness or DCs 24 or 48 h after the last treatment. In contrast, TPA induced a marked increase in epidermal thickness in DBA/2 rather than C57BL/6 and a considerably higher induction of DCs in DBA/2 (37.3 +/- 2.2%) than in C57BL/6 (9.6 +/- 2.5%) 48 h after the last treatment. The LIs after topical application of sn-1,2-DDG were elevated at 24 h, but returned to basal levels by 48 h in both strains, whereas TPA treatment significantly elevated the LI in both strains at 48 h after the last application. In addition, the effects of various doses and frequencies of application of sn-1,2-DDG were investigated using SENCAR mice. High doses (20,000 nmol) or more frequent applications (5000 nmol once daily for 7 days) of sn-1,2-DDG still produced only weak hyperplasia. These results suggest that the induction of epidermal ODC activity can be dissociated from the induction of epidermal hyperplasia and may provide an explanation for the lack of complete promoting activity presently observed with membrane permeable diacylglycerol derivatives.

Administration, Cutaneous↗