Showing papers on "7,12-Dimethylbenz[a]anthracene published in 1978"

Developmental Stage of the Rat Mammary Gland as Determinant of Its Susceptibility to 7, 12-Dimethylbenz[a]anthracene

Abstract: Postnatal development of the mammary gland was studied in 80 noninbred Sprague-Dawley virgin rats ranging in age from 2 to 112 days, and the changes induced by 7,12-dimethylbenz[a]anthracene (DMBA) were studied in 60 noninbred Sprague-Dawley virgin rats that, at the age of 55 days, were inoculated intragastrically with 10 mg DMBA/100 g body weight. To correlate the sequential structural changes in the two groups, animals of both groups were killed weekly and their mammary glands removed and processed for wholemount. Terminal endbuds (TEB), terminal ducts (TD), alveolar buds (AB), and lobules per square millimeter were counted in wholemount preparations under a stereomicroscope. During postnatal development, the mammary gland tree grew by sprouting numerous ducts ending in club-shaped TEB. The density of TEB reached a peak when the rats were 21 days old (25 +/- 2 TEB/mm2), decreased sharply until the animals were 63 days old, and then decreased slowly until they were 84 days of age. The number of TEB decreased because of their differentiation mainly into AB or their evolution to TD. AB later differentiated into lobules. AB increased in number steadily to a plateau when the animals were 70--84 days old. After DMBA was administered to the rats at 55 days of age, the number of TEB remained higher than that in the control animals and the TEB became larger and had higher mitotic activities. Such TEB were called intraductal proliferations (IDP); they evolved to adenocarcinomas. DMBA increased the number of TD and decreased the number of AB and lobules in relation to the control animals. These findings led to the conclusion that DMBA administration to 55-day-old rats alters the differentiation of TEB leads to AB leads to lobules, inducing instead the sequence TEB leads to IDP leads to adenocarcinoma.

Origin of tubular complexes developing during induction of pancreatic adenocarcinoma by 7,12-dimethylbenz(a)anthracene.

Abstract: Implantation of 7,12-dimethylbenz(a)anthracene (DMBA) into the pancreas of rats has been shown to induce adenocarcinoma. Complexes of tubules, which have the appearance of proliferated intralobular ducts, frequently appear during tumor development. These complexes were studied by light and electron microscopy to determine their method of formation. In addition, a tubular complex was reconstructed from serial sections to determine its three-dimensional configuration. Although tubular complexes have been thought by others to result from ductal proliferation, the following observation indicate that they originate from zymogen-granule-containing cells: a) there is a continuum of transitional stages between acini and tubules, b) most tubules decrease in size and are replaced by connective tissue (evidence of regression rather than proliferation), c) few mitotic figures are seen in tubular complexes, d) the tubules comprise many cells which have an abundance of rough endoplasmic reticulum, an organelle which is sparce in ducts, and e) the three-dimensional arrangement of tubules appears identical to the branching, anastomosing arrangement of zymogen-granule-containing cells of the normal rat pancreas. Control animals in which only sutures were placed in the pancreas showed minimal reaction. It is concluded that "acini" become recognized as tubules when loss of zymogen granules accompanies tumor induction by DMBA. Transformation of these cells could be erroneously interpreted as transformation from proliferating ducts.

In Vitro Development of Oncogenicity in Cell Lines Established from Tracheal Epithelium Preexposed in Vivo to 7,12-Dimethylbenz(a)anthracene

Abstract: The purpose of these studies was to determine whether carcinogenesis initiated in vivo in tracheal epithelium of rats progresses in vitro upon culturing of the epithelium. Transplanted rat tracheas were exposed to either 150 or 640 µg of 7,12-dimethylbenz( a )anthracene over a period of 2 weeks. Epithelial cell lines were derived from tracheas exposed in this manner and were tested periodically in vivo for development of oncogenicity and for phenotypic changes associated with neoplastic transformation in vitro . Three cell lines were obtained from tracheas preexposed to 150 µg 7,12-dimethylbenz( a )anthracene. Tumorigenicity was demonstrated only in the late passages of 2 cell lines maintained to 400 days or more in vitro . With these cells in vivo tumor latency was 115 to 255 days. Eight of the 9 cell lines derived from tracheas preexposed to 640 µg 7,12-dimethylbenz( a )anthracene have become tumorigenic. Several of these were found to be oncogenic after approximately 200 days in vitro and yielded palpable tumors within 9 to 80 days after inoculation. In several instances inoculation of cells from early passage into immunosuppressed isogenic recipients resulted in the development of keratinic cysts or tumors that regressed. Inoculation of later passages of the same cell lines resulted in the development of invasive tumors. Loss of anchorage dependence of growth was, in most cases, a reliable phenotypic marker for development of oncogenicity, as was colony-forming efficiency on plastic. Growth rate, saturation density, and cell and colony morphology were not. All of the cell lines were epithelial as indicated by ultrastructural characteristics, the production of keratin in vitro , and/or the formation of squamous cell carcinomas upon inoculation in vivo . The cell lines had stable morphological characteristics distinguishing each cell line from any other by growth pattern, cell shape, and degree of keratinization. Our data indicate that the process of carcinogenesis initiated in epithelial cells in vivo continues in in vitro culture. Thus it should be possible to study in detail both the evolution of the neoplastic process and factors affecting its progression.

Identification of four trans-3,4-dihydrodiol metabolites of 7,12-dimethylbenz[a]anthracene and their in vitro DNA-binding activities upon further metabolism.

Abstract: Trans-3,4-dihydrodiols of 7,12-dimethylbenz[a]anthracene (7,12-Me2BA), 7-methyl-12-hydroxymethylbenz[a]anthracene (7-Me-12-OHMeBA), 7-hydroxymethyl-12-methylbenz[a]anthracene (7-OHMe-12-MeBA), and 7,12-di(hydroxymethyl)benz[a]anthracene [7,12-(OHMe)2BA] have been identified as metabolites of the potent carcinogenic and adrenocorticolytic agent 7,12-MeBA. The four trans-3,4-dihydrodiols were identified by their (i) ultraviolet-visible absorption and fluorescence properties, (ii) different retention times on both reversed-phase and normal-phase high-pressure liquid chromatography, (iii) mass spectral analysis, and (iv) inability to form vicinal cis-acetonides. Upon further metabolism by liver microsomes, the trans-3,4-dihydrodiols of 7,12-Me2BA, 7-Me-12OHMeBA, and 7-OHMe-12-MeBA were found to give rise to products that bind more strongly to DNA in vitro than do the products of 7,12-Me2BA. The evidence suggests that one or more of the four trans-3,4-dihydrodiols may be the proximate carcinogenic and adrenocorticolytic metabolites.

Age-Related Modification of 7,12-Dimethylbenz[a]anthracene Binding to Rat Mammary Gland DNA

Abstract: The binding of 7,12-dimethylbenz[a]anthracene (DMBA) to mammary gland and liver DNA of female Sprague-Dawley rats either 35, 50, or 120 days of age at the time of carcinogen administration was studied. Following a single oral feeding of tritium-labeled DMBA, the level of binding to liver DNA of rats in all 3 age groups was significantly lower, at all times during a 6-week period, than that of binding to mammary DNA. The amount of DMBA bound to liver DNA was a function of the amount of carcinogen administered and not the age of the animal. In contrast, DMBA binding to mammary DNA was dependent on the age of the animal at the time of carcinogen feeding. Furthermore, in the age group with 100% tumor induction (50 days old), DMBA binding increased directly with the amount of carcinogen fed; this was not the case for the other 2 age groups. These results indicated that a significant correlation existed between the age of the rat, the amount of DMBA bound to DNA, and the incidence of mammary tumors following carcinogen feeding.

Androgen effects mediated by estrogen receptor in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors.

Abstract: To improve our understanding of the effects of androgens on the induction and growth of mammary tumors, the interaction of androgen on the estrogen receptor (ER) has been evaluated in the 7,12-dimethylbenz(a)anthracene-induced rat mammary tumor. In vitro competitive experiments have shown that androgens interact on ER with a low affinity but have a good stereospecificity for C19 steroids bearing a 17β- and/or 3β-hydroxyl group. The administration of one dose (⩾20 mg) of 5α-dihydrotestosterone to 1-day ovariectomized rats induced ER nuclear translocation in 92% of the mammary tumors. In 60% of these tumors, this translocation was followed by a significant stimulation of the rate of [3H]leucine incorporation into cytosoluble proteins by 5α-dihydrotestosterone or estradiol. When injected together, 5α-dihydrotestosterone did not antagonize the effect of estradiol. We conclude that one very high dose of 5α-dihydrotestosterone that stimulates leucine incorporation into proteins is also able to occupy the cytosol ER in mammary tumors and to translocate it in vivo into the nucleus. We suggest that a direct interaction of androgens with the ER located in mammary tumors is responsible, as in rat uteri, for the stimulating effect of very high doses of androgens. We cannot ascertain that the same mechanism is involved in the androgen-induced regression of the mammary tumors.

Carcinogenesis Induced by 7,12-Dimethylbenz[a]anthracene in C3H-A vyfB Mice: Influence of Different Dietary Fats

Abstract: The effect of a diet containing either sunflower-seed oil (polyunsaturated fat diet) or tallow (saturated fat diet) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced carcinogenesis in C3H-A vyfB mice was examined. After receiving either diet for 28 days, some of the mice were given an intragastric dose of 5 mg DMBA. To identify the stage of carcinogenesis that might be influenced by dietary fat, the diets of half of the mice were then interchanged so that those previously fed the saturated fat diet were fed the polyunsaturated fat diet and vice versa. The cumulative incidence of tumor-bearing mice was significantly greater among the females fed the polyunsaturated fat diet compared to those fed the saturated fat diet. This enhancement of carcinogenesis was observed only when the mice were fed the polyunsaturated fat diet after DMBA administration. Similar trends were observed in the male mice, but these mice developed fewer tumors and none of the differences between the tumor incidences were statistically significant. The most common sites for tumors in the male mice were the liver, lungs, and skin, whereas those for tumors in the females were the mammary glands and ovaries. The differences in tumor incidence suggest that carcinogenesis was enhanced by the polyunsaturated fat diet during the promotion stage of carcinogenesis.

Development of a System for Controlled Release of Benzo(a)pyrene, 7,12-Dimethylbenz(a)anthracene, and Phorbol Ester for Tumor Induction in Heterotopic Tracheal Grafts

Abstract: The utility of the tracheal transplant model as a tool in in vivo carcinogenesis studies depends largely on the development of a good drug delivery system affording reproducible, sustained carcinogen release. Previously used methods have proven to be less than satisfactory. We studied the release of benzo( a )pyrene, 7,12-dimethylbenz( a )anthracene, and 12- O -tetradecanoylphorbol-13-acetate from pellets of varying composition. In vitro release of the two polycyclic hydrocarbons (PCH) from beeswax pellets showed little variability, regardless of PCH concentration. In marked contrast, in vivo release was highly variable, particularly at high PCH concentrations. This suggested that the in vivo variability was largely due to the toxic alterations of tissues, caused by carcinogen released at high rates. Pellets composed of beeswax:cholesterol in ratios of 1:1 to 1:9 showed markedly reduced rates of PCH release. At a ratio of 1:9, the overall release rate of benzo( a )pyrene was ∼1 µg/day compared to ∼7 µg/day for pellets with a pure beeswax matrix [100 µg benzo( a )pyrene pellets]. The variability of PCH release was simultaneously diminished, supporting the suspicion that it was a result of toxic tissue changes. Similarly reduced release rates could be obtained by adsorbing the PCH to charcoal particles. Studies with the promotor 12- O -tetradecanoylphorbol-13-acetate showed a release rate of 1.6 µg/day from pure beeswax (100 µg 12- O -tetradecanoylphorbol-13-acetate per pellet). This rate may have to be diminished before promotion studies in the tracheal transplant model can be attempted. Our studies demonstrate that protracted PCH release from pellets can be achieved by using a beeswax: cholesterol matrix instead of a pure beeswax matrix or by adsorbing the PCH to charcoal particles. Such pellets release at fairly constant rates, with little pellet-to-pellet variability. Thus, the major problem of using the tracheal transplant model for quantitative tumor induction studies with PCH9s appears to be resolved.

Cyclic Nucleotide Concentrations in 7,12-Dimethylbenz[a]anthracene-Induced Pancreatic Cancer in Rats

Abstract: Pancreas cancer was induced in noninbred male Holtzman rats by the implantation of beeswax containing 7.12-dimethylbenz[a]anthracene (DMBA) into the "head" of the pancreas. The tumors that developed 4--6 months later were examined for their cyclic AMP and cyclic GMP levels. The lesions could be considered in one of two categories according to their cyclic nucleotide contents: lesions with significantly smaller amounts and those with greater amounts, compared with levels measured in the pancreas tissues of the control rats. The existence of two biochemically distinct groups may indicate different growth patterns of the DMBA-induced pancreatic neoplasia.

Reaction of 7,12-dimethylbenz(a)anthracene with DNA of fetal and maternal rat tissues in vivo.

Abstract: Pregnant BD-IX rats (21st day of gestation) received a single IV injection (15 mg/kg) of tritiated 7,12-dimethylbenz(a)anthracene (DMBA), a dose known to induce a high incidence of nervous-system tumors in the offspring. The animals were killed 12 h later and hydrocarbon-deoxyribonucleoside products from DNA of maternal and fetal tissues were separated on Sephadex LH-20 columns eluted with a 20–100% methanol gradient. Concentrations of the major DMBA-DNA adduct varied considerably, with highest values in maternal intestine, liver and lung, followed by spleen, kidney and brain. In fetal intestine and liver, concentrations were 34% and 16% lower than in the respective maternal organs whereas the reaction with cerebral DNA was 2 1/2 times higher in fetuses than in the pregnant mother. This indicates that there is no significant placental barrier to DMBA or DMBA metabolites involved in DNA binding and that rat fetuses participate in the metabolic formation of the ultimate carcinogen.

Formation of Glucuronic Acid Conjugates of 7,12-Dimethylbenz(a)-anthracene Phenols in 7,12-Dimethylbenz(a)anthracene-treated Hamster Embryo Cell Cultures

Abstract: Secondary cultures of hamster embryo cells exposed to 0.5 nmol [G- 3 H]7,12-dimethylbenz( a )anthracene (DMBA) per ml medium metabolized more than 90% of the DMBA within 48 hr. Samples of medium were extracted with chloroform, methanol, and water. The chloroform phases contained about one-third of the DMBA metabolites; the major chloroform-extractable metabolite was 8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz( a )anthracene. β-Glucuronidase treatment of the aqueous methanol-soluble metabolites converted almost one-half of them to chloroformsoluble metabolites, of which more than 80% were identified as phenolic derivatives of DMBA. Similar metabolite profiles were obtained by treating the medium with β-glucuronidase before chloroform extraction. Separation of the methyl group-hydroxylated derivatives of DMBA from the phenolic derivatives was accomplished by high-pressure liquid chromatography. Small amounts of hydroxymethyl derivatives were detected only in the chloroform-extractable material, whereas DMBA phenols were the major component of the β-glucuronidase-released material. These results indicate that the major pathway of DMBA metabolism in hamster embryo cells is oxidation of the aromatic rings and not oxidation of the methyl groups.

Cellular uptake, transport, and macromolecular binding of benzo(a)pyrene and 7,12-dimethylbenz(a)anthracene by human cells in vitro.

Abstract: Patterns of benzo( a )pyrene (BP) and 7,12-dimethylbenz( a )anthracene (DMBA) uptake and subcellular distribution by monolayer cultures of preconfluent human neonatal foreskin fibroblasts were significantly different; the maximum concentration of DMBA in the whole-cell fraction was 6% of the maximum BP concentration in that fraction, and the maximum DMBA concentration in the nuclear fraction was 2% that of maximum nuclear-associated BP. Approximately 30% of BP present in the cytoplasm of human fibroblasts was bound DMBA. In BP-treated cells the extent of polynuclear hydrocarbon uptake by the bound cytoplasmic and nuclear fractions was approximately the same; BP appeared first in the bound cytoplasmic fraction and then in the nuclear fraction. The binding of BP to cytoplasmic protein and translocation of this bound polynuclear hydrocarbon to the nucleus appeared to be a function of one or several metabolites of the parent hydrocarbon. In DMBA-treated cells the pattern and extent of uptake by the crude cytoplasmic fraction was approximately the same as that of the nuclear fraction, indicating random dispersal of DMBA throughout the cell. Microelectrophoresis of a cell extract prepared from [ 3 H]BP-treated human neonatal foreskin cells suggested that the [ 3 H]BP-cytoplasmic protein association was noncovalent.

Metabolism of 7,12-Dimethylbenz(a)anthracene by Macrophages and Uptake of Macrophage-derived Metabolites by Respiratory Tissues in Vitro

Abstract: Cultured mouse macrophages and tracheal and lung tissue each produced the same ethyl acetate-soluble derivatives of 7,12-dimethylbenz(a)anthracene (DMBA). The derivatives produced in the different cultures were indistinguishable by thin-layer chromatography and by high-pressure liquid chromatography but differed in their relative proportions. The greatest difference was seen between lungs and macrophages. The predominant metabolite produced by lungs was 8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz(a)anthracene, while macrophages produced equal quantities of both 8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz(a)anthracene and a second uncharacterized derivative, Metabolite B, at low DMBA doses ( 0.05 µg/ml medium). Macrophages released the majority of the ethyl acetate-soluble metabolites that they produced into the surrounding medium. With the exception of 8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz(a)anthracene, these derivatives were accumulated within tracheal and lung tissue when these organs were cocultivated with macrophages in the presence of DMBA.

Restraint-Induced Inhibition of 7,12-Dimethylbenz[a]anthracene-Induced Mammary Tumors: Relation to Stages of Tumor Development

Abstract: Experiments on the use of chronically applied restraint to reduce the number of mammary tumors developing in response to treatment of rats with 7,12-dimethylbenz[a]anthracene indicated that this inhibitory effect was largely due to restraint applied after the induction period; preinduction restraint and induction period restraint had no significant effect on tumor development. After termination of the restraint treatment, the rate at which new tumors appeared first increased and then decreased. Restraint did not affect the proportion of tumors regressing after ovariectomy.

Expression of RNA of an Endogenous Replication-Defective Retrovirus in Rat Mammary Adenocarcinomas Induced by 7,12-Dimethylbenz[a]anthracene

Abstract: An investigation into the possible relationship between chemical carcinogen induction of rat mammary tumors and the expression of an endogenous retroviral genome was initiated. Mammary tumors were induced in female SD rats with 7,12-dimethylbenz[a]anthracene (DMBA). Tumors, identified histologically as mammary adenocarcinomas, were analyzed for RNA of a replication-defective endogenous retrovirus or RNA of a helper-independent endogenous type C virus. Expression of RNA of the replication-defective virus was detected in mammary tumors weighing 0.2--2.0 g. Larger tumors, for which histologic examination revealed proportionally more fibroblastic tissue than epithelial cells, did not contain comparable concentrations of this viral RNA. RNA homologous to a helper-independent rat type C retrovirus was not detected in tumors of any size. A cell line was established from a primary DMBA-induced mammary adenocarcinoma and appeared similar to the small mammary tumors with respect to endogenous type C viral RNA expression. We discuss possible implications of the expression of endogenous replication-defective viruses for use as markers for the effects of chemical carcinogens.

Binding of 7,12-Dimethylbenz[a]anthracene to BALB/c Mouse Mammary Gland DNA in Organ Culture

Abstract: The second thoracic mammary glands of Immature female BALB/c mice were cultivated to alveolar development In a chemically defined medium with Insulin plus prolactin plus aldosterone plus hydrocortisone. (IPAH medium). The glands were treated with labeled PH or 14C} or unlabeled 7,12-dlmethylbenz[a]anthracene (DMBA) In dimethyl sulfoxide (DMSO) for 24 hours between days 3 and 4 of culture. For binding studies, isolated mammary gland DNA was treated with RNase and pronase and the radioactivity In DNA was measured. The DNA of glands treated with [14C]DMBA was also analyzed In a CsCI density gradient. The DNA of glands treated with labeled DMBA was found to contain bound radioactivity. UV absorption spectral analysis also showed the presence of the DMBA nucleus at the 310-nm region In the DNA of DMBA-treated glands. Nearly 100% of the Initial (3H]DMBA-DNA radioactivity was retained up to 5 months, and at 8 months 72% of the radioactivity was present In the DNA. For morphologic studies, observation of the glands after treatment with equlmolar concentrations (0.004 M) of DMBA, dibenz[a,h]anthracene, benz[a]anthracene, or anthracene In IPAH medium revealed that DMBA was most potent in Inducing nodulelike alveolar lesions (NLAL) In the mammary glands In culture. Thus the binding of DMBA to DNA corresponds to Its high nodullgenlc action In the mammary glands in the present organ culture model. The results appear to resemble DMBA-DNA Interaction associated with the carcinogenic action of DMBA. The biologic characteristics of the NLAL are being assessed by mammary fat pad transplantation.-J Natl Cancer Inst 61: 465-

Characterization of Androgen Receptors in 7,12-Dimethylbenz(a)-anthracene-induced and Transplantable Rat Mammary Tumors

Abstract: Androgen receptors have been documented and characterized in the 7,12-dimethylbenz(a)anthracene-induced rat mammary tumor and in a series of transplantable rat mammary tumors, (MTW-9A, MTW-9B, and MTW-9D). In all cases specific binding of [ 3 H]dihydrotestosterone (DHT) to tumor cytosol was saturable, and Scatchard analysis showed a single class of high-affinity, low-capacity binding sites. Bound [ 3 H]DHT sedimented at ∼7S in sucrose gradients and was completely displaced by cold DHT. By means of competition studies, the androgen receptor in the 7,12-dimethylbenz(a)anthracene tumor could be distinguished from that for other steroid hormones. Neither dexamethasone nor cortisol competed for DHT binding, indicating that binding was not to the glucocorticoid receptor or to the cortisol-binding globulin of serum. Estradiol, however, was an excellent competitor, but because diethylstilbestrol did not compete for [ 3 H]DHT binding, the androgen receptor could be distinguished from the estrogen receptor. Although testosterone has been shown to cause regression of the estrogen-dependent 7,12-dimethylbenz(a)-anthracene tumor, the estrogen-independent MTW-9B and MTW-9D tumors did not regress following androgen therapy, and the growth of the MTW-9B was actually slightly enhanced. This suggests that the pharmacological effects of androgen in mediating tumor regression may require a functional estrogen receptor and that the androgen receptor may render the tumor sensitive to the growth-promoting effects of androgen.

Inhibition of 7,12-dimethylbenz[alpha]anthracene-induced mammary tumorigenesis in rats by a synthetic protease inhibitor, N,N-dimethylamino-(p-(p'-guanidinobenzoyloxy)) benzilcarbonyloxyglycolate.

Abstract: Oral administration of N,N-dimethylamino-(p(p'-guanidinobenzoyloxy))-benzilcarbonyloxy glycolate depressed induction of breast tumors in rats by a single intravenous injection of 7,12-dimethylbenz[alpha]anthracene. The latent period was delayed in the group fed on a diet supplemented with N,N-dimethylamino-(p(p'-guanidinobenzoyloxy))benzilcarbonyloxy glycolate. Administration of this compound for 40 days after 7,12-dimethylbenz[alpha]anthracene also significantly reduced the average weight of tumors per rat. These findings suggest that protease may play an important role in the process of mammary tumorigenesis.

Dibenz[a,c]anthracene: A potent inhibitor of skin-tumor initiation by 7,12-dimethylbenz[a]anthracene

Abstract: The mechanism by which the weak tumor initiator dibenz(a,c)anthracene (DB(a,c)A) inhibits the skin-tumor-initiating activity of 7,12-dimethylbenz(a)anthracene (DMBA) was investigated. DB(a,c)A was found to be a potent inhibitor of DMBA initiation when given either 5 min, or 1, 12, or 36 hours before DMBA. Pretreatment of mice with unlabeled DB(a,c)A at either 1, 12, or 36 hours before killing increased the in vitro epidermally mediated covalent binding of (/sup 3/H)DMBA to DNA more than pretreatment with unlabeled DMBA at comparable times. Only when the tumor experiments were mimicked did a decrease in DMBA covalent binding to DNA in vitro occur. The results suggest that some competition at the level of polycyclic hydrocarbon metabolism or at the genome level may exist between metabolites of the weak carcinogen and those of the strong carcinogen.

Primary Culture of Rat Mammary Epithelial Cells. II. Cytotoxic Effect and Metabolism of 7,12-Dimethylbenz[a]anthracene and N-Nitroso-N-methylurea

Abstract: To determine the cytotoxicity of 7,12-dimethylbenz[a]anthracene (DMBA) and N-nitroso-N-methylurea (NMU) on primary cultures of rat mammary cells, cultures were exposed to various concentrations of these carcinogens. Cytotoxicity was evident after exposure for 24 hours to as little as 0.1 microgram DMBA/ml. Cytotoxicity was evident after exposure for 2 hours with NMU at concentrations between 80 and 160 microgram/ml. Primary cultures of rat mammary cells were also examined for their ability to metabolize [3H]DMBA into water-soluble products. During a 48-hour period, mammary cells could convert 2.2% [3H]DMBA to water-soluble metabolites. The cells retained (for at least 4 days) small quantities of [3H]DMBA that were insoluble in organic solvents.

Protection Against 7,12-Dimethylbenz[a]anthracene-lnduced Rat Mammary Carcinoma by Infection With Mouse Xenotropic Type C Virus

Abstract: A single ip inoculation of female, outbred Sprague-Dawley rats with a viable mouse xenotropic type C virus significantly reduced the incidence and/or retarded the development of mammary carcinoma induced by 7, 12-dimethylbenz[a]anthracene administered orally 7 days after virus. Although infectious virus could not be isolated from organs of infected rats, high titers of circulating and tumor-associated antibodies were detected against the viral internal core protein p30, and a low-grade antibody response to intact virus or envelope glycoprotein was found. Moreover, a cell-mediated immune response, measured by lymphocyte transformation, was detected with the use of intact virus but not with p30 antigen. No immunity developed after a single inoculation of UV-inactivated virus. These data indicated that inoculation of adult individuals of heterologous species with viable xenotropic mouse type C virus resulted in the rapid disappearance of infectious virus from the recipient, followed by the development of both humoral and cellular immunity to virion constituents. These events led, by unknown mechanisms, to the effective retardation of chemical carcinogenesis when infection preceded carcinogen administration.