Effect of retinyl acetate and 4-hydroxyphenylretinamide on initiation of chemically-induced mammary tumors

The anti-promotional effect of retinoids on chemically-induced mammary carcinogenesis in the rat is well established. The present studies were performed to determine the effect of long-term feeding of retinyl acetate and 4-hydroxyphenylretinamide (4-HPR) on initiation of mammary tumors induced by MNU or DMBA. Retinyl acetate (328 mg/kg of diet) or 4-HPR (782 mg/kg of diet) was added to the diet of female Sprague-Dawley rats for two months prior to the administration of the carcinogens. In the MNU model, a 50% increase in the number of mammary adenocarcinomas was observed in rats pretreated with retinyl acetate, while pretreatment with 4-HPR resulted in a 93% increase in the number of cancers. Continued treatment with 4-HPR throughout the study, however, caused a reduction in cancer number. In the DMBA mode, pretreatment with these retinoids significantly increased the number of benign mammary tumors, but not mammary cancers. These data suggest that newly synthesized retinoids should be evaluated for chemopreventive activity against mammary cancer initiation as well as for their anti promotional activity.     

Suppression of 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis by pre-initiation treatment of rats with beta-naphthoflavone coincides with decreased levels of the carcinogen-derived DNA adducts in the mammary gland

BACKGROUND: Mechanisms underlying prevention by beta-naphthoflavone (beta-NF) of mammary carcinogenesis initiated with 7,12-dimethylbenz[a]anthracene (DMBA) in the rat were elucidated. METHODS AND RESULTS: Treatment of female Sprague-Dawley rats with beta-NF at 40 mg/kg b.wt. for 4 days by oral gavage in corn oil before a single oral dose of DMBA (112 mg/kg b.wt.) suppressed mammary gland carcinogenesis as shown by an increase in the median latent period from 10 to 24 weeks and a 60% decrease in the multiplicity of mammary adenocarcinomas. In contrast, a 20-day treatment with beta-NF starting 3 weeks after DMBA had no significant effects on mammary tumorigenesis. The activities of phase I and phase II enzymes were examined in the liver and mammary gland 24 h after treatment of rats with beta-NF, DMBA, or beta-NF followed by DMBA as in the first bioassay. Treatment with either beta-NF or DMBA increased the hepatic activities of cytochrome P450 (CYP)1A1, 1A2, and 2B1/2, and glutathione S-transferase, and the mammary activity of CYP1A1. The activity of mammary CYP2B1/2 induced by DMBA was decreased by beta-NF. In the liver, the increase of UDP-glucuronosyl transferase (GT) activity in rats treated with beta-NF and DMBA was 2.3-fold greater than in rats treated with DMBA alone. Thus, treatment with beta-NF likely increased the rate of glucuronidation of DMBA dihydrodiols leading to carcinogen detoxification. The levels of the DMBA adducts determined by 32P-postlabeling of the mammary gland DNA were decreased in the beta-NF-pretreated rats. Conclusion: The beta-NF-induced increase in the hepatic UDP-GT activity and decrease in the mammary DNA-DMBA adducts occurred under the same treatment regimen that led to suppression of DMBA-induced mammary carcinogenesis.     

Inhibitory action of aminoglutethimide on DMBA-induced mammary carcinogenesis

The present communication reports the inhibitory action of aminoglutethimide on 9,10-dimethyl-1,2-benzanthracene (DMBA) induced mammary carcinogenesis in virgin female Holtzman rats. When 20 mg of DMBA is given to the rats and maintained on normal diet for 32 weeks, approximately 70% of the animals develop mammary tumors. When animals similarly treated with DMBA are put on diets containing 0.025%, 0.05%, and 0.1% of aminoglutethimide for 32 weeks, there is a decline in the number of tumor-bearing animals as well as in the number of tumors per tumor-bearing animal, especially at higher diet doses of the drug. This inhibitory action on the induction of mammary tumors by DMBA could be mainly due to the suppressive action of the drug on endocrine functions.     

Effect of dietary butylated hydroxytoluene on the in vivo distribution, metabolism and DNA-binding of 7,12-dimethylbenz[a]anthracene

The effect of dietary intake of butylated hydroxytoluene (BHT) (0.6%) on the in vivo distribution, metabolism and DNA-binding of intragastrically administered 7,12-dimethylbenz[a]anthracene (DMBA) was evaluated. Urinary excretion of DMBA increased, blood content of metabolized DMBA increased and blood content of non-metabolized DMBA decreased for rats fed the diet containing BHT as compared to rats fed the control diet. The binding of DMBA to both liver and mammary DNA decreased for rats fed the diet containing BHT as compared to controls. The liver activities of glutathione-S-transferase (GST), epoxide hydrolase (EH) and NAD(P)H-quinone reductase (QR) increased in response to BHT feeding. However, no increase in the mammary tissue activities of these enzymes was observed. These results suggest that the ability of dietary BHT to inhibit the initiation of DMBA-induced mammary carcinogenesis partly may be due to decreased binding of DMBA to mammary DNA. This effect of BHT is not due to an increase in mammary tissue activities of GST, EH and QR, enzymes involved in carcinogen detoxification, but may involve increased liver metabolism of DMBA to products that do not bind to DNA.     

Chemopreventive Potential of Neem Flowers on Carcinogen-induced Rat Mammary and Liver Carcinogenesis

We have previously reported that dietary neem flowers (Azadirachta indica A. Juss var. siamensis Valeton) caused ‍a marked increase in glutathione S-transferase (GST) activity in the liver, while resulting in a significant reduction ‍in the activities of some hepatic P450-dependent monooxygenases. These results strongly indicate that neem flowers ‍may have chemopreventive potential. In the present study, we examined the inhibitory effects of neem flowers on ‍9,10-dimethyl-1,2-benzanthracene (DMBA)-induced mammary gland carcinogenesis in female Sprague Dawley rats ‍and on aflatoxin B ‍1 ‍(AFB1)-induced hepatocarcinogenesis in male Wistar rats. Young animals were fed with AIN-76 ‍purified diets containing either 10-12.5% ground freeze-dried neem flowers for 1 week prior to, during, and for 1 ‍week after the administration of each carcinogen. Interestingly, it was found that neem flowers resulted in a marked ‍reduction of the incidence of mammary gland (about 35.2%) and liver tumors (61.7% and 80.1% for benign and ‍malignant tumors, respectively). Furthermore, the multiplicity of tumors per rats was also lower in the neem flower ‍groups, i.e. those for mammary gland tumors and benign and malignant liver tumors were reduced to 44.0%, ‍87.9% and 88.9%, respectively. These results clearly demonstrated that neem flowers contain some chemopreventive ‍agents capable of inhibiting AFB1 and DMBA induced liver and mammary gland carcinogenesis in rats.     

Spontaneous mammary tumors in aging Noble rats

Noble (Nb) rat strain has been used for the study of hormonal carcinogenesis of mammary and prostate glands, for its susceptibility to develop premalignant lesions as well as carcinomas in these organs by sex hormones. However, background information on the spontaneously developed mammary tumors in this rat strain is scarce. We report on the incidence rate, latency period and histopathology of mammary tumors spontaneously developed in the senile intact and untreated Nb rats compared with those induced by either combined treatments with sex steroids or 7,12-dimethylbenz[a]anthracene (DMBA) in the same rat strain. We observed that the incidence rate of spontaneous mammary tumors was 45% in female Nb rats and 3% in the males. The average age of the female Nb rats to develop palpable tumors was 14 months and rarely detected in animals less than 12 months old. It was also noted that the incidence rate of the spontaneous mammary tumors was similar to those induced by combined treatments with sex steroids for 8-10 months (46.7% for T+E2 and 55.6% for T+DES) but less than those by DMBA treatment in 8 months (over 80%). Histologically, majority of the spontaneous mammary tumors were fibroadenomas, which comprised 70% of all collected tumors and about 20% were carcinomas whereas tumors induced by steroid hormones and DMBA were all carcinomas. Distant metastases of spontaneous mammary carcinomas to lung, liver and lymph nodes were also noted, but rarely.     

Suppression of 7,12-dimethylbenz[alpha]anthracene-induced carcinogenesis and hypercholesterolaemia in rats by tocotrienol-rich fraction isolated from rice bran oil.

The anti-tumour and anti-cholesterol impacts of tocotrienol-rich fraction (TRF) were investigated in rats treated with the chemical carcinogen 7,12-dimethylbenz [alpha]anthracene (DMBA), which is known to induce mammary carcinogenesis and hypercholesterolaemia. DMBA administration to rats was associated with the appearance of multiple tumours on mammary glands after 6 months. Alkaline phosphatase (ALP) and glutathione-S-transferase (GST) are used as marker enzymes to monitor the severity of carcinogenesis. Although no tumours were visible on livers, hepatic ALP and GST activities of DMBA-treated rats were profoundly elevated in comparison to enzyme activities of normal control rats. Feeding of TRF (10 mg/kg body weight/day) for 6 months, isolated from rice bran oil (RBO), to DMBA-administered rats, reduced the severity and extent of neoplastic transformation in the mammary glands. Similarly, plasma and mammary ALP activities increased during carcinogenesis (95% and 43%, respectively), were significantly decreased in TRF-treated rats, whereas TRF mediated a further increase of 51% in hepatic ALP activity. TRF treatment to rats maintained low levels of GST activities in liver ( approximately 32%) and mammary glands ( approximately 21%), which is consistent with anti-carcinogenic properties of TRF. Administration of DMBA also caused a significant increase of 30% in plasma total cholesterol and 111% in LDL-cholesterol levels compared with normal control levels. Feeding of TRF to rats caused a significant decline of 30% in total cholesterol and 67% in LDL-cholesterol levels compared with the DMBA-administered rats. The experimental hypercholesterolaemia caused a significant increase in enzymatic activity (23%) and protein mass (28%) of hepatic 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase. Consistent with TRF-mediated reduction in plasma lipid levels, enzymatic activity and protein mass of HMG-CoA reductase was significantly reduced. These results indicate that TRF has potent anti-cancer and anti-cholesterol effects in rats.     

Effect of arginine on the carcinogenicity of 7, 12-dimethylbenz[a]-anthracene and N-methyl-N-nitrosourea

The effects of supplementing a 14% casein diet with 5% L-arginineon rat mammary tumors induced by 7,12-dimethylbenz[a]anthracene(DMBA) and N-methyl-N-nitrosourea (MNU) were investigated. Dietaryarginine supplementation had no significant effect on food intakeor growth. In rats treated with either DMBA or MNU, tumor incidencewas not significantly affected, but the number of new tumorsappearing each week and the cumulative tumor weight per ratwere significantly decreased in rats fed 5% arginine diets.In vitro experiments indicated that arginine had no effect onthe enzymatic conversion of DMBA to electrophilic DNA-bindingmetabolites. The decreased tumorigenicity of both MNU and DMBAin rats given supplemental arginine suggests that this aminoacid has an inhibitory effect on stage(s) of chemical carcinogenesisother than bioactivation of procarcinogens.     

Chemoprevention of 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis in rat by the combined actions of selenium, magnesium, ascorbic acid and retinyl acetate

The chemopreventive actions of sodium selenite (SS), magnesium chloride (MC), ascorbic acid (AA) and retinyl acetate (RA), given singly or in combinations, on mammary carcinogenesis induced by 30 mg of 7,12-dimethylbenz[a]anthracene (DMBA) in female adult rats were evaluated. Administration of modulators was carried out from the age of 40 +/- 3 days to 240 +/- 3 days. When DMBA alone was given 100% of the rats developed mammary tumors. When modulators were given singly the tumor incidences were reduced to 51.77% (SS), 46.4% (MC), 57.1% (AA) and 48.1% (RA). When the modulators were given in combination of twos, the tumor incidences were further reduced to 29.5% (SS + MC), 31% (SS + AA), 29.6% (SS + RA), 25.9% (MC + AA), 31.8% (MC + RA) and 34.6% (AA + RA). Administration of modulators in combinations of threes resulted in still further reduction of tumor incidences to 22.2% (SS + MC + AA), 19.2% (SS + MC + RA), 16% (MC + AA + RA) and 23.1% (AA + RA + SS). When all four modulators were given concurrently the tumor incidence was only 12%. Further, the number of tumors per tumor-bearing animal declined with the increase in the number of agents used in combination for modulation.     

Chemoprevention of 7,12-Dimethylbenz[a]anthracene-induced Mammary Carcinogenesis in Rat by the Combined Actions of Selenium, Magnesium, Ascorbic Acid and Retinyl Acetate

The chemopreventive actions of sodium selenite (SS), magnesium chloride (MC), ascorbic acid (AA) and retinyl acetate (RA), given singly or in combinations, on mammary carcinogenesis induced by 30 mg of 7,12-dimethylbenz[ a ]anthracene (DMBA) in female adult rats were evaluated. Administration of modulators was carried out from the age of 40±3 days to 240±3 days. When DMBA alone was given 100% of the rats developed mammary tumors. When modulators were given singly the tumor incidences were reduced to 51.77% (SS), 46.4% (MC), 57.1% (AA) and 48.1% (RA). When the modulators were given in combination of twos, the tumor incidences were further reduced to 29.5% (SS + MC), 31% (SS + AA), 29.6% (SS + RA), 25.9% (MC + AA), 31.8% (MC + RA) and 34.6% (AA + RA). Administration of modulators in combinations of threes resulted in still further reduction of tumor incidences to 22.2% (SS + MC + AA), 19.2% (SS + MC + RA), 16% (MC + AA + RA) and 23.1% (AA + RA + SS). When all four modulators were given concurrently the tumor incidence was only 12%. Further, the number of tumors per tumor-bearing animal declined with the increase in the number of agents used in combination for modulation.     

Promoting effects of high-fat corn oil and high-fat mixed lipid diets on 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis in F344 rats

Epidemiological studies and laboratory animal model assays suggest that a high intake of dietary fat promotes mammary carcinogenesis as well as colon tumorigenesis. Fat intake in the United States traditionally includes high amounts (30% of total caloric intake) of saturated fatty acids (SFAs) compared to polyunsaturated fatty acids (PUFAs). A recent study suggested that a high-fat mixed-lipid diet (HFML), which simulates the mixed-lipid and high SFAs composition of the average American diet, strongly promotes rat colon carcinogenesis, even when compared to another high-fat diet containing PUFA-rich corn oil. On the other hand, some reports suggest that a high-fat diet rich in n-6 PUFAs promotes mammary carcinogenesis more strongly than a high-fat diet rich in SFAs. Therefore, the present study was designed to compare the effects of HFML, high-fat corn oil diet (HFCO) that is rich in n-6 PUFAs, and a low-fat corn oil diet (LFCO) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis in female F344 rats. At 7 weeks of age, female F344 rats intended for carcinogen treatment received a gavage of DMBA at a dose level of 65 mg/kg of body weight. Beginning 1 week after carcinogen treatment, groups of rats were then maintained on experimental diets containing LFCO, HFCO or HFML. All rats were evaluated weekly by palpation of mammary tumors and sacrificed 20 weeks after the DMBA treatment. Palpable tumors of mammary glands were detected at the 8, 11, and 19 weeks in the HFCO, HFML and LFCO groups, respectively. Histopathological observation revealed that the incidence and number of mammary tumors in the HFCO group were significantly higher than in the LFCO group. Rats on the HFML diet tended towards a higher incidence and number of mammary tumors compared with the LFCO group, although the correlation was not statistically significant. These results suggest that, for this animal model, both the HFCO and HFML diets promote DMBA-induced mammary carcinogenesis when compared to the LFCO diet, and that the HFCO diet is more tumor-promotional than the HFML diet.     

Inhibition of 7,12-dimethylbenz(a)anthracene-induced tumors and DNA adduct formation in the mammary glands of female Sprague-Dawley rats by the synthetic organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate.

We synthesized a novel organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate (XSC), possessing low toxicity by comparison with inorganic Na2SeO3, and several other synthetic organoselenium compounds (K. El-Bayoumy, Cancer Res., 45: 3631-3636, 1985). We tested the effect of XSC treatment during the initiation phase on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma formation. A semipurified high-fat diet containing 80 ppm of XSC (40 ppm as selenium) was fed to 6-wk-old virgin female Sprague-Dawley rats for 2 wk, starting 1 wk before and ending 1 wk after carcinogen treatment. At 7 wk of age, rats were given a single dose of DMBA (5 mg) in 0.2 ml of olive oil by gastric intubation; the experiment was terminated 16 wk later. The development of mammary tumors in those rats that received XSC-supplemented diets was significantly inhibited when compared with the control group (fed the same diet without XSC supplements). This was evident from tumor incidence (percentage of tumor-bearing rats, 88 versus 20) and multiplicity of tumors (mean number of tumors/rats, 3.96 versus 0.28). The finding that XSC acts as a chemopreventive agent in the DMBA mammary tumor model prompted us to examine the effect of dietary XSC on DMBA-DNA binding in both the liver and mammary tissue under conditions identical to those described above for the bioassay. Rats (four/group) were killed 6, 24, 48, and 168 h after [3H]DMBA (5 mg/rat; specific activity, 51.2 mCi/mM) administration. Liver and mammary tissue were obtained and DNA was isolated. Dietary XSC was found to inhibit total DMBA-DNA binding in the mammary tissue, but not in the liver. The most profound effect was observed at early time points, i.e., 24 to 48 h after [3H]DMBA administration. The inhibition in total binding was attributed to a reduction in the formation of the three major adducts derived from bay-region diol-epoxides of DMBA; these were identified as anti-diol-epoxide:deoxyguanosine, syn-diol-epoxide:deoxyadenosine, and anti-diol-epoxide:deoxyadenosine adducts on the basis of their chromatographic characteristics on high-pressure liquid chromatography and on a boronate affinity column. The inhibition of the DMBA-DNA binding in the target tissue provides a plausible explanation for the chemopreventive effect of XSC during the initiation stage of carcinogenesis.     

Inhibition of mammary-gland tumorigenesis in the rat by caraway seeds and dried leaves of watercress

The effect of consumption of caraway seeds and dried leaves of watercress on 7,12-dimethylbenz(alpha)anthracene (DMBA)-induced mammary gland tumorigenesis in female Sprague-Dawley rats was determined. At 6 weeks of age, animals were fed a basal (control) diet and experimental diets containing caraway or watercress (20%). Animals were maintained on their diets till termination of the experiment (25 weeks after DMBA). At 8 weeks of age, all rats were given DMBA 10 mg, one dose, p.o. in oily formulation). Neither caraway nor watercress affected the body weight or the rate of growth of animals. By week 25 after DMBA, 77% of the control rats developed mammary tumors, with a mean of 2.27 tumors per rat. Caraway decreased significantly (P<0.05) the percentage of rats with tumors (42.8% protection) and the mean number of tumors per rat (50.6% protection) and increased significantly (P<0.05) the mean latency period of tumor appearance. Watercress, though decreased the percentage of rats with tumors (28.5% protection) and the mean number of tumors per rat (31.7% protection), this decrease was significant (P < 0.05) during some week intervals only. The increase in the mean latency period of tumor appearance by watercress was not significant. The results of this study suggest that caraway and watercress possess chemopreventive effects against DMBA-induced mammary gland tumorigenesis in rats.     

Long-term exposure to elevated levels of circulating TIMP-1 but not mammary TIMP-1 suppresses growth of mammary carcinomas in transgenic mice

Tissue inhibitor of metalloproteinases-1 (TIMP-1) regulates matrix metalloproteinase activity, acts as a growth stimulator and inhibits apoptosis. We developed transgenic mice to evaluate the relevance of circulating versus mammary TIMP-1 in mammary carcinogenesis. The transgene was placed under the control of the albumin (Alb) promoter for the production of large amounts of TIMP-1 in the liver and release into the systemic circulation to achieve chronically elevated blood levels. The initial 7,12-dimethylbenz[a]anthracene (DMBA) mammary carcinogenesis study showed greatly decreased tumor incidence in heterozygous Alb-TIMP-1 mice (25%), compared with their wild-type (wt) littermates (83.3%). Metastatic mammary carcinomas were induced in the Alb-TIMP-1 mice through breeding with mice expressing the polyomavirus Middle T antigen (MT) under the control of the mouse mammary tumor virus-long terminal repeat (MMTV-LTR). Both the mammary tumor burden and the incidence of lung metastases were lower in the Alb-TIMP-1/MMTV-MT mice than their MMTV-MT littermates. Analysis of the Alb-TIMP-1/MMTV-MT tumors showed evidence of decreased proliferative activity and inhibition of apoptosis, whereas microvascular density was not affected. Transgenic expression of TIMP-1 in mammary epithelial cells was accomplished by using MMTV-LTR. In contrast to the Alb-TIMP-1 mice, there was insignificant difference in the growth of both DMBA- and MT-induced mammary tumors between heterozygous MMTV-TIMP-1 mice and their wt littermates. The MT-induced mammary tumors of the MMTV-TIMP-1 mice were separated into 'low' and 'high' TIMP-1 expressing groups. The 'high' TIMP-1 expressing tumors exhibited significantly higher proliferative activity than the tumors of the MMTV-MT only mice, whereas the number of apoptotic cells and microvascular density were not different. The findings of this study show that circulating TIMP-1, but not mammary-derived TIMP-1, has growth suppressive effects on DMBA and MT-induced mammary carcinomas.     

beta-Ionone suppresses mammary carcinogenesis, proliferative activity and induces apoptosis in the mammary gland of the Sprague-Dawley rat

beta-Ionone demonstrates potent anticancer activity both in vitro and in vivo. We determined tumor incidence and the number of rats bearing tumors as well as cell proliferation and apoptosis in a rat mammary cancer model induced by 7, 12-dimethylbenz[a]anthracene (DMBA). Rats were fed an AIN-76A diet containing beta-ionone (0, 9, 18 or 36 mmol/kg), starting 2 weeks before DMBA administration and continuing for 24 weeks. A dose-dependent inhibition of mammary carcinogenesis by dietary beta-ionone was observed. Corresponding tumor incidence values were 82.1, 53.3, 25.9 and 10.0% (p < 0.01 or 0.05). Time to tumor appearance increased and tumor multiplicity decreased with increasing dietary beta-ionone. Histopathological and immunohistochemical evaluations of tumors were performed on the 64, 31, 15 and 3 tumors, respectively, identified in rats from the respective groups of 30. The proportions of adenocarcinomas, adenomas and benign masses were equally distributed in the latter group. In proportions within the other groups, the proportions of adenocarcinomas and benign masses decreased and increased with increasing dietary beta-ionone. Proliferating cell nuclear antigen (PCNA), cyclin D1 and Bcl-2 expression decreased, and Bax expression and nuclear fragmentation increased with increasing dietary beta-ionone. These results demonstrate the potent capacity of dietary beta-ionone to suppress DMBA-initiated mammary cancer in rats.     

Protective effect of dietary brussels sprouts against mammary carcinogenesis in Sprague-Dawley rats

The effect of dietary brussels sprouts (Brassica oleracea, L.) on mammary carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA) was studied in Sprague-Dawley female rats. Rats fed a 20% brussels sprouts diet only during the initiation period of carcinogenesis had a palpable mammary tumor incidence of 13%, while those fed a casein-cornstarch semi-purified diet during this initiation period had a tumor incidence of 77% after 15 weeks post DMBA dose. When the rats were switched from the semi-purified diet to the 20% brussels sprouts diet at this time, there appeared to be a regression of small mammary tumors after 6 weeks on this dietary treatment. This regression was transitory since during the final 10 weeks of this 1 year study, 100% of this group of rats developed tumors. The rats fed the 20% brussels sprouts diet during tumor initiation exhibited a 67% incidence of fibroadenomas. The rats fed the semi-purified diet during initiation, but switched later to the brussels sprouts diet, showed over a 90% incidence of adenocarcinomas.     

Danazol therapy in hormone-sensitive mammary carcinoma.

The effect of Danazol, a synthetic gonadotropin inhibitor, on two groups of Sprague-Dawley rats with dimethylbenze (a) anthracine (DMBA) induced mammary carcinoma was studied. Twenty-four (83%) of 29 control animals developed mammary tumors. Forty-four rats in one treatment group received Danazol after tumor reached 0.5 cm in diameter. Twenty-nine (66%) demonstrated tumor regression (p less than 0.005) and in 16 (36%) tumor disappeared (p less than 0.005). In a second treatment group (given Danazol daily after administration of DMBA), only seven of 50 rats (14%) developed palpable mammary carcinoma (p less than 0.0005). Danazol therapy resulted in regression of established mammary carcinoma in rats, and produced a striking inhibition of carcinogenesis in those animals treated from the time DMBA was administered. Danazol is clinically safe; studies using it in the treatment of breast cancer in women who are candidates for hormonal ablative therapy seem warranted.     

Effects of selenium on 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis and DNA adduct formation

The purpose of the present investigation was to determine the effects of dietary selenium deficiency or excess on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary neoplasia in rats and to delineate whether selenium-mediated modification of mammary carcinogenesis was associated with changes in carcinogen:DNA adduct formation and activities of liver microsomal enzymes that are involved in xenobiotic metabolism. Female Sprague-Dawley rats were divided into three groups from weaning and were maintained on one of three synthetic diets designated as follows: selenium deficient (less than 0.02 ppm); selenium adequate (0.2 ppm); or selenium excess (2.5 ppm). For the DMBA binding and DNA adduct studies, rats were given a dose of [3H]DMBA p.o. after 1 month on their respective diets. Results from the liver and the mammary gland indicated that neither selenium deficiency nor excess had any significant effect on the binding levels, which were calculated on the basis of total radioactivity isolated with the purified DNA. Furthermore, it was found that dietary selenium intake did not seem to affect quantitatively or qualitatively the formation of DMBA:DNA adducts in the liver. Similarly, in a parallel group of rats that did not receive DMBA, the activities of aniline hydroxylase, aminopyrine N-demethylase, and cytochrome c reductase were not significantly altered by dietary selenium levels. Concurrent with the above experiments, the effect of dietary selenium intake on carcinogenesis was also monitored. Results of this experiment indicated that selenium deficiency enhanced mammary carcinogenesis only when this nutritional condition was maintained in the postinitiation phase. Likewise, an excess of selenium intake inhibited neoplastic development only when this regimen was continued after DMBA administration. In either case, deficient or excess selenium at the time of carcinogenic insult failed to produce a significant effect on subsequent tumor yield, if selenium intake was returned to normal during the proliferative phase of tumor growth. Based on the results of these studies, it is suggested that selenium-mediated modification of mammary tumorigenesis is not exerted via alterations in carcinogenic initiation (i.e., metabolism or DNA adduct formation).     

Mammary tumors in splenectomized rats.

The objective of this study was to examine how splenectomy affects the immune response, particularly T cells, in chemically-induced mammary tumors. Female rats were splenectomized and then exposed to 9,10-dimethyl-1,2-benz(a)anthracene (DMBA) to induce mammary tumors. Splenectomy significantly decreased the rate of tumor appearance and their malignant transformation. The tumor latency period in splenectomized rats was 12.0+/-0.9 weeks compared to 9.7+/-0.5 wk in intact controls, and malignancy appeared in 45% of splenectomized rats, compared to 70% in controls. By the end of the experiment, the total number of tumors and their size were similar in both groups. Blood CD4+ and CD8+ T cell concentrations were similar in tumor-bearing and tumor-free splenectomized animals, but in both groups CD4- and CD8- lymphocytes decreased sharply compared to control animals. In tumor-bearing rats, splenectomy also resulted in significantly more circulating natural killer cells. The spleens of tumor-bearing control rats had significantly fewer CD4+ and CD8+ lymphocytes and more CD4- and CD8- lymphocytes and natural killer cells than did their blood. In conclusion, splenectomy inhibits the early stages of tumorigenesis and reduces the rate of malignant transformation of benign tumors, but does not prevent the progress of carcinogenesis. Differences between splenectomized (operated) and intact rats to the effect of DMBA can be explained by an increase in non-specific resistance of splenectomized rats as a result of operation.     

Inhibition of 7,12-dimethylbenzanthracene-induced rat mammary tumorigenesis by 2,5-di-O-acetyl-D-glucaro-1, 4:6,3-dilactone, an in vivo {beta}-glucuronidase inhibitor

2,5-Di-O-acetyl-D-glucaro-1,4:6,3-dilactone (DAGDL) is a slowrelease form of D-glucaro-1,4-lactone (GL), a non-toxic naturalinhibitor of ß-glucuronidase. When administered orallyto female rats in conjunction with a carcinogenic dose of 7,12-dimethylbenzanthracene(DMBA), this compound caused a 70% reduction in the number ofrats with mammary tumors and 72% reduction in the number ofmammary tumors per rat. Co-administration also reduces the inductionby DMBA of a 60 kd oncofetal protein, previously shown to beassociated with carcinogenesis and tumorigenesis. DAGDL administrationdepressed ß-glucuronidase activity both in the absenceand presence of concurrent treatment with DMBA and also markedlyreduced binding of DMBA to organ DNA. The anti-carcinogeniceffect of DAGDL appears to be independent of route of administrationof DMBA. It is proposed that inhibition of ß-glucuronidaseincreases the proportion of DMBA which is sequestered and excretedas the glucuronide and therefore unavailable for activationto the proximal carcinogen.