Lesions of the prostate glands and seminal vesicles induced by N-methylnitrosourea in F344 rats pretreated with ethinyl estradiol

In an attempt to induce a high incidence of prostate carcinoma, N-methylnitrosourea (MNU), a multipotential carcinogen, was given during the period of cell proliferation of the prostate gland induced by administration of methyltestosterone (MT) to F344 rats pretreated with ethinyl estradiol (EE). Rats were given diet containing EE for 3 weeks and then diet containing 300 ppm of MT for 5 days. On the 3rd day of MT-treatment, they were given a single intravenous injection of 50 mg/kg body wt. of MNU. Control rats (group 4) were given vehicle only. After treatment with MT for 5 days, the rats were given basal diet (group 1), diet containing MT (group 2) or diet periodically containing EE (groups 3 and 4) until the end of the experiment (week 60). Carcinoma of the prostate was found only in 1 of 17 rats in group 3. Atypical hyperplasia of the prostate was found in 1 of 10 rats in group 1 and 3 of 17 rats in group 2. The incidences of atypical hyperplasia of the seminal vesicles in groups 1-3 were 0%, 41% and 29%, respectively. No tumor promoting effect of MT or EE was observed except promotion by MT on the development of atypical hyperplasia of the seminal vesicles.     

Rat prostate as one of the target organs for 3,2'-dimethyl-4-aminobiphenyl-induced carcinogenesis: effects of dietary ethinyl estradiol and methyltestosterone

Twenty consecutive weekly sc injections of 50 mg/kg body weight of 3,2'-dimethyl-4-aminobiphenyl (DMAB), a multipotential carcinogen, were given to male F344 rats and subsequently groups of animals were treated with dietary ethinyl estradiol (EE, 2.5 ppm) or methyltestosterone (MT, 300 ppm) for up to 40 weeks. Prostate carcinomas were found in 4 out of 32 rats given DMAB followed by MT and in 2 out of 29 rats given DMAB alone. Atypical hyperplasia of the prostate epithelium in these two groups was found in 22% and 14%, respectively. Neither carcinoma nor atypical hyperplasia was seen in the prostate of animals given DMAB followed by EE. In other organs, tumors were frequently found in the ear duct, skin, and large intestine and less frequently in the lung, preputial glands, small intestine and liver. EE significantly suppressed tumor incidence of the ear duct and sebaceous glands while increasing the incidence of liver tumor and mesothelioma. The present data indicates DMAB to be a useful carcinogen for the induction of prostate carcinomas in rats.     

Variation in tumor yield in the prostate and other target organs of the rat in response to varied dosage and duration of administration of 3,2'-dimethyl-4-aminobiphenyl

The effects of varying dosages of 3,2'-dimethyl-4-aminobiphenyl (DMAB) in combination with cyclic dietary administration of ethinyl estradiol (EE) on induction of prostate carcinoma were investigated in male F344 rats. Animals received repeated treatment with 0.75 ppm of EE for 3 wk with intervals of 2 wk on basal diet. The cycle was repeated 10, 5, and 3 times in Groups 1, 2, and 3, respectively, a single s.c. injection of DMAB being given 2 days after each change to basal diet at a dose of 50 mg/kg of body weight in Group 1, 100 mg/kg of body weight in Group 2, and 167 mg/kg of body weight in Group 3. With this dosing schedule, the total dose of DMAB (500 mg/kg of body weight) per rat was the same in each group. Subsequent to the last treatment with EE, all rats were given basal diet until the end of the experiment (Wk 60) when all surviving animals were sacrificed for histological examination. Carcinoma of the prostate was found in 58.6, 45.0, and 25.9% of rats surviving for 60 wk in Groups 1 to 3, respectively, the incidences of atypical hyperplasia being 86.2, 85.0, and 74.1%. However, tumors of the small and large intestines, preputial gland, and pancreas developed in a dosage-dependent manner, the largest incidences being found in the group given 167 mg of carcinogen 3 times. Thus the present experiment confirmed that administration of DMAB combined with cyclic treatment with EE induces a high incidence of prostate carcinoma in rats and demonstrated that a low dosage of DMAB given over a long period is superior to a high dosage over a short period for specific induction of prostate lesions.     

Trial to induce prostatic cancer in ACI/Seg rats treated with a combination of 3,2'-dimethyl-4-aminobiphenyl and ethinyl estradiol.

In an attempt to induce prostatic adenocarcinoma at higher incidence in a shorter period, we administered diet containing 0.75 ppm of ethinyl estradiol (EE) for three weeks to ACI/Seg rats, which are predisposed to develop a high incidence of microscopic adenocarcinoma of the prostate at higher age. Then, feeding was changed to basal diet and a single subcutaneous injection of 50 mg/kg body weight of 3,2'-dimethyl-4-aminobiphenyl (DMAB) was given two days after the change. We repeated this schedule 10 times. The rats were killed in week 60 of the experiment and subjected to routine autopsy. The average body weight of rats in group 1 given EE and DMAB was lower than that of control rats in group 2. The incidence of adenocarcinoma was not significantly different in the two groups, i.e., 6/74 (8.1%) in group 1 and 2/54 (3.7%) in group 2. The lesions were all microscopic. The incidence of atypical hyperplasia was significantly higher in group 1 at 17 of 74 rats (23.0%) whereas in group 2, it was only 2 of 54 rats (3.7%). Simple hyperplasia was also observed in 25 of 74 rats (33.8%) in group 1, which was significantly higher than that in group 2, where six of 54 rats (11.1%) had this lesion. The reduced growth of animals due to treatments with EE and DMAB probably suppressed the development of prostate cancer in this experiment. Further studies are needed to develop an appropriate model to induce prostate carcinoma at higher incidence in a shorter period.     

Trial to Induce Prostatic Cancer in ACI/Seg Rats Treated with a Combination of 3,2'-Dimethyl-4-aminobiphenyl and Ethinyl Estradiol

In an attempt to induce prostatic adenocarcinoma at higher incidence in a shorter period, we administered diet containing 0.75 ppm of ethinyl estradiol (EE) for three weeks to ACI/Seg rats, which are predisposed to develop a high incidence of microscopic adenocarcinoma of the prostate at higher age. Then, feeding was changed to basal diet and a single subcutaneous injection of 50 mg/kg body weight of 3,2'-dimethyl-4-aminobiphenyl (DMAB) was given two days after the change. We repeated this schedule 10 times. The rats were killed in week 60 of the experiment and subjected to routine autopsy. The average body weight of rats in group 1 given EE and DMAB was lower than that of control rats in group 2. The incidence of adenocarcinoma was not significantly different in the two groups, i.e. 6/74 (8.1%) in group 1 and 2/54 (3.7%) in group 2. The lesions were all microscopic. The incidence of atypical hyperplasia was significantly higher in group 1 at 17 of 74 rats (23.0%) whereas in group 2, it was only 2 of 54 rats (3.7%). Simple hyperplasia was also observed in 25 of 74 rats (33.8%) in group 1, which was significantly higher than that in group 2, where six of 54 rats (11.1%) had this lesion. The reduced growth of animals due to treatments with EE and DMAB probably suppressed the development of prostate cancer in this experiment. Further studies are needed to develop an appropriate model to induce prostate carcinoma at higher incidence in a shorter period.     

Low tumorigenic response to 3,2'-dimethyl-4-aminobiphenyl administration in the prostate of rats castrated at birth

Six-week-old rats which had been orchiectomized at birth were given 3,2'-dimethyl-4-aminobiphenyl (DMAB) at various doses combined with a stimulus to prostate epithelial cell proliferation in the form of oral administration of methyltestosterone (MT) for 4 weeks. Thereafter MT treatment was continued or the animals received subcutaneous implants of testosterone propionate (TP) and were maintained until sacrifice at week 60. Although prostatitis and prostatic enlargement were frequently observed, especially in the TP group, numbers of atypical hyperplastic lesions were low and only one prostatic carcinoma in situ developed. Thus, despite the presence of proliferation, castration brought about a significant reduction in susceptibility to DMAB.     

Low Tumorigenic Response to 3,2'-Dimethyl-4-aminobiphenyl Administration in the Prostate of Rats Castrated at Birth

Six-week-old rats which had been orchiectomized at birth were given 3,2'-dimethyl-4-aminobiphenyl (DMAB) at various doses combined with a stimulus to prostate epithelial cell proliferation in the form of oral administration of methyltestosterone (MT) for 4 weeks. Thereafter MT treatment was continued or the animals received subcutaneous implants of testosterone propionate (TP) and were maintained until sacrifice at week 60. Although prostatitis and prostatic enlargement were frequently observed, especially in the TP group, numbers of atypical hyperplastic lesions were low and only one prostatic carcinoma in situ developed. Thus, despite the presence of proliferation, castration brought about a significant reduction in susceptibility to DMAB.     

Induction of invasive carcinomas in the accessory sex organs other than the ventral prostate of rats given 3,2'-dimethyl-4-aminobiphenyl and testosterone propionate

The promotion effects of testosterone propionate (TP) on prostate carcinogenesis were investigated in F344 rats given the prostatic carcinogen, 3,2'-dimethyl-4-aminobiphenyl (DMAB). One group of animals received s.c. DMAB injections at a dose of 50 mg/kg body weight at 2-week intervals for a total of 10 injections along with s.c. implantations of TP-containing Silastic tubes. A second experimental group of rats was given DMAB at the same dose and intervals but each injection of DMAB was combined with 3 prior consecutive daily 100-mg/kg body weight s.c. injections of TP. After cessation of carcinogen administration, animals in these two groups received TP implants from week 21 to the end of the experiment. All surviving animals were killed at week 56 and accessory sex gland tumor incidences were compared to those in DMAB alone and other appropriate control groups. The groups given TP plus DMAB and subsequent long term administration of TP developed lesions of the dorsolateral prostate, seminal vesicles, and coagulating glands which were all invasive adenocarcinomas. Incidences were 84.2% (16 of 19 rats) and 66.7% (12 of 18 rats), respectively. Macroscopic large tumors were induced in 13 animals among which 8 demonstrated metastasis to the abdominal cavity, liver, or lung. None of the control groups except for the group given TP injections plus DMAB had equivalent tumors. Development of carcinomas of the ventral prostate, which were all of in situ type, were not increased by subsequent treatment with TP. These data thus clearly showed that TP can exert strong enhancing effects on tumor development in the dorsolateral prostate, seminal vesicles, and coagulating glands but not in the ventral prostate.     

Beef Tallow, but Not Perilla or Corn Oil, Promotion of Rat Prostate and Intestinal Carcinogenesis by 3,2-Dimethyl-4-aminobiphenyl

The modifying effects of three kinds of fat (corn oil, beef tallow or perilla oil, each at 20% in the diet) on F344 rat prostate carcinogenesis induced by 3,2-dimethyl-4-aminobiphenyl (DMAB) were investigated. Non-invasive carcinomas of the ventral prostate were induced by DMAB alone and invasive carcinomas of the other prostate lobes and seminal vesicles by DMAB and testosterone propionate (TP). Eight groups of F344 rats were initiated with 50 mg/kg body weight of DMAB at 2-week intervals for the first 20 weeks, four also receiving TP, extended until week 60. The animals received basal chow powder diet or one of three high fat diets throughout the experiment (60 weeks). One further group served as a non-carcinogen-treated control maintained on basal chow powder diet. Beef tallow significantly increased the development of ventral prostate carcinomas with DMAB alone (from 15 to 45%, P<0.05), while perilla oil reduced the incidence of prostatic intraepithelial neoplasia (PIN) in the ventral lobe of rats given DMAB + TP (from 70 to 10%, P<0.01), but not in those given DMAB alone. No other effects of high fats were observed regarding PIN or invasive cancers of the dorsolateral and anterior prostate or seminal vesicles. A satellite experiment demonstrated that all high fat diets for 4 weeks increased the 5-bromo-2-deoxyuridine (BrdU) labeling index of prostate epithelial cells, suggesting that a high fat intake, irrespective of the fatty acid composition, may accelerate cell kinetics in the prostate. Of the three high fat diets, beef tallow was also found to increase intestinal carcinogenesis. Thus, the present data revealed carcinogenesis in the prostate and intestine to be promoted by beef tallow.     

Beef tallow, but not perilla or corn oil, promotion of rat prostate and intestinal carcinogenesis by 3,2'-dimethyl-4-aminobiphenyl.

The modifying effects of three kinds of fat (corn oil, beef tallow or perilla oil, each at 20% in the diet) on F344 rat prostate carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) were investigated. Non-invasive carcinomas of the ventral prostate were induced by DMAB alone and invasive carcinomas of the other prostate lobes and seminal vesicles by DMAB and testosterone propionate (TP). Eight groups of F344 rats were initiated with 50 mg / kg body weight of DMAB at 2-week intervals for the first 20 weeks, four also receiving TP, extended until week 60. The animals received basal chow powder diet or one of three high fat diets throughout the experiment (60 weeks). One further group served as a non-carcinogen-treated control maintained on basal chow powder diet. Beef tallow significantly increased the development of ventral prostate carcinomas with DMAB alone (from 15 to 45%, P < 0.05), while perilla oil reduced the incidence of prostatic intraepithelial neoplasia (PIN) in the ventral lobe of rats given DMA + TP (from 70 to 10%, P < 0.01), but not in those given DMAB alone. No other effects of high fats were observed regarding PIN or invasive cancers of the dorsolateral and anterior prostate or seminal vesicles. A satellite experiment demonstrated that all high fat diets for 4 weeks increased the 5-bromo-2-deoxyuridine (BrdU) labeling index of prostate epithelial cells, suggesting that a high fat intake, irrespective of the fatty acid composition, may accelerate cell kinetics in the prostate. Of the three high fat diets, beef tallow was also found to increase intestinal carcinogenesis. Thus, the present data revealed carcinogenesis in the prostate and intestine to be promoted by beef tallow.     

Selective induction of rat urinary bladder tumors by simultaneous administration of 3,2'-dimethyl-4-aminobiphenyl (DMAB) and butylated hydroxyanisole or butylated hydroxytoluene is associated with increased DMAB-DNA adduct formation

Modification of 3,2'-dimethyl-4-aminobiphenyl (DMAB) multi-organ carcinogenesis by simultaneous treatment with butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT) was studied using young and old male F344 rats. Animals, 4 or 54 weeks old, were given DMAB (s.c. injection of 50 mg/kg body wt once a week for 10 weeks) along with BHA (2.0% in diet for 11 weeks) or BHT (1.0% in diet for 11 weeks). The experiments were terminated 55 weeks after the commencement. Combined administration of BHA or BHT with the carcinogen resulted in development of urinary bladder tumors in greater than 90% of both young and old rats thus treated, whereas no tumors were induced in animals given DMAB alone. In contrast, the appearance of preneoplastic lesions in the liver and pancreas was reduced by BHA or BHT treatment. Tumor development (less than 30% incidence) was also evident in the small and large intestines, prostate, preputial glands, skin/subcutis and ear duct, with no modification by BHA or BHT. No ageing effects were evident. The formations of DMAB-DNA adducts, evaluated by the enzyme-linked immunosorbent assay and immunohistochemical staining, correlated well with tumorigenesis in the urinary bladder, liver and pancreas. The selective enhancement of urinary bladder tumor induction by BHA and BHT appeared to be due to both increased DMAB-DNA adduct formation caused by metabolic alteration of DMAB in the liver and increased DNA synthesis in the urothelial cells.     

Modifying effects of simultaneous treatment with butylated hydroxyanisole (BHA) on rat tumor induction by 3,2'-dimethyl-4-aminobiphenyl, 2,2'-dihydroxy-di-n-propylnitrosamine and N-methylnitrosourea

The modifying effects of concurrent treatment with high or low doses of butylated hydroxyanisole (BHA) on wide-spectrum carcinogen-induced carcinogenesis were studied in male F344 rats. Groups of 20 animals were treated with 2 or 0.04% BHA for 24 weeks. Starting 2 weeks after the commencement of BHA treatment, they were given s.c. injection of 50 mg/kg body weight 3,2'-dimethyl-4-aminobiphenyl (DMAB) once a week, i.g. administrations of 200 mg/kg body weight 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN) once every 2 weeks, or i.p. injection of 15 mg/kg body weight N-methylnitrosourea (MNU) once every 2 weeks for 22 weeks. Further groups of rats were treated with DMAB, DHPN, MNU, or 2 or 0.04% BHA alone. All surviving animals were killed 24 weeks after the beginning of the experiment and the target organs examined histopathologically. The BHA treatment dose-dependently decreased the incidence of DMAB-induced liver preneoplastic lesions but was associated with significant tumor induction in the forestomach (papillomas, 40%, P less than 0.01) and urinary bladder (papillomas, 53%, P less than 0.001; carcinomas, 80%, P less than 0.001), where no lesions were observed in the group given only DMAB. Concurrent administration of 2% BHA also significantly inhibited the development of alveolar hyperplasia (P less than 0.001) of the lung in DHPN-treated animals, while enhancing induction of forestomach papillomas (P less than 0.05) and simple hyperplasia in the urinary bladder. Neither MNU nor 2% BHA alone induced forestomach carcinoma or papillary or nodular hyperplasia (PN hyperplasia) in the urinary bladder. However, these lesions were observed in 100% (P less than 0.001) and 55% (P less than 0.001) of animals respectively, receiving the two compounds in combination. These results demonstrated that concurrent treatment with BHA not only inhibits but can also strongly enhance carcinogenesis depending on the organ, irrespective of whether the carcinogens act directly or require metabolism. The finding that BHA potently modified carcinogenesis at 0.04% in diet, 1/50 of the carcinogenic dose, suggests that actual dietary levels close to the human situation might play a significant role in tumor development in man.     

Selective Induction of Prostate Carcinomas in F344 Rats Treated with Intraperitoneal Injections of N-Hydroxy-3,2'-dimethyl-4-aminobiphenyl

Groups of F344 and Wistar rats were given an intraperitoneal injection of N-hydroxy-3,2'-dimethyl-4-aminobiphenyl (N-OH-DMAB) at a dose of 5 mg/kg body weight with a 1-week dietary pretreatment with ethinyl estradiol (EE), and this regimen was repeated 10 times at one-week intervals. Additional groups were given N-OH-DMAB 10 times without the dietary EE pretreatment. The total experimental period was 60 weeks. Carcinomas and atypical hyperplasias of the prostate developed in 8 (42%) and 16 (84%) of 19 F344 rats without the dietary EE treatment and in 1 (6%) and 7 (39%) of 18 rats with the EE diet, respectively. No prostatic tumors were found in Wistar rats, although atypical hyperplasias were observed in 6 of 18 rats with and 4 of 8 rats without the EE supplementation. Tumor yields in other organs were extremely low, resulting in good survival of the animals. A comparison of the results with those obtained for DMAB suggests that intraperitoneal administration of N-OH-DMAB in F344 provides a better induction method for models of prostate carcinogenesis.     

Selective induction of prostate carcinomas in F344 rats treated with intraperitoneal injections of N-hydroxy-3,2'-dimethyl-4-aminobiphenyl.

Groups of F344 and Wistar rats were given an intraperitoneal injection of N-hydroxy-3,2'-dimethyl-4-aminobiphenyl (N-OH-DMAB) at a dose of 5 mg/kg body weight with a 1-week dietary pretreatment with ethinyl estradiol (EE), and this regimen was repeated 10 times at one-week intervals. Additional groups were given N-OH-DMAB 10 times without the dietary EE pretreatment. The total experimental period was 60 weeks. Carcinomas and atypical hyperplasias of the prostate developed in 8 (42%) and 16 (84%) of 19 F344 rats without the dietary EE treatment and in 1 (6%) and 7 (39%) of 18 rats with the EE diet, respectively. No prostatic tumors were found in Wistar rats, although atypical hyperplasias were observed in 6 of 18 rats with and 4 of 8 rats without the EE supplementation. Tumor yields in other organs were extremely low, resulting in good survival of the animals. A comparison of the results with those obtained for DMAB suggests that intraperitoneal administration of N-OH-DMAB in F344 provides a better induction method for models of prostate carcinogenesis.     

Lack of modifying effects of 4-ter t-octylphenol and benzyl butyl phthalate on 3,2-dimethyl-4-aminobiphenyl-induced prostate carcinogenesis in rats

The modifying effects of dietary feeding of two estrogenic compounds, 4-tert-octylphenol (tOP) and benzyl butyl phthalate (BBP), on 3,2-dimethyl-4-aminobiphenol (DMAB)-induced prostatic carcinogenesis were investigated in male F344 rats. We also assessed the effects of the test compounds on the proliferating cell nuclear antigen (PCNA) index in induced neoplasms, prostatic intra-epithelial neoplasm (PIN), and non-lesional glands in the prostate. To induce prostatic neoplasms, rats were given subcutaneous injections of DMAB (25 mg/kg body weight) every other week, 10 times in total. They also received the experimental diet containing 10 or 100 ppm tOP and BBP for 40 weeks, starting 1 week after the last dosing of DMAB. DMAB exposure produced prostatic adenocarcinoma with an incidence of 41.2% at the end of the study (week 60). Dietary administration of tOP and BBP did not affect the incidence of prostatic adenocarcinoma: 43.8% in the DMAB --> 10 ppm tOP group; 25.0% in the DMAB --> 100 ppm tOP group; 43.8% in the DMAB --> 10 ppm BBP group; and 43.8% in the DMAB --> 100 ppm BBP group. The PCNA indices in adenocarcinomas, PIN, and non-lesional glands in rats treated with DMAB and tOP or BBP were slightly lower than that of the DMAB alone group, but the differences were not statistically significant. These results might suggest that dietary feeding of the estrogenic compounds tOP and BBP did not modulate DMAB-induced prostatic carcinogenesis in rats.     

Decrease of Prostaglandin E2 and 5–Bromo–2'–deoxyuridine Labeling but Not Prostate Tumor Development by Indomethacin Treatment of Rats Given 3,2'–Dimethyl-4-aminobiphenyl and Testosterone Propionate

The modifying effects of indomethacin (IM) on rat prostate carcinogenesis induced by 3,2'–dimethyl–4–aminobiphenyl (DMAB) were investigated. F344 rats were given 50 mg/kg body weight of DMAB at 2–week intervals for 20 weeks and then received IM at a dose of 20 ppm in the drinking water for 37 weeks. Separate groups additionally received testosterone propionate (TP) in Silastic tubes throughout the experiment. DMAB alone induced carcinomas in situ in the ventral lobe and in combination with TP caused invasive carcinomas of the dorso–lateral and anterior lobes and seminal vesicles. No clear suppression by IM of development of in situ carcinomas or in vasive carcinomas was observed. In a short–term satellite experiment, it was revealed that prostaglandin E₂ (PGE₂) levels in the dorso–lateral prostate and seminal vesicles, but not the ventral prostate, were significantly reduced by IM and that TP itself also suppressed PGE₂ levels. The 5–bromo–2'–deoxyuridine labeling index in the ventral prostate was significantly decreased by IM administration. These results indicate that while IM can efficiently suppress tissue PGE₂ levels, it does not inhibit tumor development in the prostate or seminal vesicles of rats in the present model.     

Organ dependent enhancement of rat 3,2'-dimethyl-4-aminobiphenyl (DMAB) carcinogenesis by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP): positive effects on the intestine but not the prostate

In order to evaluate tumor enhancing effects of the heterocyclic carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), doses of 100 and 300 p.p.m. PhIP were given for 40 weeks to male F344 rats, which initially received 3,2'-dimethyl-4-aminobiphenyl (DMAB). DMAB shows a similar carcinogenic organ spectrum to that of PhIP, including the prostate and colon. PhIP alone at a dose of 300 p.p.m. resulted in the development of prostate and intestine cancers. Furthermore, among the DMAB-treated group, enhancement of intestinal carcinogenesis by 300 p.p.m. PhIP was observed. However, no prostate enhancement was demonstrated in the DMAB + PhIP group. Since PhIP-DNA adduct formation in the prostate epithelial cells in a satellite experiment was not affected by pre-treatment with DMAB, it is speculated that the contradictory findings between the intestine and prostate may be due to the specific biological effects of PhIP. Taking into account previous data, that PhIP clearly enhanced rat 1,2-dimethylhydrazine-initiated colon tumorigenesis, the potential of PhIP to enhance colon carcinogenesis may be initiator dependent.     

Protective effect of acetaminophen against colon cancer initiation effects of 3,2'-dimethyl-4-aminobiphenyl in rats.

A previous investigation demonstrated the anticarcinogenicity of acetaminophen (APAP) against colon carcinogenesis in rats induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB). DMAB was selected as a structurally related surrogate for heterocyclic amines, formed during cooking of protein, which are believed to be involved in human colon cancer. The objective of the present study was to ascertain whether the early initiating effects of this colon carcinogen are inhibited by APAP. Six groups of male F344 rats were treated over a 6-week period as follows: (1) vehicle (corn oil) for 6 weeks; (2) APAP in the diet at 1000 ppm daily for 6 weeks; (3) 50 mg/kg DMAB by gavage once a week for the last 4 weeks; (4) 5 mg/kg DMAB as for (3); (5) 1000 ppm APAP for 6 weeks and 50 mg/kg DMAB for the last 4 weeks; and (6) 1000 ppm APAP and 5 mg/kg DMAB as for (5). Colonic tissue was within normal limits in the control and APAP groups. In the APAP only group, apical enterocytic hypertrophy and hyperaemia over the entire surface epithelium was present. In the high-dose DMAB group, in the lower third of the crypts, foci of enlarged glands with hypertrophic cells exhibiting karyomegaly and anisokaryosis (FHE) of 3+ degree of severity were evident in 100% of the animals. Also, there were increases in periglandular fibrocytes, matrix and mononuclear cells (PF). In the low-dose DMAB group both FHE and PF changes with the same degree of severity were reduced. In rats given the low dose of DMAB plus APAP, FHE and PF with the same degree of severity (3+) was absent. Both DMAB exposures increased significantly the replicating fraction of colonic enterocytes in an exposure-related fashion and the replicating fractions were significantly reduced by APAP. In 32P-postlabelling of colon, liver and urinary bladder DNA, high-dose DMAB produced 2-6 distinct dose-related spots reflecting DNA adducts. These spots were reduced or were no longer detectable in all three tissues when APAP was given 2 weeks before and during DMAB exposure. Using immunohistochemical detection of DMAB adducts in the colon, a dose-related colour intensity was present for both doses of DMAB. APAP reduced this by 94-fold. Thus, APAP produced a marked protective effect in colonic enterocytes against several parameters of neoplastic development by the carcinogen.     

Direct Effects of Testosterone, Dihydrotestosterone and Estrogen on 3,2'-Dimethyl-4-aminobiphenyl-induced Prostate Carcinogenesis in Castrated F344 Rats

The present experiment was carried out to explore the effect of endogenous androgen on rat prostate carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) and testosterone propionate (TP) or 5α-dihydrotestosterone (DHT) with or without ethinyl estradiol (EE). In order to eliminate the influence of endogenous androgen, F344 rats were orchiectomized just after initiation with the prostate carcinogen, DMAB, and then given TP, DHT, TP plus EE or DHT plus EE for 40 weeks. The results demonstrated that while administration of TP following DMAB treatment causes invasive carcinomas in the lateral and anterior prostate and seminal vesicles, DHT does not exhibit equivalent effects. Synergistic enhancement was also evident with TP plus EE, but not with DHT plus EE. The incidences of prostatic and seminal vesicle lesions in all groups of the present experiment, except for the group given castration without hormonal supplement, were equivalent to those previously found in non-castrated animals. Therefore, the present findings indicate that endogenous testosterone may not be required for promotion hy TP/EE of DMAB-initiated prostate carcinogenesis and that it may not contribute to the actions of DHT.     

Lack of modification by naturally occurring antioxidants of 3,2'-dimethyl-4-aminobiphenyl-initiated rat prostate carcinogenesis

The modifying effects of 6 naturally occurring antioxidants on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-initiated rat prostate carcinogenesis were investigated in male F344 rats. Animals were pretreated with DMAB in a 20-week initiation protocol and then administered basal diet containing 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone, 2 ppm selenium, 2% gamma-orysanol or 1% alpha-tocopherol for 40 weeks. The experiment was terminated at week 60 for histopathological assessment of lesion development. Atypical hyperplasias and carcinomas of the prostate were observed in the ventral lobe in all groups treated with DMAB. However, the incidences of these lesions were not significantly different between carcinogen control and antioxidant-treated groups. There were also no significant increases or decreases in the incidences of tumors in any other organs.