Inhibition by aspirin of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide initiation and sodium saccharin promotion of urinary bladder carcinogenesis in male F344 rats.

N-[4-(5-Nitro-2-furyl)-2-thiazolyl]formamide (FANFT) is metabolically activated by several enzyme systems, including prostaglandin H synthase. Aspirin is an inhibitor of prostaglandin H synthase and has been shown to inhibit FANFT-induced bladder carcinogenesis when coadministered in the diet. To further evaluate the effects of aspirin on bladder carcinogenesis in the rat, we have coadministered aspirin with FANFT during the initiation phase and with sodium saccharin during the promotion phase of carcinogenesis. FANFT was administered in the diet at a level of 0.2% for 6 weeks as the initiator and sodium saccharin was administered in the diet at a level of 5% for 61 weeks as promoting stimulus. Aspirin was administered at a level of 0.5% with FANFT or with sodium saccharin, and appropriate control groups were included. Weanling male Fischer 344 rats were utilized and the chemicals were added to Agway Prolab 3000 rat chow. A 1-week interval was included between the FANFT and sodium saccharin administration during which the rats received either aspirin containing diet or control chow, depending on the treatment regimen of the group. Thirty rats were included in each group at the beginning of the experiment, except for the control group which contained 40. Rats given FANFT followed by saccharin had a bladder carcinoma incidence of 83%. Rats given aspirin with FANFT but not with saccharin had a carcinoma incidence of 20% and the rats fed aspirin with the saccharin but not with the FANFT had an incidence of 28%. FANFT followed by control diet resulted in a bladder carcinoma incidence of 10%, as was true for the rats given FANFT plus aspirin followed by control diet. However, the hyperplastic effects induced in the bladder epithelium by saccharin without prior FANFT administration were inhibited by coadministration with aspirin. These results indicate that aspirin inhibits both FANFT initiation and sodium saccharin promotion of bladder carcinogenesis, but the mechanisms involved would most probably be different for each.

Effect of avitaminosis A and hypervitaminosis A on urinary bladder carcinogenicity of N-(4-(5-Nitro-2-furyl)-2-thiazolyl)formamide.

The effect of vitamin A deficiency and hypervitaminosis A on the urothelial carcinogenicity of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formanmide (FANFT) was determined in female weanling Sprague-Dawley rats. Vitamin A deficiency resulted in squamous metaplasia of the urinary bladder and high incidences of cystitis, ureteritis, and pyelonephritis. Administration of FANFT to vitamin A-deficient rats appeared to accelerate the carcinogenic process, with earlier appearance of urinary bladder tumors and the development of ureteral and renal pelvic carcinomas. Most of these tumors were squamous cell, occasionally with transitional cell foci. Hypervitaminosis A prevented the appearance of squamous metaplasia and squamous cell neoplasia in rats fed FANFT, but it did not inhibit the formation of transitional cell hyperplasia or neoplasia in comparison to rats receiving normal levels of vitamin A and FANFT.

The pathogenesis of experimental bladder cancer.

The pathogenesis of signal morphological lesions of the urinary bladder induced in several species following administration of N-butyl-N-(4-hydroxybutyl)nitrosamine, bracken fern, or N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide is presented. Incidences of bladder neoplasia exceeding 80% were generated in the rat by each compound. Bladder neoplasia was induced in the following species by each substance: by N-butyl-N-(4-hydroxybutyl)nitrosamine in the mouse, hamster, guinea pig, and dog; by bracken fern in the guinea pig, mouse, and cow; and by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide in mouse, hamster, and dog. The guinea pig appeared resistant to the bladder oncogenicity of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide. Different species displayed a gradient of bladder neoplastic responsiveness. Hyperplasia was a consistent early lesion and was usually focal. Early hyperplastic lesions regressed following removal of the carcinogenic stimulus, but later lesions appeared to be irreversible. These animal systems appear useful in providing opportunities for investigations relevant to human bladder cancer.

Enhancing effect of allopurinol on the induction of bladder cancer in rats by n-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide.

The effects of allopurinol on the induction of bladder cancer by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT), excretion of urinary tryptophan metabolites, hepatic nitroreductase activity, and the acid-soluble thiol content of liver and blood in weanling female Fischer rats were investigated. Four groups of rats were given normal diet or normal diet supplemented with 0.005% allopurinol, 0.188% FANFT, or 0.005% allopurinol-0.188% FANFT. Transitional cell carcinomas appeared in 3 of 30 rats (10%) at 15 weeks and in 7 of 44 rats (16%) at 20 weeks in the FANFT-treated group; the carcinomas appeared in 14 of 35 rats (40%) at 15 weeks and in 27 of 50 rats (54%) at 20 weeks in the FANFT-allopurinol-treated group. Growth rate was not affected by allopurinol and FANFT. Allopurinol alone caused no morphological change in the epithelial cells of the urinary bladder but decreased hepatic cytosol nitroreductase activity. FANFT alone had no effect on hepatic cytosol or microsomal nitroreductase activity but increased hepatic and blood acid-soluble thiol content. FANFT increased the urinary excretion of anthranilic acid glucuronide, kynurenine, acetylkynurenine, and 3-hydroxykynurenine and decreased indican and o-aminohippurate excretion. Allopurinol did not alter the effects of FANFT on the acid-soluble thiol content of liver and blood or the excretion of urinary tryptophan metabolites.

Tumor production in germ-free rats fed 5-nitrofurans.

Weanling female germ-free Sprague-Dawley rats were divided into 3 groups: the control group rats were fed an autoclaved 5010C diet for 2 years; the nitrofurantoin (NF) group rats were fed this diet supplemented with 0.188% NF for 2 years; and the N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide (FANFT) group rats were fed this diet supplemented with 0.188% FANFT for 20 weeks followed by 20 additional weeks of the control diet. The FANFT-group rats were killed following the early appearance of bladder tumors. Six of 11 control rats had tumors: 2 with mammary fibroadenomas, 1 with adrenal adenoma, 1 with leukemic spleen, and 2 with mesenchymal sarcoma of the colon. Ten of 12 NF-group rats had tumors: 9 with mammary fibroadenomas, 1 with adrenal adenoma, and 1 each with leukemic spleen and cervical squamous cell carcinoma. Eight of 12 FANFT-group rats had tumors: 7 with bladder and 1 with renal pelvis transitional cell carcinoma. The incidences of mammary fibroadenoma in the NF group and of lower urinary tract tumors in the FANFT group were significantly greater (P less than 0.01) than those of these tumors in the control group.

Influence of the application mode of N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide on the localization of its carcinogenic expression in female NMRI-mice.

The administration of N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide FANFT) by gavage to female NMRI-mice resulted in a high incidence of neoplasms of the forestomach. From 117 effective animals which were pooled from 3 dosed groups, 30 squamous cell carcinomas and 26/117 papillomas of the forestomach were diagnosed. Only 5/117 neoplasms of the urinary bladder occurred. The average cumulative dose administered was 1180 mg/mouse, and the mean latent period for the induction of forestomach tumours was 574 days. The mode of application seems to be an important factor in the carcinogenicity of FANFT.

Effect of phenobarbital on the carcinogenesis of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide in rats.

Male Fischer rats were fed a N-[4-(5-nitro-2-furyl]-2-thiazolyl]formamide (FANFT) diet for 6 weeks followed by a phenobarbital (PB) diet for an additional 86 weeks. PB significantly increased the incidence of bladder tumors, but not the incidence of hepatic foci and areas of cellular alterations caused by FANFT. The results suggest that PB may be a weak promoter for bladder carcinogenesis, and that FANFT may not be an initiator for hepatocarcinogenesis.

Effect of aspirin on N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide-induced epithelial proliferation in the urinary bladder and forestomach of the rat.

The co-administration of aspirin with N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide (FANFT) to rats resulted in a reduced incidence of FANFT-induced bladder carcinomas but a concomitant induction of forestomach tumors. An autoradiographic study was performed on male F-344 rats fed diet containing FANFT at a level of 0.2% and/or aspirin at a level of 0.5% to evaluate the effect of aspirin on the increased cell proliferation induced by FANFT in the forestomach and bladder. FANFT-induced cell proliferation in the bladder was significantly suppressed by aspirin co-administration after 4 weeks but not after 12 weeks. In the forestomach, and also in the liver, aspirin did not affect the FANFT-induced increase in labeling index. The present results are consistent with the carcinogenicity experiment suggesting that different mechanisms are involved in FANFT carcinogenesis in the bladder and forestomach, and that aspirin's effect on FANFT in the forestomach is not due to an irritant effect associated with increased cell proliferation. Also, there appears to be an adaptation by the rats to the chronic ingestion of aspirin.

13-cis-retinoic acid: effect on urinary bladder carcinogenesis by N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide in Fischer rats.

The failure of 13-cis-retinoic acid to inhibit either the incidence or severity of bladder carcinoma in female Fischer rate initiated with N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) suggests that inhibition of bladder carcinogenesis by natural and synthetic retinoids is carcinogen-class specific, and adds an element of complexity to approaches in chemoprevention.

Agglutination assay of bladder cells by Concanavalin A proved the high susceptibility of analbuminemic rats to bladder carcinogens.

The susceptibility of analbuminemic rats, a mutant strain of Sprague-Dawley rats, to bladder carcinogens was examined by testing the agglutinability of isolated bladder epithelial cells by Concanavalin A (Con A). One-week treatment with 0.001% N-butyl-N-(4-hydroxybutyl)nitrosamine (BHBN) in the drinking water or 0.01% N-(4-(5-nitro-2-furyl)-2-thiazolyl)-formamide (FANFT), 0.01% and 0.1% 4-aminobiphenyl, 0.1% 4-nitrobiphenyl, 0.1% benzidine, 0.1% 2-napthylamine or 5% sodium saccharin in the diet clearly induced high agglutinability of bladder cells of male analbuminemic rats but not Sprague-Dawley rats. These results suggest that male analbuminemic rats are very susceptible to bladder carcinogens in general and therefore will be very useful in screening tests for bladder carcinogens.

Production of urinary tract tumors by co-administration of uracil and N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide in F344 rats.

Co-administration of uracil and N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) to weanling female Fischer rats produced uracil stones in the bladder and significantly reduced the incidence of bladder tumors. Contrary to bladder tumors, the incidence of renal pelvic and ureteric tumors was increased by this regimen. Feeding of uracil alone produced bladder tumors, in addition to the hyperplasia of renal pelvis, ureter and bladder. The mechanism of uracil's effect on FANFT carcinogenesis is not known.

Enhancement by phenothiazine and 2,5-di-O-acetyl-D-glucosaccharo-(1,4)(6,3)-dilactone of bladder carcinogenicity of N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide in rats.

Rats concomitantly fed N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide (FANFT) and phenothiazine, or concomitantly fed FANFT and Glucaron then fed Glucaron alone had significantly greater incidences of transitional cell carcinomas of the bladder than rats fed FANFT alone. Caffeine and cysteamine did not affect FANFT bladder carcinogenesis. Phenothiazine induced nitroreductase activity of hepatic microsomes.

Use of cell proliferation data in modeling urinary bladder carcinogenesis.

A multistage, probabilistic, biologically based model of carcinogenesis has been developed involving qualitative and quantitative aspects of the process. A chemical can affect the risk of cancer by directly damaging DNA and/or increasing the number of cell divisions during which errors in DNA replication can occur. Based on this model, carcinogens are classified as genotoxic versus nongenotoxic; nongenotoxic chemicals are further divided on the basis of whether or not they act through a specific cell receptor. Nongenotoxic compounds, particularly those acting through a nonreceptor mechanism, are likely to have dose and/or species-specific thresholds. This classification also implies the existence of chemicals that will be carcinogenic at high doses in animal models, but because of dose and/or mechanistic considerations, will not be carcinogenic to humans at levels of exposure. N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide (FANFT) and 2-acetylaminofluorene (AAF) are classical genotoxic bladder carcinogens that also cause proliferative effects at higher doses. Although there is an apparent no-effect level for the urinary bladder carcinogenicity of these two compounds at low doses, in reality, DNA adducts form at these low levels, and it is likely that there is a cancer effect (no threshold), but it is below the level of detection of the bioassay. These conclusions are based on studies involving multiple doses and time points in rodents, including results from the ED01. Pellets implanted directly into the rodent bladder lumen or calculi formed in the urine as a result of an administered chemical cause abrasion of the urothelium, and a marked increase in cell proliferation and cell number, and ultimately tumors.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of nitrofurantoin on the two stages of urinary bladder carcinogenesis in the rat.

The possibility that nitrofurantoin is a complete carcinogen or is an initiator or promoter of urinary bladder carcinogenesis was evaluated in male weanling F344 rats. No increase in tumor incidence was observed in rats fed nitrofurantoin at a level of 0.187% of the diet for 2 years compared to a control group. Also, no evidence of bladder initiating activity by nitrofurantoin was observed using sodium saccharin (5% of the diet) as a promoter, and no promoting activity was observed when nitrofurantoin was fed after initiation by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (0.2% of the diet for 4 weeks). In a second experiment, nitrofurantoin (at a dose of 0.187% of the diet) was administered for 6 weeks to rats with a rapidly proliferating bladder epithelium following freeze ulceration, and then the rats were treated with 5% sodium saccharin in the diet for 98 weeks. In additional rats, labelling index following [3H]thymidine injection, determined after 12 weeks of feeding nitrofurantoin, was not increased above control levels in the urinary bladder, stomach, duodenum, or liver. Metabolism of nitrofurantoin by prostaglandin H synthase (PHS) was examined using solubilized ram seminal vesicle microsomes. The rate of nitrofurantoin metabolism by PHS was much less than that observed with benzidine, and the proportion of total metabolite bound to protein was also much less than that with benzidine. These results are consistent with previous reports describing the lack of effect of nitrofurantoin on urinary bladder carcinogenesis.

Mutagenicity of urine of various species fed N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide or 2-amino-4-(5-nitro-2-furyl)thiazole.

Rats, mice and hamsters, which are susceptible to the bladder carcinogenesis by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT), and guinea pigs, which are not, were fed a diet containing 0.188% FANFT or 0.188% 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT) for 1 week and their urine was then examined for mutagenicity for S. typhimurium TA100. The mutagenicities of the urine of these species fed FANFT were approximately equal. Similarly, that of the urine of these species fed ANFT were also approximately equal. However, the urine from FANFT-fed animals was approximately 10 times as mutagenic as that from ANFT-fed animals. ANFT was detected only in the urine of rats, mice or hamsters fed FANFT. A positive correlation between the susceptibility toward bladder carcinogenesis by FANFT and urinary ANFT excretion was demonstrated, although the correlation between this susceptibility and urine mutagenicity was lacking.

Multi-stage carcinogenesis in the urinary bladder.

Sodium saccharin has been shown to be a promoting substance for urinary bladder carcinogenesis in the rat following initiation with N-methyl-N-nitrosourea, N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT), or N-butyl-N-(4-hydroxybutyl)nitrosamine. It has been shown to have many of the properties of promoting substances in other animal models, such as the mouse skin; it lacks mutagenic activity, induces hyperplasia in the target tissue, and does not bind DNA. It has recently been demonstrated to be co-carcinogenic for the rat bladder. It has also been shown that the administration of sodium saccharin during the regenerative hyperplasia observed after freeze ulceration or cyclophosphamide administration resulted in the induction of bladder tumours, even without pre-initiation with FANFT or other known initiating substances. This model appears to be analogous to the administration of sodium saccharin to animals with a rapidly proliferating bladder mucosa as occurs in utero during the two-generation carcinogenesis experiments and in the pellet-insertion experiments in which a cholesterol pellet containing sodium saccharin is inserted into the bladder. To enhance our understanding of the complex interaction of the many variables involved in two-stage bladder carcinogenesis, a stochastic model has been formulated based on long-term carcinogenicity and in vivo tissue kinetic studies. This model indicates the importance of cell proliferation and the development of hyperplasia in carcinogenesis.

The effect of long-term administration of aspirin and sodium saccharin on the rat kidney.

In a study primarily designed to evaluate the inhibitory effects of aspirin on N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT)-initiated and saccharin-promoted bladder carcinogenesis, significant renal lesions were observed. Thus, administration in the diet of aspirin and sodium saccharin to F344 male rats for 68 weeks resulted in significant lesions of the renal papilla. In contrast to the bladder, aspirin enhanced the frequency and severity of the proliferative action of sodium saccharin on the epithelium of the renal papilla (p less than 0.05 compared to rats treated with either compound alone). The majority of rats administered the two chemicals together demonstrated moderate to severe urothelial hyperplasia of the renal papilla. Columnar metaplasia of the papillary epithelium also occurred frequently in rats fed the combination of chemicals. The rats treated with a combination of sodium saccharin and aspirin had a high incidence of renal papillary necrosis which was also present to a lesser extent among rats treated with aspirin only. Papillary calcification was also frequently observed in the rats fed the combination of aspirin and sodium saccharin. Sodium saccharin or aspirin alone reduced the light microscopic incidence and severity of rat nephropathy, a common finding in aging rats. It would appear that the hyperplastic and renal papillary toxic effects of aspirin and sodium saccharin are independent responses, and that the administration of the two chemicals together greatly accentuates these responses.

Human relevance of animal carcinogenicity studies.

Extrapolation of results from rodent bioassays involving high-dose exposures to possible carcinogenic risk in humans exposed to low doses is based on the assumptions of species relevance and high- to low-dose extrapolation. For genotoxic chemicals, such as 2-acetylaminofluorene and N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide, these assumptions appear to be appropriate, although the dose response can be greatly modified by cell proliferation effects of these chemicals at high doses. In contrast, nongenotoxic chemicals, such as chemicals causing urinary calculi or sodium saccharin and related sodium and potassium salts, frequently are carcinogenic only at high doses and/or only in specific species. Consequently, for extrapolation of results for nongenotoxic chemicals these assumptions may not be appropriate.