Acetyl transferase-mediated metabolic activation of N-hydroxy-4-aminobiphenyl by human uroepithelial cells

Metabolism and nucleic acid binding of N-hydroxy-4-aminobiphenyl (N-OH-ABP), a proximate carcinogenic metabolite of the human bladder carcinogen 4-aminobiphenyl (ABP), was investigated using cultured normal human uroepithelial cells (HUC). HPLC and TLC of the ethyl acetate extract of the media from cultured HUC after 4 h exposure to N-OH-ABP revealed the formation of two major metabolites, ABP and 4-acetylaminobiphenyl (AABP), suggesting the presence of N-acetyl transferase(s) in HUC. This was further confirmed by the formation of AABP, during the incubation of ABP with acetyl coenzyme A (AcCoA) and HUC cytosol. To test whether these enzymes also catalyze the AcCoA-dependent O-acetylation, we examined the metabolic activation of N-OH-ABP using cytosolic preparations. Cytosol from HUC catalyzed AcCoA-dependent binding of [3H]N-OH-ABP to RNA; the amount of binding was 757 pmol/mg RNA/mg protein. Binding with DNA was quantitatively similar to RNA. HPLC and TLC analyses of the enzymatic hydrolysate of [3H]N-OH-ABP-bound DNA revealed the major adduct to be N-(deoxyguanosine-8-yl)-4-aminobiphenyl, based on mobility of the radioactivity in comparison with the authentic synthetic standard. 32P-Post-labeling analysis of the DNA from the cytosol-mediated binding of N-OH-ABP revealed four radioactive spots. In contrast, post-labeling analysis of the DNA from intact HUC exposed to N-OH-ABP showed five adducts, including two of the adducts observed with HUC cytosols, suggesting the possible involvement of additional activation pathway(s) in intact HUC. These results suggest that bioactivation of N-OH-ABP could occur within the HUC, the target organ for ABP, and that cytosolic acetyl transferase(s) may play a critical role in susceptibility to arylamine-induced bladder carcinogenesis.

Schedule-dependent variations in the response of murine P388 leukemia to cyclophosphamide in combination with interferons-alpha/beta

Positive therapeutic effects of interferons (IFNs) in combination with other therapies will depend on defining modalities, doses, and timing of treatment in the setting of varied tumor burdens. When 10(4) P388 leukemia cells were inoculated i.p. on day 0 in BALB/c x DBA/2 F1 mice, all mice died within 18 days if left untreated. Murine IFN-alpha/beta (5 x 10(5) units) injected daily i.p. on days 5-9 resulted in 20% increase in life span (ILS) (P less than 0.0001). Cyclophosphamide (CY) (100, 33, or 15 mg/kg) was injected i.p. once 2 days before start (day 3), simultaneously with start (day 5), or 2 days after cessation of IFN treatment (day 11). When 100 mg/kg CY alone were injected on day 3 or 5, all mice survived more than 90 days and were considered cured. When IFN was given after this curative dose of CY, more tumor deaths occurred; up to 100% of the mice died when 100 mg/kg CY on day 3 were combined with IFN on days 5-9. Increased mortality with the combination was not due to added toxicity of CY and IFN since the mice developed abdominal tumors and ascites. Mice not inoculated with tumor cells and treated similarly suffered only a transient weight loss, had only moderate white count depression, and did not die. When IFN was injected before CY on days 1-5 (instead of days 5-9), IFN did not alter the effectiveness of CY (100 mg/kg on day 5). In contrast to these results, when CY (100 mg/kg) was administered on day 11, after IFN (days 5-9), an augmented survival occurred with 119% ILS and 40% cures (CY alone on day 11 resulted in 69% ILS but no cures). In addition, when CY at a lower dose of 15 mg/kg was injected in combination with IFN, survival was consistently augmented by IFN; e.g., CY alone on day 3 caused 40% ILS and with IFN (days 5-9) 60% ILS (P less than 0.0001). Qualitatively similar findings were obtained when P388 leukemia cells were inoculated s.c. and the drugs delivered i.p. Inhibition by IFN of antitumor effects of a second alkylating agent, 1,3-bis(2-chloroethyl)-1-nitrosourea, was also identified. Thus, IFN-alpha/beta potentiated suboptimal CY effects for P388 leukemia, had neutral effects when injected before CY treatment, and inhibited antitumor activity of curative CY or nitrosourea schedules.

Xanthine oxidase-mediated mutagenicity of the bladder carcinogen 4-nitrobiphenyl

Xanthine oxidase catalyzed mutagenicity of 4-nitrobiphenyl (NBP), a dog-bladder carcinogen, was tested in Ames assay using Salmonella typhimurium TA98 strains. NBP was active as a mutagen in the parent strain TA98 which is proficient in nitroreductase, while it was inactive in the strain TA98NR which is deficient in nitroreductase. However, preincubation of NBP at 37 degrees C with NADH and commercial preparations of xanthine oxidase for 30 min resulted in a dose-dependent increase in the mutagenic activity in TA98NR. Allopurinol blocked the xanthine oxidase catalyzed mutagenicity of NBP in TA98NR and the extent of inhibition was dependent upon the concentration of the inhibitor. Rat-liver and dog-bladder cytosol preparations also enhanced the mutagenic activity of NBP in TA98NR in a dose-dependent manner. In addition, the cytosol-mediated activity was also inhibited by allopurinol, implying that the cytosolic enzyme activity might be due to xanthine oxidase. In vitro enzymatic reduction of NBP using bacterial cell lysates of TA98 and TA98NR revealed the major product of reduction to be 4-aminobiphenyl. The transient intermediates of reduction were not detected during the in vitro incubation. The reduction intermediate N-hydroxylaminobiphenyl showed direct and equal mutagenic activity in both TA98 and TA98NR, in contrast to NBP. These results suggest that N-hydroxylaminobiphenyl is generated during the preincubation of NBP with xanthine oxidase or cytosolic preparations and the former might account for the mutagenicity of NBP. Furthermore, the occurrence of such enzyme(s) in the target tissue for NBP carcinogenesis, support the hypothesis that metabolic activation of the bladder carcinogen NBP could occur within the target organ by virtue of its intrinsic metabolic potential.

Mutagenicity of 3,4-diphenyl-5-nitrofuran analogs in Salmonella typhimurium

A new series of chemicals comprising eight different 3,4-diphenyl-substituted furan analogs, namely, methyl-3,4-diphenyl-2-furoate, methyl-3,4-diphenyl-5-nitro-2-furoate, 3,4-diphenyl-5-nitro-2-furoic acid, 3,4-diphenyl-5-nitro-2-acetylfuran, 3,4-diphenyl-5-nitro-2-bromoacetylfuran, 2-amino-4-(3,4-diphenyl-5-nitro-2-furyl)thiazole, 2-acetyl-amino-4-(3,4-diphenyl-5-nitro-2-furyl)thiazole and 2-formyl-amino-4-(3,4-diphenyl-5-nitro-2-furyl)thiazole were synthesized and their mutagenic activities tested in Salmonella typhimurium. The structure--activity relationship studies revealed that for mutagenic activity the nitro group is essential and that the potency of activity is greatly altered by the nature of the substituent at the 2-position of the furan ring. The mutagenic activities of these chemicals were generally much higher in TA100 compared to TA98. The relative order of activities for 2-substituted, 3,4-diphenyl-5-nitrofurans were COOCH3 greater than COCH2BR greater than COCH3 greater than COOH in S. typhimurium TA100. 3,4-Diphenyl-5-nitro-2-bromoacetylfuran was equally active in nitroreductase-proficient (TA98, TA100) and in nitroreductase-deficient (TA98NR, TA100NR) strains. In contrast, the acetyl and carboxymethyl ester analogs were relatively less active in nitroreductase-deficient strains. Mutagenic activities of 3,4-diphenyl-substituted furylthiazoles in comparison with the unsubstituted analogs of N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide, N-[4-(5-nitro-2-furyl)-2-thiazolyl]-acetamide and 2-amino-4-(5-nitro-2-furyl)thiazole revealed that the phenyl groups drastically reduced their mutagenic activities. However, the relative order of activities formylamino greater than or equal to acetylamino greater than amino were the were the same between phenyl-substituted and unsubstituted analogs.

A protocol for the combined biochemical and serological identification of the Ames mutagen tester strains as Salmonella typhimurium

Previously published reports have noted biochemical reactions atypical of Salmonella among the Ames tester strains of Salmonella typhimurium, and an inability to assign the strains to a specific Salmonella O (heat-stable cell wall) antigen group. We studied the biochemistry and serology of strains TA97, 98, 100, 102, 104, 1535, 1537, and 1538 in an attempt to develop a protocol to correctly speciate the strains. Biochemical reactions of all eight strains using standard media supplemented with histidine and biotin were consistent with those of the genus Salmonella. Strains TA100, 104, and 1535 were assigned to Salmonella O groups using bacteria treated with hot ethanol (White schema). H (flagellar) antigen assignments were performed successfully with seven of the eight strains. Two H antigen assignments required the use of the Craigie tube test for selection of motile revertants. Combining our biochemical and serological results obtained by this protocol, we were able to correctly speciate TA100, 104, and 1535 as Salmonella typhimurium. Our results demonstrate that representatives of the tester strains can be correctly speciated provided that procedures are followed that allow for the unusual nutrient requirements, the deep rough cell wall mutation, and the variably deficient motility of these organisms.

Urine recovery experiments with quercetin and other mutagens using the Ames test

Recovery from urine of the mutagenic activity of 2-anthramine, cyclophosphamide, 7,12-dimethylbenz[a]anthracene, 6-chloro-9-((3-(2-chloroethylamino)-propyl)amino)-2-methoxyacridin e dihydrochloride (ICR-191), mitomycin-C, nitrofurantoin, and quercetin was studied with several of the Ames tester strains using acetone-extracted XAD-2 columns with yields ranging from 27% to 79%. Dose responses of the pure chemicals were also studied, and results showed TA 97 to be far more susceptible to quercetin mutagenesis than TA 1537. Reducing pour plate agar volume enhanced mutagenesis.

Factors affecting the mutagenic activity of quercetin for Salmonella typhimurium TA98: metal ions, antioxidants and pH

The mutagenic activity of quercetin for Salmonella typhimurium TA98 was inhibited by addition of metal salts. MnCl2 was a potent inhibitor, followed by CuCl2, FeSO4, and FeCl3, the probable mechanism being facilitated catalytic oxidation of quercetin. With quercetin incorporated at a level of 100 nmoles/plate, approximate doses (nmoles/plate) to give 50% inhibition of mutagenic activity were: MnCl2 less than 10 (-S9), 18 (+S9); CuCl2 65 (-S9), greater than 100 (+S9); FeSO4 190 (-S9), greater than 300 (+S9); or FeCl3 275 (-S9), greater than 300 (+S9). Ascorbate, superoxide dismutase, and, to a lesser extent, NADH and NADPH, all enhanced the mutagenic activity of quercetin in the absence of the mammalian-microsome (S9) system, but had no significant effect in the presence of the S9 mix. The maximum enhancement of activity by ascorbate or superoxide dismutase was approximately 87% of the increase achieved by addition of the S9 mix. Tyrosinase (catechol oxidase) substantially reduced the mutagenic activity of quercetin in the absence of the S9 mix. At lower levels of tyrosinase, activity was restored by incorporation of the S9 mix. It is proposed that the S9 mix enhances the mutagenic activity of quercetin by scavenging superoxide radicals, thus inhibiting the autoxidation of quercetin, and possibly by reducing quinone oxidation products of quercetin. The mutagenic activity of quercetin increased substantially when the pH of the media was decreased. This may be due in part to a decrease in ionization of quercetin at lower pH, thereby increasing its absorption by the tester strain, to a decrease in the rate of autoxidation of quercetin at lower pH, or to a combination of these.

Quercetin, a rat intestinal and bladder carcinogen present in bracken fern (Pteridium aquilinum)

Albino noninbred weanling male and female rats were fed a basic grain diet (Group 1) or a basic diet supplemented with 33% bracken fern [BF (Group 2)] or 0.1% quercetin [purity, > 99% (Group 3)] for 58 weeks. The quantities of quercetin and kaempferol (a close structural analog) in BF as glycosides were determined to be 0.57 and 1.1 g, respectively, per kg of dried BF. Estimated mean total cumulative doses (mmol) per rat were: Group 1, quercetin, males and females < 0.03; kaempferol, males and females < 0.03; Group 2, quercetin, males 5.8, females 5.2; kaempferol, males 11.9, females 10.8; and Group 3, quercetin, males 27.8, females 25.3; kaempferol, males and females < 0.03. Growth of rats fed BF or quercetin was comparable but significantly (p < 0.01) slower after 24 weeks than that of Group 1. Mean survivals (weeks) of rats of all groups were: Group 1, 58 +/- 7 (S.D.); Group 2, 51 +/- 13; and Group 3, 56 +/- 8. They were not significantly different, although rats fed BF tended to die earlier secondary to intestinal tumor-induced intussusception and obstruction. The following incidences of intestinal or bladder neoplasms in male or female rats, respectively, were observed: Group 1, intestinal and bladder, males, 0 of 9, females, 0 of 10; Group 2, intestinal, males, 7 of 8, females, 10 of 11; bladder, males, 6 of 8, females 8 of 11; Group 3, intestinal, males, 6 of 7, females, 14 of 18; bladder, males, 2 of 7, females, 3 of 18. The histopathology of neoplasms of the 2 target organs was identical for rats of Groups 2 and 3. Multiple ileal intestinal neoplasms of rats fed quercetin included: adenoma, 4; fibroadenoma, 7; and adenocarcinoma, 9 (with mesenteric metastases, 3). The 5 bladder tumors were papillary or sessile transitional cell carcinomas.