Members of the structurally diverse class of drugs known as nonsteroidal anti-inflammatory drugs (NSAIDs) have the ability to prevent or reduce the occurrence of colorectal, certain other gastrointestinal, and perhaps other cancers. The anticarcinogenic property of NSAIDs has been shown in epidemiological studies with humans and in experimental carcinogenesis studies with animals. In addition, clinical studies of the human disease familial adenomatous polyposis have demonstrated the efficacy of NSAIDs in mediating regression of colorectal adenomas. The mechanism of the anticarcinogenic effect of these drugs is not known, but most hypotheses have involved the common property of the NSAIDs to inhibit prostaglandin synthase (PHS) enzymes and thereby cause a subsequent reduction in levels of prostaglandins (PG) in tissue. Recent reports have questioned the role of PHS inhibition in the anticarcinogenic activity of NSAIDs by showing that some NSAID-related compounds that are not PHS inhibitors can induce the same anticarcinogenic changes in cell cycle and apoptotic response as the PHS inhibitors. In this review we will examine the evidence that NSAIDs are anticarcinogenic, the evidence supporting PHS as the target of NSAIDs, and the evidence for and against inhibition of PG synthesis as the mechanism of cancer prevention by NSAIDs.
The frequency distributions of human N-acetyltransferase 1 (NAT1*) alleles in various ethnic groups are largely unknown. This lack of information is in contrast to the many studies of ethnic differences in NAT2* alleles and phenotypes. Increasing interest in NAT1 due to its potential roles in carcinogen metabolism and cancer risk makes it desirable to know the distribution of NAT1* alleles in various populations. Using a polymerase chain reaction-restriction fragment length polymorphism genotyping assay, the frequency of NAT1* alleles in a Lebanese population was determined. Of 84 NAT1* alleles assayed, 56% were NAT1*4. Alleles NAT1*3, *10, and *14 were found at frequencies of 0.036, 0.107, and 0.238, respectively. Five additional alleles (6%) differed from previously reported alleles. Nearly 50% of the population were heterozygous for a NAT1*14 allele. The unusually high frequency of NAT1*14 alleles in Lebanese may be useful for epidemiological studies of the effects of the NAT1 polymorphism in this population.
The effect of the acetylator polymorphism on hepatic 2-aminofluorene-DNA adduct formation in mice was studied using two recent developments from our laboratory. Acetylator congenic mouse lines differing from their parental inbred lines in N-acetyltransferase activity were used to separate the effect of the N-acetyltransferase polymorphism from effects of differences in other genetically polymorphic enzymes. DNA adduct formation was used as an indicator of arylamine induced DNA damage. Adduct formation was measured by HPLC analysis of 32P-postlabeled nucleotides from hepatic DNA of treated animals. At a high dose (60 mg/kg) of 2-aminofluorene for a 3 h exposure, rapid acetylator mice (C57BL/6J) accumulated twice the adducts of slow acetylators (A/J). In acetylator congenic mice this difference increased so that rapid acetylators with the slow background (A.B6-Natr) had 5- to 7-times the DNA damage of the slow acetylator congenic with the rapid background (B6.A-Nats). It was also found that within each mouse line examined, females had higher levels of adduct formation than males. Acetylator congenic mouse lines were useful in distinguishing the effect of acetylator genes from the total genetic background. Similarly, congenics were useful in demonstrating the contribution that enzymes other than N-acetyltransferase make to differences in adduct formation in inbred mouse lines.
4-Aminobiphenyl (4-ABP) is a human and mouse bladder carcinogen. Epidemiological studies have shown that individuals with a slow acetylator phenotype, especially those exposed to high levels of carcinogenic aromatic amines, show an increased susceptibility to bladder cancer. In order to determine if a slow acetylator phenotype results in increased DNA damage, congenic mouse strains C57BL/6J and B6.A-Nat(s), which differ genetically at the acetyltransferase (EC 2.3.1.5) locus as homozygous rapid (Natr/Natr) and homozygous slow (Nat(s)/Nat(s)) acetylators respectively, were continuously administered 4-ABP.HCl (55-300 p.p.m.) in their drinking water for 28 days. The levels of covalently bound N-(deoxyguanosin-8-yl)-4-ABP-DNA adducts, which are believed to be critical for the initiation of tumors, were quantitated in the liver and bladder by 32P-postlabeling analysis. The levels of the hepatic DNA adduct increased with dose in both sexes, but were independent of the mouse acetylator genotype. At comparable doses, however, the levels of DNA adducts were 2-fold higher in the liver of the female as compared to the male animals. The DNA adducts also increased with dose in bladder of the male mice, but in contrast to the liver, the adduct levels were approximately 2-fold lower in the bladder DNA of the female mice. Also in contrast to the liver, the levels of bladder DNA adducts were significantly higher (P < or = 0.03) in the phenotypic rapid acetylator females compared to the slow acetylators at both 75 and 150 p.p.m. doses; the median levels of adducts were 10-20% higher in the phenotypic slow acetylator male bladders compared to their rapid acetylator counterparts. The results of these studies are consistent with the increased carcinogenicity of 4-ABP to the liver of female mice and the bladder of male mice. They further suggest that factors other than acetylator phenotype limit the extent of DNA adduct formation from 4-ABP in these mice.
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