Carcinogens as Frameshift Mutagens: Metabolites and Derivatives of 2-Acetylaminofluorene and Other Aromatic Amine Carcinogens

Abstract

Several carcinogenic metabolites of the carcinogen 2-acetyl-aminofluorene, especially 2-nitrosofluorene and N-hydroxy-2-aminofluorene, are potent frameshift mutagens for Salmonella typhimurium. 2-Nitrosonaphthalene, 2-nitrosophenanthrene, 4-nitroso-transstilbene, 4-nitrosobiphenyl, and 4-nitrosoazobenzene, all of which are metabolites or likely metabolites of carcinogenic aromatic amines, are also potent frameshift mutagens. These compounds may be frameshift mutagens of the class that intercalates into DNA and then reacts covalently with the DNA; various ultimate carcinogens may be of this type. The utility of a set of bacterial strains for detecting carcinogens as mutagens is shown.Various planar polycyclic aromatic compounds, such as the acridines, which can intercalate in the DNA base-pair stack (1-9), are mutagens that cause additions or deletions of nucleotides (10-12). These errors appear to result from stabilization of a shifted pairing in a repetitive sequence in DNA by intercalation of the planar compound and subsequent addition or deletion of base pairs during replication or repair synthesis (11,13). Mlutagens with this property are called frameshift mutagens because of the shift in the reading frame of the mRNA synthesized from the altered DNA template; thus they differ from mutagens that cause basepair substitutions (11). The potency of an intercalating agent as a frameshift mutagen may increase by 10-to 100-fold if it also contains a side chain that can react covalently with DNA (12,(14)(15)(16)(17).Since it seemed possible that the reactive forms of some carcinogens with planar ring systems could be frameshift mutagens that both intercalate and react with DNA, epoxides of polycyclic hydrocarbons were examined and found to be mutagens of this type (16). In this paper this question is examined further with certain known and potential metabolites of 2-acetylaminofluorene (18). The striking activity of 2-nitrosofluorene as a frameshift mutagen then led to tests of nitroso derivatives related to various other aromatic amine carcinogens. These studies have made use of a set of tester strains (14-16) of Salmonella typhimurium that were developed for detection and classification of mutagens. MATERIALS AND METHODSBacterial Test for Mutagens. The mutagenicity test uses four Salmonella strains that require histidine (14-16). The test measures the effect of a mutagen on the reversion to growth on a histidine-free medium of these tester strains. Three of the tester strains (TA1531, TA1532, and TA1534) were designed for detecting frameshift mutagens with different specificities; each strain has a frameshift mutation in one of the genes of the histidine operon. The fourth strain (TA1530) has a base-pair change in the histidine G gene, and is used to detect mutagens that cause base-pair substitutions. In addition, all four strains lack the excision repair system (because of a deletion through uvrB); this makes them much more sensitive to any mutagen that alters the DNA in a way that would normally be repai...

Detection of carcinogens as mutagens: bacterial tester strains with R factor plasmids.

“…The tester strain TA1538 contains a well-characterized (16) histidine frameshift mutation and is reverted by a wide variety of aromatic carcinogens which can cause frameshift mutations. It is not reverted appreciably by simple alkylating agents which cause base-pair substitutions (2)(3)(4)6 Optimizing the Tester Strain: Other Test Mutations. We have attempted to construct a strain more sensitive than TA100 by putting the R factor pKM101 into many different histidine-requiring mutants.…”

“…A large group of carcinogens-aflatoxin B1, benzo[a]pyrene, 2-acetylaminofluorene, etc., have been detected as reactive frameshift mutagens after liver activation (4). Each activated molecule contains a ring system capable of stacking interaction with DNA and an electrophilic group that can react with DNA (5)(6)(7)(8).…”

Origin of carcinoma associated fibroblasts

“…56,57 This suggested that carcinogenesis is reliant on higher order cell-cell interactions rather than on a simple cell autonomous DNA damage phenomena as suggested by Ames and colleagues. 58 …”

Carcinogens are Mutagens: A Simple Test System Combining Liver Homogenates for Activation and Bacteria for Detection

“…With this test we have also shown that the active forms of a large number of known carcinogens are mutagens (1)(2)(3)(4)(5). The active forms of carcinogens such as aflatoxin, polycyclic hydrocarbons, dimethylnitrosamine, and various aromatic amines are formed by mammalian metabolism, in particular by the TPNH-dependent microsomal enzymes of liver (6)(7)(8)(9)(10)(11).…”