Phosphorus-proton spin-spin coupling and conformation of a dinucleoside phosphate.

The phosphorus-31 nuclear magnetic resonance spectrum of beta-adenosine-3'-beta-adenosine-5'-phosphoric acid in its aqueous solution (pH = 9.2) was studied. The signal consisted of eight peaks caused by the spin-spin coupling of the phosphorus nucleus with three protons, two on the 5' carbon, and one on the 3' carbon. The coupling constants were 3.4, 6.5, and 8.1 hertz; from these values the dihedral angles of the three P-O-C-H systems were estimated.

Induction of mutation in mouse FM3A cells by N4-aminocytidine-mediated replicational errors.

To explore the potential use of a nucleoside analog, N4-aminocytidine, in studies of cellular biology, the mechanism of mutation induced by this compound in mouse FM3A cells in culture was studied. On treatment of cells in suspension with N4-aminocytidine, the mutation to ouabain resistance was induced. The major DNA-replicating enzyme in mammalian cells, DNA polymerase alpha, was used to investigate whether the possible cellular metabolite of N4-aminocytidine, N4-aminodeoxycytidine 5'-triphosphate (dCamTP), can be incorporated into the DNA during replication. Using [3H]dCamTP in an in vitro DNA-synthesizing system, we were able to show that this nucleotide analog can be incorporated into newly formed DNA and that it can serve as a substitute for either dCTP or dTTP. dCamTP in the absence of dCTP maintained the activated calf thymus DNA-directed polymerization of deoxynucleoside triphosphates as efficiently as in its presence. Even in the presence of dCTP, dCamTP was incorporated into the polynucleotide. When dCamTP was used as a single substrate in the poly(dA)-oligo(dT)-directed polymerase reaction, it was incorporated into the polynucleotide fraction. The extent of incorporation was 4% of that of dTTP incorporation when dTTP was used as a single substrate. Even in the presence of dTTP, dCamTP incorporation was observed. A copolymer containing N4-aminocytosine residues was shown to incorporate guanine residues opposite the N4-aminocytosines. However, we were unable to observe adenine incorporation opposite N4-aminocytosine in templates. These cell-free experiments show that an AT-to-GC transition can take place in the presence of dCamTP during DNA synthesis, strongly suggesting that the mutation induced in the FM3A cells by N4-aminocytidine is due to replicational errors.

DNA strand cleavage in vitro by 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]-indole, a direct-acting mutagen formed in the metabolism of carcinogenic 3-amino-1-methyl-5H-pyrido[4,3-b]indole.

3-Hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole (N-OH-Trp-P-2) is a direct-acting mutagenic compound derived by metabolic activation from 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), a strongly mutagenic carcinogen. The action of N-OH-Trp-P-2 on DNA in vitro was investigated. N-OH-Trp-P-2 inactivated Bacillus subtilis transforming DNA and produced single-strand cuts in a supercoiled circular DNA (phi X174RFI) under neutral conditions. When mouse FM3A cells in culture were treated with a noncytotoxic dose of N-OH-Trp-P-2 and then the cellular DNA was examined by the alkaline elution technique, chain cleavages of the DNA were observed. Cysteamine inhibited the spontaneous degradation of N-OH-Trp-P-2 and enhanced the covalent binding of [3H]N-OH-Trp-P-2 to DNA. This finding offered an explanation for the previously observed enhancement of Trp-P-2 mutagenicity by cysteamine. In contrast cysteamine inhibited the N-OH-Trp-P-2-mediated inactivation of B. subtilis DNA as well as the strand cleavage in phi X174RFI DNA. The cleavage in phi X174RFI DNA was also inhibited by catalase. These observations indicate that the mutagenicity and DNA-cleaving activity of N-OH-Trp-P-2 are distinct from each other, that the inactivation of transforming DNA was caused mainly by strand cleavage, and that the DNA cleavage was probably caused by active oxygen radicals produced in the oxidative degradation of N-OH-Trp-P-2.

Mutagenic metabolites in urine and feces of rats fed with 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, a carcinogenic mutagen present in cooked meat.

To study the in vivo fate of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), a carcinogenic mutagen present in cooked meat, rats were fed MeIQx in the diet and their urine and feces were analyzed for the metabolites. The isolation procedure included specific adsorption of MeIQx derivatives to blue cotton and subsequent fractionations by thin layer chromatography on silica gel and by high pressure liquid chromatography. Attention was focused on mutagenically active metabolites. Three metabolites were isolated from the urine, and their structures were elucidated on the basis of 1H nuclear magnetic resonance, ultraviolet, and mass spectra. The first metabolite characterized was 2-amino-8-hydroxymethyl-3-methylimidazo[4,5-f]quinoxaline (Compound I), the second was 2-acetylamino-3,8-dimethylimidazo[4,5-f]quinoxaline (Compound II), and the third was 2-amino-8-methylimidazo[4,5-f]quinoxaline (Compound III). Compound I was isolated also from the feces. Compounds I-III were mutagenic to Salmonella typhimurium TA98 with metabolic activation. The mutagenic potency of Compounds I and II was as high as that of MeIQx, and that of Compound III was much lower than that of MeIQx.

Inhibition of protein synthesis in mouse myeloma cells by Ricinus communis toxin.

The mechanism of inhibition of protein synthesis in mouse myeloma cells by Ricinus communis toxin was studied. No significant disaggregation of polysomes into monosomes was detected in the toxin-treated cells. The activity of the polysomes isolated from the cells treated with the toxin in protein synthesis was remarkably lower than that of the untreated cells, while the activity of the supernatant enzyme fraction was retained. The ribosomes derived from the polysomes of the toxin-treated cells were inactive in poly(U)-dependent polyphenylalanine synthesis. The activity of ribosomes reconstituted by hybridizing subunits derived from the ribosomes of normal and toxin-treated cells were measured in poly(U)-dependent polyphenylalanine synthesis, and the 60 S subunit was revealed to be inactive. These results indicate that the target of action of the toxin towards intact cells is the 60 S ribosomal subunit.

A quantitative assay for concanavalin A- and Ricinus communis agglutinin-mediated agglutinations of rat ascites hepatoma cells. Relationship between concanavalin A binding and cell agglutination.

A simple quantitative assay method was developed for the agglutination of rat ascites hepatoma cells mediated by Concanavalin A or Ricinus communis agglutinin. This method was based on the principle that the turbidity of a cell suspension is proportional to the sum of the cross-sectional area of cells and aggregatesmas predicted by the theoretical consideration, the turbidity decreased when cells were aggregated and the decrease was a function of the average number of the cells in aggregates. The agglutinability of the cells, judged by this method, showed a maximum value at a certain concentration of the agglutinin. By further addition of the agglutinin, the agglutinability slightly decreased from the maximum. These phenomena were observed both for Concanavalin A and Ricinus communis agglutinin. The binding and the agglutination experiments using [3-H]concanavalin A revealed that the binding to approx;0% of the total receptors caused a maximal agglutination. This suggested that the receptors responsible for the agglutination constitute only a small part of the total receptors on the surface.

Cellular energy dependent agglutination of rat ascites tumor cells mediated by concanavalin A and Ricinus communis agglutinin.

Effect of various metabolic inhibitors on the agglutination of rat ascites tumor cells mediated by concanavalin A and Ricinus communis agglutinin was studied using a quantitative assay method for agglutination in which turbidity of cell suspension is measured. Cell agglutination was inhibited by low temperature, cytochalasin B and inhibitors of energy generating systems without affecting lectin binding, and agglutination was not affected by hydroxyurea, actinomycin D or cycloheximide. The inhibitors of energy generating systems decreased the cellular ATP level and inhibited macromolecular synthesis under the conditions where they inhibited the agglutinations. In contrast, cytochalasin B did not depress the cellular ATP level nor inhibit RNA and protein syntheses. These results suggest that the agglutination is associated with cellular energy dependent processes other than macromolecular synthesis; probably with some cellular surface movements participated by microfilament activity.

Spectrum of N4-aminocytidine mutagenesis.

N4-Aminocytidine, a nucleoside analog, is a potent mutagen towards phages, bacteria, Drosophila and mammalian cells in culture. In vitro, biochemical studies indicate that this reagent acts by being incorporated into DNA. To elucidate the mechanism of N4-aminocytidine mutagenesis, it is essential to identify the nature of DNA sequence alterations taking place during the mutagenesis. We have analyzed the nucleotide sequence changes in the lac promoter-lacZ alpha region of M13mp2 phage induced by treatment of phage-infected Escherichia coli with N4-aminocytidine. The sequence alterations of DNA samples from 89 mutants of the phage were determined. These mutants had single point mutations, except one mutant, in which a double point mutation was detected. Several hot spots were found: however, there are no apparent relations to particular DNA sequences regarding the locations of these spots. All the mutations are transitions; neither transversions nor deletions/insertions were found. A feature in these transitions is that the A/T to G/C and G/C to A/T changes occur at approximately equal rates. The overall picture of the mutagenesis is consistent with a scheme in which misincorporation and misreplication caused by the modified cytosine structure are the key steps in the DNA replication leading to transitions. Similar nucleotide alterations were found for the mutagenesis induced by an alkylated derivative, N'-methyl-N4-aminocytidine. N4-Aminocytidine also induced reversions of these mutants; both A/T to G/C and G/C to A/T transitions again took place.

A new reaction useful for chemical cross-linking between nucleic acids and proteins.

Cytosine in nucleic acids can be converted into N4-aminocytosine by treatment with a mixture of hydrazine and bisulfite. The hydrazino group thus formed at position 4 of the pyrimidine ring can be linked to a sulhydryl group in proteins by the use of bromopyruvate as a linker. Successful use of this scheme of chemical cross-linking between nucleic acid and protein was demonstrated in the linking of poly(C) with glutathione, and of RNA with protein in the E. coli 30 S ribosomal subunit.

Heat production as a quantitative parameter of phagocytosis.

Microcalorimetry was applied to measure phagocytosis by human peripheral blood neutrophils and monocytes. Heat production was 9.1 +/- 2.6 microW by 1 X 10(6) unstimulated neutrophils and increased to 28.4 +/- 3.2 microW in association with phagocytosis. The increase in heat production was directly proportional to the number of Saccharomyces cerevisiae particles phagocytosed as well as to the concentration of opsonizing serum. No heat increase was observed in the absence of phagocytosis. An increase in heat production by monocytes was also observed in association with phagocytosis, but it was much less obvious than that by neutrophils. Heat production can thus be used as a quantitative measure of phagocytosis.

Suppressing effect of Lactobacillus casei administration on the urinary mutagenicity arising from ingestion of fried ground beef in the human.

It is known that the ingestion of cooked meat which contains carcinogenic heterocyclic amines causes increase in urinary mutagenicity in humans. Using 6 healthy non-smokers, we examined the effect of 3-week oral administration of Lactobacillus casei (bacilli commonly present in yoghurt), on the urinary mutagenicity derived from ingestion of fried ground beef. Comparison of the urinary mutagenicity found before and after the L. casei treatment showed that the treatment resulted in a decrease (6-67%, average 47.5%) of the mutagenicity. This suppressing effect is possibly related to the changes in the intestinal microflora population.

Inhibitory effect of hemin on the mutagenic activities of carcinogens.

An inhibitory effect of hemin on mutagenicities of a range of carcinogens was found by adding hemin to the preincubation mixture of the Ames' test. Strong inhibitions were observed for benzo[alpha]pyrene, 3-methylcholanthrene, 7,10-dimethylbenz[alpha]anthracene, chrysene, 2-acetylaminofluorene, 2-nitrofluorene and aflatoxin B1. Generally, 50% inhibition was caused by an amount of hemin 1--2 equivalents to the mutagen. Excess of hemin caused complete inhibitions. Hemin did not affect the mutagenicities of 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide, 4-nitroquinoline-1-oxide, nitromin, N-methyl-N-nitrosourea, N-methyl-N'-nitro-N-nitrosoguanidine, N-nitrosodi-n-butyl-amine, quinoxaline-1,4-dioxide and carbadox. Biliverdin, bilirubin and chlorophyllin were also effective as inhibitors for the mutagenicity of benzo[alpha]pyrene.

Porphyrins as possible preventers of heterocyclic amine carcinogenesis.

Our studies have shown that hemin and chlorophyllin can directly interact with heterocyclic amines (HAs) and prevent their mutagenic actions. Hemin and chlorophyllin can trap HAs efficiently, probably by forming face-to-face complexes with them. The trapping was most clearly demonstrated by use of solid-supported porphyrins, hemin-agarose and chlorophyllin-chitosan. Furthermore, spectroscopic measurements have suggested that there are interactions in solution between the porphyrins and the HAs. A number of in vivo data have been accumulated by efforts from many laboratories for the anticarcinogenic and antigenotoxic properties of porphyrins, particularly chlorophyllin, against HAs.

Inhibitory activity of chlorophyllin on the genotoxicity of carcinogens in Drosophila.

Antimutagenic activity of copper chlorophyllin against various carcinogenic mutagens was assayed with Drosophila genotoxicity tests, i.e., the wing spot test for detecting somatic cell mutations and the DNA repair test for detecting DNA damage. In these tests, Drosophila larvae were fed carcinogens together with chlorophyllin. Polycyclic aromatic compounds, including heterocyclic amines, polycyclic aromatic hydrocarbons, aromatic amines and aromatic nitro compounds, were subject to inhibition, with a few exceptions. The results support the view that chlorophyllin traps carcinogens by forming complexes, thereby inhibiting the absorption of these compounds from the digestive tract. Consistent with this mechanism, Sepharose-supported chlorophyllin in the feed inhibited the Trp-P-2-induced wing spot formation, while Sepharose itself was ineffective.

Use of blue cotton for detection of mutagenicity in human feces excreted after ingestion of cooked meat.

Fried ground beef has been shown to contain mutagens, and the major mutagenic component has been identified as 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). Mutagens in feces of three adult volunteers were fractionated by treatment of the feces with blue cotton followed by chromatography on a carboxymethyl cellulose column. The chromatographic fraction corresponding to MeIQx in terms of the position of elution was examined for mutagenicity in S. typhimurium TA 98 with metabolic activation. When meals containing no heated meat were eaten, this fraction of feces showed little or no mutagenicity. On eating fried ground beef, the feces excreted in the next 2 days showed greatly increased mutagenicity in this fraction. By eating no-meat meals subsequent to the meat meal, the mutagenicity resumed the original low level on the fourth day after the meat meal. The components in the mutagenic fraction were analyzed by high-pressure liquid chromatography, and were shown to differ from MeIQx.

The 5,6-double bond of pyrimidine nucleosides, a fragile site in nucleic acids.

Our studies have revealed reagents that can attack the 5,6-double bond of pyrimidine nucleosides; potassium permanganate and bisulfite. This review is a personal account of these studies, with a discussion on the vulnerable nature of this particular double bond to external nucleophiles and oxidizing agents. The finding that N(4)aminocytidine, produced on treatment of cytidine with bisulfite and hydrazine, is a strong mutagen is also described.

Contamination by ATP of commercial dATP samples causing erroneous results in studies of DNA replication in isolated HeLa cell nuclei.

dATP at high concentrations was capable of replacing ATP required in the synthesis of Okazaki pieces in isolated HeLa cell nuclei. In addition, the levels of synthesis of high molecular weight DNA were observed to vary depending on the lot of dATP used. Analysis by HPLC revealed that dATP samples of a particular source contained ATP in the range of 0.25-0.43 mol%. With ATP-free dATP, almost no synthesis of high molecular weight DNA was observed, while with impure dATP, a small but significant amount of high molecular weight DNA was synthesized. While this observation confirmed our previous finding that dATP can replace ATP in the synthesis of Okazaki pieces but not in the joining of the pieces, it is also a warning to users of commercial dATP in biochemical and biological studies.

Potentiation of the antitumor activity of 5-trifluoromethyl-2'-deoxyuridine by the use of depot forms of the parent compound.

5-Trifluoromethyl-2'-deoxyuridine (CF3dUrd), an antitumor agent, is known to be short-lived in human plasma. Since its rapid elimination from the bloodstream seems to have descouraged the clinical evaluation of this drug, we explored the potential use of masked derivatives of CF3dUrd as "depot" forms of the parent compound. First, we observed that the toxicity of CF3dUrd against HeLA cells in culture was 10(4) times greater for a 24-h treatment as compared with a 1-h treatment at identical concentrations of the drug, which suggests the importance of using a prolonged treatment period. In fact, the divided dosing of CF3dUrd to L1210-bearing mice was markedly more effective than its single administration. 5'-O-Hexanoyl-, N3-p-butylbenzoyl-, 5'-O-benzyloxy-methyl-, and 3'-O-benzyl-CF3dUrd were found to be effective in maintaining the CF3dUrd concentration in plasma. The oral doses of these agents required to achieve 50% growth inhibition (ED50) in mice bearing sarcoma 180 tumors were 19, 34, 10, and 13 mg kg-1 day-1, respectively, whereas that of CF3dUrd was 63 mg kg-1 day-1. The ED50 values for these compounds were inversely correlated with the residence time of CF3dUrd in plasma. The therapeutic indices of these compounds, calculated as the dose producing a 50% inhibition of body-weight gain (IB50) divided by the ED50 value (1.89, 1.21, 1.40, and 2.15, respectively), were significantly higher than that of CF3dUrd (0.78). Consequently, these depot forms of CF3dUrd, particularly 3'-O-benzyl-CF3dUrd, are expected to be more useful than the parent compound as antitumor agents.

Antitumor activity of FTC-092, a masked 5-trifluoromethyl-2'-deoxyuridine derivative.

1-(3-O-Benzyl-2-deoxy-beta-D-ribofuranosyl)-5-trifluoromethyl-2,4(1H,3)- pyrimidinedione (FTC-092), a fluorinated pyrimidine derivative, appeared to be effective against various transplantable tumors in mice following oral administration, and its activity was superior to that of several other antitumor fluorinated pyrimidines. The ED50 value for FTC-092 the dose effective in achieving 50% inhibition of tumor growth against the solid form of sarcoma 180 was 13.3 mg/kg daily, whereas those for 5-trifluoromethyl-2'-deoxyuridine (CF3dUrd), the parent compound of FTC-092, for 1-(2-tetrahydrofuryl)-5-fluorouracil (Tegafur, FT), the prodrug of 5-fluorouracil (FUra), and for FUra were 64.1, 122, and 28 mg/kg daily, respectively. The therapeutic indices (LD10/ED50) of FTC-092, CF3dUrd, FT, and FUra were 4.39, 1.7, 1.35, and 1.65, respectively. FTC-092 itself is not an active agent. After it has been absorbed from the gastrointestinal tract, FTC-092 undergoes a gradual biotransformation, mainly via the action of liver microsomes, releasing CF3dUrd over a long period. The levels of CF3dUrd in the stomach and small intestine of mice after the oral administration of FTC-092 were undetectable, whereas those following the administration of CF3dUrd at the same dose were high for a period of several hours. In contrast, the CF3dUrd level generated in plasma after the administration of FTC-092 remained at a high level for a longer period than did that observed on the administration of CF3dUrd. The low levels of CF3dUrd measured in stomach and small-intestine tissues and the maintenance of CF3dUrd in blood over long periods after the administration of FTC-092 are features that favor the possible clinical application of FTC-092.

Formation of direct-acting mutagens from mixtures of N-nitrosomorpholine and carboxylates by UVA irradiation.

Previously, we found that a directly mutagenic compound is produced from N-nitrosopiperidine (NPIP) in phosphate buffer on exposure to near-ultraviolet light (UVA) and we identified its structure as alpha-hydroxy-N-nitrosopiperidine phosphate ester. In the present study, we show that a similar photoactivation of an N-nitrosamine can take place with carboxylates in place of phosphate. When a neutral solution of a mixture of N-nitrosomorpholine (NMOR) and sodium acetate was irradiated with UVA, the solution became directly mutagenic towards Salmonella typhimurium TA1535. O6-Alkylguanine-DNA alkyltransferase-deficient strains of S. typhimurium showed remarkably higher mutagenesis responses to this mutagen than the proficient strains. Citrate, succinate, and several other biological carboxylates were also effective in producing the mutagens. Since a treatment of the "NMOR plus acetate" photoproduct with carboxylic ester hydrolase resulted in a loss of the mutagenicity, the active principle is suggested to be an acetate-esterified derivative of NMOR. The role of the esters as intermediates in the photomutagenesis of nitrosamines is discussed.