Unscheduled DNA synthesis induced by N-acetoxy-2-acetylaminofluorene is not sensitive to regulation by ADP-ribosyl transferase

Multiple mechanisms of action of the benzamides and nicotinamides as sensitizers of radiotherapy: opportunities for drug design

The benzamides and nicotinamides are a well-known class of drugs that contain many analogs having radio- and chemosensitizing properties. This study reports on a structural analysis in order to explain the chemical features important to their mechanisms of action. In general, N-substituted analogs are distinguished from the non-N-substituted analogs because they (i) are susceptible to radiolysis, (ii) induce cytotoxicity by apoptosis but not necrosis, (iii) inhibit cell proliferation, (iv) activate poly adenosine diphosphate ribosyl transferase (poly ADPRT), and (v) have a much-reduced effect on microregional tumor blood perfusion. It was concluded that the mechanism of action of N-substituted analogs is shifted from primary effects on tumor vascularization as is seen with the non-N-substituted analogs to one where radiosensitization can be explained by selective induction of apoptosis via radiolysis and accumulation of DNA damage. This knowledge may be useful in the design of drugs possessing multiple mechanisms of radiosensitizing action.

Genetic toxicity of 2-acetylaminofluorene, 2-aminofluorene and some of their metabolites and model metabolites

2-Acetylaminofluorene and 2-aminofluorene are among the most intensively studied of all chemical mutagens and carcinogens. Fundamental research findings concerning the metabolism of 2-acetylaminofluorene to electrophilic derivatives, the interaction of these derivatives with DNA, and the carcinogenic and mutagenic responses that are associated with the resulting DNA damage have formed the foundation upon which much of genetic toxicity testing is based. The parent compounds and their proximate and ultimate mutagenic and carcinogenic derivatives have been evaluated in a variety of prokaryotic and eukaryotic assays for mutagenesis and DNA damage. The reactive derivatives are active in virtually all systems, while 2-acetylaminofluorene and 2-aminofluorene are active in most systems that provide adequate metabolic activation. Knowledge of the structures of the DNA adducts formed by 2-acetylaminofluorene and 2-aminofluorene, the effects of the adducts on DNA conformation and synthesis, adduct distribution in tissues, cells and DNA, and adduct repair have been used to develop hypotheses to understand the genotoxic and carcinogenic effects of these compounds. Molecular analysis of mutations produced in cell-free, bacterial, in vitro mammalian, and intact animal systems have recently been used to extend these hypotheses.

Mononuclear leukocyte ADP-ribosylation as an indicator of immune function in malignant-glioma patients treated with betamethasone for cerebral edema

Glioma patients receiving corticosteroids (16 mg/day betamethasone) were examined for evidence of immune cell dysfunction by using quantitative estimates of adenosine diphosphate (ADP)-ribosylation in peripheral mononuclear leukocytes as the physiological indicator. The duration of daily treatment with corticosteroids varied from 0 to 35 days at the time of collection of the blood samples. Even after adjustment for covariate factors such as age, sex, smoking habits, alcohol use, antiepileptic medications, and tumor grade, there still remained a highly significant dose-dependent inverse relationship between constitutive and hydrogen peroxide-induced mononuclear leukocyte ADP-ribosylation levels and the duration of corticosteroid treatment (beta coefficients -0.40 and -0.29, respectively; p less than 0.03). No other variable under consideration significantly influenced ADP-ribosylation levels after statistical adjustment. These data support a mutual interdependence of mononuclear leukocyte ADP-ribosylation and corticosteroid-induced immune cell dysfunction in vivo.

Elevation of ADP-ribosylation as an indicator of mononuclear leucocyte responsiveness in breast cancer patients treated with tamoxifen

82 women who had had surgery for removal of breast cancer were randomised during the primary care period before initiation of any chemotherapy or radiotherapy into two groups: no drug treatment (n = 40) and 20 mg tamoxifen per day for 2 years (n = 42). Mononuclear leucocyte (MNL) fractions from blood samples were collected during the first 368 days of the study and ADP-ribosylation was quantified. Tamoxifen treatment resulted in a dose-duration increase in ADP-ribosylation. This was true even after adjustment for covariates such as age, smoking habits, oestrogen use, menstruation and tumour size. These data suggest that part of the antitumour effects of tamoxifen treatment in vivo relates to an enhanced immune cell responsiveness, as indicated by the increased MNL ADP-ribosylation.

Mitogenic induction of ornithine decarboxylase in human mononuclear leukocytes: relationships with adenosine diphosphate ribosyltransferase

1. Relationships between ornithine decarboxylase (ODC) and adenosine diphosphate ribosyl transferase (ADPRT) in human mononuclear leukocytes (HML) were tested by statistical comparisons of their values in a group of 46 people, and by use of inhibitors of ADPRT. 2. ODC was assayed following exposure of HML, for 20 hr, to mitogens [phytohemagglutinin (PHA) and pokeweed mitogen]; ADPRT was measured following exposure of HML to H2O2 (100 microM) for 1 hr (activated ADPRT), and in parallel cultures without H2O2 (constitutive ADPRT). 3. Significant correlations were found between ODC and ADPRT values; the effects of smoking disturbed the correlations. PHA induction of ODC was negatively influenced by age (standardized beta coefficient = -2.95, P = 0.005), while age also influenced ADPRT values negatively in non-smokers (for H2O2 activated ADPRT, standardized beta coefficient = -2.74, P less than 0.008). 4. Inhibitors of ADPRT, nicotinamide, caffeine and benzamide inhibited the induction of ODC by PHA in a concentration-dependent manner, in the range (0.6-10 mM) known to inhibit ADPRT.

Hydrogen peroxide induced adenosine diphosphate ribosyl transferase (ADPRT) response in patients with inflammatory bowel disease

The sample population in this initial case control study of the adenosine diphosphate ribosyl transferase (ADPRT) response of inflammatory bowel disease patients included: 23 patients with ulcerative colitis (UC)-active and inactive, 13 patients with Crohn's disease (CD)-active and inactive, 14 first degree relatives of UC and CD patients, and 19 age-matched controls. Adenosine diphosphate ribosyl transferase activity was determined after one hour incubation with 1% plasma (the constitutive value) or with 1% plasma and 100 microM H2O2 (the activated value) with the resulting difference designated as the induced value. Statistically significant decrease in ADPRT activity was found for the constitutive, activated and induced values in human mononuclear leucocytes of UC and CD patients, compared with controls. The values in the first degree relatives of UC and CD patients were not significantly different from either the control or disease populations, indicating an intermediate ADPRT response. These results may be related to the nature of the immunological response of IBD patients and comparable with similar findings in other diseases with known DNA repair deficiencies--for example, colon cancer.

Biological effects in a chemical factory with mutagenic exposure. II. Analysis of unscheduled DNA synthesis and adenosine diphosphate ribosyl transferase, epoxide hydrolase, and glutathione transferase in resting mononuclear leukocytes

A chemical plant, where an increased number of non-Hodgkin's lymphomas and myelomas had been observed, was monitored for genotoxic effects occurring in peripheral mononuclear leukocyte samples from 76 exposed workers. Biochemical markers sensitive to DNA repair and drug metabolism were used as the indicators of genotoxic risk. Unscheduled DNA synthesis (UDS) and covalent binding induced by N-acetoxy-N-acetyl-2-aminofluorene (NA-AAF) and constitutive and gamma ray induced adenosine diphosphate ribosyl transferase (ADPRT) activities were highly and significantly elevated over the corresponding values for a control group of 48 postal workers. Microsomal and soluble epoxide hydrolases and glutathione transferase activities directed towards trans-stilbene oxide and 1-chloro-2,4-dinitrobenzene were not significantly altered in the exposed group. The exposure in this factory was complex, involving over 100 chemicals including several well known carcinogens. However, no apparent significant associations to exposure could be established.

Effects of hyperthermia and nicotinamide on DNA repair synthesis, ADP-ribosyl transferase activity, NAD+ and ATP pools, and cytotoxicity in gamma-irradiated human mononuclear leukocytes

Effects of hyperthermia and nicotinamide on ADP-ribosyl transferase activity (ADPRT), unscheduled DNA synthesis (UDS), NAD+- and ATP-pools and cytotoxicity were investigated in gamma-irradiated human mononuclear leukocytes. A significant decrease in radiation-induced UDS after heat treatment for 45 min was found. Nicotinamide increased the UDS levels in irradiated cells, but no effect of hyperthermia on these increased UDS values was observed. In the presence of 2 mM nicotinamide radiation-induced ADPRT activity was reduced to about 50 per cent. However, hyperthermia for 45 min was found to have no effect on the enzyme activity for temperatures below 46 degrees C. Nicotinamide increased the NAD+ pool in unirradiated cells. Damaging the cells with gamma-radiation leads to a severe depletion of the NAD+ pool. The NAD+ pool is restored, however, if the cells repair for 5 h at 37 degrees C. When radiation-damaged cells were treated with hyperthermia, exogenously supplied nicotinamide could not be converted to NAD+ in sufficient amounts to prevent NAD+ depletion. These data indicate that the radiosensitizing effect of heat and nicotinamide could both be explained by effects on the enzyme ADPRT, i.e. nicotinamide by directly blocking the enzyme and hyperthermia by limiting the co-substrate (NAD+).

Gamma-radiation induced ADP-ribosyl transferase activity and mammalian longevity

The levels of ADP-ribosyl transferase (ADPRT) activity following a standardized dose of 100 Gy gamma-radiation have been determined in leukocytes from 12 different mammalian species. Here, we report that the 100 Gy-induced levels of ADPRT correlated in a highly significant manner to the line spans of the mammals.

3-Aminobenzamide does not alter DNA repair in human fibroblasts through modulation of deoxynucleoside triphosphate pools

3-Aminobenzamide does not deplete cellular purine deoxynucleoside triphosphate pools as do the structurally-related ribonucleotide reductase inhibitors, the hydroxy- and amino-substituted benzohydroxamic acids. Thus, the previously reported ability of 3-aminobenzamide to inhibit de novo synthesis of DNA purines does not appear to be due to a direct effect on pools via inhibition of ribonucleotide reductase. The enhancement rather than inhibition by 3-aminobenzamide of DNA repair in the present studies, however, leaves open the possibility that pool modulation may play a role in cell systems where repair inhibitory effects are seen.