Diethyldithiocarbamate inhibits scheduled and unscheduled DNA synthesis of rat thymocytes in vitro and in vivo--dose-effect relationships and mechanisms of action

Cell cycle specific radiosensitisation by the disulfiram and copper complex

The disulfiram and copper complex (DSF:Cu) has emerged as a potent radiosensitising anti-cancer agent. The ability of copper to stabilise DSF in a planar conformation and to inhibit DNA replication enzymes stimulated our investigation of the effect of DSF:Cu on cell cycle regulation. Flow cytometry and immunoblotting were used to assess the effect of DSF:Cu on cell cycle progression of the neuroblastoma cell line SK-N-BE(2c) and the glioma cell line UVW. Treatment with 0.1 and 0.3 μM DSF:Cu inhibited DNA synthesis in SK-N-BE(2c) and UVW cells, respectively. The increased potency of ionising radiation treatment induced by DSF:Cu and/or gemcitabine was determined by clonogenic assay. Treatment with 0.3 μM DSF:Cu resulted in greater radiation kill, exemplified by dose enhancement factor values of 2.64 and 2.84 in SK-N-BE(2c) and UVW cells, respectively. Although DSF:Cu failed to sensitise S phase cells to irradiation, we observed that DSF:Cu radiosensitisation was potentiated by the S phase-specific cytotoxic drug gemcitabine. The efficacy of the combination treatment consisting of DSF:Cu, gemcitabine and ionising radiation was schedule-dependent. Together, these results describe cell cycle specific radiosensitisation by DSF:Cu. The well-established toxicity profiles of DSF and gemcitabine should facilitate their evaluation as a combination treatment in patients undergoing radiotherapy.

Anticancer Activities of bis(pyrazol-1-ylthiocarbonyl)disulfides against HeLa cells

Oxidation of the pyrazol-1-yldithiocarbamate compounds {[3,5-R2C3HN2CS2]-(R = H, Me} and indazol-1-lydithiocarbamate by iodine produces the sulfur-sulfur coupling compounds {R'C(S)S-S(S)CR'} (R’ = pyrazolyl, 3,5-dimethylpyrazolyl, indazolyl). All compounds were spectroscopically characterised, and, in some cases, structurally characterised. The X-ray structures reveal that these compounds contain a disulfide bridging the pyrazolylthiocarbonyl units. Two of the three disulfide compounds showed very good anticancer activities against HeLa cells at micromolar concentrations, with the most active compound active being 9.6 times more selective in its activity towards tumour cells than normal cells.

Radiation biochemistry of the chicken embryo: DNA synthesis and DNA degradation following X-irradiation

Chicken embryos were X-irradiated with a dose of 8 Gy. At a developmental stage of 15 days, desoxyribonucleic acid (DNA) synthesis, nucleoid sedimentation, viscosity of the alkaline cell lysates and DNA fragmentation were examined in brain and/or liver cells. Further studies aimed at the appearance of acid-soluble nucleic acid metabolites in the allantoic fluid. Complementary investigations comprised the in vitro activities of a DNase I and a DNase II of liver and brain cells as well as of the allantoic fluid of X-irradiated embryos. It could be shown for the first time that, following acute X-irradiation of the chicken embryo, the inhibition of DNA synthesis is accompanied by at least two enzymatic DNA degradation phases. The early phase comprises a period of 6 (-12) h, whereas the second phase lasts, with organ-specific peculiarities, > or = 24 h. During the early period, some apoptotic phenomena are seen, whereas at the later stages of radiation response signs of necrolysis become evident. The excretion of DNA metabolites, probably oligonucleotides, in the allantoic fluid is enhanced following X-irradiation > 2 Gy and may be used as an additional parameter of the overall radiation damage. Therefore, the chicken embryo may be regarded as a radiobiological and possibly toxicological alternative to laboratory animals with respect to the nucleic acid metabolism.

Poly(ADP-ribose)polymerase-activity of chicken embryo cells exposed to nucleotoxic agents

Poly(ADP-ribose)polymerase (PARP)-activity was assessed in vitro from the incorporation of the adenosine-diphosphate-ribose moiety of 14C-NAD+ in the acid-insoluble cell fraction. When compared to mammalian (rat) cells, chicken embryo cells exhibit an almost three- to fourfold higher constitutive PARP-activity and an about two- to threefold lower chromatin compactness as evidenced by viscometry of alkaline cell lysates and nucleoid sedimentation. X-irradiation, bleomycin and H2O2 activated PARP. Hyperthermia (43 degrees C), doxorubicin, ethidium bromide and novobiocin resulted in an inhibition of the enzyme activity. Even at the highest doses used, UV-light, monofunctionally alkylating agents and the bisbenzimide Hoechst 33258 remained without significant effects. It is suggested that, with respect to DNA-and/or chromatin-interactive agents, the chicken embryo PARP-test may be complementary to the results of morphological and biochemical studies.

Effect of antioxidants on chemiluminescence produced by reactive oxygen species

Luminol chemiluminescence was used to evaluate the scavenging of superoxide, hydroxyl and alkoxy radicals by four antioxidants: dipyridamole, diethyldithiocarbamic acid, (+)catechin, and ascorbic acid. Different concentrations of these compounds were compared with well-known oxygen radical scavengers in their capacity to inhibit the chemiluminescence produced in the reaction between luminol and specific oxygen radicals. Hydroxyl radicals were generated using the Fenton reaction and these produced chemiluminescence which was inhibited by diethyldithiocarbamate. Alkoxy radicals were generated using the reaction of tert-butyl hydroperoxide and ferrous ion and produced chemiluminescence which was inhibited equally by all of the compounds tested. For the determination of superoxide scavengers we describe a new, simple, economic, and rapid chemiluminescence method consisting of the reaction between luminol and horseradish peroxidase (HRP). With this method it was found that 40 nmol/l dipyridamole, 0.18 mumol/l ascorbic acid, 0.23 mumol/l (+)catechin, and 3 mumol/l diethyldithiocarbamic acid are equivalent to 3.9 ng/ml superoxide dismutase (specific scavenger of superoxide) in causing the same degree of chemiluminescence inhibition. These results not only indicated that the antioxidative properties of these compounds showed different degrees of effectiveness against a particular radical but also that they may exert their action against more than one radical.

Drugs effects on superoxide generation and chemiluminescence response of human leukocytes

Luminol-enhanced chemiluminescence was used to determine the effects of diethyldithiocarbamate, dipyridamole, catechin and verapamil on the generation of reactive oxygen species in human leukocytes, and on superoxide generated by chemiluminescence of the hypoxanthine xanthine-oxidase reaction. These agents reduced the luminol enhanced chemiluminescence response of activated leukocytes, most probably by inhibiting the superoxide generation reaction. On the other hand, citrate and diethylcarbamazine, produced a slight increase of the luminol enhanced chemiluminescence of leukocytes.

Viscometry of alkaline cell lysates--the hitherto simplest short-term test for chromatin-interactive agents? Investigations in rat thymic and splenic cells

Alkaline (AL) lysates from thymic cells (T-cells) and splenic cells (S-cells) of the rat were measured by low-shearing glass capillary viscometry. AL-viscometry was compared to the nucleoid sedimentation technique and the alkaline unwinding method. The results obtained in cells treated by (a) DNA strand breaking agents (X-rays, UV-light, doxorubicin, bleomycin, hydrogenperoxide, methylmethanesulfonate (MMS)), (b) intercalating and/or cross-linking substances (ethidium bromide, actinomycin D, mitomycin C, bisbenzimide), (c) the DNA repair inhibitor 3-aminobenzamide (3-AB) and (d) hyperthermia suggest that AL-viscometry may be considered as a very simple, rapid and inexpensive preliminary short-term test for detecting chromatin-interactive agents. Whereas agent- and cell-specific characteristics can be also revealed by AL-viscometry, quantification of specific lesions and conclusions as to the mechanisms of action require additional assays.