DNA cleavers

Recent studies with Euglena gracilis and human leukemia HL-60 cells have assessed the need for intracellular iron for cellular DNA damage and cell growth inhibition by BLM 40). Growth inhibition and both single- and double-strand DNA breaks were substantially reduced in iron-deficient cells. In iron-deficient HL-60 cells, metal-free BLM and Cu-BLM are mainly inactive as cellular DNA cleavers. The earlier findings that free BLM, Zn-BLM, or Cu-BLM had the same cytotoxic activity as Fe-BLM can now be explained by their conversion into Fe-BLM inside host cells 40). 

Little is known about DNA damage by Cr(III) complexes, even though these compounds are considered to be responsible for chromium mutagenicity. The [Cr (phen)2Cl2] Euid [Cr (bpy)2Cl2] complexes are both mutagenic and able to cleave a supercoiled plasmid DNA via ss breaks, whereas [Cr (CN)e] is not mutagenic and is inefficient as a DNA cleaver 162). 

Several metal complexes were prepared with the new products such complexes were evaluated for their efficiencies as DNA cleavers upon exposure to visible light. The attained results enlighten the role played by the water-solubilizing carbohydrate moieties attached to the lipophilic porphyrin macrocycle during the cleavage of the DNA target [145,146]. 

Scheme 3.93 DNA cleavage with lysine conjugates and literature examples of pH-controlled amino enediynes, the potential DNA-cleavers [360a].

Nakatani, K., Maekawa, S., Tanabe, K., and Saito, L, a-Diazo Ketones as Photochemical DNA Cleavers A Mimic for the Radical Generating System of Neocarzinostatin Chromophore, /. Am. Chem. Soc., 117, 10635,1995. 

Meunier, B., DNA and RATA Cleavers and Chemotherapy of Cancer or Viral Diseases, Kluwer Academic, 1996. 

Ligation Reaction. The nick in the phosphate backbone is repaired by DNA ligase. A similar excision repair mechanism exists in mammalian cells (see, e.g., Cleaver, 1983). 

Cleaver, J.E., DNA repair with purines and pyrimidines in radiation- and carcinogen-damaged normal and Xeroderma pigmentosum human cells, Cancer Res., 33, 362,1972. 

Antimony trifluoride, 16 181 preparation of, 7 14-15 solubility of, 7 6-7 Antimony trifluoroacetates, 17 12, 13 Antiperspirants, 36 16 Anti-Stokes emission, 35 342-343 Antitumor agents DNA and RNA cleavers, 45 252 phosphazotrihalides as, 14 90, 91... 

Cleaver, J.E. (1977). Methods for the study of excision repair of DNA damaged by physical and chemical mutagens, page 19 in Handbook on Mutagenicity Tkst Procedures, KiLBEY, B.J., LEGATOR, M., NICHOLS, W., AND Ramel, C., Eds. (Elsevier, Amsterdam). 

Wolff, S., Bodycote, J., Thomas, G.H., Cleaver, J.E. (1975). Sister chromatid exchanges in xeroderma pigmentosum cells that are defective in DNA excision repair or post-replication repair. Genetics 81,349-355. 

Cleaver, J.E. and Morgan, W.F. (1991) Poly(ADP-ribose)polymerase a perplexing participant in cellular responses to DNA breakage. Mutat. Res., 257, 1-18. 

Cleaver, J.E. Methods for studying excision repair of DNA damaged by physical and chemical mutagens, pp. 19-48. In B.J. Kilbey, M. Legator, W. Nichols, and C. Ramel, Eds. Handbook of Mutagenicity Test Procedures. Amsterdam Elsevier/North Holland, 1977. 

Cleaver, J.E. Methods for studying repair of DNA damaged by physical and chemical carcinogens. 

The endogenously synthesised dTTP dilutes the specific activity of the [3H]dTTP formed from the added [3H]thymidine. Thus on adding tritiated thymidine at 3 X 10 8M most of the DNA thymine is synthesised by the endogenous or de novo pathway, but when the [3H]thymidine concentration in the medium is raised to 0.3 mM it contributes 90% or more of the DNA thymine (Cleaver and Holford, 1965 Cooper et al., 1966 Cleaver, 1967). As the specific activity of [3H]dTTP is one of the factors which determine the amount of radioactivity incorporated into DNA (either total counts/min or grain counts) and as this varies (a) with external thymidine concentration and (b) with the state of the cells, the quantitative estimation of rates of DNA synthesis is full of pitfalls. 

By measuring the incorporation of thymidine into DNA from [3H]thymidine supplied at different concentrations to mouse L cells, Cleaver (1967) was able to show that, at about 10-5M thymidine, incorporation reached a plateau, and a similar observation has been made for CHO cells (Fig. 12.3). This has been interpreted as showing that at this concentration the contribution of endogenous dTTP to DNA thymine is negligible. Care must be taken, however, that at... 

DNA repair is best studied in a system where the background levels of replication are low. Suitable systems are cultures which have come to rest at high density, or unstimulated lymphocyte preparations where less than 1% of the cells are in S-phase. The low levels of replicative incorporation can be further repressed by 1-2 mM hydroxyurea which selectively inhibits replication (Cleaver, 1969b). This selective effect may simply be a result of the very small pools of deoxyribonucleoside triphosphates required for repair. 

Cleaver JE, Thomas GH (1981) Measurement of unscheduled synthesis by autoradiography. In Friedberg EC, Hanawalt PC (eds) DNA Repair. A laboratory Manual of Research Procedures. Marcel Dekker, New York, pp 277-287... 

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