Inhibition of DNA excision repair in human cells by arabinofuranosyl cytosine: effect on normal and xeroderma pigmentosum cells
Dunn, W.C.; Regan, J.D.
Molecular Pharmacology 15(2): 367-374
1979
ISSN/ISBN: 0026-895X PMID: 470933 Document Number: 146560
The antineoplastic agent arabinofuranosyl cytosine (ara-C) produced an inhibition of the pyrimidine dimer excision system of human DNA repair. Alkaline sucrose gradient analysis of DNA from normal human skin fibroblasts exposed to 20 J/m2 of UV radiation (254 nm) showed an accumulation of DNA single-strand breaks when DNA repair was attempted in the presence of 10 .mu.M ara-C. Cells from complementation groups of xeroderma pigmentosum that were defective in early steps of excision repair showed reduced numbers of DNA single strand breaks/108 daltons when compared with normal cells. Cesium chloride gradient analysis of radioactive precurser uptake during repair replication indicated that ara-C causes a 6-56% reduction in the number of nucleotide bases inserted into the DNA at concentrations of 1 and 10 .mu.M, respectively. These concentrations resulted in the substitution for deoxycytidine (dCyd) by ara-C of 40 and 100%, respectively, in repaired regions. Repair inhibition was reversed by 50% upon removal of ara-C and by > 95% with the addition of 100 .mu.M dCyd. Chromatography of digested DNA showed that incorporated ara-C was not removed during dCyd reversal, suggesting that ara-C incorporation per se did not play a significant role in the inhibition of repair synthesis. The repair inhibition observed here was dependent on 2 mM hydroxyurea, presumably due to reduction in the intracellular pool of dCyd. Ara-C may be a weak competitive inhibitor of DNA polymerases associated with UV induced excision repair.