Cisplatin-evoked DNA fragmentation in normal and cancer cells and its modulation by free radical scavengers and the tyrosine kinase inhibitor STI571.

Cis-diamminedichloroplatinum(II) (cisplatin, cis-DDP) is well studied anticancer drug, whose activity can be attributed to its ability to form adducts with DNA, but this drug can also form DNA-damaging free radicals, however this mechanism of cisplatin action is far less explored. Using the comet assay we studied cisplatin-induced DNA damage in the presence of spin traps: DMPO and PBN, Vitamins A, C and E as well as the tyrosine kinases inhibitor STI571 in normal human lymphocytes and leukemic K562 cells. The latter cells express the BCR/ABL fusion protein, which can be a target of the tyrosine kinase inhibitor STI571. A 20 h incubation with cisplatin at 1-10 microM induced DNA cross-links and DNA fragmentation in normal and cancer cells. Cisplatin could induce intra- and interstrand DNA-DNA cross-links as well as DNA-protein cross-links. DNA damage in K562 cells was more pronounced than in normal lymphocytes. In the presence of spin traps and vitamins we noticed a decrease in the DNA fragmentation in both cell types. Co-treatment of the lymphocytes with cisplatin at 10 microM and STI571 at 0.25 microg/ml caused an increase of DNA fragmentation in comparison with DNA fragmentation induced by cisplatin alone. In the case of K562 cells, an increase of DNA fragmentation was observed after treatment with cisplatin at 1 microM. Our results indicate that the free radicals scavengers could decrease DNA fragmentation induced by cisplatin in the normal and cancer cells, but probably they have no effect on DNA cross-linking induced by the drug. The results obtained with the BCR/ABL inhibitor suggest that K562 cells could be more sensitive towards co-treatment of cisplatin and STI571. Our results suggest also that aside from the BCR/ABL other factors such as p53 level, signal transduction pathways and DNA repair processes can be responsible for the increased sensitivity of K562 cells to cisplatin compared with normal lymphocytes.