Progressive formation of DNA lesions in cultured Ehrlich ascites tumor cells treated with hydroxyurea.

We have previously demonstrated an accumulation of strand breaks in mature DNA of cultured Ehrlich ascites tumor cells treated with methotrexate. We postulated that the strand breaks arose from unrepaired spontaneous DNA lesions. The present study describes a progressive accumulation of strand breaks in mature DNA of Ehrlich ascites cells treated with hydroxyurea (HU). Strand breaks were determined by alkaline elution. Accumulation of strand breaks was dependent on the length of incubation (0-16 h) and on HU concentration (0-10 mM). About 70% of strand breaks were repaired when cells were incubated without HU. About 67% of strand breaks were prevented by 0.4 mM deoxyadenosine, deoxyguanosine, and deoxycytidine, with or without thymidine. Prevention was less effective by deoxyadenosine and deoxyguanosine and ineffective by deoxycytidine. Free radical scavengers did not prevent strand breaks. S-phase cells accumulated about twice the number of strand breaks as non-S-phase cells. Cell survival decreased in proportion to the increase in HU concentration (0-10 mM). The results demonstrate that lack of purine, as well as of pyrimidine, nucleotides results in strand breaks in mature DNA, suggest that HU cytotoxicity is due to fragmentation of mature DNA, and caution against the use of HU in DNA repair studies.