THE KINETICS OF CHROMOSOME AND DNA-DAMAGE BY STREPTONIGRIN IN CHO CELLS

CHO cells were pulse-treated for 20 min with increasing doses of strep tonigrin (SN). First division cells analyzed 18 h after the end of tre atment showed a combination of chromosome and chromatid aberrations wi th a typical dose-response curve. The frequency of SCEs in second divi sion cells (24 h harvesting time) also exhibited a positive correlatio n with the SN dose. A high incidence of chromatid aberrations was dete cted in second and third division metaphases. This indicates that SN h as a persistent clastogenic action that lasts for at least three cell cycles after the end of treatment. The kinetics of DNA damage and repa ir was studied by the alkaline unwinding and single cell gel methods. It was found that a pulse treatment with SN elicited a triphasic respo nse characterized by repair-damage-repair. It is proposed that SN form s stable complexes with the DNA. These complexes by a continuous cycli ng redox process would produce active oxygen species inducing direct d amage to DNA.