Absence of anthracycline-induced degradation of nuclear DNA in Ehrlich ascites tumour cells.

The in vivo effects of anthracycline antibiotics on the integrity of Ehrlich ascites tumour cell DNA have been studied by sedimentation analysis of nuclear structures containing superhelical DNA in neutral sucrose gradients. These fast-sedimenting protein-DNA complexes may be released by gently lysing cells in solution containing non-ionic detergents and high NaCl concentrations (1.95 M). The supercoiled structure of DNA in these protein-DNA complexes is suggested by the characteristic sedimentation in the presence of intercalating agents. Apparently, no DNA damage could be detected in Ehrlich cells from 7-day-old tumours within 3 h after various doses of daunomycin (0.5--10 mg/kg of body wt.) were administered i.p. to mice. Sedimentation anomalies could not be observed even 15 or 30 h after administration of rtherapeutic doses of daunomycin or adriamycin. In contrast, at 30 min after administration to mice, therapeutic doses of bleomycin (2--8 mg/kg) caused extensive fragmentation of tumour cell DNA, which could be monitored as slowly sedimenting DNA structures (compared with the the control). Similarly, DNA damage could be induced by procarbazine at therapeutic doses. Exposure to bleomycin or procarbazine abolished the characteristic biphasic response to ethidium bromide. The absence of anthracycline-induced degradation of Ehrlich ascites tumour cell DNA is apparently in contrast with the DNA damage observed in L1210 tumour cells. These observations suggest that DNA damage is not a necessary condition for antitumour activity.