Binding of daunomycin to DNA and the inhibition of RNA and DNA synthesis.

With synchronized tissue culture cells (L929), daunomycin had the greatest inhibitory effect on cell growth when the drug was administered during the later stages of cell division (late S, G2, and M). The level of binding of daunomycin to DNA was not found to be influenced by the phase of the cell cycle. The highest level of radioactivity from [eH]-daunomycin was bound to DNA of the heterochromatin fraction. Both RNA and DNA syntheses were inhibited in isolated enzyme systems when daunomycin-treated DNA, from which the unbound drug was removed by passage through Sephadex column, was used. DNA polymerase was reduced to one-fifth of the control activity, while that of RNA polymerase was reduced to one-half. Similar experiments with daunomycin-treated RNA and DNA polymerase preparations showed that the drug had no effect on the activities of the enzymes per se. Hence, the reduction of RNA and DNA polymerase activities could be accounted for by the loss of template activity of the drug-treated DNA. Daunomycin caused by a marked drop in the formation of a complex between RNA polymerase and DNA, indicating that the binding of daunomycin to DNA may give rise to steric hindrance effects that interfere with the association of the template to RNA polymerase enzyme. Sedimentation profile in alkaline sucrose density gradient of DNA that had been treated with daunomycin showed that no change in the molecular weight could be demonstrated.