Ultraviolet Induced Binding of Daunomycin to Dna

Up to 10–15% of daunomycin present in solutions of DNA‐daunomycin remains irreversibly bound to DNA after 2 h of UV irradiation. Three times as much drug is irreversibly bound to DNA when oxygen is present, compared to deoxygenated solutions. Maximal amounts of the irreversibly bound drug are obtained between pH 5.5 and 7.5 and at an ionic strength of 0.76 M. Although the presence of daunomycin inhibits the extent of UV‐induced degradation of the DNA, the DNA is still extensively degraded and denatured in the time required for optimal yields of the DNA‐daunomycin photoproduct. This degradation of the DNA may impair its use as a lysosomotropic carrier of daunomycin.