Photoreactivity of chlorpromazine with native DNA in an aqueous solution.

Near-UV irradiation of a mixture of chlorpromazine and native DNA caused irreversible binding of the drug or its photoproduct (s) to DNA and double strand break of DNA. When the irradiation was performed in a reaction mixture with a low salt concentration, much more photobinding occurred. Accompanying these effects, the maximum hyperchromicity of DNA at a high temperature was decreased. This can be explained by either a partial denaturation or an inhibition of melting by a formation of complex between double helical DNA and a promazine polymer.