Chem.-Biol. Interactions, 20 (1978) 97--102 97 © Elsevier/North-Holland Scientific Publishers Ltd. INTERCALATION WITH DNA IS A PREREQUISITE FOR DAUNOMYCIN, ADRIAMYCIN AND ITS CONGENERS IN INHIBITING DNAase I TERENZIO FACCHINETTI, ALBERTO MANTOVANI, LAVINIA CANTONI, ROBERTO CANTONI and MARIO SALMONA Istituto di Ricerche Farmacologiche, 'Mario Negri', Via Eritrea, 62-20157 Milan (Italy) (Received October 14th, 1977) (Accepted November 5th, 1977) SUMMARY DNAase I from bovine pancreas is inhibited by Daunomycin, Adriamycin, Adriamycin-14-acetate and Adriamycin-14-octanoate, whereas it is not inhibited by N-trifluoroacetyladriamycin-14-valerate or N-trifluoroacetyl- adriamycin. The present study suggests that these inhibitors act not directly on the enzyme, but on DNA, forming stable complexes and thus interfering with enzyme activity. The correlation between DNA binding and enzyme inhibition is demonstrated by the fact that the compounds forming com- plexes with DNA inhibit DNAase I activity, whereas those which do not form complexes with DNA cause no inhibition. INTRODUCTION DM and AM, antibiotics of the anthracycline group, are known to form persistant complexes with DNA [1]. Intercalation with DNA and subsequent inhibition of nucleic acid synthesis have been generally accepted as their major cytotoxicity mode of action [1,2--6]. Di Marco [1] and recently Goodman et al. [6] reported that inhibition of DNA polymerase by AM is due to the DNA-drug complex and not to direct action of the drug on the enzyme. In a previous paper we reported that AM and DM inhibited DNAase I while a new analogue of AM AD32, did not [7]. The major peculiarity of this latter compound is its inability to form complexes with DNA. The Address correspondence to: Dr. Mario Salmona, Istituto di Ricerche Farmacologiche, ~Mario Negri', Via Eritrea, 62-20157 Milan, Italy. Abbreviations: AA, Adriamycin-14-acetate;AD32, N-trifluoracetyladriamycin-14-valerate; AD41, N-trifluoroacetyladriamycin; AM, adriamycin; AO, adriamycin-14-octanoate; DM, Daunomycin.