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Daunomycin is a new antibiotic isolated from cultures of Streptomyces peucetius. For its physicochemical characteristics it may belong to the group of antibiotics described by Ollis and Sutherland (11). The toxico-pharmacologic studies of Daunomycin administered i.v. to mice and rats indicated an acute LD50 value of 15-20 mg/kg. In the rat daily intravenous administration of 1-1.25 mg/kg for 8-14 days was well tolerated. Daily intravenous injection of 2-2.5 mg/kg for 8 days caused a slight decrease in the number of R.B.C. and W.B.C., but no histological damage was found in duodenal mucosa, testicles and other parenchimas. Daunomycin caused a significant inibition of 10 out of 12 tumors tested. At a daily dose of 1 or 2 mg/kg it had a marked inhibitory effect on ascites tumors (Hepatoma AH 130, Walker carcinoma, Ehrlich carcinoma, sarcoma 180 and O.G.G. myeloma) and remarkably increased the average survival time of the tumor-bearing animals. The antibiotic strongly inhibited also the growth of solid tumors (Ehrlich carcinoma 41.1%, 180 sarcoma 42.2%, Walker carcinoma 66.1%, O.G.G. myeloma 70.8 - 85.2% and MC sarcoma 67.6%). Daunomycin decreased the mitotic index of the Ehrlich ascites tumor and induced mitotic damages of tumor cells.

The synthesis of 4'-epi-daunorubicin and of 4'-epi-adriamycin was performed by condensation of 2,3,6-trideoxy-3-trifluoroacetamido-4-O-trifluoroacetyl-alpha-L-arabino-hexopyranosyl chloride with daunomycinone or the protected adriamycinone derivative 17, respectively. Both the alpha and beta anomers were obtained and characterized. All new compounds are biologically active in cultured cells and the alpha anomers display noticeable activity in experimental tumors in mice. Interestingly, 4'-epi-adriamycin (4) appears nontoxic to cultured heart cells up to a concentration of 5 mug/ml.

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The ability of daunomycin to bind to various DNA polymers has been studied by thermal denaturation, spectrophotometric analysis and inhibition of the polymerisation reactions catalysed by Escherichia coli DNA polymerase I and rat liver DNA polymerase CI. The quantitative binding measurements revealed that the antibiotic binds tightly to all synthetic polydeoxynucleotides studied.The results demonstrated that daunomycin can bind with equal affinity to dG . dC or dA . dT basepaired sequences. However, the number of binding sites per nucleotide for poly (dA) . poly(dT) is significantly lower than that found for poly (dA-dT) . poly(dA-dT), thus indicating an appreciable preference of the drug for the alternating copolymer.The inactivation of the template properties of the synthetic DNA polymers in the DNA polymerase system is consistent with their daunomycin binding ability. However, a lack of correlation was observed between the drug binding ability of different DNA polymers and the binding-induced stabilisation of the double helix to heat denaturation.Various lines of evidence strongly suggest that most of the biological effects of daunomycin can be ascribed to its binding to DNA with consequent impairment of nucleic acid synthesis [l]. Binding of daunomycin to DNA occurs by a strong primary process attributed to intercalation [2,3], i.e. insertion of the planar aromatic tetracyclic ring system into the double helix of DNA, with the plane of the chromophore parallel to the planes of the DNA base pairs and a concomitant slight untwisting of the DNA sugar-phosphate backbones [4 -61. In this binding mode, no significant preference for d A . dT or dG . dC sites has been detected [7]. However, differential inhibition of DNA-dependent reactions appeared related to polynucleotide base composition and/or nucleotide sequence [8,9]. In addition, the binding of nogalamycin and steffimycin B (two closely related anthracycline antibiotics) has been postulated to be dependent on the dA + dT content of the polymer [10,ll]. Therefore, it is important to gain more information about the nature and specificity of interaction between daunomycin and nucleic acids.In the present paper we report on the binding of daunomycin to a variety of synthetic polynucleotides Abbreviation. dNTPs, deoxyribonucleoside triphosphates. Abbreviations for polynucleotides follow IUPAC/IUB Recommendations, see Eur. J . Biochem. 15, 203 -208 (1970).Enzyme. DNA polymerase (EC 2.7.7.7).to determine what selectivity the antibiotic may display with respect to its capacity to bind to polynucleotides that have a different base composition and nucleotide sequence. The data presented show that the template inactivation by the antibiotic in the bacterial DNA polymerase system is in accordance with its binding properties. MATERIALS AND METHODS Nucleotides and Polyde0,~ynucleotidesAll of the polydeoxynucleotides used were obtained from P-L Biochemicals Inc. (Milwaukee, Wis., U.S.A.) and were dissolved in 0.01 M NaCl for thermal denaturation studies and in 0.15 M NaC...