Anthracycline Antitumor Antibiotic · Nucleic‐Acid Interactions

Abstract

The helix-to-coil transition of the synthetic DNA poly(dA-dT) in the presence of the anthracycline antitumor antibiotic daunomycin has been investigated by high-resolution proton nuclear magnetic resonance (NMR) spectroscopy in 1 M salt solution. The dissociation of the complex, containing molar ratios of phosphate to daunomycin (Pi/drug) of 50, 25, 9 and 5, with increasing temperature can be monitored independently at the nucleic acid and the antibiotic resonances under conditions of fast exchange. The antibiotic complex formation shifts suggest that either ring B and/or C of the intercalated anthracycline chromophore of daunomycin overlaps with adjacent nucleic acid base pairs. Ultraviolet/visible melting studies of daunomycin complexes with a series of synthetic DNAs substituted with halogen atoms (Br, I) at position 5 of the pyrimidine ring suggest that intercalation of the antibiotic into poly(dA-dU) is not perturbed by bulky substituents at this position. A comparison of the melting curves for the daunomycin . poly(dA-dT) complex with an analog of the antibiotic where the NH3+ group is replaced by dimethylglycine demonstrates the important contributions of electrostatic interactions between the amino sugar and backbone phosphates to the stability of the complex in low salt solution. The ultraviolet/visible and NMR studies monitor biphasic melting transitions at the nucleic acid markers in the daunomycin . poly(dA-dT) complexes, Pi/drug = 50 -9, so that antibiotic-free base-pair regions and those centered about bound daunomycin can be independently studied at the synthetic DNA level in solution.There has been considerable interest in the elucidation of the structural and kinetic aspects of complexes formed between antibiotics, mutagens and carcinogens with nucleic acids in solution. These studies include the application of ultraviolet/visible, circular dichroism and fluorescence spectroscopy, as well as, viscosity and sedimentation investigations [l -71. High-resolution NMR spectroscopy is a powerful method for investigating the structure of macromolecules in solution [8 -131 and we present below an example of the interaction of an antitumor agent with a synthetic DNA in aqueous solution.Daunomycin (Scheme 1) belongs to the class of glycosidic anthracycline antibiotics (which includes adriamycin and carminomycin) which have been successfully used in combination chemotherapy against acute leukemia and solid tumors in man 114,151. It appears that the dose-dependent cardiac toxicity of the anthracyclines may be minimized by the addition Abbreviations. NMR, nuclear magnetic resonance; P,/drug, molar ratio of phosphate in poly(dA-dT) to daunomycin, brsdU, 5-bromo-deoxyuridine ; ?dU, 5-iodo-deoxyuridine. The present study attempts to elucidate structural features of the intercalated complex of daunomycin and nucleic acids by high-resolution NMR spectro-

Hydrogen bonding, overlap geometry, and sequence specificity in anthracycline antitumor antibiotic.DNA complexes in solution.

“…By contrast, previous studies from our laboratory demonstrated that the anthracycline ring D ofdaunomycin does not overlap with adjacent base pairs of poly(dA-dT), on the basis of the small (0.1-0.3 ppm) upfield complexation shifts of the nonexchangeable protons of this ring system on complex formation (9).…”

“…The x-ray data on the daunomycin-hexanucleotide complex demonstrate binding through the minor groove, because the sugar ring is located in this groove (8). It appears that this crystallographic observation can be extended to solution, because we have previously demonstrated that stabilization of the synthetic DNA helix by bound daunomycin is unperturbed by the introduction of bulky halogen substituents at the pyrimidine 5 position, which faces the major groove (9).…”

1H-NMR study of the interaction of daunomycin with B-DNA helices of methylated oligodeoxynucleotides

“…Within this area particular attention has been directed towards the interaction of daunomycin (scheme 1) with various DNA fragments (calf thymus DNA, poly d(G-C), poly d(A-T) or shorter sequences such as d(C-G), d(G-C), d(C-G-T-A-C-G), d(A-T)3, d(G-C-G-C)), investigated by numerous techniques such as fluorescence, IR absorption, CD, X-Ray diffraction, NMR [8][9][10][11][12][13][14][15][16][17]. An X-Ray diffraction study of the crystal structure of a daunomycind(C-G-T-A-C-G) complex showed that the DNA forms a six base-pairs right handed double helix with two daunomycin intercalated in the d(C-G) sequences [8].…”

4',6-Diamidino-2-phenylindole (DAPI) interacts with rare structures of GC polymers

“…This mode of binding does not occur in oligodeoxynucleotides possessing A and T or G and C bases, because of intrinsic symmetry along the two directions of the DNA molecule for these polymers. The relevance for considering both these orientations was supported by various experimental observations (Patel and Canuel 1978;Klevit et al 1986;Coll et al 1987Coll et al , 1989. For this reason, in our experiments we used the two structural classes of GC polymers.…”