Stereoselective Covalent Binding of Anti-benzo(a)pyrene Diol Epoxide to DNA Conformation of Enantiomer Adducts

Abstract

The conformation of adducts derived from the reactions and covalent binding of the (+) and (-) enantiomers of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (anti-BaPDE) with double-stranded calf thymus DNA in vitro were investigated utilizing the electric linear dichroism technique. The linear dichroism and absorption spectra of the covalent DNA complexes are interpreted in terms of a superposition of two types of binding sites. One of these conformations (site I) is a complex in which the plane of the pyrene residue is close to parallel (within 30 degrees) to the planes of the DNA bases (quasi-intercalation), while the other (site II) is an external binding site; this latter type of adduct is attributed to the covalent binding of anti-BaPDE to the exocyclic amino group of deoxyguanine (N2-dG), while site I adducts are attributed to the O6-deoxyguanine and N6-deoxyadenine adducts identified in the product analysis of P. Brookes and M.R. Osborne (Carcinogenesis (1982) 3, 1223-1226). Site II adducts are dominant (approximately 90% in the covalent complexes derived from the (+) enantiomer), but account for only 50 +/- 5% of the adducts in the case of the (-)-enantiomer. The orientation of site II complexes is different by 20 +/- 10 degrees in the adducts derived from the binding of the (+) and the (-) enantiomers to DNA, the long axis of the pyrene chromophore being oriented more parallel to the axis of the DNA helix in the case of the (+) enantiomer. These findings support the proposals by Brookes and Osborne that the difference in spatial orientation of the N2-dG adducts of (-)-anti-BaPDE together with their lower abundance may account for the lower biological activity of the (-) enantiomer. The external site II adducts, rather than site I adducts, appear to be correlated with the biological activity of these compounds.

Conformations of Complexes Derived from the Interactions of Two Stereoisomeric Bay-Region 5-Methylchrysene Diol Epoxides with DNA

“…The highly tumorigenic polycyclic aromatic dial epoxides ( + )anti-BaPDE, 3-MCDE and DE-I are characterized by covalent adduct conformations in which the long axes of the aromatic residues are, on the average, tilted closer towards the axis of the average orientations of the DNA helix, than towards the planes of the nucleic acid bases (19,20,30). Other, biologically less active epoxides appear to give rise to covalent adducts with opposite orientations, i.e.…”

“…For both adducts the dichroism ratio decreases somewhat with increasing wavelength. If there were only one single conformation of the adducts, the ratio of the dichroism should be independent of wavelength (see (30), for example). The variation as a function of wavelength suggests that there is a heterogeneity of binding sites, each characterized by different red shifts in the absorption spectra and somewhat different orientation angles.…”

FLUORESCENCE SPECTROSCOPY OF BENZO[a]PYRENE DIOL EPOXIDE‐DNA ADDUCTS. CONFORMATION‐SPECIFIC EMISSION SPECTRA

“…Fluorescence characteristics of BPT at 77 K . The fluorescence characteristics of various BPDE-DNA adducts have been previously examined at room temperature (Geacintov et al, 1982(Geacintov et al, , 1984Undeman et al, 1983;Jernstom et al, 1984;Zinger et al, 1987;Chen, 1986Chen, , 1987. In order to improve the resolution of the fluorescence emission spectra, and especially to distinguish the fluorescence of site I and site I1 adducts, we examined the fluorescence characteristics of the BPDE-DNA adducts in 1 : 1 by volume ethylene glycol: aqueous buffer (EGB) solution at 77 K. This solvent mixture is known to form a good optical quality glass at low temperatures.…”

“…The characteristics of these adducts have been extensively studied by spectroscopic techniques (Geacintov, 1988). The (-)-BPDE-DNA adducts are characterized by extensive interactions between the pyrenyl residues and the DNA bases, while in the (+)-BPDE-DNA adducts, the pyrenyl residues are located at external, solvent-exposed binding sites (Geacintov et al, 1984;Jernstrom et al, 1984;Zinger et al, 1987;Kolubayev et al, 1987); these types of conformations have been classified as site I (or type I) Figure 1. Structures of (+)-BPDE, (-)-BPDE and pyrene.…”

The Interactions of Pyrenylmethyl Tributylphosphonium Bromide With Single Strand Polynucleotides

“…Peacocke and Skerret (1956) reported two modes of binding for cationic planar dyes to DNA; strong binding, later attributed to intercalation (Lerman, 1961) and weaker binding, due to interaction with the phosphate groups. The binding of pyrene and pyrene derivatives including benzo(a)pyrene to nucleic acids is of particular interest in this respect (Kim et al, 1984;Geacintov et al, 1984;Geacintov et al, 1982;Ibanez et al, 1980), but the low water solubility of these compounds has made it difficult to identify the binding modes, without using organic solvents which are known to modify polynucleotide structure and ligand binding strengths. This has, by necessity, led to the determination of association constants from data of very low ligand to polynucleotide binding ratios (e.g.…”