Site-specific adducts derived from the binding of anti-5-methylchrysene diol epoxide enantiomers to DNA: Synthesis and characteristics

Abstract

The direct synthesis and characterization of site-specific adducts derived from the binding of (+)-1R,2S-dihydroxy-3S,4R-epoxide-1,2,3,4-tetrahydro-5-methylchrysene and the (-)-1S,2R,3R,4S-enantiomer [(+)- and (-)-5-MeCDE, respectively], to the N2-guanine residues in the oligonucleotide d(CCATCGCTACC) are described. The spectroscopic characteristics of the 5-MeCDE-modified oligonucleotides are discussed, and it is shown that their CD characteristics can be used to distinguish between the trans-addition products of the binding of the (+)- and (-)-enantiomers of 5-MeCDE (C4 position). The 11-mer duplexes with the normal complementary strands are destabilized by the site-specific, covalently bound 5-MeCDE residues: the melting points, Tm, are 5-10 degrees lower than in the case of the unmodified duplex. Stereoselective exonuclease enzyme digestion patterns of the single-stranded (+)- and (-)-trans-5-MeCDE-modified oligonucleotides (Mao et al, 1993, Biochemistry, 32, 11785-11793) were used to probe the orientations of the covalently bound 5-MeCDE residues relative to the modified guanine and the 5'-3' strand polarity; the aromatic residues are positioned either on the 5'-side [(+)-5-MeCDE], or the 3'-side [(-)-5-MeCDE adduct] of the modified guanine residues. The electrophoretic mobilities of the (+)-5-MeCDE-modified 11-mer duplexes in native polyacrylamide gels are slower than those of unmodified and modified duplexes containing the stereoisomeric (-)-5-MeCDE-N2-dG lesions. This indicates that the lesions derived from the tumorigenic (+)-5-MeCDE induce greater degrees of bending or local flexibility than the non-tumorigenic (-)-5- MeCDE enantiomer. These differences in the orientational and structural characteristics are similar to those observed with analogous DNA adducts derived from the tumorigenic (+)-7R,8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and the non-tumorigenic 7S,8R,9R,10S-enantiomer, respectively. The adducts derived from BPDE and 5-MeCDE enantiomers thus display similar characteristics that depend primarily on the PAH diol epoxide enantiomer stereochemistry. This direct synthesis approach can be used to generate milligram quantities of site-specific 5-MeCDE-modified oligonucleotides that are suitable for NMR studies (Cosman, et al., 1995, Biochemistry, 34, 6247-6260).

Synthesis of Oligonucleotides Containing the N2-Deoxyguanosine Adduct of the Dietary Carcinogen 2-Amino-3-methylimidazo[4,5-f]quinoline

“…While there is a wide range of T m values for the dGuo-N 2 -PAH adducts, they typically destabilize the duplex by 5-12 °C as compared to unmodified (69)(70)(71)(72)(73). The (−)-and (+)-dGuo-syn-BPDE adducts have been reported to lower the T m of the duplex 5′-CCTATAGATATCC-3′ by 15.5 and 19°C relative to unmodified (72).…”

“…More data are available for the thermal stability of dGuo- N 2 -PAH adducts, and in some cases, conformational information accompanies the T m studies . While there is a wide range of T m values for the dGuo- N 2 -PAH adducts, they typically destabilize the duplex by 5–12 °C as compared to unmodified – . The (–)- and (+)-dGuo- syn -BPDE adducts have been reported to lower the T m of the duplex 5′-CCTATA G ATATCC-3′ by 15.5 and 19 °C relative to unmodified .…”

NMR Solution Structures of Stereoisomeric Covalent Polycyclic Aromatic Carcinogen−DNA Adducts: Principles, Patterns, and Diversity

“…However, these orientations are opposite to those deduced by NMR methods for BPDE-N 6 -dA adducts in various duplexes and in other sequence contexts (Table 4). Therefore, these series of adducts do not follow the pattern that indicates that the tilts of the PAH residues relative to the modified bases are similar in single-stranded and in double-stranded oligonucleotides (125,144,145). These results suggest either that adduct tilts are not always similar in single-and doublestranded oligonucleotides or that exonuclease digestion patterns may not always be indicative of adduct orientations in single-stranded DNA (146), possibly because of base sequence-dependent effects.…”

“…A stereoselective resistance to digestion by phosphodiesterase I is also exhibited by the 4(R)-(+)-and 4(S)-(-)-anti-[MC]-N 2 -dG adducts in single-stranded oligonucleotides (145); the digestion patterns are consistent with orientations of the MC aromatic ring system on the 5′-side of the modified dG residue in the case of the (+)-, and on the 3′-side in the case of the (-)-anti- Similar correlations between stereochemistry-dependent resistance to digestion by exonucleases of the 10(R)-(+)-and the 10(S)-(-)-trans-anti-[BPh]-N 6 -dA lesions (125), and adduct conformations in duplexes VI determined by NMR techniques (14,17), have also been reported. The differences in the rates of digestion by phosphodiesterases I and II suggest that the BPh residues are oriented on the 5′-side of the modified dA* residue in the 1(R)-(+)-trans-anti-[BPh]-N 6 -dA, and on the 3′-side in the 1(S)-(-)-trans-anti-[BPh]-N 6 -dA adducts in single-stranded oligonucleotides (125).…”

“…[MC]-N2 adducts. Thus, the orientation of the polycyclic MC residue in (-)-anti-[MC]-N 2 -dG adducts appears to be similar in the single-stranded(145) and in the doublestranded (18) oligonucleotides, just as in the case of the stereoisomeric (-)-trans-anti-[BP]-N 2 -dG adducts(144); however, the NMR solution structure of the (+)-anti-[MC]-N 2 -dG adducts has not yet been established, and thus analogous comparisons of adduct orientations cannot be made in this case.…”