Spectroscopic characteristics and site I/site II classification of cis and trans benzo[a]pyrene diolepoxide enantiomer-guanosine adducts in oligonucleotides and plynucleotides

Abstract

The highly tumorigenic isomer (+)-7,8-dihydroxy-anti-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE] and its non-tumorigenic enantiomer (-)-anti-BPDE are known to react predominantly with the exocyclic amino group (N2) of deoxyguanine in DNA and to form adducts of different conformations. The spectroscopic characteristics (UV absorbance, fluorescence and circular dichroism) of stereochemically defined (+)-trans, (-)-trans, (+)-cis and (-)-cis d(5'-CACATGBPDETACAC) adducts in the single-stranded form, or complexed with the complementary strand d(5'-GTGTACATGTG) in aqueous solution, were investigated. The spectroscopic characteristics of the double-stranded d(5'-CACATGBPDETACAC).d(5'-GTGTACATGTG) adducts can be interpreted in terms of two types of conformations. In site I-type conformations, there is an approximately 10 nm red shift in the absorption maxima, which is attributed to significant pyrenyl residue-base interactions; in site II-type adducts, the red shift is only approximately 2-3 nm, and the pyrene ring system is located at external, solvent-exposed binding sites. The spectroscopic characteristics of the BPDE-modified duplexes are of the site II type for the (+)- and (-)-trans, and of the site I type for the (+)- and (-)-cis adducts. In adducts derived from the binding of (+)-anti-BPDE to poly(dG-dC).(dG-dC) and poly(dG).(dC), the trans/cis BPDE-N2-dG adduct ratio is 6 +/- 1; in the case of (-)-anti-BPDE this ratio is only 0.4 +/- 0.1 and 0.6 +/- 0.15 in poly(dG-dC).(dG-dC) and poly(dG).(dC) respectively. The spectroscopic properties of these BPDE-modified polynucleotide adducts are consistent with those of the BPDE-modified oligonucleotide complexes; the cis adducts are correlated with site I adduct conformations, while the trans adducts are of the site II type. The correlations between adduct characteristics and biological activities of the two BPDE enantiomers are discussed.

Preparation, identification and analysis of stereoisomeric anti-benzo[a]pyrene diol epoxide–deoxyguanosine adducts using phenyl liquid chromatography with diode array, fluorescence and tandem mass spectrometry detection

“…Meanwhile, there is no significant difference in the ratio of four adducts between 25 and 37 • C. The yield of cis-(+)-anti-BPDE-N 2 -dG is the lowest (∼2.2-2.5% of total adducts), which is 20 times lower than that of trans-(+)-anti-BPDE-N 2 -dG (∼50% of total adducts). The low yield of the cis-(+)-anti-BPDE-N 2 -dG was consistent with its chemical instability [27]. By the established synthesis method, enzymatic digestion process is no longer required, and carcinogenic anti-BPDE (∼0.1 mg) is 10-100 fold less consumed than reported methods [19,20,23].…”

Methylation of Cytosine at C5 in a CpG Sequence Context Causes a Conformational Switch of a Benzo[a]pyrene diol epoxide-N2-guanine Adduct in DNA from a Minor Groove Alignment to Intercalation with Base Displacement

“…63 The stereo-chemical properties of the modified oligonucleotides were established by enzyme digestion of the modified oligonucleotides and HPLC co-elution of the BPDE-modified base with stereochemically defined trans-anti- [BP]G adduct standards. 64 The stereochemical properties of each mononucleotide adduct were identified by circular dichroism techniques, and by co-elution with the corresponding mononucleotide adduct standards as described earlier for the same B[a]PDE-modified oligonucleotides. 32 earlier.…”

Base sequence effects on interactions of aromatic mutagens with DNA

“…The oligonucleotides were synthesized using the phosphoramidite method, purified, reacted with BPDE, and the BPDE-oligonucleotide adducts were purified as described earlier [2,3].…”

“…We have recently succeeded in synthesizing stereospecific BPDE-oligonucleotide adducts by direct synthesis methods [2,3]. Both (+)-and (-)-BPDE give rise to N2-guanine-ClO BPDE adducts via trans and cis addition of dG relative to the 9,10-oxirane moiety of BPDE [2,4].…”