Thermodynamics of Translesion Synthesis across a Major DNA Adduct of Antitumor Oxaliplatin: Differential Scanning Calorimetric Study
Differential scanning calorimetry (DSC) was used to measure the thermodynamic changes associated with translesion synthesis across major lesion induced in DNA by antitumor oxaliplatin [1,2-d(GG) intrastrand cross-link]. Insertion of matched nucleotides dC at the primer terminus (across unique 3'- or 5'-dG in the unplatinated template) and subsequent extensions resulted in an incremental increase in thermodynamic parameters. In contrast, incorporation of dC opposite either platinated dG in the intrastrand cross-link formed in the template strand and subsequent extensions by one nucleotide resulted only in little changes in thermodynamics. A similar thermodynamic delay was observed for a control template primer containing a dG:dT mismatch across 3'- or 5'-dG in the template and subsequent WatsonCrick primer extensions. The thermodynamic scarcity generated by either the lesion or mismatches was not localized but extended to the 5'-downstream sites, which may be connected with the phenomenon termed short-term memory of replication errors retained by some DNA polymerases responding to DNA damages or mismatches. Interestingly, formation of the 1,2-d(GG) intrastrand cross-link of oxaliplatin altered the overall DSC profiles of the dG:dT mismatch template/primers only in a very small extent. While addition of matched nucleotide dC across either dG in the template strand was thermodynamically favored over the presence of a mismatched dT (??G0310 was 7.6 or 6.8 kJ?mol-1, ??H was 14 or 49 kJ?mol-1), no such thermodynamic advantage was observed with the 1,2-d(GG) intrastrand cross-link of oxaliplatin at these positions (??G0310 was 2.8 or -0.3 kJ?mol-1, ??H was 4 or 9 kJ?mol-1). The equilibrium thermodynamic data also provide insight into the processes associated with misincorporation of incorrect nucleotides during replication bypass across major cross-links of antitumor oxaliplatin. On the other hand, besides thermodynamic effects also kinetic factors play an important role in the processing of the cross-links of antitumor platinum drugs. The impact of the two effects in overall processing DNA adducts by a particular DNA polymerase will depend on its nature.