Comparative analysis of the effects of platinum compounds on thermostability of DNA

The thermal denaturation profiles of Calf Thymus DNA in the presence of binuclear compounds of bivalent platinum $\mathrm{(cis-[\{Pt(NH_3)_2Cl\}_2Pyr]Cl_2)}$ were studied by absorption spectrophotometry and differential adiabatic scanning microcalorimetry. A comparison with an active antitumor drug cis-diamminedichloroplatinum (cis-DDP) was made. Experimental data witness that small concentrations $(r<0.3)$ of binuclear platinum compound stabilized the structure of Calf Thymus DNA stronger than cis-DDP. Both the complexes tend to refold the denaturated DNA. It is rather interesting that in case of $10^{-6}M$ concentration of binuclear platinum compound $(r=0.03)$ the denaturated DNA is refolded by $77.62\%$, whereas under the same condition cis-DDP leads to $49.01\%$ refolding of denaturated DNA. Such a high percent of renaturation was probably the result of interstrand cross-links formation.