Electrochemical Study on the Interaction of Irinotecan with Calf Thymus Double Stranded DNA

Voltammetric behavior of Irinotecan （CPT-11） was studied in a phosphate buffer （0.002 mol.L^-1, pH 7.5） solution at the hanging mercury drop electrode （HMDE） using cyclic voltammetry （CV）. CPT-11 showed two irreversible cathodic peaks at - 1.01 V and - 1.09 V which involved two electrons and two protons in each reduction step. In addition, the interaction of Irinotecan with double-stranded calf thymus DNA （ds-DNA） was studied by CV at the HMDE employing an irreversible electrochemical equation. As a result of the reaction with ds-DNA, the reduc- tion peaks related to CPT-11 were shifted in a negative direction and the peak currents were decreased. The diffu- sion coefficients of CPT- 11 in the absence （Dr） and presence （Db） of ds-DNA were calculated as 2.8 ×10 5 cm2.s^- 1 and 1.6 × 10^-5 cm2·s^-1 respectively. The binding constant （K=1.0×10^4 L·mol^-1）, and binding site size （s=0.60） of CPT-11 interacting with ds-DNA were obtained simultaneously by non-linear fit analysis. The results demon strate that the main interaction mode of CPT-11 with ds-DNA is electrostatic.