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 reduction peaks related to CPT-11 were shifted in a negative direction and the peak currents were decreased. The diffusion coefficients of CPT-11 in the absence (D_f) and presence (D_b) 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=1.0×10⁴ 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 demonstrate that the main interaction mode of CPT-11 with ds-DNA is electrostatic.