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Journal of Spectroscopy
Volume 2013, Article ID 380352, 8 pages
Research Article

Spectrophotometric Studies on the Thermodynamics of the ds-DNA Interaction with Irinotecan for a Better Understanding of Anticancer Drug-DNA Interactions

1Young Researchers Club, Gachsaran Branch, Islamic Azad University, 75818-63876, Gachsaran, Iran
2Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia

Received 9 June 2012; Accepted 21 August 2012

Academic Editor: Lu Yang

Copyright © 2013 Reza Hajian and Tan Guan Huat. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The ds-DNA binding properties of irinotecan (CPT-11) including binding constant, thermodynamic parameter, and thermal denaturation () have been systematically studied by spectrophotometric methods. The binding of CPT-11 to ds-DNA is quite strong as indicated by its remarkable hypochromicity and equilibrium binding constant (). The van't Hoff plot of 1/T versus ln  suggests that the CPT-11 binds endothermically to ct-DNA which is characterized by large positive enthalpy and entropy changes. According to the polyelectrolyte theory, the charge release (Z), when ct-DNA interacts with CPT-11, is +0.98, which corresponds very well to the one positive charge carried by CPT-11. The at a low concentration of salt is dominated by electrostatic interaction (98.5%) while that at a high concentration of salt is weakly controlled by nonelectrostatic processes (19.0%). A moderate stabilization of the double helix ds-DNA occurs when CPT-11 binds to ds-DNA as indicated by the increase in of ct-DNA by approximately 15°C in the presence of CPT-11. The CPT-11 is stabilized by intercalation in the DNA (binding constant, K [irinotecan-DNA] = 5.8 × 104 mol−1 L) and displaces the NR dye from the NR-DNA complex (K [NR-DNA] = 2.7 × 104 mol−1 L) in a competitive reaction.