Structural Features of DNA Interaction with Amino Acid Conjugated Daunorubicin Derivatives

Abstract

Daunorubicin is an effective chemotherapeutic antibiotic crucial in the treatment of leukemia and breast cancer. It intercalates between base pairs and inhibits topoisomerase II. However, its lack of selectivity can induce serious side effects.Our group studies GnRH-III as carrier to facilitate selective targeting of the compound.We synthesized lysine, arginine and leucine conjugate of daunorubicin, three potential enzymatic metabolites of the larger conjugate, to evaluate the impact of these amino acids on the binding.Investigation of DNA structure alterations upon interaction is imperative in the characterization of the biological effect of these new derivatives.We conducted absorption, fluorescence, CD and optical melting measurements, using B-form DNA and T7 bacteriophage as nucleoprotein complex (NP).Absorption and fluorescence studies verify the intercalative binding of the derivatives to DNA. With the help of the fluorescence spectra binding constants were calculated. None of the conjugates bind with the same affinity as the unmodified compound, with slight differences arising also between the conjugates. Binding can be observed with NP as well, but the binding constants are smaller than with isolated DNA.CD spectroscopy reveals alterations in the DNA structure. Upon binding of the conjugates, major intensity changes of the B-form DNA spectra can be observed, at higher concentrations also with shifting and splitting of some bands. These changes can be attributed to the loss of stacking between adjacent base pairs, and at higher concentrations of the drug, distortion of the B-conformation. Changes of DNA CD bands within the NP also indicate the loss of helicity upon interaction.The binding increases the thermal denaturation temperature of the DNA, meaning that the interaction stabilizes the two stranded structure. In the case of NP, the measurements also imply binding to the capsid proteins.