AZT-DNA interaction

Oxidative DNA damage has been reported in fetal tissues by exposure to 3'-azido-3'-deoxythymidine (AZT). AZT has been used effectively for the treatment of human immunodeficiency virus-1 (HIV-1) and AIDS. It showed in vitro to block the nucleoside-binding site of the viral reverse transcriptase and to inhibit DNA replication by chain termination. It incorporates into both nuclear and mitochondrial DNA and is shown to cause cancer in vivo and in vitro. This study was designed to examine the interaction of AZT with DNA in aqueous solution at physiological condition, using different drug/DNA (phosphate) molar ratios (r) of 1/80 to 1/2 and constant DNA concentration of 12.5 mM (phosphate). Capillary electrophoresis, FTIR, and UV-visible difference spectroscopic methods and molecular modeling were used to determine the drug binding sites, the binding constants and the effects of the AZT complexation on DNA conformation. Structural analysis showed that AZT binds to DNA through G-C and A-T base pairs and the backbone PO(2) groups with two binding constants of K(1) = 2.60 x 10(5) M(-1) and K(2) = 1.20 x 10(5) M(-1). The drug distributions are 50% with G-C, 15% with A-T and 35% with the backbone phosphate group. AZT-DNA interaction is associated with a partial B- to A-DNA conformational transition.