Involvement of oxidative DNA damage and apoptosis in antitumor actions of aminosugars.

We investigated the mechanisms of apoptosis and DNA damage induced by aminosugars in relation to their antitumor actions. The order of cytotoxic effects of aminosugars was D-mannosamine (ManN) > D-galactosamine (GalN) > D-glucosamine (GlcN). A comparison of the frequency of apoptotic cells showed the same order. DNA ladders were formed by only ManN and the formation of DNA ladders was inhibited by a caspase inhibitor. Pulsed-field gel electrophoresis showed that ManN caused cellular DNA cleavage at a lower concentration than those causing apoptosis. Cellular DNA cleavage was inhibited by catalase and enhanced by a catalase inhibitor. Flow cytometry showed that ManN enhanced the production of intracellular peroxides. These results suggest that ManN-induced apoptosis is preceded by H2O2-mediated DNA damage. The order of the extent of damage to 32P-labeled DNA fragments by aminosugars plus Cu(II) was ManN > GalN > GlcN. The DNA damage was inhibited by catalase and bathocuproine, suggesting that H2O2 reacts with Cu(I) to form the metal-peroxide complex capable of causing DNA damage. Two mechanisms of H2O2 generation from aminosugars were proposed: one is the major pathway to form a dioxo compound and NH4+; the other is the minor pathway to form a pyrazine derivative through the condensation of two molecules of an aminosugar. The order of reactivity to generate these products was ManN > GalN > GlcN. On the basis of these results, it is concluded that aminosugars, especially ManN, produce H2O2 to cause DNA damage, which mediates apoptosis resulting in tumor growth inhibition.