The effect of Cu2+ on the interaction between an antitumor drug–mitoxantrone and human serum albumin

The studies on the interaction between HSA and drugs have been an interesting research field in life sciences, chemistry and clinical medicine. There are also many metal ions present in blood plasma, thus the research about the effect of metal ions on the interaction between drugs and plasma proteins is crucial. In this study, we have investigated the effect of a familiar metal ion-Cu2+ on the interaction between an antitumor drug–mitoxantrone (MTO) and human serum albumin (HSA) by using fluorescence spectroscopy, ultraviolet–visible absorption spectroscopy and circular dichroism spectroscopy, for the first time. The results showed that the quenching efficiency of MTO to HSA is higher with Cu2+ than that without Cu2+. In the presence of Cu2+, the secondary structure of HSA was changed and the α-helix content was increased. The apparent association constant (KA), the binding sites (n) and the spatial-distance (r) between MTO and HSA decreased. These results indicated that Cu2+ could affect the interaction between MTO and HSA by altering HSA molecular conformation. Further calculation indicated that the binding mode of Cu2+ in MTO–HSA system was likely to form Cu2+–HSA complex.