Understanding prodrugs: complexation in aqueous solutions of doxorubicin, bovine serum albumin and gold nanoparticles

Abstract

Aqueous solutions of doxorubicin (DOX), doxorubicin with bovine serum albumin (DOX-BSA), and DOX-BSA in solutions containing gold nanoparticles (AuNPs) with different concentrations of each system component are studied for the first time. The study of the concentration and time-resolved dependences of optical density spectra indicates that the interaction of protonated molecules of the antibiotic with the citrate-covered surface of the nanoparticles of high concentration promotes the aggregation and precipitation of AuNPs. On the other hand, protein macromolecules effectively form conjugates with nanoparticles, preventing their aggregation. Competition of these processes significantly complicates the behavior of optical density spectra at the absorption band of doxorubicin. The simultaneous processes of AuNP aggregation and BSA-AuNP association allow reasonable result of calculation of equilibrium-binding constants for the DOX-BSA complexation process to be obtained only at low nanoparticle concentrations (up to 1.3 × 10−10 M). It was found that these constants decrease to K = 1.18 × 106 M−1 compared with K = 4.74 × 106 M−1 for the DOX-BSA complex, indicating lower stability of these complexes after citrate-stabilized nanoparticles addition. The number of binding sites in DOX-BSA complexes, as shown by the analysis of the isomolar series curves, stays the same for the indicated AuNPs concentrations and is equal to n = 2. The obtained results could be useful to clarify the appropriate concentration of such type of AuNPs upon the development of oncology prodrugs.