Development of gold(III) thiosemicarbazonate complex–loaded PLGA nanoparticles: characterization and sustained release studies

The gold(III) complex [AuCl(L₁)] has been reported as a lead candidate for Chagas' disease (CD) treatment. However, in order to be effective, the drug must first reach the target tissue and then be delivered in therapeutic amounts. In this context, nanoparticles (NPs) of poly(lactic-co-glycolic acid) (PLGA) have been developed to be used as delivery systems for [AuCl(L₁)]. The [AuCl(L₁)]-PLGA-NPs were prepared via the emulsification and solvent evaporation technique and displayed encapsulation efficiency around 90% with the size range of 275 ± 5 nm, polydispersity index (PDI) around 0.115, and a higher value of zeta potential (− 6.51 ± 0.47 mV) compared to blank NPs (without gold complex), which agree with the formation of a cationic species in solution, as indicated by computational calculations. Additionally, high-resolution images obtained by SEM showed the [AuCl(L₁)]-PLGA-NPs spherical shape with average sizes close to those analyzed by the DLS technique. Stability studies for the [AuCl(L₁)]-PLGA-NPs pointed out that no significant changes in relation to size and PDI occur over almost 2 months of storage at 8 °C. The release of the complex from NPs was about 10% in 24 h, followed by a slow release. By means of the Korsmeyer-Peppas model, it was possible to identify the release mechanism as being through diffusion and relaxation of the polymeric matrix. Overall, it has been shown that the PLGA-NPs are promising carriers for delivery of [AuCl(L₁)] and are recommended to be investigated as formulations for parasite treatment in vivo experiments.