Avaliação da indução de autofagia em linhagem de câncer colorretal tratada com nanopartículas de óxido de zinco

Abstract

Nanoparticles of zinc oxide (ZnO-NPs) have attracted the attention of nanomedicine due to its promising anticancer properties, resulting from its electrostatic characteristic and the generation of reactive oxygen species, combined with a relatively easy and economical synthesis process. The molecular mechanisms of the effects of ZnO-NPs on tumor cells are still not well defined, and one of the processes involved that has been investigated is the role of autophagy. In this study, the cytotoxic effects of ZnO-NPs on human colon carcinoma cells (HCT-116) and induction of autophagy were investigated. The characterization of the commercially acquired ZnO-NPs was confirmed with the presence of wurtzite crystal structure by the X-ray Diffraction technique and its approximate size of 50 nm by Transmission Electron Microscopy. The dispersions of ZnO-NPs in DMEM medium showed low stability with tendency to agglomeration by zeta potential analysis and increase of the hydrodynamic size revealed by Dynamic Light Scattering. A concentration-dependent cell viability reduction was observed in the MTT assay, as colony formation was progressively affected with increasing ZnO-NP concentration in the clonogenic assay. Alterations in cell morphology such as loss of adhesion and cytoplasmic retraction were observed by optical microscopy in the presence of increasing concentrations of ZnO-NPs. Western blot analysis was performed to investigate autophagy, revealing a progressive increase in LC3 protein expression after 6, 12 and 18h incubation with IC50 obtained in the MTT assay, confirmed by indirect immunofluorescence test, which similarly increased the expression pattern of LC3A/B at higher concentrations (25 μg mL-1). The results indicated that ZnO-NPs was able to promote cytotoxic effects on the HCT-116 human colorectal carcinoma cell line and induce autophagy at a concentration of 25 μg ml-1. Due to the lack of studies indicating the mechanism of action after exposure to ZnO-NPs in colorectal cancer cells, the data here presented may contribute to the elucidation of the effects of nanoparticles on tumor cells and may direct further studies to better understand the role of autophagy induced by ZnO-NPs. [resumo fornecido pelo autor]