Protein functionalization of ZnO nanostructure exhibits selective and enhanced toxicity to breast cancer cells through oxidative stress-based cell death mechanism

Zinc oxide nanostructure (ZnONS) was chemically synthesized and functionalized (FZnONSBLA) with a small protein bovine α-lactalbumin (BLA) by chemical cross-linking methods. Both nano-structures were characterized using various techniques such as electron microscopy, dynamic light scattering (DLS), UV-Vis spectroscopy, FT-IR, photo-luminescence and X-ray diffraction. Electron microscopy and DLS analysis revealed their (ZnONS and FZnONSBLA) average size of 200 nm and 450 nm, respectively. When cytotoxicity of both the nanostructures were assessed in breast cancer cells MCF-7 and MDAMB231 by MTT assay and PI/Annexin V staining (FACS), FZnONSBLA demonstrated higher cell death than ZnONS primarily due to generation of intracellular reactive oxygen species (ROS). Our experimental results also suggested that such enhanced toxicity was due to the lethal structural variant of BLA in FZnONSBLA as well as higher cellular uptake than ZnONS by cancer cells. The death kinetics study with time in cancer cells further proved that FZnONSBLA caused toxicity much faster than ZnONS, thus suggested a strong role of lethal variant of BLA in FZnONSBLA as a cytotoxic agent in cancer cells. Furthermore, FZnONSBLA demonstrated excellent cytocompatibility (normal cells) and hemocompatibility compared to ZnONS. Hence, considering the biodegradable nature of ZnO nonmaterial, our results demonstrated that BLA functionalized ZnONS could be used to develop a suitable therapeutic strategy in cancer.