Targeted lipid-coated ZnO nanoparticles coupled with ultrasound: A sonodynamic approach for the treatment of osteosarcoma as 3D spheroid models

Bone cancer is a rare disease with limited treatment options. Surgery and chemotherapy frequently fail to cure the disease because metastases can develop in the former, and the latter often lacks specificity. Innovative therapeutic treatments are therefore needed to address this rare disease, which typically affects children and adolescents. Physical stimulation to remotely activate a therapeutic agent may represent a promising solution, especially for deep-seated and/or distributed tumors. In this regard, sonodynamic therapy gathers importance: it offers a valid solution to the limitations of photodynamic therapy, such as limited tissue penetration, but retains the advantages of remotely activatable cell death. In this work, we developed lipidic coated iron-doped zinc oxide nanoparticles with superior biocompatibility as remotely activated sonosensitizers for osteosarcoma sonodynamic therapy and an active targeting mechanism addressing the erythropoietin-producing hepatocellular receptor-2 overexpressed in bone cancer cells. The positively charged zinc oxide NPs are coated with a negatively charged phospholipidic shell, which significantly enhances the biocompatibility and hemocompatibility of the nanoconstruct. Most importantly, the lipidic shell is modified by grafting a targeting peptide onto it, increasing cellular uptake towards osteosarcoma cells and demonstrating the potential to address various tissues with the same system. Reactive Oxygen Species (ROS) are effectively generated upon ultrasound stimulation and measured through electron paramagnetic resonance spectroscopy. The nanoconstructs are evaluated in vitro on 3D osteosarcoma spheroids, to demonstrate the effectiveness of the combination of NPs and ultrasound stimulation in suppressing the growth of bone osteosarcoma. The biocompatibility, targeting capabilities, and potential flexibility of the nanoparticles here described open up avenues for an effective and remotely-activated cancer therapy.