Evaluation of High Intensity Focused Ultrasound assisted by metal oxide nanoparticles for their promising use in anticancer therapy

Cancer is becoming a very socially important disease. Only in Italy, one thousand of new tumor cases are diagnosed each day according to International Agency for Research on Cancer (IARC) data. Moreover, thousands of lives, that are cut short by cancer, have to be added to the previous numbers. The focal issue is that traditional medicine is actually not able to provide rapid diagnosis, with concrete and effective therapies. With the advent of nanotechnologies, an emerging branch in nanomedecine developed: theranostics. The promise of this new discipline, that exploits functionalized nanoparticles (NPs) to provide both for rapid diagnosis and/or therapies, seems to be the answer for the problem that is represented by cancer. Among all the possible anti-cancer therapies based on NPs, the one studied in this Master's thesis is the Sonodynamic Therapy (SDT). According to this treatment, NPs are administered into a patient and ultrasounds at high intensity (HIFU) are provided to enhance the cavitation in the diseased tissues, in order to induce the generation of reactive oxygen species (ROS) with consequently increase of the oxidative stress only in the diseased cells. The cavitation activity studies have been carried out using a HIFU ultrasound transducer and ZnO nanocrystals with two different surface functionalization. The first one is obtained through chemically anchoring an amino-propyl group, in order to stabilize the NPs in aqueous media with a proper chemical and colloidal stability. Instead, the second one is obtained through the self-assembly of a phospholipidic bi-layer, showing the promising purpose of mimic the double phospholipid membrane of human cells, for promoting the cell internalization for further SDT, but also helping in stabilizing the inorganic nanocrystals in biological media. In the first part of this work, some experiments have been done in order to study the contribution in cavitation activity of the above mentioned nanoparticles. More precisely, the experiments have allowed to determine the minimum input voltage provided to the HIFU that guarantee the cavitation rise and activity. These measurements have been carried out using two main instruments, an ultrasound imaging system and a hydrophone for the detection of the cavitation noise power. Then, the studies on the ROS generation have been carried out using an Electron Paramagnetic Resonance (EPR) spectrometer. These second set of experiments have been performed for the amino-propyl functionalized NPs and confirmed that a treatment with HIFU assisted with ZnO-NH2 NPs is able to induce cavitation at a lower threshold in water-based solution with consequently generation of ROS four times greater than the lonely water control. In contrast, for what concern the lipid-shielded nanocrystals, it was found that the cavitation threshold coincides with the one of water but a differential in the cavitation activity is observed. As a working mechanism, it is hypothesized that the lipidic-bilayer displaces the gas bubbles adsorbed at the nanocrystals surfaces, while these bubbles remain in contrast available when amino-propyl functionalized Nanocrystals are used under HIFU treatment. The obtained results can thus give an important contribution in the understanding of the cavitation mechanism supported by the presence of metal oxide nano