Synthesis and characterization of novel nanosystems for biomedical applications

Abstract

The present thesis is focused on the preparation and characterization of hybrid nanosystems for possible application in nanomedicine, with particular emphasis on cancer treatments by hyperthermia induced by radiofrequency magnetic fields and photodynamic therapy induced by highly energetic X-rays. The thesis has been mainly performed in the framework of the BioNiMED Project funded by the CARIPARMA foundation and coordinated by IMEM-CNR (Parma). During this years, I functionalized cubic SiC/SiO2 nanowires, grown at IMEM-CNR, with superparamagnetic nanoparticles and with porphyrins by chemical bond formation. The biocompatibility of the SiC/SiO2 was also assessed and the results have been recently published (Nano Lett., 2014, 14 (8), 4368–4375). Fe3O4 nanoparticles of different size were prepared by reductive thermal decomposition, magnetic characterization confirmed their superparamagnetic properties. Following the ligand exchange procedure, 10-undecynoic acid was added in the stabilizing shell to introduce a functional group, the carbon-carbon triple bond, able to react with an azide group to form a stable triazole heterocycle. The hyperthermia properties were measured by applying a radiofrequency magnetic field (f=250KHz H=0.016 T) to a colloidal suspension containing the NPs, observing a temperature increase of about 4.2 K. Studies on the biocompatibility showed that the internalization of the NPs occurs at intracytoplasmatic level. The magnetite NPs were then bound to the SiC/SiO2 nanowires, previously functionalized with a derivative of silane with azido group, to introduce the complementary reactive group. The Cu-catalyzed Huisgen 1,3-dipolar cycloaddition, well known as click reaction, permitted to obtain the nanowires decorated with the nanoparticles, with uniform coverage as evidenced by TEM spectroscopy. Different types of porphyrins were synthetized for possible application in PDT (photodynamic therapy), widely used approach for the treatment of superficial tumors. The aim was to anchor the porphyrin on the core-shell SiC/SiO2 nanowires in order to have energy transfer under X-ray irradiation from the nanowires to the photosensitizer, and thus the production of singlet oxygen, toxic for cells. The derivative of H2TCPP (tetra-4-carboxyphenylporphyrin) was reacted with the SiC/SiO2 nanowires, previously functionalized with alkylazide groups. The hybrid nanosystem (nanowires + porphyrin) was characterized and its activity was studied first evidencing the ability to produce singlet oxygen, cytotoxic to the cells, in response to irradiation with energetic X-rays and then conducting in vitro experiments in cancer cell lines. Thus, the potential use of this new nanosystem in Photodynamic Therapy was highlighted. The results have just been published in Scientific Reports (Nature Magazine Group) (published on 05 Jan 2015, doi:10.1038/srep07606) I also developed the synthesis of core-shell nanoparticles with a heart of magnetite and a shell of mesoporous silica oxide. MNPs of about 15 nm were prepared by thermal decomposition, obtaining well- stabilized crystalline particles dispersed in organic solvents. After phase transfer in aqueous medium, a mesoporous silica shell was formed using TEOS in the presence of a surfactant. After surfactant removal, the sample was studied in the absorption and desorption of a molecule model, the antibiotic indomethacin, and will be then studied for the absorption and release of a drug in vitro. Moreover, the NPs were covered with porphyrins for imaging studies in vitro, in collaboration with the Karolinska Institute in Stockholm.