Perillo, Emiliana (2015) Peptide based platforms for cancer drug delivery. [Tesi di dottorato]

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Abstract

Cancer remains one of main causes of death in humans, accounting for 8.2 milion deaths worldwide in 2012. Chemotherapy, the most widely used cancer therapy, is the most effective and potent strategy to treat malignant tumors, but has the disadvantage of not delivering the therapeutic agents only to tumor sites. Nanomedicine may allow the controlled release of drugs by biodegradation and self-regulation of nanomaterials in vitro and in vivo. The goal of this PhD project was to create a delivery tool, that transports the drug to the target cells not only with high efficacy, but also with minimal toxicity against normal cells and avoiding its degradation and entrapment in endosomes. The first part of this thesis was focused on the design of the strategies for the achievement of a toolbox easily to functionalize and on its obtainment. The second phase was the physico-chemical characterization of each selected nanosystem with particular attention to the size, zeta potential and drug loading and release. The third phase was to analyze in vitro the subcellular fate of the vectorized drug and the effect on the cells. Several nanosystems (liposomes, magnetic nanoparticles, polystyrene nanoparticles) were selected and functionalized with peptides both to enhance tumor targeting and facilitate intracellular uptake. In particular, we used a novel Cell Penetrating Peptide (namely, gH625) which is able to overcome the known limits of classic CPPs. In fact, gH625 is able to efficiently traverse biological membranes, promoting lipid-membrane reorganizing processes, such as fusion or pore formation and involving temporary membrane destabilization and subsequent reorganization; it is able to circumvent the endosomal entrapment either favouring the escape from the endosome or by directly translocating the drug across the membrane. In order to make the nanosystem cell and tissue specific, we have further functionalized the surface of the nanosystem with a targeting peptide. We exploited the EGB peptide, which recognizes the epidermal growth factor receptor (EGFR), a tyrosine kinase receptor overexpressed in several solid tumors. The first nanoplatform is liposome based. The presence of gH625 on the surface of liposomes is favouring their uptake in both sensitive and drug-resistant tumor cell lines allowing an increase of cell growth inhibition: in fact, a greater quantity of Doxo from functionalized liposomes is accumulated into cells. Doxo encapsulated in functionalized liposomes was able to enter in the nuclei of Doxo-resistant cancer cells indicating that the peptide gH625 was probably inducing a greater and more rapid internalization also in resistant cells, which could contribute to overcome drug resistance. The second nanoplatform is based on multifunctional magnetic nanoparticles (SPIONs). Our goal was to verify if we could also enhance the cellular uptake of this kind of cargo. We focused on optimization of the gH625 conjugation strategy, in order to find the best compromise between the colloidal stability of nanosystems, their half-life in blood and their efficient translocation into cells. We optimized several important parameters such as the concentration of gH625 on the polymeric surface of SPIONs and characterized the obtained nanosystem by Circular Dichroism (CD). Data confirmed that gH625 retains its helical structure when bound to the nanoparticle surface, suggesting that the secondary structure of the peptide was not disturbed by attachment to SPIONs. The third nanoplatform is based on polystyrene nanoparticles (NPs). We explored the possibility of using NPs functionalized with gH625 to deliver a drug across the Blood Brain Barrier (BBB). The uptake of NPs with gH625 by brain endothelial cells is greater than that of the NPs without the peptide. Moreover, gH625 plays a key role in controlling the uptake mechanism. In fact, gH625 is able to change the mechanism of uptake of the cargo and it is able to cross the BBB. In summary, these results establish that gH625 may represent a good choice for the design of promising carriers to deliver drugs for the treatment of human diseases and we have developed a nanoplatform for targeted drug delivery to be used for several pathologies.

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