Optimization of poly(disulfide) nanoparticles for siRNA delivery: the role of the stealthing lipid

Lipid nanoparticles have attracted significant interest in the last two decades because of their use as drug carriers for both hydrophobic and hydrophilic therapeutics. In particular they seem to be good candidates to deliver nucleic acids, like mRNA and siRNA, thanks to their biocompatibility and entrapment efficiency. This thesis focuses on the innovative design and synthesis of novel polymeric nanoparticles (NPs) that are similar to solid lipid nanoparticles (SLNs) in terms of constituents (ionizable lipid, cholesterol, phospholipids and stealthing lipids), but with a cross-linked poly(disulfide) covalent core. The aim of this modification was to improve the stability of SLNs by using a polymeric core instead of relying solely on hydrophobic interactions, and to selectively release the payload in the intracellular environment upon interaction with reducing agents (e.g. glutathione). The aim of the project is to investigate the role of the stealthing lipid which: contribute to particle stability by decreasing particle aggregation; prevent NPs from being opsonized and subsequently recognised and eliminated by the immune system; increase the circulation half-life thereby allowing them to interact with target cells for a longer time. In the context of siRNA encapsulation efficiency and structural properties, the first goal was to evaluate the impact of substituting saturated PEG-lipid chains with unsaturated ones within the nanoparticle formulation, while the second objective was to investigate the replacement of double-tailed PEG-lipid with differently saturated mono-tailed lipid.