Liposome nanoparticles for targeted drug delivery, gene delivery and magnetic imaging

Liposomes are spherical vesicles with an aqueous inner cavity surrounded by a lipid bilayer membrane. Liposomes of around 100 nm mean diameter can be classified as nanoparticles (we here refer to liposomes of this size as liposome nanoparticles). Liposome nanoparticles exhibit several properties such as ultra small-size, large surface-area-to-mass ratio, and high reactivity, all of which may be useful in various applications. The small diameter of the liposome nanoparticles is an important attribute that enables them to pass various in vivo barriers for systemic delivery. The present study aimed at developing multifunctional liposomes to deliver drugs and genes with peptide-driven targetability and MRI visualisation to treat inner ear disorders. In addition to the fact that liposomes can be targeted to selected cell populations, they are biodegradable, traceable in vivo, and can be used for controlled drug release. The first aim of the present study was to develop a method to prepare liposomes with diameter less than 100 nm using a novel procedure, adaptive focused ultrasound (AFU). AFU has several advantages compared to other ultrasound-based techniques; it is non-invasive and isothermal, and the energy involved is much more precisely controlled owing to focusing of the acoustic energy. The development of new methods for the efficient delivery of drugs to the inner ear represents an important step towards the treatment of cochlear diseases and injury and the amelioration of hearing loss. The second aim of this project was to analyse the efficacy of the penetration of liposomes through the round window membrane when injected into the middle ear cavity in mice and to determine whether the accumulation of liposomes in the inner ear tissues after such treatment were sufficient to elicit a therapeutic response. Our results demonstrate that liposomes are capable of carrying into the inner ear a drug, disulfiram that elicits a biological effect that is measurable by a functional readout. As its third aim, this study investigated the selective targetability of inner ear neuronal cells using the survival receptor tyrosine kinase B (TrkB) for targeted gene delivery. We demonstrate the feasibility of targeting of liposomes to TrkB-expressing cells by designed peptides that promote cellular uptake via receptor-mediated pathways. Our fourth aim was to track the dynamics and distribution of liposomes in vivo by preparing MRI-traceable liposomes. Effective MRI-traceable liposomes were developed by encapsulating gadolinium, which was visualised in vivo in the rat inner ear using a 4.7 T MR machine. The dynamics were correlated to the status of the perilymph circulation.