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Drug delivery to the posterior segment of the eye is challenging due to several anatomical and physiological barriers. Thus, there is a need for prolonged action and targeted drug delivery to treat retinal diseases. Intravitreal injections avoid anterior eye barriers, but the vitreoretinal interface and inner limiting membrane (ILM) may prevent access of drug delivery systems to the retina. Existing data on retinal permeation of intravitreal nanoparticles are sparse and probably misleading due to the inter-species differences of retinal structures in rodents and humans. To bridge this gap, retinal permeation of light-activated liposomes was studied in an ex vivo bovine explant system that simulates the structure of vitreoretinal interface and intact ILM. Our findings indicate that the particle size plays a significant role in determining the retinal penetration as the liposomes of >100 nm sized failed to overcome the ILM and could not permeate into the retina. In addition, our results demonstrate the impact of surface charge and PEG-coating on retinal penetration. Small (≈ 50 nm) anionic liposomes with PEG coating showed the most extensive distribution and cellular localization in the retina. In summary, this study extends understanding of ocular barriers, and provides valuable information to augment design of retinal drug delivery systems.

Nanoparticle morphology (size, shape, and composition) and surface chemistry are the determining factors underpinning the efficacy of such materials in therapeutic applications. The size, shape, and surface chemistry of a nanoparticle can strongly influence key properties such as interactions with diverse biological fluids and interfaces and, in turn, impact the delivery of bioactive cargo, modulating therapeutic performance. This is exemplified in ocular drug delivery, where potential therapeutics must navigate complex biological media such as the gel-like vitreal fluid and the retina. Biodegradable block copolymer amphiphiles are a robust tool for the engineering of various types of self-assembled nanoparticles with diverse morphologies ranging from spherical and tubular polymersomes to spherical and worm-like micelles. Here, we explore the effect of morphological features such as shape and surface chemistry upon the interactions of a series of copolymer nanoparticles with retinal (ARPE-19) cells and the release of a low solubility drug (dexamethasone) that is currently used in ocular therapy and study their diffusion in vitreous using ex vivo eyes. We demonstrate that both aspect ratio and surface chemistry of nanoparticles will influence their performance in terms of cell uptake, drug release, and diffusion with high aspect ratio shapes demonstrating enhanced properties in relation to their spherical counterparts.

In this study, the intravitreal pharmacokinetics of nanomaterials were investigated in vivo in rats and rabbits. Impact of particle size and shape (spherical, longitudinal) on ocular particle distribution and elimination was investigated with fundus camera, optical coherence tomography and ocular fluorophotometry. Differently sized particles showed prolonged ocular retention and remarkable differences in vitreal elimination, but size dependence was consistent, suggesting that other features have influence on their vitreal kinetics. We also demonstrate that liposomes are eliminated from the rabbit vitreous mainly via the anterior route. Simulation of drug concentrations after injection of intravitreal particles shows the importance of synchronized particle retention and drug release rate for efficient drug delivery. In conclusion, we provide kinetic insights in intravitreally administered nanoparticles to improve retinal drug delivery.

Choroidal neovascularization (CNV) is a prevalent vision-threatening vascular disorder in aging population. CNV is associated with several diseases in the posterior segment of the eye such as age-related macular degeneration (AMD). In this study we developed sunitinib-loaded liposomes to block the neovascularization signalling pathway through inhibition of tyrosine kinase of vascular endothelial growth factor receptors (VEGFRs). Liposomal sunitinib formulations were prepared by thin film hydration method and studied for their encapsulation efficiency (EE), loading capacity (LC) and drug release profile in buffer andvitreous. Our finding showed that the liposomes (mean size 104 nm) could effectively entrap sunitinib (EE approximate to 95%) at relatively high loading capacity (LC approximate to 5%) and release sunitinib over at least 3 days. Intravitreal sunitinib-loaded liposomes revealed inhibitory effect on established neovascularization in laser-induced CNV mouse model while the intravitreal injection of sunitinib solubilized with cyclodextrin was inefficient in management of neovascularization. Accordingly, liposomal sunitinib is a promising drug delivery system that should be further studied to inhibit the CNV related to AMD.

Light-activated liposomes permit site and time-specific drug delivery to ocular and systemic targets. We combined a light activation technology based on indocyanine green with a hyaluronic acid (HA) coating by synthesizing HA&ndash, lipid conjugates. HA is an endogenous vitreal polysaccharide and a potential targeting moiety to cluster of differentiation 44 (CD44)-expressing cells. Light-activated drug release from 100 nm HA-coated liposomes was functional in buffer, plasma, and vitreous samples. The HA-coating improved stability in plasma compared to polyethylene glycol (PEG)-coated liposomes. Liposomal protein coronas on HA- and PEG-coated liposomes after dynamic exposure to undiluted human plasma and porcine vitreous samples were hydrophilic and negatively charged, thicker in plasma (~5 nm hard, ~10 nm soft coronas) than in vitreous (~2 nm hard, ~3 nm soft coronas) samples. Their compositions were dependent on liposome formulation and surface charge in plasma but not in vitreous samples. Compared to the PEG coating, the HA-coated liposomes bound more proteins in vitreous samples and enriched proteins related to collagen interactions, possibly explaining their slightly reduced vitreal mobility. The properties of the most abundant proteins did not correlate with liposome size or charge, but included proteins with surfactant and immune system functions in plasma and vitreous samples. The HA-coated light-activated liposomes are a functional and promising alternative for intravenous and ocular drug delivery.

Stealth liposomes encapsulating oligonucleotides are considered as promising non-viral gene delivery carriers; however, general preparation procedures are not capable to encapsulate nucleic acids (NAs) efficiently. In this study, the lyophobic complexes of deoxythymidine20 oligonucleotide (dT20) and DOTAP were used instead of free dT20 for nano-encapsulation process by reverse phase evaporation method. Regarding the various factors that can potentially affect the liposome characteristics, Taguchi design was applied to analyze the simultaneous effects of factors comprising PEG-lipid (%), dT20/total lipid molar ratio, cholesterol (Chol%) and organic-to-aqueous phase ratio (o/w) at three levels. The response variables, hydrodynamic diameter, loading efficiency (LE%) and capacity (LC%), were studied by dynamic light scattering and ethidium bromide exclusion assay, respectively. The optimum condition described by minimum particle size as well as high LE% and LC% was obtained at 5% PEG-lipid, dT20/total lipid of 7, 20% Chol and o/w of 3 with an average size of 84 nm, LE% = 83.4% and LC% = 11.6%. Moreover, stability assessments in presence of heparin sulfate revealed the noticeable resistance, unlike DOTAP/dT20 lipoplexes, to premature release of NA. Transmission electron microscopy confirmed formation of discrete and circular vesicles encapsulating dT20.

Two iridium [Ir(NC)(2)(NN)](+) complexes with the diimine NN ligand containing a long polymethylene hydrophobic chain were synthesized and characterized by using NMR and ESI mass-spectrometry: NN - 2-(1-hexadecyl-1H-imidazol-2-yl)pyridine, NC - methyl-2-phenylquinoline-4-carboxylate (Ir1) and 2-phenylquinoline-4-carboxylic acid (Ir2). These complexes were used to prepare the luminescent PEGylated DPPC liposomes (DPPC/DSPE-PEG2000/Ir-complex = 95/4.5/1 mol%) using a thin film hydration method. The narrowly dispersed liposomes had diameters of about 110 nm. The photophysics of the complexes and labeled liposomes were carefully studied. Ir1 and Ir2 give red emission (lambda(em) = 667 and 605 nm) with a lifetime in the microsecond domain and quantum yields of 4.8% and 10.0% in degassed solution. Incorporation of the complexes into the liposome lipid bilayer results in shielding of the emitters from interaction with molecular oxygen and partial suppression of excited state nonradiative relaxation due to the effect of the relatively rigid bilayer matrix. Delivery of labeled liposomes to the cultured ARPE-19 cells demonstrated the usefulness of Ir1 and Ir2 in cellular imaging. Labeled liposomes were then injected intravitreally into rat eyes and imaged successfully with optical coherence tomography and funduscopy. In conclusion, iridium complexes enabled the successful labeling and imaging of liposomes in cells and animals.