Differentially cleaving peptides as a strategy for controlled drug release in human retinal pigment epithelial cells.

Currently, drug delivery to the posterior eye segment relies on intravitreal injections of therapeutics. This approach requires frequent injections and does not guarantee drug delivery to intracellular targets. Controlled release systems and nanoparticles are being investigated to mitigate these challenges but most of these approaches lack translational success to the clinics. In our present study, we report a peptide-based delivery system that utilizes enzyme assisted cleavable linkers to release conjugated cargo within the retinal pigment epithelial (RPE) cells. Peptide linkers with differential cleavage rates were developed and tested in the vitreous humor, RPE cell homogenates and intact RPE cells. Selected peptide linkers were conjugated to cell penetrating peptides and d-peptide cargoes. The peptide-based delivery systems were non-toxic to the RPE cells, chemically stable in porcine vitreous and delivered cargo prototypes (hydrophobic & hydrophilic) to the RPE cells. Importantly, we show quantitatively with LC/MS analytics that the intracellular cargo release is controlled by the sequence of the peptide linker. The controlled cleavage of the peptide linkers is not only a useful strategy for intracellular drug delivery to the RPE targets but might also be useful in utilizing the RPE cells as mediators of drug delivery to intracellular targets and surrounding tissues (such as neural retina and choroid).

High-throughput in vitro drug release and pharmacokinetic simulation as a tool for drug delivery system development: application to intravitreal ocular administration.

In vitro estimation of release kinetics from drug delivery systems is needed in formulation development. Cost-effective methods of assessment for delivery systems are needed particularly in the case of biologicals and drug administration routes that are difficult to screen in vivo (e.g. intraocular drug delivery). As a proof-of-concept, we demonstrate here a practical high-throughput methodology to investigate in vitro drug release and predict resulting drug concentrations in the eye after intravitreal administration. 96-well plate based assay aided with robotic sampling was used to study release of eight model drugs of varying physicochemical properties (dexamethasone, vancomycin, alpha-lactalbumin, lysozyme, myoglobin, albumin, lactoferrin, human IgG) from twelve alginate microsphere formulations. The amount of drug released over a period of time was assessed by photometric and fluorescence methods. In vitro drug release rates obtained were used in pharmacokinetic simulations using one-compartment model of the vitreal cavity with anatomical volume of distribution and clearance estimates based on the literature precedence. An integrated approach of drug release screening and pharmacokinetic simulations can prove to be a useful methodology in guiding formulation development for ocular delivery in animal models. In general, the methodology has the potential to be a cost-effective tool for early stage drug delivery system discovery and development.