Polymersome Mediated Delivery of Mitochondrial therapeutics to parkin Mutant Fibroblasts

Mutations in parkin cause autosomal recessive Parkinsonism and mitochondrial defects. A recent drug screen identified a steroid like class of hydrophobic compounds able rescue mitochondrial function in mutant parkin fibroblasts. These included Ursolic Acid, Ursocholanic Acid, and Ursodeoxycholic Acid. pH-sensitive polymersomes, nanoparticles composed of amphiphilic block co- polymer, have been shown to encapsulate hydrophobic cargoes, enter cells without detriment to viability and release their cargoes therein. PMPC25−PDPA65 nanoparticles successfully encapsulating drugs were made by thin film rehydration, and purified by hollow fibre filtration. High encapsulation efficiencies were revealed by HPLC. Particle characterisation by and Transmission Electron Microscopy revealed a spectrum of morphologies, including spherical particles, branched tubular assemblies, and large high genus lyotropic structures. Morphological fractionation was achieved through stepwise centrifugation, and mass quantification showed drug encapsulation increased the relative proportion of tubular assemblies. Polymersomes were found to enter into parkin mutant fibroblasts without cytotoxic induction, or detriment to mitochondrial function as assessed by LDH release, mitochondrial membrane potential and cellular ATP levels. Drug loaded polymersomes of both spherical and tubular morphology increased cellular ATP levels of parkin mutant fibroblasts, and were found to deliver a fluorescent steroid at least as effectively as DMSO. The results presented here suggest PMPC-PDPA nanoparticles are suitable for use as a therapeutic vector in parkin mutant cells. The production of spherical and tubular nanoparticle morphologies would be of interest to in vivo applications, each being known to show distinct properties affecting nanoparticle distribution within the body.