Quantum dots and potential therapy for Krabbe's disease

Abstract

Enzyme replacement therapy and substrate reduction therapy have proved useful in reversing many pathological consequences of many non-neural lysosomal storage diseases but have not yet reversed pathology or influenced disease outcome in Krabbe disease, We will discuss the relative merits of stem cell therapy, molecular chaperone therapy, gene therapy, substrate reduction therapy, enzyme replacement therapy and combination therapy. Given the limitations of these approaches we will introduce the idea of using tiny 6nm intensely fluorescent Quantum dots to deliver a cell-penetrating peptide and His6-tagged beta-D-galactosidase across the blood-brain barrier. We can therefore follow the fate of injected material and ensure that all targets are reached and accumulated material is degraded. Uptake of lysosomal hydrolases is a complex process and our cell-penetrating peptide JB577 is uniquely able to promote endosomal egress of the QD-cargo. We further show that uptake may depend on the charge of the coating of the Quantum dot, specifically that negative charge directs the cargo to neurons. Since Krabbe disease primarily involves glia, specifically oligodendroglia we experimented with many coatings and discovered a positive charged coating (Polyethyleneglycol 600-amino) which had a positive charge and targeted oligodendrocytes. A similar effect was achieved by treating with chondroitinase ABC to degrade the extracellular matrix, indicating that enzyme replacement has several hurdles to overcome before it can become a routine CNS therapy.Enzyme replacement therapy and substrate reduction therapy have proved useful in reversing many pathological consequences of lysosomal storage disease (LSD) in extraneural tissue of storage disease patients but have not been found to reverse pathology or influence disease outcome in a human neurological lysosomal storage disease such as Krabbe disease. Thus there is an unmet need to come up with a new approach to the delivery of either beta-Dgalactocerebrosidase enzyme protein or low molecular weight inhibitors of Ceramide: galactosyltransferase (substrate reduction therapy) to patients with Krabbe disease. Protein delivery to the CNSDelivering a protein across a cell membrane and having it retain its biological function inside the cell is a major challenge in biology and medicine because of the blood-brain barrier. Many cells have developed a type of receptor (a "coated pit") which facilitates the uptake of nutritive proteins such as lipoproteins (the Apo-E LDL receptor) and transferrin but for the most part they have not evolved to take up proteins from the extracellular space and proteins are endocytosed at a very low rate (Masliah and Spencer 2015). Notable exceptions to this rule are the lysosomal hydrolases, some of which use a phosphorylated sugar (Mannose-6-phosphate) and a specific receptor to exchange enzymes between cells. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptThis specialized system has been taken advantage of to car...

Targeting the central nervous system in lysosomal storage diseases: Strategies to deliver therapeutics across the blood-brain barrier

“…Delivery vehicles such as nanoparticles 13 , extracellular vesicles 79 , polymersomes 80,81 and quantum dots 82 have been explored to improve enzyme delivery to the CNS in LSDs. Whilst quantum dots have only been investigated in an in vitro setting 82 , successful in vivo studies have been conducted with polymersomes 81 , extracellular vesicles 79 and nanoparticles; of these, nanoparticles have been researched most extensively.…”

“…Delivery vehicles such as nanoparticles 13 , extracellular vesicles 79 , polymersomes 80,81 and quantum dots 82 have been explored to improve enzyme delivery to the CNS in LSDs. Whilst quantum dots have only been investigated in an in vitro setting 82 , successful in vivo studies have been conducted with polymersomes 81 , extracellular vesicles 79 and nanoparticles; of these, nanoparticles have been researched most extensively. Multiple studies have employed nanoparticles to successfully deliver therapeutic enzymes to the CNS of Gaucher disease 83 , Krabbe disease 84 and MPS II murine models, reporting reduction of storage products to non-pathological levels 85 (for a thorough review of the role of nanoparticles in LSD treatment up to 2016, please refer to Martin-Banderas et al 13 ).…”

Quantum dot cellular uptake and toxicity in the developing brain: implications for use as imaging probes

“…13 Furthermore, the small hydrodynamic size (10–20 nm) of functionalized QDs has been reported to be suitable for neuron and glial cell labeling and tracking. 14–15 QD applications in the brain have been widely explored in both fundamental research as well as in clinical investigation, 16–23 correlating with the interest in using functionalized QDs as drug-delivery vehicles or targeted-imaging biomarkers for central nervous system (CNS) diseases. Previous literature has shown that chemically modified QDs can deliver drugs and peptides to the developing brain.…”