Therapeutic approach to lysosomal storage disorders based on acid-labile polyrotaxanes

Abstract

Event Abstract Back to Event Therapeutic approach to lysosomal storage disorders based on acid-labile polyrotaxanes Atsushi Tamura1 and Nobuhiko Yui1 1 Tokyo Medical and Dental University, Institute of Biomaterials and Bioengineering, Japan Niemann-Pick type C (NPC) disease, one of the lysosomal storage disorders, is an autosomal recessive lysosomal trafficking disorder caused by the mutation of NPC1 protein, which shows the chronic accumulation of unesterified cholesterols within lysosomes of cells throughout the body[1]. The lysosomal cholesterol accumulation leads to various clinical symptoms, such as progressive neurodegeneration and hepatosplenomegaly, often resulting in fatality at an early age. Although there is currently no effective clinical treatment for NPC disease, hydroxypropyl-β-cyclodextrin (HP-β-CD) has received much attention as a potential therapeutics for NPC disease. The administration of HP-β-CD reduces the cholesterol content in various organs, leading to prolong a life-span of NPC disease model mice[2]. However, despite the significant therapeutic effect of HP-β-CD, it requires high dose for NPC disease therapy due to its non-specific inclusion of plasma components and rapid renal clearance. To address these problems, we have designed acid-labile Pluronic/β-CD-based polyrotaxanes (PRXs) bearing acid-cleavable terminal stoppers as a new therapeutics for NPC disease[3],[4]. The acid-labile polyrotaxanes exert degradation and the release of threaded β-CDs in response to lysosomal acidic environments (Figure 1). Additionally, the acid-labile PRXs are expected to show long blood half-life, because the molecular weight of the PRXs are remarkably high compared to β-CDs. Therefore, the acid-labile Pluronic/β-CD-based PRXs were synthesized and their therapeutic effect to NPC disease model mice were investigated. The acid-labile PRXs were synthesized by capping Pluronic P123/β-CD pseudopolyrotaxanes with (N-triphenylmethyl)glycine, followed by introducing (2-hydroxyethoxy)ethyl (HEE) groups at the threaded β-CD moieties to impart water solubility. The acid-labile HEE groups-modified PRXs (HEE-PRXs) maintained their supramolecular structure at the pH range of 7 to 9 even after 48 h of incubation. On the contrary, the terminal N-triphenylmethyl groups were completely cleaved after 24 h incubation at pH 5, and the supramolecular structure of PRXs were degraded into their constituent molecules. The HEE-PRXs showed negligible solubilization of cholesterols at pH 7.4, whereas the solubility of cholesterols increased at pH 5, due to the formation of inclusion complexes with dethreaded β-CDs (Figure 2A). The therapeutic effect of HEE-PRXs to NPC disease model mice was investigated using Npc1 knockout mice (NPC1 mice). The HEE-PRXs (500 mg/kg) and HP-β-CD (500 mg/kg) were subcutaneously administered to the NPC1 mice once a week, and the life span of the mice were monitored. The average life span of untreated NPC1 mice was 71.3 days. The administration of HP-β-CD (500 mg/kg) to NPC1 mice could not significantly prolong the life span (73.8 days), because the concentration of HP-β-CD was insufficient. However, the administration of HEE-PRXs (500 mg/kg) significantly prolonged the life span of NPC1 mice (86.5 days) (Figure 2B). This is most likely due to the retardation of systemic clearance for HEE-PRXs. Consequently, the acid-labile HEE-PRXs is considered to be an effective therapeutics for NPC disease.