Modification of aspartoacylase for potential use in enzyme replacement therapy for the treatment of Canavan disease

Abstract

Canavan disease is a fatal neurological disease without any effective treatments to slow the relentless progress of this disorder. Enzyme replacement therapy has been used effectively to treat a number of metabolic disorders, but the presence of the blood-brain-barrier presents an additional challenge in the treatment of neurological disorders. Studies have begun with the aim of establishing a treatment protocol that can effectively replace the defective enzyme in Canavan disease patients. The human enzyme, aspartoacylase, has been cloned, expressed and purified, and the surface lysyl groups modified through PEGylation. Fully active modified enzymes were administered to mice that are defective in this enzyme and that show many of the symptoms of Canavan disease. Statistically significant increases in brain enzyme activity levels have been achieved in this animal model, as well as decreases in the elevated substrate levels that mimic those found in Canavan disease patients. These results demonstrate that the modified enzyme is gaining access to the brain and functions to correct this metabolic defect. The stage is now set for a long term study to optimize this enzyme replacement approach for the development of a treatment protocol.

Canavan disease, a rare early-onset human spongiform leukodystrophy: Insights into its genesis and possible clinical interventions

“…These studies involving the off-label use of an approved human drug constitute the only record of human cases of CD where a pharmacological treatment has been found to result in a reduction in brain NAA levels and some measurable degree of improvement. In another pharmacologically oriented study aimed at restoring some ASPA activity in order to reduce brain NAA levels in CD, it was observed that a polyethylene glycol-modified ASPA protein administered by intra-peritoneal injection in a CD mouse model over a period of 7 weeks was found to reduce brain NAA levels by about half [72].…”

Enhanced brain distribution of modified aspartoacylase

“…Aspartoacylase (ASPA) was purified by a previously published protocol [21]. Reactive polyethylene glycol (PEG) reagents were purchased from NOF (Japan), amine-reactive AlexaFluor® 594 carboxylic acid, succinimidyl ester was from Life Technologies, polyclonal rabbit anti GFAP antibodies were from Millipore (catalog no.…”

“…We have begun to explore approaches that address each of these issues for the application of ERT in the treatment of CD. Preliminary studies have shown that administration of PEGylated forms of ASPA causes increased enzyme activity and decreased substrate accumulation in brain homogenates from an animal model of CD [21]. However, it has not been established if this treatment leads to uptake and transport of the modified enzyme into brain tissue.…”

Making the White Matter Matters: Progress in Understanding Canavan’s Disease and Therapeutic Interventions Through Eight Decades

“…Surface lysyl groups of human aspartoacylase were modified through PEGylation to decrease immune response and increase circulation halflife with the intention of treating CD patients (Zano et al 2011).…”