Enzyme replacement therapy in a feline model of MPS VI: Modification of enzyme structure and dose frequency

Enzyme replacement therapy (ERT) in the MPS VI cat is effective at reducing or eliminating pathology in most connective tissues. One exception is that cartilage and chondrocytes remained distended with extensive lysosomal vac uolation after long-term, high-dose ERT. In this study, we demonstrate that recombinant human N-acetylgalactosamine-4-sulphatase (4S) is taken up by c hondrocytes via a mannose-6-phosphate-dependent mechanism and is effective at removing MPS storage. In vitro, the penetration of 4S into articular car tilage is low (partitioning coefficient = 0.06) and i.v. administered enzym e does not distribute significantly into articular cartilage in vivo. To al ter the tissue distribution of 4S, the enzyme was coupled to ethylene diami ne or poly-L-lysine, increasing its overall charge and diffusion into carti lage, and the dosing frequency of unmodified 4S was increased. Modification resulted in active 4S that maintained its ability to correct MPS storage a nd increased the partitioning coefficient of 4S into cartilage by 77% and 5 0% for ethylene diamine and poly-l-lysine, respectively. However, in vivo E RT studies demonstrated that response to therapy was not significantly impr oved by either the enzyme modifications or change to the dosing regimen, wh en compared with ERT with unmodified enzyme. Distribution experiments indic ated the majority of enzyme is taken up by the liver irrespective of modifi cation. To optimize therapy and improve the amount of enzyme reaching carti lage and other tissues demonstrating poor uptake, it may be necessary to by pass the liver or prolong plasma half-life so that proportionately more enz yme is delivered to other tissues.