Platform technology for treatment of the brain in lysosomal disorders: Application to Niemann-Pick disease type A

The majority of lysosomal storage disorders (LSD) affect the brain. Intravenous enzyme replacement therapy does not treat the brain, because recombinant enzymes are large molecules that do not cross the blood-brain barrier (BBB). BBB-penetration of enzyme therapeutics is enabled by re-engineering the recombinant enzyme as a bi-functional IgG-enzyme fusion protein, wherein the IgG domain is a monoclonal antibody (MAb) that targets a specific endogenous receptor-mediated transporter within the human BBB, such as the human insulin receptor (HIR). A proof of concept phase II clinical trial in pediatric subjects with severe Hurler MPSI with a BBB penetrating HIRMAb-iduronidase fusion protein (AGT-181, valanafusp alpha) produced stabilization of cognition, and reduced hepatosplenomegaly. The aim of the present investigation was to determine if a similar BBB penetrating IgG-fusion protein can be engineered for the treatment of Niemann-Pick disease (NPD) type A, which is caused by mutations in the gene encoding for acid sphingomyelinase (ASM). Genes encoding the heavy chain and the light chain of a HIRMAb-PPT1 fusion protein were engineered followed by stable transfection of Chinese hamster ovary (CHO) cells. The identity of the CHO derived HIRMAb-ASM fusion protein (AGT-189) was confirmed by hIgG1 and ASM Western blot analyses and the purity by SDS-PAGE and SEC-HPLC. Fusion protein binding to the HIR was saturable with an ED50 in the low nM range and comparable to the binding of the parental HIRMAb. The ASM activity in the HIRMAb-ASM fusion protein was retained based on a fluorometric enzyme assay. The brain uptake of HIRMAb-lysosomal enzymes in non-human primates approximates 1% of injected dose per brain. This level of brain uptake is able to produce therapeutic levels of ASM enzyme activity in the brain. Successful development of a BBB penetrating HIRMAb-ASM fusion protein may be transformational for the treatment of the brain in NPA Disease.