Enzyme replacement with transferrin receptor-targeted α-L-iduronidase rescues brain pathology in mucopolysaccharidosis I mice.

Mucopolysaccharidosis I (MPS I), a lysosomal storage disease caused by dysfunction of α-L-iduronidase (IDUA), is characterized by the deposition of dermatan sulfate (DS) and heparan sulfate (HS) throughout the body, which causes several somatic and central nervous symptoms. Although enzyme-replacement therapy (ERT) is currently available to treat MPS I, it does not alleviate central nervous disorders, as it cannot penetrate the blood-brain barrier. Here we evaluate the brain delivery, efficacy, and safety of JR-171, a fusion protein comprising humanized anti-human transferrin receptor antibody Fab and IDUA, using monkeys and MPS I mice. Intravenously administered JR-171 was distributed in major organs, including the brain, and reduced DS and HS concentrations in the central nervous system and peripheral tissues. JR-171 exerted similar effects on peripheral disorders similar to conventional ERT and further reversed brain pathology in MPS I mice. We found that JR-171 improved spatial learning ability, which was seen to deteriorate in the vehicle-treated mice. Further, no safety concerns were noted in repeat-dose toxicity studies in monkeys. This study provides nonclinical evidence that JR-171 might potentially prevent and even improve disease conditions in patients with neuronopathic MPS I without serious safety concerns.

Clearance of heparan sulfate in the brain prevents neurodegeneration and neurocognitive impairment in MPS II mice.

Mucopolysaccharidosis II (MPS II), a lysosomal storage disease caused by mutations in iduronate-2-sulfatase (IDS), is characterized by a wide variety of somatic and neurologic symptoms. The currently approved intravenous enzyme replacement therapy with recombinant IDS (idursulfase) is ineffective for CNS manifestations due to its inability to cross the blood-brain barrier (BBB). Here, we demonstrate that the clearance of heparan sulfate (HS) deposited in the brain by a BBB-penetrable antibody-enzyme fusion protein prevents neurodegeneration and neurocognitive dysfunctions in MPS II mice. The fusion protein pabinafusp alfa was chronically administered intravenously to MPS II mice. The drug reduced HS and attenuated histopathological changes in the brain, as well as in peripheral tissues. The loss of spatial learning abilities was completely suppressed by pabinafusp alfa, but not by idursulfase, indicating an association between HS deposition in the brain, neurodegeneration, and CNS manifestations in these mice. Furthermore, HS concentrations in the brain and reduction thereof by pabinafusp alpha correlated with those in the cerebrospinal fluid (CSF). Thus, repeated intravenous administration of pabinafusp alfa to MPS II mice decreased HS deposition in the brain, leading to prevention of neurodegeneration and maintenance of neurocognitive function, which may be predicted from HS concentrations in CSF.

A Blood-Brain-Barrier-Penetrating Anti-human Transferrin Receptor Antibody Fusion Protein for Neuronopathic Mucopolysaccharidosis II.

Mucopolysaccharidosis II (MPS II) is an X-linked recessive lysosomal storage disease caused by mutations in the iduronate-2-sulfatase (IDS) gene. Since IDS catalyzes the degradation of glycosaminoglycans (GAGs), deficiency in this enzyme leads to accumulation of GAGs in most cells in all tissues and organs, resulting in severe somatic and neurological disorders. Although enzyme replacement therapy with human IDS (hIDS) has been used for the treatment of MPS II, this therapy is not effective for defects in the CNS mainly because the enzyme cannot cross the blood-brain barrier (BBB). Here, we developed a BBB-penetrating fusion protein, JR-141, which consists of an anti-human transferrin receptor (hTfR) antibody and intact hIDS. The TfR-mediated incorporation of JR-141 was confirmed by using human fibroblasts in vitro. When administrated intravenously to hTfR knockin mice or monkeys, JR-141, but not naked hIDS, was detected in the brain. In addition, the intravenous administration of JR-141 reduced the accumulation of GAGs both in the peripheral tissues and in the brain of hTfR knockin mice lacking Ids, an animal model of MPS II. These data provide a proof of concept for the translation of JR-141 to clinical study for the treatment of patients with MPS II with CNS disorders.

The endosomal Na(+)/H(+) exchanger contributes to multivesicular body formation by regulating the recruitment of ESCRT-0 Vps27p to the endosomal membrane.

Multivesicular bodies (MVBs) are late endosomal compartments containing luminal vesicles (MVB vesicles) that are formed by inward budding of the endosomal membrane. In budding yeast, MVBs are an important cellular mechanism for the transport of membrane proteins to the vacuolar lumen. This process requires a class E subset of vacuolar protein sorting (VPS) genes. VPS44 (allelic to NHX1) encodes an endosome-localized Na(+)/H(+) exchanger. The function of the VPS44 exchanger in the context of vacuolar protein transport is largely unknown. Using a cell-free MVB formation assay system, we demonstrated that Nhx1p is required for the efficient formation of MVB vesicles in the late endosome. The recruitment of Vps27p, a class E Vps protein, to the endosomal membrane was dependent on Nhx1p activity and was enhanced by an acidic pH at the endosomal surface. Taken together, we propose that Nhx1p contributes to MVB formation by the recruitment of Vps27p to the endosomal membrane, possibly through Nhx1p antiporter activity.