Pharmaceutical Analysis, Drug Discovery and Designing Chemistry

The majority of lysosomal storage disorders aff ect the brain.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 bi-functional IgG-enzyme fusion protein, wherein the IgG domain targets specifi c endogenous receptor-mediated transporter within the BBB, such as the insulin receptor. Brain penetrating IgG-enzyme fusion proteins have been engineered for Hurler Mucopolysaccharidosis (MPS) Type I (MPSI),Hunter MPSII, metachromatic leukodystrophy, Sanfi lippo MPSIIIA and Sanfi lippo MPSIIIB, and validated in Rhesus monkey in vivo and in human fi broblasts in culture. Brain uptake in non-human primates approximates 1% of Injected Dose (ID) per brain.This level of brain uptake is able to replace between 20-100% of endogenous enzyme activity in brain. Confocal microscopy shows that these brain penetrating IgG-enzyme fusion proteins target lysosomal compartments in human fi broblasts, reducing accumulation of sulfated glycosaminoglycans. Bio distribution of the IgG-enzyme fusion protein, as compared to enzyme alone, has been evaluated with whole body autoradiography in Rhesus monkeys. Although enzyme alone does not penetrate the primate brain, there is global uptake of the IgG-enzyme fusion protein throughout the brain of the non-human primate.Conversely, there is comparable uptake of either the enzyme alone or the IgG-enzyme fusion protein by peripheral tissues. The data are consistent with comparable uptake of either theIgG-enzyme fusion protein or the enzyme alone in peripheral organs mediated by the Mannose 6-Phosphate Receptor (M6PR), which recognizes the enzyme domain of the fusion protein. However, the M6PR is not expressed at the BBB. Brain penetration of the fusion protein is mediated via the IgG domain of the fusion protein, which targets the BBB insulin receptor. Successful development of a BBB-penetrating platform is transformational for MPS diseases as well as broader CNS/neurological conditions. Neurocognitive function, somatic eff ects and safety of a phase II proof of concept clinical trial in Hurler MPSI pediatric patients will be discussed. Th is represents the fi rst in human clinical trial of a fusion protein engineered to cross the BBB.