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Transport vehicle for CNS therapeutics
Delivering biotherapeutics to the brain is complicated by the presence of the blood-brain barrier (BBB). Kariolis et al. and Ullman et al. developed a transport vehicle (TV) consisting of an Fc fragment engineered to bind to the transferrin receptor, a protein highly expressed at the BBB. Utilizing the TV in the form of an antibody directed against beta-secretase enhanced brain delivery and effects in both mice and monkeys following systemic administration. Systemic delivery of a TV fusion with the iduronate 2-sulfatase enzyme was effective at reducing peripheral and central pathologies in a mouse model of mucopolysaccharidosis type II. The TV platform approach potentially offers a treatment for neurological disorders.
Abstract
Effective delivery of protein therapeutics to the central nervous system (CNS) has been greatly restricted by the blood-brain barrier (BBB). We describe the development of a BBB transport vehicle (TV) comprising an engineered Fc fragment that exploits receptor-mediated transcytosis for CNS delivery of biotherapeutics by binding a highly expressed brain endothelial cell target. TVs were engineered using directed evolution to bind the apical domain of the human transferrin receptor (hTfR) without the use of amino acid insertions, deletions, or unnatural appendages. A crystal structure of the TV-TfR complex revealed the TV binding site to be away from transferrin and FcRn binding sites, which was further confirmed experimentally in vitro and in vivo. Recombinant expression of TVs fused to anti–β-secretase (BACE1) Fabs yielded antibody transport vehicle (ATV) molecules with native immunoglobulin G (IgG) structure and stability. Peripheral administration of anti-BACE1 ATVs to hTfR-engineered mice and cynomolgus monkeys resulted in substantially improved CNS uptake and sustained pharmacodynamic responses. The TV platform readily accommodates numerous additional configurations, including bispecific antibodies and protein fusions, yielding a highly modular CNS delivery platform.
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