CA-IV-directed small-molecule shuttle enables targeted brain delivery of biologics.

The blood-brain barrier (BBB) presents a challenge for central nervous system (CNS) therapies. Receptor-mediated transcytosis offers a solution, but existing receptor targets are ubiquitous across CNS and peripheral tissues, causing unintended exposure. We identified carbonic anhydrase IV (CA-IV) as a brain-enriched receptor enabling engineered viral capsids to cross the BBB. However, it is unclear whether CA-IV can also mediate non-viral delivery. We thus designed a reactive small-molecule shuttle, derived from an FDA-approved binder, that couples to proteins and oligonucleotides in a single step. We validated the binding of conjugated molecules to multiple mammalian CA-IV orthologs and subsequent internalization in cell-based assays. After systemic dosing, CA-IV-targeted antibody conjugates crossed the BBB in mice and neonatal macaques, preferentially accumulating in the brain and sustaining parenchymal levels for at least 7 days. This BrainCAB (Brain access through Carbonic Anhydrase-binder Bioconjugation) technology offers a compact, modular shuttle for selective and prolonged CNS delivery of large molecules.