Macrocyclic TfR1 peptide offers a compact route to extrahepatic oligonucleotide delivery
- Oligonucleotide drugs reach the liver readily, but muscle and CNS delivery has relied on large antibody conjugates against TfR1.
- An Ionis/Bicycle peptide, BCY17901, binds TfR1 tightly at a site separate from where transferrin engages, and carries ASO or siRNA cargo.
- In knock-in mice, the conjugate performed comparably to antibody-fragment versions at a far smaller size, avoided the liver and allowed subcutaneous dosing.
- The perspective frames macrocycles as synthetically tractable antibody alternatives.
💡 Points Based on the abstract
Binding outside the transferrin site is the right call, since competing with endogenous ligand would hurt both uptake and iron homeostasis. But TfR1 is broadly expressed, so I would want knockdown across tissues, plus reticulocyte and bone marrow tolerability, before calling this clean. Next check: does affinity tuning change endosomal escape, the usual bottleneck for oligonucleotide delivery?