ligand-targeted delivery

A ligand is like a key cut to fit one particular lock. Ligand-targeted delivery means fixing such keys onto the outside of a drug carrier so it seeks out and binds the cells that display the matching lock.

The matching lock is a receptor or antigen on the target cell, and the key can be an antibody, a peptide, a sugar, a small molecule like folate, or an aptamer made of nucleic acid. These ligands are attached to the surface of a nanoparticle, liposome, or micelle, usually through a flexible linker so the ligand can reach and engage the receptor. When the receptor is one that the cell normally pulls inward, binding can carry the whole carrier into the cell.

Choosing the ligand is a careful trade-off. Antibodies bind strongly and selectively but are large, costly, and can be cleared by the immune system; small molecules are cheap and stable but may be less selective. The number of ligands per carrier matters too: too few and binding is weak, too many and the carrier may be recognised and removed faster. Many ligand-targeted nanomedicines work well in animals yet translate poorly to patients, so the approach remains promising but unproven for most indications.