Recombinant pentameric ligands or Peptabody

High Avidity Targeting
Improving weak monovalent binding forces between a ligand and its target can be of great importance in pharmacology. It can often be achieved by simple multimerization of the ligand. Nature takes advantage of this concept with immunoglobulin binding molecules which are naturally dimers, or even pentamerized dimers. The idea of ligand multimerization is therefore attractive for protein engineering and therapeutic applications where high avidity binding is of interest.

The peptabody technology is designed to allow pentamerization of polypeptide ligands and hence strong, cooperative target binding. Besides conferring superior binding properties, engineered multimeric molecules have also been demonstrated to improve the stability parameters of ligands.

The Peptabody Molecule
The monomeric form of a peptabody molecule consists of a fully humanized Cartilage Oligomeric Matrix Protein (hCOMP) backbone which pentamerizes spontaneously, a semi-rigid hinge region and a target binding molecule:
- a 48 amino acid fragment of the human Cartilage Oligomeric Matrix Protein (hCOMP)
- a 19 amino acid the human IgA fragment acting as hinge region
- a ligand
Target specificity is conferred by the ligand domain. This ligand can be of different forms ranging from short affinity peptides to small full length globular proteins.

Strong binding by avidity effect
The peptabody technology platform allows the production of high affinity, high avidity binding proteins which can be used as specific binders to cell-surface target proteins. Peptabodies with different ligands, ranging from short peptides with defined target binding properties to full length proteins such as the human epidermal growth factor EGF have been produced. The latter can displace an anti-EGF monoclonal antibody by cooperative binding at nM concentrations.

Displacement of Monoclonal antibody (nM affinity) by Peptabody targeting the same protein

Cell Targeting using Peptabody Technology
We took advantage of teh avidity effect to specifically target cells over-expressing an extracellular receptor molecule. For efficient cell binding a high density of receptor molecules is required. At low receptor density the peptabody molecule loses its high avidity binding advantage due to the lack of sufficient appropriate binding partners.

Potential of Peptabodies in Therapy and Diagnosis
Such molecules have a great potential in targeted diagnostics and therapy, comparable to successfully applied monoclonal antibodies. Furthermore, peptabodies have several potential advantages:
- The production of the peptabody in a bacterial system allows for a relatively easy and cost-efficient generation of the molecule
- By cooperative binding, its avidity for the target receptor is dramatically increased
- The use of a natural ligand provides a high specificity which is comparable with that obtained with mAb
- The short in vivo half-life and rapid clearance of non-tissue bound molecules increases the contrast and facilitates detection of the targeted molecule

Clearance of peptabody compared to MAbs one