The use of N-terminal immobilization of PTH(1–34) on PLGA to enhance bioactivity

The objective of this work was to control the orientation of bioactive molecules immobilized on a biodegradable substrate to improve their accessibility for binding to cell surface receptors and, therefore, to increase bioactivity. The osteotropic peptide, parathyroid hormone (1–34) (PTH(1–34)), was used to demonstrate the approach. To this end, the intrinsic N-terminal serine residue was oxidized to create an aldehyde group that specifically bound to hydrazide-derivatized poly(lactide-co-glycolide) under neutral conditions to form a hydrazone bond. Use of dihydrazide spacers significantly increased the amount of peptide immobilized compared to simple adsorption or direct, random attachment. In probing accessibility of immobilized PTH(1–34), attachment using longer dihydrazide spacers enhanced binding of an antibody against an epitope in the N-terminal region of the peptide. The longest spacer also increased binding of a C-terminal antibody. Furthermore, substrates with peptide tethered via spacers stimulated intracellular synthesis of cAMP, with activity increasing with dihydrazide length. PTH(1–34) immobilized using the longest spacer was significantly more effective than both random binding and adsorption. Site-directed binding of bioactive peptides to surfaces presents biomolecules for binding with cells so as to enhance interaction with receptors, and therefore the approach may be useful for obtaining preferred localized tissue responses.