Hydrogel Drug Delivery System Using Self-Cleaving Covalent Linkers for Once-a-Week Administration of Exenatide

We have developed a unique long-acting drug-delivery system for the GLP-1 agonist exenatide. The peptide was covalently attached to Tetra-PEG hydrogel microspheres by a cleavable β-eliminative linker; upon s.c. injection, the exenatide is slowly released at a rate dictated by the linker. A second β-eliminative linker with a slower cleavage rate was incorporated in polymer cross-links to trigger gel degradation after drug release. The uniform 40 μm microspheres were fabricated using a flow-focusing microfluidic device and in situ polymerization within droplets. The exenatide-laden microspheres were injected subcutaneously into the rat, and serum exenatide measured over a one-month period. Pharmacokinetic analysis showed a t1/2,β of released exenatide of about 7 days which represents over a 300-fold half-life extension in the rat and exceeds the half-life of any currently approved long-acting GLP-1 agonist. Hydrogel-exenatide conjugates gave an excellent Level A in vitro-in vivo correlation of release rates of the peptide from the gel, and indicated that exenatide release was 3-fold faster in vivo than in vitro. Pharmacokinetic simulations indicate that the hydrogel-exenatide microspheres should support weekly or biweekly subcutaneous dosing in humans. The rare ability to modify in vivo pharmacokinetics by the chemical nature of the linker indicates that an even longer acting exenatide is feasible.