Study Of Long-acting Sustained-release Microspheres Loading Exenatide With Closely Zero-release Behavior

Exenatide, a39-amino acid peptide and the first GLP-1receptor agonistapproved for therapeutic use in humans, is the first choice of the drugs for thetreatment of type II diabetes. The advantage of exenatide is that it neither likeinsulin induces the danger of hypoglycemia due to overdose, nor likechemical drugs increase the burden of liver due to the long-termadministration. But the disadvantage of exenatide is its short half-life in vivo,which causes to be injected twice daily. Besides, causing vomiting, diarrheaand other serious side effects in many patients treated with exenatideseriously limited its clinical application. Considering the side effects andpatient compliance, Bydureon, a once-weekly sustained release formulationof exenatide, has been developed by Amylin Pharmaceuticals and AlkemesPharmaceuticals. Even so, patients with serious side effects need build animmune tolerance by multiple injections of low dose exenatide before administration of the long-acting formulation. However, the process ofmultiple injections in itself is a compliance test for the patients.A new research in our lab makes us to reconsider developing thelong-acting formulation of exenatide. Concerning the non-injection deliverysystem for protein and peptide drugs, our lab invented phase-transitionhydrogel microneedle patch for transdermal delivery system. This technologycan deliver protein and peptide drugs safely, efficiently and conveniently inscientific research and is now under normalized evaluation before clinicaltrial. Comparing with insulin, exenatide, which has smaller molecular weightand higher solubility, seemed to be more easily to achieve success ofnon-injection delivery through phase-transition hydrogel microneedle patchso that drastically facilitate training immune tolerance for patients of type IIdiabetes. So a sustained-release microspheres formulation with more steadyrelease profile and longer release time would be an ideal choice.The author of this work analyzed the related technical parameters ofBydureon, the only one sustained-release formulation of exenatide on themarket, and found the pharmacokinetic profile of Bydureon was very poor.In SD rats Bydureon exhibited very low serum exenatide levels betweendays4and17. The weekly dose of exenatide in Bydureon (i.e., single doseof2mg/60Kg) was much higher (14-28fold) than that for exenatide twice daily injection (i.e.,5-10μg/60Kg twice-daily, which corresponds to a totalweekly dose of70-140μg/human). Therefore, development of an effectivesustained-release microsphere formulation has a great clinical significance.This study prepared PLGA microspheres loading exenatide using aS/O/W emulsion-solvent evaporation method. In SEM images, microspheresloading exenatide showed spherical shape and smooth surface. Theencapsulation efficiency of microspheres is above90%. Effects of PLGAwith different molecular weights and different kind of promoting agents onvitro-release profile of microspheres were also investigated. A formulation ofexenatide loaded microspheres with closely zero-release behavior was choseto do pharmacokinetic and pharmacodynamic research respectively in C57mice and SD rats. The burst-release of the first day was below10%and theaccumulation release rate was above90%after30days. The efficacy ofexenatide microspheres with different dose could maintain17days and theblood exenatide concentration was steady and had a small fluctuation duringthe release time. The long term stability of exenatide microspheres wasstudied at4℃. Finally, this work investigated effects of self-reparation ofexenatide microspheres incubated above the glass transition temperature ofPLGA on release rate of microspheres. These results laid some foundationsfor controlling the burst release of microspheres though this method.