A Controlled Release System for Long-Acting Intravitreal Delivery of Small Molecules.

Purpose: The short half lives of small molecules in the vitreous requires frequent repeated intravitreal injections that are impractical for treatment of chronic eye diseases. We sought to develop a method for increasing the intravitreal half-life of small-molecule drugs. Methods: We adapted a technology for controlled release of drugs from macromolecular carriers for use as a long-acting intravitreal delivery system for small molecules. As a prototype, a small molecule complement factor D inhibitor with an intravitreal half-life of 7 hours was covalently attached to a 4-arm PEG(40kDa) by a self-cleaving beta-eliminative linker with a cleavage half-life of approximately 1 week. Results: After intravitreal injection in rabbits, the drug was slowly released in the vitreous, and equilibrated with the retina and choroid. The intravitreal half-life of the intact PEG-drug conjugate in the rabbit was 7 days, and that of the released drug was 3.6 days. We simulated the anticipated pharmacokinetics of the delivery system in human vitreous, and estimated that the half-life of a 4-arm PEG(40kDa) conjugate would be approximately 2 weeks, and that of the released drug would be approximately 5 days. Conclusions: We posit that a linker with a cleavage half life of 2 weeks would confer a half life of approximately 7 days to a released small molecule drug in humans, comparable to the half life of approved intravitreal injected macromolecular drugs. Translational Relevance: With this technology, a potent small molecule with an appropriate therapeutic window should be administrable by intravitreal injections in the human at once-monthly intervals.