A novel nanoparticle-based system for sustained intravitreal drug delivery

Zusammenfassung

lntravitreal (IVT) injection of antiangiogenic proteins has become common in treating blinding neovascular intraocular diseases, but this suffers from rapid exit of active agents from the eye. Rapid drug loss is even more problematic for smaller agents to treat glaucoma or inflammation. Thus, many researchers have sought devices, usually microparticles (MP), to prolong IVT residence. These have not been approved, except with steroids, owing to foreign body reactions, especially in primates. The vitreous contains poly-anionic carbohydrates which could anchor smaller cationic nanoparticles (NP) but polycations are usually cytotoxic. Several reports now indicate greatly improved safety if the cations are derived from L-arginine (R; Arg). Our main goal has been to design and characterize R peptide NP conjugates (NPC), relating their R content and surface charge to increased duration of IVT residence, and relating these to increased IVT duration. In this thesis, we have studied the relation between the amount of positive charges of peptides loaded to the NP, how they affect the zeta potential (amount of charge that develops at the interface between a solid surface and its liquid medium) on the NP surface and its residence time in the vitreous. As an in vivo model we have used rabbit eyes, as it closely models the human eye pharmacokinetics. Our results show a half-life of <<5 days for simple NP residence in vitreous, increasing in NPC from 7 to 17 days, depending on peptide R content. Moreover, it did not show any pathology or inflammation in the rabbit ocular tissue at doses up to 360 µg per eye. To enable prodrug delivery in this system, we have synthesized different types of amino-alkoxy esters with varied ester hydrolysis rates. From our first screening, we selected four amino-alkoxy ester candidates, which we then attached to a chromophoric hexanoic acid, and then we conjugated these to the NP to study the relevant ester hydrolysis. This identified two bridging esters, with respective hydrolysis t1/2 near to 44 and 100 days, sufficient to enable sustained IVT protein delivery. We also discovered and optimized di-carboxy half-amides of small R-containing peptides, which are active in vivo in a mouse model of age-related macular degeneration (AMD). Finally, we synthesized an ester-peptide prodrug of one such peptide as an NPC, for release and efficacy studies. This NPC displayed an in vitro release t1/2 of 34 days. Preliminary efficacy studies in the AMD model showed significant efficacy favoring the NPC over the vehicle when these were injected 14 days before the laser-induced lesion. On the other hand, the free peptide also gave a favorable trend compared to vehicle, and the NPC was not clearly more efficacious than free peptide alone. This is now being repeated with earlier injection (-28 days), where no free peptide effect is expected.