Melanin-Binding-Based Discovery of Topically Instilled Carbonic Anhydrase Inhibitors for Targeted Delivery and Prolonged Action in the Eye

Glaucoma is a vision-threatening disease that is currently treated with intraocular-pressure-reducing eyedrops that are instilled once or multiple times daily. Unfortunately, the treatment is associated with low patient adherence and suboptimal treatment outcomes. We developed carbonic anhydrase II inhibitors (CAI-II) for a prolonged reduction of intraocular pressure (IOP). The long action is based on the melanin binding of the drugs that prolongs ocular drug retention and response. Overall, 63 new CAI-II compounds were synthesized and tested for melanin binding in vitro. Carbonic anhydrase affinity and IOP reduction of selected compounds were tested in rabbits. Prolonged reduction of IOP in pigmented rabbits was associated with increasing melanin binding of the compound. Installation of a single eye drop of a high melanin binder carbonic anhydrase inhibitor (CAI) resulted in ≈2 weeks' decrease of IOP, whereas the effect lasted less than 8 h in albino rabbits. Duration of the IOP response correlated with melanin binding of the compounds. Ocular pharmacokinetics of a high melanin binder compound was studied after eye drop instillation to the rat eyes. The CAI showed prolonged drug retention in the pigmented iris-ciliary body but was rapidly eliminated from the albino rat eyes. The melanin-bound drug depot maintained effective free concentrations of CAI in the ciliary body for several days after application of a single eye drop. In conclusion, melanin binding is a useful tool in the discovery of long-acting ocular drugs.