Discovery and SAR of a Class of Ocularly-active Compounds Displaying a Dual Mechanism of Activity for the Treatment of Glaucoma

Abstract

Purpose: : Inhibitors of Rho kinases (ROCKs) lower intraocular pressure exclusively by increasing aqueous outflow through the trabecular meshwork (TM). Presented here is the discovery and SAR of a class of compounds that possesses a dual-mechanism of activity in vitro and enhanced IOP-lowering efficacy in vivo.

Methods: : A large panel of compounds were synthesized and screened for protein kinase inhibitory activity, including ROCK inhibition. Select compounds were tested for ocular hypotensive activity and tolerability in normotensive Dutch Belted rabbits and Formosan Rock monkeys. From that initial set, a series was developed that had a distinct IOP-lowering profile. Representative compounds were subsequently screened for inhibitory activity against a panel of non-kinase proteins to assess whether a second target other than Rho kinase might contribute to the IOP-lowering activity.

Results: : In vivo testing of compounds demonstrated that compounds possessing a beta-amino acid had a distinct pharmacologic profile from compounds containing either an alpha, gamma, or delta amino acid skeleton. In a series of rabbit studies, mean IOP for untreated eyes ranged from 24.8 - 28.0 mm Hg. Treatment with beta-amino acid derivatives produced an initial rise in mean IOP followed by mean IOP reductions of 1 to 10 mm Hg (p +2 lasting for 24 hours. The addition of a hydrophobic side chain produced a series of compounds with maximal efficacy and improved tolerability. In 3-day monkey studies, mean IOP for untreated eyes ranged from 19.8 - 20.5 mm Hg. Treatment with selected hydrophobic compounds reduced mean IOP on Day 3 by 3-7.5 mm Hg (p<0.01) at 24 hours after dosing with no evidence of ocular irritation. Maximal IOP-lowering efficacy correlated with inhibitory activity against neurotransmitter reuptake receptors, including the norepinephrine transporter.

Conclusions: : Compounds containing beta-amino acids produced the largest reductions in IOP with the longest duration of action due to their unique profile as in vitro inhibitors of both rho kinases as well as neurotransmitter transporter proteins. Addition of hydrophobic modifications to select compounds preserved efficacy while improving tolerability in normotensive rabbits and monkeys. The best of these compounds, AR-13324, was selected for further study.

Keywords: outflow: trabecular meshwork • neurotransmitters/neurotransmitter systems • drug toxicity/drug effects