BK2A77: A novel non-peptide bradykinin B2 agonist lowers intraocular pressure in ocular hypertensive cynomolgus monkeys

Abstract

Purpose: Bradykinin (BK), a nonapeptide has been shown to regulate intraocular pressure (IOP) in different species including rabbits and monkeys. Presently we intended to characterize the IOP lowering effects of BK2A77, a novel and selective non-peptide bradykinin B2 receptor agonist in ocular hypertensive (OHT) cynomolgus monkeys.

Methods: BK2A77 was evaluated in several in-vitro efficacy and receptor binding assays using human cloned B1 and B2 CHO cells and in human ciliary smooth muscle (HCM) cells. Intracellular calcium mobilization ([Ca²⁺]_i) was assessed using FLIPR assay and prostaglandin (PG) release was measured using an EIA assay. Ocular safety assessments including slit lamp examinations were performed in monkeys following topical ocular application of BK2A77. BK2A77 or vehicle-induced IOP changes were measured using an Alcon computerized pneumatonometer in normal and hypertensive eyes of cynomolgus monkeys.

Results: BK2A77 is a selective B2 receptor agonist with EC₅₀ values of 13 ± 5 nM (E_max = 92 ± 1%; BK response was 100%) in [Ca²⁺]_i assay and 12 ± 7 nM (E_max = 100 ± 14%) in the PG release assays respectively. BK2A77 exhibited comparable high affinity binding to B2 receptors (Ki = 3 - 10 nM) with no detectable affinity towards B1 receptors. Topical ocular dosing of BK2A77 (3 μg x 3 times, 1 hour apart) to sedated cynomolgus monkeys caused no flare or cells to appear in the anterior chamber as observed up to 24h post-dose. No other adverse effects were noted. A single topical ocular application of BK2A77 (0.03 - 3 μg) caused a dose-dependent IOP reduction up to 25% from baseline between 6 - 24h post-dose in the hypertensive eyes of conscious cynomolgus monkeys. Maximal percent IOP reduction of 25% was observed at 0.9 - 3 μg doses. While the magnitude of IOP reduction with BK2A77 appeared to be similar to that observed with travoprost, the duration of action appeared to last >24h for BK2A77.

Conclusions: Unlike the issues surrounding topical ocular application of BK peptide, including non-selectivity against B1 and B2 receptors, poor ocular penetration and susceptibility to rapid degradation by angiotensin converting enzyme, BK2A77 offers several new therapeutic advantages. BK2A77 is a selective non-peptide B2 receptor agonist capable of robust and long lasting IOP reduction that appears to also be well tolerated following topical ocular dosing in OHT monkeys.

Keywords: 568 intraocular pressure • 675 receptors: pharmacology/physiology • 632 outflow: ciliary muscle