BK2A78: A novel non-peptide bradykinin B2 agonist lowers intraocular pressure (IOP) in ocular hypertensive cynomolgus monkeys.

Abstract

Purpose: Bradykinin (BK), a nonapeptide has been shown to regulate IOP in different species including rabbits and monkeys. Presently we intended to characterize the IOP lowering effects of BK2A78, a novel and selective non-peptide bradykinin B2 receptor agonist in ocular hypertensive (OHT) cynomolgus monkeys.

Methods: BK2A78 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 BK2A78. IOP changes were measured using an Alcon computerized pneumatonometer in normal and hypertensive eyes of cynomolgus monkeys.

Results: BK2A78 is a selective B2 receptor agonist with EC50 values of 13 ± 5 nM (Emax = 92 ± 1%; BK response was 100%) in [Ca2+]i assay and 12 ± 7 nM (Emax = 100 ± 14%) in the PG release assays respectively. BK2A78 exhibited comparable high affinity binding to B2 receptors (Ki = 3 - 10 nM) with no detectable affinity towards B1 receptors. Topical ocular dosing of BK2A78 (3 ug 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 BK2A78 (0.03 - 3 ug) 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 ug doses. The duration of action appeared to last >24h for BK2A78.

Conclusions: Bradykinin B2 receptor agonism appears to cause IOP lowering. 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, BK2A78 offers several new therapeutic advantages. BK2A78 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 • 456 ciliary muscle • 711 second messengers: pharmacology/physiology