Received for publication August 20, 2007.
Revised January 20, 2008.
Accepted for publication January 23, 2008.

Pharmacological Properties of 552-02, a Novel Epithelial Sodium Channel Blocker with Potential Clinical Efficacy for Cystic Fibrosis Lung Disease

Abstract

Amiloride improves mucociliary clearance (MC) by blocking airway epithelial sodium channels (ENaC) and expanding airway surface liquid (ASL). However, amiloride's low potency and rapid absorption by airway epithelia translated into a short duration of efficacy as an aerosolized therapy for cystic fibrosis (CF) patients. To improve ENaC blocker CF pharmacotherapy, a more potent and durable ENaC blocker tailored for aerosol delivery was synthesized. Parion 552-02 was tested for potency and reversibility of ENaC block, epithelial absorption and biotransformation, selectivity, durability of ASL expansion under isotonic and hypertonic conditions in canine and human CF bronchial epithelial cells, and drug dissociation on ENaC in Xenopus oocytes. Short-circuit current assessed compound potency and reversibility, patch-clamp recordings of ENaC current assessed drug off-rate (K_off), a gravimetric method and confocal microscopy measured mucosal water retention and ASL height, and drug absorption and biotransformation were assessed using LCMS. Amiloride and 552-02 were tested in vivo for MC activity in sheep immediately, and 4-6 hours after aerosol dosing. Compared to amiloride, compound 552-02 was 60 -100 fold more potent, 2-5 fold less reversible, slower at crossing the epithelium, and exhibited a 170 fold slower K_off. 552-02 exhibited greater ASL expansion over 8 h in vitro, and was more effective than amiloride at increasing MC immediately and 4-6 h post dosing. When combining hypertonic saline and 552-02, a synergistic effect on ASL expansion was measured in canine or CF bronchial epithelia. In summary, the preclinical data support the clinical utility of 552-02 ±hypertonic saline for CF lung disease.

Key words: Airway Epithelium, Airway Surface Liquid, Cystic Fibrosis, Epithelial Sodium Channel Blocker, Mucociliary Clearance, Parion Sciences