Received for publication May 7, 2004.
Revised July 15, 2004.
Accepted for publication July 23, 2004.

ABT-963, A Highly Potent and Selective Disubstituted Pyridazinone COX-2 Inhibitor

Abstract

Nonsteriodal anti-inflammatory drugs (NSAIDS) are efficacious for the treatment of pain associated with inflammatory disease. Clinical experience with marketed selective COX-2 inhibitors (celecoxib, rofecoxib, and valdecoxib) has confirmed the utility of these agents in the treatment of inflammatory pain with an improved gastrointestinal safety profile relative to NSAID comparators. These COX-2 inhibitors belong to the same structural class. Each contains a core heterocyclic ring with two appropriately substituted phenyl rings appended to adjacent atoms. Here we report the identification of vicinally disubstituted pyridazinones as potent and selective COX-2 inhibitors. The lead compound in the series, ABT-963 (2-(3,4-Difluoro-phenyl)-4-(3-hydroxy-3-methyl-butoxy)-5-(4-methanesulfonyl-phenyl)-2H-pyridazin-3-one), has excellent selectivity (ratio of 276, COX-2/COX-1) in human whole blood, improved aqueous solubility as compared to celecoxib and rofecoxib, high oral anti-inflammatory potency in vivo, and gastric safety in the animal studies. Following oral administration, ABT-963 reduced PGE2 production in the rat carrageenan air pouch model (ED₅₀ of 0.4 mg/kg) and reduced the edema in the carrageenan induced paw edema model with an ED₃₀ of 1.9 mg/kg. ABT-963 dose-dependently reduced nociception in the carrageenan hyperalgesia model (ED₅₀ of 3.1 mg/kg). After 14 days of dosing in the adjuvant arthritis model, ABT-963 had an ED₅₀ of 1.0 mg/kg in reducing the swelling of the hind paws. MRI examination of the diseased paws in the adjuvant model showed that ABT-963 significantly reduced bone loss and soft tissue destruction. ABT-963 is a highly selective COX-2 inhibitor that may have utility in the treatment of the pain and inflammation associated with arthritis.

Key words: ABT-963, COX-1, COX-2, NSAID, gastric safety, prostaglandins

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