Unexpected Nanomolar Inhibition of Carbonic Anhydrase by COX-2-Selective Celecoxib:  New Pharmacological Opportunities Due to Related Binding Site Recognition

Abstract

By optimizing binding to a selected target protein, modern drug research strives to develop safe and efficacious agents for the treatment of disease. Selective drug action is intended to minimize undesirable side effects from scatter pharmacology. Celecoxib (Celebrex), valdecoxib (Bextra), and rofecoxib (Vioxx) are nonsteroidal antiinflammatory drugs (NSAIDs) due to selective inhibition of inducible cyclooxygenase COX-2 while sparing inhibition of constitutive COX-1. While rofecoxib contains a methyl sulfone constituent, celecoxib and valdecoxib possess an unsubstituted arylsulfonamide moiety. The latter group is common to many carbonic anhydrase (CA) inhibitors. Using enzyme kinetics and X-ray crystallography, we demonstrate an unexpected nanomolar affinity of the COX-2 specific arylsulfonamide-type celecoxib and valdecoxib for isoenzymes of the totally unrelated carbonic anhydrase (CA) family, such as CA I, II, IV, and IX, whereas the rofecoxib methyl sulfone-type has no effect. When administered orally to glaucomatous rabbits, celecoxib and valdecoxib lowered intraocular pressure, suggesting that these agents may have utility in the treatment of this disorder. The crystal structure of celecoxib in complex with CA II reveals part of this inhibition to be mediated via binding of the sulfonamide group to the catalytic zinc of CA II. To investigate the structural basis for cross-reactivity of these compounds between COX-2 and CA II, we compared the molecular recognition properties of both protein binding pockets in terms of local physicochemical similarities among binding site-exposed amino acids accommodating different portions of the drug molecules. Our approach Cavbase, implemented into Relibase, detects similarities between the sites, suggesting some potential to predict unexpected cross-reactivity of drugs among functionally unrelated target proteins. The observed cross-reactivity with CAs may also contribute to differences in the pharmacological profiles, in particular with respect to glaucoma and anticancer therapy and may suggest new opportunities of these COX-2 selective NSAIDs.

Direct non-cyclooxygenase-2 targets of celecoxib and their potential relevance for cancer therapy

“…Similarly, valdecoxib, a sulphonamide-based coxib as well (Figure 1), was able to inhibit CAIX and CAXII with comparable potency, although its binding mode was entirely different from celecoxib (Di Fiore et al, 2006). In contrast, several non-sulphonamide COX inhibitors tested, including rofecoxib, a methylsulphone-type coxib (Figure 1), had no CA inhibitory activity (Knudsen et al, 2004;Weber et al, 2004). The ability of celecoxib and valdecoxib to inhibit CAs in vivo was confirmed in glaucomatous rabbits, where both drugs were able to lower intraocular pressure, suggesting that these agents may have utility in the treatment of this disorder (Weber et al, 2004).…”

“…Despite this telling chemical similarity, it came as a surprise when it was discovered that celecoxib displayed potent CA inhibitory activity in the low nanomolar range in vitro (Knudsen et al, 2004;Weber et al, 2004). In fact, its IC 50 towards the tumour-associated CAIX and CAXII enzymes was determined to be 16 and 18 nM, respectively (Di Fiore et al, 2006), and thus was more than double as potent than its inhibition of COX-2, where the IC 50 is 40 nM (Penning et al, 1997).…”

Exploring Polypharmacology Using a ROCS-Based Target Fishing Approach

“…Literature evidence shows the CA inhibitory activity of celecoxib. 44 The 2D-similarity between these two molecules has a Tanimoto value of 0.12.…”

Chemical modifications of nimesulide

“…9 Hence new COX-2 inhibitors that are chemically different from the 1,2-diaryl class but at the same time possessing more enzyme specificity and less adverse side effects are required. The diaryl or aryl-heteroaryl ethers and thioethers are also known to be selective inhibitors of COX-2.…”