Since cyclooxygenase (COX) isozymes discovery, many papers and reviews have been published to describe the structural bases of COX inhibition, and to debate on the therapeutic and adverse effects of worldwide clinically used nonsteroidal anti-inflammatory drugs (NSAIDs), included COX-2 selective inhibitors (well known as Coxibs). COX-2 inhibition has been widely investigated, whereas the role of COX-1 in human pathophysiology is mostly not yet well ascertained. As time goes on, the cliché that the constitutively expressed isoform COX-1 is only involved in normal physiological functions, such as platelet aggregation, gastric mucosa protection and renal electrolyte homeostasis is going to be shattered. Low-dose aspirin, behaving as a preferential inhibitor of platelet COX-1, allowed to enlighten the role exerted by this isoenzyme in many mammalian cell types. This review would elucidate the most recent findings on selective COX-1 inhibition and their relevance to human pathology such as cancer, neuro-inflammation, cardioprotection, fever and pain. It would also focus on the design and development of new highly selective COX-1 inhibitors, useful tools in pharmacological studies aimed at gaining a deeper insight of the role of COX-1 in human health and disease. Among the traditional NSAIDs, other then aspirin and indomethacin, only few examples of selective COX-1 inhibitors (SC-560, FR122047, mofezolac, P6 and TFAP) have been so far identified. This review has also the scope to stimulate the development of novel drugs, which activity is COX-1 mediated.

Aspirin affords cardioprotection through the acetylation of serine 529 in human cyclooxygenase-1 (COX-1) of anucleated platelets, inducing a permanent defect in thromboxane A 2 (TXA 2 )-dependent platelet function. However, heterogeneity of COX-1 suppression by aspirin has been detected in cardiovascular disease and may contribute to failure to prevent clinical events. The recent recognized capacity of platelets to make proteins de novo paves the way to identify new mechanisms involved in the variable response to aspirin. We found that in washed human platelets, the complete suppression of TXA 2 biosynthesis by aspirin, in vitro, recovered in response to thrombin and fibrinogen in a time-dependent fashion (at 0.5 and 24 hours, TXB 2 averaged 0.1؎0.03 and 3؎0.8 ng/mL; in the presence of arachidonic acid [10 mol/L], it was 2؎0.7 and 25؎7 ng/mL, respectively), and it was blocked by translational inhibitors, by rapamycin, and by inhibitors of phosphatidylinositol 3-kinase. The results that COX-1 mRNA was readily detected in resting platelets and that [ 35 S]-methionine was incorporated into COX-1 protein after stimulation strongly support the occurrence of de novo COX-1 synthesis in platelets. This process may interfere with the complete and persistent suppression of TXA 2 biosynthesis by aspirin necessary for cardioprotection.A spirin affords cardioprotection inducing a complete and permanent defect in the capacity of platelets to generate thromboxane A 2 (TXA 2 ) through the acetylation of serine 529 of cyclooxygenase-1 (COX-1). 1,2 Because of a nonlinear relationship of inhibition of platelet TXA 2 generation with inhibition of TXA 2 -mediated platelet aggregation, an excess of 95% inhibition of COX-1 activity is required to influence platelet function. 3 In fact, even tiny concentrations of TXA 2 have been shown to cause platelet activation. Thus, 10 nmol/L of the TXA 2 mimetic U46619 induces platelet adhesion and shape change, 4 and in the presence of a subthreshold concentration of collagen, U46619 (0.5 to 10 nmol/L) causes platelet aggregation. 5 Recently, Maree et al 6 showed that many patients who are treated with low-dose enteric-coated aspirin (75 mg) for secondary prevention of cardiovascular events have persistent elevated serum TXB 2 levels (Ͼ2.2 ng/mL), which translates into a more frequent occurrence of arachidonic acid (AA)-induced platelet aggregation. Reduced bioavailability of aspirin 6 and genetic variants in COX-1 7 may participate in the intersubject variable response to aspirin. The recent recognized capacity of platelets to make proteins de novo 8 paves the way to identify new mechanisms involved in aspirin failure to cause complete and persistent suppression of platelet COX-1 activity in some individuals.Thus, in the present study, we assessed, in vitro, the hypothesis that de novo synthesis of COX-1 could account for TXA 2 biosynthesis in platelets in which the activity of preformed COX-1 was blocked by pretreatment with aspirin in vitro. Materials and MethodsHealthy volunteers (nϭ9 to 22...

3,4-Diarylisoxazole analogues of valdecoxib [4-(5-methyl-3-phenylisoxazol-4-yl)-benzensulfonamide], a selective cyclooxygenase-2 (COX-2) inhibitor, were synthesized by 1,3-dipolar cycloaddition of arylnitrile oxides to the enolate ion of phenylacetone regioselectively prepared in situ with lithium diisopropylamide at 0 degrees C. The corresponding 3-aryl-5-methyl-4-phenylisoxazoles were easily generated by a dehydration/aromatization reaction under basic conditions of 3-aryl-5-hydroxy-5-methyl-4-phenyl-2-isoxazolines and further transformed into their benzenesulfonamide derivatives. The biochemical COX-1/COX-2 selectivity was evaluated in vitro by using the human whole blood assays of COX isozyme activity. Three compounds not bearing the sulfonamide group present in valdecoxib were selective COX-1 inhibitors.

The diarylisoxazole molecular scaffold is found in several NSAIDs, especially those with high selectivity for COX-1. Here, we have determined the structural basis for COX-1 binding to two diarylisoxazoles: mofezolac, which is polar and ionizable, and 3-(5-chlorofuran-2-yl)-5-methyl-4-phenylisoxazole (P6) that has very low polarity. X-ray analysis of the crystal structures of COX-1 bound to mofezolac and 3-(5-chlorofuran-2-yl)-5-methyl-4-phenylisoxazole allowed the identification of specific binding determinants within the enzyme active site, relevant to generate structure/activity relationships for diarylisoxazole NSAIDs.

3-(5-Chlorofuran-2-yl)-5-methyl-4-phenylisoxazole (P6), a known selective cyclooxygenase-1 (COX-1) inhibitor, was used to design a new series of 3,4-diarylisoxazoles in order to improve its biochemical COX-1 selectivity and antiplatelet efficacy. Structure-activity relationships were studied using human whole blood assays for COX-1 and COX-2 inhibition in vitro, and results showed that the simultaneous presence of 5-methyl (or -CF3), 4-phenyl, and 5-chloro(-bromo or -methyl)furan-2-yl groups on the isoxazole core was essential for their selectivity toward COX-1. 3g, 3s, 3d were potent and selective COX-1 inhibitors that affected platelet aggregation in vitro through the inhibition of COX-1-dependent thromboxane (TX) A2. Moreover, we characterized their kinetics of COX-1 inhibition. 3g, 3s, and 3d were more potent inhibitors of platelet COX-1 and aggregation than P6 (named 6) for their tighter binding to the enzyme. The pharmacological results were supported by docking simulations. The oral administration of 3d to mice translated into preferential inhibition of platelet-derived TXA2 over protective vascular-derived prostacyclin (PGI2).