Noncompetitive and irreversible inhibition of xanthine oxidase by benzimidazole analogs acting at the functional flavin adenine dinucleotide cofactor

Abstract

Benzimidazole derivatives possessing a leaving group in the 2 alpha-position and either 4,7-dione, 4,7-diol, or 4,7-dimethoxy substituents were examined as inhibitors of buttermilk xanthine oxidase. The quinone and hydroquinone derivatives are not inhibitors of xanthine-oxygen reductase activity, even though the latter is a powerful alkylating agent. The methoxylated hydroquinones are linear noncompetitive inhibitors, the best of which is the 2 alpha-bromo analogue (Ki = 46 microM). During xanthine-oxygen reductase activity, the 2 alpha-bromo analogue irreversibly traps the reduced enzyme. Formation of a C(4a) adduct of the reduced functional FAD cofactor is postulated on the basis of UV-visible spectral evidence and reconstitution of the enzyme after removal of the altered FAD. A probable sequence of events is reversible binding at or near the reduced cofactor followed by adduct formation. It is concluded that potent tight binding inhibitors could be designed that act at the FAD cofactor rather than the purine active site.

Xanthine Oxidase: Isolation, Assays of Activity, and Inhibition

“…Among the many known XO inhibitors, allopurinol, oxypurinol, and febuxostat have been used widely for the treatment of hyperuricemia and gout [43]. XO inhibitors can act either at the purine binding site such as allopurinol [44,45] or at the FAD cofactor site such as benzimidazole [46]. XO inhibitors act by blocking the biosynthesis of uric acid from purine in the body [47] and it is believed that either increasing the excretion of uric acid or reducing the uric acid production helps to reduce the risk of gout [48].…”

Tautomerism of xanthine and alloxanthine: A model for substrate recognition by xanthine oxidase

“…Knowledge of the molecular determinants that modulate substrate recognition is valuable in the design of inhibitors of xanthine oxidase [3,7]. For instance, purine-like inhibitors can interfere in other routes of purine metabolism [8], and information about the recognition pattern would be useful for designing specific inhibitors lacking undesirable side effects.…”

Inhibition of xanthine oxidase by Caulerpenyne from Caulerpa prolifera

“…The inhibitors of XOD function in two different mechanisms as this enzyme contains two different binding sites for substrate binding. Therefore, the inhibition of XOD occurs either with interaction of purine binding sites, like allopurinol [32], or interaction of FAD cofactor binding sites, like benzimidazole [33]. Several side effects of commercially used drugs for the treatment of hyperuricemia and gout have been reported in the literature so far [7][8][9].…”