A771726, the active metabolite of leflunomide, directly inhibits the activity of cyclo‐oxygenase‐2 in vitro and in vivo in a substrate‐sensitive manner

Abstract

1 The immunosuppressive and anti-in¯ammatory drug le¯unomide has several sites of action, although its precise mode of action is unknown. 2 Here we show in vitro and in vivo that le¯unomide and/or its active metabolite A771726, inhibit the activity of cyclo-oxygenase (COX) at doses below those that a ect protein expression. 3 In J774.2 macrophages treated with endotoxin for 24 h to induce COX-2 and iNOS, le¯unomide and A771726 inhibited more potently the accumulation of PGE 2 (A771726, IC 50 3.5 mg ml 71 ) than of NO 2 (A771726, IC 50 380 mg ml 71 ). At high concentrations (4300 mg ml 71 ) A771726 also exhibited the expression of COX-2 and iNOS proteins. 4 In A549 cells treated for 24 h with interleukin-1b, to induce COX-2, A771726 potently inhibited PGE 2 synthesis (IC 50 0.13 mg ml 71 ). In the same cells, A771726 was notably less active (IC 50 , 52 mg ml 71 ) at inhibiting the formation of PGE 2 stimulated by exposure to 30 mM arachidonic acid. 5 In a human whole blood assay, measuring the accumulation of TxB 2 in response to calcium ionophore as a measure of COX-1 activity and in response to incubation with bacterial endotoxin as a measure of COX-2 activity, le¯unomide inhibited COX-1 and COX-2 with IC 50 values of 31 and 185 mg ml 71 ; for A771726 the corresponding values were 40 and 69 mg ml 71 . 6 Pre-treatment of rats with le¯unomide or A771726 (10 mg kg 71 , i.p.) inhibited the plasma accumulation of 6-keto-PGF 1a but not NO 2 /NO 3 following infusion of endotoxin. Injection of a bolus of arachidonic acid following 6 h infusion of endotoxin caused a marked acute rise in plasma 6-keto-PGF 1a which was inhibited only by higher doses of A771726 (50 mg kg 71 , i.p.). 7 In conclusion, le¯unomide via A771726 can directly inhibit the activity of COX, an e ect that appears blunted both by increases in substrate supply and possibly by plasma binding. Only at much higher drug levels does le¯unomide and/or A771726 inhibit the induction of COX-2 or iNOS proteins.

Protective role of c-Jun N-terminal kinase 2 in acetaminophen-induced liver injury

“…It was proposed that JNK had a pathological role in AILI in part by contributing to mitochondrial injury [14,21,35]. Potential limitations of these studies, as acknowledged by the investigators [21,22] is that JNK inhibitors may not be specific and as reported can affect other signaling events that could lead to the misinterpretation of results [36][37][38][39]. Further, some of the JNK inhibitors were dissolved in vehicles containing DMSO [14,21] and polyethylene glycol [22,35], which may affect various parameters at the cellular and molecular level [34,[40][41][42][43].…”

Receptor Tyrosine Kinases as Target for Anti-Cancer Therapy

“…It was demonstrated as an effective inhibitor of PDGF-mediated signal transduction and tumor growth [56] and as an EGF receptor inhibitor [57]. Leflunomide/SU101 yields an active metabolite (SU0020 or A771726), that inhibits COX-2 activity in vitro [58]. SU101 was well tolerated in a Phase I study in cancer patients, when administered as a 24-hour continuous i.v.…”

Emerging oral immunomodulating agents – focus on teriflunomide for the treatment of multiple sclerosis

“…In addition, the COX-2 inhibition was reversed by high levels of arachidonic acid. 46 These two aspects suggest that any meaningful clinical effects of COX-2 inhibition by teriflunomide are limited.…”