The Immunosuppressive Metabolite of Leflunomide Is a Potent Inhibitor of Human Dihydroorotate Dehydrogenase
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- 作者：June P. Davis ; Gary A. Cain ; William J. Pitts ; Ronald L. Magolda ; and Robert A. Copeland
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：January 30, 1996
- 年：1996
- 卷：35
- 期：4
- 页码：1270 - 1273
- 全文大小：330K
- 年卷期：v.35,no.4(January 30, 1996)
- ISSN：1520-4995
文摘
The active metabolite of leflunomide, A771726, is a novelimmunosuppressive compoundthat has been shown to be a powerful antiproliferative agent formononuclear and T-cells. The molecularmechanism of action for this compound has not been clearly established.In vitro cellular and enzymaticassays, however, demonstrate that leflunomide is an inhibitor ofseveral protein tyrosine kinases, withIC50 values between 30 and 100 
M. The invivo properties of A771726 are reminiscent of anotherimmunosuppressive agent, brequinar sodium, which has been shown to be ananomolar inhibitor (Ki =10-30 nM) of the enzyme dihydroorotate dehydrogenase (DHODase).On this basis, we have investigatedthe effects of leflunomide and A771726 on the activity of purifiedrecombinant human DHODase. Wefind that A771726 is a potent inhibitor of DHODase(Ki = 179 ± 19 nM), while the parentcompound,leflunomide, had no inhibitory effect at concentrations as high as 1M. Studies of the dependence ofinhibition on the concentrations of the substrates ubiquinone anddihydroorotate demonstrate that A771726is a competitive inhibitor of the ubiquinone binding site and isnoncompetitive with respect todihydroorotate. The potency of A771726 as a DHODase inhibitor isthus 100-1000-fold greater thanthat reported for its inhibition of protein tyrosine kinases.These data suggest that an alternative explanationfor the immunosuppressive efficacy of A771726 may be the potentinhibition of DHODase by thiscompound.
M. The invivo properties of A771726 are reminiscent of anotherimmunosuppressive agent, brequinar sodium, which has been shown to be ananomolar inhibitor (Ki =10-30 nM) of the enzyme dihydroorotate dehydrogenase (DHODase).On this basis, we have investigatedthe effects of leflunomide and A771726 on the activity of purifiedrecombinant human DHODase. Wefind that A771726 is a potent inhibitor of DHODase(Ki = 179 ± 19 nM), while the parentcompound,leflunomide, had no inhibitory effect at concentrations as high as 1M. Studies of the dependence ofinhibition on the concentrations of the substrates ubiquinone anddihydroorotate demonstrate that A771726is a competitive inhibitor of the ubiquinone binding site and isnoncompetitive with respect todihydroorotate. The potency of A771726 as a DHODase inhibitor isthus 100-1000-fold greater thanthat reported for its inhibition of protein tyrosine kinases.These data suggest that an alternative explanationfor the immunosuppressive efficacy of A771726 may be the potentinhibition of DHODase by thiscompound.