Logo of annrheumdAnnals of the Rheumatic DiseasesVisit this articleSubmit a manuscriptReceive email alertsContact usBMJ
Ann Rheum Dis. 2000 Nov; 59(11): 841–849.
PMCID: PMC1753034

Leflunomide: mode of action in the treatment of rheumatoid arthritis


Leflunomide is a selective inhibitor of de novo pyrimidine synthesis. In phase II and III clinical trials of active rheumatoid arthritis, leflunomide was shown to improve primary and secondary outcome measures with a satisfactory safety profile. The active metabolite of leflunomide, A77 1726, at low, therapeutically applicable doses, reversibly inhibits dihydroorotate dehydrogenase (DHODH), the rate limiting step in the de novo synthesis of pyrimidines. Unlike other cells, activated lymphocytes expand their pyrimidine pool by approximately eightfold during proliferation; purine pools are increased only twofold. To meet this demand, lymphocytes must use both salvage and de novo synthesis pathways. Thus the inhibition of DHODH by A77 1726 prevents lymphocytes from accumulating sufficient pyrimidines to support DNA synthesis. At higher doses, A77 1726 inhibits tyrosine kinases responsible for early T cell and B cell signalling in the G0/G1 phase of the cell cycle. Because the immunoregulatory effects of A77 1726 occur at doses that inhibit DHODH but not tyrosine kinases, the interruption of de novo pyrimidine synthesis may be the primary mode of action. Recent evidence suggests that the observed anti-inflammatory effects of A77 1726 may relate to its ability to suppress interleukin 1 and tumour necrosis factor α selectively over their inhibitors in T lymphocyte/monocyte contact activation. A77 1726 has also been shown to suppress the activation of nuclear factor κB, a potent mediator of inflammation when stimulated by inflammatory agents. Continuing research indicates that A77 1726 may downregulate the glycosylation of adhesion molecules, effectively reducing cell-cell contact activation during inflammation.

Full Text

The Full Text of this article is available as a PDF (175K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Breedveld FC. New insights in the pathogenesis of rheumatoid arthritis. J Rheumatol Suppl. 1998 Jul;53:3–7. [PubMed]
  • Arend WP, Dayer JM. Inhibition of the production and effects of interleukin-1 and tumor necrosis factor alpha in rheumatoid arthritis. Arthritis Rheum. 1995 Feb;38(2):151–160. [PubMed]
  • Brazelton TR, Morris RE. Molecular mechanisms of action of new xenobiotic immunosuppressive drugs: tacrolimus (FK506), sirolimus (rapamycin), mycophenolate mofetil and leflunomide. Curr Opin Immunol. 1996 Oct;8(5):710–720. [PubMed]
  • Silva HT, Jr, Morris RE. Leflunomide and malononitriloamides. Expert Opin Investig Drugs. 1997 Jan;6(1):51–64. [PubMed]
  • Alcón S, Pozo MJ, Salido GM, Pariente JA. Histaminergic modulation of hormonal control in the exocrine guinea-pig pancreas. Inflamm Res. 1995 May;44(5):207–211. [PubMed]
  • Cherwinski HM, Cohn RG, Cheung P, Webster DJ, Xu YZ, Caulfield JP, Young JM, Nakano G, Ransom JT. The immunosuppressant leflunomide inhibits lymphocyte proliferation by inhibiting pyrimidine biosynthesis. J Pharmacol Exp Ther. 1995 Nov;275(2):1043–1049. [PubMed]
  • Cherwinski HM, Byars N, Ballaron SJ, Nakano GM, Young JM, Ransom JT. Leflunomide interferes with pyrimidine nucleotide biosynthesis. Inflamm Res. 1995 Aug;44(8):317–322. [PubMed]
  • Cao WW, Kao PN, Chao AC, Gardner P, Ng J, Morris RE. Mechanism of the antiproliferative action of leflunomide. A77 1726, the active metabolite of leflunomide, does not block T-cell receptor-mediated signal transduction but its antiproliferative effects are antagonized by pyrimidine nucleosides. J Heart Lung Transplant. 1995 Nov-Dec;14(6 Pt 1):1016–1030. [PubMed]
  • Williamson RA, Yea CM, Robson PA, Curnock AP, Gadher S, Hambleton AB, Woodward K, Bruneau JM, Hambleton P, Moss D, et al. Dihydroorotate dehydrogenase is a high affinity binding protein for A77 1726 and mediator of a range of biological effects of the immunomodulatory compound. J Biol Chem. 1995 Sep 22;270(38):22467–22472. [PubMed]
  • Xu X, Williams JW, Gong H, Finnegan A, Chong AS. Two activities of the immunosuppressive metabolite of leflunomide, A77 1726. Inhibition of pyrimidine nucleotide synthesis and protein tyrosine phosphorylation. Biochem Pharmacol. 1996 Aug 23;52(4):527–534. [PubMed]
  • Chong AS, Rezai K, Gebel HM, Finnegan A, Foster P, Xu X, Williams JW. Effects of leflunomide and other immunosuppressive agents on T cell proliferation in vitro. Transplantation. 1996 Jan 15;61(1):140–145. [PubMed]
  • Siemasko KF, Chong AS, Williams JW, Bremer EG, Finnegan A. Regulation of B cell function by the immunosuppressive agent leflunomide. Transplantation. 1996 Feb 27;61(4):635–642. [PubMed]
  • Elder RT, Xu X, Williams JW, Gong H, Finnegan A, Chong AS. The immunosuppressive metabolite of leflunomide, A77 1726, affects murine T cells through two biochemical mechanisms. J Immunol. 1997 Jul 1;159(1):22–27. [PubMed]
  • Siemasko K, Chong AS, Jäck HM, Gong H, Williams JW, Finnegan A. Inhibition of JAK3 and STAT6 tyrosine phosphorylation by the immunosuppressive drug leflunomide leads to a block in IgG1 production. J Immunol. 1998 Feb 15;160(4):1581–1588. [PubMed]
  • Williamson RA, Yea CM, Robson PA, Curnock AP, Gadher S, Hambleton AB, Woodward K, Bruneau JM, Hambleton P, Spinella-Jaegle S, et al. Dihydroorotate dehydrogenase is a target for the biological effects of leflunomide. Transplant Proc. 1996 Dec;28(6):3088–3091. [PubMed]
  • Silva HT, Cao W, Shorthouse R, Morris RE. Mechanism of action of leflunomide: in vivo uridine administration reverses its inhibition of lymphocyte proliferation. Transplant Proc. 1996 Dec;28(6):3082–3084. [PubMed]
  • Kuo EA, Hambleton PT, Kay DP, Evans PL, Matharu SS, Little E, McDowall N, Jones CB, Hedgecock CJ, Yea CM, et al. Synthesis, structure-activity relationships, and pharmacokinetic properties of dihydroorotate dehydrogenase inhibitors: 2-cyano-3-cyclopropyl-3-hydroxy-N-[3'-methyl-4'-(trifluoromethyl)phenyl ] propenamide and related compounds. J Med Chem. 1996 Nov 8;39(23):4608–4621. [PubMed]
  • Mladenovic V, Domljan Z, Rozman B, Jajic I, Mihajlovic D, Dordevic J, Popovic M, Dimitrijevic M, Zivkovic M, Campion G, et al. Safety and effectiveness of leflunomide in the treatment of patients with active rheumatoid arthritis. Results of a randomized, placebo-controlled, phase II study. Arthritis Rheum. 1995 Nov;38(11):1595–1603. [PubMed]
  • Küchle CC, Thoenes GH, Langer KH, Schorlemmer HU, Bartlett RR, Schleyerbach R. Prevention of kidney and skin graft rejection in rats by leflunomide, a new immunomodulating agent. Transplant Proc. 1991 Feb;23(1 Pt 2):1083–1086. [PubMed]
  • Schorlemmer HU, Seiler FR, Bartlett RR. Prolongation of allogeneic transplanted skin grafts and induction of tolerance by leflunomide, a new immunosuppressive isoxazol derivative. Transplant Proc. 1993 Feb;25(1 Pt 1):763–767. [PubMed]
  • Williams JW, Xiao F, Foster PF, Chong A, Sharma S, Bartlett R, Sankary HN. Immunosuppressive effects of leflunomide in a cardiac allograft model. Transplant Proc. 1993 Feb;25(1 Pt 1):745–746. [PubMed]
  • Popovic S, Bartlett RR. Disease modifying activity of HWA 486 on the development of SLE in MRL/1-mice. Agents Actions. 1986 Dec;19(5-6):313–314. [PubMed]
  • Vidic-Dankovic B, Kosec D, Damjanovic M, Apostolski S, Isakovic K, Bartlett RR. Leflunomide prevents the development of experimentally induced myasthenia gravis. Int J Immunopharmacol. 1995 Apr;17(4):273–281. [PubMed]
  • Bartlett RR, Anagnostopulos H, Zielinski T, Mattar T, Schleyerbach R. Effects of leflunomide on immune responses and models of inflammation. Springer Semin Immunopathol. 1993;14(4):381–394. [PubMed]
  • Bartlett RR, Schleyerbach R. Immunopharmacological profile of a novel isoxazol derivative, HWA 486, with potential antirheumatic activity--I. Disease modifying action on adjuvant arthritis of the rat. Int J Immunopharmacol. 1985;7(1):7–18. [PubMed]
  • Pasternak RD, Wadopian NS, Wright RN, Siminoff P, Gylys JA, Buyniski JP. Disease modifying activity of HWA 486 in rat adjuvant-induced arthritis. Agents Actions. 1987 Aug;21(3-4):241–243. [PubMed]
  • Hambleton P, McMahon S. Drug actions on delayed-type hypersensitivity in rats with developing and established adjuvant arthritis. Agents Actions. 1990 Mar;29(3-4):328–332. [PubMed]
  • Bartlett RR. Immunopharmacological profile of HWA 486, a novel isoxazol derivative--II. In vivo immunomodulating effects differ from those of cyclophosphamide, prednisolone, or cyclosporin A. Int J Immunopharmacol. 1986;8(2):199–204. [PubMed]
  • Chong AS, Finnegan A, Jiang X, Gebel H, Sankary HN, Foster P, Williams JW. Leflunomide, a novel immunosuppressive agent. The mechanism of inhibition of T cell proliferation. Transplantation. 1993 Jun;55(6):1361–1366. [PubMed]
  • Xu X, Williams JW, Bremer EG, Finnegan A, Chong AS. Inhibition of protein tyrosine phosphorylation in T cells by a novel immunosuppressive agent, leflunomide. J Biol Chem. 1995 May 26;270(21):12398–12403. [PubMed]
  • Cherwinski HM, McCarley D, Schatzman R, Devens B, Ransom JT. The immunosuppressant leflunomide inhibits lymphocyte progression through cell cycle by a novel mechanism. J Pharmacol Exp Ther. 1995 Jan;272(1):460–468. [PubMed]
  • Morris RE, Huang X, Cao W, Zheng B, Shorthouse RA. Leflunomide (HWA 486) and its analog suppress T- and B-cell proliferation in vitro, acute rejection, ongoing rejection, and antidonor antibody synthesis in mouse, rat, and cynomolgus monkey transplant recipients as well as arterial intimal thickening after balloon catheter injury. Transplant Proc. 1995 Feb;27(1):445–447. [PubMed]
  • Xu X, Blinder L, Shen J, Gong H, Finnegan A, Williams JW, Chong AS. In vivo mechanism by which leflunomide controls lymphoproliferative and autoimmune disease in MRL/MpJ-lpr/lpr mice. J Immunol. 1997 Jul 1;159(1):167–174. [PubMed]
  • Lang R, Wagner H, Heeg K. Differential effects of the immunosuppressive agents cyclosporine and leflunomide in vivo. Leflunomide blocks clonal T cell expansion yet allows production of lymphokines and manifestation of T cell-mediated shock. Transplantation. 1995 Feb 15;59(3):382–389. [PubMed]
  • Cao WW, Kao PN, Aoki Y, Xu JC, Shorthouse RA, Morris RE. A novel mechanism of action of the immunomodulatory drug, leflunomide: augmentation of the immunosuppressive cytokine, TGF-beta 1, and suppression of the immunostimulatory cytokine, IL-2. Transplant Proc. 1996 Dec;28(6):3079–3080. [PubMed]
  • Manna SK, Aggarwal BB. Immunosuppressive leflunomide metabolite (A77 1726) blocks TNF-dependent nuclear factor-kappa B activation and gene expression. J Immunol. 1999 Feb 15;162(4):2095–2102. [PubMed]
  • Fairbanks LD, Bofill M, Ruckemann K, Simmonds HA. Importance of ribonucleotide availability to proliferating T-lymphocytes from healthy humans. Disproportionate expansion of pyrimidine pools and contrasting effects of de novo synthesis inhibitors. J Biol Chem. 1995 Dec 15;270(50):29682–29689. [PubMed]
  • Jones ME. Pyrimidine nucleotide biosynthesis in animals: genes, enzymes, and regulation of UMP biosynthesis. Annu Rev Biochem. 1980;49:253–279. [PubMed]
  • Silva HT, Jr, Cao W, Shorthouse RA, Löffler M, Morris RE. In vitro and in vivo effects of leflunomide, brequinar, and cyclosporine on pyrimidine biosynthesis. Transplant Proc. 1997 Feb-Mar;29(1-2):1292–1293. [PubMed]
  • Peters GJ, Veerkamp JH. Purine and pyrimidine metabolism in peripheral blood lymphocytes. Int J Biochem. 1983;15(2):115–123. [PubMed]
  • Greene S, Watanabe K, Braatz-Trulson J, Lou L. Inhibition of dihydroorotate dehydrogenase by the immunosuppressive agent leflunomide. Biochem Pharmacol. 1995 Sep 7;50(6):861–867. [PubMed]
  • Davis JP, Cain GA, Pitts WJ, Magolda RL, Copeland RA. The immunosuppressive metabolite of leflunomide is a potent inhibitor of human dihydroorotate dehydrogenase. Biochemistry. 1996 Jan 30;35(4):1270–1273. [PubMed]
  • Chen SF, Perrella FW, Behrens DL, Papp LM. Inhibition of dihydroorotate dehydrogenase activity by brequinar sodium. Cancer Res. 1992 Jul 1;52(13):3521–3527. [PubMed]
  • Herrmann ML, Schleyerbach R, Kirschbaum BJ. Leflunomide: an immunomodulatory drug for the treatment of rheumatoid arthritis and other autoimmune diseases. Immunopharmacology. 2000 May;47(2-3):273–289. [PubMed]
  • Wahl GM, Linke SP, Paulson TG, Huang LC. Maintaining genetic stability through TP53 mediated checkpoint control. Cancer Surv. 1997;29:183–219. [PubMed]
  • Linke SP, Clarkin KC, Di Leonardo A, Tsou A, Wahl GM. A reversible, p53-dependent G0/G1 cell cycle arrest induced by ribonucleotide depletion in the absence of detectable DNA damage. Genes Dev. 1996 Apr 15;10(8):934–947. [PubMed]
  • Linke SP, Clarkin KC, Wahl GM. p53 mediates permanent arrest over multiple cell cycles in response to gamma-irradiation. Cancer Res. 1997 Mar 15;57(6):1171–1179. [PubMed]
  • Vey E, Zhang JH, Dayer JM. IFN-gamma and 1,25(OH)2D3 induce on THP-1 cells distinct patterns of cell surface antigen expression, cytokine production, and responsiveness to contact with activated T cells. J Immunol. 1992 Sep 15;149(6):2040–2046. [PubMed]
  • Isler P, Vey E, Zhang JH, Dayer JM. Cell surface glycoproteins expressed on activated human T cells induce production of interleukin-1 beta by monocytic cells: a possible role of CD69. Eur Cytokine Netw. 1993 Jan-Feb;4(1):15–23. [PubMed]
  • Lacraz S, Isler P, Vey E, Welgus HG, Dayer JM. Direct contact between T lymphocytes and monocytes is a major pathway for induction of metalloproteinase expression. J Biol Chem. 1994 Sep 2;269(35):22027–22033. [PubMed]
  • Li JM, Isler P, Dayer JM, Burger D. Contact-dependent stimulation of monocytic cells and neutrophils by stimulated human T-cell clones. Immunology. 1995 Apr;84(4):571–576. [PMC free article] [PubMed]
  • Vey E, Burger D, Dayer JM. Expression and cleavage of tumor necrosis factor-alpha and tumor necrosis factor receptors by human monocytic cell lines upon direct contact with stimulated T cells. Eur J Immunol. 1996 Oct;26(10):2404–2409. [PubMed]
  • Chizzolini C, Chicheportiche R, Burger D, Dayer JM. Human Th1 cells preferentially induce interleukin (IL)-1beta while Th2 cells induce IL-1 receptor antagonist production upon cell/cell contact with monocytes. Eur J Immunol. 1997 Jan;27(1):171–177. [PubMed]
  • Déage V, Burger D, Dayer JM. Exposure of T lymphocytes to leflunomide but not to dexamethasone favors the production by monocytic cells of interleukin-1 receptor antagonist and the tissue-inhibitor of metalloproteinases-1 over that of interleukin-1beta and metalloproteinases. Eur Cytokine Netw. 1998 Dec;9(4):663–668. [PubMed]
  • Rückemann K, Fairbanks LD, Carrey EA, Hawrylowicz CM, Richards DF, Kirschbaum B, Simmonds HA. Leflunomide inhibits pyrimidine de novo synthesis in mitogen-stimulated T-lymphocytes from healthy humans. J Biol Chem. 1998 Aug 21;273(34):21682–21691. [PubMed]
  • Strand V, Cohen S, Schiff M, Weaver A, Fleischmann R, Cannon G, Fox R, Moreland L, Olsen N, Furst D, et al. Treatment of active rheumatoid arthritis with leflunomide compared with placebo and methotrexate. Leflunomide Rheumatoid Arthritis Investigators Group. Arch Intern Med. 1999 Nov 22;159(21):2542–2550. [PubMed]
  • Smolen JS, Kalden JR, Scott DL, Rozman B, Kvien TK, Larsen A, Loew-Friedrich I, Oed C, Rosenburg R. Efficacy and safety of leflunomide compared with placebo and sulphasalazine in active rheumatoid arthritis: a double-blind, randomised, multicentre trial. European Leflunomide Study Group. Lancet. 1999 Jan 23;353(9149):259–266. [PubMed]
  • Emery P, Breedveld FC, Lemmel EM, Kaltwasser JP, Dawes PT, Gömör B, Van Den Bosch F, Nordström D, Bjorneboe O, Dahl R, et al. A comparison of the efficacy and safety of leflunomide and methotrexate for the treatment of rheumatoid arthritis. Rheumatology (Oxford) 2000 Jun;39(6):655–665. [PubMed]
  • Fox RI, Herrmann ML, Frangou CG, Wahl GM, Morris RE, Kirschbaum BJ. How does leflunomide modulate the immune response in rheumatoid arthritis? BioDrugs. 1999 Oct;12(4):301–315. [PubMed]
  • Chong AS, Huang W, Liu W, Luo J, Shen J, Xu W, Ma L, Blinder L, Xiao F, Xu X, et al. In vivo activity of leflunomide: pharmacokinetic analyses and mechanism of immunosuppression. Transplantation. 1999 Jul 15;68(1):100–109. [PubMed]
  • Paulus HE. The use of combinations of disease-modifying antirheumatic agents in rheumatoid arthritis. Arthritis Rheum. 1990 Jan;33(1):113–120. [PubMed]
  • Wilke WS, Clough JD. Therapy for rheumatoid arthritis: combinations of disease-modifying drugs and new paradigms of treatment. Semin Arthritis Rheum. 1991 Oct;21(2 Suppl 1):21–34. [PubMed]
  • Wilske KR. Approaches to the management of rheumatoid arthritis: rationale for early combination therapy. Br J Rheumatol. 1993 Mar;32 (Suppl 1):24–27. [PubMed]
  • Furst DE. Clinical pharmacology of combination DMARD therapy in rheumatoid arthritis. J Rheumatol Suppl. 1996 Mar;44:86–90. [PubMed]
  • Kremer JM. Methotrexate and leflunomide: biochemical basis for combination therapy in the treatment of rheumatoid arthritis. Semin Arthritis Rheum. 1999 Aug;29(1):14–26. [PubMed]
  • McChesney LP, Xiao F, Sankary HN, Foster PF, Sharma S, Haklin M, Williams JW. An evaluation of leflunomide in the canine renal transplantation model. Transplantation. 1994 Jun 27;57(12):1717–1722. [PubMed]
  • Thoss K, Henzgen S, Petrow PK, Katenkamp D, Brauer R. Immunomodulation of rat antigen-induced arthritis by leflunomide alone and in combination with cyclosporin A. Inflamm Res. 1996 Feb;45(2):103–107. [PubMed]

Figures and Tables

Figure 1
Chemical structure of leflunomide and its active metabolite A77 1726.
Figure 2
Cell cycle modulation. Some agents block signal transduction events in the resting G0 phase. Other agents interfere with ribonucleotide biosynthesis in the G1 phase. In either case, transition into the DNA replication phase, or S phase, of the cell cycle ...
Figure 3
Effect of inhibition of de novo pyrimidine synthesis on various mechanisms of activated lymphocytes. (Adapted from Herrmann et al.49a)
Figure 4
(A) Leflunomide (LEF) differentially inhibits the ability of stimulated T lymphocytes to activate THP-1 cells by direct cellular contact, favouring interleukin 1 receptor antagonist (IL1Ra) production, compared with dexamethasone (DEX). ...
Figure 5
Comparison of the effect of leflunomide with that of methotrexate on nucleotide synthesis. MTX = methotrexate, dUMP = deoxyuridine monophosphate.

Articles from Annals of the Rheumatic Diseases are provided here courtesy of BMJ Group


Save items

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


  • Compound
    PubChem chemical compound records that cite the current articles. These references are taken from those provided on submitted PubChem chemical substance records. Multiple substance records may contribute to the PubChem compound record.
  • MedGen
    Related information in MedGen
  • PubMed
    PubMed citations for these articles
  • Substance
    PubChem chemical substance records that cite the current articles. These references are taken from those provided on submitted PubChem chemical substance records.

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...