Description
Leflunomide is an orally-available disease-modifying antirheumatic drug
and was launched as Arava in the US for the treatment of rheumatoid arthritis
(RA) ; it is the first and only drug to be indicated to slow down structural joint
damage of RA, so addressing an unmet medical need.
Leflunomide is prepared in 3 steps from the appropriate acetoacetic anilide
using a nitrile oxide- enamine cycloaddition reaction to assemble the isoxazole
ring. Leflunomide is a prodrug, being extensively metabolized in vivo into the
corresponding 2-cyano-3-hydroxy-2-butenamide resulting from fragmentation of
the isoxazole ring. This cyanoenol is actually the active metabolite and several
experiments in animals have demonstrated that after oral administration,
substantial and sustained levels of this metabolite were delivered to the
systemic circulation.
In vitro, Leflunomide’s active metabolite inhibits dihydroorotate dehydrogenase,
an enzyme involved in the biosynthesis of pyrimidine nucleotides, probably
accounting for its immunosuppressive effect in vivo. Other mechanisms of action
such as inhibition of tyrosine kinase and inhibition of responsiveness to
interleukin-2 have been proposed. In diverse models of autoimmune or allergic
diseases, Leflunornide showed efficacy both prophylactically and therapeutically.
Originator
Hoechst
MarionRoussel (Germany)
Definition
ChEBI: A monocarboxylic acid amide obtained by formal condensation of the carboxy group of 5-methyl-1,2-oxazole-4-carboxylic acid with the anilino group of 4-(trifluoromethyl)aniline. The prodrug of teriflunomide.
Indications
Leflunomide (Arava) is an isoxazole derivative approved
for the treatment of rheumatoid arthritis in
1998. Limited data suggest that it is comparable in efficacy
to sulfasalazine and produces fewer adverse effects.
It has a faster onset of action (4 weeks) than other
DMARDs.
Manufacturing Process
In US Patent No. 4,284,786 is described two methods of preparation of 5-
methylisoxazole-4-carboxylic-(4-trifluoromethyl)-anilide.
The method 1
A mixture of 0.55 mole of diketene (46.3 g) and 30 ml of acetonitrile is added
dropwise, at 75°C, to a solution of 0.5 mole of 4-trifluoromethylaniline (30.6
g) in 150 ml of acetonitrile. The mixture is heated to boiling under reflux for
2.5 hours. When it has cooled to room temperature, the crystals which are
precipitated are filtered off, washed with cold ethanol and dried. This gives
79.1 g (64.5% of theory) of crystalline acetoacetic acid-4-
trifluoromethylanilide, melting point (after recrystallization from ethanol)
155°C.
The acetonitrile phase is evaporated to dryness under reduced pressure. The
crystalline residue (42.1 g) is recrystallized from 80 ml of ethanol. This gives
a further 24.1 g (19.7% of theory) of crystals. Melting point (after
recrystallization from ethanol) 155°C. Total yield: 84.2% of theory.
0.75 mole of acetoacetic acid 4-trifluoromethylanilide (183.9 g) is boiled
under reflux for 1.5 hours with 0.83 mole of orthoformic acid triethyl ester
(123 g) and 2.25 mole of acetic anhydride (229.7 g). After the mixture has
cooled to room temperature, the crystals which have precipitated are filtered
off and washed first with a small amount of acetic anhydride and then with
petroleum ether. This gives 116.1 g (51.4% of theory) of crystalline 2-
ethoxymethyleneacetoacetic acid 4-trifluoromethylanilide, melting point (after
recrystallization from toluene) 124-125°C.
The combined filtrates are concentrated under reduced pressure. The crystals
of the crystal paste which thereupon remains are filtered off, washed first with
a small amount of acetic anhydride and then with petroleum ether and dried.
A further 56.1 g (24.8% of theory) of crystals are thus obtained. Melting point
(after recrystallization from toluene) 124-125°C. Total yield: 76.2% of theory.
A solution 0.1 mole of 2-ethoxymethyleneacetoacetic acid 4-
trifluoromethylanilide (30.1 g) in 60 ml of ethanol is added dropwise at 5-
10°C to the mixture of 0.11 mole of hydroxylamine hydrochloride (7.65 g) in
50 ml of water and 0.11 mole of sodium hydroxide (4.4 g) in 10 ml of water.
The mixture is heated under reflux for 15 min. The crystals which are
precipitated after cooling are filtered off, washed with water and dried. 19.6 g
(72.6% of theory) of crystalline 5-methylisoxazole-4-carboxylic acid 4-
trifluoromethyl-anilide are thus obtained, melting point (after recrystallization
from toluene) 166.5°C.A solution 0.1 mole of 2-ethoxymethyleneacetoacetic acid 4-
trifluoromethylanilide (30.1 g) in 60 ml of ethanol is added dropwise at 5-
10°C to the mixture of 0.11 mole of hydroxylamine hydrochloride (7.65 g) in
50 ml of water and 0.11 mole of sodium hydroxide (4.4 g) in 10 ml of water.
The mixture is heated under reflux for 15 min. The crystals which are
precipitated after cooling are filtered off, washed with water and dried. 19.6 g
(72.6% of theory) of crystalline 5-methylisoxazole-4-carboxylic acid 4-
trifluoromethyl-anilide are thus obtained, melting point (after recrystallization
from toluene) 166.5°C.
The method 2
0.1 mole of 5-methylisoxazole-4-carboxylic acid chloride (14.6 g) and 20 ml of
a 5 N potassium hydroxide solution are added dropwise to 0.1 mole of
trifluoromethylaniline (16.1 g), suspended in 150 ml of water, in such a way
that the pH of the reaction mixture does not rise above 5. The mixture is
subsequently shaken with 150 ml of methylene chloride. The methylene
chloride phase is washed with water and, after drying with sodium sulfate is,
evaporated to dryness under reduced pressure. This gives 24.4 g (90.2% of
theory) of a crystalline 5-methylisoxazole-4-carboxylic acid 4-trifluoromethylanilide, melting point (after recrystallization from toluene) 166.5°C.
Brand name
Arava
(Sanofi Aventis).
Therapeutic Function
Immunosuppressive, Antiarthritic
Biological Functions
Leflunomide is inactive, but teriflunomide inhibits pyrimidine de novo synthesis at low therapeutic doses by inhibiting
dihydroorotate dehydrogenase (the rate-determining enzyme for the synthesis of UMP), decreasing DNA and RNA
synthesis, and arresting the cell proliferation cycle and production of antibodies. The reduction of dihydroorotate to
orotate occurs concurrently with the reduction of its cofactor, ubiquinone (coenzyme Q). The inhibition of
dihydroorotate dehydrogenase by teriflunomide demonstrates noncompetitive and uncompetitive kinetics.
Administration of leflunomide in patients with rheumatoid arthritis results in progressive removal of B cells and
down-regulation of the immune process. Teriflunomide not only inhibits B-cell proliferation but also T-cell
proliferation, blocking the synthesis of immunosuppressive cytokines. At high therapeutic doses, leflunomide inhibits
protein tyrosine kinases.
General Description
Leflunomide (Arava), an isoxazole prodrug, is an orally activeDMARD marketed in 1998 for the treatment of RA. Itis well absorbed and extensively metabolized in vivo to itsactive metabolite, 2-cyano-3-hydroxy-2-buteneamide (teriflunomide),resulting from a reductive ring opening of theisoxazole ring. Unlike MTX, teriflunomideblocks T-cell proliferation by inhibiting dihydroorotate dehydrogenase,the rate-limiting enzyme in the de novobiosynthesis of pyrimidine that is believed to be responsiblefor the immunosuppressive properties of leflunomide.For this reason, it is not surprising that leflunomide has avery comparable therapeutic efficacy to the first-lineDMARD, MTX as shown in several extended open clinicaltrials. However, even though leflunomide is well toleratedlike MTX, several cases of toxic neuropathy have beenobserved during its use, thus careful monitoring of the patient’sneurological status during treatment is mandatory.Like MTX, leflunomide is contraindicated in pregnancy orin women considering pregnancy.
Biological Activity
Immunosuppressant agent. In vitro the active metabolite A77 1726 (RS-61980) inhibits dihydroorotate dehydrogenase (K i = 2.7 μ M) and de novo pyrimidine synthesis in T-cells; blocks lymphocyte cell cycle progression and proliferation. A77 1726 also inhibits anti-CD3/CD28-induced cytokine production in PBMC cells (IC 50 = 21-27 μ g/ml). In vivo reduces inflammation in several animal models of autoimmune disease, arthritis, asthma and graft rejection.
Biochem/physiol Actions
Immunosuppressive; inhibits T and B cell proliferation. Activity is attributed mainly to its metabolite, a malononitrile derivative, which is believed to inhibit dihydroorotate dehydrogenase (in the de novo pyrimidine synthesis pathway) as well as several protein tyrosine kinases.
Pharmacokinetics
Leflunomide is a pro-drug that is rapidly and almost completely metabolized (half-life, <60 minutes) following oral
administration to teriflunomide, the pharmacologically active α-cyanoenol metabolite. The C3-H of the
isoxazole ring is essential for the ring opening to its active metabolite. The reaction is similar to CYP1A2-catalyzed
dehydration of aldoximes. The exact mechanism of action of leflunomide in the management of rheumatoid arthritis
has not been fully elucidated but appears to principally involve inhibition of B-lymphocyte (B-cell) proliferation,
reducing antibody formation. Activated lymphocytes must proliferate and synthesize large quantities of cytokines,
requiring increased de novo synthesis of uridine monophosphate (UMP) and other pyrimidine nucleotides for its cell
life cycle. Therefore, any substance that reduces the intracellular concentration of pyrimidine nucleotides will affect
the growth of these activated cells.
Pharmacology
Leflunomide is a prodrug that is converted to an active
malonitrilamide metabolite, A77 1726 (M1). M1 inhibits
T-cell proliferation by blocking de novo pyrimidine synthesis
and inhibiting the tyrosine kinases that are associated
with certain cytokine and growth factor receptors.
Clinical Use
Leflunomide is a DMARD with anti-inflammatory and immunosuppressive activity used for the management of
rheumatoid arthritis. It retards structural damage associated with arthritis in adults who have moderate to severe
active rheumatoid arthritis. Leflunomide also is being investigated for use in patients with solid tumors and organ
transplant recipients.
Side effects
Diarrhea occurs in approximately one-third of patients
taking this drug; indigestion, nausea, and vomiting occur
in about 10%. Other common adverse effects include
weight changes, headache, skin rashes, pruritus, and reversible
alopecia and hepatic enzyme elevation.Although
leflunomide acts as an immunosuppressive, it does not appear
to cause significant bone marrow depression.
Veterinary Drugs and Treatments
Leflunomide is an immunomodulating drug that may be useful in
dogs for treating a variety of immune-related conditions such as
IMHA, systemic and cutaneous reactive histiocytosis, granulomatous
meningoencephalitis, etc; it can be used as part of transplant
rejection protocols in dogs.
Leflunomide has been used with methotrexate to treat rheumatoid
arthritis in cats.
Drug interactions
Potentially hazardous interactions with other drugs
Hepatotoxic or haemotoxic drugs: increased risk of
toxicity.
Cytotoxics: risk of toxicity with methotrexate.
Lipid-lowering agents: effect significantly reduced by
colestyramine - avoid.
Live vaccines: avoid concomitant use.
Metabolism
After oral doses leflunomide undergoes rapid first-pass
metabolism in the liver and gut wall to teriflunomide
(A-771726), which is responsible for the majority of the
in vivo activity.
Teriflunomide is mostly eliminated as unchanged drug in
the bile and as metabolites in the urine. It is thought to
undergo enterohepatic recycling and has an elimination
half-life of about 18-19 days after repeated oral doses.
References
1) Teschner et al. (2010), Leflunomide: a drug with a potential beyond rheumatology; Immunotherapy, 2 637
2) Davis et al. (1996), The immunosuppressive metabolite of leflunomide is a potent inhibitor of human dihydroorotate dehydrogenase; Biochemistry, 35 1270
3) Latchoumycandane et al. (2007), Mitochondrial protection by the JNK inhibitor leflunomide rescues mice from acetaminophen-induced liver injury; Hepatology, 45 412
