Pharmacogenetic Approaches to Rheumatoid Arthritis a Taniguchi and N Kamatani 351

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MTX was suggested to exert its efficacy Pharmacogenetic approaches to and at least part of its toxicity through the inhibition of folate metabolism, it rheumatoid arthritis is possible that genetic polymorphisms in enzymes involved in folate metabo- A Taniguchi1 and N Kamatani1,2 lism may be related to these differen- tial effects. The enzyme 5,10-

1 2 methylenetetrahydrofolate reductase Institute of Rheumatology, Tokyo Women’s Medical University, Tokyo, Japan; Division (MTHFR) is central to folate metabo- of Statistical Genetics, Institute of Rheumatology, Tokyo Women’s Medical University, lism. Among more than 10 poly- Shinjuku-ku, Tokyo, Japan morphisms of MTHFR gene, C677T and A1298C are important because these polymorphisms are associated The Pharmacogenomics Journal (2004) 4, sponse has been reported in biologic with reduced enzyme activities.14,15 350–353. doi:10.1038/sj.tpj.6500263 response modifiers.5,6 Moreover, the The reduction in the activities of this Published online 13 July 2004 use of these agents is limited by the enzyme is likely to influence the development of unpredictable toxici- development of efficacy or toxicity of Rheumatoid arthritis (RA) is a chronic, ties that are sometimes severe. Pre- MTX. systemic inflammatory disease that viously, it was described that the A prospective study involving 236 affects 0.5–1.0% of the general popula- activities of some drug-metabolizing patients with RA in whom MTX was tion.1 As the disease progresses, the enzymes for DMARDs, such as N- administered showed the association inflammatory process of the synovium acetyltransferase 2 (NAT2) for SSZ7 between the presence of T allele in the of the joints destroys articular archi- and thiopurine methyltransferase genotype at C677T polymorphism and tecture irreversibly. In the late stage, (TPMT) for azathioprine (AZA),8 are the increased rate of the discontinua- the disease causes a significant disabil- different among individuals. Recent tion of MTX treatment because of ity and high medical costs. About half advances in genetics have clarified toxicities (relative risk (RR): 2.01; 95% of RA patients are unable to work at that these individual differences are confidence interval (CI): 1.09–3.70), some time in the disease. Lifetime based on genetic polymorphisms, and mainly due to an increased risk of costs for RA were reported to be this knowledge has encouraged the elevated liver enzyme levels (RR 2.38; comparable to those for coronary application of phamacogenetics to 95% CI: 1.06–5.34).16 Efficacy para- artery disease or stroke.2 Moreover, life the treatment of RA. meters were not significantly different expectancy is shorter than the general MTX is one of the most widely used between the patients with and without population. Unfortunately, the cause DMARDs for the treatment of RA. The the mutation. The authors speculated of RA is still unknown. However, as the principal pharmacological mechanism that impeded homocysteine metabo- understanding of the pathophysiology is thought to be the inhibition of lism introduced by intracellular con- of RA progresses, new therapeutic dihydrofolate reductase, a key enzyme version of folate was the mechanism of strategies and agents have been devel- in the generation of bioactive folate the increased frequency of toxicities in oped. The efficacy of early and aggres- compounds. Although precise me- patients with the mutant allele at sive treatment with disease-modifying chanisms of action of MTX in RA C677T polymorphism.16 antirheumatic drugs (DMARDs) is remain controversial, it is widely ac- In a retrospective study involving widely accepted. DMARDs, such as cepted that the in vivo action of MTX is 106 patients with RA receiving MTX, methotrexate (MTX), sulfasalazine tightly related to the inhibition of the the relationship between the two (SSZ) and leflunomide, have documen- folate metabolism.9–11 Several well- MTHFR gene polymorphisms, C677T ted prevention of the structural da- controlled trials revealed the efficacy and A1298C, and either the efficacy or mage of the joints.3,4 Recently, of MTX in RA. Nevertheless, the the toxicity of MTX was examined.17 biologic response modifiers targeting response rate to MTX has been re- Single-locus analysis showed that specific cytokines, such as tumor ne- ported to be only 463 to 65%,12 and the patients with 1298C were receiv- crosis factor-a (TNF-a) or interleukin-1, the dose of MTX required to suppress ing significantly lower doses of MTX have been introduced, and the results effectively RA activity differs widely compared to the patients without indicated the effective suppression of between patients. Toxicities of MTX it (Po0.05; RR 2.18; 95% CI: 1.17– the RA activity. However, the outcome can occur in some patients but not in 4.06), while a higher rate of overall of the treatment with DMARDs in RA others.13 Thus, the variabilities in both MTX toxicity was observed in patients is known to vary among efficacy and toxicity indeed exist in the patients with 677T than those patients. The difference in the re- the treatment of RA with MTX. As without it (Po0.05; RR 1.25; 95% Pharmacogenetic approaches to rheumatoid arthritis A Taniguchi and N Kamatani 351

CI: 1.05–1.49). Haplotype analysis re- (Po0.001; odds ratio (OR): 7.73; 95% of AZA in patients with RA in an vealed that the patients with the CI: 3.54–16.86). In 25% of the slow observational study. In 40 patients 677C–1298C haplotype were receiving acetylators, toxicities, such as myelo- with RA treated with AZA, three of lower doses of MTX than those with- suppression and hepatotoxicity, were five patients with mutant TPMT alleles out it (Po0.05; RR 2.14; 95% CI: 1.13– so severe that hospitalization was discontinued AZA because of gastro- 4.07), while the subjects with 677T– required (Po0.005; OR: 17.0; 95% CI: intestinal toxicities with severe nausea 1298A had a higher frequency of 2.74–105.5). It was suggested that and vomiting. Patients with mutant toxicities from MTX (Po0.05; RR pretreatment genotyping of the NAT2 TPMT alleles had developed toxicities 1.42; 95% CI: 1.11–1.92).17 These gene may reduce the incidence of more frequently than those without studies suggested that C677T and toxicities, especially severe ones, of mutant alleles (P ¼ 0.018).29 These stu- A1298C polymorphisms within the SSZ in RA patients.21 dies suggested the possibility that MTHFR gene might be useful to predict AZA is widely used to treat certain testing for TPMT genotypes before the efficacy or the toxicity of MTX in malignancies, organ transplant rejec- treatment with AZA would help clin- the treatment of RA patients. tions, inflammatory bowel diseases ical management of patients with Recently, the anti-inflammatory ef- and rheumatic diseases including RA. rheumatic diseases. Economical ana- fects of MTX medicated by adenosine However, a high discontinuation rate lyses suggested that PCR screening for metabolism have been reported to be caused by toxicities has limited its use. TPMT polymorphisms in patients with an important mechanism.18 However, Among three major enzymes involved RA prior to AZA treatment appeared to enzymes in the adenosine pathways in the metabolism of AZA, only TPMT be cost-effective.30,31 Although AZA is influenced by MTX have not been has been extensively studied pharma- now used less frequently in the treat- studied pharmacogenetically yet. cogenetically. TPMT activity is affected ment of RA than before, the genotyp- SSZ is another widely used DMARD. by allelic polymorphisms. Homozy- ing at TPMT before the treatment with The frequency of the toxicities with gotes for wild-type alleles (TPMT*1) AZA is a prototype of the individua- SSZ has been reported to be about 20– had high TPMT activities, while homo- lized drug therapy for RA patients. 30% in patients with RA.19–21 NAT2 is zygotes for mutant alleles such as Recently, biologic response modi- a key enzyme in the acetylation of SSZ. TPMT*2 (G238C), TPMT*3A (G460A fiers have been introduced for the The rate of acetylation is genetically and A719G), TPMT*3B (G460A) and treatment of RA. Since TNF-a plays a determined and follows a bimodal TPMT*3C (A719G) had low or no key role in the pathogenesis of RA, this distribution. Individuals were classi- activities. Heterozygotes with both cytokine might be one of the impor- fied as fast and slow acetylators.7 The wild-type and mutant alleles had in- tant targets of biologic response modi- NAT2 gene has several SNPs in exon 2 termediate activities.26,27 TPMT-defi- fiers. Anti-TNF-a agents including and it has been reported that slow cient patients accumulate very high etanercept, a recombinant soluble acetylation is due to mutations in the concentrations of thioguanine nucleo- TNF receptor p75 fusion protein, and NAT2 gene.22 The haplotypes of single tides, the toxic metabolites of AZA, infliximab, a chimeric anti-TNF-a individuals were inferred based on the which leads to the severe bone marrow monoclonal antibody, are available in genotypes at seven SNP loci. The toxicity. There have been several re- clinical practice. These agents proved genetic status of each individual at ports on the association between the to be effective for RA from various the NAT2 gene is most properly ex- genotypes at TPMT and the toxicity of viewpoints including the radiographic pressed as a combination of two AZA in patients with rheumatic dis- progression. However, 20–40% of pa- haplotypes, that is, a diplotype config- eases.28,29 Black et al analyzed the tients have been reported as nonre- uration.22,23 The NAT2 activity for an TPMT genotype in a prospective co- sponders.6 For biologic response individual was related to the diplotype hort of 67 patients with rheumatic modifiers targeting inflammatory cy- configuration. The presence of at least diseases that included 49 patients with tokines, polymorphisms associated one wild-type haplotype (NAT2*4)in RA. In the cohort, six of 67 patients with the genes that regulate either an individual resulted in a rapid were heterozygous and no patients the production or the function of the acetylator phenotype, whereas homo- were homozygous for mutant TPMT cytokines may influence the response zygotes for mutant haplotypes alleles. Five of the six heterozygous to these agents.6 Previous studies (NAT2*5, NAT2*6, NAT2*7, NAT2*13, patients discontinued AZA within 1 showed that A allele at À308GA poly- etc) resulted in a slow acetylator month of therapy because of the morphism within the TNF-a gene phenotype.22–24 Tanaka et al25 retro- reduced leukocyte counts. Patients (TNFA) promoter might be related to spectively examined whether the di- with wild-type TPMT alleles had re- the high production of TNF-a.32,33 plotype configurations at the NAT2 ceived treatment with AZA for signifi- Mugnier et al34 reported that A/A or gene were associated with toxicities of cantly longer periods than patients A/G genotypes at À308 position of SSZ in 144 Japanese RA patients. The with mutant alleles (P ¼ 0.018), TNFA were associated with a poor frequency of the patients with toxi- although the data limited to patients response to infliximab therapy. The cities was five of eight (62.5%) among with RA were not available.28 Coromi- combination of G allele at À308 posi- the slow acetylators and only 11 of 136 nas et al investigated the association tion in TNFA and the GG genotype at (8.1%) among the rapid acetylators between TPMT genotype and toxicities À1087 polymorphism in interleukin-10

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gene was reported to be associated morphisms and the individual differ- ate after administration of folinic acid. Ann with a good response to etanercept.6 ences in the responses to the drugs. Rheum Dis 1991; 50: 913–914. Although larger-scale studies includ- 11 Ortiz Z, Shea B, Suarez-Almazor ME, Moher D, Wells GA, Tugwell P. The efficacy of folic ing genotypes on various cytokines, DUALITY OF INTEREST acid and folinic acid in reducing methotrex- cytokine receptors or antagonists will None declared. ate gastrointestinal toxicity in rheumatoid be needed, these studies suggested that arthritis. A metaanalysis of randomized the pharmacogenetic approach may be controlled trials. J Rheumatol 1998; 25: Correspondence should be sent to: 36–43. useful for predicting efficacy of anti- Dr A Taniguchi, Institute of Rheumatology, 12 Bathon JM, Martin RW, Fleischmann RM, a TNF- treatment and for saving med- Tokyo Women’s Medical University, 10-22 Tesser JR, Schiff MH, Keystone EC et al. 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