Polymorphisms in genes involved in the mechanism of action of methotrexate: are they associated with outcome in rheumatoid arthritis patients?

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From: Pharmacogenomics(Vol. 15, Issue 8)
Publisher: Future Medicine Ltd.
Document Type: Report
Length: 6,437 words
Lexile Measure: 1360L

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Author(s): Juliana Salazar aff1 aff2 , Patricia Moya aff3 aff4 , Albert Altés aff5 , César Díaz-Torné aff3 , Jordi Casademont aff3 , Dacia Cerdà-Gabaroi aff6 , Hèctor Corominas aff6 , Montserrat Baiget [*] aff1 aff2


5-aminoimidazole-4-carboxamide ribonucleotide transformylase; 5,10-methylenetetrahydrofolate reductase; ATIC; DHFR; dihydrofolate reductase; methotrexate; MTHFR; rheumatoid arthritis


Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory autoimmune disease of unknown etiology. Although it mainly affects the diarthrodial joints, extra-articular manifestations may appear. RA pathogenesis is due to a complex interaction between environment and genes, leading to a breakdown of the immune tolerance and synovial inflammation [1 ].

Synovial tissues are the target of disease-modifying antirheumatic drugs (DMARDs), which act by modifying the course of the disease in order to achieve clinical remission or low disease activity. Methotrexate (MTX) relieves symptoms of joint pain and swelling and also protects against long-term sequelae, such as joint destruction, deformity and disability. It is used worldwide as the first-line treatment option for newly diagnosed RA patients owing to its efficacy and safety [2-5 ]. However, only 50-70% of patients respond to treatment and up to one-third discontinue treatment because of adverse drug events (ADEs) [6-10 ]. New biologic therapies are highly effective in RA, but they are expensive and have significant toxicity profiles. It is therefore of great interest to identify biomarkers that help to predict MTX efficacy and toxicity before starting therapy.

The mechanism of action through which MTX causes anti-inflammatory effects is complex (Figure 1) [11 ]. Once inside the cells, a portion of MTX is polyglutamylated and this reaction generates active forms of the drug, the MTX polyglutamates (MTXPGs) [12 ]. MTX and MTXPGs inhibit several enzymes involved in the folate pathway. The DHFR enzyme reduces dihydrofolate into tetrahydrofolate (THF) and its inhibition alters purine and thymidylate biosynthesis. TYMS catalyzes the methylation of deoxyuridine-5-monophosphate to deoxythymidine-5-monophosphate, a precursor of de novo pyrimidine synthesis. Gene expression of the DHFR and TYMS enzymes is regulated by the transcription factors E2F-1 and DP-1. The availability of these transcription factors is controlled by CCND1, a protein involved in Rb protein phosphorylation [13 ]. The enzyme MTHFR, which catalyzes the reduction reaction of 5,10-methylene-THF to 5-methyl-THF, is not directly inhibited by MTX although its functionality is influenced by the depletion of the intracellular folate pool due to DHFR inhibition. MTXPGs also target TYMS and ATIC. The ATIC enzyme catalyzes the last two steps of de novo purine synthesis. Its inhibition produces an intracellular accumulation of AICAR, increasing the release of adenosine into the circulation. Extracellular adenosine increases cAMP, which inhibits production of proinflammatory cytokines, such as TNF-[alpha], IFN-[gamma] and IL-1[beta]. These cytokines play a key role in the inflammatory process in RA and their inhibition accounts for the therapeutic effect of MTX [14 ].

The variable clinical response and the unpredictable toxicity in RA patients receiving MTX prompted us to study the role of genetic variants in the DHFR , TYMS , MTHFR , ATIC and CCND1 genes as biomarkers of response and toxicity.

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Gale Document Number: GALE|A393160092