Can we predict unresponsiveness to methotrexate in rheumatoid arthritis? A pharmacogenetic study

Objective Methotrexate (MTX) is the anchor drug in the treatment of rheumatoid arthritis (RA) and the therapeutic response to MTX has been observed to vary widely among these patients. The aim of this study was to investigate ABCB1 gene (the multidrug resistant 1 gene; MDR1 gene) polymorphism in patients with RA and to evaluate the relation between MTX unresponsiveness and this polymorphism. Methods Forty-five patients with RA administered MTX were included in this pharmacogenetic cross-sectional study. The gender, age, body mass index (BMI), rheumatoid factor (RF) positivity, anti-cyclic citrullinated peptide (anti-CCP) positivity, doses of MTX and glucocorticoids were recorded. In addition, initial and third month disease activity (DAS28, Simplified and Clinical Disease Activity Index; SDAI and CDAI) scores were evaluated. We also examined frequencies of two single-nucleotide polymorphisms (SNPs), G2677T and C3435T, within the gene encoding ABCB1. Results 22 patient's responsive and 20 patients unresponsive to MTX were enrolled. Initial demographic and disease related factors were similar between patients responsive or nonresponsive to MTX. In the third month evaluation, disease activity scores were significantly higher in patients unresponsive to MTX (p < 0.05). In addition, almost all patients unresponsive to MTX (19 of the 20 patients) presented heterozygosity in C3435T (p < 0.000). Conclusion We determined heterozygosity in C3435T SNP of ABCB1 gene (multidrug resistant 1 gene) in almost all patients with RA who were non-responders to MTX. This result may contribute to predict unresponsiveness to MTX in RA. Individualized treatment strategies based on the pharmacogenetic characteristics of MTX may lead to optimization of the treatment.