Background Methotrexate (MTX) is the first-line disease modifying anti-rheumatic drug (DMARD) for the treatment of rheumatoid arthritis (RA). By two years of treatment only 55% of patients remain on the drug, implying that many do not respond adequately or experience adverse effects (1,2). Therefore, identifying blood-based biomarkers that predict treatment response is an important research priority. DNA methylation is an epigenetic marker that modifies but does not alter DNA sequence, and should be considered for evaluation as potential biomarkers for treatment response. The mechanisms of action of MTX are unclear. However, it is thought that MTX promotes adenosine release and interferes with the intracellular methyl donor status leading to DNA hypomethylation (3).

Objectives To identify differential DNA methylation signatures in whole blood, which may act as biomarkers predictive of response to MTX in patients with RA.

Methods Epigenome-wide DNA methylation levels were measured using the HumanMethylation450 BeadChip (Illumina) in whole blood-derived DNA samples from individuals recruited to the Rheumatoid Arthritis Medication Study (RAMS), a one year observational study including patients with RA starting MTX for the first time, who had EULAR good response (n=36) or EULAR poor response (n=36) to MTX. DNA was taken from blood samples pre-treatment and following four weeks on therapy. Response was determined at six months using the DAS28 score. Differentially methylated positions (DMPs) were identified using linear regression, adjusting for gender, age, cell composition, and baseline DAS28 score.

Results Although no probe reached study-wide significance, 16 DMPs suggestive loci were associated with MTX response in the pre-treatment samples (arbitrary p<10^–4), including a DMP close to the IL6R gene (cg15633035, p=5.24x10^–5). At four weeks, 20 DMPs were associated with response, with no overlap with the DMPs reported in the pre-treatment sample. In good responders, 10 DMPs were differentially methylated between pre-treatment and four week samples. In poor responders, 17 DMPs were differentially methylated between time-points. There was no overlap of DMPs between good and poor responders

Conclusions These preliminary results suggest DNA methylation may provide a useful source of biomarkers of MTX response and now require replication in an independent dataset. Furthermore, investigation of differential methylation between baseline and four weeks reveals the potential of DNA methylation in pharmacodynamic modelling of MTX response. Further analysis is being conducted and significant findings will be validated in the total RAMS population using pyrosequencing.

1. Barrera P et al, Drug survival, efficacy and toxicity of monotherapy with a fully human anti-tumour necrosis factor-alpha antibody compared with methotrexate in long-standing rheumatoid arthritis. Rheumatology. 2002 Apr;41(4):430–9

2. Verstappen SMM, et al, Prediction of response and adverse events to methotrexate treatment in patients with rheumatoid arthritis. Int. J. Clin. Rheu. 2012;7(5):559–567

3. Kim Y, et al, DNA hypomethylation in inflammatory arthritis: reversal with methotrexate. J. Lab. Clin. Med. 1996;128:165–172

Disclosure of Interest None declared