Background Methotrexate (MTX) is the DMARD of first choice in most patients with rheumatoid arthritis (RA). However, a significant minority (30-40%) of patients do not respond to MTX therapy. Gene expression profiling may be a useful tool to predict treatment response.
Objectives To identify potential genetic expression profiles predictive of non-response to MTX in patients with RA.
Methods Samples from patients recruited to the Rheumatoid Arthritis Medication Study (RAMS), a one-year observational study investigating response to MTX in RA patients, were included. At 6 months, patients were categorized into responders (R) or non-responders (NR) based on EULAR response criteria. Whole blood samples for RNA extraction were collected at baseline (BL) and after 4 weeks on treatment. Samples were biotin labelled and amplified prior to being loaded onto Illumina HumanHT-12 v4 BeadChips, which target over 47,000 probes. GenomeStudio software was used to summarize bead level data. Differential gene expression (DGE) between response groups and sample time-points was investigated using linear regression. P-values were adjusted for multiple testing (adjP).
Results Samples of 24 R and 43 NR were analyzed. At BL, the median [IQR] symptom duration was 6 [4-18] vs. 13 [3-58] months. R had a significantly higher mean (SD) DAS28 score compared to NR (4.8 (1.0) vs. 4.1 (1.4), p=0.03) at BL, but, as expected, DAS28 at 6 months was significantly lower in the R group (2.3 (0.6) vs. 4.1 (1.3), p≤0.001). In R and NR, median starting dose MTX was respectively 12.5 [10-15] vs. 15 [10-15] mg/wk (p=0.91) and 13% vs. 23% of patients used oral steroids (p=0.29). No statistically significant DGE was observed in NR when comparing the 4-week sample with the BL sample, or when R and NR were compared at BL and 4-weeks. However, statistically significant DGE was observed between BL and 4 weeks in R in 131 genes, 70 up-regulated and 61 down-regulated with the top gene being importin 13 (IPO13); p value =7.07E-09. IPO13 is a nuclear transport receptor that mediates nuclear entry of glucocorticoids (GC) and previously it has been shown that MTX regulates the expression of GC receptor alpha and beta. An overview of the top differentially expressed genes between BL and 4-weeks in R are shown in Table 1.
Conclusions This is one of the largest studies of gene expression profiles in patients with RA starting MTX. We have identified a 131 DGE profile in R in the first few weeks after MTX commencement and we have identified IPO13 as a potentially important pharmacodynamic biomarker of good response.
Acknowledgements Funding: Pfizer I-CRP
Disclosure of Interest : None declared