P384 A higher red blood cell methotrexate polyglutamate 3 concentration is associated with methotrexate drug-survival in patients with Crohn’s Disease: first results of a prospective cohort

Abstract

Background Prediction and monitoring of drug response of methotrexate (MTX) in patients with Crohn’s disease (CD) is an unmet need. MTX-polyglutamates (MTX-PGs) in red blood cells (RBC) are potential markers for response in other immune-mediated inflammatory diseases. Our objectives were investigating the relation between MTX-PGs and efficacy and defining predictors of response in CD patients treated with MTX. Methods In a multicenter prospective cohort study, CD patients starting subcutaneous (s.c.) MTX without biologics were included and followed for 12 months or until MTX s.c. was discontinued or a concomitant step-up therapy was started. At baseline clinical and biochemical predictors were recorded. At 2, 3, 6 and 12 months after start of therapy or when dropping out, blood samples were collected and individual MTX-PGs (MTX-PG1 - MTX-PG5) were analyzed in RBC using a validated UHPLC-MS/MS method. The outcome was either MTX s.c. discontinuation or initiation concomitant step-up therapy, due to disease activity or toxicity. Predictors were analysed in an univariate Cox regression model and MTX-PGs in an extended Cox model, corrected for prednisone (at start) and budesonide. Results Eighty CD patients were included (age mean±SD 55±13y, 35% male). The median Harvey Bradshaw Index (HBI) was 4 (IQR 2-7). After 12 months 21 patients were still on MTX s.c. monotherapy, 21 patients stopped because of disease activity, 29 because of toxicity, 4 because of a combination of both and 5 patients were censored (4 ended study participation, 1 MTX was stopped on patient’s own initiative) [Figure 1]. A higher HBI at baseline was associated with an increased rate of MTX s.c. monotherapy discontinuation (HR 1.08, 95% CI 1.02-1.16). Predictors of discontinuation because of disease activity (cause specific hazards) were male sex (3.83, 1.62-9.05), baseline eGFR (1.06, 1.02-1.09), baseline HBI (1.12, 1.02-1.23) and baseline plasma folate (0.94, 0.88-0.99). Sex and plasma folate were not correlated with HBI. No cause specific hazards for stopping MTX because of toxicity were identified. MTX-PG3 was the most abundant MTX-PG subspecie with a median concentration of 51 nmol/L RBC (IQR 37-62) at month 3 and was associated with better MTX survival (HR 0.98, 95% CI 0.971-0.999). For every ten points increase in the MTX-PG3 concentration, the rate of MTX s.c. monotherapy discontinuation decreases with 14%. Conclusion Higher eGFR, higher HBI, lower plasma folate at baseline and male sex are predictors for MTX failure in the first year in CD patients. The last two parameters are likely predictors of MTX response specifically rather than prognostic disease factors. The measurement of MTX-PG3 in packed RBC holds potential as a tool for therapeutic drug monitoring in CD.