P050 METHOTREXATE POLYGLUTAMATES AS BIOMARKERS OF TREATMENT RESPONSE IN PEDIATRIC INFLAMMATORY BOWEL DISEASE

Abstract

Therapeutic drug monitoring methods are lacking for methotrexate (MTX), an immunomodulator used in Inflammatory Bowel Disease (IBD) treatment, alone or in conjunction with infliximab (IFX). Although studies demonstrate a lack of relationship between MTX plasma concentrations and efficacy/toxicity, recent studies in rheumatoid and juvenile idiopathic arthritis suggest a positive correlation between therapeutic response and accumulation of intracellular MTX metabolites, MTX polyglutamates (MTX-Glu). The aim of this cross-sectional investigation was to test the hypothesis that intracellular MTX-Glu are associated with therapeutic response in pediatric IBD. 21 children (5-21 years; 90% Crohn’s disease), receiving combination therapy with IFX and MTX for maintenance treatment of IBD, had MTX-Glu1-6 measured in erythrocytes, using HPLC-MS/MS methodologies, and serum IFX troughs and anti-IFX antibodies (Anti-IFX) measured, using a NF-kB luciferase gene-reporter assay (ARUP Laboratories). Medical records were reviewed and disease activity determined (active vs quiescent) via consensus by 2 pediatric gastroenterologists on Physician Global Assessment. Only children on stable dosing were included (i.e., no changes to dose or interval of either drug for at least 2 IFX cycles). Nonparametric tests (e.g., Mann-Whitney U) were used to compare MTX-Glu, IFX, anti-IFX, laboratory and demographic data in children with active vs quiescent disease, and associations between MTX-Glu and parameters of interest explored via Pearson’s correlation (SPSS24; α=0.05). To account for variability in standard-of-care IFX and MTX dosing, data were normalized for mg/kg and interval, as appropriate. MTX dose ranged 5-25mg weekly (86% oral) and, adjusted for weight (mg/kg), correlated with total MTX-Glu accumulation (ρ=0.6; α=0.01), especially long-chain MTX-Glu3-5(ρ=0.7; p=0.01). Children with quiescent disease (n=11) had significantly higher dose-adjusted total MTX-Glu than children with active disease (n=10), 224 ± 94.6 vs 133 ± 85.6 (p=0.04), despite receiving comparable MTX doses (0.22 ± 0.12 vs 0.31 ± 0.18 mg/kg; p=0.39). IFX troughs (μg/ml) unadjusted (24.3 ± 16.1 vs 16.7 ± 13.0) or adjusted (adj) for IFX dose and interval (86.9 ± 59.7 vs 57.4 ± 46.8) were comparable between study groups, which were also comparable for age and disease duration (p>0.25). Neither MTX dose nor MTX-Glu correlated significantly with IFX trough or adjtrough (ρ -0.09 to 0.39; p>0.1). Only 1 child, with undetectable IFX trough, had anti-IFX. The observed positive correlation between MTX dose and MTX-Glu suggests that MTX-Glu reflect systemic MTX exposure in IBD. Despite comparable IFX troughs, higher total MTX-Glu, particularly long-chain MTX-Glu, were associated with quiescent vs active disease, suggesting that MTX-Glu may be important markers of disease response in IBD.