Correlation Between Methotrexate Polyglutamates Concentrations in Red Blood Cells and Pulmonary Function in Patients Treated With Methotrexate in the PREDMETH Trial

Abstract Rationale In the PREDMETH trial we investigated the efficacy of methotrexate (MTX) compared to prednisone as first line treatment of pulmonary sarcoidosis. We recently reported, (European Respiratory Society Conference), that MTX is as effective as prednisone as assessed by forced vital capacity (FVC) after 6 months of treatment. At present, there are no biomarkers that can predict MTX treatment response within the first 6 months. MTX works as a folate antagonist and upon administration is actively transported into cells where it is metabolized to its active forms by adding up to 6 glutamate residues forming MTX-polyglutamate(n) (MTX-PG(n)) resulting in enhanced cellular retention and anti-inflammatory activity. Intracellular MTX-PG(n) concentrations take about 3 to 4 months to reach a steady state where there is a balance between the process of adding and removing glutamate groups to the MTX molecules. In this study, we therefore address the question whether different MTX-PG(n) metabolite concentrations in red blood cells (RBC) measured after 16 weeks of MTX therapy correlate with response to treatment after 6 months of MTX therapy. Methods For this study, pelleted red blood cells (RBC) from sarcoidosis patients under MTX therapy were used, (mean dosage 21mg/week, SD±4,7). Effectiveness of therapy was assessed by change in forced vital capacity (FVC) between baseline and after 24 weeks of treatment. MTX-PG(n) concentrations after 16 weeks were measured from whole blood RBC by LC-MS/MS. Spearman's rho correlation coefficients were calculated to evaluate the relationship between changes in the FVC and MTXPG(n) metabolite concentrations. Linear regression analysis was used to estimate the linear relationship between efficacy of therapy and the MTX-PG metabolite concentrations. Results Pelleted RBC at 16 weeks after initiation of therapy were available from 36 patients. MTXP-G1 and MTXP-G2 metabolite concentrations in RBC after 16 weeks of therapy showed a significant negative correlation with effectiveness of therapy, defined as change in FVC between baseline and after 24 weeks of therapy (r= -0.551, p = <0.001 and r= -0.511, p = 0.001 respectively). MTX-PG(3-5) did not correlate with effectiveness of therapy. Conclusion Our results suggest a relation between MTX-PG1 and MTX-PG2 metabolite concentrations in RBC after 4 months of MTX therapy and change in FVC after 6 months in patients with sarcoidosis. This could partly explain the variability of response to MTX and be a first step in therapeutic drug monitoring when using MTX in patient with pulmonary sarcoidosis.