Methotrexate Polyglutamate Concentrations as a Possible Predictive Marker for Effectiveness of Methotrexate Therapy in Patients with Sarcoidosis: A Pilot Study.

Introduction: Methotrexate (MTX), a folate antagonist, is often used as second-line treatment in patients with sarcoidosis. Effectiveness of MTX has large inter-patient variability and at present therapeutic drug monitoring (TDM) of MTX is not possible. Upon administration, MTX is actively transported into cells and metabolized to its active forms by adding glutamate residues forming MTXPG_(n=1-5) resulting in enhanced cellular retention. In this study we address the question whether different MTXPG_(n) concentrations in red blood cells (RBC) of patients with sarcoidosis after 3 months of MTX therapy correlate with response to treatment.

Methods: We retrospectively included patients with sarcoidosis that had started on MTX therapy and from whom blood samples and FDG-PET/CT were available 3 and 6-12 months after MTX initiation, respectively. FDG-uptake was measured by SUVmax in the heart, lungs and thoracic lymph nodes. Changes in SUVmax was used to determine anti-inflammatory response after 6-12 months of MTX therapy. MTXPG_(n) concentrations were measured from whole blood RBC using an LC-MS/MS method. Pearson correlation coefficients were calculated to evaluate the relationship between changes in the SUVmax and MTXPG_(n) concentrations.

Results: We included 42 sarcoidosis patients treated with MTX (15 mg/week); 31 with cardiac sarcoidosis and 11 with pulmonary sarcoidosis. In MTXPG₃ and MTXPG₄ a significant negative relation between the absolute changes in SUVmax and MTXPG_(n) was found r = - 0.312 (n = 42, p = 0.047) for MTXPG₃ and r = - 0.336 (n = 42, p = 0.031 for MTXPG₄). The other MTXPG_(n) did not correlate to changes in SUVmax.

Conclusion: These results suggest a relation between MTXPG_(n) concentrations and the anti-inflammatory effect in patients with sarcoidosis. Further prospective validation is warranted, but if measuring MTXPG concentrations could predict treatment effect of MTX this would be a step in the direction of personalized medicine.