Sulfasalazine is a potent inhibitor of the reduced folate carrier: Implications for combination therapies with methotrexate in rheumatoid arthritis
Article first published online: 6 JUL 2004
Copyright © 2004 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 50, Issue 7, pages 2130–2139, July 2004
How to Cite
Jansen, G., van der Heijden, J., Oerlemans, R., Lems, W. F., Ifergan, I., Scheper, R. J., Assaraf, Y. G. and Dijkmans, B. A. C. (2004), Sulfasalazine is a potent inhibitor of the reduced folate carrier: Implications for combination therapies with methotrexate in rheumatoid arthritis. Arthritis & Rheumatism, 50: 2130–2139. doi: 10.1002/art.20375
- Issue published online: 6 JUL 2004
- Article first published online: 6 JUL 2004
- Manuscript Accepted: 1 APR 2004
- Manuscript Received: 8 AUG 2003
- Dutch Arthritis Association. Grant Number: NRF 03-I-40
- 2002 Arthron Young Investigators Fellowship award
To investigate whether interactions of sulfasalazine (SSZ) with reduced folate carrier (RFC), the dominant cell membrane transporter for natural folates and methotrexate (MTX), may limit the efficacy of combination therapy with MTX and SSZ in patients with rheumatoid arthritis.
Human RFC-(over)expressing CEM cells of T cell origin were used to analyze the effect of SSZ on the RFC-mediated cellular uptake of radiolabeled MTX and the natural folate leucovorin. Moreover, both cells with and those without acquired resistance to SSZ were used to assess the antiproliferative effects of MTX in combination with SSZ.
Transport kinetic analyses revealed that SSZ was a potent noncompetitive inhibitor of RFC-mediated cellular uptake of MTX and leucovorin, with mean ± SD Ki (50% inhibitory concentration) values of 36 ± 6 μM and 74 ± 7 μM, respectively. Consistent with the inhibitory interaction of SSZ with RFC, a marked loss of MTX efficacy was observed when MTX was coadministered with SSZ: up to 3.5-fold for CEM cells in the presence of 0.25 mM of SSZ, and >400-fold for SSZ-resistant cells in the presence of 2.5 mM of SSZ. Importantly, along with diminished efficacy of MTX, evidence for cellular folate depletion was obtained by the demonstration of an SSZ dose–dependent decrease in leucovorin accumulation.
At clinically relevant plasma concentrations, interactions of SSZ with RFC provide a biochemical rationale for 2 important clinical observations: 1) the onset of (sub)clinical folate deficiency during SSZ treatment, and 2) the lack of additivity/synergism of the combination of SSZ and MTX when these disease-modifying antirheumatic drugs are administered simultaneously. Thus, when considering use of these drugs in combination therapies, the present results provide a rationale both for the use of folate supplementation and for spacing administration of these drugs over time.