Sulfasalazine is a potent inhibitor of the reduced folate carrier: Implications for combination therapies with methotrexate in rheumatoid arthritis
✍ Scribed by Gerrit Jansen; Joost van der Heijden; Ruud Oerlemans; Willem F. Lems; Ilan Ifergan; Rik J. Scheper; Yehuda G. Assaraf; Ben A. C. Dijkmans
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 170 KB
- Volume
- 50
- Category
- Article
- ISSN
- 0004-3591
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Objective
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.
Methods
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.
Results
Transport kinetic analyses revealed that SSZ was a potent noncompetitive inhibitor of RFC‐mediated cellular uptake of MTX and leucovorin, with mean ± SD K~i~ (50% inhibitory concentration) values of 36 ± 6 μ__M__ and 74 ± 7 μ__M__, 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 m__M__ of SSZ, and >400‐fold for SSZ‐resistant cells in the presence of 2.5 m__M__ 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.
Conclusion
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.