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Bioassay for detection of methotrexate in serum
S de Lathouder1, A H Gerards, E R de Groot
1Sanquin Research at CLB, and Landsteiner Laboratory, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Objective:
A bioassay is developed for the measurement of methotrexate (MTX) in serum.
Methods:
The assay is based on MTX inhibition of the proliferation of hypoxanthine-guanosine phosphoribosyl transferase (HGPRT) negative mouse B-cells (B9.H). HGPRT negative cells cannot use the salvage pathway of nucleotide synthesis to overcome inhibition by MTX.
Results:
When B9.H cells are cultured with serial dilutions of serum, inhibition of proliferation is a measure of the amount of MTX in the serum. Circulating folates do not interfere with the assay.
Conclusion:
This simple assay can detect low concentrations of MTX in serum: it is therefore useful for following the pharmacodynamics of functional MTX after low-dose MTX treatment.
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