Methotrexate (MTX) concentration in tumors following low-dose MTX

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Abstract
Methotrexate (MTX) is a folate analog competitive with reduced folates for cellular transport and metabolism. Since the normal plasma folate concentration is only 10-8 M, we tested the possibility that there may be a saturable uptake of MTX by proliferating tumor tissue at plasma MTX concentrations of only 10-7 to 10-6 M. Patients with advanced malignancies, refractory to accepted therapy, were given low-dose oral MTX (30–60 mg/m2 total dose in four to eight divided doses). Tumor tissue was biopsied 18–24 h after the last oral dose of MTX. The concentrations of MTX and its polyglutamated derivatives were measured in these samples. Forty-eight percent of the drug in the tumor samples was present as a polyglutamated derivative.