title: Preparation of 125iodine-labelled methotrexate and its use in a magnetisable particle solid-phase radioimmunoassay.
abstract: Two techniques for the iodination of methotrexate are describes, involving covalent linkage to the drug of 125I-labelled N-succinimidyl-3-(4-hydroxyphenyl)propionate (Bolton and Hunter reagent), or to 125I-labelled histamine. A rapid highly specific radioimmunoassay for methotrexate was developed, employing a specific antiserum covalently linked to magnetisable particles, and 125I-labelled methotrexate as tracer. Incubation times for the assays were 60 and 10 min for the Bolton and Hunter reagent-linked methotrexate and 125I-labelled histamine-linked methotrexate respectively. Separation of bound from free antigen was achieved by a rapid magnetic separation system. Results obtained for serum samples correlated closely with those using an enzymatic (dihydrofolate reductase) competitive protein binding assay for methotrexate. A major advantage of the assay is its potential for processing large numbers of samples rapidly, making it highly suitable for routine clinical use.
mesh_terms: D000818:Animals; D007457:Iodine Radioisotopes; D007553:Isotope Labeling / Q000379:methods; D008727:Methotrexate; D011863:Radioimmunoassay / Q000379:methods; D012756:Sheep / Q000276:immunology
chemical_list: D007457:Iodine Radioisotopes; D008727:Methotrexate