title: Measurement of 5,10-dideaza-5,6,7,8-tetrahydrofolate (lometrexol) in human plasma and urine by high-performance liquid chromatography.
abstract: Three high-performance liquid chromatographic methods are described for the detection of the novel antifolate anticancer drug (6R)-5,10-dideaza-5,6,7,8-tetrahydrofolate (lometrexol): one with fluorometric detection and two with detection by UV absorbance. An assay for plasma lometrexol using UV detection (288 nm) and reversed-phase chromatography was developed, with a quantitation limit of 0.2 microgram/ml and linearity up to 10 micrograms/ml. This assay was modified for measurement of lometrexol in urine, with a quantitation limit of 2 micrograms/ml and linearity up to 25 micrograms/ml. An alternative assay for plasma lometrexol using derivatization and fluorescence detection (excitation at 325 nm, emission at 450 nm) was also developed, which proved twenty-fold more sensitive (quantitation limit of 10 ng/ml) than the UV assay, and which was linear up to 250 ng/ml. The fluorometric method requires sample oxidation with manganese dioxide prior to analysis, and uses ion-pair chromatography with tetramethylammonium hydrogensulphate as an ion-pair reagent. All assays use a similar preliminary solid-phase extraction method (recovery as assessed by UV absorption > 73%), with C10-desmethylene lometrexol added for internal standardisation. Each assay is highly reproducible (inter-assay precision in each assay is < 10%). Applicability of the fluorescence-based assay to lometrexol in plasma and the UV-based assay to lometrexol in urine is demonstrated by pharmacokinetic studies in patients treated as part of a Phase I clinical evaluation of the drug.
authors.affiliation: Cancer Research Unit, Medical School, University of Newcastle-upon-Tyne, UK.
authors.forename: S R
authors.initials: SR
authors.lastname: Wedge
authors.forename: S
authors.initials: S
authors.lastname: Laohavinij
authors.forename: G A
authors.initials: GA
authors.lastname: Taylor
authors.forename: D R
authors.initials: DR
authors.lastname: Newell
mesh_terms: D000970:Antineoplastic Agents / Q000032:analysis* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007202:Indicators and Reagents; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013763:Tetrahydrofolates / Q000032:analysis* / Q000493:pharmacokinetics
chemical_list: D000970:Antineoplastic Agents; D007202:Indicators and Reagents; D013763:Tetrahydrofolates; C045894:lometrexol