7-hydroxymethotrexate and Brain-Neoplasms

The brain penetration of methotrexate (MTX) and its metabolite 7-hydroxymethotrexate (7OHMTX) was characterized in non-tumor bearing mice and mice bearing orthotopic Group 3 medulloblastoma. Plasma pharmacokinetic studies and cerebral and ventricular microdialysis studies were performed in animals dosed with 200 or 1000 mg/kg MTX by IV bolus. Plasma, brain/tumor extracellular fluid (ECF) and lateral ventricle cerebrospinal fluid (CSF) MTX and 7OHMTX concentration-time data were analyzed by validated LC-MS/MS methods and modeled using a population-based pharmacokinetic approach and a hybrid physiologically-based model structure for the brain compartments. Brain penetration was similar for MTX and 7OHMTX and was not significantly different between non-tumor and tumor bearing mice. Overall, mean (±SD) model-derived unbound plasma to ECF partition coefficient K

Topics: Animals; Brain Neoplasms; Cerebellar Neoplasms; Chromatography, Liquid; Medulloblastoma; Methotrexate; Mice; Tandem Mass Spectrometry

Methotrexate (MTX) is an anticancer agent that is widely used in a variety of human cancers including primary central nervous system lymphoma (PCNSL). Important pharmacological properties that directly bear on the use of MTX in PCNSL, such as mechanisms that govern its uptake into brain tumors, are poorly defined, but are amenable to investigation in mouse models. In order to pursue such preclinical pharmacological studies, a rapid and sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for the determination of MTX and its metabolite, 7-hydroxymethotrexate (7-OH MTX) in plasma and microdialysate samples from brain tumors and cerebrospinal fluid (CSF) is needed. The plasma assay was based on 10 microl samples and following a protein precipitation procedure enabled direct injection onto a LC/MS/MS system using positive electrospray ionization. A column switching technique was employed for desalting and the clean-up of microdialysate samples from brain tissues. The methods were validated for MTX and 7-OH MTX in both plasma and microdialysate samples from brain tumor and CSF, and produced lower limits of quantification (LLOQ) in plasma of 3.7 ng/ml for MTX and 7.4 ng/ml for 7-OH MTX, and in microdialysate samples of 0.7 ng/ml for both MTX and 7-OH MTX. The utility of the method was demonstrated by estimation of pharmacokinetic (PK) and brain distribution properties of MTX and 7-OH MTX in conscious mice. The method has the advantages of low sample volume, rapid clean-up, and the simultaneous measurement of MTX and 7-OH MTX in plasma and brain tissues allowing detailed PK studies to be completed in individual mice.

Topics: Animals; Antimetabolites, Antineoplastic; Brain; Brain Neoplasms; Chromatography, Liquid; Methotrexate; Mice; Mice, Inbred C57BL; Microdialysis; Molecular Structure; Reference Standards; Reproducibility of Results; Sensitivity and Specificity; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry