Tandem Mass Spectrometry (MS/MS) of Thiopurine Methyltransferase (TPMT) Reaction Products in order to Quantitate TPMT Enzyme Activity

Reference #:

2005-017

Inventors/Contributors

Richard M. Weinshilboum, M.D., Mark J. Magera, John F. O'Brien, Ph.D., Jean M. Lacey, Dietrich Matern M.D., Charles A. Kroll

Description

This invention provides methods and materials related to the measurement of TPMT enzymatic activity in biological samples. The assay involves the incubation of a cell lysate with a TPMT substrate and S-adenosyl-L-methionine (SAM), which acts as a methyl donor, and an isotopically labeled internal standard corresponding to the enzymatically produced methylation product of the TPMT substrate. The reaction products can be resolved using liquid chromatography tandem mass spectrometry (LC-MS/MS). The presence of the isotopically labeled internal standard in the sample allows for accurate identification and quantification of the enzymatically generated 6-MMP produced in patients’ samples. The value obtained for TPMT activity in a patient’s sample can be compared with standard reference levels.

Patent Status

Pending