Liquid chromatographic-mass spectrometric assay for quantitation of imatinib and its main metabolite (CGP 74588) in plasma

Imatinib mesylate (Gleevec, Glivec, STI571) is a targeted, small molecule inhibitor of the oncogenes, BCR/ABL and c-Kit, and has striking antitumor activity in patients with chronic myelogenous leukemia or gastrointestinal stromal tumors. We have developed a liquid chromatographic-electrospray ionization mass spectrometric (LC-MS) method for quantifying imatinib and its main metabolite (CGP 74588) in plasma. The assay uses deuterated imatinib as the internal standard; acetonitrile deproteination; a Phenomenex Luna C(18)(2) (5 microm, 50 x 4.6 mm) reversed-phase analytical column; a gradient mobile phase of 0.1% formic acid in methanol and water; and mass spectrometric detection using electrospray positive mode electron ionization. The assay has a lower limit of quantitation (LLOQ) of 30 ng/ml and is linear between 30 and 10000 ng/ml for both imatinib and CGP 74588. We demonstrated the suitability of this assay for imatinib using it to quantify the concentrations of imatinib and CGP 74588 in plasma of a patient given a 200-mg dose of imatinib orally. We believe that this LC-MS assay should be an important tool for future pharmacokinetic studies of imatinib.