Fragmentation study of imatinib and characterization of new imatinib metabolites by liquid chromatography-triple-quadrupole and linear ion trap mass spectrometers.

Imatinib (Gleevec) is an anticancer drug that inhibits specific protein kinases involved in cell proliferation. Whereas this drug is considered to have opened a new era, various mechanisms of resistance have been associated with imatinib relapse. Drug disposition in cancer cells including influx, efflux and drug metabolism is one mechanism that remains to be more thoroughly investigated. Moreover, recent genomic studies have revealed that some isozymes of cytochrome P450 (CYP) are possibly associated with the treatment outcome. Therefore, this research paper investigates the role of the activity of CYP1A1, 1A2, 1B1, 3A4, 4F2 and 4F3A/B on the fate of imatinib. First, a study of imatinib fragmentation was effected using electrospray triple-quadrupole and linear ion trap tandem mass spectrometers (MSn). Accurate mass determinations were performed at enhanced mass resolution for the identification of some product ions that were not predicted by two fragmentation softwares. Whereas the quadrupole MS was not designed for accurate mass measurement, delta mass errors were below 20 ppm. Then, a biotransformation study was effected in vitro. Imatinib metabolites were produced in microsomal incubations containing CYP isozymes. Imatinib and metabolites were extracted from incubation mixtures by protein precipitation, and supernatants were injected into a liquid chromatography equipment coupled with MS(n). Hydrophobic interaction liquid chromatography resolved one demethylated-, two hydroxy- and three N-oxide metabolites. Various rates of metabolite formation were observed between CYP isozymes. Liquid chromatography with deuterium oxide-containing mobile phase (H/D exchange) or incorporation of (18)O from H(2) (18)O added in the incubations was performed to elucidate the metabolite structure. Various MS(n) product scans (n < or = 4) were acquired on the linear ion trap or on the triple-quadrupole MS. Postulated structures of new metabolites are addressed.