title: Intracellular concentration of the tyrosine kinase inhibitor imatinib in gastrointestinal stromal tumor cells.
abstract: Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm in the gastrointestinal tract. In most GISTs, the underlying mechanism is a gain-of-function mutation in the KIT or the PDGFRA gene. Imatinib is a tyrosine kinase inhibitor that specifically blocks the intracellular ATP-binding sites of these receptors. A correlation exists between plasma levels of imatinib and progression-free survival, but it is not known whether the plasma concentration correlates with the intracellular drug concentration. We determined intracellular imatinib levels in two GIST cell lines: the imatinib-sensitive GIST882 and the imatinib-resistant GIST48. After exposing the GIST cells to imatinib, the intracellular concentrations were evaluated using LC-MS (TOF). The concentration of imatinib in clinical samples from three patients was also determined to assess the validity and reliability of the method in the clinical setting. Determination of imatinib uptake fits within detection levels and values are highly reproducible. The GIST48 cells showed significantly lower imatinib uptake compared with GIST882 in therapeutic doses, indicating a possible difference in uptake mechanisms. Furthermore, imatinib accumulated in the tumor tissues and showed intratumoral regional differences. These data show, for the first time, a feasible and reproducible technique to measure intracellular imatinib levels in experimental and clinical settings. The difference in the intracellular imatinib concentration between the cell lines and clinical samples indicates that drug transporters may contribute toward resistance mechanisms in GIST cells. This highlights the importance of further clinical studies to quantify drug transporter expression and measure intracellular imatinib levels in GIST patients.
authors.affiliation: aEndocrine and Sarcoma Surgery Unit, Department of Molecular Medicine and Surgery, Karolinska Institutet bDepartment of Breast and Endocrine Surgery, Karolinska University Hospital cDepartment of Oncology-Pathology, Cancer Center Karolinska, Karolinska Institutet, Stockholm dDepartment of Chemistry, Biomedical Center, Analytical Chemistry and Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Berglund
authors.forename: Sarojini Jayantha Kumari A
authors.initials: SJ
authors.lastname: Ubhayasekera
authors.forename: Fredrik
authors.initials: F
authors.lastname: Karlsson
authors.forename: Pinar
authors.initials: P
authors.lastname: Akcakaya
authors.forename: Warunika
authors.initials: W
authors.lastname: Aluthgedara
authors.forename: Jan
authors.initials: J
authors.lastname: Ahlen
authors.forename: Robin
authors.initials: R
authors.lastname: Fröbom
authors.forename: Inga-Lena
authors.initials: IL
authors.lastname: Nilsson
authors.forename: Weng-Onn
authors.initials: WO
authors.lastname: Lui
authors.forename: Catharina
authors.initials: C
authors.lastname: Larsson
authors.forename: Jan
authors.initials: J
authors.lastname: Zedenius
authors.forename: Jonas
authors.initials: J
authors.lastname: Bergquist
authors.forename: Robert
authors.initials: R
authors.lastname: Bränström
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000970:Antineoplastic Agents / Q000378:metabolism*; D001549:Benzamides / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005770:Gastrointestinal Neoplasms / Q000378:metabolism* / Q000473:pathology; D046152:Gastrointestinal Stromal Tumors / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D000068877:Imatinib Mesylate; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010879:Piperazines / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000378:metabolism*; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism*; D015203:Reproducibility of Results
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit