In vitro activity: In vitro assays for inhibition of a panel of tyrosine and serine/threonine protein kinases show that Imatinib inhibits the v-Abl tyrosine kinase and PDGFR potently with an IC50 of 0.6 and 0.1 μM, respectively. Imatinib inhibits the SLF-dependent activation of wild-type c-kit kinase activity with a IC50 for these effects of approximately 0.1 μM, which is similar to the concentration required for inhibition of PDGFR. Imatinib exhibits growth-inhibitory activity on the human bronchial carcinoid cell line NCI-H727 and the human pancreatic carcinoid cell line BON-1 with an IC50 of 32.4 and 32.8 μM, respectively. A recent study shows that Imatinib has the potential to exert its antileukemia effects in chronic myelogenous leukemia by down-regulating hERG1 K(+) channels, which are highly expressed in leukemia cells and appear of exceptional importance in favoring leukemogenesis.

Kinase Assay: PDGF receptor is immunoprecipitated from BALB/c 3T3 cell extracts with rabbit antiserum to the murine PDGF receptor for 2 hours on ice. Protein A-Sepharose beads are used to collect the antigen-antibody complexes. The immunoprecipitates are washed twice with TNET (50 mM Tris, pH 7.5, 140 mM NaCl, 5 mM EDTA, 1% Triton X-100), once with TNE (50 mM Tris, pH 7.5, 140 mM EDTA), and once with kinase buffer (20 mM Tris, pH 7.5,10 mM MgCl2). After stimulation with PDGF (50 ng/mL) for 10 minutes at 4 °C, different concentrations of drug are added to the reaction mixture. PDGF receptor kinase activity is determined by incubation with 10 μCi [7-33P]-ATP and l μM ATP for 10 minutes at 4 °C. Immune complexes are separated by SDS-PAGE on 7.5% gels.

Cell Assay: BON-1 cells and NCI-H727 cells are seeded into flat-bottomed 96-well plates in triplicate and allowed to adhere overnight in 10% fetal bovine serum-supplemented DMEM or RPMI 1640 complete medium, respectively; the medium is then exchanged for serum-free medium (negative control) or serum-free medium containing serial dilutions of Imatinib. After 48 hours (control cultures do not reach confluence), the number of metabolically active cells is determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and absorbance is measured in a Packard Spectra microplate reader at 540 nm. Growth inhibition is calculated using the following formula: inhibition rate = (1 – a / b) × 100%, where a and b are the absorbance values of the treated and control groups, respectively.

Proc Natl Acad Sci U S A. 1995 Mar 28; 92(7): 2558–2562; Int J Cancer. 2005 Feb 20;113(5):849-56.