Intracellular and extracellular level of gefitinib in NSCLC cell lines. A) Radioactivity distribution in Calu-3 and H1299 cells incubated with 0.1 μM [3H]gefitinib for 0.5 h or 24 h. The amount of radioactivity was determined in intracellular (gray), extracellular (white) and intracellular macromolecule-linked (black) compartments. Values are given as percentage versus the total amount of radioactivity. B) Intracellular level and C) extracellular concentration of gefitinib in a panel of NSCLC cell lines evaluated by LC-MS/MS. Gefitinib-sensitive cell lines (H322, H292, Calu-3) and resistant-cell lines (H460, H1299, A549, Calu-1, SKLU-1) were incubated with 0.1 μM gefitinib for 0.5 h and 24 h. Values given are the means (± SD) of four independent determinations (**P < 0.01; ***P < 0.001).