Effects of imatinib and AMN107 on histamine levels and HDC mRNA expression in CML cells. (A-B) KU812 cells were incubated in control medium (Control) or imatinib (STI571; 1 μM) for 8 hours (A), or in control medium (Control) or AMN107 (0.1 μM) for 8 hours (B). Thereafter, total RNA was isolated and subjected to Northern blot analysis using an HDC-specific cDNA probe. The β-actin loading control is also shown. (C) Cellular histamine levels in KU812 cells cultured in control medium (Control) or various concentrations of imatinib (STI571; 0.1, 0.5, or 1 μM) for 2, 4, 6, 10, or 14 days (C). (D-E) Histamine levels in KU812 cells cultured in control medium (Control), imatinib (STI571; 0.1-1 μM) or AMN107 (0.1 μM) for 24 hours (D) or 48 hours (E). Cellular histamine levels were determined by RIA. Results represent the mean ± SD from 3 independent experiments. ^*P < .05. (F-G) Peripheral-blood mononuclear cells (PBMCs) were isolated from a patient with chronic-phase CML (F) and a patient with imatinib-resistant accelerated-phase CML (G). Cells were incubated in control medium (Control) or imatinib (STI571; 1 μM) (F), or in control medium (Control) or AMN107 (0.1 μM) (G), for 14 hours. Thereafter, total RNA was isolated. Northern blotting was performed with an HDC-specific cDNA probe and a β-actin probe (loading control). (H-I) Histamine levels in CML cells obtained from patients with chronic-phase CML (n = 5) (H) and with imatinib-resistant CML in accelerated-phase (n = 4) (I). Isolated PBMCs were incubated in control medium (Control) or imatinib (STI571; 1 μM), or in control medium (Control) or AMN107 (0.1 μM), for 24 hours. Thereafter, cells were lysed in distilled water, and the content of histamine was quantified by RIA. Results represent the mean ± SD from 5 (H) or 4 (I) independent experiments, respectively. ^*P < .05 compared with controls.