In vitro activity: AG-490 inhibits HER-2 driven cell proliferation with IC50 of 3.5 μM. Corresponding to the specific dose-dependent inhibition of constitutively activated JAK2 in pre-B acute leukemia (ALL) cells, AG-490 (5 μM) almost completely blocks the growth of all ALL cells by inducing programmed cell death, with no deleterious effect on normal hematopoiesis. AG-490 does not inhibit the activities of Lck, Lyn, Btk, Syk, and Src. AG-490 (60-100 μM) blocks the constitutive activation of Stat3sm, and inhibits spontaneous as well as interleukin 2-induced growth of mycosis fungoides (MF) tumor cells with IC50 values of 75 μM and 20 μM, respectively. AG-490 potently inhibits IL-2-mediated human T cell growth with an IC50 of 25 μM by blocking the activities of JAK3 and STAT5a/b. Although AG-490 alone has no effect on proliferation of FDrv210H cells at a concentration of 5 μM, AG-490 can synergize with STI571 to enhance its inhibitory effect on p210bcr-abl driven proliferation. AG-490 significantly inhibits the constitutive activation of Stat3 in MOPC, MPC11, and S194 cells, leading to dramatic dose-dependent apoptosis. AG-490 (100 μM) inhibits Akt phosphorylation, inhibits the activation of nuclear factor-κB, and causes the activation of GSK-3β, leading to the reduction of c-Myc. AG-490 (50 μM) can induce apoptosis of imatinib-resistant BaF3 cells expressing T315I and E255K mutants of Bcr-Abl. AG-490 at 30 μM inhibits not only Epo-induced phosphorylation of wild-type JAK2 but also constitutive phosphorylation of the JAK2 V617F mutant. AG-490 also potently inhibits cytokine-independent cell growth induced by the JAK2 V617F mutant in BaF3 cells.

Kinase Assay: AG-490 is dissolved in DMSO 10%-H2O-ethanol 45%. Crude membrane extracts (0.125 μg/mL) are preactivated with EGF (20 nM) in 50 mM HEPES buffer, pH 7.6, and 125 mM NaCl, for 15 minutes at 4 °C. Autophosphorylation activity of EGFR or ErbB2 kinase is assayed at 4 °C for 30 seconds in V-shaped 96-well plates. Membrane extracts (8 μL) are added to each well containing reaction mixture (12 μL, 50mM, HEPES, pH 7.4,125 mM NaCl, 12 mM M8Ac2, 2 mM MnCl2, 1 mM NaVO3, 1 μM ATP, and 1 μCi[γ-32P]ATP, final concentrations) and increasing concentrations of AG-490 (4 μL). After termination by addition of hot sample buffer, the samples are run on a 6% SDS-polyacrylamide gel electrophoresis minigel, the gels dried, and autoradiography performed during the linear exposure time period. The receptor bands are scanned densitrometrically, and the results analyzed by the Ez-Fit program. For the analysis of autophosphorylation of JAK2, JAK2 is immunoprecipitated by using anti-JAK2 antibody from lysates of G2 cells pretreated for 16 hours with increasing concentrations of AG-490 (0-50 μM). Immune complexes are then immunoblotted with anti-phosphotyrosine antibody. A dose-dependent inhibition of in vitro kinase activity is demonstrated by assessing JAK2 autophosphorylation.

Cell Assay: Cells (Pre-B ALL) are exposed to different concentrations of AG-490 for 16 hours. For the determination of cell proliferation, [3H]tymidine (1 μCi) is added 6 hours or more before the cultures are terminated. Cells are then collected and samples counted in a liquid scintillation counter.

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