In vitro activity: Bosutinib is selective for Src over non-Src family kinases with an IC50 of 1.2 nM, and potently inhibits Src-dependent cell proliferation with an IC50 of 100 nM. Bosutinib significantly inhibits the proliferation of Bcr-Abl-positive leukemia cell lines KU812, K562, and MEG-01 but not Molt-4, HL-60, Ramos, and other leukemia cell lines, with IC50 of 5 nM, 20 nM and 20 nM, respectively, more potently than that of STI-571. Similar to STI-571, Bosutinib displays antiproliferative activity against the Abl-MLV-transformed fibroblasts with IC50 of 90 nM. Bosutinib ablates tyrosine phosphorylation of Bcr-Abl and STAT5 in CML cells and of v-Abl expressed in fibroblasts at the concentration of ~50 nM, 10-25 nM and 200 nM, respectively, leading to the Bcr-Abl downstream signaling inhibition of Lyn/Hck phosphorylation. Although unable to inhibit the proliferation and survival of breast cancer cells, Bosutinib significantly decreases the motility and invasion of breast cancer cells with IC50 of ~250 nM, involved with an increase in cell-to-cell adhesion and membrane localization of β-catenin.

Kinase Assay: The Src kinase activity is measured in an ELISA format. Src (3 units/reaction), reaction buffer (50 mM Tris-HCl pH 7.5, 10 mM MgCl2, 0.1 mM EGTA, 0.5 mM Na3VO4) and cdc2 substrate peptide are added to various concentration of Bosutinib and incubated at 30 °C for 10 minutes. The reaction is started by the addition of ATP to a final concentration of 100 μM, incubated at 30 °C for 1 hour and stopped by addition of EDTA. Instructions from the manufacturer are followed for subsequent steps. The Abl kinase assay is performed in a DELFIA solid phase europium-based detection assay format. Biotinylated peptide (2 μM) is bound to streptavidin-coated microtitration plates for 1.5 hours in 1 mg/mL ovalbumin in PBS. The plates are washed for 1 hour with PBS/0.1% Tween 80, followed by a PBS wash. The kinase reaction is incubated for 1 hour at 30°C. Abl kinase (10 units) is mixed with 50 mM Tris-HCl (pH 7.5), 10 mM MgCl2, 80 μM EGTA, 100 μM ATP, 0.5 mM Na3VO4, 1% DMSO, 1 mM HEPES (pH 7.0), 200 μg/mL ovalbumin and various concentration of Bosutinib. The reaction is stopped with EDTA at a final concentration of 50 mM. The reaction is monitored with Eu-labeled phosphotyrosine antibody and DELFIA enhancement solution.

Cell Assay: Cells ( Abl-MLV, Rat 2, KU812, K562, and MEG-01 cells) are exposed to various concentrations of Bosutinib for 72 hours. Anchorage-independent proliferation of Abl-MLV-transformed fibroblasts is measured in 96-well ultra-low binding plates treated with Sigmacote to block residual cell attachment. Cell proliferation is measured with MTS or Cell-Glo. For the determination of cell cycle or cell death, cells are prepared for FACS analysis in the CycleTest Plus DNA reagent kit and analyzed on a fluorescence-activated cell sorter flow cytometer.

Cancer Res. 2003 Jan 15;63(2):375-81; J Med Chem. 2001 Nov 8;44(23):3965-77.