AML-BMSC adhesion and protection is disrupted by ibrutinib. (A) Light and fluorescence microscopic images show cocultured calcein-AM–treated THP-1 cells and BMSCs with and without 0.5 µM ibrutinib treatment for 8 hours. (B) Percentage of AML cell lines and (C) primary AML blasts attached to the primary AML BMSCs in the coculture setting in the presence and absence of various concentrations of ibrutinib for 8 hours. (D) AML blasts from AML #17 (low p-BTK) and AML #19 (high p-BTK) were left alone or cocultured with BMSCs in the presence or absence of various concentrations of ibrutinib for 48 hours and then stained for Annexin-V and analyzed by flow cytometry. In all panels, the values indicate the mean ± SD from 3 independent experiments. *Statistical significance of P < .05 between the different treatment groups.