Induction of apoptosis by lapatinib in K562 and HL-60 cells.

<p>(A) K562 or HL-60 cells were left untreated or treated with various concentrations of lapatinib or TPA as indicated for 1–3 days. Cells were collected and resuspended in propidium iodide (PI)-containing hypotonic buffer, and then the percentage of apoptotic cells with DNA ladders (hypodiploid cells) was analyzed by flow cytometry. The data are expressed as means ± SEMs. (B) K562 cells were left untreated or treated with lapatinib for 3 days; cells were then collected, resuspended in both AnnexinV and PI containing buffer, and analyzed by flow cytometry. The percentages of PI(+)/annexin(+) or PI(−)/annexin(+) cells are indicated in each figure. (C) Induction of both apoptotic and non-apoptotic cell death by lapatinib in K562 cells. After DMSO or 10 µM lapatinib treatment for 1–3 days for K562, or 3 days for HL-60, cells were split into two tubes and resuspended in PI-containing phosphate buffered saline (upper panel in left figure, total dead cells) or PI-containing hypotonic buffer (lower panel in left figure, apoptotic cells), respectively, for simultaneously detecting total dead cells without intact plasma membranes or apoptotic cells as described in (A). The graph in the right panel represents the data as: the percentage of total dead cells (empty bars) and the percentages of apoptotic cells (solid bars). After drug treatment for 3 days, HL-60 cells were attached on slides using cytospin apparatus and observed after staining with Liu's stain (right panel of 2C). (D) After DMSO, 2.5, 5 or 10 µM lapatinib treatment for 8 or 16 h, K562 cells were stained with both PI and DiOC6₍₃₎. The mitochondrial transmembrane potential of the cells was analyzed by flow cytometry. *<i>P</i><0.05, **<i>P</i><0.01, ***<i>P</i><0.001 (<i>t</i>-test) between treated and DMSO control cells.