Pretreatment with etoposide or Ara-C enhances Apo-2L–induced apoptosis of HL-60 cells.

HL-60 cells were exposed to etoposide (5.0 μmol/L, 6 hours), Ara-C (10.0 μmol/L, 6 hours), or Apo-2L (100 ng/mL, 18 hours), and the percentage of apoptotic cells was determined at the end of 24 hours (see “Results”). Cells were also exposed to etoposide plus Apo-2L (total 24 hours), or Ara-C plus Apo-2L (total 24 hours). Alternatively, cells were treated with etoposide (5.0 μmol/L, 6 hours), followed by Apo-2L (100 ng/mL, 18 hours) or Ara-C (10.0 μmol/L, 6 hours), followed by Apo-2L (100 ng/mL, 18 hours). Following these treatments, the percentage of apoptotic cells was determined by Annexin V staining and flow cytometry (see “Results”).