Induction of apoptosis by vitamin D₃compounds.

HL-60 cells were treated for up to 4 days with different concentrations (10⁻⁸ or 10⁻⁷ M) of either 1,25(OH)₂D₃ or Gemini-19-nor and then analyzed by flow cytometry for cells that were annexin V-FITC⁺ and PI⁻, which represent those in the early stages of apoptosis. (A) The upper right quadrant of each histogram shows necrotic cells that were PI⁺ and annexin V⁺. The lower right quadrant shows apoptotic cells that were not necrotic (PI⁻) and annexin V⁺. Histograms show representative data from one experiment. (B) Percentage of apoptotic cells after 4 days. Column indicates mean (± SD) of 3 independent experiments. *P < .05 as determined by Studentt test difference compared with the control group.