Cells synchronized in G₂M display enhanced susceptibility to TNF-α–induced lethality.

(A) U937/neo and U937/ΔBcl-2 cells were exposed to aphidicolin (100 ng/mL) for 24 hours, washed 3 times, and then resuspended in fresh medium. Cell cycle analysis was performed 3 and 6 hours following the washout. (B) At 6 hours after aphidicolin washout, synchronized and untreated (asynchronized) cells were exposed to TNF-α (0.025 ng/mL) for 24 hours. Apoptosis was determined by annexin V/PI positivity as described in “Materials and methods.” Values represent the means for 3 separate experiments (± SE). *Significant difference relative to asynchronous cells (P < .01).