Lack of apoptosis inhibitory effect of triton-soluble extracts from untreated bcr-abl⁺ cell lines. Nuclei from U937 cells in which DNA was labeled with [¹⁴C]-thymidine were incubated for 30 minutes at 37°C with either triton-soluble extracts from untreated (U937) or etoposide-treated (100 μmol/L for 3 hours; U-VP) U937 cells or a mixture or an equal volume of triton-soluble extracts from etoposide-treated (100 μmol/L for 3 hours) U937 cells and triton-soluble extracts from untreated cell lines (U-VP + name of the untreated cell line). Results of a representative experiment are expressed as the mean ± SD of triplicate measurements standardized to the U-VP sample (100%).