Cytostasis of tumor cell lines by promyelocytic leukemia cell line HL60 differentiated to granulocyte lineage.

The human promyelocytic leukemia cell line HL60, when cultured in medium containing dimethyl sulfoxide (DMSO) or granulocyte colony-stimulating factor (G-CSF), stopped dividing and differentiated into cells with granulocyte characteristics. We found that differentiated HL60 cells have no detectable cytolytic activity against cultured human bladder cell line (T24 cell), as measured by release of (3H) thymidine, or against K562 cells, as measured by release of chromium-51. Differentiated HL60 cells inhibited incorporation of (3H) thymidine into the DNA of adherent T24 cells. Decreased incorporation was not caused by detachment of the target T24 cells from the culture wells. The degree of cytostasis was dependent on the E/T ratio, with a 70%-80% inhibition usually reached at the E/T ratio of 200:1. A wide variety of target cells was also shown to be sensitive to differentiated HL60 cell-mediated cytostasis.