Recombinant human GM-CSF significantly enhances the cytostatic activity of cell cycle specific anti-leukaemic drugs in HL-60 human myeloid leukaemia clonogenic cells in a capillary clonogenic micro-assay.

The effect of recombinant human GM-CSF on the cytostatic activity of the two cell cycle specific antileukaemic drugs, hydroxyurea and cytarabine, in HL-60 human myeloid leukaemic cells was studied in an agar capillary clonogenic micro assay. The ED90 concentrations which are the concentrations of hydroxyurea and cytarabine inducing a 90% maximum inhibition of colony formation and colony growth on day 7 in HL-60 cells were calculated from the logarithmic regression analysis of each dose response curve using the cricket graph version 1.3 program on an Apple Macintosh computer. Recombinant human GM-CSF significantly enhanced the cytostatic effect of hydroxyurea and cytarabine, and consequently reduced their ED90 concentrations. The present in vitro results provide a rationale for investigating the efficacy of combined recombinant human GM-CSF and hydroxyurea or cytarabine treatment in myeloid leukaemic patients.