Enhanced chemosensitivity of clonogenic blasts from patients with acute myeloid leukemia by G-CSF, IL-3 or GM-CSF stimulation.

Exposure to hemopoietic growth factors (HGFs) induces proliferation of clonogenic acute myeloid leukemia (AML) cells. Recruitment of quiescent, clonogenic blasts may improve the cytotoxic effects of cell-cycle-specific drugs like cytosine arabinoside (Ara-C). Because other studies have shown heterogeneous effects of HGF and Ara-C incubation, we analyzed the individual effects of granulocyte colony-stimulating factor (G-CSF), interleukin 3 (IL-3), and granulocyte-macrophage colony-stimulating factor (GM-CSF) combined with an S-phase and non-phase specific cytostatic agent on clonogenic blasts of 14 newly diagnosed AML patients under standardized, serum-free conditions. AML cells were incubated for 24 hours with titrated concentrations of Ara-C (0.01, 0.1, 1 microM) or mafosfamide (0, 1.0, 10, or 20 micrograms/ml) following preincubation for 48 hours with or without G-CSF, IL-3, or GM-CSF, starting at 24 hours prior to chemotherapy exposure. AML colony-forming cells (AML-CFU) were then determined in semi-solid culture in the presence of the same growth factor. The results showed significantly enhanced cytotoxicity of Ara-C to AML-CFU following stimulation by G-CSF (p < 0.002 at 0.01 microM, p < 0.002 at 0.1 microM, and p < 0.01 at 1 microM Ara-C), IL-3 (p < 0.002 at 0.01 microM, p = 0.001 at 0.1 microM, p < 0.01 at 1 microM, Ara-C), and GM-CSF (p = 0.01 at 0.01 microM, p < 0.01 at 0.1 microM, and p < 0.002 at 1 microM Ara-C). A moderate but significant enhancement of mafosfamide cytotoxicity by HGF was also observed (p < 0.05 at 1.0 microgram/ml mafosfamide by IL-3 and GM-CSF and p < 0.05 at 10 micrograms/ml mafosfamide by GM-CSF). Ara-C cytotoxicity to normal bone marrow progenitors was enhanced significantly only by G-CSF (p = 0.02 at 0.01 microM, p = 0.01 at 0.1 microM and p < 0.01 at 1 microM Ara-C), and by GM-CSF at 0.1 microM Ara-C (p = 0.045). However, the effect of HGF stimulation as studied by bromodeoxyuridine (BrdU) incorporation during the first or second 24 hours of HGF stimulation did not explain the difference between poor and good HGF enhanced Ara-C cytotoxicity, indicating that other cellular changes than cell-cycle activation as the consequence of growth factor stimulation are responsible for enhanced cytotoxicity. Our findings indicate that combining HGFs, and especially IL-3, with chemotherapy may be useful in the AML treatment.