Differential Effect of GM-CSF on the Intracellular Ara-C Metabolism in Normal Bone Marrow Mononuclear Cells and Acute Myeloid Leukemia (AML) Blasts

Abstract

This study examines the effect of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) on the intracellular metabolism of cytosine arabinoside (ara-C) in mononuclear bone marrow cells (NBMMC) from 8 healthy volunteers and leukemic blasts from 50 patients with acute myeloid leukemia (AML). Pretreatment with rh GM-CSF (100 U/ml) for 48 hrs significantly enhanced DNA synthesis: Median 3H-TdR uptake into the DNA increased from 2.15 to 3.68 pmol/105 cells in AML blasts and from 3.09 to 7.4 pmol/105 cells in NBMMC (p<0.05). 14 AML cases did not respond to GM-CSF. Median ara-C mediated inhibition of DNA synthesis was significantly higher in AML blasts as compared to NBMMC (76.5 vs 55.0% and 99.0 vs 96.0% at 0.05 and 5.0 μM ara-C, respectively, p<0.01). Similarly, intracellular ara-CTP levels were higher in AML blasts as compared to NBMMC (46.5 vs 18.7,167.8 vs 48.0 and 59.5 ng/107 cells at 1, 10, 100 μM extracellular ara-C, respectively, p< 0.01). Overall DNA polymerase and DNA polymerase α activity increased from median 80.9 to 94.1 and from 3.1 to 5.7 pmol/min × mg in AML blasts as compared to median 96.7 to 189.8 and 1.2 to 2.2 pmol/min × mg in NBMMC (p < 0.05). Median deoxycytidine and thymidine kinase activity were only slightly increased in the presence of GM-CSF. The GM-CSF induced increase of the 3H-ara-C incorporation into the DNA was slightly higher in GM-CSF responding AML blasts as compared to NBMMC (median 2.0 vs 1.7 fold at 0.06 μM ara-C, p < 0.05). The differential effect of GM-CSF on the metabolism of ara-C in normal versus leukemic cells may cause a selective increase in the antileukemic cytotoxicity of ara-C in the presence of GM-CSF.