OBJECTIVETo explore the effect of methotrexate on acute monoblastic leukemia cells, and the potential role of low-dose methotrexate in the treatment of monoblastic leukemia.

METHODSBy using U937 cell line as a model, the induced differentiation of MTX or GM-CSF or their combination was detected by NBT reduction test, morphological observation and CD(14) expression. TRAP-ELISA was used for measuring telomerase activity.

RESULTSAfter incubation with 20 nmol/L methotrexate for 24, 48, 72 and 96 hours, the size of the U937 cells increased, the nuclear/plasma ratio gradually decreased, NBT reductive test became positive, and CD(14) positive cells increased from 3% to 20% after 72 hours incubation, indicating partial differentiation. Treatment of U937 cells with 100 U/ml GM-CSF alone failed to induce differentiation. However, GM-CSF combined with low-dose methotrexate resulted in 63% of differentiated cells after 72 hours incubation, and telomerase activity of the U937 cells decreased from 2.11 (before treatment) to 1.48, 0.77, 0.24 (after treatment for 24, 48, 72 hrs respectively). The extent of the decrease of telomerase activity was in proportion with the degree of differentiation.

CONCLUSIONMonoblastic leukemia might be treated with low-dose methotrexate plus GM-CSF as a differentiation induction regimen.