Differential sensitivity to (dl)-5-methyltetrahydrofolate of normal CFU-GM and HL-60 cells.

We studied the effect of (dl)-5-methyltetrahydrofolate on clonogenic growth of HL-60 cells in comparison with human normal CFU-GM. Seven normal bone marrow samples were tested for CFU-GM assay with or without (dl)-mTHF at concentrations ranging from 1.25 X 10(-4) to 5 X 10(-4) M. (dl)-mTHF only slightly affected CFU-GM formation, while, at the same concentrations, it showed a dose related inhibition of HL-60 colony formation, up to a complete arrest of growth at the doses of 5 X 10(-4) and 1 X 10(-3) M. The same impairment of proliferation was observed in liquid culture. These results are in keeping with reported observations, describing a different membrane system mediating "folate" transport in normal and leukemic cells.