EFFECT OF A VITAMIN-D-3 ANALOG, EB1089, ON HEMATOPOIETIC STEM-CELLS FROM NORMAL AND MYELOID LEUKEMIC BLASTS

The seco-steroid 1,25 dihydroxyvitamin D-3 (1,25(OH)(2)D-3) induces di fferentiation and inhibits clonal proliferation of HL-60 cells. We ana lyzed the effect of a novel vitamin D-3 analog, EB1089, on normal myel oid and leukemic cells as well as CD34(+) cells. EB1089 showed an extr aordinary inhibition of clonal growth of HL-60 cells (ED(50)=5x10(-11) M) and AML blast cells (ED(50)=9x10(-10) M) compared to 1,25(OH)(2)D- 3 without suppression of growth of normal human bone marrow CFU-GM. Th e CD34(+) cells from acute myeloid leukemia (AML) blasts were inhibite d in a dose-dependent fashion by 1,25(OH)(2)D-3 with an ED(50) of 1.2x 10(-9) M; and even more strikingly, 10(-10) M of EB1089 inhibited all clonal growth of human CD34(+) leukemic colony-forming cells. In contr ast, both EB1089 and 1,25(OH)(2)D-3 (10(-8) M) showed little or only m ild inhibition of CD34(+) clongenic hematopoietic cells from normal hu man peripheral blood (PB); and in liquid culture, EB1089 stimulated th e proliferation of normal human CD34(+) cells about 2.5 times as compa red to control cultures. In order to evaluate the potential use of EB1 089 for purging leukemic cells from normal CD34(+) progenitor cells ti er BE stem cell transplantation (PBSCT), normal human PB mononuclear c ells (PBMNC) were contaminated with HL-60 cells, and then CD34(+) cell s purified and treated with EB1089. We found that CD34(+) purification and EB1089 purging was able to eliminate approximately 100% of HL-60 leukemic cells with no toxicity to normal CD34(+) hematopoietic progen itor cells. These data suggested that purification of CD34(+) cells an d ex vivo treatment with EB1089 might provide an effective therapeutic approach for PBSCT.