Interaction of vitamin D derivatives and granulocyte–macrophage colony-stimulating factor in leukaemic cell differentiation

Abstract

The ability of the physiologically active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) and two novel vitamin D analogues, EB1089 and KH1060 to induce the differentiation of the U937 and HL-60 leukaemic cell lines was evaluated, alone or in combination with granulocyte–macrophage colony-stimulating factor (GM-CSF). Studies revealed that following 96 h treatment, the vitamin D derivatives inhibited the proliferation, and induced the differentiation of U937 and HL-60 cells in a dose-dependent manner, as determined by cell counts and nitroblue tetrazolium (NBT) reduction assays, respectively. EB1089 and KH1060 were found to be more effective than 1,25(OH)₂D₃ in exhibiting their antiproliferative and differentiative effects. In contrast, induction of leukaemic cell differentiation with 1 ng/ml GM-CSF after 96 h was less effective when compared with the vitamin D derivatives used individually. Fluorescence activated cell scanning (FACS) analyses indicated that the vitamin D derivatives readily induced the expression of the monocyte-associated cell surface antigen, CD14, and also the β ₂-integrins, CD11b and CD18 in both cell lines after 48 h and 96 h treatment. The ability of EB1089 and KH1060 to induce these antigens was achieved with greater efficacy relative to the native hormone. When U937 and HL-60 cell cultures were cotreated for 48 h with the vitamin D compounds and GM-CSF and analysed by FACS, enhanced effects on CD14 and CD11b induction were observed compared to those of the compounds alone. These co-operative effects may occur as a consequence of molecular events which involve the transcription by vitamin D receptors (VDR) of genes required for the responsiveness of immature cells to factors such as GM-CSF, and place these and other related vitamin D analogues as potential therapeutic agents in the treatment of leukaemia.