THE ROLE OF VITAMIN-D DERIVATIVES AND RETINOIDS IN THE DIFFERENTIATION OF HUMAN LEUKEMIA-CELLS

The capabilities of 1 alpha, 25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3), and two novel vitamin D analogues, EB1089 and KH1060, to induce the d ifferentiation of two established leukaemia cell lines, U937 and HL-60 , were assessed alone or in combination with the retinoid compounds, 9 -cis retinoic acid (9-cis RA) and all-trans retinoic acid (ATRA). The vitamin D derivatives acted to increase the differentiation of U937 an d HL-60 cell cultures in a dose-dependent manner, as determined by nit roblue tetrazolium (NET) reduction, with EB1089 and KH1060 being more effective than the native hormone. As an additional index of leukaemic cell differentiation, induction of expression of the phenotypic cell surface antigen, CD14, and the beta(2)-integrins, CD11b and CD18 by th e vitamin D and retinoid compounds were monitored using fluorescence a ctivated cell sorting (FAGS) analyses. Following 96-hr treatment of U9 37 and HL-60 cells with 5 X 10(-10) M of the vitamin D derivatives, a striking increase in CD14 antigen expression was apparent, indicating the promotion by these compounds of a monocyte/macrophage lineage of c ells. CD11b and CD18 antigen expression were also raised above control levels. In contrast, both retinoid compounds used at the higher conce ntration of 1 X 10(-8) M were not effective inducers of CD14 antigen e xpression. However, CD11b and CD18 were both readily increased in U937 and HL-60 cell cultures. Treatment of U937 cell cultures with the vit amin D compounds and the retinoids resulted in cooperative effects on induction of differentiation, with correlation by both NET reduction a nd FACS analyses of CD14 antigen expression. The presence of 9-cis RA or ATRA appeared to contribute to the further increase of CD14 in thes e cells. HL-60 cell cotreatment with these compounds also displayed en hanced cooperative effects in phagocytic function by NBT reduction. Ho wever, analysis of CD14 revealed a dramatic diminution in HL-60 cells treated with the combinations of the vitamin D derivatives and the ret inoids. Assessment of HL-60 cell morphology treated with these combina tions demonstrated the presence of a mixed population of monocytes and granulocytes. CD11b and CD18 antigen expression was also enhanced in both cell lines with cotreatment. The ability of EB1089 and KH1060 to induce leukaemic cell differentiation may provide an additional option for therapeutic use alone or together with other differentiation agen ts such as 9-cis RA or ATRA. (C) 1997 Elsevier Science Inc.