Monocytic differentiation induction of HL-60 cells by MC 903, a novel vitamin D analogue.

1.25 (OH)2D3 is a potent inducer of differentiation of leukaemic cells into a monocytic direction. However, therapeutic application is difficult because of the development of hypercalcaemia. We examined a novel vitamin D analogue, MC 903, which is at least 100 times less effective on calcium metabolism in rats than 1.25 (OH)2D3. Using the HL-60 cell line, differentiation was measured with a comprehensive panel of qualitative and quantitative parameters. Development of monocytic cells was shown morphologically, immunophenotypically and functionally by increased capability of reducing NBT (vs cultures without MC 903, p less than 0.0001) and by qualitatively and quantitatively increased non-specific esterase activity. Furthermore, a concomitant decreased activity of myeloperoxidase and lactate dehydrogenase was noticed. In conclusion, MC 903 is a potent inducer of monocytic differentiation, comparable with 1.25 (OH)2D3 and will therefore be an interesting and potential therapeutic agent for studies in human acute leukaemia.