Inhibition of Differentiation and Proliferation of Colony-Stimulating Factor-Induced Clonal Growth of Normal Human Marrow Cells In Vitro by Retinoic Acid

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Abstract
Necessary for growth and differentiation in many normal tissues and capable of inducing differentiation in human promyelocytic cell lines, retinoids were the subject of this study. Specifically, effects of 13-cis-retinoic acid and 13-trans-retinoic acid on the growth of normal human bone marrow cells in a soft-agar system were studied. Both short-term incubation and continuous exposure to retinoic acid caused a decreased number of granulocyte colonies and an increased clusterto- colony ratio. This effect was concentration-dependent. Examination of specimens stained with Wright-Giemsa or nitro blue tetrazolium stains showed a progressive increase in the percentage of immature granulocytic precursors with increasing concentrations of retinoic acid. No effect of retinoic acid was seen on a number of human tumor cell lines. Retinoic acid blocked both differentiation and proliferation and appeared to do so by specific, noncytotoxic mechanisms in normal human bone marrow cells.