The retinoic acid analog CBS-211A potentiates the 1α,25-dihydroxyvitamin D3-induced differentiation of U937 cells

We report the effect of CBS-211A, a synthetic retinoid analog, designed for topical eye administration, on the growth and differentiation of myelomonocytic cells. This compound was assayed alone or in combination with 1α,25-dihydroxyvitamin D3 (1α,25(OH)₂D₃), since we previously evidenced a synergism of retinoic acid (RA) and 1α,25(OH)₂D₃ in the induction of U937 cell differentiation. Unlike RA, CBS-211A neither affected the growth of myelomonocytic cells nor differentiated them. Nevertheless, when it was associated with 1α,25(OH)₂D₃, CBS-211A strongly potentiated the 1α,25(OH)₂D₃-induced inhibition of U937 cell proliferation and caused a dramatic increase in their differentiation toward monocytes/macrophages. The co-inducing effect of CBS-211A was restricted to U937 cells.Our data suggest that CBS-211A may have therapeutic implications in the treatment of certain kinds of myelomonocytic leukemia. CBS-211A also provides an interesting tool to understand the mechanisms involved in the differentiation of myelomonocytic cells.