EFFECTS OF VESNARINONE ON THE BONE-MARROW STROMAL CELL-DEPENDENT PROLIFERATION AND DIFFERENTIATION OF HL60 CELLS IN-VITRO

It has been reported that vesnarinone, a new inotropic agent used in t he treatment of cardiac failure, causes agranulocytosis as a side effe ct. To study the mechanisms by which this complication occurs, vesnari none was introduced into a coculture system of HL60 and bone marrow (B M) stromal cells, in which HL60 cells were able to differentiate into mature granulocytes with no inducible exogenous factors added to the c ulture. When HL60 cells were cocultured with the human BM-derived stro mal cell line LP101, HL60 cells were induced to differentiate into mat ure granulocytes, and expression of the mature granulocyte-macrophage surface antigen, CD11b was increased. Conditioned medium (CM) obtained from LP101 cells also showed the capacity to induce the maturation of HL60 cells, in a dose- and time-dependent manner. The differentiation of HL60 cells induced by CM was also determined by morphological anal ysis, expression of myeloperoxidase, and a nitroblue tetrazolium (NET) reduction test. When HL60 cells were cocultured with LP101 ill the pr esence of vesnarinone, the CD11b expression was greatly suppressed. CM obtained from vesnarinone-treated LP101 (ves-CM) lost the capacity to induce the differentiation of HL60 cells, at a concentration of 1 mu g/mL of vesnarinone. Vesnarinone itself did not affect the proliferati on of HL60 cells. Furthermore, the addition of vesnarinone or ves-CM t o HL60 cultures incubated with CM did not alter the induction of CD11b expression, suggesting that vesnarinone has no effect on HL60 cells, but that it inhibits stromal cells from producing soluble factor(s) re quired for the differentiation of HL60 cells to mature granulocytes. A ll these findings indicate that vesnarinone causes the hematopoietic d isorder agranulocytosis, via impairment of stromal function.