In vitro effect of r-verapamil on acute myelogenous leukemia blast cells: studies of cytokine secretion and cytokine-dependent blast proliferation.

The in vitro effect of the dextroisomer r-verapamil on blast cells derived from patients with acute myelogenous leukemia (AML) was studied. R-verapamil caused a dose-dependent inhibition of AML blast proliferation in the presence of stem-cell factor, leukemia inhibitory factor, interleukin 4, interleukin 6, and interleukin 10 when these cytokines were tested both alone and in different combinations. R-verapamil also inhibited the growth of clonogenic AML blast cells. The antiproliferative effect was not specific for AML blast cells, because r-verapamil also inhibited cytokine-dependent proliferation of blast cells derived from patients with acute lymphoblastic leukemia. The inhibitory effects of r-verapamil and anti-IL1 serum were additive, suggesting that the antiproliferative effect of r-verapamil does not depend solely on inhibition of IL1-mediated effects. Although r-verapamil inhibited spontaneous AML blast proliferation, for a majority of patients it caused only minimal, if any, inhibition of spontaneous cytokine secretion (IL1 alpha, IL1 beta, TNF alpha, IL6) by AML blast cells. Thus, although inhibition of IL1 effects may contribute in certain patients to the antiproliferative effect of r-verapamil, mechanisms other than IL1 inhibition seem to be more important in mediating the effects of r-verapamil.