D‐verapamil and L‐verapamil are equally effective in increasing vincristine accumulation in leukemic cells in vitro

Abstract

Leukemic cells isolated from peripheral blood from 6 patients with chronic lymphocytic leukemia, immunocytoma and prolymphocytic leukemia were incubated with vincristine (10nM) with and without racemic verapamil and its L‐ and D‐ isomers (6.6 μM). Verapamil increased vincristine accumulation in all cells, the increase varying between 100 and 700%. Racemic verapamil and the L‐ and D‐isomer increased cellular vincristine accumulation to the same extent. The verapamil effect could not be reversed by increasing the calcium concentration in the incubation medium (final concentration 2.5–5.0mm). The results indicate that the mechanism behind the effect of verapamil on cellular accumulation of vincristine does not depend upon changes in calcium transport.