Inhibition of lymphocyte transformation by mepacrine and chloroquine

Mepacrine inhibited uptake and the incorporation of leucine, thymidine and uridine into acid-insoluble material in human lymphocytes stimulated by phytohaemagglutinin (PHA) in vitro. The IC50 for each uptake was of the order of 2 microM. Mepacrine was inhibitory if applied at any time up to 48 h after PHA. The inhibition differed from that produced by colchicine and prostaglandin E1. The dose-response curve was steep, nearly all incorporation being inhibited by 2 x IC50. Chloroquine also had a steep dose-response curve, was about one-fifth as potent as mepacrine and was maximally effective in the first 6 h after PHA.