A POSSIBLE MECHANISM OF ELLIPTICINE-INDUCED HEMOLYSIS

¹ Laboratory of Toxicology, National Cancer Institute, Bethesda, Maryland

Ellipticine (E) [5,11-dimethyl-6H-pyrido-(4,3-b)-carbazole, NSC-71795] is an antineoplastic agent which is active against L1210 lymphocytic leukemia in mice. Preclinical toxicologic studies demonstrated hemolysis in dogs and monkeys following intravenous administration of 1.5 mg/kg. This finding prompted this investigation of the mechanism of hemolysis and a study of the various factors that might ameliorate this effect. Initial experiments demonstrated that human red blood cells were completely hemolyzed at an E concentration of 10^-3 M, while a concentration of 10^-4 M stabilized red blood cells against 150 mOsM NaCl. The extent of hemolysis correlated well with the surface activities, lipophilic properties and cellular uptake of E and some of its derivatives (7,10-dimethylellipticine, isoellipticine, 9-methoxyellipticine and 11-demethylellipticine). The greatest hemolysis occurred with 7,10-dimethylellipticine and the least with 11-demethylellipticine. The cellular uptake of E and its derivatives was linear over a wide concentration range and was not temperature-dependent. Hemolysis could be blocked by citrate, sodium ethylenediamine tetraacetate, oxytetracycline and [(±)-1,2-bis(3,5-dioxopiperazin-1-y1)propane]. The inhibition of E uptake by citrate appears to be a noncompetitive process and has a K_i of 1.9 x 10^-3 M. These data suggest that Ca⁺⁺ might be involved in the hemolytic process and in the cellular uptake of E. The intravenous administration of ellipticine to rhesus monkey caused severe hemolysis which could be prevented by simultaneous injection of citrate.