Molecular Pharmacology, Vol 11, 883-888, Copyright © 1975 by the American Society for Pharmacology and Experimental Therapeutics

The Rifamycin Derivative AF/013 Is Cytolytic

¹ Division of Membrane Biology and Biochemistry, Institute of Experimental Pathology, German Cancer Research Center, D-69 Heidelberg, Federal Republic of Germany

When intact cells (HeLa S-3, mouse 3T3 flbroblasts, hen erythrocytes) are incubated with the rifamycin SV derivative AF/013, which is widely used as a potent inhibitor of mammalian DNA-dependent RNA polymerases, a rapid and extensive disintegration of the plasma membrane takes place. This cell disruption results, for example, in hemolysis of the erythrocytes at concentrations above 50 µg/ml, in the release of cytoplasmic components, including ribosomes, and in dramatic ultrastructural changes in the HeLa and mouse 3T3 cells. In HeLa cells incubated for 30 min in 100 µ/ml of the drug, about 70% of the RNA, 44% of the protein, and 26% of the phospholipids leak out into the medium. The permeability of the plasma membrane is markedly increased, even at relatively low AF/013 concentrations. In the presence of 20 µg/ml of the drug, for example, 70% of the trichloracetic acid-soluble radioactivity and 10% of the trichloracetic acid-precipitable RNA are released from [³H]uridine-labeled HeLa cells. The membranolytic action of AF/013 is higher than that of the nonionic surfactant Triton X-100. This high toxicity indicates that AF/013 cannot be used as a specific inhibitor of RNA polymerases in vivo.

Note:
ACKNOWLEDGMENTS I thank Mrs. Erika Schmid, Miss Stephanie Winter, and Miss Marianne Winter for excellent technical assistance; Mr. W. Rubik (Institute of Biochemistry, German Cancer Research Center, Heidelberg), for the mass spectroscopic analysis; as well as Drs. W. W. Franke and H. Zentgraf, for helpful discussions.