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Influence of Toyocamycin on Avian Leukemia Myeloblasts: Cell Growth, Ultrastructure, RNA Synthesis, and Elaboration of BAI Strain A Virus¹

R. A. Bonar, J. F. Chabot², A. J. Langlois, L. Sverak, L. Vepek and J. W. Beard

Department of Surgery, Duke University Medical Center, Durham, North Carolina 27706

Myeloblasts from chickens with BAI strain A virus leukemia were cultured in vitro and treated with the antibiotic toyocamycin. Cells exposed to 0.1 to 8 µg toyocamycin/ml were examined for effects of the drug on myeloblast growth, the occurrence of nonviable cells, elaboration of virus particles, ultrastructure, and RNA synthesis. In cultures containing about 10⁸ myeloblasts/ml in a medium with 50% chicken serum, cell growth was inhibited with an initial rate of decline of viable cell number approximately proportional to drug concentration. Survival time of the cultures, however, was similar for all concentrations above 1 µg/ml. Virus elaboration by viable cells was depressed in the same drug concentration range as that required for cell growth inhibition and inhibition of cell RNA synthesis. There was a marked suppression of uridine incorporation into 28 S RNA, a lesser effect on 18 S RNA, little or no effect on the 4 S fraction, and a very small accumulation of RNA's in the 30 to 45 S range. This pattern of RNA synthesis inhibition resembled closely that with toyocamycin treatment of uninfected chick embryo cells and of the cells infected with the MC29 avian tumor virus but differed substantially from that of mammalian cells as described in an earlier report. Marked associated ultrastructural changes consisted only of nucleolar alteration with dispersion of constituents but without notable rearrangement or quantitative change in the componenets. This was in sharp contrast to nucleolar response to treatment of avian leukemia myeloblasts or other cells with actinomycin D, but the changes resembled those in other cells induced by treatment with adenosine or ethionine.

¹ This work was aided by USPHS Grant C-4572, by the Annie Mabel Sherris Memorial Grant for Cancer Research from the American Cancer Society, Inc., by National Defense Education Act Title IV Fellowship 67-08530.0, by American Cancer Society Institutional Research Grant IN-611, and by the Dorothy Beard Research Fund.

² This paper is part of studies undertaken in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Zoology in the Graduate School of Arts and Sciences of Duke University.

Received 5/26/69. Accepted 8/19/69.