An Electron Microscopical Study of Changes Produced by Daunomycin on HeLa Cells

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Abstract
Daunomycin, a new antitumor antibiotic, was added in 1 μg/ml concentration, to culture media in which HeLa cells were proliferating. Cells were examined with the electron microscope at different times following the treatment. Specific nucleolar alterations were observed. Within 2 hours Daunomycin induced a marked fragmentation of nucleolonema and the detachment of some nucleolar RNA granules. After 4 hours of treatment the nucleolus was decreased in size and had a spherical shape. The successive observations up to 48 hours, demonstrated progressive nucleolar exhaustion while the cytoplasm remained unchanged. The alterations of the nucleolar structures included loss of RNA granules, and appearance of small clear vacuolated areas. These findings are discussed in the light of biochemical evidences which indicate that Daunomycin inhibits RNA synthesis.