Using light and electron microscopic procedures, the actions of 4-nitroquinoline 1-oxide, Actinomycin-B, and quinoxaline antibiotics (Quinomycin-A and Triostin-C) were examined on cultured JTC-13 cells after 4 hours of incubation with three dose levels ranging from 0.1 fo 10μg/ml of each chemical.
In the presence of 4-nitroquinoline 1-oxide, cytoplasmic alterations, such as vesicles in mitochondria, multivesicular bodies, and lvsosomes. appeared with a dose of 0.1μg/ml and activity of succinate dehydrogenase in cytoplasm was markedly decreased.
Intranuclear inclusion bodies and rearraneement of nucleolar components were demonstrated at concentrations more than 1μg/ml of the drug. Accompanied with these changes, there occurred loss of ribonucleoprotein granules in cytoplasm.
In contact with Actinomycin-B, dispersed nucleoli and chromatin aggregation near nuclear membranes were found by Acridine Orange staining, with a dose of 0.1μg/ml. Ultrastructural changes consisted of coalescence of nucleolonema, aggregates of granular component, and decrease of amorphous materials in nucleoli, with little variances of cytoplasm. Condensed granules were separated completely from the necleolonema within a nucleus on the exposure to 10μg/ml of the antibiotic. In comparison of the action between 4-nitroquinoline 1-oxide and Actinomycin-B, it was found that the former acted indirectly on the nucleic acid synthesis through disturbance of cytoplasmic metabolism, and the actinomycins directly.
When quinoxaline antibiotics were administered to the cultured cells, the same nucleolar changes without alterations of cytoplasmic organellae, as shown by Actinomycin-B, were observed.
The activity of Quinomycin-A was similar to that of Actinomycin-B, but that of Triostin-C was one-tenth of that of Actinomycin-B. Thus, this is the first evidence suggesting the similarity of ultrastructural effects between actinomycin and quinoxaline antibiotics at the cultured animal cell level.