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Studies on the Effect of 5-Iododeoxyuridine and p-Fluorophenylalanine on Polyoma Virus Formation in Vitro^*

( Section of Virology and Electron Microscopy, University of Texas M. D. Anderson Hospital and Tumor Institute; and Department of Microbiology, Baylor University College of Medicine, Texas Medical Center, Houston, Texas)

The formation of infectious polyoma virus in polyoma-infected mouse embryo cells grown in vitro is inhibited by 2.82 x 10^-5 M 5-iododeoxyuridine (10 µg IUDR/ml) when added to the tissue culture medium between 4 hours and 15–22 hours after virus infection.

The addition of 10 µg of IUDR at progressively later intervals of time up to 40 hours after infection results in the formation of correspondingly greater yields of infectious virus. No inhibition of infectious virus formation has been observed following addition of IUDR later than 32–40 hours after infection.

Exposure of polyoma-infected mouse embryo cell cultures to p-fluorophenylalanine (200 µg FPA/ml) from 4 to 15 hours after infection delays virus maturation by 19 hours, and at 106 hours after infection the virus yields of the infected cultures treated with FPA and infected control cultures are equal. These results suggest that a virus-associated protein synthesis occurs during the eclipse period of polyoma virus formation.

As determined by fluorescent antibody staining, synthesis of polyoma virus antigen is inhibited by 10 µg IUDR/ml in 69 per cent of the infected cells and by 20 µg IUDR/ml in 82 per cent of the infected cells, compared with the number of untreated infected cells showing polyoma virus antigen synthesis.

Uninfected mouse embryo cells exposed to 10 µg IUDR/ml of medium for 48 hours show inhibition of cell division which is not reversible with thymidine. Such cells following infection with polyoma virus produce normal or greater than normal amounts of infectious polyoma virus than do control infected cells. IUDR appears therefore to inhibit the formation of polyoma virus by directly interfering with virus initiated events and not by its effect on normal cellular processes.

The cell death of polyoma-infected mouse embryo cells is not prevented by IUDR in concentrations of 10–100 µg/ml of medium.

^* Supported in part by American Cancer Society Grants E-94-E and E-94-F, and by a U. S. Public Health Service Research Grant No. Ca-4140-06 from the National Cancer Institute.

Received 3/18/64.