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Additive Cytotoxicity of 5-Fluorouracil and -Radiation on Diploid Cell Strains¹

( Pasadena Foundation for Medical Research, Pasadena, California)

An attempt was made to quantitate the effects of -radiation, 5-fluorouracil (5-FU), and the combination of the 2 on established mammalian cell lines and euploid cell strains maintained in tissue culture.

Preliminary experiments suggested that treatment of cell lines with 100 µg/ml 5-FU for a 2-hr period produced a cytotoxic effect on the total populations, which masked the effect of combined therapy. Treatment of diploid cell strains of rabbit endothelium with 5–25 µg/ml 5-FU for 12 hr, followed by exposure of the cells to 400 r -radiation from a cobalt-60 source resulted in a population depletion equivalent to the calculated summation of each treatment alone. Therefore, it was concluded that 5-FU and -radiation, in combination, acted additively rather than synergistically. Although a heteroploid cell line showed a response analogous to the diploid cell strains, the importance of the latter as a test object is discussed.

¹ Aided in part by grant No. T-249B from the American Cancer Society, administered by C. M. Pomerat.

² Public Health Service Trainee Fellowship on USPHS grant T5 GM-3-07. Present address: Department of Ophthalmology, Washington University, St. Louis, Missouri.

Received 6/ 4/64. Revised 2/ 3/65.