Studies on the disposition of actinomycin D-3H in virus-infected and tumor-bearing mice.

Actinomycin D'-H (80,000 cpm//ug) was administered to tumor-bearing mice and the disposition of the drug determined. Radioactivity was found in all peripheral tissues examined (in cluding tumor), hut none was found in the brain. No significant metabolism of actinomvein was observed, although binding of the drug altered its extraction characteristics. Differential centrifugation of liver homogenate showed that the drug was con centrated in the nuclear fraction. Treatment with actinomycin significantly lowered the virus titer in mice infected with Rauscher virus. No significant binding of actinomycin D-3H to the virus that was present was obtained after concentration of the plasma virus particles by a density gradient separation.