Antiviral xanthate causes conformational changes in simian virus 40 DNA and chromatin

Xanthates possess a wide antiviral and antitumoral spectrum. Treatment of simian virus 40 (SV40)-infected cells with tricyclo-decan-9-yl-xanthate (D609) reduces transcription and replication. Concomitantly, we observed condensation of the SV40 minichromosomes after addition of D609 to the tissue culture. The structural change of the viral chromatin was measured as an increase in sedimentation behavior from 95-75 to 180-150 Svedberg units. A modulation of the DNA structure was detected in parallel, resulting in an increase in the topological linking number of the SV40 DNA by two superhelical turns above the average superhelicity in the infected cell. Therefore, enzyme activities responsible for topological changes (topoisomerases) were examined and an inhibition of topoisomerase I by more than 1,000-fold was detected.