Inhibitory effect of N-Phenyl-N'-3-hydroxyphenylthiourea (PTU-23) on the reproduction of encephalomyocarditis virus in Krebs-II cells

PTU-23, an effective in vivo wide-range enterovirus inhibitor, suppresses the reproduction of encephalomyocarditis (EMC) virus in Krebs-II ascites carcinoma cells at concentrations of 20–50 μg/ml, not affecting the cellular synthetic processes. The virus-specific RNA synthesis is distinctly inhibited. The studies on the kinetics of this effect point to its leading role in the inhibitory action the compound exerts on the production of infectious virions. The sedimentation profile in sucrose density gradient of the viral RNA isolated from PTU-23-treated cells by phenol extraction shows a clear inhibition of the synthesis of the single-stranded (ss) 37S RNA and to a lesser extent of the double-stranded (ds, RF) 20S RNA. The effect of the inhibitor on the RNA-dependent RNA polymerase in a cell-free RNA-synthesizing system has been studied, using as an enzyme preparation the 40 000 g fraction of a nuclear-free extract from infected Krebs-II cells, containing the enzyme bound to the endogenous RNA template. It is established that the compound does not affect the synthesis of the enzyme which could be probably explained by the incomplete (45–70%) inhibition of the viral RNA synthesis, its translatory function remaining unperturbed. The observed insignificant inhibition (20–26%) of the enzyme activity during the application of the inhibitor to the RNA-synthesizing reaction mixture cannot explain its effect on the viral RNA synthesis. An interaction of PTU-23 with another virus-specific protein component of the replication complex is suggested. N-Phenyl-N'-3-hydroxyphenylthioharnstoff (PTU-23), ein Enterovirus-Inhibitor mit breitem Wirkungsspektrum, hemmt die Reproduktion von Encephalomyocarditis (EMC)-Viren in Krebs-II Ascites-Karzinomzellen in Konzentrationen von 20–50 μg/ml. Der zelluläre Syntheseprozeß wird dabei nicht beeinflußt, sondern die virusspezifische RNS-Synthese stark gehemmt. Die Untersuchung der Kinetik dieses Prozesses weist auf die Rolle der Hemmwirkung des Virostaticums bei der Bildung infektiöser Viria. Das Sedimentations-profil im Sucrose-Dichtegradienten der mit Phenol aus PTU-23 behandelten Zellen isolierten Virus-RNS zeigt eine deutliche Hemmung der Synthese von einsträngiger (ss) 37S RNS und zu einem geringeren Grade der doppelstängigen (ds, RF) 20S RNS. Die Untersuchungen erstreckten sich auch auf die Wirkung des Inhibitors auf die RNS-abhängige RNS-Polymerase in einem zellfreien RNS-synthetisierenden System, wobei als Enzympräparation die