Antiviral activity of sulfated polysaccharides against African swine fever virus.

The polyanionic substances lambda and kappa carrageenan, pentosan polysulfate, fucoidan, dextran sulfate and heparin were investigated for their inhibitory effect on the replication of African swine fever virus (ASFV) in vitro. Lambda carrageenan was the most efficacious with a selectivity index, as based on the ratio of the 50% cytotoxic concentration to the 50% antiviral effective concentration, of 120, followed by pentosan polysulfate with 30, kappa carrageenan 13.3 and fucoidan 10. Dextran sulfate and heparin were almost inactive. In general, the substances had low toxicity for Vero cells. The studies with radiolabeled ASF virions suggest that the sulfated polysaccharides inhibit virus adsorption. Inhibition of virus replication was found for all the polysaccharides only when the substances were present during virus adsorption, with the exception of lambda and kappa carrageenan, which were also inhibitory when added immediately after the adsorption period.

Inhibition of African swine fever virus DNA synthesis by (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine.

The acyclic nucleotide analogue (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine [(S)-HPMPA] is a potent and selective inhibitor of African swine fever virus (ASFV) replication. Using the DNA-DNA hybridization technique with plasmid pRPEL-2 as probe, we have shown that (S)-HPMPA exerts a specific, dose-dependent, inhibitory effect on viral DNA synthesis. Also, (S)-HPMPA inhibits the production of late viral proteins, especially IP-73, in ASFV-infected MS and Vero cells. When evaluated under the same experimental conditions, phosphonoacetic acid (PAA) also caused an inhibition of viral DNA and late viral protein synthesis but only so at a concentration which was 10- to 20-fold higher than that required for (S)-HPMPA.

A model virus-cell system to study the persistence of African swine fever virus.

The persistence of African swine fever virus (ASFV) on Vero cells was induced by using 5-iodo-2'-deoxyuridine (IDU). After the persistence was established, several cycles of decreasing virus production were observed with intervals in which no virus could be detected. These latency-like periods could last from 15 to 25 days. After three and a half months the cells appeared to be "cured" and no virus was detected during almost three years. These "cured" cells (Vero-L) were more resistant to superinfection with the wild type virus, and when infected they always established persistence without drug addition characterized by a continuous virus production. The persistent virus isolated at passage 23rd from ASFV persistently infected Vero-L cells was different from wild type in a) the morphology of the plaque, b) its ability to replicate in Vero-L cells, and c) greater resistance to be inhibited by IDU in normal Vero cells (Vero-N). These results suggest that both, Vero cells and ASFV have changed during persistent infection.

Phosphonylmethoxyalkylpurines and -pyrimidines as inhibitors of African swine fever virus replication in vitro.

Several phosphonylmethoxyalkylpurine and -pyrimidine derivatives related to (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine [(S)-HPMPA] and 9-(2-phosphonylmethoxyethyl)adenine (PMEA) were evaluated as inhibitors of African swine fever virus (ASFV) replication in Vero cells. (S)-HPMPA has previously been shown to inhibit ASFV replication at a minimum inhibitory concentration (MIC) of 0.01 microgram/ml with a selectivity index of 15000. Of the new compounds tested, the following emerged as the most potent and selective inhibitors of ASFV replication: the cyclic phosphonate of (S)-HPMPA [(S)-cHPMPA] with an MIC of 0.2 microgram/ml and a selectivity index of 2500, the 2,6-diaminopurine analogue of (S)-HPMPA [(S)-HPMPDAP] with an MIC of 0.5 microgram/ml and a selectivity index of 1400, and the cytosine [(S)-HPMPC] and guanine [(RS)-HPMPG] analogues with an MIC of 1 microgram/ml and a selectivity index of 600-700.