Inhibition of Human Coronaviruses by Combinations of Host-Targeted and Direct-Acting Antivirals.

Antiviral compounds targeting cellular metabolism are part of the therapeutic arsenal to control the spread of virus infection, either as sole treatment or in combination with direct-acting antivirals (DAA) or vaccines. Here, we describe the effect of two of them, lauryl gallate (LG) and valproic acid (VPA) both exhibiting a wide antiviral spectrum, against infection by coronaviruses such as HCoV-229E, HCoV-OC43, and SARS-CoV-2. A consistent 2 to 4-log-decrease in virus yields was observed in the presence of each antiviral, with an average IC50 value of 1.6 µM for LG and 7.2 mM for VPA. Similar levels of inhibition were observed when adding the drug 1 h before adsorption, at the time of infection or 2 h after infection, supporting a postvirus entry mechanism of action. The specificity of the antiviral effect of LG against SARS-CoV-2, relative to other related compounds such as gallic acid (G) and epicatechin gallate (ECG), predicted to be better inhibitors according to in silico studies, was also demonstrated. The combined addition of LG, VPA, and remdesivir (RDV), a DAA with a proven effect against human coronaviruses, resulted in a robust synergistic effect between LG and VPA, and to a lesser extent between the other drug combinations. These findings reinforce the interest of these wide antiviral spectrum host-targeted compounds as a first line of defense against viral diseases or as a vaccine complement to minimize the gap in antibody-mediated protection evoked by vaccines, either in the case of SARS-CoV-2 or for other possible emerging viruses.

The African swine fever virus lectin EP153R modulates the surface membrane expression of MHC class I antigens.

We have modeled a 3D structure for the C-type lectin domain of the African swine fever virus protein EP153R, based on the structure of CD69, CD94 and Ly49A cell receptors, and this model predicts that a dimer of EP153R may establish an asymmetric interaction with one MHC-I molecule. A functional consequence of this interaction could be the modulation of MHC-I expression. By using both transfection and virus infection experiments, we demonstrate here that EP153R inhibits MHC-I membrane expression, most probably by impairing the exocytosis process, without affecting the synthesis or glycosylation of MHC antigens. Interestingly, the EP153-mediated control of MHC requires the intact configuration of the lectin domain of the viral protein, and specifically the R133 residue. Interference of EP153R gene expression during virus infection and studies using virus recombinants with the EP153R gene deleted further support the inhibitory role of the viral lectin on the expression of MHC-I antigens.

Inhibition of Porcine Viruses by Different Cell-Targeted Antiviral Drugs.

Antiviral compounds targeting cellular metabolism instead of virus components have become an interesting issue for preventing and controlling the spread of virus infection, either as sole treatment or as a complement of vaccination. Some of these compounds are involved in the control of lipid metabolism and/or membrane rearrangements. Here, we describe the effect of three of these cell-targeting antivirals: lauryl gallate (LG), valproic acid (VPA), and cerulenin (CRL) in the multiplication of viruses causing important porcine diseases. The results confirm the antiviral action in cultured cells of LG against African swine fever virus (ASFV), foot and mouth disease virus (FMDV), vesicular stomatitis virus (VSV), and swine vesicular disease virus (SVDV), as well as the inhibitory effect of VPA and CRL on ASFV infection. Other gallate esters have been also assayed for their inhibition of FMDV growth. The combined action of these antivirals has been also tested in ASFV infections, with some synergistic effects when LG and VPA were co-administered. Regarding the mode of action of the antivirals, experiments on the effect of the time of its addition in infected cell cultures indicated that the inhibition by VPA and CRL occurred at early times after ASFV infection, while LG inhibited a late step in FMDV infection. In all the cases, the presence of the antiviral reduced or abolished the induction of virus-specific proteins. Interestingly, LG also reduced mortality and FMDV load in a mouse model. The possible use of cell-targeted antivirals against porcine diseases is discussed.

Antiviral activity of lauryl gallate against animal viruses.

BACKGROUND: Antiviral compounds are needed in the control of many animal and human diseases. METHODS: We analysed the effect of the antitumoural drug lauryl gallate on the infectivity of the African swine fever virus among other DNA (herpes simplex and vaccinia) and RNA (influenza, porcine transmissible gastroenteritis and Sindbis) viruses, paying attention to its effect on the viability of the corresponding host cells. RESULTS: Viral production was strongly inhibited in different cell lines at non-toxic concentrations of the drug (1-10 microM), reducing the titres 3->5 log units depending on the multiplicity of infection. In our model system (African swine fever virus in Vero cells), the addition of the drug 1 h before virus adsorption completely abolished virus productivity in a one-step growth virus cycle. Interestingly, no inhibitory effect was observed when lauryl gallate was added after 5-8 h post-infection. Both cellular and viral DNA synthesis and late viral transcription were inhibited by the drug; however, the early viral protein synthesis and the virus-mediated increase of p53 remained unaffected. Activation of the apoptotic effector caspase-3 was not detected after lauryl gallate treatment of Vero cells. Furthermore, the presence of the drug abrogated the activation of this protease induced by the virus infection. CONCLUSIONS: Lauryl gallate is a powerful antiviral agent against several pathogens of clinical and veterinary importance. The overall results indicate that a cellular factor or function might be the target of the antiviral action of alkyl gallates.

The use of COS-1 cells for studies of field and laboratory African swine fever virus samples.

Different naturally occurring, cell adapted or genetically manipulated stocks of African swine fever virus were able to infect directly cultures of COS-1 cells, producing extensive cytopathic effects and amounts from 10(6) to 10(7) of infective progeny virus per ml. The induction of late virus-specific proteins, demonstrated by RT-PCR and immunoblotting, and the development of lysis plaques by all the virus samples tested so far, allowed the optimization of both titration and diagnostic assays, as well as the proposal of a method for selection of virus clones during the generation of virus mutants with specific gene deletions.