Identification and evaluation of antiviral activity of novel compounds targeting SARS-CoV-2 virus by enzymatic and antiviral assays, and computational analysis

The viral genome of the SARS-CoV-2 coronavirus, the aetiologic agent of COVID-19, encodes structural, non-structural, and accessory proteins. Most of these components undergo rapid genetic variations, though to a lesser extent the essential viral proteases. Consequently, the protease and/or deubiquitinase activities of the cysteine proteases Mpro and PLpro became attractive targets for the design of antiviral agents. Here, we develop and evaluate new bis(benzylidene)cyclohexanones (BBC) and identify potential antiviral compounds. Three compounds were found to be effective in reducing the SARS-CoV-2 load, with EC50 values in the low micromolar concentration range. However, these compounds also exhibited inhibitory activity IC50 against PLpro at approximately 10-fold higher micromolar concentrations. Although originally developed as PLpro inhibitors, the comparison between IC50 and EC50 of BBC indicates that the mechanism of their in vitro antiviral activity is probably not directly related to inhibition of viral cysteine proteases. In conclusion, our study has identified new potential noncytotoxic antiviral compounds suitable for in vivo testing and further improvement.

Molecular insights into host-virus interaction of human and rhesus cytomegalovirus UL144 mediated by immune checkpoint BTLA and CD160

Cell-cell communication is a crucial mode for multi-cellular organisms to accomplish complex biological functions and various signaling molecules have evolved to meet ever complicated demands to communicate extracellular stimuli with intracellular components. Thus, signaling molecules, whose expression is responsive to local environments; balance the communication between host innate cells and viral pathogens. This intimate interaction between virus and the host immune system covers a wide range of contacts. HVEM, a member of the TNF receptor superfamily, is commonly recognized as a co-stimulatory receptor for LIGHT and LTα. Interestingly, HVEM was also found to interact with BTLA and CD160, and thus deliver a suppressive signal to T cells, therefore the complex molecular network between HVEM and its cellular partners makes bidirectional signaling feasible. Here, we study the viral glycoprotein UL144 of human and rhesus cytomegalovirus that is orthologous to cellular HVEM, thus resembling some of its promiscuity on the cell surface. This molecular network is quite well described, however, the engagement of CD160 by UL144 has not yet been satisfactorily studied. We measured both human and rhesus CMV UL144 binding to BTLA or CD160 using purified HVEM or UL144 proteins and their mutants. We confirmed that human CMV UL144 only bound BTLA and not CD160, whereas HVEM bound both BTLA and CD160. Surprisingly, we have observed binding between UL144-glycan free mutant not only to BTLA but also CD160. Moreover, considering that the ectodomain of UL144 is highly polymorphic across primate CMV we examined both human and rhesus CMV UL144 selectivity for its cellular receptors. We found rhesus CMV UL144 bound CD160 with lower KD when compared to BTLA.

The power of human cytomegalovirus (HCMV) hijacked UL/b' functions lost in vitro

Viruses have evolved sophisticated strategies to subvert immunity to benefit overall viral fitness. Human cytomegalovirus (HCMV, β-herpesvirus) represents a paradigm of very effective hijacking of gene functions that imitate host encoded immunomodulatory proteins. This co-evolution with the host immune system allowed for establishment of lifelong persistence. The HCMV infection is largely asymptomatic in healthy persons; however, it can induce serious disease in immunocompromised individuals. For this reason, great attention is paid to the development of therapeutics based on HCMV immunomodulatory 'tricks' as well as to the search for active vaccine against HCMV. While comparing the HCMV clinical isolates with extensively passaged laboratory strains, the unique long (UL) b' locus was commonly found to be deleted in HCMV genome while adapted to replication in human fibroblasts in vitro. This missing region, called UL/b' region, encodes up to 22 canonical genes with different functions, as of targeting cellular tropism (e.g. UL133-UL138); viral entry and assembly (e.g. UL128, UL130, UL131A); regulation of immunological synapses (e.g. UL135); inhibition of NK and T cell function (e.g. UL141, UL142, UL148, UL144), ablating activity (e.g. UL146, UL147), but mainly aimed at manipulating the host immune response. Moreover, the presence of UL/b' genomic region dramatically correlates with adverse effects in vaccinated persons, indicating that viral genes in this region play a significant role in controlling virulence. Here, we review how HCMV shapes our immunity by hijacked genes originated from UL/b' locus, discuss their impact in immunomodulation mechanism and how this knowledge may translate to clinical applications. Keywords: immunomodulation; HCMV genes; UL/b' locus; NK cell function; HCMV vaccine; immunity; immunotherapeutics.

Chemokine-binding proteins encoded by herpesviruses

To establish infection, a wide variety of pathogens, including viruses, have evolved a number of strategies to avoid immune elimination. Viruses have acquired and optimized molecules that interact with the host chemokine network in order to disrupt immune surveillance and defense of vertebrates, helping to promote cell entry, facilitating dissemination of infected cells, and evasion the immune response. Viral immunomodulators include ligands, chemokine receptors and chemokine-binding proteins (vCKBPs) functioning as either cell surface receptor mimics, ligand mimics, or secreted chemokine-binding proteins. vCKBPs specifically modulate chemokine gradient formation and ligand-receptor recognition when they have a potential to even completely block chemokine-mediated responses to viral infection. Members of only two virus families (Herpesviridae and Poxviridae) encode vCKBPs capable of sequestering host chemokines through either the chemokine receptor, GAG-binding pocket, or both, which may result in the inhibition of chemotaxis in vivo. Here, we focused on vCKBPs encoded by α-, β-, and γ-herpesviruses, of which several have been experimentally used as anti-inflammatory or anti-immune reagents in animal models. Current results suggest that vCKBPs could be used to regulate the activity of both chemokines and chemokine receptors for the treatment of infections such as AIDS, diseases such as arthritis, neurotrauma, inflammatory CNS disorders, atherosclerosis, transplant rejection, and metastatic spread and angiogenesis. Better understanding of vCKBPs biology will help evaluate, which human diseases related to chemokine network dysregulation might be effectively treated with these novel promising immunomodulatory drugs to enable the manipulation of chemokine functions and leukocyte trafficking. Keywords: herpesviruses; chemokine-binding proteins; chemokines; immunomodulation viral infection, chemokines and viral immunomodulators.