ChemInnate

Although viral infections represent a major burden for public health, our therapeutic arsenal is quite limited. Current antiviral therapies mostly rely on nucleoside analogs, few virus-specific drugs (oseltamivir ; palivizumab), and recombinant IFN-a/ß of limited efficacy in most cases. Despite the success of direct acting antivirals (DAA) against HIV or HCV, viruses often escape drugs targeting components of their replication machinery through mutations. Added to the fact that new pathogenic viruses are emerging permanently, there is a critical need for innovative approaches to fight seasonal epidemics and unexpected outbreaks like Ebola and chikungunya crises. In this perspective, we are exploring a new concept: broad-spectrum antivirals that, instead of targeting the virus itself, block viral growth by modulating cellular defense mechanisms. To identify new chemical entities that stimulate the expression of the antiviral cluster of interferon-stimulated genes (ISGs), we developed a stable cell-line expressing luciferase under the control of an interferon-stimulated response element that is both activated by IRF1/3/7 transcription factors and type I interferons. This cellular assay was used to screen an unbiased chemical library of 10.000 compounds, and only one referred as ChX710 was found to activate the ISRE promoter in a range similar to IFN-ß. Further analyses by RT-qPCR showed that ChX710 efficiently stimulates the expression of interferon genes and ISGs in different human cell types, in particular primary monocytes and plasmacytoid dendritic cells. Such immunostimulatory properties were never reported before for this chemical series, and its mode of action is totally unknown. To decipher the signaling pathways activated by ChX710, we knocked-down cellular factors involved in the induction of ISGs by pathogen recognition receptors (MAVS, IRF1, IRF3) or type I interferons (TYK2). None of these different factors, except IRF1, seems to be involved in the activation of the ISRE promoter by ChX710. Added to the fact that our ISRE-luciferase reporter cell line does not express TLR7/8/9 or STING, our data suggest that ChX710 is targeting a novel signaling pathway to induce ISGs and the innate antiviral response. Furthermore, this molecule increased the antibody response to ovalbumin in mice, establishing its immunostimulatory properties in vivo. Although the antiviral response and the cellular stress induced by ChX710 eventually lead to cell death in vitro, this compound showed neither local nor systemic toxicity when injected to animals. Altogether, our data suggest that ChX710 is a potent stimulator of the innate antiviral response that targets some yet uncharacterized cellular pathway. Objectives of this research program are to study the immunostimulatory properties, the mode of action, and the antiviral activity of this molecule. To reach these goals, we will (i) develop chemical analogs of ChX710 that are more active and more stable in vivo, (ii) document the immunostimulatory and antiviral properties of ChX710 both in vitro on primary human cells and in vivo in mouse models of immunization and infection, and (iii) look for the mode of action of this molecule using transcriptomics and proteomics approaches. This interdisciplinary research program will require specific skills in organic chemistry, pharmacology and immuno-virology that are all well covered by the members of our consortium. Main outcomes of this program include the identification of novel cellular pathways that stimulate the host antiviral response, and the development of an innovative immunostimulatory drug of potential therapeutic interest against viral infections, or whenever the stimulation of innate immunity can be beneficial (cancer treatments, vaccine development, etc).