New Antiviral approach against SARS-CoV2 by Targeting the RNA helicase DHX9, a cofactor of SARS COV-2 – NAT_DHX9

The recent SARS CoV-2 outbreak raised awareness on the global burden of RNA viral infections and pointed out the weakness of public health systems. Inhibitors developed to target viral enzymes globally collide with the emergence of resistances that defeat these antiviral strategies. In this context, cellular factors required for optimal viral infections such as cellular RNA helicases represent valuable targets for antiviral applications. Helicases separate double helix made of DNA or RNA and allow cellular proteins to access, read, or rearrange genetic information. Brai et al. recently developed specific inhibitors of the DDX3 helicase and they demonstrated the antiviral properties of these molecules. Above all, by establishing the excellent toxicity profile of these compounds, they validated the possibility to target cellular helicases without significant adverse effects. Nevertheless, inhibitors against other cellular helicases remain to be developed. Based on these observations, and on the pleiotropic role of DHX9 in the replication of various RNA viruses, we consider DHX9 as a potential therapeutic target for the development of anti-SARS-CoV-2 molecules. In collaboration with two other teams (Dr. Briant and Dr. Chaloin) of the Institute of research in infectious diseases of Montpellier (IRIM), we have developed small molecules able to specifically bind a hydrophobic pocket in the Helicase domain of DHX9 and to inhibit its PCE activity. We also demonstrated the efficiency of our compounds on RNA viruses (CHIKV) et retroviruses (HTLV-1). These molecules are active in the micromolar range of concentrations. ADME/Tox studies showed that our inhibitors have no significant cytotoxic effect on non-infected cells. Last March at the beginning of the epidemy in France with the help of SATT AxLR and in collaboration with 3 other teams from IRIM including Dr. Briant, we set-up a model of SARS-CoV-2 infection using Vero E6 and A549-ACE2 cells. In our preliminary study, we showed that DHX9 is interacting with several proteins of the SARS-CoV-2 virus and that our DHX9 inhibitors demonstrated strong anti-SARS CoV-2 antiviral properties without any major cytotoxic effect in the A549-ACE2 model. In this project, our objectives are to further identify the molecular basis of DHX9 interactions with viral SARS-CoV-2 proteins to increase the specificity of our compounds; to improve the stability and solubility of the lead molecules developed in our proof of concept study, and to measure the antiviral activity spectrum of the optimized compounds in vitro and in vivo. The NAT_DHX9 project ultimately aims to contribute to satisfying urgent and still unmet medical needs regarding the SARS-CoV-2 virus by bringing efficient disease-modifying treatments to the clinical stage and finally to the market in case of success. It will increase the targeted-therapeutic arsenal to treat RNA viruses’ infection.