In a high throughput screening campaign, we discovered a benzodiazepine compound BDAA that potently inhibited yellow fever virus (YFV) replication in vitro and in an YFV infected hamster model. In collaboration with Dr. Ju-Tao Guo, Chemical genetic studies have revealed a novel mechanism of BDAA against YFV. We have demonstrated that BDAA’s interaction with YFV nonstructural 4B (NS4B) protein impairs the integrity of YFV replication complex, which inhibits viral RNA replication and promotes viral RNA releasing from replication complex and consequentially activates double stranded RNA mediated innate immune response. Currently we are using BDAA as a chemical probe to examine the molecular details of NS4B’s dual function in viral RNA replication and evasion of host cellular innate immune response and understand how these processes are simultaneously disrupted by small molecule compound.

Hit to lead optimization has been completed in collaboration with Dr. Yanming Du, and lead candidate and a backup compound have been nominated into preclinical development. We are currently in the process of developing the drug candidates through non-GLP toxicity and pharmacokinetics, GMP manufacturing, IND-enabling safety pharmacology and GLP toxicity studies, to first-in-human Phase 1 clinical trials.

Discovery and development of human STING agonists for treatment of chronic hepatitis B

Stimulator of interferon genes (STING) is the adaptor protein of multiple cytoplasmic DNA receptors. Cytoplasmic DNA activates cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) to produce cGAMP, which subsequently binds to STING and induces IFNs and other cytokines. Previously, we showed that 5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a small molecule mouse STING agonist, induced a type I-IFN dominant cytokine response in macrophages, which potently suppressed HBV replication in mouse hepatocytes by reducing the amount of cytoplasmic viral nucleocapsids. Moreover, intraperitoneal administration of DMXAA significantly induced the expression of IFN-stimulated genes and reduced HBV DNA replication intermediates in the livers of HBV hydrodynamically injected mice.  Our study thus proves the concept that activation of STING pathway induces a potent innate antiviral immune response against HBV, and the development of small molecular human STING agonists as immunotherapeutic agents for treatment of chronic hepatitis B is warranted. Recently, we developed a cell-based high throughput screening assay and identified several small molecule human STING agonists. Characterization of their effect on viral infection, mode of action as well as structure-activity-relationship studies are currently under way.

Host-targeting antiviral drug development: Iminosugar ER α-glucosidase inhibitors

Targeting host functions essential for viral replication has been considered as a potential broad-spectrum and resistance-refractory therapeutic approach. These host function-targeted broad-spectrum antiviral agents do not rely on time-consuming etiologic diagnosis and thus should be particularly valuable in management of viral hemorrhagic fever and respiratory tract viral infections, the medical conditions that can be caused by many different enveloped RNA viruses and with short window for medical intervention. Interestingly, despite that many inhibitors of host functions have been demonstrated to inhibit a specific virus or a broad-spectrum of viruses in cultured cells, the in vivo antiviral efficacy has only been demonstrated for the inhibitors of a few host cellular components. Endoplasmic reticulum (ER)-resident α-glucosidases I and II sequentially trim the three terminal glucose moieties on the N-linked glycans attached to the nascent glycoproteins. These reactions are the first steps of N-linked glycan processing and are essential for proper folding and function of many glycoproteins. Because most of the viral envelope glycoproteins contain N-linked glycans, inhibition of ER α-glucosidases with derivatives of 1-deoxynojirimycin (DNJ) or castanospermine (CAST), the two well-studied pharmacophores of α-glucosidase inhibitors, efficiently disrupts the morphogenesis of a broad-spectrum of enveloped viruses. Through extensive lead optimization efforts, we identified DNJ derivatives (iminosugars) with improved antiviral activity and reduced toxicity and have already demonstrated that several iminosugars efficiently suppressed the replication of dengue virus in mice and improved the survival rates of mice infected by dengue virus, Ebola virus and Marberg virus. To further improve the in vivo antiviral efficacy and reduce the intestine stress and diarrhea due to nonselective inhibition of gut glucosidases by the iminosugars, we are currently developing iminosugar prodrugs with improved bioavailability and metabolic activation in blood and targeted tissues for treatment of viral hemorrhagic fever and infection of other emerging enveloped viruses.