Small molecule-induced degradation of dengue proteins as an antiviral strategy

PROJECT SUMMARY / ABSTRACT Dengue virus (DENV) is a pathogen of high biomedical significance against which we lack effective countermeasures. Although targeted chemotherapy using combinations of direct-acting antivirals (DAAs) has proven highly successful against hepatitis C virus infection and HIV, efforts to develop analogous drugs against DENV have not been successful. The genetic diversity of DENV due to replication by an RNA-dependent RNA polymerase that lacks proofreading function presents additional challenges by making it difficult to develop vaccines and antivirals with broad-spectrum coverage of all genotypes within one viral species and facilitating the rapid development of antiviral resistance when DAAs are used as monotherapies. Recently developed methods for small molecule-induced degradation of specific proteins rely on chimeric molecules ("PROTACs," "degronimids," "degraders") that have a target-specific ligand linked to a moiety that binds an E3 ubiquitin ligase (e.g., cereblon, VHL). Small molecule-binding leads to ubiquitination and proteasomal degradation of the target. This results in event-driven rather than occupancy-driven pharmacology leading to efficient removal of the target from the cell and functional ablation of all of the protein's functions. Since pharmacological activity does not require constant, stoichiometric engagement of the target, even modest affinity ligands can be effective degraders. In addition, this mechanism of action can have higher natural barriers to resistance than conventional inhibitors, as has been demonstrated in the cancer biology field. While these potential advantages are attractive for antivirals development, it remains unclear the extent to which they can be leveraged to attain significant antiviral effects. In particular, strong viral expression and localization of viral processes (and their effectors) on or near specialized membranes may limit the susceptibility of DENV and other viruses to this pharmacological strategy. Here we propose to explore whether we can successfully deploy targeted protein degradation against three essential DENV proteins: core, NS4B, and NS5. As there are currently no approved anti-DENV drugs, there is an urgent need to find new pharmacological strategies to target this virus. Starting with known inhibitors as targeting ligands for degrader development, we will develop and validate antiviral degraders. We will then use these as tools to systematically explore potential points of differentiation between degraders and conventional inhibitors in terms of affinity, potency, selectivity, duration of action and susceptibility to resistance. We will also optimize validated antiviral degraders to test the efficacy of this antiviral approach in vivo. The overall goal is to validate degradation of one or more of these targets as an antiviral strategy with high natural barrier to resistance and to advance first-in-class degraders as leads for the development of antivirals. In pursuit of this goal, we will also establish important proof of concept and the foundation for more broadly developing antiviral degraders against other viral pathogens.