SMAC Mimetics as Broad-Spectrum Antivirals

ABSTRACT Antivirals that are currently in clinical use target a limited number of viruses or viral subgroups, have moderate efficacy and are prone to resistance. Current approaches for antiviral development mainly target viral proteins with enzymatic activity. A disadvantage of this approach, especially for RNA viruses, is that their small genomes offer few drug targets and high mutation rates lead to rapid emergence of drug-resistant strains. The discovery of potent, broad-spectrum antivirals with a high barrier to resistance therefore remains an urgent, unmet medical need for the treatment of endemic and emerging viral infections. Agents with these properties will most likely target host factors that are required for replication of multiple viruses and/or innate immune circuits that govern endogenous cellular defense mechanisms. SMAC mimetics, first developed to induce immunogenic death of tumor cells, are now emerging as such pan-antivirals. These agents simulate the activity of endogenous SMAC to block the action of inhibitor of apoptosis proteins (IAP). Although best known for their regulation of caspases during inflammation and cell death, IAPs also influence ubiquitin (Ub)-dependent signaling pathways that modulate innate immune responses. Several SMAC mimetics have already entered clinical trials for cancer treatment. As for antiviral therapy, research thus far has focused on SMAC mimetics for treatment of chronic viral infections, such as Hepatitis B virus and as latency reversal agents (LRAs) of HIV-1 infection. A recent report described the antiviral activity of a potent, monovalent SMAC mimetic against flaviviruses, SARS-CoV-2 and influenza A13. We have generated similar findings with SARS-CoV-2, Dengue 2 and influenza A using SMAC mimetics developed by our group. Owing to our current HIV-1 LRA program, we have novel compounds in hand that feature a range of activity profiles. We hypothesize that SMAC mimetics can be developed into potent pan- antivirals because they preferentially kill infected cells, which are sensitized to death due to activation of innate immune circuits. We recognize that SMAC mimetics may also affect cellular processes universally required for or inhibiting viral replication. This project will focus on RNA viruses with pandemic potential, including influenza A, flaviviruses (Dengue, Zika and West Nile), and SARS-CoV-2 variants. In Aim 1 we propose to investigate the breadth and potency of the antiviral activity of SMAC mimetics. Here, we will also delineate the stage of the viral replication cycle that is affected by SMAC mimetics and/or that triggers their antiviral properties. Aim 2 will rely on systems biology approaches to identify the host factors that are implicated in SMAC mimetic antiviral activity. Overall, the proposed studies will identify the mechanisms and pathways that are responsible for the antiviral activity of SMAC mimetics and enable their further optimization as broad-acting antivirals.