Counteracting Resistance through Host-Directed Myxovirus Inhibitors It is the overall goal of this project to spearhead an innovative small-molecule antiviral strategy that is designed to counteract the rapid emergence of viral resistance in the field. The approach is driven by the hypothesis that targeting host cell factors in the viral life cycle rather than direct targeting of viral components will create a significant barrier against spontaneous escape from inhibition. Individual viral mutations will likely fail to fully restore or replace functionality of an inhibited host factor that is essential for virus propagation. Since members of related viral families typically rely on an overlapping set of host components, a broadened target range of these inhibitors is expected. The latter constitutes a readily accessible marker to identify suitable candidate compounds in screening exercises. Pathogens associated with acute, rather than chronic, disease appear particularly desirable targets for this therapeutic approach since treatment time, and thus host exposure to the drug, is kept limited, thereby reducing the possible development of drug-related side effects. Myxoviruses have been chosen as an unmet target for three reasons: (1) myxoviruses such as influenza virus are a major threat to human health;(2) the vast majority of human myxovirus infections result in acute disease;(3) fundamentals of pathogen biology are conserved between different myxoviruses. To test the feasibility of this anti-myxovirus strategy, a large-scale high-throughput anti-measles virus drug screen was analyzed for hits with broadened target range. This has returned, among others, an exquisitely potent (nanomolar range) novel compound class with broad-range inhibition of different ortho- and paramyxoviruses including influenza A virus, human parainfluenzaviruses, measles virus and mumps virus. Further development of this compound class mandates mechanistic characterization of its antiviral effect (aim 1) and hit-to-lead chemical optimization. The current lead and optimized analogs will be subjected to pilot ADME assessment and in vivo toxicity and efficacy testing, using a small-animal model of influenza virus infection (aim 2). The relative frequency of spontaneous viral escape from inhibition and thus the long-term potential of this antiviral strategy to counteract emerging resistance will be assessed through attempts to adapt selected myxoviruses to growth in the presence of the myxovirus inhibitor class in comparison with conventional, virus-specific inhibitors (aim 3). PUBLIC HEALTH RELEVANCE: The myxovirus families contain RNA viruses such as influenza virus, respiratory syncytial virus, parainfluenza viruses, mumps virus and measles virus, which constitute major human pathogens. Emerging resistance against licensed influenza drugs, the threat of a pandemic of highly pathogenic influenza strains, lack of vaccines against parainfluenza viruses, and re-emergence of mumps and measles virus mandate the development of innovative myxovirus therapeutics that counteract resistance.