Development of an allosteric inhibitor class blocking RNA elongation by the respiratory syncytial virus polymerase complex

Robert M Cox,Mart Toots,Jeong-Joong Yoon,Julien Sourimant,Barbara Ludeke,Rachel Fearns,Elyse Bourque,Joseph Patti,Edward Lee,John Vernachio,Richard K Plemper

doi:10.1074/jbc.ra118.004862

Abstract

Respiratory syncytial virus (RSV) represents a significant health threat to infants and to elderly or immunocompromised individuals. There are currently no vaccines available to prevent RSV infections, and disease management is largely limited to supportive care, making the identification and development of effective antiviral therapeutics against RSV a priority. To identify effective chemical scaffolds for managing RSV disease, we conducted a high-throughput anti-RSV screen of a 57,000-compound library. We identified a hit compound that specifically blocked activity of the RSV RNA-dependent RNA polymerase (RdRp) complex, initially with moderate low-micromolar potency. Mechanistic characterization in an in vitro RSV RdRp assay indicated that representatives of this compound class block elongation of RSV RNA products after initial extension by up to three nucleotides. Synthetic hit-to-lead exploration yielded an informative 3D quantitative structure-activity relationship (3D-QSAR) model and resulted in analogs with more than 20-fold improved potency and selectivity indices (SIs) of >1,000. However, first-generation leads exhibited limited water solubility and poor metabolic stability. A second optimization strategy informed by the 3D-QSAR model combined with in silico pharmacokinetics (PK) predictions yielded an advanced lead, AVG-233, that demonstrated nanomolar activity against both laboratory-adapted RSV strains and clinical RSV isolates. This anti-RSV activity extended to infection of established cell lines and primary human airway cells. PK profiling in mice revealed 34% oral bioavailability of AVG-233 and sustained high drug levels in the circulation after a single oral dose of 20 mg/kg. This promising first-in-class lead warrants further development as an anti-RSV drug.

Highlights

Respiratory syncytial virus (RSV) represents a significant health threat to infants and to elderly or immunocompromised individuals
Whereas the majority of individuals have been exposed to RSV infection by 2 years of age, reinfection throughout life is common, and the elderly in particular are at high risk of developing RSV pneumonia with a potentially fatal outcome
With the overarching goal to prevent the development of severe disease and life-threatening viral pneumonia, it is the primary objective of our anti-RSV program to exploit this therapeutic window and reduce viral burden in the upper respiratory tract in the first days after infection

Summary

Introduction

Respiratory syncytial virus (RSV) represents a significant health threat to infants and to elderly or immunocompromised individuals. PK profiling in mice revealed 34% oral bioavailability of AVG-233 and sustained high drug levels in the circulation after a single oral dose of 20 mg/kg This promising first-in-class lead warrants further development as an anti-RSV drug. Clinical studies monitoring hospitalized RSV-infected children below 2 years of age revealed, for instance, that virus load in the upper respiratory tract during the first 3 days of hospitalization served as a predictor for the likelihood of patient progression to complicated disease with lower respiratory tract infection [8, 9]. With the overarching goal to prevent the development of severe disease and life-threatening viral pneumonia, it is the primary objective of our anti-RSV program to exploit this therapeutic window and reduce viral burden in the upper respiratory tract in the first days after infection. Novel therapeutic options against RSV disease are urgently required

Objectives

Results

Conclusion