Identification of a Series of Quinazolinediones as Potent, Selective, Post-Entry Inhibitors of Human Respiratory Syncytial Virus (\u3cem\u3eh\u3c/em\u3eRSV) via a Cell-Based High Throughput Screen and Chemical Optimization

Respiratory Syncytial Virus (RSV) is the most common cause of bronchiolitis and pneumonia among infants under one year of age. Most children will be infected with RSV prior to their second birthday, leading to 75,000-125,000 hospitalizations and medical costs exceeding $650 million annually. The virus is highly contagious and is associated with substantial morbidity and mortality. Nevertheless, severe lower respiratory tract disease may occur at any age, especially among the elderly or those with compromised cardiac, pulmonary, or immune systems. FDA-approved drugs for the acute infection are ribavirin and the prophylactic humanized monoclonal antibody, Synagis®, which is limited to use in high risk pediatric patients. Due to the lack of a vaccine and the presence of toxicological limitations in existing therapies, there is substantial need for effective treatments with an improved profile. Of the 313,816 Molecular Libraries Small Molecule Repository (MLSMR) compounds screened in a cell-based, RSV inhibition assay, 51 compounds were selected based on potency, selectivity and chemical tractability for further evaluation in dose response and secondary assays. Collaboration between the assay provider at the University of Louisville, the screening center at Southern Research Institute and the University of Kansas Specialized Chemistry Center narrowed the structure activity relationship (SAR) focus to three scaffolds. The probe, ML275, resulted from structural modification and optimization of a quinazolinedione chemical series, generating a compound with an antiviral EC50 value of 0.81 ± 0.75 μM and a 247-fold selectivity index (SI) for antiviral activity over HEp-2 cell cytotoxicity. Additionally, ML275 demonstrated a 6.7 log reduction of in vitro viral titer, or reduction by approximately 5,000,000-fold. ML275, determined to be a post-entry inhibitor of viral replication, has been broadly profiled for off-target liabilities and assessed for PAMPA permeability and hepatocyte toxicity