Carolin M. Lieber, Josef D. Wolf, Mugunthan Govindarajan, Jeong-Joong Yoon, Zachary M. Sticher, Claire E. Ruckel, Alexander I. Leach, Lauren Harrison, Dariia Vyshenska, Amalia A. Cruz, Meghan K. Andrews, Rebecca E. Krueger, Robert M. Cox, George R. Painter, Alexander L. Greninger, Michael G. Natchus, Plemper Richard K.
Orthoparamyxoviruses, such as human parainfluenza virus type 3 (HPIV3) and measles virus (MeV), are a major health threat. We discovered an orally efficacious broad-spectrum inhibitor of orthoparamyxovirus polymerases. However, here, we found that tolerability in higher mammals was limited. We report the development of the clinical candidate analog GHP-88310 (EIDD-3608), which combines improved oral efficacy with favorable tolerability in nonrodents (ferrets and dogs). GHP-88310 was active against HPIV3, Sendai virus (SeV), MeV, and related canine distemper virus (CDV). In 7-day tolerability studies, daily doses of 2000 mg/kg were well tolerated. Pharmacokinetic analysis revealed altered plasma exposure of GHP-88310 compared to the original hit. In HPIV3-infected cotton rats, GHP-88310 lowered the respiratory tract viral load. Dosing of ferrets infected with CDV, causing lethal measles-like disease, resulted in complete survival, reduction of viremia and shed viral load, and alleviated lymphocytopenia. Once-daily GHP-88310 was efficacious in the CDV-ferret and HPIV3-cotton rat models. The compound was sterilizing against HPIV3 at physiological concentrations in human airway epithelium organoids.