Characterization of a novel macrocyclic inhibitor of Lassa virus

Abstract

Lassa virus is a highly pathogenic virus belonging to the family Arenaviridae. It is the causative agent of Lassa hemorrhagic fever and is a significant threat to global public health. Lassa virus is endemic to West Africa but has been imported into other countries on multiple occasions. Though most cases are mild, 20% of infections cause significant disease requiring hospitalization. There are currently no approved medical countermeasures against Lassa virus. Current treatment for individuals infected with Lassa virus include supportive care and the controversial off-label use of the antiviral ribavirin. The objective of this dissertation was to assess and characterize the mechanism of action of a novel compound, Mac12895623 (Mac128), with potent anti-Lassa properties. Mac128 belongs to a class of compounds called macrocycles. They are large, circularized compounds, and can combine many desirable characteristics of small molecules with unique structural features. Unlike other classes of small molecule compounds, macrocycles may bind motifs that were thought to be ‘undruggable’, opening the door to new avenues in drug discovery. Chapter I serves as a literature review to introduce Lassa virus and elaborate on current medical countermeasures, the development of antivirals against high consequence pathogens, and macrocycles as antiviral therapeutics. Chapter II, outlines the materials and methods used for the research conducted herein. The results of the research are presented in Chapter III in which a family of structurally related macrocyclic compounds was identified to inhibit Lassa virus using a high-throughput screening campaign composed of almost 60,000 compounds. The most promising compound, Mac128, was assessed in a series of in vitro assays to characterize the inhibition of other Lassa virus clades and pertinent New and Old-World arenaviruses. We found Mac128 possessed Lassa-specific inhibition and various clades demonstrated differences in susceptibility. Mechanistic assays were used to assess the macrocycles effect on entry, replication and budding. These experiments revealed Mac128 inhibited viral replication and likely targets the viral polymerase. There are currently two drugs and two experimental compounds in clinical trials to treat Lassa hemorrhagic fever. Though these candidates are promising, there is still a need for medical countermeasure development against Lassa virus. By characterizing a novel compound class, this work aims to further the understanding in which this deadly pathogen can be inhibited and contribute to the development of efficacious therapeutics against Lassa virus.