Methionyl-tRNA synthetase inhibitor has potent in vivo activity in a novel Giardia lamblia luciferase murine infection model

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Abstract
Objectives: Methionyl-tRNA synthetase (MetRS) inhibitors are under investigation for the treatment of intestinal infections caused by Giardia lamblia . To properly analyze the therapeutic potential of the MetRS inhibitor 1717 , experimental tools including a robust cell-based assay and a murine model of infection were developed based on novel strains of G. lamblia that employ luciferase reporter systems to quantify viable parasites. Methods: Systematic screening of Giardia-specific promoters and luciferase variants led to the development of a strain expressing the click beetle green luciferase. Further modifying this strain to express NanoLuc created a dual reporter strain capable of quantifying parasites in both the trophozoite and cyst stages. These strains were used to develop a high throughput cell assay and a mouse infection model. A library of MetRS inhibitors was screened in the cell assay and 1717 was tested for efficacy in the mouse infection model. Results: Cell viability in in vitro compound screens was quantified via bioluminescence readouts while infection loads in mice were monitored with noninvasive whole-animal imaging and fecal analysis. Compound 1717 was effective in clearing mice of Giardia infection in 3 days at varying doses, which is supported by data from enzymatic and phenotypic cell assays. Conclusions: The new in vitro and in vivo assays based on luciferase expression by engineered G. lamblia strains are useful for the discovery and development of new therapeutics for giardiasis. MetRS inhibitors, as validated by 1717 , have promising anti-giardiasis properties that merit further study as alternative therapeutics.
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