A novel in vitro image-based assay identifies new drug leads for giardiasis

•We describe a new automated image-based method to enumerate Giardia trophozoites.•This method permits the assessment of parasite growth at multiple time points without staining.•The “Malaria Box” compound set was assessed for anti-Giardia activity using this approach.•Three compounds with sub-μM activity were identified.

Giardia duodenalis is an intestinal parasite that causes giardiasis, a widespread human gastrointestinal disease. Treatment of giardiasis relies on a small arsenal of compounds that can suffer from limitations including side-effects, variable treatment efficacy and parasite drug resistance. Thus new anti-Giardia drug leads are required. The search for new compounds with anti-Giardia activity currently depends on assays that can be labour-intensive, expensive and restricted to measuring activity at a single time-point. Here we describe a new in vitro assay to assess anti-Giardia activity. This image-based assay utilizes the Perkin-Elmer Operetta® and permits automated assessment of parasite growth at multiple time points without cell-staining. Using this new approach, we assessed the “Malaria Box” compound set for anti-Giardia activity. Three compounds with sub-μM activity (IC50 0.6-0.9 μM) were identified as potential starting points for giardiasis drug discovery.

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