A new photometric assay for testing trypanocidal activity in vitro

Area of Science:

• Parasitology
• Drug Discovery
• Biochemistry

Background:

• Human African trypanosomiasis (HAT) requires effective treatments.
• Assessing drug efficacy against Trypanosoma brucei is crucial for HAT drug development.
• Existing methods for evaluating trypanocidal activity can be laborious.

Purpose of the Study:

• To develop and validate a new in vitro assay for assessing trypanocidal activity.
• To enable efficient screening of compounds against Trypanosoma brucei bloodstream forms.
• To provide a cost-effective and reliable method for determining drug efficacy.

Main Methods:

• Established an in vitro test using axenically grown Trypanosoma brucei bloodstream forms.
• Utilized a microtiter plate system with serial drug dilutions and a 72-hour incubation period.
• Employed a pH indicator (phenol red) to detect metabolic activity (pyruvate production) and assess growth inhibition.
• Quantified results using visual inspection or an enzyme-linked immunosorbent assay (ELISA) reader by measuring extinction values at 560 nm.

Main Results:

• The assay demonstrated a linear correlation between pH indicator changes, pyruvate concentration, and drug inhibition.
• IC50 (half-maximal inhibitory concentration) values were determined by comparing extinction changes in test and control cultures.
• Minimal inhibitory concentrations (MICs) were readily determined by visual inspection.
• Photometric evaluation results were comparable to those obtained from growth inhibition and radiolabeled hypoxanthine incorporation assays.

Conclusions:

• The developed in vitro test accurately assesses the trypanocidal activity of compounds against Trypanosoma brucei.
• This assay provides a reliable, efficient, and potentially cost-effective method for drug screening in the context of HAT.
• The photometric readout offers a standardized and quantifiable approach to evaluating drug efficacy.