Propidium iodide-based methods for monitoring drug action in the kinetoplastidae: Comparison with the Alamar Blue assay

The urgent need for new drug development for African trypanosomiasis is widely recognized. This requires reliable and informative high-throughput assays. Currently, drug action is determined with a fluorimetric/colorimetric assay based on the metabolism of the dye Alamar Blue (resazurin) by live cells. However, this assay does not easily distinguish between cell death and growth arrest, or supply information about the rate at which test compounds affect these parameters. We report here an alternative fluorimetric assay, based on the interaction of propidium iodide with DNA, that allows either real-time monitoring of cell viability or the generation of EC50 values at a predetermined time-point. The assay is highly sensitive and fluorescence readings easily correlate to numbers of parasites or DNA content. The EC50 values were highly similar to those obtained with the standard Alamar Blue assay. The procedure lends itself readily to applications in drug development or resistance monitoring.