Liver and blood-stage malaria parasites have different gene expression profiles and infect different host cells. The authors exploited these differences to try to specifically identify compounds that were active against the parasite while it was still in the liver, the idea being that any drug-based prevention strategy needs to be effective against the parasites in the liver in order to eradicate infection.
The authors screened a library of over 1300 kinase inhibitors that included several compounds already being used in clinical trials for anti-cancer activity. Initial screening was performed in human liver-derived HepG2 cells infected with Plasmodium berghei expressing a luciferase reporter. Compounds that decreased parasite load by more than 95% were further characterized in dose-response experiments, and promising hits were tested in using luminescent and fluorescent cell based assays to identify compounds that were not toxic to liver cells.
Further characterization identified a few kinase inhibitors that were effective only against liver-stage parasites, but most of the hits were effective against parasites at both life cycle stages. Two candidate compounds–a CDK inhuibitor and an Aurora kinase inhibitor—were then further evaluated in a mouse model of infection to test performance in vivo. These two inhibitors were also the subject of clinical trials evaluating activity against certain cancers. Both were effective in decreasing the load of liver-stage parasites in the mouse model.
The results are exciting because they demonstrated that the Plasmodium kinome does have potential as a target for anti-malarial drugs. The authors identified more than 30 compounds as liver-stage malaria inhibitors, many of which were also active against the blood-borne stages of the infection. In this instance the use of high-throughput screening and subsequent bioinformatics analysis enabled exploration of a large pool of compounds in a phenotypic screen, increasing the chances of finding hits. Information on the human kinase targets of any promising inhibitors was then exploited using BLAST searches to find candidate Plasmodium kinases with significant sequence homology to the known human targets of the relevant inhibitor.
The identification of candidate inhibitors that are already the subject of clinical trials for a different purpose is also exciting –some of the work has already been done, potentially expediting the process of development (and decreasing the cost) if the inhibitor does turn out to me a good therapeutic candidate.
Here’s the Paper
Derbyshire, E., Zuzarte-Luís, V., Magalhães, A., Kato, N., Sanschagrin, P., Wang, J., Zhou, W., Miduturu, C., Mazitschek, R., Sliz, P., Mota, M., Gray, N., & Clardy, J. (2014). Chemical Interrogation of the Malaria Kinome ChemBioChem DOI: 10.1002/cbic.201400025