High throughput screening (HTS) has recently provided hundreds of new compounds that have been shown to disrupt formation ?-hematin, the synthetic counterpart of hemozoin, a crucial heme detoxification product in the malaria parasite believed to be an important drug target. The prototype hemozoin inhibitor, chloroquine, has recently been shown to cause a significant increase in free heme in the malaria parasite Plasmodium falciparum and to disrupt b-hematin formation via adsorption onto the hemozoin crystal surface. We hypothesize that hemozoin inhibition occurs through adsorption onto the crystal face and that parasite growth inhibition is directly related to free heme present in the parasite. The wealth of diverse new ?-hematin inhibiting scaffolds found by HTS thus provides a unique opportunity to probe and understand the relationships between structure, adsorption, free heme levels and parasite growth inhibition. To achieve this, the following specific aims are proposed:
SPECIFIC AIM 1. Investigate whether hits from HTS inhibit the heme detoxification pathway.
SPECIFIC AIM 2. Study the kinetic effects and adsorption behavior of HTS hits on b-hematin.
SPECIFIC AIM 3. Synthesize derivatives of hit compounds to probe structure-activity relationships between Kads, increased free heme in the cell and parasite IC50. In order to achieve these goals, the research will be conducted as a collaborative project between Timothy J. Egan at the University of Cape Town (UCT), Katherine A. de Villiers-Chen at Stellenbosch University (SU), South Africa and David W. Wright at Vanderbilt University (VU), Nashville, TN. Development of the free heme assay and synthesis of new compounds to probe these relationships will be conducted UCT. Screening of the effects of diverse scaffolds on free heme levels in the parasite will be performed largely at VU, while kinetic and molecular docking studies will be performed at SU. The collaboration between the three groups will be strongly synergistic and builds on existing strong links and active collaboration between all three. The considerable expertise in measurement of parasite free heme and kinetics will be transferred from UCT and SU to VU. Conversely, expertise on screening technology will be transferred from VU to UCT and SU, extending existing expertise transfer.
Malaria is the most important human parasitic disease, affecting hundreds of millions of people. The malaria parasite feeds on hemoglobin in the host red blood cell with the consequent need to detoxify heme. Recent high-throughput screening has revealed hundreds of new compounds that inhibit the detoxification process in the test tube. These provide an invaluable resource for understanding relationships between molecular structure and inhibition of the parasite heme detoxification process. We propose to undertake research to determine how these hit compounds target the detoxification process in the parasite and to develop an understanding of the relationship between their structures, the presence of free heme in the parasite and antimalarial activity as a crucial step towards eventual rational design of antimalarials.