Title: Small molecule inhibitors of Plasmodium falciparum
Description: Malaria, a vector-borne parasitic disease spread by the Anopheles mosquito, is responsible for approximately two million deaths annually with the majority of infections concentrated in Asia, South America, and sub-Saharan Africa. The causative agent of malaria is a protozoan organism of the genus Plasmodium , of which four species can infect humans. Plasmodium falciparum accounts for the majority of morbidity and mortality; however, the benign human malaria parasite Plasmodium vivax also inflicts a significant disease burden throughout many disease-endemic countries. The continued development of novel anti-malarial chemotherapies, particularly those aimed at new pathways, is necessary for the successful treatment of malaria as resistance to presently utilized drugs becomes more widespread. Here we describe three projects that address this need and represent a small portion of a larger anti-malarial drug discovery effort between Harvard University, Genzyme Corporation, and the Broad Institute. Target-based screens provide the ability to systematically develop multiple compound series addressing an identified essential protein or pathway thereby broadening the opportunity to find inhibitors with differing physico-chemical properties or reduced off-target effects. The two campaigns described herein are focused on P. falciparum dihydroorotate dehydrogenase and histone deacetylase 1. In both cases, we have identified and characterized a series of drug candidates that selectively inhibit the target enzyme with high efficacy and possess anti-malarial activity. Structure-activity relationship exploration is underway to develop lead compounds with improved pharmacological properties.

Our third goal was to identify new or under-exploited drug targets within the malaria parasite. To that end, we found P. falciparum heat shock protein 90 (pfHSP90) to be a molecular target of halofuginone (HF), a potent anti-malarial agent plagued with a poor therapeutic index. We determined that HF tightly and specifically binds pfHSP90 and found a significant correlation between ex vivo parasite sensitivities to geldanamycin, a known HSP90 inhibitor, and HF suggesting a similar mechanism of action. Although additional work is necessary to fully understand the interaction between HF and pfHSP90, a number of candidate compounds have been identified to interact with pfHSP90 and inhibit P. falciparum growth. These compounds are being pursued for improved species selectivity.