g Malaria remains a significant risk in many areas of the world, with resistance to the current antimalarial pharmacopeia an everincreasing problem. The M1 alanine aminopeptidase (PfM1AAP) and M17 leucine aminopeptidase (PfM17LAP) are believed to play a role in the terminal stages of digestion of host hemoglobin and thereby generate a pool of free amino acids that are essential for parasite growth and development. Here, we show that an orally bioavailable aminopeptidase inhibitor, CHR-2863, is efficacious against murine malaria. Malaria is a major cause of morbidity and mortality worldwide, with as many as 1 million deaths each year (3). While four Plasmodium species commonly infect humans, malaria caused by Plasmodium falciparum is responsible for most deaths, particularly in children under the age of 5 and pregnant women (2, 24). Both prevention and treatment of P. falciparum malaria are under threat because of the spread of drug-resistant parasites. Resistance to chloroquine is now considered almost universal (36), while the efficacy of affordable antimalarial drugs, such as sulfadoxine-pyrimethamine, the major drug used for intermittent preventative therapy, is declining (19,22). Artemisinin and its derivatives may be our last line of drug defense, although recent reports have indicated signs of reduced effectiveness of artemisinin combination therapies (ACTs) (23,28). For the development of the next generation of antimalarial agents, new targets and pathways susceptible to interruption by chemotherapy need to be identified.The asexual intraerythrocytic stages of Plasmodium development are responsible for the clinical symptoms attributable to malaria, and most antimalarial drugs target these stages of the parasite's life cycle (15,30). Many laboratories have focused on the hydrolytic process of hemoglobin (Hb) digestion within the parasite's specialized digestive vacuole as a target for drug discovery (4,7,16,18,32). During the asexual development phase, malaria parasites degrade 65 to 75% of their host cell's Hb, a process that ultimately results in the release of amino acids that are used by the parasite for protein anabolism (29) and the maintenance of osmotic pressure within the infected erythrocyte (14). Two metalloaminopeptidase enzymes, the P. falciparum M1 alanine aminopeptidase (PfM1AAP) and the P. falciparum M17 leucine aminopeptidase (PfM17LAP), may be critical in the terminal stages of Hb degradation and the release of free amino acids (6, 21). We have shown that inhibitors of these aminopeptidases, such as the natural Phe-Leu dipeptide analog bestatin, derived from the fungus Streptomyces olivoretticuli, and several synthetic phosphinate dipeptide analogs, can kill P. falciparum parasites in culture. These compounds are also effective against the rodent malaria parasite Plasmodium chabaudi chabaudi in vivo when administered intraperitoneally (i.p.) (32,33). We have also recently reported the production and characterization of functionally active recombinant P. falciparum M1 alanine aminopeptidas...

The M1 alanyl aminopeptidase and M17 leucyl aminopeptidase are critical to the growth and development of malaria parasites inside host erythrocytes. Potent aminopeptidase inhibitors kill malaria parasites in culture and are also active in vivo against murine malaria. Functional recombinant enzyme studies have been used to decipher the three-dimensional structures of both enzymes that together with new and specific inhibitors are facilitating structure-activityrelationship (SAR) and functional studies. Here we review the progress made in our knowledge of these two enzymes which is bringing them closer to being validated anti-malarial drug targets.

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