Chemical target validation studies of aminopeptidase in malaria using alpha-aminoalkylphosphonate and phosphonopeptide inhibitors

Department of Microbiology, School of Genetics and Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, Dublin 2, Ireland; and Faculty of Chemistry, Biochemistry and Biotechnology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland

^* To whom correspondence should be addressed. Email: abell{at}tcd.ie.

	Abstract

During its intra-erythrocytic phase, the most lethal human malarial parasite Plasmodium falciparum digests host cell hemoglobin as a source of some of the amino acids required for its own protein synthesis. A number of parasite endopeptidases (including plasmepsins and falcipains) process the globin into small peptides. These peptides appear to be further digested to free amino acids by aminopeptidases, enzymes that catalyse the sequential cleavage of N-terminal amino acids from peptides. Aminopeptidases are classified into different evolutionary families according to their sequence motifs and preferred substrates. The aminopeptidase inhibitor bestatin can disrupt parasite development, suggesting that this group of enzymes might be a chemotherapeutic target. Two bestatin-susceptible aminopeptidase activities, associated with gene products belonging to the M1 and M17 families, have been described in blood-stage P. falciparum but it is not known whether one or both is/are required for parasite development. To establish whether inhibition of the M17 aminopeptidase is sufficient to confer antimalarial activity, we evaluated 35 aminoalkylphosphonate and phosphonopeptide compounds designed to be specific inhibitors of M17 aminopeptidases. The compounds had a range of activities against cultured P. falciparum with 50% inhibitory concentrations down to 14 µM. Some of the compounds were also potent inhibitors of parasite aminopeptidase activity, though it appeared that many were capable of inhibiting the M1 enzyme as well as the M17 one. There was a strong correlation between the potency of the compounds against whole parasites and enzyme, suggesting that M17 and/or M1 aminopeptidases may be valid antimalarial drug targets.