title: Antimalarial activities of novel synthetic cysteine protease inhibitors.
abstract: Among promising new targets for antimalarial chemotherapy are the cysteine protease hemoglobinases falcipain-2 and falcipain-3. We evaluated the activities of synthetic peptidyl aldehyde and alpha-ketoamide cysteine protease inhibitors against these proteases, against cultured Plasmodium falciparum parasites, and in a murine malaria model. Optimized compounds inhibited falcipain-2 and falcipain-3, blocked hemoglobin hydrolysis, and prevented the development of P. falciparum at nanomolar concentrations. The compounds were equally active against multiple strains of P. falciparum with varied sensitivities to standard antimalarial agents. The peptidyl inhibitors were consistently less active against vinckepain-2, the putative falcipain-2 and falcipain-3 ortholog of the rodent malaria parasite Plasmodium vinckei. The lead compound morpholinocarbonyl-leucine-homophenylalanine aldehyde, which blocked P. falciparum development at low nanomolar concentrations, was tested in a murine P. vinckei model. When infused continuously at a rate of 30 mg/kg of body weight/day, the compound delayed the progression of malaria but did not eradicate infections. Our data demonstrate the potent antimalarial activities of novel cysteine protease inhibitors. Additionally, they highlight the importance of consideration of the specific enzyme targets of animal model parasites. In the case of falcipains, differences between P. falciparum and rodent parasites complicate the use of the rodent malaria model in the drug discovery process.
authors.affiliation: Department of Medicine, San Francisco General Hospital, University of California, San Francisco, San Francisco, California 94143-0811, USA.
authors.forename: Belinda J
authors.initials: BJ
authors.lastname: Lee
authors.forename: Ajay
authors.initials: A
authors.lastname: Singh
authors.forename: Peggy
authors.initials: P
authors.lastname: Chiang
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Kemp
authors.forename: Erick A
authors.initials: EA
authors.lastname: Goldman
authors.forename: Michael I
authors.initials: MI
authors.lastname: Weinhouse
authors.forename: George P
authors.initials: GP
authors.lastname: Vlasuk
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Rosenthal
mesh_terms: D000447:Aldehydes / Q000494:pharmacology; D000577:Amides / Q000494:pharmacology; D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D003546:Cysteine Endopeptidases / Q000378:metabolism / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D010963:Plasmodium falciparum / Q000187:drug effects*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D013329:Structure-Activity Relationship
chemical_list: D000447:Aldehydes; D000577:Amides; D000962:Antimalarials; D015853:Cysteine Proteinase Inhibitors; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases; C416224:falcipain 2