Molecular and Biochemical Parasitology, 9 (1983) 59-72 59 Elsevier MBP 352 INHIBITION OF THE GROWTH OF PLASMODIUMFALCIPARUM ~ IN VITRO BY COVALENT MODIFICATION OF HEMOGLOBIN* TIMOTHY G. GEARY 1, EDWARD J. DELANEY 2, IRVING M. KLOTZ 2 and JAMES B. JENSEN ~ Department of Microbiology and Public Health, Michigan Slate University, East Lansing, MI 48824-1101, U.S.A., and 2 Department of Chemistry, Northwestern University, Evanston, IL 60201, U.S.A. (Received 17 January 1983; accepted 4 March 1983) Antimalarial effects might be expected from compounds that modify hemoglobin. Dibromoaspirin and bis(dibromosalicyl) diesters decrease gelation of hemoglobin by specific covalent modification (acetylation and crosslinking) of this protein but do not interfere with oxygen transport. These compounds were toxic to malaria parasites when continuously present in culture, as were drugs with similar pharmacological effects such as indomethacin, ibuprofen, and phenylbutazone. Aspirin and acetaminophen were much less effective. When erythrocytes were pretreated with these compounds prior to parasite exposure, only dibromoaspirin and dibromosalicyl diesters prevented parasite development. The modified hemoglobin was highly resistant to digestion by cathepsin D and parasite proteases, suggesting that covalent modifications of hemoglobin that do not disrupt normal hemoglobin function have antimalarial effects. Key words: Plasmodium falciparum; Growth in vitro; Covalent modification of hemoglobin INTRODUCTION The serious problem of resistance of Plasmodiumfalciparum to the commonly used antimalarial drugs has threatened the control of this disease [1-4]. Such drugs apparently act directly against the parasite. Another route of antimalarial attack, one frequently proposed but rarely utilized, is to modify erythrocytes to render them unsuitable for parasite invasion or development. A number of genetic conditions which affect erythrocytes [5-13] prevent or limit the ability of P.falciparum to survive intracellularly. These observations support the hypothesis that modifications of hemoglobin (Hb) or red cell metabolism might have antimalarial effects. Some drugs are available that can ameliorate erythrocyte sickling in individuals * This is Journal Article No. 10349 from the Michigan Agricultural Experiment Station. Abbreviations: DBA, O-acetyl-3,5-dibromo salicylate; DBF, bis(3,5-dibromosalicyl) fumarate; DBNF, bis(3,5-dibromo-m-aminobenzyl) fumarate; DBS, bis(3,5-dibromosalicyl) succinate; DBSE, dibromosa- licyl diesters; Hb, hemoglobin; PHS, pooled human serum. 0166-6851/83/$03.00 © 1983 Elsevier Science Publishers B.V.