TY - JOUR
T1 - Inhibition of heme crystal growth by antimalarials and other compounds
T2 - Implications for drug discovery
AU - Chong, Curtis Robert
AU - Sullivan, David Joseph
N1 - Funding Information:
D.J.S. received financial assistance from the Burroughs Wellcome Career Award in Biomedical Sciences, Pew Scholars Program in Biomedical Sciences and NIH RO1 AI45774-01. An NCCR Grant GPDGCRC RR0052 supports the use of RBC for culturing P. falciparum . The authors thank Lirong Shi for assistance with Plasmodium culture. C.R.C. gratefully acknowledges the encouragement of Drs. Patrick, Patricia, and Joao Okinedo.
PY - 2003/12/1
Y1 - 2003/12/1
N2 - During intraerythrocytic infection, Plasmodium falciparum parasites crystallize toxic heme released during hemoglobin catabolism. The proposed mechanism of quinoline inhibition of crystal growth is either by a surface binding or a substrate sequestration mechanism. The kinetics of heme crystal growth was examined in this work using a new high-throughput crystal growth determination assay based on the differential solubility of free vs. crystalline FP in basic solutions. Chloroquine (IC50=4.3μM) and quinidine (IC50=1.5μM) showed a previously not recognized reversible inhibition of FP crystal growth. This inhibition decreased by increasing amounts of heme crystal seed, but not by greater amounts of FP substrate. Crystal growth decreases as pH rises from 4.0 to 6.0, except for a partial local maxima reversal from pH 5.0 to 5.5 that coincides with increased FP solubility. The new crystal growth determination assay enabled a partial screen of existing clinical drugs. Nitrogen heterocycle cytochrome P450 inhibitors also reversibly blocked FP crystal growth, including the azole antifungal drugs clotrimazole (IC50=12.9μM), econazole (IC 50=19.7μM), ketoconazole (IC50=6.5μM), and miconazole (IC50=21.4μM). Fluconazole did not inhibit. Both subcellular fractionation of parasites treated with subinhibitory concentrations of ketoconazole and in vitro hemozoin growth assays demonstrated copurification of hemozoin and ketoconazole. The chemical diversity of existing CYP inhibitor libraries that bind FP presents new opportunities for the discovery of antimalarial drugs that block FP crystal growth by a surface binding mechanism and possibly interfere with other FP-sensitive Plasmodium pathways.
AB - During intraerythrocytic infection, Plasmodium falciparum parasites crystallize toxic heme released during hemoglobin catabolism. The proposed mechanism of quinoline inhibition of crystal growth is either by a surface binding or a substrate sequestration mechanism. The kinetics of heme crystal growth was examined in this work using a new high-throughput crystal growth determination assay based on the differential solubility of free vs. crystalline FP in basic solutions. Chloroquine (IC50=4.3μM) and quinidine (IC50=1.5μM) showed a previously not recognized reversible inhibition of FP crystal growth. This inhibition decreased by increasing amounts of heme crystal seed, but not by greater amounts of FP substrate. Crystal growth decreases as pH rises from 4.0 to 6.0, except for a partial local maxima reversal from pH 5.0 to 5.5 that coincides with increased FP solubility. The new crystal growth determination assay enabled a partial screen of existing clinical drugs. Nitrogen heterocycle cytochrome P450 inhibitors also reversibly blocked FP crystal growth, including the azole antifungal drugs clotrimazole (IC50=12.9μM), econazole (IC 50=19.7μM), ketoconazole (IC50=6.5μM), and miconazole (IC50=21.4μM). Fluconazole did not inhibit. Both subcellular fractionation of parasites treated with subinhibitory concentrations of ketoconazole and in vitro hemozoin growth assays demonstrated copurification of hemozoin and ketoconazole. The chemical diversity of existing CYP inhibitor libraries that bind FP presents new opportunities for the discovery of antimalarial drugs that block FP crystal growth by a surface binding mechanism and possibly interfere with other FP-sensitive Plasmodium pathways.
KW - Chloroquine
KW - Heme crystal
KW - Hemozoin
KW - Ketoconazole
KW - Malaria
KW - Plasmodium falciparum
KW - Quinidine
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U2 - 10.1016/j.bcp.2003.08.009
DO - 10.1016/j.bcp.2003.08.009
M3 - Article
C2 - 14609745
AN - SCOPUS:0242408771
SN - 0006-2952
VL - 66
SP - 2201
EP - 2212
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 11
ER -