TY - JOUR
T1 - Deferoxamine
T2 - Stimulation of hematin polymerization and antagonism of its inhibition by chloroquine
AU - Vippagunta, Sudha R.
AU - Dorn, Arnulf
AU - Bubendorf, André
AU - Ridley, Robert G.
AU - Vennerstrom, Jonathan L.
N1 - Funding Information:
This work was supported, in part, by NIAID Grant 1 R15 AI39670–01 to J. L. V.
PY - 1999/9/1
Y1 - 1999/9/1
N2 - The iron chelator deferoxamine enhances the clearance of Plasmodium falciparum parasitemia and may be useful in drug combinations for the treatment of cerebral malaria. However, the deferoxamine-chloroquine drug combination is antagonistic, or at best additive, against P. falciparum in vitro. As chloroquine is thought to exert its antimalarial activity by interacting with hematin released from the proteolytic degradation of hemoglobin in the parasite food vacuole, we hypothesized that deferoxamine might interfere with the ability of chloroquine to inhibit hematin polymerization, since it was reported that deferoxamine interacts with hematin. Therefore, we assessed deferoxamine-hematin binding in more detail and investigated the effect of deferoxamine on hematin polymerization in the presence and absence of chloroquine. Isothermal titration calorimetry (ITC) experiments demonstrated an enthalpy-driven deferoxamine:hematin μ-oxo dimer binding with an association constant of 2.8 x 104 M-1 at pH 6.5, a binding affinity 14-fold lower than that measured for chloroquine. At least two of the three hydroxamic acid functional groups of deferoxamine must be unionized for effective binding. We also discovered that deferoxamine antagonized chloroquine-mediated inhibition of hematin polymerization. Unexpectedly, deferoxamine increased the concentration of soluble forms of hematin and enhanced the rate of hematin polymerization. Deferoxamine also could initiate hematin polymerization. In contrast, chloroquine decreased the concentration of soluble forms of hematin and inhibited hematin polymerization. This work supports the postulate that initiation of hematin polymerization requires a higher concentration of soluble hematin monomer than does the elongation phase of polymerization and provides one possible explanation for the observed antagonism between deferoxamine and chloroquine against parasites in culture. Copyright (C) 1999 Elsevier Science Inc.
AB - The iron chelator deferoxamine enhances the clearance of Plasmodium falciparum parasitemia and may be useful in drug combinations for the treatment of cerebral malaria. However, the deferoxamine-chloroquine drug combination is antagonistic, or at best additive, against P. falciparum in vitro. As chloroquine is thought to exert its antimalarial activity by interacting with hematin released from the proteolytic degradation of hemoglobin in the parasite food vacuole, we hypothesized that deferoxamine might interfere with the ability of chloroquine to inhibit hematin polymerization, since it was reported that deferoxamine interacts with hematin. Therefore, we assessed deferoxamine-hematin binding in more detail and investigated the effect of deferoxamine on hematin polymerization in the presence and absence of chloroquine. Isothermal titration calorimetry (ITC) experiments demonstrated an enthalpy-driven deferoxamine:hematin μ-oxo dimer binding with an association constant of 2.8 x 104 M-1 at pH 6.5, a binding affinity 14-fold lower than that measured for chloroquine. At least two of the three hydroxamic acid functional groups of deferoxamine must be unionized for effective binding. We also discovered that deferoxamine antagonized chloroquine-mediated inhibition of hematin polymerization. Unexpectedly, deferoxamine increased the concentration of soluble forms of hematin and enhanced the rate of hematin polymerization. Deferoxamine also could initiate hematin polymerization. In contrast, chloroquine decreased the concentration of soluble forms of hematin and inhibited hematin polymerization. This work supports the postulate that initiation of hematin polymerization requires a higher concentration of soluble hematin monomer than does the elongation phase of polymerization and provides one possible explanation for the observed antagonism between deferoxamine and chloroquine against parasites in culture. Copyright (C) 1999 Elsevier Science Inc.
KW - Association constant
KW - Chloroquine
KW - Deferoxamine
KW - Hematin polymerization
KW - Hematin μ-oxo dimer
KW - Malaria
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U2 - 10.1016/S0006-2952(99)00161-6
DO - 10.1016/S0006-2952(99)00161-6
M3 - Article
C2 - 10449192
AN - SCOPUS:0032770944
SN - 0006-2952
VL - 58
SP - 817
EP - 824
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 5
ER -