Iron Chelators: Role in Sickle Cell Malaria (pilot)

Howard University, Washington DC

Investigators

Linked publications & trials

Abstract

Plasmodium falciparum (P. falciparum) causes the most widespread and virulent form of human malaria, and drug resistance is a major factor in reduced effectiveness of our current treatment options. Our goal is to determine how new iron (Fe) chelators: 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), 2- hydroxy-1 -naphthylaldehyde-4-phenyl-3-thiosemicarbazone (N4pT), and (2-hydroxy-1 -naphthylaldehyde-4- methyl-3-thiosemicarbazone (N4mT) interact with hemoglobin S (HbS) in sickle erythrocytes to inhibit plasmodial growth. Our overall hypothesis is that the presence of HbS in sickle red blood cells (RBCs) will further enhance the antimalarial effects of 311, N4pT and N4mT in AS- and SS-infected RBCs than in HbAA-infected RBCs. Sickle erythrocytes are associated with accumulation of Hb degradative products (Fe deposits) on the inner cytoplasmic surface of the membrane which favor oxidative reaction, and P. falciparum is sensitive to oxidative stress. Fe chelators are used to treat many clinical and infectious conditions including malaria, and desferrioxamine (DFO) has clinically detectable antimalarial activity in human malaria. Poor membrane permeability and other problems have precluded DFO from being used as anti-malarial. Hence new Fe chelators are being developed. The mechanism (s) of antiplasmodial actions of Fe chelators is not clear. Initial data showed a significantly greater anti-malarial activity of 311, N4pT and N4mT over DFO in chloroquine-resistant (CQ-R) and -sensitive (CQ-S) clones of P. falciparum in HbAA RBCs and also in HbS-infected RBCs. Evidence that the Fe-complexes of these chelators have oxidative properties makes them good antimalarial candidates. Aim 1: will compare the anti-parasite effects of 311, N4pT and N4mT on CQ-S and CQ-R clones of P. falciparum-infected HbAS, HbSS and HbAA RBCs in vitro by (a) measuring the time of onset of parasite growth inhibition and the 50% inhibitory concentration (IC50), (b) examining chelator effects on red cell membrane shape. Aim 2: Determine mechanism of parasite growth inhibition by 311, N4pT and N4mT. We will (a) examine the effects of iron complexation of chelators and analysis of labile iron pools in HbAS, HbSS and HbAA RBCs compared to uninfected RBCs, (b) measure oxidant effects of the chelators on infected RBCs. Fe chelators may suppress parasite growth by interfering with Hb breakdown, thus we will (c) evaluate the effect of chelators for their inhibition of the polymerization of hematin to beta-hematin in cell-free systems. Aim 3: Determine the uptake, cellular distribution, and retention of chelators in infected and non-infected RBCs. We will measure drug levels within cells and parasite using radioactive chelators ([14C]-chelators). Studies will shed insight into role of abnormal hemoglobin in antimalaria responses and also antimalaria mechanism of action of Fe chelators. Data will enable us apply for RO1 to do animal studies and opportunity to design treatment programs towards patient's genetic status.