In Vitro Potentiation of Antibiotic Activities by a Catecholate Iron Chelator against Chloroquine-Resistant Plasmodium falciparum

Abstract

FR160, a catechol iron chelator, and tetracyclines or norfloxacin exert in vitro additive or synergistic activity against a chloroquine-resistant Plasmodium falciparum clone. FR160 shows antagonistic effects in association with macrolides, ofloxacin, and rifampin.The emergence and spread of parasite resistance to currently used antimalarial drugs indicates that novel compounds need to be discovered and developed by identification of novel chemotherapeutic targets (18). Iron chelation therapy was considered a suitable treatment for various infectious diseases, including malaria (10). Iron is needed for catalysis of DNA synthesis and for a variety of enzymes involved in electron transport and energy metabolism. Recent experimental observations obtained in vitro (9,25), in rodent (6) and primate (19) models, and in clinical studies (8,15) showed antimalarial activity of desferrioxamine. However, the time window of action of desferrioxamine is relatively limited, and the antimalarial activity is slow to develop, even after continuous in vitro or in vivo exposure to desferrioxamine (4). Various iron chelators were assessed to improve the drug lipophilicity, leading to increased access of drug to intracellular parasites and to faster action (13,14). In addition, several studies explored the possibility of improving the antimalarial efficacy of iron chelators by using them in various combinations of iron chelators with different speeds of action, stage dependences, and degrees of reversibility of effects (7,27,28). The in vitro activity of FR160, a catecholate siderophore derived from spermidine, was shown previously (21). Use of combinations of antimalarials that do not have the same resistance mechanisms will reduce the chance of selection because the chance of a resistant mutant surviving is the product of the per-parasite mutation rates for the individual drugs multiplied by the number of parasites in an infection that are exposed to the drugs (29).In this study, we assessed the combined action of FR160 with antibiotics against Plasmodium falciparum.Parasites. When required for drug assays, the chloroquineresistant clone W2 (Indochina) was synchronized by sorbitol lysis (12). Susceptibilities to FR160 and antibiotics were determined after suspension in RPMI 1640 medium (Life Technologies, Paisley, United Kingdom) supplemented with 10% human serum (pooled from different A ϩ or AB sera from nonimmune donors) and buffered with 25 mM HEPES and 25 mM NaHCO 3 (hematocrit of 1.5% and parasitemia of 0.5%).Drugs. The synthesis of FR160 was previously described (21). All antibiotics were obtained from Sigma Chemical (St. Louis, Mo.). Stock solutions were prepared in methanol for FR160, tetracycline, doxycycline, minocycline, oxytetracycline, erythromycin, spiramycin, roxithromycin, and rifampin and in dimethyl sulfoxide for ofloxacin, norfloxacin, and rolitetracycline. Twofold serial dilutions were prepared in sterile distilled water or RPMI for all these drugs. Final concentrations were distributed in triplicate into Falcon...

Anti-plasmodial activity of aroylhydrazone and thiosemicarbazone iron chelators: Effect on erythrocyte membrane integrity, parasite development and the intracellular labile iron pool

“…Assays were conducted according to the method of Pradines and colleagues [27] with modifications. Human erythrocytes were washed three times and resuspended in RPMI-1640 medium (without phenol red) supplemented with 10% human serum and buffered to pH 7.4 with 25 mM HEPES and 25 mM NaHCO 3 to a hematocrit of 2–2.5%.…”

Malaria Chemotherapeutics Part I: History of Antimalarial Drug Development, Currently Used Therapeutics, and Drugs in Clinical Development

“…This effect has been observed in laboratory strains with IC 50 values between 0.56 and 4.53 nm. [298] In different studies with field isolates, mean IC 50 values of 1.1, [172] 3.56, [299] and 6.2 nm [49] were obtained. The mammalian cytochrome complex is up to 1000-fold less sensitive against atovaquone (88).…”

The Fe2+‐Mediated Decomposition, PfATP6 Binding, and Antimalarial Activities of Artemisone and Other Artemisinins: The Unlikelihood of C‐Centered Radicals as Bioactive Intermediates

“…The idea that iron is required for activation of artemisinins appears to rely in large measure on reports that iron chelators such as desferrioxamine B (DFO) antagonize the antimalarial activities of artemisinins in vitro 29. 30 DFO is a hydrophilic chelating agent with exceptional affinity for Fe 3+ . The Fe 3+ chelate ferrioxamine B (FO) possesses a stability constant of 10 31 , which is 10 24 times greater than that of the Fe 2+ chelate 31.…”

“…We also examined the effects of DFO on PfATP6 inhibition and antimalarial activity of the artemisinins of Figure 2, and the effect of ascorbic acid on the aqueous Fe 2+ ‐mediated decomposition of the artemisinin derivatives. Ascorbic acid antagonizes in vitro antimalarial activity of the clinically used artemisinins,30, 52 but it is also a potent reductant for Fe 3+ to Fe 2+ in aqueous solutions, even where the former is associated with normally stable Fe 3+ chelates 35. 53…”