Synthesis, physicochemical characterization, and biological evaluation of 2-(1'-hydroxyalkyl)-3-hydroxypyridin-4-ones: novel iron chelators with enhanced pFe(3+) values.

The synthesis of a range of 2-(1'-hydroxyalkyl)-3-hydroxypyridin-4-ones as bidentate iron(III) chelators with potential for oral administration is described. The pK(a) values of the ligands and the stability constants of their iron(III) complexes have been determined. Results indicate that the introduction of a 1'-hydroxyalkyl group at the 2-position leads to a significant improvement in the pFe(3+) values.

6-Alkoxymethyl-3-hydroxy-4H-pyranones: potential ligands for cell-labelling with indium.

We have identified ligands for cell labelling with indium-111: 3-hydroxy-6-propoxymethyl-4H-pyran-4-one and 6-butoxymethyl-3-hydroxy-4H-pyran-4-one. The leucocyte labelling efficiencies of (111)In complexes of these ligands were higher and label stabilities were found to be similar compared with those obtained using (111)In-tropolonate. High labelling efficiencies of neutrophils and lymphocytes were achieved with (111)In complexes of pyranones.

Quantification of non-transferrin-bound iron in the presence of unsaturated transferrin.

Non-transferrin-bound iron (NTBI) has been reported to be associated with several clinical states such as thalassemia, hemochromatosis, and in patients receiving chemotherapy. We have investigated a number of ligands as potential alternatives to nitrilotriacetic acid (NTA) to capture NTBI without chelating transferrin- or ferritin-bound iron in plasma. We have established, however, that NTA is the optimal ligand to chelate the different forms of NTBI present in sera and can be adopted for utilization in the NTBI assay.

Gradient ion-pair high-performance liquid chromatographic method for analysis of 3-hydroxypyridin-4-one iron chelators.

A gradient ion-pair HPLC separation of highly hydrophilic 3-hydroxypyridin-4-one (HPO) iron chelators is described. The separation of HPOs was performed using a reversed-phase polymer HPLC column (PLRP-S 100 A, 15x0.46 cm ID, 5 microm).

Synthesis, physicochemical properties and biological evaluation of aromatic ester prodrugs of 1-(2'-hydroxyethyl)-2-ethyl-3-hydroxypyridin-4-one (CP102): orally active iron chelators with clinical potential.

The synthesis of seven aromatic ester derivatives of 1-(2'-hydroxyethyl)-2-ethyl-3-hydroxypyridin-4-one is described. These ester prodrugs have been designed to target iron chelators to the liver, the major iron storage organ. In principle this should improve chelation efficacy and minimize toxicity.

Synthesis and properties of (6,7-dimethoxy-4-coumaryl)alanine: a fluorescent peptide label.

The synthesis of racemic and l-(6,7-dimethoxy-4-coumaryl)alanine (Dmca) is described and some spectral and physicochemical properties are reported. The utility of Dmca as a highly sensitive and specific label for the quantitative detection of synthetic peptides in HPLC and in minimal essential media (MEM) is also described.

Investigation into the correlation between the structure of hydroxypyridinones and blood-brain barrier permeability.

Bidentate hydroxypyridinones are under active development as orally active iron chelators. With applications for the treatment of general body iron overload, for instance with thalassaemia, the distribution of the chelators should be limited to peripheral tissue and they should not enter the central nervous system. This study compares the predictive abilities of LogPoctanol and LogPcyclohexane and reports the existence of good correlations between blood-brain barrier (BBB) permeability and both values for N-alkylpyridinones.

Nicotianamine chelates both FeIII and FeII. Implications for metal transport in plants.

Nicotianamine (NA) occurs in all plants and chelates metal cations, including FeII, but reportedly not FeIII. However, a comparison of the FeII and ZnII affinity constants of NA and various FeIII-chelating aminocarboxylates suggested that NA should chelate FeIII. High-voltage electrophoresis of the FeNA complex formed in the presence of FeIII showed that the complex had a net charge of 0, consistent with the hexadentate chelation of FeIII.

In vivo iron mobilisation evaluation of hydroxypyridinones in 59Fe-ferritin-loaded rat model.

Although there are a number of well-characterised animal models available for testing and comparing the efficacy of iron chelators, most are expensive to operate and are not capable of providing rapid and reproducible results. The method described herein is based on the labelling of rat liver with 59Fe using rat 59Fe-ferritin. This method produces highly reproducible data of the type necessary for dose-response investigations, comparison of the efficacies of different administration routes, and structure activity studies.

Comparison of the stability of technetium-labeled peptides to challenge with cysteine.

We have labeled a series of short peptides with technetium-99m either by direct labeling at pH 11 or by exchange from [99mTc]technetium glucoheptonate. Typical labeling yields obtained were as follows: N-acetyl-Gly-Cys(S-Acm)-Gly-Cys(S-Acm)-Gly-NH2 (Acm = acetamidomethyl) 99%, S-benzoyl-mercaptoacetyltriglycine (S-Benzoyl-MAG3) 95%, mercaptoacetyldiglycine-NH2 (MAG2-NH2) 94%, MAG3 92%, N-acetyl-Aib-Aib-Cys-NH2 (Aib = aminoisobutyric acid) 91%, Gly-Gly-Gly-Gly 90%, N-acetyl-Gly-Gly-Cys-Gly 87%, cyclo-1, 4-(Gly-Gly-Gly-Gln) 40%, S-methyl-MAG2-NH2 0%. In the absence of cysteine, all of the labeled peptides were quite stable in solution, with at least 80-90% of the labeled peptide remaining at 24 h.

Synthesis, physicochemical properties, and evaluation of N-substituted-2-alkyl-3-hydroxy-4(1H)-pyridinones.

The synthesis of a range of 3-hydroxy-4(1H)-pyridinones with potential for the chelation of iron(III) is described. The pKa values of respective ligands and the stability constants of their iron(III) complexes are presented. The distribution coefficient values of a range of 48 hydroxypyridinones and their corresponding iron(III) complexes between 1-octanol and MOPS buffer (pH 7.

Comparative radical scavenging ability of bidentate iron (III) chelators.

Iron chelators can reduce radical damage inflicted on cells by two mechanisms, either direct scavenging of the radicals or by scavenging loosely bound iron which under aerobic conditions can generate radicals. Frequently it is not possible to distinguish between these two modes of action. 3-Hydroxypyridin-4-ones, in contrast to many iron(III) chelators are poor radical scavengers and therefore have potential in analysing mechanisms involved in biochemical and physiological processes which are centered on radical-induced cell injury.

Structural dependence of flavonoid interactions with Cu2+ ions: implications for their antioxidant properties.

The flavonoids constitute a large group of polyphenolic phytochemicals with antioxidant properties in vitro. The interactions of four structurally related flavonoids (quercetin, kaempferol, rutin and luteolin) with Cu2+ ions were investigated in terms of the extent to which they undergo complex formation through chelation or modification through oxidation, as well as in their structural dependence. The ortho 3',4'-dihydroxy substitution in the B ring is shown to be important for Cu2+-chelate formation, thereby influencing the antioxidant activity.

Non-transferrin-bound iron induced by myeloablative chemotherapy.

Previous studies have suggested that non-transferrin-bound plasma iron (NTBI) is present in patients undergoing cytotoxic chemotherapy, and that this may exacerbate untoward organ damage and increase the risk of bacterial infections following chemotherapy. However, the source of NTBI during myelosuppressive chemotherapy is controversial. In this study we have examined the kinetics of the appearance and disappearance of NTBI with chemotherapy.

Novel orally active iron chelators (3-hydroxypyridin-4-ones) enhance the biliary excretion of plasma non-transferrin-bound iron in rats.

Background/aims: It is well documented that levels of plasma non-transferrin-bound iron (NTBI), a particularly toxic form of iron, are increased in iron overload disorders. In light of the pathogenetic importance of NTBI in chronic iron overload, we have studied the ability of new orally active iron chelators to promote the biliary excretion of iron originating as plasma 55Fe-NTBI.

Methods: Biliary iron kinetics of plasma 55Fe-labeled NTBI and cumulative recoveries of 55Fe in bile were determined in normal and carbonyl iron-loaded rats receiving a single intragastric dose of iron chelator.

Chelation and mobilization of cellular iron by different classes of chelators.

Iron chelators belonging to three distinct chemical families were assessed in terms of their physicochemical properties and the kinetics of iron chelation in solution and in two biological systems. Several hydroxypyridinones, reversed siderophores, and desferrioxamine derivatives were selected to cover agents with different iron-binding stoichiometry and geometry and a wide range of lipophilicity, as determined by the octanol-water partition coefficients. The selection also included highly lipophilic chelators with potentially cell-cleavable ester groups that can serve as precursors of hydrophilic and membrane-impermeant chelators.

Metabolism and pharmacokinetics of 1-(2'-trimethylacetoxyethyl)-2-ethyl-3-hydroxypyridin-4-one (CP117) in the rat.

Metabolism and pharmacokinetics of 1-(2'-trimethylacetoxyethyl]-2-ethyl-3-hydroxypyridin-4-one (CP117) were studied in the rat. Urinary recovery studies were conducted in normal (oral and intravenous) and iron-overloaded rats (500 mg Fe/kg body weight; oral only). In normal rats, the majority of the dose recovered in the urine was as the hydrophilic metabolite, CP102, accounting for 69.

Protoporphyria induced by the orally active iron chelator 1,2-diethyl-3-hydroxypyridin-4-one in C57BL/10ScSn mice.

Administration in the drinking water of the orally-active iron chelator 1,2-diethyl-3-hydroxypyridin-4-one (CP94) to C57BL/10ScSn mice caused the development of hepatic protoporphyria. This was detected after 1 week and continued as long as the chelator was given (15 weeks). The more hydrophilic 1,2-dimethyl- and 1-hydroxyethyl,2-ethyl-analogues (CP20 and CP102) were also tested, but they were both inactive in inducing accumulation of protoporphyrin in the liver.

Flow cytometric assessment of hydroxypyridinone iron chelators on in vitro growth of drug-resistant malaria.

The resurgence of drug-resistant malaria makes urgent the evaluation of new antimalarial agents. This study describes a flow cytometric method (FCM) for testing in vitro drug susceptibility of Plasmodium falciparum malaria to several orally active hydroxypyridinone (CP) iron chelators and to the parenteral iron chelator desferrioxamine (DF). After exposure of parasites to various concentrations of iron chelating agents, aliquots of cultures were fixed with glutaraldehyde.

Chromatographic method for the determination of non-transferrin-bound iron suitable for use on the plasma and bronchoalveolar lavage fluid of preterm babies.

1. Non-protein-bound iron has been implicated in the aetiology of chronic lung disease of prematurity. 2.

Synthesis, physicochemical properties, and biological evaluation of hydroxypyranones and hydroxypyridinones: novel bidentate ligands for cell-labeling.

The synthesis of a range of hydroxypyranones and hydroxypyridinones with potential for the chelation of indium(III) is described. The crystal structures of two of the indium complexes are presented. The distribution coefficients of the ligands and the corresponding iron(III), gallium(III), and indium(III) complexes are reported.

The relationship of intracellular iron chelation to the inhibition and regeneration of human ribonucleotide reductase.

The depletion of cellular iron can lead to the inhibition of ribonucleotide reductase, preventing new DNA synthesis and hence inhibiting cell proliferation. Electron paramagnetic resonance (EPR) spectroscopy has been used to examine simultaneously for the first time the relationship between chelation of intracellular iron and the rate of removal and regeneration of the tyrosyl radical of ribonucleotide reductase within intact human leukemia K562 cells. The different physiochemical characteristics of relatively hydrophobic low molecular weight bidentate hydroxypyridinone chelators and the higher molecular weight hexadentate ferrioxamine have been exploited to elucidate these interactions further.

Kinetics of removal and reappearance of non-transferrin-bound plasma iron with deferoxamine therapy.

The rapidity and duration of the response of non-transferrin-bound iron (NTBPI) to chelation therapy are largely unknown and have important implications for the design of optimal chelation regimens. Methodology was developed to measure simultaneously NTBPI, deferoxamine (DFO), and its major metabolite. NTBPI was present in all but 2 of 28 thalassaemia major (TM) patients who had received conventional subcutaneous DFO the previous night, suggesting a short duration of NTBPI clearance by DFO.