Synthesis of 2-amido-3-hydroxypyridin-4(1H)-ones: novel iron chelators with enhanced pFe3+ values

Hydroxypyridinone-Based Iron Chelators with Broad-Ranging Biological Activities

Iron plays an essential role in all living cells because of its unique chemical properties. It is also the most abundant trace element in mammals. However, when iron is present in excess or inappropriately located, it becomes toxic. Excess iron can become involved in free radical formation, resulting in oxidative stress and cellular damage. Iron chelators are used to treat serious pathological disorders associated with systemic iron overload. Hydroxypyridinones stand out for their outstanding chelation properties, including high selectivity for Fe³⁺ in the biological environment, ease of derivatization, and good biocompatibility. Herein, we overview the potential for multifunctional hydroxypyridinone-based chelators to be used as therapeutic agents against a wide range of diseases associated either with systemic or local elevated iron levels.

CN128: A New Orally Active Hydroxypyridinone Iron Chelator

Deferoxamine, deferiprone, and deferasirox are used for the treatment of systemic iron overload, although they possess limitations due to lack of oral activity, lower efficacy, and side effects. These limitations led to a search for an orally active iron chelator with an improved therapeutic index. The lower efficacy of deferiprone is due to rapid glucuronidation, leading to the formation of a nonchelating metabolite. Here, we demonstrate that the influence of metabolism can be reduced by introducing a sacrificial site for glucuronidation. A log P-guided investigation of 20 hydroxpyridinones led to the identification of CN128. The Fe(III) affinity and metal selectivity of CN128 are similar to those of deferiprone, the log P value is more lipophilic, and its iron scavenging ability is superior. Overall, CN128 was demonstrated to be safe in a range of toxicity assessments and is now in clinical trials for the treatment of β-thalassemia after regular blood transfusion.

Synthesis, Molecular Modelling and Biological Studies of 3-hydroxypyrane- 4-one and 3-hydroxy-pyridine-4-one Derivatives as HIV-1 Integrase Inhibitors

BACKGROUND

Despite the progress in the discovery of antiretroviral compounds for treating HIV-1 infection by targeting HIV integrase (IN), a promising and well-known drug target against HIV-1, there is a growing need to increase the armamentarium against HIV, for avoiding the drug resistance issue.

OBJECTIVE

To develop novel HIV-1 IN inhibitors, a series of 3-hydroxy-pyrane-4-one (HP) and 3- hydroxy-pyridine-4-one (HPO) derivatives have been rationally designed and synthesized.

METHODS

To provide a significant characterization of the novel compounds, in-depth computational analysis was performed using a novel HIV-1 IN/DNA binary 3D-model for investigating the binding mode of the newly conceived molecules in complex with IN. The 3D-model was generated using the proto-type foamy virus (PFV) DNA as a structural template, positioning the viral polydesoxyribonucleic chain into the HIV-1 IN homology model. Moreover, a series of in vitro tests were performed including HIV-1 activity inhibition, HIV-1 IN activity inhibition, HIV-1 IN strand transfer activity inhibition and cellular toxicity.

RESULTS

Bioassay results indicated that most of HP analogues including HPa, HPb, HPc, HPd, HPe and HPg, showed favorable inhibitory activities against HIV-1-IN in the low micromolar range. Particularly halogenated derivatives (HPb and HPd) offered the best biological activities in terms of reduced toxicity and optimum inhibitory activities against HIV-1 IN and HIV-1 in cell culture.

CONCLUSION

Halogenated derivatives, HPb and HPd, displayed the most promising anti-HIV profile, paving the way to the optimization of the presented scaffolds for developing new effective antiviral agents.

Synthesis and Structure-Activity Relationships of the Novel Antimalarials 5-Pyridinyl-4(1 H)-Pyridones

Malaria is still one of the most prevalent parasitic infections in the world, with half of the world's population at risk for malaria. The effectiveness of current antimalarial therapies, even that of the most recent class of antimalarial drugs (artemisinin-combination therapies, ACTs), is under continuous threat by the spread of resistant Plasmodium strains. As a consequence, there is still an urgent requirement for new antimalarial drugs. We previously reported the identification of 4(1 H)-pyridones as a novel series with potent antimalarial activities. The low solubility was identified as an issue to address. In this paper, we describe the synthesis and biological evaluation of 4(1 H)-pyridones with potent antimalarial activities in vitro and in vivo and improved pharmacokinetic profiles. Their main structural novelties are the presence of polar moieties, such as hydroxyl groups, and the replacement of the lipophilic phenyl rings with pyridines on their lipophilic side chains.

Preparation of 5-Functionalised Pyridine Derivatives using a Br/Mg Exchange Reaction: Application to the Synthesis of an Iron-Chelator Prodrug

A novel preparation of 5-functionalised pyridine derivatives is reported from 5-bromo-4-tosyloxypyridines via a Br/Mg exchange procedure with i-PrMgCl·LiCl, followed by addition of an electrophile. The reaction was carried out under mild conditions and gave good to high yields. The resulting 5-functionalised pyridine derivatives enrich the library of pyridinone-type iron-chelator prodrugs.

Investigation of the complexation of natZr(iv) and 89Zr(iv) by hydroxypyridinones for the development of chelators for PET imaging applications

Three hydroxypyridinone (HOPO) positional isomers - 1,2-HOPO (L1H) and its water soluble analogue (L1'H), 3,2-HOPO (L2H) and 3,4-HOPO (L3H) have been investigated for the complexation of Zr(iv). Potentiometric and UV-Vis spectrometric studies show a higher thermodynamic stability for the formation of Zr(L1')4 in comparison with Zr(L2)4 and Zr(L3)4 as well as a higher kinetic inertness in competition studies with EDTA or Fe3+ at a radiotracer concentration with 89Zr. Besides the low pKa of L1H or L1'H (pKa = 5.01) in comparison with L2H and L3H (pKa = 8.83 and 9.55, respectively), the higher stability of Zr(L1')4 can be attributed in part to the presence of the amide group next to the chelating oxygen that induces intramolecular H-bond and amide/π interactions that were observed by X-ray crystallography and confirmed by quantum chemical calculations. The data presented here indicate that the 1,2-HOPO L1' exhibits the best characteristics for Zr(iv) complexation. However, 3,2-HOPO and 3,4-HOPO patterns, if appropriately tuned, for instance with the addition of an amide group as in the 1,2-HOPO ligand, may also become interesting alternatives for the design of Zr(iv) chelators with improved characteristics for applications in nuclear imaging with 89Zr.

Hydroxypyridinone Chelators: From Iron Scavenging to Radiopharmaceuticals for PET Imaging with Gallium-68

Derivatives of 3,4-hydroxypyridinones have been extensively studied for in vivo Fe3+ sequestration. Deferiprone, a 1,2-dimethyl-3,4-hydroxypyridinone, is now routinely used for clinical treatment of iron overload disease. Hexadentate tris(3,4-hydroxypyridinone) ligands (THP) complex Fe3+ at very low iron concentrations, and their high affinities for oxophilic trivalent metal ions have led to their development for new applications as bifunctional chelators for the positron emitting radiometal, 68Ga3+, which is clinically used for molecular imaging in positron emission tomography (PET). THP-peptide bioconjugates rapidly and quantitatively complex 68Ga3+ at ambient temperature, neutral pH and micromolar concentrations of ligand, making them amenable to kit-based radiosynthesis of 68Ga PET radiopharmaceuticals. 68Ga-labelled THP-peptides accumulate at target tissue in vivo, and are excreted largely via a renal pathway, providing high quality PET images.

Synthesis and Validation of a Hydroxypyrone-Based, Potent, and Specific Matrix Metalloproteinase-12 Inhibitor with Anti-Inflammatory Activity In Vitro and In Vivo

A hydroxypyrone-based matrix metalloproteinase (MMP) inhibitor was synthesized and assayed for its inhibitory capacity towards a panel of ten different MMPs. The compound exhibited selective inhibition towards MMP-12. The effects of inhibition of MMP-12 on endotoxemia and inflammation-induced blood-cerebrospinal fluid barrier (BCSFB) disruption were assessed both in vitro and in vivo. Similar to MMP-12 deficient mice, inhibitor-treated mice displayed significantly lower lipopolysaccharide- (LPS-) induced lethality compared to vehicle treated controls. Following LPS injection Mmp-12 mRNA expression was massively upregulated in choroid plexus tissue and a concomitant increase in BCSFB permeability was observed, which was restricted in inhibitor-treated mice. Moreover, an LPS-induced decrease in tight junction permeability of primary choroid plexus epithelial cells was attenuated by inhibitor application in vitro. Taken together, this hydroxypyrone-based inhibitor is selective towards MMP-12 and displays anti-inflammatory activity in vitro and in vivo.

Tripodal tris(hydroxypyridinone) ligands for immunoconjugate PET imaging with (89)Zr(4+): comparison with desferrioxamine-B

Due to its long half-life (78 h) and decay properties (77% electron capture, 23% β(+), Emax = 897 keV, Eav = 397 keV, Eγ = 909 keV, Iγ = 100%) (89)Zr is an appealing radionuclide for immunoPET imaging with whole IgG antibodies. Derivatives of the siderophore desferrioxamine-B (H3DFO) are the most widely used bifunctional chelators for coordination of (89)Zr(4+) because the radiolabeling of the resulting immunoconjugates is rapid under mild conditions. (89)Zr-DFO complexes are reportedly stable in vitro but there is evidence that (89)Zr(4+) is released in vivo, and subsequently taken up by the skeleton. We have evaluated a novel tripodal tris(hydroxypyridinone) chelator, H3CP256 and its bifunctional maleimide derivative, H3YM103, for coordination of Zr(4+) and compared the NMR spectra, and the (89)Zr(4+) radiolabeling, antibody conjugation, serum stability and in vivo distribution of radiolabelled immunoconjugates with those of H3DFO and its analogues. H3CP256 coordinates (89)Zr(4+) at carrier-free concentrations forming [(89)Zr(CP256)](+). Both H3DFO and H3CP256 were efficiently radiolabelled using [(89)Zr(C2O4)4](4-) at ambient temperature in quantitative yield at pH 6-7 at millimolar concentrations of chelator. Competition experiments demonstrate that (89)Zr(4+) dissociates from [(89)Zr(DFO)](+) in the presence of one equivalent of H3CP256 (relative to H3DFO) at pH 6-7, resulting largely in [(89)Zr(CP256)](+). To assess the stability of H3DFO and H3YM103 immunoconjugates radiolabelled with (89)Zr, maleimide derivatives of the chelators were conjugated to the monoclonal antibody trastuzumab via reduced cysteine side chains. Both immunoconjugates were labelled with (89)Zr(4+) in >98% yield at high specific activities and the labeled immunoconjugates were stable in serum with respect to dissociation of the radiometal. In vivo studies in mice indicate that (89)Zr(4+) dissociates from YM103-trastuzumab with significant amounts of activity becoming associated with bones and joints (25.88 ± 0.58% ID g(-1) 7 days post-injection). In contrast, <8% ID g(-1) of (89)Zr activity becomes associated with bone in animals administered (89)Zr-DFO-trastuzumab over the course of 7 days. The tris(hydroxypyridinone) chelator, H3CP256, coordinates (89)Zr(4+) rapidly under mild conditions, but the (89)Zr-labelled immunoconjugate, (89)Zr-YM103-trastuzumab was observed to release appreciable amounts of (89)Zr(4+)in vivo, demonstrating inferior stability when compared with (89)Zr-DFO-trastuzumab. The significantly lower in vivo stability is likely to be a result of lower kinetic stability of the Zr(4+) tris(hydroxypyridinone complex) relative to that of DFO and its derivatives.

Antimalarial 4(1H)-pyridones bind to the Qi site of cytochrome bc1

Cytochrome bc1 is a proven drug target in the prevention and treatment of malaria. The rise in drug-resistant strains of Plasmodium falciparum, the organism responsible for malaria, has generated a global effort in designing new classes of drugs. Much of the design/redesign work on overcoming this resistance has been focused on compounds that are presumed to bind the Q(o) site (one of two potential binding sites within cytochrome bc1 using the known crystal structure of this large membrane-bound macromolecular complex via in silico modeling. Cocrystallization of the cytochrome bc1 complex with the 4(1H)-pyridone class of inhibitors, GSK932121 and GW844520, that have been shown to be potent antimalarial agents in vivo, revealed that these inhibitors do not bind at the Q(o) site but bind at the Q(i )site. The discovery that these compounds bind at the Q(i) site may provide a molecular explanation for the cardiotoxicity and eventual failure of GSK932121 in phase-1 clinical trial and highlight the need for direct experimental observation of a compound bound to a target site before chemical optimization and development for clinical trials. The binding of the 4(1H)-pyridone class of inhibitors to Q(i) also explains the ability of this class to overcome parasite Q(o)-based atovaquone resistance and provides critical structural information for future design of new selective compounds with improved safety profiles.

Desferrithiocin: a search for clinically effective iron chelators

The successful search for orally active iron chelators to treat transfusional iron-overload diseases, e.g., thalassemia, is overviewed. The critical role of iron in nature as a redox engine is first described, as well as how primitive life forms and humans manage the metal. The problems that derive when iron homeostasis in humans is disrupted and the mechanism of the ensuing damage, uncontrolled Fenton chemistry, are discussed. The solution to the problem, chelator-mediated iron removal, is clear. Design options for the assembly of ligands that sequester and decorporate iron are reviewed, along with the shortcomings of the currently available therapeutics. The rationale for choosing desferrithiocin, a natural product iron chelator (a siderophore), as a platform for structure-activity relationship studies in the search for an orally active iron chelator is thoroughly developed. The study provides an excellent example of how to systematically reengineer a pharmacophore in order to overcome toxicological problems while maintaining iron clearing efficacy and has led to three ligands being evaluated in human clinical trials.

Potent antimalarial 4-pyridones with improved physico-chemical properties

Antimalarial 4-pyridones are a novel class of inhibitors of the plasmodial mitochondrial electron transport chain targeting Cytochrome bc1 (complex III). In general, the most potent 4-pyridones are lipophilic molecules with poor solubility in aqueous media and low oral bioavailability in pre-clinical species from the solid dosage form. The strategy of introducing polar hydroxymethyl groups has enabled us to maintain the high levels of antimalarial potency observed for other more lipophilic analogues whilst improving the solubility and the oral bioavailability in pre-clinical species.

Preparation and quality control of the [sm]-samarium maltolate complex as a lanthanide mobilization product in rats

Development of lanthanide detoxification agents and protocols is of great importance in management of overdoses. Due to safety of maltol as a detoxifying agent in metal overloads, it can be used as a lanthanide detoxifying agent. In order to demonstrate the biodistribution of final complex, [¹⁵³Sm]-samarium maltolate was prepared using Sm-153 chloride (radiochemical purity >99.9%; ITLC and specific activity). The stability of the labeled compound was determined in the final solution up to 24h as well as the partition coefficient. Biodistribution studies of Sm-153 chloride, [¹⁵³Sm]-samarium maltolate were carried out in wild-type rats comparing the critical organ uptakes. Comparative study for Sm³⁺ cation and the labeled compound was conducted up to 48 h, demonstrating a more rapid wash out for the labeled compound. The effective and biological half lives of 2.3 h and 2.46h were calculated for the complex. The data suggest the detoxification property of maltol formulation for lanthanide overdoses.

Kojic acid derivatives as histamine H(3) receptor ligands

The histamine H(3) receptor (H(3)R) is a promising target in the development of new compounds for the treatment of mainly centrally occurring diseases. However, emerging novel therapeutic concepts have been introduced and some indications in the H(3)R field, e.g. migraine, pain or allergic rhinitis, might take advantage of peripherally acting ligands. In this work, kojic acid-derived structural elements were inserted into a well established H(3)R antagonist/inverse agonist scaffold to investigate the bioisosteric potential of γ-pyranones with respect to the different moieties of the H(3)R pharmacophore. The most affine compounds showed receptor binding in the low nanomolar concentration range. Evaluation and comparison of kojic acid-containing ligands and their corresponding phenyl analogues (3-7) revealed that the newly integrated scaffold greatly influences chemical properties (S Log P, topological polar surface area (tPSA)) and hence, potentially modifies the pharmacokinetic profile of the different derivatives. Benzyl-1-(4-(3-(piperidin-1-yl)propoxy)phenyl)methanamine ligands 3 and 4 belong to the centrally acting diamine-based class of H(3)R antagonist/inverse agonist, whereas kojic acid analogues 6 and 7 might act peripherally. The latter compounds state promising lead structures in the development of H(3)R ligands with a modified profile of action.

Identifying chelators for metalloprotein inhibitors using a fragment-based approach

Fragment-based lead design (FBLD) has been used to identify new metal-binding groups for metalloenzyme inhibitors. When screened at 1 mM, a chelator fragment library (CFL-1.1) of 96 compounds produced hit rates ranging from 29% to 43% for five matrix metalloproteases (MMPs), 24% for anthrax lethal factor (LF), 49% for 5-lipoxygenase (5-LO), and 60% for tyrosinase (TY). The ligand efficiencies (LE) of the fragment hits are excellent, in the range of 0.4-0.8 kcal/mol. The MMP enzymes all generally elicit the same chelators as hits from CFL-1.1; however, the chelator fragments that inhibit structurally unrelated metalloenzymes (LF, 5-LO, TY) vary considerably. To develop more advanced hits, one hit from CFL-1.1, 8-hydroxyquinoline, was elaborated at four different positions around the ring system to generate new fragments. 8-Hydroxyquinoline fragments substituted at either the 5- or 7-positions gave potent hits against MMP-2, with IC(50) values in the low micromolar range. The 8-hydroxyquinoline represents a promising new chelator scaffold for the development of MMP inhibitors that was discovered by use of a metalloprotein-focused chelator fragment library.

Amido-3-hydroxypyridin-4-ones as iron(III) ligands

The synthesis and physicochemical properties of a range of 2- and 6-amido-3-hydroxypyridin-4-ones are described. All the amido-substituted 3-hydroxypyridin-4-ones have lower pK(a) values than 1,2-dimethyl-3-hydroxypyridin-4-one (deferiprone). This is due to the inductive effect of the amido group. Furthermore, the pK(a) values of the 3-hydroxy group in 1-nonsubstituted pyridinones are dramatically lower than those of the corresponding 1-alkyl analogues, indicating that a strong hydrogen bond exists between the 2-amido function and the 3-oxygen anion, which stabilises the anion. As a result of the decreased competition with protons, the pFe(3+) values of this group of molecules are higher than that of deferiprone. The distribution coefficients of these molecules are also increased despite the lack of a hydrophobic 1-alkyl substituent and this is ascribed to the intramolecular hydrogen bond. X-ray diffraction studies confirm the existence of the intramolecular hydrogen bond.

The selective quantification of iron by hexadentate fluorescent probes

The synthesis of four hexadentate fluorescent probes is described, where the fluorescent moiety is based on either coumarin or fluorescein and the chelating moiety is based on either 3-hydroxypyridin-4-one or 3-hydroxypyran-4-one. The fluorescence is quenched when the probe chelating moieties bind iron. The probes were found to be selective for iron over other metals such as Cu, Zn, Ni, Mn and Co. The effect of Cu on fluorescence quenching can be eliminated in the presence of N,N,N',N'-tetrakis(2-pyridylmethyl)-ethylenediamine. Competition studies demonstrate that the exchange of iron between pyridinone-based probes and apotransferrin is very slow. The ability to scavenge iron from oligomeric iron(III) citrate complexes demonstrate that the pyridinone probes scavenges iron faster than deferiprone and desferrioxamine. The fluorescence intensity of the fluorescein-based probe is quantitatively related to the iron concentration with the limit of detection being 10(-8)M.

Synthesis of hydroxypyrone- and hydroxythiopyrone-based matrix metalloproteinase inhibitors: developing a structure-activity relationship

The zinc(II)-dependent matrix metalloproteinases (MMPs) are associated with a variety of diseases. Development of inhibitors to modulate MMP activity has been an active area of investigation for therapeutic development. Hydroxypyrones and hydroxythiopyrones are alternative zinc-binding groups (ZBGs) that, when combined with peptidomimetic backbones, comprise a novel class of MMP inhibitors (MMPi). In this report, a series of hydroxypyrone- and hydroxythiopyrone-based MMPi with aryl backbones at the 2-, 5-, and 6-positions of the hydroxypyrone ring have been synthesized. Synthetic routes for developing inhibitors with substituents at two of these positions (so-called double-handed inhibitors) are also explored. The MMP inhibition profiles and structure-activity relationship of synthesized hydroxypyrones and hydroxythiopyrones have been analyzed. The results here show that the ZBG, the position of the backbone on the ZBG, and the nature of the linker between the ZBG and backbone are critical for MMPi activities.

Design, synthesis and evaluation of new 6-substituted-5-benzyloxy-4-oxo-4H-pyran-2-carboxamides as potential Src inhibitors

Src family kinases (SFKs) are nonreceptor tyrosine kinases that are reported to be critical for cancer progression. Inhibiting the catalytic activity of these proteins has become one of the major therapeutic concepts in contemporary drug discovery. We report here the design and the synthesis of novel 6-substituted-5-benzyloxy-4-oxo-4H-pyran-2-carboxamides as potential inhibitors of Src kinase. The synthesis of these derivatives and the preliminary results of biological activity will be discussed.

Efficient synthesis of 5-amido-3-hydroxy-4-pyrones as inhibitors of matrix metalloproteinases

3-hydroxy-4-pyrones are a class of important metal chelators with versatile medicinal applications. An efficient pathway for the preparation of new 5-amido-3-hydroxy-4-pyrone derivatives has been developed. The synthesized 5-amido-3-hydroxy-4-pyrones have been evaluated as inhibitors of matrix metalloproteinases.

Chelation and determination of labile iron in primary hepatocytes by pyridinone fluorescent probes

A series of fluorescent iron chelators has been synthesized such that a fluorescent function is covalently linked to a 3-hydroxypyridin-4-one. In the present study, the fluorescent iron chelators were loaded into isolated rat hepatocytes. The intracellular fluorescence was not only quenched by an addition of a highly lipophilic 8-hydroxyquinoline-iron(III) complex but also was dequenched by the addition of an excess of the membrane-permeable iron chelator CP94 (1,2-diethyl-3-hydroxypyridin-4-one). The time course of uptake of iron and iron chelation in single, intact cells was recorded on-line by using digital fluorescence microscopy. Intracellular concentrations of various fluorescent iron chelators were determined by using a spectrofluorophotometer subsequent to lysis of probe-loaded cells and were found to depend on their partition coefficients; the more hydrophobic the compound, the higher the intracellular concentration. An ex situ calibration method was used to determine the chelatable iron pool of cultured rat hepatocytes. CP655 (7-diethylamino-N-[(5-hydroxy-6-methyl-4-oxo-1,4-dihydropyridin-3-yl)methyl]-N-methyl-2-oxo-2H-chromen-3-carboxamide), which is a moderately lipophilic fluorescent chelator, was found to be the most sensitive probe for monitoring chelatable iron, as determined by the intracellular fluorescence increase induced by the addition of CP94. The concentration of the intracellular chelatable iron pool in hepatocytes was determined by this probe to be 5.4+/-1.3 microM.

Metal complexes of maltol and close analogues in medicinal inorganic chemistry

The family of hydroxypyrones and close congeners, the hydroxypyridinones, is a particularly versatile class of ligands. The most widely investigated for medicinal applications are the 3-hydroxy-4-pyrones and the 1,2- 3,2- and 3,4-hydroxypyridinones. Key features of these ligands are: a six-membered ring, with a ring N or O atom either ortho or para to a ketone group, and two ortho exocyclic oxygen atoms. Readily functionalizable, the hydroxypyrones and hydroxypyridinones allow one to achieve a range of di- and trivalent metallocomplex stabilities and can include tissue or molecular targeting features by design. Research over the past several decades has greatly expanded the array of ligands that are the subject of this critical review. Ligand applications as diverse as iron removal or supplementation, contrast agents in imaging applications, and mobilization of undesirable excess metal ions will be surveyed herein.

The Evolution of Iron Chelators for the Treatment of Iron Overload Disease and Cancer

The evolution of iron chelators from a range of primordial siderophores and aromatic heterocyclic ligands has lead to the formation of a new generation of potent and efficient iron chelators. For example, various siderophore analogs and synthetic ligands, including ICL670A [4-[3,5-bis-(hydroxyphenyl)-1,2,4-triazol-1-yl]-benzoic acid], 4'-hydroxydesazadesferrithiocin, and Triapine, have been developed from predecessors and illustrate potent iron-mobilizing or antineoplastic activities. This review focuses on the evolution of iron chelators from initial lead compounds through to the development of novel chelating agents, many of which show great potential to be clinically applied in the treatment of iron overload disease and cancer.

Improved high-performance liquid chromatographic method for the pharmacokinetic studies of a novel iron chelator, CP502, in rats

An improved reverse-phase high-performance liquid chromatographic method (RP-HPLC) for the determination of a novel iron chelator CP502 (1,6-dimethyl-3-hydroxy-4-(1H)-pyridinone-2-carboxy-(N-methyl)-amide hydrochloride) in rat plasma, urine and feces was developed and validated. The separation was performed on a polymeric column using a mobile phase composed of 1mM ethylenediaminetetra-acetic acid disodium salt (EDTA), acetonitrile, methanol and methylene chloride. Separation of CP502 from plasma, urine or feces endogenous compounds was achieved by gradient elution. Retention times of CP502 and its major metabolite (glucuronide) were about 13 and 4 min, respectively. The method was validated in terms of limit of detection (LOD), limit of quantification (LOQ), selectivity (endogenous from plasma, urine or feces), linearity, extraction recovery, robustness (column selection, mobile phase composition, detection mode, internal standard (IS) selection, analyte stability), day-to-day reproducibility and system suitability (repeatability, peak symmetry and resolution). The method is applicable to bioavailability and pharmacokinetic studies of CP502 in rats.

Human immunodeficiency virus type 1 replication inhibition by the bidentate iron chelators CP502 and CP511 is caused by proliferation inhibition and the onset of apoptosis

BACKGROUND

The iron chelators deferoxamine (DF) and deferiprone (CP20) have been shown to inhibit human immunodeficiency virus type 1 (HIV-1) replication in human peripheral blood lymphocytes (PBL). The orally active bidentate chelators CP502 and CP511, which also belong to the 3-hydroxypyridin-4-one family, but with higher affinities for iron than CP20, were monitored for their antiviral properties by checking for p24 antigen production and nuclear factor (NF)-kappaB activation, and their ability to induce apoptosis.

MATERIALS AND METHODS

Human PBLs were isolated from HIV-1 seronegative donors and subsequently infected with HIV-1(Ba-L) for 2 h. After 5 days' incubation, HIV-1 replication was monitored by p24 antigen production. Cellular proliferation as well as caspase-3 activity were monitored in uninfected cells after a period of 5 days and after 1 day infection, respectively. NF-kappaB activity was also monitored by electromobility shift assays (EMSA) performed on nuclear extracts of Jurkat cells treated with the different chelators for 4 h.

RESULTS

CP502 and CP511 decrease HIV-1 replication by decreasing cellular proliferation in a similar manner to DF and CP20. CP511 seemed to be more potent than either CP502 or CP20. Due to the reduction in cellular proliferation, there was an increase in caspase-3 activity after 24 h incubation. NF-kappaB activity was not affected by any of the chelators.

CONCLUSIONS

Iron chelators with high affinities for iron, which are under development for the treatment of iron overload, could contribute to the reduction of HIV-1 replication in infected patients by cellular proliferation inhibition rather than by a direct antiviral action.

Design of clinically useful iron(III)-selective chelators

Iron overload is a serious clinical condition which can be largely prevented by the use of iron-specific chelating agents. Desferrioxamine-B, the most widely used iron chelator in haematology over the past 30 years, has a major disadvantage of being orally inactive. Consequently, the successful design of an orally active, nontoxic, selective iron chelator has become a much sought after goal. In order to identify an ideal iron chelator for clinical use, a range of specifications must be considered such as metal selectivity and affinity, kinetic stability of the complex, bioavailability and toxicity. A wide range of chelator types bind iron(III) and of these, hexa-, tri-, and bidentate are capable of providing iron(III) with the favoured octahedral environment. In this review, the comparative properties of such ligands are discussed, examples being selected from hydroxamates, aminocarboxylates, hydroxypyridinones, orthosubstituted phenols and triazoles.

Secondary iron overload

Transfusion therapy for inherited anemias and acquired refractory anemias both improves the quality of life and prolongs survival. A consequence of chronic transfusion therapy is secondary iron overload, which adversely affects the function of the heart, the liver and other organs. This session will review the use of iron chelating agents in the management of transfusion-induced secondary iron overload. In Section I Dr. John Porter describes techniques for the administration of deferoxamine that exploit the pharmacokinetic properties of the drug and minimize potential toxic side effects. The experience with chelation therapy in patients with thalassemia and sickle cell disease will be reviewed and guidelines will be suggested for chelation therapy of chronically transfused adults with refractory anemias. In Section II Dr. Nancy Olivieri examines the clinical consequences of transfusion-induced secondary iron overload and suggests criteria useful in determining the optimal timing of the initiation of chelation therapy. Finally, Dr. Olivieri discusses the clinical trials evaluating orally administered iron chelators.