Recent developments on 3-hydroxy-4-pyridinones with respect to their clinical applications

An update on the novel and approved drugs for Alzheimer disease

Introduction

Given the severity of the condition and the increasing number of patients, developing effective therapies for Alzheimer's disease has become a significant necessity. Aggregation of Amyloid-Beta (Aβ) plaques and Tau Protein Tangles in the brain's nerve tissue are two of the most histopathological/pathophysiological symptoms. Another important element involved in the etiology of Alzheimer's disease is the reduction in acetylcholine (ACh) levels in the brain. Currently available medications for Alzheimer's disease treatment, such as cholinesterase inhibitors and an antagonist of the N-methyl-d-aspartate receptor, can temporarily reduce dementia symptoms but not stop or reverse disease development. In addition, several medicinal plants have been shown to diminish the degenerative characteristics associated with Alzheimer's disease, either in its crude form or as isolated chemicals.

Aim

This review summarises the results from previous studies that reflect an array of novel therapies underway in various phases of clinical trials. Many are discontinued due to non-adherence to the designed endpoints or the surfacing of unavoidable side effects. The present piece of article focuses on the approved drugs for the treatment of Alzheimer's disease and their related mode of action as well as the promising therapies for the treatment of the said disease. Special attention has been placed on the researched herbal drugs, with the pipeline of novel therapies underway in various phases of clinical trials.

Result

The current article includes a list of approved pharmaceuticals for treating Alzheimer's disease, prospective therapies for the illness's treatment, and a pipeline of novel therapies in various stages of clinical trials.

Conclusion

The results suggest that the drugs under clinical trials may open new pathways for the effective treatment of patients with Alzheimer's disease while improving their quality of life.

Hydroxypyrone derivatives in drug discovery: from chelation therapy to rational design of metalloenzyme inhibitors

The versatile structural motif of hydroxypyrone is found in natural products and can be easily converted into hydroxypyridone and hydroxythiopyridone analogues. The favourable toxicity profile and ease of functionalization to access a vast library of compounds make them an ideal structural scaffold for drug design and discovery. This versatile scaffold possesses excellent metal chelating properties that can be exploited for chelation therapy in clinics. Deferiprone [1,2-dimethyl-3-hydroxy-4(1H)-one] was the first orally active chelator to treat iron overload in thalassemia major. Metal complexes of hydroxy-(thio)pyr(id)ones have been investigated as magnetic resonance imaging contrast agents, and anticancer and antidiabetic agents. In recent years, this compound class has demonstrated potential in discovering and developing metalloenzyme inhibitors. This review article summarizes recent literature on hydroxy-(thio)pyr(id)ones as inhibitors for metalloenzymes such as histone deacetylases, tyrosinase and metallo-β-lactamase. Different approaches to the design of hydroxy-(thio)pyr(id)ones and their biological properties against selected metalloenzymes are discussed.

Synthesis, physicochemical characterization and neuroprotective evaluation of novel 1-hydroxypyrazin-2(1H)-one iron chelators in an in vitro cell model of Parkinson's disease

Iron dysregulation, dopamine depletion, cellular oxidative stress and α-synuclein protein mis-folding are key neuronal pathological features seen in the progression of Parkinson's disease. Iron chelators endowed with one or more therapeutic modes of action have long been suggested as disease modifying therapies for its treatment. In this study, novel 1-hydroxypyrazin-2(1H)-one iron chelators were synthesized and their physicochemical properties, iron chelation abilities, antioxidant capacities and neuroprotective effects in a cell culture model of Parkinson's disease were evaluated. Physicochemical properties (log β, log D7.4, pL0.5) suggest that these ligands have a poorer ability to penetrate cell membranes and form weaker iron complexes than the closely related 1-hydroxypyridin-2(1H)-ones. Despite this, we show that levels of neuroprotection provided by these ligands against the catecholaminergic neurotoxin 6-hydroxydopamine in vitro were comparable to those seen previously with the 1-hydroxypyridin-2(1H)-ones and the clinically used iron chelator Deferiprone, with two of the ligands restoring cell viability to ≥89% compared to controls. Two of the ligands were endowed with additional phenol moieties in an attempt to derive multifunctional chelators with dual iron chelation/antioxidant activity. However, levels of neuroprotection with these ligands were no greater than ligands lacking this moiety, suggesting the neuroprotective properties of these ligands are due primarily to chelation and passivation of intracellular labile iron, preventing the generation of free radicals and reactive oxygen species that otherwise lead to the neuronal cell death seen in Parkinson's disease.

High Antiproliferative Activity of Hydroxythiopyridones over Hydroxypyridones and Their Organoruthenium Complexes

Hydroxypyr(id)ones are a pharmaceutically important class of compounds that have shown potential in diverse areas of drug discovery. We investigated the 3-hydroxy-4-pyridones 1a-1c and 3-hydroxy-4-thiopyridones 1d-1f as well as their Ru(η⁶-p-cymene)Cl complexes 2a-2f, and report here the molecular structures of 1b and 1d as determined by X-ray diffraction analysis. Detailed cell biological investigations revealed potent cytotoxic activity, in particular of the 3-hydroxy-4-thiopyridones 1d-1f, while the Ru complexes of both compound types were less potent, despite still showing antiproliferative activity in the low μM range. The compounds did not modulate the cell cycle distribution of cancer cells but were cytostatic in A549 and cytotoxic in NCI-H522 non-small lung cancer cells, among other effects on cancer cells.

Speciation Studies of Bifunctional 3-Hydroxy-4-Pyridinone Ligands in the Presence of Zn2+ at Different Ionic Strengths and Temperatures

The acid–base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn²⁺, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and ¹H NMR spectroscopic titrations, carried out at 0.15 ≤ I/mol ⁻¹ ≤ 1.00 and 288.15 ≤ T/K ≤ 310.15. A study at I = 0.15 mol L⁻¹ and T = 298.15 K was also performed for other three Zn²⁺/L^z− systems, with ligands belonging to the same family of compounds. The processing of experimental data allowed the determination of protonation and stability constants, which showed accordance with the data obtained from the different analytical techniques used, and with those reported in the literature for the same class of compounds. ESI-MS spectrometric measurements provided support for the formation of the different Zn²⁺/ligand species, while computational molecular simulations allowed information to be gained on the metal–ligand coordination. The dependence on ionic strength and the temperature of equilibrium constants were investigated by means of the extended Debye–Hückel model, the classical specific ion interaction theory, and the van’t Hoff equations, respectively.

Functionalization of Ruthenium(II)(η6 -p-cymene)(3-hydroxy-2-pyridone) Complexes with (Thio)Morpholine: Synthesis and Bioanalytical Studies

Hydroxypyr(id)ones constitute an emerging platform for the design of drug molecules, owing to their favorable biocompatibility and toxicity profiles. Herein, [Ru^II (η⁶ -p-cymene)] complexes with 3-hydroxy-2-pyridinone functionalized with morpholine and thiomorpholine, as a means often used in medicinal chemistry to alter the physicochemical properties of drug compounds, are reported. The compounds underwent hydrolysis of the Ru-Cl bond and the aqua species were stable for up to 48 h in aqueous solution, as observed by ¹ H NMR spectroscopy and ESI-MS. The compounds formed adducts with amino acids and proteins through cleavage of the pyridinone ligand. Binding experiments to the nucleosome core particle by means of X-ray crystallography revealed similar reactivity and exclusive binding to histidine moieties of the histone proteins. Preliminary cyclin-dependent kinase 2 (CDK2)/cyclin A kinase inhibitory studies revealed promising activity similar to that of structurally related organometallic compounds.

A new tetrapodal 3-hydroxy-4-pyridinone ligand for complexation of 89zirconium for positron emission tomography (PET) imaging

The first octadentate 3-hydroxy-4-pyridinone chelator was prepared and its monometallic ⁸⁹Zr(iv)-complex was studied in vitro and in vivo.

Synthesis of New Bis(3-hydroxy-4-pyridinone) Ligands as Chelating Agents for Uranyl Complexation

Five new bis(3-hydroxy-4-pyridinone) tetradentate chelators were synthesized in this study. The structures of these tetradentate chelators were characterized by ¹H-NMR, (13)C-NMR, FT-IR, UV-vis, and mass spectral analyses. The binding abilities of these tetradentate chelators for uranyl ion at pH 7.4 were also determined by UV spectrophotometry in aqueous media. Results showed that the efficiencies of these chelating agents are dependent on the linker length. Ligand 4b is the best chelator and suitable for further studies.

The binding, transport and fate of aluminium in biological cells

Aluminium is the most abundant metal in the Earth's crust and yet, paradoxically, it has no known biological function. Aluminium is biochemically reactive, it is simply that it is not required for any essential process in extant biota. There is evidence neither of element-specific nor evolutionarily conserved aluminium biochemistry. This means that there are no ligands or chaperones which are specific to its transport, there are no transporters or channels to selectively facilitate its passage across membranes, there are no intracellular storage proteins to aid its cellular homeostasis and there are no pathways which evolved to enable the metabolism and excretion of aluminium. Of course, aluminium is found in every compartment of every cell of every organism, from virus through to Man. Herein we have investigated each of the 'silent' pathways and metabolic events which together constitute a form of aluminium homeostasis in biota, identifying and evaluating as far as is possible what is known and, equally importantly, what is unknown about its uptake, transport, storage and excretion.

Identification of the structural determinants for anticancer activity of a ruthenium arene peptide conjugate

Organometallic Ru(arene)-peptide bioconjugates with potent in vitro anticancer activity are rare. We have prepared a conjugate of a Ru(arene) complex with the neuropeptide [Leu(5)]-enkephalin. [Chlorido(η(6)-p-cymene)(5-oxo-κO-2-{(4-[(N-tyrosinyl-glycinyl-glycinyl-phenylalanyl-leucinyl-NH2)propanamido]-1H-1,2,3-triazol-1-yl)methyl}-4H-pyronato-κO)ruthenium(II)] (8) shows antiproliferative activity in human ovarian carcinoma cells with an IC50 value as low as 13 μM, whereas the peptide or the Ru moiety alone are hardly cytotoxic. The conjugation strategy for linking the Ru(cym) (cym=η(6)-p-cymene) moiety to the peptide involved N-terminal modification of an alkyne-[Leu(5)]-enkephalin with a 2-(azidomethyl)-5-hydroxy-4H-pyran-4-one linker, using Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC), and subsequent metallation with the Ru(cym) moiety. The ruthenium-bioconjugate was characterized by high resolution top-down electrospray ionization mass spectrometry (ESI-MS) with regard to peptide sequence, linker modification and metallation site. Notably, complete sequence coverage was obtained and the Ru(cym) moiety was confirmed to be coordinated to the pyronato linker. The ruthenium-bioconjugate was analyzed with respect to cytotoxicity-determining constituents, and through the bioconjugate models [{2-(azidomethyl)-5-oxo-κO-4H-pyronato-κO}chloride (η(6)-p-cymene)ruthenium(II)] (5) and [chlorido(η(6)-p-cymene){5-oxo-κO-2-([(4-(phenoxymethyl)-1H-1,2,3-triazol-1-yl]methyl)-4H-pyronato-κO}ruthenium(II)] (6) the Ru(cym) fragment with a triazole-carrying pyronato ligand was identified as the minimal unit required to achieve in vitro anticancer activity.

Organometallic ruthenium and osmium compounds of pyridin-2- and -4-ones as potential anticancer agents

Organometallic Ru(II) compounds are among the most widely studied anticancer agents. Functionalizing metal centers with biomolecule-derived ligands has been shown to be a promising strategy to improve the antiproliferative activity of metal-based chemotherapeutics. Herein, the synthesis of a series of novel 3-hydroxypyridin-2-one-derived ligands and their M(II)(η(6)-p-cymene) half-sandwich complexes (M = Ru, Os) is described. The compounds were characterized by 1D- and 2D-NMR spectroscopy, and elemental analysis.

Iron(III) selective molecular and supramolecular fluorescent probes

Iron is one of the most important elements in metabolic processes, being indispensable for all living systems and therefore it is extensively distributed in environmental and biological materials. However, both its deficiency and excess from the normal permissible limit can induce serious disorders. Therefore, several analytical techniques have been adopted for the detection of iron. Among the various techniques used for its detection, the method based on fluorescent sensors has received considerable interest in recent years because of its ability to provide online monitoring of very low concentrations without any pre-treatment of the sample together with the advantages of spatial and temporal resolution. In this article, efforts have been made to review the various molecular and supramolecular fluorescent sensors that have been developed for the selective detection of iron(III).

New hydroxypyridinone-functionalized sepharoses as sorbing agents for hard metal ions

Two new polymeric matrices functionalized with 3-hydroxy-4-pyridinone chelating units (HP-NH-SEPH and HP-C=NH-SEPH) have been prepared and studied for their chelating ability towards a set of metal ions (e.g. Fe(III), Al(III), and Th(IV)). Both matrices demonstrated excellent ability to complex these metal ions, but HP-NH-SEPH evidenced higher chelating capacity than HP-C=NH-SEPH. The corresponding metal-complex gels presented high stability in the pH range 3-7, and their chelating capacity followed the order, Fe(III)≈Th(IV)>Al(III), in agreement with previously reported thermodynamics of the corresponding monomeric ligand-metal complexes in aqueous solution. These functionalized supports also showed capacity to be regenerated and reused. Thus, there are good perspectives for potential environmental and medical applications of these new metal sorbents.

Is the reactivity of M(II)-arene complexes of 3-hydroxy-2(1H)-pyridones to biomolecules the anticancer activity determining parameter?

Hydroxypyr(id)ones are versatile ligands for the synthesis of organometallic anticancer agents, equipping them with fine-tunable pharmacological properties. Herein, we report on the preparation, mode of action, and in vitro anticancer activity of Ru(II)- and Os(II)-arene complexes with alkoxycarbonylmethyl-3-hydroxy-2-pyridone ligands. The hydrolysis and binding to amino acids proceed quickly, as characterized by NMR spectroscopy and ESI mass spectrometry. However, the reaction with amino acids causes cleavage of the pyridone ligands from the metal center because the amino acids act as multidentate ligands. A similar behavior was also observed during the reactions with the model proteins ubiquitin and cytochrome c, yielding mainly [protein + M(eta(6)-p-cymene)] adducts (M = Ru, Os). Notably the ligand cleavage of the Os derivative was significantly slower than of its Ru analogue, which could explain its higher activity in in vitro anticancer assays. Furthermore, the reaction of the compounds to 5'-GMP was characterized and coordination to the N7 of the guanine moiety was demonstrated by (1)H NMR spectroscopy and X-ray diffraction analysis. CDK2/Cyclin A protein kinase inhibition studies revealed potent activity of the Ru and Os complexes.

Diaqua-(2,6-dihy-droxy-benzoato-κO,O)bis-(2,6-dihy-droxy-benzoato-κO)bis-(1,10-phenanthroline-κN,N')lanthanum(III)-1,10-phenanthroline (1/1)

In the title compound, [La(C(7)H(5)O(4))(3)(C(12)H(8)N(2))(3)(H(2)O)(2)]·C(12)H(8)N(2), the La(III) atom is coordinated by four N atoms from two chelating 1,10-phenanthroline (phen) ligands, four O atoms from three 2,6-dihy-droxy-benzoate (DHB) anions (one monodentate, the other bidentate) and two water O atoms, completing a distorted LaN(4)O(6) bicapped square-anti-prismatic geometry. Within the mononuclear complex mol-ecule, intra-molecular π-π stacking inter-actions are observed, the first between a coordinated phen mol-ecule and a DHB ligand [centroid-centroid distance = 3.7291 (16) Å], and the second between a coordinated phen mol-ecule and an uncoordinated phen ligand [centroid-centroid distance = 3.933 (2) Å]. Inter-molecular π-π stacking is observed between adjacent complexes [inter-planar distance = 3.461 (3) Å]. Intra- and inter-molecular O-H⋯O hydrogen bonds are observed in the DHB ligands and between a water mol-ecule and DHB ligands, respectively. O-H⋯N hydrogen bonds are also observed in the DHB ligands and between uncoordinated phen mol-ecules and aqua ligands.

A gallium complex with a new tripodal tris-hydroxypyridinone for potential nuclear diagnostic imaging: solution and in vivo studies of 67Ga-labeled species

The gallium(III) complex of a new tripodal 3-hydroxy-4-pyridinone (3,4-HP) chelator has been studied in terms of its physico-chemical and in vivo properties aimed at potential application as probe for nuclear imaging. In particular, based on spectrophotometric titrations, the hexa-coordinated (1:1) gallium complex appeared as the major species in a wide physiological acid-neutral pH range and its high stability (pGa=27.5) should avoid drug-induced toxicity resulting from Ga(III) accumulation in tissues due to processes of transmetallation with endogenenous ligands or demetallation. A multinuclear ((1)H and (71)Ga) NMR study gave some insights into the structure and dynamics of the gallium(III) chelate in solution, which are consistent with the tris-(3,4-HP) coordination and an eventual pseudo-octahedral geometry. Biodistribution and scintigraphic studies of the (67)Ga(III) labelled chelate, performed in Wistar rats, confirmed the in vivo stability of the radiolabelled complex, its non interaction with blood proteins and its quick renal clearance. These results indicate good perspectives for potential application of extrafunctionalized analogues in radiodiagnostic techniques.

Influence of the Arene Ligand and the Leaving Group on the Anticancer Activity of (Thio)maltol Ruthenium(II)–(η6-Arene) Complexes

Maltol and its metal complexes have shown promising applications in medicinal chemistry. We report here the synthesis and characterization of Ru(η6-arene)(halido) coordination compounds bearing maltol or thiomaltol ligands and studies on their behaviour in aqueous solution, their reactions with the DNA model guanosine 5′-monophosphate (5′-GMP) and their in vitro anticancer activity in human tumour cell lines. The compounds hydrolyze rapidly and quantitatively to the respective aqua species by exchange of the halido ligand. With pKa values of >8, such species would also be present in biological media and they proved reactive to 5′-GMP. The thiomaltol compounds show promising in vitro activity with IC50 values (50% inhibitory concentration) in the low micromolar range, whereas activity of the maltol complexes is marginal. Variation of the arene ligand (benzene, toluene, p-cymene or biphenyl) resulted only in minor changes in activity.

Complexes of hydroxy(thio)pyrone and hydroxy(thio)pyridinone with Zn(II) and Mo(VI). Thermodynamic stability and insulin-mimetic activity

The development of metal-containing pharmaceuticals as insulin-mimetics has been the object of recent worldwide research. We have examined a series of zinc(II) and molybdenum(VI) complexes with model O,S-donor ligands (thiomaltol and 1,2-dimethyl-3-hydroxypyridine-4-thione (DMHTP)) and the corresponding O,O-analogues (maltol and DMHP) for their insulin-mimetic activity. Aimed at getting structure-activity relationships, some physical-chemical properties were also studied, such as metal-complex formation, speciation at different pH conditions and ligand lipophilicity. The Zn-complexes exhibit considerably higher insulin-mimetic activity than the corresponding Mo-analogues. Particularly, the bis(thiomaltolato)zinc(II) complex reveals a very high activity, ascribed to the effect of the thione π character and to the soft nature of the sulfur donor atom enhancing the Zn(II)-ligand affinity and the ligand/complex lipophilicity, two determinant parameters for delivering the metal-drug into the cells. Hence, these preliminary studies indicate that the Zn(thiomaltol)₂ complex can be considered a potential drug candidate for treatment of diabetes mellitus, upon in vivo evaluations.

New tripodal hydroxypyridinone based chelating agents for Fe(III), Al(III) and Ga(III): Synthesis, physico-chemical properties and bioevaluation

Two new tris-hydroxypyridinone based compounds (KEMPPr(3,4-HP)(3) and KEMPBu(3,4-HP)(3)) have been developed and studied as strong sequestering agents for iron and the group III of metal ions, aimed as potential pharmacological applications on metal-chelation therapy. Their structure is based on the KEMP acid scaffold to which three 3-hydroxy-4-pyridinone chelating moieties are attached via two different size spacers. After the preparation and characterization of the compounds their physico-chemical properties were studied, in relation with their metal binding affinity and lipophilicity. The KEMPPr(3,4-HP)(3) ligand was also bioassayed to evaluate its in vivo metal sequestering capacity from most organs using an animal model overload with (67)Ga. These studies showed that, for both in solution and in vivo conditions, the compounds have higher metal chelating efficacy than Deferriprone, the commercially available iron chelator in medical application, thus some perspectives are envisaged as potential pharmaceutical drug candidates for chelating therapy.