8-Hydroxyquinolines in medicinal chemistry: A structural perspective

Enhanced selectivity towards melanoma cells with zinc(II)-Schiff bases containing imidazole derivatives

Zinc(II)-complexes with the general formula [Zn(L)2] containing 8-hydroxyquinoline Schiff bases functionalized with 1-(3-aminopropyl)imidazole or 1-(3-aminopropyl)-2-methyl-1H-imidazole on 2-position and their respective ligands (HL1 or HL2) were synthesized and characterized by NMR, UV-Vis, FTIR and CD spectroscopies as well as ESI-MS spectrometry. Single crystals of HL2 and [Zn(L1)2]n were analysed by SC-XRD. [Zn(L1)2]n shows a 1D polymeric chain structure of alternating Zn(II) cations and bridging Schiff base ligands, in contrast to previously reported monomeric structures of analogous complexes. DFT calculations were performed to rationalize the polymeric X-ray structure of Zn(L1)2. Results showed that the ligands can bind as bi- or tridentate to Zn(II) and there is the possibility of a dynamic behavior for the complexes in solution. Both ligands and complexes present limited stability in aqueous media, however, in the presence of bovine serum albumin the complexes are stable. Molecular docking simulations and circular dichroism spectroscopic studies suggest binding to this protein in close proximity to the Trp213 residue. Biological studies on a panel of cancer cells revealed that the Zn(II)-complexes have a lower impact on cell viability than cisplatin, except for triple-negative breast cancer cells in which they were comparable. Notwithstanding, they display much higher selectivity towards cancer cells vs. normal cells, than cisplatin. They induce the generation of ROS and DNA double-strand breaks, primarily through apoptosis as the mode of cell death. Overall, the novel Zn(II)-complexes demonstrate improved induction of apoptosis and higher selectivity, particularly for melanoma cells, compared to previously reported analogues, making them promising candidates for clinical application.

Complex formation of ML324, the histone demethylase inhibitor, with essential metal ions: Relationship between solution chemistry and anticancer activity

N-(3-(dimethylamino)propyl-4-(8-hydroxyquinolin-6-yl)benzamide (ML324, HL) is a potent inhibitor of the iron-containing histone demethylase KDM4, a recognized potential target of cancer therapeutics. Herein, we report the proton dissociation and complex formation processes of ML324 with essential metal ions such as Fe(II), Fe(III), Cu(II) and Zn(II) using UV-visible, fluorescence, electron paramagnetic resonance and 1H NMR spectroscopic methods. The electrochemical behaviour of the copper and iron complexes was characterized by cyclic voltammetry and spectroelectrochemistry. The solid phase structure of ML324 analysed by X-ray crystallography is also provided. Based on the solution equilibrium data, ML324 is present in solution in H2L+ form with a protonated dimethylammonium moiety at pH 7.4, and this (N,O) donor bearing ligand forms mono and bis complexes with all the studied metal ions and the tris-ligand species is also observed with Fe(III). At pH 7.4 the metal binding ability of ML324 follows the order: Fe(II) < Zn(II) < Cu(II) < Fe(III). Complexation with iron resulted in a negative redox potential (E'1/2 = -145 mV vs. NHE), further suggesting that the ligand has a preference for Fe(III) over Fe(II). ML324 was tested for its anticancer activity in chemosensitive and resistant human cancer cells overexpressing the efflux pump P-glycoprotein. ML324 exerted similar activity in all tested cells (IC50 = 1.9-3.6 μM). Co-incubation and complexation of the compound with Cu(II) and Zn(II) had no impact on the cytotoxicity of ML324, whereas Fe(III) decreased the toxicity in a concentration-dependent manner, and this effect was more pronounced in the multidrug resistant cells.

Development of a topical treatment for tegumentary leishmaniasis using 8-hydroxyquinoline

In the context of neglected diseases, tegumentary leishmaniasis (TL) presents an emerging and re-emerging character in the national territory and in the world. The treatment of TL has limitations, such as intravenous administration route, high toxicity, and high treatment costs. Thus, several researchers work on new therapeutic strategies to improve the effectiveness of the treatment of leishmaniasis. In this light, the present study used a topical formulation, containing 8-hydroquinoline (8-HQN), for the treatment of Balb/c mice infected with L. amazonensis. After the treatment, the mean diameter of the lesion was measured, as well as the parasite load in organs and immunological parameters associated with the treatment. The results showed that the animals treated with 8-HQN 5%, when compared to controls, showed a reduction in the mean diameter of the lesion and in the parasite load. The animals treated with the ointment showed a type 1 cellular immune response profile associated with the production of cytokines such as INF-γ and TNF-α. In addition, the treatment did not demonstrate toxicity to mice. Therefore, the topical formulation containing 8-HQN 5% is a promising candidate in the topical treatment and could be considered, in the future, as an alternative for the treatment of TL.

Tailoring the Use of 8-Hydroxyquinolines for the Facile Separation of Iron, Dysprosium and Neodymium

Permanent magnets (PMs) containing rare earth elements (REEs) can generate energy in a sustainable manner. With an anticipated tenfold increase in REEs demand by 2050, one of the crucial strategies to meet the demand is developing of efficient recycling methods. NdFeB PMs are the most widely employed, however, the similar chemical properties of Nd (20-30 % wt.) and Dy (0-10 % wt.) make their recycling challenging, but possible using appropriate ligands. In this work, we investigated commercially available 8-hydroxyquinolines (HQs) as potential Fe/Nd/Dy complexing agents enabling metal separation by selective precipitation playing on specific structure/property (solubility) relationship. Specifically, test ethanolic solutions of nitrate salts, prepared to mimic the main components of a PM leachate, were treated with functionalized HQs. We demonstrated that Fe3+ can be separated as insoluble [Fe(QCl,I)3] from soluble [REE(QCl,I)4]- complexes (QCl,I -: 5-Cl-7-I-8-hydoxyquinolinate). Following that, QCl - (5-Cl-8-hydroxyquinolinate) formed insoluble [Nd3(QCl)9] and soluble (Bu4N)[Dy(QCl)4]. The process ultimately gave a solution phase containing Dy with only traces of Nd. In a preliminary attempt to assess the potentiality of a low environmental impact process, REEs were recovered as oxalates, while the ligands as well as Bu4N+ ions, were regenerated and internally reused, thus contributing to the sustainability of a possible metal recovery process.

A Pt(II) complex bearing N-heterocycle ring induced ferroptotic cell death in ovarian cancer

Cisplatin is a widely used chemotherapeutic agent which interacts with DNA to form Pt-DNA adducts, leading to DNA double-strand breaks and apoptosis. Resistance is the major obstacle in the clinical application of cisplatin. A quinoline derivative based Pt(II) complex PtQ was synthesized and characterized. As an analogue of cisplatin, PtQ demonstrated a novel anticancer mechanism in ovarian cancer. PtQ caused excessive production of reactive oxygen species (ROS), which triggered ferroptotic cell death in ovarian cancer. Cystine/glutamate antiporter SLC7A11 and glutathione peroxidase 4 (GPX4) which alleviate lipid peroxidation were both downregulated in PtQ-treated SKOV3 cells. Furthermore, PtQ induced DNA single-strand breaks and suppressed the expression of single-strand breaks repair protein PARP1. Mechanism studies demonstrated that PtQ can hopefully bypass the signaling pathways mediated cisplatin resistance in ovarian cancer.

Synthesis, characterization, and cancer cell-selective cytotoxicity of mixed-ligand cobalt(III) complexes of 8-hydroxyquinolines and phenanthroline bases

Transition metal complexes exhibiting selective toxicity towards a broad range of cancer types are highly desirable as potential anticancer agents. Herein, we report the synthesis, characterization, and cytotoxicity studies of six new mixed-ligand cobalt(III) complexes of general formula [Co(B)2(L)](ClO4)2 (1-6), where B is a N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), and L is the monoanion of 8-hydroxyquinoline (HQ in 1, 3, 5) and 5-chloro-7-iodo-8-hydroxyquinoline (CQ in 2, 4, 6). The X-ray single crystal structures of complexes 1 and 2 as PF6- salts revealed a distorted octahedral CoN5O coordination environment. Complexes demonstrated good stability in an aqueous buffer medium and in the presence of ascorbic acid as a reductant. Cytotoxicity studies using a panel of nine cancer cell lines showed that complex 6, with the dppz and CQ ligands, was significantly toxic against most cancer cell types, yielding IC50 values in the range of 2 to 14 μM. Complexes 1, 3, and 5, containing the HQ ligand, displayed lower toxicity compared to their CQ counterparts. The phenanthroline complexes demonstrated marginal toxicity towards the tested cell lines, while the dpq complexes exhibited moderate toxicity. Interestingly, all complexes demonstrated negligible toxicity towards normal HEK-293 kidney cells (IC50 > 100 μM). The observed cytotoxicity of the complexes correlated well with their lipophilicities (dppz > dpq > phen). The cytotoxicity of complex 6 was comparable to that of the clinical drug cisplatin under similar conditions. Notably, neither the HQ nor the CQ ligands alone demonstrated noticeable toxicity against any of the tested cell lines. The Annexin-V-FITC and DCFDA assays revealed that the cell death mechanism induced by the complexes involved apoptosis, which could be attributed to the metal-assisted generation of reactive oxygen species. Overall, the dppz complex 6, with its remarkable cytotoxicity against a broad range of cancer cells and negligible toxicity toward normal cells, holds significant potential for cancer chemotherapeutic applications.

Synergistic activity of clioquinol with voriconazole and amphotericin B against fungi of interest in eye infections

Keratoplasty represents a risk factor for fungal eye infections, despites the antibacterial actives in the corneal tissue preservation means, it does not contain active substances with antifungal action. Among the most commonly associated fungal agents are the species belonging to the genera Fusarium and Candida. These agents can trigger an infectious process characterized by swift progression associated with high rates of morbidity, causing irreversible damage. Polyene and azole antifungals are the main agents of ocular therapy, however, they demonstrate some limitations, such as their toxicity and fungal resistance. In this context, drug repositioning and the combination of antifungals may be an alternative. Hence, the goal of this study was to investigate the potential activity of clioquinol (CLQ), a derivative of 8-hydroxyquinoline with previously described antifungal activity, along with its triple and quadruple combinations with antifungal agents commonly used in ophthalmic fungal therapy, natamycin (NAT), voriconazole (VRC), and amphotericin B (AMB), against main fungal pathogens in eye infections. The MICs for CLQ ranged from 0.25 to 2.0 μg/mL, for NAT from 4.0 to 32.0 μg/mL, for AMB it ranged from 0.25 to 16.0 μg/mL and for VRC from 0.03125 to 512.0 µg/mL. Among the tested combinations, the VRC-AMB-CLQ combination stands out, which showed a synergistic effect for more than 50 % of the tested strains and did not present antagonistic results against any of them. Toxicity data were similar to those antifungals already used, even with lower potential toxicity. Therefore, both clioquinol and the triple combination VCR-AMB-CLQ exhibited promising profiles for use as active components in corneal tissue preservation medium.

Therapeutic Activity of a Topical Formulation Containing 8-Hydroxyquinoline for Cutaneous Leishmaniasis

Cutaneous leishmaniasis exhibits a wide spectrum of clinical manifestations; however, only a limited number of drugs are available and include Glucantime® and amphotericin B, which induce unacceptable side effects in patients, limiting their use. Thus, there is an urgent demand to develop a treatment for leishmaniasis. Recently, it was demonstrated that 8-hydroxyquinoline (8-HQ) showed significant leishmanicidal effects in vitro and in vivo. Based on that, this work aimed to develop a topical formulation containing 8-HQ and assess its activity in experimental cutaneous leishmaniasis. 8-HQ was formulated using a Beeler base at 1 and 2% and showed an emulsion size with a D50 of 25 and 51.3 µm, respectively, with a shear-thinning rheological behaviour. The creams were able to permeate artificial Strat-M membranes and excised porcine skin without causing any morphological changes in the porcine skin or murine skin tested. In BALB/c mice infected with L. (L.) amazonensis, topical treatment with creams containing 1 or 2% of 8-HQ was found to reduce the parasite burden and lesion size compared to infected controls with comparable efficacy to Glucantime® (50 mg/kg) administered at the site of the cutaneous lesion. In the histological section of the skin from infected controls, a diffuse inflammatory infiltrate with many heavily infected macrophages that were associated with areas of necrosis was observed. On the other hand, animals treated with both creams showed only moderate inflammatory infiltrate, characterised by few infected macrophages, while tissue necrosis was not observed. These histological characteristics in topically treated animals were associated with an increase in the amount of IFN-γ and a reduction in IL-4 levels. The topical use of 8-HQ was active in decreasing tissue parasitism and should therefore be considered an interesting alternative directed to the treatment of leishmaniasis, considering that this type of treatment is non-invasive, painless, and, importantly, does not require hospitalisation, improving patient compliance by allowing the treatment to be conducted.

In vitro evaluation of the efficacy of 8-hydroxyquinoline derivatives for the control of Phaeomoniella chlamydospora, the causative agent of Petri disease in grapevines

AIM

This study evaluates the in vitro efficacy of 8-hydroxyquinoline (8HQ) derivatives in controlling the phytopathogenic fungus Phaeomoniella chlamydospora.

METHODS AND RESULTS

The in vitro tests assessed the susceptibility to the minimum inhibitory concentration (MIC), checkerboard assay, mycelial growth (MG) inhibition, and EC50 determination. Among the seven agricultural fungicides tested, tebuconazole (TEB) displayed the lowest MIC, 1.01 µg mL-1, followed by captan (CAP), thiophanate methyl (TM), and mancozeb with MICs of 4.06, 5.46, and 10.62 µg mL-1, respectively. The 8HQ derivatives used in this study were clioquinol and PH 151 (PH) with MICs of 1.09 and 2.02 µg mL-1, respectively. PH associated with TEB and CAP showed synergism and inhibited 95.8% of MG at the highest dose. TEB inhibited 100% of MG at the three highest doses, while associated with PH exhibited the lowest EC50 (0.863 + 0.0381 µg mL-1).

CONCLUSIONS

We concluded that the 8HQ derivatives tested controlled effectively the P. chlamydospora in vitro. PH associated with CAP and TEB exhibited a synergistic effect. The association between PH and TM was considered indifferent.

IMPACT STATEMENT

This study expands the list of active ingredients tested against P. chlamydospora, with the PH 151 and clioquinol derivatives being tested for the first time. The in vitro efficacy and synergistic action with other fungicides suggest a potential use as a grapevine wound protectant. This association makes it possible to reduce doses and increase the potency of both drugs, reducing the risk of resistance development and harm to humans and the environment.

Cu(II) and Zn(II) Complexes of New 8-Hydroxyquinoline Schiff Bases: Investigating Their Structure, Solution Speciation, and Anticancer Potential

We report the synthesis and characterization of three novel Schiff bases (L1-L3) derived from the condensation of 2-carbaldehyde-8-hydroxyquinoline with amines containing morpholine or piperidine moieties. These were reacted with CuCl₂ and ZnCl₂ yielding six new coordination compounds, with the general formula ML₂, where M = Cu(II) or Zn(II) and L = L1-L3, which were all characterized by analytical, spectroscopic (Fourier transform infrared (FTIR), UV-visible absorption, nuclear magnetic resonance (NMR), or electron paramagnetic resonance (EPR)), and mass spectrometric techniques, as well as by single-crystal X-ray diffraction. In the solid state, two Cu(II) complexes, with L1 and L2, are obtained as dinuclear compounds, with relatively short Cu-Cu distances (3.146 and 3.171 Å for Cu₂(L1)₄ and Cu₂(L2)₄, respectively). The free ligands show moderate lipophilicity, while their complexes are more lipophilic. The pK_a values of L1-L3 and formation constants of the complex (for ML and ML₂) species were determined by spectrophotometric titrations, with the Cu(II) complexes showing higher stability than the Zn(II) complexes. EPR indicated the presence of several species in solution as pH varied and binding modes were proposed. The binding of the complexes to bovine serum albumin (BSA) was evaluated by fluorescence and circular dichroism (CD) spectroscopies. All complexes bind BSA, and as demonstrated by CD, the process takes several hours to reach equilibrium. The antiproliferative activity was evaluated in malignant melanoma cells (A375) and in noncancerous keratinocytes (HaCaT). All complexes display significant cytotoxicity (IC₅₀ < 10 μM) but modest selectivity. The complexes show higher activity than the free ligands, the Cu(II) complexes being more active than the Zn(II) complexes, and approximately twice more cytotoxic than cisplatin. A Guava ViaCount assay corroborated the antiproliferative activity.

Synthesis, cytotoxicity, and biomacromolecule binding: Three isomers of nitrosylruthenium complexes with bidentate bioactive molecules as co-ligands

Three isomeric nitrosylruthenium complexes [RuNO(Qn)(PZA)Cl] (P1, P2, and P3) with bioactive small molecules 8-hydroxyquinoline (Qn) and pyrazinamide (PZA) as co-ligands were synthesized, and their crystal structures were determined using X-ray diffraction technique. The cellular toxicity of the isomeric complexes was compared to understand the effects of the geometries on the biological activity of the complexes. Both the complexes and the human serum albumin (HSA) complex adducts affected the extent of proliferation of HeLa cells (IC₅₀: 0.77-1.45 μM). P2 showed prominent activity-induced cell apoptosis and arrested cell cycles at the G1 phase. The binding constants (K_b) of the complex with calf thymus DNA (CT-DNA) and HSA were quantitatively evaluated using fluorescence spectroscopy in the range of 0.17-1.56 × 10⁴ M^-1 and 0.88-3.21 × 10⁵ M^-1, respectively. The average binding site (n) number was close to 1. Moreover, the structure of HSA and the P2 complex adduct solved at the resolution of 2.48 Å revealed that one PZA-coordinated nitrosylruthenium complex bound at the subdomain I of HSA via a noncoordinative bond. HSA could serve as a potential nano-delivery system. This study provides a framework for the rational design of metal-based drugs.

In vitro and in vivo antitumor activity of novel half-sandwich ruthenium complexes containing quinoline derivative ligands

A series of half-sandwich ruthenium complexes containing quinoline derivative ligands was synthesized, which had excellent antitumor toxicity toward a variety of cell lines and could localize lysosomes. The damage of lysosomes promotes the release of cathepsin B and initiates downstream apoptotic cascade signals. The increase in reactive oxygen species (ROS) caused by the decrease in mitochondrial membrane potential (ΔΨ_m) synergistically amplified the damage degree of lysosomes. In addition, the complex could inhibit cell transfer and clone formation. In vivo results showed that the complex had excellent biological effects in tested mouse samples as the body weight of mice did not change much during the treatment, and the mean tumor volume was significantly lower than the control group.

Terpyridine Glycoconjugates and Their Metal Complexes: Antiproliferative Activity and Proteasome Inhibition

Metal terpyridine complexes have gained substantial interest in many application fields, such as catalysis and supramolecular chemistry. In recent years, the biological activity of terpyridine and its metal complexes has aroused considerable regard. On this basis, we synthesised new terpyridine derivatives of trehalose and glucose to improve the water solubility of terpyridine ligands and target them in cancer cells through glucose transporters. Glucose derivative and its copper(II) and iron(II) complexes showed antiproliferative activity. Interestingly, trehalose residue reduced the cytotoxicity of terpyridine. Moreover, we tested the ability of parent terpyridine ligands and their copper complexes to inhibit proteasome activity as an antineoplastic mechanism.

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.

Development of a Clioquinol Nanocarrier as a New, Promising Option for the Treatment of Dermatomycosis

Dermatomycosis is a common fungal infection, and its treatment is limited by few antifungal agents. Clioquinol (CQ) is an antiparasitic agent that has been studied for new uses, such as antifungal and antiviral applications. CQ was incorporated into a lipid-based nanocarrier as a new, promising option for dermatomycosis. This study aimed to develop a CQ-loaded lipid-based nanocarrier for cutaneous application and to evaluate its antifungal activity. CQ-loaded nanoformulation (LBN-CQ) was developed using the ultrasonication method, and the particle size, polydispersity index (PDI), pH, zeta potential, and drug content were monitored for 45 days. To evaluate antifungal activity, broth microdilution and a time-kill assay were performed. LBN-CQ presented a particle size of 91 ± 3 nm and PDI of 0.102 ± 0.009. The zeta potential and pH values were -9.7 ± 2.0 mV and 6.0 ± 0.1, respectively. The drug content was 96.4 ± 2.3%, and the encapsulation efficiency was 98.4%. LBN-CQ was able to reduce the minimum inhibitory concentration (MIC) in a 2-fold or 4-fold manner in most of the tested strains. Additionally, LBN-CQ presented stable fungistatic action that was not concentration- or time-dependent. In conclusion, the developed CQ-loaded nanocarrier is a promising treatment for skin fungal infections and a promising candidate for future randomized clinical trials.

Insights of metal 8-hydroxylquinolinol complexes as the potential anticancer drugs

8-Hydroxyquinoline and its derivatives, which belong to a well-known class of quinoline based drugs with varied biological activities, have been extensively explored for the treatments of cancer, Alzheimer's disease, neurodegenerative diseases and other life-threatening diseases. In virtue of the existence of bicyclic heterocyclic scaffold, their bidentate chelators can further bind to metal ions via O- and N-donors from 8-hydroxylquinolinol skeletons to yield a variety of metal 8-hydroxylquinolinol complexes appealing as the anticancer drugs with low toxicity, due to their better biological effects and higher anticancer activities than free 8-hydroxylquinolinol ligands and cis-diammine-dichloro-platinum. The present review summarizes the recent developments in the syntheses, crystal structures, and anticancer activities of metal 8-hydroxylquinolinol complexes, attempting to discover a correlation between their structures and anticancer activities, and to provide an evidence for their potential application perspectives. It means to offer the helpful and meaningful guidance for the researchers in the future syntheses of new and highly efficient anticancer metal 8-hydroxylquinolinol complexes based drugs.

Promising anticancer agents based on 8-hydroxyquinoline hydrazone copper(II) complexes

We report the synthesis and characterization of a group of benzoylhydrazones (Lⁿ) derived from 2-carbaldehyde-8-hydroxyquinoline and benzylhydrazides containing distinct para substituents (R = H, Cl, F, CH₃, OCH₃, OH and NH₂, for L^1-7, respectively; in L⁸ isonicotinohydrazide was used instead of benzylhydrazide). Cu(II) complexes were prepared by reaction of each benzoylhydrazone with Cu(II) acetate. All compounds were characterized by elemental analysis and mass spectrometry as well as by FTIR, UV-visible absorption, NMR or electron paramagnetic resonance spectroscopies. Complexes isolated in the solid state (1-8) are either formulated as [Cu(HL)acetate] (with L¹ and L⁴) or as [Cu(Lⁿ)]₃ (n = 2, 3, 5, 6, 7 and 8). Single crystal X-ray diffraction studies were done for L⁵ and [Cu(L⁵)]₃, confirming the trinuclear formulation of several complexes. Proton dissociation constants, lipophilicity and solubility were determined for all free ligands by UV-Vis spectrophotometry in 30% (v/v) DMSO/H₂O. Formation constants were determined for [Cu(LH)], [Cu(L)] and [Cu(LH_-1)] for L = L¹, L⁵ and L⁶, and also [Cu(LH_-2)] for L = L⁶, and binding modes are proposed, [Cu(L)] predominating at physiological pH. The redox properties of complexes formed with L¹, L⁵ and L⁶ are investigated by cyclic voltammetry; the formal redox potentials fall in the range of +377 to +395 mV vs. NHE. The binding of the Cu(II)-complexes to bovine serum albumin was evaluated by fluorescence spectroscopy, showing moderate-to-strong interaction and suggesting formation of a ground state complex. The interaction of L¹, L³, L⁵ and L⁷, and of the corresponding complexes with calf thymus DNA was evaluated by thermal denaturation. The antiproliferative activity of all compounds was evaluated in malignant melanoma (A-375) and lung (A-549) cancer cells. The complexes show higher activity than the corresponding free ligand, and most complexes are more active than cisplatin. Compounds 1, 3, 5, and 8 were selected for additional studies: while these complexes induce reactive oxygen species and double-strand breaks in both cancer cells, their ability to induce cell-death by apoptosis varies. Within the set of compounds tested, 8 emerges as the most promising one, presenting low IC₅₀ values, and high induction of oxidative stress and DNA damage, which eventually lead to high rates of apoptosis.

Metal Complexes of a 5-Nitro-8-Hydroxyquinoline-Proline Hybrid with Enhanced Water Solubility Targeting Multidrug Resistant Cancer Cells

Multidrug resistance (MDR) in cancer is one of the major obstacles of chemotherapy. We have recently identified a series of 8-hydroxyquinoline Mannich base derivatives with MDR-selective toxicity, however with limited solubility. In this work, a novel 5-nitro-8-hydroxyquinoline-proline hybrid and its Rh(η5-C5Me5) and Ru(η6-p-cymene) complexes with excellent aqueous solubility were developed, characterized, and tested against sensitive and MDR cells. Complex formation of the ligand with essential metal ions was also investigated using UV-visible, circular dichroism, 1H NMR (Zn(II)), and electron paramagnetic resonance (Cu(II)) spectroscopic methods. Formation of mono and bis complexes was found in all cases with versatile coordination modes, while tris complexes were also formed with Fe(II) and Fe(III) ions, revealing the metal binding affinity of the ligand at pH 7.4: Cu(II) > Zn(II) > Fe(II) > Fe(III). The ligand and its Rh(III) complex displayed enhanced cytotoxicity against the resistant MES-SA/Dx5 and Colo320 human cancer cell lines compared to their chemosensitive counterparts. Both organometallic complexes possess high stability in solution, however the Ru(II) complex has lower chloride ion affinity and slower ligand exchange processes, along with the readiness to lose the arene ring that is likely connected to its inactivity.

New multifunctional Ru(II) organometallic compounds show activity against Trypanosoma brucei and Leishmania infantum

Human African trypanosomiasis (sleeping sickness) and leishmaniasis are prevalent zoonotic diseases caused by genomically related trypanosomatid protozoan parasites (Trypanosoma brucei and Leishmania spp). Additionally, both are co-endemic in certain regions of the world. Only a small number of old drugs exist for their treatment, with most of them sharing poor safety, efficacy, and pharmacokinetic profiles. In this work, new multifunctional Ru(II) ferrocenyl compounds were rationally designed as potential agents against these trypanosomatid parasites by including in a single molecule 1,1'-bis(diphenylphosphino)ferrocene (dppf) and two bioactive bidentate ligands: 8-hydroxyquinoline derivatives (8HQs) and polypyridyl ligands (NN). Three [Ru(8HQs)(dppf)(NN)](PF₆) compounds were synthesized and fully characterized. They showed in vitro activity on bloodstream Trypanosoma brucei (IC₅₀ 140-310 nM) and on Leishmania infantum promastigotes (IC₅₀ 3.0-4.8 μM). The compounds showed good selectivity towards T. brucei in respect to J774 murine macrophages as mammalian cell model (SI 15-38). Changing hexafluorophosphate counterion by chloride led to a three-fold increase in activity on both parasites and to a two to three-fold increase in selectivity towards the pathogens. The compounds affect in vitro at least the targets of the individual bioactive moieties included in the new chemical entities: DNA and generation of ROS. The compounds are stable in solution and are more lipophilic than the free bioactive ligands. No clear correlation between lipophilicity, interaction with DNA or generation of ROS and activity was detected, which agrees with their overall similar anti-trypanosoma potency and selectivity. These compounds are promising candidates for further drug development.

Co-Delivery of 8-Hydroxyquinoline Glycoconjugates and Doxorubicin by Supramolecular Hydrogel Based on α-Cyclodextrin and pH-Responsive Micelles for Enhanced Tumor Treatment

The sustained release of multiple anti-cancer drugs using a single delivery carrier to achieve a synergistic antitumor effect remains challenging in biomaterials and pharmaceutics science. In this study, a supramolecular hydrogel based on the host-guest complexes between pH-responsive micelle derived poly(ethylene glycol) chains and α-cyclodextrin was designed for codelivery of two kinds of anti-cancer agents, hydrophilic 8-hydroxyquinoline glycoconjugate and hydrophobic doxorubicin. The host-guest interactions were characterized using X-ray diffraction and differential scanning calorimetry techniques. The resultant supramolecular hydrogel showed thixotropic properties, which are advantageous to drug delivery systems. In vitro release studies revealed that the supramolecular hydrogel exhibited faster drug release profiles in acidic conditions. The MTT assay demonstrated a synergistic cancer cell proliferation inhibition of DOX/8HQ-Glu mixture. In vitro cytotoxicity studies indicated excellent biocompatibility of the supramolecular hydrogel matrix, whereas the DOX/8HQ-Glu-loaded supramolecular hydrogel showed a sustained inhibition efficacy against cancer cells. The codelivery of hydrophobic anti-cancer drugs and hydrophilic anti-cancer drug glycoconjugates via a pH-responsive supramolecular hydrogel opens up new possibilities for the development of an effective cancer treatment based on the tumor-specific Warburg effect.

Synthesis of Indenoquinolinones and 2-Substituted Quinolines via [4 + 2] Cycloaddition Reaction

We have reported a metal-free protocol for the synthesis of indenoquinolinones and 2-substituted quinolines via [4 + 2] cycloaddition reaction using readily available 2-aminobenzaldehydes and ketones as starting materials. Different quinoline derivatives can be selectively synthesized by changing the type of ketones. O₂ and dimethyl sulfoxide (DMSO) as co-oxidants play an important role in the synthesis of indenoquinolinones. This condensation/oxidation strategy involves the formation of C-N, C-C, and C-O bonds, with the advantages of high yields and a broad substrate range.

New ternary Fe(III)-8-hydroxyquinoline-reduced Schiff base complexes as selective anticancer drug candidates

Due to the growing prevalence of cancer diseases, new therapeutic options are urgently needed, and drugs based on metal ions other than platinum are alternatives with exciting possibilities. We report the synthesis, characterization and biological effect of mixed-ligand Fe(III)-aminophenolate complexes derived from salicylaldehyde and L-tryptophan with quinoline derivatives as co-ligands, namely 8-hydroxyquinoline (8HQ), [Fe(L)(8HQ)(H₂O)] (1) and its 5-cloro derivative (Cl8HQ), [Fe(L)(Cl8HQ)(H₂O)] (2). The complex bearing the aminophenolate and lacking the quinoline co-ligand, [Fe(L)(Cl)(H₂O)₂] (3), was prepared for comparison. The analytical and spectroscopic characterization revealed that 1 and 2 are octahedral Fe(III) complexes with the aminophenolate acting as a dianionic tridentate ligand and 8HQ co-ligands as bidentate chelates. Spectroscopic techniques and molecular docking studies were used to evaluate the ability of these complexes to bind bovine serum albumin (BSA) and calf thymus DNA. Complex 2 [Fe(L)(Cl8HQ)(H₂O)] was the one showing higher affinity for both biomolecules. Cell viability was assessed in breast, colorectal and bone human cancer cell lines. 1 and 2 were found to be more active than cisplatin in all cell lines tested. A non-tumoral fibroblast line (L929, mouse non-tumoral fibroblasts) was used to evaluate selectivity. The results evidence that 2 shows much higher selectivity than 1 in all cell lines tested, but particularly in bone cancer cells in which selectivity index (SI) values are 8.0 and 18.8 for 1 and 2, respectively.

New anti-cancer explorations based on metal ions

Due to the urgent demand for more anti-cancer methods, the new applications of metal ions in cancer have attracted increasing attention. Especially the three kinds of the new mode of cell death, including ferroptosis, calcicoptosis, and cuproptosis, are of great concern. Meanwhile, many metal ions have been found to induce cell death through different approaches, such as interfering with osmotic pressure, triggering biocatalysis, activating immune pathways, and generating the prooxidant effect. Therefore, varieties of new strategies based on the above approaches have been studied and applied for anti-cancer applications. Moreover, many contrast agents based on metal ions have gradually become the core components of the bioimaging technologies, such as MRI, CT, and fluorescence imaging, which exhibit guiding significance for cancer diagnosis. Besides, the new nano-theranostic platforms based on metal ions have experimentally shown efficient response to endogenous and exogenous stimuli, which realizes simultaneous cancer therapy and diagnosis through a more controlled nano-system. However, most metal-based agents have still been in the early stages, and controlled clinical trials are necessary to confirm or not the current expectations. This article will focus on these new explorations based on metal ions, hoping to provide some theoretical support for more anti-cancer ideas.

Glycoconjugation of Quinoline Derivatives Using the C-6 Position in Sugars as a Strategy for Improving the Selectivity and Cytotoxicity of Functionalized Compounds

Based on the Warburg effect and the increased demand for glucose by tumor cells, a targeted drug delivery strategy was developed. A series of new glycoconjugates with increased ability to interact with GLUT transporters, responsible for the transport of sugars to cancer cells, were synthesized. Glycoconjugation was performed using the C-6 position in the sugar unit, as the least involved in the formation of hydrogen bonds with various aminoacids residues of the transporter. The carbohydrate moiety was connected with the 8-hydroxyquinoline scaffold via a 1,2,3-triazole linker. For the obtained compounds, several in vitro biological tests were performed using HCT-116 and MCF-7 cancer cells as well as NHDF-Neo healthy cells. The highest cytotoxicity of both cancer cell lines in the MTT test was noted for glycoconjugates in which the triazole-quinoline was attached through the triazole nitrogen atom to the d-glucose unit directly to the carbon at the C-6 position. These compounds were more selective than the analogous glycoconjugates formed by the C-1 anomeric position of d-glucose. Experiments with an EDG inhibitor have shown that GLUTs can be involved in the transport of glycoconjugates. The results of apoptosis and cell cycle analyses by flow cytometry confirmed that the new type of glycoconjugates shows pro-apoptotic properties, without significantly affecting changes in the distribution of the cell cycle. Moreover, glycoconjugates were able to decrease the clonogenic potential of cancer cells, inhibit the migration capacity of cells and intercalate with DNA.

Quinoline, with the active site of 8-hydroxyl, efficiently inhibits Micropterus salmoides rhabdovirus (MSRV) infection in vitro and in vivo

Micropterus salmoides rhabdovirus (MSRV) is an significant pathogen that causes high mortality and related economic losses in bass aquaculture. There is no effective or approved therapy to date. In this study, we evaluated the anti-MSRV effects of 22 quinoline derivatives in grass carp ovary (GCO) cells. Among these compounds, 8-hydroxyquinoline exhibited valid inhibition in decreasing MSRV nucleoprotein gene expression levels of 99.3% with a half-maximal inhibitory concentrations (IC₅₀ ) value of 4.66 μM at 48 h. Moreover, 8-hydroxyquinoline significantly enhanced a protective effect in GCO cells by reducing the cytopathic effect (CPE). By comparing the anti-MSRV activity of 22 quinoline derivatives, we found that 8-hydroxyquinoline possessed the efficient active site of 8-hydroxyl and inhibited MSRV infection in vitro. For in vivo studies, 8-hydroxyquinoline via intraperitoneal injection exhibited an antiviral effect in MSRV-infected largemouth bass by substantially enhancing the survival rate by 15.0%. Importantly, the viral loads in the infected largemouth bass notably reduced in the spleen on the third days post-infection. Overall, 8-hydroxyquinoline was considered to be an efficient agent against MSRV in aquaculture.

[Ru(η6-p-cymene)(N^O 8-hydroxyquinoline)(PTA)] complexes as rising stars in medicinal chemistry: synthesis, properties, biomolecular interactions, in vitro anti-tumor activity toward human brain carcinomas, and in vivo biodistribution and toxicity in a zebrafish model

Herein, we have introduced a class of half-sandwich [Ru(η⁶-p-cymene)(N^O 8-hydroxyquinoline)(PTA)] complexes for brain cancer therapy. Among all the complexes, [RuL3PTA] and [RuL4PTA] exhibited excellent cytotoxicity profiles against T98G, LN229, and U87MG cancer cells. Notably, the antiproliferative activities of the relevant complexes were also supported by neurosphere, DNA intercalation, agarose gel electrophoresis, and time-dependent ROS detection assay studies. Detailed molecular assays were obtained via real-time reverse transcription (RT)-polymerase chain reaction (PCR) experiments. Moreover, the in vivo biodistribution of the [RuL4PTA] complex in different organs and the morphological patterns of zebrafish embryos due to toxic effects have been evaluated.

Structure-Activity Relationships of 8-Hydroxyquinoline-Derived Mannich Bases with Tertiary Amines Targeting Multidrug-Resistant Cancer

A recently proposed strategy to overcome multidrug resistance (MDR) in cancer is to target the collateral sensitivity of otherwise resistant cells. We designed a library of 120 compounds to explore the chemical space around previously identified 8-hydroxyquinoline-derived Mannich bases with robust MDR-selective toxicity. We included compounds to study the effect of halogen and alkoxymethyl substitutions in R5 in combination with different Mannich bases in R7, a shift of the Mannich base from R7 to R5, as well as the introduction of an aromatic moiety. Cytotoxicity tests performed on a panel of parental and MDR cells highlight a strong influence of experimentally determined pK_a values of the donor atom moieties, indicating that protonation and metal chelation are important factors modulating the MDR-selective anticancer activity of the studied compounds. Our results identify structural requirements increasing MDR-selective anticancer activity, providing guidelines for the development of more effective anticancer chelators targeting MDR cancer.

Direct Cell Radiolabeling for in Vivo Cell Tracking with PET and SPECT Imaging

The arrival of cell-based therapies is a revolution in medicine. However, its safe clinical application in a rational manner depends on reliable, clinically applicable methods for determining the fate and trafficking of therapeutic cells in vivo using medical imaging techniques─known as in vivo cell tracking. Radionuclide imaging using single photon emission computed tomography (SPECT) or positron emission tomography (PET) has several advantages over other imaging modalities for cell tracking because of its high sensitivity (requiring low amounts of probe per cell for imaging) and whole-body quantitative imaging capability using clinically available scanners. For cell tracking with radionuclides, ex vivo direct cell radiolabeling, that is, radiolabeling cells before their administration, is the simplest and most robust method, allowing labeling of any cell type without the need for genetic modification. This Review covers the development and application of direct cell radiolabeling probes utilizing a variety of chemical approaches: organic and inorganic/coordination (radio)chemistry, nanomaterials, and biochemistry. We describe the key early developments and the most recent advances in the field, identifying advantages and disadvantages of the different approaches and informing future development and choice of methods for clinical and preclinical application.

Antibacterial and synergistic activity of a new 8-hydroxyquinoline derivative against methicillin-resistant Staphylococcus aureus

Aim: To evaluate the antibacterial and synergistic effect of a new 8-hydroxyquinoline derivative (PH176) against MRSA. Materials & methods: PH176 activity was determined by broth microdilution against 38 Staphylococcus aureus clinical isolates. The antibacterial and synergistic effects with oxacillin and nitroxoline were evaluated by time-kill assays to five MRSA isolates. Toxicity was evaluated by in vitro and ex vivo models. Results: The MIC₅₀ and MIC₉₀ of PH176 were 16 and 32 μg/ml, respectively. The PH176 and nitroxoline led to a reduction in colony count for four isolates and the combination of PH176 and oxacillin acted synergically for three isolates. Furthermore, PH176 was determined to be noncytotoxic/nonirritant. Conclusion: These results demonstrate that PH176 has revealed promising results to be a potential candidate to treat MRSA infections.

Design, synthesis, and evaluation of 8-aminoquinoline-melatonin derivatives as effective multifunctional agents for Alzheimer's disease

Background

Alzheimer’s disease (AD) is thought to be a complex, multifactorial syndrome with many related molecular lesions contributing to its pathogenesis. Thus, multi-target-directed ligands are considered an effective way of treating AD. This study sought to evaluate 8-aminoquinoline-melatonin derivatives as effective multifunctional agents for AD.

Methods

Thioflavin-T fluorescence assays were used to detect the inhibitory potency of 8-aminoquinoline-melatonin hybrids (a1–a5, b1–b5, and c1–c5) on self- and acetylcholinesterase (AChE)-induced amyloid-β (Aβ) aggregation. The AChE and butyrylcholinesterase (BuChE) inhibitory potency within the compounds was evaluated by Ellman’s assays. Methyl thiazolyl tetrazolium (MTT) assays were performed to evaluate the cytotoxicity of the compounds to C17.2 cells. MTT assay was used to detect the cell viability of HT22 cells to evaluate the antioxidant effect of the compounds. Metal chelation property was measured by ultraviolet-visible spectrophotometry.

Results

Compounds c3 and c5 had superior inhibitory activity against self-induced Aβ aggregation (with inhibitory rates of 41.4±2.1 and 25.5±3.2 at 10 µM, respectively) compared to the other compounds. Compounds in the carbamate group (i.e., a4, a5, b4, b5, c4, and c5) showed significant BuChE inhibitory activity and excellent selectivity over AChE. Most of the compounds exhibited low cytotoxicity in the C17.2 cells. Notably, a2, a3, b2, and b3 and series c (c1–c5) exhibited strong protective effects. Additionally, a3 and c1 specifically chelated with copper ions.

Conclusions

Taking all of the promising results together, 8-aminoquinoline-melatonin hybrids can serve as lead molecules in the further development of new multi-functional anti-AD agents.

Exploration of Nitroaromatic Antibiotics via Sanger's Reagent: Synthesis, In Silico, and Antimicrobial Evaluation

Facile synthesis of molecular hybrids containing a 2,4-dinitrophenyl moiety was achieved via nucleophilic aromatic substitution of the fluoride anion of Sanger's reagent (2,4-dinitrofluorobenzene) with various N, S, and O nucleophiles, considered as bioactive moieties. Antimicrobial evaluation of the new hybrids was carried out using amoxicillin and nystatin as antibacterial and antifungal reference standards, respectively. MIC test results identified the compounds 3, 4, and 7 as the most active hybrids against standard strains and multidrug-resistant strains (MDR) of Staphylococcus aureus, Escherichia coli, and Pseudomonas aurginosa. Most of the hybrids displayed two times the antibacterial activity of AMOX against MDR Pseudomonas aeruginosa, E. coli, and a standard strain of P. aeruginosa (ATCC 29853), while demonstrating a weak antifungal profile against Candida albicans. Selectivity profiles of the promising compounds 3, 4, 6, 7, 8, and 11 on WI-38 human cells were characterized, which indicated that compound 3 is the safest one (CC₅₀ 343.72 μM). The preferential anti-Gram-negative activity of our compounds led us to do docking studies on DNA gyrase B. Docking revealed that the potential antimicrobial compounds fit well into the active site of DNA gyrase B. Furthermore, in silico absorption, distribution, metabolism, and excretion (ADME) predictions revealed that most of the new compounds have high gastrointestinal absorption and a good oral bioavailability with no BBB permeability.

Styrylquinolines Derivatives: SAR study and Synthetic Approaches

Abstract:

In the present-day scenario, heterocyclic derivatives have revealed the primary function of various medicinal agents precious for humanity. Out of a diverse range of heterocycles, Styrylquinolines scaffolds have been proved to play an essential role in a broad range of biological activities, includinganti-HIV-1, antimicrobial, anti-inflammatory, anti-Alzheimer activity with antiproliferative effects on tumor cell lines. Due to the immense pharmacological importance, distinct synthetic methods have been executed to attain new drug entities from Styrylquinolines. Various schemes for synthesizing Styrylquinolines derivatives like one-pot, ultrasound-promoted heterogeneous acid-catalysed, microwave-assisted, solvent-free, and green synthesis were discussed in the present review. Some products of Styrylquinolines are in clinical trials, and patents are also granted for the novel synthesis of Styrylquinolines. According to the structure-activity relationship, replacement at the R-7 and R-8 positions is required for various activities. In this review, recent synthetic approaches in the medicinal chemistry of Styrylquinolines and potent Styrylquinolines derivatives based on structural activity relationships (SAR) are outlined. Moreover, their primary methods and modifications are also discussed.

Synthesis and Preliminary Evaluation of the Cytotoxicity of Potential Metabolites of Quinoline Glycoconjugates

The design of prodrugs is one of the important strategies for selective anti-cancer therapies. When designing prodrugs, attention is paid to the possibility of their targeting tumor-specific markers such as proteins responsible for glucose uptake. That is why glycoconjugation of biologically active compounds is a frequently used strategy. Glycoconjugates consisting of three basic building blocks: a sugar unit, a linker containing a 1,2,3-triazole ring, and an 8-hydroxyquinoline fragment was described earlier. It is not known whether their cytotoxicity is due to whole glycoconjugates action or their metabolites. To check the biological activity of products that can be released from glycoconjugates under the action of hydrolytic enzymes, the synthetically obtained potential metabolites were tested in vitro for the inhibition of proliferation of HCT-116, MCF-7, and NHDF-Neo cell lines using the MTT assay. Research shows that for the full activity of glycoconjugates, the presence of all three building blocks in the structure of a potential drug is necessary. For selected derivatives, additional tests of targeted drug delivery to tumor cells were carried out using polymer nanocarriers in which they are encapsulated. This approach significantly lowered the determined IC₅₀ values of the tested compounds and improved their selectivity and effectiveness.

Electrospun 5-Chloro-7-iodo-8-hydroxyquinoline (Clioquinol)-Containing Poly(3-hydroxybutyrate)/Polyvinylpyrrolidone Antifungal Materials Prospective as Active Dressings against Esca

Esca is a grapevine disease known for centuries which pertains to the group of so-called vine trunk diseases. Phaeomoniella chlamydospora (P. chlamydospora) and Phaeoacremonium aleophilum (P. aleophilum) are the two main fungal pathogens associated with esca. Novel fibrous materials with antifungal properties based on poly(3-hydroxybutyrate) (PHB), polyvinylpyrrolidone (PVP) and 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol, CQ) were developed. One-pot electrospinning (“in” strategy) or electrospinning in conjunction with electrospraying (“on” strategy) were applied to obtain the materials. The materials’ morphology and their surface chemical composition were examined using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). CQ incorporated in the bulk of the fibers or in PVP particles deposited on the fibers was in the amorphous phase, which was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD). The in vitro release of CQ depended on the composition of the electrospun materials and on their design. The performed microbiological screening revealed that, unlike the non-loaded mats, the fibrous mats loaded with CQ were effective in inhibiting the growth of the pathogenic P. chlamydospora and P. aleophilum fungi. Therefore, the created materials are promising as active dressings for grapevine protection against esca.

Nitroxoline and its derivatives are potent inhibitors of metallo-β-lactamases

Carbapenemases such as metallo-β-lactamases (MBLs) are spreading among Gram-negative bacterial pathogens. Infections due to these multidrug-resistant bacteria constitute a major global health challenge. Therapeutic strategies against carbapenemase producing bacteria include β-lactamase inhibitor combinations. Nitroxoline is a broad-spectrum antibiotic with restricted indication for urinary tract infections. In this study, we report on nitroxoline as an inhibitor of MBLs. We investigate the structure-activity relationships of nitroxoline derivatives considering in vitro MBL inhibitory potency in a fluorescence based assay using purified recombinant MBLs, NDM-1 and VIM-1. We investigated the most potent nitroxoline derivative in combination with imipenem against clinical isolates as well as transformants producing MBL by broth microdilution and time-kill kinetics. Our findings demonstrate that nitroxoline derivatives are potent MBL inhibitors and in combination with imipenem overcome MBL-mediated carbapenem resistance.

2-(2-(4-Methoxyphenyl)furo[3,2-h]quinolin-3-yl)acetic Acid

A simple and efficient protocol for the synthesis of the previously unknown 2-(2-(4-methoxyphenyl)furo[3,2-h]quinolin-3-yl)acetic acid was elaborated. The suggested method is based on the telescoped multicomponent reaction of 8-hydroxyquinoline, 4-methylglyoxal, and Meldrum’s acid. The studied process includes the initial interaction of the starting compounds in MeCN followed by intramolecular cyclization to the target product in refluxing acetic acid. The advantage of this approach is the application of readily available starting materials, atom economy, and a simple work-up procedure. The structure of the synthesized furylacetic acid derivative was proven by 1H, 13C, 2D-NMR, IR spectroscopy, and high-resolution mass spectrometry.