Quinolin-4(1H)-imines are potent antiplasmodial drugs targeting the liver stage of malaria

Dependence on linkers' flexibility designed for benzenesulfonamides targeting discovery of novel hCA IX inhibitors as potent anticancer agents

Herein we reported the design and synthesis of two series comprising twenty-two benzenesulfonamides that integrate the s-triazine moiety. Target compounds successfully suppressed the hCA IX, with IC₅₀ ranging from 28.6 to 871 nM. Compounds 5d, 11b, 5b, and 7b were the most active analogues, which inhibited hCA IX isoform in the low nanomolar range (K_I = 28.6, 31.9, 33.4, and 36.6 nM, respectively). Furthermore, they were assessed for their cytotoxic activity against a panel of 60 cancer cell lines following US-NCI protocol. According to five-dose assay, 13c showed significant anticancer activity than 5c with GI₅₀-MID values of 25.08 and 189.01 µM, respectively. Additionally, 13c's effects on wound healing, cell cycle disruption, and apoptosis induction in NCI-H460 cancer cells were examined. Further, docking studies combined with molecular dynamic simulation showed a stable complex with high binding affinity of 5d to hCA IX, exploiting a favourable H-bond and lipophilic interactions.HIGHLIGHTSCarbonic anhydrase (CA) inhibitors comprising rigid and flexible linkers were developed.Compound 5d is the most potent CA IX inhibitor in the study (IC50: 28.6 nM).Compounds 5c and 13c displayed the greatest antiproliferative activity towards 60 cell lines.Compound 13c exposed constructive outcomes on normal cell lines, metastasis, and wound healing.Molecular docking and molecular dynamics (MDs) simulation was utilised to study binding mode.

New targets for antimalarial drug discovery

Phenotypic screening methods have placed numerous preclinical candidates into the antimalarial drug-discovery pipeline. As more chemically validated targets become available, efforts are shifting to target-based drug discovery. Here, we briefly review some of the most attractive targets that have been identified in recent years.

Biological Evaluation and Mechanistic Studies of Quinolin-(1H)-Imines as a New Chemotype against Leishmaniasis

Leishmaniasis is one of the most challenging neglected tropical diseases and remains a global threat to public health. Currently available therapies for leishmaniases present significant drawbacks and are rendered increasingly inefficient due to parasite resistance, making the need for more effective, safer, and less expensive drugs an urgent one. In our efforts to identify novel chemical scaffolds for the development of antileishmanial agents, we have screened in-house antiplasmodial libraries against axenic and intracellular forms of Leishmania infantum, Leishmania amazonensis, and Leishmania major. Several of the screened compounds showed half-maximal inhibitory concentrations (IC₅₀s) against intracellular L. infantum parasites in the submicromolar range (compounds 1h, IC₅₀ = 0.9 μM, and 1n, IC₅₀ = 0.7 μM) and selectivity indexes of 11 and 9.7, respectively. Compounds also displayed activity against L. amazonensis and L. major parasites, albeit in the low micromolar range. Mechanistic studies revealed that compound 1n efficiently inhibits oxygen consumption and significantly decreases the mitochondrial membrane potential in L. infantum axenic amastigotes, suggesting that this chemotype acts, at least in part, by interfering with mitochondrial function. Structure-activity analysis suggests that compound 1n is a promising antileishmanial lead and emphasizes the potential of the quinoline-(1H)-imine chemotype for the future development of new antileishmanial agents.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Effects of Ferrocenyl 4-(Imino)-1,4-Dihydro-quinolines on Xenopus laevis Prophase I - Arrested Oocytes: Survival and Hormonal-Induced M-Phase Entry

Xenopus oocytes were used as cellular and molecular sentinels to assess the effects of a new class of organometallic compounds called ferrocenyl dihydroquinolines that have been developed as potential anti-cancer agents. One ferrocenyl dihydroquinoline compound exerted deleterious effects on oocyte survival after 48 h of incubation at 100 μM. Two ferrocenyl dihydroquinoline compounds had an inhibitory effect on the resumption of progesterone induced oocyte meiosis, compared to controls without ferrocenyl groups. In these inhibited oocytes, no MPF (Cdk1/cyclin B) activity was detected by western blot analysis as shown by the lack of phosphorylation of histone H3. The dephosphorylation of the inhibitory Y15 residue of Cdk1 occurred but cyclin B was degraded. Moreover, two apoptotic death markers, the active caspase 3 and the phosphorylated histone H2, were detected. Only 7-chloro-1-ferrocenylmethyl-4-(phenylylimino)-1,4-dihydroquinoline (8) did not show any toxicity and allowed the assembly of a histologically normal metaphase II meiotic spindle while inhibiting the proliferation of cancer cell lines with a low IC₅₀, suggesting that this compound appears suitable as an antimitotic agent.

Role of Trifluoromethyl Substitution in Design of Antimalarial Quinolones: a Comprehensive Review

Malaria represents a significant health issue, and novel effective drugs are needed to address parasite resistance that has emerged to the current drug arsenal. The most popular antimalarial drugs are focused on the 7-chloro-4-aminoquinoline [e.g., chloroquine (CQ), amodiaquine (AQ), isoquine (IQ), and tebuquine (TBQ)], artemisinin, and atovaquone systems. Recently, endochin has been used as a platform to design a variety of novel potent and safe antimalarial agents named endochin-like quinolones (ELQs). Also, antimalarial quinolones have been constructed from other quinolones drugs such as ICI-56780 and floxacrine. Trifluoromethyl substitution has provided a significant increase in the antimalarial response of many of the designed ELQs against Plasmodium-resistant strains and for in vivo models. In particular, attachment of a substituted trifluoromethoxy (or trifluoromethyl in some cases) biaryl side chain at 2-, 3-, 4-, or 6-position of the quinolone core has shown to be crucially important to generate selective and potent novel ELQs. Furthermore, 6-chloro and 7-methoxy moieties on the quinolone core have been identified as essential pharmacophores when the trifluoromethoxy biaryl side chain is placed at 2- or 3-position of the quinolone core. Methyl or ethyl ester attached at 3-position is essential when the trifluoromethoxy aryl side chain is attached at 6- or 7-position of the quinolone core. Some promising ELQs are currently under clinical trials, representing an excellent platform for the design of new potent, selective, effective, and safe antimalarial drugs against emergent resistance malarial models.

Improvement of Aqueous Solubility of Lapatinib-Derived Analogues: Identification of a Quinolinimine Lead for Human African Trypanosomiasis Drug Development

Lapatinib, an approved epidermal growth factor receptor inhibitor, was explored as a starting point for the synthesis of new hits against Trypanosoma brucei, the causative agent of human African trypanosomiasis (HAT). Previous work culminated in 1 (NEU-1953), which was part of a series typically associated with poor aqueous solubility. In this report, we present various medicinal chemistry strategies that were used to increase the aqueous solubility and improve the physicochemical profile without sacrificing antitrypanosomal potency. To rank trypanocidal hits, a new assay (summarized in a cytocidal effective concentration (CEC50)) was established, as part of the lead selection process. Increasing the sp3 carbon content of 1 resulted in 10e (0.19 μM EC50 against T. brucei and 990 μM aqueous solubility). Further chemical exploration of 10e yielded 22a, a trypanocidal quinolinimine (EC50: 0.013 μM; aqueous solubility: 880 μM; and CEC50: 0.18 μM). Compound 22a reduced parasitemia 109 fold in trypanosome-infected mice; it is an advanced lead for HAT drug development.

Platinum(ii)-chloroquine complexes are antimalarial agents against blood and liver stages by impairing mitochondrial function

Chloroquine is an antimalarial agent with strong activity against the blood stage of Plasmodium infection, but with low activity against the parasite's liver stage. In addition, the resistance to chloroquine limits its clinical use. The discovery of new molecules possessing multistage activity and overcoming drug resistance is needed. One possible strategy to achieve this lies in combining antimalarial quinolones with the pharmacological effects of transition metals. We investigated the antimalarial activity of four platinum(ii) complexes composed of chloroquine and phosphine ligands, denoted as WV-90, WV-92, WV-93 and WV-94. In comparison with chloroquine, the complexes were less potent against the chloroquine-sensitive 3D7 strain but they were as active as chloroquine in inhibiting the chloroquine-resistant W2 strain of P. falciparum. Regarding selectivity, the complexes WV-90 and WV-93 displayed higher indexes. Unlike chloroquine, the complexes act as irreversible parasiticidal agents against trophozoites and the WV-93 complex displayed activity against the hepatic stage of P. berghei. The in vivo suppression activity against P. berghei in the Peters 4 day test displayed by the complexes was similar to that of chloroquine. However, the efficacy in an established P. berghei infection in the Thompson test was superior for the WV-93 complex compared to chloroquine. The complexes' antimalarial mechanism of action is initiated by inhibiting the hemozoin formation. While chloroquine efficiently inhibits hemozoin, parasites treated with the platinum complexes display residual hemozoin crystals. This is explained since the interaction of the platinum complexes with ferriprotoporphyrin is weaker than that of chloroquine. However, the complexes caused a loss of mitochondrial integrity and subsequent reduction in mitochondrial activity, and their effects on mitochondria were more pronounced than those in the chloroquine-treated parasites. The dual effect of the platinum complexes may explain their activity against the hemozoin-lacking parasites (hepatic stage), where chloroquine has no activity. Our findings indicate that the platinum(ii)-chloroquine complexes are multifunctional antimalarial compounds and reinforce the importance of metal complexes in antimalarial drug discovery.

Antileishmanial activity, structure-activity relationship of series of 2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-ones

Trifluoromethyl-substituted quinolones and their analogues have emerged as an interesting platform in the last 6 years to design antiparasite agents. Many of their derivatives have been demonstrated to display excellent efficacy against flagellate parasites such as Plasmodium spp. In order to identify new analogues of trifluoromethyl-substituted quinolones to treat the American cutaneous leishmaniasis, we evaluated the antiproliferative activity of a series of 2-(trifluoromethyl)benzo[b]-[1,8]naphthyridin-4(1H)-ones on the Leishmania braziliensis and Leishmania mexicana parasites. The mentioned derivatives have never been evaluated against any parasite strain. In general, an in vitro evaluation on L.(L)mexicana and L.(V)braziliensis showed that L.(L)mexicana was more sensitive to the action of the compounds than L.(V)braziliensis, either in the promastigote or in the amastigote form. Five compounds exhibited moderate efficacy against L.(L)mexicana promastigotes, with IC50 values ranging from 9.65 to 14.76 µM. From the mentioned molecules, three compounds, 1e, 1f, and 1h, showed a discrete response against axenic and intracellular amastigotes, with LD50 values between 19 and 24 µM. Moreover, an in vitro evaluation was performed on an antimony-resistant amastigote strain and a human isolate amastigote strain. These three compounds showed discrete toxicity on peritoneal macrophages; however, their relatively good antiamastigote response compared to the drug glucantime promoted our trifluoromethyl-substituted benzo[b][1,8]naphthyridin-4(1H)-ones as a potential platform to design potent antileishmanial agents.

Antiplasmodial and antimalarial activities of quinolone derivatives: An overview

Malaria remains one of the most deadly infectious diseases globally. Considering the growing spread of resistance, development of new and effective antimalarials remains an urgent priority. Quinolones, which are emerged as one of the most important class of antibiotics in the treatment of various bacterial infections, showed potential in vitro antiplasmodial and in vivo antimalarial activities, making them promising candidates for the chemoprophylaxis and treatment of malaria. This review presents the current progresses and applications of quinolone-based derivatives as potential antimalarials to pave the way for the development of new antimalarials.

Synthesis of spiro[pyrazole-4,8′-pyrazolo [3,4-f]quinolin]-5(1H)-ones by the reaction of aldehydes with 1H-indazol-6-amine and 1H-pyrazol-5(4H)-one

A four-component reaction including two equivalents of aldehyde, 1

Reinvestigating Old Pharmacophores: Are 4-Aminoquinolines and Tetraoxanes Potential Two-Stage Antimalarials?

The syntheses and antiplasmodial activities of various substituted aminoquinolines coupled to an adamantane carrier are described. The compounds exhibited pronounced in vitro and in vivo activity against Plasmodium berghei in the Thompson test. Tethering a fluorine atom to the aminoquinoline C(3) position afforded fluoroaminoquinolines that act as intrahepatocytic parasite inhibitors, with compound 25 having an IC50 = 0.31 μM and reducing the liver load in mice by up to 92% at 80 mg/kg dose. Screening our peroxides as inhibitors of liver stage infection revealed that the tetraoxane pharmacophore itself is also an excellent liver stage P. berghei inhibitor (78: IC50 = 0.33 μM). Up to 91% reduction of the parasite liver load in mice was achieved at 100 mg/kg. Examination of tetraoxane 78 against the transgenic 3D7 strain expressing luciferase under a gametocyte-specific promoter revealed its activity against stage IV-V Plasmodium falciparum gametocytes (IC50 = 1.16 ± 0.37 μM). To the best of our knowledge, compounds 25 and 78 are the first examples of either an 4-aminoquinoline or a tetraoxane liver stage inhibitors.

Synthesis of New 4-Aminoquinolines and Evaluation of Their In Vitro Activity against Chloroquine-Sensitive and Chloroquine-Resistant Plasmodium falciparum

The efficacy of chloroquine, once the drug of choice in the fight against Plasmodium falciparum, is now severely limited due to widespread resistance. Amodiaquine is one of the most potent antimalarial 4-aminoquinolines known and remains effective against chloroquine-resistant parasites, but toxicity issues linked to a quinone-imine metabolite limit its clinical use. In search of new compounds able to retain the antimalarial activity of amodiaquine while circumventing quinone-imine metabolite toxicity, we have synthesized five 4-aminoquinolines that feature rings lacking hydroxyl groups in the side chain of the molecules and are thus incapable of generating toxic quinone-imines. The new compounds displayed high in vitro potency (low nanomolar IC50), markedly superior to chloroquine and comparable to amodiaquine, against chloroquine-sensitive and chloroquine-resistant strains of P. falciparum, accompanied by low toxicity to L6 rat fibroblasts and MRC5 human lung cells, and metabolic stability comparable or higher than that of amodiaquine. Computational studies indicate a unique mode of binding of compound 4 to heme through the HOMO located on a biphenyl moeity, which may partly explain the high antiplasmodial activity observed for this compound.

Antiplasmodial drugs in the gas phase: a CID and DFT study of quinolon-4(1H)-imine derivatives

The gas-phase behavior of 12 quinolon-4(1H)-imine derivatives with antiplasmodial activity was investigated using electrospray ionization tandem mass spectrometry together with collision induced dissociation and density functional theory (DFT) calculations. The most probable protonation site was predicted by calculating the proton affinity (PA) values for each possible protonation site and it was found to be the imine nitrogen for all compounds under study. Fragmentation pathways of the protonated molecules were proposed and the assignment of product ion structures was performed taking into account theoretical calculations. The nature of the quinoline substituent was found to influence the gas-phase behavior of the compounds under study. The data acquired allowed to bracket the proton affinity of the quinolin-4-imine scaffold, which can be a useful starting point to choose appropriate references for determining PA values of this scaffold.

Assessment of dual life stage antiplasmodial activity of british seaweeds

Terrestrial plants have proven to be a prolific producer of clinically effective antimalarial drugs, but the antimalarial potential of seaweeds has been little explored. The main aim of this study was to assess the in vitro chemotherapeutical and prophylactic potential of the extracts of twenty-three seaweeds collected from the south coast of England against blood stage (BS) and liver stage (LS) Plasmodium parasites. The majority (14) of the extracts were active against BS of P. falciparum, with brown seaweeds Cystoseira tamariscifolia, C. baccata and the green seaweed Ulva lactuca being the most active (IC(50)s around 3 μg/mL). The extracts generally had high selectivity indices (>10). Eight seaweed extracts inhibited the growth of LS parasites of P. berghei without any obvious effect on the viability of the human hepatoma (Huh7) cells, and the highest potential was exerted by U. lactuca and red seaweeds Ceramium virgatum and Halopitys incurvus (IC50 values 14.9 to 28.8 μg/mL). The LS-active extracts inhibited one or more key enzymes of the malarial type-II fatty acid biosynthesis (FAS-II) pathway, a drug target specific for LS. Except for the red seaweed Halopitys incurvus, all LS-active extracts showed dual activity versus both malarial intracellular stage parasites. This is the first report of LS antiplasmodial activity and dual stage inhibitory potential of seaweeds.

Structural optimization of quinolon-4(1H)-imines as dual-stage antimalarials: toward increased potency and metabolic stability

Discovery of novel effective and safe antimalarials has been traditionally focused on targeting erythrocytic parasite stages that cause clinical symptoms. However, elimination of malaria parasites from the human population will be facilitated by intervention at different life-cycle stages of the parasite, including the obligatory developmental phase in the liver, which precedes the erythrocytic stage. We have previously reported that N-Mannich-based quinolon-4(1H)-imines are potent antiplasmodial agents but present several stability liabilities. We now report our efforts to optimize quinolon-4(1H)-imines as dual-stage antiplasmodial agents endowed with chemical and metabolic stability. We report compounds active against both the erythrocytic and exoerythrocytic forms of malaria parasites, such as the quinolon-4(1H)-imine 5p (IC50 values of 54 and 710 nM against the erythrocytic and exoerythrocytic forms), which constitute excellent starting points for further lead optimization as dual-stage antimalarials.

Flavones as isosteres of 4(1H)-quinolones: discovery of ligand efficient and dual stage antimalarial lead compounds

Malaria is responsible for nearly one million deaths annually, and the increasing prevalence of multi-resistant strains of Plasmodium falciparum poses a great challenge to controlling the disease. A diverse set of flavones, isosteric to 4(1H)-quinolones, were prepared and profiled for their antiplasmodial activity against the blood stage of P. falciparum W2 strain, and the liver stage of the rodent parasite Plasmodium berghei. Ligand efficient leads were identified as dual stage antimalarials, suggesting that scaffold optimization may afford potent antiplasmodial compounds.

Cell-based medicinal chemistry optimization of high-throughput screening (HTS) hits for orally active antimalarials. Part 1: challenges in potency and absorption, distribution, metabolism, excretion/pharmacokinetics (ADME/PK)

Malaria represents a significant health issue, and novel and effective drugs are needed to address parasite resistance that has emerged to the current drug arsenal. Antimalarial drug discovery has historically benefited from a whole-cell (phenotypic) screening approach to identify lead molecules. This approach has been utilized by several groups to optimize weakly active antimalarial pharmacophores, such as the quinolone scaffold, to yield potent and highly efficacious compounds that are now poised to enter clinical trials. More recently, GNF/Novartis, GSK, and others have employed the same approach in high-throughput screening (HTS) of large compound libraries to find novel scaffolds that have also been optimized to clinical candidates by GNF/Novartis. This perspective outlines some of the inherent challenges in cell-based medicinal chemistry optimization, including optimization of oral exposure and hERG activity.