Acridine and acridinones: old and new structures with antimalarial activity

N-(9-Acridinyl) Amino Acid Derivatives: Synthesis and In Vitro Evaluation of Anti-Toxoplasma gondii Activity

Background/Objectives: Acridine, an aromatic heterocyclic compound, serves as a basis for the synthesis of potent bioactive derivatives, displaying a broad spectrum of biological activity, such as antibacterial, antitumor, and antiparasitic activity. With the ability to undergo various types of electrophilic substitutions, introducing different side chains could lead to compounds being active towards various and potentially multiple biotargets. Toxoplasma gondii, a ubiquitous protozoan parasite with worldwide distribution, poses a major health threat, particularly in immunocompromised patients and fetuses. Current treatment options for toxoplasmosis are scarce, with notable limitations, especially regarding side myelotoxicity and inactivity towards T. gondii cysts, causing a need for novel drug candidates. The aim of this study was to evaluate selected N-(9-acrydinil) amino acid derivatives as potential anti-T. gondii agents. Methods: Synthesis of new derivatives was performed using a two-step method, with the initial mixing of 9-chloroacridine with methanol and sodium alkoxide solution and subsequent adding of appropriate amino acids. Cytotoxicity of the tested compounds was evaluated on the Vero cell line using a MTT assay, while their anti-T. gondii activity was investigated using T. gondii RH strain tachyzoites. Results: CC50 values of the derivatives ranged from 41.72 to 154.10 µM. Anti-T. gondii activity, displayed as a reduction in the number of viable tachyzoites compared to the untreated control, ranged from 0 to 33.3%. One of the derivatives displayed activity comparable to the standard treatment option while retaining acceptable cytotoxicity. Esterification, presence of aromatic substituents and the length of the amino acid side chain were identified as key factors that affect both toxicity and activity of these derivatives. Conclusions: Promising results obtained throughout this study provide guidelines for further structural modifications of N-(9-acrydinil) amino acid derivatives in order to synthesize drug candidates competitive to standard treatment options for toxoplasmosis.

Pyronaridine: a review of its clinical pharmacology in the treatment of malaria

Pyronaridine-artesunate was recently strongly recommended in the 2022 update of the WHO Guidelines for the Treatment of Malaria, becoming the newest artemisinin-based combination therapy (ACT) for both uncomplicated Plasmodium falciparum and Plasmodium vivax malaria. Pyronaridine-artesunate, available as a tablet and paediatric granule formulations, is being adopted in regions where malaria treatment outcome is challenged by increasing chloroquine resistance. Pyronaridine is an old antimalarial agent that has been used for more than 50 years as a blood schizonticide, which exerts its antimalarial activity by interfering with the synthesis of the haemozoin pigment within the Plasmodium digestive vacuole. Pyronaridine exhibits a high blood-to-plasma distribution ratio due to its tendency to accumulate in blood cells. This feature is believed to play a crucial role in its pharmacokinetic (PK) properties and pharmacological activity. The PK characteristics of pyronaridine include rapid oral absorption, large volumes of distribution and low total body clearance, resulting in a long terminal apparent half-life. Moreover, differences in PK profiles have been observed between healthy volunteers and malaria-infected patients, indicating a potential disease-related impact on PK properties. Despite a long history, there is only limited knowledge of the clinical PK and pharmacodynamics of pyronaridine, particularly in special populations such as children and pregnant women. We here provide a comprehensive overview of the clinical pharmacology of pyronaridine in the treatment of malaria.

Demystifying the potential of inhibitors targeting DNA topoisomerases in unicellular protozoan parasites

DNA topoisomerases are a group of enzymes omnipresent in all organisms. They maintain the DNA topology during replication, repair, recombination, and transcription. However, the structure of topoisomerase in protozoan parasites differs significantly from that of human topoisomerases; thus, this enzyme acts as a crucial target in drug development against parasitic diseases. Although the therapeutic potential of drugs targeting the parasitic topoisomerase is well known, to manage the shortcomings of currently available therapeutics and the emergence of drug resistance, the discovery of novel antiparasitic molecules is an urgent need. In this review, we describe various investigational and repurposed topoisomerase inhibitors developed against protozoan parasites over the past few years. Teaser: Fatal parasitic diseases are an increasing cause for concern; here, we provide a compilation of different inhibitors targeting DNA topoisomerases, enzymes that are essential for, and unique to, protozoan parasites; therefore, inhibitors are efficient and have few adverse effects.

Anti-amoebic effects of synthetic acridine-9(10H)-one against brain-eating amoebae

Pathogenic A. castellanii and N. fowleri are opportunistic free-living amoebae. Acanthamoeba spp. are the causative agents of granulomatous amebic encephalitis (GAE) and amebic keratitis (AK), whereas Naegleria fowleri causes a very rare but severe brain infection called primary amebic meningoencephalitis (PAM). Acridinone is an important heterocyclic scaffold and both synthetic and naturally occurring derivatives have shown various valuable biological properties. In the present study, ten synthetic Acridinone derivatives (I-X) were synthesized and assessed against both amoebae for anti-amoebic and cysticidal activities in vitro. In addition, excystation, encystation, cytotoxicity, host cell pathogenicity was also performed in-vitro. Furthermore, molecular docking studies of these compounds with three cathepsin B paralogous enzymes of N. fowleri were performed in order to predict the possible docking mode with pathogen. Compound VII showed potent anti-amoebic activity against A. castellanii with IC₅₀ 53.46 µg/mL, while compound IX showed strong activity against N. fowleri in vitro with IC₅₀ 72.41 µg/mL. Compounds II and VII showed a significant inhibition of phenotypic alteration of A. castellanii, while compound VIII significantly inhibited N. fowleri cysts. Cytotoxicity assessment showed that these compounds caused minimum damage to human keratinocyte cells (HaCaT cells) at 100 µg/mL, while also effectively reduced the cytopathogenicity of Acanthamoeba to HaCaT cells. Moreover, Cathepsin B protease was investigated in-silico as a new molecular therapeutic target for these compounds. All compounds showed potential interactions with the catalytic residues. These results showed that acridine-9(10H)-one derivatives, in particular compounds II, VII, VIII and IX hold promise in the development of therapeutic agents against these free-living amoebae.

ACW-02 an Acridine Triazolidine Derivative Presents Antileishmanial Activity Mediated by DNA Interaction and Immunomodulation

The present study proposed the synthesis of a novel acridine derivative not yet described in the literature, chemical characterization by NMR, MS, and IR, followed by investigations of its antileishmanial potential. In vitro assays were performed to assess its antileishmanial activity against L. amazonensis strains and cytotoxicity against macrophages through MTT assay and annexin V-FITC/PI, and the ability to perform an immunomodulatory action using CBA. To investigate possible molecular targets, its interaction with DNA in vitro and in silico targets were evaluated. As results, the compound showed good antileishmanial activity, with IC50 of 6.57 (amastigotes) and 94.97 (promastigotes) µg mL-1, associated with non-cytotoxicity to macrophages (CC50 > 256.00 µg mL-1). When assessed by flow cytometry, 99.8% of macrophages remained viable. The compound induced an antileishmanial effect in infected macrophages and altered TNF-α, IL-10 and IL-6 expression, suggesting a slight immunomodulatory activity. DNA assay showed an interaction with the minor grooves due to the hyperchromic effect of 47.53% and Kb 1.17 × 106 M-1, and was sustained by docking studies. Molecular dynamics simulations and MM-PBSA calculations propose cysteine protease B as a possible target. Therefore, this study demonstrates that the new compound is a promising molecule and contributes as a model for future works.

Solvent Effect on the spectral and photophysical properties of the Acridone

UV/Vis absorption, emission, and excitation spectroscopy with various solvents (dimethyl sulfoxide (DMSO), N,N-Dimethylformamide (DMF), and tetrahydrofuran (THF) and Acetone) at two concentrations (10−4 and 10−5) Mol/L were used to investigate the spectra and photophysical properties of Acridone. Using the integrated emission spectra, the fluorescence quantum yields are calculated. The emission maxima were determined using the red absorption band’s positions and bandwidths. The maximum absorption and emission wavelengths were found to be 390–399 nm and 399–413 nm, respectively, resulting in Stokes shifts of 318.05 and 1142.62 cm-1. Fluorescence spectra have a broad spectral range so that as concentration is increased, each peak shifts toward a long wavelength. It has been discovered that as concentrations increase, the quantum efficiency decreases. The fluorescence quantum yield magnitude is affected by solvents, with THF having the highest value.

Synthesis and investigation on optical and electrochemical properties of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridines

A facile synthesis of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridine derivatives is reported which is based on POCl₃-mediated cyclodehydration followed by double Suzuki-Miyaura cross-coupling. The absorption and fluorescence properties of the obtained products were investigated and their HOMO/LUMO energy levels were estimated by cyclic voltammetry measurements. Besides, density functional theory calculations were carried out for further exploration of their electronic properties.

In vitro anti-Leishmania activity and molecular docking of spiro-acridine compounds as potential multitarget agents against Leishmania infantum

Leishmaniasis is an infectious disease with several limitations regarding treatment schemes. This work reports the anti-Leishmania activity of spiroacridine compounds against the promastigote (IC₅₀ = 1.1 to 6.0 µg / mL) and amastigote forms of the best compounds (EC₅₀ = 4.9 and 0.9 µg / mL) inLeishmania (L.) infantumand proposes an in-silico study with possible selective therapeutic targets for L. infantum. The substituted dimethyl-amine compound (AMTAC 11) showed the best leishmanicidal activity in vitro, and was found to interact with TryRandLdTopoI. comparisons with standard inhibitors were performed, and its main interactions were elucidated. Based on the biological assessment and the structure-activity relationship study, the spiroacridine compounds appear to be promisinganti-leishmaniachemotherapeutic agents to be explored.

Synthesis of Novel Biologically Active Proflavine Ureas Designed on the Basis of Predicted Entropy Changes

A novel series of proflavine ureas, derivatives 11a–11i, were synthesized on the basis of molecular modeling design studies. The structure of the novel ureas was obtained from the pharmacological model, the parameters of which were determined from studies of the structure-activity relationship of previously prepared proflavine ureas bearing n-alkyl chains. The lipophilicity (LogP) and the changes in the standard entropy (ΔS°) of the urea models, the input parameters of the pharmacological model, were determined using quantum mechanics and cheminformatics. The anticancer activity of the synthesized derivatives was evaluated against NCI-60 human cancer cell lines. The urea derivatives azepyl 11b, phenyl 11c and phenylethyl 11f displayed the highest levels of anticancer activity, although the results were only a slight improvement over the hexyl urea, derivative 11j, which was reported in a previous publication. Several of the novel urea derivatives displayed GI₅₀ values against the HCT-116 cancer cell line, which suggest the cytostatic effect of the compounds azepyl 11b–0.44 μM, phenyl 11c–0.23 μM, phenylethyl 11f–0.35 μM and hexyl 11j–0.36 μM. In contrast, the novel urea derivatives 11b, 11c and 11f exhibited levels of cytotoxicity three orders of magnitude lower than that of hexyl urea 11j or amsacrine.

2,4-Bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridines: synthesis and photophysical properties

Acridine derivatives have attracted considerable interest in numerous areas owing to their attractive physical and chemical properties. Herein, starting from readily available anthranilic acid, an efficient synthesis of 2,4-bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridine derivatives was accomplished via a one-pot double Sonogashira cross-coupling method. The UV-visible absorption and emission properties of the synthesized molecules have been examined. Additionally, theoretical studies based on density functional theory (DFT/B3LYP/6-31G(d)) were carried out.

Repurposing the Ebola and Marburg Virus Inhibitors Tilorone, Quinacrine, and Pyronaridine: In Vitro Activity against SARS-CoV-2 and Potential Mechanisms

Severe acute respiratory coronavirus 2 (SARS-CoV-2) is a newly identified virus that has resulted in over 2.5 million deaths globally and over 116 million cases globally in March, 2021. Small-molecule inhibitors that reverse disease severity have proven difficult to discover. One of the key approaches that has been widely applied in an effort to speed up the translation of drugs is drug repurposing. A few drugs have shown in vitro activity against Ebola viruses and demonstrated activity against SARS-CoV-2 in vivo. Most notably, the RNA polymerase targeting remdesivir demonstrated activity in vitro and efficacy in the early stage of the disease in humans. Testing other small-molecule drugs that are active against Ebola viruses (EBOVs) would appear a reasonable strategy to evaluate their potential for SARS-CoV-2. We have previously repurposed pyronaridine, tilorone, and quinacrine (from malaria, influenza, and antiprotozoal uses, respectively) as inhibitors of Ebola and Marburg viruses in vitro in HeLa cells and mouse-adapted EBOV in mice in vivo. We have now tested these three drugs in various cell lines (VeroE6, Vero76, Caco-2, Calu-3, A549-ACE2, HUH-7, and monocytes) infected with SARS-CoV-2 as well as other viruses (including MHV and HCoV 229E). The compilation of these results indicated considerable variability in antiviral activity observed across cell lines. We found that tilorone and pyronaridine inhibited the virus replication in A549-ACE2 cells with IC50 values of 180 nM and IC50 198 nM, respectively. We used microscale thermophoresis to test the binding of these molecules to the spike protein, and tilorone and pyronaridine bind to the spike receptor binding domain protein with K d values of 339 and 647 nM, respectively. Human Cmax for pyronaridine and quinacrine is greater than the IC50 observed in A549-ACE2 cells. We also provide novel insights into the mechanism of these compounds which is likely lysosomotropic.

Crystal structure and Hirshfeld surface analysis of ethyl 2-[9-(2-hy-droxy-phen-yl)-3,3,6,6-tetra-methyl-1,8-dioxo-2,3,4,4a,5,6,7,8a,9,9a,10,10a-dodeca-hydro-acridin-10-yl]acetate

In the title compound, C27H33NO5, a 3,3,6,6-tetra-methyl-tetra-hydro-acridine-1,8-dione ring system carries an ethyl acetate substituent on the acridine N atom and an o-hy-droxy-phenyl ring on the central methine C atom of the di-hydro-pyridine ring. The benzene ring is inclined to the acridine ring system at an angle of 80.45 (7)° and this conformation is stabilized by an intra-molecular O-H⋯O hydrogen bond between the hy-droxy substituent on the benzene ring and one of the carbonyl groups of the acridinedione unit. The ester C=O oxygen atom is disordered over major and minor orientations in a 0.777 (9):0.223 (9) ratio and the terminal -CH3 unit of the ethyl side chain is disordered over two sets of sites in a 0.725 (5): 0.275 (5) ratio. In the crystal, C-H⋯O hydrogen bonds combine to link the mol-ecules into a three-dimensional network. van der Waals H⋯H contacts contribute the most to the Hirshfeld surface (66.9%) followed by O⋯H/H⋯O (22.1%) contacts associated with weak hydrogen bonds.

A new look at 9-substituted acridines with various biological activities

Heterocycles have long been the focus of intensive study in attempts to develop novel therapeutic compounds, and acridine, a polynuclear nitrogen molecule containing a heterocycle, has attracted a considerable amount of scientific attention. Acridine derivatives have been studied in detail and have been found to possess multitarget properties, which inhibit topoisomerase enzymes that regulate topological changes in DNA and interfere with the essential biological function of DNA. This article describes some recent advancements in the field of new 9-substituted acridine heterocyclic agents and describes both the structure and the structure-activity relationship of the most promising molecules. The article will also present the IC₅₀ values of the novel derivatives against various human cancer cell lines. The mini review also investigates the topoisomerase inhibition and antibacterial and antimalarial activity of these polycyclic aromatic derivatives.

Evaluation of Antiplasmodial Potential of C2 and C8 Modified Quinolines: in vitro and in silico Study

BACKGROUND

Malaria remains a common life-threatening infectious disease across the globe due to the development of resistance by Plasmodium parasite against most antimalarial drugs. The situation demands new and effective drug candidates against Plasmodium.

OBJECTIVES

The objective of this study is to design, synthesize and test novel quinoline based molecules against the malaria parasite.

METHODS

C2 and C8 modified quinoline analogs obtained via C-H bond functionalization approach were synthesized and evaluated for inhibition of growth of P. falciparum grown in human red blood cells using SYBR Green microtiter plate based screening. Computational molecular docking studies were carried out with top fourteen molecules using Autodoc software.

RESULTS

The biological evaluation results revealed good activity of quinoline-8-acrylate 3f (IC50 14.2 µM), and the 2-quinoline-α-hydroxypropionates 4b (IC50 6.5 µM), 4j (IC50 5.5 µM) and 4g (IC50 9.5 µM), against chloroquine sensitive Pf3D7 strain. Top fourteen molecules were screened also against chloroquine resistant Pf INDO strain and the observed resistant indices were found to lie between 1 and 7.58. Computational molecular docking studies indicated a unique mode of binding of these quinolines to Falcipain-2 and heme moiety, indicating these to be the probable targets of their antiplasmodial action.

CONCLUSION

An important finding of our work is the fact that unlike Chloroquine which shows a resistance Index of 15, the resistance indices for the most promising molecules studied by us were about one indicating equal potency against drug sensitive and resistant strains of the malaria parasite.

A novel alkaloid glycoside isolated from Atalantia buxifolia

From the dried root and rhizomes of Atalantia buxifolia afford 11 compounds, one new compound 1 and ten known compounds 2-11 were isolated and identified. The novel compound 1 was alkaloid glycoside. Its mother nuclear was the acridone, which was relatively rare. The structure of compound 1 was established identified by spectrum and elucidated as β-D-Glu-4,5-dimethoxy-1,6-dihydroxy-10-methyl-acridone. The compound 1 enriched the compound library and laid the material foundation for the subsequent study of pharmacological activities.

Acridone suppresses the proliferation of human breast cancer cells in vitro via ATP-binding cassette subfamily G member 2

In the past decades, the tricyclic acridone ring system has become a focus of major research by medicinal chemists due to the biological significance of this moiety in drug design and discovery. Acridone has substantial bio-potential since it performs crucial functions, including antibacterial, antimalarial, antiviral and anti-neoplastic activities. However, the anticancer effect and the underlying mechanisms of acridone on breast cancer cells remains unclear. In the present study, the anti-tumor function and the underlying mechanisms of acridone were evaluated in vitro. Firstly, an MTT assay was used to evaluate the inhibitory effect of acridone. Subsequently, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to investigate whether ATP binding cassette subfamily G member 2 (ABCG2) was associated with the function of acridone. Finally, western blotting was used to confirm the results of RT-qPCR. The present study demonstrated that acridone may decrease the proliferation of MDA-MB-231 cells dose-dependently. Further experiments revealed that acridone may downregulate the mRNA and protein expression levels of ABCG2, supporting the potential application of acridone in breast cancer treatment. These findings suggested that acridone is a potential agent in the treatment of human breast cancer.

Metal-Free Synthesis of 2-Substituted 3-(2-Hydroxyaryl)quinolines and 4-(2-Hydroxyaryl)acridines via Benzyne Chemistry

A metal-free approach for the synthesis of 3-aryl-2-substituted quinolines and 4-arylacridines has been developed via the 1,3-dipolar cycloaddition reactions of arynes with N-oxides. Reactions of various 2-substitued quinoline N-oxides with ortho-(trimethylsilyl)aryltriflates in the presence of KF gave 3-(2-hydroxyaryl)quinoline derivatives in good yields. Acridine N-oxides also reacted with arynes to furnish 4-(2-hydroxyaryl)acridines, albeit in moderate yields.

Amino acid or peptide conjugates of acridine/acridone and quinoline/quinolone-containing drugs. A critical examination of their clinical effectiveness within a twenty-year timeframe in antitumor chemotherapy and treatment of infectious diseases

Acridines/acridones, quinolines/quinolones (chromophores) and their derivatives constitute extremely important family of compounds in current medicine. Great significance of the compounds is connected with antimicrobial and antitumor activities. Combining these features together in one drug seems to be long-term benefit, especially in oncology therapy. The attractiveness of the chromophore drugs is still enhanced by elimination their toxicity and improvement not only selectivity, specificity but also bioavailability. The best results are reached by conjugation to natural peptides. This paper highlights significant advance in the study of amino acid or peptide chromophore conjugates that provide highly encouraging data for novel drug development. The structures and clinical significance of amino acid or peptide chromophore conjugates are widely discussed.

9-AAA inhibits growth and induces apoptosis in human melanoma A375 and rat prostate adenocarcinoma AT-2 and Mat-LyLu cell lines but does not affect the growth and viability of normal fibroblasts

The present study found that, similarly to 5-fluorouracil, low concentrations (1-10 µM) of 9-aminoacridine (9-AAA) inhibited the growth of the two rat prostate cancer AT-2 and Mat-LyLu cell lines and the human melanoma A375 cell line. However, at the same concentrations, 9-AAA had no effect on the growth and apoptosis of normal human skin fibroblasts (HSFs). The differences between the cellular responses of the AT-2 and Mat-LyLu cell lines, which differ in malignancy, were found to be relatively small compared with the differences between normal HSFs and the cancer cell lines. Visible effects on the cell growth and survival of tumor cell lines were observed after 24-48 h of treatment with 9-AAA, and increased over time. The inhibition of cancer cell growth was found to be due to the gradually increasing number of cells dying by apoptosis, which was observed using two methods, direct counting and FlowSight analysis. Simultaneously, cell motile activity decreased to the same degree in cancer and normal cells within the first 8 h of incubation in the presence of 9-AAA. The results presented in the current study suggest that short-lasting tests for potential anticancer substances can be insufficient; which may result in cell type-dependent differences in the responses of cells to tested compounds that act with a delay being overlooked. The observed differences in responses between normal human fibroblasts and cancer cells to 9-AAA show the requirement for additional studies to be performed simultaneously on differently reacting cancer and normal cells, to determine the molecular mechanisms responsible for these differences.

Antibiotics in malaria therapy: which antibiotics except tetracyclines and macrolides may be used against malaria?

Malaria, a parasite vector-borne disease, is one of the most significant health threats in tropical regions, despite the availability of individual chemoprophylaxis. Malaria chemoprophylaxis and chemotherapy remain a major area of research, and new drug molecules are constantly being developed before drug-resistant parasites strains emerge. The use of anti-malarial drugs is challenged by contra-indications, the level of resistance of Plasmodium falciparum in endemic areas, clinical tolerance and financial cost. New therapeutic approaches are currently needed to fight against this disease. Some antibiotics that have shown potential effects on malaria parasite have been recently studied in vitro or in vivo intensively. Two families, tetracyclines and macrolides and their derivatives have been particularly studied in recent years. However, other less well-known have been tested or are being used for malaria treatment. Some of these belong to older families, such as quinolones, co-trimoxazole or fusidic acid, while others are new drug molecules such as tigecycline. These emerging antibiotics could be used to prevent malaria in the future. In this review, the authors overview the use of antibiotics for malaria treatment.

Design, Synthesis and Evaluation of Bifunctional Acridinine-Naphthalenediimide Redox-Active Conjugates as Antimalarials

A novel class of bifunctional molecules was synthesized integrating acridine (Ac) and redox-active naphthalenediimide (NDI) scaffolds directly and through a flexible linker (en). We evaluated in vitro antiplasmodial activity, physicochemical properties, and a possible mode of action. Theoretical studies suggested electronic segmentation between the electron-rich Ac and electron-deficient NDI scaffolds. Orthogonal Ac-NDI molecules showed activities in the micromolar to submicromolar range against a chloroquine (CQ)-sensitive strain of human malaria pathogen Plasmodium falciparum (maximum activity, IC₅₀: 0.419 μM). The flexible Ac-en-NDI molecules were most potent and showed activity in the nanomolar range against both CQ-sensitive (with most effective compounds, IC₅₀: 3.65 and 4.33 nM) as well as CQ-resistant (with most effective compounds, IC₅₀: 52.20 and 28.53 nM) strains of P. falciparum. Significantly, with CQ-resistant strains, the activity of the most effective compounds was 1 order of magnitude better than that of standard drug CQ. Ac-en-NDI-conjugated molecules were significantly more potent than the individual NDI and Ac-based molecules. The structure-activity relationship (SAR) suggests that the flexible spacer (en) linking the Ac and NDI scaffolds plays a vital role in exhibiting improved potency. None of the molecules triggered hemolysis in culture, and the most potent compounds did not show cytotoxicity in vitro against mammalian fibroblast NIH3T3 cells at their respective IC₅₀ values. The other significant outcome of this work is that some of the investigated molecules have the potential to affect multiple processes in the parasite including the hemozoin formation in digestive vacuoles (DVs), mitochondrial membrane potential, and the redox homeostasis of the parasite.

Pyrrolidine-Acridine hybrid in Artemisinin-based combination: a pharmacodynamic study

Aiming to develop new artemisinin-based combination therapy (ACT) for malaria, antimalarial effect of a new series of pyrrolidine-acridine hybrid in combination with artemisinin derivatives was investigated. Synthesis, antimalarial and cytotoxic evaluation of a series of hybrid of 2-(3-(substitutedbenzyl)pyrrolidin-1-yl)alkanamines and acridine were performed and mode of action of the lead compound was investigated. In vivo pharmacodynamic properties (parasite clearance time, parasite reduction ratio, dose and regimen determination) against multidrug resistant (MDR) rodent malaria parasite and toxicological parameters (median lethal dose, liver function test, kidney function test) were also investigated. 6-Chloro-N-(4-(3-(3,4-dimethoxybenzyl)pyrrolidin-1-yl)butyl)-2-methoxyacridin-9-amine (15c) has shown a dose dependent haem bio-mineralization inhibition and was found to be the most effective and safe compound against MDR malaria parasite in Swiss mice model. It displayed best antimalarial potential with artemether (AM) in vitro as well as in vivo. The combination also showed favourable pharmacodynamic properties and therapeutic response in mice with established MDR malaria infection and all mice were cured at the determined doses. The combination did not show toxicity at the doses administered to the Swiss mice. Taken together, our findings suggest that compound 15c is a potential partner with AM for the ACT and could be explored for further development.

Verapamil-Sensitive Transport of Quinacrine and Methylene Blue via the Plasmodium falciparum Chloroquine Resistance Transporter Reduces the Parasite's Susceptibility to these Tricyclic Drugs

BACKGROUND

It is becoming increasingly apparent that certain mutations in the Plasmodium falciparum chloroquine resistance transporter (PfCRT) alter the parasite's susceptibility to diverse compounds. Here we investigated the interaction of PfCRT with 3 tricyclic compounds that have been used to treat malaria (quinacrine [QC] and methylene blue [MB]) or to study P. falciparum (acridine orange [AO]).

METHODS

We measured the antiplasmodial activities of QC, MB, and AO against chloroquine-resistant and chloroquine-sensitive P. falciparum and determined whether QC and AO affect the accumulation and activity of chloroquine in these parasites. We also assessed the ability of mutant (PfCRT(Dd2)) and wild-type (PfCRT(D10)) variants of the protein to transport QC, MB, and AO when expressed at the surface of Xenopus laevis oocytes.

RESULTS

Chloroquine resistance-conferring isoforms of PfCRT reduced the susceptibility of the parasite to QC, MB, and AO. In chloroquine-resistant (but not chloroquine-sensitive) parasites, AO and QC increased the parasite's accumulation of, and susceptibility to, chloroquine. All 3 compounds were shown to bind to PfCRT(Dd2), and the transport of QC and MB via this protein was saturable and inhibited by the chloroquine resistance-reverser verapamil.

CONCLUSIONS

Our findings reveal that the PfCRT(Dd2)-mediated transport of tricyclic antimalarials reduces the parasite's susceptibility to these drugs.

From hybrid compounds to targeted drug delivery in antimalarial therapy

The discovery of new drugs to treat malaria is a continuous effort for medicinal chemists due to the emergence and spread of resistant strains of Plasmodium falciparum to nearly all used antimalarials. The rapid adaptation of the malaria parasite remains a major limitation to disease control. Development of hybrid antimalarial agents has been actively pursued as a promising strategy to overcome the emergence of resistant parasite strains. This review presents the journey that started with simple combinations of two active moieties into one chemical entity and progressed into a delivery/targeted system based on major antimalarial classes of drugs. The rationale for providing different mechanisms of action against a single or additional targets involved in the multiple stages of the parasite's life-cycle is highlighted. Finally, a perspective for this polypharmacologic approach is presented.

Antiprotozoal activity and DNA binding of dicationic acridones

Dicationic acridone derivatives were synthesized and their antiparasitic activity was evaluated. Acridones displayed in vitro nanomolar IC50 values against Trypanosoma brucei rhodesiense STIB900 with selectivity indices >1000. Compounds 1b, 3a, and 3b were as potent as the reference drug melarsoprol in this assay. Submicromolar-range activities were observed against wild-type (NF54) and resistant (K1) strains of Plasmodium falciparum, whereas no significant activity was detected against Trypanosoma cruzi or Leishmania donovani. Compounds 1a and 1b were curative in the STIB900 mouse model for human African trypanosomiasis. UV spectrophotometric titrations and circular dichroism (CD) experiments with fish sperm (FS) DNA showed that these compounds form complexes with DNA with binding affinities in the 10(4) M(-1) range. Biological and biophysical data show that antiparasitic activity, toxicity, and DNA binding of this series of acridones are dependent on the relative position of both imidazolinium cations on the heterocyclic scaffold.

Quinoline-based antimalarial hybrid compounds

Quinoline-containing compounds, such as quinine and chloroquine, have a long-standing history as potent antimalarial agents. However, the increasing resistance of the Plasmodium parasite against these drugs and the lack of licensed malaria vaccines have forced chemists to develop synthetic strategies toward novel biologically active molecules. A strategy that has attracted considerable attention in current medicinal chemistry is based on the conjugation of two biologically active molecules into one hybrid compound. Since quinolines are considered to be privileged antimalarial building blocks, the synthesis of quinoline-containing antimalarial hybrids has been elaborated extensively in recent years. This review provides a literature overview of antimalarial hybrid molecules containing a quinoline core, covering publications between 2009 and 2014.

Comparison of hematin-targeting properties of pynacrine, an acridine analog of the benzonaphthyridine antimalarial pyronaridine

The hematin-targeting properties of pynacrine, an acridine analog of the schizontocidal antimalarial drug, pyronaridine, were evaluated to probe the role of the latter's benzonaphthyridine moiety. Pynacrine was as active as pyronaridine in inhibiting glutathione-induced hematin degradation and in enhancing hematin-mediated membrane lysis. It formed a 1:2 complex with hematin but was 50-fold less effective in inhibiting β-hematin formation. However, pynacrine was as potent as pyronaridine in inhibiting intra-erythrocytic Plasmodium falciparum growth in culture, suggesting that it has other off-target(s) effects.

Targeting G-quadruplex nucleic acids with heterocyclic alkaloids and their derivatives

G-Quadruplex nucleic acids or G-quadruplexes (G4s) are four-stranded DNA or RNA secondary structures that are formed in guanine-rich sequences. They are widely distributed in functional regions of the human genome, such as telomeres, ribosomal DNA (rDNA), transcription start sites, promoter regions and untranslated regions of mRNA, suggesting that G-quadruplex structures may play a pivotal role in the control of a variety of cellular processes. G-Quadruplexes are viewed as valid therapeutic targets in human cancer diseases. Small molecules, from naturally occurring to synthetic, are exploited to specifically target G-quadruplexes and have proven to be a new class of anticancer agents. Notably, alkaloids are an important source of G-quadruplex ligands and have significant bioactivities in anticancer therapy. In this review, the authors provide a brief, up-to-date summary of heterocyclic alkaloids and their derivatives targeting G-quadruplexes.

Recent progress in the development of anti-malarial quinolones

Available anti-malarial tools have over the ten-year period prior to 2012 dramatically reduced the number of fatalities due to malaria from one million to less than six-hundred and thirty thousand. Although fewer people now die from malaria, emerging resistance to the first-line anti-malarial drugs, namely artemisinins in combination with quinolines and arylmethanols, necessitates the urgent development of new anti-malarial drugs to curb the disease. The quinolones are a promising class of compounds, with some demonstrating potent in vitro activity against the malaria parasite. This review summarizes the progress made in the development of potential anti-malarial quinolones since 2008. The efficacy of these compounds against both asexual blood stages and other stages of the malaria parasite, the nature of putative targets, and a comparison of these properties with anti-malarial drugs currently in clinical use, are discussed.

Gametocytocidal screen identifies novel chemical classes with Plasmodium falciparum transmission blocking activity

Discovery of transmission blocking compounds is an important intervention strategy necessary to eliminate and eradicate malaria. To date only a small number of drugs that inhibit gametocyte development and thereby transmission from the mosquito to the human host exist. This limitation is largely due to a lack of screening assays easily adaptable to high throughput because of multiple incubation steps or the requirement for high gametocytemia. Here we report the discovery of new compounds with gametocytocidal activity using a simple and robust SYBR Green I- based DNA assay. Our assay utilizes the exflagellation step in male gametocytes and a background suppressor, which masks the staining of dead cells to achieve healthy signal to noise ratio by increasing signal of viable parasites and subtracting signal from dead parasites. By determining the contribution of exflagellation to fluorescent signal and using appropriate cutoff values, we were able to screen for gametocytocidal compounds. After assay validation and optimization, we screened an FDA approved drug library of approximately 1500 compounds, as well as the 400 compound MMV malaria box and identified 44 gametocytocidal compounds with sub to low micromolar IC₅₀s. Major classes of compounds with gametocytocidal activity included quaternary ammonium compounds with structural similarity to choline, acridine-like compounds similar to quinacrine and pyronaridine, as well as antidepressant, antineoplastic, and anthelminthic compounds. Top drug candidates showed near complete transmission blocking in membrane feeding assays. This assay is simple, reproducible and demonstrated robust Z-factor values at low gametocytemia levels, making it amenable to HTS for identification of novel and potent gametocytocidal compounds.

Amsacrine suppresses matrix metalloproteinase-2 (MMP-2)/MMP-9 expression in human leukemia cells

This study explores the suppression mechanism of amsacrine (4-(9-Acridinylamino)-N-(methanesulfonyl)-m-anisidine hydrochloride) on matrix metalloproteinase-2 (MMP-2) and MMP-9 expression in human leukemia cells. Amsacrine attenuated cell invasion with decreased MMP-2/MMP-9 protein expression and mRNA levels in U937, Jurkat, HL-60, K562, KU812, and MEG-01 cells. Moreover, amsacrine reduced both MMP-2/MMP-9 promoter luciferase activity and MMP-2/MMP-9 mRNA stability in leukemia cells. Studies on amsacrine-treated U937 cells revealed that amsacrine-elicited ROS generation induced JNK and p38 MAPK activation but reduced the phospho-ERK level. Amsacrine-induced ERK inactivation and p38 MAPK/JNK activation were demonstrated to suppress MMP-2/MMP-9 promoter luciferase activity and promote MMP-2/MMP-9 mRNA decay, respectively. p38 MAPK/JNK activation led to up-regulation of protein phosphatase 2A catalytic subunit α (PP2Acα) in amsacrine-treated U937 cells. Okadaic acid (PP2A inhibitor) treatment increased MMP-2/MMP-9 mRNA stability in amsacrine-treated cells, whereas PP2Acα over-expression increased MMP-2/MMP-9 mRNA decay. Amsacrine-induced MMP-2/MMP-9 down-regulation was also related to PP2Acα up-regulation on Jurkat, HL-60, K562, KU812, and MEG-01 cells. Collectively, our data indicate that amsacrine induces MMP-2/MMP-9 down-regulation via simultaneous suppression of genetic transcription and mRNA stability in human leukemia cells.

Analgesic, anti-inflammatory, and GC-MS studies on Castanospermum australe A. Cunn. & C. Fraser ex Hook

The present study was aimed to evaluate the analgesic and anti-inflammatory properties of Castanospermum australe and to profile phytochemicals by GC-MS. The ethanolic extracts were prepared by successive solvent extraction using Soxhlet apparatus. The analgesic activity was analyzed by hot plate method and acetic acid-induced writhing test whereas anti-inflammatory study was done by carrageenan induced paw oedema model. The acute toxicity study revealed that ethanol extracts of leaf and bark of C. australe were safe even at a higher dose of 2000 mg/kg whereas ethanol extract of seed was toxic at the same dose. In both hot plate method (5.85 s) and acetic acid-induced writhing test (57%), the leaf ethanol extract exhibited significant analgesic activity (P < 0.001) at a dose of 400 mg/kg. The anti-inflammatory activity of leaf extract was exhibited by the reduction in paw linear diameter by 64.76% at 400 mg/kg in carrageenan induced paw oedema. The GC-MS analysis of the ethanol extract of leaf revealed sixteen major compounds of which 1,7-dimethyl-4,10-dioxa-1,7-diazacyclododecane, (+)-N-methylephedrine, and permethylspermine were found to be pharmaceutically and the most important. These findings justify that C. australe can be a valuable natural analgesic and anti-inflammatory source which seemed to provide potential phytotherapeutics against various ailments.

Solvatochromic properties of 3,6-di-tert-butyl-8H-indolo[3,2,1-de]acridin-8-one

The spectral and photophysical properties of newly synthesized 3,6-di-tert-butyl-8H-indolo[3,2,1-de]acridin-8-one were studied.

N-cinnamoylation of antimalarial classics: quinacrine analogues with decreased toxicity and dual-stage activity

Plasmodium falciparum, the causative agent of the most lethal form of malaria, is becoming increasingly resistant to most available drugs. A convenient approach to combat parasite resistance is the development of analogues of classical antimalarial agents, appropriately modified in order to restore their relevance in antimalarial chemotherapy. Following this line of thought, the design, synthesis and in vitro evaluation of N-cinnamoylated quinacrine surrogates, 9-(N-cinnamoylaminobutyl)-amino-6-chloro-2-methoxyacridines, is reported. The compounds were found to be highly potent against both blood-stage P.falciparum, chloroquine-sensitive 3D7 (IC50 =17.0-39.0 nM) and chloroquine-resistant W2 and Dd2 strains (IC50 =3.2-41.2 and 27.1-131.0 nM, respectively), and liver-stage P.berghei (IC50 =1.6-4.9 μM) parasites. These findings bring new hope for the possible future "rise of a fallen angel" in antimalarial chemotherapy, with a potential resurgence of quinacrine-related compounds as dual-stage antimalarial leads.