Targeting Asexual and Sexual Blood Stages of the Human Malaria Parasite P. falciparum with 7-Chloroquinoline-Based 1,2,3-Triazoles

Biological evaluation of novel side chain containing CQTrICh-analogs as antimalarials and their development as PfCDPK1 kinase inhibitors

The rapid emergence of resistance to existing frontline antimalarial drugs emphasizes a need for the development of target-oriented molecules with novel modes of action. Given the importance of a plant-like Calcium-Dependent Protein Kinase 1 (PfCDPK1) as a stand-alone multistage signalling regulator of P. falciparum, we designed and synthesized 7-chloroquinoline-indole-chalcones tethered with a triazole (CQTrICh-analogs 7 (a-s) and 9) directed towards PfCDPK1. This was accomplished by reacting substituted 1-phenyl-3-(1-(prop-2-yn-1-yl)-1H-indol-3-yl) prop-2-en-1-one and 1-(prop-2-yn-1-yl)-1H-indole-3-carbaldehyde with 4-azido-7-chloroquinoline, respectively via a 'click' reaction. The selected CQTrICh-analogs: 7l and 7r inhibited the growth of chloroquine-sensitive 3D7 strain and -resistant RKL-9 isolate of Plasmodium falciparum, with IC50 values of 2.4 μM & 1.8 μM (7l), and 3.5 μM & 2.7 μM (7r), respectively, and showed no apparent hemolytic activity and cytotoxicity in mammalian cells. Intra-erythrocytic progression studies revealed that the active hybrids: 7l and 7r are effective against the mature stages of the parasite. 7l and 7r were found to stably interact with the catalytically active ATP-binding pocket of PfCDPK1 via energetically favourable H-bonds. The interaction was confirmed in vitro by microscale thermophoresis and kinase assays, which demonstrated that the active hybrids interact with PfCDPK1 and inhibit its kinase activity which is presumably responsible for the parasite growth inhibition. Interestingly, 7l and 7r showed no inhibitory effect on the human kinases, indicating their selectivity for the parasite kinase. We report the antiplasmodial potential of novel kinase-targeting bio-conjugates, a step towards developing pan-kinase inhibitors which is a prerequisite for multistage anti-malarial protection.

Exploring diverse frontiers: Advancements of bioactive 4-aminoquinoline-based molecular hybrids in targeted therapeutics and beyond

Amongst heterocyclic compounds, quinoline and its derivatives are advantaged scaffolds that appear as a significant assembly motif for developing new drug entities. Aminoquinoline moiety has gained significant attention among researchers in the 21stcentury. Considering the biological and pharmaceutical importance of aminoquinoline derivatives, herein, we review the recent developments (since 2019) in various biological activities of the 4-aminoquinoline scaffold hybridized with diverse heterocyclic moieties such as quinoline, pyridine, pyrimidine, triazine, dioxine, piperazine, pyrazoline, piperidine, imidazole, indole, oxadiazole, carbazole, dioxole, thiazole, benzothiazole, pyrazole, phthalimide, adamantane, benzochromene, and pyridinone. Moreover, by gaining knowledge about SARs, structural insights, and molecular targets, this review may help medicinal chemists design cost-effective, selective, safe, and more potent 4-aminoquinoline hybrids for diverse biological activities.

Triazole hybrid compounds: A new frontier in malaria treatment

Reviewing the advancements in malaria treatment, the emergence of triazole hybrid compounds stands out as a groundbreaking development. Combining the advantages of triazole and other moieties, these hybrid compounds offer a new frontier in the battle against malaria. Their potential as effective antimalarial agents has captured the attention of researchers and holds promise for overcoming the challenges posed by drug-resistant malaria strains. We focused on their broad spectrum of antimalarial activity of diverse hybridized 1,2,3-triazoles and 1,2,4-triazoles, structure-activity relationship (SAR), drug-likeness, bioavailability and pharmacokinetic properties reported since 2018 targeting multiple stages of the Plasmodium life cycle. This versatility makes them highly effective against both drug-sensitive and drug-resistant strains of P. falciparum, making them invaluable tools in regions where resistance is prevalent. The synergistic effects of combining the triazole moiety with other pharmacophores have resulted in even greater antimalarial potency. This approach has the potential to circumvent existing resistance mechanisms and provide a more sustainable solution to malaria treatment. While triazole hybrid compounds show great promise, further research and clinical trials are warranted to fully evaluate their safety, efficacy and long-term effects. As research progresses, these compounds can potentially revolutionize the field and contribute to global efforts to eradicate malaria, ultimately saving countless lives worldwide.

Current development of 1,2,3-triazole derived potential antimalarial scaffolds: Structure- activity relationship (SAR) and bioactive compounds

Malaria is among one of the most devastating and deadliest parasitic disease in the world claiming millions of lives every year around the globe. It is a mosquito-borne infectious disease caused by various species of the parasitic protozoan of the genus Plasmodium. The indiscriminate exploitation of the clinically used antimalarial drugs led to the development of various drug-resistant and multidrug-resistant strains of plasmodium which severely reduces the therapeutic effectiveness of most frontline medicines. Therefore, there is urgent need to develop novel structural classes of antimalarial agents acting with unique mechanism of action(s). In this context, design and development of hybrid molecules containing pharmacophoric features of different lead molecules in a single entity represents a unique strategy for the development of next-generation antimalarial drugs. Research efforts by the scientific community over the past few years has led to the identification and development of several heterocyclic small molecules as antimalarial agents with high potency, less toxicity and desired efficacy. Triazole derivatives have become indispensable units in the medicinal chemistry due to their diverse spectrum of biological profiles and many triazole based hybrids and conjugates have demonstrated potential in vitro and in vivo antimalarial activities. The manuscript compiled recent developments in the medicinal chemistry of triazole based small heterocyclic molecules as antimalarial agents and discusses various reported biologically active compounds to lay the groundwork for the rationale design and discovery of triazole based antimalarial compounds. The article emphasised on biological activities, structure activity relationships, and molecular docking studies of various triazole based hybrids with heterocycles such as quinoline, artemisinins, naphthyl, naphthoquinone, etc. as potential antimalarial agents which could act on the dual stage and multi stage of the parasitic life cycle.

Recent developments in the synthesis of hybrid antimalarial drug discovery

In this 21st century, Malaria remains a global burden and causes massive economic trouble to disease-endemic nations. The control and eradication of malaria is a major challenge that requires an urgent need to develop novel antimalarial drugs. To overcome the aforementioned situation, several researchers have given significant effort to develop hybrid antimalarial agents in the search for new antimalarial drugs. Hence, we have summarized those developments of hybrid antimalarial agents from 2017 to till date. This review illustrates the current progress in the recent synthesis of hybrid antimalarial agents along with focusing on their antimalarial evaluation to find the most potent hybrids. This present mini-review will also be useful for the scientific community for the development of new antimalarial drugs to eradicate malaria.

Recent developments in antimalarial activities of 4-aminoquinoline derivatives

Malaria is the fifth most lethal parasitic infection in the world. Antimalarial medications have played a crucial role in preventing and eradicating malaria. Numerous heterocyclic moieties have been incorporated into the creation of effective antimalarial drugs. The 4-aminoquinoline moiety is favoured in antimalarial drug discovery due to the diverse biological applications of its derivative. Since the 1960s, 4-aminoquinoline has been an important antimalarial drug due to its low toxicity, high tolerability, and rapid absorption after administration. This review focused on the antimalarial efficacy of the 4-aminoquinoline moiety hybridised with various heterocyclic scaffolds developed by scientists since 2018 against diverse Plasmodium clones. It could aid in the future development of more effective antimalarial agents.

Synthesis and antimalarial activity of 7-chloroquinoline-tethered sulfonamides and their [1,2,3]-triazole hybrids

Aim & background: Drugs with multiple bioactive moieties have the advantages of multiple modes of action and fewer chances of drug resistance. In continuation of our previous work of developing hybrid antimalarials, we present herein the synthesis and antimalarial activity of two different series of 7-chloroquinoline-sulfonamide hybrids. Materials & methods: The first series of compounds were synthesized by using p-dodecylbenzenesulfonic acid as a Bronsted acid catalyst in ethanol. The second series' compounds were synthesized by 1,3-dipolar cycloaddition of azides and alkynes under click reaction conditions. Results & conclusion: The majority of these compounds demonstrated noncytotoxicity and significant antimalarial activity against Plasmodium falciparum (3D7) with IC₅₀ values in the range of 1.49-13.49 μM. The most promising hybrids (12d, 13a and 13c) may be good starting points for next-generation antimalarials.

Synthesis, Biocidal and Antibiofilm Activities of New Isatin-Quinoline Conjugates against Multidrug-Resistant Bacterial Pathogens along with Their In Silico Screening

Isatin-quinoline conjugates 10a-f and 11a-f were assembled by the reaction of N-(bromobutyl) isatin derivatives 3a, b with aminoquinolines 6a-c and their corresponding hydrazinyl 9a-c in good yields. The structures of the resulting conjugates were established by spectroscopic tools and showed data consistent with the proposed structures. In vitro antibacterial activity against different bacterial strains was evaluated. All tested conjugates showed significant biocidal activity with lower MIC than the first line drugs chloramphenicol and ampicillin. Conjugates 10a, 10b and 10f displayed the most potent activity against all clinical isolates. The antibiofilm activity for all tested conjugates was screened against the reference drug vancomycin using the MRSA strain. The results revealed that all conjugates had an inhibitory activity against biofilm formation and conjugate. Conjugate 11a showed 83.60% inhibition at 10 mg/mL. In addition, TEM studies were used to prove the mechanism of antibacterial action of conjugates 10a and 11a against (MRSA). Modeling procedures were performed on 10a-f and 11a-f and interestingly the results were nearly consistent with the biological activities. In addition, in silico pharmacokinetic evaluation was performed and revealed that the synthesized compounds 10a-f and 11a-f were considered drug-like molecules with promising bioavailability and high GI absorption. The results confirmed that the title compounds caused the disruption of bacterial cell membranes and could be used as potential leads for the further development and optimization of antibacterial agents.

Recent contributions of quinolines to antimalarial and anticancer drug discovery research

Quinoline, a privileged scaffold in medicinal chemistry, has always been associated with a multitude of biological activities. Especially in antimalarial and anticancer research, quinoline played (and still plays) a central role, giving rise to the development of an array of quinoline-containing pharmaceuticals in these therapeutic areas. However, both diseases still affect millions of people every year, pointing to the necessity of new therapies. Quinolines have a long-standing history as antimalarial agents, but established quinoline-containing antimalarial drugs are now facing widespread resistance of the Plasmodium parasite. Nevertheless, as evidenced by a massive number of recent literature contributions, they are still of great value for future developments in this field. On the other hand, the number of currently approved anticancer drugs containing a quinoline scaffold are limited, but a strong increase and interest in quinoline compounds as potential anticancer agents can be seen in the last few years. In this review, a literature overview of recent contributions made by quinoline-containing compounds as potent antimalarial or anticancer agents is provided, covering publications between 2018 and 2020.

Investigation of factors affecting the production of P. falciparum gametocytes in an Indian isolate

The fundamental requirement of every gametocytocidal drug screening assay is the sufficient numbers of healthy and viable gametocytes. The number of in vitro gametocytes grossly depends on the genetic capacity of parasites to produce gametocytes and on various environmental factors that are not precisely elucidated. In the present study, we tested multiple environmental factors that are reported, hypothesized, or predicted to influence gametocyte numbers. We observed that hypoxanthine and the use of freshly drawn human blood significantly enhance gametocytemia (p < 0.05) in vitro. However, other tested factors did not significantly affect gametocytemia. The addition of N-acetyl glucosamine to the culture enriched the gametocytes but d-sorbitol (5% v/v) in amounts and duration of incubation tested was unable to do so without negatively affecting the maturity and health of the gametocytes. Although the in vitro gametocyte production depends on the genetic capability of the parasite strain tested, various environmental factors also control the ability of the strain to produce gametocytes up to a certain extent. This is the first study testing the role of various environmental factors that might affect the gametocyte development in a gametocyte producing strain. The results presented herein will help in the optimization of gametocyte production procedures for various gametocytocidal drug screening assays.

Diterpenoids as potential anti-malarial compounds from Andrographis paniculata

Background

The objectives of the current study are to evaluate the traditionally used medicinal plants Andrographis paniculata for in vitro anti-malarial activity against human malarial parasite Plasmodium falciparum and to further characterize the anti-malarial active extract of A. paniculata using spectroscopic and chromatographic methods.

Results

The chloroform extract of A. paniculata displayed anti-malarial activity with IC50 values 6.36 μg/ml against 3D7 strain and 5.24 μg/ml against K1 strains respectively with no evidence of significant cytotoxicity against mammalian cell line (CC50 > 100 μg/ml). LC-MS analysis of the extract led to the identification of 59 compounds based on their chromatographic and mass spectrometric features (a total of 35 compounds are present in positive ion and 24 compounds in negative ion mode). We have identified 5 flavonoids and 30 compounds as diterpenoids in positive ion mode, while in the negative mode all identified compounds were diterpenoids. Characterization of the most promising class of compound diterpenoids using HPLC-LC-ESI-MS/MS was also undertaken.

Conclusions

The in vitro results undoubtedly validate the traditional use of A. paniculata for the treatment of malaria. The results have led to the identification of diterpenoids from IGNTU_06 extract as potential anti-malarial compounds that need to be further purified and analyzed in anti-malarial drug development programs.

Graphical abstract

Medicinal chemistry updates on quinoline- and endoperoxide-based hybrids with potent antimalarial activity

The resistance of conventional antimalarial drugs against the malarial parasite continues to pose a challenge to control the disease. The indiscriminate exploitation of the available antimalarials has resulted in increasing treatment failures, which urges on the search for novel lead molecules. Artemisinin-based combination therapy (ACT) is the current WHO-recommended first-line treatment for the majority of malaria cases. Hybrid molecules offer a newer strategy for the development of next-generation antimalarial drugs. These comprise molecules, each with an individual pharmacological activity, linked together into a single hybrid molecule. This approach has been utilized by several research groups to develop molecules with potent antimalarial activity. In this review, we provide an overview of the pivotal roles of quinoline- and endoperoxide-based hybrids as inhibitors of the life-cycle progression of Plasmodium. Based on the exhaustive literature reports, we have collated the structural and functional analyses of quinoline- and endoperoxide-based hybrid molecules that show potency equal to or greater than those of the individual compounds, offering an effective therapeutics option for clinical use.

Recent accomplishments on the synthetic/biological facets of pharmacologically active 1H-1,2,3-triazoles

The continuous demand of medicinally important scaffolds has prompted the synthetic chemists to identify simple and efficient routes for their synthesis. 1H-1,2,3-triazole, obtained by highly versatile, efficacious and selective "Click Reaction" has become a synthetic/medicinal chemist's favorite not only because of its ability to mimic different functional groups but also due to enhancement in the targeted biological activities. Triazole ring has also been shown to play a critical role in biomolecular mimetics, fragment-based drug design, and bioorthogonal methodologies. In addition, the availability of triazole containing drugs such as fluconazole, furacyclin, etizolam, voriconazole, triozolam etc. in market has underscored the potential of this biologically enriched core in expediting development of new scaffolds. The present review, therefore, is an attempt to highlight the recent synthetic/biological advancements in triazole derivatives that could facilitate the in-depth understanding of its role in the drug discovery process.

Discovery of fast-acting dual-stage antimalarial agents by profiling pyridylvinylquinoline chemical space via copper catalyzed azide-alkyne cycloadditions

To identity fast-acting, multistage antimalarial agents, a series of pyridylvinylquinoline-triazole analogues have been synthesized via CuAAC. Most of the compounds display significant inhibitory effect on the drug-resistant malarial Dd2 strain at low submicromolar concentrations. Among the tested analogues, compound 60 is the most potent molecule with an EC₅₀ value of 0.04 ± 0.01 μM. Our current study indicates that compound 60 is a fast-acting antimalarial compound and it demonstrates stage specific action at the trophozoite phase in the P. falciparum asexual life cycle. In addition, compound 60 is active against both early and late stage P. falciparum gametocytes. From a mechanistic perspective, compound 60 shows good activity as an inhibitor of β-hematin formation. Collectively, our findings suggest that fast-acting agent 60 targets dual life stages of the malarial parasites and warrant further investigation of pyridylvinylquinoline hybrids as new antimalarials.

Malaria transmission-blocking drugs: implications and future perspectives

As the world gets closer to eliminating malaria, the scientific community worldwide has begun to realize the importance of malaria transmission-blocking interventions. The onus of breaking the life cycle of the human malaria parasite Plasmodium falciparum predominantly rests upon transmission-blocking drugs because of emerging resistance to commonly used schizonticides and insecticides. This third part of our review series on malaria transmission-blocking entails transmission-blocking potential of preclinical transmission-blocking antimalarials and other non-malaria drugs/experimental compounds that are not in clinical or preclinical development for malaria but possess transmission-blocking potential. Collective analysis of the structure and the activity of these experimental compounds might pave the way toward generation of novel prototypes of next-generation transmission-blocking drugs.

Recent advances in transmission-blocking drugs for malaria elimination

The scientific community worldwide has realized that malaria elimination will not be possible without development of safe and effective transmission-blocking interventions. Primaquine, the only WHO recommended transmission-blocking drug, is not extensively utilized because of the toxicity issues in G6PD deficient individuals. Therefore, there is an urgent need to develop novel therapeutic interventions that can target malaria parasites and effectively block transmission. But at first, it is imperative to unravel the existing portfolio of transmission-blocking drugs. This review highlights transmission-blocking potential of current antimalarial drugs and drugs that are in various stages of clinical development. The collective analysis of the relationships between the structure and the activity of transmission-blocking drugs is expected to help in the design of new transmission-blocking antimalarials.

Hybrid molecules with potential in vitro antiplasmodial and in vivo antimalarial activity against drug-resistant Plasmodium falciparum

Malaria is a tropical disease, leading to around half a million deaths annually. Antimalarials such as quinolines are crucial to fight against malaria, but malaria control is extremely challenged by the limited pipeline of effective pharmaceuticals against drug-resistant strains of Plasmodium falciparum which are resistant toward almost all currently accessible antimalarials. To tackle the growing resistance, new antimalarial drugs are needed urgently. Hybrid molecules which contain two or more pharmacophores have the potential to overcome the drug resistance, and hybridization of quinoline privileged antimalarial building block with other antimalarial pharmacophores may provide novel molecules with enhanced in vitro and in vivo activity against drug-resistant (including multidrug-resistant) P falciparum. In recent years, numerous of quinoline hybrids were developed, and their activities against a panel of drug-resistant P falciparum strains were screened. Some of quinoline hybrids were found to possess promising in vitro and in vivo potency. This review emphasized quinoline hybrid molecules with potential in vitro antiplasmodial and in vivo antimalarial activity against drug-resistant P falciparum, covering articles published between 2010 and 2019.