A primaquine-chloroquine hybrid with dual activity against Plasmodium liver and blood stages

Rh(iii)-catalyzed sp3/sp2-C-H heteroarylations via cascade C-H activation and cyclization

The development of an efficient strategy for facile access to quinoline-based bis-heterocycles holds paramount importance in medicinal chemistry. Herein, we describe a unified approach for accessing 8-(indol-3-yl)methyl-quinolines by integrating Cp*Rh(iii)-catalyzed C(sp3)-H bond activation of 8-methylquinolines followed by nucleophilic cyclization with o-ethynylaniline derivatives. Remarkably, methoxybiaryl ynones under similar catalytic conditions delivered quinoline tethered spiro[5.5]enone scaffolds via a dearomative 6-endo-dig C-cyclization. Moreover, leveraging this method for C8(sp2)-H bond activation of quinoline-N-oxide furnished biologically relevant oxindolyl-quinolines. This reaction proceeds via C(sp2)-H bond activation, regioselective alkyne insertion, oxygen-atom-transfer (OAT) and intramolecular nucleophilic cyclization in a cascade manner. One C-C, one C-N and one C[double bond, length as m-dash]O bond were created with concomitant formation of a quaternary center.

Potential Benefits of Lycopene Consumption: Rationale for Using It as an Adjuvant Treatment for Malaria Patients and in Several Diseases

Malaria is a disease that affects thousands of people around the world every year. Its pathogenesis is associated with the production of reactive oxygen and nitrogen species (RONS) and lower levels of micronutrients and antioxidants. Patients under drug treatment have high levels of oxidative stress biomarkers in the body tissues, which limits the use of these drugs. Therefore, several studies have suggested that RONS inhibition may represent an adjuvant therapeutic strategy in the treatment of these patients by increasing the antioxidant capacity of the host. In this sense, supplementation with antioxidant compounds such as zinc, selenium, and vitamins A, C, and E has been suggested as part of the treatment. Among dietary antioxidants, lycopene is the most powerful antioxidant among the main carotenoids. This review aimed to describe the main mechanisms inducing oxidative stress during malaria, highlighting the production of RONS as a defense mechanism against the infection induced by the ischemia-reperfusion syndrome, the metabolism of the parasite, and the metabolism of antimalarial drugs. Furthermore, the effects of lycopene on several diseases in which oxidative stress is implicated as a cause are outlined, providing information about its mechanism of action, and providing an evidence-based justification for its supplementation in malaria.

Quantitative Analysis of the Potency of Equimolar Two-Drug Combinations and Combi-Molecules Involving Kinase Inhibitors In Vitro: The Concept of Balanced Targeting

The median-effect principle proposed by Chou and Talalay is the most effective approach to parameterize interactions between several agents in combination. However, this method cannot be used to evaluate the effectiveness of equimolar drug combinations, which are comparative references for dual-targeting molecular design. Here, using data acquired through the development of “combi-molecules” blocking two kinases (e.g., EGFR-c-Src and EGFR-c-Met), we established potency indices for equimolar and dual-targeted inhibitors. If the fold difference (κ) between the IC50 of the two individual kinase inhibitors was >6, the IC50 of their equimolar combination resembled that of the more potent inhibitor. Hence, the “combi-targeting” of the two kinases was considered “imbalanced” and the combination ineffective. However, if κ ≤ 6, the IC50 of the combination fell below that of each individual drug and the combi-targeting was considered “balanced” and the combination effective. We also showed that combi-molecules should be compared with equimolar combinations only under balanced conditions and propose a new parameter Ω for validating their effectiveness. A multi-targeted drug is effective if Ω < 1, where Ω is defined as the IC50 of the drug divided by that of the corresponding equimolar combination. Our study provides a methodology to determine the in vitro potency of equimolar two-drug combinations as well as combi-/hybrid molecules inhibiting two different kinase targets.

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.

Itaconic acid hybrids as potential anticancer agents

Abstract

In this paper, we report the synthesis of novel hybrids 2–14 based on itaconic acid and fluoroaniline, pyridine, indole and quinoline scaffolds. Itaconic acid is a naturally occurring compound with a Michael acceptor moiety, a key structural feature in several anticancer and antiviral drugs, responsible for the covalent binding of a drug to the cysteine residue of a specific protein. Aromatic parts of the hybrids also come from the substances reported as anticancer or antiviral agents. The synthetic route employed to access the amido-ester hybrids 2–13 used monomethyl itaconate or monomethyl itaconyl chloride and corresponding amines as the starting materials. Dimers 14 and 15 with two aminoindole or mefloquine moieties were prepared from itaconic acid and corresponding amino derivative, using standard coupling conditions (HATU/DIEA). All hybrids exerted anticancer effects in vitro against almost all the tumour cell lines that were evaluated (MCF-7, HCT 116, H460, LN-229, Capan-1, DND-41, HL-60, K-562, Z-138). Solid tumour cells were, in general, more responsive than the haematological cancer cells. The MCF-7 breast adenocarcinoma cell line appeared the most sensitive. Amido-ester 12 with chloroquine core and mefloquine homodimer 15 showed the highest activity with GI₅₀ values between 0.7 and 8.6 µM. In addition, compound 15 also exerted antiviral activity against Zika virus and Coxsackievirus B4 in low micromolar concentrations.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s11030-020-10147-6) contains supplementary material, which is available to authorized users.

Structural hybridization as a facile approach to new drug candidates

Structural hybridization of preclinically and clinically validated pharmacologically active molecules has emerged as a promising tool to develop new generations of safe and highly efficient drug candidates against various diseases including microbial infections, virus infections and cancer. Strategies of drug-drug combinations have been adopted to generate hybrid conjugates of many clinically used drugs, designed to address inherent problems associated with these drugs. Thus, the design of hybrids was aimed to achieve higher efficacy through possible multi-target interactions, selective delivery of the drug to the site of action with the aim to improve bioavailability, alleviate toxicity and circumvent drug resistances. In this review article, we summarize the progress made in recent years in the rapidly growing field of drug discovery, focusing on the rationality of the hybrid design with particular emphasis on the linker architecture, which plays a crucial role in the overall success of a hybrid drug.

Pyridine and Pyrimidine Derivatives as Privileged Scaffolds in Biologically Active Agents

Pyridine and pyrimidine derivatives have received great interest in recent pharmacological research, being effective in the treatment of various malignancies, such as myeloid leukemia, breast cancer and idiopathic pulmonary fibrosis. Most of the FDA approved drugs show a pyridine or pyrimidine core bearing different substituents. The aim of this review is to describe the most recent reports in this field, with reference to the newly discovered pyridineor pyrimidine-based drugs, to their synthesis and to the evaluation of the most biologically active derivatives. The corresponding benzo-fused heterocyclic compounds, i.e. quinolines and quinazolines, are also reported.

Primaquine derivatives: Modifications of the terminal amino group

Numerous modifications of the well-known antimalarial drug primaquine, both at the quinoline ring and at the primary amino group, have been reported, mostly to obtain antimalarial agents with improved bioavailability, reduced toxicity and/or prolonged activity. Modifications of the terminal amino group were made with the main idea to prevent the metabolic pathway leading to inactive and toxic carboxyprimaquine (follow-on strategy), but also to get compounds with different activity (repurposing strategy). The modifications undertaken until 2009 were included in a review published in the same year. The present review covers various classes of primaquine N-derivatives with diverse biological profiles, prepared in the last decade by our research group as well as the others. We have summarized the synthetic procedures applied for their preparation and discussed the main biological results. Several hits for the development of novel antiplasmodial, anticancer, antimycobacterial and antibiofilm agents were identified.

Malaria Hybrids: A Chronological Evolution

Malaria, an upsetting malaise caused by a diverse class of Plasmodium species affects about 40% of the world's population. The distress associated with it has reached colossal scales owing to the development of resistance to most of the clinically available agents. Hence, the search for newer molecules for malaria treatment and cure is an incessant process. After the era of a single molecule for malaria treatment ended, there was an advent of combination therapy. However, lately there had been reports of the development of resistance to many of these agents as well. Subsequently, at present most of the peer groups working on malaria treatment aim to develop novel molecules, which may act on more than one biological processes of the parasite life cycle, and these scaffolds have been aptly termed as Hybrid Molecules or Double Drugs. These molecules may hold the key to hitherto unknown ways of showing a detrimental effect on the parasite. This review enlists a few of the recent advances made in malaria treatment by these hybrid molecules in a sequential manner.

Primaquine homodimers as potential antiplasmodial and anticancer agents

Primaquine homodimers, e.g. symmetric PQ-diamides of dicarboxylic acids containing 4 to 8 carbon atoms, were evaluated against Plasmodium berghei hepatic stages and P. falciparum blood stages, as well as against three cancer cell lines. Novel PQ-homodimers exerted much higher activity against hepatic stages, but less pronounced activity against blood stages in comparison to the parent drug. The submicromolar activity of succinic, fumaric and maleic derivatives against P. berghei was determined (IC₅₀ values: 726.2, 198.1 and 358.4 nM, respectively). Our results indicated that the length and type of spacer between two PQ moieties highly modified the antiproliferative activities of PQ-homodimers. The general antiproliferative activity of the adipic and mesaconic derivatives against three cancer cell lines (MCF-7, HCT116, H 460) was observed (GI₅₀ = 1.78-13.7 and 2.36-4.31 µM, respectively), but adipic derivative was less toxic to human embryonic kidney cells (HEK 293). High selectivity of fumaric and suberic derivatives against breast adenocarcinoma cell line MCF-7 was detected. These two compounds have shown no antiproliferative activity against other tumor cells and HEK 293.

Antiplasmodial Activity and In Vivo Bio-Distribution of Chloroquine Molecules Released with a 4-(4-Ethynylphenyl)-Triazole Moiety from Organometallo-Cobalamins

We have explored the possibility of using organometallic derivatives of cobalamin as a scaffold for the delivery of the same antimalarial drug to both erythro- and hepatocytes. This hybrid molecule approach, intended as a possible tool for the development of multi-stage antimalarial agents, pivots on the preparation of azide-functionalized drugs which, after coupling to the vitamin, are released with a 4-(4-ethynylphenyl)-triazole functionality. Three chloroquine and one imidazolopiperazine derivative (based on the KAF156 structure) were selected as model drugs. One hybrid chloroquine conjugate was extensively studied via fluorescent labelling for in vitro and in vivo bio-distribution studies and gave proof-of-concept for the design. It showed no toxicity in vivo (zebrafish model) as well as no hepatotoxicity, no cardiotoxicity or developmental toxicity of the embryos. All 4-(4-ethynylphenyl)-triazole derivatives of chloroquine were equally active against chloroquine-resistant (CQR) and chloroquine-sensitive (CQS) Plasmodium falciparum strains.

Primaquine-quinoxaline 1,4-di-N-oxide hybrids with action on the exo-erythrocytic forms of Plasmodium induce their effect by the production of reactive oxygen species

Background

The challenge in anti-malarial chemotherapy is based on the emergence of resistance to drugs and the search for medicines against all stages of the life cycle of Plasmodium spp. as a therapeutic target. Nowadays, many molecules with anti-malarial activity are reported. However, few studies about the cellular and molecular mechanisms to understand their mode of action have been explored. Recently, new primaquine-based hybrids as new molecules with potential multi-acting anti-malarial activity were reported and two hybrids of primaquine linked to quinoxaline 1,4-di-N-oxide (PQ–QdNO) were identified as the most active against erythrocytic, exoerythrocytic and sporogonic stages.

Methods

To further understand the anti-malarial mode of action (MA) of these hybrids, hepg2-CD81 were infected with Plasmodium yoelii 17XNL and treated with PQ–QdNO hybrids during 48 h. After were evaluated the production of ROS, the mitochondrial depolarization, the total glutathione content, the DNA damage and proteins related to oxidative stress and death cell.

Results

In a preliminary analysis as tissue schizonticidals, these hybrids showed a mode of action dependent on peroxides production, but independent of the activation of transcription factor p53, mitochondrial depolarization and arrest cell cycle.

Conclusions

Primaquine–quinoxaline 1,4-di-N-oxide hybrids exert their antiplasmodial activity in the exoerythrocytic phase by generating high levels of oxidative stress which promotes the increase of total glutathione levels, through oxidation stress sensor protein DJ-1. In addition, the role of HIF1a in the mode of action of quinoxaline 1,4-di-N-oxide is independent of biological activity.

Potent Antimalarial Activity of Two Arenes Linked with Triamine Designed To Have Multiple Interactions with Heme

Based on the idea that compounds designed to exhibit high affinity for heme would block hemozoin formation, a critical heme-detoxification process for malarial parasites, we synthesized a series of compounds with two π-conjugated moieties at terminal amino groups of triamine. These compounds exhibited moderate to high antimalarial activities in vitro toward both chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum. In a P. berghei-infected mouse model, 3a and 12a showed potent antimalarial activities compared to artesunate, as well as a prolonged duration of antimalarial effect. We found a good correlation between protective activity against hemin degradation and antimalarial activity. Compounds 8b and 3a strongly inhibited hemozoin formation catalyzed by heme detoxification protein.

Novel antimalarial chloroquine- and primaquine-quinoxaline 1,4-di-N-oxide hybrids: Design, synthesis, Plasmodium life cycle stage profile, and preliminary toxicity studies

Emergence of drug resistance and targeting all stages of the parasite life cycle are currently the major challenges in antimalarial chemotherapy. Molecular hybridization combining two scaffolds in a single molecule is an innovative strategy for achieving these goals. In this work, a series of novel quinoxaline 1,4-di-N-oxide hybrids containing either chloroquine or primaquine pharmacophores was designed, synthesized and tested against both chloroquine sensitive and multidrug resistant strains of Plasmodium falciparum. Only chloroquine-based compounds exhibited potent blood stage activity with compounds 4b and 4e being the most active and selective hybrids at this parasite stage. Based on their intraerythrocytic activity and selectivity or their chemical nature, seven hybrids were then evaluated against the liver stage of Plasmodium yoelii, Plasmodium berghei and Plasmodium falciparum infections. Compound 4b was the only chloroquine-quinoxaline 1,4-di-N-oxide hybrid with a moderate liver activity, whereas compound 6a and 6b were identified as the most active primaquine-based hybrids against exoerythrocytic stages, displaying enhanced liver activity against P. yoelii and P. berghei, respectively, and better SI values than primaquine. Although both primaquine-quinoxaline 1,4-di-N-oxide hybrids slightly reduced the infection of mosquitoes, they inhibited sporogony of P. berghei and compound 6a showed 92% blocking of transmission. In vivo liver efficacy assays revealed that compound 6a showed causal prophylactic activity affording parasitaemia reduction of up to 95% on day 4. Absence of genotoxicity and in vivo acute toxicity were also determined. These results suggest the approach of primaquine-quinoxaline 1,4-di-N-oxide hybrids as new potential dual-acting antimalarials for further investigation.

Are Antimalarial Hybrid Molecules a Close Reality or a Distant Dream?

Emergence of drug-resistant Plasmodium falciparum strains has led to a situation of haste in the scientific and pharmaceutical communities. Hence, all their efforts are redirected toward finding alternative chemotherapeutic agents that are capable of combating multidrug-resistant parasite strains. In light of this situation, scientists have come up with the concept of hybridization of two or more active pharmacophores into a single chemical entity, resulting in "antimalarial hybrids." The approach has been applied widely for generation of lead compounds against deadly diseases such as cancer and AIDS, with a proven potential for use as novel drugs, but is comparatively new in the sphere of antimalarial drug discovery. A sudden surge has been evidenced in the number of studies on the design and synthesis of hybrids for treating malaria and may be regarded as proof of their potential advantages over artemisinin-based combination therapy (ACT). However, it is evident from recent studies that most of the potential advantages of antimalarial hybrids, such as lower toxicity, better pharmacokinetics, and easier formulation, have yet to be realized. A number of questions left unaddressed at present need to be answered before this approach can progress to the late stages of clinical development and prove their worth in the clinic. To the best of our knowledge, this compilation is the first attempt to shed light on the shortcomings that are surfacing as more and more studies on molecular hybridization of the active pharmacophores of known antimalarials are being published.

Malaria treatment using novel nano-based drug delivery systems

We reside in an era of technological innovation and advancement despite which infectious diseases like malaria remain to be one of the greatest threats to the humans. Mortality rate caused by malaria disease is a huge concern in the twenty-first century. Multiple drug resistance and nonspecific drug targeting of the most widely used drugs are the main reasons/drawbacks behind the failure in malarial therapy. Dose-related toxicity because of high doses is also a major concern. Therefore, to overcome these problems nano-based drug delivery systems are being developed to facilitate site-specific or target-based drug delivery and hence minimizing the development of resistance progress and dose-dependent toxicity issues. In this review, we discuss about the shortcomings in treating malaria and how nano-based drug delivery systems can help in curtailing the infectious disease malaria.

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.

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.

Quinine conjugates and quinine analogues as potential antimalarial agents

Malaria is a tropical disease, prevalent in Southeast Asia and Africa, resulting in over half a million deaths annually; efforts to develop new antimalarial agents are therefore particularly important. Quinine continues to play a role in the fight against malaria, but quinoline derivatives are more widely used. Drugs based on the quinoline scaffold include chloroquine and primaquine, which are able to act against the blood and liver stages of the parasite's life cycle. The purpose of this review is to discuss reported biologically active compounds based on either the quinine or quinoline scaffold that may have enhanced antimalarial activity. The review emphasises hybrid molecules, and covers advances made in the last five years. The review is divided into three sections: modifications to the quinine scaffold, modifications to aminoquinolines and finally metal-containing antimalarial compounds.

Design and Synthesis of Novel Hybrid Molecules against Malaria

The effective treatment of malaria can be very complex: Plasmodium parasites develop in multiple stages within a complex life cycle between mosquitoes as vectors and vertebrates as hosts. For the full and effective elimination of parasites, an effective drug should be active against the earliest stages of the Plasmodium infection: liver stages (reduce the progress of the infection), blood stages (cure the clinical symptoms), and gametocytes (inhibit the transmission cycle). Towards this goal, here we report the design, the synthetic methodology, and the characterization of novel hybrid agents with combined activity against Plasmodium liver stages and blood stages and gametocytes. The divergent synthetic approach allows the access to differently linked primaquine-chloroquine hybrid templates in up to eight steps.

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.

Reemergence of chloroquine (CQ) analogs as multi-targeting antimalarial agents: a review

Amongst several communicable diseases (CDs), malaria is one of the deadliest parasitic disease all over the world, particularly in African and Asian countries. To curb this menace, numbers of antimalarial agents are being sold as over the counter (OTC) drugs. Chloroquine (CQ) is one of them and is one of the oldest, cheapest, and easily available synthetic agents used to curb malaria. Unfortunately, after the reports of CQ-resistance against different strains of malarial parasite strains worldwide, scientist are continuously modifying the core structure of CQ to get an efficient drug. Interestingly, several new drugs have been emerged in due course having unique and enhanced properties (like dual stage inhibitors, resistance reversing ability etc.) and are ready to enter into the clinical trial. In this course, some new agents have also been discovered which are; though inactive against CQS strain, highly active against CQR strains. The present article describes the role of modification of the core structure of CQ and its effects on the biological activities. Moreover, the attempt has also been made to predict the future prospects of such drugs to reemerge as antimalarial agents.

Interaction of a biguanide compound with membrane model interface systems: probing the properties of antimalaria and antidiabetic compounds

Since membrane penetration is important for drug efficacy, how antimalarial precursor material 1-phenylbiguanide (PBG) interacts with an interface was characterized using a reverse micelle (RM) model system. (1)H NMR studies show that PBG partitions across the membrane interface. Specifically, the (1)H NMR studies showed that the 1-phenylbiguanide compound in an aqueous environment changed when placed near an interface. PBG is known to affect hydrogen bonding in water, and as the size of the RMs changes, the water organization in the water pool is changed. The NOESY spectrum of PBG in AOT RM contains cross-peak signals between the PBG protons and AOT protons, which is consistent with the penetration of the PBG into the interface. At the same time, there is a cross peak between the biguanide moiety and the HOD signal. This shows that these NH protons are near the HOD protons, placing the biguanide functional group in the water pool. Preliminary differential FTIR spectroscopic studies confirmed this location. In summary, we found that PBG interacts with different regions of the interface, with the phenyl group penetrating the hydrophobic interface while the biguanide remains in the water pool.