Next-Generation Antimalarial Drugs: Hybrid Molecules as a New Strategy in Drug Design

Antimalarial and antioxidant activities of novel artesunate-ellagic acid hybrid compound in vitro and in vivo

Introduction: Emergence of drug resistant strains of Plasmodium species has necessitated the search for novel antimalarials with unique mechanisms of action. Synthesis of hybrid compounds has been one approach to tackling this challenge. In this study, the synthesis of artesunate-ellagic acid hybrid compound (EA31) from ellagic acid and artesunate and its evaluation for antimalarial and antioxidant activities using in vitro and in vivo models were carried out. Method: EA31 was synthesized from artesunate and ellagic acid. The activities of the hybrid compound against Plasmodium falciparum W2 and P. berghei NK65 were evaluated, and its antioxidant activities were also determined. Results: The results revealed that EA31 was more active against P. falciparum W2 (chloroquine resistant) clone and less cytotoxic to buffalo green monkey kidney cell line compared to artesunate. EA31 was also active against Plasmodium berghei NK65 in vivo. The results revealed inhibition of β-hematin formation as one of the mechanisms of action of EA31. EA31 also exhibited antioxidant activities. Conclusion: The results revealed that EA31 may exert dual action of killing malaria parasite and mopping the reactive oxygen species that mediate the secondary complications of malaria.

Probing the Antiplasmodial Properties of Plakortinic Acids C and D: An Uncommon Pair of Marine Peroxide-Polyketides Isolated from a Two-Sponge Association of Plakortis symbiotica and Xetospongia deweerdtae Collected near Puerto Rico

Plakortinic acids C (1) and D (2), an unseparable pair of endoperoxide polyketides isolated and purified from the symbiotic association of Caribbean Sea sponges Plakortis symbiotica-Xestospongia deweerdtae, underwent in vitro evaluation for antiplasmodial activity against the malaria parasite Plasmodium berghei using a drug luminescence assay. Initial screening at 10 µM revealed 50% in vitro parasite growth inhibition. The title compounds displayed antiplasmodial activity with an EC50 of 5.3 µM toward P. berghei parasites. The lytic activity against erythrocytes was assessed through an erythrocyte cell lysis assay, which showed non-lytic activity at lower concentrations ranging from 1.95 to 3.91 µM. The antiplasmodial activity and the absence of hemolytic activity support the potential of plakortinic acids C (1) and D (2) as promising lead compounds. Moreover, drug-likeness (ADMET) properties assessed through the pkCSM server predicted high intestinal absorption, hepatic metabolism, and volume of distribution, indicating favorable pharmacokinetic profiles for oral administration. These findings suggest the potential suitability of these metabolites for further investigations of antiplasmodial activity in multiple parasitic stages in the mosquito and Plasmodium falciparum. Notably, this study represents the first report of a marine natural product exhibiting the unique 7,8-dioxatricyclo[4.2.2.02,5]dec-9-ene motif being evaluated against malaria.

Recent Trends in the Synthesis and Bioactivity of Coumarin, Coumarin-Chalcone, and Coumarin-Triazole Molecular Hybrids

Molecular hybridization represents a new approach in drug discovery in which specific chromophores are strategically combined to create novel drugs with enhanced therapeutic effects. This innovative strategy leverages the strengths of individual chromophores to address complex biological challenges, synergize beneficial properties, optimize pharmacokinetics, and overcome limitations associated with single-agent therapies. Coumarins are documented to possess several bioactivities and have therefore been targeted for combination with other active moieties to create molecular hybrids. This review summarizes recent (2013-2023) trends in the synthesis of coumarins, as well as coumarin-chalcone and coumarin-triazole molecular hybrids. To cover the wide aspects of this area, we have included differently substituted coumarins, chalcones, 1,2,3- and 1,2,4-triazoles in this review and considered the point of fusion/attachment with coumarin to show the diversity of these hybrids. The reported syntheses mainly relied on well-established chemistry without the need for strict reaction conditions and usually produced high yields. Additionally, we discussed the bioactivities of the reported compounds, including antioxidative, antimicrobial, anticancer, antidiabetic, and anti-cholinesterase activities and commented on their IC50 where possible. Promising bioactivity results have been obtained so far. It is noted that mechanistic studies are infrequently found in the published work, which was also mentioned in this review to give the reader a better understanding. This review aims to provide valuable information to enable further developments in this field.

Novel quinolinepiperazinyl-aryltetrazoles targeting the blood stage of Plasmodium falciparum

The emergence of drug resistance against the frontline antimalarials is a major challenge in the treatment of malaria. In view of emerging reports on drug-resistant strains of Plasmodium against artemisinin combination therapy, a dire need is felt for the discovery of novel compounds acting against novel targets in the parasite. In this study, we identified a novel series of quinolinepiperazinyl-aryltetrazoles (QPTs) targeting the blood stage of Plasmodium. In vitro anti-plasmodial activity screening revealed that most of the compounds showed IC50 < 10 μM against chloroquine-resistant PfINDO strain, with the most promising lead compounds 66 and 75 showing IC50 values of 2.25 and 1.79 μM, respectively. Further, compounds 64-66, 68, 75-77 and 84 were found to be selective (selectivity index >50) in their action against Pf over a mammalian cell line, with compounds 66 and 75 offering the highest selectivity indexes of 178 and 223, respectively. Explorations into the action of lead compounds 66 and 75 revealed their selective cidal activity towards trophozoites and schizonts. In a ring-stage survival assay, 75 showed cidal activity against the early rings of artemisinin-resistant PfCam3.1R539T. Further, 66 and 75 in combination with artemisinin and pyrimethamine showed additive to weak synergistic interactions. Of these two in vitro lead molecules, only 66 restricted rise in the percentage of parasitemia to about 10% in P. berghei-infected mice with a median survival time of 28 days as compared to the untreated control, which showed the percentage of parasitemia >30%, and a median survival of 20 days. Promising antimalarial activity, high selectivity, and additive interaction with artemisinin and pyrimethamine indicate the potential of these compounds to be further optimized chemically as future drug candidates against malaria.

Curcumin hybrid molecules for the treatment of Alzheimer's disease: Structure and pharmacological activities

Alzheimer's disease (AD) is the most common neurodegenerative disease among the elderly. Contemporary treatments can only relieve symptoms but fail to delay disease progression. Curcumin is a naturally derived compound that has demonstrated significant therapeutic effects in AD treatment. Recently, molecular hybridization has been utilized to combine the pharmacophoric groups present in curcumin with those of other AD drugs, resulting in a series of novel compounds that enhance the therapeutic efficacy through multiple mechanisms. In this review, we firstly provide a concise summary of various pathogenetic hypotheses of AD and the mechanism of action of curcumin in AD, as well as the concept of molecular hybridization. Subsequently, we focus on the recent development of hybrid molecules derived from curcumin, summarizing their structures and pharmacological activities, including cholinesterase inhibitory activity, Aβ aggregation inhibitory activity, antioxidant activity, and other activities. The structure-activity relationships were further discussed.

Synthesis, Antimalarial, Antileishmanial, and Cytotoxicity Activities and Preliminary In Silico ADMET Studies of 2-(7-Chloroquinolin-4-ylamino)ethyl Benzoate Derivatives

A series of heterocyclic chloroquine hybrids, containing a chain of two carbon atoms at position four of the quinolinic chain and acting as a link between quinoline and several benzoyl groups, is synthesized and screened in vitro as an inhibitor of β-hematin formation and in vivo for its antimalarial activity against chloroquine-sensitive strains of Plasmodium berghei ANKA in this study. The compounds significantly reduced haeme crystallization, with IC50 values < 10 µM. The values were comparable to chloroquine's, with an IC50 of 1.50 ± 0.01 µM. The compounds 4c and 4e prolonged the average survival time of the infected mice to 16.7 ± 2.16 and 14.4 ± 1.20 days, respectively. We also studied the effect of the compounds 4b, 4c, and 4e on another important human parasite, Leishmania mexicana, which is responsible for cutaneous leishmaniasis, demonstrating a potential leishmanicidal effect against promasigotes, with an IC50 < 10 µM. Concerning the possible mechanism of action of these compounds on Lesihmania mexicana, we performed experiments demonstrating that these three compounds could induce the collapse of the parasite mitochondrial electrochemical membrane potential (Δφ). The in vitro cytotoxicity assays against mammalian cancerous and noncancerous human cell lines showed that the studied compounds exhibit low cytotoxic effects. The ADME/Tox analysis predicted moderate lipophilicity values, low unbound fraction values, and a poor distribution for these compounds. Therefore, moderate bioavailability was expected. We calculated other molecular descriptors, such as the topological polar surface area, according to Veber's rules, and except for 2 and 4i, the rest of the compounds violated this descriptor, demonstrating the low antimalarial activity of our compounds in vivo.

Antimalarial activity assay of artesunate-3-chloro-4(4-chlorophenoxy) aniline in vitro and in mice models

The global spread of multi-drug resistant P. falciparum, P. vivax, and P. malariae strains and absence of long-term effective vaccine makes chemotherapy the mainstay of malaria control strategies in endemic settings. The Mossman's assay and the Organization for Economic Co-operation and Development (OECD), 2001 guideline 423, were used to determine the cytotoxicity and acute oral toxicity of a novel hybrid drug, artesunate-3-Chloro-4(4-chlorophenoxy) aniline (ATSA), in vitro and in vivo, respectively. A modified Desjardins method was used to screen for antiplasmodial activity using P. falciparum (3D₇ and W₂) strains in vitro. The Peter's 4-day suppressive tests (4DTs) was used to evaluate the in vivo antimalaria activity using P. berghei ANKA strain, lumefantrine resistant (LuR), and piperaquine resistant (PQR) P. berghei lines. In silico prediction of absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles was assayed using PreADMET online prediction tool. The reference drug in all experiments was artesunate (ATS). Statistical significance between ATSA's activities in treated and control mice was evaluated by one-way analysis of variance (ANOVA). Results show that inhibitory concentrations-50 (IC₅₀) of ATSA is 11.47 ± 1.3 (3D₇) and 1.45 ± 0.26 (W₂) against 4.66 ± 0.93 (3D₇) and 0.60 ± 0.15 (W₂) ng/ml of ATS with a selective index of 2180.91(3D₇) and a therapeutic index (TI) of > 71). No mortalities were observed in acute oral toxicity assays and mean weight differences for test and controls were statistically insignificant (P > 0.05). The in vivo activity of ATSA was above 40% with effective dosage-50 (ED₅₀) of 4.211, 2.601, and 3.875 mg/kg body weight against P. berghei ANKA, LuR, and PQR lines, respectively. The difference between treated and control mice was statistically significant (P < 0.05). ATSA has high intestinal absorption (HIA) > 95% and has medium human ether-a-go-go related gene (hERG) K⁺ channel inhibition risks. Preclinical and clinical studies on ATSA are recommended to evaluate its value in developing novel drugs for future management of multi-drug resistant malaria parasites.

Squaramide Tethered Clindamycin, Chloroquine, and Mortiamide Hybrids: Design, Synthesis, and Antimalarial Activity

Malaria remains one of the major health problems in the world. In this work, a series of squaramide tethered chloroquine, clindamycin, and mortiamide D hybrids have been synthesized to assess their in vitro antiplasmodial activity against 3D7 (chloroquine-sensitive) and Dd2 strains of Plasmodium falciparum. The most active compound, a simple chloroquine analogue, displayed low nanomolar IC50 value against both strains (3 nM for 3D7 strain and 18 nM for Dd2 strain). Moreover, all molecular hybrids incorporating the hydroxychloroquine scaffold showed the most potent activities, exemplified with a chloroquine dimer, IC50 = 31 nM and 81 nM against 3D7 and Dd2 strains, respectively. These results highlight the first time use of clindamycin and mortiamide D as antimalarial molecular hybrids and establish these valuable hits for future optimization.

Hybrid Molecules as Potential Drugs for the Treatment of HIV: Design and Applications

Human immunodeficiency virus (HIV) infection is a major problem for humanity because HIV is constantly changing and developing resistance to current drugs. This necessitates the development of new anti-HIV drugs that take new approaches to combat an ever-evolving virus. One of the promising alternatives to combination antiretroviral therapy (cART) is the molecular hybrid strategy, in which two or more pharmacophore units of bioactive scaffolds are combined into a single molecular structure. These hybrid structures have the potential to have higher efficacy and lower toxicity than their parent molecules. Given the potential advantages of the hybrid molecular approach, the development and synthesis of these compounds are of great importance in anti-HIV drug discovery. This review focuses on the recent development of hybrid compounds targeting integrase (IN), reverse transcriptase (RT), and protease (PR) proteins and provides a brief description of their chemical structures, structure–activity relationship, and binding mode.

Upregulation of BAX and caspase-3, as well as downregulation of Bcl-2 during treatment with indeno[1,2-b]quinoxalin derivatives, mediated apoptosis in human cancer cells

Cancer is the world's foremost cause of death. There are over 100 different forms of cancer. Cancers are frequently named after the organs or tissues in which they develop. As a part of our aim to develop promising anticancer agents, a series of new indeno[1,2-b]quinoxaline derivatives were synthesized. All of the synthesized compounds were tested for anticancer activity in vitro in three human cancer cell lines: the HCT-116 colon cancer cell line, the HepG-2 liver cancer cell line, and the MCF-7 breast cancer cell line. Among the tested derivatives, 2, 3, 5, 12, 21, and 22 showed exceptional antiproliferative activities against the three tested cell lines compared to the reference standard imatinib. These compounds were, therefore, selected for further investigations. Evaluation of their cytotoxicity against a normal human cell line (WI-38) was performed, to ensure their safety and selectivity (IC₅₀  > 92 μM). Then, induction of apoptosis by the most active compounds was found to be accomplished by downregulation of Bcl-2 and upregulation of BAX and caspase-3. After that, the most promising apoptotic compound that increases the caspase-3 and BAX expression and downregulates Bcl-2 activity (3) was assessed for its impact on the cell cycle distribution in HepG-2 cells: The most potent derivative (3) induced cell cycle arrest at the G2/M phase. Finally, in silico evaluation of the ADME properties indicated that compound 3 is orally bioavailable and can be readily synthesized on a large scale.

Quinoline-dihydropyrimidin-2(1H)-one hybrids: Synthesis, biological activity and mechanistic studies

A novel class of quinoline-dihydropyrimidin-2(1H)-one (DHPM) hybrids was synthesized and in vitro antiplasmodial activity was evaluated against chloroquine sensitive (D10) and chloroquine resistant (Dd2) strains of Plasmodium falciparum, the human malaria parasite. The antiplasmodial activity was compared to previously reported DHPM based molecular hybrids. Dual mode of antiplasmodial action of the most active member has been evaluated through heme binding study and in silico docking in the active site of dihydrofolate enzymes (wild-type as well as mutant). Favourable pharmacokinetic parameters were predicted in the ADMET evaluation. The new hybrids were also tested against a number of DNA and RNA viruses. No antiviral activity was found, except for one hybrid  that showed mild inhibitory activity against two strains of cytomegalovirus (AD-169 and Davis), The most active hybrid  was found to be a selective inhibitor of the growth of P. falciparum as well as a modest inhibitor of varicella zoster virus in HEL cells. Cytotoxicity of all hybrids was assessed in HEL, HeLa, Vero, MDCK, and CRFK cell cultures.

Artemisinin inspired synthetic endoperoxide drug candidates: Design, synthesis, and mechanism of action studies

Artemisinin combination therapies (ACTs) have been used as the first-line treatments against Plasmodium falciparum malaria for decades. Recent advances in chemical proteomics have shed light on the complex mechanism of action of semi-synthetic artemisinin (ARTs), particularly their promiscuous alkylation of parasite proteins via previous heme-mediated bioactivation of the endoperoxide bond. Alarmingly, the rise of resistance to ART in South East Asia and the synthetic limitations of the ART scaffold have pushed the course for the necessity of fully synthetic endoperoxide-based antimalarials. Several classes of synthetic endoperoxide antimalarials have been described in literature utilizing various endoperoxide warheads including 1,2-dioxanes, 1,2,4-trioxanes, 1,2,4-trioxolanes, and 1,2,4,5-tetraoxanes. Two of these classes, the 1,2,4-trioxolanes (arterolane and artefenomel) and the 1,2,4,5-tetraoxanes (N205 and E209) based antimalarials, have been explored extensively and are still in active development. In contrast, the most recent publication pertaining to the development of the 1,2-dioxane, Arteflene, and 1,2,4-trioxanes fenozan-50F, DU1301, and PA1103/SAR116242 was published in 2008. This review summarizes the synthesis, biological and clinical evaluation, and mechanistic studies of the most developed synthetic endoperoxide antimalarials, providing an update on those classes still in active development.

Isatin Hybrids and Their Pharmacological Investigations

Hybridization is an important strategy to design molecules that can be effectively used to treat fatal diseases known to mankind. Molecular hybrids and their pharmacological investigations aided in discovering several potent isatin (Indole 2, 3 dione) derivatives with anti-HIV, antimalarial, antitubercular, antibacterial, and anticancer activities. Indole-2,3-dione and their derivatives have diverse pharmacological properties and have a prominent role in the discovery of new drugs. To understand the various approaches for designing new molecules based on isatin nucleus analysis of various pharmacophore hybrids, spacers/linkers between pharmacophores and isatin for hybridization and their biological activities are important. This review discusses the progress in developing isatin hybrids as biologically effective agents and their crucial aspects of design and structure-activity relationships.

Microwave-assisted synthesis of hybrid PABA-1,3,5-triazine derivatives as an antimalarial agent

The present manuscript deals with the development of novel p-aminobenzoic acid (PABA) associated 1,3,5-triazine derivatives as antimalarial agents. The molecules were developed via microwave-assisted synthesis and structures of compounds were ascertained via numerous analytical and spectroscopic techniques. The synthesized compounds were also subjected to ADMET analysis. In a docking analysis, the title compounds showed high and diverse binding affinities towards wild (-162.45 to -369.38 kcal/mol) and quadruple mutant (-165.36 to -209.47 kcal/mol) Pf-DHFR-TS via interacting with Phe58, Arg59, Ser111, Ile112, Phe116. The in vitro antimalarial activity suggested that compounds 4e, 4b, and 4h showed IC₅₀ ranging from 4.18 to 8.66 μg/ml against the chloroquine-sensitive (3D7) strain of Plasmodium falciparum. Moreover, compounds 4g, 4b, 4e, and 4c showed IC₅₀ ranging from 8.12 to 12.09 μg/ml against chloroquine-resistant (Dd2) strain. In conclusion, our study demonstrated the development of hybrid PABA substituted 1,3,5-triazines as a novel class of Pf-DHFR inhibitor for antimalarial drug discovery.

Synthesis and Evaluation of Chalcone-Quinoline Based Molecular Hybrids as Potential Anti-Malarial Agents

Molecular hybridization is a drug discovery strategy that involves the rational design of new chemical entities by the fusion (usually via a covalent linker) of two or more drugs, both active compounds and/or pharmacophoric units recognized and derived from known bioactive molecules. The expected outcome of this chemical modification is to produce a new hybrid compound with improved affinity and efficacy compared to the parent drugs. Additionally, this strategy can result in compounds presenting modified selectivity profiles, different and/or dual modes of action, reduced undesired side effects and ultimately lead to new therapies. In this study, molecular hybridization was used to generate new molecular hybrids which were tested against the chloroquine sensitive (NF54) strain of P. falciparum. To prepare the new molecular hybrids, the quinoline nucleus, one of the privileged scaffolds, was coupled with various chalcone derivatives via an appropriate linker to produce a total of twenty-two molecular hybrids in 11%–96% yield. The synthesized compounds displayed good antiplasmodial activity with IC₅₀ values ranging at 0.10–4.45 μM.

Design, synthesis, crystal structure and anti-plasmodial evaluation of tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidine derivatives

Effective chemotherapy is essential for controlling malaria. However, resistance of Plasmodium falciparum to existing antimalarial drugs has undermined attempts to control and eventually eradicate the disease. In this study, a series of 2-((substituted)(4-(5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4-yl)piperazin-1-yl)methyl)-6-substitutedphenol derivatives were prepared using Petasis reaction with a view to evaluate their activities against P. falciparum. The development of synthesized compounds (F1-F16) was justified through the study of H¹ NMR, C¹³ NMR, mass spectra. Compound F1 and F2 were also structurally validated by single crystal X-ray diffraction analysis. All the compounds were evaluated for their in vitro antiplasmodial assessment against the W2 strain (chloroquine-resistant) of P. falciparum IC₅₀ values ranging from 0.74-6.4 μM. Two compounds, F4 and F16 exhibited significant activity against W2 strain of P. falciparum with 0.75 and 0.74 μM. The compounds (F3-F6 and F16) were also evaluated for in vitro cytotoxicity against two cancer cell lines, human lung (A549) and cervical (HeLa) cells, which demonstrated non-cytotoxicity with significant selectivity indices. In addition, in silico ADME profiling and physiochemical properties predicts drug-like properties with a very low toxic effect. Thus, all these results indicate that tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidine scaffolds may serve as models for the development of antimalarial agents.

Synthesis of 2-(N-cyclicamino)quinoline combined with methyl (E)-3-(2/3/4-aminophenyl)acrylates as potential antiparasitic agents

A rationally designed series of 2-(N-cyclicamino)quinolines coupled with methyl (E)-3-(2/3/4-aminophenyl)acrylates was synthesized and subjected to in vitro screening bioassays for potential antiplasmodial and antitrypanosomal activities against a chloroquine-sensitive (3D7) strain of Plasmodium falciparum and nagana Trypanosoma brucei brucei 427, respectively. Substituent effects on activity were evaluated; meta-acrylate 24 and the ortho-acrylate 29 exhibited the highest antiplasmodial (IC₅₀  = 1.4 µM) and antitrypanosomal (IC₅₀  = 10.4 µM) activities, respectively. The activity against HeLa cells showed that the synthesized analogs are not cytotoxic at the maximum tested concentration. The ADME (absorption, distribution, metabolism, and excretion) drug-like properties of the synthesized compounds were predicted through the SwissADME software.

Ferroptosis: A Novel Mechanism of Artemisinin and its Derivatives in Cancer Therapy

BACKGROUND

Artemisinin is a sesquiterpene lactone compound with a special peroxide bridge that is tightly linked to the cytotoxicity involved in fighting malaria and cancer. Artemisinin and its derivatives (ARTs) are considered to be potential anticancer drugs that promote cancer cell apoptosis, induce cell cycle arrest and autophagy, inhibit cancer cell invasion and migration. Additionally, ARTs significantly increase intracellular Reactive Oxygen Species (ROS) in cancer cells, which result in ferroptosis, a new form of cell death, depending on the ferritin concentration. Ferroptosis is regarded as a cancer suppressor and as well as considered a new mechanism for cancer therapy.

METHODS

The anticancer activities of ARTs and reference molecules were compared by literature search and analysis. The latest research progress on ferroptosis was described, with a special focus on the molecular mechanism of artemisinin-induced ferroptosis.

RESULTS

Artemisinin derivatives, artemisinin-derived dimers, hybrids and artemisinin-transferrin conjugates, could significantly improve anticancer activity, and their IC50 values are lower than those of reference molecules such as doxorubicin and paclitaxel. The biological activities of linkers in dimers and hybrids are important in the drug design processes. ARTs induce ferroptosis mainly by triggering intracellular ROS production, promoting the lysosomal degradation of ferritin and regulating the System Xc-/Gpx4 axis. Interestingly, ARTs also stimulate the feedback inhibition pathway.

CONCLUSION

Artemisinin and its derivatives could be used in the future as cancer therapies with broader applications due to their induction of ferroptosis. Meanwhile, more attention should be paid to the development of novel artemisinin-related drugs based on the mechanism of artemisinininduced ferroptosis.

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.

Amide Tethered 4-Aminoquinoline-naphthalimide Hybrids: A New Class of Possible Dual Function Antiplasmodials

A series of amide tethered 4-aminoquinoline-naphthalimide hybrids has been synthesized to assess their in vitro antiplasmodial potential against chloroquine-susceptible (3D7) and chloroquine-resistant (W2) strains of Plasmodium falciparum. The most active and noncytotoxic compound had an IC₅₀ value of 0.07 μM against W2 strain and was more active than standard antimalarial drugs, including chloroquine, desethylamodiaquine, and quinine, particularly for drug resistant malaria. The promising scaffold, when subjected to heme binding and molecular modeling studies, was identified as a possible potent inhibitor of hemozoin formation and P. falciparum chloroquine resistance transporter (PfCRT), respectively, and, therefore, could act as a dual function antiplasmodial.

Indole: The After Next Scaffold of Antiplasmodial Agents?

Malaria remains a global public health problem due to the uphill fight against the causative Plasmodium parasites that are relentless in developing resistance. Indole-based antiplasmodial compounds are endowed with multiple modes of action, of which inhibition of hemozoin formation is the major mechanism of action reported for compounds such as cryptolepine, flinderoles, and isosungucine. Indole-based compounds exert their potent activity against chloroquine-resistant Plasmodium strains by inhibiting hemozoin formation in a mode of action different from that of chloroquine or through a novel mechanism of action. For example, dysregulating the sodium and osmotic homeostasis of Plasmodium through inhibition of PfATP4 is the novel mechanism of cipargamin. The potential of developing multi-targeted compounds through molecular hybridization ensures the existence of indole-based compounds in the antimalarial pipeline.

Artemisinins as Anticancer Drugs: Novel Therapeutic Approaches, Molecular Mechanisms, and Clinical Trials

Artemisinin and its derivatives have shown broad-spectrum antitumor activities in vitro and in vivo. Furthermore, outcomes from a limited number of clinical trials provide encouraging evidence for their excellent antitumor activities. However, some problems such as poor solubility, toxicity and controversial mechanisms of action hamper their use as effective antitumor agents in the clinic. In order to accelerate the use of ARTs in the clinic, researchers have recently developed novel therapeutic approaches including developing novel derivatives, manufacturing novel nano-formulations, and combining ARTs with other drugs for cancer therapy. The related mechanisms of action were explored. This review describes ARTs used to induce non-apoptotic cell death containing oncosis, autophagy, and ferroptosis. Moreover, it highlights the ARTs-caused effects on cancer metabolism, immunosuppression and cancer stem cells and discusses clinical trials of ARTs used to treat cancer. The review provides additional insight into the molecular mechanism of action of ARTs and their considerable clinical potential.

Synthesis of Tamoxifen-Artemisinin and Estrogen-Artemisinin Hybrids Highly Potent Against Breast and Prostate Cancer

In the search for new and effective treatments of breast and prostate cancer, a series of hybrid compounds based on tamoxifen, estrogens, and artemisinin were successfully synthesized and analyzed for their in vitro activities against human prostate (PC-3) and breast cancer (MCF-7) cell lines. Most of the hybrid compounds exhibit a strong anticancer activity against both cancer cell lines - for example, EC50 (PC-3) down to 1.07 μM, and EC50 (MCF-7) down to 2.08 μM - thus showing higher activities than their parent compounds 4-hydroxytamoxifen (afimoxifene, 7; EC50 =75.1 (PC-3) and 19.3 μM (MCF-7)), dihydroartemisinin (2; EC50 =263.6 (PC-3) and 49.3 μM (MCF-7)), and artesunic acid (3; EC50 =195.1 (PC-3) and 32.0 μM (MCF-7)). The most potent compounds were the estrogen-artemisinin hybrids 27 and 28 (EC50 =1.18 and 1.07 μM, respectively) against prostate cancer, and hybrid 23 (EC50 =2.08 μM) against breast cancer. These findings demonstrate the high potential of hybridization of artemisinin and estrogens to further improve their anticancer activities and to produce synergistic effects between linked pharmacophores.

Hybrid Compounds & Oxidative Stress Induced Apoptosis in Cancer Therapy

Elevated Reactive Oxygen Species (ROS) generated by the conventional cancer therapies and the endogenous production of ROS have been observed in various types of cancers. In contrast to the harmful effects of oxidative stress in different pathologies other than cancer, ROS can speed anti-tumorigenic signaling and cause apoptosis of tumor cells via oxidative stress as demonstrated in several studies. The primary actions of antioxidants in cells are to provide a redox balance between reduction-oxidation reactions. Antioxidants in tumor cells can scavenge excess ROS, causing resistance to ROS induced apoptosis. Various chemotherapeutic drugs, in their clinical use, have evoked drug resistance and serious side effects. Consequently, drugs having single-targets are not able to provide an effective cancer therapy. Recently, developed hybrid anticancer drugs promise great therapeutic advantages due to their capacity to overcome the limitations encountered with conventional chemotherapeutic agents. Hybrid compounds have advantages in comparison to the single cancer drugs which have usually low solubility, adverse side effects, and drug resistance. This review addresses two important treatments strategies in cancer therapy: oxidative stress induced apoptosis and hybrid anticancer drugs.

Synthesis of Novel Ciprofloxacin-Based Hybrid Molecules toward Potent Antimalarial Activity

Antimalarial drug resistance is a serious obstacle in the persistent quest to eradicate malaria. There is a need for potent chemical agents that are able to act on drug-resistant Plasmodium falciparum populations at reasonable concentrations without any related toxicity to the host. By rational drug design, we envisaged to address this issue by generating a novel hybrid drug possessing two pharmacophores that can act on two unique and independent targets within the cell. We synthesized a new class of ciprofloxacin-based hybrid molecules, which have been integrated with acridine, quinolone, sulphonamide, and cinnamoyl pharmacophores (1-4). We realized a potent chloroquinolone-ciprofloxacin-based antimalarial hybrid (2, CQ-CFX) whose mechanism of action is unlike that of its parent molecules indicating a unique biological target. CQ-CFX is not only potent against CQ-resistant and susceptible strains of Plasmodium falciparum at low nanomolar concentrations (IC₅₀ values are 63.17 ± 1.2 nM and 25.52 ± 4.45 nM, respectively) but is also not toxic to mammalian and bacterial systems up to 20 μM and 1 μM, respectively.

In silico modeling of tetraoxane-8-aminoquinoline hybrids active against Plasmodium falciparum

Background

Quantitative structure-activity relationships (QSAR) is a technique that is used to produce a model that connects biological activities of compounds to their chemical structures, and molecular docking is a technique that reveals the binding mode and interactions between a drug and its target enzyme. These techniques have been successfully applied in the design and development of many drug candidates and herein were employed to build a model that could help in the development of more potent antimalaria drugs.

Results

Descriptors of the compounds were calculated using the PaDEL-Descriptor software, and Genetic Function Algorithm (GFA) was used to select descriptors and build the model. A robust and reliable model was generated and validated to have internal and external squared correlation coefficient (R2) of 0.9622 and 0.8191, respectively, adjusted squared correlation coefficient (Radj) of 0.9471, and leave-one-out (LOO) cross-validation coefficient (Q2cv) of 0.9223. The model revealed that the antiplasmodial activities of 1,2,4,5-tetraoxane-8-aminoquinoline hybrids depend on MATS3m, GATS8p, GATS8i, and RDF50s descriptors. MATS3m, GATS8i, and RDF50s influenced the antiplasmodial activities of the compounds positively while GATS8p negatively with the greatest influence. The docking result shows strong interactions between 1,2,4,5-tetraoxane-8-aminoquinoline hybrids and Plasmodium falciparum lactate dehydrogenase (pfLDH) with binding affinities ranging from − 6.3 to − 10.9 kcal/mol which were better than that of chloroquine (− 6.1 kcal/mol), suggesting that these compounds could be better inhibitors of pfLDH than chloroquine.

Conclusion

The results of this study could serve as a model for designing new potent 1,2,4,5-tetraoxane-8-aminoquinolines with better antiplasmodial activities for the development of highly active antimalaria drugs.

An epigrammatic status of the 'azole'-based antimalarial drugs

The development of multidrug resistance in the malarial parasite has sabotaged majority of the eradication efforts by restraining the inhibition profile of first line as well as second line antimalarial drugs, thus necessitating the development of novel pharmaceutics constructed on appropriate scaffolds with superior potency against the drug-resistant and drug-susceptible Plasmodium parasite. Over the past decades, the infectious malarial parasite has developed resistance against most of the contemporary therapeutics, thus necessitating the rational development of novel approaches principally focused on MDR malaria. This review presents an epigrammatic collation of the epidemiology and the contemporary antimalarial therapeutics based on the 'azole' motif.

Synthesis and Antileishmanial Activity of 1,2,4,5-Tetraoxanes against Leishmania donovani

A chemically diverse range of novel tetraoxanes was synthesized and evaluated in vitro against intramacrophage amastigote forms of Leishmania donovani. All 15 tested tetraoxanes displayed activity, with IC₅₀ values ranging from 2 to 45 µm. The most active tetraoxane, compound LC140, exhibited an IC₅₀ value of 2.52 ± 0.65 µm on L. donovani intramacrophage amastigotes, with a selectivity index of 13.5. This compound reduced the liver parasite burden of L. donovani-infected mice by 37% after an intraperitoneal treatment at 10 mg/kg/day for five consecutive days, whereas miltefosine, an antileishmanial drug in use, reduced it by 66%. These results provide a relevant basis for the development of further tetraoxanes as effective, safe, and cheap drugs against leishmaniasis.

Feitosa L, O. Gandi M, F. Silveira F, Boechat N. The Development of Novel Compounds Against Malaria: Quinolines, Triazolpyridines, Pyrazolopyridines and Pyrazolopyrimidines

Based on medicinal chemistry tools, new compounds for malaria treatment were designed. The scaffolds of the drugs used to treat malaria, such as chloroquine, primaquine, amodiaquine, mefloquine and sulfadoxine, were used as inspiration. We demonstrated the importance of quinoline and non-quinoline derivatives in vitro with activity against the W2 chloroquine-resistant (CQR) Plasmodium falciparum clone strain and in vivo against Plasmodium berghei-infected mouse model. Among the quinoline derivatives, new hybrids between chloroquine and sulfadoxine were designed, which gave rise to an important prototype that was more active than both chloroquine and sulfadoxine. Hybrids between chloroquine-atorvastatin and primaquine-atorvastatin were also synthesized and shown to be more potent than the parent drugs alone. Additionally, among the quinoline derivatives, new mefloquine derivatives were synthesized. Among the non-quinoline derivatives, we obtained excellent results with the triazolopyrimidine nucleus, which gave us prototype I that inspired the synthesis of new heterocycles. The pyrazolopyrimidine derivatives stood out as non-quinoline derivatives that are potent inhibitors of the P. falciparum dihydroorotate dehydrogenase (PfDHODH) enzyme. We also examined the pyrazolopyridine and pyrazolopyrimidine nuclei.

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.

Diene-Transmissive Diels-Alder Sequences with Benzynes

Diene-transmissive Diels-Alder (DTDA) sequences are extraordinarily powerful processes for the generation of fused bicyclic systems. Nonetheless, only stable dienophiles have previously been deployed. Herein we report DTDA sequences with a variety of substituted [3]dendralenes in the first study to deploy arynes as dienophiles. We demonstrate the one-flask generation of complex, aromatic-ring-containing, multicyclic systems of relevance to medicinal chemistry. These synthetic operations provide numerous successful examples of the otherwise challenging and rarely reported intermolecular Diels-Alder reaction of acyclic 1,3-butadienes with arynes, which is made possible due to the exalted reactivity of dendralenic dienes.

Molecular docking and QSAR studies for modeling the antimalarial activity of hybrids 4-anilinoquinoline-triazines derivatives with the wild-type and mutant receptor pf-DHFR

Plasmodium falciparum dihydrofolate reductase (pf-DHFR) is one of the several targets in the treatment of malaria. Double and quadruple mutations at residues 51, 59, 108, and 164 of pf-DHFR have been linked to antifolate resistance. Several efforts are underway to overcome this drug resistance and to produce potential inhibitors. In this regard, the quantitative structure-activity relationship (QSAR) and docking studies were performed for previously reported 4-anilinoquinoline and 1,3,5-triazines based molecular hybrids. The generated model showed good correlation coefficients (R2 = 0.70) and test set prediction coefficient (R2 = 0.74). These outcomes showed the good predictive competence of the established QSAR model. Based on these results we docked into active site of pf-DHFR protein with the most active (4) and the less active (5) compounds. The docking results revealed that these molecules interact specifically with SER108 and ILE164 in the pf-DHFR binding pocket as that of best active compound but also showed additional interactions with LEU40 and GLY44.

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.

SAHAquines, Novel Hybrids Based on SAHA and Primaquine Motifs, as Potential Cytostatic and Antiplasmodial Agents

We report the synthesis of SAHAquines and related primaquine (PQ) derivatives. SAHAquines are novel hybrid compounds that combine moieties of suberoylanilide hydroxamic acid (SAHA), an anticancer agent with weak antiplasmodial activity, and PQ, an antimalarial drug with low antiproliferative activity. The preparation of SAHAquines is simple, cheap, and high yielding. It includes the following steps: coupling reaction between primaquine and a dicarboxylic acid monoester, hydrolysis, a new coupling reaction with O-protected hydroxylamine, and deprotection. SAHAquines 5 a-d showed significant reduction in cell viability. Among the three human cancer cell lines (U2OS, HepG2, and MCF-7), the most responsive were the MCF-7 cells. The antibodies against acetylated histone H3K9/H3K14 in MCF-7 cells revealed a significant enhancement following treatment with N-hydroxy-N'-{4-[(6-methoxyquinolin-8-yl)amino]pentyl}pentanediamide (5 b). Ethyl (2E)-3-({4-[(6-methoxyquinolin-8-yl)amino]pentyl}carbamoyl)prop-2-enoate (2 b) and SAHAquines were the most active compounds against both the hepatic and erythrocytic stages of Plasmodium parasites, some of them at sub-micromolar concentrations. The results of our research suggest that SAHAquines are promising leads for new anticancer and antimalarial agents.

Synthesis, docking and anticancer activity of azo-linked hybrids of 1,3,4-thia-/oxadiazoles with cyclic imides

A series of novel analogues based on a diazole-imide pharmacophore were synthesized by diazotizing substituted 1,3,4-thia-/oxadiazol-2-amines and subsequently coupling the resulting diazonium salts with N-substituted cyclic imides. The resulting compounds C1 to C28 were characterized by various spectral methods, viz. IR, NMR and mass spectroscopy. All the synthesized compounds were tested against two human cancer cell lines: human breast adenocarcinoma cell line MCF-7 and colorectal adenocarcinoma cell line HT-29. Among the synthesized compounds, C14 (2-(4-chloro-3-((5-(4-nitrophenyl)-1,3,4-thiadiazol-2-yl)diazenyl)phenyl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione) emerged as a potential candidate against both MCF-7 and HT-29 with [Formula: see text] values of 0.09 ± 0.02 [Formula: see text]M and 0.11 ± 0.03 [Formula: see text]M, respectively. Similarly, compound C16 displayed highest anticancer activity against MCF-7 cell line with [Formula: see text] = 0.07 ± 0.02 [Formula: see text]M. Target fishing (inverse docking) using ChemMapper server identified EGFR tyrosine and CDK2 kinases as high priority targets for this pharmacophore. Computational docking (AutoDock 4.2) was used to analyse the interactions between the target proteins and active compounds.

Molecular Modeling of Antimalarial Agents by 3D-QSAR Study and Molecular Docking of Two Hybrids 4-Aminoquinoline-1,3,5-triazine and 4-Aminoquinoline-oxalamide Derivatives with the Receptor Protein in Its Both Wild and Mutant Types

Modeling studies using 3D-QSAR and molecular docking methods were performed on a set of 34 hybrids of 4-aminoquinoline derivatives previously studied as effective antimalarial agents of wild type and quadruple mutant Plasmodium falciparum dihydrofolate reductase (DHFR). So, the famous mathematical method multiple linear regression (MLR) was explored to build the QSAR model. The DFT-B3LYP method with the basis set 6-31G was used to calculate the quantum chemical descriptors, chosen to represent the electronic descriptors of molecular structures. On the contrary, the MM2 method was used to calculate lipophilic, geometrical, physicochemical, and steric descriptors. The QSAR model tested with artificial neural network (ANN) method shows high performance towards its predictability. The predicted model was confirmed by three validation methods: leave-one-out (LOO) cross validation, Y-randomization, and validation external. The molecular docking study of three compounds 9, 11, and 26 on both wild and quadruple mutant types of pf-DHFR-TS as the protein target helps to understand more and then predict the binding modes with the binding sites.

Synthesis of Thymoquinone-Artemisinin Hybrids: New Potent Antileukemia, Antiviral, and Antimalarial Agents

A series of hybrid compounds based on the natural products artemisinin and thymoquinone was synthesized and investigated for their biological activity against the malaria parasite Plasmodium falciparum 3D7 strain, human cytomegalovirus (HCMV), and two leukemia cell lines (drug-sensitive CCRF-CEM and multidrug-resistant subline CEM/ADR5000). An unprecedented one-pot method of selective formation of C-10α-acetate 14 starting from a 1:1 mixture of C-10α- to C-10β-dihydroartemisinin was developed. The key step of this facile method is a mild decarboxylative activation of malonic acid mediated by DCC/DMAP. Ether-linked thymoquinone-artemisinin hybrids 6a/b stood out as the most active compounds in all categories, while showing no toxic side effects toward healthy human foreskin fibroblasts and thus being selective. They exhibited EC₅₀ values of 0.2 μM against the doxorubicin-sensitive as well as the multidrug-resistant leukemia cells and therefore can be regarded as superior to doxorubicin. Moreover, they showed to be five times more active than the standard drug ganciclovir and nearly eight times more active than artesunic acid against HCMV. In addition, hybrids 6a/b possessed excellent antimalarial activity (EC₅₀ = 5.9/3.7 nM), which was better than that of artesunic acid (EC₅₀ = 8.2 nM) and chloroquine (EC₅₀ = 9.8 nM). Overall, most of the presented thymoquinone-artemisinin-based hybrids exhibit an excellent and broad variety of biological activities (anticancer, antimalarial, and antiviral) combined with a low toxicity/high selectivity profile.

Molecular Consortia-Various Structural and Synthetic Concepts for More Effective Therapeutics Synthesis

The design and discovery of novel drug candidates are the initial and most probably the crucial steps in the drug development process. One of the tasks of medicinal chemistry is to produce new molecules that have a desired biological effect. However, even today the search for new pharmaceuticals is a very complicated process that is hard to rationalize. Literature provides many scientific reports on future prospects of design of potentially useful drugs. Many trends have been proposed for the design of new drugs containing different structures (dimers, heterodimers, heteromers, adducts, associates, complexes, biooligomers, dendrimers, dual-, bivalent-, multifunction drugs and codrugs, identical or non-identical twin drugs, mixed or combo drugs, supramolecular particles and various nanoindividuals. Recently much attention has been paid to different strategies of molecular hybridization. In this paper, various molecular combinations were described e.g., drug–drug or drug-non-drug combinations which are expressed in a schematic multi-factor form called a molecular matrix, consisting of four factors: association mode, connection method, and the number of elements and linkers. One of the most popular trends is to create small–small molecule combinations such as different hybrids, codrugs, drug–drug conjugates (DDCs) and small-large molecule combinations such as antibody-drug conjugates (ADCs), polymer-drug conjugates (PDCs) or different prodrugs and macromolecular therapeutics. A review of the structural possibilities of active framework combinations indicates that a wide range of potentially effective novel-type compounds can be formed. What is particularly important is that new therapeutics can be obtained in fast, efficient, and selective methods using current trends in chemical synthesis and the design of drugs such as the “Lego” concept or rational green approach.

Quinoline-Based Hybrid Compounds with Antimalarial Activity

The application of quinoline-based compounds for the treatment of malaria infections is hampered by drug resistance. Drug resistance has led to the combination of quinolines with other classes of antimalarials resulting in enhanced therapeutic outcomes. However, the combination of antimalarials is limited by drug-drug interactions. In order to overcome the aforementioned factors, several researchers have reported hybrid compounds prepared by reacting quinoline-based compounds with other compounds via selected functionalities. This review will focus on the currently reported quinoline-based hybrid compounds and their preclinical studies.

Ni(II) Complexes with Schiff Base Ligands: Preparation, Characterization, DNA/Protein Interaction and Cytotoxicity Studies

In this study, two Ni(II) complexes, namely [Ni(HL1)₂(OAc)₂] (1) and [Ni(L2)₂] (2) (where HL1 and HL2 are (E)-1-((1-(2-hydroxyethyl)-1H-pyrazol-5-ylimino)methyl)-naphthalen-2-ol) and (E)-ethyl-5-((2-hydroxynaphthalen-1-yl)methyleneamino)-1-methyl-1H-pyrazole-4-carboxylate, respectively), were synthesized and characterized by X-ray crystallography, Electrospray Ionization Mass Spectrometry (ESI-MS), elemental analysis, and IR. Their uptake in biological macromolecules and cancer cells were preliminarily investigated through electronic absorption (UV-Vis), circular dichroism (CD) and fluorescence quenching measurements. Bovine serum albumin (BSA) interaction experiments were investigated by spectroscopy which showed that the complexes and ligands could quench the intrinsic fluorescence of BSA through an obvious static quenching process. The spectroscopic studies indicated that these complexes could bind to DNA via groove, non-covalent, and electrostatic interactions. Furthermore, in vitro methyl thiazolyl tetrazolium (MTT) assays and Annexin V/PI flow cytometry experiments were performed to assess the antitumor capacity of the complexes against eight cell lines. The results show that both of the complexes possess reasonable cytotoxicities.