Design, synthesis, and biological evaluation of novel 7-deazapurine nucleoside derivatives as potential anti-dengue virus agents

Development in the Inhibition of Dengue Proteases as Drug Targets

BACKGROUND

Viral infections continue to increase morbidity and mortality severely. The flavivirus genus has fifty different species, including the dengue, Zika, and West Nile viruses that can infect 40% of individuals globally, who reside in at least a hundred different countries. Dengue, one of the oldest and most dangerous human infections, was initially documented by the Chinese Medical Encyclopedia in the Jin period. It was referred to as "water poison," connected to flying insects, i.e., Aedes aegypti and Aedes albopictus. DENV causes some medical expressions like dengue hemorrhagic fever, acute febrile illness, and dengue shock syndrome.

OBJECTIVE

According to the World Health Organization report of 2012, 2500 million people are in danger of contracting dengue fever worldwide. According to a recent study, 96 million of the 390 million dengue infections yearly show some clinical or subclinical severity. There is no antiviral drug or vaccine to treat this severe infection. It can be controlled by getting enough rest, drinking plenty of water, and using painkillers. The first dengue vaccine created by Sanofi, called Dengvaxia, was previously approved by the USFDA in 2019. All four serotypes of the DENV1-4 have shown re-infection in vaccine recipients. However, the usage of Dengvaxia has been constrained by its adverse effects.

CONCLUSION

Different classes of compounds have been reported against DENV, such as nitrogen-containing heterocycles (i.e., imidazole, pyridine, triazoles quinazolines, quinoline, and indole), oxygen-containing heterocycles (i.e., coumarins), and some are mixed heterocyclic compounds of S, N (thiazole, benzothiazine, and thiazolidinediones), and N, O (i.e., oxadiazole). There have been reports of computationally designed compounds to impede the molecular functions of specific structural and non-structural proteins as potential therapeutic targets. This review summarized the current progress in developing dengue protease inhibitors.

Dapoxetine, a Selective Serotonin Reuptake Inhibitor, Suppresses Zika Virus Infection In Vitro

Zika virus (ZIKV) belongs to the Flavivirus genus of the Flaviviridae family, and is a pathogen posing a significant threat to human health. Currently, there is a lack of internationally approved antiviral drugs for the treatment of ZIKV infection, and symptomatic management remains the primary clinical approach. Consequently, the exploration of safe and effective anti-ZIKV drugs has emerged as a paramount imperative in ZIKV control efforts. In this study, we performed a screening of a compound library consisting of 1789 FDA-approved drugs to identify potential agents with anti-ZIKV activity. We have identified dapoxetine, an orally administered selective serotonin reuptake inhibitor (SSRI) commonly employed for the clinical management of premature ejaculation (PE), as a potential inhibitor of ZIKV RNA-dependent RNA polymerase (RdRp). Consequently, we conducted surface plasmon resonance (SPR) analysis to validate the specific binding of dapoxetine to ZIKV RdRp, and further evaluated its inhibitory effect on ZIKV RdRp synthesis using the ZIKV Gluc reporter gene assay. Furthermore, we substantiated the efficacy of dapoxetine in suppressing intracellular replication of ZIKV, thereby demonstrating a concentration-dependent antiviral effect (EC50 values ranging from 4.20 μM to 12.6 μM) and negligible cytotoxicity (CC50 > 50 μM) across diverse cell lines. Moreover, cell fluorescence staining and Western blotting assays revealed that dapoxetine effectively reduced the expression of ZIKV proteins. Collectively, our findings suggest that dapoxetine exhibits anti-ZIKV effects by inhibiting ZIKV RdRp activity, positioning it as a potential candidate for clinical therapeutic intervention against ZIKV infection.

Design, synthesis, and biological evaluation of a series of new anthraquinone derivatives as anti-ZIKV agents

The major severe complications linked to Zika virus (ZIKV) cause the global public health problems, including microcephaly and other congenital abnormalities in newborns, and Guillain-Barré syndrome, meningoencephalitis, multi-organ failure in adults. However, neither approved vaccines nor drugs are available for ZIKV. In this study, we describe the design, synthesis and the anti-ZIKV activities of a series of anthraquinone analogs. Most of the newly synthesized compounds demonstrated moderate to excellent potency against ZIKV. Among all, compound 22, showed the most potent anti-ZIKV activity (EC₅₀ value from 1.33 μM to 5.72 μM) with low cytotoxicity (CC₅₀＞50 μM) in multiple cellular model. Importantly, 22 significantly improved the survival of ZIKV-infected mice (Ifnar1^-/-), alleviated ZIKV-associated pathological damages and suppressed the excessive inflammatory response and pyroptosis induced by ZIKV in vivo and in vitro. Furthermore, the molecular docking simulation analysis and the surface plasmon resonance results demonstrated the direct binding between 22 and ZIKV RdRp, and the mechanistic study revealed that 22 suppressed viral RNA synthesis by ZIKV NS5 in cells. Taken together, this study highlights that 22 may be a novel anti-ZIKV drug candidate and provides treatment options for ZIKV-associated diseases.

Identification of Montelukast as flavivirus NS2B-NS3 protease inhibitor by inverse virtual screening and experimental validation

Flavivirus, such as Dengue Virus (DENV) and Zika virus (ZIKV), infects millions of people and cause the death of thousands of people every year. Despite many efforts, there is no approved anti-flaviviral treatment available. In particular, some antiflavivirus compounds were investigated the cellular activities of DENV and ZIKV, but lacking the exploration of specific target enzyme, thereby resulting in the hindrance of structure-based drug design. One example is Montlukast, which was found to inhibit the replicon replication in DENV and ZIKV infected cells, with EC₅₀ values as 1.03 μM (DENV) and 1.14 μM (ZIKV), while the underlying mechanism remains unclear. In our study, the inhibitory mechanisms of Montelukast against the replicon replication of DENV and ZIKV infected cells were studied by using in silico approaches including inverse virtual screening (IVS), molecular dynamics (MD) simulations and binding free energy calculation, and validated through in vitro protease assay, confirming Montelukast could bind to NS2B-NS3 proteases of DENV and ZIKV as a competitive inhibitor (IC₅₀ for DENV: 25.65 μM, for ZIKV: 15.57 μM). Moreover, Montelukast has no potential off-target effect on NS2B-NS3 protease from thrombin and trypsin inhibitory assay. Overall, Montelukast may be used as a potential candidate to block NS2B-NS3 protease as well as lead for structural modification.

The Fellowship of Privileged Scaffolds-One Structure to Inhibit Them All

Over the past few years, the application of privileged structure has emerged as a powerful approach to the discovery of new biologically active molecules. Privileged structures are molecular scaffolds with binding properties to the range of different biological targets. Moreover, privileged structures typically exhibit good drug-like properties, thus assuring more drug-like properties of modified compound. Our main objective is to discuss the privileged structures used for the development of antiviral agents.

6-Methyl-7-deazapurine nucleoside analogues as broad-spectrum antikinetoplastid agents

Kinetoplastid parasites are the causative agents of Chagas disease (CD), leishmaniasis and human African trypanosomiasis (HAT). Despite a sustained decrease in the number of HAT cases, more efforts are needed to discover safe and effective therapies against CD and leishmaniasis. Kinetoplastid parasites lack the capability to biosynthesize purines de novo and thus critically depend on uptake and processing of purines from host cells. As such, modified purine nucleoside analogues may act as broad-spectrum antikinetoplastid agents. This study assessed the in vitro activity profile of 7-modified 6-methyl tubercidin derivatives against Trypanosoma cruzi, Leishmania infantum, Trypanosoma brucei brucei and T. b. rhodesiense, and led to the identification of analogues that display activity against all these species, such as 7-ethyl (13) and 7-chloro (7) analogues. These selected analogues also proved sufficiently stable in liver microsomes to warrant in vivo follow-up evaluation.

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New safe and effective therapies are needed for Chagas disease and leishmaniasis.

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The causative agents rely on the acquisition of purine nucleobases and nucleosides from host cells to grow and multiply.

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New 7-substituted 6-methyl-7-deazapurine ribonucleosides were synthesized.

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A 7-ethyl and 7-chloro analogue display low to submicromolar activity against T. brucei, T. cruzi and L. infantum.

6-Methyl-7-Aryl-7-Deazapurine Nucleosides as Anti-Trypanosoma cruzi Agents: Structure-Activity Relationship and in vivo Efficacy

Chagas disease is a tropical infectious disease resulting in progressive organ-damage and currently lacks efficient treatment and vaccine options. The causative pathogen, Trypanosoma cruzi, requires uptake and processing of preformed purines from the host because it cannot synthesize these de novo, instigating the evaluation of modified purine nucleosides as potential trypanocides. By modifying the pyrimidine part of a previously identified 7-aryl-7-deazapurine nucleoside, we found that substitution of a 6-methyl for a 6-amino group allows retaining T. cruzi amastigote growth inhibitory activity but confers improved selectivity towards mammalian cells. By keeping the 6-methyl group unaltered, and introducing different 7-aryl groups, we identified several analogues with sub-micromolar antitrypanosomal activity. The 7-(4-chlorophenyl) analogue 14, which was stable in microsomes, was evaluated in an acute mouse model. Oral administration of 25 mg/kg b.i.d. suppressed peak parasitemia and protected mice from infection-related mortality, gave similar reductions as the reference drug of blood parasite loads determined by qPCR, but as benznidazole failed to induce sterile cure in the short time period of drug exposure (5 days).

Antiviral Activity of 7-Substituted 7-Deazapurine Ribonucleosides, Monophosphate Prodrugs, and Triphoshates against Emerging RNA Viruses

A series of 7-deazaadenine ribonucleosides bearing alkyl, alkenyl, alkynyl, aryl, or hetaryl groups at position 7 as well as their 5'-O-triphosphates and two types of monophosphate prodrugs (phosphoramidates and S-acylthioethanol esters) were prepared and tested for antiviral activity against selected RNA viruses (Dengue, Zika, tick-borne encephalitis, West Nile, and SARS-CoV-2). The modified triphosphates inhibited the viral RNA-dependent RNA polymerases at micromolar concentrations through the incorporation of the modified nucleotide and stopping a further extension of the RNA chain. 7-Deazaadenosine nucleosides bearing ethynyl or small hetaryl groups at position 7 showed (sub)micromolar antiviral activities but significant cytotoxicity, whereas the nucleosides bearing bulkier heterocycles were still active but less toxic. Unexpectedly, the monophosphate prodrugs were similarly or less active than the corresponding nucleosides in the in vitro antiviral assays, although the bis(S-acylthioethanol) prodrug 14h was transported to the Huh7 cells and efficiently released the nucleoside monophosphate.

Synthesis and Biological Profiling of Pyrazolo-Fused 7-Deazapurine Nucleosides

A series of 8-substituted 1-methyl-1,4-dihydropyrazolo[3',4':4,5]pyrrolo[2,3-d]pyrimidine (methylpyrazolo-fused 7-deazapurine) ribonucleosides have been designed and synthesized. Two synthetic approaches to the key heterocyclic aglycon 7, (i) a six-step classical heterocyclization starting from 5-chloro-1-methyl-4-nitropyrazole and (ii) a three-step cross-coupling and cyclization approach starting from the zincated 4,6-dichloropyrimidine, gave comparable total yields of 18% vs 13%. The glycosylation of 7 was attempted by three different methods but only the Vorbrüggen silyl-base protocol was efficient and stereoselective to give desired β-anomeric nucleoside intermediate 17A. Its nucleophilic substitutions or cross-coupling reactions at position 8 and deprotection of the sugar moiety gave eight derivatives of pyrazolo-fused deazapurine ribonucleosides, some of which were weakly fluorescent. Methyl, amino, and methylsulfanyl derivatives exerted submicromolar cytotoxic effects in vitro against a panel of cancer and leukemia cell lines as well as antiviral effects against hepatitis C virus in the replicon assay.

Synthesis, Photophysical Properties, and Biological Profiling of Benzothieno-Fused 7-Deazapurine Ribonucleosides

Two isomeric series of benzothieno-fused 7-deazapurine (benzo[4',5']thieno[3',2':4,5]- and benzo[4',5']thieno[2',3':4,5]pyrrolo[2,3-d]pyrimidine) ribonucleosides were designed and synthesized. Key steps of the synthesis included the Negishi coupling of zincated dichloropyrimidine with 2- or 3-iodobenzothiophene followed by azidation, thermal or photochemical cyclization, glycosylation, and final functionalization at position 6 through cross-couplings or nucleophilic substitutions. Deprotection gave the final nucleosides, some of which showed moderate cytotoxic and antiviral activity. Most of the free nucleosides showed moderate to strong fluorescence with emission maxima of 362-554 nm. 2'-Deoxyribonucleoside and its 5'-O-triphosphate were also prepared from benzothieno-fused 7-deazaadenine derivative, and the triphosphate was a good substrate for KOD XL DNA polymerase in primer extension synthesis of modified DNA which exerted a weak fluorescence which was slightly enhanced in double-stranded DNA as compared to single-stranded oligonucleotides.

Recent update on anti-dengue drug discovery

Dengue is the most important arthropod-borne viral disease of humans, with more than half of the global population living in at-risk areas. Despite the negative impact on public health, there are no antiviral therapies available, and the only licensed vaccine, Dengvaxia^®, has been contraindicated in children below nine years of age. In an effort to combat dengue, several small molecules have entered into human clinical trials. Here, we review anti-DENV molecules and their drug targets that have been published within the past five years (2014-2018). Further, we discuss their probable mechanisms of action and describe a role for classes of clinically approved drugs and also an unclassified class of anti-DENV agents. This review aims to enhance our understanding of novel agents and their cognate targets in furthering innovations in the use of small molecules for dengue drug therapies.

Synthesis and biological evaluation of novel imidazole nucleosides as potential anti-dengue virus agents

In this work, we developed imidazole nucleoside derivatives with anti-dengue virus (DENV) activity was examined. First, compounds in a nucleosides library were screened to find lead compounds which inhibit replication of DENV. As a result, 5-ethynyl-(1-β-d-ribofuranosyl)imidazole-4-carboxamide (1; EICAR) and its 4-carbonitrile derivative EICNR (2) were selected as promising antiviral compounds. However, both of them also exhibited cytotoxicity. In order to develop an effective and less toxic compound, 4'-thio and 4'-seleno derivatives of EICAR and EICNR 3-6 were prepared. The resulting 4'-thioEICAR and 4'-thioEICNR showed inhibitory effect on DENV replication without cytotoxicity as potent as ribavirin, a positive control.

Dengue drug discovery: Progress, challenges and outlook

In the context of the only available vaccine (DENGVAXIA) that was marketed in several countries, but poses higher risks to unexposed individuals, the development of antivirals for dengue virus (DENV), whilst challenging, would bring significant benefits to public health. Here recent progress in the field of DENV drug discovery made in academic laboratories and industry is reviewed. Characteristics of an ideal DENV antiviral molecule, given the specific immunopathology provoked by this acute viral infection, are described. New chemical classes identified from biochemical, biophysical and phenotypic screens that target viral (especially NS4B) and host proteins, offer promising opportunities for further development. In particular, new methodologies ("omics") can accelerate the discovery of much awaited flavivirus specific inhibitors. Challenges and opportunities in lead identification activities as well as the path to clinical development of dengue drugs are discussed. To galvanize DENV drug discovery, collaborative public-public partnerships and open-access resources will greatly benefit both the DENV research community and DENV patients.