Inhibition Of Viral DNA Polymerase Research Articles

Management of Cytomegalovirus Infections in the Era of the Novel Antiviral Players, Letermovir and Maribavir.

Cytomegalovirus (CMV) infections may increase morbidity and mortality in immunocompromised patients. Until recently, standard antiviral drugs against CMV were limited to viral DNA polymerase inhibitors (val)ganciclovir, foscarnet and cidofovir with a risk for cross-resistance. These drugs may also cause serious side effects. This narrative review provides an update on new antiviral agents that were approved for the prevention and treatment of CMV infections in transplant recipients. Letermovir was approved in 2017 for CMV prophylaxis in CMV-seropositive adults who received an allogeneic hematopoietic stem cell transplant. Maribavir followed four years later, with an indication in the treatment of adult and pediatric transplant patients with refractory/resistant CMV disease. The target of letermovir is the CMV terminase complex (constituted of pUL56, pUL89 and pUL51 subunits). Letermovir prevents the cleavage of viral DNA and its packaging into capsids. Maribavir is a pUL97 kinase inhibitor, which interferes with the assembly of capsids and the egress of virions from the nucleus. Both drugs have activity against most CMV strains resistant to standard drugs and exhibit favorable safety profiles. However, high-level resistance mutations may arise more rapidly in the UL56 gene under letermovir than low-grade resistance mutations. Some mutations emerging in the UL97 gene under maribavir can be cross-resistant with ganciclovir. Thus, letermovir and maribavir now extend the drug arsenal available for the management of CMV infections and their respective niches are currently defined.

Monkeypox: Virology, laboratory diagnosis and therapeutic approach.

Monkeypox infection outbreaks have been observed sporadically in Africa, usually as a result of interaction with wildlife reservoirs. The genomes of the new strain range in size from 184.7 to 198.0kb and are identified with 143-214 open reading frames. Viral cores are rapidly carried on microtubules away from the cell's perimeter and deeper into the cytoplasm once the virus and cell membranes fuse. Depending on the kind of exposure, patients with monkeypox may experience a febrile prodrome 5-13 days after exposure, which frequently includes lymphadenopathy, malaise, headaches, and muscle aches. A different diagnostic approach is available for monkeypox, including histopathological analysis, electron microscopy, immunoassays, polymerase chain reaction, genome sequencing, microarrays, loop-mediated isothermal amplification technology and CRISPR (i.e., "clustered regularly interspaced short palindromic repeats"). There are currently no particular, clinically effective treatments available for the monkeypox virus. An initial treatment is cidofovir. As a monophosphate nucleotide analog, cidofovir is transformed into an inhibitor of viral DNA polymerase by cellular kinases, which is analogous to cidofovir's function in inhibiting viral DNA synthesis. The European Medicine Agency and the Food and Drug Administration have both granted permission for IMVAMUNE, a replication-deficient, attenuated third-generation modified vaccinia Ankara vaccine, to be used for the prevention of smallpox and monkeypox in adults.

Combination prophylaxis in CMV high risk heart transplant recipients: A single center experience.

Cytomegalovirus (CMV) is the most clinically relevant infectious agent following heart transplantation (HTX). Data on the beneficial effects of prophylactic use of CMV immunoglobulins (CMVIG) are scarce. In this single-center, retrospective study, we reported patient outcomes following cardiac transplantation using prophylactic CMV treatment, including CMVIG. Distinct clinically relevant outcomes were compared across different CMV risk groups (CMV D-/R-, CMV D-/R+, CMV D+/R+, and CMV D+/R- or CMV high risk group). We included 272 heart transplant procedures, performed between 1/1/2009 and 1/11/2020. Sixty-one (22%) procedures belonged to the CMV high risk group, while 96 (35%), 50 (18%), and 65 (24%) were CMV D-/R-, CMV D-/R+, and CMV D+/R+, respectively. Baseline donor and recipient characteristics (sex, age, body mass index, cause of death, indication for HTX), ischemia times and baseline immunosuppressive regimens were similar across the different CMV risk groups, yet fewer patients were bridged with a mechanical circulatory support in the CMV D+/R- group. CMV disease following cardiac transplantation was more common in the CMV D+/R- risk group (n=40 or 66.7%; p<.001), yet mortality and re-transplantation rates, cardiac allograft vasculopathy (CAV) severity, rejection episodes, and development of donor-specific antibodies (DSA), post-transplant lymphoproliferative diseases (PTLD), and EBV infections were similar across all four CMV risk groups. High risk CMV D+/R- patients had a similar survival compared to low and intermediate CMV risk groups using a prophylactic strategy combining CMVIG and viral DNA polymerase inhibitors. This may be related to a number of factors unrelated to prophylaxis strategy as two out of three CMV D+/R- recipients developed CMV primary infection after prophylaxis was discontinued.

Artificial stem cells mediated inflammation-tropic delivery of antiviral drugs for pneumonia treatment

BackgroundCytomegalovirus (CMV) pneumonia is a major cause of morbidity and mortality in immunodeficiency individuals, including transplant recipients and Acquired Immune Deficiency Syndrome patients. Antiviral drugs ganciclovir (GCV) and phosphonoformate (PFA) are first-line agents for pneumonia caused by herpesvirus infection. However, the therapy suffers from various limitations such as low efficiency, drug resistance, toxicity, and lack of specificity.MethodsThe antiviral drugs GCV and PFA were loaded into the pH-responsive nanoparticles fabricated by poly(lactic-co-glycolic acid) (PLGA) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), and further coated with cell membranes derived from bone marrow mesenchymal stem cells to form artificial stem cells, namely MPDGP. We evaluated the viral suppression effects of MPDGP in vitro and in vivo.ResultsMPDGP showed significant inflammation tropism and efficient suppression of viral replication and virus infection-associated inflammation in the CMV-induced pneumonia model. The synergistic effects of the combination of viral DNA elongation inhibitor GCV and viral DNA polymerase inhibitor PFA on suppressing the inflammation efficiently.ConclusionThe present study develops a novel therapeutic intervention using artificial stem cells to deliver antiviral drugs at inflammatory sites, which shows great potential for the targeted treatment of pneumonia. To our best knowledge, we are the first to fabricate this kind of artificial stem cell to deliver antiviral drugs for pneumonia treatment.Graphical

Foscarnet-Type Inorganic-Organic Hybrid Nanoparticles for Effective Antiviral Therapy.

[ZrO]2+[(FCN)0.4(OH)0.8]2- and Gd3+[FCN]3- inorganic-organic hybrid nanoparticles (IOH-NPs) are novel saline antiviral nanocarriers with foscarnet (FCN) as a drug anion. FCN as a pyrophosphate analogue serves as a prototype of a viral DNA polymerase inhibitor. FCN is used for the treatment of herpesvirus infections, including the drug-resistant cytomegalovirus (CMV) and herpes simplex viruses, HSV-1 and HSV-2. The novel [ZrO]2+[(FCN)0.4(OH)0.8]2- and Gd3+[FCN]3- IOH-NPs are characterized by aqueous synthesis, small size (20-30 nm), low material complexity, high biocompatibility, and high drug load (up to 44 wt % FCN per nanoparticle). The antiviral activity of the FCN-type IOH-NPs is probed for the human cytomegalovirus (HCMV). Moreover, the uptake of FCN-type IOH-NPs into vesicles, cytoplasm, and nuclei of nonphagocytic lung epithelial cells is evaluated. As a result, a promising antiviral activity of the FCN-type IOH-NPs that significantly outperforms freely dissolved FCN at the level of clinical formulations is observed, encouraging a future use of FCN-type IOH-NPs for the delivery of antivirals against respiratory viruses.

The Clinically Approved Antifungal Drug Posaconazole Inhibits Human Cytomegalovirus Replication.

Posaconazole (PCZ) is a clinically approved drug used predominantly for prophylaxis and salvage therapy of fungal infections. Here, we report its previously undescribed anti-human cytomegalovirus (HCMV) activity. By using antiviral assays, we demonstrated that PCZ, along with other azolic antifungals, has a broad anti-HCMV activity, being active against different strains, including low-passage-number clinical isolates and strains resistant to viral DNA polymerase inhibitors. Using a pharmacological approach, we identified the inhibition of human cytochrome P450 51 (hCYP51), or lanosterol 14α demethylase, a cellular target of posaconazole in infected cells, as a mechanism of anti-HCMV activity of the drug. Indeed, hCYP51 expression was stimulated upon HCMV infection, and the inhibition of its enzymatic activity by either the lanosterol analog VFV {(R)-N-(1-(3,4'-difluoro-[1,1'-biphenyl]-4-yl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide} or PCZ decreased HCMV yield and infectivity of released virus particles. Importantly, we observed that the activity of the first-line anti-HCMV drug ganciclovir was boosted tenfold by PCZ and that ganciclovir (GCV) and PCZ act synergistically in inhibiting HCMV replication. Taken together, these findings suggest that this clinically approved drug deserves further investigation in the development of host-directed antiviral strategies as a candidate anti-HCMV drug with a dual antimicrobial effect.

Have the Starting Lineup of Five for Hepatitis B Virus Covalently Closed Circular DNA Synthesis Been Identified?

The persistence of covalently closed circular (ccc) DNA after a long-term therapy of viral DNA polymerase inhibitors attributes to their failure of curing chronic hepatitis B virus (HBV) infection. However, lack of knowledge on the molecular mechanism of cccDNA biosynthesis, metabolic stability and transcriptional regulation impedes the discovery of therapeutics for selective eradication or silencing of cccDNA minichromosomes.

THYMIDINE KINASE AS A CAUSATIVE FACTOR FOR TYPE 1 HERPES SIMPLEX VIRUS RESISTANCE AGAINST ACYCLOVIR

ABSTRACTBackground: Herpes Simplex Virus (HSV) infection demonstrates a high prevalence in the world. Acyclovir, one of guanine synthetic analogues, is commonly used to treat infections caused by HSV. HSV resistance against acyclovir may occur, especially in immunocompromised and immunocompetent patients, as the consequence of viral mutations. Thymidine kinase (TK) is an HSV tegument protein which plays an important role in HSV-1 resistance against acyclovir. Purpose: The purpose of this article is to review the mechanisms of TK mutation that cause HSV-1 resistance against acyclovir. Review: Acyclovir involves three stages of viral thymidine kinase phosphorylation to form acyclovir triphosphate. It prevents HSV replication by acting as a competitive inhibitor of viral DNA polymerase and a chain terminator in viral DNA synthesis. Resistance is associated with viral TK mutation that is encoded by UL23 gene. Long-term use of acyclovir may promote thymidine kinase mutation in immunocompromised and immunocompetent patients via three mechanisms, namely absolute insufficiency in TK activity (TK-negative), depletion in TK synthesis, and inability in TK phosphorylation which consequently hinders the phosphorylation of acyclovir. Herpes TK gene contains a series of cytosine and guanosine, that are important for the function and the mutation of HSV by producing incomplete or fewer enzymes as the result of nucleotide addition or elimination in homopolymer process. Conclusion: HSV-1 resistance against acyclovir is evolved from TK mutations, in the form of TK-negative, TK low-producing, and TK altered mutants, that are unable to phosphorylate TK and accordingly disrupt acyclovir phosphorylation to convert acyclovir triphosphate. Keyword : Acyclovir, Herpes simplex virus, Resistance, Thymidine kinase

Alpha-carboxynucleoside phosphonates: direct-acting inhibitors of viral DNA polymerases.

Acyclic nucleoside phosphonates represent a well-defined class of clinically used nucleoside analogs. All acyclic nucleoside phosphonates need intracellular phosphorylation before they can bind viral DNA polymerases. Recently, a novel class of alpha-carboxynucleoside phosphonates have been designed to mimic the natural 2'-deoxynucleotide 5'-triphosphate substrates of DNA polymerases. They contain a carboxyl group in the phosphonate moiety linked to the nucleobase through a cyclic or acyclic bridge. Alpha-carboxynucleoside phosphonates act as viral DNA polymerase inhibitors without any prior requirement of metabolic conversion. Selective inhibitory activity against retroviral reverse transcriptase and herpesvirus DNA polymerases have been demonstrated. These compounds have a unique mechanism of inhibition of viral DNA polymerases, and provide possibilities for further modifications to optimize and fine tune their antiviral DNA polymerase spectrum.

Possibilities Of Prevention And Treatment Of Human Cytomegalovirus Infections Including New Drugs And Compounds With Potential Application

Abstract Human Cytomegalovirus (hCMV) or human herpesvirus 5 (HHV5) is one of the most common pathogens. Studies indicate the presence of infection in 60–100% of individuals. The ability to cause asymptomatic, infection and a latency promotes the persistence and spread of the virus. hCMV infection is usually asymptomatic and does not require treatment, but in some cases especially in immunocompromised persons (e.g., transplant recipients, patients with hematological malignancies, untreated HIV infected individuals) symptoms can be serious and life-threatening. The paper presents drugs currently used for treatment or prevention of hCMV infection, as well as the prospect of new treatment options. Currently, ganciclovir or valganciclovir are used as the first-line drugs and foscarnet and cidofovir are used alternatively. These drugs usually allow to control hCMV infections, however, there are important limitations. These include the toxicity and the possibility of the development of resistance, including the cross-resistance to all four drugs because they have a common mechanism of action, inhibition of viral DNA polymerase. Therefore, the creation of new drugs, with different mechanisms of action, lower toxicity and better pharmacokinetic parameters is important. Recently, the new drug, letermovir have been registered. Letermovir acts as hCMV DNA terminase inhibitor and due to the different mechanism of action the drug is active against hCMV strains resistant to DNA polymerase inhibitors, and potentially can act synergistically with them. The other drugs that are in the research stage or clinical studies include: brincidofovir, a cidofovir derivative, maribavir, a competitive inhibitor of ATP, cyclopropavir, a guanosine analog and antiviral peptides. 1. Introduction – epidemiology of hCMV infections and prophylaxis schemes. 2. Drugs approved for use in the prevention and treatment of hCMV infections. 2.1. Nucleoside analogues: ganciclovir and valganciclovir. 2.2. Foscarnet. 2.3. Cidofovir. 2.4. Letermovir. 3. Compounds with potential use in the treatment of hCMV infections. 3.1. Brincidofovir. 3.2. Maribavir. 3.3. Cyclopropavir 3.4. Antiviral peptides. 4. Summary

In vitro evaluation of current and novel antivirals in combination against human cytomegalovirus

Human cytomegalovirus (HCMV) can cause severe disease in patients with compromised or immature immune systems. Currently approved pharmacotherapies for the treatment of systemic HCMV infections [ganciclovir (GCV), cidofovir (CDV), foscarnet] are limited by a high incidence of adverse effects and/or the development of drug resistance. Given that many of these drugs have the same viral target (HCMV-encoded DNA polymerase), cross-resistance is relatively common. The primary means to combat drug resistance is combination pharmacotherapy using therapeutics with different molecular mechanisms of action with the expectation that those combinations result in an additive or synergistic enhancement of effect; combinations that result in antagonism can, in many cases, be detrimental to the outcome of the patient. We therefore tested select combinations of approved (GCV, CDV, letermovir (LMV)) and experimental (brincidofovir (BCV), cyclopropavir (CPV), maribavir (MBV), BDCRB) drugs with the hypothesis that combinations of drugs with different and distinct molecular mechanisms of action will produce an additive and/or synergistic enhancement of antiviral effect against HCMV in vitro. Using MacSynergy II (a statistical package that measures enhancement or lessening of effect relative to zero/additive), select drug combination studies demonstrated combination indices ranging from 160 to 372 with 95% confidence intervals greater than zero indicating that these combinations elicit a synergistic enhancement of effect against HCMV in vitro. These data suggest that administration of a viral DNA polymerase inhibitor, MBV, and/or a viral terminase inhibitor in combination has the potential to address the resistance/cross-resistance problems associated with currently available therapeutics.

Synthesis of Guanine α-Carboxy Nucleoside Phosphonate (G-α-CNP), a Direct Inhibitor of Multiple Viral DNA Polymerases.

The synthesis of guanine α-carboxy nucleoside phosphonate (G-α-CNP) is described. Two routes provide access to racemic G-α-CNP 9, one via base construction and the other utilizing Tsuji-Trost allylic substitution. The latter methodology was also applied to the enantiopure synthesis of both antipodes of G-α-CNP, each of which showing interesting antiviral DNA polymerase activity. Additionally, we report an improved multigram scale preparation of the cyclopentene building block 10, starting material for the preferred Tsuji-Trost route to 9.

Xanthine-based acyclic nucleoside phosphonates with potent antiviral activity against varicella-zoster virus and human cytomegalovirus.

While noncanonic xanthine nucleotides XMP/dXMP play an important role in balancing and maintaining intracellular purine nucleotide pool as well as in potential mutagenesis, surprisingly, acyclic nucleoside phosphonates bearing a xanthine nucleobase have not been studied so far for their antiviral properties. Herein, we report the synthesis of a series of xanthine-based acyclic nucleoside phosphonates and evaluation of their activity against a wide range of DNA and RNA viruses. Two acyclic nucleoside phosphonates within the series, namely 9-[2-(phosphonomethoxy)ethyl]xanthine (PMEX) and 9-[3-hydroxy-2-(phosphonomethoxy)propyl]xanthine (HPMPX), were shown to possess activity against several human herpesviruses. The most potent compound was PMEX, a xanthine analogue of adefovir (PMEA). PMEX exhibited a single digit µM activity against VZV (EC50 = 2.6 µM, TK+ Oka strain) and HCMV (EC50 = 8.5 µM, Davis strain), while its hexadecyloxypropyl monoester derivative was active against HSV-1 and HSV-2 (EC50 values between 1.8 and 4.0 µM). In contrast to acyclovir, PMEX remained active against the TK– VZV 07–1 strain with EC50 = 4.58 µM. PMEX was suggested to act as an inhibitor of viral DNA polymerase and represents the first reported xanthine-based acyclic nucleoside phosphonate with potent antiviral properties.

Interferon-\u03b3-inducible protein 16 (IFI16) is required for the maintenance of Epstein-Barr virus latency

BackgroundEpstein-Barr virus (EBV) exhibits both lytic and latent (Lat. I, II, and III) phases in an infected individual. It’s during the latent phase of EBV that all EBV-associated cancers, including Burkitt’s lymphoma, nasopharyngeal carcinoma and lymphoproliferative disease arise. Interferon-γ-inducible protein 16 (IFI16) is a well-established innate immune sensor and viral transcriptional regulator involved in response to invading DNA viruses. During latency, IFI16 remains in the nucleus, in part bound to the EBV genome; however, neither its role in EBV lytic cycle or latency has been established.MethodsShort interfering RNA against IFI16 and IFI16 overexpression were used to identify the role of IFI16 in the maintenance of EBV latency I. We also studied how induction of the lytic cycle affected IFI16 using the EBV positive, latently infected Akata or MUTU-1 cell lines. Akata cells were induced with TPA and MUTU-1 cells with TGF-β up to 96 h and changes in IFI16 protein were analyzed by Western blotting and immunofluorescence microscopy. To assess the mechanism of IFI16 decrease, EBV DNA replication and late lytic transcripts were blocked using the viral DNA polymerase inhibitor phosphonoacetic acid.ResultsKnockdown of IFI16 mRNA by siRNA resulted in enhanced levels of EBV lytic gene expression from all temporal gene classes, as well as an increase in the total EBV genome abundance, whereas overexpression of exogenous IFI16 reversed these effects. Furthermore, 96 h after induction of the lytic cycle with either TPA (Akata) or TGF-β (MUTU-1), IFI16 protein levels decreased up to 80% as compared to the EBV-negative cell line BJAB. Reduction in IFI16 was observed in cells expressing EBV lytic envelope glycoprotein. The decreased levels of IFI16 protein do not appear to be dependent on late lytic transcripts of EBV but suggest involvement of the immediate early, early, or a combination of both gene classes.ConclusionsReduction of IFI16 protein levels following lytic cycle induction, as well as reactivation from latency after IFI16 mRNA knockdown suggests that IFI16 is crucial for the maintenance of EBV latency. More importantly, these results identify IFI16 as a unique host factor protein involved in the EBV lifecycle, making it a potential therapeutic target to combat EBV-related malignancies.

Guanine α-carboxy nucleoside phosphonate (G-α-CNP) shows a different inhibitory kinetic profile against the DNA polymerases of human immunodeficiency virus (HIV) and herpes viruses

α-Carboxy nucleoside phosphonates (α-CNPs) are modified nucleotides that represent a novel class of nucleotide-competing reverse transcriptase (RT) inhibitors (NcRTIs). They were designed to act directly against HIV-1 RT without the need for prior activation (phosphorylation). In this respect, they differ from the nucleoside or nucleotide RTIs [N(t)RTIs] that require conversion to their triphosphate forms before being inhibitory to HIV-1 RT. The guanine derivative (G-α-CNP) has now been synthesized and investigated for the first time. The (L)-(+)-enantiomer of G-α-CNP directly and competitively inhibits HIV-1 RT by interacting with the substrate active site of the enzyme. The (D)-(−)-enantiomer proved inactive against HIV-1 RT. In contrast, the (+)- and (−)-enantiomers of G-α-CNP inhibited herpes (i.e. HSV-1, HCMV) DNA polymerases in a non- or uncompetitive manner, strongly indicating interaction of the (L)-(+)- and the (D)-(−)-G-α-CNPs at a location different from the polymerase substrate active site of the herpes enzymes. Such entirely different inhibition profile of viral polymerases is unprecedented for a single antiviral drug molecule. Moreover, within the class of α-CNPs, subtle differences in their sensitivity to mutant HIV-1 RT enzymes were observed depending on the nature of the nucleobase in the α-CNP molecules. The unique properties of the α-CNPs make this class of compounds, including G-α-CNP, direct acting inhibitors of multiple viral DNA polymerases.

Characterization of novel hepadnaviral RNA species accumulated in hepatoma cells treated with viral DNA polymerase inhibitors

Inhibitors of hepadnaviral DNA polymerases are predicted to inhibit both minus and plus strand of viral DNA synthesis and arrest viral DNA replication at the stage of pregenomic (pg) RNA-containing nucleocapsids. However, analyses of the RNA species of human and duck hepatitis B viruses (HBV and DHBV, respectively) in hepatoma cells treated with viral DNA polymerase inhibitors revealed the genesis of novel RNA species migrating slightly faster than the full-length pgRNA. The DNA polymerase inhibitor-induced accumulation of these RNA species were abolished in the presence of alpha-interferon or HBV nucleocapsid assembly inhibitors. Moreover, they were protected from microccocal nuclease digestion and devoid of a poly-A tail. These characteristics suggest that the novel RNA species are most likely generated from RNase H cleavage of encapsidated pgRNA, after primer translocation and synthesis of the 5′ terminal portion of minus strand DNA. In support of this hypothesis, DNA polymerase inhibitor treatment of chicken hepatoma cells transfected with a DHBV genome encoding an RNase H inactive DNA polymerase (E696H) failed to produce such RNA species. Our results thus suggest that the currently available DNA polymerase inhibitors do not efficiently arrest minus strand DNA synthesis at the early stage in hepatocytes. Hence, development of novel antiviral agents that more potently suppress viral DNA synthesis or viral nucleocapsid assembly inhibitors that are mechanistically complementary to the currently available DNA polymerase inhibitors are warranted.

Pronounced Inhibition Shift from HIV Reverse Transcriptase to Herpetic DNA Polymerases by Increasing the Flexibility of α-Carboxy Nucleoside Phosphonates.

Alpha-carboxynucleoside phosphonates (α-CNPs) are novel viral DNA polymerase inhibitors that do not need metabolic conversion for enzyme inhibition. The prototype contains a cyclopentyl linker between nucleobase and α-carboxyphosphonate and preferentially (50- to 100-fold) inhibits HIV-1 RT compared with herpetic DNA polymerases. A synthesis methodology involving three steps has been developed for the synthesis of a series of novel α-CNPs, including a Rh(II)-catalyzed O-H insertion that connects the carboxyphosphonate group to a linker moiety and an attachment of a nucleobase to the other end of the linker by a Mitsunobu reaction followed by final deprotection. Replacing the cyclopentyl moiety in the prototype α-CNPs by a more flexible entity results in a selectivity shift of ∼ 100-fold in favor of the herpetic DNA polymerases when compared to selectivity for HIV-1 RT. The nature of the kinetic interaction of the acyclic α-CNPs against the herpetic DNA polymerases differs from the nature of the nucleobase-specific kinetic interaction of the cyclopentyl α-CNPs against HIV RT.

KSHV targeted therapy: an update on inhibitors of viral lytic replication.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi’s sarcoma, primary effusion lymphoma and multicentric Castleman’s disease. Since the discovery of KSHV 20 years ago, there is still no standard treatment and the management of virus-associated malignancies remains toxic and incompletely efficacious. As the majority of tumor cells are latently infected with KSHV, currently marketed antivirals that target the virus lytic cycle have shown inconsistent results in clinic. Nevertheless, lytic replication plays a major role in disease progression and virus dissemination. Case reports and retrospective studies have pointed out the benefit of antiviral therapy in the treatment and prevention of KSHV-associated diseases. As a consequence, potent and selective antivirals are needed. This review focuses on the anti-KSHV activity, mode of action and current status of antiviral drugs targeting KSHV lytic cycle. Among these drugs, different subclasses of viral DNA polymerase inhibitors and compounds that do not target the viral DNA polymerase are being discussed. We also cover molecules that target cellular kinases, as well as the potential of new drug targets and animal models for antiviral testing.

Polysaccharides from leaves of Stevia rebaudiana (Bertoni) and anti-herpesvirus properties

Herpes simplex virus type 1 (HSV-1) is an enveloped DNA virus that is able to establish latent infection. The prevalence of infection is more than 80% among adults, typically causing oral and eye lesions and even life-threatening disease in immunocompromised individuals. The drugs used to treat HSV-1, including viral DNA polymerase inhibitors, are not always effective or well-tolerated by patients, increasing cases of viral resistance to the drugs. Natural compounds, such as polysaccharides, are being investigated as potential drugs to treat viral infections. Crude aqueous and homogeneous alkaline polysaccharide fractions (i.e., SFW and SSFK-10RM, respectively) from the leaves of Stevia rebaudiana (Bertoni) were analyzed to elucidate their anti-HSV-1 action using a plaque reduction assay, cell-cell virus spread analysis, and Western blot of viral glycoprotein expression. The fractions were active in the adsorption and viral penetration phases, with an EC50 of 14 and 22 µg/mL for SSFK-10RM and SFW, respectively. Both polysaccharides neutralized viral particles. The assessment of cell-cell virus spread demonstrated that 50 µg/mL of SSFK-10RM and SFW inhibited the lateral spread of infection by 40% and 70%, respectively. Both fractions inhibited the lateral spread of infection by 100% when tested at a concentration of 100 µg/mL. A partial reduction of the expression of viral glycoproteins gB, gC, and gD was observed during the adsorption phase and after virus penetration in the cell. Complete inhibition was observed when the cells were treated during all stages of infection. Our results suggest that S. rebaudiana polysaccharides are able to both inhibit the early steps of the infection and exert significant antiviral activity after virus entry into the cell by an unknown mechanism. Thus, S. rebaudiana polysaccharides are promising for future research that seeks to treat infections caused by HSV-1 in vivo. Acknowledgements: CNPq, FINEP, CAPES, Fundação Araucária.

Design, Synthesis, and Evaluation of WC5 Analogues as Inhibitors of Human Cytomegalovirus Immediate‐Early 2 Protein, a Promising Target for Anti‐HCMV Treatment

Although human cytomegalovirus (HCMV) infection is mostly asymptomatic for immunocompetent individuals, it remains a serious threat for those who are immunocompromised, in whom it is associated with various clinical manifestations. The therapeutic utility of the few available anti-HCMV drugs is limited by several drawbacks, including cross-resistance due to their common mechanism of action, i.e., inhibition of viral DNA polymerase. Therefore, compounds that target other essential viral events could overcome this problem. One example of this is the 6-aminoquinolone WC5, which acts by directly blocking the transactivation of essential viral Early genes by the Immediate-Early 2 (IE2) protein. In this study, the quinolone scaffold of the lead compound WC5 was investigated in depth, defining more suitable substituents for each of the scaffold positions explored and identifying novel, potent and nontoxic compounds. Some compounds showed potent anti-HCMV activity by interfering with IE2-dependent viral E gene expression. Among them, naphthyridone 1 was also endowed with potent anti-HIV activity in latently infected cells. Their antiviral profile along with their innovative mechanism of action make these anti-HCMV quinolones a very promising class of compounds to be exploited for more effective antiviral therapeutic treatment.