Enhanced inhibition of orthopoxvirus replication in vitro by alkoxyalkyl esters of cidofovir and cyclic cidofovir

Divergent synthesis of benzoxaphospholenes and phosphacoumarins via the reaction of 2-alkenylphenols with phosphorus(III/V) chlorides

The divergent synthesis of benzo[e]-1,2-oxaphosphinines or benzo[d]-1,2-oxaphospholenes along with spirocyclic quasiphosphonium compounds based on 2-alkenylphenols and phosphorus(III/V) chlorides is presented. The reaction is condition-dependent and determined by the biphility of the phosphorus(III) derivative and the dual reactivity of 2-alkenylphenol. The procedures are applicable for obtaining benzo[e]-1,2-oxaphosphinines substituted at position 4 and disubstituted at positions 4 and 5 as well as 3,3-disubstituted benzo[d]-1,2-oxaphospholenes with good to high yields.

The Overview of Potential Antiviral Bioactive Compounds in Poxviruses

Poxviruses belong to the family of double-stranded DNA viruses, and it is pathogenic for humans and spread worldwide. These viruses cause infections and various diseases in human. So, it is required to develop new drugs for the treatment of smallpox or other poxvirus infections. Very few potential compounds for the treatment of poxvirus such as smallpox, chickenpox, and monkeypox have been reported. Most of the compounds has used as vaccines. Cidofovir is most commonly used as a vaccine for the treatment of poxviruses. There are no phytochemicals reported for the treatment of poxviruses. Very few phytochemicals are under investigation for the treatment of poxviruses.

Current Status of Epidemiology, Diagnosis, Therapeutics, and Vaccines for the Re-Emerging Human Monkeypox Virus

Monkeypox (Mpox) virus, a member of the Poxviridae family, causes a severe illness similar to smallpox, which is characterized by symptoms such as high fever, rash, and pustules. Human-to-human transmission cases have been reported but remained low since the first recorded case of human infection occurred in the Congo in 1970. Recently, Mpox has re-emerged, leading to an alarming surge in infections worldwide since 2022, originating in the United Kingdom. Consequently, the World Health Organization (WHO) officially declared the '2022-23 Mpox outbreak'. Currently, no specific therapy or vaccine is available for Mpox. Therefore, patients infected with Mpox are treated using conventional therapies developed for smallpox. However, the vaccines developed for smallpox have demonstrated only partial efficacy against Mpox, allowing viral transmission among humans. In this review, we discuss the current epidemiology of the ongoing Mpox outbreak and provide an update on the progress made in diagnosis, treatment, and development of vaccines for Mpox.

Disulfide-incorporated lipid prodrugs of cidofovir: Synthesis, antiviral activity, and release mechanism

The double-stranded DNA (dsDNA) viruses represented by adenovirus and monkeypox virus, have attracted widespread attention due to their high infectivity. In 2022, the global outbreak of mpox (or monkeypox) has led to the declaration of a Public Health Emergency of International Concern. However, to date therapeutics approved for dsDNA virus infections remain limited and there are still no available treatments for some of these diseases. The development of new therapies for treating dsDNA infection is in urgent need. In this study, we designed and synthesized a series of novel disulfide-incorporated lipid conjugates of cidofovir (CDV) as potential candidates against dsDNA viruses including vaccinia virus (VACV) and adenovirus (AdV) 5. The structure-activity relationship analyses revealed that the optimum linker moiety was C₂H₄ and the optimum aliphatic chain length was 18 or 20 atoms. Among the synthesized conjugates, 1c exhibited more potency against VACV (IC₅₀ = 0.0960 μM in Vero cells; IC₅₀ = 0.0790 μM in A549 cells) and AdV5 (IC₅₀ = 0.1572 μM in A549 cells) than brincidofovir (BCV). The transmission electron microscopy (TEM) images revealed that the conjugates could form micelles in phosphate buffer. The stability studies in the GSH environment demonstrated that the formation of micelles in phosphate buffer might protect the disulfide bond from glutathione (GSH) reduction. The dominant means of the synthetic conjugates to liberate the parent drug CDV was by enzymatic hydrolysis. Furthermore, the synthetic conjugates remained sufficiently stable in simulated gastric fluid (SGF), simulated intestinal fluid (SIF), and pooled human plasma, which indicated the possibility for oral administration. These results indicated 1c may be a broad-spectrum antiviral candidate against dsDNA viruses with potential oral administration. Moreover, modification of the aliphatic chain attached to the nucleoside phosphonate group was involved as an efficient prodrug strategy for the development of potent antiviral candidates.

An Overview of Antivirals against Monkeypox Virus and Other Orthopoxviruses

The current monkeypox outbreaks during the COVID-19 pandemic have reignited interest in orthopoxvirus antivirals. Monkeypox belongs to the Orthopoxvirus genus of the Poxviridae family, which also includes the variola virus, vaccinia virus, and cowpox virus. Two orally bioavailable drugs, tecovirimat and brincidofovir, have been approved for treating smallpox infections. Given their human safety profiles and in vivo antiviral efficacy in animal models, both drugs have also been recommended to treat monkeypox infection. To facilitate the development of additional orthopoxvirus antivirals, we summarize the antiviral activity, mechanism of action, and mechanism of resistance of orthopoxvirus antivirals. This perspective covers both direct-acting and host-targeting antivirals with an emphasis on drug candidates showing in vivo antiviral efficacy in animal models. We hope to speed the orthopoxvirus antiviral drug discovery by providing medicinal chemists with insights into prioritizing proper drug targets and hits for further development.

Human mpox: Biology, epidemiology, therapeutic options, and development of small molecule inhibitors

Although monkeypox (mpox) has been endemic in Western and Central Africa for 50 years, it has not received sufficient prophylactic and therapeutical attention to avoid evolving into an epidemic. From January 2022 to January 2023, more than 84,000 of mpox cases were reported from 110 countries worldwide. Case numbers appear to be rising every day, making mpox an increasing global public health threat for the foreseeable future. In this perspective, we review the known biology and epidemiology of mpox virus, together with the latest therapeutic options available for mpox treatment. Further, small molecule inhibitors against mpox virus and the future directions in this field are discussed as well.

NPP-669, a Novel Broad-Spectrum Antiviral Therapeutic with Excellent Cellular Uptake, Antiviral Potency, Oral Bioavailability, Preclinical Efficacy, and a Promising Safety Margin

DNA viruses are responsible for many diseases in humans. Current treatments are often limited by toxicity, as in the case of cidofovir (CDV, Vistide), a compound used against cytomegalovirus (CMV) and adenovirus (AdV) infections. CDV is a polar molecule with poor bioavailability, and its overall clinical utility is limited by the high occurrence of acute nephrotoxicity. To circumvent these disadvantages, we designed nine CDV prodrug analogues. The prodrugs modulate the polarity of CDV with a long sulfonyl alkyl chain attached to one of the phosphono oxygens. We added capping groups to the end of the alkyl chain to minimize β-oxidation and focus the metabolism on the phosphoester hydrolysis, thereby tuning the rate of this reaction by altering the alkyl chain length. With these modifications, the prodrugs have excellent aqueous solubility, optimized metabolic stability, increased cellular permeability, and rapid intracellular conversion to the pharmacologically active diphosphate form (CDV-PP). The prodrugs exhibited significantly enhanced antiviral potency against a wide range of DNA viruses in infected human foreskin fibroblasts. Single-dose intravenous and oral pharmacokinetic experiments showed that the compounds maintained plasma and target tissue levels of CDV well above the EC₅₀ for 24 h. These experiments identified a novel lead candidate, NPP-669. NPP-669 demonstrated efficacy against CMV infections in mice and AdV infections in hamsters following oral (p.o.) dosing at a dose of 1 mg/kg BID and 0.1 mg/kg QD, respectively. We further showed that NPP-669 at 30 mg/kg QD did not exhibit histological signs of toxicity in mice or hamsters. These data suggest that NPP-669 is a promising lead candidate for a broad-spectrum antiviral compound.

Synthesis and Evaluation of Prodrugs of α-Carboxy Nucleoside Phosphonates

A range of lipophilic prodrugs of α-carboxy nucleoside phosphonates, potent inhibitors of HIV-1 reverse transcriptase without requiring prior phosphorylation, were synthesized to evaluate their in vivo potency against HIV in cell culture. A series of prodrug derivatives bearing a free carboxylic acid where the phosphonate was masked with bispivaloyloxymethyl, diisopropyloxycarbonyloxymethyl, bisamidate, aryloxyphosphoramidate, hexadecyloxypropyl, CycloSal, and acycloxybenzyl moieties were synthesized, adapting existing methodologies for phosphonate protection to accommodate the adjacent carboxylic acid moiety. The prodrugs were assayed for anti-HIV activity in CEM cell cultures─the bispivaloyloxymethyl free acid monophosphonate prodrug exhibited some activity (inhibitory concentration-50 (IC₅₀) 59 ± 17 μM), while the other prodrugs were inactive at 100 μM. A racemic bispivaloyloxymethyl methyl ester monophosphonate prodrug was also prepared to assess the suitability of the methyl ester as a carboxylic acid prodrug. This compound exhibited no activity against HIV in cellular assays.

New challenges in human monkeypox outside Africa: A review and case report from Italy

BACKGROUND

Human monkeypox (MPX) is a neglected zoonotic disease caused by the MPX virus a double-stranded DNA virus which belongs to the Poxviridae family genus Orthopoxvirus. It is endemic in the rural rainforests of Central and Western Africa where it is responsible of human sporadic cases and outbreaks since 1970. Outside Africa MPXV caused an outbreak in 2003 in the United States linked to importation of infected rodents from Ghana and a few travel-related cases in the USA, United Kingdom, Israel and Singapore. Actually, a worldwide outbreak with more than 1200 confirmed cases mainly concentrated among men who have sex with men is ongoing.

CASE REPORT

We present the case of an Italian man living in Portugal that was diagnosed with MPX at our clinic in Milan, Italy. Monkeypox virus infection was confirmed by a specific homemade Real-Time PCR. Samples obtained from different sites (pharynx, skin lesions, anal ulcer, seminal fluid) turned all positive with different viral load.

CONCLUSIONS

Our report illustrates the challenge of a disease that seems to present in a different way from classic description with possible human-to-human transmission through sexual contact.

Antivirals With Activity Against Mpox: A Clinically Oriented Review

Mpox virus is an emergent human pathogen. While it is less lethal than smallpox, it can still cause significant morbidity and mortality. In this review, we explore 3 antiviral agents with activity against mpox and other orthopoxviruses: cidofovir, brincidofovir, and tecovirimat. Cidofovir, and its prodrug brincidofovir, are inhibitors of DNA replication with a broad spectrum of activity against multiple families of double-stranded DNA viruses. Tecovirimat has more specific activity against orthopoxviruses and inhibits the formation of the extracellular enveloped virus necessary for cell-to-cell transmission. For each agent, we review basic pharmacology, data from animal models, and reported experience in human patients.

Efficient Method for Generating Point Mutations in the Vaccinia Virus Genome Using CRISPR/Cas9

The vaccinia virus (VACV) was previously used as a vaccine for smallpox eradication. Nowadays, recombinant VACVs are developed as vaccine platforms for infectious disease prevention and cancer treatment. The conventional method for genome editing of the VACV is based on homologous recombination, which is poorly efficient. Recently, the use of CRISPR/Cas9 technology was shown to greatly improve the speed and efficiency of the production of recombinant VACV expressing a heterologous gene. However, the ability to rapidly recover viruses bearing single nucleotide substitutions is still challenging. Notwithstanding, ongoing studies on the VACV and its interaction with the host cell could benefit from viral gene targeted mutagenesis. Here, we present a modified version of the CRISPR/Cas9 system for the rapid selection of mutant VACV carrying point mutations. For this purpose, we introduced a silent mutation into the donor gene (which will replace the wildtype gene) that serves a double function: it is located in the PAM (NGG) sequence, which is essential for Cas9 cleavage, and it alters a restriction site. This silent mutation, once introduced into the VACV genome, allows for rapid selection and screening of mutant viruses carrying a mutation of interest in the targeted gene. As a proof of concept, we produced several recombinant VACVs, with mutations in the E9L gene, upon which, phenotypic analysis was performed.

Development and Validation of a Method of Liquid Chromatography Coupled with Tandem Mass Spectrometry for Quantification of ST-246 (Tecovirimat) in Human Plasma

The aim of this work was to develop and validate a sensitive and robust method of liquid chromatography coupled with tandem mass spectrometry to quantitate ST-246 (tecovirimat) in plasma using an internal standard (2-hydroxy-N-{3,5-dioxo-4-azatetracyclo [5.3.2.02.6.08.10]dodec-11-en-4-yl}-5-methylbenzamide). The method was validated in negative multiple reaction monitoring mode following recommendations of the European Medicines Agency for the validation of bioanalytical methods. The calibration curve for the analyte was linear in the 10−2500 ng/mL range with determination coefficient R2 > 0.99. Intra- and inter-day accuracy and precision for three concentrations of quality control were <15%. Testing of long-term stability of ST-246 (tecovirimat) in plasma showed no degradation at −20 °C for at least 3 months. The method was applied to a clinical assay of a new antipoxvirus compound, NIOCH-14. Thus, the proposed method is suitable for therapeutic drug monitoring of ST-246 (tecovirimat) itself and of NIOCH-14 as its metabolic precursor.

Phosphonates and Phosphonate Prodrugs in Medicinal Chemistry: Past Successes and Future Prospects

Compounds with a phosphonate group, i.e., -P(O)(OH)₂ group attached directly to the molecule via a P-C bond serve as suitable non-hydrolyzable phosphate mimics in various biomedical applications. In principle, they often inhibit enzymes utilizing various phosphates as substrates. In this review we focus mainly on biologically active phosphonates that originated from our institute (Institute of Organic Chemistry and Biochemistry in Prague); i.e., acyclic nucleoside phosphonates (ANPs, e.g., adefovir, tenofovir, and cidofovir) and derivatives of non-nucleoside phosphonates such as 2-(phosphonomethyl) pentanedioic acid (2-PMPA). Principal strategies of their syntheses and modifications to prodrugs is reported. Besides clinically used ANP antivirals, a special attention is paid to new biologically active molecules with respect to emerging infections and arising resistance of many pathogens against standard treatments. These new structures include 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy]pyrimidines or so-called "open-ring" derivatives, acyclic nucleoside phosphonates with 5-azacytosine as a base moiety, side-chain fluorinated ANPs, aza/deazapurine ANPs. When transformed into an appropriate prodrug by derivatizing their charged functionalities, all these compounds show promising potential to become drug candidates for the treatment of viral infections. ANP prodrugs with suitable pharmacokinetics include amino acid phosphoramidates, pivaloyloxymethyl (POM) and isopropoxycarbonyloxymethyl (POC) esters, alkyl and alkoxyalkyl esters, salicylic esters, (methyl-2-oxo-1,3-dioxol-4-yl) methyl (ODOL) esters and peptidomimetic prodrugs. We also focus on the story of cytostatics related to 9-[2-(phosphonomethoxy)ethyl]guanine and its prodrugs which eventually led to development of the veterinary drug rabacfosadine. Various new ANP structures are also currently investigated as antiparasitics, especially antimalarial agents e.g., guanine and hypoxanthine derivatives with 2-(phosphonoethoxy)ethyl moiety, their thia-analogues and N-branched derivatives. In addition to ANPs and their analogs, we also describe prodrugs of 2-(phosphonomethyl)pentanedioic acid (2-PMPA), a potent inhibitor of the enzyme glutamate carboxypeptidase II (GCPII), also known as prostate-specific membrane antigen (PSMA). Glutamate carboxypeptidase II inhibitors, including 2-PMPA have been found efficacious in various preclinical models of neurological disorders which are caused by glutamatergic excitotoxicity. Unfortunately its highly polar character and hence low bioavailability severely limits its potential for clinical use. To overcome this problem, various prodrug strategies have been used to mask carboxylates and/or phosphonate functionalities with pivaloyloxymethyl, POC, ODOL and alkyl esters. Chemistry and biological characterization led to identification of prodrugs with 44-80 fold greater oral bioavailability (tetra-ODOL-2-PMPA).

Alkoxylalkyl Esters of Nucleotide Analogs Inhibit Polyomavirus DNA Replication and Large T Antigen Activities

Polyomavirus infections occur commonly in humans and are normally nonfatal. However, in immunocompromised individuals, they are intractable and frequently fatal. Due to a lack of approved drugs to treat polyomavirus infections, cidofovir, a phosphonate nucleotide analog approved to treat cytomegalovirus infections, has been repurposed as an antipolyomavirus agent. Cidofovir has been modified in various ways to improve its efficacies as a broad-spectrum antiviral agent. However, the actual mechanisms and targets of cidofovir and its modified derivatives as antipolyomavirus agents are still under research. Here, polyomavirus large tumor antigen (Tag) activities were identified as the viral target of cidofovir derivatives. The alkoxyalkyl ester derivatives of cidofovir efficiently inhibit polyomavirus DNA replication in cell-free human extracts and a viral in vitro replication system utilizing only purified proteins. We present evidence that DNA helicase and DNA binding activities of polyomavirus Tags are diminished in the presence of low concentrations of alkoxyalkyl ester derivatives of cidofovir, suggesting that the inhibition of viral DNA replication is at least in part mediated by inhibiting single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) binding activities of Tags. These findings show that the alkoxyalkyl ester derivatives of cidofovir are effective in vitro without undergoing further conversions, and we conclude that the inhibitory mechanisms of nucleotide analog-based drugs are more complex than previously believed.

Overview of Biologically Active Nucleoside Phosphonates

The use of the phosphonate motif featuring a carbon-phosphorous bond as bioisosteric replacement of the labile P–O bond is widely recognized as an attractive structural concept in different areas of medicinal chemistry, since it addresses the very fundamental principles of enzymatic stability and minimized metabolic activation. This review discusses the most influential successes in drug design with special emphasis on nucleoside phosphonates and their prodrugs as antiviral and cancer treatment agents. A description of structurally related analogs able to interfere with the transmission of other infectious diseases caused by pathogens like bacteria and parasites will then follow. Finally, molecules acting as agonists/antagonists of P2X and P2Y receptors along with nucleotidase inhibitors will also be covered. This review aims to guide readers through the fundamentals of nucleoside phosphonate therapeutics in order to inspire the future design of molecules to target infections that are refractory to currently available therapeutic options.

Phosphonate prodrugs: an overview and recent advances

Phosphonates, often used as isosteric replacements for phosphates, can provide important interactions with an enzyme. Due to their high charge at physiological pH, however, permeation into cells can be a challenge. Protecting phosphonates as prodrugs has shown promise in drug delivery. Thus, a variety of structures and cleavage/activation mechanisms exist, enabling release of the active compound. This review describes the structural diversity of these pro-moieties, relevant cleavage mechanisms and recent advances in the design of phosphonate prodrugs.

Drug Development against Smallpox: Present and Future

Forty years after the last endemic smallpox case, variola virus (VARV) is still considered a major threat to humans due to its possible use as a bioterrorism agent. For many years, the risk of disease reemergence was thought to solely be through deliberate misuse of VARV strains kept in clandestine laboratories. However, recent experiments using synthetic biology have proven the feasibility of recreating a poxvirus de novo, implying that VARV could, in theory, be resurrected. Because of this new perspective, the WHO Advisory Committee on VARV Research released new recommendations concerning research on poxviruses that strongly encourages pursuing the development of new antiviral drugs against orthopoxviruses. In 2018, the U.S. FDA advised in favor of two molecules for smallpox treatment, tecovirimat and brincidofovir. This review highlights the difficulties to develop new drugs targeting an eradicated disease, especially as it requires working under the FDA "animal efficacy rule" with the few, and imperfect, animal models available.

Smallpox in the Post-Eradication Era

Widespread vaccination programmes led to the global eradication of smallpox, which was certified by the World Health Organisation (WHO), and, since 1978, there has been no case of smallpox anywhere in the world. However, the viable variola virus (VARV), the causative agent of smallpox, is still kept in two maximum security laboratories in Russia and the USA. Despite the eradication of the disease smallpox, clandestine stocks of VARV may exist. In a rapidly changing world, the impact of an intentional VARV release in the human population would nowadays result in a public health emergency of global concern: vaccination programmes were abolished, the percentage of immunosuppressed individuals in the human population is higher, and an increased intercontinental air travel allows for the rapid viral spread of diseases around the world. The WHO has authorised the temporary retention of VARV to enable essential research for public health benefit to take place. This work aims to develop diagnostic tests, antiviral drugs, and safer vaccines. Advances in synthetic biology have made it possible to produce infectious poxvirus particles from chemicals in vitro so that it is now possible to reconstruct VARV. The status of smallpox in the post-eradication era is reviewed.

In vitro comparison of currently available and investigational antiviral agents against pathogenic human double-stranded DNA viruses: A systematic literature review

BACKGROUND

Double-stranded (ds) DNA virus infections often occur concomitantly in immunocompromised patients. We performed a systematic search of published in vitro activity for nine approved and investigational antivirals to understand the spectrum of in vitro activity against dsDNA viruses.

METHODS

A literature search was performed (PubMed and the WoS Core Collection) using keywords related to: 1) targeted approved/developmental antivirals (acyclovir, artesunate, brincidofovir, cidofovir, cyclopropavir (filociclovir), foscarnet, ganciclovir, letermovir, and maribavir); 2) pathogenic dsDNA viruses; 3) in vitro activity. We summarized data from 210 publications.

RESULTS

Activity against ≤3 viruses was documented for maribavir (cytomegalovirus, Epstein-Barr virus), and letermovir, while activity against > 3 viruses was shown for ganciclovir, cidofovir, acyclovir, foscarnet, cyclopropavir, artesunate, and brincidofovir. The EC₅₀ values of brincidofovir were the lowest, ranging from 0.001 to 0.27 μM, for all viruses except papillomaviruses. The next most potent agents included cidofovir, ganciclovir, foscarnet, and acyclovir with EC₅₀ values between 0.1 μM and >10 μM for cytomegalovirus, herpes simplex virus, and adenovirus.

CONCLUSION

Most of the identified antivirals had in vitro activity against more than one dsDNA virus. Brincidofovir and cidofovir have broad-spectrum activity, and brincidofovir has the lowest EC₅₀ values. These findings could assist clinical practice and developmental research.

A Randomized, Double-Blind, Placebo-Controlled Phase 3 Trial of Oral Brincidofovir for Cytomegalovirus Prophylaxis in Allogeneic Hematopoietic Cell Transplantation

Cytomegalovirus (CMV) infection is a common complication of allogeneic hematopoietic cell transplantation (HCT). In this trial, we randomized adult CMV-seropositive HCT recipients without CMV viremia at screening 2:1 to receive brincidofovir or placebo until week 14 post-HCT. Randomization was stratified by center and risk of CMV infection. Patients were assessed weekly through week 15 and every third week thereafter through week 24 post-HCT. Patients who developed clinically significant CMV infection (CS-CMVi; CMV viremia requiring preemptive therapy or CMV disease) discontinued the study drug and began anti-CMV treatment. The primary endpoint was the proportion of patients with CS-CMVi through week 24 post-HCT; patients who discontinued the trial or with missing data were imputed as primary endpoint events. Between August 2013 and June 2015, 452 patients were randomized at a median of 15 days after HCT and received study drug. The proportion of patients who developed CS-CMVi or were imputed as having a primary endpoint event through week 24 was similar between brincidofovir-treated patients and placebo recipients (155 of 303 [51.2%] versus 78 of 149 [52.3%]; odds ratio, .95 [95% confidence interval, .64 to 1.41]; P = .805); fewer brincidofovir recipients developed CMV viremia through week 14 compared with placebo recipients (41.6%; P < .001). Serious adverse events were more frequent among brincidofovir recipients (57.1% versus 37.6%), driven by acute graft-versus-host disease (32.3% versus 6.0%) and diarrhea (6.9% versus 2.7%). Week 24 all-cause mortality was 15.5% among brincidofovir recipients and 10.1% among placebo recipients. Brincidofovir did not reduce CS-CMVi by week 24 post-HCT and was associated with gastrointestinal toxicity.

The French Armed Forces Virology Unit: A Chronological Record of Ongoing Research on Orthopoxvirus

Since the official declaration of smallpox eradication in 1980, the general population vaccination has ceased worldwide. Therefore, people under 40 year old are generally not vaccinated against smallpox and have no cross protection against orthopoxvirus infections. This naïve population may be exposed to natural or intentional orthopoxvirus emergences. The virology unit of the Institut de Recherche Biomédicale des Armées (France) has developed research programs on orthopoxviruses since 2000. Its missions were conceived to improve the diagnosis capabilities, to foster vaccine development, and to develop antivirals targeting specific viral proteins. The role of the virology unit was asserted in 2012 when the responsibility of the National Reference Center for the Orthopoxviruses was given to the unit. This article presents the evolution of the unit activity since 2000, and the past and current research focusing on orthopoxviruses.

The Role of Brincidofovir in Preparation for a Potential Smallpox Outbreak

Smallpox (variola) virus is considered a Category A bioterrorism agent due to its ability to spread rapidly and the high morbidity and mortality rates associated with infection. Current recommendations recognize the importance of oral antivirals and call for having at least two smallpox antivirals with different mechanisms of action available in the event of a smallpox outbreak. Multiple antivirals are recommended due in large part to the propensity of viruses to become resistant to antiviral therapy, especially monotherapy. Advances in synthetic biology heighten concerns that a bioterror attack with variola would utilize engineered resistance to antivirals and potentially vaccines. Brincidofovir, an oral antiviral in late stage development, has proven effective against orthopoxviruses in vitro and in vivo, has a different mechanism of action from tecovirimat (the only oral smallpox antiviral currently in the US Strategic National Stockpile), and has a resistance profile that reduces concerns in the scenario of a bioterror attack using genetically engineered smallpox. Given the devastating potential of smallpox as a bioweapon, preparation of a multi-pronged defense that accounts for the most obvious bioengineering possibilities is strategically imperative.

Short-term clinical safety profile of brincidofovir: A favorable benefit-risk proposition in the treatment of smallpox

Brincidofovir (BCV, CMX001) is an orally available, long-acting, broad-spectrum antiviral that has been evaluated in healthy subjects in Phase I studies and in hematopoietic cell transplant recipients and other immunocompromised patients in Phase II/III clinical trials for the prevention and treatment of cytomegalovirus and adenovirus infections. BCV has also shown in vitro activity against orthopoxviruses such as variola (smallpox) virus, and is under advanced development as a treatment for smallpox under the US FDA's 'Animal Rule'. The anticipated treatment regimen for smallpox is a total weekly dose of 200 mg administered orally for 3 consecutive weeks. To assess the benefit-to-risk profile of BCV for the treatment of smallpox, we evaluated short-term safety data associated with comparable doses from Phase I studies and from adult and pediatric subjects in the cytomegalovirus and adenovirus clinical programs. When administered at doses and durations similar to that proposed for the treatment of smallpox, BCV was generally well tolerated in both adults and pediatric subjects. The most common adverse events were mild gastrointestinal events and asymptomatic, transient, and reversible elevations in serum transaminases. The data presented herein indicate a favorable safety profile for BCV for the treatment of smallpox, and support its continued development for this indication.

Treatment of alpha and beta herpesvirus infections in solid organ transplant recipients

INTRODUCTION

Human herpesviruses frequently cause infections in solid organ transplant (SOT) recipients. Areas covered: We provide an overview of the clinical impact of alpha and beta herpesviruses and highlight the mechanisms of action, pharmacokinetics, clinical indications, and adverse effects of antiviral drugs for the management of herpes simplex virus, varicella zoster virus and cytomegalovirus. We comprehensively evaluated key clinical trials that led to drug approval, and served as the foundation for management guidelines. We further provide an update on investigational antiviral agents for alpha and beta herpesvirus infections after SOT. Expert commentary: The therapeutic armamentarium for herpes infections is limited by the emergence of drug resistance. There have been major efforts for discovery of new drugs against these viruses, but the results of early-phase clinical trials have been less than encouraging. We believe, however, that more antiviral drug options are needed given the adverse side effects associated with current antiviral agents, and the emergence of drug-resistant virus populations in SOT recipients. Likewise, optimized use and strategies are needed for existing and novel antiviral drugs against alpha and beta-herpesviruses in SOT recipients.

Preliminary Evaluation of the Effect of Investigational Ebola Virus Disease Treatments on Viral Genome Sequences

BACKGROUND

Several patients with Ebola virus disease (EVD) managed in the United States have received ZMapp monoclonal antibodies, TKM-Ebola small interfering RNA, brincidofovir, and/or convalescent plasma as investigational therapeutics.

METHODS

To investigate whether treatment selected for Ebola virus (EBOV) mutations conferring resistance, viral sequencing was performed on RNA extracted from clinical blood specimens from patients with EVD following treatment, and putative viral targets were analyzed.

RESULTS

We observed no major or minor EBOV mutations within regions targeted by therapeutics.

CONCLUSIONS

This small subset of patients and clinical specimens suggests that evolution of resistance is not a direct consequence of antiviral treatment. As EVD antiviral treatments are introduced into wider use, it is essential that continuous viral full-genome surveillance is performed, to monitor for the emergence of escape mutations.

Improved safety of a replication-competent poxvirus-based HIV vaccine with the introduction of the HSV-TK/GCV suicide gene system

INTRODUCTION

Replication-competent vaccinia viruses (VACVs) show prolonged antigen expression time and greater stimulation of immune responses than their replication-incompetent counterparts. However, there is the potential risk of serious post-vaccination complications, especially for children and immunocompromised individuals, leading to safety concerns about the reintroduction of VACV as a vaccine vector. In this study, we improved the safety of the vaccinia virus TianTan (VACV-TT) based HIV vaccine by introducing the HSV-TK/GCV suicide gene system, which is composed of the herpes simplex virus type 1 thymidine kinase gene (HSV-tk) and the antiviral drug ganciclovir (GCV).

MATERIALS AND METHODS

By inserting the HSV-tk gene into the replication-competent VACV-TT genome, a new vector, TT-TK (VACV-TT expressing the HSV-tk gene), and a candidate vaccine, TT-EnvTK (TT-TK expressing the HIV-1 env gene), were constructed.

RESULTS

The new vector TT-TK exhibited reduced replication capacity both in vitro and in vivo in the presence of GCV. GCV inhibited the replication of TT-TK in the brains of mice and skin of rabbits, and provided 100% protection in mice against lethal challenge with TT-TK at a dose of 80mg/kg/day. Furthermore, the candidate vaccine TT-EnvTK induced cellular and humoral immunity against HIV-1 antigen that was comparable to the immunity induced by VTKgpe (VACV-TT expressing HIV-1 env, gag, and pol genes).

DISCUSSION

These promising results suggest a new strategy to mitigate the potential risk of post-vaccination complications from replication-competent VACV-based HIV vaccines.

Anti-viral therapy for congenital cytomegalovirus infection: pharmacokinetics, efficacy and side effects

Congenital cytomegalovirus (CMV) infection is the most common congenital infection in the world with approximately 0.5-2% of all live born infants, and can cause early or late severe neurological and neurisensorial damage. Although no drug has been licensed for therapy of congenital CMV infection, ganciclovir (GCV) and its oral pro-drug, valganciclovir (val-GCV), is increasingly being administrated to symptomatic infants, to improve neurodevelopmental and auditory outcome. Other potentially efficacious for therapy of congenital CMV disease are foscarnet and cidofovir, which have only been administered in few cases. A literature search was performed to look for evidence based or scientific articles evaluating pharmacokinetics, efficacy, and side effects of GCV/val-GCVand the other two anti-viral drugs.

Postchallenge administration of brincidofovir protects healthy and immune-deficient mice reconstituted with limited numbers of T cells from lethal challenge with IHD-J-Luc vaccinia virus

Protection from lethality by postchallenge administration of brincidofovir (BCV, CMX001) was studied in normal and immune-deficient (nude, nu/nu) BALB/c mice infected with vaccinia virus (VACV). Whole-body bioluminescence imaging was used to record total fluxes in the nasal cavity, lungs, spleen, and liver and to enumerate pox lesions on tails of mice infected via the intranasal route with 10(5) PFU of recombinant IHD-J-Luc VACV expressing luciferase. Areas under the flux curve (AUCs) were calculated for individual mice to assess viral loads. A three-dose regimen of 20 mg/kg BCV administered every 48 h starting either on day 1 or day 2 postchallenge protected 100% of mice. Initiating BCV treatment earlier was more efficient in reducing viral loads and in providing protection from pox lesion development. All BCV-treated mice that survived challenge were also protected from rechallenge with IHD-J-Luc or WRvFire VACV without additional treatment. In immune-deficient mice, BCV protected animals from lethality and reduced viral loads while animals were on the drug. Viral recrudescence occurred within 4 to 9 days, and mice succumbed ∼10 to 20 days after treatment termination. Nude mice reconstituted with 10(5) T cells prior to challenge with 10(4) PFU of IHD-J-Luc and treated with BCV postchallenge survived the infection, cleared the virus from all organs, and survived rechallenge with 10(5) PFU of IHD-J-Luc VACV without additional BCV treatment. Together, these data suggest that BCV protects immunocompetent and partially T cell-reconstituted immune-deficient mice from lethality, reduces viral dissemination in organs, prevents pox lesion development, and permits generation of VACV-specific memory.

IMPORTANCE

Mass vaccination is the primary element of the public health response to a smallpox outbreak. In addition to vaccination, however, antiviral drugs are required for individuals with uncertain exposure status to smallpox or for whom vaccination is contraindicated. Whole-body bioluminescence imaging was used to study the effect of brincidofovir (BCV) in normal and immune-deficient (nu/nu) mice infected with vaccinia virus, a model of smallpox. Postchallenge administration of 20 mg/kg BCV rescued normal and immune-deficient mice partially reconstituted with T cells from lethality and significantly reduced viral loads in organs. All BCV-treated mice that survived infection were protected from rechallenge without additional treatment. In immune-deficient mice, BCV extended survival. The data show that BCV controls viral replication at the site of challenge and reduces viral dissemination to internal organs, thus providing a shield for the developing adaptive immunity that clears the host of virus and builds virus-specific immunological memory.

Potential of acyclic nucleoside phosphonates in the treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates [HPMPC: cidofovir, Vistide; PMEA: adefovir dipivoxil, Hepsera; and PMPA: tenofovir, Viread] have proven to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections, for example, cidofovir against herpesvirus [herpes simplex virus type 1 and 2, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus type 6, 7 and 8), polyoma-, papilloma-, adeno- and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus and orf) infections; adefovir against herpesvirus, hepadnavirus [human hepatitis B virus] and retrovirus [HIV type-1 and 2, simian immunodeficiency virus and feline immunodeficiency virus] infections; and tenofovir against both hepadna- and retrovirus infections. Cidofovir has been officially approved for the treatment of cytomegalovirus retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) for the treatment of HIV infections (i.e., AIDS) and adefovir dipivoxil for the treatment of chronic hepatitis B.

Highlights in antiviral drug research: antivirals at the horizon

This review highlights ten "hot topics" in current antiviral research: (i) new nucleoside derivatives (i.e., PSI-352938) showing high potential as a direct antiviral against hepatitis C virus (HCV); (ii) cyclopropavir, which should be further pursued for treatment of human cytomegalovirus (HCMV) infections; (iii) North-methanocarbathymidine (N-MCT), with a N-locked conformation, showing promising activity against both α- and γ-herpesviruses; (iv) CMX001, an orally bioavailable prodrug of cidofovir with broad-spectrum activity against DNA viruses, including polyoma, adeno, herpes, and pox; (v) favipiravir, which is primarily pursued for the treatment of influenza virus infections, but also inhibits the replication of other RNA viruses, particularly (-)RNA viruses such as arena, bunya, and hanta; (vi) newly emerging antiarenaviral compounds which should be more effective (and less toxic) than the ubiquitously used ribavirin; (vii) antipicornavirus agents in clinical development (pleconaril, BTA-798, and V-073); (viii) natural products receiving increased attention as potential antiviral drugs; (ix) antivirals such as U0126 targeted at specific cellular kinase pathways [i.e., mitogen extracellular kinase (MEK)], showing activity against influenza and other viruses; and (x) two structurally unrelated compounds (i.e., LJ-001 and dUY11) with broad-spectrum activity against virtually all enveloped RNA and DNA viruses.

CMX001 to prevent cytomegalovirus disease in hematopoietic-cell transplantation

BACKGROUND

The use of available antiviral agents for the prevention of cytomegalovirus (CMV) disease is limited by frequent toxic effects and the emergence of resistance. CMX001 has potent in vitro activity against CMV and other double-stranded DNA viruses. We evaluated the safety and anti-CMV activity of CMX001 in patients who had undergone allogeneic hematopoietic-cell transplantation.

METHODS

From December 2009 through June 2011, a total of 230 patients with data that could be evaluated were enrolled in the study. We randomly assigned these adult CMV-seropositive transplant recipients from 27 centers to oral administration of CMX001 or placebo. Patients were assigned in a 3:1 ratio to five sequential study cohorts according to a dose-escalating, double-blind design. Randomization was stratified according to the presence or absence of acute graft-versus-host disease and CMV DNA in plasma. Patients received the study drug after engraftment for 9 to 11 weeks, until week 13 after transplantation. Polymerase-chain-reaction analysis of CMV DNA in plasma was performed weekly. Patients in whom CMV DNA was detected at a level that required treatment discontinued the study drug and received preemptive treatment against CMV infection. The primary end point was a CMV event, defined as CMV disease or a plasma CMV DNA level greater than 200 copies per milliliter when the study drug was discontinued. The analysis was conducted in the intention-to-treat population.

RESULTS

The incidence of CMV events was significantly lower among patients who received CMX001 at a dose of 100 mg twice weekly than among patients who received placebo (10% vs. 37%; risk difference, -27 percentage points; 95% confidence interval, -42 to -12; P=0.002). Diarrhea was the most common adverse event in patients receiving CMX001 at doses of 200 mg weekly or higher and was dose-limiting at 200 mg twice weekly. Myelosuppression and nephrotoxicity were not observed.

CONCLUSIONS

Treatment with oral CMX001 at a dose of 100 mg twice weekly significantly reduced the incidence of CMV events in recipients of hematopoietic-cell transplants. Diarrhea was dose-limiting in this population at a dose of 200 mg twice weekly. (Funded by Chimerix; CMX001-201 ClinicalTrials.gov number, NCT00942305.).

Camelpox, an emerging orthopox viral disease

Camelpox is considered as emerging public health problem during this decade due to increased reported cases and outbreaks in camels. Camelpox is a contagious, often sporadic, and notifiable skin disease of camelids and is socio-economically significant as it incurs considerable loss in terms of morbidity, mortality, loss of weight and reduction in milk yield and confined to camel-rearing countries. The causative agent, camelpox virus (CMLV) is genetically closely related to variola virus and has gained much attention from researchers due to its recent emergence in human. The virus carrying genes responsible for host immune evasion mechanisms owing to the threat posed by potential bio-warfare agents. Although the disease can be diagnosed based on clinical features, the similar confounding skin lesions necessitate identification, detection and differentiation of the CMLV by molecular techniques. Vaccines are available in some countries and the available live attenuated vaccine provides long-lasting immunity. Further, novel highly sensitive and specific techniques would be useful in the identification of emerging and re-emerging virus, thereby therapeutic, prophylactic, preventive measures would be applied in time to curtail further spread of camelpox like other zoonotic diseases. This review provide overview of the camelpox particularly on its epidemiology, pathogenesis and biology of the disease, diagnostic approaches and control measures.

Prodrug strategies in ocular drug delivery

Poor bioavailability of topically instilled drug is the major concern in the field of ocular drug delivery. Efflux transporters, static and dynamic ocular barriers often possess rate limiting factors for ocular drug therapy. Different formulation strategies like suspension, ointment, gels, nanoparticles, implants, dendrimers and liposomes have been employed in order to improve drug permeation and retention by evading rate limiting factors at the site of absorption. Chemical modification such as prodrug targeting various nutrient transporters (amino acids, peptide and vitamin) has evolved a great deal of interest to improve ocular drug delivery. In this review, we have discussed various prodrug strategies which have been widely applied for enhancing therapeutic efficacy of ophthalmic drugs. The purpose of this review is to provide an update on the utilization of prodrug concept in ocular drug delivery. In addition, this review will highlight ongoing academic and industrial research and development in terms of ocular prodrug design and delivery.

Increased susceptibility of Cantagalo virus to the antiviral effect of ST-246®

Cantagalo virus (CTGV) is the etiologic agent of a pustular disease in dairy cows and dairy workers in Brazil with important economical and occupational impacts. Nevertheless, no antiviral therapy is currently available. ST-246 is a potent inhibitor of orthopoxvirus egress from cells and has proved its efficacy in cell culture and in animal models. In this work, we evaluated the effect of ST-246 on CTGV replication. Plaque reduction assays indicated that CTGV is 6-38 times more susceptible to the drug than VACV-WR and cowpox virus, respectively, with an EC50 of 0.0086μM and a selective index of >11,600. The analysis of β-gal activity expressed by recombinant viruses in the presence of ST-246 confirmed these results. In addition, ST-246 had a greater effect on the reduction of CTGV spread in comet tail assays and on the production of extracellular virus relative to VACV-WR. Infection of mice with CTGV by tail scarification generated primary lesions at the site of scarification that appeared less severe than those induced by VACV-WR. Animals infected with CTGV and treated with ST-246 at 100mg/kg for 5days did not develop primary lesions and virus yields were inhibited by nearly 98%. In contrast, primary lesions induced by VACV-WR were not affected by ST-246. The analysis of F13 (p37) protein from CTGV revealed a unique substitution in residue 217 (D217N) not found in other orthopoxviruses. Construction of recombinant VACV-WR containing the D217N polymorphism did not lead to an increase in the susceptibility to ST-246. Therefore, it is still unknown why CTGV is more susceptible to the antiviral effects of ST-246 compared to VACV-WR. Nonetheless, our data demonstrates that ST-246 is a potent inhibitor of CTGV replication that should be further evaluated as a promising anti-CTGV therapy.

The antiviral activity and mechanism of action of (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides

One class of compounds that has shown promise as antiviral agents are the (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides, members of the broader class of acyclic nucleoside phosphonates. These HPMP nucleosides are nucleotide analogs and have been shown to be effective inhibitors of a wide range of DNA viruses. Prodrugs of these compounds, which achieve higher levels of the active metabolites within the cell, have an expanded activity spectrum that also includes RNA viruses and retroviruses. Because they are analogs of natural nucleotide substrates, HPMP nucleosides are predicted to target polymerases (DNA polymerases, RNA polymerases and reverse transcriptases), resulting in the inhibition of viral genome replication. Previous work using the replicative enzymes of different viruses including human cytomegalovirus (HCMV) and vaccinia virus DNA polymerases and human immunodeficiency virus type 1 (HIV-1) reverse transcriptase has shown that the activated forms of these compounds are substrates for viral polymerases and that incorporation of these compounds into either the primer strand or the template strand inhibits, but does not necessarily terminate, further nucleic acid synthesis. The activity of these compounds against other viruses that do not encode their own polymerases, like polyoma viruses and papilloma viruses, suggests that host cell DNA polymerases are also targeted. This complex mechanism of action and broad activity spectrum has implications for the development of resistance and host cell genome replication, and suggests these compounds may be effective against other viruses such as influenza virus, respiratory syncytial virus and Dengue virus. This class of nucleotide analogs also points to a potential avenue for the development of newer antivirals.

A single cidofovir treatment rescues animals at progressive stages of lethal orthopoxvirus disease

BACKGROUND

In an event of a smallpox outbreak in humans, the window for efficacious treatment by vaccination with vaccinia viruses (VACV) is believed to be limited to the first few days post-exposure (p.e.). We recently demonstrated in a mouse model for human smallpox, that active immunization 2-3 days p.e. with either VACV-Lister or modified VACV Ankara (MVA) vaccines, can rescue animals from lethal challenge of ectromelia virus (ECTV), the causative agent of mousepox. The present study was carried out in order to determine whether a single dose of the anti-viral cidofovir (CDV), administered at different times and doses p.e. either alone or in conjunction with active vaccination, can rescue ECTV infected mice.

METHODS

Animals were infected intranasally with ECTV, treated on different days with various single CDV doses and monitored for morbidity, mortality and humoral response. In addition, in order to determine the influence of CDV on the immune response following vaccination, both the "clinical take", IFN-gamma and IgG Ab levels in the serum were evaluated as well as the ability of the mice to withstand a lethal challenge of ECTV. Finally the efficacy of a combined treatment regime of CDV and vaccination p.e. was determined.

RESULTS

A single p.e. CDV treatment is sufficient for protection depending on the initiation time and dose (2.5 - 100 mg/kg) of treatment. Solid protection was achieved by a low dose (5 mg/kg) CDV treatment even if given at day 6 p.e., approximately 4 days before death of the control infected untreated mice (mean time to death (MTTD) 10.2). At the same time point complete protection was achieved by single treatment with higher doses of CDV (25 or 100 mg/kg). Irrespective of treatment dose, all surviving animals developed a protective immune response even when the CDV treatment was initiated one day p.e.. After seven days post treatment with the highest dose (100 mg/kg), virus was still detected in some organs (e.g. lung and liver) yet all animals survived, suggesting that efficacious single CDV treatment requires a potent immune system. The combination of CDV and vaccination provided no additional protection over CDV alone. Yet, combining CDV and vaccination maintained vaccination efficacy.

CONCLUSIONS

Altogether, our data substantiate the feasibility of single post-exposure antiviral treatment to face orthopoxvirus infection.

Mutations conferring resistance to viral DNA polymerase inhibitors in camelpox virus give different drug-susceptibility profiles in vaccinia virus

Cidofovir or (S)-HPMPC is one of the three antiviral drugs that might be used for the treatment of orthopoxvirus infections. (S)-HPMPC and its 2,6-diaminopurine counterpart, (S)-HPMPDAP, have been described to select, in vitro, for drug resistance mutations in the viral DNA polymerase (E9L) gene of vaccinia virus (VACV). Here, to extend our knowledge of drug resistance development among orthopoxviruses, we selected, in vitro, camelpox viruses (CMLV) resistant to (S)-HPMPDAP and identified a single amino acid change, T831I, and a double mutation, A314V+A684V, within E9L. The production of recombinant CMLV and VACV carrying these amino acid substitutions (T831I, A314V, or A314V+A684V) demonstrated clearly their involvement in conferring reduced sensitivity to viral DNA polymerase inhibitors, including (S)-HPMPDAP. Both CMLV and VACV harboring the A314V change showed comparable drug-susceptibility profiles to various antivirals and similar impairments in viral growth. In contrast, the single change T831I and the double change A314V+A684V in VACV were responsible for increased levels of drug resistance and for cross-resistance to viral DNA polymerase antivirals that were not observed with their CMLV counterparts. Each amino acid change accounted for an attenuated phenotype of VACV in vivo. Modeling of E9L suggested that the T→I change at position 831 might abolish hydrogen bonds between E9L and the DNA backbone and have a direct impact on the incorporation of the acyclic nucleoside phosphonates. Our findings demonstrate that drug-resistance development in two related orthopoxvirus species may impact drug-susceptibility profiles and viral fitness differently.

Medicinal Chemistry of Nucleoside Phosphonate Prodrugs for Antiviral Therapy

Considerable attention has been focused on the development of phosphonate-containing drugs for application in many therapeutic areas. However, phosphonate diacids are deprotonated at physiological pH and thus phosphonate-containing drugs are not ideal for oral administration, an extremely desirable requisite for the treatment of chronic diseases. To overcome this limitation several prodrug structures of biologically active phosphonate analogues have been developed. The rationale behind the design of such agents is to achieve temporary blockade of the free phosphonic functional group until their systemic absorption and delivery, allowing the release of the active drug only once at the target. In this paper, an overview of acyclic and cyclic nucleoside phosphonate prodrugs, designed as antiviral agents, is presented.

In vitro characterization of a nineteenth-century therapy for smallpox

In the nineteenth century, smallpox ravaged through the United States and Canada. At this time, a botanical preparation, derived from the carnivorous plant Sarracenia purpurea, was proclaimed as being a successful therapy for smallpox infections. The work described characterizes the antipoxvirus activity associated with this botanical extract against vaccinia virus, monkeypox virus and variola virus, the causative agent of smallpox. Our work demonstrates the in vitro characterization of Sarracenia purpurea as the first effective inhibitor of poxvirus replication at the level of early viral transcription. With the renewed threat of poxvirus-related infections, our results indicate Sarracenia purpurea may act as another defensive measure against Orthopoxvirus infections.

Orthopoxvirus targets for the development of new antiviral agents

Investments in the development of new drugs for orthopoxvirus infections have fostered new avenues of research, provided an improved understanding of orthopoxvirus biology and yielded new therapies that are currently progressing through clinical trials. These broad-based efforts have also resulted in the identification of new inhibitors of orthopoxvirus replication that target many different stages of viral replication cycle. This review will discuss progress in the development of new anti-poxvirus drugs and the identification of new molecular targets that can be exploited for the development of new inhibitors. The prototype of the orthopoxvirus group is vaccinia virus and its replication cycle will be discussed in detail noting specific viral functions and their associated gene products that have the potential to serve as new targets for drug development. Progress that has been achieved in recent years should yield new drugs for the treatment of these infections and might also reveal new approaches for antiviral drug development with other viruses.

A modified MS2 bacteriophage plaque reduction assay for the rapid screening of antiviral plant extracts

Introduction:

Traditional methods of screening plant extracts and purified components for antiviral activity require up to a week to perform, prompting the need to develop more rapid quantitative methods to measure the ability of plant based preparations to block viral replication. We describe an adaption of an MS2 plaque reduction assay for use in S. aureus.

Results:

MS2 bacteriophage was capable of infecting and replicating in B. cereus, S. aureus and F + E. coli but not F- E. coli. Indeed, both B. cereus and S. aureus were more sensitive to MS2 induced lysis than F+ E. coli. When MS2 bacteriophage was mixed with Camellia sinensis extract (1 mg/ml), Scaevola spinescens extract (1 mg/ml) or Aloe barbadensis juice and the mixtures inoculated into S. aureus, the formation of plaques was reduced to 8.9 ± 3.8%, 5.4 ± 2.4% and 72.7 ± 20.9% of the untreated MS2 control values respectively.

Conclusions:

The ability of the MS2 plaque reduction assay to detect antiviral activity in these known antiviral plant preparations indicates its suitability as an antiviral screening tool. An advantage of this assay compared with traditionally used cytopathic effect reduction assays and replicon based assays is the more rapid acquisition of results. Antiviral activity was detected within 24 h of the start of testing. The MS2 assay is also inexpensive and non-pathogenic to humans making it ideal for initial screening studies or as a simulant for pathogenic viruses.