Single-dose safety and pharmacokinetics of ST-246, a novel orthopoxvirus egress inhibitor

Nonhuman primates as valuable models for mpox drug and vaccine discovery

INTRODUCTION

In recent months, monkeypox (mpox) virus (MPXV) infections has grown to be a major worldwide concern. Cynomolgus monkeys, rhesus macaques, marmosets, and baboons are the nonhuman primate (NHP) models that provide the much needed means for developing new therapies against MPXV due to their genetic proximity to humans.

AREA COVERED

In this review, the authors discuss epidemiology, transmission, clinical presentation, and the use of NHP in studying the treatment of MPXV over the past two decades on Google Scholar. NHP models have been widely used to evaluate the efficacy of antiviral drugs and antibodies, providing important information regarding immune responses and disease. NHPs continue to be an important mainstay in preclinical testing, enabling the optimization of the efficacy and safety of drugs, antibodies, and vaccines to accelerate the development of effective MPXV treatments for humans.

EXPERT OPINION

The intravenous forms of medications like cidofovir, brincidofovir, and Vaccinia Immune Globulin (VIG) constitute the basis of MPXV therapy. Additionally, antibodies such as HAI, PN, and CF assess the efficacy of smallpox vaccination against MPXV in primates. This would help both the development of diagnostic tools and the optimization of vaccine strategies. Moreover, the similarities between MPXV and vaccinia or variola can play a role in developing targeted antiviral treatment methods.

Monkeypox: Origin, Transmission, Clinical Manifestations, Prevention, and Therapeutic Options

Monkeypox is a rapidly spreading transmissible disease induced by the monkeypox virus (MPXV), a major public health problem worldwide. The origin of monkeypox might be tracked to the continent of Africa, where it first afflicted primate species prior to spreading to the world. Severe health issues for the public have been raised as a result of the disease's current breakouts in nonendemic areas and its subsequent dissemination to several nations throughout the globe. Monkeypox spreads by having contact with infected creatures or people, as well as respiratory droplets and contaminated things. Symptoms of monkeypox in young children and adults are different. While the symptoms are similar to smallpox, monkeypox has a reduced mortality rate. Proper diagnosis, suitable care, and focused preventative efforts all depend on becoming cognizant of those distinctions. Numerous promising therapeutic approaches have been recently investigated. Antiviral drugs such as tecovirimat, cidofovir, and brincidofovir, which were initially developed to treat smallpox, were found to have been effective in treating MPXV cases. Moreover, vaccinations continue to be an important preventative step. The purpose of this article is to offer the most recent and thorough information available on monkeypox, including its possible causes, modes of transfer, and potential treatments. By identifying the distinct forms of monkeypox and exploring potential treatment options, this work contributes to the ongoing battle against MPXVs and the management of this novel viral disease. To stop the propagation of monkeypox, greater research and communication are needed to provide stronger treatments and effective vaccinations.

Clinical considerations on monkeypox antiviral medications: An overview

Monkeypox (mpox), a virus belonging to the orthopoxvirus family, can cause a zoonotic infectious disease with morbidity and cosmetic complications. Therefore, effective antiviral drugs with appropriate safety profiles are important for the treatment of patients with mpox. To date, there is no FDA-approved drug for the treatment of mpox. However, tecovirimat, brincidofovir, and cidofovir are the candidate therapies for the management of mpox. Given the safety concerns following the use of these medications, we aimed to review evidence on the clinical considerations of mpox antiviral medications that will be useful to guide clinicians in the treatment approach. Based on the current evidence, tecovirimat has favorable clinical efficacy, safety, and side effect profile and it can be considered as first-line treatment for mpox.

Pharmacokinetics of tecovirimat in subjects with Mpox

OBJECTIVE

To investigate the pharmacokinetics (PK) of tecovirimat in subjects with Mpox.

METHODS

This monocentric, prospective, observational study enrolled subjects with Mpox who received standard treatment with oral tecovirimat. Plasma samples for PK assessment were collected at steady state (5-8 days after initiation of antiviral therapy), before and 3, 5, 7 and 12 h after tecovirimat administration. Drug concentrations were determined by validated liquid chromatography coupled with tandem mass spectrometry. PK parameters were calculated using Phoenix 8.1.

RESULTS

Overall, 14 male patients hospitalized for severe Mpox with ongoing tecovirimat treatment were enrolled in this study. Six of the 14 patients were living with human immunodeficiency virus (HIV), all of whom were on antiretroviral therapy (ART) and virologically suppressed at the time of hospitalization. Significant differences in tecovirimat PK were observed in subjects without HIV compared with subjects with HIV. In subjects with HIV, the maximum tecovirimat plasma concentration (39%, P≤0.0001), minimum tecovirimat plasma concentration (42%, P=0.0079) and area under the curve from zero to the last measured time-point (40%, P≤0.0001) were significantly lower compared with subjects without HIV, but all concentrations remained above the in-vitro calculated 90% inhibitory concentration. No significant associations were found between demographic/clinical data and tecovirimat PK. All patients recovered completely within 14 (range 6-36) days of treatment initiation.

CONCLUSIONS

This study found a significant decrease in plasma exposure of tecovirimat in Mpox patients with HIV on effective ART compared with those without HIV, with no evident impact on clinical outcomes. Although these results need to be confirmed in larger studies, they may provide useful information on the PK of tecovirimat.

Challenges in the treatment and prevention of Monkeypox infection; a comprehensive review

Human monkeypox (HMPX) is a zoonotic disease, literally meaning that it can be passed on from animals (non-primate) to human (primate). All the reported and recorded cases have been traced back either to international travel or import of African animals. In the Unites states, sporadic monkeypox cases have been reported in specific over the past 50 years, starting its first identification in the Democratic Republic of the Congo (D.R.C.) in 1970. Due to its extreme versatility, this disease poses threat as a serious public health issue that needs to be monitored, researched and prevented. Data indicate that prior immunization with the smallpox vaccine is beneficial and may provide protection against the monkeypox virus. JYNNEOSTM is a live viral vaccine that has been approved to improve clinical manifestations of the infection. On the other hand, public ignorance about safety precaution towards monkeypox post-COVID is another challenge that needs to be overcome in tackling HMPX as a possible re-emergent infection. This review is a collation of the epidemiology, etiology, transmission, clinical features and treatment of human monkeypox (HMPX).

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.

Safety and Pharmacokinetics of the Substance of the Anti-Smallpox Drug NIOCH-14 after Oral Administration to Laboratory Animals

BACKGROUND

Since most of the modern human population has no anti-smallpox immunity, it is extremely important to develop and implement effective drugs for the treatment of smallpox and other orthopoxvirus infections. The objective of this study is to determine the main characteristics of the chemical substance NIOCH-14 and its safety and bioavailability in the body of laboratory animals.

METHODS

The safety of NIOCH-14 upon single- or multiple-dose intragastric administration was assessed according to its effect on the main hematological and pathomorphological parameters of laboratory mice and rats. In order to evaluate the pharmacokinetic parameters of NIOCH-14 administered orally, a concentration of ST-246, the active metabolite of NIOCH-14, in mouse blood and organs was determined by tandem mass spectrometry and liquid chromatography.

RESULTS

The intragastric administration of NIOCH-14 at a dose of 5 g/kg body weight caused neither death nor signs of intoxication in mice. The intragastric administration of NIOCH-14 to mice and rats at doses of 50 and 150 µg/g body weight either as a single dose or once daily during 30 days did not cause animal death or critical changes in hematological parameters and the microstructure of internal organs. The tissue availability of NIOCH-14 administered orally to the mice at a dose of 50 µg/g body weight, which was calculated according to concentrations of its active metabolite ST-246 for the lungs, liver, kidney, brain, and spleen, was 100, 69.6, 63.3, 26.8 and 20.3%, respectively. The absolute bioavailability of the NIOCH-14 administered orally to mice at a dose of 50 µg/g body weight was 22.8%.

CONCLUSION

Along with the previously determined efficacy against orthopoxviruses, including the smallpox virus, the substance NIOCH-14 was shown to be safe and bioavailable in laboratory animal experiments.

The land-scape of immune response to monkeypox virus

Human monkeypox is a viral zoonotic smallpox-like disease caused by the monkeypox virus (MPXV) and has become the greatest public health threat in the genus Orthopoxvirus after smallpox was eradicated. The host immune response to MPXV plays an essential role in disease pathogenesis and clinical manifestations. MPXV infection leads to skin lesions with the genital area as the main feature in the current outbreak and triggers a strong immune response that results in sepsis, deep tissue abscess, severe respiratory disease, and injuries to multiple immune organs. Emerging evidence shows that the immunopathogenesis of MPXV infection is closely associated with impaired NK-cell function, lymphopenia, immune evasion, increased antibodies, increased blood monocytes and granulocytes, cytokine storm, inhibition of the host complement system, and antibody-dependent enhancement. In this overview, we discuss the immunopathology and immunopathogenesis of monkeypox to aid the development of novel immunotherapeutic strategies against monkeypox.

Monkeypox Virus Infections in Humans

Human monkeypox is a viral zoonosis endemic to West and Central Africa that has recently generated increased interest and concern on a global scale as an emerging infectious disease threat in the midst of the slowly relenting COVID-2019 disease pandemic. The hallmark of infection is the development of a flu-like prodrome followed by the appearance of a smallpox-like exanthem. Precipitous person-to-person transmission of the virus among residents of 100 countries where it is nonendemic has motivated the immediate and widespread implementation of public health countermeasures. In this review, we discuss the origins and virology of monkeypox virus, its link with smallpox eradication, its record of causing outbreaks of human disease in regions where it is endemic in wildlife, its association with outbreaks in areas where it is nonendemic, the clinical manifestations of disease, laboratory diagnostic methods, case management, public health interventions, and future directions.

New Perspectives on Antimicrobial Agents: Tecovirimat for Treatment of Human Monkeypox Virus

Tecovirimat is an antiviral drug initially developed against variola virus (VARV) to treat smallpox infection. Due to its mechanism of action, it has activity against the family of orthopoxviruses, including vaccinia and the human monkeypox virus (HMPXV). Efficacy studies have thus far been limited to animal models, with human safety trials showing no serious adverse events. Currently approved by the FDA only for the treatment of smallpox, tecovirimat shows promise for the treatment of HMPXV. Tecovirimat has been prescribed via an expanded access for an investigational new drug protocol during the 2022 outbreak. This review will examine the literature surrounding tecovirimat's mechanism of action, pharmacokinetics, safety, efficacy, and potential for resistance.

Therapeutic strategies for human poxvirus infections: Monkeypox (mpox), smallpox, molluscipox, and orf

Therapeutic and vaccine development for human poxvirus infections (e.g., monkeypox (mpox) virus, variola virus, molluscum contagiosum virus, orf virus) has been largely deserted, especially after the eradication of smallpox by 1980. Human mpox is a self-limited disease confined to Central and West Africa for decades. However, since April 2022, mpox has quickly emerged as a multi-country outbreak, urgently calling for effective antiviral agents and vaccines to control mpox. Here, this review highlights possible therapeutic options (e.g., tecovirimat, brincidofovir, cidofovir) and other strategies (e.g., vaccines, intravenous vaccinia immune globulin) for the management of human poxvirus infections worldwide.

An Update on the Pharmacological Aspects of Vaccines and Antivirals for the Management of Monkeypox

Monkeypox is a self-limiting zoonotic disease caused by the monkeypox virus belonging to the genus of orthopox viruses. Initially considered an ‘African disease’, this infection has crossed the boundaries to affect other continents and it has raised tremendous concerns among the general public as well as the medical fraternity all over the world, particularly because of the lack of specific vaccinations and drugs for the management of the illness. Epidemiological evaluation of the current infection has reported that it is mainly transmitted through sexual contact in bisexual men, mostly whites, and in those with pre-existing human immunodeficiency virus infection. The most common presentations were skin rash, anogenital lesions, or mucosal lesions along with systemic symptoms. It has been established that the vaccines and drugs approved for the management of smallpox could be used for the management of the current monkeypox outbreak. Vaccinia Immune Globulin (VIG) and vaccines like JYNNEOS and ACAM2000 and antiviral drugs like tecovirimat, cidofovir (CDV), and brincidofovir are being considered for those patients with serious diseases. It is imperative for physicians to understand the pharmacological aspects of these drugs for delivering better care to patients with monkeypox, which is eventually essential for the containment of this infection. This review covers updates on vaccines as well as drugs for the prevention and management of monkeypox.

Monkeypox in humans: a new outbreak

Infection caused by Monkeypox Virus (MPVX) has small rodents as its natural reservoir and both monkeys and humans are occasional hosts. The causative agent is an Orthopoxvirus (MPVX) that was isolated in monkeys in 1958 and proved capable of passing to humans in 1970. It remained contained in Africa, causing isolated episodes of infection, until 2003 when an outbreak occurred in the United States following importation of animals from that continent. Since then, anecdotal cases have continued to be reported outside Africa, usually very clearly linked to travelers to those countries, but in May 2022, a broad outbreak of this disease has begun, now affecting several continents, with the emergence of human cases of MPVX (H-MPVX) infection mainly among Men that have Sex with Men (MSM). The disease has an incubation time ranging from 5 to 15 days and is characterized by the presence of pustules, fever, malaise and headache. The presence of significant regional lymphadenopathy is a differential feature with episodes of classical smallpox. Proctitis and pharyngitis, with minimal skin lesions, may be another form of presentation. Diagnosis can be confirmed by PCR testing of lesions or by demonstration of MPVX in other body fluids or tissues, although in the appropriate epidemiologic setting the clinical picture is highly suggestive of the disease. Effective drug treatment has been developed as part of programs to protect against potential bioterrorist agents and smallpox vaccinees are known to have high protection against monkeypox. New vaccines are available, but neither the drugs nor the vaccines are yet freely available on the market. The prognosis of the disease appears, at least in adults in developed countries, to be good, with very low mortality figures and much less aggressive behavior than that described in classical smallpox. Isolation measures, essential for the control of the outbreak, have been published by the health authorities.

Monkeypox-What Pediatricians Need to Know

Monkeypox is a zoonotic disease, presenting with fever, lymphadenopathy and vesicular-pustular skin lesions, that historically has rarely been reported outside the endemic regions of Central and West Africa. It was previously thought that human-to-human transmission was too low to sustain spread. During 2022, the number of cases of monkeypox, caused by clade II, rose rapidly globally, predominantly among men who have sex with men. In previous outbreaks with monkeypox clade 1 in endemic areas, children were disproportionately more affected with higher morbidity and mortality. It is unclear whether children are at similarly higher risk from monkeypox clade II. Nonetheless, children and pregnant women are considered high-risk groups and antiviral treatment should be considered for those affected. While smallpox vaccination offers good protection against monkeypox, the duration of protection is unknown, and infection occurs in vaccinated individuals. Should the current outbreak spread to children, authorities should be prepared to rapidly implement vaccination for children. In this review, we summarize epidemiological and clinical features, as well as the pathogenesis, treatment, and prevention options for monkeypox with a focus on considerations for children.

Management of patients with monkeypox virus infection and contacts in the community and in healthcare settings: a French position paper

SCOPE

Since April 2022, a large number of monkeypox (MPX) cases have emerged across the globe in regions that are known to be totally free of zoonotic reservoir. The High Council for Public Health is a national institute commissioned to provide guidelines to the French Ministry of Health. The objective of these guidelines and recommendations is to inform the public, people at risk of severe MPX infection, infected patients and their families and contacts and healthcare workers in charge of infected patients.

METHODS

A review of the literature from the MEDLINE database was carried out using the single keyword 'monkeypox', including recent and older articles from January 2000 to June 2022. There was no filter for the type of study, except English language. The titles and summaries of all the articles were read by the experts to select articles of interest. The High Council for Public Health brought together specialists with expertise in the field to analyse the scientific literature and international recommendations. Recommendations were classified with clinical practice methodology using four levels (strong recommendation, recommendation, optional recommendation and no recommendation) without grading the level of evidence. To develop and methodologically validate the recommendations, the Appraisal of Guidelines for Research and Evaluation Instrument (AGREE-II)chart was partially used. QUESTIONS ADDRESSED BY THE GUIDELINES AND RECOMMENDATIONS: (a) What are the therapeutic management measures for hospitalized patients with severe forms of MPX infection, and what are the preventive measures to protect healthcare professionals? (b) What are the isolation and prevention measures in the community for patients with mild or moderate severity MPX infection? (c) what are the preventive measures for contacts of an MPX-infected person? (d) Who should be vaccinated? (e) What are the specific prevention measures for children and schools?

Monkeypox: A Comprehensive Review

The 2022 multi-country monkeypox outbreak in humans has brought new public health adversity on top of the ongoing coronavirus disease 2019 (COVID-19) pandemic. The disease has spread to 104 countries throughout six continents of the world, with the highest burden in North America and Europe. The etiologic agent, monkeypox virus (MPXV), has been known since 1959 after isolation from infected monkeys, and virulence among humans has been reported since the 1970s, mainly in endemic countries in West and Central Africa. However, the disease has re-emerged in 2022 at an unprecedented pace, with particular concern on its human-to-human transmissibility and community spread in non-endemic regions. As a mitigation effort, healthcare workers, public health policymakers, and the general public worldwide need to be well-informed on this relatively neglected viral disease. Here, we provide a comprehensive and up-to-date overview of monkeypox, including the following aspects: epidemiology, etiology, pathogenesis, clinical features, diagnosis, and management. In addition, the current review discusses the preventive and control measures, the latest vaccine developments, and the future research areas in this re-emerging viral disease that was declared as a public health emergency of international concern.

Neurologic Complications of Smallpox and Monkeypox: A Review

Importance

Orthopox viruses include smallpox virus, a once feared but now eradicated virus, as well as monkeypox virus. Monkeypox is an emerging virus initially isolated in 1958, previously unrecognized outside sub-Saharan Africa until a worldwide outbreak in May 2022. It is important to review known neurologic consequences of both these viruses, as complications of smallpox may be relevant to monkeypox, though complications of monkeypox may be rarer and perhaps less severe.

Observations

This was a literature review of the known neurologic complications of smallpox, which include encephalitis, transverse myelitis, and acute disseminated encephalomyelitis among others; historical complications of smallpox vaccination, including postvaccinal encephalomyelitis; and the known neurologic complications of monkeypox, which include headaches and mood disturbances, as well as rare presentations of encephalitis, transverse myelitis, and seizures. Of concern is the possibility of viral persistence and systemic complications in immunocompromised individuals. Also provided were considerations for diagnosis, current treatment, and prevention of monkeypox.

Conclusions and Relevance

Monkeypox should be considered in high-risk populations who present with neurologic syndromes. Diagnosis may require serology and polymerase chain reaction testing of blood and spinal fluid. Antiviral therapy should be initiated early in the course of the illness.

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.

A brief on new waves of monkeypox and vaccines and antiviral drugs for monkeypox

Monkeypox virus (MPXV), genetic closely linked to the notorious variola (smallpox) virus, currently causes several clusters and outbreaks in the areas outside Africa and is noted to be phylogenetically related to the West African clade. To prepare for the upsurge of the cases of monkeypox in the Europe and North America, two vaccines, Jynneos® in the U.S. (Imvamune® in Canada or Imvanex® in the Europe) and ACAM2000® (Acambis, Inc.) initially developed in the smallpox eradication program, can provide protective immunity to monkeypox, and their production and availability are rapidly scaled up in the response to the emerging threat. So far, these two vaccines are recommended for people at a high risk for monkeypox, instead of universal vaccination. Tecovirimat, an inhibitor of extracellular virus formation, and brincidofovir, a lipid conjugate of cidofovir, both are in vitro and in vivo active against MPXV, and are suggested for immunocompromised persons, who are at risk to develop severe diseases. However, current general consensus in the response to the monkeypox outbreak among public health systems is early identification and isolation of infected patients to prevent its spread.

A Glance at the Development and Patent Literature of Tecovirimat: The First-in-Class Therapy for Emerging Monkeypox Outbreak

Monkeypox disease (MPX) is currently considered a global threat after COVID-19. European Medicines Agency (EMA) approved Tecovirimat in capsule dosage form (200 mg) as the first treatment for MPX in January 2022. This article highlights Tecovirimat’s development and patent literature review and is believed to benefit the scientists working on developing MPX treatments. The literature for Tecovirimat was gathered from the website of SIGA Technologies (developer of Tecovirimat), regulatory agencies (EMA, United States Food and Drug Administration (USFDA), and Health Canada), PubMed, and freely accessible clinical/patent databases. Tecovirimat was first recognized as an anti-orthopoxvirus molecule in 2002 and developed by SIGA Technologies. The USFDA and Health Canada have also recently approved Tecovirimat to treat smallpox in 2018 and 2021, respectively. The efficacy of Tecovirimat was verified in infected non-human primates (monkeys) and rabbits under the USFDA’s Animal Rule. Most clinical studies have been done on Tecovirimat’s safety and pharmacokinetic parameters. The patent literature has revealed inventions related to the capsule, injection, suspension, crystalline forms, amorphous form, and drug combinations (Tecovirimat + cidofovir) and process for preparing Tecovirimat. The authors foresee the off-label use of Tecovirimat in the USA and Canada for MPX and other orthopoxvirus infections. The authors also trust that there is immense scope for developing new Tecovirimat-based treatments (new drug combinations with other antivirals) for orthopoxvirus and other viral diseases. Drug interaction studies and drug resistance studies on Tecovirimat are also recommended. Tecovirimat is believed to handle the current MPX outbreak and is a new hope of biosecurity against smallpox or orthopoxvirus-related bioterrorism attack.

Therapeutic strategies to address monkeypox

Introduction

Monkeypox is a viral zoonosis, with symptoms similar to those seen in smallpox patients, although the clinical presentation may be less severe. Until recently, human monkeypox infection was rare, and primarily occurred in Central and West Africa.

Areas covered

An international outbreak began in May 2022, and monkeypox has now been detected on every continent except Antarctica. The first recognized case from the current outbreak was confirmed in the United Kingdom on 6 May 2022, in an adult with travel links to Nigeria, but it has been suggested that cases had been spreading in Europe for months. On 23 July 2022 the Director-General of the World Health Organization declared the monkeypox outbreak a public health emergency of international concern.

Expert opinion

There are no treatments specifically for monkeypox virus infections. However, monkeypox and smallpox viruses are genetically similar, and therapeutics developed to combat smallpox may be used to treat monkeypox. This manuscripts reviews what is known about these potential treatments, including tecovirimat and brincidofovir, based on a literature search of PubMed through 9 August 2022, and explores how these therapeutics may be used in the future to address the expanding monkeypox pandemic.

A PBPK Model of Ternary Cyclodextrin Complex of ST-246 Was Built to Achieve a Reasonable IV Infusion Regimen for the Treatment of Human Severe Smallpox

ST-246 is an oral drug against pathogenic orthopoxvirus infections. An intravenous formulation is required for some critical patients. A ternary complex of ST-246/meglumine/hydroxypropyl-β-cyclodextrin with well-improved solubility was successfully developed in our institute. The aim of this study was to achieve a reasonable intravenous infusion regimen of this novel formulation by a robust PBPK model based on preclinical pharmacokinetic studies. The pharmacokinetics of ST-246 after intravenous injection at different doses in rats, dogs, and monkeys were conducted to obtain clearances. The clearance of humans was generated by using the allometric scaling approach. Tissue distribution of ST-246 was conducted in rats to obtain tissue partition coefficients (K_p). The PBPK model of the rat was first built using in vivo clearance and K_p combined with in vitro physicochemical properties, unbound fraction, and cyclodextrin effect parameters of ST-246. Then the PBPK model was transferred to a dog and monkey and validated simultaneously. Finally, pharmacokinetic profiles after IV infusion at different dosages utilizing the human PBPK model were compared to the observed oral PK profile of ST-246 at therapeutic dosage (600 mg). The mechanistic PBPK model described the animal PK behaviors of ST-246 via intravenous injection and infusion with fold errors within 1.2. It appeared that 6h-IV infusion at 5 mg/kg BID produced similar C_max and AUC as oral administration at 600 mg. A PBPK model of ST-246 was built to achieve a reasonable regimen of IV infusion for the treatment of severe smallpox, which will facilitate the clinical translation of this novel formulation.

A human recombinant analogue to plasma-derived vaccinia immunoglobulin prophylactically and therapeutically protects against lethal orthopoxvirus challenge

Orthopoxviruses such as variola and monkeypox viruses continue to threaten the human population. Monkeypox virus is endemic in central and western Africa and outbreaks have reached as far as the U.S. Although variola virus, the etiologic agent of smallpox, has been eradicated by a successful vaccination program, official and likely clandestine stocks of the virus exist. Moreover, studies with ectromelia virus (the etiological agent of mousepox) have revealed that IL-4 recombinant viruses are significantly more virulent than wild-type viruses even in mice treated with vaccines and/or antivirals. For these reasons, it is critical that antiviral modalities are developed to treat these viruses should outbreaks, or deliberate dissemination, occur. Currently, 2 antivirals (brincidofovir and tecovirimat) are in the U.S. stockpile allowing for emergency use of the drugs to treat smallpox. Both antivirals have advantages and disadvantages in a clinical and emergency setting. Here we report on the efficacy of a recombinant immunoglobulin (rVIG) that demonstrated efficacy against several orthopoxviruses in vitro and in vivo in both a prophylactic and therapeutic fashion. A single intraperitoneal injection of rVIG significantly protected mice when given up to 14 days before or as late as 6 days post challenge. Moreover, rVIG reduced morbidity, as measured by weight-change, as well as several previously established biomarkers of disease. In rVIG treated mice, we found that vDNA levels in blood were significantly reduced, as was ALT (a marker of liver damage) and infectious virus levels in the liver. No apparent adverse events were observed in rVIG treated mice, suggesting the immunoglobulin is well tolerated. These findings suggest that recombinant immunoglobulins could be candidates for further evaluation and possible licensure under the FDA Animal Rule.

Asymmetric Intramolecular Dearomatization of Nonactivated Arenes with Ynamides for Rapid Assembly of Fused Ring System under Silver Catalysis

Arene dearomatization is a straightforward method for converting an aromatic feedstock into functionalized carbocycles. Enantioselective dearomatizations of chemically inert arenes, however, are quite limited and underexplored relative to those of phenols and indoles. We developed a method for diazo-free generation of silver-carbene species from an ynamide and applied it to the dearomatization of nonactivated arenes. Transiently generated norcaradiene could be trapped by intermolecular [4 + 2] cycloaddition, synthesizing polycycles with five consecutive stereogenic centers. This protocol constitutes the first highly enantioselective reaction based on the diazo-free generation of silver-carbene species. Mechanistic investigations revealed a dearomatization followed by two different classes of pericyclic reactions, as well as the origin of the chemo- and enantioselectivity.

An overview of tecovirimat for smallpox treatment and expanded anti-orthopoxvirus applications

Introduction

Tecovirimat (TPOXX®; ST-246) was approved for the treatment of symptomatic smallpox by the USFDA in July of 2018 and has been stockpiled by the US government for use in a smallpox outbreak. While there has not been a reported case of smallpox since 1978 it is still considered a serious bioterrorism threat.

Areas covered

A brief history of smallpox from its proposed origins as a human disease through its eradication in the late 20th century is presented. The current smallpox threat and the current public health response plans are described. The discovery, and development of tecovirimat through NDA submission and subsequent approval for treatment of smallpox are discussed. Google Scholar and PubMed were searched over all available dates for relevant publications.

Expert opinion

Approval of tecovirimat to treat smallpox represents an important milestone in biosecurity preparedness. Incorporating tecovirimat into the CDC smallpox response plan, development of pediatric liquid and intravenous formulations, and approval for post-exposure prophylaxis would provide additional health security benefit.

Tecovirimat shows broad efficacy against orthopoxviruses in vitro and in vivo and could be developed for use against emerging orthopoxvirus diseases such as monkeypox, vaccination-associated adverse events, and side effects of vaccinia oncolytic virus therapy.

Catalytic, Asymmetric Dearomative Synthesis of Complex Cyclohexanes via a Highly Regio- and Stereoselective Arene Cyclopropanation Using α-Cyanodiazoacetates

Arene cyclopropanation offers a direct route to higher-order, non-aromatic carbocycles; however, the inherent issue of dictating site selectivity has cumbered the development of novel intermolecular reactions that directly engage the arene pool. This paper describes a highly regio- and stereoselective, Rh₂[(S)-PTTL]₄-catalyzed arene cyclopropanation using α-cyanodiazoacetates to afford stable norcaradienes bearing three stereogenic centers, one of which is an all-carbon quaternary center. The enantioenriched norcaradienes served as tunable templates for further transformation into stereochemically dense, fused and bicyclic carbocycles containing transmutable functionality.

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.

Oral Tecovirimat for the Treatment of Smallpox

BACKGROUND

Smallpox was declared eradicated in 1980, but variola virus (VARV), which causes smallpox, still exists. There is no known effective treatment for smallpox; therefore, tecovirimat is being developed as an oral smallpox therapy. Because clinical trials in a context of natural disease are not possible, an alternative developmental path to evaluate efficacy and safety was needed.

METHODS

We investigated the efficacy of tecovirimat in nonhuman primate (monkeypox) and rabbit (rabbitpox) models in accordance with the Food and Drug Administration (FDA) Animal Efficacy Rule, which was interpreted for smallpox therapeutics by an expert advisory committee. We also conducted a placebo-controlled pharmacokinetic and safety trial involving 449 adult volunteers.

RESULTS

The minimum dose of tecovirimat required in order to achieve more than 90% survival in the monkeypox model was 10 mg per kilogram of body weight for 14 days, and a dose of 40 mg per kilogram for 14 days was similarly efficacious in the rabbitpox model. Although the effective dose per kilogram was higher in rabbits, exposure was lower, with a mean steady-state maximum, minimum, and average (mean) concentration (Cmax, Cmin, and Cavg, respectively) of 374, 25, and 138 ng per milliliter, respectively, in rabbits and 1444, 169, and 598 ng per milliliter in nonhuman primates, as well as an area under the concentration-time curve over 24 hours (AUC0-24hr) of 3318 ng×hours per milliliter in rabbits and 14,352 ng×hours per milliliter in nonhuman primates. These findings suggested that the nonhuman primate was the more conservative model for the estimation of the required drug exposure in humans. A dose of 600 mg twice daily for 14 days was selected for testing in humans and provided exposures in excess of those in nonhuman primates (mean steady-state Cmax, Cmin, and Cavg of 2209, 690, and 1270 ng per milliliter and AUC0-24hr of 30,632 ng×hours per milliliter). No pattern of troubling adverse events was observed.

CONCLUSIONS

On the basis of its efficacy in two animal models and pharmacokinetic and safety data in humans, tecovirimat is being advanced as a therapy for smallpox in accordance with the FDA Animal Rule. (Funded by the National Institutes of Health and the Biomedical Advanced Research and Development Authority; ClinicalTrials.gov number, NCT02474589 .).

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.

Co-administration of the broad-spectrum antiviral, brincidofovir (CMX001), with smallpox vaccine does not compromise vaccine protection in mice challenged with ectromelia virus

Natural orthopoxvirus outbreaks such as vaccinia, cowpox, cattlepox and buffalopox continue to cause morbidity in the human population. Monkeypox virus remains a significant agent of morbidity and mortality in Africa. Furthermore, monkeypox virus’s broad host-range and expanding environs make it of particular concern as an emerging human pathogen. Monkeypox virus and variola virus (the etiological agent of smallpox) are both potential agents of bioterrorism. The first line response to orthopoxvirus disease is through vaccination with first-generation and second-generation vaccines, such as Dryvax and ACAM2000. Although these vaccines provide excellent protection, their widespread use is impeded by the high level of adverse events associated with vaccination using live, attenuated virus. It is possible that vaccines could be used in combination with antiviral drugs to reduce the incidence and severity of vaccine-associated adverse events, or as a preventive in individuals with uncertain exposure status or contraindication to vaccination. We have used the intranasal mousepox (ectromelia) model to evaluate the efficacy of vaccination with Dryvax or ACAM2000 in conjunction with treatment using the broad spectrum antiviral, brincidofovir (BCV, CMX001). We found that co-treatment with BCV reduced the severity of vaccination-associated lesion development. Although the immune response to vaccination was quantifiably attenuated, vaccination combined with BCV treatment did not alter the development of full protective immunity, even when administered two days following ectromelia challenge. Studies with a non-replicating vaccine, ACAM3000 (MVA), confirmed that BCV’s mechanism of attenuating the immune response following vaccination with live virus was, as expected, by limiting viral replication and not through inhibition of the immune system. These studies suggest that, in the setting of post-exposure prophylaxis, co-administration of BCV with vaccination should be considered a first response to a smallpox emergency in subjects of uncertain exposure status or as a means of reduction of the incidence and severity of vaccine-associated adverse events.

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.

Safety and pharmacokinetics of the anti-orthopoxvirus compound ST-246 following a single daily oral dose for 14 days in human volunteers

ST-246 is being evaluated as a treatment for pathogenic orthopoxvirus infections in humans. To this end, a phase 2, double-blind, randomized, placebo-controlled, multicenter trial was conducted to assess the safety, tolerability, and pharmacokinetics (PK) of ST-246 when administered as a single daily oral dose (400 mg or 600 mg) for 14 days in fed adult volunteers. ST-246 was safe and well tolerated, with no deaths or serious adverse events reported during the study. There was a low incidence of treatment-emergent adverse events (TEAEs), the most common of which were mild nausea and headache. There were no clinically significant results from laboratory assessments, vital sign measurements, physical examinations, or electrocardiograms. The PK and dose proportionality of ST-246 were determined. The PK analysis showed that steady state was achieved by day 5 for the ST-246 400-mg treatment group and by day 6 for the 600-mg group. The dose proportionality analysis showed that the 400- and 600-mg ratio of dose-normalized peak drug concentration in plasma (C(max)) and relative exposure for each dosing interval (AUC(τ)) ranged from 80% to 85%. However, the 90% confidence intervals did not include 1.0, so dose proportionality could not be concluded. Overall, ST-246 was shown to be safe, and the PK was predictable. These results support further testing of ST-246 in a multicenter pivotal clinical safety study for licensure application.

Pharmacokinetic comparison of a single oral dose of polymorph form i versus form V capsules of the antiorthopoxvirus compound ST-246 in human volunteers

ST-246, a novel compound that inhibits egress of orthopoxvirus from mammalian cells, is being tested as a treatment for pathogenic orthopoxvirus infections in humans. This phase I, double-blind, randomized, crossover, exploratory study was conducted to compare the pharmacokinetics (PK) of a single daily 400-mg oral dose of ST-246 polymorph form I versus polymorph form V administered to fed, healthy human volunteers. Both forms appeared to be well tolerated, with no serious adverse events. The order of administration of the two forms had no effect on the results of the PK analyses. Form I and form V both exhibited comparable plasma concentration versus time profiles, but complete bioequivalence between the two forms was not found. Maximum drug concentration (C(max)) met the bioequivalence criteria, as the 90% confidence interval (CI) was 80.6 to 96.9%. However, the area under the concentration-time curve from time zero to time t (AUC(0-t)) and AUC(0-∞) did not meet the bioequivalence criteria (CIs of 67.8 to 91.0% and 73.9 to 104.7%, respectively). The extent of absorption of form I, as defined by AUC(0-∞), was 11.7% lower than that of form V. Since ST-246 form I is more thermostable than form V, form I was selected for further development and use in all future studies.

Deletion of the vaccinia virus F13L gene results in a highly attenuated virus that mounts a protective immune response against subsequent vaccinia virus challenge

Vaccinia virus F13L encodes the envelope protein p37, which is the target of the anti-pox virus drug ST-246 (Yang et al., 2005) and that is required for production of extracellular vaccinia virus. The F13L (p37)-deleted (and ST-246 resistant) vaccinia virus recombinant (Vac-ΔF13L) produced smaller plaques than the wild-type vaccinia (Western Reserve vaccinia). In addition, Vac-ΔF13L proved, when inoculated either intravenously or intracutaneously in both immunocompetent and immunodeficient (athymic nude or SCID) mice, to be severely attenuated. Intravenous or intracutaneous inoculation of immunocompetent mice with the ΔF13L virus efficiently protected against a subsequent intravenous, intracutaneous or intranasal challenge with vaccinia WR (Western Reserve). This was corroborated by the observation that Vac-ΔF13L induced a humoral immune response against vaccinia following either intravenous or intracutaneous challenge. In conclusion, F13L-deleted vaccinia virus may have the potential to be developed as a smallpox vaccine.

SP600125 inhibits Orthopoxviruses replication in a JNK1/2 -independent manner: Implication as a potential antipoxviral

The pharmacological inhibitor SP600125 [anthra(1,9-cd)pyrazol-6(2H)-one 1,9-pyrazoloanthrone] has been largely employed as a c-JUN N-terminal kinase (JNK1/2) inhibitor. In this study, we evaluated whether pretreatment with SP600125 was able to prevent Orthopoxviruses Vaccinia virus (VACV), Cowpox virus (CPXV) and modified Vaccinia virus Ankara (MVA) replication. We found that incubation with SP600125 not only blocked virus-stimulated JNK phosphorylation, but also, significantly reduced virus production. We observed 1-3 log decline in viral yield depending on the cell line infected (A31, BSC-40 or BHK-21). The reduction in viral yield correlated with a dramatic impact on virus morphogenesis progress, intracellular mature viruses (IMV) were barely detected. Despite the fact that SP600125 can act as an efficient anti-orthopoxviral compound, we also provide evidence that this antiviral effect is not specifically exerted through JNK1/2 inhibition. This conclusion is supported by the fact that viral titers measured after infections of JNK1/2 knockout cells were not altered as compared to those of wild-type cells. In contrast, a decline in viral titers was verified when the infection of KO cells was carried out in the presence of the pharmacological inhibitor. SP600125 has been the focus of recent studies that have evaluated its action on diverse viral infections including DNA viruses. Our data support the notion that SP600125 can be regarded as a potential antipoxviral compound.

Comparison of the safety and pharmacokinetics of ST-246® after i.v. infusion or oral administration in mice, rabbits and monkeys

BACKGROUND

ST-246® is an antiviral, orally bioavailable small molecule in clinical development for treatment of orthopoxvirus infections. An intravenous (i.v.) formulation may be required for some hospitalized patients who are unable to take oral medication. An i.v. formulation has been evaluated in three species previously used in evaluation of both efficacy and toxicology of the oral formulation.

METHODOLOGY/PRINCIPAL FINDINGS

The pharmacokinetics of ST-246 after i.v. infusions in mice, rabbits and nonhuman primates (NHP) were compared to those obtained after oral administration. Ten minute i.v. infusions of ST-246 at doses of 3, 10, 30, and 75 mg/kg in mice produced peak plasma concentrations ranging from 16.9 to 238 µg/mL. Elimination appeared predominately first-order and exposure dose-proportional up to 30 mg/kg. Short i.v. infusions (5 to 15 minutes) in rabbits resulted in rapid distribution followed by slower elimination. Intravenous infusions in NHP were conducted at doses of 1 to 30 mg/kg. The length of single infusions in NHP ranged from 4 to 6 hours. The pharmacokinetics and tolerability for the two highest doses were evaluated when administered as two equivalent 4 hour infusions initiated 12 hours apart. Terminal elimination half-lives in all species for oral and i.v. infusions were similar. Dose-limiting central nervous system effects were identified in all three species and appeared related to high C(max) plasma concentrations. These effects were eliminated using slower i.v. infusions.

CONCLUSIONS/SIGNIFICANCE

Pharmacokinetic profiles after i.v. infusion compared to those observed after oral administration demonstrated the necessity of longer i.v. infusions to (1) mimic the plasma exposure observed after oral administration and (2) avoid C(max) associated toxicity. Shorter infusions at higher doses in NHP resulted in decreased clearance, suggesting saturated distribution or elimination. Elimination half-lives in all species were similar between oral and i.v. administration. The administration of ST-246 was well tolerated as a slow i.v. infusion.

Severe ear chondritis due to cowpox virus transmitted by a pet rat

We describe a case of cowpox virus infection leading to severe acute inflammation and chondritis of the outer ear, complicated by local necrosis and facial cellulitis. Secondary lesions occurred on a finger and the abdomen. Apart from scarring, outcome was favorable after repeated surgical excision of necrotic tissue.

Development of the small-molecule antiviral ST-246 as a smallpox therapeutic

Naturally occurring smallpox has been eradicated, yet it remains as one of the highest priority pathogens due to its potential as a biological weapon. The majority of the US population would be vulnerable in a smallpox outbreak. SIGA Technologies, Inc. has responded to the call of the US government to develop and supply to the Strategic National Stockpile a smallpox antiviral to be deployed in the event of a smallpox outbreak. ST-246(®) (tecovirimat) was initially identified via a high-throughput screen in 2002, and in the ensuing years, our drug-development activities have spanned in vitro analysis, preclinical safety, pharmacokinetics and efficacy testing (all according to the 'animal rule'). Additionally, SIGA has conducted Phase I and II clinical trials to evaluate the safety, tolerability and pharmacokinetics of ST-246, bringing us to our current late stage of clinical development. This article reviews the need for a smallpox therapeutic and our experience in developing ST-246, and provides perspective on the role of a smallpox antiviral during a smallpox public health emergency.

Polycyclic N-benzamido imides with potent activity against vaccinia virus

The synthesis and antiviral activity of a series of novel polycyclic analogues of the orthopoxvirus egress inhibitor tecovirimat (ST-246) is presented. Several of these compounds display sub-micromolar activity against vaccinia virus, and were more potent than cidofovir (CDV). The more active compounds were about 10-fold more active than CDV, with minimum cytotoxic concentrations above 100 μM. Chemical manipulations of the two carbon-carbon double bonds present in the compounds were carried out to further explore the structure-activity relationships of these new polycyclic imides. Hydrogenation of the two carbon-carbon double bonds decreases antiviral activity, whereas either cyclopropanation or epoxidation of the double bonds fully eliminates the antiviral activity.

[Necrotic skin lesions caused by pet rats in two teenagers]

We report 2 observations in young girls who, after exposure to domestic rats from the same pet shop, presented with inflammatory and necrotic skin wounds in the neck and face. Since lesions did not improve with antibiotic therapy, surgical excision of necrosis healed the wounds, with a 2nd intervention necessary in 1 patient. All bacteriological investigations appeared to be negative; finally, electron microscopy of excised subepidermal tissue and PCR characterization provided the diagnosis of cowpox virus (CPXV) infection. CPXV is part of the Orthopox virus genus, like variola virus, and is generally transmitted to humans by infected cats or rodents. CPXV infection should be kept in mind when macular, vesicular, or necrotic cutaneous wounds do not improve with antibiotics.

Impact of ST-246® on ACAM2000™ smallpox vaccine reactogenicity, immunogenicity, and protective efficacy in immunodeficient mice

Although a highly effective vaccine against smallpox, vaccinia virus (VV) is not without adverse events, some of which can be life-threatening, particularly in immunocompromised individuals. We have recently demonstrated that the immunogenicity and protective efficacy of Dryvax(®) in immunocompetent mice is preserved even when co-administered with ST-246, an orally bioavailable small-molecule inhibitor of orthopoxvirus egress and dissemination. In addition, ST-246 markedly reduced the reactogenicity of the smallpox vaccine ACAM2000 and the highly neurovirulent VV strain Western Reserve (VV-WR). Here, we evaluated the impact of ST-246 co-administration on ACAM2000 reactogenicity, immunogenicity, and protective efficacy in seven murine models of varying degrees of humoral and cellular immunodeficiency: BALB/c and B-cell deficient (JH-KO) mice depleted of CD4(+) or CD8(+) or both subsets of T cells. We observed that ST-246 reduced vaccine lesion severity and time to complete resolution in all of the immunodeficient models examined, except in those lacking both CD4(+) and CD8(+) T cells. Although VV-specific humoral responses were moderately reduced by ST-246 treatment, cellular responses were generally comparable or slightly enhanced at both 1 and 6 months post-vaccination. Most importantly, in those models in which vaccination given alone conferred protection against lethal VV challenge, similar levels of protection were observed at both time points when vaccination was given with ST-246. These data suggest that, with the exception of individuals with irreversible, combined CD4(+) and CD8(+) T-cell deficiency, ST-246 co-administered at the time of vaccination may help reduce vaccine reactogenicity--even in those lacking humoral immunity--without impeding the induction of protective immunity.

Principles of antidote pharmacology: an update on prophylaxis, post-exposure treatment recommendations and research initiatives for biological agents

The use of biological agents has generally been confined to military-led conflicts. However, there has been an increase in non-state-based terrorism, including the use of asymmetric warfare, such as biological agents in the past few decades. Thus, it is becoming increasingly important to consider strategies for preventing and preparing for attacks by insurgents, such as the development of pre- and post-exposure medical countermeasures. There are a wide range of prophylactics and treatments being investigated to combat the effects of biological agents. These include antibiotics (for both conventional and unconventional use), antibodies, anti-virals, immunomodulators, nucleic acids (analogues, antisense, ribozymes and DNAzymes), bacteriophage therapy and micro-encapsulation. While vaccines are commercially available for the prevention of anthrax, cholera, plague, Q fever and smallpox, there are no licensed vaccines available for use in the case of botulinum toxins, viral encephalitis, melioidosis or ricin. Antibiotics are still recommended as the mainstay treatment following exposure to anthrax, plague, Q fever and melioidosis. Anti-toxin therapy and anti-virals may be used in the case of botulinum toxins or smallpox respectively. However, supportive care is the only, or mainstay, post-exposure treatment for cholera, viral encephalitis and ricin - a recommendation that has not changed in decades. Indeed, with the difficulty that antibiotic resistance poses, the development and further evaluation of techniques and atypical pharmaceuticals are fundamental to the development of prophylaxis and post-exposure treatment options. The aim of this review is to present an update on prophylaxis and post-exposure treatment recommendations and research initiatives for biological agents in the open literature from 2007 to 2009.

Inhibition of poxvirus spreading by the anti-tumor drug Gefitinib (Iressa)

The threat of smallpox virus as a bioterrorist weapon is raising international concerns again since the anthrax attacks in the USA in 2001. The medical readiness of treating patients suffering from such infections is a prerequisite of an effective civil defense system. Currently the only therapeutic option for the treatment of poxvirus infections relies on the virostatic nulceosid analog cidofovir, although severe side effects and drug resistant strains have been described. A growing understanding of poxvirus pathogenesis raises the possibility to explore other appropriate targets involved in the viral replication cycle. Poxvirus encoded growth factors such as the Vaccinia Growth Factor (VGF) stimulate host cells via the Epidermal Growth Factor Receptor (EGFR) and thereby facilitate viral spreading. In this study we could visualize for the first time the paracrine priming of uninfected cells for subsequent infection by orthopoxviruses directly linked to EGFR phosphorylation. Since EGFR is a well known target for anti-tumor therapy small molecules for inhibition of its tyrosine kinase (TK) activity are readily available and clinically evaluated. In this study we analyzed three different EGFR receptor tyrosine kinase inhibitors for inhibition of orthopoxvirus infection in epithelial cells. The inhibitor shown to be most effective was Gefitinib (Iressa) which is already approved as a drug for anti-tumor medication in the USA and in Europe. Thus Gefitnib may provide a new therapeutic option for single or combination therapy of acute poxvirus infections, acting on a cellular target and thus reducing the risk of viral resistance to treatment.

Update on new antivirals under development for the treatment of double-stranded DNA virus infections

All the currently available antiviral agents used in the treatment of double-stranded (ds) DNA viruses, with the exception of interferon-α, inhibit the same target, the viral DNA polymerase. With increasing reports of the development of resistance of herpes simplex virus (HSV), cytomegalovirus (CMV), and hepatitis B virus (HBV) to some of these drugs, new antiviral agents are needed to treat these infections. Additionally, no drugs have been approved to treat several DNA virus infections, including those caused by adenovirus, smallpox, molluscum contagiosum, and BK virus. We report the status of 10 new antiviral drugs for the treatment of dsDNA viruses. CMX-001 has broad activity against dsDNA viruses; 3 helicase-primase inhibitors, maribavir, and FV-100 have activity against certain herpesviruses; ST-246 inhibits poxviruses; GS-9191 inhibits papillomaviruses; and clevudine and emtricitabine are active against HBV. Most of these drugs have completed at least phase I trials in humans, and many are in additional clinical trials.

Development of ST-246® for Treatment of Poxvirus Infections

ST-246 (Tecovirimat) is a small synthetic antiviral compound being developed to treat pathogenic orthopoxvirus infections of humans. The compound was discovered as part of a high throughput screen designed to identify inhibitors of vaccinia virus-induced cytopathic effects. The antiviral activity is specific for orthopoxviruses and the compound does not inhibit the replication of other RNA- and DNA-containing viruses or inhibit cell proliferation at concentrations of compound that are antiviral. ST-246 targets vaccinia virus p37, a viral protein required for envelopment and secretion of extracellular forms of virus. The compound is orally bioavailable and protects multiple animal species from lethal orthopoxvirus challenge. Preclinical safety pharmacology studies in mice and non-human primates indicate that ST-246 is readily absorbed by the oral route and well tolerated with the no observable adverse effect level (NOAEL) in mice measured at 2000 mg/kg and the no observable effect level (NOEL) in non-human primates measured at 300 mg/kg. Drug substance and drug product processes have been developed and commercial scale batches have been produced using Good Manufacturing Processes (GMP). Human phase I clinical trials have shown that ST-246 is safe and well tolerated in healthy human volunteers. Based on the results of the clinical evaluation, once a day dosing should provide plasma drug exposure in the range predicted to be antiviral based on data from efficacy studies in animal models of orthopoxvirus disease. These data support the use of ST-246 as a therapeutic to treat pathogenic orthopoxvirus infections of humans.

Inhibition of poxvirus growth by Terameprocol, a methylated derivative of nordihydroguaiaretic acid

Terameprocol (TMP) is a methylated derivative of nordihydroguaiaretic acid, a phenolic antioxidant originally derived from creosote bush extracts. TMP has previously been shown to have antiviral and anti-inflammatory activities, and has been proven safe in phase I clinical trials conducted to evaluate TMP as both a topical and parenteral therapeutic. In the current study, we examined the ability of TMP to inhibit poxvirus growth in vitro, and found that TMP potently inhibited the growth of both cowpox virus and vaccinia virus in a variety of cell lines. TMP treatment was highly effective at reducing infectious virus yield in multi-step virus growth assays, but it did not substantially inhibit the synthesis of infectious progeny viruses in individual infected cells. These contrasting results showed that TMP inhibits poxvirus growth in vitro by preventing the efficient spread of virus particles from cell to cell. The canonical mechanism of poxvirus cell-to-cell spread requires morphogenesis of cell-associated, enveloped virions. The virions then trigger the formation of actin tails to project them from the cell surface. The number of actin tails present at the surface of poxvirus-infected cells was reduced dramatically by treatment with TMP. Whether TMP inhibits poxvirus morphogenesis, or subsequent events required for actin tail formation, remains to be determined. The results of this study, together with the clinical safety record of TMP, support further evaluation of TMP as a poxvirus therapeutic.