Protease inhibitors broadly effective against feline, ferret and mink coronaviruses

Potent small molecule inhibitors against the 3C protease of foot-and-mouth disease virus

Foot-and-mouth disease (FMD) is one of the most devastating diseases of livestock which can cause significant economic losses, especially when introduced to FMD-free countries. FMD virus (FMDV) belongs to the family Picornaviridae and is antigenically heterogeneous with seven established serotypes. The prevailing preventive and control strategies are limited to restriction of animal movement and elimination of infected or exposed animals, which can be potentially combined with vaccination. However, FMD vaccination has limitations including delayed protection and lack of cross-protection against different serotypes. Recently, antiviral drug use for FMD outbreaks has increasingly been recognized as a potential tool to augment the existing early response strategies, but limited research has been reported on potential antiviral compounds for FMDV. FMDV 3C protease (3Cpro) cleaves the viral-encoded polyprotein into mature and functional proteins during viral replication. The essential role of viral 3Cpro in viral replication and the high conservation of 3Cpro among different FMDV serotypes make it an excellent target for antiviral drug development. We have previously reported multiple series of inhibitors against picornavirus 3Cpro or 3C-like proteases (3CLpros) encoded by coronaviruses or caliciviruses. In this study, we conducted structure-activity relationship studies for our in-house focused compound library containing 3Cpro or 3CLpro inhibitors against FMDV 3Cpro using enzyme and cell-based assays. Herein, we report the discovery of aldehyde and α-ketoamide inhibitors of FMDV 3Cpro with high potency. These data inform future preclinical studies that are related to the advancement of these compounds further along the drug development pathway.IMPORTANCEFood-and-mouth disease (FMD) virus (FMDV) causes devastating disease in cloven-hoofed animals with a significant economic impact. Emergency response to FMD outbreaks to limit FMD spread is critical, and the use of antivirals may overcome the limitations of existing control measures by providing immediate protection for susceptible animals. FMDV encodes 3C protease (3Cpro), which is essential for virus replication and an attractive target for antiviral drug discovery. Here, we report a structure-activity relationship study on multiple series of protease inhibitors and identified potent inhibitors of FMDV 3Cpro. Our results suggest that these compounds have the potential for further development as FMD antivirals.

Immunoinformatics-aided rational design of a multi-epitope vaccine targeting feline infectious peritonitis virus

Feline infectious peritonitis (FIP) is a grave and frequently lethal ailment instigated by feline coronavirus (FCoV) in wild and domestic feline species. The spike (S) protein of FCoV assumes a critical function in viral ingress and infection, thereby presenting a promising avenue for the development of a vaccine. In this investigation, an immunoinformatics approach was employed to ascertain immunogenic epitopes within the S-protein of FIP and formulate an innovative vaccine candidate. By subjecting the amino acid sequence of the FIP S-protein to computational scrutiny, MHC-I binding T-cell epitopes were predicted, which were subsequently evaluated for their antigenicity, toxicity, and allergenicity through in silico tools. Our analyses yielded the identification of 11 potential epitopes capable of provoking a robust immune response against FIPV. Additionally, molecular docking analysis demonstrated the ability of these epitopes to bind with feline MHC class I molecules. Through the utilization of suitable linkers, these epitopes, along with adjuvants, were integrated to design a multi-epitope vaccine candidate. Furthermore, the stability of the interaction between the vaccine candidate and feline Toll-like receptor 4 (TLR4) was established via molecular docking and molecular dynamics simulation analyses. This suggests good prospects for future experimental validation to ascertain the efficacy of our vaccine candidate in inducing a protective immune response against FIP.

The research progress of SARS-CoV-2 main protease inhibitors from 2020 to 2022

The novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread worldwide. The main protease (M^pro) of SARS-CoV-2 plays a central role in viral replication and transcription and represents an attractive drug target for fighting COVID-19. Many SARS-CoV-2 M^pro inhibitors have been reported, including covalent and noncovalent inhibitors. The SARS-CoV-2 M^pro inhibitor PF-07321332 (Nirmatrelvir) designed by Pfizer has been put on the market. This paper briefly introduces the structural characteristics of SARS-CoV-2 M^pro and summarizes the research progress of SARS-CoV-2 M^pro inhibitors from the aspects of drug repurposing and drug design. These information will provide a basis for the drug development of treating the infection of SARS-CoV-2 and even other coronaviruses in the future.

Recent updates on the biological efficacy of approved drugs and potent synthetic compounds against SARS-CoV-2

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), also known as COVID-19, has triggered a global pandemic that has prompted severe public health concerns. Researchers worldwide are continuously trying to find options that could be effective against COVID-19. The main focus of research during the initial phase of the pandemic was to use the already approved drugs as supportive care, and efforts were made to find new therapeutic options. Nirmatrelvir (PF-07321332), a Pfizer chemical, recently received approval for usage in conjunction with ritonavir. This mini-review summarises the biological effectiveness of vital synthetic compounds and FDA-approved medications against SARS-CoV-2. Understanding how functional groups are included in the creation of synthetic compounds could help enhance the biological activity profile of those compounds to increase their efficacy against SARS-CoV-2. This opened the way for researchers to explore opportunities to develop better therapeutics by investigating synthetic analogs.

Potent Protease Inhibitors of Highly Pathogenic Lagoviruses: Rabbit Hemorrhagic Disease Virus and European Brown Hare Syndrome Virus

Rabbit hemorrhagic disease (RHD) and European brown hare syndrome (EBHS) are highly contagious diseases caused by lagoviruses in the Caliciviridae family. These infectious diseases are associated with high mortality and a serious threat to domesticated and wild rabbits and hares, including endangered species such as riparian brush rabbits (Sylvilagus bachmani riparius). In the United States (U.S.), only isolated cases of RHD had been reported until Spring 2020. However, RHD caused by GI.2/rabbit hemorrhagic disease virus (RHDV)2/b was unexpectedly reported in April 2020 in New Mexico and has subsequently spread to several U.S. states, infecting wild rabbits and hares and making it highly likely that RHD will become endemic in the U.S. Vaccines are available for RHD; however, there is no specific treatment for this disease. Lagoviruses encode a 3C-like protease (3CLpro), which is essential for virus replication and a promising target for antiviral drug development. We have previously generated focused small-molecule libraries of 3CLpro inhibitors and demonstrated the in vitro potency and in vivo efficacy of some protease inhibitors against viruses encoding 3CLpro, including caliciviruses and coronaviruses. Here, we report the development of the enzyme and cell-based assays for the 3CLpro of GI.1c/RHDV, recombinant GI.3P-GI.2 (RHDV2/b), and GII.1/European brown hare syndrome virus (EBHSV) as well as the identification of potent lagovirus 3CLpro inhibitors, including GC376, a protease inhibitor being developed for feline infectious peritonitis. In addition, structure-activity relationship study and homology modeling of the 3CLpro and inhibitors revealed that lagovirus 3CLpro share similar structural requirements for inhibition with other calicivirus 3CLpro. IMPORTANCE Rabbit hemorrhagic disease (RHD) and European brown hare syndrome (EBHS) are viral diseases that affect lagomorphs with significant economic and ecological impacts. RHD vaccines are available, but specific antiviral treatment for these viral infections would be a valuable addition to the current control measures. Lagoviruses encode 3C-like protease (3CLpro), which is essential for virus replication and an attractive target for antiviral drug discovery. We have screened and identified potent small-molecule inhibitors that block lagovirus 3CLpro in the enzyme- and cell-based assays. Our results suggest that these compounds have the potential for further development as antiviral drugs for lagoviruses.

Bio-Guided Isolation of SARS-CoV-2 Main Protease Inhibitors from Medicinal Plants: In Vitro Assay and Molecular Dynamics

Since the emergence of the pandemic of the coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the discovery of antiviral phytoconstituents from medicinal plants against SARS-CoV-2 has been comprehensively researched. In this study, thirty-three plants belonging to seventeen different families used traditionally in Saudi Arabia were tested in vitro for their ability to inhibit the SARS-CoV-2 main protease (M^PRO). Major constituents of the bio-active extracts were isolated and tested for their inhibition potential against this enzyme; in addition, their antiviral activity against the SARS-CoV-2 Egyptian strain was assessed. Further, the thermodynamic stability of the best active compounds was studied through focused comparative insights for the active metabolites regarding ligand–target binding characteristics at the molecular level. Additionally, the obtained computational findings provided useful directions for future drug optimization and development. The results revealed that Psiadia punctulata, Aframomum melegueta, and Nigella sativa extracts showed a high percentage of inhibition of 66.4, 58.7, and 31.5%, against SARS-CoV-2 M^PRO, respectively. The major isolated constituents of these plants were identified as gardenins A and B (from P. punctulata), 6-gingerol and 6-paradol (from A. melegueta), and thymoquinone (from N. sativa). These compounds are the first to be tested invitro against SARS-CoV-2 M^PRO. Among the isolated compounds, only thymoquinone (THY), gardenin A (GDA), 6-gingerol (GNG), and 6-paradol (PAD) inhibited the SARS-CoV-2 M^PRO enzyme with inhibition percentages of 63.21, 73.80, 65.2, and 71.8%, respectively. In vitro assessment of SARS-CoV-2 (hCoV-19/Egypt/NRC-03/2020 (accession number on GSAID: EPI_ISL_430820) revealed a strong-to-low antiviral activity of the isolated compounds. THY showed relatively high cytotoxicity and was anti-SARS-CoV-2, while PAD demonstrated a cytotoxic effect on the tested VERO cells with a selectivity index of CC₅₀/IC₅₀ = 1.33 and CC₅₀/IC₅₀ = 0.6, respectively. Moreover, GNG had moderate activity at non-cytotoxic concentrations in vitro with a selectivity index of CC₅₀/IC₅₀ = 101.3/43.45 = 2.3. Meanwhile, GDA showed weak activity with a selectivity index of CC₅₀/IC₅₀ = 246.5/83.77 = 2.9. The thermodynamic stability of top-active compounds revealed preferential stability and SARS-CoV-2 M^PRO binding affinity for PAD through molecular-docking-coupled molecular dynamics simulation. The obtained results suggest the treating potential of these plants and/or their active metabolites for COVID-19. However, further in-vivo and clinical investigations are required to establish the potential preventive and treatment effectiveness of these plants and/or their bio-active compounds in COVID-19.

Thiazole/Thiadiazole/Benzothiazole Based Thiazolidin-4-One Derivatives as Potential Inhibitors of Main Protease of SARS-CoV-2

Since the time of its appearance until present, COVID-19 has spread worldwide, with over 71 million confirmed cases and over 1.6 million deaths reported by the World Health Organization (WHO). In addition to the fact that cases of COVID-19 are increasing worldwide, the Delta and Omicron variants have also made the situation more challenging. Herein, we report the evaluation of several thiazole/thiadiazole/benzothiazole based thiazolidinone derivatives which were chosen from 112 designed derivatives by docking as potential molecules to inhibit the main protease of SARS-CoV-2. The contained experimental data revealed that among the fifteen compounds chosen, five compounds (k3, c1, n2, A2, A1) showed inhibitory activity with IC50 within the range of 0.01-34.4 μΜ. By assessing the cellular effects of these molecules, we observed that they also had the capacity to affect the cellular viability of human normal MRC-5 cells, albeit with a degree of variation. More specifically, k3 which is the most promising compound with the higher inhibitory capacity to SARS-CoV-2 protease (0.01 μΜ) affects in vitro cellular viability only by 57% at the concentration of 0.01 μM after 48 h in culture. Overall, these data provide evidence on the potential antiviral activity of these molecules to inhibit the main protease of SARS-CoV-2, a fact that sheds light on the chemical structure of the thiazole/thiadiazole/benzothiazole based thiazolidin-4-one derivatives as potential candidates for COVID-19 therapeutics.

Crystallization of Feline Coronavirus Mpro With GC376 Reveals Mechanism of Inhibition

Coronaviruses infect a variety of hosts in the animal kingdom, and while each virus is taxonomically different, they all infect their host via the same mechanism. The coronavirus main protease (Mpro, also called 3CLpro), is an attractive target for drug development due to its essential role in mediating viral replication and transcription. An Mpro inhibitor, GC376, has been shown to treat feline infectious peritonitis (FIP), a fatal infection in cats caused by internal mutations in the feline enteric coronavirus (FECV). Recently, our lab demonstrated that the feline drug, GC373, and prodrug, GC376, are potent inhibitors of SARS-CoV-2 Mpro and solved the structures in complex with the drugs; however, no crystal structures of the FIP virus (FIPV) Mpro with the feline drugs have been published so far. Here, we present crystal structures of FIPV Mpro-GC373/GC376 complexes, revealing the inhibitors covalently bound to Cys144 in the active site, similar to SARS-CoV-2 Mpro. Additionally, GC376 has a higher affinity for FIPV Mpro with lower nanomolar Ki values compared to SARS-CoV and SARS-CoV-2 Mpro. We also show that improved derivatives of GC376 have higher potency for FIPV Mpro. Since GC373 and GC376 represent strong starting points for structure-guided drug design, determining the crystal structures of FIPV Mpro with these inhibitors are important steps in drug optimization and structure-based broad-spectrum antiviral drug discovery.

Nanotechnology-based therapeutic formulations in the battle against animal coronaviruses: an update

Outbreak of infectious diseases imposes a serious threat to human population and also causes a catastrophic impact on global economy. Animal coronaviruses remain as one of the intriguing problems, known to cause deadly viral diseases on economically important animal population, and also these infections may spread to other animals and humans. Through isolation of the infected animals from others and providing appropriate treatment using antiviral drugs, it is possible to prevent the virus transmission from animals to other species. In recent times, antiviral drug-resistant strains are being emerged as a deadly virus which are known to cause pandemic. To overcome this, nanoparticles-based formulations are developed as antiviral agent which attacks the animal coronaviruses at multiple sites in the virus replication cycle. Nanovaccines are also being formulated to protect the animals from coronaviruses. Nanoformulations contain particles of one or more dimensions in nano-scale (few nanometers to 1000 nm), which could be inorganic or organic in nature. This review presents the comprehensive outline of the nanotechnology-based therapeutics formulated against animal coronaviruses, which includes the nanoparticles-based antiviral formulations and nanoparticles-based adjuvant vaccines. The mechanism of action of these nanoparticles-based antivirals against animal coronavirus is also discussed using relevant examples. In addition, the scope of repurposing the existing nano-enabled antivirals and vaccines to combat the coronavirus infections in animals is elaborated.

Improved SARS-CoV-2 Mpro inhibitors based on feline antiviral drug GC376: Structural enhancements, increased solubility, and micellar studies

Replication of SARS-CoV-2, the coronavirus causing COVID-19, requires a main protease (Mpro) to cleave viral proteins. Consequently, Mpro is a target for antiviral agents. We and others previously demonstrated that GC376, a bisulfite prodrug with efficacy as an anti-coronaviral agent in animals, is an effective inhibitor of Mpro in SARS-CoV-2. Here, we report structure-activity studies of improved GC376 derivatives with nanomolar affinities and therapeutic indices >200. Crystallographic structures of inhibitor-Mpro complexes reveal that an alternative binding pocket in Mpro, S4, accommodates the P3 position. Alternative binding is induced by polar P3 groups or a nearby methyl. NMR and solubility studies with GC376 show that it exists as a mixture of stereoisomers and forms colloids in aqueous media at higher concentrations, a property not previously reported. Replacement of its Na+ counter ion with choline greatly increases solubility. The physical, biochemical, crystallographic, and cellular data reveal new avenues for Mpro inhibitor design.

Two Inhibitors Against the 3C-Like Proteases of Swine Coronavirus and Feline Coronavirus

Coronaviruses (CoVs) are important human and animal pathogens that cause respiratory and gastrointestinal diseases. Porcine epidemic diarrhoea (PED), characterized by severe diarrhoea and vomiting in pigs, is a highly lethal disease caused by porcine epidemic diarrhoea virus (PEDV) and causes substantial losses in the swine industry worldwide. However, currently available commercial drugs have not shown great therapeutic effects. In this study, a fluorescence resonance energy transfer (FRET)-based assay was applied to screen a library containing 1,590 compounds and identified two compounds, 3-(aminocarbonyl)-1-phenylpyridinium and 2,3-dichloronaphthoquinone, that target the 3C-like protease (3CL^pro) of PEDV. These compounds are of low molecular weight (MW) and greatly inhibited the activity of this enzyme (IC₅₀ values were obtained in this study). Furthermore, these compounds exhibited antiviral capacity against another member of the CoV family, feline infectious peritonitis virus (FIPV). Here, the inhibitory effects of these compounds against CoVs on Vero cells and feline kidney cells were identified (with EC₅₀ values) and cell viability assays were performed. The results of putative molecular docking models indicate that these compounds, labeled compound 1 and compound 2, contact the conserved active sites (Cys144, Glu165, Gln191) of 3CL^pro via hydrogen bonds. These findings provide insight into the antiviral activities of compounds 1 and 2 that may facilitate future research on anti-CoV drugs.

N-Terminal Finger Stabilizes the S1 Pocket for the Reversible Feline Drug GC376 in the SARS-CoV-2 Mpro Dimer

The main protease (Mpro, also known as 3CL protease) of SARS-CoV-2 is a high priority drug target in the development of antivirals to combat COVID-19 infections. A feline coronavirus antiviral drug, GC376, has been shown to be effective in inhibiting the SARS-CoV-2 main protease and live virus growth. As this drug moves into clinical trials, further characterization of GC376 with the main protease of coronaviruses is required to gain insight into the drug's properties, such as reversibility and broad specificity. Reversibility is an important factor for therapeutic proteolytic inhibitors to prevent toxicity due to off-target effects. Here we demonstrate that GC376 has nanomolar Ki values with the Mpro from both SARS-CoV-2 and SARS-CoV strains. Restoring enzymatic activity after inhibition by GC376 demonstrates reversible binding with both proteases. In addition, the stability and thermodynamic parameters of both proteases were studied to shed light on physical chemical properties of these viral enzymes, revealing higher stability for SARS-CoV-2 Mpro. The comparison of a new X-ray crystal structure of Mpro from SARS-CoV complexed with GC376 reveals similar molecular mechanism of inhibition compared to SARS-CoV-2 Mpro, and gives insight into the broad specificity properties of this drug. In both structures, we observe domain swapping of the N-termini in the dimer of the Mpro, which facilitates coordination of the drug's P1 position. These results validate that GC376 is a drug with an off-rate suitable for clinical trials.

The preclinical inhibitor GS441524 in combination with GC376 efficaciously inhibited the proliferation of SARS-CoV-2 in the mouse respiratory tract

The unprecedented coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a serious threat to global public health. Development of effective therapies against SARS-CoV-2 is urgently needed. Here, we evaluated the antiviral activity of a remdesivir parent nucleotide analog, GS441524, which targets the coronavirus RNA-dependent RNA polymerase enzyme, and a feline coronavirus prodrug, GC376, which targets its main protease, using a mouse-adapted SARS-CoV-2 infected mouse model. Our results showed that GS441524 effectively blocked the proliferation of SARS-CoV-2 in the mouse upper and lower respiratory tracts via combined intranasal (i.n.) and intramuscular (i.m.) treatment. However, the ability of high-dose GC376 (i.m. or i.n. and i.m.) was weaker than GS441524. Notably, low-dose combined application of GS441524 with GC376 could effectively protect mice against SARS-CoV-2 infection via i.n. or i.n. and i.m. treatment. Moreover, we found that the pharmacokinetic properties of GS441524 is better than GC376, and combined application of GC376 and GS441524 had a synergistic effect. Our findings support the further evaluation of the combined application of GC376 and GS441524 in future clinical studies.

SARS-CoV-2 Seroprevalence in Household Domestic Ferrets (Mustela putorius furo)

Simple Summary

Animal infections with SARS-CoV-2 have been reported in different countries and several animal species have been proven to be susceptible to infection with SARS-CoV-2 both naturally or by experimental infection. Moreover, infections under natural conditions in more than 20 mink farms have been reported where humans could have been the source of infection for minks. However, little information is available about the susceptibility of pet animals under natural conditions and currently there is no SARS-CoV-2 epidemiological assessment occurrence in household ferrets. In this study, the presence of SARS-CoV-2 antibodies was evaluated in serum samples obtained from 127 household ferrets (Mustela putorius furo) in the Province of Valencia (Spain). Two ferrets tested positive to SARS-CoV-2 (1.57%) by in-house enzyme-linked immunosorbent assay based on receptor binding domain (RBD) of Spike antigen. Furthermore, anti-RBD SARS-CoV-2 antibodies persisted at detectable levels in a seropositive SARS-CoV-2 domestic ferret beyond 129 days since the first-time antibodies were detected. This study reports for the first time the evidence of household pet ferrets exposure to SARS-CoV-2 in Spain to date.

Abstract

Animal infections with SARS-CoV-2 have been reported in different countries and several animal species have been proven to be susceptible to infection with SARS-CoV-2 both naturally and by experimental infection. Moreover, infections under natural conditions in more than 20 mink farms have been reported where humans could have been the source of infection for minks. However, little information is available about the susceptibility of pet animals under natural conditions and currently there is no SARS-CoV-2 epidemiological assessment occurrence in household ferrets. In this study, the presence of SARS-CoV-2 antibodies was evaluated in serum samples obtained from 127 household ferrets (Mustela putorius furo) in the Province of Valencia (Spain). Two ferrets tested positive to SARS-CoV-2 (1.57%) by in-house enzyme-linked immunosorbent assay based on receptor binding domain (RBD) of Spike antigen. Furthermore, anti-RBD SARS-CoV-2 antibodies persisted at detectable levels in a seropositive SARS-CoV-2 domestic ferret beyond 129 days since the first time antibodies were detected. This study reports for the first time the evidence of household pet ferrets exposure to SARS-CoV-2 in Spain to date.

Coronaviruses Associated with the Superfamily Musteloidea

Among the animal superfamily Musteloidea, which includes those commonly known as mustelids, naturally occurring and species-specific alphacoronavirus infections have been observed in both mink (Mustela vison/Neovison vison) and domestic ferrets (Mustela putorius furo). Ferret systemic coronavirus (FRSCV), in particular, has been associated with a rare but fatal systemic disease. In recent months, it has become apparent that both minks and ferrets are susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a betacoronavirus and the cause of the coronavirus disease 2019 (COVID-19) pandemic. Several mink farms have experienced SARS-CoV-2 outbreaks, and experimental models have demonstrated susceptibility of ferrets to SARS-CoV-2. The potential for pet ferrets to become infected with SARS-CoV-2, however, remains elusive. During the 2002-2003 SARS epidemic, it was also apparent that ferrets were susceptible to SARS-CoV and could be utilized in vaccine development. From a comparative standpoint, understanding the relationships between different infections and disease pathogenesis in the animal superfamily Musteloidea may help elucidate viral infection and transmission mechanisms, as well as treatment and prevention strategies for coronaviruses.

COVID-19: What Should the General Practitioner Know?

BACKGROUND

SARS-CoV-2 infection is currently the most significant public health challenge. Its presentation ranges from mild to severe respiratory failure and septic shock. Rapid transmission of the virus is dangerous with a high possibility of life-threatening complications. Lack of treatment standards for SARS-CoV-2 is responsible for the current dilemma in clinical medicine.

METHODS

An electronic literature search was done using PubMed to gather information on the pathogenesis, transmission of infection, clinical symptoms, diagnosis, and therapeutic options for COVID-19. Search items included "SARS-CoV-2", "COVID-19" and "coronavirus infection".

RESULTS

In light of the current global crisis caused by SARS-CoV-2, the exchange of information within the scientific community should be quick and extremely transparent. Thus, this review presents the available information necessary for a general practitioner. Such presentation of data should allow the reader quick access to basic and crucial information related to epidemiology, viral transmission, clinical symptoms, diagnostics, treatment, and complications that may occur in the course of COVID-19.

CONCLUSION

Rapidly increasing amounts of information about the diagnosis and treatment of patients with SARS-CoV-2 allow a better understanding of the etiology and course of the infection. In the current epidemiological situation, readily accessible information helps minimize the time to acquire knowledge and focus on prevention methods, diagnostic and treatment options. Thus, this review highlights key issues related to SARS-CoV-2 infection and contains the most useful data for daily medical practice.

Protease inhibitor GC376 for COVID-19: Lessons learned from feline infectious peritonitis

The main protease (M^pro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an important therapeutic target as it plays a major role in the processing and maturation of the viral polyprotein. GC376 is a pre-clinical dipeptide-based protease inhibitor that has been previously used for managing feline infectious peritonitis virus (FIPV). Since both GC373 and GC376 have already been successfully used in treating animal coronavirus infection, they can be considered as strong drug candidates for COVID-19 in humans. GC376 is a broad-spectrum antiviral drug that inhibits M^pro of several viruses, including the coronaviruses like feline coronavirus, porcine epidemic diarrhoea virus, severe acute respiratory syndrome coronavirus, Middle East respiratory syndrome coronavirus, ferret, and mink coronavirus. However, further studies should be conducted to evaluate the potency, efficacy, and safety of these broad-spectrum M^pro inhibitors in patients with COVID-19. The lessons learned from the successful use of drug candidates for treating animal coronavirus infections will help us to develop framework for their use in human trials.

Drawing Comparisons between SARS-CoV-2 and the Animal Coronaviruses

The COVID-19 pandemic, caused by a novel zoonotic coronavirus (CoV), SARS-CoV-2, has infected 46,182 million people, resulting in 1,197,026 deaths (as of 1 November 2020), with devastating and far-reaching impacts on economies and societies worldwide. The complex origin, extended human-to-human transmission, pathogenesis, host immune responses, and various clinical presentations of SARS-CoV-2 have presented serious challenges in understanding and combating the pandemic situation. Human CoVs gained attention only after the SARS-CoV outbreak of 2002-2003. On the other hand, animal CoVs have been studied extensively for many decades, providing a plethora of important information on their genetic diversity, transmission, tissue tropism and pathology, host immunity, and therapeutic and prophylactic strategies, some of which have striking resemblance to those seen with SARS-CoV-2. Moreover, the evolution of human CoVs, including SARS-CoV-2, is intermingled with those of animal CoVs. In this comprehensive review, attempts have been made to compare the current knowledge on evolution, transmission, pathogenesis, immunopathology, therapeutics, and prophylaxis of SARS-CoV-2 with those of various animal CoVs. Information on animal CoVs might enhance our understanding of SARS-CoV-2, and accordingly, benefit the development of effective control and prevention strategies against COVID-19.

Feline coronavirus drug inhibits the main protease of SARS-CoV-2 and blocks virus replication

The main protease, M^pro (or 3CL^pro) in SARS-CoV-2 is a viable drug target because of its essential role in the cleavage of the virus polypeptide. Feline infectious peritonitis, a fatal coronavirus infection in cats, was successfully treated previously with a prodrug GC376, a dipeptide-based protease inhibitor. Here, we show the prodrug and its parent GC373, are effective inhibitors of the M^pro from both SARS-CoV and SARS-CoV-2 with IC₅₀ values in the nanomolar range. Crystal structures of SARS-CoV-2 M^pro with these inhibitors have a covalent modification of the nucleophilic Cys145. NMR analysis reveals that inhibition proceeds via reversible formation of a hemithioacetal. GC373 and GC376 are potent inhibitors of SARS-CoV-2 replication in cell culture. They are strong drug candidates for the treatment of human coronavirus infections because they have already been successful in animals. The work here lays the framework for their use in human trials for the treatment of COVID-19.

3C-like protease inhibitors block coronavirus replication in vitro and improve survival in MERS-CoV-infected mice

Coronavirus 3C-like proteases (3CLpro) are attractive therapeutic targets because they play a vital role in coronavirus replication. Rathnayake et al. now report a series of optimized coronavirus 3CLpro inhibitors that blocked replication of the human coronaviruses MERS-CoV and SARS-CoV-2 in cultured cells. Administration of a lead compound to a MERS-CoV mouse model demonstrated proof-of-concept efficacy. These findings suggest that this lead compound should be investigated further as a potential therapeutic for human coronavirus infection.

Pathogenic coronaviruses are a major threat to global public health, as exemplified by severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and the newly emerged SARS-CoV-2, the causative agent of coronavirus disease 2019 (COVID-19). We describe herein the structure-guided optimization of a series of inhibitors of the coronavirus 3C-like protease (3CLpro), an enzyme essential for viral replication. The optimized compounds were effective against several human coronaviruses including MERS-CoV, SARS-CoV, and SARS-CoV-2 in an enzyme assay and in cell-based assays using Huh-7 and Vero E6 cell lines. Two selected compounds showed antiviral effects against SARS-CoV-2 in cultured primary human airway epithelial cells. In a mouse model of MERS-CoV infection, administration of a lead compound 1 day after virus infection increased survival from 0 to 100% and reduced lung viral titers and lung histopathology. These results suggest that this series of compounds has the potential to be developed further as antiviral drugs against human coronaviruses.

Persistent infection and pancytopenia associated with ferret systemic coronaviral disease in a domestic ferret

Ferret systemic coronaviral disease (FSCD) is a well-established cause of mortality in domestic ferrets. We describe herein novel findings in a case of FSCD that was diagnosed and medically managed following virus detection by immunohistochemical (IHC) staining of surgical biopsy samples. Hematologic changes in this ferret suggested spread of the virus to the bone marrow, which was confirmed by IHC staining of a postmortem sample. Genotyping of the virus indicated that the virus grouped with alphacoronaviruses and was most closely related to ferret enteric coronavirus (FRECV) MSU-2. Our clinical case demonstrates that a FRECV MSU-2-like ferret coronavirus associated previously with the enteric pathotype may cause systemic disease, including bone marrow involvement causing persistent pancytopenia.

Current knowledge about the antivirals remdesivir (GS-5734) and GS-441524 as therapeutic options for coronaviruses

Recent international epidemics of coronavirus-associated illnesses underscore the urgent medical and public health need for vaccine development and regulatory body approved therapies. In particular, the current coronavirus disease 2019 (COVID-19) pandemic has quickly intensified interest in developing treatment options to mitigate impact on human life. Remdesivir (GS-5734™) is a broad-spectrum antiviral drug that is now being tested as a potential treatment for COVID-19 in international, multi-site clinical trials. Currently available evidence about the antiviral effects of remdesivir against coronaviruses is primarily based on in vitro and in vivo studies (including some on a chemically related compound, GS-441524™), which have demonstrated largely favorable findings. As the pandemic progresses, information from human compassionate use cases will continue to accumulate before the clinical trials are concluded. It is imperative for public health practitioners and the One Health community to stay up to date on the most promising potential therapeutic options that are under investigation. Thus, the purpose of this review is to synthesize the knowledge to date about remdesivir as a therapeutic option for coronaviruses, with a special focus on information relevant to the One Health community.