Identification of one peptide which inhibited infectivity of avian infectious bronchitis virus in vitro

Discovery of Antivirals Using Phage Display

The latest coronavirus disease outbreak, COVID-19, has brought attention to viral infections which have posed serious health threats to humankind throughout history. The rapid global spread of COVID-19 is attributed to the increased human mobility of today's world, yet the threat of viral infections to global public health is expected to increase continuously in part due to increasing human-animal interface. Development of antiviral agents is crucial to combat both existing and novel viral infections. Recently, there is a growing interest in peptide/protein-based drug molecules. Antibodies are becoming especially predominant in the drug market. Indeed, in a remarkably short period, four antibody therapeutics were authorized for emergency use in COVID-19 treatment in the US, Russia, and India as of November 2020. Phage display has been one of the most widely used screening methods for peptide/antibody drug discovery. Several phage display-derived biologics are already in the market, and the expiration of intellectual property rights of phage-display antibody discovery platforms suggests an increment in antibody drugs in the near future. This review summarizes the most common phage display libraries used in antiviral discovery, highlights the approaches employed to enhance the antiviral potency of selected peptides/antibody fragments, and finally provides a discussion about the present status of the developed antivirals in clinic.

Phage Display Technique as a Tool for Diagnosis and Antibody Selection for Coronaviruses

Phage display is one of the important and effective molecular biology techniques and has remained indispensable for research community since its discovery in the year 1985. As a large number of nucleotide fragments may be cloned into the phage genome, a phage library may harbour millions or sometimes billions of unique and distinctive displayed peptide ligands. The ligand–receptor interactions forming the basis of phage display have been well utilized in epitope mapping and antigen presentation on the surface of bacteriophages for screening novel vaccine candidates by using affinity selection-based strategy called biopanning. This versatile technique has been modified tremendously over last three decades, leading to generation of different platforms for combinatorial peptide display. The translation of new diagnostic tools thus developed has been used in situations arising due to pathogenic microbes, including bacteria and deadly viruses, such as Zika, Ebola, Hendra, Nipah, Hanta, MERS and SARS. In the current situation of pandemic of Coronavirus disease (COVID-19), a search for neutralizing antibodies is motivating the researchers to find therapeutic candidates against novel SARS-CoV-2. As phage display is an important technique for antibody selection, this review presents a concise summary of the very recent applications of phage display technique with a special reference to progress in diagnostics and therapeutics for coronavirus diseases. Hopefully, this technique can complement studies on host–pathogen interactions and assist novel strategies of drug discovery for coronaviruses.

Antiviral Peptides: Identification and Validation

Despite rapid advances in the human healthcare, the infection caused by certain viruses results in high morbidity and mortality accentuate the importance for development of new antivirals. The existing antiviral drugs are limited, due to their inadequate response, increased rate of resistance and several adverse side effects. Therefore, one of the newly emerging field “peptide-based therapeutics” against viruses is being explored and seems promising. Over the last few years, a lot of scientific effort has been made for the identification of novel and potential peptide-based therapeutics using various advanced technologies. Consequently, there are more than 60 approved peptide drugs available for sale in the market of United States, Europe, Japan, and some Asian countries. Moreover, the number of peptide drugs undergoing the clinical trials is rising gradually year by year. The peptide-based antiviral therapeutics have been approved for the Human immunodeficiency virus (HIV), Influenza virus and Hepatitis virus (B and C). This review enlightens the various peptide sources and the different approaches that have contributed to the search of potential antiviral peptides. These include computational approaches, natural and biological sources (library based high throughput screening) for the identification of lead peptide molecules against their target. Further the applications of few advanced techniques based on combinatorial chemistry and molecular biology have been illustrated to measure the binding parameters such as affinity and kinetics of the screened interacting partners. The employment of these advanced techniques can contribute to investigate antiviral peptide therapeutics for emerging infections.

Antiviral activity of phage display-selected peptides against Japanese encephalitis virus infection in vitro and in vivo

Japanese Encephalitis virus (JEV) is a zoonotic flavivirus that is the most significant etiological agent of childhood viral neurological infections. However, no specific antiviral drug is currently available to treat JEV infections. The JEV envelope (E) protein is a class II viral fusion protein that mediates host cell entry, making interference with the interaction between the E protein of JEV and its cognate receptors an attractive strategy for anti-JEV drug development. In this study, we identified a peptide derived from a phage display peptide library against the E protein of JEV, designated P1, that potentially inhibits in vitro and in vivo JEV infections. P1 inhibits JEV infection in BHK-21 cells with 50% inhibitory capacity at a concentration of 35.9 μM. The time-of-addition assay indicates that JEV replication is significantly inhibited during pre-infection and co-infection of P1 with JEV while post-infection treatments with P1 have very little impact on JEV proliferation, showing that P1 inhibits JEV infection at early stages and indicating the potential prophylactic effect of P1. We adapted an in vitro BiFC assay system and demonstrated that P1 interacts with JEV E proteins and blocks their entry into cells. We also evaluated the therapeutic efficacy of P1 in a lethal JEV mouse model exhibiting systemic and brain infections. Interestingly, P1 treatment protected C57BL/6 mice against mortality, markedly reduced the viral loads in blood and brain, and diminished the histopathological lesions in the brain cells. In addition to controlling systemic infection, P1 has a very low level of cytotoxicity and acts in a sequence-specific manner, as scrambled peptide sP1 does not show any antiviral activity. In conclusion, our in vitro and in vivo experimental findings show that P1 possesses antiviral activity against JEV infections, is safe to use, and has potential for further development as an antiviral treatment against JEV infections.

Phage-Displayed Peptides Selected to Bind Envelope Glycoprotein Show Antiviral Activity against Dengue Virus Serotype 2

Dengue virus is a growing public health threat that affects hundreds of million peoples every year and leave huge economic and social damage. The virus is transmitted by mosquitoes and the incidence of the disease is increasing, among other causes, due to the geographical expansion of the vector's range and the lack of effectiveness in public health interventions in most prevalent countries. So far, no highly effective vaccine or antiviral has been developed for this virus. Here we employed phage display technology to identify peptides able to block the DENV2. A random peptide library presented in M13 phages was screened with recombinant dengue envelope and its fragment domain III. After four rounds of panning, several binding peptides were identified, synthesized, and tested against the virus. Three peptides were able to block the infectivity of the virus while not being toxic to the target cells. Blind docking simulations were done to investigate the possible mode of binding, showing that all peptides appear to bind domain III of the protein and may be mostly stabilized by hydrophobic interactions. These results are relevant to the development of novel therapeutics against this important virus.

Characterization and utility of phages bearing peptides with affinity to porcine reproductive and respiratory syndrome virus nsp7 protein

High-affinity peptides to porcine reproductive and respiratory syndrome virus (PRRSV) nonstructural protein (nsp) 7 were identified using phage-display technology. Five 12-amino-acid peptide sequences were identified after six rounds of biopanning. A putative CD##WC motif was found in two different consensus peptides borne by phages 4 and 5. The peptides borne by phages 4, 5, and 6 were synthesized for subsequent experiments, according to the results of the binding assays. Immunofluorescence assay revealed that all these peptides recognized nsp7 in PRRSV-infected cells. Furthermore, the peptides demonstrated antiviral activities, with peptides 5 and 6 showing effective inhibition. Early peptide stimulation was associated with strong antiviral activity, and the inhibitory effects of the peptides were dose-dependent at 36 and 48 h post-infection. Peptide 5 was selected to detect the intracellular localization of nsp7 by confocal microscopy. This peptide had a similar effect to anti-nsp7 monoclonal antibody on nsp7. These results suggest that high-affinity peptides to PRRSV nsp7 could mimic the potential of nsp7 antibody as a diagnostic reagent for virus detection. Moreover, the peptides selected in this study represented a potentially effective antiviral candidate to inhibit PRRSV.

Phage display of combinatorial peptide libraries: application to antiviral research

Given the growing number of diseases caused by emerging or endemic viruses, original strategies are urgently required: (1) for the identification of new drugs active against new viruses and (2) to deal with viral mutants in which resistance to existing antiviral molecules has been selected. In this context, antiviral peptides constitute a promising area for disease prevention and treatment. The identification and development of these inhibitory peptides require the high-throughput screening of combinatorial libraries. Phage-display is a powerful technique for selecting unique molecules with selective affinity for a specific target from highly diverse combinatorial libraries. In the last 15 years, the use of this technique for antiviral purposes and for the isolation of candidate inhibitory peptides in drug discovery has been explored. We present here a review of the use of phage display in antiviral research and drug discovery, with a discussion of optimized strategies combining the strong screening potential of this technique with complementary rational approaches for identification of the best target. By combining such approaches, it should be possible to maximize the selection of molecules with strong antiviral potential.

Priming with a DNA vaccine and boosting with an inactivated vaccine enhance the immune response against infectious bronchitis virus

The methods of repeated immunization with inactivated vaccines have been used widely to increase antibody protection against infectious bronchitis virus (IBV). However, compared with DNA vaccines, these methods usually induce poor cellular responses. In the present study, specific pathogen-free (SPF) chickens were immunized intramuscularly with a DNA vaccine carrying the main IBV structural genes (pVAX1-S1, pVAX1-M, and pVAX1-N, respectively) and boosted with the IBV M41 strain inactivated vaccine to assess whether such a new strategy could enhance the immune responses against IBV. The protection efficacy of the DNA vaccine carrying different structural genes for priming was evaluated further. The chickens were immunized primely on day 7 and boosted 2 weeks later. After that, distribution of the DNA vaccine in vivo, the percentage of CD4+CD3+ and CD8+CD3+ subgroups of peripheral blood T-lymphocytes, and the specific IgG and virus neutralizing antibodies were measured. Chickens were then challenged by the nasal-ocular route with the IBV M41 strain 4 weeks after booster immunization. The results demonstrated that priming with a DNA vaccine encoding nucleocapsid protein (pVAX1-N) and boosting with the inactivated IBV vaccine led to the dramatic augmentation of humoral and cellular responses, and provided up to 86.7% rate of immune protection, providing an effective approach to protect chickens from IBV.

The immunoreactivity of a chimeric multi-epitope DNA vaccine against IBV in chickens

Epitope-based vaccines designed to induce cellular immune response and antibody responses specific for infectious bronchitis virus (IBV) are being developed as a means for increasing vaccine potency. In this study, we selected seven epitopes from the spike (S1), spike (S2), and nucleocapsid (N) protein and constructed a multi-epitope DNA vaccine. The 7-day-old chickens were immunized intramuscularly with multi-epitope DNA vaccine encapsulated by liposome and boosted two weeks later, and were challenged by virulent IBV strain five weeks post booster. The results showed that multi-epitope DNA vaccine led to a dramatic augmentation of humoral and cellular responses, and provided up to 80.0% rate of immune protection. The novel immunogenic chimeric multi-epitope DNA vaccine revealed in this study provided a new candidate target for IBV vaccine development.

Infection of HeLa cells by avian infectious bronchitis virus is dependent on cell status

To investigate the adaptation of avian infectious bronchitis virus (IBV) in a human cell line may be beneficial to understanding the potential mechanisms of coronavirus interspecies infection. The current study addressed the poor replication of IBV in the HeLa human cell line demonstrated in previous reports. We showed that IBV strains M41, H52, H120 and Gray could be propagated in HeLa cells with distinct cytopathic effect. The virus titre in freshly dispersed HeLa cells was 1000-fold higher than in cell monolayers. Trypsin was not the determinant for the viral replication, suggesting that the restriction of IBV replication in HeLa cells is the result of intracellular events rather than the binding to or fusion with host cells. These IBV strains replicated to an average titre of 10(3.4+/-0.2)/0.1 ml median tissue culture infectious doses in freshly dispersed HeLa cells and maintained this titre for the first 12 passages. Then an approximately 10-fold increase (10(4.20+/-0.19)/0.1 ml) occurred in passage 13, which was maintained to passage 16, after which there was another, bigger rise to 10(6.6+/-0.3)/0.1 ml in passage 17. This titre was maintained until passage 24 when the experiment was terminated. The IBV M41 S1 gene was amplified and sequenced for passages 0, 5 and 21. There was only one amino acid replacement in the S1 protein, in passage 21. The presence of sialic acid on HeLa cells contributed to efficient virus replication, while human aminopeptidase N was not involved in the infection. Haemagglutinin activity gradually reduced with increased passages. These results indicated that the virus adaptation would probably be determined by host cell modification such as receptor glycosylation and different receptor utilization instead of viral gene mutation.