The Bottlenecks of Preparing Virus Particles by Size Exclusion for Antibody Generation.

Enterovirus 71 (EV71) is the major etiological agent contributing to the development of hand-foot-mouth disease (HFMD). There are not any global available vaccines or antibody drugs against EV71 released yet. In this study, we perform the virus immunization in a cost-effective and convenient approach by preparing virus particles from size exclusion and immunization of chicken. Polyclonal yolk-immunoglobulin (IgY) was simply purified from egg yolk and monoclonal single-chain variable fragments (scFv) were selected via phage display technology with two scFv libraries containing 6.0 × 106 and 1.3 × 107 transformants. Specific clones were enriched after 5 rounds of bio-panning and four identical genes were classified after the sequence analysis. Moreover, the higher mutation rates were revealed in the CDR regions, especially in the CDR3. IgY showed specific binding activities to both EV71-infected and Coxsackievirus 16-infected cell lysates and high infectivity inhibitory activity of EV71. However, while IgY detected a 37 kDa protein, the selected scFv seemingly detected higher size proteins which could be cell protein instead of EV71 proteins. Despite the highly effective chicken antibody generation, the purity of virus particles prepared by size exclusion is the limitation of this study, and further characterization should be carried out rigorously.

In Vitro Characterization of Neutralizing Hen Antibodies to Coxsackievirus A16.

Coxsackievirus A16 (CA16) is one of the major causative agents of hand, foot, and mouth disease (HFMD). Children aged <5 years are the most affected by CA16 HFMD globally. Although clinical symptoms of CA16 infections are usually mild, severe complications, such as aseptic meningitis or even death, have been recorded. Currently, no vaccine or antiviral therapy for CA16 infection exists. Single-chain variable fragment (scFv) antibodies significantly inhibit viral infection and could be a potential treatment for controlling the infection. In this study, scFv phage display libraries were constructed from splenocytes of a laying hen immunized with CA16-infected lysate. The pComb3X vector containing the scFv genes was introduced into ER2738 Escherichia coli and rescued by helper phages to express scFv molecules. After screening with five cycles of bio-panning, an effective scFv antibody showing favorable binding activity to proteins in CA16-infected lysate on ELISA plates was selected. Importantly, the selected scFv clone showed a neutralizing capability against the CA16 virus and cross-reacted with viral proteins in EV71-infected lysate. Intriguingly, polyclonal IgY antibody not only showed binding specificity against proteins in CA16-infected lysate but also showed significant neutralization activities. Nevertheless, IgY-binding protein did not cross-react with proteins in EV71-infected lysate. These results suggest that the IgY- and scFv-binding protein antibodies provide protection against CA16 viral infection in in vitro assays and may be potential candidates for treating CA16 infection in vulnerable young children.

Effect of a Neuropilin-1-Derived Virus Receptor Trap on Enterovirus A71 Infection In Vitro.

We discovered that neuropilin 1 (NRP1) is a new receptor candidate to mediate enterovirus A71 (EVA71) into cells. In the engineered form as a decoy receptor, NRP1 was able to recognize and neutralize EVA71 but not enterovirus D68 or coxsackievirus B3 (CVB3). NRP1 recognizes EVA71 through a novel domain on the VP3 capsid protein. The principle in the design, engineering, and refinement of the NRP1-based decoy receptor described in this study represents a general and well-suited antiviral strategy.

Antiviral Activity of a Llama-Derived Single-Domain Antibody against Enterovirus A71.

In the past few decades, enterovirus A71 (EVA71) has caused devastating outbreaks in the Asia-Pacific region, resulting in serious sequelae in infected young children. No preventive or therapeutic interventions are currently available for curing EVA71 infection, highlighting a great unmet medical need for this disease. Here, we showed that one novel single-domain antibody (sdAb), F1, isolated from an immunized llama, could alleviate EVA71 infection both in vitro and in vivo We also confirmed that the sdAb clone F1 recognizes EVA71 through a novel conformational epitope comprising the highly conserved region of VP3 capsid protein by using competitive-binding and overlapping-peptide enzyme-linked immunosorbent assays (ELISAs). Because of the virion's icosahedral structure, we reasoned that adjacent epitopes must be clustered within molecular ranges that may be simultaneously bound by an engineered antibody with multiple valency. Therefore, two single-domain binding modules (F1) were fused to generate an sdAb-in-tandem design so that the capture of viral antigens could be further increased by valency effects. We showed that the tetravalent construct F1×F1-hFc, containing two sdAb-in-tandem on a fragment crystallizable (Fc) scaffold, exhibits more potent neutralization activity against EVA71 than does the bivalent sdAb F1-hFc by at least 5.8-fold. We also demonstrated that, using a human scavenger receptor class B member 2 (hSCARB2) transgenic mouse model, a half dose of the F1×F1-hFc provided better protection against EVA71 infection than did the F1-hFc. Thus, our study furnishes important insights into multivalent sdAb engineering against viral infection and provides a novel strategic deployment approach for preparedness of emerging infectious diseases such as EVA71.

Engineering a novel IgG-like bispecific antibody against enterovirus A71.

Frequent outbreaks of enterovirus A71 (EVA71) occur in the Asia-Pacific area, and these are closely associated with severe neurological symptoms in young children. No effective antiviral therapy is currently available for the treatment of EVA71 infection. The development of monoclonal antibodies (mAbs) has demonstrated promise as a novel therapy for the prevention and treatment of infectious diseases. Several medical conditions have been treated using bispecific or multi-specific antibodies that recognize two or more distinct epitopes simultaneously. However, bispecific or multi-specific antibodies often encounter protein expression and product stability problems. In this study, we developed an IgG-like bispecific antibody (E18-F1) comprising two anti-EVA71 antibodies: E18 mAb and llama-derived F1 single-domain antibody. E18-F1 was demonstrated to exhibit superior binding affinity and antiviral activity compared with E18 or F1. Additionally, E18-F1 not only improved survival rate, but also reduced clinical signs in human SCARB2 receptor (hSCARB2) transgenic mice challenged with a lethal dose of EVA71. Altogether, our results reveal that E18-F1 is a simple format bispecific antibody with promising antiviral activity for EVA71.

Design, synthesis, and antipicornavirus activity of 1-[5-(4-arylphenoxy)alkyl]-3-pyridin-4-ylimidazolidin-2-one derivatives.

A series of pyridylimidazolidinone derivatives was synthesized and tested in vitro against enterovirus 71 (EV71). On the basis of compound 33 (DBPR103), introduction of a methyl group at the 2- or 3-position of the linker between the imidazolidinone and the biphenyl resulted in markedly improved antiviral activity toward EV71 with IC(50) values of 5.0 nM (24b) and 9.3 nM (14a), respectively. Increasing the branched chain to propyl resulted in a progressive decrease in activity, while inserting different heteroatoms entirely rendered the compound only weakly active. The introduction of a bulky group (cyclohexyl, phenyl, or benzyl) led to loss of activity against EV71. The 4-chlorophenyl moiety in 14a was replaced with bioisosteric groups such as oxadiazole (28a-d) or tetrazole (32a,b), dramatically improving anti-EV71 activity and selectivity indices. Compounds 14a, 24b, 28b, 28d, and 32a exhibited a strong activity against lethal EV71, and no apparent cellular toxicity was observed. Three of the more potent imidazolidinone compounds, 14a, 28b, and 32b, were subjected to a large group of picornaviruses to determine their spectrum of antiviral activity.

Mutation in enterovirus 71 capsid protein VP1 confers resistance to the inhibitory effects of pyridyl imidazolidinone.

Enterovirus 71 is one of the most important pathogens in the family of Picornaviridae that can cause severe complications in the postpoliovirus era, such as encephalitis, pulmonary edema, and even death. Pyridyl imidazolidinone is a novel class of potent and selective human enterovirus 71 inhibitor. Pyridyl imidazolidinone was identified by using computer-assisted drug design. This virologic investigation demonstrates that BPR0Z-194, one of the pyridyl imidazolidinones, targets enterovirus 71 capsid protein VP1. Time course experiments revealed that BPR0Z-194 effectively inhibited virus replication in the early stages, implying that the compound can inhibit viral adsorption and/or viral RNA uncoating. BPR0Z-194 was used to select and characterize the drug-resistant viruses. Sequence analysis of the VP1 region showed that the resistant variants differed consistently by seven amino acids in VP1 region from their parental drug-sensitive strains. Site-directed mutagenesis of enterovirus 71 infectious cDNA revealed that a single amino acid alteration at the position 192 of VP1 can confer resistance to the inhibitory effects of BPR0Z-194.

Design, synthesis, and structure-activity relationships of pyrazolo[3,4-d]pyrimidines: a novel class of potent enterovirus inhibitors.

A series of pyrazolo[3,4-d]pyrimidines were synthesized and their antiviral activity was evaluated in a plaque reduction assay. It is very interesting that this class of compounds provide remarkable evidence that they are very specific for human enteroviruses, in particular, coxsackieviruses. Some derivatives proved to be highly effective in inhibiting enterovirus replication at nanomolar concentrations. SAR studies revealed that the phenyl group at the N-1 position and the hydrophobic diarylmethyl group at the piperazine largely influenced the in vitro antienteroviral activity of this new class of potent antiviral agents. It was found that the pyrazolo[3,4-d]pyrimidines with a thiophene substituent, such as compounds 20-24, in general exhibited high activity against coxsackievirus B3 (IC(50) = 0.063-0.089 microM) and moderate activity against enterovirus 71 (IC(50) = 0.32-0.65 microM) with no apparent cytotoxic effect toward RD (rhabdomyosarcoma) cell lines (CC(50) > 25 microM).

Design, synthesis, and structure-activity relationship of pyridyl imidazolidinones: a novel class of potent and selective human enterovirus 71 inhibitors.

When skeletons of Win compounds were used as templates, computer-assisted drug design led to the identification of a novel series of imidazolidinone derivatives with significant antiviral activity against enterovirus 71 (EV 71), the infection of which had resulted in about 80 fatalities during the 1998 epidemic outbreak in Taiwan. In addition to inhibiting all the genotypes (A, B, and C) of EV 71 in the submicromolar to low micromolar range, compounds 1 and 8 were extensively evaluated against a variety of viruses, showing potent activity against coxsackievirus A9 (IC(50) = 0.47-0.55 microM) and coxsackievirus A24 (IC(50) = 0.47-0.55 microM) as well as moderate activity against enterovirus 68 (IC(50) = 2.13 microM) and echovirus 9 (IC(50) = 2.6 microM). Our SAR studies revealed that imidazolidinone analogues with an aryl substituent at the para position of the phenoxyl ring, such as compounds 20, 21, 27, 57, 58, and 61, in general exhibited the highest activity against EV 71. Among them, compound 20 and its corresponding hydrochloride salt 57, in terms of potency and selectivity index, appear to be the most promising candidates in this series for further development of anti-EV-71 agents. Preliminary results of the study on the mode of action by a time-course experiment suggest that test compounds 1 and 8 can effectively inhibit the virus replication at the early stages, referring to virus attachment or uncoating. This indicates that the surface protein may be the target for this type of compounds.