Title:The use of Pseudotyped Coronaviruses for the Screening of Entry
Inhibitors: Green Tea Extract Inhibits the Entry of SARS-CoV-1, MERSCoV,
and SARS-CoV-2 by Blocking Receptor-spike Interaction
Volume: 23
Issue: 8
Author(s): Jeswin Joseph, Thankamani Karthika, Valiyathara Rajan Akshay Das and Victor Stalin Raj*
Affiliation:
- Virology Scientific Research (VSR) Laboratory, School of Biology, Indian Institute of Science Education and Research (IISER-TVM), Thiruvananthapuram, India
Keywords:
SARS-CoV-2, SARS-CoV-1, MERS-CoV, antivirals, green tea, pseudoviruses.
Abstract:
Background: Coronaviruses (CoVs) infect a wide range of animals and birds. Their tropism
is primarily determined by the ability of the spike protein to bind to a host cell surface receptor. The
ongoing outbreak of SARS-CoV-2 inculcates the need for the development of effective intervention
strategies.
Objectives: In this study, we aim to produce pseudotyped coronaviruses of SARS-CoV-1, MERS-CoV,
and SARS-CoV-2 and show its applications, including virus entry, neutralization, and screening of
entry inhibitors from natural products.
Methods: Here, we generated VSV-based pseudotyped coronaviruses (CoV-PVs) for SARS-CoV-1,
MERS-CoV, and SARS-CoV-2. Recombinant spike proteins of SARS-CoV-1, MERS-CoV, and
SARS-CoV-2 were transiently expressed in HEK293T cells followed by infection with recombinant
VSV. High titer pseudoviruses were harvested and subjected to distinct validation assays, which
confirms the proper spike pseudotyping. Further, specific receptor-mediated entry was confirmed by
antibody neutralization and soluble form of receptor inhibition assay on Vero E6 cells. Next, these
CoV-PVs were used for screening of antiviral activity of natural products such as green tea and
Spirulina extract.
Results: Medicinal plants and natural compounds have been traditionally used as antiviral agents. In
the first series of experiments, we demonstrated that pseudotyped viruses specifically bind to their
receptors for cellular entry. SARS-CoV-1 and MERS-CoV anti-sera neutralize SARS-CoV-1-PV and
SARS-CoV-2-PV, and MERS-CoV-PV, respectively. Incubation of soluble ACE2 with CoV-PVs
inhibited entry of SARS-CoV-1 and SARS-CoV-2 PVs but not MERS-CoV-PV. Also, transient
expression of ACE2 and DPP4 in non-permissive BHK21 cells enabled infection by SARS-CoV-1-PV,
SARS-CoV-2-PV, and MERS-CoV-PV, respectively. Next, we showed the antiviral properties of
known entry inhibitors of enveloped viruses, Spirulina, and green tea extracts against CoV-PVs. SARSCoV-
1-PV, MERS-CoV-PV, and SARS-CoV-2-PV entry was blocked with higher efficiency when
preincubated with either green tea or Spirulina extracts. Green tea provided a better inhibitory effect by
binding to the S1 domain of the spike and blocking the spike interaction with its receptor.
Conclusion: In summary, we demonstrated that pseudotyped viruses are an ideal tool for studying viral
entry, quantification of neutralizing antibodies, and screening of entry inhibitors in a BSL-2 facility.
Moreover, green tea might be a promising natural remedy against emerging coronaviruses.