Tracking Live Virus by Targeting the Fusion Intermediate of Six-Helix Boundle Of  SARS-CoV-2

Abstract

Background: Molecular imaging specifically detecting SARS-CoV-2 in live subjects may aid theranostics for Coronavirus Disease 2019 (COVID-19). Herein, we developed novel molecular probes, Cy5-EK1 and [64 Cu]-NOTA-EK1, based on 36-mer EK1 peptide derived from the S2 subunit of spike (S) protein of SARS-CoV-2, an element of the six-helix bundle of S-protein for virus entry in vivoMethods: Enzyme-linked immunosorbent assay (ELISA) and immunostaining were performed to evaluate the potency of binding between these probes and recombinant full-length S-protein in vitro. HEK293 cells expressing S-protein of SARS-CoV-2 tumor-bearing mouse models were established to test the imaging target engagement in vivo.Findings: The potency of binding between NOTA-EK1 and S-protein was very strong, for which K d was 3.56 ± 0.38 nM and IC50 was 15.7 ± 0.6 nM. The uptake of [64Cu]-NOTA-EK1 in S-protein-positive tumors was greatly increased as early as 1 h post-injection and maintained at a high level until 24 h, while no signal was observed for S-protein-negative tumors. These differences were further confirmed by ex vivo imaging from both fluorescence and PET post-imaging studies. Immunofluorescent staining confirmed the colocalization of Cy5-EK1 with cell surface S-protein of SARS-CoV-2 in S-protein-positive HEK293 cells.Interpretation: Cy5-EK1 and [ 64Cu]-NOTA-EK1 could be used as specific molecular imaging probes for tracking SARS-CoV-2, which may have potential for the imaging and quantification of COVID-19 in a clinical context.Funding: This work was financially supported by the National Key R&D Program of China (2018YFC0910600).Declaration of Interest: None to declare. Ethical Approval: All animal experiments were carried out in accordance with the Institutional Ethical Guidelines for Animal Experiments of the Fifth Affiliated Hospital of Sun Yat-sen University(approval number: 00065).