Unfractionated heparin inhibits live wild-type SARS-CoV-2 cell infectivity at therapeutically relevant concentrations.

Background and purpose Currently there are no licensed vaccines and limited antivirals for the treatment of COVID-19. Heparin (delivered systemically) is currently used to treat anticoagulant anomalies in COVID-19 patients. In addition, in the UK, Brazil and Australia, nebulised unfractionated heparin (UFH) is being trialled in COVID-19 patients as a potential treatment. A systematic comparison of the potential antiviral effect of various heparin preparations on live wild-type SARS-CoV-2, in vitro, is needed. Experimental approach Seven different heparin preparations including UFH and low molecular weight heparins (LMWH) of porcine or bovine origin were screened for antiviral activity against live SARS-CoV-2 (Australia/VIC01/2020) using a plaque inhibition assay with Vero E6 cells. Interaction of heparin with spike protein RBD was studied using differential scanning fluorimetry, and the inhibition of RBD binding to human ACE2 protein using ELISA assays was examined. Key results All the UFH preparations had potent antiviral effects, with IC50 values ranging between 25-41 μg ml-1 whereas LMWHs were less inhibitory by ~150-fold (IC50 range 3.4 - 7.8 mg ml-1 ). Mechanistically we observed that heparin binds and destabilizes the RBD protein, and furthermore we show heparin directly inhibits the binding of RBD to the human ACE2 protein receptor. Conclusions and implications This comparison of clinically relevant heparins shows UFH has significantly stronger SARS-CoV-2 antiviral activity compared to LMWHs. UFH acts to directly inhibit binding of spike protein to the human ACE2 protein receptor. Overall the data strongly support further clinical investigation of UFH as a potential treatment for patients with COVID-19.