1 INTRODUCTION
Currently there are no licensed vaccines and limited antivirals for the treatment of COVID-19. Repurposing existing clinical drugs with proven safety profiles provides a rapid approach to address this gap in treatment. Throughout the COVID-19 pandemic anticoagulant drugs such as unfractionated heparin (UFH) and low molecular weight heparin (LMWH) delivered systemically, have been widely used across the world as part of standard treatment for patients in intensive care units (ICU). Use of these drugs has been shown to be effective for dealing with coagulopathies seen during the late stage of the disease (Kollias, Kyriakoulis et al., 2020; Tang, Li et al., 2020). Furthermore, heparin exhibits a wide range of anti-inflammatory properties (Mulloy, Hogwood et al., 2016), thus providing an additional rationale of its clinical use to treat the hyperinflammatory response observed in patients with COVID-19.
There is a recent and growing body of evidence suggesting that UFH has antiviral properties against SARS-CoV-2, the causative agent of COVID-19. UFH has been shown to bind to the receptor binding domain (RBD) of the SARS-CoV2 spike protein, which induces a conformational change (Mycroft-West, Su et al., 2020a) and also inhibits binding of spike protein to cells (Mycroft-West, Su et al., 2020b; Partridge, Green et al., 2020). Additional work with a pseudotyped assay indicated that UFH has an IC50 of 0.6 μg/ml (Tandon, Sharp et al., 2020). Recent studies, performed with live SARS-CoV-2 and Vero E6 cells, were limited to one heparin brand (Celsus, USA) and showed SARS-CoV-2 virus was inhibited by 44 - 80% with 6.25 μg - 200 μg/ml of UFHin vitro (Mycroft-West, Su et al., 2020b). Taking these interesting results together, there is an urgent need for a systematic assessment of the antiviral activity of a variety of clinically relevant heparins, in vitro , with live wild-type SARS-CoV-2, to establish the relative antiviral potencies of different heparins.
Independent from the systemic use of heparin in COVID-19 patients, nebulised heparin has also been proposed as a unique and potentially effective treatment for different stages of COVID-19 disease (van Haren, Page et al., 2020). In the UK a clinical trial evaluating the effectiveness of nebulised UFH in hospitalised COVID-19 patients is currently underway (https://accord-trial.org). The strategy underpinning this treatment stems from the positive observations made, based on anticoagulant and anti-inflammatory activity, when running trials of nebulised heparin in patients with acute lung injury and related conditions (van Haren, Page et al., 2020). The delivery of an aerosolised antiviral agent directly to the lungs where SARS-COV-2 virus is known to be present (both upper and lower respiratory tract) (Schaefer, Padera et al., 2020) may help to treat the alveolar coagulopathy that is often a feature of COVID-19, reduce the hyperinflammatory response and prevent patients from developing acute respiratory distress syndrome (ARDS) and pulmonary fibrosis (PF), the major complications of coronavirus infection.
Here we report for the first time a systematic assessment of the antiviral activity of a range of heparins (UFH and LMWH) in vitroagainst live wild-type SARS-CoV-2 thereby shedding light on the antiviral potency of a range of different heparin preparations, including the nebulised UFH already undergoing clinical trials in COVID-19 patients.