Synthetic Heparan Sulfate Mimetic Pixatimod (PG545) Potently Inhibits SARS-CoV-2 By Disrupting The Spike-ACE2 interaction

Heparan sulfate (HS) is a cell surface polysaccharide recently identified as a co-receptor with the ACE2 protein for recognition of the S1 spike protein on SARS-CoV2 virus, revealing an attractive new target for therapeutic intervention. Clinically-used heparins demonstrate relevant inhibitory activity, but world supplies are limited, necessitating a synthetic solution. The HS mimetic pixatimod is synthetic drug candidate for cancer with immunomodulatory and heparanase-inhibiting properties. Here we show that pixatimod binds directly to the SARS-CoV-2 spike protein receptor binding domain (S1-RBD), altering its conformation and destabilizing its structure. Molecular modelling identified a binding site overlapping with the ACE2 receptor site. Consistent with this, pixatimod inhibits binding of S1-RBD to ACE2-expressing cells and displays a direct mechanism of action by inhibiting binding of S1-RBD to human ACE2. Assays with four different clinical isolates of live SARS-CoV-2 virus show that pixatimod potently inhibits infection of Vero cells at doses well within its safe therapeutic dose range. This demonstration of potent anti-SARS-CoV-2 activity establishes that synthetic HS mimetics can target the HS-Spike protein-ACE2 axis. Together with other known activities of pixatimod our data provides a strong rationale for its further investigation as a potential multimodal therapeutic to address the COVID-19 pandemic.