SARS Epidemiology Provides Clues to Potential Treatment for COVID-19

Mark S. Lesney

March 05, 2020

A team of researchers has discovered important commonalities between SARS-CoV-2 and SARS-CoV infection that could lead to a potential target for antiviral intervention.

Markus Hoffmann, of the Leibniz Institute for Primate Research, Göttingen, Germany, and a team of investigators also found that antibody responses raised against SARS-S during infection or vaccination might offer some level of protection against SARS-CoV-2 infection. Their findings were published in Cell.

In order for coronaviruses to enter a cell, they must first bind their viral spike (S) proteins to cellular receptors and depend on S protein priming by host cell proteases. The study found that the SARS-CoV-2, causal agent for COVID-19, uses the same SARS-CoV receptor, ACE2, for entry and uses the serine protease TMPRSS2 for S protein priming as the original SARS-CoV-1 (SARS). Importantly, the researchers also found that the cellular serine protease TMPRSS2 primes SARS-CoV-2-S for entry and that a serine protease inhibitor blocks SARS-CoV-2 infection of lung cells, providing opportunities for potential therapeutic intervention.

The researchers performed a sequence analysis that showed SARS-CoV-2 clusters with SARS-CoV–related viruses from bats, of which some — but not all — can use ACE2 for host cell entry. Further analysis of the receptor binding motif known to make contact with ACE2 showed that most amino acid residues essential for ACE2 binding by SARS-S were conserved in SARS-2-S but were absent from S proteins of those SARS-related coronaviruses previously found not to use ACE2.

In addition, the researchers found that SARS-CoV-2–infected BHK-21 cells transfected to express ACE2 with high efficiency, but not the parental BHK-21 cells indicating that SARS-CoV-2-S, like the original SARS virus S protein, uses ACE2 for cellular entry.

Using cultured cells, the researchers found that the protease inhibitor, camostat mesylate, inhibited SARS-S and SARS-2-S entry into primary human lung cells, demonstrating that SARS-CoV-2 can use TMPRSS2 for S protein priming and that camostat mesylate can block SARS-CoV-2 infection of lung cells. Camostat mesylate has been used as a therapy for some forms of cancer and other viral infections.

In addition to their research on the protease inhibitor, the researchers also found that sera from convalescent SARS patients cross-neutralized SARS-2-S–driven entry. They found that four sera obtained from three convalescent SARS patients inhibited SARS-S entry into cell lines in a concentration dependent fashion.

"We demonstrate that SARS-CoV-2 uses the SARS55 CoV receptor, ACE2, for entry and the serine protease TMPRSS2 for S protein priming. A TMPRSS2 inhibitor approved for clinical use blocked entry and might constitute a treatment option. Finally, we show that the sera from convalescent SARS patients cross-neutralized SARS-2-S–driven entry," the authors concluded.

The study was supported by BMBF (RAPID Consortium) and German Research Foundation (DFG). The authors reported that they had no conflicts.

Cell. Published online March 5, 2020. Full text

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