- Proteins and Peptides
- Lysates and Cell Lines
By Jamshed Arslan, Pharm. D., PhD.
Coronaviruses are a family of enveloped RNA viruses. Some family members circulate in human populations, but others like severe acute respiratory syndrome coronavirus (SARS-CoV) are transmitted from animals to humans. A new strain of coronaviruses called novel coronavirus (nCOV) or SARS-CoV-2 is also transmitted zoonotically. SARS-CoV-2 has caused a global infectious disease called COVID-19. A person catches this notorious illness when he/she comes in contact with respiratory droplets from an infected person. SARS-CoV-2 in cough or sneeze droplets can survive on surfaces for several days. The most common symptoms of COVID-19 are dry cough, fever, tiredness and difficulty breathing. Good news is that 80% of the infected people recover without any special treatment, but sadly, we do not have any approved antiviral drug or vaccine against SARS-CoV-2. Similar to the strategies adopted during the SARS epidemic of 2002/2003, authorities are trying to halt COVID-19 by travel restrictions and patient isolation. However, an antiviral breakthrough might be our best bet against the COVID-19 pandemic.
Coronaviruses use their spike (S) protein to enter the target cell. The S protein binds to a cellular receptor to facilitate viral attachment to the target cell surface. The consequent viral entry depends on S protein priming. As far as SARS-CoV is concerned, the entry receptor for S protein is angiotensin-converting enzyme 2 (ACE2) and the S protein priming is done by a cellular enzyme called transmembrane protease serine 2 (TMPRSS2). Since SARS-CoV and SARS-CoV-2 share about 76% amino acid similarity, a team affiliated with German, Austrian and Russian institutes hypothesized that SARS-CoV-2 cell entry would also depend on ACE2 and TMPRSS2.
(Left) Western blot detection of ACE-2 in tissue lysates of human ovary, human testis, and human kidney. Goat Anti-Human ACE‑2 Polyclonal Antibody (Catalog AF933) was used at 1 µg/mL to probe the PVDF membrane and was followed by HRP-conjugated Anti-Goat IgG Secondary Antibody (Catalog HAF019). Analysis was conducted under reducing conditions. (Right) Immunohistochemical detection of ACE‑2 in immersion fixed paraffin-embedded sections of human kidney. (A) Goat Anti-Human ACE‑2 Polyclonal Antibody (Catalog AF933) was used at 15 µg/mL for overnight incubation at 4 °C followed by staining with Anti-Goat HRP-DAB Cell & Tissue Staining Kit (brown; Catalog CTS008) and counterstaining using hematoxylin (blue). (B) Omission of the primary antibody and tissue staining only with secondary antibody and detection reagents.
Indeed, SARS-CoV-2 was found to use the same mechanism. That is, SARS-CoV-2 uses ACE2 for entry and TMPRSS2 primes the viral S protein. Investigators used ACE-2 polyclonal antibody (Catalog AF933) at 2 or 20 mg/mL to block SARS-S- and SARS-2-S- driven entry into Vero cells. Interestingly, a clinically used TMPRSS2 inhibitor, camostat mesylate , was found to block SARS-CoV-2 entry into the target cells.
Camostat mesylate is an orally active protease inhibitor which inhibits transmembrane serine protease TMPRSS2 and partially blocks entry of SARS-Cov-2 (COVID-19) into lung cells in vitro.
This means that there is a glimmer of hope, but only time will tell if blocking viral entry by inhibiting TMPRSS2 is a viable strategy for treating COVID-19. However, the fact that the infection mechanism is similar to SARS-CoV may provide a significant step forward in identifying effective strategies to battle this new threat.
Jamshed Arslan, Pharm D, PhD
Dr Arslan is an Assistant Professor at Barrett Hodgson University, Pakistan,
where he uses various pedagogical methods to teach Pharm D students.
Research in focus
Hoffmann M, Kleine-Weber H, Schroeder S, et al. (2020). SARS-CoV-2 Cell Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a Clinically Proven Protease Inhibitor. Cell, S0092-8674(20)30229-4. doi:10.1016/j.cell.2020.02.052