Pfizer's Anti-Viral 3CL Protease Inhibitor Shows Antiviral Potential Against SARS-CoV-2 | Virus World | Scoop.it
From www.news-medical.net - September 16, 2020 11:27 AM

Now, a new study by researchers from Pfizer, University of Arizona, Purdue University, The Scripps Research Institute, and UC San Diego School of Medicine and published on the preprint server bioRxiv in September 2020 reports that an enzyme inhibitor may act in synergism with the approved antiviral remdesivir to suppress viral replication in COVID-19. Remdesivir is an RNA-dependent RNA polymerase (RdRp) inhibitor that has received emergency use authorization by the US Food and Drug Administration (FDA) in May 2020 for the treatment of SARS-CoV-2. Remdesivir trials have revealed that this drug reduces the time to recovery for COVID-19 patients, but not the severity of the disease. To enhance its clinical impact, it is necessary to find other drugs that may add to its therapeutic efficacy. The drug candidate PF-00835231 discussed in the current study acts on the SARS-CoV-2 main protease or 3C-like protease (3CL protease or 3CLpro). This is required for viral replication since it causes the large viral polyprotein p1a/p1ab to be cleaved at 10 or more junctions. The result is the production of several non-structural proteins that play a crucial part in viral replication and transcription. These include RdRp, the helicase, and the 3CLpro itself. Also, viral 3CLpro has no comparable human analogs. These two properties make it an ideal candidate for further investigation as a potential COVID-19 therapeutic.

 

Protease inhibitors have played a similar role in HIV and HCV therapeutics. Following this lead, the current researchers identified a small molecule protease inhibitor PF-00835231 that was active against SARS-CoV, the virus responsible for the earlier respiratory illness outbreak of 2002.  Produced by structure-based drug design, this drug never saw the light of day because of the rapid termination of the outbreak by stringent public health measures. Now, the researchers are taking a fresh look at it because of the high degree of identity between the SARS-CoV and SARS-CoV-2 3CLpro. In fact, they have entirely identical active sites. The researchers found that both PF-00835231 and its phosphate prodrug has antiviral activity against a broad spectrum of coronaviruses (CoVs). It binds tightly to the enzyme at the catalytic cysteine residue, potently suppressing its activity. This enzyme being conserved across several CoVs. This allows it to inhibit several CoV 3CLpro enzymes in vitro, from alpha-, beta- and gamma-CoVs. However, it is inactive against human and HIV proteases, indicating its specificity of activity.

 

The researchers examined the ability of PF-00835231 to exert antiviral activity against SARS-CoV-2 in cell culture, using a cytopathic effect (CPE) assay. As expected from experience with other viral protease inhibitors, they found that there was a dose-dependent but steep suppression of viral activity with this molecule. When repeated using cell lines, which are more similar to the human lung cells, they obtained similarly promising results. Thus, this drug candidate has in vitro antiviral activity even as a single agent.  When antiviral agents are combined, especially when they act on different steps of the replication cycle, the effects are often much more significant than when used alone. Evaluation of the combined activity of these drugs led to the finding that while the in vitro EC50 for PF-00835231 alone was 0.14 μM, and for remdesivir, it was 0.074μM, in combination, they showed a mix of synergistic and additive effects. This could be because different convalescent sera were used for the detection process...

 

Preprint available at bioRxiv (Sept.13, 2020):

https://www.biorxiv.org/content/10.1101/2020.09.12.293498v2