Pfizer Inc. announced that it is progressing to multiple ascending doses after completing the dosing of single ascending doses in a Phase 1 study in healthy adults to evaluate the safety and tolerability of an investigational, novel oral antiviral therapy for SARS-CoV-2, the virus that causes COVID-19. This Phase 1 trial is being conducted in the United States. The oral antiviral clinical candidate PF-07321332, a SARS-CoV2-3CL protease inhibitor, has demonstrated potent in vitro anti-viral activity against SARS-CoV-2, as well as activity against other coronaviruses, suggesting potential for use in the treatment of COVID-19 as well as potential use to address future coronavirus threats.

“Tackling the COVID-19 pandemic requires both preventions via vaccine and targeted treatment for those who contract the virus. Given the way that SARS-CoV-2 is mutating and the continued global impact of COVID-19, it appears likely that it will be critical to have access to therapeutic options both now and beyond the pandemic,” said Mikael Dolsten, MD, PhD., Chief Scientific Officer and President, Worldwide Research, Development and Medical of Pfizer.

“We have designed PF-07321332 as a potential oral therapy that could be prescribed at the first sign of infection, without requiring that patients are hospitalized or in critical care. At the same time, Pfizer’s intravenous antiviral candidate is a potential novel treatment option for hospitalized patients. Together, the two have the potential to create an end to end treatment paradigm that complements vaccination in cases where disease still occurs.”

Protease inhibitors bind to a viral enzyme (called a protease), preventing the virus from replicating in the cell. Protease inhibitors have been effective at treating other viral pathogens such as HIV and hepatitis C virus, both alone and in combination with other antivirals. Currently marketed therapeutics that target viral proteases are not generally associated with toxicity and as such, this class of molecules may potentially provide well-tolerated treatments against COVID-19.

The Phase 1 trial is a randomized, double-blind, sponsor-open, placebo-controlled, single- and multiple-dose escalation study in healthy adults evaluating the safety, tolerability and pharmacokinetics of PF-07321332.

Initiation of this study is supported by preclinical studies that demonstrated the antiviral activity of this potential first-in-class SARS-CoV-2 therapeutic designed specifically to inhibit replication of the SARS-CoV2 virus. The structure of PF-07321332, together with the pre-clinical data, will be shared in a COVID-19 session of the Spring American Chemical Society meeting on April 6.

Pfizer is also investigating an intravenously administered investigational protease inhibitor, PF-07304814, which is currently in a Phase 1b multi-dose trial in hospitalized clinical trial participants with COVID-19.