Pfizer research-and-development chief Mikael Dolsten told the Wall Street Journal in an interview that laboratory research suggests the drug candidate blocks the new coronavirus from replicating.
The findings indicate the experimental drug could slow or stop the spread of the virus in patients with mild-to-moderate symptoms, though testing on humans will be necessary for proof.
The New York pharma giant this week will also start testing an approved rheumatoid-arthritis drug, Xeljanz, in coronavirus patients in Italy to see whether the therapy has a benefit, The Journal said.
The company is also planning to publish research on whether one of its antibiotics helps.
American depositary receipts of BioNTech at last check were up 7.5% to $48.30, while Pfizer shares were 1.7% higher at $35.20.
Pfizer said it planned to move into clinical trials as early as the end of this month with four different vaccines simultaneously, and it aims to move the best one forward in future studies.
Under the terms of the agreement, Pfizer will pay BioNTech $185 million up front, including $72 million cash and $113 million in an equity investment.
BioNTech is eligible to receive future milestone payments of up to $563 million for a potential total of $748 million.
Pfizer and BioNTech will share development costs equally. Initially, Pfizer will fund 100% of the development costs, and BioNTech will repay Pfizer its 50% share of these costs when the vaccine is commercialized.
Dozens of companies and university researchers are working to develop therapies for or vaccines against the virus.
More than 140 are in development worldwide, most in early stages, including about a dozen already in clinical trials, the Journal said, citing Informa Pharma Intelligence.