Purple Biotech (PPBT) said in a regulatory filing Friday it plans to offer "on a reasonable best efforts" basis up to 2,702,702 American Depositary Shares representing 540,540,400 common shares at a currently assumed estimated combined price of $2.22 per ADS, and accompanying and other prefunded warrants, 'from time-to-time.'

Each ADS represents 200 Purple Biotech common shares, the company said.

The company has hired H.C. Wainwright & Co as "placement agent" in connection with the offering, which will expire Oct. 3, unless the company decides to terminate it at any time earlier, according to the F-1 filing.

If and when sold, the company said, it plans to use the proceeds from the offering to develop its oncology therapeutic candidates, and for general working capital and corporate purposes.

Shares of Purple Biotech were down 8% in recent Friday trading.

Price: 2.19, Change: -0.08, Percent Change: -3.52