Pfizer informed Icagen’s board on Friday that its final offer price for the company is $6 per share. The drugmaker also indicated that it wouldn’t raise its takeover offer, which was announced in July and is scheduled to expire on August 31, even if a majority of shares in Icagen aren’t tendered.

In a letter to Icagen’s board, Douglas Giordano, Pfizer’s senior vice president of worldwide business development, noted that “we thought it appropriate to reaffirm unambiguously, as we made clear when negotiating the merger agreement with you, that $6 per share is our best and final price.” The drugmaker went on to note that although the tender offer requires that a majority of Icagen investors agree to the deal, “if a majority of shares are not tendered, however, we still will not raise our offer.”

Icagen CEO P. Kay Wagoner has written to investors urging them to tender their shares. However, several large investors have stated that the drugmaker’s offer is too low, with two investment firms suggesting that Icagen could be worth three times as much based on data from trials of an experimental pain drug that Pfizer and Icagen are developing together. The firms, which own more than 10 percent of Icagen stock, have said they will not tender their shares at the current offer price.