Pfizer reported Friday that is has completed its acquisition of Durham-based Icagen.

Icagen is now a wholly-owned subsidiary of Pfizer. Icagen's stock ceased trading on NASDAQ on Friday.

Icagen and Pfizer announced the $56 million deal in July, but some large investors complained the $6 share price was too low.

Pfizer was able to convince enough shareholders to go along with the deal after extending the deadline twice.

Icagen was founded in 1992 by P. Kay Wagoner, a former GlaxoSmithKline Plc research executive who focused on developing new ways to treat pain.

None of the company's drugs have been approved by the U.S. Food and Drug Administration for sale in the U.S. market.

Pfizer announced today that all the remaining outstanding shares of Icagen have been tendered, setting the stage for the Durham-based drug company to become a wholly-owned subsidiary of Pfizer.

Nearly 5.4 million shares of Icagen common stock were tendered as of 6 p.m. Monday.

Pfizer already owned more than a million shares before the Monday deadline, and the additional shares bring the company's ownership stake in the company to 70 percent.

Pfizer expects to complete the acquisition once the merger agreement is approved at an Icagen stockholders meeting.

It took some wooing but Pfizer was finally able to convince Icagen shareholders that its $56 million offer for Icagen was a good deal.

The companies announced this morning that enough shareholders had tendered their shares for the acquisition to go through. Pfizer had to extend the deadline twice to make it happen.

Pfizer now owns 64 percent of the outstanding shares of Durham-based Icagen.

In announcing the completion of the deal, Pfizer also announced a subsequent offering period that expires at 6 p.m. Sept. 12, for any remaining shares. Sellers today will also receive $6 a share.

Icagen and Pfizer announced the $56 million deal in July. But some large investors complained the $6 share price was too low. They argued the business could be worth three times as much because of the promising results for experimental pain medications that Icagen is developing in a partnership with Pfizer.

Pfizer has one again extended the deadline for its $6-per-share offer for Durham's Icagen.

The pharmaceutical company announced this morning that it was extending the offer until 6 p.m. today in hopes of winning the support of more shareholders so it can complete the deal.

On Thursday, Pfizer officials said the offer would expire at midnight.

According to a Pfizer press release this morning, shareholders holding 49.6 percent of Icagen's fully-diluted shares had agreed to tender their holdings. The company needs 39,799 more shares to be tendered to close the deal.

Icagen and Pfizer announced the $56 million deal in July. But some large investors complained the $6 share price was too low. They argued the business could be worth three times as much because of the promising results for experimental pain medications that Icagen is developing in a partnership with Pfizer.

Pfizer, however, has not been willing to increase its offer.

Shareholders holding roughly 4.1 million shares of Icagen common stock, including shares owned by Icagen directors and officers, have agreed to tender their shares. In addition, Pfizer owns nearly 1.1 million shares.

Icagen shares were trading at $6 this morning.

Pfizer, which has offered to buy Durham's Icagen for $6 per share, wants to be clear: It won't pay a dime more.

In response to pressure from Icagen investors who are unhappy with the value of the offer, Pfizer sent a letter today to Icagen's board.

With the takeover offer set to expire on Aug. 31, "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 letter states. "Pfizer will not pay more."

The so-called 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," wrote Douglas Giordano, Pfizer's senior vice president of worldwide business development.

Durham drug-development company Icagen approached dozens of companies during the past three years about a possible acquisition before finally announcing its takeover by Pfizer last month.

But Icagen and its investment adviser J.P. Morgan Securities were rejected repeatedly, Icagen reported in a filing with the Securities and Exchange Commission. In the summer and fall of 2009 alone, the quest involved contacting about 40 companies "to discuss possible strategic alternatives."

The SEC filing describes Icagen's long struggle to find a larger partner that would provide money needed for further research of experimental drugs to treat epilepsy and other ailments.

In July, Icagen and Pfizer announced the deal worth $56 million, or $6 per share.

But the companies are facing pressure from several large investors who say that price is too low. 

Two large Icagen investors say that Pfizer's $56 million takeover offer for the Durham drug-development company is too low and will push for a higher price.

Pfizer announced on July 20 that it planned to buy the remaining shares of Icagen it doesn't already own for $6 each.

But Merlin Nexus and New Leaf Venture Partners believe that Icagen's shares could be worth up to three time as much, the investment firms wrote in a letter last week to Icagen's board and chairman Charles Sanders. The firms disclosed the letter in a Securities and Exchange Commission filing on Friday.

"We believe the purchase price dramatically undervalues Icagen’s assets, and is not in the best interests of all stockholders," they wrote.

Icagen agreed to be bought by its larger partner Pfizer for $6 per share, or about $56 million, a price that's less than what Wall Street was expecting.

Shares of Icagen, a small, Durham-based drug-development company, surged last month after Pfizer disclosed the companies were in discussions about a "strategic transaction."

On Tuesday, Icagen shares closed at $7.75, more than triple the price of a month ago.

But its shares fell 23 percent to $5.95 in midday trading today, after the companies announced that Pfizer, which already owns more than 1 million Icagen shares, will buy the remaining 8.3 million shares for $6 each.

"The price is really on the low range of what investors had been expecting," said Christopher James, who follows Icagen for McNicoll Lewis Vlak. He doesn't own Icagen or Pfizer shares.

Icagen shares surged today, as investors bet that the Durham company will be bought for a premium by larger partner Pfizer.

Late Friday, Pfizer disclosed that it's in discussions about a "strategic transaction" with Icagen. Pfizer, the world's largest drugmaker, first formed a partnership with Icagen in 2007 to develop new pain medicines.

Icagen could be worth $50 million to $100 million in a takeover, McNicoll, Lewis & Vlak analyst Christopher James told Bloomberg News. That would make Icagen's shares worth up to $13 each.

In midday trading, Icagen's stock rose $3.09 to $5.49. That's the highest level in more than a year.

Icagen, a Durham drug development company that has struggled financially, is in discussions about a possible takeover by its much-larger partner Pfizer.

Pfizer disclosed in a regulatory filing this afternoon that it is "evaluating the possibility of entering into a strategic transaction with Icagen."

Icagen began a collaboration with Pfizer in 2007 to develop new pain medicines. As part of that partnership, Pfizer has paid Icagen millions of dollars in milestone fees. It also bought more than 1 million Icagen shares and now owns a 14 percent stake in the company.

In a prepared statement late today, Icagen acknowledged that its executives are in talks with Pfizer, but that no agreement has been reached. The company "does not plan to make future announcements with respect to this matter" until a deal is reached, the current partnership agreement with Pfizer is extended or the discussions have terminated.