SEATTLE (AP) ¿ Drug developer Cell Therapeutics Inc. said Monday it has adopted a shareholder rights plan, or "poison pill" plan, to block hostile takeover efforts as it waits for a regulatory decision on its cancer drug candidate pixantrone.

The Seattle company said the plan was adopted on Thursday and will prevent a potential buyer from acquiring Cell Therapeutics without making a fair offer to its shareholders. The plan will go into effect on Jan. 7, 2010.

On that date, the company will give out options that would allow its shareholders to buy a fraction of a share of preferred stock if any one person or group acquires more than 20 percent of the company's shares.

If an acquisition happens, the board of Cell Therapeutics can decide that all the rights can be redeemed for common stock at a higher price. A potential acquirer would not be allowed to exercise those rights.

The company said the plan would not block a takeover, but should force a potential buyer to talk to Cell Therapeutics' board of directors before trying to acquire the company instead of taking its bid directly to shareholders.

Cell Therapeutics is seeking Food and Drug Administration marketing approval for pixantrone as a treatment for aggressive non-Hodgkin's lymphoma that has returned after previous treatments, or not responded to other drugs. An advisory panel is scheduled to review the company's application on Feb. 10. The review could be a key step in bringing pixantrone to market, while a negative panel vote could damage its chances of approval.

The FDA is not required to follow the advice of its panels, but it often does.

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