(AOM) - Get Report

said its board unanimously rejected a buyout offer from



, but that isn't deterring its suitor.

Just hours after Genzyme learned its bid was turned down by the Canadian biopharmaceutical company, it said it would go around the board and take its $8.55-a-share proposal directly to AnorMED's stockholders.

Word of the hostile takeover attempt sent shares of AnorMED skyrocketing $4.55, or 90%, to $9.58. More than 4.5 million shares had traded. On a normal day, about 28,000 shares change hands. During the last year, AnorMED has traded between $3.35 and $7.45.

Meanwhile, shares of Genzyme were losing 49 cents, or 0.7%, to $66.18.

Genzyme said it plans to start a tender offer to acquire AnorMED at a price that represents a 70% premium over its close on Tuesday. The deal would be worth around $380 million.

If it manages to buy AnorMED, Genzyme would gain a product called Mozobil, which could improve the viability of hematopoietic stem cell transplants and enlarge the pool of patients for whom transplantation is an option.

Enrollment is complete in a Phase III trial for Mozobil against multiple myeloma, and a Phase III trial studying the drug in non-Hodgkin's lymphoma is expected to conclude later this year. Mozobil has been granted special protocol assessment and orphan drug status in the U.S. and European Union.

Genzyme has been in discussions with AnorMED regarding Mozobil since last October, and it offered to buy the company in April.