Genzyme raised the stakes once again in the tussle to acquire Canadian drugmaker AnorMed yesterday, with a $13.50 per share offer that trumps a $12 offer from rival Millennium Pharmaceuticals.

The new offer is raised by $200 million to around $580 million, more than 12% higher than Millennium’s $515 million offer.

AnorMed had earlier recommended that its shareholders plump for Millennium, despite Genzyme’s assertions that it would be making a counter-offer, but now has a deadline of this evening to review the two bids side by side.

Genzyme’s sweetened offer comes after it was given access to AnorMed’s files on Mozobil (AMD3100), a drug designed to improve the success of stem cell transplantation procedures used to serious malignancies, in order to carry out proper due diligence. However, shares in the US biotech dipped on the announcement as analysts expressed concern that the price being paid for the business was too high.

Both companies are trying to get their hands on Mozobil because it complements their existing product ranges. Millennium believes that Mozobil will sit well alongside its Velcade (bortezomib), which is sold for the haematological cancer multiple myeloma. Mozobil's lead indications are in multiple myeloma and non-Hodgkin’s lymphoma.

Meanwhile, Genzyme has a heritage in selling drugs for transplantation with its Thymoglobulin product, and says Mozobil would complement that franchise. It is also interested in Mozobil as a potential treatment for leukaemia, on the premise that the drug can mobilise leukaemic cells out of the bone marrow and into the blood, where they become more susceptible to chemotherapy.

Genzyme chief executive Henri Termeer said that his company’s international presence made it a much better partner for Mozobil, as less than 40% of all hematopoietic stem cell transplants occur in the USA.

AnorMed also has an HIV entry inhibitor AMD070 which is in Phase II, and the winning company will also be able to tap into a royalty stream from kidney failure drug Fosrenol (lanthanum carbonate), sold by Shire of the UK.