Amgen Inc. Tuesday reduced the competition fordevelopment of thrombopoietin by licensing rights toZymoGenetics Inc.'s version of the platelet growth factorfor an undisclosed sum.

Thrombopoietin, or TPO, stimulates production ofplatelets, which are involved in blood clotting. Theprotein hormone is in early stage development forrestoring platelets destroyed during cancer chemotherapytreatments.

In addition to Amgen and ZymoGenetics, which is asubsidiary of Denmark-based Novo Nordisk A/S, theother company developing TPO to combatthrombocytopenia, which is a reduction of platelets, isGenentech Inc., of South San Francisco.

Amgen, of Thousand Oaks, Calif., is developing itsversion of thrombopoietin, called megakaryocyte growthand development factor (MGDF), with Kirin Brewery Co.Ltd., of Tokyo. The drug is in Phase I clinical trials.Genentech expects to begin clinical studies with itsproduct toward the end of the third quarter.

In licensing ZymoGenetics' product, Amgen "makes it atwo-player field instead of a three-player field," saidMatthew Geller, an analyst with Oppenheimer & Co. inNew York. The drugs basically are the same.

In addition to thrombopoietin, interleukins are beingtested by other companies as platelet productionstimulators and are far more advanced in clinicaldevelopment. Immunex Corp., of Seattle, and GeneticsInstitute Inc., of Cambridge, Mass., have interleukins inPhase III trials for restoring platelets. Switzerland-basedSandoz Ltd. also is conducting clinical studies withinterleukins.

Immunex's drug, Pixy321, is a combination ofinterleukin-3 (IL-3) and granulocyte macrophage-colonystimulating factor (GM-CSF). Genetics Institute's productis recombinant human interleukin-11. Sandoz Ltd. istesting interleukin-6 as well as a combination of IL-3 andGM-CSF.

Analysts have estimated the initial market for plateletstimulating drugs at about $500 million worldwide.Currently platelet transfusions are used to boost plateletcounts.

Neither Amgen nor Novo Nordisk would disclosefinancial details of the TPO agreement.

Henrik Aagaard, president of Novo Nordisk NorthAmerica in New York, said the deal gives Amgenworldwide rights to sell and market TPO from hiscompany's patents. He said Novo Nordisk has U.S. andEuropean patents on its version of thrombopoietin.

Novo Nordisk's decision to license out TPO, Aagaardadded, was based on the company's strategy, announcedin December, of refocusing resources on three coredevelopment areas _ diabetes, human growth hormoneand hormone replacement therapy.

As other drug candidates, such as TPO, emerge fromNovo Nordisk's research, Aagaard said the company willcontinue to explore licensing agreements.

ZymoGenetics' president, Bruce Carter, said the Amgenagreement does affect his company's potential $50million collaboration with Progenitor Inc., of Columbus,Ohio, for developing blood stem growth factors fortreating cancer patients.

Amgen's stock (NASDAQ:AMGN), which splits two forone today, closed Tuesday at $94.13, down $1.38. NovoNordisk (NYSE:NVO) was up 25 cents to $28.63. n

-- Charles Craig

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