Portola Pharmaceuticals, Inc. Data on Its Novel Syk Inhibitors and Novel Universal Factor Xa Inhibitor Antidote to be Presented at 2008 American Society of Hematology Meeting

SOUTH SAN FRANCISCO, Calif., Dec. 3 /PRNewswire/ -- Portola Pharmaceuticals, a biopharmaceutical company developing innovative drugs that provide significant advances in cardiovascular disease, inflammatory disease and cancer, today announced that data related to the Company’s series of novel compounds that inhibit spleen tyrosine kinase (Syk) and its novel universal Factor Xa inhibitor antidote will be presented at the annual meeting of the American Society of Hematology (ASH) at the Moscone Center in San Francisco during December 6-9, 2008.

Portola’s Syk inhibitor program is focused on developing specific oral inhibitors of this key signaling pathway, which modulate inflammation, certain cancers and thrombosis. The Company plans to study its compounds initially in rheumatoid arthritis and non-Hodgkin’s Lymphoma and eventually intends to explore their potential in other inflammatory diseases and cancers. Portola is developing its universal Factor Xa inhibitor antidote to neutralize the effect of small molecule Factor Xa inhibitors in patients experiencing major bleeding and for patients undergoing emergent or elective surgery.

Details of the ASH presentations are below and full abstracts can be viewed on the ASH website at http://www.hematology.org.

Syk Inhibitor Program

“Specific Inhibition of Syk is Sufficient to Disrupt Proliferation and Survival of Non-Hodgkin’s Lymphoma Cell Lines without Concomitant Inhibition of JAK” (abstract # 1794)

Saturday, December 6, 5:30 PM

Hall A (Moscone Center)

“PRT060318, a Novel Syk Inhibitor, Prevents Heparin-Induced Thrombocytopenia in a Transgenic Mouse Model” (abstract # 269)

Monday, December 8, 7:00 AM

3007-3009-3011 - West (Moscone Center)

“Specific Pharmacological Targeting of the Syk Kinase Activity in Platelets: A Novel, Safe Anti-Thrombotic Strategy” (abstract # 409)

Monday, December 8, 11:00 AM

3002-3004 - West (Moscone Center)

“Inhibition of Syk Activity is Sufficient for Inhibitory Effect in Animal Models of Autoimmune Diseases” (abstract # 680)

“Recombinant Antidote for Reversal of Anticoagulation by Factor Xa Inhibitors” (abstract # 983)

About Portola Pharmaceuticals, Inc.

Portola Pharmaceuticals develops innovative therapeutics based on targets with established proof of concept that are engineered to provide significant advances over current treatments for cardiovascular and inflammatory diseases and cancer.

Portola’s two lead Phase II compounds, betrixaban, an oral Factor Xa inhibitor and PRT060128, an ADP receptor antagonist, target the global multi- billion dollar antithrombotic market. Both product candidates have best-in- class features versus current and novel agents in development and address the hospital, specialty, and chronic care markets. The Company’s earlier-stage programs are leveraging its chemistry capability to develop specific Syk and JAK inhibitors to treat cancer and inflammatory diseases. The company also has a novel Factor Xa inhibitor antidote program with the potential to help manage the more than 20 million patients expected to be treated with anticoagulants worldwide in the next decade. For additional information, visit http://www.portola.com.

CONTACT: Mardi Dier - CFO, Portola Pharmaceuticals, +1-650-246-7236,
mdier@portola.com, or Julie Normart, Invigorate Communications,
+1-415-946-1087, jnormart@invigoratepr.com, for Portola

Web site: http://www.portola.com/

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