Portola Enters Into Clinical Collaboration Agreement With Bayer and Janssen for Phase 2 Study of Universal Factor Xa Inhibitor

Portola Enters Into Clinical Collaboration Agreement With Bayer and Janssen for 
Phase 2 Study of Universal Factor Xa Inhibitor Antidote,
PRT4445, and XARELTO(R) 
SOUTH SAN FRANCISCO, CA -- (Marketwire) -- 02/05/13 --  Portola
Pharmaceuticals, Inc. today announced a clinical collaboration
agreement with Bayer HealthCare and Janssen Pharmaceuticals, Inc. for
a Phase 2 study evaluating the safety and effectiveness of PRT4445,
Portola's universal antidote for Factor Xa inhibitors, in healthy
volunteers who have been administered the U.S. Food and Drug
Administration-approved oral Factor Xa inhibitor XARELTO(R)
(rivaroxaban). PRT4445 is designed to reverse the anticoagulant
activity of Factor Xa inhibitors in patients experiencing an
uncontrolled bleeding episode or requiring emergency surgery. There
are no currently approved agents to reverse the activity of oral
Factor Xa inhibitors, and PRT4445 is the only universal Factor Xa
inhibitor antidote in clinical development. 
The collaboration will be in effect throughout the Phase 2 study,
which is scheduled to be completed in the second half of 2013. The
study is designed to demonstrate the safety of PRT4445 at several
different doses and its ability to reverse the anticoagulant activity
of XARELTO. Bayer and Janssen will make an undisclosed cash payment
to Portola and will provide development and regulatory guidance for
the study. Portola retains all global development and
commercialization rights for PRT4445.  
"Oral Factor Xa inhibitors are a major advance over standard
therapies such as warfarin and enoxaparin, but there is an important
unmet medical need for an antidote to help manage patients if they
require their anticoagulant to be reversed," said William Lis, chief
executive officer of Portola. "Our goal is to accelerate the
development and regulatory approval of PRT4445 as the first universal
reversal agent for all Factor Xa inhibitors. We are pleased to be
working with our Bayer and Janssen colleagues to help achieve this
objective with XARELTO." 
Clinical trial results suggest that, annually, between 1-4 percent of
patients treated with Factor Xa inhibitors will experience
uncontrolled bleeding, and an additional 1 percent will require
emergency surgery, depending on the patient's underlying medical
ition. Currently, standard clinical measures are employed to
manage these events. Development of an agent specifically designed to
reverse the activity of Factor Xa inhibitors may provide an important
treatment option for patients who experience an uncontrolled major
bleeding event or require emergency surgery.  
About PRT4445
 PRT4445 is a novel recombinant protein designed to
reverse the anticoagulant activity in Factor Xa inhibitor-treated
patients suffering from an uncontrolled bleeding episode or
undergoing emergency surgery. It is similar to native Factor Xa but
has structural modifications intended to restrict its biological
activity to reverse the effects of Factor Xa inhibitors. PRT4445
works by acting as a decoy for Factor Xa inhibitors in the blood,
thereby preventing them from inhibiting the activity of native Factor
Xa. As a result, the native Factor Xa is available to participate in
the coagulation process and restore normal clotting.  
Results of a Phase 1 single ascending dose safety and tolerability
study, conducted by Portola in 32 healthy volunteers in the United
States, showed that PRT4445 was generally well tolerated with no
apparent safety signals.  
About XARELTO(R) (rivaroxaban)
  XARELTO works by blocking the blood
clotting enzyme Factor Xa. XARELTO does not require routine blood
monitoring and is approved for six distinct uses: 
 1. To reduce the
risk of blood clots in the legs and lungs of people who have just had
knee replacement surgery. 
 2. To reduce the risk of blood clots in
the legs and lungs of people who have just had hip replacement
 3. To reduce the risk of both hemorrhagic and thrombotic
strokes as well as other blood clots in people with atrial
fibrillation not caused by a heart valve problem. There is limited
information on how XARELTO(R) compares to a medicine called warfarin
in reducing the risk of stroke when the effects of warfarin are well
 4. To treat people with pulmonary embolism (PE).
 5. To
treat people with deep vein thrombosis (DVT).
 6. To reduce the risk
of recurrence of DVT or PE following an initial six months of
treatment for acute venous thromboembolism. 
The extensive program of clinical trials evaluating rivaroxaban makes
the compound the most studied oral Factor Xa inhibitor in the world
today. By the time of its completion, more than 100,000 patients will
have participated in the rivaroxaban clinical development program.
There are two additional indications currently submitted and under
review at the FDA. 
About Portola Pharmaceuticals, Inc.
 Portola Pharmaceuticals is a
biopharmaceutical company focused on developing and commercializing
novel therapeutics in the areas of thrombosis, other hematologic
disorders and inflammation for patients that currently have limited
or no approved treatments. In thrombosis, Portola is developing
betrixaban, a novel, oral, once-daily inhibitor of Factor Xa in
development for extended duration prophylaxis of venous
thromboembolism (VTE) in acute medically ill patients; and PRT4445, a
universal antidote for Factor Xa inhibitors. Portola has a clinical
collaboration agreement with Bristol-Myers Squibb and Pfizer for the
initial Phase 2 proof-of-concept study of PRT4445 in combination with
ELIQUIS(R) (apixaban). Portola retains full commercial rights for
Portola's two other product candidates are orally available kinase
inhibitors with unique pharmacologic properties targeting hematologic
cancers and inflammatory disorders: PRT2070, which inhibits both
spleen tyrosine kinase (Syk) and Janus kinases (JAK) enzymes, which
regulate important signaling pathways; and PRT2607, which selectively
inhibits Syk. Portola is developing PRT2070 for treatment of certain
B-cell hematologic cancers, with a particular focus on patients who
have mutations that cause failure or relapse with existing treatments
and those in development. Portola has a collaboration agreement with
Biogen Idec to develop specific inhibitors of Syk, including PRT2607.
For more information, visit www.portola.com. 
Mardi Dier
CFO, Portola Pharmaceuticals
Paul Laland
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