Portola Pharmaceuticals, a therapeutics company focused on thrombosis, inflammatory disease and cancer, global biopharmaceutical company Bristol-Myers Squibb (BMS) and Pfizer have signed a clinical collaboration agreement to conduct a proof-of-concept study of PRT4445 and the investigational oral Factor Xa inhibitor Elquis (apixaban).

The collaboration will be in effect during the clinical proof-of-concept study, which is anticipated to start by the end of 2012. The study is designed to demonstrate the safety of PRT4445 and its ability to reverse the anticoagulation activity of Elquis and other Factor Xa inhibitors, including betrixaban, Portola's phase III oral Factor Xa inhibitor. BMS and Pfizer will make an undisclosed cash payment to Portola upon initiation of the study and will provide development and regulatory guidance. Portola retains 100% global development and commercialization rights for PRT4445.

"Oral Factor Xa inhibitors address an important unmet need for patients requiring anticoagulant therapy, but as with all anticoagulants, there is a need for an antidote to help manage the concerns physicians have around infrequent but serious bleeding events," said William Lis, CEO of Portola.

Major bleeding events occur infrequently in patients taking Factor Xa inhibitors (1-4% per year in clinical studies) and standard measures are employed to manage these events. Development of an agent specifically designed to reverse the activity of Factor Xa inhibitors may provide an antidote for patients who, in rare instances, experience an uncontrolled major bleeding event or require emergency surgery.