Onyx Pharmaceuticals signs definitive agreement to acquire Proteolix

Proteolix, Inc. today announced that it has signed a definitive agreement to be acquired by Onyx Pharmaceuticals, Inc. (Nasdaq: ONXX). Proteolix is a privately-held biopharmaceutical company focused on discovering and developing novel therapies that target the proteasome for the treatment of hematological malignancies and solid tumors. Proteolix's lead compound, carfilzomib, is a proteasome inhibitor currently in multiple clinical trials, including an advanced Phase 2b clinical trial for patients with relapsed and refractory multiple myeloma.

"Proteolix has succeeded in pioneering a new class of potent proteasome inhibitors, as demonstrated by the promising data achieved in multiple studies of our lead candidate, carfilzomib. We believe Onyx truly shares our vision for carfilzomib as an important new therapy in oncology and recognizes Proteolix's scientific leadership in proteasome inhibition," said John A. Scarlett, M.D., President and Chief Executive Officer of Proteolix. "Onyx's proven track record and commercial resources in oncology are impressive. We are excited to join forces and together we are poised to advance carfilzomib through regulatory approval and achieve our ultimate objective of helping patients."

Under the terms of the transaction, Onyx will make a $276 million cash payment upon closing of the transaction. Additional payments include $40 million payable in 2010 based on the achievement of a development milestone and up to $535 million contingent upon the achievement of anticipated approvals for carfilzomib in the U.S. and Europe. Of the potential $535 million, a payment of $170 million is based upon the achievement of accelerated U.S. Food and Drug Administration approval. The transaction is expected to close in the fourth quarter of 2009, subject to the receipt of clearance under the Hart-Scott-Rodino Act and customary closing conditions.

Proteolix is a leader in developing therapeutics that inhibit the cellular proteasome, a validated and well-characterized approach to treating certain hematologic cancers. Carfilzomib is the first in a new class of selective and irreversible proteasome inhibitors. To date, carfilzomib has demonstrated strong response rates in multiple studies and a potentially more tolerable safety profile than currently approved agents. An ongoing accelerated approval Phase 2b trial in patients with relapsed and refractory multiple myeloma is expected to complete enrollment in 2009 with data anticipated in the second half of 2010. Carfilzomib is also being evaluated in a companion Phase 2 trial in relapsed multiple myeloma. A Phase 3 trial evaluating carfilzomib in combination with lenalidomide and dexamethasone as a potential treatment option for patients with multiple myeloma is expected to begin in 2010. Carfilzomib is also being evaluated in a Phase 1b/2 study for solid tumor cancers. In addition, Proteolix has discovered additional next-generation proteasome inhibitors to which it holds worldwide development and commercialization rights, including an oral proteasome inhibitor and a selective immunoproteasome inhibitor.

"Treatment options in multiple myeloma have historically been limited, and there is a tremendous need to expand the treatment paradigm with agents offering an improved efficacy and safety profile," said Michael Kauffman, M.D., Ph.D., Chief Medical Officer at Proteolix. "Carfilzomib is in multiple ongoing clinical studies and has revealed clear single-agent activity in a heavily pre-treated multiple myeloma patient population, as well as being well tolerated alone, or in combination with Revlimid. Upcoming data for carfilzomib could support the potential near-term introduction of a novel therapy for this debilitating disease."

Cooley Godward Kronish LLP acted as legal advisor to Proteolix on this transaction.