Bayer’s blockbuster hopeful regorafenib, an oral multi-kinase inhibitor and marketed as Stivarga, was approved by the U.S. Food and Drug Administration (FDA) on September 27, 2012 for the treatment of patients with metastatic colorectal cancer (mCRC).

Regorafenib (aka BAY 73-4506, DAST, Fluoro-Sorafenib) has the same chemical structure as the blockbuster cancer therapy Nexavar marketed jointly by Onyx and Bayer, except for the new cancer drug with the substitution of a single fluorine atom in place of a hydrogen atom.

Germany-based Bayer AG and South San Francisco-based Onyx began working together in 1994, and their collaboration on Nexavar brings Onyx all of its revenue.

Nexavar (sorafenib) approved by US FDA against kidney cancer in 2005 and advanced liver cancer in 2007, sells for about $5,000 a month in the United States. Worldwide sales of the drug grew to $481.1 million in the first six months of 2011.

Onyx Pharmaceuticals filed a lawsuit in May 2009, accusing its partner Bayer of trying to cut it out of the collaboration by developing a drug that was almost identical to the their approved cancer drug Nexavar without informing Onyx so it would not have to make royalty payments to Onyx.

The case is Onyx Pharmaceuticals Inc. vs. Bayer Corp., Case No. 3:09-cv-02145 MHP, U.S. District Court, Northern District of California (San Francisco).

Both companies reached an agreement in 2011 with Bayer paying Onyx a one-time $160 million fee plus a royalty of 20% of future regorafenib sales. 

Bayer is developing regorafenib as a treatment for gastrointestinal stromal tumors, which mostly occur in the stomach or small intestine. Bayer has applied for FDA approval of the drug for use in patients who have not been helped by treatment with Novartis AG’s drug Gleevec and Pfizer Inc.’s Sutent.