Bayer's contested kidney cancer drug shows promise -study

FRANKFURT, May 30 (Reuters) - A sister compound to Bayer BAYG.DE and Onyx Pharmaceuticals' (ONXX.O) potential blockbuster Nexavar has showed promise against kidney cancer in a Phase II study, raising the stakes in a legal row between the two partners.

Preliminary results of the mid-stage study that started in October 2008 show that 27 percent of the 33 patients evaluated saw their tumours shrink and that the cancer was kept stable in a further 42 percent of cases, according to documents released by the U.S. oncologist association ASCO on its Web site.

The results encouraged Bayer to take the compound into the third and last phase of testing usually required for regulatory approval, the German drug company said on Saturday.

The drug, dubbed BAY 73-4506 by Bayer, has become a bone of contention between the German drugmaker and its U.S. biotech partner because Bayer is developing the drug on its own while Onyx claims the compound should be treated as an offshoot of the joint Nexavar project.

Onyx sued Bayer this month over the rights to BAY 73-4506, which Onyx refers to as fluoro-sorafenib, claiming its molecular structure differs from Nexavar, or sorafenib, only in one atom.

BAY 73-4506 is similar to Bayer's Nexavar drug, scientifically known as sorafenib, and both drugs are so-called multikinase inhibitors that quell cancer cell growth and prevent new blood vessels that could feed tumours.

Doctors use Nexavar, which is taken as a pill, to treat liver cancer and advanced kidney cancer and Bayer expects to generate more than 2 billion euros ($2.80 billion) in peak annual sales from it.

Phase II trial participants were suffering from previously untreated kidney tumours that could not be removed surgically or that had started spreading.

Side effects, which included rash, diarrhoea, and anorexia, were manageable and typical of the drug class, according to ASCO.

Bayer is testing BAY 73-4506 against bowel cancer as well. (Reporting by Ludwig Burger, editing by Mike Peacock)