Wyeth has signed a licensing agreement with US biotechnology firm Trubion for rights to a portfolio of injectable drugs for diseases such as arthritis and cancer.

The $800 million dollar deal, including a signing fee of $40 million, gives Wyeth co-development and co-marketing rights to a series of drugs - known as Small Modular Immunopharmaceuticals or ‘SMIPs’ - developed at Trubion.

SMIPs are molecules that behave in a similar manner to antibodies but are smaller and therefore easier to deliver. They can reach areas of the body that antibodies cannot, and are more stable so will require less frequent dosing. Trubion’s lead compound, TRU-015, is a SMIP in Phase II testing as a treatment for rheumatoid arthritis.

TRU-015 interacts with CD20, a protein on B lymphocytes that is already a validated target in rheumatoid arthritis. Genentech/Roche and Biogen Idec’s Rituxan/MabThera (rituximab) works by this mechanism: it is already approved for use in cancer and has been filed as a treatment for rheumatoid arthritis on the back of some compelling clinical data.

Analysts have suggested that Rituxan could achieve sales in excess of $1 billion in rheumatoid arthritis, so Wyeth and Trubion could be on to a winner if TRU-015 fulfils its potential. Meanwhile, the overall market for RA treatments is tipped to double in size from $5.5 billion at present to $10.5 billion in 2008.

This is the third licensing deal for Wyeth in recent weeks. In late December it agreed to pay up to $417 million to Progenics Pharmaceuticals in return for rights to methylnaltrexone, an experimental treatment for constipation and other side-effects of opioid use. Meanwhile, earlier in the month it signed a $158 million deal with Exelixis for a series of compounds with potential in the treatment of metabolic diseases.