Pfizer has told Trubion Pharmaceuticals it is dropping one rheumatoid arthritis drug from their alliance but will keep developing a next-generation therapy for the disease.

The New York-headquartered giant is to discontinue development of TRU-015, an investigational drug, and Trubion’s lead candidate, for the treatment of RA developed under the companies' CD20 collaboration. Pfizer's decision is based on preliminary results from a Phase IIb study which “did not meet the internally predefined primary endpoint”, a 20% difference in ACR50 response (a standard criteria for evaluating the effectiveness of RA treatments) compared with placebo at week 24.

Trubion said that a previously-conducted interim analysis of the trial data on 50% of the patient population revealed that the primary endpoint had been met. Also no significant safety issues were reported, “and they were not a factor in Pfizer's decision to discontinue development”, the Seattle-headquartered company said.

Nevertheless, given the higher than usual placebo response, TRU-015 did not meet the internal hurdle for continued development,” said Scott Stromatt, Trubion’s chief medical officer. He claimed it is “evident that the drug has significant biological and clinical activity with no significant safety concerns, but market dynamics dictate that we pursue a differentiated and best-in-class product to bring into Phase III development”.

This is the good news for Trubion as Pfizer confirmed that it will continue to develop SBI-087, a next-generation, humanised, subcutaneous CD20 RA product candidate which is in Phase II. Evan Loh, senior vice president of BioTherapeutics R&D at Pfizer, said “we are encouraged by our analysis to date of SBI-087”, adding that “the goal of our collaboration with Trubion continues to be the development of best-in-class CD20 therapies, and we look forward to the results of the ongoing Phase II study”.

The companies will be hoping that SBI-087 will one day grab some of the CD20 market dominated by Roche and Biogen Idec’s blockbuster Rituxan/MabThera (rituximab), which is approved for non-Hodgkin’s lymphoma and chronic lymphocytic leukaemia as well as RA. Pfizer inherited the Trubion pact following its merger with Wyeth last year.