Background Mitogen-activated protein (MAP) kinases are key regulators of cytokine production, and are therefore potential targets for treatment of rheumatoid arthritis (RA).

Objective This two-part phase II study investigated the efficacy and safety of a once-daily 50 mg GLPG0259 (an inhibitor of MAP kinase-activated protein kinase 5) dose vs placebo (part A). An interim analysis after part A would determine whether the dose-finding part (part B) would be performed.

Methods In part A, eligible methotrexate (MTX)-refractory patients with RA were randomised to receive either a once-daily 50 mg dose of GLPG0259 or placebo, in addition to a stable dose of MTX, for 12 weeks. The primary efficacy end point was the percentage of patients achieving an American College of Rheumatology 20% improvement (ACR20) response after 12 weeks.

Results The interim analysis showed no difference between the percentage of subjects achieving the primary efficacy variable of ACR20 or the secondary efficacy variables (ACR50, ACR70 and Disease Activity Score 28) at week 12 in the GLPG0259-treated (n=19) and placebo-treated (n=11) groups. Owing to lack of efficacy, the study was terminated, and part B was not initiated.

Conclusions This innovative study design quickly provided conclusive results on the lack of efficacy of GLPG0259 in patients with RA.