Atacicept in Patients With Rheumatoid Arthritis and an Inadequate Response to Tumor Necrosis Factor Antagonist Therapy Results of a Phase II, Randomized, Placebo-Controlled, Dose-Finding Trial

Objective. To assess the efficacy, safety, and biologic activity of atacicept in patients with rheumatoid arthritis (RA) in whom the response to treatment with tumor necrosis factor antagonists was inadequate. Methods. The Atacicept for Reduction of Signs and Symptoms in Rheumatoid Arthritis Trial (AUGUST I) was a multicenter, phase II, double-blind, placebo-controlled dose-finding study involving 256 patients randomized 1:1:1:1 to receive atacicept (25 mg, 75 mg, or 150 mg) or placebo twice weekly for 4 weeks, then weekly for 21 weeks, with a 13-week treatment-free followup period (week 38). The primary end point was a response at week 26 according to the American College of Rheumatology criteria for 20% improvement in disease severity, using the C-reactive protein level. Results. No statistically significant differences were observed in the efficacy end points at week 26 (P = 0.410 for overall treatment effect). However, atacicept significantly reduced immunoglobulin and rheumatoid factor (RF) levels, but not anti-citrullinated protein antibody levels, in a dose-dependent manner, with levels returning toward baseline values during followup. The effects of treatment on IgG-RF and IgA-RF were more pronounced than the effects on total IgG and IgA. Adverse events (AEs), including serious AEs, leading to withdrawal were more common among patients treated with atacicept compared with placebo. AEs were variable in nature, and no dose-dependent trends were observed. The frequency of infection-related AEs was similar across treatments. No notable effect of treatment on immunization status (protective versus non-protective titer) was observed after initiation of treatment. Conclusion. This study did not meet the primary efficacy end point. However, clear biologic activity consistent with the proposed mechanism of action was observed. The results suggest that decreasing the expression of RF may not be sufficient to induce clinical improvement in RA. The safety of atacicept was considered acceptable in this patient population.