Tumor necrosis factor (TNF) is the dominant mediator of the cytokine cascade that causes inflammation and joint destruction in rheumatoid arthritis. A new class of agents under investigation, the biologic TNF inhibitors, inhibits the activity of TNF. Recombinant human TNF receptor p75 Fc fusion protein (TNFR:Fc; Enbrel) blocks the activity of the cytokine TNF. The preclinical, Phase I, and Phase II data of TNFR:Fc in rheumatoid arthritis are reviewed in this article.
All available data on TNFR:Fc in rheumatoid arthritis were reviewed. These data included published literature and data on file at the manufacturer.
TNFR:Fc has been effective in many models of inflammation, including animal models of rheumatoid arthritis and in clinical rheumatoid arthritis trials. Conclusions from a study with TNFR "knockout" mice (genetically altered mice incapable of producing TNFR proteins) demonstrated that p75 TNFR is a natural antagonist of TNF-mediated inflammation. A placebo-controlled, dose-escalation, Phase I trial evaluated the safety and efficacy of TNFR:Fc in patients with rheumatoid arthritis. There were no serious adverse effects reported. A Phase II, randomized, double-blind, placebo-controlled trial evaluated 180 patients with active rheumatoid arthritis whose previous therapy had failed. A dose-response relationship was observed in the number of tender and swollen joints; patients who received the highest dose (16 mg/m2) of TNFR:Fc had the greatest improvement. Treatment was generally well tolerated. TNFR:Fc is nonimmunogenic; no antibodies to TNFR:Fc have been detected thus far in human studies.
Preliminary data indicate that TNFR:Fc is an excellent candidate for future long-term studies in the treatment of rheumatoid arthritis.