Sprifermin for Treatment of Osteoarthritis: Recombinant Fibroblast Growth Factor 18 as a Possible Disease-Modifying Knee Osteoarthritis Drug

Osteoarthritis (OA) is a major cause of pain and disability in adults, affecting approximately 150 million people worldwide. It is most prevalent in knees and hips. Major risk factors are age, female sex, prior joint injury, and obesity. OA causes significant personal and steeply rising socio-economical costs in ageing populations. OA is characterized by progressive cartilage damage and inflammation. In later stages, it affects the subchondral bone, bone marrow, ligaments, tendons, and nerves und eventually leads to joint failure. Symptoms include pain, joint swelling, and stiffness. Therapies are symptomatic and focus on pain relief and measures to improve mobility, or, ultimately, joint replacement. So far, no drugs that could prevent or slow down disease progression are available. Based on promising in vitro and preclinical studies, recombinant fibroblast growth factor (FGF) 18 (sprifermin; Merck Serono) has come into focus as a potential disease-modifying OA drug (DMOAD). Three randomized controlled trials (RCTs) investigating the safety and efficacy of intraarticularly (i.a.) injected sprifermin application in patients with knee OA have been completed so far. Data from these trials, post hocanalyses and follow-ups provide have evidenced that i.a. sprifermin induced a significant and sustained increase in cartilage thickness and volume without specific adverse effects, but in terms of clinical symptoms or physical joint function sprifermin did not cause significant improvements compared to placebo treatment in whole study populations. However, significant pain reduction was observed in a “subgroup at risk” of patients with more severe disease states, indicating that under certain disease conditions the structural benefit improvements could translate into clinical benefit. This calls for larger RCTs allowing e.g., for disease state or risk factor-specific stratification of patients and longer follow-ups to substantiate the efficacy of sprifermin as a possible DMOAD. This review gives an overview on the prevalence, etiology and socio-economic burden of OA, its pathogenesis as well as the current treatment options of the disease. It summarizes the role of FGF-18 in chondrocyte and cartilage (patho)physiology and addresses the question of evidence for the efficacy and safety of i.a. sprifermin injection in patients with knee OA based on trial outcomes and literature data.