Abstract
Ubiquitination is a common post-translational modification, tagging proteins for degradation. The ubiquitin proteasome system is activated in Crohn’s Disease (CD), and modulation of its components might be a novel strategy for therapeutic intervention to control inflammation. The conjugation of ubiquitin to a target protein is orchestrated by a series of enzymatic reactions, the last step being catalyzed by a selective ubiquitin E3 ligase. Among ubiquitin E3 ligases, Fbxl2 serves as a sentinel gatekeeper to limit inflammation by targeting and enhancing the degradation of tumor necrosis factor receptor associated factors (TRAF) proteins, which link cell surface signals (through NFkB signaling) to cytokine secretion. In addition, Fbxl2 controls the ubiquitination of the inflammasome, NOD-like receptor protein 3 (NLRP3), which mediates the release of interleukin (IL)1β and IL18 (Fig.1). Fbxl2 protein itself is ubiquitinated and degraded by another protein, called Fbxo3. Inhibition of Fbxo3 results in increased Fbxl2 levels and decreased TRAF and NLRP3. Individuals with a natural occurring polymorphism within Fbxo3V221Ihave decreased lipopolysaccharide(LPS)-induced cytokine (TNFα, IL1β & IL6) production, Fbxo3 and TRAF levels and increased Fbxl2, providing human genetic target validation for Fbxo3-Fbxl2 axis modulation in inflammatory conditions. BC1261 is a first-in-class, selective, orally available Fbxo3 inhibitor in clinical development for the treatment of CD.
In vitro data demonstrated that BC1261 binds to Fbxo3, prevents Fbxo3/Fbxl2 association and produces a concentration-dependent inhibition of LPS-induced release of TNFα and IL1β from human peripheral blood mononuclear cells. In an acute DSS-mouse model, administration of BC-1261 via drinking water ad libitum (30 μg/ml) or by daily intraperitoneal (IP) injection (150 μg) for 5 days resulted in the attenuation of the shortening of colonic length, tissue damage (Fig2.A), and TNFα and IL6 tissue levels (Fig.2B). In a repeated DSS-mouse model, BC-1261 (10 mg/kg bid) given orally for 19 days was comparable to the positive control (anti-p40) in the DAI composite (Fig2.C), stool consistency (Fig2.D), and histopathology score in the proximal colon (Fig2.E). BC-1261 also lead to clinically relevant reductions on endoscopy score (Fig2.F).
Mechanism and Impact of Fbxo3-Fbxl2 Axis Modulation
BC-1261 is Effective in Mice Models of Colitis
BC1261, a Fbxo3 inhibitor, was efficacious in both acute and chronic preclinical models of colitis. Taken together, these results suggest the potential utility of selective Fbxo3-Fbxl2 modulation in the treatment of CD.
