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The nuclear transcription factorκB (NFκB) is a potential molecular target for anti-inflammatory therapy. The NFκB pathway is crucial to the transcriptional activation of multiple mediators involved in the initiation and maintenance of inflammatory processes such as arthritis. The present study was undertaken to investigate the potency of a novel class of NFκB inhibitors that interfere with the NFκB signalling pathway selectively in endothelial cells, a cell type that plays an important role in the extravasation of leucocytes in inflammation.
A multimodular recombinant protein that specifically binds cytokine-activated endothelium consists of three domains: (1) an endothelial cell-specific binding domain; (2) the translocation domain of pseudomonas exotoxin A (ETA II) that facilitates the endosomal release of the construct into the cytosol; and (3) the NEMO-binding peptide (NFκB inhibiting effector domain). This multimodular protein is also named ‘ligand-sneaking construct’. The influence of this E-selectin specific construct (LSC1) on NFκB activation was analysed in vitro by an NFκB-luciferase reporter gene assay and EMSA. Two different mouse models of arthritis were used to investigate the effect of LSC1 in vivo.
ELISA experiments showed specific binding of this LSC1 on E-selectin expressing CHO cells (CHO_E) versus wildtype CHO cells. The inhibitory effect of the NFκB transcriptional activity in LSC1 treated CHO_E cells was observed using an NFκB-luciferase reporter gene assay. Additionally, EMSA analysis indicated a reduced nuclear translocation of NFκB upon cytokine stimulation after LSC1 pretreatment of CHO_E cells. Furthermore, leucocytes adhesion on cytokine-activated and LSC1 treated mouse endothelial cells was significantly diminished. In vivo, joint swelling was significantly reduced after treatment with this LSC1 in the acute and flare-up phase of mBSA-induced arthritis in mice. In contrast, treatment of the mice with the control constructs did not ameliorate arthritis.
Moreover, we show that the systemic administration of the endothelium-specific NFκB inhibitor LSC1 leads to an amelioration of inflammatory joint disease induced by G6PI containing serum. Strong evidence for specific in vivo binding to the endothelium of LSC1 was shown by in vivo imaging.
Our results demonstrate that endothelial cell-specific NFκB inhibition can be achieved using the ‘ligand-sneaking concept’. We presented for the first time an E-selectin-specific NFκB inhibitor that shows therapeutic potential to treat inflammatory joint diseases in two different mouse model of arthritis. The ligand-sneaking concept can be modified to target other cell types and to interfere with distinct signalling pathways.