ABSTRACT
Endothelial Notch signaling is critical for tumor angiogenesis. Notch1 blockade can interfere with tumor vessel function but causes tissue hypoxia and gastrointestinal toxicity. Notch4 is primarily expressed in endothelial cells, where it may promote angiogenesis; however, effective therapeutic targeting of Notch4 has not been successful. We developed highly specific Notch4-blocking antibodies, 6-3-A6 and humanized E7011, allowing therapeutic targeting of Notch4 to be assessed in tumor models. Notch4 was expressed on tumor endothelial cells in multiple cancer models, and endothelial expression was associated with response to E7011/6-3-A6. Anti-Notch4 treatment significantly delayed tumor growth in mouse models of breast, skin, and lung cancer. Enhanced tumor inhibition occurred when anti-Notch4 treatment was used in combination with chemotherapeutics. Endothelial transcriptomic analysis of murine breast tumors treated with 6-3-A6 identified significant changes in pathways of vascular function but caused only modest change in canonical Notch signaling. Analysis of early and late treatment timepoints revealed significant differences in vessel area and perfusion in response to anti-Notch4 treatment. We conclude that targeting Notch4 improves tumor growth control through endothelial intrinsic mechanisms.
ABSTRACT
Rheumatoid arthritis (RA) is an autoimmune disorder that affects joints and is characterized by synovial hyperplasia and bone erosion associated with neovascularization and infiltration of proinflammatory cells. The introduction of biological disease-modifying anti-rheumatic drugs has dramatically changed the treatment of RA over the last 20 years. However, fewer than 50% of RA patients enter remission, and 10-15% are treatment refractory. There is currently no cure for RA. Fractalkine (FKN, also known as CX3CL1) is a cell membrane-bound chemokine that can be induced on activated vascular endothelial cells. FKN has dual functions as a cell adhesion molecule and a chemoattractant. FKN binds specifically to the chemokine receptor CX3CR1, which is selectively expressed on subsets of immune cells such as patrolling monocytes and killer lymphocytes. The FKN-CX3CR1 axis is thought to play important roles in the initiation of the inflammatory cascade and can contribute to exacerbation of tissue injury in inflammatory diseases. Accordingly, studies in animal models have shown that inhibition of the FKN-CX3CR1 axis not only improves rheumatic diseases but also reduces associated complications, such as pulmonary fibrosis and cardiovascular disease. Recently, a humanized anti-FKN monoclonal antibody, E6011, showed promising efficacy with a dose-dependent clinical response and favorable safety profile in a Phase 2 clinical trial in patients with RA (NCT02960438). Taken together, the preclinical and clinical results suggest that E6011 may represent a new therapeutic approach for rheumatic diseases by suppressing a major contributor to inflammation and mitigating concomitant cardiovascular and fibrotic diseases. In this review, we describe the role of the FKN-CX3CR1 axis in rheumatic diseases and the therapeutic potential of anti-FKN monoclonal antibodies to fulfill unmet clinical needs.
ABSTRACT
OBJECTIVE: To elucidate the role of the fractalkine (FKN)/CX3 CR1 pathway in joint destruction in rheumatoid arthritis. METHODS: We examined the effect of treatment with anti-mouse FKN (anti-mFKN) monoclonal antibody (mAb) on joint destruction and the migration of osteoclast precursors (OCPs) into the joint, using the collagen-induced arthritis (CIA) model. DBA/1 mice were immunized with bovine type II collagen to induce arthritis, and then treated with anti-mFKN mAb. Disease severity was monitored by arthritis score, and joint destruction was evaluated by soft x-ray and histologic analyses. Plasma levels of joint destruction markers were assessed by enzyme-linked immunosorbent assay. FKN expression on endothelial cells was detected by immunohistochemistry. Bone marrow-derived OCPs were labeled with fluorescein and transferred to mice with CIA, and the migration of the OCPs to the joints was then analyzed. RESULTS: Both prophylactic and therapeutic treatment with anti-mFKN mAb significantly decreased the arthritis and soft x-ray scores. Plasma levels of cartilage oligomeric matrix protein and matrix metalloproteinase 3 decreased after treatment with anti-mFKN mAb. Histologic analysis revealed that anti-mFKN mAb inhibited synovitis, pannus formation, and cartilage destruction, as well as suppressed bone damage, with a marked reduction in the number of tartrate-resistant acid phosphatase-positive osteoclasts. Anti-mFKN mAb strongly inhibited the migration of bone marrow-derived OCPs into the affected synovium. CONCLUSION: Anti-mFKN mAb notably ameliorates arthritis and joint destruction in the CIA model, as well as inhibits migration of OCPs into the synovium. These results suggest that inhibition of the FKN/CX3 CR1 pathway could be a novel strategy for treatment of both synovitis and joint destruction in rheumatoid arthritis.
