Endothelial-Specific Molecule 1 Inhibition Lessens Productive Angiogenesis and Tumor Metastasis to Overcome Bevacizumab Resistance

Simple Summary Bevacizumab mediated anti-angiogenesis provides a new chance of survival for patients with a tumor. However, most patients have acquired bevacizumab resistance after continuous treatment, and there is no available clinical therapy to overcome drug resistance. In this study, we analyzed unique expression patterns of genes from bevacizumab-sensitive or acquired bevacizumab-resistant cancer cells using RNA-seq analysis to identify the potential molecules and mechanism of bevacizumab resistance. We found that endothelial-specific molecule 1 expression elevated bevacizumab-resistant tumor cells, and endothelial-specific molecule 1 further regulates MMP9, VEGF, and DLL4 to promote metastasis and angiogenesis in vitro and in vivo. The anti-ESM1 monoclonal antibody developed by us significantly strengthened the efficacy of bevacizumab in vivo. This research has an important theoretical and clinical application value for elucidating the resistance mechanism and overcoming the bevacizumab resistance. The development of drug resistance in malignant tumors leads to disease progression, creating a bottleneck in treatment. Bevacizumab is widely used clinically, and acts by inhibiting angiogenesis to "starve" tumors. Continuous treatment can readily induce rebound proliferation of tumor blood vessels, leading to drug resistance. Previously, we found that the fragment crystallizable (Fc) region of bevacizumab cooperates with the Toll-like receptor-4 (TLR4) ligand to induce M2b polarization in macrophages and secrete tumor necrosis factor-alpha (TNF alpha), which promotes immunosuppression, tumor metastasis, and angiogenesis. However, the downstream mechanism underlying TNF alpha-mediated bevacizumab resistance requires further investigation. Our RNA-Seq analysis results revealed that the expression of endothelial cell specific molecule-1 (ESM1) increased significantly in drug-resistant tumors and promoted metastasis and angiogenesis in vitro and in vivo. Furthermore, TNF alpha induced the upregulation of ESM1, which promotes metastasis and angiogenesis and regulates matrix metalloprotease-9 (MMP9), vascular endothelial growth factor (VEGF), and delta-like ligand-4 molecules (DLL4). Accordingly, the curative effect of bevacizumab improved by neutralizing ESM1 with high-affinity anti-ESM1 monoclonal antibody 1-2B7 in bevacizumab-resistant mice. This study provides important insights regarding the molecular mechanism by which TNF alpha-induced ESM1 expression promotes angiogenesis, which is significant for elucidating the mechanism of bevacizumab drug resistance and possibly identifying appropriate biosimilar molecules.