Despite the fact that the role of endoglin on endothelial cells has been extensively described, its expression and biological role on (epithelial) cancer cells is still debatable. Especially its... Show moreDespite the fact that the role of endoglin on endothelial cells has been extensively described, its expression and biological role on (epithelial) cancer cells is still debatable. Especially its function on squamous cell carcinoma (SCC) cells is largely unknown. Therefore, we investigated SCC endoglin expression and function in three types of SCCs; head and neck (HNSCC), esophageal (ESCC) and vulvar (VSCC) cancers. Endoglin expression was evaluated in tumor specimens and 14 patient-derived cell lines. Next to being expressed on angiogenic endothelial cells, endoglin is selectively expressed by individual SCC cells in tumor nests. Patient derived HNSCC, ESCC and VSCC cell lines express varying levels of endoglin with high interpatient variation. To assess the function of endoglin in signaling of TGF-beta ligands, endoglin was overexpressed or knocked out or the signaling was blocked using TRC105, an endoglin neutralizing antibody. The endoglin ligand BMP-9 induced strong phosphorylation of SMAD1 independent of expression of the type-I receptor ALK1. Interestingly, we observed that endoglin overexpression leads to strongly increased soluble endoglin levels, which in turn decreases BMP-9 signaling. On the functional level, endoglin, both in a ligand dependent and independent manner, did not influence proliferation or migration of the SCC cells. In conclusion, these data show endoglin expression on individual cells in the tumor nests in SCCs and a role for (soluble) endoglin in paracrine signaling, without directly affecting proliferation or migration in an autocrine manner. Show less
The TME has increasingly been recognized as an important player in tumor progression and metastasis and a possible target for therapy. The TME consists of multiple cell types secreting growth... Show moreThe TME has increasingly been recognized as an important player in tumor progression and metastasis and a possible target for therapy. The TME consists of multiple cell types secreting growth factors and cytokines that exert either pro- or anti-tumor effects. This thesis mainly focuses on studies of the TME, especially the effects of Endoglin, on several cell types within the TME, including endothelial cells, fibroblasts, and immune cells.The TME has increasingly been recognized as an important player in tumor progression and metastasis and a possible target for therapy. The TME consists of multiple cell types secreting growth factors and cytokines that exert either pro- or anti-tumor effects. This thesis mainly focusses on studies of the TME, especially the effects of Endoglin, on several cell types within the TME, including endothelial cells, fibroblasts, and immune cells. This thesis aims to unravel the role of Endoglin as a possible target on various cell types within the TME of solid tumors. Endoglin is known for its role during angiogenesis, however, an increasing number of studies have shown the importance of Endoglin expression on several other cell types (e.g., immune cells, CAFs, tumor cells). Show less
Liu, Y.M.; Paauwe, M.; Nixon, A.B.; Hawinkels, L.J.A.C. 2021
Approximately 30 years ago, endoglin was identified as a transforming growth factor (TGF)-beta coreceptor with a crucial role in developmental biology and tumor angiogenesis. Its selectively high... Show moreApproximately 30 years ago, endoglin was identified as a transforming growth factor (TGF)-beta coreceptor with a crucial role in developmental biology and tumor angiogenesis. Its selectively high expression on tumor vessels and its correlation with poor survival in cancer patients led to the exploration of endoglin as a therapeutic target for cancer. The endoglin neutralizing antibody TRC105 (Carotuximab(R), Tracon Pharmaceuticals (San Diego, CA, USA) was subsequently tested in a wide variety of preclinical cancer models before being tested in phase I-III clinical studies in cancer patients as both a monotherapy and in combination with other chemotherapeutic and anti-angiogenic therapies. The combined data of these studies have revealed new insights into the role of endoglin in angiogenesis and its expression and functional role on other cells in the tumor microenvironment. In this review, we will summarize the preclinical work, clinical trials and biomarker studies of TRC105 and explore what these studies have enabled us to learn and what questions remain unanswered. Show less
Schoonderwoerd, M.J.A.; Hakuno, S.K.; Sassen, M.; Kuhlennaijer, E.B.; Paauwe, M.; Slingerland, M.; ... ; Hawinkels, L.J.A.C. 2021
Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal forms of cancer and is known to have low immunogenicity and an immunosuppressive microenviron-ment. It is also... Show moreBackground: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal forms of cancer and is known to have low immunogenicity and an immunosuppressive microenviron-ment. It is also characterized by high accumulation of dense stroma, composed of mostly cancer-associated fibroblasts (CAFs). Multiple subsets of CAFs are described, with one of them expressing the transforming growth factor (TGF)-beta co-receptor endoglin. In previous work, we and others have shown that endoglin-expressing CAFs stimulate tumor progression and metastasis. Therefore, in this study, we set out to investigate the role of endoglin-expressing CAFs in pancreatic cancer progression. Methods: First, we investigated the expression of endoglin on CAFs in both human tissues as well as a mouse model for PDAC. Since CAF-specific endoglin expression was high, we targeted endoglin by using the endoglin neutralizing antibody TRC105 in the murine KPC model for PDAC. Results: Although some signs of immune activation were observed, TRC105 did not affect tumor growth. Since 90% of the CD8+ T-cells expressed the immune checkpoint PD-1, we investigated the combination with a PD1 checkpoint inhibitor, which did not enhance therapeutic responses. Finally, genetic deletion of endoglin from collagen 1a1 expressing cells also did not affect the growth of the mouse KPC tumors. Conclusion: Our results show that although endoglin is highly expressed on PDAC-CAFs and signaling is efficiently inhibited by TRC105, this does not result in decreased tumor growth in the KPC model for pancreatic cancer. Show less
Endoglin, a type-III accessory receptor for the Transforming Growth Factor (TGF)-beta superfamily pathway, is known for its crucial role during angiogenesis. Extensive work has shown the important... Show moreEndoglin, a type-III accessory receptor for the Transforming Growth Factor (TGF)-beta superfamily pathway, is known for its crucial role during angiogenesis. Extensive work has shown the important roles that endoglin plays in balancing the TGF-beta signaling pathway, thereby regulating endothelial cell proliferation and migration. However, recent work indicates a far more widespread role for endoglin beyond the endothelial cells. In this review, we will provide a summary of recent publications on endoglin expression on epithelial (cancer) cells, cancer-associated fibroblasts, and mesenchymal stem cells. Additionally, we will discuss the role of endoglin in innate and adaptive immunity. Finally, we will discuss the results of clinical trials using the endoglin targeting antibody (TRC105), focusing on the effects observed beyond the endothelium. In conclusion, although endoglin was initially identified as an endothelial marker, additional roles for endoglin on other cell types have been shown, although the number of studies is still limited, with sometimes conflicting data. Future studies will further establish the roles of endoglin beyond the endothelium. Show less
