Translational Value of Tumor-Associated Lymphangiogenesis in Cholangiocarcinoma

Abstract

The prognosis of cholangiocarcinoma remains poor in spite of the advances in immunotherapy and molecular profiling, which has led to the identification of several targetable genetic alterations. Surgical procedures, including both liver resection and liver transplantation, still represent the treatment with the best curative potential, though the outcomes are significantly compromised by the early development of lymph node metastases. Progression of lymphatic metastasis from the primary tumor to tumor-draining lymph nodes is mediated by tumor-associated lymphangiogenesis, a topic largely overlooked until recently. Recent findings highlight tumor-associated lymphangiogenesis as paradigmatic of the role played by the tumor microenvironment in sustaining cholangiocarcinoma invasiveness and progression. This study reviews the current knowledge about the intercellular signaling and molecular mechanism of tumor-associated lymphangiogenesis in cholangiocarcinoma in the hope of identifying novel therapeutic targets to halt a process that often limits the success of the few available treatments.

Keywords: VEGF-C; VEGFR-3; biliary neoplasia; cancer-associated fibroblasts; lymphatic vessel; tumor microenvironment.

Figure 1

Histological evidence of lymphoinvasion with lymph node metastasis and spatial configuration of the lymphatic vascularization within the tumor microenvironment. (A–D). H&E showing examples of intra-tumoral (A) and peri-tumoral lymphatic vessel invasion in iCCA (B); lymphatic invasion can also be observed in portal tracts of adjacent non-tumoral liver (C). Neoplastic lympho-invasion in iCCA eventually leads to lymph node metastases (D–F). Dual immunohistochemistry for Podoplanin (PDPN) (blue) and α-SMA (brown) shows the close alignment of PDPN⁺ lymphatic endothelial cells with α-SMA⁺ cancer-associated fibroblasts in the same area taken at different magnifications, to highlight the intense functional link between the two stromal cell types. Original magnifications: (A–C,E): 10×; (D): 1.25×; (F): 20×.

Figure 2

Molecular mechanisms regulating lymphangiogenesis in CCA. The recruitment of the lymphatic plexus in CCA is mediated by the coordinated action of neoplastic cells and stromal cells hosted in the tumor microenvironment. Tumor cholangiocytes (CCA), in response to a hypoxic stimulus, upregulate HIF-1α, which is responsible for the increased secretion of VEGF-A, PDGF-B, and PDGF-D. These mediators recruit CAFs, which in turn are induced to secrete VEGF-A and VEGF-C via an ERK/JNK-mediated pathway, ultimately responsible for the vascular assembly of LECs. CCA cells are also able to directly recruit LECs through a RIPK1/p38/JNK/AP-1-mediated pathway that stimulates VEGF-C and PEDF hypersecretion. This same pathway is also able to stimulate the secretion of proinflammatory cytokines such as TNF-α and IL-6, with effects on the inflammatory milieu of the tumor microenvironment. Finally, the secretion of THBS1 and THBS2 by CCA cells, which inhibit the release of VEGF-A by the other components of the tumor microenvironment (matrix), dampens tumor blood angiogenesis in CCA. See the main text for further description of the mechanisms involved. CCA, cholangiocarcinoma; TME, tumor microenvironment; Hif-1α, hypoxia-inducible factor-1α; VEGF, vascular endothelial growth factor; PDGF, platelet-derived growth factor; CAFs, cancer-associated fibroblasts; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; LECs, lymphatic endothelial cells; RIPK1, receptor-interacting protein kinase 1; AP-1, activation protein-1; PEDF, pigment epithelium-derived factor; THBS, thrombospondin. Legend: ↑, upregulation.