Hepatic tumor growth: target for angiogenesis inhibition?

Microvessel density correlates with lymph node metastases and prognosis in hilar cholangiocarcinoma

BACKGROUND

Neovascularization was shown to be critically involved in the progression of multiple cancers, and treatment approaches targeting tumor-associated neovascularization provide convincing results in recent years in some tumor entities. However, little is known about the tumor-associated neovascularization in hilar cholangiocarcinoma. The present study was conducted to analyze tumor-associated neovascularization in hilar cholangiocarcinoma and to determine its influence on tumor growth, metastasis, recurrence, and prognosis.

METHODS

We analyzed tissue specimens of hilar cholangiocarcinoma (n = 60) by immunohistochemistry using the endothelial-specific antibody CD31 and subsequently quantified the microvessel density (MVD). The MVD was correlated with clinicopathological characteristics and recurrence pattern of the tumors as well as survival of patients.

RESULTS

Hilar cholangiocarcinoma revealed a high degree of vascularization, with a calculated mean MVD of 28.1 +/- 14.5 vessels. Tumors with a high MVD had a significant higher incidence of lymph node involvement (P = 0.009) and local recurrence (P < 0.001). Furthermore, a high MVD was identified to be a significant overall survival disadvantage (3-year, 28% vs. 93%; 5-year, 8% vs. 78%; P < 0.001) as well as disease-free survival disadvantage (3-year, 7% vs. 88%, 5-year, 7% vs. 72%; P < 0.001), with MVD representing an independent prognostic factor for survival.

CONCLUSIONS

Neovascularization is associated with nodal spread as well as local recurrence and serves as an independent prognostic factor for survival after curative resection of hilar cholangiocarcinoma. Therefore, tumor-associated neovascularization seems to be critically involved in the progression of this tumor entity. In addition, neovascularization may represent a potential target in he development of new therapeutic approaches in hilar cholangiocarcinoma.

A comparison of antiangiogenic therapies for the prevention of liver metastases

Angiogenesis is essential for solid tumor growth. Although successful antiangiogenic therapies have been demonstrated in animal models, a systematic comparison of the efficacy of different antiangiogenic factors has not been described in the hepatic environment. To address this issue, CT26 murine colon carcinoma cells were transfected with retroviral vectors encoding murine endostatin (mEndostatin), human angiostatin (hAngiostatin), murine-soluble vascular endothelial growth factor receptor-2, (msFlk-1), or murine-soluble Tie2 (msTie2). The transfected cells were then subjected to another round of transfection with a luciferase cDNA-encoding retroviral vector. Expression of these putative antiangiogenic proteins inhibited the proliferation of human umbilical vein endothelial cells in vitro but not tumor cells. To examine effects on tumor growth in vivo, modified cells were delivered via intrasplenic injection into BALB/c mice to induce liver metastases. Tumor burden was measured weekly by bioluminescence. Growth of hepatic metastases in vivo was significantly reduced in mice that were administered cells expressing msTie2 (76% reduction compared with control cells 21 days after intrasplenic inoculation; P < 0.05). Similar results were observed with cells that expressed msFlk-1 and hAngiostatin. However, expression of mEndostatin had no significant effect on the growth of liver metastases compared with control animals. These findings indicate that multiple antiangiogenic pathways are necessary for the growth of hepatic metastases, and each of these pathways is a potential clinically relevant antiangiogenic target for the treatment of this disease.