Role of angiopoietins in mesothelioma progression

BACKGROUND AND OBJECTIVE

Anti-angiogenic treatment has been recently shown to be clinically beneficial for mesothelioma patients. Angiopoietins-1 and -2 are key regulators of tumor angiogenesis. Ang-1 is mainly known to promote angiogenesis and vessel stability, while Ang-2 could serve as an antagonist of Ang-1 causing vessel regression and destabilization or enhance angiogenesis in a context-dependent manner. We hypothesized that Ang-1 would promote and Ang2 would halt experimental mesothelioma by affecting tumor angiogenesis.

METHODS

To examine the effects of angiopoietins in mesothelioma angiogenesis and in vivo growth we constructed Ang-1 or Ang-2 overexpressing AE17 and AB1 mesothelioma cells and implanted them in the respective syngeneic animals. We also explored the clinical relevance of our observations using the human tumoral mRNAseq data available in the TCGA database.

RESULTS AND CONCLUSIONS

Ang-1 promotes mesothelioma angiogenesis and growth while the effect of Ang-2 is context-dependent. Low Ang-1 levels in human mesotheliomas are associated with the epitheloid subtype. Tumors of high Ang-1, or concurrent high Ang-2 and VEGF expression present high PECAM-1 and CDH5 expression, markers of vascularity and vascular stability, respectively. Our results highlight the importance of angiopoietins in mesothelioma pathophysiology and pave the way for the clinical development of novel anti-angiogenic strategies.

Targeting Tie-2/angiopoietin axis in experimental mesothelioma confers differential responses and raises predictive implications

Malignant pleural mesothelioma is resistant to currently used treatment. Angiopoieitn-1 directly promotes mesothelioma cell growth in a Tie-2-dependent fashion. Angiopoietin/Tie-2 axis may thus be valid targets for therapeutic interventions against mesothelioma. We hypothesized that a soluble angiopoietin inhibitor (Murine Tek-deltaFc) would halt mesothelioma progression in vivo by enhancing mesothelioma cell proliferation and inhibiting tumor angiogenesis. Our hypothesis was challenged on two syngeneic mesothelioma in vivo models (AB1 cells-Balb/c mice and AE17 cells-C57BL/6 mice. Even though both mesothelioma cell lines express the Angiopoietin-1/-2 and Tie-2, murine Tek-deltaFc hampered AB1 but not AE17 mesothelioma growth in vivo by enhancing tumor cell apoptosis and limiting tumor angiogenesis. Neither angiopoietins (Angs)-1 and -2 nor the inhibitor affected mesothelioma cell growth in vitro. AB1 (responding) tumors were more vascularized and displayed higher endothelial Tie-2 and lower tumor Ang-1 expression than the (non-responding) AE17 tumors. Angiopoietins-1 and -2 are expressed in tumors and pleural cavity of mesothelioma patients demonstrating the clinical relevance of our experimental observations. In conclusion, disrupting Ang-Tie-2 signaling limits mesothelioma angiogenesis and halts tumor progression. Tumor vascularity, endothelial Tie-2 expression and tumor Ang-1 expression may predict mesothelioma response to Tek-deltaFc.

Icmt inhibition exerts anti-angiogenic and anti-hyperpermeability activities impeding malignant pleural effusion

Small GTPases are pivotal regulators of several aspects of tumor progression. Their implication in angiogenesis, vascular permeability and tumor-associated inflammatory responses is relevant to the pathobiology of Malignant Pleural Effusion (MPE). Inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt) abrogates small GTPase activation. We therefore hypothesized that cysmethynil, an Icmt inhibitor would limit pleural fluid accumulation in two models, a lung-adenocarcinoma and a mesothelioma-induced MPE. Cysmethynil significantly reduced MPE volume in both models and tumor burden in the adenocarcinoma model. It inhibited pleural vascular permeability and tumor angiogenesis in vivo and reduced endothelial cell proliferation, migration and tube formation in vitro. Cysmethynil also promoted M1 anti-tumor macrophage homing in the pleural space in vivo, and inhibited tumor-induced polarization of macrophages towards a M2 phenotype in vitro. In addition, the inhibitor promoted adenocarcinoma cell apoptosis in vivo. Inhibition of small GTPase might thus represent a valuable strategy for pharmacotherapy of MPE.

Mammalian target of rapamycin (mTOR) inhibition does not prevent lung adenocarcinoma-induced malignant pleural effusion

The impact of temsirolimus was investigated in a murine model of malignant pleural effusion (MPE) created with intrapleural injection of Lewis Lung Cancer (LLC) cells. Temsirolimus (1 or 20 mg/kg) did not affect the pleural fluid volume or the number of pleural tumour foci. In addition, temsirolimus did not affect vascular endothelial growth factor expression by LLC cells in vitro. In conclusion, temsirolimus did not curtail experimental lung-adenocarcinoma-induced MPE.