Expression and secretion of endostatin in thyroid cancer

In thyroid cancer (TC) endostatin was identified as a powerful negative regulator of tumor angiogenesis in vitro. It is currently being evaluated in phase I trials for antiangiogenic therapy in various solid tumors. The aim of this study was to evaluate endostatin expression in archival TC specimens and its secretion following stimulation with thyrotropin (TSH) and epidermal growth factor (EGF) in TC cell lines.

Tissue microarrays of 44 differentiated and 7 anaplastic TC and their metastasis were immunostained for endostatin protein expression and compared with corresponding non-neoplastic thyroid tissue (NT). In vitro, six differentiated (FTC133, FTC236, HTC, HTC-TSHr, XTC, and TPC1) and three anaplastic (C643, Hth74, Kat4.0) TC cell lines were evaluated for basal as well as TSH (1-100 mU/ml) and EGF stimulated (1-100 ng/ml) endostatin.

Endostatin was detected in all TC and more than half of the NT. Endostatin expression was more frequent and intense in differentiated as compared to anaplastic TC. In vitro, basal endostatin secretion varied between 33 +/- 5 pg/ml (FTC236) and 549 +/- 65 pg/ml (TPC1) and was doubled in FTC, when the "primary" (FTC133) was compared with the metastasis (FTC236). Some cell lines showed TSH-induced (e.g., 60% in XTC) or EGF-induced (e.g., 120% in TPC1) upregulation of endostatin secretion, while others did not, despite documented receptor expression.

This study demonstrates endostatin expression in TC, metastasis and--less frequently and intensely--in NT, suggesting a possible association to tumor progression. In vitro, endostatin secretion of some cell lines is regulated by TSH and EGF, however the individual differences deserve further functional studies. These results support rather tumor-specific than histotype-specific expression and regulation of endostatin in TC.