Effects of Thyroid Stimulating Hormone on Tumor Growth by Modulating Tumor Microenvironment in Thyroid Cancer

Abstract

Introduction: The stimulatory effect of thyroid stimulating hormone (TSH) through TSH receptor signal pathways on the growth of thyrocytes is well-demonstrated. Differentiated thyroid cancer (DTC) expresses TSH receptors and retains responsiveness to TSH. Thus, TSH suppression has been used as an important and effective treatment in patients with DTC. Since tumor microenvironment including angiogenesis has a crucial role in cancer progression and metastasis, we investigated whether the effects of TSH on tumor growth are also mediated by tumor microenvironment using a mouse model of DTC. Materials and Methods: BHP10-3SC DTC cells, which express TSH receptors, were subcutaneously implanted on 7-week-old BALB/c nu/nu mice. When the greater diameter of tumor became 5 mm or larger, recombinant human TSH (rhTSH, 1.5 μg/g) or vehicle was started to be injected intraperitoneally. Tumor size was measured every 3 days. After 15 days, tumor histology was examined and vascular endothelial growth factor (VEGF) mRNA expression was analyzed using real time-PCR. For supporting in vivo results, in vitro experiments to demonstrate TSH effects on angiogenesis were performed in BHP10-3SC and human endothelial cells. Results: Tumors in rhTSH group grew more rapidly than controls, and there was a significant difference in the tumor volume (on day 15, 1733.4 ± 793.5 mm3 vs. 1148.8 ± 471.1 mm3, respectively, P = 0.010). The vascular density in tumors was significantly increased in rhTSH group (13.8 ± 0.8% vs. 5.7 ± 0.8% in control, P = 0.021). Moreover, more tortuous and dilated vessels were observed in tumors of rhTSH group compared with controls (23.0 ± 1.7 μm vs. 7.4 ± 0.5 μm in vascular diameter, respectively, P <0.001). In addition, the macrophage infiltration in tumors was significantly increased in rhTSH group (27.6 ± 11.6% vs. 12.1 ± 4.3% in control, P = 0.004). In vitro experiments showed that TSH induced a significant up-regulation of VEGF-A mRNA expression in BHP10-3SC cells. Conditioned medium of TSH-treated BHP10-3SC cells (TSH-CM) contained higher concentration of VEGF-A than saline-treated CM (control-CM). Finally, treatment of TSH-CM significantly enhance potentials of cell migration and tube formation in human endothelial cells, HMVEC or HUVEC. Conclusions: TSH supports the growth of thyroid cancer via enhancing abnormal vasculature and subsequent recruitment of macrophages in tumor microenvironments.