Possible contributions of thyroid hormone replacement to specific behaviors of cancer

Sunitinib-Induced Hypothyroidism and Survival in Pancreatic Neuroendocrine Tumors

Sunitinib has been approved for the treatment of pancreatic neuroendocrine tumors, renal-cell carcinoma, and gastrointestinal stromal tumors. The elevation of thyroid-stimulating hormone serum levels is a common side effect. Studies suggest a correlation between sunitinib-induced hypothyroidism and treatment outcome in patients with renal-cell carcinoma and gastrointestinal stromal tumors. This study assessed whether sunitinib-induced hypothyroidism is a predictive marker of the objective response rate, progression-free survival, and overall survival in pancreatic neuroendocrine tumor patients. Twenty-nine patients treated with sunitinib for advanced pancreatic neuroendocrine tumors were included. The incidence of sunitinib-induced hypothyroidism was 33%. The median progression-free survival of patients who developed hypothyroidism was 16 months (95% confidence interval: 6.2-25.8 months) as compared with six months among euthyroid patients (95% confidence interval: 0.1-12.2 months) (p=0.02). The median overall survival was 77 months (95% confidence interval: 31.4-122.6 months) in hypothyroid patients but 12 months (95% confidence interval: 5.9-18.1 months) in subjects with euthyroidism (p=0.001). The median overall survival from the time of initial diagnosis ranged from 247 months in patients with hypothyroidism to 65 months in euthyroid subjects (p=0.015). Elevated thyroid-stimulating hormone levels are a prognostic biomarker of improved outcomes of sunitinib therapy in pancreatic neuroendocrine tumor patients.

Tetrac as an anti-angiogenic agent in cancer

The thyroid hormones T3 and T4 have emerged as pro-angiogenic hormones with important implications for cancer management. Endogenous circulating hormone levels may help stimulate cancer progression and limit the effectiveness of anticancer therapy, though clinical data remain inconclusive. The capacity of thyroid hormones to modulate angiogenesis is mediated through non-canonical mechanisms initiated at the cell surface receptor integrin αvβ3. This integrin is predominantly expressed on tumour cells, proliferating endothelial cells and tumour stroma-associated cells, emphasising its potential relevance in angiogenesis and tumour biology. Thyroid hormone/integrin αvβ3 signalling results in the activation of intracellular pathways that are commonly associated with angiogenesis and are mediated through classical pro-angiogenic molecules such as vascular endothelial growth factor. The naturally occurring T4 analogue tetrac blocks the pro-angiogenic actions of thyroid hormones at the integrin receptor, in addition to agonist-independent anti-angiogenic effects. Tetrac reduces endothelial cell proliferation, migration and tube formation through a reduction in the transcription of vascular growth factors/growth factor receptors, hypoxia-inducible factor-1α, pro-angiogenic cytokines and a number of other pro-angiogenic genes, while at the same time stimulating the expression of endogenous angiogenesis inhibitors. It further modulates vascular growth factor activity by disrupting the crosstalk between integrin αvβ3 and adjacent growth factor receptors. Moreover, tetrac disrupts thyroid hormone-stimulated tumour recruitment, differentiation and the pro-angiogenic signalling of tumour stroma-associated mesenchymal stem cells. Tetrac affects tumour-associated angiogenesis via multiple mechanisms and interferes with other cancer cell survival pathways. In conjunction with its low toxicity and high tissue selectivity, tetrac is a promising candidate for clinical application.

Non-genomic Actions of Thyroid Hormones Regulate the Growth and Angiogenesis of T Cell Lymphomas

T-cell lymphomas (TCL) are a heterogeneous group of aggressive clinical lymphoproliferative disorders with considerable clinical, morphological, immunophenotypic, and genetic variation, including ~10-15% of all lymphoid neoplasms. Several evidences indicate an important role of the non-neoplastic microenvironment in promoting both tumor growth and dissemination in T cell malignancies. Thus, dysregulation of integrin expression and activity is associated with TCL survival and proliferation. We found that thyroid hormones acting via the integrin αvβ3 receptor are crucial factors in tumor microenvironment (TME) affecting the pathophysiology of TCL cells. Specifically, TH-activated αvβ3 integrin signaling promoted TCL proliferation and induced and an angiogenic program via the up-regulation of the vascular endothelial growth factor (VEGF). This was observed both on different TCL cell lines representing the different subtypes of human hematological malignancy, and in preclinical models of TCL tumors xenotransplanted in immunodeficient mice as well. Moreover, development of solid tumors by inoculation of murine TCLs in syngeneic hyperthyroid mice, showed increased tumor growth along with increased expression of cell cycle regulators. The genomic or pharmacological inhibition of integrin αvβ3 decreased VEGF production, induced TCL cell death and decreased in vivo tumor growth and angiogenesis. Here, we review the non-genomic actions of THs on TCL regulation and their contribution to TCL development and evolution. These actions not only provide novel new insights on the endocrine modulation of TCL, but also provide a potential molecular target for its treatment.

Clinical Implications and Impact of Discovery of the Thyroid Hormone Receptor on Integrin αvβ3-A Review

Hypothyroidism has been reported to improve survival in cancer patients but only recently has the putative mechanism been identified as a receptor for thyroxine and tri-iodothyronine on integrin αvβ3. Recognition of divergence of action of the pro-oncogenic L-thyroxine (T4) from pro-metabolic 3,5,3'-triiodo-L-thyronine (T3) has enabled clinical implementation whereby exogenous T3 may replace exogenous (or endogenous) T4 to maintain clinical euthyroid hypothyroxinemia that results in significantly better survival in advanced cancer patients without the morbidity of clinical hypothyroidism.