Aleck Hercbergs

Crosstalk between integrin αvβ3 and estrogen receptor-α is involved in thyroid hormone-induced proliferation in human lung carcinoma cells.

A cell surface receptor for thyroid hormone that activates extracellular regulated kinase (ERK) 1/2 has been identified on integrin αvβ3. We have examined the actions of thyroid hormone initiated at the integrin on human NCI-H522 non-small cell lung carcinoma and NCI-H510A small cell lung cancer cells. At a physiologic total hormone concentration (10−7 M), T4 significantly increased proliferating cell nuclear antigen (PCNA) abundance in these cell lines, as did 3, 5, 3′-triiodo-L-thyronine (T3) at a supraphysiologic concentration. Neutralizing antibody to integrin αvβ3 and an integrin-binding Arg-Gly-Asp (RGD) peptide blocked thyroid hormone-induced PCNA expression. Tetraiodothyroacetic acid (tetrac) lacks thyroid hormone function but inhibits binding of T4 and T3 to the integrin receptor; tetrac eliminated thyroid hormone-induced lung cancer cell proliferation and ERK1/2 activation. In these estrogen receptor-α (ERα)-positive lung cancer cells, thyroid hormone (T4>T3) caused phosphorylation of ERα; the specific ERα antagonist ICI 182,780 blocked T4-induced, but not T3-induced ERK1/2 activation, as well as ERα phosphorylation, proliferating-cell nuclear antigen (PCNA) expression and hormone-dependent thymidine uptake by tumor cells. Thus, in ERα-positive human lung cancer cells, the proliferative action of thyroid hormone initiated at the plasma membrane is at least in part mediated by ERα. In summary, thyroid hormone may be one of several endogenous factors capable of supporting proliferation of lung cancer cells. Activity as an inhibitor of lung cancer cell proliferation induced at the integrin receptor makes tetrac a novel anti-proliferative agent.

Erythrocyte glutathione and tumour response to chemotherapy

There is much evidence that tumour glutathione (GSH) concentration is an important factor in resistance to cancer chemotherapy. Since measurement of tumour GSH would require an invasive procedure in every patient, we have tried to find out whether GSH concentrations in peripheral-blood erythrocytes are related to the response to chemotherapy and thus whether they reflect those in tumour cells. Erythrocyte GSH concentrations were measured by spectrophotometry in peripheral blood from 28 patients with advanced breast cancer and 40 patients with other tumours before and after treatment with various conventional chemotherapeutic regimens. The mean pretreatment GSH concentration was lower in patients who showed a complete or partial response to chemotherapy than in those with stable or progressive disease in both the breast-cancer group (8.69 [95% confidence interval 5.99-11.39] vs 2.32 [1.23-3.41] mumol/g haemoglobin; p less than 0.01) and the group with other tumours (5.94 [4.14-7.74] vs 2.83 [1.71-3.95] mumol/g; p less than 0.01). The correlation of erythrocyte GSH concentration with response rate suggests that this measurement may be helpful in prediction of response to therapy.

Modulation of angiogenesis by thyroid hormone and hormone analogues: implications for cancer management

Acting via a cell surface receptor on integrin αvβ3, thyroid hormone is pro-angiogenic. Nongenomic mechanisms of actions of the hormone and hormone analogues at αvβ3 include modulation of activities of multiple vascular growth factor receptors and their ligands (vascular endothelial growth factor, basic fibroblast growth factor, platelet-derived growth factor, epidermal growth factor), as well as of angiogenic chemokines (CX3 family). Thyroid hormone also may increase activity of small molecules that support neovascularization (bradykinin, angiotensin II) and stimulate endothelial cell motility. Therapeutic angio-inhibition in the setting of cancer may be opposed by endogenous thyroid hormone, particularly when a single vascular growth factor is the treatment target. This may be a particular issue in management of aggressive or recurrent tumors. It is desirable to have access to chemotherapies that affect multiple steps in angiogenesis and to examine as alternatives in aggressive cancers the induction of subclinical hypothyroidism or use of antagonists of the αvβ3 thyroid hormone receptor that are under development.

Cancer Cell Gene Expression Modulated from Plasma Membrane Integrin αvβ3 by Thyroid Hormone and Nanoparticulate Tetrac

Integrin αvβ3 is generously expressed by cancer cells and rapidly dividing endothelial cells. The principal ligands of the integrin are extracellular matrix proteins, but we have described a cell surface small molecule receptor on αvβ3 that specifically binds thyroid hormone and thyroid hormone analogs. From this receptor, thyroid hormone (l-thyroxine, T4; 3,5,3′-triiodo-l-thyronine, T3) and tetraiodothyroacetic acid (tetrac) regulate expression of specific genes by a mechanism that is initiated non-genomically. At the integrin, T4 and T3 at physiological concentrations are pro-angiogenic by multiple mechanisms that include gene expression, and T4 supports tumor cell proliferation. Tetrac blocks the transcriptional activities directed by T4 and T3 at αvβ3, but, independently of T4 and T3, tetrac modulates transcription of cancer cell genes that are important to cell survival pathways, control of the cell cycle, angiogenesis, apoptosis, cell export of chemotherapeutic agents, and repair of double-strand DNA breaks. We have covalently bound tetrac to a 200 nm biodegradable nanoparticle that prohibits cell entry of tetrac and limits its action to the hormone receptor on the extracellular domain of plasma membrane αvβ3. This reformulation has greater potency than unmodified tetrac at the integrin and affects a broader range of cancer-relevant genes. In addition to these actions on intra-cellular kinase-mediated regulation of gene expression, hormone analogs at αvβ3 have additional effects on intra-cellular protein-trafficking (cytosol compartment to nucleus), nucleoprotein phosphorylation, and generation of nuclear coactivator complexes that are relevant to traditional genomic actions of T3. Thus, previously unrecognized cell surface-initiated actions of thyroid hormone and tetrac formulations at αvβ3 offer opportunities to regulate angiogenesis and multiple aspects of cancer cell behavior.

Overlapping nongenomic and genomic actions of thyroid hormone and steroids

Nuclear receptors for thyroid hormone and steroids are members of a receptor superfamily with similar molecular organization, but discrete transcriptional functions that define genomic actions of these nonpeptide hormones. Nongenomic actions of thyroid hormone and estrogens and androgens are initiated outside the nucleus, at receptors in the plasma membrane or in cytoplasm; these actions are largely regarded to be unique to the respective hormones. However, there is an increasing number of descriptions of overlapping nongenomic and genomic effects of thyroid hormone and estrogens and testosterone. These effects are concentrated in tumor cells, where, for example, estrogens and thyroid hormone have similar mitogen-activate protein kinase (MAPK)-dependent proliferative actions on ERα-positive human breast cancer cells, and where dihydrotestosterone also can stimulate proliferation. Steroids and thyroid hormone have similar anti-apoptotic effects in certain tumors. But thyroid hormone and steroids also have overlapping or interacting nongenomic and genomic actions in heart and brain cells. These various effects of thyroid hormone and estrogens and androgens are reviewed here and their possible clinical consequences are enumerated.

Thyroid Hormone Is a MAPK-Dependent Growth Factor for Human Myeloma Cells Acting via αvβ3 Integrin

Experimental and clinical observations suggest that thyroid hormone [l-thyroxine (T4) and 3,5,3′-triiodo-l-thyronine (T3)] can support cancer cell proliferation. T3 and T4 promote both tumor cell division and angiogenesis by activating mitogen-activated protein kinase (MAPK) via binding to a hormone receptor on the αvβ3 integrin, overexpressed on many cancer cells. We have studied the responsiveness of several MM cell lines to T3 and T4 and characterized hormonal effects on cell survival, proliferation, and MAPK activation. Overnight T3 (1–100 nmol/L) and T4 (100 nmol/L) incubation enhanced, up to 50% (P < 0.002), MM cell viability (WST-1 assay) and increased cell proliferation by 30% to 60% (P < 0.01). Short exposure (10 minutes) to T3 and T4 increased MAPK activity by 2.5- to 3.5-fold (P < 0.03). Pharmacologic MAPK inhibition blocked the proliferative action of T3 and T4. Antibodies to the integrin αvβ3 dimer and αv and β3 monomers (but not β1) inhibited MAPK activation and subsequent cell proliferation in response to thyroid hormone, indicating dependence upon this integrin. Moreover, tetraiodothyroacetic acid (tetrac), a non-agonist T4 analogue previously shown to selectively block T3/T4 binding to αvβ3 receptor site, blocked induction of MAPK by the hormones in a dose-dependent manner. This demonstration of the role of thyroid hormones as growth factors for MM cells may offer novel therapeutic approaches. Mol Cancer Res; 9(10); 1385–94. ©2011 AACR.

Cell-surface receptor for thyroid hormone and tumor cell proliferation

Integrin αVβ3 is a structural protein of the plasma membrane that transduces signals from extracellular matrix proteins and has recently been shown to contain a novel receptor for thyroid hormone. Thyroid hormone signals are converted by αVβ3 into mitogen-activated protein kinase (MAPK) (ERK1/2) activation and downstream intracellular events in the cell nucleus. The latter include post-translational modification of the nuclear thyroid hormone receptor (TRβ1) and complex cellular or tissue responses, such as hormone-induced angiogenesis via basic fibroblast growth factor release. The integrin receptor for thyroid hormone has been shown to mediate proliferative effects of the hormone on certain tumor cell lines, including murine glioma/glioblastoma cells and human breast cancer (MCF-7) cells. More than one mechanism may account for this hormonal action, but in vitro studies indicate a direct hormonal action on cellular proliferation. Other possible mechanisms involve indirect actions via the release of tumor growth factors and effects on cell migration. In the intact organism, support of tumor growth by thyroid hormone is postulated to include angiogenesis. Crosstalk between the integrin thyroid hormone receptor and the epidermal growth factor receptor on the plasma membrane may be another mechanism by which thyroid hormone may modify tumor cell growth. Tetraiodothyroacetic acid (tetrac) is an iodothyronine analog that has no agonist activity at the integrin receptor, but inhibits binding of l-thyroxine and 3,5,3´-triiodo-l-thyronine to the receptor, preventing MAPK activation and consequent actions downstream of MAPK. In vitro studies and a preliminary in vivo experiment indicate that tetrac blocks the action of thyroid hormone on tumor cell proliferation. Both unmodified tetrac and tetrac reformulated as a nanoparticle that does not gain access to the cell interior are under investigation in animal models as anticancer agents. Also under study is the susceptibility of other human cancer cell lines to induction of proliferation by physiological concentrations of thyroid hormone.

Nanotetrac targets integrin αvβ3 on tumor cells to disorder cell defense pathways and block angiogenesis

The extracellular domain of integrin αvβ3 contains a receptor for thyroid hormone and hormone analogs. The integrin is amply expressed by tumor cells and dividing blood vessel cells. The proangiogenic properties of thyroid hormone and the capacity of the hormone to promote cancer cell proliferation are functions regulated nongenomically by the hormone receptor on αvβ3. An L-thyroxine (T4) analog, tetraiodothyroacetic acid (tetrac), blocks binding of T4 and 3,5,3′-triiodo-L-thyronine (T3) by αvβ3 and inhibits angiogenic activity of thyroid hormone. Covalently bound to a 200 nm nanoparticle that limits its activity to the cell exterior, tetrac reformulated as Nanotetrac has additional effects mediated by αvβ3 beyond the inhibition of binding of T4 and T3 to the integrin. These actions of Nanotetrac include disruption of transcription of cell survival pathway genes, promotion of apoptosis by multiple mechanisms, and interruption of repair of double-strand deoxyribonucleic acid breaks caused by irradiation of cells. Among the genes whose expression is suppressed by Nanotetrac are EGFR, VEGFA, multiple cyclins, catenins, and multiple cytokines. Nanotetrac has been effective as a chemotherapeutic agent in preclinical studies of human cancer xenografts. The low concentrations of αvβ3 on the surface of quiescent nonmalignant cells have minimized toxicity of the agent in animal studies.

Relevance of the thyroid hormones-αvβ3 pathway in primary myeloma bone marrow cells and to bortezomib action.

Abstract Thyroid hormones (T3 and T4) induce proliferation in multiple myeloma (MM) cell lines via the αvβ3 integrin–mitogen-activated protein kinase (MAPK) pathway. We further show in primary MM bone marrow (BM) samples (n = 9) induction of cell viability by 1 nM T3 (13%, p < 0.002) and more potently by 100 nM T4 (21–45%, p < 0.0002) and a quick (1 h) and long-lasting (24 h) pERK activation, which was inhibited in the presence of β3 but not β1 blocking antibodies. Involvement of the integrin was further shown by two disintegrins, Arg-Gly-Asp (RGD) and echistatin peptides, which occluded the effects of T3/T4 on viability, proliferating cell nuclear antigen (PCNA) (proliferation marker) and apoptotic gene expression. Lastly, T3/T4 significantly opposed bortezomib (25 nM) cytotoxicy, as confirmed by several methods. In summary, our results imply that endogenous thyroid hormones in myeloma are factors that may support cell growth, with relevance to bortezomib action.

Long-term response in high-grade optic glioma treated with medically induced hypothyroidism and carboplatin: a case report and review of the literature.

Glioblastoma multiforme (GBM) is the most malignant and frequent brain tumor, with an aggressive growth pattern and poor prognosis despite best treatment modalities. Long-term survival of patients with GBM is rare. Optic glioma represents 0.6-1.2% of all brain tumors. Unlike low-grade optic gliomas in children, optic gliomas in adults are highly aggressive and death usually occurs in less than a year. Prolonged progression-free survival and survival rates have been reported in association with induced hypothyroidism in two clinical trials for recurrent GBM. We present the clinical, radiological, and pathological findings in a patient with inoperable GBM of the optic chiasm. Following failure of initial, standard radiation and temozolomide therapy, chemical hypothyroidism was induced using the antithyroid thioamide, propylthiouracil, followed by carboplatin chemotherapy. Initial thyroid stimulating hormone, free T4, and free T3 analysis was carried out and then monthly. This patient responded rapidly to treatment (clinically and with tumor regression within 4 weeks) on two separate occasions with an extended remission period (2.5 years) and prolonged overall survival (4.5 years). We report the successful long-term tumor response to medically induced chemical hypothyroidism in conjunction with carboplatinum chemotherapy of an adult patient with grade IV GBM of the optic chiasm. These clinical observations find mechanistic support from the recent identification of potent mitogenic actions of the thyroid hormone, L-thyroxine, in malignant glioma through binding to a cognate thyroid hormone receptor on the αvβ3 integrin. Approaches to block its activity are now explored in preclinical studies.