Increased I-131 uptake in local recurrence and distant metastases after second treatment with retinoic acid

The Thyroid Na+/I- Symporter: Molecular Characterization and Genomic Regulation

Iodide (I-) is an essential constituent of the thyroid hormones triiodothyronine (T₃) and thyroxine (T₄), and the iodide concentrating mechanism of the thyroid gland is essential for the synthesis of these hormones. In addition, differential uptake of iodine isotopes (radioiodine) is a key modality for the diagnosis and therapy of thyroid cancer. The sodium dependent iodide transport activity of the thyroid gland is mainly attributed to the functional expression of the Na+/I- Symporter (NIS) localized at the basolateral membrane of thyrocytes. In this paper, we review and summarize current data on molecular characterization, on structure and function of NIS protein, as well as on the transcriptional regulation of NIS encoding gene in the thyroid gland. We also propose that a better and more precise understanding of NIS gene regulation at the molecular level in both healthy and malignant thyroid cells may lead to the identification of small molecule candidates. These could then be translated into clinical practice for better induction and more effective modulation of radioiodine uptake in dedifferentiated thyroid cancer cells and in their distant metastatic lesions.

Unliganded estrogen receptor-alpha activates transcription of the mammary gland Na+/I- symporter gene

The function of sodium iodide symporter (Na(+)/I(-) symporter, or NIS) in mammary epithelial cells is essential for the accumulation of I(-) in milk; the newborn's first source of I(-) for thyroid hormone synthesis. Furthermore, increased mammary gland NIS expression has previously been shown in human breast cancer. Several hormones and factors including all-trans-retinoic acid (tRA) regulate the expression of NIS. In this study, using breast cancer cell lines, we established that tRA-responsive NIS expression is confined to estrogen receptor-alpha (ERalpha) positive cells and we investigated the role of ERalpha in the regulation of NIS expression. We showed that the suppression of endogenous ERalpha by RNA interference downregulates NIS expression in ERalpha positive mammary cells. Besides, in an ERalpha negative cell line, reintroduction of ERalpha resulted in the expression of NIS in a ligand-independent manner. We also identified a novel estrogen-responsive element in the promoter region of NIS that specifically binds ERalpha and mediates ERalpha-dependent activation of transcription. Our results indicate that unliganded ERalpha (apo-ERalpha) contributes to the regulation of NIS gene expression.

The promoter of the human sodium/iodide-symporter gene responds to retinoic acid

It was shown previously that hNIS mRNA expression is stimulated by retinoic acid (RA) in human follicular thyroid carcinoma cell lines FTC-133 and FTC-238, and patients with thyroid carcinomas lacking iodide uptake respond to RA treatment with increased radioiodide transport. Here, in transient transfection experiments using FTC-238 cells, hNIS promoter/luciferase reporter constructs showed an up to 2.5-fold increase in transcriptional activity after incubation with 1 microM RA. Stimulation by 10 nM T3 was up to 2.4-fold. Deletion or block mutation of a putative nuclear receptor recognition site, 'DR10', abolished RA and T3 responses. Four copies of the DR10 cloned 5' to the thymidine kinase promoter gave a 2.6-fold and a 1.4-fold increase in transcriptional activity after RA and T3 stimulation, respectively. In electrophoretic mobility shifts, a wildtype DR10 oligonucleotide, but not block mutants of either DR10 halfsite, interacted with nuclear receptors. Thus, RA redifferentiation of advanced thyroid carcinomas may reinduce iodide uptake by stimulating hNIS expression and thereby make tumours accessible for radioiodide therapy again.

[Therapeutic advances of nuclear medicine in oncology]

With the development of new radiopharmaceuticals there is a tendency to apply nuclear medicine therapy for malignancies of higher incidence (lymphoma, prostate) than the ones which have been treated for many years (thyroid cancer, neuroendocrine tumours). One of the most important areas of current development in radionuclide cancer therapy is the monotherapeutic use of new or already available radiopharmaceuticals in preclinical or phase I studies and to a lesser degree in phase II trials. In this context, the radioimmunotherapy is showing important advances in the treatment of medullary thyroid carcinoma, malignant lymphomas en brain tumours with potential extension to neuroblastoma therapy. The development of DOTA as a chelating agent has lead to the use of Y-90-DOTATOC in the treatment of neuroendocrine tumours, particularly carcinoid tumours, and non-I131I-avid thyroid carcinomas. In an effort to improve tumour targeting together with simultaneous reduction of physiological organ uptake, 131I-MIBG is being used in combination with interferon a and pre-targeting with unlabelled MIBG in the treatment of carcinoid tumours. New routes of administration of radiopharmaceuticals (intratumoral, intra-arterial) have enhanced the treatment of malignancies of liver, pancreas and brain as well as the potential use of radioimmunotherapy by intravesical administration for bladder carcinoma. Another significant tendency in radionuclide therapy is its evolution from monotherapy towards a combined application with other anticancer modalities. Some recent examples of combined therapy with demonstrated anti-tumour effect are found in neuroblastoma (131I-MIBG and chemotherapy), bone metastases of prostatic carcinoma (addition of 89Sr to chemotherapy schedules), brain malignancies (adjuvant use of radioimmnunotherapy in relation to surgery and external radiotherapy) and lymphoma (radioimmunotherapy combined with chemotherapy or immunotherapy). Reinforcing this trend in phase II and III studies as well as the planning of multicenter trials following the guidelines and criteria of clinical oncology will determine the future advances in this field.

Sodium iodide symporter-based strategies for diagnosis and treatment of thyroidal and nonthyroidal malignancies

The recent cloning and molecular characterization of the sodium iodide-symporter (NIS) has inspired novel approaches to the diagnosis and treatment of thyroidal and nonthyroidal malignancies. This article briefly reviews the physiologic regulation of NIS expression by cytokines, the expression in benign and malignant thyroidal diseases, and the expression in extrathyroidal tissues. Current concepts for NIS-based cancer therapy in thyroidal and extrathyroidal tumors are presented. The recent discovery of NIS expression in a majority of breast cancers as well as its promising application for prostate cancer imply potential applications in diagnostic imaging and radioiodine anticancer therapy for these highly common and lethal malignancies.