Sodium/iodide-symporter: distribution in different mammals and role in entero-thyroid circulation of iodide

Development and evaluation of a theranostic probe with RGD peptide introduced platinum complex to enable tumor-specific accumulation

Cisplatin (CDDP) has been widely used for chemotherapy. However, it has several unfavorable side effects due to its low tumor selectivity. In this study, we designed, synthesized, and evaluated Pt(IV)-[c(RGDyK)]₂ (9), in which two molecules of an RGD peptide are introduced as a carrier molecule to cancer into oxoplatin, a Pt(IV) prodrug of CDDP, to enhance cancer selectivity. Furthermore, we prepared and evaluated Pt(IV)-[c(RGDyK)]{[¹²⁵I]c[RGDy(3-I)K]} ([¹²⁵I]10) for a preliminary step of nuclear medicine imaging and theranostics. Compound 9 inhibited cell growth in the cell viability assay and, [¹²⁵I]10 was highly accumulated in tumor tissues (1 h: 3.53 ± 0.53 %ID/g) in the biodistribution study. These results indicate that implementing RGD peptides into oxoplatin enabled tumor-specific accumulation, and combining [^123/124I]10 and 9 for diagnostic imaging and therapy could be useful for cancer theranostics.

Synthesis and Evaluation of Radioiodine-Labeled pH (Low) Insertion Peptide Variant 7-Like Peptide as a Noninvasive Tumor Microenvironment Imaging Agent in a Mouse MDA-MB-231 Triple-Negative Breast Cancer Model

PURPOSE

The pH (low) insertion peptide (pHLIP) family can target the tumor microenvironment (TME). If pHLIP can be labeled with radioiodine, the imaging and treatment of tumors can be considered. However, tyrosine and tryptophan can bind with iodine in the insertion region of pHLIP, and radioiodine labeling may affect the formation of α-helix structures in acidic environments; therefore, it is necessary to adjust the structure of pHLIP. This study aims to develop an ¹²⁵I-labeled pH (low) insertion peptide variant 7-like peptide (pHLIP (Var7) LP) for imaging the TME in MDA-MB-231 triple-negative breast cancer (TNBC) xenograft tumor models.

PROCEDURES

Based on pHLIP (Var7), a new peptide sequence, pHLIP (Var7) LP, was obtained by the sequence modification method and then characterized. The binding of pHLIP (Var7) LP to MDA-MB-231 cells was analyzed. pHLIP (Var7) LP was labeled with ¹²⁵I by the iodogen iodination method. Serial biodistribution studies and small-animal single photon emission computed tomography (SPECT)/computed tomography (CT) imaging in subcutaneous MDA-MB-231 TNBC-bearing mice were performed using [¹²⁵I] I-pHLIP (Var7) LP.

RESULTS

A novel peptide, pHLIP (Var7) LP, has the characteristics of an α-helix structure, electronegativity, and amphiphilicity. Circular dichroism (CD) spectroscopy showed that the peptide presented a typical pH-dependent transition from an unstructured conformation to an α-helix structure when the pH was reduced from 8.0 to 4.0. The relative fluorescence intensities of 5-carboxytetramethylrhodamine (5-TAMRA)-pHLIP(var7) LP at pH = 6.0, 6.6, and 7.4 were 100.00 ± 5.98%, 72.10 ± 4.65%, and 13.72 ± 1.41%, respectively. The distribution of [¹²⁵I] I-pHLIP (Var7) LP in tumors reached the highest level (8.7 ± 1.6% ID/g) at 2 h after injection, and the tumor-to-muscle ratios and tumor-to-blood ratios increased with time. Of the measured off-target organs, the stomach, kidney, and bladder showed higher uptake levels. SPECT imaging revealed rapid and sustained tumor uptake of [¹²⁵I] I-pHLIP (Var7) LP in breast cancer-bearing mice.

CONCLUSIONS

This study showed that [¹²⁵I]I-pHLIP (Var7)LP had rapid and sustained tumor uptake in MDA-MB-231 TNBC and provided a new method for TNBC imaging and further treatment.

Radionuclide, magnetic resonance and computed tomography imaging in European round back slugs (Arionidae) and leopard slugs (Limacidae)

Other than in animal models of human disease, little functional imaging has been performed in most of the animal world. The aim of this study was to explore the functional anatomy of the European round back slug (Arionidae) and leopard slug (Limacidae) and to establish an imaging protocol for comparative species study. Radionuclide images with single photon emission computed tomography (SPECT) and positron emission tomography (PET) were obtained after injections of standard clinical radiopharmaceuticals ^99mtechnetium dicarboxypropane diphosphonate (bone scintigraphy), ^99mtechnetium mercaptoacetyltriglycine (kidney function), ^99mtechnetium diethylenetriaminepentaacetic acid (kidney function), ^99mtechnetium pertechnetate (mediated by the sodium-iodide symporter), ^99mtechnetium sestamibi (cardiac scintigraphy) or ¹⁸F-fluoro-deoxyglucose (glucose metabolism) in combination with magnetic resonance imaging (MRI) and computed tomography (CT) for uptake anatomic definition. Images were compared with anatomic drawings for the Arionidae species. Additionally, organ uptake data was determined for a description of slug functional anatomy in comparison to human tracer biodistribution patterns identifying the heart, the open circulatory anatomy, calcified shell remnant, renal structure (nephridium), liver (digestive gland) and intestine. The results show the detailed functional anatomy of Arionidae and Limacidae, and describe an in vivo whole-body imaging procedure for invertebrate species.

A brief review of reporter gene imaging in oncolytic virotherapy and gene therapy

Reporter gene imaging (RGI) can accelerate development timelines for gene and viral therapies by facilitating rapid and noninvasive in vivo studies to determine the biodistribution, magnitude, and durability of viral gene expression and/or virus infection. Functional molecular imaging systems used for this purpose can be divided broadly into deep-tissue and optical modalities. Deep-tissue modalities, which can be used in animals of any size as well as in human subjects, encompass single photon emission computed tomography (SPECT), positron emission tomography (PET), and functional/molecular magnetic resonance imaging (f/mMRI). Optical modalities encompass fluorescence, bioluminescence, Cerenkov luminescence, and photoacoustic imaging and are suitable only for small animal imaging. Here we discuss the mechanisms of action and relative merits of currently available reporter gene systems, highlighting the strengths and weaknesses of deep tissue versus optical imaging systems and the hardware/reagents that are used for data capture and processing. In light of recent technological advances, falling costs of imaging instruments, better availability of novel radioactive and optical tracers, and a growing realization that RGI can give invaluable insights across the entire in vivo translational spectrum, the approach is becoming increasingly essential to facilitate the competitive development of new virus- and gene-based drugs.

An Experimental Study on [125I]I-pHLIP (Var7) for SPECT/CT Imaging of an MDA-MB-231 Triple-Negative Breast Cancer Mouse Model by Targeting the Tumor Microenvironment

Objective

To evaluate the diagnostic efficacy of MDA-MB-231 triple-negative breast cancer with ¹²⁵I-labeled pHLIP (Var7) by single-photon emission computed tomography/computed tomography (SPECT/CT) imaging.

Methods

The binding fraction of [¹²⁵I]I-pHLIP (Var7) and MDA-MB-231 cells was measured at pH 7.4 and pH 6.0, and tumor-bearing mice were subjected to small-animal SPECT/CT imaging studies.

Results

At pH = 6.0, the binding fractions of [¹²⁵I]I-pHLIP (Var7) and MDA-MB-231 cells at 10 min, 40 min, 1 h, and 2 h were 1.9 ± 0.1%, 3.5 ± 0.1%, 6.3 ± 0.8%, and 6.6 ± 0.3%, respectively. At pH = 7.4, there was no measured binding between [¹²⁵I]I-pHLIP (Var7) and MDA-MB-231 cells. Small-animal SPECT/CT imaging showed clearly visible tumors at 1 and 2 h after injection.

Conclusions

[¹²⁵I]I-pHLIP (Var7) could bind to MDA-MB-231 cells in an acidic environment, and small-animal SPECT/CT imaging showed clear tumors at 1 and 2 h after probe injection.

Expression of the sodium iodide symporter (NIS) in reproductive and neural tissues of teleost fish

Iodine, an essential component of thyroid hormones, can only be obtained through the diet. The sodium iodide symporter (NIS) transports iodide across mammalian intestinal and thyroid epithelia to deliver iodide for thyroid hormone production. Using reverse transcription-polymerase chain reaction (RT-PCR) we confirmed that mRNA for a homolog of mammalian NIS is expressed in comparable locations, both sub-pharyngeal thyroid tissue and intestine, in multiple teleost fish species, supporting a conserved mechanism for intestinal-thyroid iodine transport across vertebrates. To determine when in embryogenesis NIS expression is initiated we utilized in situ hybridization (ISH) during development of zebrafish (Danio rerio) embryos. This revealed expression of nis as early as 2 days post fertilization (dpf) along the dorsal surface of the yolk sac, suggesting a function to import iodine from yolk. To evaluate the potential for maternal deposition of iodine in yolk, RT-PCR and further in situ staining of ovarian tissue in gravid female zebrafish confirmed NIS mRNA presence in the ooplasm and granulosa layer of early stage follicles. This further suggests that maternally-deposited NIS mRNA may be available for early embryogenesis. Unexpectedly, ISH in embryos revealed robust nis expression in the central nervous system throughout days 2-5 days post fertilization, with adult whole brain ISH localizing expression in the hypothalamus, cerebellum, and optic tectum. RT-PCR on whole brain tissue from five species of adult fish representing three taxonomic orders likewise revealed robust CNS expression. These unexpected locations of nis expression suggest novel, as yet undescribed reproductive and neural functions of NIS in teleost species.

Human dosimetry of free 211At and meta-[211At]astatobenzylguanidine (211At-MABG) estimated using preclinical biodistribution from normal mice

BACKGROUND

211At is one of the ideal nuclides for targeted radionuclide therapies (TRTs). Meta-[211At]astatobenzylguanidine (211At-MABG) has been proposed for the treatment of pheochromocytoma. To effectively use these radiopharmaceuticals, dosimetry must be performed. It is important to determine the absorbed doses of free 211At and 211At-MABG to determine the organs that may be at risk when using TRTs. The aim of this study was to estimate human dosimetry from preclinical biodistribution of free 211At and 211At-MABG in various organs in normal mice.

METHODS

Male C57BL/6 N mice were administered 0.13 MBq of free 211At or 0.20 MBq of 211At-MABG by tail-vein injection. The mice were sacrificed at 5 min, and at 1, 3, 6, and 24 h after the injection (n = 5 for each group). The percentage of injected activity per mass in organs and blood (%IA/g) was determined. The human absorbed doses of free 211At and 211At-MABG were calculated using the Organ Level INternal Dose Assessment/EXponential Modeling (OLINDA/EXM) version 2.0 and IDAC-Dose 2.1.

RESULTS

High uptake of free 211At was observed in the lungs, spleen, salivary glands, stomach, and thyroid. The absorbed doses of free 211At in the thyroid and several tissues were higher than those of 211At-MABG. The absorbed doses of 211At-MABG in the adrenal glands, heart wall, and liver were higher than those of free 211At.

CONCLUSIONS

The absorbed doses of 211At-MABG in organs expressing the norepinephrine transporter were higher than those of free 211At. In addition, the biodistribution of free 211At was different from that of 211At-MABG. The absorbed dose of free 211At may help predict the organs potentially at risk during TRTs using 211At-MABG due to deastatination.

Functional analysis and clinical significance of sodium iodide symporter expression in gastric cancer

BACKGROUND

Recent studies have described important roles for the sodium iodide symporter (NIS) in tumor behavior. The objectives of the present study were to investigate the role of NIS in the regulation of genes involved in tumor progression and the clinicopathological significance of its expression in gastric cancer (GC).

METHODS

In human GC cell lines, knockdown experiments were conducted using NIS siRNA, and the effects on proliferation, survival, and cellular movement were analyzed. The gene expression profiles of cells were examined using a microarray analysis. An immunohistochemical analysis was performed on 145 primary tumor samples obtained from GC patients.

RESULTS

NIS was strongly expressed in MKN45 and MKN74 cells. The depletion of NIS inhibited cell proliferation, migration, and invasion and induced apoptosis. The results of the microarray analysis revealed that various interferon (IFN) signaling-related genes, such as STAT1, STAT2, IRF1, and IFIT1, were up-regulated in NIS-depleted MKN45 cells. Furthermore, the down-regulation of NIS affected the phosphorylation of MAPKs and NF-kB. Immunohistochemical staining showed that NIS was primarily located in the cytoplasm or cell membranes of carcinoma cells, and its expression was related to the histological type or venous invasion. Prognostic analyses revealed that the strong expression of NIS was associated with shorter postoperative survival.

CONCLUSIONS

These results suggest that NIS regulates tumor progression by affecting IFN signaling, and that its strong expression is related to a worse prognosis in patients with GC. These results provide an insight into the role of NIS as a mediator and/or a biomarker for GC.

Single-Photon Emission Computed Tomography for Preclinical Assessment of Thyroid Radioiodide Uptake Following Various Combinations of Preparative Measures

BACKGROUND

MicroSPECT/CT imaging was used to quantitatively evaluate how iodide uptake in the mouse thyroid is influenced by (i) route of iodine administration; (ii) injection of recombinant human thyrotropin (rhTSH); and (iii) low iodide diet (LID) in euthyroid and triiodothyronine (T3)-treated mice.

METHODS

Pertechnetate (^99mTcO₄^-) and ¹²³I thyroid uptake in euthyroid and T3-treated animals fed either a normal-iodine diet (NID) or an LID, treated or not with rhTSH, and radiotracer administered intravenously, subcutaneously, intraperitoneally or by gavage, were assessed using microSPECT/CT imaging. Western blotting was performed to measure sodium/iodide symporter expression levels in the thyroid.

RESULTS

Systemic administration of radioiodide resulted in a higher (2.35-fold in NID mice) accumulation of iodide in the thyroid than oral administration. Mice fed LID with systemic radioiodide administration showed a further two-fold increase in thyroid iodide uptake to yield a ∼5-fold increase in uptake compared to the standard NID/oral route. Although rhTSH injections stimulated thyroid activity in both euthyroid and T3-treated mice fed the NID, uptake levels for T3-treated mice remained low compared with those for the euthyroid mice. Combining LID and rhTSH in T3-treated mice resulted in a 2.8-fold higher uptake compared with NID/T3/rhTSH mice and helped restore thyroid activity to levels equivalent to those of euthyroid animals.

CONCLUSIONS

Systemic radioiodide administration results in higher thyroidal iodide levels than oral administration, particularly in LID-fed mice. These data highlight the importance of LID, both in euthyroid and T3-treated, rhTSH-injected mice. Extrapolated to human patients, and in the context of clinical guidelines for the preparation of differentiated thyroid cancer patients, our data indicate that LID can potentiate the efficacy of rhTSH treatment in T3-treated patients.

Developmental timing of perchlorate exposure alters threespine stickleback dermal bone

Adequate levels of thyroid hormone are critical during development and metamorphosis, and for maintaining metabolic homeostasis. Perchlorate, a common contaminant of water sources, inhibits thyroid function in vertebrates. We utilized threespine stickleback (Gasterosteus aculeatus) to determine if timing of perchlorate exposure during development impacts adult dermal skeletal phenotypes. Fish were exposed to water contaminated with perchlorate (30mg/L or 100mg/L) beginning at 0, 3, 7, 14, 21, 42, 154 or 305days post fertilization until sexual maturity at 1year of age. A reciprocal treatment moved stickleback from contaminated to clean water on the same schedule providing for different stages of initial exposure and different treatment durations. Perchlorate exposure caused concentration-dependent significant differences in growth for some bony traits. Continuous exposure initiated within the first 21days post fertilization had the greatest effects on skeletal traits. Exposure to perchlorate at this early stage can result in small traits or abnormal skeletal morphology of adult fish which could affect predator avoidance and survival.

Comparison of radioactive iodide uptake in the rat thyroid between oral and intravenous bolus administration

OBJECTIVE

Radioiodide is commonly used to diagnose and treat hyperthyroidism and thyroid carcinoma. However, we could not find any experimental data that strictly compared the biodistribution and thyroid uptake of radioactive iodide between the oral and intravenous (iv) routes with time. This prompted us to compare (123)I biodistribution and thyroid uptake to clarify the differences between oral and iv bolus administration in rats.

METHODS

The rats were divided into two groups, A and B (n = 5, each). In the first imaging experiment, Na(123)I solution (35 MBq/200 μL) was administered as a bolus to the rats orally in group A and intravenously in group B. Two weeks later, the second imaging experiment was performed as a crossover experiment. (123)I biodistribution was evaluated visually and quantitatively with a gamma camera at 10 min, 3, 6, 12, 24, and 48 h after (123)I administration. Thyroid uptake was compared between oral and iv groups. Correlation of (123)I thyroid uptake and whole-body excretion was evaluated. The area under the curve (AUC) of thyroid uptake was also calculated.

RESULTS

(123)I biodistribution differed visually during 6 h between the two groups. (123)I thyroid uptake was significantly higher in the iv group at 10 min (P < 0.05) and in the oral group at 6 or more hour time points (P < 0.005-P < 0.0001) and peaked at 12 h in both groups (oral: 24.4 ± 2.8 %ID, iv: 15.2 ± 2.8 %ID). (123)I thyroid uptake showed significant inverse correlations with whole-body excretion from 6 h (r = -0.799, P < 0.0001), and thereafter [12 h (r = -0.957, P < 0.0001), 24 h (r = -0.905, P < 0.0001) and 48 h (r = -0.893, P < 0.0001)], respectively. (123)I whole-body excretion was significantly higher in the iv group at each time point (P < 0.0001). The AUC of (123)I thyroid uptake was 1.6 times higher in the oral group than the iv group.

CONCLUSIONS

These results suggest that radioiodide accumulates in the rat thyroid more effectively by oral than iv administration probably due to slower and lower (123)I clearance from the body in the oral administration when administered in a bolus fashion.

Sodium iodide symporter (NIS) in extrathyroidal malignancies: focus on breast and urological cancer

Background

Expression and function of sodium iodide symporter (NIS) is requisite for efficient iodide transport in thyrocytes, and its presence in cancer cells allows the use of radioiodine as a diagnostic and therapeutic tool in thyroid neoplasia. Discovery of NIS expression in extrathyroidal tissues, including transformed cells, has opened a novel field of research regarding NIS-expressing extrathyroidal neoplasia. Indeed, expression of NIS may be used as a biomarker for diagnostic, prognostic, and therapeutic purposes. Moreover, stimulation of endogenous NIS expression may permit the radioiodine treatment of extrathyroidal lesions by concentrating this radioisotope.

Results

This review describes recent findings in NIS research in extrathyroidal malignancies, focusing on breast and urological cancer, emphasizing the most relevant developments that may have clinical impact.

Conclusions

Given the recent progress in the study of NIS regulation as molecular basis for new therapeutic approaches in extrathyroidal cancers, particular attention is given to studies regarding the relationship between NIS and clinical-pathological aspects of the tumors and the regulation of NIS expression in the experimental models.

⁹⁹mTcO₄--, auger-mediated thyroid stunning: dosimetric requirements and associated molecular events

Low-energy Auger and conversion electrons deposit their energy in a very small volume (a few nm³) around the site of emission. From a radiotoxicological point of view the effects of low-energy electrons on normal tissues are largely unknown, understudied, and generally assumed to be negligible. In this context, the discovery that the low-energy electron emitter, ^99mTc, can induce stunning on primary thyrocytes in vitro, at low absorbed doses, is intriguing. Extrapolated in vivo, this observation suggests that a radioisotope as commonly used in nuclear medicine as ^99mTc may significantly influence thyroid physiology. The aims of this study were to determine whether ^99mTc pertechnetate (^99mTcO₄⁻) is capable of inducing thyroid stunning in vivo, to evaluate the absorbed dose of ^99mTcO₄⁻ required to induce this stunning, and to analyze the biological events associated/concomitant with this effect. Our results show that ^99mTcO₄⁻–mediated thyroid stunning can be observed in vivo in mouse thyroid. The threshold of the absorbed dose in the thyroid required to obtain a significant stunning effect is in the range of 20 Gy. This effect is associated with a reduced level of functional Na/I symporter (NIS) protein, with no significant cell death. It is reversible within a few days. At the cellular and molecular levels, a decrease in NIS mRNA, the generation of double-strand DNA breaks, and the activation of the p53 pathway are observed. Low-energy electrons emitted by ^99mTc can, therefore, induce thyroid stunning in vivo in mice, if it is exposed to an absorbed dose of at least 20 Gy, a level unlikely to be encountered in clinical practice. Nevertheless this report presents an unexpected effect of low-energy electrons on a normal tissue in vivo, and provides a unique experimental setup to understand the fine molecular mechanisms involved in their biological effects.

Development and characterization of [123I]iodotiagabine for in-vivo GABA-transporter imaging

The increased knowledge of molecular changes associated with different neurological disorders calls for the development of novel radioligands. Tiagabine (Gabitril) is an anticonvulsive drug that binds selectively to GABA transporter-1 and thereby inhibits GABA uptake. As radioligands for in-vivo imaging of the GABA transporter are not yet available, we radiolabelled tiagabine and assessed its efficacy for in-vivo imaging of these transporters. Tiagabine was first brominated at its vinylic part, which was then exchanged with I. Next, anaesthetized rats received a bolus injection of [I]iodotiagabine in their tail vein, which was immediately followed by acquisition of planar and high-resolution micro-single-photon emission computed tomography (SPECT) images of the total body with special focus on the brain. Uptake in anatomical regions was assessed by coregistration of micro-SPECT with micro-CT images. Tiagabine labelling with I resulted in 50% yield and 99.7% radiochemical purity. Within 3 h after injection, SPECT demonstrated an increased signal-to-background ratio in the nasal mucosa and/or the Harderian glands but not in the brain. In addition we observed an increased signal-to-background ratio in organs such as the thyroid, heart, liver, kidney and bladder. More than 99% pure I-labelled tiagabine can be obtained and applied in animal micro-SPECT studies. However, this new radioligand is not taken up sufficiently by the brain and therefore cannot be used to successfully detect cerebral GABA transporters.

Treatment of medulloblastoma using an oncolytic measles virus encoding the thyroidal sodium iodide symporter shows enhanced efficacy with radioiodine

Background

Medulloblastoma is the most common malignant brain tumor of childhood. Although the clinical outcome for medulloblastoma patients has improved significantly, children afflicted with the disease frequently suffer from debilitating side effects related to the aggressive nature of currently available therapy. Alternative means for treating medulloblastoma are desperately needed. We have previously shown that oncolytic measles virus (MV) can selectively target and destroy medulloblastoma tumor cells in localized and disseminated models of the disease. MV-NIS, an oncolytic measles virus that encodes the human thyroidal sodium iodide symporter (NIS), has the potential to deliver targeted radiotherapy to the tumor site and promote a localized bystander effect above and beyond that achieved by MV alone.

Methods

We evaluated the efficacy of MV-NIS against medulloblastoma cells in vitro and examined their ability to incorporate radioiodine at various timepoints, finding peak uptake at 48 hours post infection. The effects of MV-NIS were also evaluated in mouse xenograft models of localized and disseminated medulloblastoma. Athymic nude mice were injected with D283med-Luc medulloblastoma cells in the caudate putamen (localized disease) or right lateral ventricle (disseminated disease) and subsequently treated with MV-NIS. Subsets of these mice were given a dose of ¹³¹I at 24, 48 or 72 hours later.

Results

MV-NIS treatment, both by itself and in combination with ¹³¹I, elicited tumor stabilization and regression in the treated mice and significantly extended their survival times. Mice given ¹³¹I were found to concentrate radioiodine at the site of their tumor implantations. In addition, mice with localized tumors that were given ¹³¹I either 24 or 48 hours after MV-NIS treatment exhibited a significant survival advantage over mice given MV-NIS alone.

Conclusions

These data suggest MV-NIS plus radioiodine may be a potentially useful therapy for the treatment of medulloblastoma.

Dietary iodide controls its own absorption through post-transcriptional regulation of the intestinal Na+/I- symporter

Dietary I(-) absorption in the gastrointestinal tract is the first step in I(-) metabolism. Given that I(-) is an essential constituent of the thyroid hormones, its concentrating mechanism is of significant physiological importance. We recently described the expression of the Na(+)/I(-) symporter (NIS) on the apical surface of the intestinal epithelium as a central component of the I(-) absorption system and reported reduced intestinal NIS expression in response to an I(-)-rich diet in vivo. Here, we evaluated the mechanism involved in the regulation of NIS expression by I(-) itself in enterocytes. Excess I(-) reduced NIS-mediated I(-) uptake in IEC-6 cells in a dose- and time-dependent fashion, which was correlated with a reduction of NIS expression at the plasma membrane. Perchlorate, a competitive inhibitor of NIS, prevented these effects, indicating that an increase in intracellular I(-) regulates NIS. Iodide induced rapid intracellular recruitment of plasma membrane NIS molecules and NIS protein degradation. Lower NIS mRNA levels were detected in response to I(-) treatment, although no transcriptional effect was observed. Interestingly, I(-) decreased NIS mRNA stability, affecting NIS translation. Heterologous green fluorescent protein-based reporter constructs revealed a significant repressive effect of the I(-)-targeting NIS mRNA 3 untranslated region. In conclusion, excess I(-) downregulates NIS expression in enterocytes by virtue of a complex mechanism. Our data suggest that I(-) regulates intestinal NIS mRNA expression at the post-transcriptional level as part of an autoregulatory effect of I(-) on its own metabolism.

The sodium iodide symporter (NIS) as an imaging reporter for gene, viral, and cell-based therapies

Preclinical and clinical tomographic imaging systems increasingly are being utilized for non-invasive imaging of reporter gene products to reveal the distribution of molecular therapeutics within living subjects. Reporter gene and probe combinations can be employed to monitor vectors for gene, viral, and cell-based therapies. There are several reporter systems available; however, those employing radionuclides for positron emission tomography (PET) or singlephoton emission computed tomography (SPECT) offer the highest sensitivity and the greatest promise for deep tissue imaging in humans. Within the category of radionuclide reporters, the thyroidal sodium iodide symporter (NIS) has emerged as one of the most promising for preclinical and translational research. NIS has been incorporated into a remarkable variety of viral and non-viral vectors in which its functionality is conveniently determined by in vitro iodide uptake assays prior to live animal imaging. This review on the NIS reporter will focus on 1) differences between endogenous NIS and heterologously-expressed NIS, 2) qualitative or comparative use of NIS as an imaging reporter in preclinical and translational gene therapy, oncolytic viral therapy, and cell trafficking research, and 3) use of NIS as an absolute quantitative reporter.

The sodium iodide symporter (NIS): regulation and approaches to targeting for cancer therapeutics

Expression of the sodium iodide symporter (NIS) is required for efficient iodide uptake in thyroid and lactating breast. Since most differentiated thyroid cancer expresses NIS, β-emitting radioactive iodide is routinely utilized to target remnant thyroid cancer and metastasis after total thyroidectomy. Stimulation of NIS expression by high levels of thyroid-stimulating hormone is necessary to achieve radioiodide uptake into thyroid cancer that is sufficient for therapy. The majority of breast cancer also expresses NIS, but at a low level insufficient for radioiodine therapy. Retinoic acid is a potent NIS inducer in some breast cancer cells. NIS is also modestly expressed in some non-thyroidal tissues, including salivary glands, lacrimal glands and stomach. Selective induction of iodide uptake is required to target tumors with radioiodide. Iodide uptake in mammalian cells is dependent on the level of NIS gene expression, but also successful translocation of NIS to the cell membrane and correct insertion. The regulatory mechanisms of NIS expression and membrane insertion are regulated by signal transduction pathways that differ by tissue. Differential regulation of NIS confers selective induction of functional NIS in thyroid cancer cells, as well as some breast cancer cells, leading to more efficient radioiodide therapy for thyroid cancer and a new strategy for breast cancer therapy. The potential for systemic radioiodide treatment of a range of other cancers, that do not express endogenous NIS, has been demonstrated in models with tumor-selective introduction of exogenous NIS.

Micro-single-photon emission computed tomography image acquisition and quantification of sodium-iodide symporter-mediated radionuclide accumulation in mouse thyroid and salivary glands

BACKGROUND

Micro-single-photon emission computed tomography (SPECT) provides a noninvasive way to evaluate the effects of genetic and/or pharmacological modulation on sodium-iodide symporter (NIS)-mediated radionuclide accumulation in mouse thyroid and salivary glands. However, parameters affecting image acquisition and analysis of mouse thyroids and salivary glands have not been thoroughly investigated. In this study, we investigated the effects of region-of-interest (ROI) selection, collimation, scan time, and imaging orbit on image acquisition and quantification of thyroidal and salivary radionuclide accumulation in mice.

METHODS

The effects of data window minima and maxima on thyroidal and salivary ROI selection using a visual boundary method were examined in SPECT images acquired from mice injected with (123)I NaI. The effects of collimation, scan time, and imaging orbit on counting linearity and signal intensity were investigated using phantoms filled with various activities of (123)I NaI or Tc-99m pertechnetate. Spatial resolution of target organs in whole-animal images was compared between circular orbit with parallel-hole collimation and spiral orbit with five-pinhole collimation. Lastly, the inter-experimental variability of the same mouse scanned multiple times was compared with the intra-experimental variability among different mice scanned at the same time.

RESULTS

Thyroid ROI was separated from salivary glands by empirically increasing the data window maxima. Counting linearity within the range of 0.5-14.2 μCi was validated by phantom imaging using single- or multiple-pinhole collimators with circular or spiral imaging orbit. Scanning time could be shortened to 15 minutes per mouse without compromising counting linearity despite proportionally decreased signal intensity. Whole-animal imaging using a spiral orbit with five-pinhole collimators achieved a high spatial resolution and counting linearity. Finally, the extent of inter-experimental variability of NIS-mediated radionuclide accumulation in the thyroid and salivary glands by SPECT imaging in the same mouse was less than the magnitude of variability among the littermates.

CONCLUSIONS

The impacts of multiple variables and experimental designs on micro-SPECT imaging and quantification of radionuclide accumulation in mouse thyroid and salivary glands can be minimized. This platform will serve as an invaluable tool to screen for pharmacologic reagents that differentially modulate thyroidal and salivary radioiodine accumulation in preclinical mouse models.

[Stable iodine as a prophylaxis therapy following exposure to radioactive iodines: pharmacological and pharmaceutical characteristics]

More or less rapid radio-induction of thyroidian cancers is the main pathological consequence of an accidental exposure to ingested or inhaled radioactive iodines following a nuclear power plant accident. The prophylactic administration of potassium iodine in a single oral dose has to be practiced as soon as possible after the nuclear accident. The efficacy of this therapy depends on pharmacokinetics of radioidines. Iodines are rapidly and completely absorbed as iodides. The radioactive iodines, mainly iodine 131, concentrate in the thyroid gland because of a carrier-mediated transport by the Na-I symporter. Administration of stable iodine results in the symporter blockade, which limits the uptake of radioactive iodines by the thyroid and the duration of the internal irradiation. This irradiation will never exceed 3days if the therapy is started between 6h before the accidental exposure and 1h after. The pharmacist asked to dispense the tablets of stable iodine has a important place because, besides his advices on the optimal modalities of taking stable iodine and the risks of unwanted effects, he extend these advices to information on the radioactive risk and on measures of civil and sanitary protection.

Effective radiovirotherapy for malignant gliomas by using oncolytic measles virus strains encoding the sodium iodide symporter (MV-NIS)

Engineered measles virus (MV) strains deriving from the vaccine lineage represent a promising oncolytic platform and are currently being tested in phase I trials. In this study, we have demonstrated that MV strains genetically engineered to express the human sodium iodide symporter (NIS) have significant antitumor activity against glioma lines and orthotopic xenografts; this compares favorably with the MV strain expressing the human carcinoembryonic antigen, which is currently in clinical testing. Expression of NIS protein in infected cells results in effective concentration of radioactive iodine, which allows for in vivo monitoring of localization of MV-NIS infection by measuring uptake of (123)I or (99m)Tc. In addition, radiovirotherapy with MV-NIS followed by (131)I administration resulted in significant increase of MV-NIS antitumor activity as compared with virus alone in both subcutaneous (p=0.0003) and orthotopic (p=0.004) glioblastoma models. In conclusion, MV-NIS-based radiovirotherapy has significant antitumor activity against glioblastoma multiforme and represents a promising candidate for clinical translation.

Mechanism of immunopotentiation by aluminum-containing adjuvants elucidated by the relationship between antigen retention at the inoculation site and the immune response

The relationship between depot formation and immunopotentiation was studied by comparing the retention of antigen at the inoculation site with antibody production in rats. A model (111)In-labeled alpha casein (IDCAS) antigen was formulated into four vaccines: IDCAS adsorbed onto either aluminum hydroxide adjuvant (AH) or aluminum phosphate adjuvant (AP); non-adsorbed IDCAS with phosphate-treated AP (PTAP); and IDCAS solution. Gamma scintigraphy showed the order of retention following subcutaneous administration to be: AH adsorbed>AP adsorbed>non-adsorbed with PTAP=solution. The antibody titers followed the order: non-adsorbed with PTAP=AP adsorbed>AH adsorbed>>solution. The presence of an aluminum-containing adjuvant was essential for immunopotentiation, but retention of the antigen at the inoculation site was not required.

Iodine in evolution of salivary glands and in oral health

The authors hypothesize that dietary deficiency or excess of iodine (I) has an important role in oral mucosa and in salivary glands physiology. Salivary glands derived from primitive I-concentrating oral cells, which during embryogenesis, migrate and specialize in secretion of saliva and iodine. Gastro-salivary clearance and secretions of iodides are a considerable part of "gastro-intestinal cycle of iodides", which constitutes about 23% of iodides pool in the human body. Salivary glands, stomach and thyroid share I-concentrating ability by sodium iodide symporter (NIS) and peroxidase activity, which transfers electrons from iodides to the oxygen of hydrogen peroxide and so protects the cells from peroxidation. Iodide seems to have an ancestral antioxidant function in all I-concentrating organisms from primitive marine algae to more recent terrestrial vertebrates. The high I-concentration of thymus supports the important role of iodine in the immune system and in the oral immune defence. In Europe and in the world, I-deficiency is surprisingly present in a large part of the population. The authors suggest that the trophic, antioxidant and apoptosis-inductor actions and the presumed antitumour activity of iodides might be important for prevention of oral and salivary glands diseases, as for some other extrathyroidal pathologies.

Iodide deficiency-induced angiogenic stimulus in the thyroid occurs via HIF- and ROS-dependent VEGF-A secretion from thyrocytes

Vascular supply is an obvious requirement for all organs. In addition to oxygen and nutrients, blood flow also transports essential trace elements. Iodine, which is a key element in thyroid hormone synthesis, is one of them. An inverse relationship exists between the expansion of the thyroid microvasculature and the local availability of iodine. This microvascular trace element-dependent regulation is unique and contributes to keep steady the iodide delivery to the thyroid. Signals involved in this regulation, such as VEGF-A, originate from thyrocytes as early TSH-independent responses to iodide scarcity. The question raised in this paper is how thyrocytes, facing an acute drop in intracellular stores of iodine, generate angiogenic signals acting on adjacent capillaries. Using in vitro models of rat and human thyroid cells, we show for the first time that the deficit in iodine is related to the release of VEGF-A via a reactive oxygen species/hypoxia-inducible factor-1-dependent pathway.

The Slc26a4 transporter functions as an electroneutral Cl-/I-/HCO3- exchanger: role of Slc26a4 and Slc26a6 in I- and HCO3- secretion and in regulation of CFTR in the parotid duct

Transcellular Cl(-) and HCO(3)(-) transport is a vital function of secretory epithelia and exit across the luminal membrane is mediated by members of the SLC26 transporters in conjunction with cystic fibrosis transmembrane conductance regulator (CFTR) channel. Typically, secretory epithelia express several SLC26 transporters in the same tissue; however, how their specific function is determined in vivo is not known. In the present work we used the parotid gland duct which expressed Slc26a4 and Slc26a6 and the model systems of Slc26a4(-/-) and Slc26a6(-/-) mice to study the role and regulation of these SLC26 transporters. We examined the transport modes of SLC26A4 expressed in Xenopus oocytes and report that SLC26A4 functions as a coupled, electroneutral I(-)/Cl(-), I(-)/HCO(3)(-) and Cl(-)/HCO(3)(-) exchanger with 1: 1 stoichiometry, with I(-) as the preferred anion. In the duct, Slc26a4 is expressed in the luminal membrane and mainly mediates I(-) secretion with minimal role in luminal HCO(3)(-) transport. By contrast, Slc26a6 mediates luminal Cl(-)/HCO(3)(-) exchange activity with minimal role in I(-) secretion. Furthermore, silencing of CFTR altered Cl(-)/HCO(3)(-) exchange by Slc26a6, but had no effect on I(-) secretion by Slc26a4. Accordingly, deletion of Slc26a6, but not deletion of Slc26a4, results in dysregulation of CFTR. These findings provide the first evidence for a selective role of the SLC26 transporters expressed in the same tissue in epithelial anion transport and suggest that transport specificity is achieved by both the properties of the transporters and the composition of the complexes they form.

Radiolabeling and biodistribution of a nasopharyngeal carcinoma-targeting peptide identified by in vivo phage display

A dodecapeptide EDIKPKTSLAFR ligand targeting CEN-1 human nasopharyngeal carcinoma (NPC) was identified by in vivo phage display. Two tridecapeptides and their derivatives, named YR13 (YEDIKPKTSLAFR), EY13 (EDIKPKTSLAFRY), EY13-NH2 (EDIKPKTSLAFRY-NH2) and Fmoc-YR13 (Fmoc-YEDIKPKTSLAFR), were synthesized and radiolabeled with 131I. The stability in vitro, biodistribution and tissue distribution of selected phage particles in mice bearing NPC tumor were determined, and plasma metabolites analysis of radiolabeled peptides was carried out. Although Fmoc and NH2 groups could protect the peptide from deiodination, only Fmoc group inhibited the binding of Fmoc-YR13 to NPC tumors. The compound EY13-NH2, the C-terminal amide of peptide EY13, had the greatest serum stability, the least deiodination, and showed favorable tumor/blood ratios. The selected phage particles (phage 3 or phage 5) were more concentrated in NPC tumors than the control phage (initial phage display peptide library). EY13 could also inhibit the binding of selected phage particles to tumors. The results indicated that EDIKPKTSLAFR was a good candidate in diagnostic and therapeutic NPC.

Effects of perchlorate on sodium-iodide symporter and pendrin gene expression in deer mice

Effects of perchlorate on sodium-iodide symporter (NIS) and pendrin gene expression in deer mice kidney and stomach were investigated. This was accomplished by isolating a partial cDNA sequence of deer mice NIS gene of 425 bps, and quantitatively analyzing NIS mRNA expression in various deer mouse tissues. The highest NIS expression level was in the stomach, followed by testes, brain, and large intestine; very low expression of NIS was observed in the lung, kidney, heart, and liver. Exposure to perchlorate through drinking water for 28 days did not significantly increase NIS gene expression in the kidney and stomach, and pendrin gene expression in the kidney. In a depuration experiment in which deer mice were exposed to perchlorate for 8-h followed by an 88-h depuration period, no significant difference was observed between the low and high exposure groups in terms of NIS or pendrin gene expression in the kidney or stomach at the end of the experiment. Furthermore, no significant linear relationship was observed between gene expression (either NIS or pendrin) in the kidney and perchlorate mass excreted via urine at day 28, average daily excretion, or total excretion mass over the 28 day exposure. Several factors could influence the effect of perchlorate exposure on NIS and pendrin gene expression in the stomach and kidney, including (1) pre-exposure to trace perchlorate through food and water perhaps resulting in adaptation (or tolerance) in these animals; (2) metabolism of perchlorate in deer mice causing only 46-61% perchlorate excreted into urine. It is also possible that there is no effect of perchlorate exposure and/or urinary excretion on NIS and pendrin gene expression, particularly in the kidney.

A gamma camera re-evaluation of potassium iodide blocking efficiency in mice

The protection of the thyroid against radioiodine uptake has been an important safety concern for decades. After several studies examined potassium iodide blockade efficacy in the 1960's and 1970's, a standard dosage was prescribed by both the World Health Organization and the U.S. Food and Drug Administration. In this paper, we tested the effectiveness of a scaled version of that standard dosage in comparison to higher doses in mice. A novel gamma camera was employed with a high spatial resolution for precisely quantifying activity within the thyroid and a field of view large enough to image the entire mouse body. Thyroid and whole-body 125I biodistribution was analyzed immediately after exposure and 1 and 7 days later. It was found that 1 h after exposure five times the scaled human dose blocked thyroid uptake about 40% more effectively than the 1X scaled dose. Even after 1 d and 7 d, five times the recommended scaled human dose blocked approximately 10% more effectively than the 1X dose. These data suggest the need for continued evaluation of the effectiveness of KI as a blocking agent and the application of novel, non-invasive technologies to this important human health issue.

t-Butyloxycarbonyl: An ordinary but promising group for protecting peptides from deiodination

In order to protect directly radioiodinated peptides from in vivo deiodination, a novel procedure was explored. Two peptides, Try-Gly-Gly-Gly-Gly-Gly-Cys-Asn-Gly-Arg-Cys (YG5) and t-Boc-Try-Gly-Gly-Gly-Gly-Gly-Cys-Asn-Gly-Arg-Cys (t-BOC-YG5) were synthesized and radiolabeled. A paired-label biodistribution study using [131I]t-BOC-YG5 and [125I]YG5 was undertaken in normal mice. Compared to [125I]YG5, [131I]t-BOC-YG5 was quite resistant to in vivo deiodination, resulting in rapid reduction of the radioactive background and negligible radioactivity accumulation in both thyroid and stomach. [131I]t-BOC-YG5 was also stable in human serum even after 24 h. In conclusion, the t-BOC group has the potential to protect peptide from deiodination.

Sodium-iodide symporter mediates iodide secretion in rat gastric mucosa in vitro

In vivo studies on rats have demonstrated that considerable amounts of iodide are transported from the bloodstream into the gastric lumen. The mechanisms for and functional significance of this transport are poorly understood. Active (driven by Na(+)/K(+)-ATPase) iodide transport into thyroid follicular cells is mediated by the sodium-iodide symporter (NIS), which is also abundantly expressed in gastric mucosa. We aimed to further investigate the iodide transport in gastric mucosa and the possible role of NIS in this transport process. Iodide transport in rat gastric mucosa was studied in vitro in an Ussing chamber system using (125)I as a marker. The system allows measurements in both directions over a mucosal specimen. A considerable transport of iodide (from the serosal to the mucosal side) was established across the gastric mucosa, whereas in the opposite direction (mucosa to serosa), iodide transport was negligible. Sodium perchlorate (NaClO(4)), a competitive inhibitor of NIS, and ouabain, an inhibitor of the Na(+)/K(+)-ATPase, both attenuated gastric iodide transport from the serosal to the mucosal side. To investigate a possible neuroendocrine regulation of the iodide transport identified to occur from the serosal to the mucosal side of the stomach, thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH), vasoactive intestinal peptide (VIP), histamine, or nitric oxide donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) was added. None of these substances influenced the iodide transport. We conclude that iodide is actively transported into the gastric lumen and that this transport is at least partly mediated by NIS. Additional investigations are needed to understand the regulation and significance of this transport.

Synthesis and in vitro and in vivo evaluation of three radioiodinated nitroimidazole analogues as tumor hypoxia markers

Three novel nitroimidazole-based thioflavin-T derivatives, N-[4-(benzothiazol-2-yl)phenyl]-3-(4-nitroimidazole-1-yl)propanamide, N-[4-(benzothiazol-2-yl) phenyl]-3-(4-nitroimidazole-1-yl)-N-methylpropanamide and N-[4-(benzothiazol-2-yl)phenyl]-3-(2-nitroimidazole-1-yl) propanamide were synthesized and radiolabeled with iodine-131. Three (131)I-labeled compounds continuously accumulated in hypoxic murine sarcoma S180 cells in vitro but not in aerobic cells. Biodistribution results in mice bearing S180 tumor indicated that the tracers could localize in the tumor and eliminate from it slowly. In contrast, the uptake in other organs (stomach excluded) was little and the clearance was quick. The tumor-to-tissue ratios of three compounds all increased with time.

Imaging of metastatic pulmonary tumors following NIS gene transfer using single photon emission computed tomography

The Na+/I- symporter (NIS) is a membrane glycoprotein that facilitates the uptake of iodine into thyroid follicular cells. Recently, we and others have demonstrated the feasibility of imaging subcutaneous xenografts expressing exogenous NIS, suggesting that NIS may serve as an imaging reporter gene to monitor vector delivery and therapeutic gene expression. In this study, we established NIS-expressing pulmonary tumors in nude mice to investigate the minimal tumor size required for in vivo detection of pulmonary tumors by single photon emission computed tomography (SPECT) with pinhole collimation. In order to define the anatomic location of NIS-expressing tumor nodules detectable by SPECT, we performed simultaneous, dual-isotope imaging. We injected 1 mCi 99mTc-MAA via tail vein to image pulmonary perfusion and injected 1 mCi Na125I intraperitoneally to image NIS-expressing tumors. Fused images showed that 99mTc-MAA perfusion defects correlated with NIS-mediated 125I uptake. Post-mortem analysis revealed that tumors 3 mm in diameter could be detected by SPECT with pinhole collimation. These studies demonstrate the feasibility of SPECT to detect pulmonary tumors expressing exogenous NIS in mice.

Biodistribution of radioiodinated adenovirus fiber protein knob domain after intravenous injection in mice

The knob domains from the fiber proteins of adenovirus serotypes 2 and 12 were labeled with radioiodine and then injected into the bloodstreams of mice. Knob proteins with functional binding sites for the coxsackie and adenovirus receptor (CAR) were cleared rapidly from the circulation, with radioactivity appearing predominantly in the stomach, while knob mutants unable to bind to CAR remained in the blood circulation for a prolonged period. The clearance of radiolabeled wild-type knob from the blood was slowed by coinjecting an excess of unlabeled wild-type knob protein. An earlier study showed that (99m)Tc-labeled knob protein with intact CAR-binding activity also cleared rapidly from the blood circulation of mice, with radioactivity accumulating predominantly in the liver (K. R. Zinn et al., Gene Ther. 5:798-808, 1998). Together these results suggest that rapid clearance of knob protein from the blood results from specific binding to CAR in the liver and that the bound knob then enters a degradative pathway. The elevated levels of radioiodine in the stomach observed in our experiments are consistent with deiodination of labeled knob by dehalogenases in hepatocyte microsomes and uptake of the resultant free radioiodine by Na/I symporters in the gastric mucosa. Although CAR has been shown to localize in tight junctions of polarized epithelial cells, where it functions in intercellular adhesion, the results of our study suggest that a subset of CAR molecules in the liver is highly accessible to ligands in the blood and able to rapidly deliver bound ligand to an intracellular degradative compartment.

Interspecies differences in susceptibility to perturbation of thyroid homeostasis: a case study with perchlorate

Despite many physiological similarities, humans and rats exhibit notably different susceptibilities to thyroid perturbation. Considerable research has recently been conducted on the thyroid-active chemical perchlorate, a chemical of emerging environmental and regulatory interest. While the data indicate humans and rats exhibit similar dose-response relationships in terms of acute inhibition of thyroidal iodide uptake, the two species appear to exhibit notable differences in terms of thyroid hormone response, the toxicologically significant consequence of iodide uptake inhibition. We analyzed dose-response data for changes in serum T(3), T(4), and TSH levels from studies in humans, rats, mice, and rabbits. We found that thyroid homeostasis in the rat appears to be strikingly more sensitive to perchlorate than any of the other species. Rats exhibited an increase in serum TSH at 0.1mg/kg-day whereas other species remained unresponsive even at doses of 10mg/kg-day. Less pronounced but consistent effects were seen with serum T(3) and T(4). These cross-species comparisons provide strong evidence that data obtained from rat studies should be critically evaluated for their relevance to humans. If rat data are used to develop toxicity criteria for perchlorate, we propose that this is an instance where an inter-species uncertainty factor less than one is supportable. DISCLOSURE STATEMENT: One of the authors (BDB) has been hired by Lockheed Martin Corporation as an expert in litigation involving perchlorate. A portion of the initial research presented in this paper was conducted in conjunction with her role in that matter.

Effects of dose, intervention time, and radionuclide on sodium iodide symporter (NIS)-targeted radionuclide therapy

The sodium iodide symporter (NIS) mediates iodide uptake into thyrocytes and is the molecular basis of thyroid radioiodine therapy. We previously have shown that NIS gene transfer into the F98 rat gliomas facilitated tumor imaging and increased survival by radioiodine. In this study, we show that: (1) the therapeutic effectiveness of (131)I in prolonging the survival time of rats bearing F98/hNIS gliomas is dose- and treatment-time-dependent; (2) the number of remaining NIS-expressing tumor cells decreased greatly in RG2/hNIS gliomas post (131)I treatment and was inversely related to survival time; (3) 8 mCi each of (125)I/(131)I is as effective as 16 mCi (131)I alone, despite a smaller tumor absorbed dose; (4) (188)ReO(4), a potent beta(-) emitter, is more efficient than (131)I to enhance the survival of rats bearing F98/hNIS gliomas. These studies demonstrate the importance of radiopharmaceutical selection, dose, and timing of treatment to optimize the therapeutic effectiveness of NIS-targeted radionuclide therapy following gene transfer into gliomas.

[The sodium-iodide symporter. Pathophysiologic, diagnostic and therapeutic significance]

The sodium iodide symporter NIS) is an intrinsic plasma membrane protein that mediates the active transport of iodide in the thyroid gland and a number of extrathyrioidal tissues, in particular lactating mammary gland. Because of its crucial role in the ability of thyroid follicular cells to trap iodide of NIS opened an exciting and extensivenew field of thyroid-related research. Cloning and molecular characterization of NIS allowed investigation of its expression and regulation in thyroidal and nonthyroidal tissues, and its potential pathophysiological and therepeutic implications is benign and malignant thyroid diseases. In addition, NIS-mediated iodide accumulation allows diagnostic thyroid scintigraphy as well as effective therapeutic application of radio-iodide in benign and malignant thyroid disease. characterization and application of NIS as a novel therapeutic gene for cytoreductive gene therapy of extrathyroidal tumors, and the presence of high endogenous NIS expression in the majority of breast cancers further suggest a promising role of NIS in diagnosis and therapy of cancer outside the thyroid gland.