Approaches to gene therapy with sodium/iodide symporter

Role of iodide metabolism in physiology and cancer

Iodide (I^-) metabolism is crucial for the synthesis of thyroid hormones (THs) in the thyroid and the subsequent action of these hormones in the organism. I^- is principally transported by the sodium iodide symporter (NIS) and by the anion exchanger PENDRIN, and recent studies have demonstrated the direct participation of new transporters including anoctamin 1 (ANO1), cystic fibrosis transmembrane conductance regulator (CFTR) and sodium multivitamin transporter (SMVT). Several of these transporters have been found expressed in various tissues, implicating them in I^- recycling. New research supports the exciting idea that I^- participates as a protective antioxidant and can be oxidized to hypoiodite, a potent oxidant involved in the host defense against microorganisms. This was possibly the original role of I^- in biological systems, before the appearance of TH in evolution. I^- per se participates in its own regulation, and new evidence indicates that it may be antineoplastic, anti-proliferative and cytotoxic in human cancer. Alterations in the expression of I^- transporters are associated with tumor development in a cancer-type-dependent manner and, accordingly, NIS, CFTR and ANO1 have been proposed as tumor markers. Radioactive iodide has been the mainstay adjuvant treatment for thyroid cancer for the last seven decades by virtue of its active transport by NIS. The rapid advancement of techniques that detect radioisotopes, in particular I^-, has made NIS a preferred target-specific theranostic agent.

Hypoxia-targeted 131I therapy of hepatocellular cancer after systemic mesenchymal stem cell-mediated sodium iodide symporter gene delivery

Adoptively transferred mesenchymal stem cells (MSCs) home to solid tumors. Biologic features within the tumor environment can be used to selectively activate transgenes in engineered MSCs after tumor invasion. One of the characteristic features of solid tumors is hypoxia. We evaluated a hypoxia-based imaging and therapy strategy to target expression of the sodium iodide symporter (NIS) gene to experimental hepatocellular carcinoma (HCC) delivered by MSCs.

MSCs engineered to express transgenes driven by a hypoxia-responsive promoter showed robust transgene induction under hypoxia as demonstrated by mCherry expression in tumor cell spheroid models, or radioiodide uptake using NIS. Subcutaneous and orthotopic HCC xenograft mouse models revealed significant levels of perchlorate-sensitive NIS-mediated tumoral radioiodide accumulation by tumor-recruited MSCs using ¹²³I-scintigraphy or ¹²⁴I-positron emission tomography. Functional NIS expression was further confirmed by ex vivo¹²³I-biodistribution analysis. Administration of a therapeutic dose of ¹³¹I in mice treated with NIS-transfected MSCs resulted in delayed tumor growth and reduced tumor perfusion, as shown by contrast-enhanced sonography, and significantly prolonged survival of mice bearing orthotopic HCC tumors. Interestingly, radioiodide uptake into subcutaneous tumors was not sufficient to induce therapeutic effects. Our results demonstrate the potential of using tumor hypoxia-based approaches to drive radioiodide therapy in non-thyroidal tumors.

Nucleic acid therapeutics: concepts for targeted delivery to solid tumors

Solid tumors form a heterogeneous group of diseases, although common features such as hyperproliferation, overexpression of certain growth factor receptors and deregulated vessel formation including leaky vasculature give the opportunity to target macromolecular drug and nucleic acid carriers to tumor tissue. Similar to other macromolecular drugs, nucleic acid carriers have to be designed to enable tumor targeting after systemic injection. Chemical modification of nucleic acids makes them resistant towards enzymatic degradation. Cationic lipids or polycations condense nucleic acids into small, virus-like structures and the surface modification with hydrophilic polymers allows passive accumulation in tumor tissue; tumor cell binding ligands allow cellular targeting. To avoid toxic side effects, biodegradable and biocompatible carriers were designed. The design of thermoresponsive gene carriers allowed their selective tumor accumulation by locoregional hyperthermia. As a therapeutic concept, tumor-specific delivery of antitumoral RNA was realized in an orthotopic brain tumor model. The combination of gene- and radio-therapy enabled selective accumulation of radionuclides in tumors and boosted antitumoral effects. Hence, combining a smart delivery concept for nucleic acids with a suitable therapeutic strategy will allow successful treatment of otherwise incurable malignant diseases.

Enhanced anti-tumor effects of combined MDR1 RNA interference and human sodium/iodide symporter (NIS) radioiodine gene therapy using an adenoviral system in a colon cancer model

Using an adenoviral system as a delivery mediator of therapeutic gene, we investigated the therapeutic effects of the use of combined MDR1 shRNA and human NIS (hNIS) radioiodine gene therapy in a mouse colon xenograft model. In vitro uptake of Tc-99m sestamibi was increased approximately two-fold in cells infected with an adenovirus vector that expressed MDR1 shRNA (Ad-shMDR1) and I-125 uptake was 25-fold higher in cells infected with an adenovirus vector that expressed human NIS (Ad-hNIS) as compared with control cells. As compared with doxorubicin or I-131 treatment alone, the combination of doxorubicin and I-131 resulted in enhanced cytotoxicity for both Ad-shMDR1- and Ad-hNIS-infected cells, but not for control cells. In vivo uptake of Tc-99m sestamibi and Tc-99m pertechnetate was twofold and 10-fold higher for Ad-shMDR1 and Ad-hNIS-infected tumors as compared with tumors infected with a control adenovirus construct that expressed β-galactrosidase (Ad-LacZ), respectively. In mice treated with either doxorubicin or I-131 alone, there was a slight delay in tumor growth as compared to mice treated with Ad-LacZ. However, combination therapy with doxorubicin and I-131 induced further significant inhibition of tumor growth as compared with mice treated with Ad-LacZ. We have shown successful therapeutic efficacy of combined MDR shRNA and hNIS radioiodine gene therapy using an adenoviral vector system in a mouse colon cancer model. Adenovirus-mediated cancer gene therapy using MDR1 shRNA and hNIS would be a useful tool for the treatment of cancer cells expressing multi-drug resistant genes.

Sodium/iodide symporter expression in primary lung cancer and comparison with glucose transporter 1 expression

The aim of the present study was to evaluate the expression of sodium/iodide symporter (NIS) and glucose transporter 1 (Glut1) in 139 primary lung cancers on immunohistochemistry, and to determine the diagnostic utility of NIS as an imaging reporter. Immunoreactivity for NIS and Glut1 was noted in 75 (54.0%) and 72 (51.8%) of the 139 cases, respectively. Analysis of NIS expression on Western blot confirmed the immunohistochemistry. NIS expression was significantly higher in the adenocarcinomas than in the other carcinomas, and Glut1 expression was significantly higher in the squamous cell carcinomas than in the other carcinomas (each P < 0.0001). The frequency of NIS expression in those carcinomas lacking Glut1 expression was significantly higher than in those with Glut1 expression (P = 0.012). Among 64 adenocarcinomas, the frequency of the NIS(+)/Glut1(-) phenotype was 61.0%, which was the most frequent expression pattern. By studying the expression pattern of NIS in lung cancer, the present paper provides a helpful foundation for examining the potential utility of NIS-mediated radioiodide as an alternative diagnostic modality, especially for the management of patients with lung adenocarcinoma lacking Glut1 expression.

The importance of sodium/iodide symporter (NIS) for thyroid cancer management

The thyroid gland has the ability to uptake and concentrate iodide, which is a fundamental step in thyroid hormone biosynthesis. Radioiodine has been used as a diagnostic and therapeutic tool for several years. However, the studies related to the mechanisms of iodide transport were only possible after the cloning of the gene that encodes the sodium/iodide symporter (NIS). The studies about the regulation of NIS expression and the possibility of gene therapy with the aim of transferring NIS gene to cells that normally do not express the symporter have also become possible. In the majority of hypofunctioning thyroid nodules, both benign and malignant, NIS gene expression is maintained, but NIS protein is retained in the intracellular compartment. The expression of NIS in non-thyroid tumoral cells in vivo has been possible through the transfer of NIS gene under the control of tissue-specific promoters. Apart from its therapeutic use, NIS has also been used for the localization of metastases by scintigraphy or PET-scan with 124I. In conclusion, NIS gene cloning led to an important development in the field of thyroid pathophysiology, and has also been fundamental to extend the use of radioiodine for the management of non-thyroid tumors.

Cell-based imaging of sodium iodide symporter activity with the yellow fluorescent protein variant YFP-H148Q/I152L

The sodium iodide symporter (NIS) mediates iodide (I−) transport in the thyroid gland and other tissues and is of increasing importance as a therapeutic target and nuclear imaging reporter. NIS activity in vitro is currently measured with radiotracers and electrophysiological techniques. We report on the development of a novel live cell imaging assay of NIS activity using the I−-sensitive and genetically encodable yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In FRTL-5 thyrocytes stably expressing YFP-H148Q/I152L, I− induced a rapid and reversible decrease in cellular fluorescence characterized by 1) high affinity for extracellular I− (35 μM), 2) inhibition by the NIS inhibitor perchlorate, 3) extracellular Na+ dependence, and 4) TSH dependence, suggesting that fluorescence changes are due to I− influx via NIS. Individual cells within a population of FRTL-5 cells exhibited a 3.5-fold variation in the rate of NIS-mediated I− influx, illustrating the utility of YFP-H148Q/I152L to detect cell-to-cell difference in NIS activity. I− also caused a perchlorate-sensitive decrease in YFP-H148Q/I152L fluorescence in COS-7 cells expressing NIS but not in cells lacking NIS. These results demonstrate that YFP-H148Q/I152L is a sensitive biosensor of NIS-mediated I− uptake in thyroid cells and in nonthyroidal cells following gene transfer and suggest that fluorescence detection of cellular I− may be a useful tool by which to study the pathophysiology and pharmacology of NIS.

Engineered measles virus as a novel oncolytic viral therapy system for hepatocellular carcinoma

The oncolytic measles virus Edmonston strain (MV-Edm), a nonpathogenic virus targeting cells expressing abundant CD46, selectively destroys neoplastic tissue. Clinical development of MV-Edm would benefit from noninvasive monitoring strategies to determine the speed and extent of the spread of the virus in treated patients and the location of virus-infected cells. We evaluated recombinant MV-Edm expressing carcinoembryonic antigen (CEA) or the human sodium iodide symporter (hNIS) for oncolytic potential in hepatocellular carcinoma (HCC) and efficiency in tracking viruses in vivo by noninvasive monitoring. CD46 expression in human HCC and primary hepatocytes was assessed by flow cytometry and immunohistochemistry. Infectivity, syncytium formation, and cytotoxicity of recombinant MV-Edm in HCC cell lines were evaluated by fluorescence microscopy, crystal violet staining, and the MTS assay. Transgene expression in HCC cell lines after infection with recombinant MV-Edm in vitro and in vivo was assessed by CEA concentration, 125I-uptake, and 123I-imaging studies. Toxicology studies were performed in Ifnar(KO)xCD46 transgenic mice. The CD46 receptor was highly expressed in HCC compared to nonmalignant hepatic tissue. Recombinant MV-Edm efficiently infected HCC cell lines, resulting in extensive syncytium formation followed by cell death. Transduction of HCC cell lines and subcutaneous HCC xenografts with recombinant MV-Edm resulted in high-level expression of transgenes in vitro and in vivo. MV-Edm was nontoxic in susceptible mice. Intratumoral and intravenous therapy with recombinant MV-Edm resulted in inhibition of tumor growth and prolongation of survival with complete tumor regression in up to one third of animals. In conclusion, engineered MV-Edm may be a potent and novel cancer gene therapy system for HCC. MV-Edm expressing CEA or hNIS elicited oncolytic effects in human HCC cell lines in vitro and in vivo, enabling the spread of the virus to be monitored in a noninvasive manner.

Combined I-124 Positron Emission Tomography/Computed Tomography Imaging of NIS Gene Expression in Animal Models of Stably Transfected and Intravenously Transfected Tumor

PURPOSE

With the advent of replication competent viruses for cancer gene therapy, it has become imperative to monitor the biodistribution, expression and replication of these vectors in living organisms. We evaluated the potential of I-124 positron emission tomography (PET)/computed tomography (CT) imaging in gene therapy animal models utilizing the sodium iodide symporter (NIS) and compared the findings to I-123 gamma camera imaging.

PROCEDURES

CB17 SCID mice were implanted with myeloma cell lines expressing NIS or infected by MV-NIS given systemically. Mice were imaged by both gamma camera (I-123) and PET/CT (I-124 ) and image quality assessed.

RESULTS

NIS expressing tumors concentrated 7.1% of the injected activity while tumors infected with the control virus had only 0.3% of the activity injected.

CONCLUSIONS

I-124 PET/CT in combination with NIS allows the tracking of stably transfected tumors or intravenously transfected tumors. Combined modality imaging using PET/CT allows accurate and non-invasive imaging of the distribution and gene expression of a replicating viral vector in living systems.

Noninvasive radiological imaging of pulmonary gene transfer and expression using the human sodium iodide symporter

PURPOSE

In this study we investigated the application of the human sodium iodide symporter (hNIS) as a reporter gene to noninvasively image in vivo gene transfer and expression in lung tissue in real time.

METHODS

Human NIS-expressing adenoviruses (Ad-hNIS) or empty adenoviruses (Ad-Bgl II) were instilled into the lungs of Cotton rats via the nostrils. After 3, 10, and 17 days post infection, gamma camera scintigraphy with 99mTcO4- was performed to observe the distribution and duration of gene transfer. At 20 days after infection, reverse transcription polymerase chain reaction was performed to detect hNIS gene expression. Dual expressing vector Ad-hNIS-eGFP was used to detect transgene expression by fluorescence photomicroscopy in infected lung tissue. Positron emission tomography (PET) imaging of gene transfer to the lungs was performed using 124I- as tracer. Finally, hNIS transfer to a polarized human airway epithelial cell layer was evaluated by phosphorimaging.

RESULTS

Lungs in animals infected with Ad-hNIS were clearly visible on scintigraphy and PET scans, while those infected with Ad-Bgl II were undetectable. Lungs in Ad-hNIS infected animals could still be visualized at 17 days but were no longer detectable at 20 days. Fluorescence microscopy showed that lung tissue infected with Ad-hNIS-eGFP had significantly higher GFP signal intensity than that infected with Ad-Bgl II.

CONCLUSION

It is feasible to use the hNIS gene as a reporter gene to monitor the location, magnitude, and timing of expression of genes delivered during pulmonary gene therapy. The ability to noninvasively visualize gene expression tomographically in real time has significant translational implications in human gene therapy.

The Na/I symporter (NIS): imaging and therapeutic applications

The Na(+)/I(-) symporter (NIS) is the plasma membrane glycoprotein that mediates the active uptake of I(-) in the thyroid, ie, the crucial first step in thyroid hormone biosynthesis. NIS also mediates I(-) uptake in other tissues, such as salivary glands, gastric mucosa, and lactating (but not nonlactating) mammary gland. The ability of thyroid cancer cells to actively transport I(-) via NIS provides a unique and effective delivery system to detect and target these cells for destruction with therapeutic doses of radioiodide. Breast cancer is the only malignancy other than thyroid cancer to have been shown to functionally express NIS endogenously. The considerable potential diagnostic and therapeutic use of radioiodide in breast cancer is currently being assessed. On the other hand, exogenous NIS gene transfer has successfully been carried out into a variety of other cell lines and tumors, including A375 human melanoma tumors, and SiHa cervix cancer, human glioma, and hepatoma cell lines. Most notably, significant radioiodine therapy results have been obtained in the NIS-transfected human prostatic adenocarcinoma cell line LNCaP and in NIS-transfected myeloma cells, both of which exhibited prolonged retention of radio iodide even in the absence of I(-) organification. The therapeutic potential of alternative NIS-transported radioisotopes with different decay properties and a shorter, physical half-life than 131I(-), such as beta-emitter 188Rhenium (188ReO(4)-) and alpha-emitter 211Astatine (211At(-)), has been evaluated. In conclusion, it is clear that the remarkable progress made in the last few years in the molecular characterization of NIS has created new opportunities for the development of diagnostic and therapeutic applications for NIS in nuclear medicine.

Primer on medical genomics. Part X: Gene therapy

Gene therapy is defined as any therapeutic procedure in which genes are intentionally introduced into human somatic cells. Both preclinical and clinical gene therapy research have been progressing rapidly during the past 15 years; gene therapy is now a highly promising new modality for the treatment of numerous human disorders. Since the first clinical test of gene therapy in 1989, more than 600 gene therapy protocols have been approved, and more than 3000 patients have received gene therapy. However, at the time of writing this article, no gene therapy products have been approved for clinical use. This article explains the potential clinical scope of gene therapy and the underlying pharmacological principles, describes some of the major gene transfer systems (or vectors) that are used to deliver genes to their target sites, and discusses the various strategies for controlling expression of therapeutic transgenes. Safety issues regarding clinical use of gene therapy are explored, and the most important technical challenges facing this field of research are highlighted. This review should serve as an introduction to the subject of gene therapy for clinician investigators, physicians and medical scientists in training, practicing clinicians, and other students of medicine.

Micro-PET imaging and small animal models of disease

Positron emission tomography (PET) has been used clinically to measure enzyme reactions, ligand-receptor interactions, cellular metabolism and cell proliferation. Until recently, however, PET has not been suitable for small animal models because of resolution limitations. Development of micro-PET instrumentation for small animal imaging and the availability of positron-emitting tracers has made this technology accessible for the non-invasive, quantitative and repetitive imaging of biological function in living animals. The development of new probes and positron-imaging based reporter genes has extended micro-PET applications to investigations of metabolism, enzyme activity, receptor-ligand interactions, protein-protein interactions, gene expression, adoptive cell therapy and somatic gene therapy. Because small animal PET is immediately extrapolatable to the clinic, laboratory advances should rapidly be translated to clinical practice.

Tumour-specific activation of the sodium/iodide symporter gene under control of the glucose transporter gene 1 promoter (GTI-1.3)

Targeted transfer of a functionally active sodium iodide symporter (NIS) into tumour cells may be used for radioiodine therapy of cancer. Therefore, we investigated radioiodine uptake in a hepatoma cell line in vitro and in vivo after transfer of the sodium iodide symporter ( hNIS) gene under the control of a tumour-specific regulatory element, the promoter of the glucose transporter 1 gene (GTI-1.3). Employing a self-inactivating bicistronic retroviral vector for the transfer of the hNIS and the hygromycin resistance genes, rat Morris hepatoma (MH3924A) cells were infected with retroviral particles and hNIS-expressing cell lines were generated by hygromycin selection. (125)I(-) uptake and efflux were determined in genetically modified and wild type hepatoma cells. In addition, the iodide distribution in rats bearing wild type and genetically modified hepatomas was monitored. hNIS-expressing MH3924A cell lines accumulated up to 30 times more iodide than wild type hepatoma cells, with a maximal iodide uptake after 30 min incubation time. Competition experiments in the presence of sodium perchlorate revealed a decrease in the iodide uptake (80-84% decrease). Moreover, ouabain led to a loss of accumulated I(-) (81% decrease) whereas 4,4'-diisothiocyano-2,2'-disulphonic acid stilbene (DIDS) increased the I(-) uptake into cells (87% increase). However, a rapid efflux of the radioactivity (70%) was observed 20 min after (125)I(-)-containing medium had been replaced by non-radioactive medium. Lithium had no significant effect on iodide efflux. In rats, the hNIS-expressing tumours accumulated 22 times more iodide than the contralateral wild type tumour. In accordance with the in vitro data, we also observed a rapid efflux of the radioactivity out of the tumour in vivo. Dosimetric calculations resulted in an absorbed dose of 85 mGy in the wild type tumour and 830 mGy in the hNIS-expressing tumour after administration of 18.5 MBq (131)I. In conclusion, transduction of the hNIS gene under the control of the GLUT1 promoter element induces iodide transport in Morris hepatoma cells in vitro and in vivo. However, for therapeutic application additional conditions need to be defined which inhibit the iodide efflux out of the tumour cells.

Well differentiated thyroid cancer

Cancers of follicular cell origin are the most common of the endocrine malignancies. Thyroid cancers are seen with increased frequency after radiation exposure and in some familial syndromes. Interestingly, the prognosis of thyroid carcinoma is highly dependent on the age of the patient at the time of examination: several clinical staging systems facilitate appropriate treatment planning. The ability of the follicular cell to take up iodine permits the use of radioactive iodine for follow-up and therapy. After thyroidectomy and radioiodine ablation, thyroglobulin becomes a sensitive marker for the presence of recurrent or metastatic disease. Patients who are thyroglobulin-positive but radioiodine-negative or who have antithyroglobulin antibodies are a clinical challenge. Improvement in imaging studies can help in the treatment of these patients. New treatments, such as the use of agents to improve iodine uptake in follicular cell tumors, are in early clinical investigation; others are in experimental development but hold promise for the treatment of aggressive thyroid malignancies.

Transfectant mosaic spheroids: a new model for evaluation of tumour cell killing in targeted radiotherapy and experimental gene therapy

BACKGROUND

We describe an in vitro tumour model for targeted radiotherapy and gene therapy that incorporates cell population heterogeneity.

MATERIALS AND METHODS

Transfectant mosaic spheroids (TMS) and transfected mosaic monolayers (TMM) are composed of two cell populations derived from a single cell line. The cells of one population were transfected with the noradrenaline transporter gene (NAT), allowing active uptake of a radiolabelled targeting agent meta-[131I]iodobenzylguanidine ([131I]MIBG); the other population of cells was derived from the same parent line and transfected with a marker gene - green fluorescent protein (GFP). After treatment with [131I]MIBG, cell kill was determined in TMM by clonogenic assay and in TMS by clonogenic assay and spheroid growth delay.

RESULTS

We have used the TMS model to assess the 'radiological bystander effect' (radiation cross-fire) conferred by the beta-emitting radiopharmaceutical [131I] MIBG whose cellular uptake is facilitated by the transfected gene encoding NAT. We show that cell killing by [131I]MIBG in both TMS and TMM cultures increased in direct proportion to the fraction of NAT-transfected cells and that the degree of cell killing against fraction transfected was greater in TMS, suggestive of a greater bystander effect in the three-dimensional culture system.

CONCLUSIONS

TMS provide a useful model for assessment of the effectiveness of targeted radiotherapy in combination with gene therapy when less than 100% of the target cell population is expressing the NAT transgene. Further, this novel model offers the unique opportunity to investigate radiation-induced bystander effects and their contribution to cell cytotoxicity in radiotherapy and other gene therapy applications.