Application of 188rhenium as an alternative radionuclide for treatment of prostate cancer after tumor-specific sodium iodide symporter gene expression

The sodium iodide symporter (NIS) as theranostic gene: its emerging role in new imaging modalities and non-viral gene therapy

Cloning of the sodium iodide symporter (NIS) in 1996 has provided an opportunity to use NIS as a powerful theranostic transgene. Novel gene therapy strategies rely on image-guided selective NIS gene transfer in non-thyroidal tumors followed by application of therapeutic radionuclides. This review highlights the remarkable progress during the last two decades in the development of the NIS gene therapy concept using selective non-viral gene delivery vehicles including synthetic polyplexes and genetically engineered mesenchymal stem cells. In addition, NIS is a sensitive reporter gene and can be monitored by high resolution PET imaging using the radiotracers sodium [¹²⁴I]iodide ([¹²⁴I]NaI) or [¹⁸F]tetrafluoroborate ([¹⁸F]TFB). We performed a small preclinical PET imaging study comparing sodium [¹²⁴I]iodide and in-house synthesized [¹⁸F]TFB in an orthotopic NIS-expressing glioblastoma model. The results demonstrated an improved image quality using [¹⁸F]TFB. Building upon these results, we will be able to expand the NIS gene therapy approach using non-viral gene delivery vehicles to target orthotopic tumor models with low volume disease, such as glioblastoma.

Trial registration not applicable.

A Human-derived Dual MRI/PET Reporter Gene System with High Translational Potential for Cell Tracking

PURPOSE

Reporter gene imaging has been extensively used to longitudinally report on whole-body distribution and viability of transplanted engineered cells. Multi-modal cell tracking can provide complementary information on cell fate. Typical multi-modal reporter gene systems often combine clinical and preclinical modalities. A multi-modal reporter gene system for magnetic resonance imaging (MRI) and positron emission tomography (PET), two clinical modalities, would be advantageous by combining the sensitivity of PET with the high-resolution morphology and non-ionizing nature of MRI.

PROCEDURES

We developed and evaluated a dual MRI/PET reporter gene system composed of two human-derived reporter genes that utilize clinical reporter probes for engineered cell detection. As a proof-of-concept, breast cancer cells were engineered to co-express the human organic anion transporter polypeptide 1B3 (OATP1B3) that uptakes the clinical MRI contrast agent gadolinium ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA), and the human sodium iodide symporter (NIS) which uptakes the PET tracer, [18F] tetrafluoroborate ([18F] TFB).

RESULTS

T1-weighted MRI results in mice exhibited significantly higher MRI signals in reporter-gene-engineered mammary fat pad tumors versus contralateral naïve tumors (p < 0.05). No differences in contrast enhancement were observed at 5 h after Gd-EOB-DTPA administration using either intravenous or intraperitoneal injection. We also found significantly higher standard uptake values (SUV) in engineered tumors in comparison to the naïve tumors in [18F]TFB PET images (p < 0.001). Intratumoral heterogeneity in signal enhancement was more conspicuous in relatively higher resolution MR images compared to PET images.

CONCLUSIONS

Our study demonstrates the ability to noninvasively track cells engineered with our human-derived dual MRI/PET reporter system, enabling a more comprehensive evaluation of transplanted cells. Future work is focused on applying this tool to track therapeutic cells, which may one day enable the broader application of cell tracking within the healthcare system.

Selective sodium iodide symporter (NIS) genetherapy of glioblastoma mediatedby EGFR-targeted lipopolyplexes

Lipo-oligomers, post-functionalized with ligands to enhance targeting, represent promising new vehicles for the tumor-specific delivery of therapeutic genes such as the sodium iodide symporter (NIS). Due to its iodide trapping activity, NIS is a powerful theranostic tool for diagnostic imaging and the application of therapeutic radionuclides. ¹²⁴I PET imaging allows non-invasive monitoring of the in vivo biodistribution of functional NIS expression, and application of ¹³¹I enables cytoreduction. In our experimental design, we used epidermal growth factor receptor (EGFR)-targeted polyplexes (GE11) initially characterized in vitro using ¹²⁵I uptake assays. Mice bearing an orthotopic glioblastoma were treated subsequently with mono-dibenzocyclooctyne (DBCO)-PEG₂₄-GE11/NIS or bisDBCO-PEG₂₄-GE11/NIS, and 24-48 h later, ¹²⁴I uptake was assessed by positron emission tomography (PET) imaging. The best-performing polyplex in the imaging studies was then selected for ¹³¹I therapy studies. The in vitro studies showed EGFR-dependent and NIS-specific transfection efficiency of the polyplexes. The injection of monoDBCO-PEG₂₄-GE11/NIS polyplexes 48 h before ¹²⁴I application was characterized to be the optimal regime in the imaging studies and was therefore used for an ¹³¹I therapy study, showing a significant decrease in tumor growth and a significant extension of survival in the therapy group. These studies demonstrate the potential of EGFR-targeted polyplex-mediated NIS gene therapy as a new strategy for the therapy of glioblastoma.

Molecular imaging of cellular immunotherapies in experimental and therapeutic settings

Cell-based cancer immunotherapies are becoming a routine part of the armamentarium against cancer. While remarkable successes have been seen, including durable remissions, not all patients will benefit from these therapies and many can suffer from life-threatening side effects. These differences in efficacy and safety across patients and across tumor types (e.g., blood vs. solid), are thought to be due to differences in how well the immune cells traffic to their target tissue (e.g., tumor, lymph nodes, etc.) whilst avoiding non-target tissues. Across patient variability can also stem from whether the cells interact with (i.e., communicate with) their intended target cells (e.g., cancer cells), as well as if they proliferate and survive long enough to yield potent and long-lasting therapeutic effects. However, many cell-based therapies are monitored by relatively simple blood tests that lack any spatial information and do not reflect how many immune cells have ended up at particular tissues. The ex vivo labeling and imaging of infused therapeutic immune cells can provide a more precise and dynamic understanding of whole-body immune cell biodistribution, expansion, viability, and activation status in individual patients. In recent years numerous cellular imaging technologies have been developed that may provide this much-needed information on immune cell fate. For this review, we summarize various ex vivo labeling and imaging approaches that allow for tracking of cellular immunotherapies for cancer. Our focus is on clinical imaging modalities and summarize the progression from experimental to therapeutic settings. The imaging information provided by these technologies can potentially be used for many purposes including improved real-time understanding of therapeutic efficacy and potential side effects in individual patients after cell infusion; the ability to more readily compare new therapeutic cell designs to current designs for various parameters such as improved trafficking to target tissues and avoidance of non-target tissues; and the long-term ability to identify patient populations that are likely to be positive responders and at low-risk of side effects.

Quantitative imaging and dynamics of tumor therapy with viruses

Cancer therapy remains challenging due to the myriad presentations of the disease and the vast genetic diversity of tumors that continuously evolve and often become resistant to therapy. Viruses can be engineered to specifically infect, replicate, and kill tumor cells (tumor virotherapy). Moreover, the viruses can be "armed" with therapeutic genes to enhance their oncolytic effect. Using viruses to treat cancer is exciting and novel and in principle can be used for a broad variety of tumors. However, the approach is distinctly different from other cancer therapies since success depends on establishment of an infection within the tumor and ongoing propagation of the oncolytic virus within the tumor itself. Therefore, the target itself amplifies the therapy. This introduces complex dynamics especially when the immune system is taken into consideration as well as the physical and other biological barriers to virus growth. Understanding these dynamics not only requires mathematical and computational models but also approaches for the noninvasive monitoring of the virus and tumor populations. In this perspective, we discuss strategies and current results to achieve this important goal of understanding these dynamics in pursuit of optimization of oncolytic virotherapy.

Integrin αvβ3-Mediated Effects of Thyroid Hormones on Mesenchymal Stem Cells in Tumor Angiogenesis

Background: Several clinical and experimental studies have implicated thyroid hormones in cancer progression. Cancer-relevant effects, including stimulation of tumor growth and new blood vessel formation by angiogenesis, are thought to be mediated by a nonclassical signaling pathway initiated through integrin αvβ3 expressed on cancer cells and proliferating endothelium. In an earlier study, we established mesenchymal stem cells (MSCs), important contributors to the fibrovascular network of tumors, as new thyroid hormone-dependent targets. Here, we evaluated the effects of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) versus Tetrac, an integrin-specific inhibitor of thyroid hormone action, on MSCs in tumor angiogenesis. Methods: Modulation of the expression and secretion of angiogenesis-relevant factors by thyroid hormones in primary human MSCs and their effect on endothelial cell tube formation were tested in vitro. We further engineered MSCs to express the sodium iodide symporter (NIS) reporter gene under control of a hypoxia-responsive promoter and the vascular endothelial growth factor (VEGF) promoter to test effects on these pathways in vitro and, for VEGF, in vivo in an orthotopic hepatocellular carcinoma (HCC) xenograft mouse model by positron emission tomography imaging. Results: T3 and T4 increased the expression of pro-angiogenic genes in MSCs and NIS-mediated radioiodide uptake in both NIS reporter MSC lines in the presence of HCC cell-conditioned medium. Supernatant from thyroid hormone-treated MSCs significantly enhanced endothelial cell tube formation. Tetrac and/or inhibitors of signaling pathways downstream of the integrin reversed all these effects. Tumoral radioiodide uptake in vivo demonstrated successful recruitment of MSCs to tumors and VEGF promoter-driven NIS expression. Hyperthyroid mice showed an increased radioiodide uptake compared with euthyroid mice, while tracer uptake was markedly reduced in hypothyroid and Tetrac-treated mice. Conclusions: Our data suggest that thyroid hormones influence angiogenic signaling in MSCs via integrin αvβ3 and further substantiate the anti-angiogenic activity of Tetrac in the tumor microenvironment.

Rhenium-188 Labeled Radiopharmaceuticals: Current Clinical Applications in Oncology and Promising Perspectives

Rhenium-188 (¹⁸⁸Re) is a high energy beta-emitting radioisotope with a short 16.9 h physical half-life, which has been shown to be a very attractive candidate for use in therapeutic nuclear medicine. The high beta emission has an average energy of 784 keV and a maximum energy of 2.12 MeV, sufficient to penetrate and destroy targeted abnormal tissues. In addition, the low-abundant gamma emission of 155 keV (15%) is efficient for imaging and for dosimetric calculations. These key characteristics identify ¹⁸⁸Re as an important therapeutic radioisotope for routine clinical use. Moreover, the highly reproducible on-demand availability of ¹⁸⁸Re from the ¹⁸⁸W/¹⁸⁸Re generator system is an important feature and permits installation in hospital-based or central radiopharmacies for cost-effective availability of no-carrier-added (NCA) ¹⁸⁸Re. Rhenium-188 and technetium-99 m exhibit similar chemical properties and represent a “theranostic pair.” Thus, preparation and targeting of ¹⁸⁸Re agents for therapy is similar to imaging agents prepared with ^99mTc, the most commonly used diagnostic radionuclide. Over the last three decades, radiopharmaceuticals based on ¹⁸⁸Re-labeled small molecules, including peptides, antibodies, Lipiodol and particulates have been reported. The successful application of these ¹⁸⁸Re-labeled therapeutic radiopharmaceuticals has been reported in multiple early phase clinical trials for the management of various primary tumors, bone metastasis, rheumatoid arthritis, and endocoronary interventions. This article reviews the use of ¹⁸⁸Re-radiopharmaceuticals which have been investigated in patients for cancer treatment, demonstrating that ¹⁸⁸Re represents a cost effective alternative for routine clinical use in comparison to more expensive and/or less readily available therapeutic radioisotopes.

Radiation-Induced Amplification of TGFB1-Induced Mesenchymal Stem Cell-Mediated Sodium Iodide Symporter (NIS) Gene 131I Therapy

PURPOSE

The innate tumor homing potential of mesenchymal stem cells (MSCs) has been used for a targeted delivery of the theranostic sodium iodide symporter (NIS) transgene into solid tumors. We have previously shown that external beam radiotherapy (EBRT) results in the enhanced recruitment of NIS-expressing MSCs into human hepatocellular carcinoma (HuH7). In parallel, the tumor-associated cytokine TGFB1 becomes strongly upregulated in HuH7 tumors in response to EBRT.

EXPERIMENTAL DESIGN

We therefore evaluated the effects of combining focused EBRT (5 Gy) with MSC-mediated systemic delivery of the theranostic NIS transgene under control of a synthetic TGFB1-inducible SMAD-responsive promoter (SMAD-NIS-MSCs) using ¹²³I-scintigraphy followed by ¹³¹I therapy in CD1 nu/nu mice harboring subcutaneous human hepatocellular carcinoma (HuH7).

RESULTS

Following tumor irradiation and SMAD-NIS-MSC application, tumoral iodide uptake monitored in vivo by ¹²³I-scintigraphy was enhanced as compared with nonirradiated tumors. Combination of EBRT and SMAD-NIS-MSC-mediated ¹³¹I therapy resulted in a significantly improved delay in tumor growth and prolonged survival in therapy mice as compared with the combined therapy using CMV-NIS-MSCs or to control groups receiving EBRT or saline only, or EBRT together with SMAD-NIS-MSCs and saline applications.

CONCLUSIONS

MSC-based NIS-mediated ¹³¹I therapy after EBRT treatment dramatically enhanced therapeutic efficacy when a TGFB1-inducible SMAD-responsive promoter was used to drive NIS expression in adoptively applied MSCs. The remarkable therapeutic effect seen is thought to be linked in large part to the enhanced TGFB1 produced in this context, which leads to a highly selective and focused amplification of MSC-based NIS expression within the tumor milieu.

A Novel Chimeric Poxvirus Encoding hNIS Is Tumor-Tropic, Imageable, and Synergistic with Radioiodine to Sustain Colon Cancer Regression

Colon cancer has a high rate of recurrence even with good response to modern therapies. Novel curative adjuncts are needed. Oncolytic viral therapy has shown preclinical promise against colon cancer but lacks robust efficacy in clinical trials and raises regulatory concerns without real-time tracking of viral replication. Novel potent vectors are needed with adjunctive features to enhance clinical efficacy. We have thus used homologous recombination and high-throughput screening to create a novel chimeric poxvirus encoding a human sodium iodide symporter (hNIS) at a redundant tk locus. The resulting virus (CF33-hNIS) consistently expresses hNIS and demonstrates replication efficiency and immunogenic cell death in colon cancer cells in vitro. Tumor-specific CF33-hNIS efficacy against colon cancer results in tumor regression in vivo in colon cancer xenograft models. Early expression of hNIS by infected cells makes viral replication reliably imageable via positron emission tomography (PET) of I-124 uptake. The intensity of I-124 uptake mirrors viral replication and tumor regression. Finally, systemic delivery of radiotherapeutic I-131 isotope following CF33-hNIS infection of colon cancer xenografts enhances and sustains tumor regression compared with virus treatment alone in HCT116 xenografts, demonstrating synergy of oncolytic viral therapy with radioablation in vivo.

Systemic tumor-targeted sodium iodide symporter (NIS) gene therapy of hepatocellular carcinoma mediated by B6 peptide polyplexes

BACKGROUND

Nonviral polymer-based gene transfer represents an adaptable system for tumor-targeted gene therapy because various design strategies of shuttle systems, together with the mechanistic concept of active tumor targeting, lead to improved gene delivery vectors resulting in higher tumor specificity, efficacy and safety.

METHODS

Using the sodium iodide symporter (NIS) as a theranostic gene, nonviral gene delivery vehicles based on linear polyethylenimine (LPEI), polyethylene glycol (PEG) and coupled to the synthetic peptide B6 (LPEI-PEG-B6), which specifically binds to tumor cells, were investigated in a hepatocellular carcinoma xenograft model for tumor selectivity and transduction efficiency.

RESULTS

In vitro incubation of three different tumor cell lines with LPEI-PEG-B6/NIS resulted in significant increase in iodide uptake activity compared to untargeted and empty vectors. After establishment of subcutaneous HuH7 tumors, NIS-conjugated nanoparticles were injected intravenously followed by analysis of radioiodide biodistribution using ¹²³ I-scintigraphy showing significant perchlorate-sensitive iodide accumulation in tumors of LPEI-PEG-B6/NIS-treated mice (8.0 ± 1.5% ID/g ¹²³ I; biological half-life of 4 h). After four cycles of repetitive polyplex/¹³¹ I applications, a significant delay of tumor growth was observed, which was associated with markedly improved survival in the therapy group.

CONCLUSIONS

These results clearly demonstrate that systemic in vivo NIS gene transfer using nanoparticle vectors coupled to B6 tumor targeting ligand is capable of inducing tumor-specific radioiodide uptake. This promising gene therapy approach opens the exciting prospect of NIS-mediated radionuclide therapy in metastatic cancer, together with the possibility of combining several targeting ligands to enhance selective therapeutic efficacy in a broad field of cancer types with various receptor expression profiles.

Human sodium iodide transporter gene-mediated imaging and therapy of mouse glioma, comparison between 188Re and 131I

Novel treatment options are urgently required for patients with glioma who are not effectively treated through standard therapy. Human sodium iodide symporter (hNIS) is a molecular target of certain tumors types. Compared with ¹³¹I, ¹⁸⁸Re possesses a higher energy and shorter half-life; therefore, the effects of ¹⁸⁸Re and ¹³¹I were compared in hNIS-mediated gene imaging and therapy in the present study. Recombinant human brain glioma cell line U87 was transfected with a recombinant lentiviral vector containing hNIS (U87-hNIS). U87-0 cell line transfected with blank lentivirus was prepared as a control. In vitro, the ¹⁸⁸Re and ¹³¹I uptake of U87-hNIS cells were 21.3-times and 25.9-times that of the control groups, however the excretion rate of the two nuclides was very rapid, and the half-life was only ~4 min. Sodium perchlorate inhibited hNIS-mediated ¹⁸⁸Re and ¹³¹I uptake to levels observed in the control groups. ¹⁸⁸Re and ¹³¹I were able to kill U87-hNIS cells selectively, with a survival of only 21.6 and 36.2%, respectively. U87-hNIS nude mice appeared to accumulate ¹⁸⁸Re, with a ratio of radioactivity counts between tumor and non-tumor sites of ~13.5 compared with 10.3 of ¹³¹I 1 h after radionuclide injection. In contrast with in vitro studies, U87-hNIS cells demonstrated a notable increase in ¹⁸⁸Re retention in vivo, even 24 h after ¹⁸⁸Re injection. U87-hNIS cells also exhibited increased ¹³¹I retention in vivo; however, as the time increased, ¹³¹I was rapidly released with the tumor no longer able to be imaged 24 h after ¹³¹I injection. Following treatment, U87-hNIS tumors experienced a volume reduction of 24.1%, whereas U87-0 cells demonstrated an increase of 28.8%. ¹⁸⁸Re and ¹³¹I were revealed to be effective at decreasing tumor volume compared with the control. However, ¹⁸⁸Re was significantly more potent compared with ¹³¹I (P<0.01). The present study indicated that the U87-hNIS cell line is sufficient to induce specific ¹⁸⁸Re and ¹³¹I uptake, which may kill cells in vitro and in vivo. ¹⁸⁸Re exhibited an increased retention time in vivo compared with ¹³¹I, which facilitates the imaging and therapy of U87-hNIS tumors.

Reintroducing the Sodium-Iodide Symporter to Anaplastic Thyroid Carcinoma

BACKGROUND

Anaplastic thyroid carcinoma (ATC), the most aggressive form of thyroid cancer, is unresponsive to radioiodine therapy. The current study aimed to extend the diagnostic and therapeutic application of radioiodine beyond the treatment of differentiated thyroid cancer by targeting the functional sodium-iodide symporter (NIS) to ATC.

METHODS

The study employed nanoparticle vectors (polyplexes) based on linear polyethylenimine (LPEI), shielded by polyethylene glycol (PEG) and coupled to the synthetic peptide GE11 as an epidermal growth factor receptor (EGFR)-specific ligand in order to target a NIS-expressing plasmid (LPEI-PEG-GE11/NIS) to EGFR overexpressing human thyroid carcinoma cell lines. Using ATC xenograft mouse models, transfection efficiency by ¹²³I scintigraphy and potential for systemic radioiodine therapy after systemic polyplex application were evaluated.

RESULTS

In vitro iodide uptake studies in SW1736 and Hth74 ATC cells, and, for comparison, in more differentiated follicular (FTC-133) and papillary (BCPAP) thyroid carcinoma cells demonstrated high transfection efficiency and EGFR-specificity of LPEI-PEG-GE11/NIS that correlated well with EGFR expression levels. After systemic polyplex injection, in vivo ¹²³I gamma camera imaging revealed significant tumor-specific accumulation of radioiodine in an SW1736 and an Hth74 xenograft mouse model. Radioiodine accumulation was found to be higher in SW1736 tumors, reflecting in vitro results, EGFR expression levels, and results from ex vivo analysis of NIS staining. Administration of ¹³¹I in LPEI-PEG-GE11/NIS-treated SW1736 xenograft mice resulted in significantly reduced tumor growth associated with prolonged survival compared to control animals.

CONCLUSIONS

The data open the exciting prospect of NIS-mediated radionuclide imaging and therapy of ATC after non-viral reintroduction of the NIS gene. The high tumor specificity after systemic application makes the strategy an attractive alternative for the treatment of highly metastatic ATC.

Imaging and targeted therapy of pancreatic ductal adenocarcinoma using the theranostic sodium iodide symporter (NIS) gene

The theranostic sodium iodide symporter (NIS) gene allows detailed molecular imaging of transgene expression and application of therapeutic radionuclides. As a crucial step towards clinical application, we investigated tumor specificity and transfection efficiency of epidermal growth factor receptor (EGFR)-targeted polyplexes as systemic NIS gene delivery vehicles in an advanced genetically engineered mouse model of pancreatic ductal adenocarcinoma (PDAC) that closely reflects human disease. PDAC was induced in mice by pancreas-specific activation of constitutively active KrasG12D and deletion of Trp53. We used tumor-targeted polyplexes (LPEI-PEG-GE11/NIS) based on linear polyethylenimine, shielded by polyethylene glycol and coupled with the EGFR-specific peptide ligand GE11, to target a NIS-expressing plasmid to high EGFR-expressing PDAC. In vitro iodide uptake studies in cell explants from murine EGFR-positive and EGFR-ablated PDAC lesions demonstrated high transfection efficiency and EGFR-specificity of LPEI-PEG-GE11/NIS. In vivo 123I gamma camera imaging and three-dimensional high-resolution 124I PET showed significant tumor-specific accumulation of radioiodide after systemic LPEI-PEG-GE11/NIS injection. Administration of 131I in LPEI-PEG-GE11/NIS-treated mice resulted in significantly reduced tumor growth compared to controls as determined by magnetic resonance imaging, though survival was not significantly prolonged. This study opens the exciting prospect of NIS-mediated radionuclide imaging and therapy of PDAC after systemic non-viral NIS gene delivery.

MR molecular imaging of tumours using ferritin heavy chain reporter gene expression mediated by the hTERT promoter

Objectives

Using the human telomerase reverse transcriptase (hTERT) promoter and the modified ferritin heavy chain (Fth) reporter gene, reporter gene expression for MRI was examined in telomerase positive and negative tumour cells and xenografts.

Methods

Activity of the reporter gene expression vector Lenti-hTERT-Fth1-3FLAG-Puro was compared to constitutive CMV-driven expression and to the untransfected parental control in five tumour cell lines: A549, SKOV3, 293T, U2OS and HPDLF. In vitro, transfected cells were evaluated for FLAG-tagged protein expression, iron accumulation and transverse relaxation. In vivo, tumours transduced by lentiviral vector injection were imaged using T2*WI. Changes in tumour signal intensity were validated by histology.

Results

Only telomerase positive tumour cells expressed FLAG-tagged Fth and displayed an increase in R2* above the parental control, with a corresponding change in T2*WI. In addition, only telomerase positive tumours, transduced by injection of the reporter gene expression construct, exhibited a change in signal intensity on T2*WI. Tumour histology verified the expression of FLAG-tagged Fth and iron accumulation in telomerase positive tissue.

Conclusion

Reporter gene expression for MRI, using the Fth reporter and the hTERT promoter, may be a useful strategy for the non-invasive diagnosis of many types of cancer.

Key points

• Modified heavy chain of ferritin can serve as an MR reporter gene

• hTERT promoter can direct the expression of reporter gene in cancer cells

• MR reporter imaging mediated by hTERT promoter can be used for cancer diagnosis

Mesenchymal stem cell-mediated, tumor stroma-targeted radioiodine therapy of metastatic colon cancer using the sodium iodide symporter as theranostic gene

The tumor-homing property of mesenchymal stem cells (MSCs) allows targeted delivery of therapeutic genes into the tumor microenvironment. The application of sodium iodide symporter (NIS) as a theranostic gene allows noninvasive imaging of MSC biodistribution and transgene expression before therapeutic radioiodine application. We have previously shown that linking therapeutic transgene expression to induction of the chemokine CCL5/RANTES allows a more focused expression within primary tumors, as the adoptively transferred MSC develop carcinoma-associated fibroblast-like characteristics. Although RANTES/CCL5-NIS targeting has shown efficacy in the treatment of primary tumors, it was not clear if it would also be effective in controlling the growth of metastatic disease.

METHODS

To expand the potential range of tumor targets, we investigated the biodistribution and tumor recruitment of MSCs transfected with NIS under control of the RANTES/CCL5 promoter (RANTES-NIS-MSC) in a colon cancer liver metastasis mouse model established by intrasplenic injection of the human colon cancer cell line LS174t. RANTES-NIS-MSCs were injected intravenously, followed by (123)I scintigraphy, (124)I PET imaging, and (131)I therapy.

RESULTS

Results show robust MSC recruitment with RANTES/CCL5-promoter activation within the stroma of liver metastases as evidenced by tumor-selective iodide accumulation, immunohistochemistry, and real-time polymerase chain reaction. Therapeutic application of (131)I in RANTES-NIS-MSC-treated mice resulted in a significant delay in tumor growth and improved overall survival.

CONCLUSION

This novel gene therapy approach opens the prospect of NIS-mediated radionuclide therapy of metastatic cancer after MSC-mediated gene delivery.

The Na+/I- symporter (NIS): mechanism and medical impact

The Na(+)/I(-) symporter (NIS) is the plasma membrane glycoprotein that mediates active I(-) transport in the thyroid and other tissues, such as salivary glands, stomach, lactating breast, and small intestine. In the thyroid, NIS-mediated I(-) uptake plays a key role as the first step in the biosynthesis of the thyroid hormones, of which iodine is an essential constituent. These hormones are crucial for the development of the central nervous system and the lungs in the fetus and the newborn and for intermediary metabolism at all ages. Since the cloning of NIS in 1996, NIS research has become a major field of inquiry, with considerable impact on many basic and translational areas. In this article, we review the most recent findings on NIS, I(-) homeostasis, and related topics and place them in historical context. Among many other issues, we discuss the current outlook on iodide deficiency disorders, the present stage of understanding of the structure/function properties of NIS, information gleaned from the characterization of I(-) transport deficiency-causing NIS mutations, insights derived from the newly reported crystal structures of prokaryotic transporters and 3-dimensional homology modeling, and the novel discovery that NIS transports different substrates with different stoichiometries. A review of NIS regulatory mechanisms is provided, including a newly discovered one involving a K(+) channel that is required for NIS function in the thyroid. We also cover current and potential clinical applications of NIS, such as its central role in the treatment of thyroid cancer, its promising use as a reporter gene in imaging and diagnostic procedures, and the latest studies on NIS gene transfer aimed at extending radioiodide treatment to extrathyroidal cancers, including those involving specially engineered NIS molecules.

EGFR-Targeted Adenovirus Dendrimer Coating for Improved Systemic Delivery of the Theranostic NIS Gene

We recently demonstrated tumor-selective iodide uptake and therapeutic efficacy of combined radiovirotherapy after systemic delivery of the theranostic sodium iodide symporter (NIS) gene using a dendrimer-coated adenovirus. To further improve shielding and targeting we physically coated replication-selective adenoviruses carrying the hNIS gene with a conjugate consisting of cationic poly(amidoamine) (PAMAM) dendrimer linked to the peptidic, epidermal growth factor receptor (EGFR)-specific ligand GE11. In vitro experiments demonstrated coxsackie-adenovirus receptor-independent but EGFR-specific transduction efficiency. Systemic injection of the uncoated adenovirus in a liver cancer xenograft mouse model led to high levels of NIS expression in the liver due to hepatic sequestration, which were significantly reduced after coating as demonstrated by ¹²³I-scintigraphy. Reduction of adenovirus liver pooling resulted in decreased hepatotoxicity and increased transduction efficiency in peripheral xenograft tumors. ¹²⁴I-PET-imaging confirmed EGFR-specificity by significantly lower tumoral radioiodine accumulation after pretreatment with the EGFR-specific antibody cetuximab. A significantly enhanced oncolytic effect was observed following systemic application of dendrimer-coated adenovirus that was further increased by additional treatment with a therapeutic dose of ¹³¹I. These results demonstrate restricted virus tropism and tumor-selective retargeting after systemic application of coated, EGFR-targeted adenoviruses therefore representing a promising strategy for improved systemic adenoviral NIS gene therapy.

Stromal targeting of sodium iodide symporter using mesenchymal stem cells allows enhanced imaging and therapy of hepatocellular carcinoma

The tumor-homing property of mesenchymal stem cells (MSC) has lead to their use as delivery vehicles for therapeutic genes. The application of the sodium iodide symporter (NIS) as therapy gene allows noninvasive imaging of functional transgene expression by (123)I-scintigraphy or PET-imaging, as well as therapeutic application of (131)I or (188)Re. Based on the critical role of the chemokine RANTES (regulated on activation, normal T-cell expressed and presumably secreted)/CCL5 secreted by MSCs in the course of tumor stroma recruitment, use of the RANTES/CCL5 promoter should allow tumor stroma-targeted expression of NIS after MSC-mediated delivery. Using a human hepatocellular cancer (HCC) xenograft mouse model (Huh7), we investigated distribution and tumor recruitment of RANTES-NIS-engineered MSCs after systemic injection by gamma camera imaging. (123)I-scintigraphy revealed active MSC recruitment and CCL5 promoter activation in the tumor stroma of Huh7 xenografts (6.5% ID/g (123)I, biological half-life: 3.7 hr, tumor-absorbed dose: 44.3 mGy/MBq). In comparison, 7% ID/g (188)Re was accumulated in tumors with a biological half-life of 4.1 hr (tumor-absorbed dose: 128.7 mGy/MBq). Administration of a therapeutic dose of (131)I or (188)Re (55.5 MBq) in RANTES-NIS-MSC-treated mice resulted in a significant delay in tumor growth and improved survival without significant differences between (131)I and (188)Re. These data demonstrate successful stromal targeting of NIS in HCC tumors by selective recruitment of NIS-expressing MSCs and by use of the RANTES/CCL5 promoter. The resulting tumor-selective radionuclide accumulation was high enough for a therapeutic effect of (131)I and (188)Re opening the exciting prospect of NIS-mediated radionuclide therapy of metastatic cancer using genetically engineered MSCs as gene delivery vehicles.

Systemic image-guided liver cancer radiovirotherapy using dendrimer-coated adenovirus encoding the sodium iodide symporter as theranostic gene

Currently, major limitations for the clinical application of adenovirus-mediated gene therapy are high prevalence of neutralizing antibodies, widespread expression of the coxsackie-adenovirus receptor (CAR), and adenovirus sequestration by the liver. In the current study, we used the sodium iodide symporter (NIS) as a theranostic gene to investigate whether coating of adenovirus with synthetic dendrimers could be useful to overcome these hurdles in order to develop adenoviral vectors for combination of systemic oncolytic virotherapy and NIS-mediated radiotherapy.

METHODS

We coated replication-deficient (Ad5-CMV/NIS) (CMV is cytomegalovirus) and replication-selective (Ad5-E1/AFP-E3/NIS) adenovirus serotype 5 carrying the hNIS gene with poly(amidoamine) dendrimers generation 5 (PAMAM-G5) in order to investigate transduction efficacy and altered tropism of these coated virus particles by (123)I scintigraphy and to evaluate their therapeutic potential for systemic radiovirotherapy in a liver cancer xenograft mouse model.

RESULTS

After dendrimer coating, Ad5-CMV/NIS demonstrated partial protection from neutralizing antibodies and enhanced transduction efficacy in CAR-negative cells in vitro. In vivo (123)I scintigraphy of nude mice revealed significantly reduced levels of hepatic transgene expression after intravenous injection of dendrimer-coated Ad5-CMV/NIS (dcAd5-CMV/NIS). Evasion from liver accumulation resulted in significantly reduced liver toxicity and increased transduction efficiency of dcAd5-CMV/NIS in hepatoma xenografts. After PAMAM-G5 coating of the replication-selective Ad5-E1/AFP-E3/NIS, a significantly enhanced oncolytic effect was observed after intravenous application (virotherapy) that was further increased by additional treatment with a therapeutic dose of (131)I (radiovirotherapy) and was associated with markedly improved survival.

CONCLUSION

These results demonstrate efficient liver detargeting and tumor retargeting of adenoviral vectors after coating with synthetic dendrimers, thereby representing a promising innovative strategy for systemic NIS gene therapy. Moreover, our study-based on the function of NIS as a theranostic gene allowing the noninvasive imaging of NIS expression by (123)I scintigraphy-provides detailed characterization of in vivo vector biodistribution and localization, level, and duration of transgene expression, essential prerequisites for exact planning and monitoring of clinical gene therapy trials that aim to individualize the NIS gene therapy concept.

Sodium iodide symporter (NIS)-mediated radiovirotherapy of hepatocellular cancer using a conditionally replicating adenovirus

In this study, we determined the in vitro and in vivo efficacy of sodium iodide symporter (NIS) gene transfer and the therapeutic potential of oncolytic virotherapy combined with radioiodine therapy using a conditionally replicating oncolytic adenovirus. For this purpose, we used a replication-selective adenovirus in which the E1a gene is driven by the mouse alpha-fetoprotein (AFP) promoter and the human NIS gene is inserted in the E3 region (Ad5-E1/AFP-E3/NIS). Human hepatocellular carcinoma cells (HuH7) infected with Ad5-E1/AFP-E3/NIS concentrated radioiodine at a level that was sufficiently high for a therapeutic effect in vitro. In vivo experiments demonstrated that 3 days after intratumoral (i.t.) injection of Ad5-E1/AFP-E3/NIS HuH7 xenograft tumors accumulated approximately 25% ID g(-1) (percentage of the injected dose per gram tumor tissue) (123)I as shown by (123)I gamma camera imaging. A single i.t. injection of Ad5-E1/AFP-E3/NIS (virotherapy) resulted in a significant reduction of tumor growth and prolonged survival, as compared with injection of saline. Combination of oncolytic virotherapy with radioiodine treatment (radiovirotherapy) led to an additional reduction of tumor growth that resulted in markedly improved survival as compared with virotherapy alone. In conclusion, local in vivo NIS gene transfer using a replication-selective oncolytic adenovirus is able to induce a significant therapeutic effect, which can be enhanced by additional (131)I application.

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.

Combining transfer of TTF-1 and Pax-8 gene: a potential strategy to promote radioiodine therapy of thyroid carcinoma

Cotransfer of thyroid-specific transcription factor (TTF)-1 and Pax-8 gene to tumor cells, resulting in the re-expression of iodide metabolism-associated proteins, such as sodium iodide symporter (NIS), thyroglobulin (Tg), thyroperoxidase (TPO), offers the possibility of radioiodine therapy to non-iodide-concentrating tumor because the expression of iodide metabolism-associated proteins in thyroid are mediated by the thyroid transcription factor TTF-1 and Pax-8. The human TTF-1 and Pax-8 gene were transducted into the human thyroid carcinoma (K1 and F133) cells by the recombinant adenovirus, AdTTF-1 and AdPax-8. Re-expression of NIS mRNA and protein, but not TPO and Tg mRNA and protein, was detected in AdTTF-1-infected F133 cells, following with increasing radioiodine uptake (6.1-7.4 times), scarcely iodide organification and rapid iodide efflux (t(1/2) ≈ 8-min in vitro, t(1/2) ≈ 4.7-h in vivo). On contrast, all of the re-expression of NIS, TPO and Tg mRNA and proteins were detected in F133 cells coinfected with AdTTF-1 and AdPax-8. AdTTF-1- and AdPax-8-coinfected K1 and F133 cells could effectively accumulate radioiodine (6.6-7.5 times) and obviously retarded radioiodine retention (t(1/2) ≈ 25-30-min in vitro, t(1/2) ≈ 12-h in vivo) (P<0.05). Accordingly, the effect of radioiodine therapy of TTF-1 and Pax-8 cotransducted K1 and F133 cells (21-25% survival rate in vitro) was better than that of TTF-1-transducted cells (40% survival rate in vitro) (P<0.05). These results indicate that single TTF-1 gene transfer may have limited efficacy of radioiodine therapy because of rapid radioiodine efflux. The cotransduction of TTF-1 and Pax-8 gene, with resulting NIS-mediated radioiodine accumulation and TPO and Tg-mediated radioiodine organification and intracellular retention, may lead to effective radioiodine therapy of thyroid carcinoma.

Image-guided tumor-selective radioiodine therapy of liver cancer after systemic nonviral delivery of the sodium iodide symporter gene

We reported the induction of tumor-selective iodide uptake and therapeutic efficacy of (131)I in a hepatocellular carcinoma (HCC) xenograft mouse model, using novel polyplexes based on linear polyethylenimine (LPEI), shielded by polyethylene glycol (PEG), and coupled with the epidermal growth factor receptor-specific peptide GE11 (LPEI-PEG-GE11). The aim of the current study in the same HCC model was to evaluate the potential of biodegradable nanoparticle vectors based on pseudodendritic oligoamines (G2-HD-OEI) for systemic sodium iodide symporter (NIS) gene delivery and to compare efficiency and tumor specificity with LPEI-PEG-GE11. Transfection of HCC cells with NIS cDNA, using G2-HD-OEI, resulted in a 44-fold increase in iodide uptake in vitro as compared with a 22-fold increase using LPEI-PEG-GE11. After intravenous application of G2-HD-OEI/NIS HCC tumors accumulated 6-11% ID/g (123)I (percentage of the injected dose per gram tumor tissue) with an effective half-life of 10 hr (tumor-absorbed dose, 281 mGy/MBq) as measured by (123)I scintigraphic gamma camera or single-photon emission computed tomography computed tomography (SPECT CT) imaging, as compared with 6.5-9% ID/g with an effective half-life of only 6 hr (tumor-absorbed dose, 47 mGy/MBq) for LPEI-PEG-GE11. After only two cycles of G2-HD-OEI/NIS/(131)I application, a significant delay in tumor growth was observed with markedly improved survival. A similar degree of therapeutic efficacy had been observed after four cycles of LPEI-PEG-GE11/(131)I. These results clearly demonstrate that biodegradable nanoparticles based on OEI-grafted oligoamines show increased efficiency for systemic NIS gene transfer in an HCC model with similar tumor selectivity as compared with LPEI-PEG-GE11, and therefore represent a promising strategy for NIS-mediated radioiodine therapy of HCC.

Radioiodine therapy of thyroid carcinoma following Pax-8 gene transfer

The thyroid transcription factor Pax-8 could bind with the promoter/enhancer of thyroid-specific genes such as thyroglobulin (Tg), thyroperoxidase (TPO) and sodium iodide symporter (NIS), and regulate the expression of these proteins in thyrocyte. Promoting iodide accumulation in tumor cells by re-expression of Pax-8 provides a possible strategy for radioiodine therapy of tumor. Therefore, we investigated the effect of Pax-8 gene transfer on radioiodine therapy of thyroid carcinoma. The human Pax-8 gene was transfected into the human thyroid carcinoma (K1 and F133) cells by the recombinant adenovirus vector. Although the NIS mRNA was not detected, the expression of mRNA and proteins of Tg and TPO in AdPax-8-infected F133 cells were activated by Pax-8. Iodide uptake in thyroid carcinoma cells was reactivated by Pax-8 (increasing 3.3-fold in K1 cells and 5.7-fold in F133 cells). Moreover, Pax-8 promoted iodide organification and the retention time of iodine in Pax-8-expressing cells apparently prolonged in vitro and in vivo (P<0.05). Pax-8-expressing thyroid carcinoma cells were selectively killed by radioiodine. The AdPax-8-infected tumors in vivo clearly visualized in scanning images at 12 h after administration of radioiodine. These results indicate that Pax-8 can promote iodide uptake, and specifically prolong the retention time of iodide in thyroid cancer in vitro and in vivo by promoting the expression of TPO and Tg proteins. Pax-8 gene transfection may lead to effective radioiodine therapy of tumor.

Sodium iodide symporter (NIS)-mediated radionuclide ((131)I, (188)Re) therapy of liver cancer after transcriptionally targeted intratumoral in vivo NIS gene delivery

We reported the therapeutic efficacy of (131)I in hepatocellular carcinoma (HCC) cells stably expressing the sodium iodide symporter (NIS) under the control of the tumor-specific α-fetoprotein (AFP) promoter. In the current study we investigated the efficacy of adenovirus-mediated in vivo NIS gene transfer followed by (131)I and (188)Re administration for the treatment of HCC xenografts. We used a replication-deficient adenovirus carrying the human NIS gene linked to the mouse AFP promoter (Ad5-AFP-NIS) for in vitro and in vivo NIS gene transfer. Functional NIS expression was confirmed by in vivo γ-camera imaging, followed by analysis of NIS protein and mRNA expression. Human HCC (HepG2) cells infected with Ad5-AFP-NIS concentrated 50% of the applied activity of (125)I, which was sufficiently high for a therapeutic effect in an in vitro clonogenic assay. Four days after intratumoral injection of Ad5-AFP-NIS (3×10(9) plaque-forming units) HepG2 xenografts accumulated 14.5% injected dose (ID)/g (123)I with an effective half-life of 13 hr (tumor-absorbed dose, 318 mGy/MBq (131)I). In comparison, 9.2% ID/g (188)Re was accumulated in tumors with an effective half-life of 12.8 hr (tumor-absorbed dose, 545 mGy/MBq). After adenovirus-mediated NIS gene transfer in HepG2 xenografts administration of a therapeutic dose of (131)I or (188)Re (55.5 MBq) resulted in a significant delay in tumor growth and improved survival without a significant difference between (188)Re and (131)I. In conclusion, a therapeutic effect of (131)I and (188)Re was demonstrated in HepG2 xenografts after tumor-specific adenovirus-mediated in vivo NIS gene transfer.

Image-guided, tumor stroma-targeted 131I therapy of hepatocellular cancer after systemic mesenchymal stem cell-mediated NIS gene delivery

Due to its dual role as reporter and therapy gene, the sodium iodide symporter (NIS) allows noninvasive imaging of functional NIS expression by (123)I-scintigraphy or (124)I-PET imaging before the application of a therapeutic dose of (131)I. NIS expression provides a novel mechanism for the evaluation of mesenchymal stem cells (MSCs) as gene delivery vehicles for tumor therapy. In the current study, we stably transfected bone marrow-derived CD34(-) MSCs with NIS cDNA (NIS-MSC), which revealed high levels of functional NIS protein expression. In mixed populations of NIS-MSCs and hepatocellular cancer (HCC) cells, clonogenic assays showed a 55% reduction of HCC cell survival after (131)I application. We then investigated body distribution of NIS-MSCs by (123)I-scintigraphy and (124)I-PET imaging following intravenous (i.v.) injection of NIS-MSCs in a HCC xenograft mouse model demonstrating active MSC recruitment into the tumor stroma which was confirmed by immunohistochemistry and ex vivo γ-counter analysis. Three cycles of systemic MSC-mediated NIS gene delivery followed by (131)I application resulted in a significant delay in tumor growth. Our results demonstrate tumor-specific accumulation and therapeutic efficacy of radioiodine after MSC-mediated NIS gene delivery in HCC tumors, opening the prospect of NIS-mediated radionuclide therapy of metastatic cancer using MSCs as gene delivery vehicles.

Evaluation of [18F]-tetrafluoroborate as a potential PET imaging agent for the human sodium/iodide symporter in a new colon carcinoma cell line, HCT116, expressing hNIS

PURPOSE

Accumulation of iodide and other substrates via the human sodium/iodide symporter (hNIS) is fundamental to imaging and therapy of thyroid disease, hNIS reporter gene imaging and hNIS-mediated gene therapy. There is no readily available positron emission tomography (PET) tracer for hNIS. Our aim was to develop a colon carcinoma cell line stably expressing hNIS, and use it to evaluate a novel hNIS PET tracer, [18F]-tetrafluoroborate.

METHODS

Colon carcinoma cell line, HCT116, was stably transfected with hNIS, thus producing a cell line, HCT116-C19, with high hNIS expression. A Fisher rat thyroid cell line, FRTL5, which expresses rat sodium/iodide symporter when stimulated with thyroid-stimulating hormone, was used for comparison. Accumulation of [188Re]-perrhenate, [99mTc]-pertechnetate and [18F]-tetrafluoroborate was evaluated with and without perchlorate inhibition using an automated radioimmune assay system, LigandTracer. The affinity of [18F]-tetrafluoroborate for hNIS, and its half-maximal inhibitory concentration (IC50) for the inhibition of [99mTc]-pertechnetate transport were determined from the plateau accumulation of [18F]-tetrafluoroborate and [99mTc]-pertechnetate, respectively, as a function of tetrafluoroborate concentration.

RESULTS

[18F]-tetrafluoroborate accumulated effectively in both FRTL5 and HCT116-C19 cells. The accumulation in HCT116-C19 cells (plateau accumulation 31%) was comparable to that of [188Re]-perrhenate (41%) and [99mTc]-pertechnetate (46%). Its affinity for hNIS and half-maximal inhibitory concentration (IC50) for the inhibition of pertechnetate uptake was approximately micromolar.

CONCLUSION

We have produced a human colon cell line with a stable constitutive expression of functional hNIS (HCT116-hNIS-C19). [18F]-tetrafluoroborate accumulates in cells expressing hNIS or rat sodium/iodide symporter and is a potential PET imaging agent in thyroid disease and hNIS reporter gene imaging.

Epidermal growth factor receptor-targeted (131)I-therapy of liver cancer following systemic delivery of the sodium iodide symporter gene

We recently demonstrated tumor-selective iodide uptake and therapeutic efficacy of radioiodine in neuroblastoma tumors after systemic nonviral polyplex-mediated sodium iodide symporter (NIS) gene delivery. In the present study, we used novel polyplexes based on linear polyethylenimine (LPEI), polyethylene glycol (PEG), and the synthetic peptide GE11 as an epidermal growth factor receptor (EGFR)-specific ligand to target a NIS-expressing plasmid to hepatocellular carcinoma (HCC) (HuH7). Incubation of HuH7 cells with LPEI-PEG-GE11/NIS polyplexes resulted in a 22-fold increase in iodide uptake, which was confirmed in other cancer cell lines correlating well with EGFR expression levels. Using (123)I-scintigraphy and ex vivo γ-counting, HuH7 xenografts accumulated 6.5-9% injected dose per gram (ID/g) (123)I, resulting in a tumor-absorbed dose of 47 mGray/Megabecquerel (mGy/MBq) (131)Iodide ((131)I) after intravenous (i.v.) application of LPEI-PEG-GE11/NIS. No iodide uptake was observed in other tissues. After pretreatment with the EGFR-specific antibody cetuximab, tumoral iodide uptake was markedly reduced confirming the specificity of EGFR-targeted polyplexes. After three or four cycles of polyplex/(131)I application, a significant delay in tumor growth was observed associated with prolonged survival. These results demonstrate that systemic NIS gene transfer using polyplexes coupled with an EGFR-targeting ligand is capable of inducing tumor-specific iodide uptake, which represents a promising innovative strategy for systemic NIS gene therapy in metastatic cancers.

Targeting of tumor radioiodine therapy by expression of the sodium iodide symporter under control of the survivin promoter

To test the feasibility of using the survivin promoter to induce specific expression of sodium/iodide symporter (NIS) in cancer cell lines and tumors for targeted use of radionuclide therapy, a recombinant adenovirus, Ad-SUR-NIS, that expressed the NIS gene under control of the survivin promoter was constructed. Ad-SUR-NIS mediating iodide uptake and cytotoxicity was performed in vitro. Scintigraphic, biodistribution and radioiodine therapy studies were performed in vivo. PC-3 (prostate); HepG2 (hepatoma) and A375 (melanoma) cancer cells all exhibited perchlorate-sensitive iodide uptake after infection with Ad-SUR-NIS, ∼50 times higher than that of negative control Ad-CMV-GFP-infected cells. No significant iodide uptake was observed in normal human dental pulp fibroblast (DPF) cells after infection with Ad-SUR-NIS. Clonogenic assays demonstrated that Ad-SUR-NIS-infected cancer cells were selectively killed by exposure to ¹³¹I. Ad-SUR-NIS-infected tumors show significant radioiodine accumulation (13.3±2.85% ID per g at 2 h post-injection), and the effective half-life was 3.1 h. Moreover, infection with Ad-SUR-NIS in combination with ¹³¹I suppressed tumor growth. These results indicate that expression of NIS under control of the survivin promoter can likely be used to achieve cancer-specific expression of NIS in many types of cancers. In combination with radioiodine therapy, this strategy is a possible method of cancer gene therapy.

The biology of the sodium iodide symporter and its potential for targeted gene delivery

The sodium iodide symporter (NIS) is responsible for thyroidal, salivary, gastric, intestinal and mammary iodide uptake. It was first cloned from the rat in 1996 and shortly thereafter from human and mouse tissue. In the intervening years, we have learned a great deal about the biology of NIS. Detailed knowledge of its genomic structure, transcriptional and post-transcriptional regulation and pharmacological modulation has underpinned the selection of NIS as an exciting approach for targeted gene delivery. A number of in vitro and in vivo studies have demonstrated the potential of using NIS gene therapy as a means of delivering highly conformal radiation doses selectively to tumours. This strategy is particularly attractive because it can be used with both diagnostic (99mTc, 125I, 124I)) and therapeutic (131I, 186Re, 188Re, 211At) radioisotopes and it lends itself to incorporation with standard treatment modalities, such as radiotherapy or chemoradiotherapy. In this article, we review the biology of NIS and discuss its development for gene therapy.

Genetics and phenomics of hypothyroidism and goiter due to NIS mutations

Molecular cloning of the NIS gene in 1996 allowed examination of the molecular basis of congenital hypothyroidism due to iodide transport defect (ITD) many years after the first case was described by Federman et al. in 1958. Since 1997, when the first NIS mutation causing ITD was identified and characterized, 12 different NIS molecular defects have been described in 31 ITD patients. Interestingly, marked clinical heterogeneity between patients with the same NIS mutation and in patients with different mutations in the NIS gene without a clear genotype-phenotype correlation has been observed. The study of NIS mutations as the molecular basis of ITD has not only yielded extremely valuable structure/function information on NIS, but has also provided an important tool for preclinical diagnosis and genetic counseling of ITD patients.

Therapeutic effect of sodium iodide symporter gene therapy combined with external beam radiotherapy and targeted drugs that inhibit DNA repair

Adenoviral (AdV) transfer of sodium iodide symporter (NIS) gene has translational potential, but relatively low levels of transduction and subsequent radioisotope uptake limit the efficacy of the approach. In previous studies, we showed that combining NIS gene delivery with external beam radiotherapy (EBRT) and DNA damage repair inhibitors increased viral gene expression and radioiodide uptake. Here, we report the therapeutic efficacy of this strategy. An adenovirus expressing NIS from a telomerase promoter (Ad-hTR-NIS) was cytotoxic combined with relatively high-dose (50 microCi) (131)I therapy and enhanced the efficacy of EBRT combined with low-dose (10 and 25 microCi) (131)I therapy in colorectal and head and neck cancer cells. Combining this approach with ataxia-telangiectasia mutated (ATM) or DNA-dependent protein kinase (DNA-PK) inhibition caused maintenance of double-stranded DNA breaks (DSBs) at 24 hours and increased cytotoxicity on clonogenic assay. When the triplet of NIS-mediated (131)I therapy, EBRT, and DNA-PKi was used in vivo, 90% of mice were tumor-free at 5 weeks. Acute radiation toxicity in the EBRT field was not exacerbated. In contrast, DNA-PKi did not enhance the therapeutic efficacy of EBRT plus adenovirus-mediated HSVtk/ganciclovir (GCV). Therefore, combining NIS gene therapy and EBRT represents an ideal strategy to exploit the therapeutic benefits of novel radiosensitizers.

Synthesis and biological evaluation of [(18)F]tetrafluoroborate: a PET imaging agent for thyroid disease and reporter gene imaging of the sodium/iodide symporter

Purpose

The human sodium/iodide symporter (hNIS) is a well-established target in thyroid disease and reporter gene imaging using gamma emitters ¹²³I-iodide, ¹³¹I-iodide and ^99mTc-pertechnetate. However, no PET imaging agent is routinely available. The aim of this study was to prepare and evaluate ¹⁸F-labelled tetrafluoroborate ([¹⁸F]TFB) for PET imaging of hNIS.

Methods

[¹⁸F]TFB was prepared by isotopic exchange of BF₄⁻ with [¹⁸F]fluoride in hot hydrochloric acid and purified using an alumina column. Its identity, purity and stability in serum were determined by HPLC, thin-layer chromatography (TLC) and mass spectrometry. Its interaction with NIS was assessed in vitro using FRTL-5 rat thyroid cells, with and without stimulation by thyroid-stimulating hormone (TSH), in the presence and absence of perchlorate. Biodistribution and PET imaging studies were performed using BALB/c mice, with and without perchlorate inhibition.

Results

[¹⁸F]TFB was readily prepared with specific activity of 10 GBq/mg. It showed rapid accumulation in FRTL-5 cells that was stimulated by TSH and inhibited by perchlorate, and rapid specific accumulation in vivo in thyroid (SUV = 72 after 1 h) and stomach that was inhibited 95% by perchlorate.

Conclusion

[¹⁸F]TFB is an easily prepared PET imaging agent for rodent NIS and should be evaluated for hNIS PET imaging in humans.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-010-1523-0) contains supplementary material, which is available to authorized users.

Sodium iodide symporter and the radioiodine treatment of thyroid carcinoma

Since the specific accumulation of iodide in thyroid was found in 1915, radioiodine has been widely applied to diagnose and treat thyroid cancer. Iodide uptake occurs across the membrane of the thyroid follicular cells and cancer cells through an active transporter process mediated by the sodium iodide symporter (NIS). The NIS coding genes were cloned and identified from rat and human in 1996. Evaluation of the NIS gene and protein expression is critical in the management of thyroid cancer, and several approaches have been tried to increase NIS levels. Identification of the NIS gene has provided a means of expanding its role in the radionuclide gene therapy of nonthyroidal cancers as well as thyroid cancer. In this article, we explain the relationship between NIS expression and the treatment of thyroid carcinoma with I-131, and we include a review of the results of our experimental and clinical trials.

Targeted radioiodine therapy of neuroblastoma tumors following systemic nonviral delivery of the sodium iodide symporter gene

PURPOSE

We recently reported the significant therapeutic efficacy of radioiodine therapy in various tumor mouse models following transcriptionally targeted sodium iodide symporter (NIS) gene transfer. These studies showed the high potential of NIS as a novel diagnostic and therapeutic gene for the treatment of extrathyroidal tumors. As a next crucial step towards clinical application of NIS-mediated radionuclide therapy we aim at systemic delivery of the NIS gene to target extrathyroidal tumors even in the metastatic stage.

EXPERIMENTAL DESIGN

In the current study, we used synthetic polymeric vectors based on pseudodendritic oligoamines with high intrinsic tumor affinity (G2-HD-OEI) to target a NIS-expressing plasmid (CMV-NIS-pcDNA3) to neuroblastoma (Neuro2A) cells.

RESULTS

Incubation with NIS-containing polyplexes (G2-HD-OEI/NIS) resulted in a 51-fold increase in perchlorate-sensitive iodide uptake activity in Neuro2A cells in vitro. Through (123)I-scintigraphy and ex vivo gamma counting Neuro2A tumors in syngeneic A/J mice were shown to accumulate 8% to 13% ID/g (123)I with a biological half-life of 13 hours, resulting in a tumor-absorbed dose of 247 mGy/MBq (131)I after i.v. application of G2-HD-OEI/NIS. Nontarget organs, including liver, lung, kidneys, and spleen revealed no significant iodide uptake. Moreover, two cycles of systemic NIS gene transfer followed by (131)I application (55.5 MBq) resulted in a significant delay in tumor growth associated with markedly improved survival.

CONCLUSIONS

In conclusion, our data clearly show the high potential of novel pseudodendritic polymers for tumor-specific NIS gene delivery after systemic application, opening the prospect of targeted NIS-mediated radionuclide therapy of nonthyroidal tumors even in metastatic disease.

Internal radiotherapy of liver cancer with rat hepatocarcinoma-intestine-pancreas gene as a liver tumor-specific promoter

The hepatocarcinoma-intestine-pancreas (HIP) gene, also called pancreatitis-associated protein-1 (PAP1) or Reg IIIalpha, is activated in most human hepatocellular carcinomas (HCCs) but not in normal liver, which suggests that HIP regulatory sequence could be used as efficient liver tumor-specific promoters to express a therapeutic polynucleotide in liver cancer. The sodium iodide symporter (NIS), which has recognized therapeutic and reporter gene properties, is appropriate to evaluate the transcriptional strength and specificity of the HIP promoter in HCC. For this purpose, we constructed a recombinant rat HIP-NIS adenoviral vector (AdrHIP-NIS), and evaluated its performance as a mediator of selective radioiodide uptake in tumor hepatocytes. Western blot, immunofluorescence, and iodide uptake assays were performed in AdrHIP-NIS-infected primary hepatocytes and transformed hepatic and nonhepatic cells. Nuclear imaging, tissue counting and immunohistochemistry were performed in normal and HCC-bearing Wistar rats infected with AdrHIP-NIS intratumorally or via the hepatic artery. In AdrHIP-NIS-infected transformed hepatic cells, functional NIS was strongly expressed, as in cells infected with a cytomegalovirus-NIS vector. No NIS expression was found in AdrHIP-NIS-infected normal hepatocytes or transformed nonhepatic cells. In rats bearing multinodular HCC, AdrHIP-NIS triggered functional NIS expression that was preferential in tumor hepatocytes. Administration of 18 mCi of (131)I resulted in the destruction of AdrHIP-NIS-injected nodules. This study has identified the rHIP regulatory sequence as a potent liver tumor-specific promoter for the transfer of therapeutic genes, and AdrHIP-NIS-mediated (131)I therapy as a valuable option for the treatment of multinodular HCC.

Microvascular free tissue transfer for gene delivery: in vivo evaluation of different routes of plasmid and adenoviral delivery

Transfer of healthy autologous tissue as a microvascular free flap facilitates reconstruction during ablative cancer surgery. In addition to filling surgical defects, free flaps might concentrate viral vectors at the tumour bed and mediate local therapeutic effects. We evaluated the magnitude, topography and duration of luciferase gene expression after plasmid and adenoviral delivery in rat superficial inferior epigastric (SIE) flaps. For plasmid delivery, luciferase expression was significantly increased by all transduction routes (topical, intraflap injection, intravascular) (P<0.01) at day 1, but not at day 7. The spread of luciferase expression was significantly different between the 4 groups at 1 day (P=0.026) and was greatest for flaps transduced by intravascular injection. For adenoviral transduction, total radiance was significantly different between the transduced groups at 1, 14 and 28 days (P<0.05 for all comparisons). The highest levels of radiance were seen in the intravascular group. There was a statistically significant difference in the spread of light emission between the 3 groups at 1 (P=0.009) and 14 (P=0.013) days, but this was no longer evident at 28 days. Intravascular adenoviral delivery yields high-level, diffuse and durable gene expression in rat SIE flaps and is suitable for examination in therapeutic models.

The potential of 211Astatine for NIS-mediated radionuclide therapy in prostate cancer

PURPOSE

We reported recently the induction of selective iodide uptake in prostate cancer cells (LNCaP) by prostate-specific antigen (PSA) promoter-directed sodium iodide symporter (NIS) expression that allowed a significant therapeutic effect of (131)I. In the current study, we studied the potential of the high-energy alpha-emitter (211)At, also transported by NIS, as an alternative radionuclide after NIS gene transfer in tumors with limited therapeutic efficacy of (131)I due to rapid iodide efflux.

METHODS

We investigated uptake and therapeutic efficacy of (211)At in LNCaP cells stably expressing NIS under the control of the PSA promoter (NP-1) in vitro and in vivo.

RESULTS

NP-1 cells concentrated (211)At in a perchlorate-sensitive manner, which allowed a dramatic therapeutic effect in vitro. After intraperitoneal injection of (211)At (1 MBq), NP-1 tumors accumulated approximately 16% ID/g (211)At (effective half-life 4.6 h), which resulted in a tumor-absorbed dose of 1,580+/-345 mGy/MBq and a significant tumor volume reduction of up to 82+/-19%, while control tumors continued their growth exponentially.

CONCLUSIONS

A significant therapeutic effect of (211)At has been demonstrated in prostate cancer after PSA promoter-directed NIS gene transfer in vitro and in vivo suggesting a potential role for (211)At as an attractive alternative radioisotope for NIS-targeted radionuclide therapy, in particular in smaller tumors with limited radionuclide retention time.