99mTc-pertechnetate uptake in hepatoma cells due to tissue-specific human sodium iodide symporter gene expression

Visualization research on ENT1/NIS dual-function gene therapy to reverse drug resistance mediated by MUC1 in GEM-resistant pancreatic cancer

PURPOSE

To use bifunctional target genes to increase the intracellular transport of gemcitabine (GEM) to reverse chemotherapy resistance and to simultaneously use reporter gene imaging to localize therapeutic genes. The therapeutic effect was evaluated by [¹⁸F]FLT PET/CT to visualize the effect of gene therapy.

METHODS

A viral gene vector containing the pancreatic cancer-targeting promoter MUC1 for specific transcription of equilibrative nucleoside transporter 1 (ENT1) and NIS (nuclide transport channel) was employed. [¹²⁵I]NaI uptake tests and [¹³¹I]NaI SPECT imaging were performed to verify the function of NIS and the target function of MUC1. The correlation between [¹⁸F]FLT uptake and GEM resistance were assessed, and the influence ENT1 and thymidine kinase 1 (TK1) expression on [¹⁸F]FLT micro-PET/CT was measured, which provides a theoretical basis for the use of [¹⁸F]FLT micro-PET/CT to evaluate the efficacy of gene therapy.

RESULTS

First, functions of gene therapy were confirmed: ENT1 reversed the drug resistance of GEM-resistant pancreatic cancer cells by increasing GEM intracellular transport; MUC1 drove NIS target gene expression in pancreatic cancer; and therapeutic genes could be localized using [¹³¹I]NaI SPECT reporter gene imaging. Second, the [¹⁸F]FLT uptake ratio was affected by drug resistance and GEM treatment. The mechanism underlying this effect was related to ENT1 and TK1. Increased expression of ENT1 inhibited the expression of TK1 after GEM chemotherapy to reduce the uptake of [¹⁸F]FLT. Finally, micro-PET/CT indicated that the SUV_max of [¹⁸F]FLT could predict survival time. SUV_max exhibited an increasing trend in resistant pancreatic cancer but a trend of inhibition after upregulation of ENT1, which was more significant after GEM treatment.

CONCLUSIONS

Bifunctional targeted genes can localize therapeutic genes through reporter gene imaging, reverse the drug resistance of GEM-resistant pancreatic cancer and be visually evaluated through [¹⁸F]FLT micro-PET/CT.

Targeting uptake transporters for cancer imaging and treatment

Cancer cells reprogram their gene expression to promote growth, survival, proliferation, and invasiveness. The unique expression of certain uptake transporters in cancers and their innate function to concentrate small molecular substrates in cells make them ideal targets for selective delivering imaging and therapeutic agents into cancer cells. In this review, we focus on several solute carrier (SLC) transporters known to be involved in transporting clinically used radiopharmaceutical agents into cancer cells, including the sodium/iodine symporter (NIS), norepinephrine transporter (NET), glucose transporter 1 (GLUT1), and monocarboxylate transporters (MCTs). The molecular and functional characteristics of these transporters are reviewed with special emphasis on their specific expressions in cancers and interaction with imaging or theranostic agents [e.g., I-123, I-131, ¹²³I-iobenguane (mIBG), ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and ¹³C pyruvate]. Current clinical applications and research areas of these transporters in cancer diagnosis and treatment are discussed. Finally, we offer our views on emerging opportunities and challenges in targeting transporters for cancer imaging and treatment. By analyzing the few clinically successful examples, we hope much interest can be garnered in cancer research towards uptake transporters and their potential applications in cancer diagnosis and treatment.

Reporter PET Images Bortezomib Treatment-Mediated Suppression of Cancer Cell Proteasome Activity

Proteasomal protein degradation is a promising target for cancer therapy. Here, we developed a positron emission tomography (PET) technique based on the sodium-iodide symporter (NIS) gene fused with the carboxyl-terminal of ornithine decarboxylase (cODC) that noninvasively images cancer cells with inhibited proteasome activity. A retroviral vector was constructed in which the murine cODC degron was fused to the human NIS gene (NIS-cODC). Transiently transduced CT26 and HT29 colon cancer cells and stably expressing CT26/NIS-cODC cells were prepared. In cancer cells transiently transduced with NIS-cODC, NIS expression and transport activity was low at baseline, but NIS protein and ¹²⁵I uptake was significantly increased by inhibition of proteasome activity with bortezomib. Stable CT26/NIS-cODC cells also showed increased cytosolic and membrane NIS by bortezomib, and four different stable clones displayed bortezomib dose-dependent stimulation of ¹²⁵I and ^99mTc-0₄⁻ uptake. Importantly, bortezomib dose-dependently suppressed survival of CT26/NIS-cODC clones in a manner that closely correlated to the magnitudes of ¹²⁵I and ^99mTc-0₄⁻ uptake. CT26/NIS-cODC tumors of bortezomib-treated mice demonstrated greater ¹²⁴I uptake on PET images and increased NIS expression on tissue staining compared to vehicle-injected animals. NIS-cODC PET imaging may allow noninvasive quantitative monitoring of proteasome activity in cancer cells treated with bortezomib.

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.

Imaging grafted cells with [18F]FHBG using an optimized HSV1-TK mammalian expression vector in a brain injury rodent model

INTRODUCTION

Cell transplantation is an innovative therapeutic approach after brain injury to compensate for tissue damage. To have real-time longitudinal monitoring of intracerebrally grafted cells, we explored the feasibility of a molecular imaging approach using thymidine kinase HSV1-TK gene encoding and [18F]FHBG as a reporter probe to image enzyme expression.

METHODS

A stable neuronal cell line expressing HSV1-TK was developed with an optimised mammalian expression vector to ensure long-term transgene expression. After [18F]FHBG incubation under defined parameters, calibration ranges from 1 X 104 to 3 X 106 Neuro2A-TK cells were analysed by gamma counter or by PET-camera. In parallel, grafting with different quantities of [18F]FHBG prelabelled Neuro2A-TK cells was carried out in a rat brain injury model induced by stereotaxic injection of malonate toxin. Image acquisition of the rats was then performed with PET/CT camera to study the [18F]FHBG signal of transplanted cells in vivo.

RESULTS

Under the optimised incubation conditions, [18F]FHBG cell uptake rate was around 2.52%. In-vitro calibration range analysis shows a clear linear correlation between the number of cells and the signal intensity. The PET signal emitted into rat brain correlated well with the number of cells injected and the number of surviving grafted cells was recorded via the in-vitro calibration range. PET/CT acquisitions also allowed validation of the stereotaxic injection procedure. Technique sensitivity was evaluated under 5 X 104 grafted cells in vivo. No [18F]FHBG or [18F]metabolite release was observed showing a stable cell uptake even 2 h post-graft.

CONCLUSION

The development of this kind of approach will allow grafting to be controlled and ensure longitudinal follow-up of cell viability and biodistribution after intracerebral injection.

Longitudinal Assessment of Lung Cancer Progression in Mice Using the Sodium Iodide Symporter Reporter Gene and SPECT/CT Imaging

Lung cancer has the highest mortality rate of any tissue-specific cancer in both men and women. Research continues to investigate novel drugs and therapies to mitigate poor treatment efficacy, but the lack of a good descriptive lung cancer animal model for preclinical drug evaluation remains an obstacle. Here we describe the development of an orthotopic lung cancer animal model which utilizes the human sodium iodide symporter gene (hNIS; SLC5A5) as an imaging reporter gene for the purpose of non-invasive, longitudinal tumor quantification. hNIS is a glycoprotein that naturally transports iodide (I-) into thyroid cells and has the ability to symport the radiotracer 99mTc-pertechnetate (99mTcO4-). A549 lung adenocarcinoma cells were genetically modified with plasmid or lentiviral vectors to express hNIS. Modified cells were implanted into athymic nude mice to develop two tumor models: a subcutaneous and an orthotopic xenograft tumor model. Tumor progression was longitudinally imaged using SPECT/CT and quantified by SPECT voxel analysis. hNIS expression in lung tumors was analyzed by quantitative real-time PCR. Additionally, hematoxylin and eosin staining and visual inspection of pulmonary tumors was performed. We observed that lentiviral transduction provided enhanced and stable hNIS expression in A549 cells. Furthermore, 99mTcO4- uptake and accumulation was observed within lung tumors allowing for imaging and quantification of tumor mass at two-time points. This study illustrates the development of an orthotopic lung cancer model that can be longitudinally imaged throughout the experimental timeline thus avoiding inter-animal variability and leading to a reduction in total animal numbers. Furthermore, our orthotopic lung cancer animal model is clinically relevant and the genetic modification of cells for SPECT/CT imaging can be translated to other tissue-specific tumor animal models.

Sodium/iodide symporter gene transfection increases radionuclide uptake in human cisplatin-resistant lung cancer cells

The sodium/iodide symporter (NIS) is involved in iodide uptake and has been used for the diagnosis and treatment of thyroid cancer. Transfection of the NIS gene in A549 human lung cancer cells can induce radioactive iodine ((131)I) and radioactive technetium ((99m)Tc) uptake. The aim of the present study was to assess the role of NIS in (99m)Tc and (131)I uptake by the A549/DDP human cisplatin-resistant lung cancer cell line. To do so, recombinant adenovirus, adenovirus-enhanced green fluorescent protein-human NIS (Ad-eGFP-hNIS) and Ad-eGFP-rat NIS (Ad-eGFP-rNIS) vectors were established. These vectors were transfected into A549/DDP cells and xenograft tumors in nude mice. Assessment of (99m)Tc and (131)I uptake was performed. Results showed that the transfection efficiency of Ad-eGFP-hNIS and Ad-eGFP-rNIS in A549/DDP cells was at least 90 % in all experiments, and that the uptake ability of (99m)Tc and (131)I was highly enhanced (14-18 folds for (99m)Tc, and 12-16 folds for (131)I). However, the radionuclide concentration in transfected NIS genes' A549/DDP cells reached a plateau within 30-60 min, indicating that NIS transport led rapidly to (99m)Tc and (131)I saturation in cells. In xenograft tumor models, uptake of (99m)TcO4 (-) was obviously higher in the hNIS and rNIS groups compared with controls. In conclusion, these results support the hypothesis that A549/DDP cells can effectively uptake (99m)Tc and (131)I when transfected with the hNIS and rNIS gene. The rNIS or hNIS gene could be used as an effective method for the effective delivery of radioactive products to specific tissues for imagery and/or treatment.

Theranostic studies of human sodium iodide symporter imaging and therapy using 188Re: a human glioma study in mice

Objective

To investigate the role of ¹⁸⁸Re in human sodium iodide symporter (hNIS) theranostic gene-mediated human glioma imaging and therapy in model mice.

Methods

The human glioma cell line U87 was transfected with recombinant lentivirus encoding the hNIS gene under the control of cytomegalovirus promoter (U87-hNIS). The uptake and efflux of ¹⁸⁸Re were determined after incubating the cells with ¹⁸⁸Re. ¹⁸⁸Re uptake experiments in the presence of various concentrations of sodium perchlorate were carried out. In vitro cell killing tests with ¹⁸⁸Re were performed. U87-hNIS mediated ¹⁸⁸Re distribution, imaging and therapy in nude mice were also tested.

Results

U87-hNIS cell line was successfully established. The uptake of ¹⁸⁸Re in U87-hNIS cells increased up to 26-fold compared to control cells, but was released rapidly with a half-life of approximately 4 minutes. Sodium perchlorate reduced hNIS-mediated ¹⁸⁸Re uptake to levels of control cell lines. U87-hNIS cells were selectively killed following exposure to ¹⁸⁸Re, with a survival of 21.4%, while control cells had a survival of 92.1%. Unlike in vitro studies, U87-hNIS tumor showed a markedly increased ¹⁸⁸Re retention even 48 hours after ¹⁸⁸Re injection. In the therapy study, there was a significant difference in tumor size between U87-hNIS mice (317±67 mm³) and control mice (861±153 mm³) treated with ¹⁸⁸Re for 4 weeks (P<0.01).

Conclusion

The results indicate that inserting the hNIS gene into U87 cells is sufficient to induce specific ¹⁸⁸Re uptake, which has a cell killing effect both in vitro and in vivo. Moreover, our study, based on the function of hNIS as a theranostic gene allowing noninvasive imaging of hNIS expression by ¹⁸⁸Re scintigraphy, provides detailed characterization of in vivo vector biodistribution and level, localization, essential prerequisites for precise planning and monitoring of clinical gene therapy that aims to individualize gene therapy concept.

Monitoring adenoviral based gene delivery in rat glioma by molecular imaging

AIM: To determine whether endothelial progenitor cells (EPCs) can be used as delivery vehicle for adenoviral vectors and imaging probes for gene therapy in glioblastoma.

METHODS: To use cord blood derived EPCs as delivery vehicle for adenoviral vectors and imaging probes for glioma gene therapy, a rat model of human glioma was made by implanting U251 cells orthotopically. EPCs were transfected with an adenovirus (AD5/carrying hNIS gene) and labeled with iron oxide and inoculated them directly into the tumor 14 d following implantation of U251 cells. Magnetic resonance imaging (MRI) was used to in vivo track the migration of EPCs in the tumor. The expression of gene products was determined by in vivo Tc-99m single photon emission computed tomography (SPECT). The findings were validated with immunohistochemistry (IHC).

RESULTS: EPCs were successfully transfected with the adenoviral vectors carrying hNIS which was proved by significantly (P < 0.05) higher uptake of Tc-99m in transfected cells. Viability of EPCs following transfection and iron labeling was not altered. In vivo imaging showed the presence of iron positive cells and the expression of transgene (hNIS) product on MRI and SPECT, respectively, all over the tumors following administration of transfected and iron labeled EPCs in the tumors. IHC confirmed the distribution of EPC around the tumor away from the injection site and also showed transgene expression in the tumor. The results indicated the EPCs’ ability to deliver adenoviral vectors into the glioma upon intratumor injection.

CONCLUSION: EPCs can be used as vehicle to deliver adenoviral vector to glioma and also act as imaging probe at the same time.

Cord blood endothelial progenitor cells as therapeutic and imaging probes

Numerous studies demonstrated that neovascularization processes associated with severe tissue ischemia commonly found in conditions such as cardiovascular disorders and tumor growth occur via angiogenic and vasculogenic mechanisms. Over the past decade, it has been demonstrated that endothelial progenitor cells (EPCs) play a significant role in neo-angiogenic and neovasculogenic processes. Due to their ability to self-renew, circulate, home to the ischemic sites and differentiate into mature endothelial cells, EPCs derived from various sources hold enormous potential to be used as therapeutic agents in pro- or anti-angiogenic strategies for the treatment of ischemic and tumor conditions, respectively. However, the development of EPC-based therapies requires accompanying, noninvasive imaging protocol for in vivo tracking of transplanted cells. Hence, this review focuses on cord blood-derived EPCs and their role in neovascularization with emphasis on the potential use of EPCs as a therapeutic and imaging probe.

Normalisation to blood activity is required for the accurate quantification of Na/I symporter ectopic expression by SPECT/CT in individual subjects

The utilisation of the Na/I symporter (NIS) and associated radiotracers as a reporter system for imaging gene expression is now reaching the clinical setting in cancer gene therapy applications. However, a formal assessment of the methodology in terms of normalisation of the data still remains to be performed, particularly in the context of the assessment of activities in individual subjects in longitudinal studies. In this context, we administered to mice a recombinant, replication-incompetent adenovirus encoding rat NIS, or a human colorectal carcinoma cell line (HT29) encoding mouse NIS. We used (99m)Tc pertechnetate as a radiotracer for SPECT/CT imaging to determine the pattern of ectopic NIS expression in longitudinal kinetic studies. Some animals of the cohort were culled and NIS expression was measured by quantitative RT-PCR and immunohistochemistry. The radioactive content of some liver biopsies was also measured ex vivo. Our results show that in longitudinal studies involving datasets taken from individual mice, the presentation of non-normalised data (activity expressed as %ID/g or %ID/cc) leads to 'noisy', and sometimes incoherent, results. This variability is due to the fact that the blood pertechnetate concentration can vary up to three-fold from day to day. Normalisation of these data with blood activities corrects for these inconsistencies. We advocate that, blood pertechnetate activity should be determined and used to normalise the activity measured in the organ/region of interest that expresses NIS ectopically. Considering that NIS imaging has already reached the clinical setting in the context of cancer gene therapy, this normalisation may be essential in order to obtain accurate and predictive information in future longitudinal clinical studies in biotherapy.

Endothelial progenitor cells (EPCs) as gene carrier system for rat model of human glioma

Background

Due to their unique property to migrate to pathological lesions, stem cells are used as a delivery vehicle for therapeutic genes to tumors, especially for glioma. It is critically important to track the movement, localization, engraftment efficiency and functional capability or expression of transgenes of selected cell populations following transplantation. The purposes of this study were to investigate whether 1) intravenously administered, genetically transformed cord blood derived EPCs can carry human sodium iodide symporter (hNIS) to the sites of tumors in rat orthotopic model of human glioma and express transgene products, and 2) whether accumulation of these administered EPCs can be tracked by different in vivo imaging modalities.

Methods and Results

Collected EPCs were cultured and transduced to carry hNIS. Cellular viability, differential capacity and Tc-99m uptake were determined. Five to ten million EPCs were intravenously administered and Tc-99-SPECT images were acquired on day 8, to determine the accumulation of EPCs and expression of transgenes (increase activity of Tc-99m) in the tumors. Immunohistochemistry was performed to determine endothelial cell markers and hNIS positive cells in the tumors. Transduced EPCs were also magnetically labeled and accumulation of cells was confirmed by MRI and histochemistry. SPECT analysis showed increased activity of Tc-99m in the tumors that received transduced EPCs, indicative of the expression of transgene (hNIS). Activity of Tc-99m in the tumors was also dependent on the number of administered transduced EPCs. MRI showed the accumulation of magnetically labeled EPCs. Immunohistochemical analysis showed iron and hNIS positive and, human CD31 and vWF positive cells in the tumors.

Conclusion

EPC was able to carry and express hNIS in glioma following IV administration. SPECT detected migration of EPCs and expression of the hNIS gene. EPCs can be used as gene carrier/delivery system for glioma therapy as well as imaging probes.

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.

Sodium butyrate enhances the expression of baculovirus-mediated sodium/iodide symporter gene in A549 lung adenocarcinoma cells

OBJECTIVE

Increased expression of sodium/iodide symporter (NIS) is required for reporter gene imaging and effective radioiodine treatment of tumor. We investigated whether increased accumulation of iodine can be induced by sodium butyrate through a newly developed baculoviral transfer of the human NIS (hNIS) gene in A549 human lung adenocarcinoma.

METHODS

A recombinant baculovirus [Bac-cytomegalovirus (CMV)-hNIS] encoding hNIS gene under the control of the CMV promoter was constructed. After A549 cells were transfected with Bac-CMV-hNIS in the presence of sodium butyrate, the expression of hNIS protein was detected by immunofluorescence and western blot analysis. The uptake and efflux of iodine were determined after the incubation of the transfected cells with I-iodide in the presence or absence of sodium butyrate.

RESULTS

Immunocytochemical staining and western blot analysis showed increased hNIS protein expression in A549 cells transfected with Bac-CMV-hNIS after sodium butyrate treatment. Bac-CMV-hNIS transfected A549 cells accumulated up to about nine times more I than nontransfected cells; the amount of I uptake increased in a sodium butyrate in dose-dependent manner (P<0.001). However, rapid efflux of radioactivity was observed, with 50% lost during the first 2 min after I-containing medium had been replaced by a nonradioactive medium.

CONCLUSION

Our results indicated that an improved efficiency of baculovirus-mediated hNIS reporter gene imaging in lung adenocarcinoma is possible with treatment with sodium butyrate. However, additional conditions need to be defined to reduce the rapid efflux of radioiodine for the purpose of radionuclide therapy.

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.

Assessment of the Na/I symporter as a reporter gene to visualize oncolytic adenovirus propagation in peritoneal tumours

PURPOSE

In vivo imaging of the spread of oncolytic viruses using the Na/I symporter (NIS) has been proposed. Here, we assessed whether the presence of NIS in the viral genome affects the therapeutic efficacy of the oncolytic adenovirus dl922-947 following intraperitoneal administration, in a mouse model of peritoneal ovarian carcinoma.

METHODS

We generated AdAM7, a dl922-947 oncolytic adenovirus encoding the NIS coding sequence. Iodide uptake, NIS expression, infectivity and cell-killing activity of AdAM7, as well as that of relevant controls, were determined in vitro. In vivo, the propagation of this virus in the peritoneal cavity of tumour-bearing mice was determined using SPECT/CT imaging and its therapeutic efficacy was evaluated.

RESULTS

In vitro infection of ovarian carcinoma IGROV-1 cells with ADAM7 led to functional expression of NIS. However, the insertion of NIS into the viral genome resulted in a loss of efficacy of the virus in terms of replication and cytotoxicity. In vivo, on SPECT/CT imaging AdAM7 was only detectable in the peritoneal cavity of animals bearing peritoneal ovarian tumours for up to 5 days after intraperitoneal administration. Therapeutic experiments in vivo demonstrated that AdAM7 is as potent as its NIS-negative counterpart.

CONCLUSION

This study demonstrated that despite the detrimental effect observed in vitro, insertion of the reporter gene NIS in an oncolytic adenovirus did not affect its therapeutic efficacy in vivo. We conclude that NIS is a highly relevant reporter gene to monitor the fate of oncolytic adenovectors in live subjects.

Radioiodine gene therapy of hepatocellular carcinoma targeted human alpha fetoprotein

INTRODUCTION

We conducted a molecular imaging and gene therapy method in alpha-fetoprotein (AFP)-producing hepatocellular carcinoma (HCC) by tumor-specific expression of the human sodium/iodide symporter (hNIS) using an AFP promoter.

METHODS

The tumor-specific expression of hNIS gene by the AFP enhancer/promoter was constructed as pcDNA3-AFP/hNIS. The pcDNA3-AFP/hNIS was stably transfected to human HCC (Huh-7/AN) and rat glioma cells (C6/AN). Functional hNIS expression was confirmed by radioiodine uptake. The mRNA and protein-expression level of hNIS were measured. Biodistribution of 131I was evaluated, and scintigraphic images of 99mTc were obtained in xenografted mice. A clonogenic assay was performed by 131I. And, the in vivo therapeutic effect of 131I was evaluated in xenografted mice.

RESULTS

In Huh-7/AN cells, iodine was highly accumulated and completely blocked by perchlorate. The protein and mRNA expression levels were correlated with iodine uptake. Radioiodine uptake in Huh-7/AN tumors was higher than those of control tumors and clearly visualized. The survival rate was significantly decreased in Huh-7/AN cells by 131I. Moreover, a growth of Huh-7/AN tumors was inhibited by 131I in mice.

CONCLUSIONS

AFP-producing hepatoma can be targeted and treated with radionuclides and hNIS, using AFP enhancer/promoter. This targeted hNIS gene therapy and molecular imaging have the potential to be used in the management of AFP-producing HCC.