Non-invasive radioiodine imaging for accurate quantitation of NIS reporter gene expression in transplanted hearts

[18F]tetrafluoroborate-PET/CT enables sensitive tumor and metastasis in vivo imaging in a sodium iodide symporter-expressing tumor model

Cancer cell metastasis is responsible for most cancer deaths. Non-invasive in vivo cancer cell tracking in spontaneously metastasizing tumor models still poses a challenge requiring highest sensitivity and excellent contrast. The goal of this study was to evaluate if the recently introduced PET radiotracer [18F]tetrafluoroborate ([18F]BF4-) is useful for sensitive and specific metastasis detection in an orthotopic xenograft breast cancer model expressing the human sodium iodide symporter (NIS) as a reporter. In vivo imaging was complemented by ex vivo fluorescence microscopy and γ-counting of harvested tissues. Radionuclide imaging with [18F]BF4- (PET/CT) was compared to the conventional tracer [123I]iodide (sequential SPECT/CT). We found that [18F]BF4- was superior due to better pharmacokinetics, i.e. faster tumor uptake and faster and more complete clearance from circulation. [18F]BF4--PET was also highly specific as in all detected tissues cancer cell presence was confirmed microscopically. Undetected comparable tissues were similarly found to be free of metastasis. Metastasis detection by routine metabolic imaging with [18F]FDG-PET failed due to low standard uptake values and low contrast caused by adjacent metabolically active organs in this model. [18F]BF4--PET combined with NIS expressing disease models is particularly useful whenever preclinical in vivo cell tracking is of interest.

Molecular In Vivo Imaging Using a Noninvasive Cardiac-Specific MLC-2v Promoter Driven Dual-Gene Recombinant Lentivirus Monitoring System

Background

Our study aimed to demonstrate the feasibility of using the sodium/iodide symporter (NIS) to monitor vascular endothelial growth factor (VEGF₁₆₅) expression in vivo.

Methods

We constructed a recombinant lentivirus plasmid with the MLC-2v promoter driving the sodium/iodide symporter (NIS) reporter gene linked to the VEGF₁₆₅ gene. Expression of NIS and VEGF gene were identified by Western blot. On days 2 and 54, ^99mTc-MIBI imaging was used to evaluate changes in myocardial ischemia. Noninvasive ¹²⁵I micro-SPECT/CT imaging was used to assess the expression of NIS reporter gene dynamically over the next 2 months.

Results

Western blot analysis showed that both NIS and VEGF₁₆₅ were highly expressed in rat cardiomyoblast H9C2 cells transduced with Lenti-MLC-2v-NIS--VEGF₁₆₅. ¹²⁵I micro-SPECT/CT reporter imaging showed higher uptake in mouse myocardium transduced with Lenti-MLC-2v-VEGF₁₆₅-IRES-NIS. NIS expression peaked on day 1 after transduction followed by a progressive decline to negligible levels by day 21. On day 1, mean ¹²⁵I activity value in group 1 was higher than that in group 2 (P<0.05). The mean ¹²⁵I activity value in group 3 was statically lower than that in group 1 and 2 (P<0.01). On day 60, ¹²⁵I uptakes in test and positive control groups became very low, and no significant differences in the mean ¹²⁵I activity values were detected between group 1 and group 2 (P = 0.531 > 0.05). In group 1 (test group), ^99mTc-MIBI SPECT/CT revealed improvements in perfusion and wall thickening in the apical anterior wall. Mean IOD values of NIS and CD₃₄ were significantly higher in group 1 than group 3 (P<0.05). Our study proved mean I-125 uptake was significantly correlated with mean IOD value of NIS and CD34 (P<0.05).

Conclusion

This study demonstrates the feasibility of using the NIS gene to monitor VEGF₁₆₅ expression in a mouse myocardial ischemia model.

Cardiac AAV9 Gene Delivery Strategies in Adult Canines: Assessment by Long-term Serial SPECT Imaging of Sodium Iodide Symporter Expression

Heart failure is a leading cause of morbidity and mortality, and cardiac gene delivery has the potential to provide novel therapeutic approaches. Adeno-associated virus serotype 9 (AAV9) transduces the rodent heart efficiently, but cardiotropism, immune tolerance, and optimal delivery strategies in large animals are unclear. In this study, an AAV9 vector encoding canine sodium iodide symporter (NIS) was administered to adult immunocompetent dogs via epicardial injection, coronary infusion without and with cardiac recirculation, or endocardial injection via a novel catheter with curved needle and both end- and side-holes. As NIS mediates cellular uptake of clinical radioisotopes, expression was tracked by single-photon emission computerized tomography (SPECT) imaging in addition to Western blot and immunohistochemistry. Direct epicardial or endocardial injection resulted in strong cardiac expression, whereas expression after intracoronary infusion or cardiac recirculation was undetectable. A threshold myocardial injection dose that provides robust nonimmunogenic expression was identified. The extent of transmural myocardial expression was greater with the novel catheter versus straight end-hole needle delivery. Furthermore, the authors demonstrate that cardiac NIS reporter gene expression and duration can be quantified using serial noninvasive SPECT imaging up to 1 year after vector administration. These data are relevant to efforts to develop cardiac gene delivery as heart failure therapy.

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.

Heart failure gene therapy: the path to clinical practice

Gene therapy, aimed at the correction of key pathologies being out of reach for conventional drugs, bears the potential to alter the treatment of cardiovascular diseases radically and thereby of heart failure. Heart failure gene therapy refers to a therapeutic system of targeted drug delivery to the heart that uses formulations of DNA and RNA, whose products determine the therapeutic classification through their biological actions. Among resident cardiac cells, cardiomyocytes have been the therapeutic target of numerous attempts to regenerate systolic and diastolic performance, to reverse remodeling and restore electric stability and metabolism. Although the concept to intervene directly within the genetic and molecular foundation of cardiac cells is simple and elegant, the path to clinical reality has been arduous because of the challenge on delivery technologies and vectors, expression regulation, and complex mechanisms of action of therapeutic gene products. Nonetheless, since the first demonstration of in vivo gene transfer into myocardium, there have been a series of advancements that have driven the evolution of heart failure gene therapy from an experimental tool to the threshold of becoming a viable clinical option. The objective of this review is to discuss the current state of the art in the field and point out inevitable innovations on which the future evolution of heart failure gene therapy into an effective and safe clinical treatment relies.

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.

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.

Secreted blood reporters: insights and applications

Secreted reporters detected in body fluids (blood, serum or urine) have shown to be simple and useful tools for ex vivo real-time monitoring of in vivo biological processes. Here we explore the most commonly used secreted blood reporters in experimental animals: secreted alkaline phosphatase, soluble marker peptides derived from human carcinoembryonic antigen and human chorionic gonadotropin, as well as Gaussia luciferase. We also comment on other recently discovered secreted luciferases and their potential use as blood reporters for multiplexing applications.

Prolonged cardiac allograft survival using iodine 131 after human sodium iodide symporter gene transfer in a rat model

BACKGROUND

Radioiodine is efficiently concentrated by tissues expressing the human sodium iodide symporter (hNIS).

OBJECTIVE

To analyze the effects of iodine 131 on acute cardiac allograft rejection after ex vivo hNIS gene transfer in a rat model of cardiac allotransplantation.

MATERIALS AND METHODS

Hearts from Brown Norway rats were perfused ex vivo either with UW (University of Wisconsin) solution (n = 9) or UW solution containing 1 x 10(9) pfu/mL of adenovirus 5 plus NIS (Ad-NIS) (n = 18). Donor hearts were transplanted heterotopically into the abdomen of Lewis rats, and recipients were treated on postoperative day 3 with either 15,000 microCi of (131)I or saline solution. The hearts were explanted when no longer beating, and were evaluated histologically for evidence of rejection and other changes.

RESULTS

Grafts perfused with the Ad-NIS vector survived significantly longer in recipients injected with (131)I (mean [SD], 11.3 [1.9] days) compared with control animals not treated with (131)I (5.7 [0.65] days) (P < .001). Treatment with (131)I did not prolong graft survival in recipients of hearts that were not perfused with Ad-NIS (5.5 [1.0] vs 5.3 [0.8] days). In Ad-NIS (131)I-treated transplants, the level of myocardial damage on day 6 after surgery, when control hearts were rejected, was significantly lower (60.8 [28.0] vs 99.7 [0.8]; P < .05).

CONCLUSION

Our findings indicate that (131)I, after NIS gene transfer, can effectively prolong cardiac allograft survival. To our knowledge, this is the first report of the use of NIS-targeted (131)I therapy in cardiac transplantation. Further studies are required to determine the mechanism of this effect and its potential for clinical application.

Glutamate release predicts ongoing myocardial ischemia of rat hearts

BACKGROUND

Glutamate metabolism is associated with myocardial ischemia-reperfusion, but it is not clear whether glutamate reveals ongoing ischemia (OI). We evaluated whether microdialysis would detect OI induced by coronary artery ligation in a rat cardiac transplantation model.

MATERIAL AND METHODS

A total of 24 Fischer 344 rats underwent syngeneic heterotopic cardiac transplantation. Of these, 16 rats underwent ligation of the left anterior coronary artery (LAD) of the heart to induce ongoing ischemia (OI), of which eight grafts received intra-aortally Gabapentin (12 mg/graft), a glutamate-release inhibitor and eight grafts with transplantation only served as the control. With a microdialysis catheter samples for glucose, lactate, pyruvate, glutamate, and glycerol were analysed spectrophotometrically. Histology and aquaporin 7 evaluations were performed after graft harvesting.

RESULTS

Glutamate was elevated after 15 min of reperfusion in OI as compared with Control (14.31 +/- 5.03 microM vs 6.75 +/- 2.21 microM, p = 0.05), respectively. Glycerol remained high in OI (61.89 +/- 46.13 microM to 15.84 +/- 0.85 microM, p = ns) and low in Control (12.33 +/- 3.36 microM to 5.52 +/- 0.25 microM, p = ns). Gabapentin decreased glutamate release from 7.32 +/- 1.57 microM to 2.71 +/- 0.64 microM, (p < 0.05) and resulted in decrease of glycerol levels from 24.64 +/- 4.03 microM to 10.43 +/- 2.49 microM, (p < 0.05) in OI. The expression of aquaporin 7 and histology confirmed OI.

CONCLUSIONS

We suggest that glutamate release may be used as an early indicator of OI after cardiac arrest.

Evaluation of adenovirus capsid labeling versus transgene expression

Adenoviral vectors have been utilized for a variety of gene therapy applications. Our group has incorporated bioluminescent, fluorographic reporters, and/or suicide genes within the adenovirus genome for analytical and/or therapeutic purposes. These molecules have also been incorporated as capsid components. Recognizing that incorporations at either locale yield potential advantages and disadvantages, our report evaluates the benefits of transgene incorporation versus capsid incorporation. To this end, we have genetically incorporated firefly luciferase within the early region 3 or at minor capsid protein IX and compared vector functionality by means of reporter readout.