SPECT/CT imaging of oncolytic adenovirus propagation in tumours in vivo using the Na/I symporter as a reporter gene

The Basics of Visualizing, Analyzing, and Reporting Preclinical PET/CT Imaging Data

Positron emission tomography (PET) has transformed medical imaging, and while first developed and applied to the human setting, it has found widespread application at the preclinical level over the past two decades. Its strength is that it offers noninvasive 3D tomographic imaging in a quantitative manner at very high sensitivity. Paired with the right molecular probes, invaluable insights into physiology and pathophysiology have been accessible and therapeutic development has been enhanced through preclinical PET imaging. PET imaging is now often routinely combined with either computed tomography (CT) or magnetic resonance imaging (MRI) to provide additional anatomical context. All these developments were accompanied by the provision of ever more complex and powerful analysis software enabling users to visualize and quantify signals from PET imaging data. Aside from experimental complexities, there are also various pitfalls in PET image data analysis, which can negatively impact on reporting and reproducibility.Here, we provide a protocol intended to guide the inexperienced user through PET/CT data analysis. We describe the general principles and workflows required for PET/CT image data visualization and quantitative analysis using various software packages popular in the field. Moreover, we present recommendations for reporting of preclinical PET/CT data including examples of good and poor practice.

Imaging of T-cell Responses in the Context of Cancer Immunotherapy

Immunotherapy, which promotes the induction of cytotoxic T lymphocytes and enhances their infiltration into and function within tumors, is a rapidly expanding and evolving approach to treating cancer. However, many of the critical denominators for inducing effective anticancer immune responses remain unknown. Efforts are underway to develop comprehensive ex vivo assessments of the immune landscape of patients prior to and during response to immunotherapy. An important complementary approach to these efforts involves the development of noninvasive imaging approaches to detect immune targets, assess delivery of immune-based therapeutics, and evaluate responses to immunotherapy. Herein, we review the merits and limitations of various noninvasive imaging modalities (MRI, PET, and single-photon emission tomography) and discuss candidate targets for cellular and molecular imaging for visualization of T-cell responses at various stages along the cancer-immunity cycle in the context of immunotherapy. We also discuss the potential use of these imaging strategies in monitoring treatment responses and predicting prognosis for patients treated with immunotherapy.

Applications of nuclear-based imaging in gene and cell therapy: probe considerations

Several types of gene- and cell-based therapeutics are now emerging in the cancer immunotherapy, transplantation, and regenerative medicine landscapes. Radionuclear-based imaging can be used as a molecular imaging tool for repetitive and non-invasive visualization as well as in vivo monitoring of therapy success. In this review, we discuss the principles of nuclear-based imaging and provide a comprehensive overview of its application in gene and cell therapy. This review aims to inform investigators in the biomedical field as well as clinicians on the state of the art of nuclear imaging, from probe design to available radiopharmaceuticals and advances of direct (probe-based) and indirect (transgene-based) strategies in both preclinical and clinical settings. Notably, as the nuclear-based imaging toolbox is continuously expanding, it will be increasingly incorporated into the clinical setting where the distribution, targeting, and persistence of a new generation of therapeutics can be imaged and ultimately guide therapeutic decisions.

Spatiotemporal PET Imaging Reveals Differences in CAR-T Tumor Retention in Triple-Negative Breast Cancer Models

Chimeric antigen receptor T cell therapy (CAR-T) has been rolled out as a new treatment for hematological malignancies. For solid tumor treatment, CAR-T has been disappointing so far. Challenges include the quantification of CAR-T trafficking, expansion and retention in tumors, activity at target sites, toxicities, and long-term CAR-T survival. Non-invasive serial in vivo imaging of CAR-T using reporter genes can address several of these challenges. For clinical use, a non-immunogenic reporter that is detectable with exquisite sensitivity by positron emission tomography (PET) using a clinically available non-toxic radiotracer would be beneficial. Here, we employed the human sodium iodide symporter to non-invasively quantify tumor retention of pan-ErbB family targeted CAR-T by PET. We generated and characterized traceable CAR T cells and examined potential negative effects of radionuclide reporter use. We applied our platform to two different triple-negative breast cancer (TNBC) models and unexpectedly observed pronounced differences in CAR-T tumor retention by PET/CT (computed tomography) and confirmed data ex vivo. CAR-T tumor retention inversely correlated with immune checkpoint expression in the TNBC models. Our platform enables highly sensitive non-invasive PET tracking of CAR-T thereby addressing a fundamental unmet need in CAR-T development and offering to provide missing information needed for future clinical CAR-T imaging.

Non-invasive Reporter Gene Imaging of Cell Therapies, including T Cells and Stem Cells

Cell therapies represent a rapidly emerging class of new therapeutics. They are intended and developed for the treatment of some of the most prevalent human diseases, including cancer, diabetes, and for regenerative medicine. Currently, they are largely developed without precise assessment of their in vivo distribution, efficacy, or survival either clinically or preclinically. However, it would be highly beneficial for both preclinical cell therapy development and subsequent clinical use to assess these parameters in situ to enable enhancements in efficacy, applicability, and safety. Molecular imaging can be exploited to track cells non-invasively on the whole-body level and can enable monitoring for prolonged periods in a manner compatible with rapidly expanding cell types. In this review, we explain how in vivo imaging can aid the development and clinical translation of cell-based therapeutics. We describe the underlying principles governing non-invasive in vivo long-term cell tracking in the preclinical and clinical settings, including available imaging technologies, reporter genes, and imaging agents as well as pitfalls related to experimental design. Our emphasis is on adoptively transferred T cell and stem cell therapies.

How Non-invasive in vivo Cell Tracking Supports the Development and Translation of Cancer Immunotherapies

Immunotherapy is a relatively new treatment regimen for cancer, and it is based on the modulation of the immune system to battle cancer. Immunotherapies can be classified as either molecular or cell-based immunotherapies, and both types have demonstrated promising results in a growing number of cancers. Indeed, several immunotherapies representing both classes are already approved for clinical use in oncology. While spectacular treatment successes have been reported, particularly for so-called immune checkpoint inhibitors and certain cell-based immunotherapies, they have also been accompanied by a variety of severe, sometimes life-threatening side effects. Furthermore, not all patients respond to immunotherapy. Hence, there is the need for more research to render these promising therapeutics more efficacious, more widely applicable, and safer to use. Whole-body in vivo imaging technologies that can interrogate cancers and/or immunotherapies are highly beneficial tools for immunotherapy development and translation to the clinic. In this review, we explain how in vivo imaging can aid the development of molecular and cell-based anti-cancer immunotherapies. We describe the principles of imaging host T-cells and adoptively transferred therapeutic T-cells as well as the value of traceable cancer cell models in immunotherapy development. Our emphasis is on in vivo cell tracking methodology, including important aspects and caveats specific to immunotherapies. We discuss a variety of associated experimental design aspects including parameters such as cell type, observation times/intervals, and detection sensitivity. The focus is on non-invasive 3D cell tracking on the whole-body level including aspects relevant for both preclinical experimentation and clinical translatability of the underlying methodologies.

Preclinical SPECT and SPECT-CT in Oncology

Molecular imaging enables both spatial and temporal understanding of the complex biologic systems underlying carcinogenesis and malignant spread. Single-photon emission tomography (SPECT) is a versatile nuclear imaging-based technique with ideal properties to study these processes in vivo in small animal models, as well as to identify potential drug candidates and characterize their antitumor action and potential adverse effects. Small animal SPECT and SPECT-CT (single-photon emission tomography combined with computer tomography) systems continue to evolve, as do the numerous SPECT radiopharmaceutical agents, allowing unprecedented sensitivity and quantitative molecular imaging capabilities. Several of these advances, their specific applications in oncology as well as new areas of exploration are highlighted in this chapter.

Imaging of T-cells and their responses during anti-cancer immunotherapy

Immunotherapy has proven to be an effective approach in a growing number of cancers. Despite durable clinical responses achieved with antibodies targeting immune checkpoint molecules, many patients do not respond. The common denominator for immunotherapies that have successfully been introduced in the clinic is their potential to induce or enhance infiltration of cytotoxic T-cells into the tumour. However, in clinical research the molecules, cells and processes involved in effective responses during immunotherapy remain largely obscure. Therefore, in vivo imaging technologies that interrogate T-cell responses in patients represent a powerful tool to boost further development of immunotherapy. This review comprises a comprehensive analysis of the in vivo imaging technologies that allow the characterisation of T-cell responses induced by anti-cancer immunotherapy, with emphasis on technologies that are clinically available or have high translational potential. Throughout we discuss their respective strengths and weaknesses, providing arguments for selecting the optimal imaging options for future research and patient management.

In vitro study on human umbilical cord mesenchymal stem cells transfected with lentivirus-mediated hNIS-EGFP dual reporter gene and co-labeled with superparamagnetic iron oxide

The aim of the present study was to establish a stem cell line for multi-mode imaging (in vivo fluorescence imaging, magnetic resonance imaging and ^99mTc single-photon emission computed tomography) and to study the biological activity, stemness, proliferative activity and differentiation ability of superparamagnetic iron oxide (SPIO), human sodium/iodide symporter (hNIS) and enhanced green fluorescent protein (EGFP) co-labeled human umbilical cord mesenchymal stem cells (hUCMSCs). The EGFP reporter gene was selected to indirectly reflect the expression of target gene hNIS, and hUCMSCs were re-transfected with the successfully constructed recombinant plasmid pCMV-NIS-EF1-GFP-PGK-puro. When a stem cell line stably expressing hNIS and EGFP was obtained, the cells were incubated with 30 µg/ml SPIO to obtain hNIS, EGFP and SPIO co-labeled stem cells. The protein expressions of hNIS and EGFP were identified using western blot analysis, and the protein function of hNIS was identified by ¹²⁵I influx and ¹²⁵I efflux experiments. hNIS-EGFP-hUCMSCs were labeled with SPIO under the mediation of poly-L-lysine, and SPIO, hNIS and EGFP co-labeled hUCMSCs were established successfully. Staining with Prussian blue confirmed that 98% of cells were successfully labeled with SPIO. Western blotting results demonstrated positive hNIS and EGFP protein expression levels, and ¹²⁵I influx and ¹²⁵I efflux experiments confirmed that the protein function of hUCMSCs after expressing hNIS was normal. The uptake of ¹²⁵I was higher in cell lines hNIS-EGFP-hUCMSCs than in control hUCMSCs (fold change: 16.43±2.30 times; P<0.05). The stemness of hNIS-EGFP-hUCMSCs was found to be slightly decreased but not statistically significant; the overall characteristics of stem cells remained unchanged. The assessments of adipogenic and osteogenic differentiation suggest that hNIS-EGFP-hUCMSCs have no significantly different characteristics compared with primary hUCMSCs.

Cousins at work: How combining medical with optical imaging enhances in vivo cell tracking

Microscopy and medical imaging are related in their exploitation of electromagnetic waves, but were developed to satisfy differing needs, namely to observe small objects or to look inside subjects/objects, respectively. Together, these techniques can help elucidate complex biological processes and better understand health and disease. A current major challenge is to delineate mechanisms governing cell migration and tissue invasion in organismal development, the immune system and in human diseases such as cancer where the spatiotemporal tracking of small cell numbers in live animal models is extremely challenging. Multi-modal multi-scale in vivo cell tracking integrates medical and optical imaging. Fuelled by basic research in cancer biology and cell-based therapeutics, it has been enabled by technological advances providing enhanced resolution, sensitivity and multiplexing capabilities. Here, we review which imaging modalities have been successfully used for in vivo cell tracking and how this challenging task has benefitted from combining macroscopic with microscopic techniques.

The importance of imaging strategies for pre-clinical and clinical in vivo distribution of oncolytic viruses

Oncolytic viruses (OVs) are an emergent and unique therapy for cancer patients. Similar to chemo- and radiation therapy, OV can lyse (kill) cancer cell directly. In general, the advantages of OVs over other treatments are primarily: a higher safety profile (as shown by less adverse effects), ability to replicate, transgene(s) delivery, and stimulation of a host’s immune system against cancer. The latter has prompted successful use of OVs with other immunotherapeutic strategies in a synergistic manner. In spite of extended testing in pre-clinical and clinical setting, using biologically derived therapeutics like virus always raises potential concerns about safety (replication at non-intended locations) and bio-availability of the product. Recent advent in in vivo imaging techniques dramatically improves the convenience of use, quality of pictures, and amount of information acquired. Easy assessing of safety/localization of the biotherapeutics like OVs became a new potential weapon in the physician’s arsenal to improve treatment outcome. Given that OVs are typically replicating, in vivo imaging can also track virus replication and persistence as well as precisely mapping tumor tissues presence. This review discusses the importance of imaging in vivo in evaluating OV efficacy, as well as currently available tools and techniques.

Radionuclide-fluorescence Reporter Gene Imaging to Track Tumor Progression in Rodent Tumor Models

Metastasis is responsible for most cancer deaths. Despite extensive research, the mechanistic understanding of the complex processes governing metastasis remains incomplete. In vivo models are paramount for metastasis research, but require refinement. Tracking spontaneous metastasis by non-invasive in vivo imaging is now possible, but remains challenging as it requires long-time observation and high sensitivity. We describe a longitudinal combined radionuclide and fluorescence whole-body in vivo imaging approach for tracking tumor progression and spontaneous metastasis. This reporter gene methodology employs the sodium iodide symporter (NIS) fused to a fluorescent protein (FP). Cancer cells are engineered to stably express NIS-FP followed by selection based on fluorescence-activated cell sorting. Corresponding tumor models are established in mice. NIS-FP expressing cancer cells are tracked non-invasively in vivo at the whole-body level by positron emission tomography (PET) using the NIS radiotracer [18F]BF4-. PET is currently the most sensitive in vivo imaging technology available at this scale and enables reliable and absolute quantification. Current methods either rely on large cohorts of animals that are euthanized for metastasis assessment at varying time points, or rely on barely quantifiable 2D imaging. The advantages of the described method are: (i) highly sensitive non-invasive in vivo 3D PET imaging and quantification, (ii) automated PET tracer production, (iii) a significant reduction in required animal numbers due to repeat imaging options, (iv) the acquisition of paired data from subsequent imaging sessions providing better statistical data, and (v) the intrinsic option for ex vivo confirmation of cancer cells in tissues by fluorescence microscopy or cytometry. In this protocol, we describe all steps required for routine NIS-FP-afforded non-invasive in vivo cancer cell tracking using PET/CT and ex vivo confirmation of in vivo results. This protocol has applications beyond cancer research whenever in vivo localization, expansion and long-time monitoring of a cell population is of interest.

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.

The Novel Oncolytic Adenoviral Mutant Ad5-3Δ-A20T Retargeted to αvβ6 Integrins Efficiently Eliminates Pancreatic Cancer Cells

Metastatic pancreatic ductal adenocarcinomas (PDAC) are incurable due to the rapid development of resistance to all current therapeutics. Oncolytic adenoviral mutants have emerged as a promising new strategy that negates such resistance. In contrast to normal tissue, the majority of PDACs express the αvβ6 integrin receptor. To exploit this feature, we modified our previously reported oncolytic adenovirus, AdΔΔ, to selectively target αvβ6 integrins to facilitate systemic delivery. Structural modifications to AdΔΔ include the expression of the small but potent αvβ6-binding peptide, A20FMDV2, and ablation of binding to the native coxsackie and adenovirus receptor (CAR) within the fiber knob region. The resultant mutant, Ad5-3Δ-A20T, infected and killed αvβ6 integrin-expressing cells more effectively than the parental wild-type (Ad5wt) virus and AdΔΔ. Viral uptake through αvβ6 integrins rather than native viral receptors (CAR, αvβ3 and αvβ5 integrins) promoted viral propagation and spread. Superior efficacy of Ad5-3Δ-A20T compared with Ad5wt was demonstrated in 3D organotypic cocultures, and similar potency between the two viruses was observed in Suit-2 in vivo models. Importantly, Ad5-3Δ-A20T infected pancreatic stellate cells at low levels, which may further facilitate viral spread and cancer cell elimination either as a single agent or in combination with the chemotherapy drug, gemcitabine. We demonstrate that Ad5-3Δ-A20T is highly selective for αvβ6 integrin-expressing pancreatic cancer cells, and with further development, this new and exciting strategy can potentially be extended to improve the systemic delivery of adenoviruses to pancreatic cancer patients. Mol Cancer Ther; 17(2); 575-87. ©2018 AACR.

EGFR-targeted nonviral NIS gene transfer for bioimaging and therapy of disseminated colon cancer metastases

Liver metastases present a serious problem in the therapy of advanced colorectal cancer (CRC), as more than 20% of patients have distant metastases at the time of diagnosis with less than 5% being cured. Consequently, new therapeutic approaches are of major need together with high-resolution imaging methods that allow highly specific detection of small metastases.

The unique combination of reporter and therapy gene function of the sodium iodide symporter (NIS) may represent a promising theranostic strategy for CRC liver metastases allowing non-invasive imaging of functional NIS expression and therapeutic application of ¹³¹I.

For targeted NIS gene transfer polymers containing linear polyethylenimine (LPEI), polyethylene glycol (PEG) and the epidermal growth factor receptor (EGFR)-specific ligand GE11 were complexed with human NIS DNA (LPEI-PEG-GE11/NIS). Tumor specificity and transduction efficiency were examined in high EGFR-expressing LS174T metastases by non-invasive imaging using ¹⁸F-tetrafluoroborate (¹⁸F-TFB) as novel NIS PET tracer. Mice that were injected with LPEI-PEG-GE11/NIS 48 h before ¹⁸F-TFB application showed high tumoral levels (4.8±0.6% of injected dose) of NIS-mediated radionuclide uptake in comparison to low levels detected in mice that received untargeted control polyplexes. Three cycles of intravenous injection of EGFR-targeted NIS polyplexes followed by therapeutic application of 55.5 MBq ¹³¹I resulted in marked delay in metastases spread, which was associated with improved animal survival.

In conclusion, these preclinical data confirm the enormous potential of EGFR-targeted synthetic polymers for systemic NIS gene delivery in an advanced multifocal CRC liver metastases model and open the exciting prospect of NIS-mediated radionuclide therapy in metastatic disease.

[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.

Cell penetrating peptide of sodium-iodide symporter effect on the I-131 radiotherapy on thyroid cancer

The aim of the present study was to clarify whether the cell penetrating peptide of sodium-iodide symporter (NIS) has an effect on the I-131 radiotherapy of thyroid cancer. Firstly, we combined the HIV-1 TAT peptide (a cell penetrating peptide, dTAT) and established a nanoparticle vector (dTAT NP) to study the delivery efficiency of this cell-penetrating strategy for tumor-targeted gene delivery. dTAT NP was transfected into cultured TPC-1 cells as a model to study the effects of I-131 radiotherapy on thyroid cancer. Reverse transcription-quantitative polymerase chain reaction and western blotting results showed that the mRNA and protein expression levels of NIS in the transfected TPC-1 cells were substantially higher than in the negative control cells. MTT and flow cytometric analyses demonstrated that the cell growth and apoptosis rates of the TPC-1 cells were significantly inhibited and activated, respectively, by treatment with dTAT NP. The results of DAPI staining showed that treatment with dTAT NP visibly increased the nuclear apoptosis rate of the TPC-1 cells. The effect of dTAT NP on TPC-1 cells was associated with the promotion of caspase-3 and downregulation of the PI3K/Akt signaling pathway. In summary, the present data provide a pre-clinical proof-of-concept for a novel gene delivery system that efficiently delivers NIS to the targeted cancer cells and presents a satisfactory efficacy. This approach may offer an effective strategy for improving thyroid cancer gene therapy.

Sequence-defined cMET/HGFR-targeted Polymers as Gene Delivery Vehicles for the Theranostic Sodium Iodide Symporter (NIS) Gene

The sodium iodide symporter (NIS) as well-characterized theranostic gene represents an outstanding tool to target different cancer types allowing noninvasive imaging of functional NIS expression and therapeutic radioiodide application. Based on its overexpression on the surface of most cancer types, the cMET/hepatocyte growth factor receptor serves as ideal target for tumor-selective gene delivery. Sequence-defined polymers as nonviral gene delivery vehicles comprising polyethylene glycol (PEG) and cationic (oligoethanoamino) amide cores coupled with a cMET-binding peptide (cMBP2) were complexed with NIS-DNA and tested for receptor-specificity, transduction efficiency, and therapeutic efficacy in hepatocellular cancer cells HuH7. In vitro iodide uptake studies demonstrated high transduction efficiency and cMET-specificity of NIS-encoding polyplexes (cMBP2-PEG-Stp/NIS) compared to polyplexes without targeting ligand (Ala-PEG-Stp/NIS) and without coding DNA (cMBP2-PEG-Stp/Antisense-NIS). Tumor recruitment and vector biodistribution were investigated in vivo in a subcutaneous xenograft mouse model showing high tumor-selective iodide accumulation in cMBP2-PEG-Stp/NIS-treated mice (6.6 ± 1.6% ID/g (123)I, biological half-life 3 hours) by (123)I-scintigraphy. Therapy studies with three cycles of polyplexes and (131)I application resulted in significant delay in tumor growth and prolonged survival. These data demonstrate the enormous potential of cMET-targeted sequence-defined polymers combined with the unique theranostic function of NIS allowing for optimized transfection efficiency while eliminating toxicity.

Perfusion Pressure Is a Critical Determinant of the Intratumoral Extravasation of Oncolytic Viruses

Antitumor efficacy of oncolytic virotherapy is determined by the density and distribution of infectious centers within the tumor, which may be heavily influenced by the permeability and blood flow in tumor microvessels. Here, we investigated whether systemic perfusion pressure, a key driver of tumor blood flow, could influence the intratumoral extravasation of systemically administered oncolytic vesicular stomatitis virus (VSV) in myeloma tumor-bearing mice. Exercise was used to increase mean arterial pressure, and general anesthesia to decrease it. A recombinant VSV expressing the sodium iodide symporter (NIS), which concentrates radiotracers at sites of infection, was administered intravenously to exercising or anesthetized mice, and nuclear NIS reporter gene imaging was used to noninvasively track the density and spatial distribution of intratumoral infectious centers. Anesthesia resulted in decreased intratumoral infection density, while exercise increased the density and uniformity of infectious centers. Perfusion state also had a significant impact on the antitumor efficacy of the VSV therapy. In conclusion, quantitative dynamic radiohistologic imaging was used to noninvasively interrogate delivery of oncolytic virotherapy, highlighting the critical importance of perfusion pressure as a driver of intratumoral delivery and efficacy of oncolytic viruses.

The use of the NIS reporter gene for optimizing oncolytic virotherapy

Introduction: Oncolytic viruses are experimental cancer therapies being translated to the clinic. They are unique in their ability to amplify within the body, therefore requiring careful monitoring of viral replication and biodistribution. Traditional monitoring strategies fail to recapitulate the dynamic nature of oncolytic virotherapy. Consequently, clinically relevant, noninvasive, high resolution strategies are needed to effectively track virotherapy in real time.

Areas covered: The expression of the sodium iodide symporter (NIS) reporter gene is tightly coupled to viral genome replication and mediates radioisotope concentration, allowing noninvasive molecular nuclear imaging of active viral infection with high resolution. This provides insight into replication kinetics, biodistribution, the impact of vector design, administration, and dosing on therapeutic outcomes, and highlights the heterogeneity of spatial distribution and temporal evolution of infection. NIS-mediated imaging in clinical trials confirms the feasibility of this technology to noninvasively and longitudinally observe oncolytic virus infection, replication, and distribution.

Expert opinion: NIS-mediated imaging provides detailed functional and molecular information on the evolution of oncolytic virus infection in living animals. The use of NIS reporter gene imaging has rapidly advanced to provide unparalleled insight into the spatial and temporal context of oncolytic infection which will be integral to optimization of oncolytic treatment strategies.

Molecular imaging of oncolytic viral therapy

Oncolytic viruses have made their mark on the cancer world as a potential therapeutic option, with the possible advantages of reduced side effects and strengthened treatment efficacy due to higher tumor selectivity. Results have been so promising, that oncolytic viral treatments have now been approved for clinical trials in several countries. However, clinical studies may benefit from the ability to noninvasively and serially identify sites of viral targeting via molecular imaging in order to provide safety, efficacy, and toxicity information. Furthermore, molecular imaging of oncolytic viral therapy may provide a more sensitive and specific diagnostic technique to detect tumor origin and, more importantly, presence of metastases. Several strategies have been investigated for molecular imaging of viral replication broadly categorized into optical and deep tissue imaging, utilizing several reporter genes encoding for fluorescence proteins, conditional enzymes, and membrane protein and transporters. Various imaging methods facilitate molecular imaging, including computer tomography, magnetic resonance imaging, positron emission tomography, single photon emission CT, gamma-scintigraphy, and photoacoustic imaging. In addition, several molecular probes are used for medical imaging, which act as targeting moieties or signaling agents. This review will explore the preclinical and clinical use of in vivo molecular imaging of replication-competent oncolytic viral therapy.

Genetically engineering adenoviral vectors for gene therapy

Adenoviral (Ad) vectors are commonly used for various gene therapy applications. Significant advances in the genetic engineering of Ad vectors in recent years has highlighted their potential for the treatment of metastatic disease. There are several methods to genetically modify the Ad genome to incorporate retargeting peptides which will redirect the natural tropism of the viruses, including homologous recombination in bacteria or yeast. However, homologous recombination in yeast is highly efficient and can be achieved without the need for extensive cloning strategies. In addition, the method does not rely on the presence of unique restriction sites within the Ad genome and the reagents required for this method are widely available and inexpensive. Large plasmids containing the entire adenoviral genome (~36 kbp) can be modified within Saccharomyces cerevisiae yeast and genomes easily rescued in Escherichia coli hosts for analysis or amplification. A method for two-step homologous recombination in yeast is described in this chapter.

Monitoring of biodistribution and persistence of conditionally replicative adenovirus in a murine model of ovarian cancer using capsid-incorporated mCherry and expression of human somatostatin receptor subtype 2 gene

A significant limiting factor to the human clinical application of conditionally replicative adenovirus (CRAd)-based virotherapy is the inability to noninvasively monitor these agents and their potential persistence. To address this issue, we proposed a novel imaging approach that combines transient expression of the human somatostatin receptor (SSTR) subtype 2 reporter gene with genetic labeling of the viral capsid with mCherry fluorescent protein. To test this dual modality system, we constructed the Ad5/3Δ24pIXcherry/SSTR CRAd and validated its capacity to generate fluorescent and nuclear signals in vitro and following intratumoral injection. Analysis of 64Cu-CB-TE2A-Y3-TATE biodistribution in mice revealed reduced uptake in tumors injected with the imaging CRAd relative to the replication-incompetent, Ad-expressing SSTR2 but significantly greater uptake compared to the negative CRAd control. Optical imaging demonstrated relative correlation of fluorescent signal with virus replication as determined by viral genome quantification in tumors. Positron emission tomography/computed tomography studies demonstrated that we can visualize radioactive uptake in tumors injected with imaging CRAd and the trend for greater uptake by standardized uptake value analysis compared to control CRAd. In the aggregate, the plasticity of our dual imaging approach should provide the technical basis for monitoring CRAd biodistribution and persistence in preclinical studies while offering potential utility for a range of clinical applications.

Microdistribution of MC1R-targeted polyplexes in murine melanoma tumor tissue

Targeted sodium-iodide symporter (NIS) gene transfer can be considered as a promising approach for diagnostics of specific types of cancer. For this purpose we used targeted polyplexes based on PEI-PEG-MC1SP block-copolymer containing MC1SP-peptide, a ligand specific for melanocortin receptor-1 (MC1R) overexpressed on melanoma cells. Targeted polyplexes demonstrated enhanced NIS gene transfer compared to non-targeted (lacking MC1SP) ones in vitro. Using dorsal skinfold chamber and intravital microscopy we evaluated accumulation and microdistribution of quantum dot-labeled polyplexes in tumor and normal subcutaneous tissues up to 4 h after intravenous injection. Polyplexes demonstrated significantly higher total accumulation in tumor tissue in comparison with subcutaneous ones (control). Targeted and non-targeted polyplexes extravasated and penetrated into the tumor tissue up to 20 μm from the vessel walls. In contrast, in normal subcutaneous tissue polyplexes penetrated not more than 3 μm from the vessel walls with the level of extravasated polyplexes 400-fold less than in tumor. Accumulated polyplexes in tumor tissue caused NIS gene expression. Subsequent (123)I(-) intravenous injection resulted in 6.8 ± 1.1 and 4.5 ± 0.8% ID/g (p < 0.001) iodide accumulation in tumors in the case of targeted and non-targeted polyplexes, respectively, as was shown using SPECT/CT.

Adrenal gland infection by serotype 5 adenovirus requires coagulation factors

Recombinant, replication-deficient serotype 5 adenovirus infects the liver upon in vivo, systemic injection in rodents. This infection requires the binding of factor X to the capsid of this adenovirus. Another organ, the adrenal gland is also infected upon systemic administration of Ad, however, whether this infection is dependent on the cocksackie adenovirus receptor (CAR) or depends on the binding of factor X to the viral capsid remained to be determined. In the present work, we have used a pharmacological agent (warfarin) as well as recombinant adenoviruses lacking the binding site of Factor X to elucidate this mechanism in mice. We demonstrate that, as observed in the liver, adenovirus infection of the adrenal glands in vivo requires Factor X. Considering that the level of transduction of the adrenal glands is well-below that of the liver and that capsid-modified adenoviruses are unlikely to selectively infect the adrenal glands, we have used single-photon emission computed tomography (SPECT) imaging of gene expression to determine whether local virus administration (direct injection in the kidney) could increase gene transfer to the adrenal glands. We demonstrate that direct injection of the virus in the kidney increases gene transfer in the adrenal gland but liver transduction remains important. These observations strongly suggest that serotype 5 adenovirus uses a similar mechanism to infect liver and adrenal gland and that selective transgene expression in the latter is more likely to be achieved through transcriptional targeting.

Differential biodistribution of oncolytic poxvirus administered systemically in an autochthonous model of hepatocellular carcinoma

BACKGROUND

Preclinical studies have demonstrated that, unlike oncolytic adenoviruses, oncolytic vaccinia viruses can reach implanted tumors upon systemic injection. However, the biodistribution of this oncolytic agent in in situ autochthonous tumor models remains poorly characterized. In the present study, we assessed this biodistribution in a model of mouse hepatocellular carcinoma (HCC) obtained after injection of the carcinogen diethylnitrosamine (DEN).

METHODS

Twelve months after DEN administration, histology, quantitative reverse transcription-polymerase chain reaction, in situ hybridization and viral titration were used to characterize tumors, as well as to assess the viral load of the livers upon either intravenous or intraperitoineal injection.

RESULTS

The results obtained showed that the architecture of the liver was lost, with a noticeable absence of sinusoids, as well as the presence of steatosis and α-fetoprotein-positive HCC tumor nodules. Bioluminescence imaging and measures of the infective virus load demonstrated that intravenous injection of 10(8)  plaque-forming units of the recombinant vaccinia virus led to a predominant transduction of the liver, whereas intraperitoneal injection resulted in a lower level of liver transduction accompanied by an increased infection of the lungs, spleen, kidneys and bowels. Immunohistochemical analysis of liver sections of animals injected intravenously with the virus revealed a preferential localization of vaccinia-specific immunoreactivity in the tumors.

CONCLUSIONS

The findings of the present study emphasize the importance of the route of administration of the vector and highlight the relevance of systemic injection of oncolytic vaccinia virus in the context of hepatocellular carcinoma.

A vaccinia virus encoding the human sodium iodide symporter facilitates long-term image monitoring of virotherapy and targeted radiotherapy of pancreatic cancer

To assess therapeutic response and potential toxicity of oncolytic virotherapy, a noninvasive, deep-tissue imaging modality is needed. This study aimed to assess the feasibility, parameters, and determining factors of serial imaging and long-term monitoring of virotherapy and the therapeutic response of pancreatic cancer xenografts treated with a vaccinia virus carrying the human sodium iodide symporter GLV-1h153.

METHODS

Pancreatic cancer xenografts (PANC-1) in nude mice were treated systemically or intratumorally with GLV-1h153 and serially imaged using (124)I PET at 1, 2, 3, and 5 wk after viral injection. Signal intensity was compared with tumor therapeutic response and optical imaging, and tumors were histologically analyzed for morphology and the presence of virus. Autoradiography was performed using technetium-pertechnetate and γ-scintigraphy to assess determining factors for radiouptake in tumors. Finally, the enhanced therapeutic effect of combination therapy with GLV-1h153 and systemic radioiodine was assessed.

RESULTS

GLV-1h153 successfully facilitated serial long-term imaging of virotherapy, with PET signal intensity correlating to tumor response. GLV-1h153 colonization of tumors mediated radioiodine uptake at potentially therapeutic doses. Successful radiouptake required the presence of virus, adequate blood flow, and viable tissue, whereas loss of signal intensity was linked to tumor death and necrosis. Finally, combining systemically administered GLV-1h153 and (131)I led to enhanced tumor kill when compared with virus or (131)I alone (P < 0.01).

CONCLUSION

GLV-1h153 is a promising oncolytic agent for the treatment, long-term imaging, and monitoring of therapeutic response in a xenograft model of pancreatic cancer. GLV-1h153 provided insight into tumor biologic activity and facilitated enhanced tumor kill when combined with systemic targeted radiotherapy. These results warrant further investigation into parameters and potential synergistic effects of combination therapy.

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.

Chapter five--The development of transcription-regulated adenoviral vectors with high cancer-selective imaging capabilities

A clear benefit of molecular imaging is to enable noninvasive, repetitive monitoring of intrinsic signals within tumor cells as a means to identify the lesions as malignant or to assess the ability of treatment to perturb key pathways within the tumor cells. Due to the promising utility of molecular imaging in oncology, preclinical research to refine molecular imaging techniques in small animals is a blossoming field. We will first discuss the several imaging modalities such as fluorescent imaging, bioluminescence imaging, and positron emission tomography that are now commonly used in small animal settings. The indirect imaging approach, which can be adapted to a wide range of imaging reporter genes, is a useful platform to develop molecular imaging. In particular, reporter gene-based imaging is well suited for transcriptional-targeted imaging that can be delivered by recombinant adenoviral vectors. In this review, we will summarize transcription-regulated strategies used in adenoviral-mediated molecular imaging to visualize metastasis and monitor oncolytic therapy in preclinical models.

Imaging characteristics, tissue distribution, and spread of a novel oncolytic vaccinia virus carrying the human sodium iodide symporter

Introduction

Oncolytic viruses show promise for treating cancer. However, to assess therapy and potential toxicity, a noninvasive imaging modality is needed. This study aims to determine the in vivo biodistribution, and imaging and timing characteristics of a vaccinia virus, GLV-1h153, encoding the human sodium iodide symporter (hNIS.

Methods

GLV-1h153 was modified from GLV-1h68 to encode the hNIS gene. Timing of cellular uptake of radioiodide ¹³¹I in human pancreatic carcinoma cells PANC-1 was assessed using radiouptake assays. Viral biodistribution was determined in nude mice bearing PANC-1 xenografts, and infection in tumors confirmed histologically and optically via Green Fluorescent Protein (GFP) and bioluminescence. Timing characteristics of enhanced radiouptake in xenografts were assessed via ¹²⁴I-positron emission tomography (PET). Detection of systemic administration of virus was investigated with both ¹²⁴I-PET and 99m-technecium gamma-scintigraphy.

Results

GLV-1h153 successfully facilitated time-dependent intracellular uptake of ¹³¹I in PANC-1 cells with a maximum uptake at 24 hours postinfection (P<0.05). In vivo, biodistribution profiles revealed persistence of virus in tumors 5 weeks postinjection at 10⁹ plaque-forming unit (PFU)/gm tissue, with the virus mainly cleared from all other major organs. Tumor infection by GLV-1h153 was confirmed via optical imaging and histology. GLV-1h153 facilitated imaging virus replication in tumors via PET even at 8 hours post radiotracer injection, with a mean %ID/gm of 3.82±0.46 (P<0.05) 2 days after intratumoral administration of virus, confirmed via tissue radiouptake assays. One week post systemic administration, GLV-1h153-infected tumors were detected via ¹²⁴I-PET and 99m-technecium-scintigraphy.

Conclusion

GLV-1h153 is a promising oncolytic agent against pancreatic cancer with a promising biosafety profile. GLV-1h153 facilitated time-dependent hNIS-specific radiouptake in pancreatic cancer cells, facilitating detection by PET with both intratumoral and systemic administration. Therefore, GLV-1h153 is a promising candidate for the noninvasive imaging of virotherapy and warrants further study into longterm monitoring of virotherapy and potential radiocombination therapies with this treatment and imaging modality.

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.

In vivo positron emission tomography imaging using the sodium iodide symporter as a reporter gene

Information regarding the biodistribution and kinetics of spread of oncolytic viruses is crucial for safety considerations in the design of future, more efficient reagents. Although optical imaging can be used to gain this information in rodent models, imaging with radioactive isotopes presents the advantage of being directly applicable to humans, and preclinical imaging data can provide a basis for the design of clinical protocols. In this chapter, we describe the use of the Na/I symporter as a reporter gene, associated with (124)I-NaI as a radiotracer, to monitor the anatomical localization, as well as the propagation, of oncolytic viruses using dedicated, preclinical positron emission tomography scanners.

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.

Telomerase-driven expression of the sodium iodide symporter (NIS) for in vivo radioiodide treatment of cancer: a new broad-spectrum NIS-mediated antitumor approach

CONTEXT

Telomerase promoters (hTERT and hTR) are useful for transcriptional targeting in gene therapy models of cancer. Telomerase-driven expression of the sodium iodide symporter (NIS) in tumor cells has been successfully used as a reporter gene in vivo using positron emission tomography (PET) imaging.

OBJECTIVE

The aim of this study was to investigate the NIS-mediated therapeutic effect of telomerase promoters in a wide variety of human cancer cell lines.

DESIGN AND METHODS

Promoter fragments from either hTERT or hTR were used to drive the expression of NIS in cell lines derived from melanoma (M14), breast (MDA-MB-231), colon (HT-29), lung (H460), ovarian (OVCAR-3), and thyroid (TPC-1) carcinomas. Iodide uptake assays, protein immunodetection, and clonigenic assays were used to confirm NIS functional expression and the (131)I-mediated cytopathic effect. Tumor xenografts in mice were infected with hTERT and hTR and then treated using radioiodide.

RESULTS

Both promoters were selectively active in cancer cells that were effectively killed by exposure to (131)I. One single dose of 1 mCi (131)I markedly suppressed tumor growth of melanoma-derived tumor xenografts compared with controls. This effect was more modest in colon cancer-derived xenografts in part due to the reduced infectivity and the tumor cystic nature. The therapeutic effect of hTR promoter was found to be stronger than that of hTERT promoter.

CONCLUSIONS

These results demonstrate that telomerase-driven expression of NIS could potentially have applications for (131)I therapy of a wide variety of cancers. Additionally, this is the first study to report NIS-mediated (131)I therapy of melanoma tumors in vivo.

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.

Genetic incorporation of human metallothionein into the adenovirus protein IX for non-invasive SPECT imaging

As the limits of existing treatments for cancer are recognized, clearly novel therapies must be considered for successful treatment; cancer therapy using adenovirus vectors is a promising strategy. However tracking the biodistribution of adenovirus vectors in vivo is limited to invasive procedures such as biopsies, which are error prone, non-quantitative, and do not give a full representation of the pharmacokinetics involved. Current non-invasive imaging strategies using reporter gene expression have been applied to analyze adenoviral vectors. The major drawback to approaches that tag viruses with reporter genes is that these systems require initial viral infection and subsequent cellular expression of a reporter gene to allow non-invasive imaging. As an alternative to conventional vector detection techniques, we developed a specific genetic labeling system whereby an adenoviral vector incorporates a fusion between capsid protein IX and human metallothionein. Our study herein clearly demonstrates our ability to rescue viable adenoviral particles that display functional metallothionein (MT) as a component of their capsid surface. We demonstrate the feasibility of ^99mTc binding in vitro to the pIX-MT fusion on the capsid of adenovirus virions using a simple transchelation reaction. SPECT imaging of a mouse after administration of a ^99mTc-radiolabeled virus showed clear localization of radioactivity to the liver. This result strongly supports imaging using pIX-MT, visualizing the normal biodistribution of Ad primarily to the liver upon injection into mice. The ability we have developed to view real-time biodistribution in their physiological milieu represents a significant tool to study adenovirus biology in vivo.

Optical imaging of reporter gene expression using a positron-emission-tomography probe

Reporter gene∕reporter probe technology is one of the most important techniques in molecular imaging. Lately, many reporter gene∕reporter probe systems have been coupled to different imaging modalities such as positron emission tomography (PET) and optical imaging (OI). It has been recently found that OI techniques could be used to monitor radioactive tracers in vitro and in living subjects. In this study, we further demonstrate that a reporter gene∕nuclear reporter probe system [herpes simplex virus type-1 thymidine kinase (HSV1-tk) and 9-(4-(18)F-fluoro-3-[hydroxymethyl] butyl) guanine ([(18)F]FHBG)] could be successfully imaged by OI in vitro and in vivo. OI with radioactive reporter probes will facilitate and broaden the applications of reporter gene∕reporter probe techniques in medical research.

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.

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.

Intelligent design: combination therapy with oncolytic viruses

Metastatic cancer remains an incurable disease in the majority of cases and thus novel treatment strategies such as oncolytic virotherapy are rapidly advancing toward clinical use. In order to be successful, it is likely that some type of combination therapy will be necessary to have a meaningful impact on this disease. Although it may be tempting to simply combine an oncolytic virus with the existing standard radiation or chemotherapeutics, the long-term goal of such treatments must be to have a rational, potentially synergistic combination strategy that can be safely and easily used in the clinical setting. The combination of oncolytic virotherapy with existing radiotherapy and chemotherapy modalities is reviewed along with novel biologic therapies including immunotherapies, in order to help investigators make intelligent decisions during the clinical development of these products.

Targeted radionuclide therapy using a Wnt-targeted replicating adenovirus encoding the Na/I symporter

PURPOSE

The Na/I symporter (hNIS) promotes concentration of iodine in cells. In cancer gene therapy, this transgene has potential as a reporter gene for molecular imaging of viral biodistribution and as a therapeutic protein promoting (131)I-mediated radiotherapy. Here, we combined the imaging and therapeutic potential of hNIS in an oncolytic adenoviruses targeting colorectal cancer cells.

EXPERIMENTAL DESIGN

We generated an adenovirus (AdIP2) encoding hNIS and capable of selective replication in colorectal carcinoma cells. The selectivity of this virus was verified in vitro and in vivo. Its spread in tumors was monitored in vivo using single-photon emission computed tomography/CT imaging upon (99m)TcO(4)(-) injection and confirmed by immunohistochemistry. Metabolic radiotherapy was done through injection of therapeutic doses of (131)I(-).

RESULTS

We showed in vitro and in vivo the selectivity of AdIP2 and that hNIS expression is restricted to the target cells. Imaging and immunohistochemical data showed that viral spread is limited and that the point of maximal hNIS expression is reached 48 hours after a single intratumoral injection. Administration of a single therapeutic dose of (131)I at this time point led to a dramatic reduction in tumor size not observed in hNIS-negative viruses.

CONCLUSIONS

This report showed for the first time that the combination of the imaging and therapeutic potentials of hNIS can be applied to oncolytic adenoviruses in experimental models of cancer.

Visualization of gene expression in the live subject using the Na/I symporter as a reporter gene: applications in biotherapy

Biotherapies involve the utilization of antibodies, genetically modified viruses, bacteria or cells for therapeutic purposes. Molecular imaging has the potential to provide unique information that will guarantee their biosafety in humans and provide a rationale for the future development of new generations of reagents. In this context, non-invasive imaging of gene expression is an attractive prospect, allowing precise, spacio-temporal measurements of gene expression in longitudinal studies involving gene transfer vectors. With the emergence of cell therapies in regenerative medicine, it is also possible to track cells injected into subjects. In this context, the Na/I symporter (NIS) has been used in preclinical studies. Associated with a relevant radiotracer ((123)I(-), (124)I(-), (99m)TcO4(-)), NIS can be used to monitor gene transfer and the spread of selectively replicative viruses in tumours as well as in cells with a therapeutic potential. In addition to its imaging potential, NIS can be used as a therapeutic transgene through its ability to concentrate therapeutic doses of radionuclides in target cells. This dual property has applications in cancer treatment and could also be used to eradicate cells with therapeutic potential in the case of adverse events. Through experience acquired in preclinical studies, we can expect that non-invasive molecular imaging using NIS as a transgene will be pivotal for monitoring in vivo the exact distribution and pharmacodynamics of gene expression in a precise and quantitative way. This review highlights the applications of NIS in biotherapy, with a particular emphasis on image-guided radiotherapy, monitoring of gene and vector biodistribution and trafficking of stem cells.

Targeted radiotherapy for prostate cancer with an oncolytic adenovirus coding for human sodium iodide symporter

PURPOSE

Oncolytic adenoviruses are promising tools for cancer therapy. Although several clinical reports have indicated both safety and promising antitumor capabilities for these viruses, there are only a few examples of complete tumor eradication. Thus, the antitumor efficacy of oncolytic adenoviruses needs to be improved. One potentially useful approach is combination with radiotherapy.

EXPERIMENTAL DESIGN

To target systemically administered radioiodide to tumors, we created Ad5/3-Delta24-human sodium iodide symporter (hNIS), a Rb-p16 pathway selective infectivity enhanced oncolytic adenovirus encoding hNIS.

RESULTS

Ad5/3-Delta24-hNIS replication effectively killed prostate cancer cells in vitro and in vivo. Also, the virus-mediated radioiodide uptake into prostate cancer cells in vitro and into tumors in vivo. Furthermore, Ad5/3-Delta24-hNIS with radioiodide was significantly more effective than virus alone in mice with prostate cancer xenografts.

CONCLUSIONS

These results suggest that oncolytic adenovirus-mediated targeted radiotherapy might be a potentially useful option for enhancing the efficacy or adenoviral virotherapy.

In vivo functional and anatomic imaging for assessment of in vivo gene transfer

PURPOSE

To assess whether a combination of in vivo anatomic and functional imaging can help quantify expression of somatostatin receptor type 2 (SSTR2)-based reporters after in vivo gene transfer.

MATERIALS AND METHODS

All animal experiments were approved by an institutional animal care and use committee. Six nude mice bearing two subcutaneous L3.6pl (human pancreatic cancer) tumors were injected intratumorally with an adenovirus containing a human somatostatin receptor type 2 gene chimera (Ad-HA-SSTR2) or a control adenovirus containing green fluorescent protein (Ad-GFP). Two days later, magnetic resonance (MR) imaging was performed to derive tumor weight and analyze morphology. Intravenous injection of Food and Drug Administration-approved indium 111 octreotide was followed by gamma camera imaging (planar imaging and single photon emission computed tomography [SPECT]) the next day. Region-of-interest analysis followed. The procedure was also performed in six nude mice with slow-growing MDA-MB-435 (human breast carcinoma) tumors, which allowed serial imaging 3 days and 2 weeks after adenovirus injection. After imaging, excised tumor weight and biodistribution were assessed. Statistical analyses included a Student t test and linear regression.

RESULTS

With both tumor types, ex vivo and image-based in vivo biodistribution demonstrated greater uptake (percentage of injected dose per gram) in tumors infected with Ad-HA-SSTR2 than in those infected with Ad-GFP (P < .05). Furthermore, in vivo and ex vivo biodistribution analysis correlated (ex vivo vs planar and MR imaging: r = 0.87, P < .05, n = 24; ex vivo vs SPECT and MR imaging: r = 0.84, P < .05, n = 24). Moreover, in vivo biodistribution distinguished greater expression at the earlier time point in MDA-MB-435 tumors infected with Ad-HA-SSTR2 from waning expression at the later time point (P < .05).

CONCLUSION

A combination of in vivo functional and anatomic imaging methods can help quantify gene expression after in vivo gene transfer.

Molecular imaging with bioconjugates in mouse models of cancer

The definition of molecular imaging provided by the Society of Nuclear Medicine is "the visualization, characterization and measurement of biological processes at the molecular and cellular levels in humans and other living systems". This review gives an overview of the technologies available for and the potential benefits from molecular imaging at the preclinical stage. It focuses on the use of imaging probes based on bioconjugates and for reasons of brevity confines itself to discussion of applications in the field of oncology, although molecular imaging can be equally useful in many fields including cardiovascular medicine, neurosciences, infection, and others.

In vivo retargeting of adenovirus type 5 to alphavbeta6 integrin results in reduced hepatotoxicity and improved tumor uptake following systemic delivery

A key impediment to successful cancer therapy with adenoviral vectors is the inefficient transduction of malignant tissue in vivo. Compounding this problem is the lack of cancer-specific targets, coupled with a shortage of corresponding high-efficiency ligands, permitting selective retargeting. The epithelial cell-specific integrin alphavbeta6 represents an attractive target for directed therapy since it is generally not expressed on normal epithelium but is upregulated in numerous carcinomas, where it plays a role in tumor progression. We previously have characterized a high-affinity, alphavbeta6-selective peptide (A20FMDV2) derived from VP1 of foot-and-mouth disease virus. We generated recombinant adenovirus type 5 (Ad5) fiber knob, incorporating A20FMDV2 in the HI loop, for which we validated the selectivity of binding and functional inhibition of alphavbeta6. The corresponding alphavbeta6-retargeted virus Ad5-EGFP(A20) exhibited up to 50-fold increases in coxsackievirus- and-adenovirus-receptor-independent transduction and up to 480-fold-increased cytotoxicity on a panel of alphavbeta6-positive human carcinoma lines compared with Ad5-EGFP(WT). Using an alphavbeta6-positive (DX3-beta6) xenograft model, we observed a approximately 2-fold enhancement in tumor uptake over Ad5-EGFP(WT) following systemic delivery. Furthermore, approximately 5-fold-fewer Ad5-EGFP(A20) genomes were detected in the liver (P = 0.0002), correlating with reduced serum transaminase levels and E1A expression. Warfarin pretreatment, to deplete coagulation factors, did not improve tumor uptake significantly with either virus but did significantly reduce liver sequestration and hepatic toxicity. The ability of Ad5-EGFP(A20) to improve delivery to alphavbeta6, combined with its reduced hepatic tropism and toxicity, highlights its potential as a prototype virus for future clinical investigation.