Molecular pathology of malignant gliomas

Red-Shifted Coumarin Luciferins for Improved Bioluminescence Imaging

Multicomponent bioluminescence imaging in vivo requires an expanded collection of tissue-penetrant probes. Toward this end, we generated a new class of near-infrared (NIR) emitting coumarin luciferin analogues (CouLuc-3s). The scaffolds were easily accessed from commercially available dyes. Complementary mutant luciferases for the CouLuc-3 analogues were also identified. The brightest probes enabled sensitive imaging in vivo. The CouLuc-3 scaffolds are also orthogonal to popular bioluminescent reporters and can be used for multicomponent imaging applications. Collectively, this work showcases a new set of bioluminescent tools that can be readily implemented for multiplexed imaging in a variety of biological settings.

Near-Infrared Fluorescent Probe Activated by Nitroreductase for In Vitro and In Vivo Hypoxic Tumor Detection

Tumor hypoxia is correlated with increased resistance to chemotherapy and poor overall prognoses across a number of cancer types. We present here a cancer cell-selective and hypoxia-responsive probe (fol-BODIPY) designed on the basis of density functional theory (DFT)-optimized quantum chemical calculations. The fol-BODIPY probe was found to provide a rapid fluorescence "off-on" response to hypoxia relative to controls, which lack the folate or nitro-benzyl moieties. In vitro confocal microscopy and flow cytometry analyses, as well as in vivo near-infrared optical imaging of CT26 solid tumor-bearing mice, provided support for the contention that fol-BODIPY is more readily accepted by folate receptor-positive CT26 cancer cells and provides a superior fluorescence "off-on" signal under hypoxic conditions than the controls. Based on the findings of this study, we propose that fol-BODIPY may serve as a tumor-targeting, hypoxia-activatable probe that allows for direct cancer monitoring both in vitro and in vivo.

Noninvasive in vivo cell tracking using molecular imaging: A useful tool for developing mesenchymal stem cell-based cancer treatment

Mounting evidence has emphasized the potential of cell therapies in treating various diseases by restoring damaged tissues or replacing defective cells in the body. Cell therapies have become a strong therapeutic modality by applying noninvasive in vivo molecular imaging for examining complex cellular processes, understanding pathophysiological mechanisms of diseases, and evaluating the kinetics/dynamics of cell therapies. In particular, mesenchymal stem cells (MSCs) have shown promise in recent years as drug carriers for cancer treatment. They can also be labeled with different probes and tracked in vivo to assess the in vivo effect of administered cells, and to optimize therapy. The exact role of MSCs in oncologic diseases is not clear as MSCs have been shown to be involved in tumor progression and inhibition, and the exact interactions between MSCs and specific cancer microenvironments are not clear. In this review, a multitude of labeling approaches, imaging modalities, and the merits/demerits of each strategy are outlined. In addition, specific examples of the use of MSCs and in vivo imaging in cancer therapy are provided. Finally, present limitations and future outlooks in terms of the translation of different imaging approaches in clinics are discussed.

Cellular and molecular imaging for stem cell tracking in neurological diseases

Stem cells (SCs) are cells with strong proliferation ability, multilineage differentiation potential and self-renewal capacity. SC transplantation represents an important therapeutic advancement for the treatment strategy of neurological diseases, both in the preclinical experimental and clinical settings. Innovative and breakthrough SC labelling and tracking technologies are widely used to monitor the distribution and viability of transplanted cells non-invasively and longitudinally. Here we summarised the research progress of the main tracers, labelling methods and imaging technologies involved in current SC tracking technologies for various neurological diseases. Finally, the applications, challenges and unresolved problems of current SC tracing technologies were discussed.

Seeing (and Using) the Light: Recent Developments in Bioluminescence Technology

Bioluminescence has long been used to image biological processes in vivo. This technology features luciferase enzymes and luciferin small molecules that produce visible light. Bioluminescent photons can be detected in tissues and live organisms, enabling sensitive and noninvasive readouts on physiological function. Traditional applications have focused on tracking cells and gene expression patterns, but new probes are pushing the frontiers of what can be visualized. The past few years have also seen the merger of bioluminescence with optogenetic platforms. Luciferase-luciferin reactions can drive light-activatable proteins, ultimately triggering signal transduction and other downstream events. This review highlights these and other recent advances in bioluminescence technology, with an emphasis on tool development. We showcase how new luciferins and engineered luciferases are expanding the scope of optical imaging. We also highlight how bioluminescent systems are being leveraged not just for sensing-but also controlling-biological processes.

A novel luminescent Ir(iii) complex for dual mode imaging: synergistic response to hypoxia and acidity of the tumor microenvironment

The early detection of cancer shows great promise for the control and prevention of cancer. For early detection, one of the challenges that still exists is searching for methods that can illuminate tumors with high sensitivity. Here, acidity and hypoxia, two typical features that exist universally in a solid tumor microenvironment, were focused on to attain synergistic imaging with an enhanced signal-to-noise ratio. This was realized using an iridium(iii) based optical probe (Ir-1) that could sense acidity and hypoxia simultaneously and synergistically. Through the synergistic sensing of acidic pH and hypoxia, stronger emission signals or larger lifetime changes can be obtained than if a single factor (acidity or hypoxia) is used to induce variations. Furthermore, its potential for biological applications was confirmed by employing Ir-1 for phosphorescence synergistic intensity and lifetime imaging of acidity and hypoxia in live monolayer cells and 3D multicellular spheroids.

Molecular Imaging of Stem Cells

Regenerative medicine with the use of stem cells has appeared as a potential therapeutic alternative for many disease states. Despite initial enthusiasm, there has been relatively slow transition to clinical trials. In large part, numerous questions remain regarding the viability, biology and efficacy of transplanted stem cells in the living subject. The critical issues highlighted the importance of developing tools to assess these questions. Advances in molecular biology and imaging have allowed the successful non-invasive monitoring of transplanted stem cells in the living subject. Over the years these methodologies have been updated to assess not only the viability but also the biology of transplanted stem cells. In this review, different imaging strategies to study the viability and biology of transplanted stem cells are presented. Use of these strategies will be critical as the different regenerative therapies are being tested for clinical use.

Mycobacterium tuberculosis Reporter Strains as Tools for Drug Discovery and Development

Reporter strains have proven to be powerful tools to study Mycobacterium tuberculosis (Mtb) physiology. Transcriptional and translational reporter strains are engineered by fusing a readout gene, encoding a fluorescent, luminescent or enzymatic protein, downstream of a promoter or in-frame with a gene of interest. When the reporter is expressed, it generates a signal that acts as a synthetic phenotype, enabling the study of physiologies that might have otherwise been hidden. This review will discuss approaches for generating reporter strains in Mtb and how they can be used as tools for high-throughput genetic and small molecule screening and as biomarkers for examining Mtb responses to drug or immune stresses during animal infections. Fluorescent reporter strains have an added benefit in that they can be used for single-cell studies both in vitro and in vivo, thus enabling the study of mechanisms underlying phenotypic heterogeneity. Recent examples of the use of Mtb reporter strains will be presented with a focus on how they can be used as tools for drug discovery and development. © 2018 IUBMB Life, 70(9):818-825, 2018.

Non-invasive imaging of engineered human tumors in the living chicken embryo

The growing interest in engineered tumor models prompted us to devise a method for the non-invasive assessment of such models. Here, we report on bioluminescence imaging (BLI) for the assessment of engineered tumor models in the fertilized chicken egg, i.e, chick chorioallantoic membrane (CAM) assay. One prostate cancer (PC-3) and two osteosarcoma (MG63 and HOS) cell lines were modified with luciferase reporter genes. To create engineered tumors, these cell lines were seeded either onto basement membrane extract (BME) or gelfoam scaffolds, and subsequently grafted in vivo onto the CAM. BLI enabled non-invasive, specific detection of the engineered tumors on the CAM in the living chicken embryo. Further, BLI permitted daily, quantitative monitoring of the engineered tumors over the course of up to 7 days. Data showed that an extracellular matrix (ECM) composed of BME supported growth of reporter gene marked PC-3 tumors but did not support MG63 or HOS tumor growth. However, MG63 tumors engineered on the collagen-based gelfoam ECM showed a temporal proliferation burst in MG63 tumors. Together, the data demonstrated imaging of engineered human cancer models in living chicken embryos. The combination of CAM assay and BLI holds significant potential for the examination of a broad range of engineered tumor models.

Fluorescent probes and materials for detecting formaldehyde: from laboratory to indoor for environmental and health monitoring

Formaldehyde (FA), as a vital industrial chemical, is widely used in building materials and numerous living products.

Monitoring the Growth of an Orthotopic Tumour Xenograft Model: Multi-Modal Imaging Assessment with Benchtop MRI (1T), High-Field MRI (9.4T), Ultrasound and Bioluminescence

BACKGROUND

Research using orthotopic and transgenic models of cancer requires imaging methods to non-invasively quantify tumour burden. As the choice of appropriate imaging modality is wide-ranging, this study aimed to compare low-field (1T) magnetic resonance imaging (MRI), a novel and relatively low-cost system, against established preclinical techniques: bioluminescence imaging (BLI), ultrasound imaging (US), and high-field (9.4T) MRI.

METHODS

A model of colorectal metastasis to the liver was established in eight mice, which were imaged with each modality over four weeks post-implantation. Tumour burden was assessed from manually segmented regions.

RESULTS

All four imaging systems provided sufficient contrast to detect tumours in all of the mice after two weeks. No significant difference was detected between tumour doubling times estimated by low-field MRI, ultrasound imaging or high-field MRI. A strong correlation was measured between high-field MRI estimates of tumour burden and all the other modalities (p < 0.001, Pearson).

CONCLUSION

These results suggest that both low-field MRI and ultrasound imaging are accurate modalities for characterising the growth of preclinical tumour models.

Synthesis of Firefly Luciferin Analogues and Evaluation of the Luminescent Properties

Five new firefly luciferin (1) analogues were synthesized and their light emission properties were examined. Modifications of the thiazoline moiety in 1 were employed to produce analogues containing acyclic amino acid side chains (2-4) and heterocyclic rings derived from amino acids (5 and 6) linked to the benzothiazole moiety. Although methyl esters of all of the synthetic derivatives exhibited chemiluminescence activity, only carboluciferin (6), possessing a pyrroline-substituted benzothiazole structure, had bioluminescence (BL) activity (λmax =547 nm). Results of bioluminescence studies with AMP-carboluciferin (AMP=adenosine monophosphate) and AMP-firefly luciferin showed that the nature of the thiazoline mimicking moiety affected the adenylation step of the luciferin-luciferase reaction required for production of potent BL. In addition, BL of 6 in living mice differed from that of 1 in that its luminescence decay rate was slower.

Novel Bioluminescent Activatable Reporter for Src Tyrosine Kinase Activity in Living Mice

Aberrant activation of the Src kinase is implicated in the development of a variety of human malignancies. However, it is almost impossible to monitor Src activity in an in vivo setting with current biochemical techniques. To facilitate the noninvasive investigation of the activity of Src kinase both in vitro and in vivo, we developed a genetically engineered, activatable bioluminescent reporter using split-luciferase complementation. The bioluminescence of this reporter can be used as a surrogate for Src activity in real time. This hybrid luciferase reporter was constructed by sandwiching a Src-dependent conformationally responsive unit (SH2 domain-Srcpep) between the split luciferase fragments. The complementation bioluminescence of this reporter was dependent on the Src activity status. In our study, Src kinase activity in cultured cells and tumor xenografts was monitored quantitatively and dynamically in response to clinical small-molecular kinase inhibitors, dasatinib and saracatinib. This system was also applied for high-throughput screening of Src inhibitors against a kinase inhibitor library in living cells. These results provide unique insights into drug development and pharmacokinetics/phoarmocodynamics of therapeutic drugs targeting Src signaling pathway enabling the optimization of drug administration schedules for maximum benefit. Using both Firefly and Renilla luciferase imaging, we have successfully monitored Src tyrosine kinase activity and Akt serine/threonine kinase activity concurrently in one tumor xenograft. This dual luciferase reporter imaging system will be helpful in exploring the complex signaling networks in vivo. The strategies reported here can also be extended to study and image other important kinases and the cross-talks among them.

Visualizing cell proximity with genetically encoded bioluminescent reporters

Cell-cell interactions underlie diverse physiological processes ranging from immune function to cell migration. Dysregulated cellular crosstalk also potentiates numerous pathologies, including infections and metastases. Despite their ubiquity in organismal biology, cell-cell interactions are difficult to examine in tissues and whole animals without invasive procedures. Here, we report a strategy to noninvasively image cell proximity using engineered bioluminescent probes. These tools comprise "split" fragments of Gaussia luciferase (Gluc) fused to the leucine zipper domains of Fos and Jun. When cells secreting the fragments draw near one another, Fos and Jun drive the assembly of functional, light-emitting Gluc. Photon production thus provides a readout on the distance between two cell types. We used the split fragments to visualize cell-cell interactions over time in vitro and in macroscopic models of cell migration. Further application of these tools in live organisms will refine our understanding of cell contacts relevant to basic biology and disease.

Bioresponsive probes for molecular imaging: concepts and in vivo applications

Molecular imaging is a powerful tool to visualize and characterize biological processes at the cellular and molecular level in vivo. In most molecular imaging approaches, probes are used to bind to disease-specific biomarkers highlighting disease target sites. In recent years, a new subset of molecular imaging probes, known as bioresponsive molecular probes, has been developed. These probes generally benefit from signal enhancement at the site of interaction with its target. There are mainly two classes of bioresponsive imaging probes. The first class consists of probes that show direct activation of the imaging label (from "off" to "on" state) and have been applied in optical imaging and magnetic resonance imaging (MRI). The other class consists of probes that show specific retention of the imaging label at the site of target interaction and these probes have found application in all different imaging modalities, including photoacoustic imaging and nuclear imaging. In this review, we present a comprehensive overview of bioresponsive imaging probes in order to discuss the various molecular imaging strategies. The focus of the present article is the rationale behind the design of bioresponsive molecular imaging probes and their potential in vivo application for the detection of endogenous molecular targets in pathologies such as cancer and cardiovascular disease.

Optogenetic inhibition of neurons by internal light production

Optogenetics is an extremely powerful tool for selective neuronal activation/inhibition and dissection of neural circuits. However, a limitation of in vivo optogenetics is that an animal must be tethered to an optical fiber for delivery of light. Here, we describe a new method for in vivo, optogenetic inhibition of neural activity using an internal, animal-generated light source based on firefly luciferase. Two adeno-associated viruses encoding luciferase were tested and both produced concentration-dependent light after administration of the substrate, luciferin. Mice were co-infected with halorhodopsin- and luciferase-expressing viruses in the striatum, and luciferin administration significantly reduced Fos activity compared to control animals infected with halorhodopsin only. Recordings of neuronal activity in behaving animals confirmed that firing was greatly reduced after luciferin administration. Finally, amphetamine-induced locomotor activity was reduced in halorhodopsin/luciferase mice pre-injected with luciferin compared to controls. This demonstrates that virally encoded luciferase is able to generate sufficient light to activate halorhodopsin and suppress neural activity and change behavior. This approach could be used to generate inhibition in response to activation of specific molecular pathways.

Multimodality molecular imaging to monitor transplanted stem cells for the treatment of ischemic heart disease

PURPOSE

Non-invasive techniques to monitor the survival and migration of transplanted stem cells in real-time is crucial for the success of stem cell therapy. The aim of this study was to explore multimodality molecular imaging to monitor transplanted stem cells with a triple-fused reporter gene [TGF; herpes simplex virus type 1 thymidine kinase (HSV1-tk), enhanced green fluorescence protein (eGFP), and firefly luciferase (FLuc)] in acute myocardial infarction rat models.

METHODS

Rat myocardial infarction was established by ligating the left anterior descending coronary artery. A recombinant adenovirus carrying TGF (Ad5-TGF) was constructed. After transfection with Ad5-TGF, 5 × 10(6) bone marrow mesenchymal stem cells (BMSCs) were transplanted into the anterior wall of the left ventricle (n = 14). Untransfected BMSCs were as controls (n = 8). MicroPET/CT, fluorescence and bioluminescence imaging were performed. Continuous images were obtained at day 2, 3 and 7 after transplantation with all three imaging modalities and additional images were performed with bioluminescence imaging until day 15 after transplantation.

RESULTS

High signals in the heart area were observed using microPET/CT, fluorescence and bioluminescence imaging of infarcted rats injected with Ad5-TGF-transfected BMSCs, whereas no signals were observed in controls. Semi-quantitative analysis showed the gradual decrease of signals in all three imaging modalities with time. Immunohistochemistry assays confirmed the location of the TGF protein expression was the same as the site of stem cell-specific marker expression, suggesting that TGF tracked the stem cells in situ.

CONCLUSIONS

We demonstrated that TGF could be used as a reporter gene to monitor stem cells in a myocardial infarction model by multimodality molecular imaging.

Secreted Gaussia princeps luciferase as a reporter of Escherichia coli replication in a mouse tissue cage model of infection

Measurement of bacterial burden in animal infection models is a key component for both bacterial pathogenesis studies and therapeutic agent research. The traditional quantification means for in vivo bacterial burden requires frequent animal sacrifice and enumerating colony forming units (CFU) recovered from infection loci. To address these issues, researchers have developed a variety of luciferase-expressing bacterial reporter strains to enable bacterial detection in living animals. To date, all such luciferase-based bacterial reporters are in cell-associated form. Production of luciferase-secreting recombinant bacteria could provide the advantage of reporting CFU from both infection loci themselves and remote sampling (eg. body fluid and plasma). Toward this end, we have genetically manipulated a pathogenic Escherichia coli (E. coli) strain, ATCC25922, to secrete the marine copepod Gaussia princeps luciferase (Gluc), and assessed the use of Gluc as both an in situ and ex situ reporter for bacterial burden in mouse tissue cage infections. The E. coli expressing Gluc demonstrates in vivo imaging of bacteria in a tissue cage model of infection. Furthermore, secreted Gluc activity and bacterial CFUs recovered from tissue cage fluid (TCF) are correlated along 18 days of infection. Importantly, secreted Gluc can also be detected in plasma samples and serve as an ex situ indicator for the established tissue cage infection, once high bacterial burdens are achieved. We have demonstrated that Gluc from marine eukaryotes can be stably expressed and secreted by pathogenic E. coli in vivo to enable a facile tool for longitudinal evaluation of persistent bacterial infection.

Blood-based assay with secreted Gaussia luciferase to monitor tumor metastasis

Only a few techniques are currently available for quantifying systemic metastases in preclinical models. Cancer cell expression of naturally secreted Gaussia luciferase (Gluc) provides a useful circulating biomarker that enables the monitoring of metastatic tumor burden and of treatment response from minimal drops of blood. This blood-based Gluc assay exhibits several distinct advantages: (1) It is highly sensitive in quantifying metastatic tumor growth, particularly when compared to whole-body bioluminescence imaging (BLI) alone; (2) It is quantitative by nature and reflects viable tumor burden in a minimally invasive manner; (3) Through longitudinal collection of blood samples, treatment response can be monitored in real-time; and (4) Gluc bioluminescence provides a means to localize and assess metastatic colonization using BLI. By elucidating the progression of systemic metastases and therapeutic response in animal models, the blood-based Gluc assay is emerging as a valuable quantitative tool for novel drug development.

Reporter gene technologies for imaging cell fates in hematopoiesis

Advances in noninvasive imaging technologies that allow for in vivo dynamic monitoring of cells and cellular function in living research subjects have revealed new insights into cell biology in the context of intact organs and their native environment. In the field of hematopoiesis and stem cell research, studies of cell trafficking involved in injury repair and hematopoietic engraftment have made great progress using these new tools. Stem cells present unique challenges for imaging since after transplantation, they proliferate dramatically and differentiate. Therefore, the imaging modality used needs to have a large dynamic range, and the genetic regulatory elements used need to be stably expressed during differentiation. Multiple imaging technologies using different modalities are available, and each varies in sensitivity, ease of data acquisition, signal to noise ratios (SNR), substrate availability, and other parameters that affect utility for monitoring cell fates and function. For a given application, there may be several different approaches that can be used. For mouse models, clinically validated technologies such as magnetic resonance imaging (MRI) and positron emission tomography (PET) have been joined by optical imaging techniques such as in vivo bioluminescence imaging (BLI) and fluorescence imaging (FLI), and all have been used to monitor bone marrow and stem cells after transplantation into mice. Photoacoustic imaging that utilizes the sound created by the thermal expansion of absorbed light to generate an image best represents hybrid technologies. Each modality requires that the cells of interest be marked with a genetic reporter that acts as a label making them uniquely visible using that technology. For each modality, there are several labels to choose from. Multiple methods for applying these different labels are available. This chapter provides an overview of the imaging technologies and commonly used labels for each, as well as detailed protocols for gene delivery into hematopoietic cells for the purposes of applying these specific labels to cell trafficking. The goal of this chapter is to provide adequate background information to allow the design and implementation of an experimental system for in vivo imaging in mice.

Academic radiology in the new health care delivery environment

RATIONALE AND OBJECTIVES

Ongoing concerns over the rising cost of health care are driving large-scale changes in the way that health care is practiced and reimbursed in the United States.

MATERIALS AND METHODS

To effectively implement and thrive within this new health care delivery environment, academic medical institutions will need to modify financial and business models and adapt institutional cultures. In this article, we review the expected features of the new health care environment from the perspective of academic radiology departments.

CONCLUSIONS

Our review will include background on accountable care organizations, identify challenges associated with the new managed care model, and outline key strategies-including expanding the use of existing information technology infrastructure, promoting continued medical innovation, balancing academic research with clinical care, and exploring new roles for radiologists in efficient patient management-that will ensure continued success for academic radiology.

Gene transfer in the liver using recombinant adeno-associated virus

Liver-directed gene transfer and gene therapy are rapidly gaining attention primarily because the liver is centrally involved in a variety of metabolic functions that are affected in various inherited disorders. Recombinant adeno-associated virus (rAAV) is a popular gene delivery vehicle for gene therapy, and intravenous delivery of some rAAV serotypes results in very efficient transduction in the liver. rAAV-mediated gene transfer to the liver can be used to create somatic transgenic animals or disease models for studying the function of various genes and miRNAs. The liver is the target tissue for gene therapy of many inborn metabolic diseases and may also be exploited as a "biofactory" for production of coagulation factors, insulin, growth hormones, and other non-hepatic proteins. Hence, efficient delivery of transgenes and small RNAs to the liver by rAAV vectors has been of long-standing interest to research scientists and clinicians alike. This unit describes methods for delivery of rAAV vectors by several injection routes, followed by a range of analytical methods for assessing the expression, activity, and effects of the transgene and its product.

Visualizing cellular interactions with a generalized proximity reporter

Interactions among neighboring cells underpin many physiological processes ranging from early development to immune responses. When these interactions do not function properly, numerous pathologies, including infection and cancer, can result. Molecular imaging technologies, especially optical imaging, are uniquely suited to illuminate complex cellular interactions within the context of living tissues in the body. However, no tools yet exist that allow the detection of microscopic events, such as two cells coming into close proximity, on a global, whole-animal scale. We report here a broadly applicable, longitudinal strategy for probing interactions among cells in living subjects. This approach relies on the generation of bioluminescent light when two distinct cell populations come into close proximity, with the intensity of the optical signal correlating with relative cellular location. We demonstrate the ability of this reporter strategy to gauge cell-cell proximity in culture models in vitro and then evaluate this approach for imaging tumor-immune cell interactions using a murine breast cancer model. In these studies, our imaging strategy enabled the facile visualization of features that are otherwise difficult to observe with conventional imaging techniques, including detection of micrometastatic lesions and potential sites of tumor immunosurveillance. This proximity reporter will facilitate probing of numerous types of cell-cell interactions and will stimulate the development of similar techniques to detect rare events and pathological processes in live animals.

A concise review of magnetic resonance molecular imaging of tumor angiogenesis by targeting integrin αvβ3 with magnetic probes

Angiogenesis is an essential step for the growth and spread of malignant tumors. Accurate detection and quantification of tumor angiogenesis is important for early diagnosis of cancers as well as post therapy assessment of antiangiogenic drugs. The cell adhesion molecule integrin αvβ3 is a specific marker of angiogenesis, which is highly expressed on activated and proliferating endothelial cells, but generally not on quiescent endothelial cells. Therefore, in recent years, many different approaches have been developed for imaging αvβ3 expression, for the detection and characterization of tumor angiogenesis. The present review provides an overview of the current status of magnetic resonance molecular imaging of integrin αvβ3, including the new development of high sensitive contrast agents and strategies for improving the specificity of targeting probes and the biological effects of imaging probes on αvβ3 positive cells.

Imaging blood-brain barrier dysfunction in animal disease models

The blood-brain barrier (BBB) is a highly complex structure, which separates the extracellular fluid of the central nervous system (CNS) from the blood of CNS vessels. A wide range of neurologic conditions, including stroke, epilepsy, Alzheimer's disease, and brain tumors, are associated with perturbations of the BBB that contribute to their pathology. The common consequence of a BBB dysfunction is increased permeability, leading to extravasation of plasma constituents and vasogenic brain edema. The BBB impairment can persist for long periods, being involved in secondary inflammation and neuronal dysfunction, thus contributing to disease pathogenesis. Therefore, reliable imaging of the BBB impairment is of major importance in both clinical management of brain diseases and in experimental research. From landmark studies by Ehrlich and Goldman, the use of dyes (probes) has played a critical role in understanding BBB functions. In recent years methodologic advances in morphologic and functional brain imaging have provided insight into cellular and molecular interactions underlying BBB dysfunction in animal disease models. These imaging techniques, which range from in situ staining to noninvasive in vivo imaging, have different spatial resolution, sensitivity, and capacity for quantitative and kinetic measures of the BBB impairment. Despite significant advances, the translation of these techniques into clinical applications remains slow. This review outlines key recent advances in imaging techniques that have contributed to the understanding of BBB dysfunction in disease and discusses major obstacles and opportunities to advance these techniques into the clinical realm.

Rapid clinical bacteriology and its future impact

Clinical microbiology has always been a slowly evolving and conservative science. The sub-field of bacteriology has been and still is dominated for over a century by culture-based technologies. The integration of serological and molecular methodologies during the seventies and eighties of the previous century took place relatively slowly and in a cumbersome fashion. When nucleic acid amplification technologies became available in the early nineties, the predicted "revolution" was again slow but in the end a real paradigm shift did take place. Several of the culture-based technologies were successfully replaced by tests aimed at nucleic acid detection. More recently a second revolution occurred. Mass spectrometry was introduced and broadly accepted as a new diagnostic gold standard for microbial species identification. Apparently, the diagnostic landscape is changing, albeit slowly, and the combination of newly identified infectious etiologies and the availability of innovative technologies has now opened new avenues for modernizing clinical microbiology. However, the improvement of microbial antibiotic susceptibility testing is still lagging behind. In this review we aim to sketch the most recent developments in laboratory-based clinical bacteriology and to provide an overview of emerging novel diagnostic approaches.

Making the brain glow: in vivo bioluminescence imaging to study neurodegeneration

Bioluminescence imaging (BLI) takes advantage of the light-emitting properties of luciferase enzymes, which produce light upon oxidizing a substrate (i.e., D-luciferin) in the presence of molecular oxygen and energy. Photons emitted from living tissues can be detected and quantified by a highly sensitive charge-coupled device camera, enabling the investigator to noninvasively analyze the dynamics of biomolecular reactions in a variety of living model organisms such as transgenic mice. BLI has been used extensively in cancer research, cell transplantation, and for monitoring of infectious diseases, but only recently experimental models have been designed to study processes and pathways in neurological disorders such as Alzheimer disease, Parkinson disease, or amyotrophic lateral sclerosis. In this review, we highlight recent applications of BLI in neuroscience, including transgene expression in the brain, longitudinal studies of neuroinflammatory responses to neurodegeneration and injury, and in vivo imaging studies of neurogenesis and mitochondrial toxicity. Finally, we highlight some new developments of BLI compounds and luciferase substrates with promising potential for in vivo studies of neurological dysfunctions.

A multimode optical imaging system for preclinical applications in vivo: technology development, multiscale imaging, and chemotherapy assessment

PURPOSE

Several established optical imaging approaches have been applied, usually in isolation, to preclinical studies; however, truly useful in vivo imaging may require a simultaneous combination of imaging modalities to examine dynamic characteristics of cells and tissues. We developed a new multimode optical imaging system designed to be application-versatile, yielding high sensitivity, and specificity molecular imaging.

PROCEDURES

We integrated several optical imaging technologies, including fluorescence intensity, spectral, lifetime, intravital confocal, two-photon excitation, and bioluminescence, into a single system that enables functional multiscale imaging in animal models.

RESULTS

The approach offers a comprehensive imaging platform for kinetic, quantitative, and environmental analysis of highly relevant information, with micro-to-macroscopic resolution. Applied to small animals in vivo, this provides superior monitoring of processes of interest, represented here by chemo-/nanoconstruct therapy assessment.

CONCLUSIONS

This new system is versatile and can be optimized for various applications, of which cancer detection and targeted treatment are emphasized here.

Cascade of tau toxicity in inducible hippocampal brain slices and prevention by aggregation inhibitors

Mislocalization and aggregation of the axonal protein tau are hallmarks of Alzheimer's disease and other tauopathies. Here, we studied the relationship between tau aggregation, loss of spines and neurons, and reversibility by aggregation inhibitors. To this end we established an in vitro model of tauopathy based on regulatable transgenic hippocampal organotypic slice cultures prepared from mice expressing proaggregant Tau repeat domain with mutation ΔK280 (Tau(RD)ΔK). Transgene expression was monitored by a bioluminescence reporter assay. We observed abnormal tau phosphorylation and mislocalization of exogenous and endogenous tau into the somatodendritic compartment. This was paralleled by a reduction of dendritic spines, altered dendritic spine morphology, dysregulation of Ca(++) dynamics and elevated activation of microglia. Neurotoxicity was mediated by Caspase-3 activation and correlated with the expression level of proaggregant Tau(RD)ΔK. Finally, tau aggregates appeared in areas CA1 and CA3 after three weeks in vitro. Neurodegeneration was relieved by aggregation inhibitors or by switching off transgene expression. Thus the slice culture model is suitable for monitoring the development of tauopathy and the therapeutic benefit of antiaggregation drugs.

Cognitive defects are reversible in inducible mice expressing pro-aggregant full-length human Tau

Neurofibrillary lesions of abnormal Tau are hallmarks of Alzheimer disease and frontotemporal dementias. Our regulatable (Tet-OFF) mouse models of tauopathy express variants of human full-length Tau in the forebrain (CaMKIIα promoter) either with mutation ΔK280 (pro-aggregant) or ΔK280/I277P/I308P (anti-aggregant). Co-expression of luciferase enables in vivo quantification of gene expression by bioluminescence imaging. Pro-aggregant mice develop synapse loss and Tau-pathology including missorting, phosphorylation and early pretangle formation, whereas anti-aggregant mice do not. We correlated hippocampal Tau pathology with learning/memory performance and synaptic plasticity. Pro-aggregant mice at 16 months of gene expression exhibited severe cognitive deficits in Morris water maze and in passive-avoidance paradigms, whereas anti-aggregant mice were comparable to controls. Cognitive impairment of pro-aggregant mice was accompanied by loss of hippocampal LTP in CA1 and CA3 areas and by a reduction of synaptic proteins and dendritic spines, although no neuronal loss was observed. Remarkably, memory and LTP recovered when pro-aggregant Tau was switched-OFF for ~4 months, Tau phosphorylation and missorting were reversed, and synapses recovered. Moreover, soluble and insoluble pro-aggregant hTau40 disappeared, while insoluble mouse Tau was still present. This study links early Tau pathology without neurofibrillary tangles and neuronal death to cognitive decline and synaptic dysfunction. It demonstrates that Tau-induced impairments are reversible after switching-OFF pro-aggregant Tau. Therefore, our mouse model may mimic an early phase of AD when the hippocampus does not yet suffer from irreversible cell death but cognitive deficits are already striking. It offers potential to evaluate drugs with regard to learning and memory performance.

Expedient synthesis of electronically modified luciferins for bioluminescence imaging

Bioluminescence imaging with luciferase enzymes requires access to light-emitting, small-molecule luciferins. Here, we describe a rapid method to synthesize d-luciferin, the substrate for firefly luciferase (Fluc), along with a novel set of electronically modified analogues. Our procedure utilizes a relatively rare, but synthetically useful dithiazolium reagent to generate heteroaromatic scaffolds in a divergent fashion. Two of the luciferin analogues produced with this approach emit light with Fluc in vitro and in live cells. Collectively, our work increases the number of substrates that can be used for bioluminescence imaging and provides a general strategy for synthesizing new collections of luciferins.

A multimodality reporter gene for monitoring transplanted stem cells

INTRODUCTION

The aim of this study is to explore the feasibility of a triple-fused reporter gene, termed TGF [herpes simplex virus type 1 thymidine kinase (HSV1-tk), enhanced green fluorescent protein (eGFP) and firefly luciferase (Fluc)], to monitor stem cells using multimodality molecular imaging.

METHODS

A recombinant adenovirus vector carrying the triple-fused reporter gene (Ad5-TGF) was constructed. Bone marrow mesenchymal stem cells (BMSCs) were transfected with different virus titers of Ad5-TGF [multiplicities of infection (MOIs) were 0, 50, 100, 150, 200 and 250]. The mRNA and protein expressions of HSV1-tk, eGFP and Fluc in the transfected BMSCs were evaluated using polymerase chain reaction and Western blot. After the transfection of the BMSCs with different virus titers of Ad5-TGF (MOIs were 25, 50, 75, 100 and 125), their uptake rates of (131)I-FIAU were measured. Whole-body fluorescence, bioluminescence and micro-positron emission tomography (PET) images were acquired 1 day after the transfected BMSCs were injected into the left forelimb of rats.

RESULTS

After the transfection with different titers of Ad5-TGF, the positive transfection rate reached a peak (70%) when the MOI was 100. HSV1-tk, eGFP and Fluc mRNA and protein were detected in the Ad5-TGF-transfected BMSCs, which implies their successful transfection and expression. The BMSCs uptake of (131)I-FIAU increased with the adenovirus titer and incubation time and reached a plateau (approximately 5.3%) after 3 h. Strong signals were observed in the injected left forearms in the fluorescence, bioluminescence and micro-PET images.

CONCLUSIONS

A triple-fused reporter gene, TGF, can be used as a multifunctional molecular probe for multimodality imaging.

Detection of the onset of ischemia and carcinogenesis by hypoxia-inducible transcription factor-based in vivo bioluminescence imaging

An animal model for the early detection of common fatal diseases such as ischemic diseases and cancer is desirable for the development of new drugs and treatment strategies. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that regulates oxygen homeostasis and plays key roles in a number of diseases, including cancer. Here, we established transgenic (Tg) mice that carry HRE/ODD-luciferase (HOL) gene, which generates bioluminescence in an HIF-1-dependent manner and was successfully used in this study to monitor HIF-1 activity in ischemic tissues. To monitor carcinogenesis in vivo, we mated HOL mice with rasH2 Tg mice, which are highly sensitive to carcinogens and are used for short-term carcinogenicity assessments. After rasH2-HOL Tg mice were treated with N-methyl-N-nitrosourea, bioluminescence was detected noninvasively as early as 9 weeks in tissues that contained papillomas and malignant lesions. These results suggest that the Tg mouse lines we established hold significant potential for monitoring the early onset of both ischemia and carcinogenesis and that these lines will be useful for screening chemicals for carcinogenic potential.

Visualizing the dynamic of adoptively transferred T cells during the rejection of large established tumors

Adoptive T-cell therapy (ATCT) can result in tumor rejection, yet the behavior and fate of the introduced T cells remain unclear. We developed a novel bioluminescence mouse model, which enabled highly sensitive detection of T-cell signals at the single-cell level. Transferred T cells preferentially accumulated within antigen-positive tumors, relative to the unaffected areas in each mouse, and remarkably, expanded within both lymphopenic and P14 mice. This expansion was controlled and efficient, as evaluated by bioluminescence imaging (BLI) of the T-cell signals and by tumor rejection respectively. Analysis of the population dynamics of transferred T cells in ATCT of large tumors revealed that proliferation did not always follow a simple linear pattern of expansion, but showed an oscillating pattern of expansion and contraction that was often followed by a rebound, until full tumor rejection was achieved. Furthermore, visualizing the recall response showed that the transferred T cells responded expeditiously, indicating the ability of these cells to survive, establish memory and compete with endogenous T cells for as long as 1 year after rejecting the tumor.

Molecular imaging of cell therapy for gastroenterologic applications

Stem cell therapy has appeared as a possible therapeutic alternative for numerous diseases. Furthermore, cancer stem cells are a focus of significant interest as they may allow for a better understanding of the genesis of different malignancies. The ultimate goal of stem cell therapeutics is to ensure the viability and functionality of the transplanted cells. Similarly, the ultimate goal of understanding cancer stem cells is to understand how they behave in the living subject. Until recently, the efficacy of stem cell therapies has been assessed by overall organ function recovery. Understanding the behavior and biology of stem cells directly in the living subject can also lead to therapy optimization. Thus, there is a critical need for reliable and accurate methods to understand stem cell biology in vivo. Recent advances in both imaging and molecular biology have enabled transplanted stem cells to be successfully monitored in the living subject. The use of molecular imaging modalities has the capability to answer these questions and may one day be translated to patients. In this review, we will discuss the potential imaging strategies and how they can be utilized, depending on the questions that need to be answered.

In vivo bioluminescence for tracking cell fate and function

Tracking the fate and function of cells in vivo is paramount for the development of rational therapies for cardiac injury. Bioluminescence imaging (BLI) provides a means for monitoring physiological processes in real time, ranging from cell survival to gene expression to complex molecular processes. In mice and rats, BLI provides unmatched sensitivity because of the absence of endogenous luciferase expression in mammalian cells and the low background luminescence emanating from animals. In the field of stem cell therapy, BLI provides an unprecedented means to monitor the biology of these cells in vivo, giving researchers a greater understanding of their survival, migration, immunogenicity, and potential tumorigenicity in a living animal. In addition to longitudinal monitoring of cell survival, BLI is a useful tool for semiquantitative measurements of gene expression in vivo, allowing a better optimization of drug and gene therapies. Overall, this technology not only enables rapid, reproducible, and quantitative monitoring of physiological processes in vivo but also can measure the influences of therapeutic interventions on the outcome of cardiac injuries.

Multimode Optical Imaging for Translational Chemotherapy: In Vivo Tumor Detection and Delineation by Targeted Gallium Corroles

We report the feasibility of tumor detection and delineation in vivo using multimode optical imaging of targeted gallium corrole (HerGa). HerGa is highly effective for targeted HER2+ tumor elimination in vivo, and it emits intense fluorescence. These unique characteristics of HerGa prompted us to investigate the potential of HerGa for tumor detection and delineation, by performing multimode optical imaging ex vivo and in vivo; the imaging modes included fluorescence intensity, spectral (including ratiometric), lifetime, and two-photon excited fluorescence, using our custom-built imaging system. While fluorescence intensity imaging provided information about tumor targeting capacity and tumor retention of HerGa, ratiometric spectral imaging offered more quantitative and specific information about HerGa location and accumulation. Most importantly, the fluorescence lifetime imaging of HerGa allowed us to discriminate between tumor and non-tumor regions by fluorescence lifetime differences. Finally, two-photon excited fluorescence images provided highly resolved and thus topologically detailed information around the tumor regions where HerGa accumulates. Taken together, the results shown in this report suggest the feasibility of tumor detection and delineation by multimode optical imaging of HerGa, and fluorescent chemotherapy agents in general. Specifically, the multimode optical imaging can offer complementary and even synergetic information simultaneously in the tumor detection and delineation by HerGa, thus enhancing contrast.

In vivo imaging of HIF-active tumors by an oxygen-dependent degradation protein probe with an interchangeable labeling system

Hypoxia-inducible factor (HIF) functions as a master transcriptional regulator for adaptation to hypoxia by inducing adaptive changes in gene expression for regulation of proliferation, angiogenesis, apoptosis and energy metabolism. Cancers with high expression of the alpha subunit of HIF (HIFα) are often malignant and treatment-resistant. Therefore, the development of a molecular probe that can detect HIF activity has great potential value for monitoring tumor hypoxia. HIF prolyl hydroxylases (HPHDs) act as oxygen sensors that regulate the fate of HIFα protein through its oxygen-dependent degradation (ODD) domain. We constructed a recombinant protein PTD-ODD-HaloTag (POH) that is under the same ODD regulation as HIFα and contains protein transduction domain (PTD) and an interchangeable labeling system. Administration of near-infrared fluorescently labeled POH (POH-N) to mouse models of cancers allowed successful monitoring of HIF-active regions. Immunohistochemical analysis for intratumoral localization of POH probe revealed its specificity to HIF-active cells. Furthermore, lack of the PTD domain or a point mutation in the ODD domain abrogated the specificity of POH-N to HIF-active cells. Overall results indicate that POH is a practical probe specific to HIF-active cell in cancers and suggest its large potential for imaging and targeting of HIF-related diseases.

Molecular imaging: current status and emerging strategies

In vivo molecular imaging has a great potential to impact medicine by detecting diseases in early stages (screening), identifying extent of disease, selecting disease- and patient-specific treatment (personalized medicine), applying a directed or targeted therapy, and measuring molecular-specific effects of treatment. Current clinical molecular imaging approaches primarily use positron-emission tomography (PET) or single photon-emission computed tomography (SPECT)-based techniques. In ongoing preclinical research, novel molecular targets of different diseases are identified and, sophisticated and multifunctional contrast agents for imaging these molecular targets are developed along with new technologies and instrumentation for multi-modality molecular imaging. Contrast-enhanced molecular ultrasound (US) with molecularly-targeted contrast microbubbles is explored as a clinically translatable molecular imaging strategy for screening, diagnosing, and monitoring diseases at the molecular level. Optical imaging with fluorescent molecular probes and US imaging with molecularly-targeted microbubbles are attractive strategies as they provide real-time imaging, are relatively inexpensive, produce images with high spatial resolution, and do not involve exposure to ionizing irradiation. Raman spectroscopy/microscopy has emerged as a molecular optical imaging strategy for ultrasensitive detection of multiple biomolecules/biochemicals with both in vivo and ex vivo versatility. Photoacoustic imaging is a hybrid of optical and US techniques involving optically-excitable molecularly-targeted contrast agents and quantitative detection of resulting oscillatory contrast agent movement with US. Current preclinical findings and advances in instrumentation, such as endoscopes and microcatheters, suggest that these molecular imaging methods have numerous potential clinical applications and will be translated into clinical use in the near future.