MicroPET/SPECT/CT imaging of small animal models of disease

A pH-responsive magnetic resonance tuning probe for precise imaging of bacterial infection in vivo

Accurate and sensitive detection of bacteria is essential for treating bacterial infections. Herein, a pH-responsive magnetic resonance tuning (MRET) probe, whose T₁-weighted signal is activated in the bacteria-infected acid microenvironment, is developed for in situ accurately magnetic resonance imaging (MRI) of bacterial infection in vivo. The MRET probe (MDVG-1) is an assembly of paramagnetic enhancer (gadolinium-modified i-motif DNA₃, abbreviated as Gd-DNA₃-Gd) and the precursor of superparamagnetic quencher (DNA and vancomycin-modified magnetic nanoparticle, abbreviated as MDV). The T₁-weighted signal of Gd-DNA₃-Gd is quenched once the formation of MDVG-1 (MRET ON). Interestingly, the MDVG-1 probe was disassembled into the monomers of Gd-DNA₃-Gd and MDV under the bacteria-infected acid microenvironment, resulting significantly enhanced T₁-weighted signal at the infected site (MRET OFF). The pH-responsive MRET probe-based enhanced MRI signal and bacteria targeting significantly improve the distinction between bacterial infectious tissues and sterile inflamed tissues, which provides a promising approach for accurately detecting bacterial infection in vivo. STATEMENT OF SIGNIFICANCE: : Detecting pathogenic bacteria in vivo based on magnetic resonance imaging (MRI) strategy has been exploring recently. Although various bacterial-targeted MRI probes have been developed to image bacteria in vivo, the MRI signal of these MRI probes is always "on", which inevitably generates nonspecific background MRI signals, affecting the accuracy of MRI to a certain extent. In the current study, based on the magnetic resonance tuning (MRET) phenomenon, we present a pH-responsive MRET probe (MDVG-1) with T₂-weighted imaging to T₁-weighted imaging switchable properties to achieve in situ precise imaging of bacterial infection in vivo.

Non-invasive photoacoustic computed tomography of rat heart anatomy and function

Complementary to mainstream cardiac imaging modalities for preclinical research, photoacoustic computed tomography (PACT) can provide functional optical contrast with high imaging speed and resolution. However, PACT has not been demonstrated to reveal the dynamics of whole cardiac anatomy or vascular system without surgical procedure (thoracotomy) for tissue penetration. Here, we achieved non-invasive imaging of rat hearts using the recently developed three-dimensional PACT (3D-PACT) platform, demonstrating the regulated illumination and detection schemes to reduce the effects of optical attenuation and acoustic distortion through the chest wall; thereby, enabling unimpeded visualization of the cardiac anatomy and intracardiac hemodynamics following rapidly scanning the heart within 10 s. We further applied 3D-PACT to reveal distinct cardiac structural and functional changes among the healthy, hypertensive, and obese rats, with optical contrast to uncover differences in cardiac chamber size, wall thickness, and hemodynamics. Accordingly, 3D-PACT provides high imaging speed and nonionizing penetration to capture the whole heart for diagnosing the animal models, holding promises for clinical translation to cardiac imaging of human neonates.

New Enclosure for in vivo Medical Imaging of Zebrafish With Vital Signs Monitoring

Lately, the use of zebrafish has gained increased interest in the scientific community as an animal model in preclinical research. However, there is a lack of in vivo imaging tools that ensure animal welfare during acquisition procedures. The use of functional imaging techniques, like Positron Emission Tomography (PET), in zebrafish is limited since it requires the animal to be alive, representing a higher instrumentation complexity when compared to morphological imaging systems. In the present work, a new zebrafish enclosure was developed to acquire in vivo images while monitoring the animal’s welfare through its heartbeat. The temperature, dissolved oxygen, and pH range in a closed aquatic environment were tested to ensure that the conditions stay suitable for animal welfare during image acquisitions. The developed system, based on an enclosure with a bed and heartbeat sensors, was tested under controlled conditions in anesthetized fishes. Since the anesthetized zebrafish do not affect the water quality over time, there is no need to incorporate water circulation for the expected time of PET exams (about 30 min). The range of values obtained for the zebrafish heart rate was 88–127 bpm. The developed system has shown promising results regarding the zebrafish’s heart rate while keeping the fish still during the long imaging exams. The zebrafish enclosure ensures the animal’s well-being during the acquisition of in vivo images in different modalities (PET, Computer Tomography, Magnetic Resonance Imaging), contributing substantially to the preclinical research.

PET Use in Cancer Diagnosis, Treatment, and Prognosis

Tumorigenesis is a multistep process marked by variations in numerous metabolic pathways that affect cellular architectures and functions. Cancer cells reprogram their energy metabolism to enable several basic molecular functions, including membrane biosynthesis, receptor regulations, bioenergetics, and redox stress. In recent years, cancer diagnosis and treatment strategies have targeted these specific metabolic changes and the tumor's interactions with its microenvironment. Positron emission tomography (PET) captures all molecular alterations leading to abnormal function and cancer progression. As a result, the development of PET radiotracers increasingly focuses on irregular biological pathways or cells that overexpress receptors that have the potential to function as biomarkers for early diagnosis and treatment measurements as well as research. This chapter reviews both established and evolving PET radiotracers used to image tumor biology. We have also included a few advantages and disadvantages of the routinely used PET radiotracers in cancer imaging.

PET/CT Technology in Adult Zebrafish: A Pilot Study Toward Live Longitudinal Imaging

Decades of research have confirmed the beneficial and advantageous use of zebrafish (Danio rerio) as a model of human disease in biomedical studies. Not only are 71% of human genes shared with the zebrafish many of these genes are linked to human diseases. Currently, numerous transgenic and mutant genetic zebrafish lines are now widely available for use in research. Furthermore, zebrafish are relatively inexpensive to maintain compared to rodents. However, a limiting factor to fully utilising adult zebrafish in research is not the fish but the technological imaging tools available. In order to increase the utilisation of adult zebrafish, which are not naturally transparent, requires new imaging approaches. Therefore, this feasibility study: (1) presents an innovative designed PET/CT adult zebrafish imaging platform, capable of maintaining normal aquatic physiology during scanning; (2) assesses the practical aspects of adult zebrafish imaging; and (3) set basic procedural guidelines for zebrafish imaging during a PET/CT acquisition. Methods: With computer aided design (CAD) software an imaging platform was developed for 3D printing. A 3D printed zebrafish model was created from a CT acquisition of a zebrafish using the CAD software. This model and subsequently euthanised zebrafish were imaged post-injection using different concentrations of the radiotracer [18F]FDG with CT contrast. Results: PET/CT imaging was successful, revealing levels as low as 0.01 MBq could be detected in the fish. In the zebrafish imaging post-injection distribution of the radiotracer was observed away from the injection site as well as tissue uptake. Potential preliminary husbandry and welfare guidelines for the fish during and after PET/CT imaging were determined. Conclusion: Using PET/CT for adult zebrafish imaging as a viable non-invasive technological tool is feasible. Adult zebrafish PET/CT imaging has the potential to be a key imaging technique offering the possibilities of enhanced biomedical understanding and new translational data sets.

The Potential of OMICs Technologies for the Treatment of Immune-Mediated Inflammatory Diseases

Immune-mediated inflammatory diseases (IMIDs), such as inflammatory bowel diseases and inflammatory arthritis (e.g., rheumatoid arthritis, psoriatic arthritis), are marked by increasing worldwide incidence rates. Apart from irreversible damage of the affected tissue, the systemic nature of these diseases heightens the incidence of cardiovascular insults and colitis-associated neoplasia. Only 40–60% of patients respond to currently used standard-of-care immunotherapies. In addition to this limited long-term effectiveness, all current therapies have to be given on a lifelong basis as they are unable to specifically reprogram the inflammatory process and thus achieve a true cure of the disease. On the other hand, the development of various OMICs technologies is considered as “the great hope” for improving the treatment of IMIDs. This review sheds light on the progressive development and the numerous approaches from basic science that gradually lead to the transfer from “bench to bedside” and the implementation into general patient care procedures.

Role of Nuclear Imaging to Understand the Neural Substrates of Brain Disorders in Laboratory Animals: Current Status and Future Prospects

Molecular imaging, which allows the real-time visualization, characterization and measurement of biological processes, is becoming increasingly used in neuroscience research. Scintigraphy techniques such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) provide qualitative and quantitative measurement of brain activity in both physiological and pathological states. Laboratory animals, and rodents in particular, are essential in neuroscience research, providing plenty of models of brain disorders. The development of innovative high-resolution small animal imaging systems together with their radiotracers pave the way to the study of brain functioning and neurotransmitter release during behavioral tasks in rodents. The assessment of local changes in the release of neurotransmitters associated with the performance of a given behavioral task is a turning point for the development of new potential drugs for psychiatric and neurological disorders. This review addresses the role of SPECT and PET small animal imaging systems for a better understanding of brain functioning in health and disease states. Brain imaging in rodent models faces a series of challenges since it acts within the boundaries of current imaging in terms of sensitivity and spatial resolution. Several topics are discussed, including technical considerations regarding the strengths and weaknesses of both technologies. Moreover, the application of some of the radioligands developed for small animal nuclear imaging studies is discussed. Then, we examine the changes in metabolic and neurotransmitter activity in various brain areas during task-induced neural activation with special regard to the imaging of opioid, dopaminergic and cannabinoid receptors. Finally, we discuss the current status providing future perspectives on the most innovative imaging techniques in small laboratory animals. The challenges and solutions discussed here might be useful to better understand brain functioning allowing the translation of preclinical results into clinical applications.

Rapidly (and Successfully) Translating Novel Brain Radiotracers From Animal Research Into Clinical Use

The advent of preclinical research scanners for in vivo imaging of small animals has added confidence into the multi-step decision-making process of radiotracer discovery and development. Furthermore, it has expanded the utility of imaging techniques available to dissect clinical questions, fostering a cyclic interaction between the clinical and the preclinical worlds. Significant efforts from medicinal chemistry have also made available several high-affinity and selective compounds amenable for radiolabeling, that target different receptors, transporters and enzymes in vivo. This substantially increased the range of applications of molecular imaging using positron emission tomography (PET) or single photon emission computed tomography (SPECT). However, the process of developing novel radiotracers for in vivo imaging of the human brain is a multi-step process that has several inherent pitfalls and technical difficulties, which often hampers the successful translation of novel imaging agents from preclinical research into clinical use. In this paper, the process of radiotracer development and its relevance in brain research is discussed; as well as, its pitfalls, technical challenges and future promises. Examples of successful and unsuccessful translation of brain radiotracers will be presented.

Improving glucose metabolism in the auditory cortex delays the aging of auditory function of guinea pig

The glucose homeostasis is essential for brain function, and energy deficiency is a key feature of brain aging. We investigated whether improving glucose metabolism in the auditory cortex can delay the aging of auditory function of guinea pigs with age-related hearing loss (ARHL) by d-galactose. Auditory function was assessed by auditory brainstem response (ABR), glucose metabolism was detected by micro PET/CT, and the proteome were identified in auditory cortex by two-dimensional electrophoresis and matrix assisted laser desorption/ionization mass spectrometry. Glucose metabolism decreased in the auditory cortex of d-galactose group, and improving glucose metabolism can delay the aging of auditory function by upregulating seven metabolism-related proteins including ATP synthase subunit beta, triosephosphate isomerase, creatine kinase U-type, pyruvate dehydrogenase E1 component subunit beta, alpha-enolase, phosphoglycerate kinase, and tubulin beta-2A chain. These results suggest that the decrease of glucose metabolism in the auditory cortex may be an important role in the aging of auditory function, and improving glucose metabolism in the auditory cortex can delay the aging of auditory function of guinea pig with ARHL induced by d-galactose.

Terrestrial acclimation and exercise lead to bone functional response in Polypterus senegalus pectoral fins

The ability of bones to sense and respond to mechanical loading is a central feature of vertebrate skeletons. However, the functional demands imposed on terrestrial and aquatic animals differ vastly. The pectoral girdle of the basal actinopterygian fish Polypterus senegalus was previously shown to exhibit plasticity following terrestrial acclimation, but the pectoral fin itself has yet to be examined. We investigated skeletal plasticity in the pectoral fins of P. senegalus after exposure to terrestrial loading. Juvenile fish were divided into three groups: a control group was kept under aquatic conditions without intervention, an exercised group was also kept in water but received daily exercise on land, and a terrestrial group was kept in a chronic semi-terrestrial condition. After 5 weeks, the pectoral fins were cleared and stained with Alcian Blue and Alizarin Red to visualize cartilage and bone, allowing measurements of bone length, bone width, ossification and curvature to be taken for the endochondral radial bones. Polypterus senegalus fin bones responded most strongly to chronic loading in the terrestrial condition. Fish that were reared in a terrestrial environment had significantly longer bones compared with those of aquatic controls, wider propterygia and metapterygia, and more ossified metapterygia and medial radials, and they showed changes in propterygial curvature. Exercised fish also had longer and more ossified medial radials compared with those of controls. Polypterus senegalus fin bones exhibit plasticity in response to novel terrestrial loading. Such plasticity could be relevant for transitions between water and land on evolutionary scales, but key differences between fish and tetrapod bone make direct comparisons challenging.

Injectable hydrogels based on MPEG–PCL–RGD and BMSCs for bone tissue engineering

The aim of this study was to investigate the osteogenic potential of BMSCs seeded on RGD-conjugated methoxy polyethylene glycol-polycaprolactone (MP–RGD) in vitro and in vivo.

Imaging the Injured Lung: Mechanisms of Action and Clinical Use

Acute respiratory distress syndrome (ARDS) consists of acute hypoxemic respiratory failure characterized by massive and heterogeneously distributed loss of lung aeration caused by diffuse inflammation and edema present in interstitial and alveolar spaces. It is defined by consensus criteria, which include diffuse infiltrates on chest imaging-either plain radiography or computed tomography. This review will summarize how imaging sciences can inform modern respiratory management of ARDS and continue to increase the understanding of the acutely injured lung. This review also describes newer imaging methodologies that are likely to inform future clinical decision-making and potentially improve outcome. For each imaging modality, this review systematically describes the underlying principles, technology involved, measurements obtained, insights gained by the technique, emerging approaches, limitations, and future developments. Finally, integrated approaches are considered whereby multimodal imaging may impact management of ARDS.

Metabolism of Stem and Progenitor Cells: Proper Methods to Answer Specific Questions

Stem cells can stay quiescent for a long period of time or proliferate and differentiate into multiple lineages. The activity of stage-specific metabolic programs allows stem cells to best adapt their functions in different microenvironments. Specific cellular phenotypes can be, therefore, defined by precise metabolic signatures. Notably, not only cellular metabolism describes a defined cellular phenotype, but experimental evidence now clearly indicate that also rewiring cells towards a particular cellular metabolism can drive their cellular phenotype and function accordingly. Cellular metabolism can be studied by both targeted and untargeted approaches. Targeted analyses focus on a subset of identified metabolites and on their metabolic fluxes. In addition, the overall assessment of the oxygen consumption rate (OCR) gives a measure of the overall cellular oxidative metabolism and mitochondrial function. Untargeted approach provides a large-scale identification and quantification of the whole metabolome with the aim to describe a metabolic fingerprinting. In this review article, we overview the methodologies currently available for the study of invitro stem cell metabolism, including metabolic fluxes, fingerprint analyses, and single-cell metabolomics. Moreover, we summarize available approaches for the study of in vivo stem cell metabolism. For all of the described methods, we highlight their specificities and limitations. In addition, we discuss practical concerns about the most threatening steps, including metabolic quenching, sample preparation and extraction. A better knowledge of the precise metabolic signature defining specific cell population is instrumental to the design of novel therapeutic strategies able to drive undifferentiated stem cells towards a selective and valuable cellular phenotype.

Effect of methotrexate on collagen-induced arthritis in male Wistar rats

To evaluate the effect of methotrexate on collagen-induced arthritis, micro-computed tomography (micro-CT) and histopathological analyses were used in male Wistar rats. Rats were divided randomly into three groups. Group 1 was treated with 0.9% saline, and groups 2 and 3 were boosted with type Ⅱ collagen. From day 21 to 42, groups 1 and 2 were orally treated with 0.9% saline and group 3 was orally treated with 1.5 mg/kg methotrexate. All rats were sacrificed at day 42 after the first collagen treatment. Micro-CT analyses showed bony parameters, such as bone volume and trabecular number, were decreased in group 2 compared to group 1, and these parameters were recovered in group 3. Histopathological examination and pathological parameter scoring showed that the knee joints of rats in group 2 had severe joint destruction, showing cartilage and bone erosion, enlarged cavities with inflammatory cell infiltration and activation of synovial fibroblasts. By contrast, these changes were reduced in group 3. Taken together, methotrexate treatment showed therapeutic potential in male rat collagen-induced arthritis model, and micro-CT analysis and histopathological tools could be integrated to assess the quantification/qualification of arthritic lesions.

Replacement, Refinement, and Reduction in Animal Studies With Biohazardous Agents

Animal models are critical to the advancement of our knowledge of infectious disease pathogenesis, diagnostics, therapeutics, and prevention strategies. The use of animal models requires thoughtful consideration for their well-being, as infections can significantly impact the general health of an animal and impair their welfare. Application of the 3Rs—replacement, refinement, and reduction—to animal models using biohazardous agents can improve the scientific merit and animal welfare. Replacement of animal models can use in vitro techniques such as cell culture systems, mathematical models, and engineered tissues or invertebrate animal hosts such as amoeba, worms, fruit flies, and cockroaches. Refinements can use a variety of techniques to more closely monitor the course of disease. These include the use of biomarkers, body temperature, behavioral observations, and clinical scoring systems. Reduction is possible using advanced technologies such as in vivo telemetry and imaging, allowing longitudinal assessment of animals during the course of disease. While there is no single method to universally replace, refine, or reduce animal models, the alternatives and techniques discussed are broadly applicable and they should be considered when infectious disease animal models are developed.

Application of a novel in vivo imaging approach to measure pulmonary vascular responses in mice

Noninvasive imaging of the murine pulmonary vasculature is challenging due to the small size of the animal, limits of resolution of the imaging technology, terminal nature of the procedure, or the need for intravenous contrast. We report the application of laboratory-based high-speed, high-resolution x-ray imaging, and image analysis to detect quantitative changes in the pulmonary vascular tree over time in the same animal without the need for intravenous contrast. Using this approach, we detected an increased number of vessels in the pulmonary vascular tree of animals after 30 min of recovery from a brief exposure to inspired gas with 10% oxygen plus 5% carbon dioxide (mean ± standard deviation: 2193 ± 382 at baseline vs. 6177 ± 1171 at 30 min of recovery; P < 0.0001). In a separate set of animals, we showed that the total pulmonary blood volume increased (P = 0.0412) while median vascular diameter decreased from 0.20 mm (IQR: 0.15-0.28 mm) to 0.18 mm (IQR: 0.14-0.26 mm; P = 0.0436) over the respiratory cycle from end-expiration to end-inspiration. These findings suggest that the noninvasive, nonintravenous contrast imaging approach reported here can detect dynamic responses of the murine pulmonary vasculature and may be a useful tool in studying these responses in models of disease.

Molecular Imaging of Smoke-Induced Changes in Nuclear Factor-Kappa B Expression in Murine Tissues Including the Lung

Many inflammatory responses are mediated by activation of the transcription factor, nuclear factor-kappa B (NF-κB), and a wide variety of human diseases involve abnormal regulation of its expression. In this investigation, we evaluated the effect of smoke inhalation injury on NF-κB expression in lung using two strains of NF-κB reporter mice. Groups of reporter mice with viral thymidine kinase (TK) or "fire fly" luciferase (Luc) genes under control by the NF-κB promoter (TK/NF-κB mice and Luc/NF-κB mice) were subjected to nonlethal smoke inhalation injury. Sham-treated animals served as controls. Twenty-four hours (each animal was injected intravenously with either 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine (FHBG) (~ 1.0 mCi) or luciferin (1.0 mg). One hour later, the TK/NF-κB mice were studied by micro-positron emission tomography (µ-PET) imaging using a Concord P4 µ-PET camera, and the Luc/NF-κB mice were studied by bioluminescence imaging with a charge-coupled device camera. The µ-PET data demonstrated that smoke injury produced massive increases in NF-κB expression (FHBG-standardized uptake value: 3.1 vs 0.0) 24 hours after smoke inhalation, which was reduced 48 hours after smoke inhalation, but still significantly different than the control. Qualitative analysis of the bioluminescence data revealed a remarkably similar effect of burn NF-κB luciferase expression in vivo. Biodistribution studies of FHBG uptake and luciferase activity in lung tissue demonstrated a similar increase 24 hours after injury, which was reduced 48 hours later, but still significantly higher than the sham. The present data with these models providing longitudinal imaging data on the same mouse may prove useful in the examination of the factors producing lung injury by smoke inhalation, as well as the treatment(s) for the damage produced with and without burn injury.

Novel imaging approaches for small animal models of lung disease (2017 Grover Conference series)

Imaging in small animal models of lung disease is challenging, as existing technologies are limited either by resolution or by the terminal nature of the imaging approach. Here, we describe the current state of small animal lung imaging, the technological advances of laboratory-sourced phase contrast X-ray imaging, and the application of this novel technology and its attendant image analysis techniques to the in vivo imaging of the large airways and pulmonary vasculature in murine models of lung health and disease.

Gadolinium-Labeled Aminoglycoside and Its Potential Application as a Bacteria-Targeting Magnetic Resonance Imaging Contrast Agent

Magnetic resonance imaging (MRI) is a powerful diagnostic technique that can penetrate deep into tissue providing excellent spatial resolution without the need for ionizing radiation or harmful radionuclides. However, diagnosing bacterial infections in vivo with clinical MRI is severely hampered by the lack of contrast agents with high relaxivity, targeting capabilities, and bacterial penetration and specificity. Here, we report the development of the first gadolinium (Gd)-based bacteria-specific targeting MRI contrast agent, probe 1, by conjugating neomycin, an aminoglycoside antibiotic, with Dotarem (Gd-DOTA, an FDA approved T₁-weighted MRI contrast agent). The T₁ relaxivity of probe 1 was found to be comparable to that of Gd-DOTA; additionally, probe 1-treated bacteria generated a significantly brighter T₁-weighted MR signal than Gd-DOTA-treated bacteria. More importantly, in vitro cellular studies and preliminary in vivo MRI demonstrated probe 1 exhibits the ability to efficiently target bacteria over macrophage-like cells, indicating its great potential for high-resolution imaging of bacterial infections in vivo.

Surfactant-stripped naphthalocyanines for multimodal tumor theranostics with upconversion guidance cream

Surfactant-stripped, nanoformulated naphthalocyanines (nanonaps) can be formed with Pluronic F127 and low temperature membrane processing, resulting in dispersed frozen micelles with extreme contrast in the near infrared region. Here, we demonstrate that nanonaps can be used for multifunctional cancer theranostics. This includes lymphatic mapping and whole tumor photoacoustic imaging following intradermal or intravenous injection in rodents. Without further modification, pre-formed nanonaps were used for positron emission tomography and passively accumulated in subcutaneous murine tumors. Because the nanonaps used absorb light beyond the visible range, a topical upconversion skin cream was developed for anti-tumor photothermal therapy with laser placement that can be guided by the naked eye.

Tactics for preclinical validation of receptor-binding radiotracers

INTRODUCTION

Aspects of radiopharmaceutical development are illustrated through preclinical studies of [125I]-(E)-1-(2-(2,3-dihydrobenzofuran-5-yl)ethyl)-4-(iodoallyl)piperazine ([125I]-E-IA-BF-PE-PIPZE), a radioligand for sigma-1 (σ1) receptors, coupled with examples from the recent literature. Findings are compared to those previously observed for [125I]-(E)-1-(2-(2,3-dimethoxy-5-yl)ethyl)-4-(iodoallyl)piperazine ([125I]-E-IA-DM-PE-PIPZE).

METHODS

Syntheses of E-IA-BF-PE-PIPZE and [125I]-E-IA-BF-PE-PIPZE were accomplished by standard methods. In vitro receptor binding studies and autoradiography were performed, and binding potential was predicted. Measurements of lipophilicity and protein binding were obtained. In vivo studies were conducted in mice to evaluate radioligand stability, as well as specific binding to σ1 sites in brain, brain regions and peripheral organs in the presence and absence of potential blockers.

RESULTS

E-IA-BF-PE-PIPZE exhibited high affinity and selectivity for σ1 receptors (Ki = 0.43 ± 0.03 nM, σ2/σ1 = 173). [125I]-E-IA-BF-PE-PIPZE was prepared in good yield and purity, with high specific activity. Radioligand binding provided dissociation (koff) and association (kon) rate constants, along with a measured Kd of 0.24 ± 0.01 nM and Bmax of 472 ± 13 fmol/mg protein. The radioligand proved suitable for quantitative autoradiography in vitro using brain sections. Moderate lipophilicity, Log D7.4 2.69 ± 0.28, was determined, and protein binding was 71 ± 0.3%. In vivo, high initial whole brain uptake, >6% injected dose/g, cleared slowly over 24 h. Specific binding represented 75% to 93% of total binding from 15 min to 24 h. Findings were confirmed and extended by regional brain biodistribution. Radiometabolites were not observed in brain (1%).

CONCLUSIONS

Substitution of dihydrobenzofuranylethyl for dimethoxyphenethyl increased radioligand affinity for σ1 receptors by 16-fold. While high specific binding to σ1 receptors was observed for both radioligands in vivo, [125I]-E-IA-BF-PE-PIPZE displayed much slower clearance kinetics than [125I]-E-IA-DM-PE-PIPZE. Thus, minor structural modifications of σ1 receptor radioligands lead to major differences in binding properties in vitro and in vivo.

Surfactant-Stripped Frozen Pheophytin Micelles for Multimodal Gut Imaging

Edible, surfactant-stripped, frozen micelles are formed from pheophytin (demetallated chlorophyll), a pigment that is naturally consumed in human diets. Pheophytin nanoparticles pass completely and safely through the gastrointestinal tract and enable trimodal gut contrast imaging via photoacoustic, fluorescence, and positron emission tomography techniques.

Intra-iliac Artery Injection for Efficient and Selective Modeling of Microscopic Bone Metastasis

Intra-iliac artery (IIA) injection is an efficient approach to introduce metastatic lesions of various cancer cells in animals. Compared to the widely used intra-cardiac and intra-tibial injections, IIA injection brings several advantages. First, it can deliver a large quantity of cancer cells specifically to hind limb bones, thereby providing spatiotemporally synchronized early-stage colonization events and allowing robust quantification and swift detection of disseminated tumor cells. Second, it injects cancer cells into the circulation without damaging the local tissues, thereby avoiding inflammatory and wound-healing processes that confound the bone colonization process. Third, IIA injection causes very little metastatic growth in non-bone organs, thereby preventing animals from succumbing to other vital metastases, and allowing continuous monitoring of indolent bone lesions. These advantages are especially useful for the inspection of progression from single cancer cells to multi-cell micrometastases, which has largely been elusive in the past. When combined with cutting-edge approaches of biological imaging and bone histology, IIA injection can be applied to various research purposes related to bone metastases.

Detecting Tumor Metastases: The Road to Therapy Starts Here

Metastasis is the complex process by which primary tumor cells migrate and establish secondary tumors in an adjacent or distant location in the body. Early detection of metastatic disease and effective therapeutic options for targeting these detected metastases remain impediments to effectively treating patients with advanced cancers. If metastatic lesions are identified early, patients might maximally benefit from effective early therapeutic interventions. Further, monitoring patients whose primary tumors are effectively treated for potential metastatic disease onset is also highly valuable. Finally, patients with metastatic disease can be monitored for efficacy of specific therapeutic interventions through effective metastatic detection techniques. Thus, being able to detect and visualize metastatic lesions is key and provides potential to greatly improve overall patient outcomes. In order to achieve these objectives, researchers have endeavored to mechanistically define the steps involved in the metastatic process as well as ways to effectively detect metastatic progression. We presently overview various preclinical and clinical in vitro and in vivo assays developed to more efficiently detect tumor metastases, which provides the foundation for developing more effective therapies for this invariably fatal component of the cancerous process.

Recent Advances of Radionuclide-Based Molecular Imaging of Atherosclerosis

Atherosclerosis is a systemic disease characterized by the development of multifocal plaque lesions within vessel walls and extending into the vascular lumen. The disease takes decades to develop symptomatic lesions, affording opportunities for accurate detection of plaque progression, analysis of risk factors responsible for clinical events, and planning personalized treatment. Of the available molecular imaging modalities, radionuclidebased imaging strategies have been favored due to their sensitivity, quantitative detection and pathways for translational research. This review summarizes recent advances of radiolabeled small molecules, peptides, antibodies and nanoparticles for atherosclerotic plaque imaging during disease progression.

Ratiometric mechanosensitive fluorescent dyes: Design and applications

Fluorescent molecules, with their almost instantaneous response to external influences and relatively low-cost measurement instrumentation, have been attractive analytical tools and biosensors for centuries. More recently, advanced chemical synthesis and targeted design have accelerated the development of fluorescent probes. This article focuses on dyes with segmental mobility (known as fluorescent molecular rotors) that act as mechanosensors, which are known for their relationship of emission quantum yield with microviscosity. Fluorescence lifetime is directly related to quantum yield, but steady-state emission intensity is not. To remove confounding factors with steady-state instrumentation, dual-band emission dyes can be used, and molecular rotors have been developed that either have intrinsic dual emission or that have a non-sensitive reference unit to provide a calibration emission band. We report on theory, chemical structure, applications and targeted design of several classes of dual-emission molecular rotors.

TSPO expression in brain tumours: is TSPO a target for brain tumour imaging?

Positron emission tomography (PET) alone or in combination with MRI is increasingly assuming a central role in the development of diagnostic and therapeutic strategies for brain tumours with the aim of addressing tumour heterogeneity, assisting in patient stratification, and contributing to predicting treatment response. The 18 kDa translocator protein (TSPO) is expressed in high-grade gliomas, while its expression is comparatively low in normal brain. In addition, the evidence of elevated TSPO in neoplastic cells has led to studies investigating TSPO as a transporter of anticancer drugs for brain delivery and a selective target for tumour tissue. The TSPO therefore represents an ideal candidate for molecular imaging studies. Knowledge of the biology of TSPO in normal brain cells, in-depth understanding of TSPO functions and biodistribution in neoplastic cells, accurate methods for quantification of uptake of TSPO tracers and pharmacokinetic data regarding TSPO-targeted drugs are required before introducing TSPO PET and TSPO-targeted treatment in clinical practice. In this review, we will discuss the impact of preclinical PET studies and the application of TSPO imaging in human brain tumours, the advantages and disadvantages of TSPO imaging compared to other imaging modalities and other PET tracers, and pathology studies on the extent and distribution of TSPO in gliomas. The suitability of TSPO as molecular target for treatment of brain tumours will also be the appraised.

Molecular Imaging of Pancreatic Cancer with Antibodies

Development of novel imaging probes for cancer diagnostics remains critical for early detection of disease, yet most imaging agents are hindered by suboptimal tumor accumulation. To overcome these limitations, researchers have adapted antibodies for imaging purposes. As cancerous malignancies express atypical patterns of cell surface proteins in comparison to noncancerous tissues, novel antibody-based imaging agents can be constructed to target individual cancer cells or surrounding vasculature. Using molecular imaging techniques, these agents may be utilized for detection of malignancies and monitoring of therapeutic response. Currently, there are several imaging modalities commonly employed for molecular imaging. These imaging modalities include positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance (MR) imaging, optical imaging (fluorescence and bioluminescence), and photoacoustic (PA) imaging. While antibody-based imaging agents may be employed for a broad range of diseases, this review focuses on the molecular imaging of pancreatic cancer, as there are limited resources for imaging and treatment of pancreatic malignancies. Additionally, pancreatic cancer remains the most lethal cancer with an overall 5-year survival rate of approximately 7%, despite significant advances in the imaging and treatment of many other cancers. In this review, we discuss recent advances in molecular imaging of pancreatic cancer using antibody-based imaging agents. This task is accomplished by summarizing the current progress in each type of molecular imaging modality described above. Also, several considerations for designing and synthesizing novel antibody-based imaging agents are discussed. Lastly, the future directions of antibody-based imaging agents are discussed, emphasizing the potential applications for personalized medicine.

From mice to men: Murine models of colorectal cancer for use in translational research

Colorectal cancer (CRC) is the third most common carcinoma worldwide and despite advances in treatment, survival for patients with metastatic disease remains poor. With nearly 50% of patients developing metastases, in vivo investigation is essential to improve outcomes for these patients and numerous murine models of CRC have been developed to allow the study of chemoprevention and chemotherapy, in addition to improving our understanding of the pathogenesis of CRC. Selecting the most appropriate murine model for a specific application will maximize the conversion of potential therapies from the laboratory to clinical practice and requires an understanding of the various models available. This review will provide an overview of the murine models currently used in CRC research, discussing the limitations and merits of each and their most relevant application. It is aimed at the developing researcher, acting as a guide to prompt further reading in planning a specific study.

Animal models for photodynamic therapy (PDT)

Photodynamic therapy (PDT) combines visible light and photosensitizing dyes. Different animal models have been used to test PDT for cancer, infectious disease and cardiovascular disease. Mouse models of tumours include subcutaneous, orthotopic, syngeneic, xenograft, autochthonous and genetically modified.

Photodynamic therapy (PDT) employs non-toxic dyes called photosensitizers (PSs), which absorb visible light to give the excited singlet state, followed by the long-lived triplet state that can undergo photochemistry. In the presence of ambient oxygen, reactive oxygen species (ROS), such as singlet oxygen and hydroxyl radicals are formed that are able to kill cancer cells, inactivate microbial pathogens and destroy unwanted tissue. Although there are already several clinically approved PSs for various disease indications, many studies around the world are using animal models to investigate the further utility of PDT. The present review will cover the main groups of animal models that have been described in the literature. Cancer comprises the single biggest group of models including syngeneic mouse/rat tumours that can either be subcutaneous or orthotopic and allow the study of anti-tumour immune response; human tumours that need to be implanted in immunosuppressed hosts; carcinogen-induced tumours; and mice that have been genetically engineered to develop cancer (often by pathways similar to those in patients). Infections are the second biggest class of animal models and the anatomical sites include wounds, burns, oral cavity, ears, eyes, nose etc. Responsible pathogens can include Gram-positive and Gram-negative bacteria, fungi, viruses and parasites. A smaller and diverse group of miscellaneous animal models have been reported that allow PDT to be tested in ophthalmology, atherosclerosis, atrial fibrillation, dermatology and wound healing. Successful studies using animal models of PDT are blazing the trail for tomorrow's clinical approvals.

Multimodal imaging analysis of an orthotopic head and neck cancer mouse model and application of anti-CD137 tumor immune therapy

BACKGROUND

Recent technical progress makes sophisticated noninvasive imaging methods available for murine models. For the first time, in this study, we applied fluorodeoxyglucose (FDG)-positron emission tomography (PET)-CT and FDG-PET-MRI to a murine orthotopic model of head and neck cancer immunotherapy.

METHODS

Tumor growth of floor of the mouth tumors was evaluated by multimodal small-animal imaging using FDG-PET-CT and FDG-PET-MRI. The immunotherapeutic effects of anti-CD137 antibody therapy were examined on body weight, tumor growth, and tumor-infiltrating immune cells in longitudinal imaging studies and immunohistochemical analyses.

RESULTS

Imaging revealed aggressive, fast-growing tumors without evidence of local or distant metastases. CD137 immunotherapy decreased tumor take and growth and stabilized body weight over time. A clear case of tumor regression was demonstrated by longitudinal PET-CT.

CONCLUSION

The murine model mimics the characteristics of head and neck cancer in humans and offers excellent opportunities to investigate immunomodulatory anticancer drugs. The CD137 antibody showed antitumor effects in some therapy-responsive mice.

Animal Models of Bone Metastasis

Bone is one of the most common sites of cancer metastasis in humans and is a significant source of morbidity and mortality. Bone metastases are considered incurable and result in pain, pathologic fracture, and decreased quality of life. Animal models of skeletal metastases are essential to improve the understanding of the molecular pathways of cancer metastasis and growth in bone and to develop new therapies to inhibit and prevent bone metastases. The ideal animal model should be clinically relevant, reproducible, and representative of human disease. Currently, an ideal model does not exist; however, understanding the strengths and weaknesses of the available models will lead to proper study design and successful cancer research. This review provides an overview of the current in vivo animal models used in the study of skeletal metastases or local tumor invasion into bone and focuses on mammary and prostate cancer, lymphoma, multiple myeloma, head and neck squamous cell carcinoma, and miscellaneous tumors that metastasize to bone.

Effect of methotrexate on collagen-induced arthritis assessed by micro-computed tomography and histopathological examination in female rats

We tested the hypothesis that micro-computed tomography (micro-CT) analysis provides a better quantitative readout of the therapeutic potential of methotrexate (MTX) for treating collagen-induced arthritis (CIA) in rats and compared to conventional histopathological examination. Rats were divided into three groups: Group 1 (G1) was treated with 0.9% saline, whereas groups 2 (G2) and 3 (G3) were boosted with type II collagen at days 0 and 7. Following the first collagen immunization, rats in G1 and G2 were treated with 0.9% saline and those in G3 were treated with 1.5 mg/kg MTX from day 14 to 28. All rats were sacrificed on day 28, at which point and all hind knee joints were analyzed by micro-CT and histopathological examination. Micro-CT analyses showed that bone volume and trabecular number were significantly decreased in G2 and G3 compared to G1 (p<0.01), as was percent bone volume (p<0.05 and p<0.01, respectively). However, bone surface/bone volume was significantly increased in G2 and G3 compared to G1 (p<0.05 and p<0.01, respectively). Trabecular separation was significantly increased in G3 compared to G1 (p<0.05). Histopathological examination showed that knee joints of rats in G2 and G3 showed severe joint destruction with inflammatory cell infiltration. However, cartilage destruction was slightly reduced in G3 compared to G2. Taken together, these results suggest that MTX treatment reduced cartilage destruction in rats with CIA, and micro-CT analyses made it possible to quantify arthritic bony lesion.

Micro-computed tomography evaluation and pathological analyses of female rats with collagen-induced arthritis

Imaging techniques have been introduced to assess the efficacy and toxicity of developing pharmaceuticals. The purpose of this study was to perform a comprehensive characterization of collagen-induced arthritis (CIA) in rats using micro-computed tomography (micro-CT) and to compare the results with data from conventional pathological examination. Arthritis was induced by collagen in 24 female Wistar rats. Micro-CT and pathological analyses were performed to assess arthritis progression. Micro-CT analysis showed marked joint destruction occurring in a time-dependent manner following collagen administration. Bone volume was significantly decreased in the tibia at weeks 3 and 4 compared to week 0 (p < 0.05 and p < 0.01, respectively). Additionally, percent bone volume was significantly reduced in the tibia at week 4 compared to week 0 (p < 0.05). In contrast, bone surface/bone volume and trabecular separation were significantly increased in the tibia of the animals at week 4 compared to week 0 (p < 0.05). Severe joint destruction with extensive inflammation, erosion of cartilage and bone, and infiltration of inflammatory cells were observed in the knee joints of the collagen-treated rats. Taken together, micro-CT made it possible to quantify CIA lesions and should be performed with pathological examination in rats.

Imaging preclinical tumour models: improving translational power

Recent developments and improvements of multimodal imaging methods for use in animal research have substantially strengthened the options of in vivo visualization of cancer-related processes over time. Moreover, technological developments in probe synthesis and labelling have resulted in imaging probes with the potential for basic research, as well as for translational and clinical applications. In addition, more sophisticated cancer models are available to address cancer-related research questions. This Review gives an overview of developments in these three fields, with a focus on imaging approaches in animal cancer models and how these can help the translation of new therapies into the clinic.

Real-time assessment of tissue hypoxia in vivo with combined photoacoustics and high-frequency ultrasound

Purpose: In preclinical cancer studies, non-invasive functional imaging has become an important tool to assess tumor development and therapeutic effects. Tumor hypoxia is closely associated with tumor aggressiveness and is therefore a key parameter to be monitored. Recently, photoacoustic (PA) imaging with inherently co-registered high-frequency ultrasound (US) has reached preclinical applicability, allowing parallel collection of anatomical and functional information. Dual-wavelength PA imaging can be used to quantify tissue oxygen saturation based on the absorbance spectrum differences between hemoglobin and deoxyhemoglobin.

Experimental Design: A new bi-modal PA/US system for small animal imaging was employed to test feasibility and reliability of dual-wavelength PA for measuring relative tissue oxygenation. Murine models of pancreatic and colon cancer were imaged, and differences in tissue oxygenation were compared to immunohistochemistry for hypoxia in the corresponding tissue regions.

Results: Functional studies proved feasibility and reliability of oxygenation detection in murine tissue in vivo. Tumor models exhibited different levels of hypoxia in localized regions, which positively correlated with immunohistochemical staining for hypoxia. Contrast-enhanced imaging yielded complementary information on tissue perfusion using the same system.

Conclusion: Bimodal PA/US imaging can be utilized to reliably detect hypoxic tumor regions in murine tumor models, thus providing the possibility to collect anatomical and functional information on tumor growth and treatment response live in longitudinal preclinical studies.

MicroSPECT and MicroPET Imaging of Small Animals for Drug Development

The process of drug discovery and development requires substantial resources and time. The drug industry has tried to reduce costs by conducting appropriate animal studies together with molecular biological and genetic analyses. Basic science research has been limited to in vitro studies of cellular processes and ex vivo tissue examination using suitable animal models of disease. However, in the past two decades new technologies have been developed that permit the imaging of live animals using radiotracer emission, Xrays, magnetic resonance signals, fluorescence, and bioluminescence. The main objective of this review is to provide an overview of small animal molecular imaging, with a focus on nuclear imaging (single photon emission computed tomography and positron emission tomography). These technologies permit visualization of toxicodynamics as well as toxicity to specific organs by directly monitoring drug accumulation and assessing physiological and/or molecular alterations. Nuclear imaging technology has great potential for improving the efficiency of the drug development process.