Ratio imaging of enzyme activity using dual wavelength optical reporters

The design of near-infrared fluorescent (NIRF) probes that are activated by specific proteases has, for the first time, allowed enzyme activity to be imaged in vivo. In the current study, we report on a method of imaging enzyme activity using two fluorescent probes that, together, provide improved quantitation of enzymatic activity. The method employs two chemically similar probes that differ in their degradability by cathepsin B. One probe consists of the NIRF dye Cy5.5 attached to a particulate carrier, a crosslinked iron oxide nanoparticle (CLIO), through cathepsin B cleavable L-arginyl peptides. A second probe consists of Cy3.5 attached to a CLIO through proteolytically resistant D-arginyl peptides. Using mixtures of the two probes, we have shown that the ratio of Cy5.5 to Cy3.5 fluorescence can be used to determine levels of cathepsin B in the environment of nanoparticles with macrophages in suspension. After intravenous injection, tissue fluorescence from the nondegradable Cy3.5-D-arginyl probe reflected nanoparticle accumulation, while fluorescence of the Cy5.5-L-arginyl probe was dependent on both accumulation and activation by cathepsin B. Dual wavelength ratio imaging can be used for the quantitative imaging of a variety of enzymes in clinically important settings, while the magnetic properties of the probes allow their detection by MR imaging.     

Oleyl-chitosan nanoparticles based on a dual probe for optical/MR imaging in vivo

Oleic acid-conjugated chitosan (oleyl-chitosan) is a powerful platform for encapsulating oleic acid-decorated iron oxide nanoparticles (ION), resulting in a good magnetic resonance imaging (MRI) probe. Oleyl-chitosan could self-assemble into core-shell structures in aqueous solution and provide the effective core compartment for loading ION. ION-loaded oleyl-chitosan nanoparticles showed good enhanced MRI sensitivity in a MR scanner. Cy5.5 dye was accessed to the oleyl-chitosan conjugate for near-infrared (NIR) in vivo optical imaging. After intravenous injection of ION-loaded Cy5.5-conjugated oleyl-chitosan (ION-Cy5.5-oleyl-chitosan) nanoparticles in tumor-bearing mice, both NIRF and MR imaging showed the detectable signal intensity and enhancement in tumor tissues via enhanced permeability and retention (EPR) effect. Tumor accumulation of the nanoparticles was confirmed through ex vivo fluorescence images and Prussian blue staining images in tumor tissues. It is concluded that ION-Cy5.5-oleyl-chitosan nanoparticle is highly an effective imaging probe for detecting tumor in vivo.     

In vivo imaging of siRNA delivery and silencing in tumors

With the increased potential of RNA interference (RNAi) as a therapeutic strategy, new noninvasive methods for detection of siRNA delivery and silencing are urgently needed. Here we describe the development of dual-purpose probes for in vivo transfer of siRNA and the simultaneous imaging of its accumulation in tumors by high-resolution magnetic resonance imaging (MRI) and near-infrared in vivo optical imaging (NIRF). These probes consisted of magnetic nanoparticles labeled with a near-infrared dye and covalently linked to siRNA molecules specific for model or therapeutic targets. Additionally, these nanoparticles were modified with a membrane translocation peptide for intracellular delivery. We show the feasibility of in vivo tracking of tumor uptake of these probes by MRI and optical imaging in two separate tumor models. We also used proof-of-principle optical imaging to corroborate the efficiency of the silencing process. These studies represent the first step toward the advancement of siRNA delivery and imaging strategies, essential for cancer therapeutic product development and optimization.     

A dual fluorochrome probe for imaging proteases

Near-infrared fluorescence (NIRF) optical probes have been able to provide a noninvasive assessment of enzyme activity for a number of different enzymes and types of pathology. Here we describe a dual fluorochrome enzyme-activatable probe featuring one NIRF fluorochrome that is activated by protease activity and a second fluorochrome that is protease resistant and serves as an internal standard. The probe was prepared by attaching Cy7 directly to an amino-CLIO, an amine functional cross-linked iron oxide (CLIO) nanoparticle carrier, in a protease resistant manner. Cy5.5 was attached to a protease sensitive polyarginine peptide spacer, also attached to amino-CLIO. In vitro and in vivo the ratio of the Cy5.5 to Cy7 fluorescence was increased by protease, reflecting the increase in Cy5.5 fluorescence by protease in the vicinity of the probe. In vitro and in vivo the absolute values of the Cy5.5 and Cy7 fluorescence reflected lesion size and the distance of lesions from the surface, while the ratio of Cy5.5 to Cy7 fluorescence obtained was constant and independent of lesion size and depth. The dual fluorochrome probe, and related dual wavelength imaging method, represents a novel approach for imaging protease activity in vivo.     

Preparation of a cathepsin D sensitive near-infrared fluorescence probe for imaging.

A variety of proteases are overexpressed or activated during pathogenesis and represent important targets for therapeutic drugs. We have previously shown that optical imaging probes sensitive in the near-infrared fluorescence (NIRF) spectrum can be used for in vivo imaging of enzyme activity. In the current study, we show that these probes can be designed with specificity for specific enzymes, for example, cathepsin D which is known to be overexpressed in many tumors. A NIR cyanine fluorochrome served as the optical reporter and was attached to the amino terminal of an 11 amino acid peptide sequence with specificity for cathepsin D. The peptides were subsequently attached to a synthetic graft copolymer for efficient tumoral delivery. The close spatial proximity of the multiple fluorochromes resulted in quenching of fluorescence in the bound state. A 350-fold signal amplification was observed post cleavage during in vitro testing. Cell culture experiments using a rodent tumor cell line stably transfected with human cathepsin D confirmed enzyme specific activation within cells. This sequence but not a scrambled control sequence showed enzyme specificity in vitro. We conclude that activatable NIRF optical probes can be synthesized to potentially probe for specific enzymes in living organisms.     

Long-circulating near-infrared fluorescence core-cross-linked polymeric micelles: synthesis, characterization, and dual nuclear/optical imaging

We report the synthesis of PEG-coated, core-cross-linked polymeric micelles (CCPMs) derived from an amine-terminated amphiphilic block copolymer, poly(PEG-methacrylate)-b-poly(triethoxysilyl propylmethacrylate). The block copolymer self-assembled to form micellar nanoparticles, and a Cy-7-like near-infrared fluorescence (NIRF) dye was entrapped in the core bearing reactive ethoxysilane functional groups through a subsequent sol-gel process. The fluorescent signal of CCPMs on the molar basis was 16-fold brighter than that of Cy7. With an average diameter of 24 +/- 8.9 nm, CCPMs exhibited a prolonged blood half-life (t1/2,alpha = 1.25 h; t1/2,beta = 46.18 h) and moderate uptake by the mononuclear phagocytic system. Significant accumulation of CCPMs in human breast tumor xenografts allowed noninvasive monitoring of the uptake kinetics with both NIRF optical and gamma imaging techniques. Our data suggest that Cy7-entrapped CCPM nanoparticles are suitable for NIRF imaging of solid tumors and have potential applications in the imaging of tumor-associated molecular markers.     

Improvement of MRI probes to allow efficient detection of gene expression

Recently, it has been demonstrated that magnetic resonance imaging (MRI) utilizing monocrystalline iron oxide nanoparticles (MIONs) targeted to an engineered transferrin receptor enables imaging of gene expression. However, the relatively high doses of iron oxides used indicated the need for improved MR imaging probes to monitor changes in gene expression in vivo. Using alternative conjugation chemistries to link targeting ligands and iron oxide nanoparticles, we present the development and characterization as well as improved receptor binding and MRI detection of a novel imaging probe. Iron oxide nanoparticles with a cross-linked dextran coat were conjugated to transferrin (Tf) through the linker molecule N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) to yield Tf-S-S-CLIO. The characteristics of this conjugate were evaluated in comparison to Tf-MION and Tf-CLIO generated by oxidative activation of the dextran-coat with subsequent reduction of Schiff's base. SPDP conjugation allowed approximately a 4-fold increase in the number of Tf molecules attached per iron oxide nanoparticle and resulted in a more than 10-fold improvement of binding and uptake by cells. This translated into an imaging probe that was 16 times better for imaging gene expression in a cellular MRI assay. This novel probe for MRI may substantially increase the sensitivity for the detection of endogenous or genetically induced transferrin receptor expression in small numbers of cells and may significantly reduce the imaging dose from over 100 mg/kg to doses of iron oxides that are currently used in clinical imaging.     

Near-infrared imaging of flare-up arthritis with native fluorochrome Cy5.5 and albumin-bound Cy5.5

The aim of the study was to visualize chronic experimental arthritis with near-infrared fluorescence imaging (NIRF) in a murine experimental arthritis model of rheumatoid arthritis (RA) (flare-up arthritis). The flare-up arthritis model is a modification of the primary antigen-induced arthritis (AIA) model. NIRF was done for two preparations of the fluorochrome Cy5.5, one native and the other albumin conjugated. Histological features of flare-up arthritis were evaluated.AIA was induced in 16 mice (strain C57/Bl6); flare-up arthritis was induced in a subgroup of eight. On day 7 after induction of flare-up arthritis, four mice received 50 nmol/kg native dye and four mice equimolar concentrations of the dye as albumin-dye conjugate intravenously. NIRF imaging was performed immediately before injection (baseline) and until 72 h thereafter. Arthritis severity was evaluated histologically for primary AIA and flare-up arthritis mice.NIRF imaging revealed higher fluorochrome uptake in all inflamed knees compared to contralateral ones. The signal intensities induced by native Cy5.5 were higher than those generated by albumin-Cy5.5 conjugate. Histological evaluation of arthritic joints showed similar abnormalities in flare-up arthritis and in primary AIA joints.Imaging of flare-up arthritis in the near-infrared range was successful for both fluorochrome preparations, but albumin conjugation prior to injection does not improve the uptake of dye in arthritic joints. Flare-up arthritis is a feasible model of chronic relapse of arthritis in human RA.     

Manufacture of IRDye800CW-coupled Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and their applications in cell labeling and <Emphasis Type="Italic">in vivo</Emphasis> imaging

Background  

In recent years, near-infrared fluorescence (NIRF)-labeled iron nanoparticles have been synthesized and applied in a number of applications, including the labeling of human cells for monitoring the engraftment process, imaging tumors, sensoring the in vivo molecular environment surrounding nanoparticles and tracing their in vivo biodistribution. These studies demonstrate that NIRF-labeled iron nanoparticles provide an efficient probe for cell labeling. Furthermore, the in vivo imaging studies show excellent performance of the NIR fluorophores. However, there is a limited selection of NIRF-labeled iron nanoparticles with an optimal wavelength for imaging around 800 nm, where tissue autofluorescence is minimal. Therefore, it is necessary to develop additional alternative NIRF-labeled iron nanoparticles for application in this area.     

Synthesis of 64Cu-labeled magnetic nanoparticles for multimodal imaging

Complementary imaging modalities provide more information than either method alone can yield and we have developed a dual-mode imaging probe for combined magnetic resonance (MR) and positron emission tomography (PET) imaging. We have developed dual-mode PET/MRI active probes targeted to vascular inflammation and present synthesis of (1) an aliphatic amine polystyrene bead and (2) a novel superparamagnetic iron oxide nanoparticle targeted to macrophages that were both coupled to positron-emitting copper-64 isotopes. The amine groups of the polystyrene beads were directly conjugated with an amine-reactive form (isothiocyanate) of aza-macrocycle 1,4,7,10-tetraazacyclo-dodecane-1,4,7,10-tetraacetic acid (DOTA). Iron oxide nanoparticles are dextran sulfate coated, and the surface was modified to contain aldehyde groups to conjugate to an amine-activated DOTA. Incorporation of chelated Cu-64 to nanoparticles under these conditions, which is routinely used to couple DOTA to macromolecules, was unexpectedly difficult and illustrates that traditional conjugation methods do not always work in a nanoparticle environment. Therefore, we developed new methods to couple Cu-64 to nanoparticles and demonstrate successful labeling to a range of nanoparticle types. We obtained labeling yields of 24% for the amine polystyrene beads and 21% radiolabeling yield for the anionic dextran sulfate iron oxide nanoparticles. The new coupling chemistry can be generalized for attaching chelated metals to other nanoparticle platforms.     

In vivo imaging of tumors with protease-activated near-infrared fluorescent probes

We have developed a method to image tumor-associated lysosomal protease activity in a xenograft mouse model in vivo using autoquenched near-infrared fluorescence (NIRF) probes. NIRF probes were bound to a long circulating graft copolymer consisting of poly-L-lysine and methoxypolyethylene glycol succinate. Following intravenous injection, the NIRF probe carrier accumulated in solid tumors due to its long circulation time and leakage through tumor neovasculature. Intratumoral NIRF signal was generated by lysosomal proteases in tumor cells that cleave the macromolecule, thereby releasing previously quenched fluorochrome. In vivo imaging showed a 12-fold increase in NIRF signal, allowing the detection of tumors with submillimeter-sized diameters. This strategy can be used to detect such early stage tumors in vivo and to probe for specific enzyme activity.     

Noninvasive near-infrared imaging of fluorochromes within the brain of live mice: an in vivo phantom study

Near-infrared fluorescence (NIRF) imaging has great potential for studying physiological and pathophysiological processes noninvasively in several locations of the body. In this study, we evaluated the feasibility of NIRF imaging to visualize fluorescent compounds within the brains of live mice commonly used in brain research. To simulate the presence of a molecular NIRF reporter agent at the site of a lesion, we developed a new in vivo phantom model wherein capsules containing different amounts of an NIRF dye (Cy5.5) were stereotactically implanted deep into the left hemispheres of living mice. To precisely locate the implanted capsules, magnetic resonance imaging (MRI) was performed. Fluorescence reflectance imaging (FRI) and transillumination fluorescence imaging (TFI) were conducted to analyze and compare sensitivity and target-to-background ratios of the two methods. The sensitivities of FRI and TFI to background fluorescence from circulating dye was tested by imaging fluorescent capsules in mice intravenously injected with increasing amounts of long-circulating Cy5.5-dextran. The results show that capsules containing dye amounts as low as 10(-12) mol can be detected. TFI yielded significantly higher target-to-background ratios than FRI at 10(-11) mol (p < .05). Comparatively low amounts of fluorescence in the blood vessels can extinguish the signal. We conclude that keeping the signal from circulating NIRF dye low, NIRF imaging offers high sensitivity in detecting fluorochromes noninvasively within brains of mice, especially by using TFI. This encourages the application of NIRF for molecular imaging in the mouse brain using NIRF reporters.     

In vivo near-infrared imaging of fibrin deposition in thromboembolic stroke in mice

Objectives

Thrombus and secondary thrombosis plays a key role in stroke. Recent molecular imaging provides in vivo imaging of activated factor XIII (FXIIIa), an important mediator of thrombosis or fibrinolytic resistance. The present study was to investigate the fibrin deposition in a thromboembolic stroke mice model by FXIIIa–targeted near-infrared fluorescence (NIRF) imaging.

Materials and Methods

The experimental protocol was approved by our institutional animal use committee. Seventy-six C57B/6J mice were subjected to thromboembolic middle cerebral artery occlusion or sham operation. Mice were either intravenously injected with the FXIIIa-targeted probe or control probe. In vivo and ex vivo NIRF imaging were performed thereafter. Probe distribution was assessed with fluorescence microscopy by spectral imaging and quantification system. MR scans were performed to measure lesion volumes in vivo, which were correlated with histology after animal euthanasia.

Results

In vivo significant higher fluorescence intensity over the ischemia-affected hemisphere, compared to the contralateral side, was detected in mice that received FXIIIa-targeted probe, but not in the controlled mice. Significantly NIRF signals showed time-dependent processes from 8 to 96 hours after injection of FXIIIa-targeted probes. Ex vivo NIRF image showed an intense fluorescence within the ischemic territory only in mice injected with FXIIIa-targeted probe. The fluorescence microscopy demonstrated distribution of FXIIIa-targeted probe in the ischemic region and nearby micro-vessels, and FXIIIa-targeted probe signals showed good overlap with immune-fluorescent fibrin staining images. There was a significant correlation between total targeted signal from in vivo or ex vivo NIRF images and lesion volume.

Conclusion

Non-invasive detection of fibrin deposition in ischemic mouse brain using NIRF imaging is feasible and this technique may provide an in vivo experimental tool in studying the role of fibrin in stroke.     

Dual-wavelength imaging of tumor progression by activatable and targeting near-infrared fluorescent probes in a bioluminescent breast cancer model

Bioluminescence imaging (BLI) has shown its appeal as a sensitive technique for in vivo whole body optical imaging. However, the development of injectable tumor-specific near-infrared fluorescent (NIRF) probes makes fluorescence imaging (FLI) a promising alternative to BLI in situations where BLI cannot be used or is unwanted (e.g., spontaneous transgenic tumor models, or syngeneic mice to study immune effects).In this study, we addressed the questions whether it is possible to detect tumor progression using FLI with appropriate sensitivity and how FLI correlates with BLI measurements. In addition, we explored the possibility to simultaneously detect multiple tumor characteristics by dual-wavelength FLI (~700 and ~800 nm) in combination with spectral unmixing. Using a luciferase-expressing 4T1-luc2 mouse breast cancer model and combinations of activatable and targeting NIRF probes, we showed that the activatable NIRF probes (ProSense680 and MMPSense680) and the targeting NIRF probes (IRDye 800CW 2-DG and IRDye 800CW EGF) were either activated by or bound to 4T1-luc2 cells. In vivo, we implanted 4T1-luc2 cells orthotopically in nude mice and were able to follow tumor progression longitudinally both by BLI and dual-wavelength FLI. We were able to reveal different probe signals within the tumor, which co-localized with immuno-staining. Moreover, we observed a linear correlation between the internal BLI signals and the FLI signals obtained from the NIRF probes. Finally, we could detect pulmonary metastases both by BLI and FLI and confirmed their presence histologically.Taken together, these data suggest that dual-wavelength FLI is a feasible approach to simultaneously detect different features of one tumor and to follow tumor progression with appropriate specificity and sensitivity. This study may open up new perspectives for the detection of tumors and metastases in various experimental models and could also have clinical applications, such as image-guided surgery.     

Magnetic resonance and near-infrared imaging using a novel dual-modality nano-probe for dendritic cell tracking in vivo

Background aimsThe effect of cellular-based immunotherapy is highly correlated with the success of dendritic cells (DCs) homing to the draining lymph nodes (LNs) and interacting with antigen-specific CD4⁺ T cells. In this study, a novel magneto-fluorescent nano-probe was used to track the in vivo migration of DCs to the draining LNs.MethodsA dual-modality nano-probe composed of superparamagnetic iron oxide (SPIO) and near-infrared fluorescent (NIRF) dye (NIR797) was developed, and its magnetic and optical contrasting properties were characterized. DCs generated from mouse bone marrow were co-cultured with the probe at a lower concentration of 10 μg/mL. The cell phenotype and function of DCs were also investigated by fluorescence-activated cell sorting analysis and mixed leukocyte reactivity assay. Labeled DCs were injected into the footpad of C57BL/6 mice. Afterward, magnetic resonance imaging, NIRF imaging, Perls staining and CD11c immunofluorescence were used to observe the migration of the labeled DCs into draining LNs.ResultsThe synthetic SPIO-NIR797 nano-probe had a desirable superparamagnetic and near-infrared behavior. Perls staining showed perfect labeling efficiency. The cell phenotypes, including CD11c, CD80, CD86 and major histocompatibility complex class II, as well as the T-cell activation potential of the mature DCs were insignificantly affected after incubation (P > 0.05). Labeled DCs migrating into LNs could be detected by both magnetic resonance imaging and NIRF imaging simultaneously, which was further confirmed by Perls staining and immunofluorescence.ConclusionsThe novel dual-modality SPIO-NIR797 nano-probe has highly biocompatible characteristics for labeling and tracking DCs, which can be used to evaluate cancer immunotherapy in clinical applications.     

Targeting and cellular trafficking of magnetic nanoparticles for prostate cancer imaging

Antibody-conjugated iron oxide nanoparticles offer a specific and sensitive tool to enhance magnetic resonance (MR) images of both local and metastatic cancer. Prostate-specific membrane antigen (PSMA) is predominantly expressed on the neovasculature of solid tumors and on the surface of prostate cells, with enhanced expression following androgen deprivation therapy. Biotinylated anti-PSMA antibody was conjugated to streptavidin-labeled iron oxide nanoparticles and used in MR imaging and confocal laser scanning microscopic imaging studies using LNCaP prostate cancer cells. Labeled iron oxide nanoparticles are internalized by receptor-mediated endocytosis, which involves the formation of clathrin-coated vesicles. Endocytosed particles are not targeted to the Golgi apparatus for recycling but instead accumulate within lysosomes. In T(1)-weighted MR images, the signal enhancement owing to the magnetic particles was greater for cells with magnetic particles bound to the cell surface than for cells that internalized the particles. However, the location of the particles (surface vs internal) did not significantly alter their effect on T(2)-weighted images. Our findings indicate that targeting prostate cancer cells using PSMA offers a specific and sensitive technique for enhancing MR images.     

Magnetically labeled insulin-secreting cells

Iron oxide nanoparticles have been shown to magnetically label cells in order to visualize them in vivo via MR imaging. This technology has yet to be implemented in insulin secreting cells, thus it is not known whether the presence of these nanoparticles in the cytoplasm of the cells affects insulin secretion. This study investigates the effectiveness and consequence of labeling mouse insulinoma betaTC3 and betaTC-tet cells with monocrystalline iron oxide nanoparticles (MION). Our data show that MION can be internalized in both betaTC3 and betaTC-tet cells following a 24h exposure to 0.02mg/ml MION solution. The metabolic and secretory activities of both MION-labeled cell lines were statistically indistinguishable from sham treatment. Furthermore, cell viability and apoptosis remained constant throughout the cell's exposure to MION. Finally, MR images demonstrated significant contrast between labeled and sham-treated cells. Thus, labeling murine insulinoma cell lines with magnetic iron oxide nanoparticles does not hinder their insulin secretion, while it provides MR imaging contrast.     

Glycol chitosan/heparin immobilized iron oxide nanoparticles with a tumor-targeting characteristic for magnetic resonance imaging

We described the preparation of the glycol chitosan/heparin immobilized iron oxide nanoparticles (composite NPs) as a magnetic resonance imaging agent with a tumor-targeting characteristic. The iron oxide nanoseeds used clinically as a magnetic resonance imaging agent were immobilized into the glycol chitosan/heparin network to form the composite NPs. To induce the ionic interaction between the iron oxide nanoseeds and glycol chitosan, gold was deposited on the surface of iron oxide nanoseeds. After the immobilization of gold-deposited iron oxide NPs into the glycol chitosan network, the NPs were stabilized with heparin based on the ionic interaction between cationic glycol chitosan and anionic heparin. FE-SEM (field emission-scanning electron microscopy) and a particle size analyzer were used to observe the formation of the stabilized composite NPs, and a Jobin-Yvon Ultima-C inductively coupled plasma-atomic emission spectrometer (ICP-AES) was used to measure the contents (%) of formed iron oxide nanoseeds as a function of reaction temperature and formed gold deposited on the iron oxide nanoparticles. We also evaluated the time-dependent excretion profile, in vivo biodistribution, circulation time, and tumor-targeting ability of the composite NPs using a noninvasive NIR fluorescence imaging technology. To observe the MRI contrast characteristic, the composite NPs were injected into the tail veins of tumor-bearing mice to demonstrate their selective tumoral distribution. The MR images were collected with conventional T(2)-weighted spin echo acquisition parameters.     

Formulation of novel lipid-coated magnetic nanoparticles as the probe for in vivo imaging

Background  

Application of superparamagnetic iron oxide nanoparticles (SPIOs) as the contrast agent has improved the quality of magnetic resonance (MR) imaging. Low efficiency of loading the commercially available iron oxide nanoparticles into cells and the cytotoxicity of previously formulated complexes limit their usage as the image probe. Here, we formulated new cationic lipid nanoparticles containing SPIOs feasible for in vivo imaging.     

磁性氧化铁纳米颗粒及其磁共振成像应用

磁性氧化铁纳米颗粒在磁共振成像方面的应用,已经在全世界范围内得到了广泛的关注,相关研究也被各国科学家高度重视.目前,磁性氧化铁纳米颗粒正在从早期的基于被动识别的肝部磁共振造影,快速转向基于主动识别的磁共振分子影像应用.本文将围绕磁性氧化铁纳米颗粒的生物体内应用,着重介绍磁性纳米颗粒的制备及其在疾病诊断,尤其是在肿瘤早期...