Comparison of noninvasive fluorescent and bioluminescent small animal optical imaging

Optical imaging is a modality that is cost-effective, rapid, easy to use, and can be readily applied to studying disease processes and biology in vivo. For this study, we used a green fluorescent protein (GFP)- and luciferase-expressing mouse tumor model to compare and contrast the quantitative and qualitative capabilities of a fluorescent reporter gene (GFP) and a bioluminescent reporter gene (luciferase). We describe the relationship between tumor volume, tumor mass, and bioluminescent/fluorescent intensity for both GFP and luciferase. Bioluminescent luciferase imaging was shown to be more sensitive than fluorescent GFP imaging. Luciferase-expressing tumors were detected as early as 1 day after tumor cell inoculation, whereas GFP-expressing tumors were not detected until 7 days later. Both bioluminescent and fluorescent intensity correlated significantly and linearly with tumor volume and tumor weight, as measured by caliper. Compared to bioluminescent imaging, fluorescent imaging does not require the injection of a substrate and may be appropriate for applications where sensitivity is not as critical. Knowing the relative strengths of each imaging modality will be important in guiding the decision to use fluorescence or bioluminescence.     

人宫颈癌细胞Hela移植模型肿瘤生长的荧光分析和卡尺测量的比较

目的建立稳定表达绿色荧光蛋白的人宫颈癌细胞系,建立移植瘤模型并比较移植模型肿瘤生长的荧光分析和卡尺测量的优缺点。方法以Lipofectamine 2000介导chickenβ-actin-GFP-NEO转染人宫颈癌细胞Hela,经梯度浓度G418筛选获得稳定表达绿色荧光蛋白的细胞克隆并扩大培养。BALB/cA-nu裸鼠皮下接种1×10^6个发光细胞使其成瘤,利用活体荧光成像系统和游标卡尺观察肿瘤的生长情况。结果获得了稳定表达GFP的人宫颈癌细胞株,将其接种到裸鼠体内可成瘤。活体荧光成像观察发现,1至3周随着肿瘤体积逐渐增大,平均荧光光子数逐渐增加;4周时随着肿瘤出现明显坏死,平均荧光光子数呈现下降趋势,而游标卡尺测量结果显示肿瘤在4至5周仍然不断的增大。结论绿色荧光蛋白能够在人宫颈癌细胞Hela中长期稳定表达,用绿色荧光蛋白标记的人宫颈癌细胞Hela建立的裸鼠肿瘤模型可以为人宫颈癌研究提供理想的实验材料,应用小动物活体成像系统能够客观定量评价活的肿瘤细胞在动物体内的生长情况,而不是肿瘤体积的变化。     

慢病毒介导荧光素酶表达的人鼻咽癌细胞小鼠模型的建立

目的：建立荧光素酶标记的人鼻咽癌细胞裸鼠模型,活体成像系统监测肿瘤的生长并与肿瘤的体积进行对比。方法：构建表达荧光素酶基因2（1uc2）的慢病毒载体,与辅助质粒共转染293T细胞以制备慢病毒,感染人鼻咽癌SUNEl细胞后经嘌呤霉素筛选获得表达luc2的细胞株。活体成像设备体外检测不同数量细胞的发光强度,最后以5×10 6个细胞皮下接种BALB／cnu／nu裸鼠,活体成像系统动态记录接种后肿瘤的信号并与肿瘤的体积对比。结果：成功构建慢病毒表达质粒pLenti．1uc2并包装出慢病毒颗粒,病毒感染后嘌呤霉素筛选6天得到鼻咽癌细胞株SUNEl一luc2。细胞株传代后有稳定的发光强度,且经活体检测的每秒光子数与细胞数成正相关（R2=0．96）;活体成像观察发现裸鼠接种第2天接种部位的发光强度就达到3-2×10^8,而且成瘤过程中发光强度的变化与肿瘤大小一致。结论：成功构建适用于活体成像的人鼻咽癌SUNEl细胞的裸鼠成瘤模型,该模型从细胞接种开始即可有效动态监测鼻咽癌皮下瘤的生长及转移,从而为鼻咽癌的成瘤机制及药物干预研究提供一个新的手段。     

2-Nitroimidazole-tricarbocyanine conjugate as a near-infrared fluorescent probe for in vivo imaging of tumor hypoxia

We developed a novel near-infrared (NIR) fluorescent probe, GPU-167, for in vivo imaging of tumor hypoxia. GPU-167 comprises a tricarbocyanine dye as an NIR fluorophore and two 2-nitroimidazole moieties as exogenous hypoxia markers that undergo bioreductive activation and then selective entrapment in hypoxic cells. After treatment with GPU-167, tumor cells contained significantly higher levels of fluorescence in hypoxia than in normoxia. In vivo fluorescence imaging specifically detected GPU-167 in tumors 24 h after administration. Ex vivo analysis revealed that fluorescence showed a strong correlation with hypoxia inducible factor (HIF)-1 active hypoxic regions. These data suggest that GPU-167 is a promising in vivo optical imaging probe for tumor hypoxia.     

Caliper and ultrasonographic measurements of bovine testicles and a mathematical formula for determining testicular volume and weight in vivo

This study quantified the relationship between calibrated caliper and ultrasonographic derived measurements of bovine testicles in vivo with actual testicular length, width, volume and weight. The prolate spheroid formula was tested to accurately predict testicular volume and a modification to predict weight. Ten bulls were employed to derive caliper and ultrasound testicle (n = 20) length and width measurements in vivo. Caliper length measurements were more reliable than ultrasound derived lengths, with correlations of r2 = 0.8023; P < 0.05 and r2 = 0.5111; P < 0.05, respectively. Width for both the calipers and ultrasound measurements when compared to actual width measurements were r2 = 0.7313; P < 0.05 and r2 = 0.8310; P < 0.05, respectively. The prolate spheroid formula is reliable in determining testicle (n = 116) volume (r2 = 0.8928; P < 0.05). Testicular volume and weight are highly correlated (r2 = 0.9776; P < 0.05); therefore, a modification of the prolate spheroid formula was used to predict weight (r2 = 0.9084; P < 0.05) against the actual weight. Caliper-derived length and width measurements used in the prediction of volume and weight had correlation coefficients against actual volume and weight of r2 = 0.5497; P < 0.05 and r2 = 0.6340; P < 0.05, respectively. Ultrasound in vivo measurements for prediction of testicular volume and testicular weight had a correlation of r2 = 0.3276; P < 0.05 and r2 = 0.6249; P < 0.05, respectively. A testicular (n = 116) length to width ratio of 1.8:1 (SEM = 0.01) was determined for both slaughterhouse and castrated animals. Caliper measurements are reliable, inexpensive and much simpler to obtain than ultrasound determinations for in vivo testicle length, width, volume and weight. The two-dimensional measurement of length and width would be a more accurate predictor of testicle volume and weight than the one-dimensional measurement of scrotal circumference (SC), especially in bulls with variation in testicular shape.     

Near-infrared fluorescence imaging of mammalian cells and xenograft tumors with SNAP-tag

Fluorescence in the near-infrared (NIR) spectral region is suitable for in vivo imaging due to its reduced background and high penetration capability compared to visible fluorescence. SNAP(f) is a fast-labeling variant of SNAP-tag that reacts with a fluorescent dye-conjugated benzylguanine (BG) substrate, leading to covalent attachment of the fluorescent dye to the SNAP(f). This property makes SNAP(f) a valuable tool for fluorescence imaging. The NIR fluorescent substrate BG-800, a conjugate between BG and IRDye 800CW, was synthesized and characterized in this study. HEK293, MDA-MB-231 and SK-OV-3 cells stably expressing SNAP(f)-Beta-2 adrenergic receptor (SNAP(f)-ADRβ2) fusion protein were created. The ADRβ2 portion of the protein directs the localization of the protein to the cell membrane. The expression of SNAP(f)-ADRβ2 in the stable cell lines was confirmed by the reaction between BG-800 substrate and cell lysates. Microscopic examination confirmed that SNAP(f)-ADRβ2 was localized on the cell membrane. The signal intensity of the labeled cells was dependent on the BG-800 concentration. In vivo imaging study showed that BG-800 could be used to visualize xenograph tumors expressing SNAP(f)-ADRβ2. However, the background signal was relatively high, which may be a reflection of non-specific accumulation of BG-800 in the skin. To address the background issue, quenched substrates that only fluoresce upon reaction with SNAP-tag were synthesized and characterized. Although the fluorescence was successfully quenched, in vivo imaging with the quenched substrate CBG-800-PEG-QC1 failed to visualize the SNAP(f)-ADRβ2 expressing tumor, possibly due to the reduced reaction rate. Further improvement is needed to apply this system for in vivo imaging.     

Correlation of in vivo testicle and seminal vesicle size with post mortem dimensions in bulls

This study was conducted to quantify the relationships between in vivo measurements of testicular and seminal vesicle size and post mortem size of these organs in 30 Santa Gertrudis bulls. The in vivo measurements of testicles were obtained by transrectal ultrasonography and palpation per rectum, while scrotal circumference was measured by scrotal tape. Linear post mortem dimensions were obtained by direct measurements of the excised organs. Volume was assessed by water displacement while the testicles were weighed. Seminal vesicle length, determined by palpation, had the highest correlation with post mortem measurements (r = 0.70; P = 0.0001). Accurate estimation of the thickness of the vesicles (1.47 vs 1.55 cm for in vivo and post mortem, respectively) was performed by ultrasonograph. Of all seminal vesicle linear measurements, width had the highest correlations with volume measured by water displacement (r = 0.67; P = 0.0001 and r = 0.38; P = 0.04 for post mortem and in vivo, respectively). Testicular diameter was accurately measured by ultrasonography (5.54 vs 4.58 cm in vivo and post mortem, respectively) and was highly correlated (range r = 0.84 to 0.89; P = 0.0001) with post mortem measurements of testicular volume, weight and circumference. The correlation between scrotal circumference and diameter of the testicle was 0.75 (P = 0.0001). The correlations of testicular diameter measured by ultrasound with the post mortem measurements of testicular weight and circumference were similar to the correlations between scrotal circumference and those 2 post mortem measurements. We conclude that palpation of vesicle length is highly correlated with volume of the seminal vesicle in situ. Individual linear measurements do not seem to be an accurate predictor of the relativ size of the seminal vesicle. Furthermore, ultrasonography does not seem to be a more accurate measure of testicular size than scrotal circumference for evaluation of breeding soundness.     

Multimodality imaging of somatostatin receptor-positive tumors with nuclear and bioluminescence imaging

Multimodal bioluminescence (BLI) and single-photon emission computed tomography/computed tomography (SPECT/CT) imaging were investigated as means to monitor somatostatin receptor subtype 2 (SST2)-positive neuroendocrine tumors as both a subcutaneously implanted and a liver metastasis animal model in mice and rats. Ultimately, such a model will be of use for studying SST2-targeted peptide receptor radionuclide therapy (PRRT). CA20948 cells were transfected with a green fluorescent protein/luciferase plasmid construct. Cells were inoculated subcutaneously in the shoulder of nude mice: nontransfected cells in the left shoulder and transfected cells in the right shoulder. BLI, SPECT/CT imaging, biodistribution analysis, and ex vivo autoradiography of the tumors were performed. BLI and SPECT/CT imaging were also performed on an intrahepatic tumor model in the rat. Caliper volume measurement of transfected tumors could be correlated with BLI measurements (R2 = .76). SPECT/CT imaging showed high levels of accumulation of 111In-DTPA-octreotide in control and transfected tumors, which was confirmed by biodistribution analysis and autoradiography. Subcapsular inoculation of transfected cells in rat liver resulted in an intrahepatic tumor, which could be visualized by both SPECT/CT and BLI. Transfection of CA20948 tumor cells did not alter the growth properties of the cell line or the expression of SST2. Transfected tumors could be clearly visualized by BLI and SPECT/CT imaging. The transfected SST2-positive tumor cell line could represent a novel preclinical model for tumor monitoring in studies that aim at further optimizing PRRT for neuroendocrine tumors.     

On-line bioprocess monitoring with a multi-wavelength fluorescence sensor using multivariate calibration

Cultivations of Pseudomonas fluorescens were monitored with a multi-wavelength on-line fluorescence sensor. The multi-wavelength fluorometer used excitation light from 270 to 550 nm with 20 nm steps and measured fluorescence emission from 310 to 590 nm. The fluorescence, on-line exhaust gas measurements and off-line analysis of nitrate, succinate, optical density and protein were compared chemometrically by multivariate calibration, i.e. computing partial least square (PLS) regression models. Based on the multivariate regression models, it was possible to determine CO2 and O2 composition in the exhaust gas (the correlation coefficients, R2 between the predicted values by the PLS model and the measured values was 0.97 for CO(2) and 0.97 for O2, respectively). Also to make quantitative determinations of succinate (R(2) = 0.97), protein (R(2) = 0.94), optical density (R(2) = 1.0) and nitrate (R(2) = 0.98) in the medium based on the fluorescence spectra. Only a limited data set was available but the results indicated that the sensor could indirectly determine non-fluorescent compounds, i.e. nitrate and succinate, which probably is due to the stoichiometric relationship between fluorescent cellular components and non-fluorescent compounds. Consequently multi-wavelength fluorescence is an interesting technique for a wide range of applications.     

In vivo resolution of multiexponential decays of multiple near-infrared molecular probes by fluorescence lifetime-gated whole-body time-resolved diffuse optical imaging

The biodistribution of two near-infrared fluorescent agents was assessed in vivo by time-resolved diffuse optical imaging. Bacteriochlorophyll a (BC) and cypate-glysine-arginine-aspartic acid-serine-proline-lysine-OH (Cyp-GRD) were administered separately or combined to mice with subcutaneous xenografts of human breast adenocarcinoma and slow-release estradiol pellets for improved tumor growth. The same excitation (780 nm) and emission (830 nm) wavelengths were used to image the distinct fluorescence lifetime distribution of the fluorescent molecular probes in the mouse cancer model. Fluorescence intensity and lifetime maps were reconstructed after raster-scanning whole-body regions of interest by time-correlated single-photon counting. Each captured temporal point-spread function (TPSF) was deconvolved using both a single and a multiexponental decay model to best determine the measured fluorescence lifetimes. The relative signal from each fluorophore was estimated for any region of interest included in the scanned area. Deconvolution of the individual TPSFs from whole-body fluorescence intensity scans provided corresponding lifetime images for comparing individual component biodistribution. In vivo fluorescence lifetimes were determined to be 0.8 ns (Cyp-GRD) and 2 ns (BC). This study demonstrates that the relative biodistribution of individual fluorophores with similar spectral characteristics can be compartmentalized by using the time-domain fluorescence lifetime gating method.     

Near-infrared fluorescence-labeled anti-PD-L1-mAb for tumor imaging in human colorectal cancer xenografted mice

The expression of programmed death ligand-1 (PD-L1) in tumor has been used as a biomarker to predict the anti-PD-L1 immunotherapy response. To develop a noninvasive imaging technique to monitor the dynamic changes in PD-L1 expression in colorectal cancer (CRC), we labeled an anti-PD-L1 monoclonal antibody with near-infrared (NIR) dye and tested the ability of the NIR-PD-L1-mAb probe to monitor the PD-L1 expression in CRC-xenografted mice by performing optical imaging. Consistent with the expression levels of PD-L1 protein in three CRC cell lines in vitro by flow cytometry and Western blot analyses, our in vivo imaging showed the highest fluorescence signal of the xenografted tumors in mice bearing SW620 CRC cells, followed by tumors derived from SW480 and HCT8 cell lines. We detected the highest fluorescent intensity of the tumor at 120 hours after injection of NIR-PD-L1-mAb. The highest fluorescence intensity was seen in the tumor, followed by the spleen and the liver in SW620 xenografted mice. In SW480 and HCT8 xenografted mice, however, the highest fluorescent signals were detected in the spleen, followed by the liver and the tumor. Our findings indicate that SW620 cells express a higher level of PD-L1, and the NIR-PD-L1-mAb binding to PD-L1 on the surface of CRC cells was specific. The technique was safe and could provide valuable information on PD-L1 expression of the tumor for development of a therapeutic strategy of personized targeted immunotherapies as well as treatment response of patients with CRC.     

hNIS-IRES-eGFP dual reporter gene imaging

The human and rodent sodium iodide symporters (NIS) have recently been cloned and are being investigated as potential therapeutic and reporter genes. We have extended this effort by constructing an internal ribosomal entry site (IRES)-linked human NIS (hNIS)-enhanced green fluorescent protein (eGFP) hybrid reporter gene for both nuclear and optical imaging. A self-inactivating retroviral vector, termed pQCNIG, containing hNIS-IRES-eGFP dual reporter gene, driven by a constitutive CMV promoter, was constructed and used to generate RG2-pQCNIG cells and RG2-pQCNIG tumors. 131I-iodide and 99mTcO4-pertechnetate accumulation studies plus fluorescence microscopy and intensity assays were performed in vitro, and gamma camera imaging studies in RG2-pQCNIG and RG2 tumor-bearing athymic rats were performed. RG2-pQCNIG cells expressed high levels of hNIS protein and showed high intensity of eGFP fluorescence compared with RG2 wild-type cells. RG2-pQCNIG cells accumulated Na131I and 99mTcO4- to a 50:1 and a 170:1 tissue/medium ratio at 10 min, compared with 0.8:1.2 tissue/medium ratio in wild-type RG2 cells. A significant correlation between radiotracer accumulation and eGFP fluorescence intensity was demonstrated. RG2-pQCNIG and RG2 tumors were readily differentiated by in vivo gamma camera imaging; radiotracer uptake increased in RG2-pQCNIG but declined in RG2 tumors over the 50-min imaging period. Stomach and thyroid were the major organs of radionuclide accumulation. The IRES-linked hNIS-eGFP dual reporter gene is functional and stable in transduced RG2-pQCNIG cells. Optical and nuclear imaging of tumors produced from these cell lines provides the opportunity to monitor tumor growth and response to therapy. These studies indicate the potential for a wider application of hNIS reporter imaging and translation into patient studies using radioisotopes that are currently available for human use for both SPECT and PET imaging.     

Metabolic imaging of tumors using intrinsic and extrinsic fluorescent markers

One of the biochemical "hallmarks" of malignancy is enhanced tumor glycolysis, which is primary due to the overexpression of glucose transporters (GLUTs) and the increased activity of mitochondria-bound hexokinase in tumors. Easy methods for assessing glucose utilization in vitro and in vivo should find widespread application in biological and biomedical studies, as illustrated by the adoption of FDG PET imaging in medicine. We have recently synthesized a new NIR fluorescent pyropheophorbide conjugate of 2-deoxyglucose (2DG), Pyro-2DG, as a GLUT-targeted photosensitizer. In this study, we have evaluated the in vivo uptake of Pyro-2DG and found that Pyro-2DG selectively accumulated in two tumor models, 9L glioma in the rat and c-MYC-induced mammary tumor in the mouse, compared to surrounding normal muscle tissues at a ratio of about 10:1. By simultaneously performing redox ratio and fluorescence imaging, a high degree of correlation between the PN/(Fp+PN) redox ratio, where PN denotes reduced pyridine nucleotides (NADH) and Fp denotes oxidized flavoproteins, and the Pyro-2DG uptake was found in both murine tumor models, indicating that Pyro-2DG could serve as an extrinsic NIR fluorescent metabolic index for the tumors. The fact that only a low level of correlation was observed between the redox ratio and the uptake of Pyro-acid (the free fluorophore without the 2-deoxyglucose moiety) supports the hypothesis that Pyro-2DG is an index of the mitochondrial status (extent of PN reduction) of a tumor.     

Arthritis imaging using a near-infrared fluorescence folate-targeted probe

A recently developed near-infrared fluorescence-labeled folate probe (NIR2-folate) was tested for in vivo imaging of arthritis using a lipopolysaccharide intra-articular injection model and a KRN transgenic mice serum induction mouse model. In the lipopolysaccharide injection model, the fluorescence signal intensity of NIR2-folate (n = 12) and of free NIR2 (n = 5) was compared between lipopolysaccharide-treated and control joints. The fluorescence signal intensity of the NIR2-folate probe at the inflammatory joints was found to be significantly higher than the control normal joints (up to 2.3-fold, P < 0.001). The NIR2-free dye injection group showed a persistent lower enhancement ratio than the NIR2-folate probe injection group. Excessive folic acid was also given to demonstrate a competitive effect with the NIR2-folate. In the KRN serum transfer model (n = 4), NIR2-folate was applied at different time points after serum transfer, and the inflamed joints could be detected as early as 30 hours after arthritogenic antibody transfer (1.8-fold increase in signal intensity). Fluorescence microscopy, histology, and immunohistochemistry validated the optical imaging results. We conclude that in vivo arthritis detection was feasible using a folate-targeted near-infrared fluorescence probe. This receptor-targeted imaging method may facilitate improved arthritis diagnosis and early assessment of the disease progress by providing an in vivo characterization of active macrophage status in inflammatory joint diseases.     

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.     

Osteopontin-targeted probe detects orthotopic breast cancers using optoacoustic imaging

Improved detection of breast cancer using highly sensitive, tumor-specific imaging would facilitate diagnosis, surveillance and assessment of response to treatment. We conjugated osteopontin peptide to an infrared fluorescent dye to serve as a contrast agent for detection of breast cancer by multispectral optoacoustic tomography (MSOT). Selective binding of the osteopontin-based probe was identified using flow cytometry and near infrared fluorescent imaging in triple negative and HER2 positive breast cancer cell lines in vitro. Osteopontin-750 accumulation was evaluated in vivo using MSOT with secondary confirmation of signal accumulation using near infrared fluorescent imaging. The osteopontin-based probe demonstrated binding to breast cancer cells in vitro. Similarly, after intravenous administration of the osteopontin-750 probe, it accumulated preferentially in the subcutaneous breast tumor in nude mice (557 MSOT a.u. compared to untargeted organs such as kidney (53.7 MSOT a.u.) and liver (32.1 MSOT a.u.). At 2.5 h post-injection, signal intensity within the tumor was 9.7 and 17 times greater in the tumor bed than in the kidney or liver, respectively. Fluorescence imaging ex vivo comparing tumor signal to that of nontarget organs confirmed the results in vivo. MSOT imaging demonstrated selective accumulation of the fluorescent osteopontin targeting probe to tumor sites both in vitro and in vivo, and provided high-resolution images. Further development of this tool is promising for advanced diagnostic imaging, disease surveillance and therapeutic models that limit nontarget toxicity.     

Cellular imaging of inflammation in atherosclerosis using magnetofluorescent nanomaterials

OBJECTIVE: Magnetofluorescent nanoparticles (MFNPs) offer the ability to image cellular inflammation in vivo. To better understand their cellular targeting and imaging capabilities in atherosclerosis, we investigated prototypical dextran-coated near-infrared fluorescent MFNPs in the apolipoprotein E-deficient (apo E-/-) mouse model. METHODS AND RESULTS: In vitro MFNP uptake was highest in activated murine macrophages (p < .001). Apo E-/- mice (n = 11) were next injected with the MFNP (15 mg/kg iron) or saline. In vivo magnetic resonance imaging (MRI) demonstrated strong plaque enhancement by the MFNPs (p < .001 vs. saline), which was confirmed by multimodality ex vivo MRI and fluorescence reflectance imaging. On fluorescence microscopy, MFNPs were found in cellular-rich areas of atheroma and colocalized with immunofluorescent macrophages over endothelial cells and smooth muscle cells (p < .001). CONCLUSIONS: Here we show that (1) the in vitro and in vivo cellular distribution of atherosclerosis-targeted MFNPs can be quantified by using fluorescence imaging methods; (2) in atherosclerosis, dextranated MFNPs preferentially target macrophages; and (3) MFNP deposition in murine atheroma can be noninvasively detected by in vivo MRI. This study thus provides a foundation for using MFNPs to image genetic and/or pharmacological perturbations of cellular inflammation in experimental atherosclerosis and for the future development of novel targeted nanomaterials for atherosclerosis.     

In Vivo Imaging and Quantification of Carbonic Anhydrase IX Expression as an Endogenous Biomarker of Tumor Hypoxia

Carbonic anhydrase IX (CA IX) is a transmembrane protein that has been shown to be greatly upregulated under conditions of hypoxia in many tumor cell lines. Tumor hypoxia is associated with impaired efficacy of cancer therapies making CA IX a valuable target for preclinical and diagnostic imaging. We have developed a quantitative in vivo optical imaging method for detection of CA IX as a marker of tumor hypoxia based on a near-infrared (NIR) fluorescent derivative of the CA IX inhibitor acetazolamide (AZ). The agent (HS680) showed single digit nanomolar inhibition of CA IX as well as selectivity over other CA isoforms and demonstrated up to 25-fold upregulation of fluorescent CA IX signal in hypoxic versus normoxic cells, which could be blocked by 60%–70% with unlabeled AZ. CA IX negative cell lines (HCT-116 and MDA-MB-231), as well as a non-binding control agent on CA IX positive cells, showed low fluorescent signal under both conditions. In vivo FMT imaging showed tumor accumulation and excellent tumor definition from 6–24 hours. In vivo selectivity was confirmed by pretreatment of the mice with unlabeled AZ resulting in >65% signal inhibition. HS680 tumor signal was further upregulated >2X in tumors by maintaining tumor-bearing mice in a low oxygen (8%) atmosphere. Importantly, intravenously injected HS680 signal was co-localized specifically with both CA IX antibody and pimonidazole (Pimo), and was located away from non-hypoxic regions indicated by a Hoechst stain. Thus, we have established a spatial correlation of fluorescence signal obtained by non-invasive, tomographic imaging of HS680 with regions of hypoxia and CA IX expression. These results illustrate the potential of HS680 and combined with FMT imaging to non-invasively quantify CA IX expression as a hypoxia biomarker, crucial to the study of the underlying biology of hypoxic tumors and the development and monitoring of novel anti-cancer therapies.     

In vivo time domain optical imaging of renal ischemia-reperfusion injury: discrimination based on fluorescence lifetime

Fluorescence lifetime is an intrinsic parameter of the fluorescent probe, independent of the probe concentration but sensitive to changes in the surrounding microenvironment. Therefore, fluorescence lifetime imaging could potentially be applied to in vivo diagnostic assessment of changes in the tissue microenvironment caused by disease, such as ischemia. The aim of this study was to evaluate the utility of noninvasive fluorescence lifetime imaging in distinguishing between normal and ischemic kidney tissue in vivo. Mice were subjected to 60-minute unilateral kidney ischemia followed by 6-hour reperfusion. Animals were then injected with the near-infrared fluorescence probe Cy5.5 or saline and imaged using a time-domain small-animal optical imaging system. Both fluorescence intensity and lifetime were acquired. The fluorescence intensity of Cy5.5 was clearly reduced in the ischemic compared with the contralateral kidney, and the fluorescence lifetime of Cy5.5 was not detected in the ischemic kidney, suggesting reduced kidney clearance. Interestingly, the two-component lifetime analysis of endogenous fluorescence at 700 nm distinguished renal ischemia in vivo without the need for Cy5.5 injection for contrast enhancement. The average fluorescence lifetime of endogenous tissue fluorophores was a sensitive indicator of kidney ischemia ex vivo. The study suggests that fluorescence lifetime analysis of endogenous tissue fluorophores could be used to discriminate ischemic or necrotic tissues by noninvasive in vivo or ex vivo organ imaging.     

Visualization of pulmonary inflammation using noninvasive fluorescence molecular imaging.

The ability to visualize molecular processes and cellular regulators of complex pulmonary diseases such as asthma, chronic obstructive pulmonary disease (COPD), or adult respiratory distress syndrome (ARDS), would aid in the diagnosis, differentiation, therapy assessment and in small animal-based drug-discovery processes. Herein we report the application of normalized transillumination and fluorescence molecular tomography (FMT) for the noninvasive quantitative imaging of the mouse lung in vivo. We demonstrate the ability to visualize and quantitate pulmonary response in a murine model of LPS-induced airway inflammation. Twenty-four hours prior to imaging, BALB/c female mice were injected via tail vein with 2 nmol of a cathepsin-sensitive activatable fluorescent probe (excitation: 750 nm; emission: 780 nm) and 2 nmol of accompanying intravascular agent (excitation: 674 nm; emission: 694 nm). Six hours later, the mice were anesthetized with isoflurane and administered intranasal LPS in sterile 0.9% saline in 25 microl aliquots (one per nostril). Fluorescence molecular imaging revealed the in vivo profile of cysteine protease activation and vascular distribution within the lung typifying the inflammatory response to LPS insult. Results were correlated with standard in vitro laboratory tests (Western blot, bronchoalveolar lavage or BAL analysis, immunohistochemistry) and revealed good correlation with the underlying activity. We demonstrated the capacity of fluorescence tomography to noninvasively and longitudinally characterize physiological, cellular, and subcellular processes associated with inflammatory disease burden in the lung. The data presented herein serve to further evince fluorescence molecular imaging as a technology highly appropriate for the biomedical laboratory.