Small Animal Imaging System Research Articles

Abstract 2386: TROP2-targeted photoimmunotherapy in experimental human pancreatic cancer

Abstract Background: Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed cancer therapy that employs a selective monoclonal antibody (mAb) conjugated to a photosensitizer phthalocyanine dye, IR700. The complex mAb-IR700 binds to the specific antigen on the cellular membrane, and then NIR light is delivered, leading to rapid and target-selective cell death. The type I trans-membrane protein, TROP2, is found to be expressed at high levels in many epithelial cancers, including pancreatic carcinoma. Further, TROP2 overexpression correlates with poor prognosis and tumor aggressiveness. In this study, we investigated the antitumor effect of TROP2-targeted PIT in an experimental human pancreatic cancer model using anti-TROP2 mAb-IR700 conjugate. Methods: The experiments were performed on TROP2-overexpressing human pancreatic cancer cells (PK-59 and KP-3L) and 3T3/HER2 cells were used as the negative control. Anti-TROP2 antibody (Chiome Bioscience, Tokyo, Japan) was conjugated with IR700 and purified (TROP2-IR700). The expression and localization of TROP2 were determined by fluorescence microscopy and flow cytometry. LIVE/DEAD assay was performed to determine cytotoxicity exerted by NIR light irradiation in vitro. Subsequently, for in vivo studies, PIT was tested on a mouse tumor xenograft model (PK-59 cells). Specifically, tumor-bearing mice were intravenously injected with TROP2-IR700 and tumors were irradiated with NIR laser light, 1 day after the injection. Distribution of TROP2-IR700 was then monitored with small animal imaging system and the antitumor effects were determined by measuring the tumor diameter using a caliper. Additionally, the expression patterns of TROP2 and EGFR in human pancreatic cancer were analyzed by immunohistochemistry, using tissue microarray samples. Results: We found that TROP2-IR700 specifically localized on the cellular membrane as well as on lysosomes, in TROP2-overexpressing PK-59 and KP-3L cells, whereas no specific signals were observed in TROP2-negative 3T3/HER2 cells. Moreover, TROP2-IR700-mediated PIT was able to induce a strong cytotoxic effect in PK-59 and KP-3L cells, which was NIR-light dose dependent. The localization of TROP2-selective IR700 fluorescence was observed in the mouse xenograft, 1 day after intravenous injection with TROP2-IR700, and the tumor growth was significantly inhibited by NIR light irradiation compared to the control groups. Moreover, pancreatic cancer tissue microarray analysis revealed that 80% of the tumors were positive for TROP2 and 50% were positive for EGFR and the expression patterns were independent from each other. Conclusions: We demonstrated that TROP2-IR700-targeted PIT exerts an antitumor effect against TROP2 positive pancreatic cancer, both in vitro and in vivo, and could be a promising therapeutic option for human pancreatic cancer. Citation Format: Takashi Nishimura, Makoto Mitsunaga. TROP2-targeted photoimmunotherapy in experimental human pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2386.

NEMA NU 4-2008 and in vivo imaging performance of RAYCAN trans-PET/CT X5 small animal imaging system

The RAYCAN Trans-PET/CT X5 is a preclinical positron emission tomography and computed tomography (PET/CT) system intended for in vivo imaging of rats and mice, featuring all-digital readout electronics for PET data acquisition.The National Electrical Manufacturers Association (NEMA) NU 4-2008 performance evaluation was conducted on the RAYCAN Trans-PET/CT X5 in addition to assessing in vivo imaging performance of the system on live animals. The performance characteristics of the system were evaluated, including system spatial resolution, count rate performance, sensitivity and image quality. The system imaging performance is assessed in dynamic in vivo PET imaging.The system resolution defined as full width half maximum (FWHM) was 2.07 mm, 2.11 mm and 1.31 mm for the tangential, radial and axial resolution, respectively, at the center of the field of view. The peak noise equivalent count rate (NECR) values measured were 61 kcps at 0.19 MBq ml−1 for the rat size phantom and 126 kcps at 1.53 MBq ml−1 for the mouse size phantom. Scatter fractions were 24% and 14% for the rat and mouse phantom. The measured peak sensitivity of the system was 1.70%. Image quality in static imaging was deemed sufficient based on the image quality phantom study, with average activity concentration of 155 ± 8.6 kBq ml−1 and image uniformity of 5.57% when using two-dimensional filtered backprojection algorithm (2D-FBP). Rods in the image quality phantom were visualized easily up to 2 mm in size. In dynamic in vivo PET imaging, time-activity-curves from several regions were successfully measured, characterizing the radioactivity distribution in myocardial blood pool, liver, left ventricle and the lung.In conclusion, the RAYCAN Trans-PET/CT X5 system can be considered a suitable option for basic imaging needs in preclinical imaging.

Accurate assessment of LV function using the first automated 2D-border detection algorithm for small animals - evaluation and application to models of LV dysfunction

Echocardiography is the most commonly applied technique for non-invasive assessment of cardiac function in small animals. Manual tracing of endocardial borders is time consuming and varies with operator experience. Therefore, we aimed to evaluate a novel automated two-dimensional software algorithm (Auto2DE) for small animals and compare it to the standard use of manual 2D-echocardiographic assessment (2DE). We hypothesized that novel Auto2DE will provide rapid and robust data sets, which are in agreement with manually assessed data of animals.2DE and Auto2DE were carried out using a high-resolution imaging-system for small animals. First, validation cohorts of mouse and rat cine loops were used to compare Auto2DE against 2DE. These data were stratified for image quality by a blinded expert in small animal imaging. Second, we evaluated 2DE and Auto2DE in four mouse models and four rat models with different cardiac pathologies.Automated assessment of LV function by 2DE was faster than conventional 2DE analysis and independent of operator experience levels. The accuracy of Auto2DE-assessed data in healthy mice was dependent on cine loop quality, with excellent agreement between Auto2DE and 2DE in cine loops with adequate quality. Auto2DE allowed for valid detection of impaired cardiac function in animal models with pronounced cardiac phenotypes, but yielded poor performance in diabetic animal models independent of image quality.Auto2DE represents a novel automated analysis tool for rapid assessment of LV function, which is suitable for data acquisition in studies with good and very good echocardiographic image quality, but presents systematic problems in specific pathologies.

Non-invasive in vivo fluorescence imaging of apoptotic retinal photoreceptors

Phosphatidylserine externalization is an early molecular signature for apoptosis. In many retinal degenerative diseases, photoreceptor neurons die by apoptosis. Here, we report utility of the phosphatidylserine-binding conjugate of Bis(zinc(II)-dipicolylamine (Zn-DPA) with Texas-red (PSVue-550) in transiently labeling apoptotic photoreceptors in living pigmented or albino rats and mice with retinal degeneration. Applying PSVue-550 as eyedrop is non-toxic and eliminates need for intraocular injection. PSVue-550 fluorescence specifically and transiently labeling dying retinal photoreceptors is detectable in anesthetized animals using standard retinal or whole small animal imaging systems. Importantly, prior PSVue-550 eyedrop administration and imaging does not affect repeat testing. Altogether, our results establish PSVue-550 imaging as a completely non-invasive method that provides the opportunity to longitudinally monitor retinal photoreceptor cell death in preclinical studies.

Recombinant human calcineurin B inhibits orthotopic hepatocellular carcinoma xenograt growth in mice by promoting apoptosis

Objective: To explore the effects of recombinant human calcineurin B (rhCNB) on hepatocellular carcinoma in mice. Methods: An in vivo mouse model with hepatocellular carcinoma was established, and the mice were randomized into the rhCNB, positive control and vehicle treatments groups. Tumor growth was assessed via bioluminescence using a small animal imaging system. Relative tumor proliferation rate and tumor growth inhibition were calculated. The expression of p53 and caspase-9 proteins in tumors were detected by immunohistochemistry. In vitro, flow cytometry was used to quantify the cell-cycle stages and rate of apoptosis. Western blotting and quantitative real-time PCR assays were used to evaluate the effects of rhCNB on protein and gene expression of CDK1, cyclin B1, p53 and caspase-9. Results: rhCNB at the higher dose significantly reduced tumor growth in vivo and caused tumor cell apoptosis in vitro. The rhCNB at the higher dose was as effective as cisplatin, and was safer. Conclusions: rhCNB has potent pro-apoptotic effects on tumor cells in vivo and in vitro and is well tolerated in vivo.

Photoacoustic and acousto-optic tomography for quantitative and functional imaging

Optical absorption contrast, large imaging depth at ultrasonic resolution, and the potential of functional/quantitative imaging are the features driving the rapid development of photoacoustic (PA) imaging. For quantitative and functional PA imaging, the fluence distribution is required to transform a PA image to a map of absorption coefficients. A suitable method to estimate the fluence for in vivo applications must not require a priori knowledge of the medium optical properties, should work for various illumination conditions, and must be applicable to different PA imaging geometries. Existing methods of estimating fluence in tissue do not meet these requirements simultaneously. Here we present a method to measure the fluence distribution in tissue using acousto-optics (AO) that meets all the above requirements. We developed a PA and AO tomography system for small-animal imaging to investigate the potential and the feasibility of fluence-corrected PA imaging using our method in a single instrument. We performed experiments on phantoms, an ex vivo tissue sample, and freshly sacrificed mice. We demonstrate that the correction for spatial and spectral fluence variations in PA images establishes the direct relation between image value and optical absorption, which in turns improves the quantitative estimation of blood oxygen saturation.

Characterization of three layer depth of interaction PET detectors for small animal imaging

High sensitivity and spatial resolution are two main parameters of each small animal imaging system. Multi-layers phoswich detectors have been developed to measure the depth of interaction and to improve system spatial resolution. In the past, efforts have been made to develop these kinds of detectors with different crystal materials and lengths. In this work, three layers phoswich detectors based on GE Healthcare eXplore VISTA PET scanner geometry composing LYSO, GSO and BGO scintillators with different crystal orders and lengths were investigated to find the optimum case with the highest sensitivity and uniform spatial resolution. All simulations were performed using the Monte Carlo simulation tool, the Geant4 Application for Tomographic Emission (GATE). In order to validate GATE simulation package, the GE eXplore VISTA small animal PET system was modeled and output results were compared with the experimental data. The length of each of the three layers varied, while the total length (LYSO + GSO + BGO) was fixed at 15 mm. The order of these crystal layers was also changed, so that totally we have considered 55 × 6 = 330 different configurations. Using three layer phoswich detector, a 25%–68% improvement in the sensitivity at central slice was found compared to the dual layer VISTA PET scanner, dependent on different detector configurations. In this study, among all posible configurations, detector length permutations with higher efficiency values (12 × 6 = 72 cases) were choosen to evaluate spatial resolution. The radial and tangential spatial resolutions were markedly improved for all studied different detector configurations compared to the VISTA PET scanner. Among all the possible selected detector configurations, LYSO (4 mm) + GSO (4 mm) + BGO (7 mm) and BGO (5 mm) + LYSO (5 mm) + GSO (5 mm) cases gave the best DOI radial and tangential resolutions for an energy threshold of 250 keV, respectively. In the LYSO (4 mm) + GSO (4 mm) + BGO (7 mm) scanner configuration, the radial resolution was kept below 1.154 mm, over 25 mm field of view (FOV). The tangential resolution variations were minimized to less than 1.029 mm, over 25 mm FOV, using the BGO (5 mm) + LYSO (5 mm) + GSO (5 mm) detector type. As a result, our new designed three layers phoswich detectors with excellent DOI resolution will lead to small animal PET scanners with higher sensitivity and uniform spatial resolution across the FOV.

Danhong Injection Enhances the Therapeutic Efficacy of Mesenchymal Stem Cells in Myocardial Infarction by Promoting Angiogenesis

Stem cell-based therapies have the potential to dramatically transform the treatment and prognosis of myocardial infarction (MI), and mesenchymal stem cells (MSCs) have been suggested as a promising cell population to ameliorate the heart remodeling in post-MI. However, poor implantation and survival in ischemic myocardium restrict its efficacy and application. In this study, we sought to use the unique mode of action of Chinese medicine to improve this situation. Surrounding the myocardial infarct area, we performed a multi-point MSC transplantation and administered in conjunction with Danhong injection, which is mainly used for the treatment of MI. Our results showed that the MSC survival rate and cardiac function were improved significantly through the small animal imaging system and echocardiography, respectively. Moreover, histological analysis showed that MSC combined with DHI intervention significantly reduced myocardial infarct size in myocardial infarcted mice and significantly increased MSC resident. To investigate the mechanism of DHI promoting MSC survival and cell migration, PCR and WB experiments were performed. Our results showed that DHI could promote the expression of CXC chemokine receptor 4 in MSC and enhance the expression of stromal cell–derived factor-1 in myocardium, and this effect can be inhibited by AMD3100 (an SDF1/CXCR4 antagonist). Additionally, MSC in combination with DHI interfered with MI in mice and this signifies that when combined, the duo could the expression of vascular endothelial growth factor (VEGF) in the marginal zone of infarction compared with when either MSC or DHI are used individually. Based on these results, we conclude that DHI enhances the residence of MSCs in cardiac tissue by modulating the SDF1/CXCR4 signaling pathway. These findings have important therapeutic implications for Chinese medicine-assisted cell-based therapy strategies.

Stable silencing of dll4 gene suppresses the growth and metastasis of esophagus cancer cells by attenuating Akt phosphorylation.

δ‑Like ligand4 (DLL4) has recently been reported to be involved in the process of cancer angiogenesis and considered to play a vital role in vascular endothelial growth factor (VEGF) signaling, while the role of DLL4 in cancer metastasis and growth has not been systematically studied. In the present study, the esophagus cancer cell line Eca109 was infected invitro with a lentiviral vector loaded with dll4‑shRNA to obtain a stable cell line of DLL4 expression which was downregulated through puromycin screening. The migration and invasion ability of the Eca109 dll4‑shRNA cells were evaluated by scratch and Transwell assays, respectively. The underlying signaling pathway was further explored by western blotting. Subsequently, to explore the role of dll4 in the development of esophagus cancer cells invivo, a xenograft model was established by intraperitoneal injection with Eca109 dll4‑shRNA cells containing luciferase activity in nude mice. Then, small animal imaging system was used to evaluate the volume and metastatic potential of the tumors. Additionally, the overall survival rate of the nude mice was also recorded. Following infection with lentivirus, the expression of DLL4 in the Eca109 cells could be stably silenced through screening with puromycin, which was confirmed by western blotting. The scratch and Transwell assays demonstrated that downregulated DLL4 significantly diminished the aggressive invasion and migration properties of the Eca109 cells. The underlying mechanisms may be attributed to the inactivation of the PI3K/Akt/E‑cadherin pathway by western blotting. Finally, the results from the invivo study indicated that the tumor growth rate in the Eca109 dll4‑shRNA group, as displayed by the tumor volume and the weak staining of the proliferating cell nuclear antigen (PCNA), was significantly slower than the control group, and the metastasis ability of the Eca109 dll4‑shRNA cells was also dramatically abolished invivo. It was also observed that downregulated DLL4 led to the formation of less pulmonary nodules in mice lungs and to a prolonged survival rate of nude mice. In summary, this study revealed that DLL4 has pathophysiological roles on the progression of esophagus cancer cells, including migration, invasion and apoptosis, which indicated that DLL4 may be considered as a potent therapeutic target for the treatment of malignant esophageal cancer.

Introduction of image-guided stereotactic radiotherapy systems for small animals

The theory and application of small animal radiotherapy models is critical for the research and development of radiobiology and clinical radiotherapy. Considering universality and cost effects, mouse models are widely used to explore the radiobiological mechanisms of cancerous and normal tissues. In recent years, there has been tremendous progress in image-guided stereotactic radiotherapy equipment for small animals, which could simulate the human radiotherapy process. This article introduces stereotactic radiotherapy systems for small animals guided by different imaging modalities, such as cone-beam computed tomography and magnetic resonance imaging, and then reviews small animal fluorescence imaging technology and summarizes the application of different bioluminescence and fluorescence imaging equipment in small animal imaging systems. Finally, we put forward the prospect of optimization direction of radiotherapy equipment for small animals in future. Key words: Small animal radiotherapy system; Bioluminescence and Fluorescence; Reconstruction

Tumor-targeting Salmonella typhimurium A1-R Inhibits Osteosarcoma Angiogenesis in the In Vivo Gelfoam® Assay Visualized by Color-coded Imaging.

We previously developed a color-coded imaging model that can quantify the length of nascent blood vessels using Gelfoam® implanted in nestin-driven green fluorescent protein (ND-GFP) nude mice. In this model, nascent blood vessels selectively express GFP. We also previously showed that osteosarcoma cells promote angiogenesis in this assay. We have also previously demonstrated the tumor-targeting bacteria Salmonella typhimurium A1-R (S. typhimurium A1-R) can inhibit or regress all tested tumor types in mouse models. The aim of the present study was to determine if S. typhimurium A1-R could inhibit osteosarcoma angiogenesis in the in vivo Gelfoam® color-coded imaging assay. Gelfoam® was implanted subcutaneously in ND-GFP nude mice. Skin flaps were made 7 days after implantation and 143B-RFP human osteosarcoma cells expressing red fluorescent protein (RFP) were injected into the implanted Gelfoam. After establishment of tumors in the Gelfoam®, control-group mice were treated with phosphate buffered saline via tail-vein injection (iv) and the experimental group was treated with S. typhimurium A1-R iv Skin flaps were made at day 7, 14, 21, and 28 after implantation of the Gelfoam® to allow imaging of vascularization in the Gelfoam® using a variable-magnification small-animal imaging system and confocal fluorescence microscopy. Nascent blood vessels expressing ND-GFP extended into the Gelfoam® over time in both groups. However, the extent of nascent blood-vessel growth was significantly inhibited by S. typhimurium A1-R treatment by day 28. The present results indicate S. typhimurium A1-R has potential for anti-angiogenic targeted therapy of osteosarcoma.

Synthesis of Biotin-Modified Galactosylated Chitosan Nanoparticles and Their Characteristics in Vitro and in Vivo

Background/Aims: Our previous study found that a nanoparticle drug delivery system that operates as a drug carrier and controlled release system not only improves the efficacy of the drugs but also reduces their side effects. However, this system could not efficiently target hepatoma cells. The aim of this study was to synthesize biotin-modified galactosylated chitosan nanoparticles (Bio-GC) and evaluate their characteristics in vitro and in vivo. Methods: Bio-GC nanomaterials were synthesized, and confirmed by fourier transform infrared spectroscopy (FT-IR) and hydrogen-¹ nuclear magnetic resonance (¹H-NMR). The liver position and cancer target property of Bio-GC nanoparticles in vitro and in vivo was tested by confocal laser and small animal imaging system. The characteristics of Bio-GC/5-fluorouracil (5-FU) nanoparticles in vitro and in vivo were explored by cell proliferation, migration and cytotoxicity test, or by animal experiment. Results: Bio-GC nanoparticles were synthesized with biodegradable chitosan as the nanomaterial skeleton with biotin and galactose grafts. Bio-GC was confirmed by FT-IR and ¹H-NMR. Bio-GC/5-FU nanoparticles were synthesized according to the optimal mass ratio for Bio-GC/5-FU (1: 4) and had a mean particle size of 81.1 nm, zeta potential of +39.2 mV, and drug loading capacity of 8.98%. Bio-GC/5-FU nanoparticles had sustained release properties (rapid, steady, and slow release phases). Bio-GC nanoparticles targeted liver and liver cancer cell in vitro and in vivo, and this was confirmed by confocal laser scanning and small animal imaging system. Compared with GC/5-FU nanoparticles, Bio-GC/5-FU nanoparticles showed more specific cytotoxic activity in a dose- and time-dependent manner and a more obvious inhibitory effect on the migration of liver cancer cells. In addition, Bio-GC/5-FU nanoparticles significantly prolonged the survival time of mice in orthotopic liver cancer transplantation model compared with other 5-FU nanoparticles or 5-FU alone. Bio-GC (0.64%) nanomaterial had no obvious cytotoxic effects on cells; thus, the concentration of Bio-GC/5-FU nanoparticles used was only 0.04% and showed no toxic effects on the cells. Conclusion: Bio-GC is a liver- and cancer-targeting nanomaterial. Bio-GC/5-FU nanoparticles as drug carriers have stronger inhibitory effects on the proliferation and migration of liver cancer cells compared with 5-FU in vitro and in vivo.

Cell-penetrating Peptide-modified Targeted Drug-loaded Phase-transformation Lipid Nanoparticles Combined with Low-intensity Focused Ultrasound for Precision Theranostics against Hepatocellular Carcinoma.

Objective: Prepare a multifunctional ultrasound molecular probe, hyaluronic acid-mediated cell-penetrating peptide-modified 10-hydroxycamptothecin-loaded phase-transformation lipid nanoparticles (HA/CPPs-10-HCPT-NPs), and to combine HA/CPPs-10-HCPT-NPs with low-intensity focused ultrasound (LIFU) for precision theranostics against hepatocellular carcinoma (HCC).Methods: HA/CPPs-10-HCPT-NPs were prepared using thin-film dispersion, ultrasound emulsification, and electrostatic effects. HA/CPPs-10-HCPT-NPs were characterized for particle size, zeta potential, encapsulation efficiency and drug-loading efficiency. In vitro, HA/CPPs-10-HCPT-NPs were tested for acoustic droplet vaporization (ADV) at different time points/acoustic intensities; the ability of HA/CPPs-10-HCPT-NPs to target SMMC-7721 cells was detected by confocal laser scanning microscopy (CLSM); the penetrating ability of CG-TAT-GC-modified NPs was verified by CLSM in a 3D multicellular tumor spheroid (MCTS) model; the effect of HA/CPPs-10-HCPT-NPs combined with LIFU on killing SMMC-7721 cells was measured by CCK-8 and flow cytometry. In vivo, the tumor-target efficiency of HA/CPPs-10-HCPT-NPs was evaluated by a small-animal fluorescence imaging system and CLSM; the enhanced ultrasound imaging efficiency of HA/CPPs-10-HCPT-NPs combined with LIFU was measured by an ultrasound imaging analyzer; the therapeutic effect of HA/CPPs-10-HCPT-NPs combined with LIFU was evaluated by tumor volume, tumor inhibition rate, and staining (hematoxylin and eosin (H & E), proliferating cell nuclear antigen (PCNA) and TUNEL).Results: Mean particle size and mean zeta potential of HA/CPPs-10-HCPT-NPs were 284.2±13.3 nm and - 16.55±1.50 mV, respectively. HA/CPPs-10-HCPT-NPs could bind to SMMC-7721 cells more readily than CPPs-10-HCPT-NPs. Penetration depth into 3D MCTS of HA/CPPs-10-HCPT-NPs was 2.76-fold larger than that of NPs without CG-TAT-GC. HA/CPPs-10-HCPT-NPs could enhance ultrasound imaging by undergoing ADV triggered by LIFU. HA/CPPs-10-HCPT-NPs+LIFU group demonstrated significantly higher efficiency of anti-proliferation and apoptosis percentage than all other groups. In mouse liver tumor xenografts, HA/CPPs-10-HCPT-NPs could target tumor sites and enhance ultrasound imaging under LIFU. HA/CPPs-10-HCPT-NPs+LIFU group had a significantly smaller tumor volume, lower proliferative index (PI), and higher tumor inhibition and apoptotic index (AI) than all other groups.Conclusions: Combined application of HA/CPPs-10-HCPT-NPs and LIFU should be a valuable and promising strategy for precise HCC theranostics.

ESTRO ACROP: Technology for precision small animal radiotherapy research: Optimal use and challenges

Many radiotherapy research centers have recently installed novel research platforms enabling the investigation of the radiation response of tumors and normal tissues in small animal models, possibly in combination with other treatment modalities. Many more research institutes are expected to follow in the coming years. These novel platforms are capable of mimicking human radiotherapy more closely than older technology. To facilitate the optimal use of these novel integrated precision irradiators and various small animal imaging devices, and to maximize the impact of the associated research, the ESTRO committee on coordinating guidelines ACROP (Advisory Committee in Radiation Oncology Practice) has commissioned a report to review the state of the art of the technology used in this new field of research, and to issue recommendations. This report discusses the combination of precision irradiation systems, small animal imaging (CT, MRI, PET, SPECT, bioluminescence) systems, image registration, treatment planning, and data processing. It also provides guidelines for reporting on studies.

Optimization of a Protease Activated Probe for Optical Surgical Navigation.

Molecularly targeted optical contrast agents have the potential to enable surgeons to visualize specific molecular markers that can help improve surgical precision and thus outcomes. Fluorescently quenched substrates can be used to highlight tumor lesions by targeting proteases that are highly abundant in the tumor microenvironment. However, the majority of these and other molecularly targeted optical contrast agents are labeled with reporter dyes that are not ideally matched to the properties of clinical camera systems, which are typically optimized for detection of indocyanine-green (ICG). While a wide range of near-infrared (NIR) dyes are suitable for use with highly sensitive and highly tunable research-focused small animal imaging systems, most have not been evaluated for use with commonly used clinical imaging systems. Here we report the optimization of a small molecule fluorescently quenched protease substrate probe 6QC-ICG, which uses the indocyanine green (ICG) dye as its optical reporter. We evaluated dosing and kinetic parameters of this molecule in tumor-bearing mice and observed optimal tumor over background signals in as little as 90 min with a dose of 2.3 mg/kg. Importantly, the fluorescence intensity of the probe signal in tumors did not linearly scale with dose, suggesting the importance of detailed dosing studies. Furthermore, when imaged using the FDA approved da Vinci Si surgical system with Firefly detection, signals were significantly higher for the ICG probe compared to a corresponding probe containing a dye with similar quantum yield but with a slightly shifted excitation and emission profile. The increased signal intensity generated by the optimal dye and dose of the ICG labeled probe enabled detection of small, flat lesions that were less than 5 mm in diameter. Therefore, 6QC-ICG is a highly sensitive probe that performs optimally with clinical imaging systems and has great potential for applications in optical surgical navigation.

Hand-held Clinical Photoacoustic Imaging System for Real-time Non-invasive Small Animal Imaging.

Translation of photoacoustic imaging into the clinic is a major challenge. Handheld real-time clinical photoacoustic imaging systems are very rare. Here, we report a combined photoacoustic and clinical ultrasound imaging system by integrating an ultrasound probe with light delivery for small animal imaging. We demonstrate this by showing sentinel lymph node imaging in small animals along with minimally invasive real-time needle guidance. A clinical ultrasound platform with access to raw channel data allows the integration of photoacoustic imaging leading to a handheld real-time clinical photoacoustic imaging system. Methylene blue was used for sentinel lymph node imaging at 675 nm wavelength. Additionally, needle guidance with dual modal ultrasound and photoacoustic imaging was shown using the imaging system. Depth imaging of up to 1.5 cm was demonstrated with a 10 Hz laser at a photoacoustic imaging frame rate of 5 frames per second.

Hand-held Clinical Photoacoustic Imaging System for Real-time Non-invasive Small Animal Imaging

Hand-held Clinical Photoacoustic Imaging System for Real-time Non-invasive Small Animal Imaging

Near-infrared–conjugated humanized anti-carcinoembryonic antigen antibody targets colon cancer in an orthotopic nude-mouse model

BackgroundThe success of a curative surgery for cancer is dependent on the complete removal of all cancer cells. Tumor visualization by the surgeon can be enhanced through fluorescent-antibody targeting. To further develop such technology, we selected humanized anti-carcinoembryonic antigen (CEA) conjugated to a near-infrared dye to target orthotopically-implanted human colon cancer in nude mice. Materials and methodsThe HT-29 human colon cancer cell line was grown in culture and subcutaneously injected in mice. After 3 wk of growth, tumors were resected and cut into 2 mm3 fragments that were sutured to the cecum of five additional nude mice for orthotopic implantation. The tumors were allowed to grow for 4 wk at which point 3 had successful orthotopic tumor growth and were selected for injection of the humanized anti-CEA antibody conjugated to the near-infrared dye IRDye800CW (anti-CEA-IRDye800CW). The antibody-dye conjugate (75 μg) was administered via tail vein injection. Images were obtained with the Pearl Trilogy Small Animal Imaging System with both 700 and 800 nm channels and evaluated using Image Studio. ResultsLaparotomy was performed 24 h after labeling the tumors. When imaged through the 800 nm channel, the tumors were observed to be strongly labeled with anti-CEA-IRDye800. At 48 h, laparotomy was repeated which again demonstrated strong labeling of the tumors through the 800 nm channel, but with a lower absolute intensity (in relative units), than at 24 h. ConclusionsHumanized anti-CEA-IRDye800CW can rapidly and effectively label CEA-expressing human colon cancer in an orthotopic nude mouse model. Given the ability of this technology to target and label tumors with great specificity, the anti-CEA-IRDye800CW is currently being developed for clinical use in fluorescence-guided surgery.

PKU-PET-II: A novel SiPM-based PET imaging system for small animals

The objective of this study was to introduce, describe, and validate the performance of a novel preclinical silicon photomultiplier (SiPM)-based PET system (PKU-PET-II). Briefly, the detector assembly consisted of cerium-doped lutetium–yttrium oxyorthosilicate (LYSO) crystals, with dimensions of 2×2×15 mm3, that offered a 60 mm transaxial field of view (FOV) and 32 mm axial FOV, respectively. The compact front-end electronics readout and digital controller implemented architecture in the FPGA were noteworthy improvements in PKU-PET-II over its predecessor (PKU-PET-I). Based on the National Electrical Manufacturers Association (NEMA) NU 04-2008 standards, the design of the PKU-PET-II system was validated by a phantom experiment. The results presented spatial resolution (evaluated as full width at half maximum) with a system range from 1.68±0.07 to 2.31±0.03 mm at the FOV center and from 1.43±0.02 to 2.10±0.10 mm at the 1/4th axial FOV, respectively. The system’s absolute sensitivity at the center position was 1.35% with the coincidence window of 6 ns and energy window of 300–700 keV. In addition, the NEMA image quality phantom and an animal study results validated the system imaging performance in preclinical imaging application. In conclusion, this SiPM-based, small-animal PET system (PKU-PET-II) provided higher-resolution, adequate sensitivity, and excellent image quality and has potential as a useful tool for real-time imaging of disease progression and development in vivo.

The Distribution of Transplanted Umbilical Cord Mesenchymal Stem Cells in Large Blood Vessel of Experimental Design With Traumatic Brain Injury.

The authors aim to track the distribution of human umbilical cord mesenchymal stem cells (MSCs) in large blood vessel of traumatic brain injury -rats through immunohistochemical method and small animal imaging system. After green fluorescent protein (GFP) gene was transfected into 293T cell, virus was packaged and MSCs were transfected. Mesenchymal stem cells containing GFP were transplanted into brain ventricle of rats when the infection rate reaches 95%. The immunohistochemical and small animal imaging system was used to detect the distribution of MSCs in large blood vessels of rats. Mesenchymal stem cells could be observed in large vessels with positive GFP expression 10 days after transplantation, while control groups (normal group and traumatic brain injury group) have negative GFP expression. The vascular endothelial growth factor in transplantation group was higher than that in control groups. The in vivo imaging showed obvious distribution of MSCs in the blood vessels of rats, while no MSCs could be seen in control groups. The intravascular migration and homing of MSCs could be seen in rats received MSCs transplantation, and new angiogenesis could be seen in MSCs-transplanted blood vessels.