In vivo molecular imaging of gastric cancer in human-murine xenograft models with confocal laser endomicroscopy using a tumor vascular homing peptide

Near-infrared-dye labeled tumor vascular-targeted dimer GEBP11 peptide for image-guided surgery in gastric cancer

Introduction

Positive resection margins occur in about 2.8%-8.2% gastric cancer surgeries and is associated with poor prognosis. Intraoperative guidance using Nearinfrared (NIR) fluorescence imaging is a promising technique for tumor detection and margin assessment. The goal of this study was to develop a tumor-specific probe for real-time intraoperative NIR fluorescence imaging guidance.

Methods

The tumor vascular homing peptide specific for gastric cancer, GEBP11, was conjugated with a near-infrared fluorophore, Cy5.5. The binding specificity of the GEBP11 probes to tumor vascular endothelial cells were confirmed by immunofluorescent staining. The ability of the probe to detect tumor lesions was evaluated in two xenograft models. An orthotopic gastric cancer xenograft model was used to evaluate the efficacy of the GEBP11 NIR probes in real-time surgical guidance.

Results

In vitro assay suggested that both mono and dimeric GEBP11 NIR probes could bind specifically to tumor vascular epithelial cells, with dimeric peptides showed better affinity. In tumor xenograft mice, live imaging suggested that comparing with free Cy5.5 probe, significantly stronger NIR signals could be detected at the tumor site at 24-48h after injection of mono or dimeric GEBP11 probes. Dimeric GEBP11 probe showed prolonged and stronger NIR signals than mono GEBP11 probe. Biodistribution assay suggested that GEBP11 NIR probes were enriched in gastric cancer xenografts. Using dimeric GEBP11 NIR probes in real-time surgery, the tumor margins and peritoneal metastases could be clearly visualized. Histological examination confirmed the complete resection of the tumor.

Conclusion

(GEBP11)2-ACP-Cy5.5 could be a potential useful probe for intraoperative florescence guidance in gastric cancer surgery.

Confocal laser endomicroscopy in gastro-intestinal endoscopy: technical aspects and clinical applications

Confocal laser endomicroscopy (CLE) is an advanced endoscopic imaging technology that provides a magnified, cellular level view of gastrointestinal epithelia. In conjunction with topical or intravenous fluorescent dyes, CLE allows for an "optical biopsy" for real-time diagnosis. Two different CLE system have been used in clinical endoscopy, probe-based CLE (pCLE) and endoscope-based CLE (eCLE). Using pCLE, the device can be delivered: (I) into the luminal gastrointestinal tract through the working channel of standard endoscopes; (II) into extraluminal cystic and solid parenchymal lesions through an endoscopic ultrasound (EUS) needle; or (III) into the biliary system through an endoscopic retrograde cholangiopancreatography (ERCP) accessory channel. With eCLE, the probe is directly integrated into the tip of a conventional endoscope, however, these endoscopes are no longer commercially available. CLE has moderate to high diagnostic accuracy for neoplastic and inflammatory conditions through the gastrointestinal tract including: oesophageal, gastric and colonic neoplasia, pancreatic cysts and solid lesions, malignant pancreatobiliary strictures and inflammatory bowel disease. Some studies have demonstrated the diagnostic benefit of CLE imaging when combined with either conventional white light endoscopy or advanced imaging technologies. Therefore, optical biopsies using CLE can resolve diagnostic dilemmas in some cases where conventional imaging fails to achieve conclusive results. CLE could also reduce the requirement for extensive tissue sampling during surveillance procedures. In the future, CLE in combination with molecular probes, could allow for the molecular characterization of diseases and assess response to targeted therapy. However, the narrow field of view, high capital costs and specialized operator training requirements remain the main limitations. Future multi-center, randomized trials with a focus on conventional diagnostic applications, cost-effectiveness and standardized training will be required for definitive evidence. The objective of this review is to evaluate the technical aspects and current applications of CLE in patients with gastrointestinal and pancreatobiliary diseases and discuss future directions for this technique.

LncRNA NORAD Promotes Proliferation And Inhibits Apoptosis Of Gastric Cancer By Regulating miR-214/Akt/mTOR Axis

PURPOSE

In previous studies, we confirmed that the overexpression of lncRNA NORAD was associated with the occurrence and development of gastric cancer (GC). The aim of the present study was to explore the molecular mechanism of lncRNA NORAD on GC cell proliferation and apoptosis in vitro and in vivo.

PATIENTS AND METHODS

The quantitative Real-Time PCR (qRT-PCR) was used to determine the expression levels of lncRNA NORAD and miR-214 in GC tissues and cells. The interaction between lncRNA NORAD and miR-214 was investigated by biological information and Dual-Luciferase gene reporter assay. Effect of lncRNA NORAD on GC tumor growth in vivo was studied in tumor xenograft model mice. The apoptosis of GC cells was determined by flow cytometry. The proliferation of GC cells was determined by 5-ethynyl-2´-deoxyuridine (EDU) and colony formation assays. Western Blot was used to determine the expressions of caspase-3, Akt and mTOR in GC tissues and cells.

RESULTS

The qRT-PCR results showed that lncRNA NORAD was highly expressed in human GC tissues and cell lines, while miR-214 was significantly down-regulated. Meanwhile, there was a direct interaction between lncRNA NORAD and miR-214. In addition, lncRNA NORAD could promote the growth and proliferation of GC cells both in vivo and in vitro. NOARD could also inhibit the apoptosis of GC cells by down-regulating caspase-3; however, miR-214 overexpression attenuated this effect. Moreover, lncRNA NORAD promoted the phosphorylation of Akt and mTOR in mouse GC tissues and GC cell lines, while miR-214 mimics inhibited that promotion.

CONCLUSION

These results suggested that NORAD could promote the development of GC by inhibiting miR-214 expression and activating the Akt/mTOR signaling pathway.

Molecular endoscopic imaging: the future is bright

The prediction and final survival rate of gastrointestinal cancers are dependent on the stage of disease. The ideal would be to detect those gastrointestinal lesions at early stage or even premalignant forms which are difficult to detect by conventional endoscopy with white light optical imaging as they show minimum or no changes in morphological characteristics and are thus left untreated. The introduction of molecular imaging has greatly changed the pattern for detecting gastrointestinal lesions from purely macroscopic structural imaging to the molecular level. It allows microscopic examination of the gastrointestinal mucosa with endoscopy after the topical or systemic application of molecular probes. In recent years, major advancements in endoscopic instruments and specific molecular probes have been achieved. This review focuses on the current status of endoscopic imaging and highlights the application of molecular imaging in gastrointestinal and hepatic disease in the context of diagnosis and therapy based on recently published literature in this field. We also discuss the challenges of molecular endoscopic imaging, its future directions and potential that could have a tremendous impact on endoscopic research and clinical practice in future.

Magnetic Semiconductor Gd-Doping CuS Nanoparticles as Activatable Nanoprobes for Bimodal Imaging and Targeted Photothermal Therapy of Gastric Tumors

Targeted delivery of enzyme-activatable probes into cancer cells to facilitate accurate imaging and on-demand photothermal therapy (PTT) of cancers with high spatiotemporal precision promises to advance cancer diagnosis and therapy. Here, we report a tumor-targeted and matrix metalloprotease-2 (MMP-2)-activatable nanoprobe (T-MAN) formed by covalent modification of Gd-doping CuS micellar nanoparticles with cRGD and an MMP-2-cleavable fluorescent substrate. T-MAN displays a high r₁ relaxivity (∼60.0 mM^-1 s^-1 per Gd³⁺ at 1 T) and a large near-infrared (NIR) fluorescence turn-on ratio (∼185-fold) in response to MMP-2, allowing high-spatial-resolution magnetic resonance imaging (MRI) and low-background fluorescence imaging of gastric tumors as well as lymph node (LN) metastasis in living mice. Moreover, T-MAN has a high photothermal conversion efficiency (PCE, ∼70.1%) under 808 nm laser irradiation, endowing it with the ability to efficiently generate heat to kill tumor cells. We demonstrate that T-MAN can accumulate preferentially in gastric tumors (∼23.4% ID%/g at 12 h) after intravenous injection into mice, creating opportunities for fluorescence/MR bimodal imaging-guided PTT of subcutaneous and metastatic gastric tumors. For the first time, accurate detection and laser irradiation-initiated photothermal ablation of orthotopic gastric tumors in intraoperative mice was also achieved. This study highlights the versatility of using a combination of dual biomarker recognition (i.e., α_vβ₃ and MMP-2) and dual modality imaging (i.e., MRI and NIR fluorescence) to design tumor-targeting and activatable nanoprobes with improved selectivity for cancer theranostics in vivo.

A CD44-specific peptide, RP-1, exhibits capacities of assisting diagnosis and predicting prognosis of gastric cancer

Early diagnosis and evaluation of prognosis are both crucial for preventing poor prognosis of patients with gastric cancer (GC), a leading cause of cancer-related deaths worldwide. Cluster of differentiation 44 (CD44), an indicator of cancer stem cells, can be specifically targeted by molecular probes and detected in tissues of GC in a large quantity. In current study we found that RP-1, a specific peptide binding to CD44 protein, exhibited the potentials of specific binding to CD44 high-expressing cancer cells both in vitro and in vivo, and the capacity of predicting prognosis of human GC in a microarray assay. Results showed that RP-1 was characterized by high affinity, sensitivity and specificity, and low toxicity, suggesting RP-1 could be an ideal bio-probe for accessory diagnosis of GC. Further immunohistochemical studies and statistical analysis of tissue microarray of human GC demonstrated similar sensitivity and specificity of RP-1 with the monoclonal anti-CD44 antibody in the diagnosis of GC, and even proved that positive RP-1 could be an independent risk factor. Therefore, this study suggests RP-1 has the potentials of binding to CD44 protein expressed on the membrane of GC cells, and demonstrates the feasibility and reliability of its further application in molecular diagnosis and prognostic prediction of GC.

Multimodality Imaging of Angiogenesis in a Rabbit Atherosclerotic Model by GEBP11 Peptide Targeted Nanoparticles

Background and Aims: Angiogenesis is an important pathological process during progression of plaque formation, which can result in plaque hemorrhage and vulnerability. This study aims to explore non-invasive imaging of angiogenesis in atherosclerotic plaque through magnetic resonance imaging (MRI) and positron emission tomography (PET) by using GEBP11 peptide targeted magnetic iron oxide nanoparticles in a rabbit model of atherosclerosis.

Methods: The dual-modality imaging probe was constructed by coupling 2, 3-dimercaptosuccinnic acid-coated paramagnetic nanoparticles (DMSA-MNPs) and the PET ⁶⁸Ga chelator 1,4,7-triazacyclononane-N, N', N''-triacetic acid (NOTA) to GEBP11 peptide. The atherosclerosis model was induced in New Zealand white rabbits by abdominal aorta balloon de-endothelialization and atherogenic diet for 12 weeks. The plaque areas in abdominal artery were detected by ultrasound imaging and Oil Red O staining. Immunofluorescence staining and Prussian blue staining were applied respectively to investigate the affinity of GEBP11 peptide. MTT and flow cytometric analysis were performed to detect the effects of NGD-MNPs on cell proliferation, cell cycle and apoptosis in Human umbilical vein endothelial cells (HUVECs). In vivo MRI and PET imaging of atherosclerotic plaque were carried out at different time points after intravenous injection of nanoparticles.

Results: The NGD-MNPs with hydrodynamic diameter of 130.8 nm ± 7.1 nm exhibited good imaging properties, high stability, low immunogenicity and little cytotoxicity. In vivo PET/MR imaging revealed that ⁶⁸Ga-NGD-MNPs were successfully applied to visualize atherosclerotic plaque angiogenesis in the rabbit abdominal aorta. Prussian blue and CD31 immunohistochemical staining confirmed that NGD-MNPs were well co-localized within the blood vessels' plaques.

Conclusion:⁶⁸Ga-NGD-MNPs might be a promising MR and PET dual imaging probe for visualizing the vulnerable plaques.

Improved Tumor Targeting and Longer Retention Time of NIR Fluorescent Probes Using Bioorthogonal Chemistry

The traditional labeling method for targeted NIR fluorescence probes requires directly covalent-bonded conjugation of targeting domains and fluorophores in vitro. Although this strategy works well, it is not sufficient for detecting or treating cancers in vivo, due to steric hindrance effects that relatively large fluorophore molecules exert on the configurations and physiological functions of specific targeting domains. The copper-free, “click-chemistry”-assisted assembly of small molecules in living systems may enhance tumor accumulation of fluorescence probes by improving the binding affinities of the targeting factors. Here, we employed a vascular homing peptide, GEBP11, as a targeting factor for gastric tumors, and we demonstrate its effectiveness for in vivo imaging via click-chemistry-mediated conjugation with fluorescence molecules in tumor xenograft mouse models. This strategy showed higher binding affinities than those of the traditional conjugation method, and our results showed that the tumor accumulation of click-chemistry-mediated probes are 11-fold higher than that of directly labeled probes. The tracking life was prolonged by 12-fold, and uptake of the probes into the kidney was reduced by 6.5-fold. For lesion tumors of different sizes, click-chemistry-mediated probes can achieve sufficient signal-to-background ratios (3.5-5) for in vivo detection, and with diagnostic sensitivity approximately 3.5 times that of traditional labeling probes. The click-chemistry-assisted detection strategy utilizes the advantages of “small molecule” probes while not perturbing their physiological functions; this enables tumor detection with high sensitivity and specific selectivity.

Three-Dimensional High-Frequency Ultrasonography for Early Detection and Characterization of Embryo Implantation Site Development in the Mouse

Ultrasonography is a powerful tool to non-invasively monitor in real time the development of the human fetus in utero. Although genetically engineered mice have served as valuable in vivo models to study both embryo implantation and pregnancy progression, such studies usually require sacrifice of parous mice for subsequent phenotypic analysis. To address this issue, we used three-dimensional (3-D) reconstruction in silico of high-frequency ultrasound (HFUS) imaging data for early detection and characterization of murine embryo implantation sites and their development in utero. With HFUS imaging followed by 3-D reconstruction, we were able to precisely quantify embryo implantation site number and embryonic developmental progression in pregnant C57BL6J/129S mice from as early as 5.5 days post coitus (d.p.c.) through to 9.5 d.p.c. using a VisualSonics Vevo 2100 (MS550S) transducer. In addition to measurements of implantation site number, location, volume and spacing, embryo viability via cardiac activity monitoring was also achieved. A total of 12 dams were imaged with HFUS with approximately 100 embryos examined per embryonic day. For the post-implantation period (5.5 to 8.5 d.p.c.), 3-D reconstruction of the gravid uterus in mesh or solid overlay format enabled visual representation in silico of implantation site location, number, spacing distances, and site volume within each uterine horn. Therefore, this short technical report describes the feasibility of using 3-D HFUS imaging for early detection and analysis of post-implantation events in the pregnant mouse with the ability to longitudinally monitor the development of these early pregnancy events in a non-invasive manner. As genetically engineered mice continue to be used to characterize female reproductive phenotypes, we believe this reliable and non-invasive method to detect, quantify, and characterize early implantation events will prove to be an invaluable investigative tool for the study of female infertility and subfertility phenotypes based on a defective uterus.

Multifunctional SPIO/DOX-loaded A54 Homing Peptide Functionalized Dextran-g-PLGA Micelles for Tumor Therapy and MR Imaging

Specific delivery of chemotherapy drugs and magnetic resonance imaging (MRI) contrast agent into tumor cells is one of the issues to highly efficient tumor targeting therapy and magnetic resonance imaging. Here, A54 peptide-functionalized poly(lactic-co-glycolic acid)-grafted dextran (A54-Dex-PLGA) was synthesized. The synthesized A54-Dex-PLGA could self-assemble to form micelles with a low critical micelle concentration of 22.51 μg. mL⁻¹ and diameter of about 50 nm. The synthetic A54-Dex-PLGA micelles can encapsulate doxorubicin (DOX) as a model anti-tumor drug and superparamagnetic iron oxide (SPIO) as a contrast agent for MRI. The drug-encapsulation efficiency was about 80% and the in vitro DOX release was prolonged to 72 hours. The DOX/SPIO-loaded micelles could specifically target BEL-7402 cell line. In vitro MRI results also proved the specific binding ability of A54-Dex-PLGA/DOX/SPIO micelles to hepatoma cell BEL-7402. The in vivo MR imaging experiments using a BEL-7402 orthotopic implantation model further validated the targeting effect of DOX/SPIO-loaded micelles. In vitro and in vivo anti-tumor activities results showed that A54-Dex-PLGA/DOX/SPIO micelles revealed better therapeutic effects compared with Dex-PLGA/DOX/SPIO micelles and reduced toxicity compared with commercial adriamycin injection.

Endoscopic molecular imaging of gastrointestinal tumors

In China, the incidence and mortality of gastrointestinal cancers are high, and early diagnosis is the key to improving the survival rate. In recent years, endoscopic molecular imaging in tumor diagnosis with its unique advantages has attracted more and more attention. With the rapid development of molecular biology, the mechanism of tumor occurrence and development has been gradually elucidated. The advent of fluorescent labeled molecular probes and targeted binding to molecular targets of gastrointestinal tumors makes it possible achieve real-time endoscopic molecular diagnosis of digestive tract tumors, which has a significant impact on tumor targeted therapy. In this paper, we review the progress in endoscopic molecular imaging of digestive tract tumors.

Characterization of lesions in the stomach: will confocal laser endomicroscopy replace the pathologist?

Confocal laser endomicroscopy (CLE) permits microscopic visualization of the mucosa during endoscopy at an approximately 1000fold magnification, permitting endoscopists to obtain microscopic analysis during gastroscopy. This can result in optimized diagnosis of diffuse alterations such as gastric atrophy and intestinal metaplasia and may limit the sampling error of untargeted biopsies. It also allows risk stratification prior to endoscopic therapy of neoplastic lesions of the stomach. In these areas, CLE represents a valuable adjunct for targeted histopathology. In addition, CLE allows on-site in vivo imaging, and by this insight into physiologic and pathophysiologic as well as molecular events of the stomach without major artifacts.

Endoscopic imaging

OPINION STATEMENT

The most important tools are the eye and the brain. A detailed white-light high-resolution examination and ability to recognize subtle lesions provide the foundation of the ability to detect lesions in the gastrointestinal tract. Novel technologies are now available to provide additional information with the goals of detection, delineation, or classification often with a focus on neoplasia in the gastrointestinal tract. The observer using these new tools must still recognize, interpret, and then make a clinically relevant conclusion. Therefore, the assessment of these tools may focus on both the technical feasibility to use the respective equipment to obtain an image and then also the associated cognitive-based criteria for image interpretation.

Ultrasensitive in vivo detection of primary gastric tumor and lymphatic metastasis using upconversion nanoparticles

Lymphatic metastasis is an important prognostic factor regarding long-term survival rate of gastric cancer (GC) patients. Pretreatment knowledge of lymph node status is extremely helpful for planning treatment and prognosis. However, to date, no imaging method has been demonstrated to be effective for detecting lymphatic metastasis in GC. Molecular imaging probes based on upconversion nanoparticles with unique optical and magnetic properties have provided great hope for early tumor detection. Herein we report highly sensitive detection of lymphatic spread using core@shell structured NaGdF4:Yb,Er@NaGdF4 upconversion nanoparticles coated with polyethylene glycol (PEG). A GC-specific probe was constructed through "click" reaction between the maleimide moiety of PEG ligand and the thiol group from partly reduced antigastric cancer antibody MGb2. The primary tumor and adjacent lymphatic metastasis site were clearly differentiated by upconversion luminescence imaging after the GC-specific probe was delivered through tail vein injection into tumor-bearing mice. Moreover, lymphatic metastases smaller than 1 mm were successfully detected, owing to the ultralow background under 980 nm excitation. It has been demonstrated that both primary and lymphatic metastatic sites in an orthotopic mouse model of human gastric cancer can be optically detected by using GC-specific upconversion luminescence nanoprobes. The current studies may therefore provide a highly effective approach for GC diagnosis.

In vivo molecular imaging of colorectal cancer using quantum dots targeted to vascular endothelial growth factor receptor 2 and optical coherence tomography/laser-induced fluorescence dual-modality imaging

Optical coherence tomography/laser induced fluorescence (OCT/LIF) dual-modality imaging allows for minimally invasive, nondestructive endoscopic visualization of colorectal cancer in mice. This technology enables simultaneous longitudinal tracking of morphological (OCT) and biochemical (fluorescence) changes as colorectal cancer develops, compared to current methods of colorectal cancer screening in humans that rely on morphological changes alone. We have shown that QDot655 targeted to vascular endothelial growth factor receptor 2 (QD655-VEGFR2) can be applied to the colon of carcinogen-treated mice and provides significantly increased contrast between the diseased and undiseased tissue with high sensitivity and specificity ex vivo. QD655-VEGFR2 was used in a longitudinal in vivo study to investigate the ability to correlate fluorescence signal to tumor development. QD655-VEGFR2 was applied to the colon of azoxymethane (AOM-) or saline-treated control mice in vivo via lavage. OCT/LIF images of the distal colon were taken at five consecutive time points every three weeks after the final AOM injection. Difficulties in fully flushing unbound contrast agent from the colon led to variable background signal; however, a spatial correlation was found between tumors identified in OCT images, and high fluorescence intensity of the QD655 signal, demonstrating the ability to detect VEGFR2 expressing tumors in vivo.