Monitoring E-selectin-mediated adhesion using green and red fluorescent proteins

Purified polysaccharide from Ginkgo biloba leaves inhibits P-selectin-mediated leucocyte adhesion and inflammation

AIM

To investigate the anti-inflammatory mechanism of the polysaccharides of Ginkgo biloba leaves (PGBL) by inhibiting leucocyte adhesion.

METHODS

The rough PGBL were isolated and purified. The anti-inflammatory effects of purified PGBL (p-PGBL) were assayed by ear edema induced by xylol and the acute peritonitis model in mice. The effect of p-PGBL on inhibiting the interaction between P-selectin and its ligands was investigated by flow cytometry and flow chamber.

RESULTS

p-PGBL could effectively inhibit the acute inflammation in mice and interfere with the adhesion of HL-60 cells, a human leukaemia cell line, or neutrophils to P-selectin in static conditions, as well as the adhesion of neutrophils to Chinese hamster ovary cells expressing human P-selectin and human umbilical vein endothelial cells in flow conditions in a dose-dependant manner.

CONCLUSIONS

p-PGBL can inhibit the inflammatory process through interfering with the interaction between P-selectin and its ligands.

Flow cytometric assay for quantitative and qualitative evaluation of adhesive interactions of tumor cells with endothelial cells

The purpose of the study was to develop a flow cytometric assay for quantitative determination of adhesive interactions of human endothelial cells (ECs) with tumor cells. EC lines established from human lymph node, appendix, lung, skin and intestine microvessels, labeled with PKH26-GL fluorescent dye, were grown to confluency in 24-well TC plates. Human colon adenocarcinoma cell suspension was overlaid onto labeled ECs, and allowed to adhere for 20 min at 4 degrees C under static conditions. Non-adhering cells were collected first, and adhering tumor cells together with ECs were detached from the culture plate. Collected cell fractions were evaluated by flow cytometry. Results were re-calculated as a ratio (R) of adhering colon carcinoma cells per one EC. We demonstrated that immortalized human microvascular ECs preserved their organ specificity. Colon carcinoma cells adhere preferentially to ECs of intestine origin. The immunofluorescent staining of adhering and non-adhering cancer cell subpopulations has revealed an augmented level of Lewis(x) antigen on adhering cancer cells. The organ specificity of endothelial cell interactions with colon carcinoma cells demonstrated in static conditions was verified and confirmed with flow adhesion assay. The method elaborated is suitable for quantifying of tumor cells adhering to ECs, with simultaneous evaluation of cell surface phenotypic markers of both partner cells participating in adhesive interactions. Validated by comparison to dynamic shear stress adhesion assay in blood flow reconstituted conditions this assay greatly facilitates evaluation of tumor cell-endothelial cell mutual interactions taking place during metastatic process.

Molecular imaging: reporter gene imaging

Non-invasive in-vivo molecular genetic imaging developed over the past decade and predominantly utilises radiotracer (PET, gamma camera, autoradiography), magnetic resonance and optical imaging technology. Molecular genetic imaging has its roots in both molecular biology and cell biology. The convergence of these disciplines and imaging modalities has provided the opportunity to address new research questions, including oncogenesis, tumour maintenance and progression, as well as responses to molecular-targeted therapy. Three different imaging strategies are described: (1) "bio-marker" or "surrogate" imaging; (2) "direct" imaging of specific molecules and pathway activity; (3) "indirect" reporter gene imaging. Examples of each imaging strategy are presented and discussed. Several applications of PET- and optical-based reporter imaging are demonstrated, including signal transduction pathway monitoring, oncogenesis in genetic mouse models, endogenous molecular genetic/biological processes and the response to therapy in animal models of human disease. Molecular imaging studies will compliment established ex-vivo molecular-biological assays that require tissue sampling by providing a spatial and a temporal dimension to our understanding of disease development and progression, as well as response to treatment. Although molecular imaging studies are currently being performed primarily in experimental animals, we optimistically expect they will be translated to human subjects with cancer and other diseases in the near future.

Multi-Modality Molecular Imaging of Tumors

Noninvasive in vivo molecular-genetic imaging uses nuclear, magnetic resonance, and optical imaging techniques. Described and discussed are "direct" imaging of specific molecules and pathway activity, "indirect" reporter gene imaging, and "bio-marker" or "surrogate" imaging. Applications of PET- and optical-based reporter imaging are demonstrated, including imaging of oncogenesis in genetic mouse models, endogenous molecular-genetic-biological properties, and response to therapy in animal models of human disease. Molecular imaging studies complement established ex vivo molecular-biological assays that require tissue sampling by providing a spatial as well as temporal dimension to our understanding of oncogenesis, and the progression and treatment of cancer. Molecular imaging studies being performed in experimental animals will be translated to animals in the near future.

Optical tomographic imaging of small animals

Diffuse optical tomography is emerging as a viable new biomedical imaging modality. Using visible and near-infrared light this technique can probe the absorption and scattering properties of biological tissues. The main applications are currently in brain, breast, limb and joint imaging; however, optical tomographic imaging of small animals is attracting increasing attention. This interest is fuelled by recent advances in the transgenic manipulation of small animals that has led to many models of human disease. In addition, an ever increasing number of optically reactive biochemical markers has become available, which allow diseases to be detected at the molecular level long before macroscopic symptoms appear. The past three years have seen an array of novel technological developments that have led to the first optical tomographic studies of small animals in the areas of cerebral ischemia and cancer.

Multimodality in Vivo Molecular-Genetic Imaging

Multimodality imaging is increasingly being used in molecular-genetic studies in small animals. The coupling of nuclear and optical reporter genes represents the beginning of a far wider application of this technology. Optical imaging and optical reporter systems are cost-effective and time-efficient, they require less resources and space than PET or MRI, and they are particularly well suited for small animal imaging and for in vitro assays to validate different reporter systems. However, optical imaging techniques are limited by depth of light penetration and scatter and do not yet provide optimal quantitative or tomographic information. These issues are not limiting for PET- or MRI-based reporter systems, and PET- and MRI-based animal studies are more easily generalized to human applications. Many of the shortcomings of each modality alone can be overcome by the use of dual- or triple-modality reporter constructs that incorporate the opportunity for PET, fluorescence and bioluminescence imaging. We optimistically expect that some form of tomographic, small animal optical imaging capability will be developed soon, and that this will provide the opportunity for the colocalization of optical signals to anatomical structures provided by tomographic CT and MR imaging.

In vivo molecular-genetic imaging: multi-modality nuclear and optical combinations

Multi-modality, noninvasive in vivo imaging is increasingly being used in molecular-genetic studies and will soon become the standard approach for reporter gene imaging studies in small animals. The coupling of nuclear and optical reporter genes, as described here, represents only the beginning of a far wider application of this technology in the future. Optical imaging and optical reporter systems are cost-effective and time-efficient; they require less resources and space than PET or MRI, and are particularly well suited for imaging small animals, such as mice. Optical reporter systems are also very useful for the quantification and selection of transduced cells using FACS, and for performing in vitro assays to validate the function and sensitivity of constitutive and specific-inducible reporter systems. However, optical imaging techniques are limited by depth of light penetration and do not yet provide optimal quantitative or tomographic information. These issues are not limiting for PET- or MRI-based reporter systems, and PET- and MRI-based animal studies are more easily generalized to human applications. Many of the shortcomings of each modality alone can be overcome by the use of dual- or triple-modality reporter constructs that incorporate the opportunity for PET, fluorescence and bioluminescence imaging.

Transgene expression of alpha(1,2)-fucosyltransferase-I (FUT1) in tumor cells selectively inhibits sialyl-Lewis x expression and binding to E-selectin without affecting synthesis of sialyl-Lewis a or binding to P-selectin

During inflammation, E- and P-selectins appear on activated endothelial cells to interact with leukocytes through sialyl-Lewis x and sialyl-Lewis a antigens (sLe(x/a)). These selectins can also interact with tumor cells in a sialyl-Lewis-dependent manner and for this reason, they are thought to play a key role in metastasis. Diverting the biosynthesis of sialyl-Lewis antigens toward nonadhesive structures is an attractive gene therapy for preventing the hematogenous metastatic spread of cancers. We have previously shown that transfection of alpha(1,2)-fucosyltransferase-I (FUT1) in Chinese hamster ovary (CHO) cells had a slight effect on the overall sialylation while the synthesis of sLE(x) was dramatically prevented. We herein delivered the gene of FUT1 by a human immunodeficiency virus-derived lentiviral vector to three human cancer cell lines including pancreatic (BxPC3), hepatic (HepG2), and colonic (HT-29) cancer cells. We found that on FUT1 transduction, all cells exhibited a dramatic decrease in sLe(x) synthesis with a concomitant increase in Le(y) and Le(b) expression, without any detectable effect on the level of cell surface sLe(a) antigens. In parallel, FUT1-transduced HT-29 and HepG2 cells, but not BxPC3 cells, failed to interact with E-selectin as assessed by E-selectin-binding assay or dynamic adhesion to activated endothelial cells. We show also that transduced FUT1 efficiently fucosylates the P-selectin ligand PSGL-1 without altering P-selectin binding. These results have important implications for understanding cell-specific reactions underlying the synthesis of selectin ligands in cancer cells and may provide a basis for the development of anti-metastatic gene therapy.

A novel triple-modality reporter gene for whole-body fluorescent, bioluminescent, and nuclear noninvasive imaging

Two genetic reporter systems were developed for multimodality reporter gene imaging of different molecular-genetic processes using fluorescence, bioluminescence (BLI), and nuclear imaging techniques. The eGFP cDNA was fused at the N-terminus with HSV1-tk cDNA bearing a nuclear export signal from MAPKK (NES-HSV1-tk) or with truncation at the N-terminus of the first 45 amino acids (Delta45HSV1-tk) and with firefly luciferase at the C-terminus. A single fusion protein with three functional subunits is formed following transcription and translation from a single open reading frame. The NES-TGL (NES-TGL) or Delta45HSV1-tk/GFP/luciferase (Delta45-TGL) triple-fusion gene cDNAs were cloned into a MoMLV-based retrovirus, which was used for transduction of U87 human glioma cells. The integrity, fluorescence, bioluminescence, and enzymatic activity of the TGL reporter proteins were assessed in vitro. The predicted molecular weight of the fusion proteins (~130 kDa) was confirmed by western blot. The U87-NES-TGL and U87-Delta45-TGL cells had cytoplasmic green fluorescence. The in vitro BLI was 7- and 13-fold higher in U87-NES-TGL and U87-Delta45-TGL cells compared to nontransduced control cells. The Ki of (14)C-FIAU was 0.49+/-0.02, 0.51+/-0.03, and 0.003+/-0.001 ml/min/g in U87-NES-TGL, U87-Delta45-TGL, and wild-type U87 cells, respectively. Multimodality in vivo imaging studies were performed in nu/ nu mice bearing multiple s.c. xenografts established from U87-NES-TGL, U87-Delta45-TGL, and wild-type U87 cells. BLI was performed after administration of d-luciferin (150 mg/kg i.v.). Gamma camera or PET imaging was conducted at 2 h after i.v. administration of [(131)I]FIAU (7.4 MBq/animal) or [(124)I]FIAU (7.4 MBq/animal), respectively. Whole-body fluorescence imaging was performed in parallel with the BLI and radiotracer imaging studies. In vivo BLI and gamma camera imaging showed specific localization of luminescence and radioactivity to the TGL transduced xenografts with background levels of activity in the wild-type xenografts. Tissue sampling yielded values of 0.47%+/-0.08%, 0.86%+/-0.06%, and 0.03%+/-0.01%dose/g [(131)I]FIAU in U87-NES-TGL, U87-Delta45-TGL, and U87 xenografts, respectively. The TGL triple-fusion reporter gene preserves the functional activity of its subunits and is very effective for multimodality imaging. It provides for the seamless transition from fluorescence microscopy and FACS to whole-body bioluminescence imaging, to nuclear (PET, SPET, gamma camera) imaging, and back to in situ fluorescence image analysis.

Cytoplasmically retargeted HSV1-tk/GFP reporter gene mutants for optimization of noninvasive molecular-genetic imaging

To optimize the sensitivity of imaging HSV1-tk/GFP reporter gene expression, a series of HSV1-tk/GFP mutants was developed with altered nuclear localization and better cellular enzymatic activity, compared to that of the native HSV1-tk/GFP fusion protein (HSV1-tk/GFP). Several modifications of HSV1-tk/GFP reporter gene were performed, including targeted inactivating mutations in the nuclear localization signal (NLS), the addition of a nuclear export signal (NES), a combination of both mutation types, and a truncation of the first 135 bp of the native hsv1-tk coding sequence containing a "cryptic" testicular promoter and the NLS. A recombinant HSV1-tk/GFP protein and a highly sensitive sandwich enzyme-linked immunosorbent assay for HSV1-tk/GFP were developed to quantitate the amount of reporter gene product in different assays to allow normalization of the data. These different mutations resulted in various degrees of nuclear clearance, predominant cytoplasmic distribution, and increased total cellular enzymatic activity of the HSV1-tk/GFP mutants, compared to native HSV1-tk/GFP when expressed at the same levels. This appears to be the result of improved metabolic bioavailability of cytoplasmically retargeted mutant HSV1-tk/GFP enzymes for reaction with the radiolabeled probe (e.g., FIAU). The analysis of enzymatic properties of different HSV1-tk/GFP mutants using FIAU as a substrate revealed no significant differences from that of the native HSV1-tk/GFP. Improved total cellular enzymatic activity of cytoplasmically retargeted HSV1-tk/GFP mutants observed in vitro was confirmed by noninvasive imaging of transduced subcutaneous tumor xenografts bearing these reporters using [(131)I]FIAU and a gamma-camera.