Molecular imaging of angiogenesis

Perspectives: MRI of angiogenesis

Angiogenesis, the expansion of the vascular bed, is an important component in remodeling of tissues and organs. Such remodeling is essential for coping with substantial and sustained increase in the demands for supply of oxygen and nutrients and the timely removal of waste products. The vasculature, and its effectiveness in systemic delivery to all parts of the body, regulates the distribution of immune cells and the delivery of therapeutics as well as the dissemination of disease. Therefore, the vascular bed is possibly one of the key organs involved in homeostasis, in health and disease. The critical role of the vasculature in health, and the accessibility to non invasive probing by MRI, renders MRI as a modality of choice for monitoring the vasculature and its adaption to challenges.

Genetically modified lentiviruses that preserve microvascular function protect against late radiation damage in normal tissues

Improvements in cancer survival mean that long-term toxicities, which contribute to the morbidity of cancer survivorship, are being increasingly recognized. Late adverse effects (LAEs) in normal tissues after radiotherapy (RT) are characterized by vascular dysfunction and fibrosis causing volume loss and tissue contracture, for example, in the free flaps used for immediate breast reconstruction after mastectomy. We evaluated the efficacy of lentivirally delivered superoxide dismutase 2 (SOD2) overexpression and connective tissue growth factor (CTGF) knockdown by short hairpin RNA in reducing the severity of LAEs in an animal model of free flap LAEs. Vectors were delivered by intra-arterial injection, ex vivo, to target the vascular compartment. LVSOD2 and LVshCTGF monotherapy before irradiation resulted in preservation of flap volume or reduction in skin contracture, respectively. Flaps transduced with combination therapy experienced improvements in both volume loss and skin contracture. Both therapies reduced the fibrotic burden after irradiation. LAEs were associated with impaired vascular perfusion, loss of endothelial permeability, and stromal hypoxia, which were all reversed in the treatment model. Using a tumor recurrence model, we showed that SOD2 overexpression in normal tissues did not compromise the efficacy of RT against tumor cells but appeared to enhance it. LVSOD2 and LVshCTGF combination therapy by targeted, intravascular delivery reduced LAE severities in normal tissues without compromising the efficacy of RT and warrants translational evaluation as a free flap-targeted gene therapy.

Melanin-Based Contrast Agents for Biomedical Optoacoustic Imaging and Theranostic Applications

Optoacoustic imaging emerged in early 1990s as a new biomedical imaging technology that generates images by illuminating tissues with short laser pulses and detecting resulting ultrasound waves. This technique takes advantage of the spectroscopic approach to molecular imaging, and delivers high-resolution images in the depth of tissue. Resolution of the optoacoustic imaging is scalable, so that biomedical systems from cellular organelles to large organs can be visualized and, more importantly, characterized based on their optical absorption coefficient, which is proportional to the concentration of absorbing chromophores. Optoacoustic imaging was shown to be useful in both preclinical research using small animal models and in clinical applications. Applications in the field of molecular imaging offer abundant opportunities for the development of highly specific and effective contrast agents for quantitative optoacoustic imaging. Recent efforts are being made in the direction of nontoxic biodegradable contrast agents (such as nanoparticles made of melanin) that are potentially applicable in clinical optoacoustic imaging. In order to increase the efficiency and specificity of contrast agents and probes, they need to be made smart and capable of controlled accumulation in the target cells. This review was written in recognition of the potential breakthroughs in medical optoacoustic imaging that can be enabled by efficient and nontoxic melanin-based optoacoustic contrast agents.

Characterization of the Tumor Microenvironment and Tumor-Stroma Interaction by Non-invasive Preclinical Imaging

Tumors are often characterized by hypoxia, vascular abnormalities, low extracellular pH, increased interstitial fluid pressure, altered choline-phospholipid metabolism, and aerobic glycolysis (Warburg effect). The impact of these tumor characteristics has been investigated extensively in the context of tumor development, progression, and treatment response, resulting in a number of non-invasive imaging biomarkers. More recent evidence suggests that cancer cells undergo metabolic reprograming, beyond aerobic glycolysis, in the course of tumor development and progression. The resulting altered metabolic content in tumors has the ability to affect cell signaling and block cellular differentiation. Additional emerging evidence reveals that the interaction between tumor and stroma cells can alter tumor metabolism (leading to metabolic reprograming) as well as tumor growth and vascular features. This review will summarize previous and current preclinical, non-invasive, multimodal imaging efforts to characterize the tumor microenvironment, including its stromal components and understand tumor-stroma interaction in cancer development, progression, and treatment response.

Assessing tumor vascularization as a potential biomarker of imatinib resistance in gastrointestinal stromal tumors by dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND

Most metastatic gastrointestinal stromal tumors (GISTs) develop resistance to the first-line imatinib treatment. Recently, increased vessel density and angiogenic markers were reported in GISTs with a poor prognosis, suggesting that angiogenesis is implicated in GIST tumor progression and resistance. The purpose of this study was to investigate the relationship between tumor vasculature and imatinib resistance in different GIST mouse models using a noninvasive magnetic resonance imaging (MRI) functional approach.

METHODS

Immunodeficient mice (n = 8 for each cell line) were grafted with imatinib-sensitive (GIST882 and GIST-T1) and imatinib-resistant (GIST430) human cell lines. Dynamic contrast-enhanced MRI (DCE-MRI) was performed on GIST xenografts to quantify tumor vessel permeability (K ^trans) and vascular volume fraction (v _p). Microvessel density (MVD), permeability (mean dextran density, MDD), and angiogenic markers were evaluated by immunofluorescence and western blot assays.

RESULTS

Dynamic contrast-enhanced magnetic resonance imaging showed significantly increased vessel density (P < 0.0001) and permeability (P = 0.0002) in imatinib-resistant tumors compared to imatinib-sensitive ones. Strong positive correlations were observed between MRI estimates, K ^trans and v _p, and their related ex vivo values, MVD (r = 0.78 for K ^trans and r = 0.82 for v _p) and MDD (r = 0.77 for K ^trans and r = 0.94 for v _p). In addition, higher expression of vascular endothelial growth factor receptors (VEGFR2 and VEFGR3) was seen in GIST430.

CONCLUSIONS

Dynamic contrast-enhanced magnetic resonance imaging highlighted marked differences in tumor vasculature and microenvironment properties between imatinib-resistant and imatinib-sensitive GISTs, as also confirmed by ex vivo assays. These results provide new insights into the role that DCE-MRI could play in GIST characterization and response to GIST treatment. Validation studies are needed to confirm these findings.

Imaging preclinical tumour models: improving translational power

Recent developments and improvements of multimodal imaging methods for use in animal research have substantially strengthened the options of in vivo visualization of cancer-related processes over time. Moreover, technological developments in probe synthesis and labelling have resulted in imaging probes with the potential for basic research, as well as for translational and clinical applications. In addition, more sophisticated cancer models are available to address cancer-related research questions. This Review gives an overview of developments in these three fields, with a focus on imaging approaches in animal cancer models and how these can help the translation of new therapies into the clinic.

Imaging aspects of the tumor stroma with therapeutic implications

Cancer cells rely on extensive support from the stroma in order to survive, proliferate and invade. The tumor stroma is thus an important potential target for anti-cancer therapy. Typical changes in the stroma include a shift from the quiescence promoting-antiangiogenic extracellular matrix to a provisional matrix that promotes invasion and angiogenesis. These changes in the extracellular matrix are induced by changes in the secretion of extracellular matrix proteins and glucose amino glycans, extravasation of plasma proteins from hyperpermeable vessels and release of matrix modifying enzymes resulting in cleavage and cross-linking of matrix macromolecules. These in turn alter the rigidity of the matrix and the exposure and release of cytokines. Changes in matrix rigidity and vessel permeability affect drug delivery and mediate resistance to cytotoxic therapy. These stroma changes are brought about not only by the cancer cells, but also through the action of many cell types that are recruited by tumors including immune cells, fibroblasts and endothelial cells. Within the tumor, these normal host cells are activated resulting in loss of inhibitory and induction of cancer promoting activities. Key to the development of stroma-targeted therapies, selective biomarkers were developed for specific imaging of key aspects of the tumor stroma.

Genetic tools to manipulate MRI contrast

Advances in molecular biology in the early 1970s revolutionized research strategies for the study of complex biological processes, which, in turn, created a high demand for new means to visualize these dynamic biological changes noninvasively and in real time. In this respect, MRI was a perfect fit, because of the versatile possibility to alter the different contrast mechanisms. Genetic manipulations are now being translated to MRI through the development of reporters and sensors, as well as the imaging of transgenic and knockout mice. In the past few years, a new molecular biology toolset, namely optogenetics, has emerged, which allows for the manipulation of cellular behavior using light. This technology provides a few particularly attractive features for combination with newly developed MRI techniques for the probing of in vivo cellular and, in particular, neural processes, specifically the ability to control focal, genetically defined cellular populations with high temporal resolution using equipment that is magnetically inert and does not interact with radiofrequency pulses. Recent studies have demonstrated that the combination of optogenetics and functional MRI (fMRI) can provide an appropriate platform to investigate in vivo, at the cellular and molecular levels, the neuronal basis of fMRI signals. In addition, this novel combination of optogenetics with fMRI has the potential to resolve pre-synaptic versus post-synaptic changes in neuronal activity and changes in the activity of large neuronal networks in the context of plasticity associated with development, learning and pathophysiology.

Multifunctional magnetic resonance imaging probes

Magnetic resonance imaging (MRI) is a key imaging modality in cancer diagnostics and therapy monitoring. MRI-based tumor detection and characterization is commonly achieved by exploiting the compositional, metabolic, cellular, and vascular differences between malignant and healthy tissue. Contrast agents are frequently applied to enhance this contrast. The last decade has witnessed an increasing interest in novel multifunctional MRI probes. These multifunctional constructs, often of nanoparticle design, allow the incorporation of multiple imaging agents for complementary imaging modalities as well as anti-cancer drugs for therapeutic purposes. The composition, size, and surface properties of such constructs can be tailored as to improve biodistribution and ensure optimal delivery to the tumor microenvironment by passive or targeted mechanisms. Multifunctional MRI probes hold great promise to facilitate more specific tumor diagnosis, patient-specific treatment planning, the monitoring of local drug delivery, and the early evaluation of therapy. This chapter reviews the state-of-the-art and new developments in the application of multifunctional MRI probes in oncology.

Preclinical molecular imaging using PET and MRI

Molecular imaging fundamentally changes the way we look at cancer. Imaging paradigms are now shifting away from classical morphological measures towards the assessment of functional, metabolic, cellular, and molecular information in vivo. Interdisciplinary driven developments of imaging methodology and probe molecules utilizing animal models of human cancers have enhanced our ability to non-invasively characterize neoplastic tissue and follow anti-cancer treatments. Preclinical molecular imaging offers a whole palette of excellent methodology to choose from. We will focus on positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques, since they provide excellent and complementary molecular imaging capabilities and bear high potential for clinical translation. Prerequisites and consequences of using animal models as surrogates of human cancers in preclinical molecular imaging are outlined. We present physical principles, values and limitations of PET and MRI as molecular imaging modalities and comment on their high potential to non-invasively assess information on hypoxia, angiogenesis, apoptosis, gene expression, metabolism, and cell trafficking in preclinical cancer research.

Opportunities and pitfalls of cancer imaging in clinical trials

Cancer treatment strategies have changed considerably over the past two decades, with increasing emphasis on cancer-specific biological therapies. This situation has led to the incorporation of biomarkers, including those obtained by medical imaging, into trial designs to better understand mechanisms of action and, hopefully, to provide early evidence of treatment efficacy at a molecular or physiological level. Unlike blood tests and tissue samples, an imaging biomarker allows assessment of treatment in the whole tumor, in all tumors in the body, and at multiple time points. This situation has increased the complexity of clinical trials, as each imaging modality has issues related to cost, ease of use, patient compatibility, data analysis, and interpretation. This article reviews strengths and limitations of the current imaging methods available in clinical cancer trials, including MRI, CT, PET, and ultrasonography. The information gained by each test, and the difficulties in acquiring the data and interpreting it are also discussed in order to help researchers plan imaging in clinical trials and interpret data from such studies.

HiSStology: high spectral and spatial resolution magnetic resonance imaging detection of vasculature validated by histology and micro-computed tomography

High spectral and spatial resolution (HiSS) data, acquired with echo-planar spectroscopic imaging (EPSI), can be used to acquire water spectra from each small image voxel. These images are sensitive to changes in local susceptibility caused by superparamagnetic iron oxide particles (SPIO); therefore, we hypothesized that images derived from HiSS data are very sensitive to tumor neovasculature following injection of SPIO. Accurate image registration was used to validate HiSS detection of neovasculature with histology and micro-computed tomographic (microCT) angiography. Athymic nude mice and Copenhagen rats were inoculated with Dunning AT6.1 prostate tumor cells in the right hind limb. The tumor region was imaged pre- and post-intravenous injection of SPIO. Three-dimensional assemblies of the CD31-stained histologic slices of the mouse legs and the microCT images of the rat vascular casts were registered with EPSI. The average distance between HiSS-predicted regions of high vascular density on magnetic resonance imaging and CD31-stained regions on histology was 200 μm. Similarly, vessels identified by HiSS in the rat images coincided with vasculature in the registered microCT image. The data demonstrate a strong correlation between tumor vasculature identified using HiSS and two gold standards: histology and microCT angiography.

Relationship between serum heparanase and microscopic venous invasion in patients with hepatocellular carcinoma

The serum heparanase level of 92 patients with hepatocellular carcinoma (HCC) measured by enzyme-linked immunosorbent assay (median, 91.4 U/mL) was higher than that of 19 healthy control subjects. Serum heparanase levels were higher in patients with HCC characterized by large tumors (>5 cm), advanced pTNM stage (III and IV), tumor capsule absence, and portal vein invasion. Positive correlations between serum heparanase and tumor heparanase expression were observed in 92 patients with HCC, 53 among them treated with tumor resection. In these 53 patients, the rate of microscopic venous invasion was significantly higher in 18 cases with high serum heparanase levels (>91.4 U/mL) than in the other 35 cases with low heparanase levels (14/18 vs 10/35; P = .001). Serum heparanase and vascular endothelial growth factor were identified as independent predictive factors for HCC microscopic venous invasion. The postoperative recurrence-free time (median, 8.7 months; range, 4.1-22.9 months), recurrence rate (72% [13/18]), 1.5-year disease-free survival rate (29.7%) were significantly worse in these 18 patients.

A comparison of tracer kinetic models for T1-weighted dynamic contrast-enhanced MRI: application in carcinoma of the cervix

The Tofts tracer kinetic models are often used to analyze dynamic contrast-enhanced MRI data. They are derived from a general two-compartment exchange model (2CXM) but assume negligible plasma mean transit time. The 2CXM estimates tissue plasma perfusion and capillary permeability-surface area; the Tofts models estimate the transfer constant K(trans), which reflects a combination of these two parameters. The aims of this study were to compare the 2CXM and Tofts models and report microvascular parameters in patients with cervical cancer. Thirty patients were scanned pretreatment using a dynamic contrast-enhanced MRI protocol with a 3 sec temporal resolution and a total scan duration of 4 min. Whole-tumor parameters were estimated with both models. The 2CXM provided superior fits to the data for all patients (all 30 P values < 0.005), and significantly different parameter estimates were obtained (P < 0.01). K(trans) (mean = 0.35 +/- 0.26 min(-1)) did not equal absolute values of tissue plasma perfusion (mean = 0.65 +/- 0.56 mL/mL/min) or permeability-surface area (mean = 0.14 +/- 0.09 mL/mL/min) but correlated strongly with tissue plasma perfusion (r = 0.944; P = 0.01). Average plasma mean transit time, calculated with the 2CXM, was 22 +/- 16 sec, suggesting the assumption of negligible plasma mean transit time is not appropriate in this dataset and the 2CXM is better suited for its analysis than the Tofts models. The results demonstrate the importance of selecting an appropriate tracer kinetic model in dynamic contrast-enhanced MRI.

Cellular characterization of the peritumoral edema zone in malignant brain tumors

Brain edema is a hallmark of human malignant brain tumors and contributes to the clinical course and outcome of brain tumor patients. The so-called perifocal edema or brain swelling imposes in T2-weighted MR scans as high intensity areas surrounding the bulk tumor mass. The mechanisms of this increased fluid attraction and the cellular composition of the microenvironment are only partially understood. In this study, we focus on imaging perifocal edema in orthotopically implanted gliomas in rodents and correlate perifocal edema with immunohistochemical markers. We identified that areas of perifocal edema not only include the tumor invasion zone, but also are associated with increased glial fibrillary acidic protein (GFAP) and aquaporin-4 expression surrounding the bulk tumor mass. Moreover, a high number of activated microglial cells expressing CD11b and macrophage migration inhibitory factor (MIF) accumulate at the tumor border. Thus, the area of perifocal edema is mainly dominated by reactive changes of vital brain tissue. These data corroborate that perifocal edema identified in T2-weighted MR scans are characterized with alterations in glial cell distribution and marker expression forming an inflammatory tumor microenvironment.

Monitoring angiogenesis in human melanoma xenograft model using contrast-enhanced ultrasound imaging

The potential for noninvasive monitoring and quantification of tumor angiogenesis with contrast-enhanced ultrasound imaging has been investigated in a murine cancer model. Seventy athymic nude mice were implanted with the human melanoma cell line DB-1 but only 30 of these were available for the final study. The 30 mice were divided into three groups (10 mice/group), which were studied with contrast-enhanced ultrasound imaging 4, 5 or 6 weeks post-implantation. Power Doppler and pulse inversion harmonic imaging (PIHI) were performed (in real time and intermittently) with a Sonoline Elegra scanner (Siemens Medical Solutions, Issaquah, WA) following injection of Optison (dose: 0.4-0.6 ml/kg; GE Healthcare, Princeton, NJ). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between the percent area stained with VEGF and ultrasound measures of tumor neovascularity obtained with all three techniques (p < 0.01). Contrast-enhanced ultrasound imaging of tumor neovascularity appears to provide a noninvasive marker of angiogenesis corresponding to the expression of VEGF in the DB-1 model and may become a useful tool for monitoring clinical anti-angiogenic therapies.

Molecular profiling of angiogenesis with targeted ultrasound imaging: early assessment of antiangiogenic therapy effects

Molecular ultrasound is capable of elucidating the expression of angiogenic markers in vivo. However, the capability of the method for volumetric "multitarget quantification" and for the assessment of antiangiogenic therapy response has rather been investigated. Therefore, we generated cyanoacrylate microbubbles linked to vascular endothelial growth factor receptor 2 (VEGFR2) and alphavbeta3 integrin binding ligands and quantified their accumulation in squamous cell carcinoma xenografts (HaCaT-ras-A-5RT3) in mice with the quantitative volumetric ultrasound scanning technique, sensitive particle acoustic quantification. Specificity of VEGFR2 and alphavbeta3 integrin binding microbubbles was shown, and changes in marker expression during matrix metalloproteinase inhibitor treatment were investigated. In tumors, accumulation of targeted microbubbles was significantly higher compared with nonspecific ones and could be inhibited competitively by addition of the free ligand in excess. Also, multimarker imaging could successfully be done during the same imaging session. Molecular ultrasound further indicated a significant increase of VEGFR2 and alphavbeta3 integrin expression during tumor growth and a considerable decrease in both marker densities after matrix metalloproteinase inhibitor treatment. Histologic data suggested that the increasing VEGFR2 and alphavbeta3 integrin concentrations in tumors during growth are related to an up-regulation of its expression by the endothelial cells, whereas its decrease under therapy is more related to the decreasing relative vessel density. In conclusion, targeted ultrasound appears feasible for the longitudinal molecular profiling of tumor angiogenesis and for the sensitive assessment of therapy effects in vivo.

The effects of tumor-derived platelet-derived growth factor on vascular morphology and function in vivo revealed by susceptibility MRI

Platelet-derived growth factors (PDGF) play a major role in pericyte recruitment in tumor capillaries. Pericytes are required for proper vessel development, and contribute to tumor angiogenesis by promoting stabilization and maturation of newly formed vessels. To investigate the effects of pericyte coverage on tumor vessel morphology and function in vivo, tumors derived from B16 melanoma cells transfected with either control plasmid (B16/ctr) or plasmid encoding full-length PDGF-BB (B16/PDGF), the latter previously shown to have enhanced blood vessel pericyte coverage and an increased tumor growth rate, were assessed using histopathological methods, Hoechst 33342-based perfusion analyses, and two noninvasive susceptibility magnetic resonance imaging (MRI) methods. Susceptibility-contrast MRI, incorporating the use of ultrasmall superparamagnetic iron oxide particles, revealed a significant (p < 0.05) reduction in vessel size index (R(v)) of B16/PDGF tumors, and which was validated histologically by the presence of significantly smaller (p < 0.001), more punctate blood vessels identified by fluorescence microscopy of the perfusion marker Hoechst 33342. Intrinsic-susceptibility MRI was used to measure the transverse MRI relaxation rate R(2)*, sensitive to changes in endogenous paramagnetic [deoxyhaemoglobin], and used to probe for vascular maturation and function. Hypercapnia (5% CO(2)/95% air) induced a negligible Delta R(2)* response in the B16/ctr and B16/PDGF tumors. In contrast, hyperoxia (5% CO(2)/95% O(2)) induced a significantly greater R(2)* reduction in the B16/PDGF tumors (p < 0.02). Together the susceptibility MRI-derived biomarkers reveal novel pericyte-dependent changes in the morphology and function of the perfused tumor vasculature in vivo.

Volumetric high-frequency Doppler ultrasound enables the assessment of early antiangiogenic therapy effects on tumor xenografts in nude mice

The sensitivity of Doppler ultrasound below 10 MHz to assess antiangiogenic therapy effects in tumor xenografts has been shown to be limited. Thus, our aim was to evaluate high-frequency volumetric power-Doppler ultrasound (HF-VPDU) for monitoring antiangiogenic treatments. Squamous cell carcinoma xenografts grown in nude mice were scanned with HF-VPDU at a center frequency of 30 MHz. Images with 200-microm slice thicknesses were recorded and merged into a three-dimensional dataset, of which the relative color pixel density was determined. Animals received either VEGFR2 antibodies or 0.9% NaCl and were examined at days 0, 3 and 6 of treatment. After the last examination, tumors were resected and their vascularization characterized by immunohistology. At day 6, the volumes of treated and untreated tumors were not significantly different yet. In contrast, mean tumor vascularization in treated animals had decreased to 44%, while in the control group it had increased to 152% (P < 0.01). In correspondence, vessel density, as determined by CD31 staining, was 0.19 +/- 0.10% in treated and 0.92 +/- 0.41% in untreated tumors (P < 0.01). Additionally, the fraction of mature (SMA-positive) vessels increased under therapy. Thus, HF-VPDU can be considered as an easily applicable and fast method to screen high animal numbers for antiangiogenic therapy effects.

Lymphatic vessel density and function in experimental bladder cancer

BACKGROUND

The lymphatics form a second circulatory system that drains the extracellular fluid and proteins from the tumor microenvironment, and provides an exclusive environment in which immune cells interact and respond to foreign antigen. Both cancer and inflammation are known to induce lymphangiogenesis. However, little is known about bladder lymphatic vessels and their involvement in cancer formation and progression.

METHODS

A double transgenic mouse model was generated by crossing a bladder cancer-induced transgenic, in which SV40 large T antigen was under the control of uroplakin II promoter, with another transgenic mouse harboring a lacZ reporter gene under the control of an NF-kappaB-responsive promoter (kappaB-lacZ) exhibiting constitutive activity of beta-galactosidase in lymphatic endothelial cells. In this new mouse model (SV40-lacZ), we examined the lymphatic vessel density (LVD) and function (LVF) during bladder cancer progression. LVD was performed in bladder whole mounts and cross-sections by fluorescent immunohistochemistry (IHC) using LYVE-1 antibody. LVF was assessed by real-time in vivo imaging techniques using a contrast agent (biotin-BSA-Gd-DTPA-Cy5.5; Gd-Cy5.5) suitable for both magnetic resonance imaging (MRI) and near infrared fluorescence (NIRF). In addition, IHC of Cy5.5 was used for time-course analysis of co-localization of Gd-Cy5.5 with LYVE-1-positive lymphatics and CD31-positive blood vessels.

RESULTS

SV40-lacZ mice develop bladder cancer and permitted visualization of lymphatics. A significant increase in LVD was found concomitantly with bladder cancer progression. Double labeling of the bladder cross-sections with LYVE-1 and Ki-67 antibodies indicated cancer-induced lymphangiogenesis. MRI detected mouse bladder cancer, as early as 4 months, and permitted to follow tumor sizes during cancer progression. Using Gd-Cy5.5 as a contrast agent for MRI-guided lymphangiography, we determined a possible reduction of lymphatic flow within the tumoral area. In addition, NIRF studies of Gd-Cy5.5 confirmed its temporal distribution between CD31-positive blood vessels and LYVE-1 positive lymphatic vessels.

CONCLUSION

SV40-lacZ mice permit the visualization of lymphatics during bladder cancer progression. Gd-Cy5.5, as a double contrast agent for NIRF and MRI, permits to quantify delivery, transport rates, and volumes of macromolecular fluid flow through the interstitial-lymphatic continuum. Our results open the path for the study of lymphatic activity in vivo and in real time, and support the role of lymphangiogenesis during bladder cancer progression.

Discovery of gliotoxin as a new small molecule targeting thioredoxin redox system

Thioredoxin redox system has been implicated as an intracellular anti-oxidant defense system leading to reduction of cellular oxidative stresses utilizing electrons from NADPH. From high content screening of small molecules targeting the system, gliotoxin, a fungal metabolite, was identified as an active compound. Gliotoxin potently accelerates NADPH oxidation and reduces H(2)O(2). The compound reduces H(2)O(2) to H(2)O by replacing the function of peroxiredoxin in vitro and decreases intracellular level of H(2)O(2) in HeLa cells. The anti-oxidant activity of gliotoxin was further validated H(2)O(2)-mediated cellular phenotype of angiogenesis. The proliferation of endothelial cells was inhibited by the compound at nanomolar range. In addition, H(2)O(2)-induced tube formation and invasion of the cells were blocked by gliotoxin. Together, these results demonstrate that gliotoxin is a new small molecule targeting thioredoxin redox system.

Autonomously vascularized cellular constructs in tissue engineering: opening a new perspective for biomedical science

In tissue engineering cell cultures play a crucial role besides the matrix materials for the end of substituting lost tissue functions. The cell itself is situated at the cross-roads leading to different orders of scale, from molecule to organism and different levels of function, from biochemistry to macrophysiology. Extensive in vitro investigations have dissected a vast amount of cellular phenomena and the role of a number of bioactive substances has been elucidated in the past. Further, recombinant DNA technologies allow modulation of the expression profiles of virtually all kinds of cells. However, issues of vascularization in vivo limit transferability of these observations and restrict upscaling into clinical applications. Novel in vivo models of vascularization have evolved inspired from reconstructive microsurgical concepts and they encompass axial neovascularization by means of vascular induction. This work represents a brief description of latest developments and potential applications of neovascularization and angiogenesis in tissue engineering.