Vascular structure and microcirculation of experimental pancreatic carcinoma in rats

Synergistic treatment strategy: combining CAR-NK cell therapy and radiotherapy to combat solid tumors

Immunotherapy, notably chimeric antigen receptor (CAR) modified natural killer (NK) cell therapy, has shown exciting promise in the treatment of hematologic malignancies due to its unique advantages including fewer side effects, diverse activation mechanisms, and wide availability. However, CAR-NK cell therapies have demonstrated limited efficacy against solid tumors, primarily due to challenges posed by the solid tumor microenvironment. In contrast, radiotherapy, a well-established treatment modality, has been proven to modulate the tumor microenvironment and facilitate immune cell infiltration. With these observations, we hypothesize that a novel therapeutic strategy integrating CAR-NK cell therapy with radiotherapy could enhance the ability to treat solid tumors. This hypothesis aims to address the obstacles CAR-NK cell therapies face within the solid tumor microenvironment and explore the potential efficacy of their combination with radiotherapy. By capitalizing on the synergistic advantages of CAR-NK cell therapy and radiotherapy, we posit that this could lead to improved prognoses for patients with solid tumors.

Anticancer Effect of Heparin-Taurocholate Conjugate on Orthotopically Induced Exocrine and Endocrine Pancreatic Cancer

Simple Summary

Pancreatic cancer has a less than 9% 5-year survival rate among patients because it is very difficult to detect and diagnose early. Combinatorial chemotherapy with surgery or radiotherapy is a potential remedy to treat pancreatic cancer. However, these strategies still have side effects such as hair loss, skin soreness and fatigue. To overcome these side effects, angiogenesis inhibitors such as sunitinib are used to deliver targeted blood vessels around tumor tissues, including pancreatic cancer tumors. It is still controversial whether antiangiogenesis therapy is sufficient to treat pancreatic cancer. So far, many scientists have not been focused on the tumor types of pancreatic cancer when they have developed antipancreatic cancer medication. Here, we used heparin–taurocholate (LHT) as an anticancer drug to treat pancreatic cancer through inhibition of angiogenic growth factors. In this study, we examined the anticancer efficacy of LHT on various types of pancreatic cancer in an orthotopic model.

Abstract

Pancreatic cancers are classified based on where they occur, and are grouped into those derived from exocrine and those derived from neuroendocrine tumors, thereby experiencing different anticancer effects under medication. Therefore, it is necessary to develop anticancer drugs that can inhibit both types. To this end, we developed a heparin–taurocholate conjugate, i.e., LHT, to suppress tumor growth via its antiangiogenic activity. Here, we conducted a study to determine the anticancer efficacy of LHT on pancreatic ductal adenocarcinoma (PDAC) and pancreatic neuroendocrine tumor (PNET), in an orthotopic animal model. LHT reduced not only proliferation of cancer cells, but also attenuated the production of VEGF through ERK dephosphorylation. LHT effectively reduced the migration, invasion and tube formation of endothelial cells via dephosphorylation of VEGFR, ERK1/2, and FAK protein. Especially, these effects of LHT were much stronger on PNET (RINm cells) than PDAC (PANC1 and MIA PaCa-2 cells). Eventually, LHT reduced ~50% of the tumor weights and tumor volumes of all three cancer cells in the orthotopic model, via antiproliferation of cancer cells and antiangiogenesis of endothelial cells. Interestingly, LHT had a more dominant effect in the PNET-induced tumor model than in PDAC in vivo. Collectively, these findings demonstrated that LHT could be a potential antipancreatic cancer medication, regardless of pancreatic cancer types.

Endothelial capture using antibodies and nanoparticles in human tissues: Antigen identification and liver segment imaging

BACKGROUND

The unique phenomenon of endothelial antibody capture (endocapt) leads to site-specific accumulation of antibodies on the endothelium after its locoregional injection. The potential of this phenomenon has already been demonstrated in animal models. In the present study, the translational potential of several human endothelium-specific antibodies for their use in the endocapt-based approach was analysed.

METHODS

The binding of different endothelium-surface specific monoclonal antibody clones was analysed in human tissue and in endothelial cells using image-based immunofluorescence and the determination of half-maximal effective concentration (EC₅₀). The potential of endocapt-based locoregional application of antibodies or antibody-coated liposomes was analysed ex vivo using isolated mouse liver perfusion and in vivo using superselective injection in tumour models.

RESULTS

Eight out of ten antibody clones were assigned to the group of "fast binding antibodies". Different antibody clones showed various binding kinetics to the same endothelial marker whereas the binding kinetics of single antibody clones was independent from the tissue type. Anti-CD49e, anti-CD31, anti-CD34 and anti-CD102 antibodies showed the lowest EC₅₀ of antibody binding concentration and constant results in EC₅₀ determination of antibody binding to cells and human tissue. Experimental studies using anti-mouse CD49e antibody and coated immunoliposomes confirmed their effective capture by endothelial cells in vitro and in vivo by which fluorescent liver segment labelling was achieved.

CONCLUSIONS

Our findings identify the high potential of several human antibody clones, especially anti-CD49e, -CD31, -CD34 and -CD102, for endocapt technology. We also propose important translational implications of these antibodies for image-guided liver surgery and for use of nanoparticles/immunoliposomes. Toxicological studies are indispensable for further translational development of new antibodies for endocapt.

STATEMENT OF SIGNIFICANCE

The phenomenon of endothelial antibody capture (endocapt) leads to site-specific accumulation of antibodies on the endothelium after its locoregional injection. This phenomenon broadly prevents systemic circulation of the antibody or antibody-drug conjugates. In the present study, our findings identify several human antibody clones promising for endothelial capture technology. This study provided the experimental demonstration of liver segment labelling ex vivo using isolated mouse liver perfusion and in vivo using superselective injection in tumor models. In addition, this study proposed the important translational implications of selected antibodies for image-guided liver surgery and for use of nanoparticles/immunoliposomes.

Impact of wall shear stress and ligand avidity on binding of anti-CD146-coated nanoparticles to murine tumor endothelium under flow

The endothelial phenotype of tumor blood vessels differs from the liver and forms an important base for endothelium-specific targeting by antibody-coated nanoparticles. Although differences of shear stress and ligand avidity can modulate the nanoparticle binding to endothelium, these mechanisms are still poorly studied. This study analyzed the binding of antibody-coated nanoparticles to tumor and liver endothelium under controlled flow conditions and verified this binding in tumor models in vivo. Binding of anti-CD146-coated nanoparticles, but not of antibody was significantly reduced under increased wall shear stress and the degree of nanoparticle binding correlated with the avidity of the coating. The intravascular wall shear stress favors nanoparticle binding at the site of higher avidity of endothelial epitope which additionally promotes the selectivity to tumor endothelium. After intravenous application in vivo, pegylated self-coated nanoparticles showed specific binding to tumor endothelium, whereas the nanoparticle binding to the liver endothelium was very low. This study provides a rationale that selective binding of mAb-coated nanoparticles to tumor endothelium is achieved by two factors: higher expression of endothelial epitope and higher nanoparticle shearing from liver endothelium. The combination of endothelial marker targeting and the use of shear stress-controlled nanoparticle capture can be used for selective intratumoral drug delivery.

Pancreatic ductal adenocarcinoma: From genetics to biology to radiobiology to oncoimmunology and all the way back to the clinic

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death. Despite improvements in the clinical management, the prognosis of PDAC remains dismal. In the present comprehensive review, we will examine the knowledge of PDAC genetics and the new insights into human genome sequencing and clonal evolution. Additionally, the biology and the role of the stroma in tumour progression and response to treatment will be presented. Furthermore, we will describe the evidence on tumour chemoresistance and radioresistance and will provide an overview on the recent advances in PDAC metabolism and circulating tumour cells. Next, we will explore the characteristics and merits of the different mouse models of PDAC. The inflammatory milieu and the immunosuppressive microenvironment mediate tumour initiation and treatment failure. Hence, we will also review the inflammatory and immune escaping mechanisms and the new immunotherapies tested in PDAC. A better understanding of the different mechanisms of tumour formation and progression will help us to identify the best targets for testing in future clinical studies of PDAC.

Diffusion-weighted magnetic resonance imaging of the pancreas: diagnostic benefit from an intravoxel incoherent motion model-based 3 b-value analysis

OBJECTIVES

The objective of this study was to evaluate the diagnostic benefit of an intravoxel incoherent motion (IVIM) model-based characterization of pancreatic masses from diffusion-weighted imaging (DWI) with 3 b values.

MATERIALS AND METHODS

This retrospective study had an approval from the institutional review board, and informed patient consent was waived. The 1.5-T DWI data of 42 patients with or without pancreatic disease, acquired by a respiratory-gated spin-echo echo-planar imaging sequence with 3 b values (0, 50, 800 s/mm²), were retrospectively analyzed. The IVIM-related parameters D', which is the apparent diffusion coefficient [ADC(50,800)], and f', as well as ADC(0,50), and conventional ADC(0,800) were calculated voxelwise. Regions of interest were analyzed in pancreatic adenocarcinomas (CAs, n = 12), neuroendocrine pancreatic tumors (NETs, n = 9), and chronic pancreatitis (CPs, n = 11), not affected tissue of each pathologic group, and in the head, body, and tail of the healthy pancreas (n = 10).

RESULTS

By ADC(0,800) and D', CAs could hardly be distinguished from neuroendocrine pancreatic tumors and chronic pancreatitis. However, CAs revealed very low ADC(0,50) and f' values, which differed significantly from all other groups. In the healthy pancreas, ADC(0,800) and D' values were significantly higher for the head than for the body and tail, but no significant differences were found for ADC(0,50) and f'.

CONCLUSIONS

The determination of IVIM-based microcirculation-sensitive parameter maps from DWI with 3 b values significantly improved the discrimination of CAs from NETs, CPs, and the healthy tissue.

Monitoring the effects of anti-angiogenesis on the radiation sensitivity of pancreatic cancer xenografts using dynamic contrast-enhanced computed tomography

PURPOSE

To image the intratumor vascular physiological status of pancreatic tumors xenografts and their response to anti-angiogenic therapy using dynamic contrast-enhanced computed tomography (DCE-CT), and to identify parameters of vascular physiology associated with tumor x-ray sensitivity after anti-angiogenic therapy.

METHODS AND MATERIALS

Nude mice bearing human BxPC-3 pancreatic tumor xenografts were treated with 5 Gy of radiation therapy (RT), either a low dose (40 mg/kg) or a high dose (150 mg/kg) of DC101, the anti-VEGF receptor-2 anti-angiogenesis antibody, or with combination of low or high dose DC101 and 5 Gy RT (DC101-plus-RT). DCE-CT scans were longitudinally acquired over a 3-week period post-DC101 treatment. Parametric maps of tumor perfusion and fractional plasma volume (Fp) were calculated and their averaged values and histogram distributions evaluated and compared to controls, from which a more homogeneous physiological window was observed 1-week post-DC101. Mice receiving a combination of DC101-plus-RT(5 Gy) were imaged baseline before receiving DC101 and 1 week after DC101 (before RT). Changes in perfusion and Fp were compared with alternation in tumor growth delay for RT and DC101-plus-RT (5 Gy)-treated tumors.

RESULTS

Pretreatment with low or high doses of DC101 before RT significantly delayed tumor growth by an average 7.9 days compared to RT alone (P ≤ .01). The increase in tumor growth delay for the DC101-plus-RT-treated tumors was strongly associated with changes in tumor perfusion (ΔP>-15%) compared to RT treated tumors alone (P=.01). In addition, further analysis revealed a trend linking the tumor's increased growth delay to its tumor volume-to-DC101 dose ratio.

CONCLUSIONS

DCE-CT is capable of monitoring changes in intratumor physiological parameter of tumor perfusion in response to anti-angiogenic therapy of a pancreatic human tumor xenograft that was associated with enhanced radiation response.

Endothelial plasticity governs the site-specific leukocyte recruitment in hepatocellular cancer

The correct programming of the endothelial cell phenotype is crucial for efficient leukocyte recruitment to tumor tissue. It has been previously described that T cells infiltrated hepatocellular cancer (HCC) tissue mainly in peritumoral, stromal and tumor border areas. In the current study, phenotype features of tumor endothelial cells and their potential impact on leukocyte recruitment were analyzed in murine tissue of HCC. In the murine model, proinflammatory stimulation with IL-1β induced leukocyte recruitment in the blood vessels of peripheral tumor areas and in nonmalignant liver tissue, but not in deeper tumor blood vessels. Furthermore, peripheral tumor endothelium, but not deeper tumor blood vessels exhibited a "normalized" hepatic sinusoidal endothelial cell (HSEC)-like phenotype with regard to the expression of adhesion molecules and liver sinusoidal endothelial markers. When tumor endothelial cells were isolated and incubated in vitro, their phenotype rapidly changed and became almost identical to normal hepatic endothelial cells. Interestingly, cytokine production in HCC was strongly dysregulated as compared to normal liver, with IL-1RN exhibiting the most prominent elevation. Experiments with isolated hepatic endothelial cells showed that IL-1RN effectively antagonized the activating action of IL-1β on the expression of adhesion molecules and T cell attachment. These novel insights indicate that tumor endothelium of HCC represents a plastic system that is susceptible to microenvironmental changes. The peritumoral and tumor border areas have distinct endothelial cell phenotype, which promotes leukocyte recruitment to HCC tissue.

Contrast-enhanced endoscopic ultrasound

The European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) introduced guidelines on the use of contrast-enhanced ultrasound (CEUS) in 2004. This EFSUMB-document focused mainly on liver applications. However, new applications extending beyond the liver were developed thereafter. Increased interest in recent years in CEUS technique and in the application of CEUS in novel fields like endoscopic ultrasound (EUS) has revolutionized indications and applications. As a result, the EFSUMB initiated a new update of the guidelines in 2011 to include this additional knowledge. Some of the contrast-enhanced EUS (CE-EUS) indications are established, whereas others are preliminary; these latter indications are categorized as emergent CEUS applications since the available evidence is insufficient for general recommendation. This article focuses on the use of CE-EUS in various clinical settings. The reader will get an overview of current indications and possible applications of CE-EUS. This involves the introduction of different contrast studies including color Doppler techniques (known as contrast-enhanced high mechanical index endosonography or CEHMI-EUS) as well as more modern high-resolution contrast-enhanced techniques (known as contrast-enhanced low mechanical index endosonography or CELMI EUS).

Contrast enhanced endoscopic ultrasound: More than just a fancy Doppler

Contrast enhanced endoscopic ultrasound (CEUS) is a new modality that takes advantage of vascular structure and blood flow to distinguish different clinical entities. Contrast agents are microbubbles that oscillate when exposed to ultrasonographic waves resulting in characteristic acoustic signals that are then converted to colour images. This permits exquisite imaging of macro- and microvasculature, providing information to help delineate malignant from non-malignant processes. The use of CEUS may significantly increase the sensitivity and specificity over conventional endoscopic ultrasound. Currently available contrast agents are safe, with infrequent adverse effects. This review summarizes the theory and technique behind CEUS and the current and future clinical applications.

Endoscopic ultrasound-guided fine-needle aspiration biopsy and trucut biopsy in gastroenterology - An overview

Endoscopic ultrasound (EUS)-guided biopsies are reliable, safe and effective techniques in obtaining samples for cytological or histological examinations either as a primary procedure or in cases where other biopsy techniques have failed. Endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNA), as well as endoscopic ultrasound-guided trucut biopsy (EUS-TCB), has proven to be of significant value in the diagnostic evaluation of benign and malignant diseases, as well as in staging of the malignant tumours of the gastrointestinal tract and of adjacent organs. The diagnostic yield of EUS-guided biopsies depends on site, size and characteristics of target tissues as well as technical and procedural factors (type of needle, biopsy technique and material processing). Other weighting factors include expertise, training and interaction between the endosonographer and cytopathologist. Rapid on-site cytological evaluation has proven to be successful in optimising the diagnostic efficiency of EUS-FNA. A sensible alternative is to collect specimens for histological and immunohistochemical investigations in addition to the cytological smears. EUS-FNA using a 22-gauge needle is successful in harvesting core biopsies in approximately three out of four cases. Therefore, the use of 19-gauge needles for EUS-FNA or EUS-TCB may only be necessary in selected cases. The reproducibility of cytopathological diagnosis among pathologists with special experience in assessing material obtained by EUS-guided biopsies is very high. False-positive diagnosis of malignancy in EUS-guided biopsy is rare. False-negative diagnosis appears with variable frequency depending on the target tissue, technical factors and expertise of the endosonographer and cytopathologist. There are numerous challenges and pitfalls in the differential diagnostic classification of benign and malignant lesions. These problems are related to the characteristics of samples obtained by EUS-guided biopsy, as well as to the multiple diagnoses with similar or overlapping cytological or histological characteristics. The high prognostic and therapeutic relevance of the cytopathological diagnoses resulting from EUS-guided biopsy calls for a shared responsibility of an endosonographer and a cytopathologist.

Contrast-enhanced endoscopic ultrasound in discrimination between focal pancreatitis and pancreatic cancer

AIM: To evaluate the contrast-enhanced endosonography as a method of differentiating inflammation from pancreatic carcinoma based on perfusion characteristics of microvessels.

METHODS: In 86 patients with suspected chronic pancreatitis (age: 62 ± 12 years; sex: f/m 38/48), pancreatic lesions were examined by conventional endoscopic B-mode, power Doppler ultrasound and contrast-enhanced power mode (Hitachi EUB 525, SonoVue^®, 2.4 mL, Bracco) using the following criteria for malignant lesions: no detectable vascularisation using conventional power Doppler scanning, irregular appearance of arterial vessels over a short distance using SonoVue^® contrast-enhanced technique and no detectable venous vessels inside the lesion. A malignant lesion was assumed if all criteria were detectable [gold standard endoscopic ultrasound (EUS)-guided fine needle aspiration cytology, operation]. The criteria of chronic pancreatitis without neoplasia were defined as no detectable vascularisation before injection of SonoVue^®, regular appearance of vessels over a distance of at least 20 mm after injection of SonoVue^® and detection of arterial and venous vessels.

RESULTS: The sensitivity and specificity of conventional EUS were 73.2% and 83.3% respectively for pancreatic cancer. The sensitivity of contrast-enhanced EUS increased to 91.1% in 51 of 56 patients with malignant pancreatic lesion and the specificity increased to 93.3% in 28 of 30 patients with chronic inflammatory pancreatic disease.

CONCLUSION: Contrast-enhanced endoscopic ultrasound improves the differentiation between chronic pancreatitis and pancreatic carcinoma.

Expansion of endothelial surface by an increase of vessel diameter during tumor angiogenesis in experimental hepatocellular and pancreatic cancer

AIM: A low vessel density is a common feature of malignant tumors. We suggested that the expansion of vessel diameter might reconstitute the oxygen and nutritient’s supply in this situation. The aim of the present study was to compare the number and diameter of blood vessels in pancreatic and liver carcinoma with normal tissue.

METHODS: Tumor induction of pancreatic (DSL6A) or hepatocellular (Morris-hepatoma) carcinoma was performed in male Lewis (pancreatic cancer) and ACI (hepatoma) rats by an orthotopic inoculation of solid tumor fragments (pancreatic cancer) or tumor cells (hepatoma). Six weeks (pancreatic cancer) or 12 d (hepatoma) after tumor implantation, the tumor microvasculature as well as normal pancreatic or liver blood vessels were investigated by intravital microscopy. The number of perfused blood vessels in tumor and healthy tissue was assessed by computer-assisted image analysis.

RESULTS: The vessel density in healthy pancreas (565 ± 89 n/mm²) was significantly higher compared to pancreatic cancer (116 ± 36 n/mm²) (P < 0.001). Healthy liver showed also a significantly higher vessel density (689 ± 36 n/mm²) compared to liver carcinoma (286 ± 32 n/mm²) (P < 0.01). The comparison of diameter frequency showed a significant increase of vessel diameter in both malignant tumors compared to normal tissue (P < 0.05).

CONCLUSION: The expansion of endothelial cells during tumor angiogenesis is accompanied to a large extent by an increase of vessel diameter rather than by formation of new blood vessels. This may be a possible adaptive mechanism by which experimental pancreatic and hepatocellular cancers expand their endothelial diffusion surface of endothelium to compensate for inadequate neoangiogenesis.

Radiation-induced leukocyte adhesion to endothelium in normal pancreas and in pancreatic carcinoma of the rat

High-dose radiation is known to induce an inflammatory reaction in normal and malignant tissue including leukocyte infiltration. The influence of radiation on leukocyte-endothelium interaction in tumor tissue, which precedes leukocyte migration, has not yet been investigated to our knowledge. In our study, intravital microscopy was used to compare the radiogenic effects on leukocyte-endothelium interaction and leukocyte migration in healthy and malignant pancreatic tissue in vivo. An established model of ductlike pancreatic cancer (DSL6A) of syngeneic Lewis rats was utilized. Irradiation with 15 Gy increased the high-affinity leukocyte-endothelium interaction both in normal and malignant tissue. The low-affinity leukocyte-endothelium interaction was not significantly altered. Radiation-induced tumor cell death 12 days after radiation was significantly higher in tumors with moderate and severe leukocyte infiltration compared to low leukocyte infiltration. Thus, radiation-induced leukocyte infiltration in pancreatic carcinoma correlates with the extent of tumor cell death.

Different radiogenic effects on microcirculation in healthy pancreas and in pancreatic carcinoma of the rat

OBJECTIVE

To compare the radiogenic effects on microcirculation in healthy and malignant pancreatic tissue.

SUMMARY BACKGROUND DATA

Vascular injury is an important effect of radiotherapy, which has been suggested for antiangiogenic tumor therapy.

METHODS

An established model of duct-like pancreatic cancer (DSL6A) was used. Investigation was performed in 12 healthy and 24 tumor-bearing Lewis rats. The tumors were locally irradiated with 15 Gy in 12 animals 4 weeks after intraperitoneal inoculation. Additionally, local radiation of the normal pancreas was performed in six healthy animals. Intravital microscopy of tumor and normal pancreatic microcirculation was performed 5 days after radiation. Relevant parameters were erythrocyte velocity and functional vessel density. Tumor apoptosis and the fraction of vital tumor cells were estimated histologically 5 and 12 days after radiation.

RESULTS

Local radiation with 15 Gy caused a pronounced impairment of blood flow and functional capillary density in the normal pancreas 5 days after radiation, while the tumor blood flow was not significantly changed. A significant reduction in the fraction of vital tumor cells and a significant increase in tumor apoptosis were observed 12 days after radiation.

CONCLUSIONS

Local radiation impairs blood flow in healthy pancreas but not in pancreatic cancer tissue. Tumor cell death is the leading consequence of radiation injury in malignant pancreatic tissue without affecting the vascular system of the tumor. The authors conclude that external beam radiation does not appear to be a useful adjunct for a vascular-targeted therapy in pancreatic carcinoma but causes distinct hypoperfusion in the healthy pancreas.

Angiogenesis inhibition with TNP-470, 2-methoxyestradiol, and paclitaxel in experimental pancreatic carcinoma

INTRODUCTION

Inhibition of tumor angiogenesis is a novel therapeutic modality for various malignancies.

AIM

To investigate the effect of different antiangiogenic agents (TNP-470, 2-methoxyestradiol, and paclitaxel) on growth and neovascularization of experimental pancreatic cancer.

METHODOLOGY

In 25 male Lewis rats, tumor induction was achieved by orthotopic and subcutaneous tumor fragment implantation of ductlike pancreatic cancer DSL6A. Four weeks after tumor implantation, the animals were randomly treated with TNP-470, 2-methoxyestradiol, or paclitaxel. After 2 weeks of antiangiogenic therapy, total tumor volume, vital tumor surface, vascular density, and apoptosis were measured.

RESULTS

Total tumor volume and vital tumor surface were not significantly different in any of the treatment groups. Similarly, vascular density and apoptosis were not altered by treatment with the various angiogenesis inhibitors at the specific doses used.

CONCLUSION

We conclude that in contrast to many earlier studies, angiogenesis inhibition by a single-drug application and by the doses used in the present model did not reveal a favorable therapeutic effect on pancreatic cancer DSL6A. The combination of different angiogenesis inhibitors or higher doses might be more effective.

Evaluation of morphology and microcirculation of the pancreas by ex vivo and in vivo reflectance confocal microscopy

BACKGROUND

Near-infrared reflectance confocal microscopy (CM) provides non-invasive real-time images of thin virtual horizontal tissue sections with high resolution and contrast.

AIM

Aim of the study was to characterize morphology, microcirculation and leukocyte-endothelial interaction (LEI) in normal pancreas by in vivo and ex vivo CM.

METHODS

For CM we used water immersion objective lenses of high numerical aperture and near-infrared wavelengths. Experimentally measured lateral optical resolution is 0.5-1 micron and the axial resolution is 3-5 microns. The maximum depth of resolution was 300-400 microns. For ex vivo imaging, freshly excised pancreatic tissue from rats was studied by reflectance CM and conventional histopathology. For in vivo CM, the pancreatic head was exteriorized on a specially constructed stage for imaging the microcirculation and LEI. Images were obtained in real time at rates of 30 frames/s and later analyzed off-line to evaluate LEI and functional capillary density (FCD).

RESULTS

CM allowed high resolution visualization of normal pancreas acinar cells, ducts, islets, capillaries and LEI in postcapillary venules. Histological images and optical sections from ex vivo CM can be correlated. Cellular morphology is better analyzed by conventional histology, but angioarchitecture and connective tissue structure are better evaluated by CM. FCD (265.7 +/- 16.6 cm-1) and LEI (rolling leukocytes 5.3 +/- 1.6/100 microns/sticking leukocytes 1.5 +/- 0.9/100 microns) were evaluated by in vivo CM in the normal pancreas.

CONCLUSIONS

CM findings in tissues ex vivo correlate with those of classical histology but add informative details of connective tissue structure and angioarchitecture. Potential future applications for in vivo CM include real-time analysis of microcirculation, leukocyte-endothelial interaction and angiostructure in inflammatory and malignant pancreatic diseases.

Transformation of the microvascular system during multistage tumorigenesis

Simian virus SV40 large T Antigen expression in the islets of Langerhans of transgenic mice results in beta-cell hyperproliferation, onset of new blood vessel formation and the development of highly vascularized solid tumors. Angiogenesis in the RIPTag mouse model, as well as in human cancer, is a hallmark of multistage tumorigenesis and precedes the development of solid tumors. In our study, intravital microscopy was used to monitor changes in the blood vessel phenotype, microcirculation and leukocyte adhesion during the progression from normal islets to angiogenic islets and solid tumors. In RIP1-Tag5 mice, an aberrant microangioarchitecture becomes apparent in early stages during spontaneous tumor development. Notably, the transition from normal to angiogenic islets is characterized by an increase in vessel diameter rather than vessel numbers. Thus, dilatation of existing vessels precedes vessel sprouting. Once initiated, neovascularization in angiogenic islets results in loss of vessel hierarchy and differentiation. Solid insulinomas display a higher vessel density and even more dramatic vessel heterogeneity as revealed by local "hot spots" of neovascularization and irregular vessel diameters. Strikingly, profound changes in the microangioarchitecture are already observed in early angiogenic islets suggesting that key features of the angiogenic vasculature are established prior to the expansion of tumor mass. Moreover, adhesion of leukocytes was found to be dramatically decreased in both angiogenic islets and solid tumors and correlates with morphological alterations of the vasculature. Thus, vessel transformation and reduced leukocyte-endothelium interactions are not exclusively features of solid tumors but represent early events during tumorigenesis.