Pathology: cancer cells compress intratumour vessels

Tracer kinetic model-driven registration for dynamic contrast-enhanced MRI time-series data

Dynamic contrast-enhanced MRI (DCE-MRI) time series data are subject to unavoidable physiological motion during acquisition (e.g., due to breathing) and this motion causes significant errors when fitting tracer kinetic models to the data, particularly with voxel-by-voxel fitting approaches. Motion correction is problematic, as contrast enhancement introduces new features into postcontrast images and conventional registration similarity measures cannot fully account for the increased image information content. A methodology is presented for tracer kinetic model-driven registration that addresses these problems by explicitly including a model of contrast enhancement in the registration process. The iterative registration procedure is focused on a tumor volume of interest (VOI), employing a three-dimensional (3D) translational transformation that follows only tumor motion. The implementation accurately removes motion corruption in a DCE-MRI software phantom and it is able to reduce model fitting errors and improve localization in 3D parameter maps in patient data sets that were selected for significant motion problems. Sufficient improvement was observed in the modeling results to salvage clinical trial DCE-MRI data sets that would otherwise have to be rejected due to motion corruption.

Towards solid tumor treatment by irreversible electroporation: intrinsic redistribution of fields and currents in tissue

Local and drug-free tissue treatment by irreversible electroporation (IRE) involves the creation of aqueous pores in a cell's plasma membrane (PM) and leads to non-thermal cell death by necrosis. To investigate explicit pore-based effects we use two-dimensional system models with different spatial scales. The first is a multicellular system model (spatial scale 100 mum) that has irregularly shaped cells, and quantitatively describes dynamic (creation and destruction, evolution in pore size) pore behavior at the PM. The second is a tissue model (spatial scale 200 mm) that is constructed from a unit cell and uses the asymptotic (fixed pore size) electroporation model. Both system models show that significant redistribution of fields and currents occurs through transient PM pores. Pore histograms for the multicellular model demonstrate the simultaneous presence of small and large pores during IRE pulses. The associated significant increase of PM permeability may prove to be essential to understanding how cell death by necrosis occurs. The averaged tissue conductivity in both models increases during IRE pulses because of electroporation. This leads to greater electrical dissipation (heating) and, thus, to larger temperature increases than suggested by tissue models with passive and static electrical properties.

Antiangiogenics: the potential role of integrating this novel treatment modality with chemoradiation for solid cancers

Although still in very early stages of clinical development, the combination of antiangiogenics with contemporary chemoradiotherapy regimens has emerged as a feasible and promising approach to many cancers. We review the rationale and the current understanding of antiangiogenics and their therapeutic potential in combination with chemoradiotherapy. Finally, we offer a perspective on future research directions aimed at making this complex therapeutic approach successful in the clinic.

Time-course-dependent microvascular alterations in a model of myeloid leukemia in vivo

Functional and morphological properties of tumor microcirculation play a pivotal role in tumor progression, metastasis and inefficiency of tumor therapies. Despite enormous insights into tumor angiogenesis in solid tumors, little is known about the time-course-dependent properties of tumor vascularization in hematologic malignancies. The aim of this study was to establish a model of myeloid leukemia, which allows long-term monitoring of tumor progression and associated microcirculation. Red fluorescent protein-transduced human leukemic cell lines (M-07e) were implanted into cranial windows of severe combined immunodeficient mice. Intravital microscopy was performed over 55 days to measure functional (microvascular permeability, tissue perfusion rate and leukocyte-endothelium interactions) and morphological vascular parameters (vessel density, distribution and diameter). Tumor progression was associated with elevated microvascular permeability and an initial angiogenic wave followed by decreased vessel density combined with reduced tissue perfusion due to loss in small vessels and development of heterogenous tumor vascularization. Following altered geometric resistance of microcirculation, leukocyte-endothelium interactions were more frequent without increased leukocyte extravasation. It was concluded that time-dependent alterations of leukemic tumor vascularization exhibit strong similarities to those found in solid tumors. The potential contribution to the development of barriers to drug delivery in leukemic tumors is discussed.

Drug Resistance and the Solid Tumor Microenvironment

Resistance of human tumors to anticancer drugs is most often ascribed to gene mutations, gene amplification, or epigenetic changes that influence the uptake, metabolism, or export of drugs from single cells. Another important yet little-appreciated cause of anticancer drug resistance is the limited ability of drugs to penetrate tumor tissue and to reach all of the tumor cells in a potentially lethal concentration. To reach all viable cells in the tumor, anticancer drugs must be delivered efficiently through the tumor vasculature, cross the vessel wall, and traverse the tumor tissue. In addition, heterogeneity within the tumor microenvironment leads to marked gradients in the rate of cell proliferation and to regions of hypoxia and acidity, all of which can influence the sensitivity of the tumor cells to drug treatment. In this review, we describe how the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and discuss potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumor microenvironment.

Polydisulfide Gd(III) chelates as biodegradable macromolecular magnetic resonance imaging contrast agents

Macromolecular gadolinium (Gd)(III) complexes have a prolonged blood circulation time and can preferentially accumulate in solid tumors, depending on the tumor blood vessel hyperpermeability, resulting in superior contrast enhancement in magnetic resonance (MR) cardiovascular imaging and cancer imaging as shown in animal models. Unfortunately, safety concerns related to these agents’ slow elimination from the body impede their clinical development. Polydisulfide Gd(III) complexes have been designed and developed as biodegradable macromolecular magnetic resonance imaging (MRI) contrast agents to facilitate the clearance of Gd(III) complexes from the body after MRI examinations. These novel agents can act as macromolecular contrast agents for in vivo imaging and excrete rapidly as low-molecular-weight agents. The rationale and recent development of the novel biodegradable contrast agents are reviewed here. Polydisulfide Gd(III) complexes have relatively long blood circulation time and gradually degrade into small Gd(III) complexes, which are rapidly excreted via renal filtration. These agents result in effective and prolonged in vivo contrast enhancement in the blood pool and tumor tissue in animal models, yet demonstrate minimal Gd(III) tissue retention as the clinically used low-molecular-weight agents. Structural modification of the agents can readily alter the contrast-enhancement kinetics. Polydisulfide Gd(III) complexes are promising for further clinical development as safe, effective, biodegradable macromolecular MRI contrast agents for cardiovascular and cancer imaging, and for evaluation of therapeutic response.

Modelling the role of angiogenesis and vasculogenesis in solid tumour growth

Recent experimental evidence suggests that vasculogenesis may play an important role in tumour vascularisation. While angiogenesis involves the proliferation and migration of endothelial cells (ECs) in pre-existing vessels, vasculogenesis involves the mobilisation of bone-marrow-derived endothelial progenitor cells (EPCs) into the bloodstream. Once blood-borne, EPCs home in on the tumour site, where subsequently they may differentiate into ECs and form vascular structures. In this paper, we develop a mathematical model, formulated as a system of nonlinear ordinary differential equations (ODEs), which describes vascular tumour growth with both angiogenesis and vasculogenesis contributing to vessel formation. Submodels describing exclusively angiogenic and exclusively vasculogenic tumours are shown to exhibit similar growth dynamics. In each case, there are three possible scenarios: the tumour remains in an avascular steady state, the tumour evolves to a vascular equilibrium, or unbounded vascular growth occurs. Analysis of the full model reveals that these three behaviours persist when angiogenesis and vasculogenesis act simultaneously. However, when both vascularisation mechanisms are active, the tumour growth rate may increase, causing the tumour to evolve to a larger equilibrium size or to expand uncontrollably. Alternatively, the growth rate may be left unaffected, which occurs if either vascularisation process alone is able to keep pace with the demands of the growing tumour. To clarify further the effects of vasculogenesis, the full model is also used to compare possible treatment strategies, including chemotherapy and antiangiogenic therapies aimed at suppressing vascularisation. This investigation highlights how, dependent on model parameter values, targeting both ECs and EPCs may be necessary in order to effectively reduce tumour vasculature and inhibit tumour growth.

Non-uniform plasma leakage affects local hematocrit and blood flow: implications for inflammation and tumor perfusion

Vessel leakiness is a hallmark of inflammation and cancer. In inflammation, plasma extravasation and leukocyte adhesion occur in a coordinated manner to enable the immune response, but also to maintain tissue perfusion. In tumors, similar mechanisms operate, but they are not well regulated. Therefore, blood perfusion in tumors is non-uniform, and delivery of blood-borne therapeutics is difficult. In order to analyze the interplay among plasma leakage, blood viscosity, and vessel geometry, we developed a mathematical model that explicitly includes blood cells, vessel branching, and focal leakage. The results show that local hemoconcentration due to plasma leakage can greatly increase the flow resistance in individual vascular segments, diverting flow to other regions. Similarly, leukocyte rolling can increase flow resistance by partially blocking flow. Vessel dilation can counter these effects, and likely occurs in inflammation to maintain blood flow. These results suggest that potential strategies for improving perfusion through tumor networks include (i) eliminating non-uniform plasma leakage, (ii) inhibiting leukocyte interactions, and (iii) preventing RBC aggregation in sluggish vessels. Normalization of tumor vessels by anti-angiogenic therapy may improve tumor perfusion via the first two mechanisms.

The role of tumor microenvironment in prostate cancer bone metastasis

Prostate cancer (PCa) epithelial cells require a number of factors to facilitate their establishment and growth at a distant site of metastasis. Their ability to adapt to their microenvironment, proliferate and recruit an underlying stroma is integral to the survival and growth of the metastasis. PCa predominantly metastasizes to the bone, and bone metastases are the main cause of morbidity. The bone marrow provides a permissive environment for the formation of a metastasis. In some cases, the cells may remain dormant for some time, eventually proliferating in response to an unknown "trigger." The marrow is rich in progenitor cells that differentiate into numerous cell types, producing new blood vessels, supporting fibroblasts, and an underlying extracellular matrix (ECM) that form the reactive stroma. By secreting a number of cytokines, growth factors and proteases they recruit auxiliary cells required to produce a functional stroma. These components are involved in a reciprocal interaction between the stroma and the PCa cells, allowing for the growth and survival of the tumor. Left unchecked, once a PCa tumor has established itself in the bone marrow it will eventually replace the marrow, interrupting bone homeostasis and typically promoting an osteoblastic response in the bone including osteoclastic events. The abundant deposition of new woven bone results in nerve compression, bone pain and an increase in fractures in patients with PCa bone metastases. This review will examine the tumor microenvironment, its role in facilitating tumor dissemination, growth and the resultant pathologies associated with PCa bone metastasis.

The relevance of circulating epithelial tumor cells (CETC) for therapy monitoring during neoadjuvant (primary systemic) chemotherapy in breast cancer

BACKGROUND

Having demonstrated in a previous report that the response of circulating epithelial tumor cells (CETC) during the first cycles of primary (neoadjuvant) chemotherapy perfectly reflects the response of the tumor, in the present study the changes in cell numbers during subsequent cycles and their possible impact on the therapy's outcome were examined.

PATIENTS AND METHODS

In 58 breast cancer patients CETC were quantified during therapy with either EC (epirubicin/ cyclophosphamid) or dose intensified E (epirubicin) followed by taxane, with or without trastuzumab, and subsequent CMF (cyclophosphamid/methorexate/ fluorouracil).

RESULTS

CETC numbers declined more than 10-fold (good response) in 65% (her2/neu-negative) and 55% (her2/neu-positive) of patients during EC, and in 60% during dose intensified E, respectively, followed by an increase of CETC in all patients. CETC remained increased, decreasing only when adding CMF. A good initial response correlated with estrogen-receptor negativity, a poor response with early distant relapse (P < 0,0001, hazard ratio = 11.91).

CONCLUSION

Response of CETC already during the first cycles of neoadjuvant treatment predicts the final response of the tumor. Hitherto unknown effects of the release of tumor cells during therapy further our understanding of tumor-blood interaction and may improve access of agents like antibodies to cells. The impact on the further course of disease remains to be evaluated.

Real-time imaging of tumor-cell shedding and trafficking in lymphatic channels

In the present report, we show real-time imaging of cancer cell trafficking in lymphatic vessels. Cancer cells labeled with both green fluorescent protein (GFP) in the nucleus and red fluorescent protein (RFP) in the cytoplasm or with GFP only or RFP only were injected into the inguinal lymph node of nude mice. The labeled cancer cells trafficked through lymphatic vessels where they were imaged via a skin flap in real time at the cellular level until they entered the axillary lymph node. The bright fluorescence of the cancer cells and the real-time microscopic imaging capability of the Olympus OV100 small-animal imaging system enabled imaging of the trafficking cancer cells in the lymphatics. Using this imaging strategy, two different cancer cell lines, one expressing GFP and the other expressing RFP, were simultaneously injected in the inguinal lymph node. Fluorescence imaging readily distinguished the two color-coded cell lines and their different abilities to survive in the lymphatic system. Using this imaging technology, we also investigated the role of pressure on tumor-cell shedding into lymphatic vessels. Pressure was generated by placing 25- and 250-g weights for 10 s on the bottom surface of a tumor-bearing footpad. Tumor cell fragments, single cells, and emboli shed from the footpad tumor were easily distinguished with the labeled cells and OV100 imaging system. Increasing pressure on the tumor increased the numbers of shed cells, fragments, and emboli. Pressure also deformed the shed emboli, increasing their maximum major axis. Imaging lymphatic trafficking of cancer cells can reveal critical steps of lymph node metastasis.

Angiogenesis in brain tumours

Despite aggressive surgery, radiotherapy and chemotherapy, malignant gliomas remain uniformly fatal. To progress, these tumours stimulate the formation of new blood vessels through processes driven primarily by vascular endothelial growth factor (VEGF). However, the resulting vessels are structurally and functionally abnormal, and contribute to a hostile microenvironment (low oxygen tension and high interstitial fluid pressure) that selects for a more malignant phenotype with increased morbidity and mortality. Emerging preclinical and clinical data indicate that anti-VEGF therapies are potentially effective in glioblastoma--the most frequent primary brain tumour--and can transiently normalize tumour vessels. This creates a window of opportunity for optimally combining chemotherapeutics and radiation.

[Magnetic resonance imaging of angiogenesis in tumors]

Tumor angiogenesis induces the proliferation of immature blood vessels that are both heterogeneous and leaky. These characteristics can be demonstrated by measuring the perfusion parameters with MRI. Perfusion MRI is usually performed with in T1-weighted dynamic imaging after bolus injection of an exogenous contrast agent such as gadolinium chelate. The perfusion parameters are obtained by semi-quantitative or quantitative analysis of the enhancement curves in the tumor and the arterial input. Perfusion can also be assessed without injecting a contrast agent using arterial spin labeling techniques, diffusion MRI, or BOLD (blood oxygen level dependent) MRI. However, these latter methods are limited by a low signal-to-noise ratio and problems with quantification. The main indication for perfusion MRI is the assessment of antiangiogenic and antivascular treatments. New possibilities for demonstrating angiogenic blood vessels are being opened by molecular imaging.

Intermittent hypoxia changes HIF-1alpha phosphorylation pattern in endothelial cells: unravelling of a new PKA-dependent regulation of HIF-1alpha

Vascularized tumors are exposed to intermittent hypoxia, that is, hypoxia followed by periods of reoxygenation. Abnormal structure and dysfunction of tumor blood vessels are responsible for these conditions. These repeated short periods of hypoxia concern tumor cells as well as endothelial cells. However, the effects of intermittent hypoxia are poorly understood. The aim of this study was to investigate the effects of intermittent hypoxia on endothelial cells and particularly on HIF-1alpha, a central actor in adaptive response to hypoxia. For that, endothelial cells were exposed to four repeated cycles of 1-h hypoxia followed by 30 min of reoxygenation. We showed that repeated cycles of hypoxia/reoxygenation induced a modification in HIF-l alpha phosphorylation pattern: a progressive increase in HIF-1alpha phosphorylated form was observed during the hypoxic periods. Activation of p42/p44, Akt and PKA was observed in parallel. PKA was shown to be involved in the phosphorylation of HIF-lalpha under intermittent hypoxia, while p42/p44 and Akt were not. As HIF-1 activity is often associated with enhanced cell survival, a better knowledge of the effects of intermittent hypoxia on endothelial cells and the highlight of particular mechanisms induced by intermittent hypoxia are essential to understand the behavior of endothelial cells during neo-angiogenesis.

Active versus passive mechanisms in metastasis: do cancer cells crawl into vessels, or are they pushed?

Although millions of cells are shed from a tumour every day, haematogenous metastasis is believed to be very inefficient. This inefficiency is widely assumed to be a result of the destruction of cells in the bloodstream by shear stress and the immune system and a slow rate of extravasation and proliferation in the stroma at a secondary site. Here, we propose that, whereas active intravasation of cells into the circulation is important in some tumours, others might shed cells passively into the blood or lymphatic vessels without the involvement of active cell migration. We discuss the evidence for and against this passive-shedding hypothesis and the implications for future treatments.

Distinctive Features of Angiogenesis and Lymphangiogenesis Determine Their Functionality during De novo Tumor Development

Blood and lymphatic vasculature are essential components of all organs, responsible for maintaining organ fluid dynamics and tissue homeostasis. Although both vessel systems are composed of similar lineages of endothelial cells whose crude functions include fluid and cell transport, each system also possesses distinctive physiologic properties, enabling their distinctive functions in tissues. The role of hematogenous vasculature and development of angiogenic blood vessels during cancer development is well established; however, the role of lymphangiogenesis and structural/functional alterations occurring within lymphatic vessels during cancer development are incompletely understood. To assess premalignant versus malignant alterations in blood and lymphatic vasculature associated with squamous epithelial skin carcinogenesis, we assessed architectural and functional features of both vascular systems using a mouse model of de novo carcinoma development. We report that, as vasculature acquires angiogenic and/or lymphangiogenic properties, angiogenic blood vessels become leaky in premalignant tissue and at peripheries of carcinomas, where enlarged lymphatic capillaries efficiently drain increased tissue fluid, thereby maintaining tissue hemodynamics. In contrast, central regions of carcinomas exhibit elevated tissue fluid levels, compressed lymphatic lumina, and decreased vascular leakage, thus indicating impaired hemodynamics within solid tumors. Together, these data support the notion that therapeutic delivery of anticancer agents is best realized in premalignant tissues and/or at the peripheries of solid tumors where hemodynamic forces support drug delivery. Strategies to normalize intratumoral hemodynamics would therefore enhance therapeutic delivery to otherwise poorly accessible central regions of solid tumors.

RK. Tumor microvasculature and microenvironment: targets for anti-angiogenesis and normalization

A solid tumor forms an organ-like entity comprised of neoplastic cells and non-transformed host stromal cells embedded in an extracellular matrix. Similar to normal tissues, blood vessels nourish cells residing in tumors. However, unlike normal blood vessels, tumor vasculature has abnormal organization, structure, and function. Tumor vessels are leaky and blood flow is heterogeneous and often compromised. Vascular hyperpermeability and the lack of functional lymphatic vessels inside tumors cause elevation of interstitial fluid pressure in solid tumors. Each of these abnormalities forms a physiological barrier to the delivery of therapeutic agents to tumors. Furthermore, elevated tumor interstitial fluid pressure increases fluid flow from the tumor margin into the peri-tumor area and may facilitate peri-tumor lymphatic hyperplasia and metastasis. Abnormal microcirculation in tumors also leads to a hostile microenvironment characterized by hypoxia and acidosis, which hinder the effectiveness of anti-tumor treatments such as radiation therapy and chemotherapy. In addition, host-tumor interactions regulate expression of pro- and anti-angiogenic factors and hence contribute to their imbalance and resulting pathophysiological characteristics of the tumor. Restoration of pro- and anti-angiogenic balance in tumors may "normalize" tumor vasculature and thus improve its function. Indeed, anti-angiogenic treatments directly targeting angiogenic signaling pathways as well as indirectly modulating angiogenesis show normalization of tumor vasculature and microenvironment at least transiently in both preclinical and clinical settings. Combination of cytotoxic therapy and anti-angiogenic treatment during the vascular normalization exhibits synergistic effect.

Use of an artificial lymphatic system during carboplatin infusion to improve canine osteosarcoma blood flow and clinical response

BACKGROUND

The artificial lymphatic system (ALS), a mechanical system designed to reduce increased interstitial fluid pressure in solid tumors and enhance the delivery of chemotherapy, was evaluated within a randomized clinical trial treating spontaneously occurring canine appendicular osteosarcoma (OS), a tumor similar to its human OS counterpart.

METHODS

An ALS was investigated for its ability to increase OS blood flow and increase uptake of intravenously administered carboplatin.

RESULTS

Blood flow increased by 314% in tumors with active ALS drains versus 126% in control tumors (P < .03). Tumor carboplatin uptake increased by 51% after drain activation (P = .07). Microvascular density (MVD) was measured in tumors after surgical amputation and in corresponding bone regions in a cohort of normal dogs. The OS tumors had equivalent MVD as normal bone, and MVD was higher in the humerus than the femur (P < .03) in both tumor and normal bone. Median survival between the ALS-treated and control cohorts was not different despite increased drug uptake or ALS manipulation. Compared with historic controls, ALS drain insertion into tumors to reduce interstitial fluid pressure did not worsen the prognosis.

CONCLUSIONS

The findings in canine spontaneously occurring OS indicate that an ALS may be of value as a chemotherapy adjunct for enhancing the delivery of chemotherapy to tumor interstitium.

Effect of vascular normalization by antiangiogenic therapy on interstitial hypertension, peritumor edema, and lymphatic metastasis: insights from a mathematical model

Preclinical and clinical evidence shows that antiangiogenic agents can decrease tumor vessel permeability and interstitial fluid pressure (IFP) in a process of vessel "normalization." The resulting normalized vasculature has more efficient perfusion, but little is known about how tumor IFP and interstitial fluid velocity (IFV) are affected by changes in transport properties of the vessels and interstitium that are associated with antiangiogenic therapy. By using a mathematical model to simulate IFP and IFV profiles in tumors, we show here that antiangiogenic therapy can decrease IFP by decreasing the tumor size, vascular hydraulic permeability, and/or the surface area per unit tissue volume of tumor vessels. Within a certain window of antiangiogenic effects, interstitial convection within the tumor can increase dramatically, whereas fluid convection out of the tumor margin decreases. This would result in increased drug convection within the tumor and decreased convection of drugs, growth factors, or metastatic cancer cells from the tumor margin into the peritumor fluid or tissue. Decreased convection of growth factors, such as vascular endothelial growth factor-C (VEGF-C), would limit peritumor hyperplasia, and decreased VEGF-A would limit angiogenesis in sentinel lymph nodes. Both of these effects would reduce the probability of lymphatic metastasis. Finally, decreased fluid convection into the peritumor tissue would decrease peritumor edema associated with brain tumors and ascites accumulation in the peritoneal or pleural cavity, a major complication with a number of malignancies.

Nanotechnology platforms and physiological challenges for cancer therapeutics

Nanotechnology is considered to be an emerging, disruptive technology that will have significant impact in all industrial sectors and across-the-board applications in cancer research. There has been tremendous investment in this area and an explosion of research and development efforts in recent years, particularly in the area of cancer research. At the National Institutes of Health, nanomedicine is one of the priority areas under its Roadmap Initiatives. Moreover, in 2005 the National Cancer Institute alone committed $144.3 million over 5 years for its Alliance for Nanotechnology in Cancer program. Much research and development is progressing in the areas of cancer diagnostics, devices, biosensors, and microfluidics, but this review will focus on therapeutics. Current nanotechnology platforms for cancer therapeutics encompass a vast array of nanomaterials and nanodevices. This review will focus on six of the most prominent and most widely studied: nanoshells, carbon nanotubes, dendrimers, quantum dots, superparamagnetic nanoparticles, and liposomes. All of these nanotechnology platforms can be multifunctional, so they are frequently touted as "smart" or "intelligent." This review will discuss the shared approaches in the design and development of these nanotechnology platforms that bestow such characteristics to the nanoparticles. Finally, the review will raise awareness of the physiological challenges for the application of these therapeutic nanotechnologies, in light of some recent advances in our understanding of tumor biology.

Methodology for quantifying interactions between perfusion evaluated by DCE-US and hypoxia throughout tumor growth

The objective was to validate a combination of two new technologies to depict tumor physiology both temporally and spatially with dynamic contrast-enhanced sonography and an oximeter. Human cancer prostate tumors xenografted onto mice were followed for three weeks using dynamic contrast-enhanced ultrasonography (DCE-US) to detect tumor perfusion. Time intensity curves in linear data were quantified on four regions-of-interest (ROI, main tumor section and its anterior, central and posterior intra-tumoral areas) to extract three indices of perfusion. An oxygen sensor was guided by sonography to obtain accurate pO(2) measurements in the three predefined areas of tumors during their development. No impact on tumor growth of subsequent pO(2) probe insertion was detected. Among the four ROIs studied, the local central tumor showed significant perfusion and oxygenation variations throughout the experiment. A correlation was observed between local central tumor perfusion and pO(2), both of them decreasing through time (p = 0.0068; r = 0.66). The methodology which we developed demonstrated the potential of combining DCE-US with direct tissue pO(2) measurements, improving the description of complex intratumoral dynamic behavior.

Computer simulation of glioma growth and morphology

Despite major advances in the study of glioma, the quantitative links between intra-tumor molecular/cellular properties, clinically observable properties such as morphology, and critical tumor behaviors such as growth and invasiveness remain unclear, hampering more effective coupling of tumor physical characteristics with implications for prognosis and therapy. Although molecular biology, histopathology, and radiological imaging are employed in this endeavor, studies are severely challenged by the multitude of different physical scales involved in tumor growth, i.e., from molecular nanoscale to cell microscale and finally to tissue centimeter scale. Consequently, it is often difficult to determine the underlying dynamics across dimensions. New techniques are needed to tackle these issues. Here, we address this multi-scalar problem by employing a novel predictive three-dimensional mathematical and computational model based on first-principle equations (conservation laws of physics) that describe mathematically the diffusion of cell substrates and other processes determining tumor mass growth and invasion. The model uses conserved variables to represent known determinants of glioma behavior, e.g., cell density and oxygen concentration, as well as biological functional relationships and parameters linking phenomena at different scales whose specific forms and values are hypothesized and calculated based on in vitro and in vivo experiments and from histopathology of tissue specimens from human gliomas. This model enables correlation of glioma morphology to tumor growth by quantifying interdependence of tumor mass on the microenvironment (e.g., hypoxia, tissue disruption) and on the cellular phenotypes (e.g., mitosis and apoptosis rates, cell adhesion strength). Once functional relationships between variables and associated parameter values have been informed, e.g., from histopathology or intra-operative analysis, this model can be used for disease diagnosis/prognosis, hypothesis testing, and to guide surgery and therapy. In particular, this tool identifies and quantifies the effects of vascularization and other cell-scale glioma morphological characteristics as predictors of tumor-scale growth and invasion.

Angiogenesis in cancer

New growth in the vascular network is important since the proliferation, as well as metastatic spread, of cancer cells depends on an adequate supply of oxygen and nutrients and the removal of waste products. New blood and lymphatic vessels form through processes called angiogenesis and lymphangiogenesis, respectively. Angiogenesis is regulated by both activator and inhibitor molecules. More than a dozen different proteins have been identified as angiogenic activators and inhibitors. Levels of expression of angiogenic factors reflect the aggressiveness of tumor cells. The discovery of angiogenic inhibitors should help to reduce both morbidity and mortality from carcinomas. Thousands of patients have received antiangiogenic therapy to date. Despite their theoretical efficacy, antiangiogeic treatments have not proved beneficial in terms of long-term survival. There is an urgent need for a new comprehensive treatment strategy combining antiangiogenic agents with conventional cytoreductive treatments in the control of cancer.

Tumor cell transendothelial passage in the absorbing lymphatic vessel of transgenic adenocarcinoma mouse prostate

The distribution and fine structure of the tumor-associated absorbing lymphatic vessel in the tumor mass of prostate adenocarcinoma and of seminal vesicle metastasis in transgenic mice was studied for the purpose of understanding the modality of tumor cell transendothelial passage from the extravasal matrix into the lymphatic vessel. In the tumor mass, two main cell populations were identified: stromal tumor cells and the invasive phenotype tumor (IPT) cells, having characteristics such as a highly electron-dense matrix rich in small granules lacking a dense core and massed nuclear chromatin, which is positive to immunostaining with anti-SV40 large T antigen antibody. Based on the ultrastructural pictures of different moments of the IPT cell transendothelial passage by ultrathin serial sections of the tumor-associated absorbing lymphatic vessel, the manner of its transendothelial passage through the intraendothelial channel, without involving intercellular contacts, was demonstrated. The presence of IPT cells in the parenchyma of satellite lymph node highlights its significant role in metastatic diffusion. The intraendothelial channel is the reply to the lack of knowledge regarding the intravasation of the tumor cell into the lymphatic circulation. The lymphatic endothelium would organize this channel on the basis of tumor cell-endothelial cell-extravasal matrix molecular interactions, which are as yet unidentified.

Angiogenesis inhibition with bevacizumab and the surgical management of colorectal cancer

BACKGROUND

Bevacizumab is an angiogenesis inhibitor and a new therapy for the treatment of colorectal cancer. It is a humanized monoclonal antibody that targets vascular endothelial growth factor.

METHODS

This review is based on a literature search of Medline, Pubmed, ISI web of knowledge and other published work for original articles, reviews and abstracts relevant to the surgical management of colorectal cancer with bevacizumab.

RESULTS AND CONCLUSION

Combined with current chemotherapy regimens, bevacizumab offers a significant survival advantage, making it likely to see widespread use. Despite being generally well tolerated, serious toxicities, including wound complications and gastrointestinal perforation, have been reported that affect surgical management. Consideration should be given to the timing of surgical and adjuvant intervention when using this drug.

Thermographic assessment of tumor growth in mouse xenografts

In human breast tumors, a 1-2 degrees C increase in skin surface temperature is usually observed at the periphery; it has been proposed that this change is due to the hypervascularity and increased blood flow resulting from tumor-associated angiogenesis. Here we tested the hypothesis that thermal imaging might represent a useful adjunctive technique in monitoring the growth dynamics of human tumor xenografts. Xenografts were established in immunocomprised nude mice using MDA-MB-231 or MCF7 breast cancer cells. We exploited the inherent noncontact and noninvasive advantages of infrared thermography to detect skin surface temperature changes. Continuous thermographic investigation was performed to detect and monitor tumor growth in vivo and high resolution digital images were analyzed to measure the tumor temperature dynamics. In contrast to the skin temperature increases associated with human breast cancer, a consistent temperature decrease was found in the xenograft mice. In one case, a smaller secondary tumor, otherwise undetectable, was clearly evident by thermal imaging. The tumors were cooler than the surrounding tissue with a maximum temperature reduction of 1.5 degrees C for MDA-MB-231 tumor and 3 degrees C for MCF7 tumors observed on day 14. In addition, the temperature of the xenograft tumors decreased progressively as they grew throughout the observation period. It was demonstrated that thermographic imaging could detect temperature changes as small as 0.1 degrees C on the skin surface at an early stage of tumor development. The findings of the study indicate that thermographic imaging might have considerable potential in monitoring human tumor xenografts and their response to anticancer drugs.

Tumor microenvironment abnormalities: Causes, consequences, and strategies to normalize

A solid tumor is an organ-like entity comprised of neoplastic cells and non-transformed host stromal cells embedded in an extracellular matrix. The expression of various genes is influenced by interactions among these cells, surrounding matrix, and their local physical and biochemical microenvironment. The products encoded by these genes, in turn, control the pathophysiological characteristics of the tumor, and give rise to the abnormal organization, structure, and function of tumor blood vessels. These abnormalities contribute to heterogeneous blood flow, vascular permeability, and microenvironment. Proliferating tumor cells produce solid stress which compresses blood and lymphatic vessels. As a result of vessel leakiness and lack of functional lymphatics, interstitial fluid pressure is significantly elevated in solid tumors. Each of these abnormalities forms a physiological barrier to the delivery of therapeutic agents to tumors. Furthermore, the metabolic microenvironment in tumors such as hypoxia and acidosis hinder the efficacy of anti-tumor treatments such as radiation therapy and chemotherapy. A judicious application of anti-angiogenic therapy has the potential to overcome these problems by normalizing the tumor vessels and making them more efficient for delivery of oxygen and drugs. Combined anti-angiogenic and conventional therapies have shown promise in the clinic.

Long-term lowering of tumour interstitial fluid pressure reduces Ki-67 expression

High tumour interstitial fluid pressure (TIFP) is a characteristic of most solid tumours. Recent data give first evidence that mechanical stretch induced by TIFP triggers proliferation in solid tumours. In the present study we compared two protocols of TIFP reduction on the expression of the tumour proliferation marker Ki-67: (a) short-term lowering of TIFP by a singular puncture and (b) long-term lowering of TIFP by catheterization. Utilizing two experimental tumours (A431, A549) it was found that the TIFP broke down rapidly after a singular puncture but recovered within 6h. In case of permanent catheterization no TIFP recovery was observed. After 24h tumours were excised and stained against the proliferation marker Ki-67. While a singular puncture had no effect catheterized tumours showed a significant decrease in Ki-67 expression. Our data suggest that long-term lowering of TIFP is required to reduce tumour proliferation.

Lowering of tumor interstitial fluid pressure reduces tumor cell proliferation in a xenograft tumor model

High tumor interstitial fluid pressure (TIFP) is a characteristic of most solid tumors. TIFP may hamper adequate uptake of macromolecular therapeutics in tumor tissue. In addition, TIFP generates mechanical forces affecting the tumor cortex, which might influence the growth parameters of tumor cells. This seems likely as, in other tissues (namely, blood vessels or the skin), mechanical stretch is known to trigger proliferation. Therefore, we hypothesize that TIFP-induced stretch modulates proliferation-associated parameters. Solid epithelial tumors (A431 and A549) were grown in Naval Medical Research Institute nude mice, generating a TIFP of about 10 mm Hg (A431) or 5 mm Hg (A549). Tumor drainage of the central cystic area led to a rapid decline of TIFP, together with visible relaxation of the tumor cortex. It was found by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analysis that TIFP lowering yields a decreased phosphorylation of proliferation-associated p44/42 mitogen-activated protein kinase and tumor relaxation. In confirmation, immunohistochemical staining showed a decrease of tumor-associated proliferation marker Ki-67 after TIFP lowering. These data suggest that the mechanical stretch induced by TIFP is a positive modulator of tumor proliferation.

Molecular imaging strategies for drug discovery and development

Recent advances in non-invasive molecular imaging provide exciting opportunities for discovery, validation and development of novel therapeutics. As the arsenal of detection devices and strategies, injectable probes, genetically encoded reporters and animal models rapidly expands, molecular imaging is becoming indispensable for drug discovery and development. Not only do such strategies reduce the time, cost and workload associated with conventional destructive end-point assays, but they also enable spatial and temporal monitoring of in vivo gene expression, signaling pathways, biochemical reactions and targets as they relate to the pharmacokinetics and pharmacodynamics of novel drugs.

Drug penetration in solid tumours

To be most effective anticancer drugs must penetrate tissue efficiently, reaching all the cancer cells that comprise the target population in a concentration sufficient to exert a therapeutic effect. Most research into the resistance of cancers to chemotherapy has concentrated on molecular mechanisms of resistance, whereas the role of limited drug distribution within tumours has been neglected. We summarize the evidence that indicates that the distribution of many anticancer drugs in tumour tissue is incomplete, and we suggest strategies that might be used either to improve drug penetration through tumour tissue or to select compounds based on their abilities to penetrate tissue, thereby increasing the therapeutic index.

Lymph node metastasis in breast cancer xenografts is associated with increased regions of extravascular drain, lymphatic vessel area, and invasive phenotype

Interactions between the tumor stromal compartment and cancer cells play an important role in the spread of cancer. In this study, we have used noninvasive in vivo magnetic resonance imaging (MRI) of two human breast cancer models with significantly different invasiveness, to quantify and understand the role of interstitial fluid transport, lymphatic-convective drain, and vascularization in the regional spread of breast cancer to the axillary lymph nodes. Quantitative fluorescence microscopy was done to morphometrically characterize lymphatic vessels in these tumors. Significant differences in vascular and extravascular transport variables as well as in lymphatic vessel morphology were detected between the two breast cancer models, which also exhibited significant differences in lymph node and lung metastasis. These data are consistent with a role of lymphatic drain in lymph node metastasis and suggest that increased lymph node metastasis may occur due to a combination of increased invasiveness, and reduced extracellular matrix integrity allowing increased pathways of least resistance for the transport of extravascular fluid, as well as tumor cells. It is also possible that lymph node metastasis occurred via the cancer cell-bearing tumoral lymphatic vessels. The congestion of these tumoral lymphatics with cancer cells may have restricted the entry and transport of macromolecules.

A two-tiered physiologically based model for dually labeled single-chain Fv-Fc antibody fragments

Monoclonal antibodies (mAb) are being used at an increasing rate in the treatment of cancer, with current efforts focused on developing engineered antibodies that exhibit optimal biodistribution profiles for imaging and/or radioimmunotherapy. We recently developed the single-chain Fv-Fc (scFv-Fc) mAb, which consists of a single-chain antibody Fv fragment (light-chain and heavy-chain variable domains) coupled to the IgG1 Fc region. Point mutations that attenuate binding affinity to FcRn were introduced into the Fc region of the wild-type scFv-Fc mAb, resulting in several new antibodies, each with a different half-life. Here, we describe the construction of a two-tiered physiologically based pharmacokinetic model capable of simulating the apparent biodistribution of both (111)In- and (125)I-labeled scFv-Fc mAbs, where (111)In-labeled metabolites from degraded (111)In-labeled mAbs tend to become trapped within the lysosomal compartment, whereas free (125)I from degraded (125)I-labeled mAbs is quickly eliminated via the urinary pathway. The different concentration-time profiles of (111)In- and (125)I-labeled mAbs permits estimation of the degradation capacity of each organ and elucidates the dependence of cumulative degradation in liver, muscle, and skin on FcRn affinity and tumor mass. Liver is estimated to account for approximately 50% of all degraded mAb when tumor is small (approximately 0.1 g) and drops to about 35% when tumor mass is larger (approximately 0.3 g). mAb degradation in residual carcass (primarily skin and muscle) decreases from approximately 45% to 16% as FcRn affinity of the three mAb variants under consideration increases. In addition, elimination of a small amount of mAb in the kidneys is shown to be required for a successful fit of model to data.

The role of nitric oxide in tumour progression

Nitric oxide (NO) and nitric oxide synthases are ubiquitous in malignant tumours and are known to exert both pro- and anti-tumour effects. We summarize our current understanding of the role of NO in tumour progression, especially in relation to angiogenesis and vascular functions. We also discuss potential strategies for cancer treatment that modulate NO production and/or its downstream signalling pathways.

Three-dimensional visualization of microvessel architecture of whole-mount tissue by confocal microscopy

The three-dimensional architecture of the nascent microvascular network is a critical determinant of vascular perfusion in the setting of regenerative growth, vasculopathies and cancer. Current methods for microvessel visualization are limited by insufficient penetration and instability of endothelial immunolabels, inadequate vascular perfusion by the high-viscosity polymers used for vascular casting, and destruction of tissue stroma during the processing required for scanning electron microscopy. The aim of this study was to develop whole-mount tissue processing methods for 3D in situ visualization of the microvasculature that were also compatible with supplementary labeling for other structures of interest in the tissue microenvironment. Here, we present techniques that allow imaging of the microvasculature by confocal microscopy, to depths of up to 1500 mum below the specimen surface. Our approach includes labeling luminal surfaces of endothelial cells by i.v. injection of fluorescently conjugated lectin and filling the microvasculature with carbon or fluorescent nanoparticles/Mercox, followed by optical clearing of thick tissue sections to reduce light scatter and permit 3D visualization of microvessel morphology deep into the sample. Notably, tissue stroma is preserved, allowing simultaneous labeling of other structures by immunohistochemistry or nuclear dyes. Results are presented for various murine tissues including fat, muscle, heart and brain under conditions of normal health, as well as in the setting of a glioma model growing in the subcutaneous space or orthotopically in the brain parenchyma.

QxDB: a generic database to support mathematical modelling in biology

QxDB (quantitative x-modelling database) is a web-based generic database package designed especially to house quantitative and structural information. Its development was motivated by the need for centralized access to such results for development of mathematical models, but its usefulness extends to the general research community of both modellers and experimentalists. Written in PHP (Hyper Preprocessor) and MYSQL, the database is easily adapted to new fields of research and ported to Apache-based web servers. Unlike most existing databases, experimental and observational results curated in QxDB are supplemented by comments from the experts who contribute input to the database, giving their evaluations of experimental techniques, breadth of validity of results, experimental conditions, and the like, thus providing the visitor with a basis for gauging the quality (or appropriateness) of each item for his/her needs. QxDB can be easily customized by adapting the contents of the database table containing the descriptors that characterize each data record according to an informal ontology of the research domain. We will illustrate this adaptability of QxDB by presenting two examples, the first dealing with modelling in oncology and the second with mechanical properties of cells and tissues.

Chronic effects of mechanical force on airways

Airways are embedded in the mechanically dynamic environment of the lung. In utero, this mechanical environment is defined largely by fluid secretion into the developing airway lumen. Clinical, whole lung, and cellular studies demonstrate pivotal roles for mechanical distention in airway morphogenesis and cellular behavior during lung development. In the adult lung, the mechanical environment is defined by a dynamic balance of surface, tissue, and muscle forces. Diseases of the airways modulate both the mechanical stresses to which the airways are exposed as well as the structure and mechanical behavior of the airways. For instance, in asthma, activation of airway smooth muscle abruptly changes the airway size and stress state within the airway wall; asthma also results in profound remodeling of the airway wall. Data now demonstrate that airway epithelial cells, smooth muscle cells, and fibroblasts respond to their mechanical environment. A prominent role has been identified for the epithelium in transducing mechanical stresses, and in both the fetal and mature airways, epithelial cells interact with mesenchymal cells to coordinate remodeling of tissue architecture in response to the mechanical environment.

Antiangiogenesis and drug delivery to tumors: bench to bedside and back

After over 30 years of preclinical and clinical development, antiangiogenic agents have recently entered the clinic as attractive targeted therapeutics for the treatment of cancer. Fueled by exciting new developments in the field, the AACR Special Conference was designed to broadly survey critical scientific advances in the antiangiogenic therapy of cancer. Because these advances have come primarily with the use of combinations of antiangiogenic agents with chemotherapy, or with antiangiogenic agents that also directly target the cancer cells, the central theme included the issue of drug delivery to tumors. These two major issues were addressed in concert, from basic mechanisms of action of antiangiogenic agents to new combination approaches to cancer treatment. Nearly 300 participants from 20 countries registered for the conference, drawn both from academia and industry, with a wide range in experience and background. Dr. Rakesh Jain, along with conference co-chairs, Drs. Lee Ellis and Luisa Iruela-Arispe, assembled an outstanding lineup of speakers for this conference that included many of the pioneers in the fields of angiogenesis and drug delivery from the U.S. and abroad. This resulted in an excellent overview of the advances in our understanding of cellular and molecular aspects of tumor angiogenesis and antiangiogenic therapy of cancer in combination with conventional therapy.

On the transendothelial passage of tumor cell from extravasal matrix into the lumen of absorbing lymphatic vessel

The aim of the research is the study of ultrastructural characteristics of the absorbing lymphatic vessel and of tumor cell passage through the endothelial lymphatic wall in (a) subcutaneous xenografts of T84 colon adenocarcinoma and B16 melanoma cell lines in nude mice and (b) human colorectal cancer. It was found that the tumor-associated absorbing lymphatic (TAAL) vessel has the same ultrastructural characteristics as the absorbing lymphatic vessel in normal organs, and it is provided with an endothelial wall wholly lacking a continuous basement membrane, pores, fenestrations, and open junctions. The TAAL vessel is always missing in the studied tumor masses as far as the central stroma is concerned, whereas it is always present in the peripheral area of the tumor and in the peritumoral connective tissue. The factors of extravasal matrix that play an active role in migration process of invasive phenotype tumor (IPT) cell after its detachment from tumor mass, as well as the role of cytoplasmic protrusions (pseudopod-like) in lymphatic recognition, were considered. For the first time, this study demonstrated the transendothelial passage of IPT cell inside the TAAL vessel lumen, which takes place by means of the intraendothelial channel (approximately 1.8-2.1 mum in diameter and 6.8-7.2 microm in length). This channel is to be considered a transient morphological entity organized by TAAL vessel endothelium by means of still unidentified molecular mechanisms. Therefore, it appears to be ascertained that the intraendothelial channel represents a step forward in the knowledge of the drainage into lymphatic circulation of interstitial fluid and the answer to the lack of knowledge expressed till today by researchers concerning the modality of passage of the tumor cell through the endothelial wall of the TAAL vessel.

Onset of abnormal blood and lymphatic vessel function and interstitial hypertension in early stages of carcinogenesis

Recent improvements in diagnostic methods have opened avenues for detection and treatment of (pre)malignant lesions at early stages. However, due to the lack of spontaneous tumor models that both mimic human carcinogenesis and allow direct optical imaging of the vasculature, little is known about the function of blood and lymphatic vessels during the early stages of cancer development. Here, we used a spontaneous carcinogenesis model in the skin of DNA polymerase eta-deficient mice and found that interstitial fluid pressure was already elevated in the hyperplastic/dysplastic stage. This was accompanied by angiogenic blood vasculature that exhibited altered permeability, vessel compression, and decreased alpha-smooth muscle actin-positive perivascular cell coverage. In addition, the lymphatic vessels in hyperplastic/dysplastic lesions were partly compressed and nonfunctional. These novel insights may aid early detection and treatment strategies for cancer.

Lymphatic or hematogenous dissemination: how does a metastatic tumor cell decide?

The formation of distant metastases is the deadliest phase of cancer progression. Although numerous studies have identified genes and mechanisms that affect metastasis after tumors have reached secondary sites, our knowledge about how cancer cells initially gain access to systemic circulation is limited. Since tumors can enter the blood directly by intravasating into venous capillaries or indirectly via lymphatics, it is important to evaluate the relative contributions of both pathways as routes of egress from the primary site. Insights into tumor and stromal factors governing the intravasation process may help explain why certain tumors exhibit "preferred" pathways for metastatic dissemination, both clinically and in experimental animal models.

Fluctuations in pO2 in irradiated human melanoma xenografts

Several studies have demonstrated that untreated tumors may show significant fluctuations in tissue oxygen tension (pO(2)). Radiation treatment may induce changes in the tumor microenvironment that alter the pO(2) fluctuation pattern. The purpose of the present study was to investigate whether pO(2) fluctuations may also occur in irradiated tumors. A-07 human melanoma xenografts were irradiated with single doses of 0, 5 or 10 Gy. Fluctuations in pO(2) were recorded with OxyLite probes prior to irradiation and 24 and 72 h after the radiation exposure. Radiation-induced changes in the tumor microenvironment (i.e. blood perfusion and extracellular volume fraction) were assessed by dynamic contrast-enhanced magnetic resonance imaging. Seventy-two hours after 10 Gy, tumor blood perfusion had decreased to approximately 40% of that prior to irradiation, whereas the extracellular volume fraction had increased by approximately 25%. Fluctuations in pO(2) were seen in most tumors, irrespective of radiation dose and time after irradiation. The mean pO(2), the number of fluctuations around the mean pO(2), the number of fluctuations around threshold pO(2) values of 1, 2, 3, 5, 7 and 10 mmHg, and the amplitude of the fluctuations were determined for each pO(2) trace. No significant differences were detected between irradiated and unirradiated tumors. The results showed that pO(2) fluctuations may occur in irradiated tumors and that the pO(2) fluctuation pattern in A-07 tumors exposed to 5 or 10 Gy is similar to that in untreated tumors. Consequently, these doses did not induce changes in the tumor microenvironment that were sufficient to cause detectable alterations in the pO(2) fluctuation pattern.

Morphologic instability and cancer invasion

PURPOSE

A solid tumor embedded in host tissue is a three-dimensional arrangement of cells and extracellular matrix that acts as a sink of oxygen and cell nutrients, thus establishing diffusional gradients. This and variations in vascular density and blood flow typically produce intratumoral regions of hypoxia and acidosis, and may result in spatially heterogeneous cell proliferation and migration. Here, we formulate the hypothesis that through these mechanisms, microenvironmental substrate gradients may drive morphologic instability with separation of cell clusters from the tumor edge and infiltration into surrounding normal tissue.

EXPERIMENTAL DESIGN

We used computer simulations and in vitro experiments.

RESULTS

We provide evidence that morphologic instability could be suppressed in vivo by spatially homogeneous oxygen and nutrient supply because normoxic conditions act both by decreasing gradients and increasing cell adhesion and, therefore, the mechanical forces that maintain a well-defined tumor boundary. A properly working tumor microvasculature can help maintain compact noninfiltrating tumor morphologies by minimizing oxygen and nutrient gradients. In contrast, antiangiogenic therapy, by increasing microenvironmental heterogeneity, may promote morphologic instability, leading to invasive patterns even under conditions in which the overall tumor mass shrinks.

CONCLUSIONS

We conclude that therapeutic strategies focused solely on reduction of vascular density may paradoxically increase invasive behavior. This theoretical model accounts for the highly variable outcome of antiangiogenic therapy in multiple clinical trials. We propose that antiangiogenic strategies will be more consistently successful when aimed at "normalizing" the vasculature and when combined with therapies that increase cell adhesion so that morphologic instability is suppressed and compact, noninvasive tumor morphologies are enforced.

Lymphangiogenesis in development and human disease

The lymphatic vasculature forms a vessel network that drains interstitial fluid from tissues and returns it to the blood. Lymphatic vessels are also an essential part of the body's immune defence. They have an important role in the pathogenesis of several diseases, such as cancer, lymphoedema and various inflammatory conditions. Recent biological and technological developments in lymphatic vascular biology will lead to a better understanding and treatment of these diseases.

Changes in the tumor microenvironment during low-dose-rate permanent seed implantation iodine-125 brachytherapy

PURPOSE

There is a lack of data regarding how the tumor microenvironment (e.g., perfusion and oxygen partial pressure [pO2]) changes in response to low-dose-rate (LDR) brachytherapy. This may be why some clinical issues remain unresolved, such as the appropriate use of adjuvant external beam radiation therapy (EBRT). The purpose of this work was to obtain some basic preclinical data on how the tumor microenvironment evolves in response to LDR brachytherapy.

METHODS AND MATERIALS

In an experimental mouse tumor, pO2 (measured by electron paramagnetic resonance) and perfusion (measured by dynamic contrast-enhanced magnetic resonance imaging) were monitored as a function of time (0-6 days) and distance (0-2 mm and 2-4 mm) from an implanted 0.5 mCi iodine-125 brachytherapy seed.

RESULTS

For most of the experiments, including controls, tumors remained hypoxic at all times. At distances of 2-4 mm from radioactive seeds ( approximately 1.5 Gy/day), however, there was an early, significant increase in pO2 within 24 h. The pO2 in that region remained elevated through Day 3. Additionally, the perfusion in that region was significantly higher than for controls starting at Day 3.

CONCLUSION

It may be advantageous to give adjuvant EBRT shortly (approximately 1 to 2 days) after commencement of clinical LDR brachytherapy, when the pO2 in the spatial regions between seeds should be elevated. If chemotherapy is given adjuvantly, it may best be administered just a little later (approximately 3 or 4 days) after the start of LDR brachytherapy, when perfusion should be elevated.

Tumours can adapt to anti-angiogenic therapy depending on the stromal context: lessons from endothelial cell biology

It has long been recognized that interference with the blood supply of a tumour is an effective way to halt tumour progression, and even induce tumour regression. This can be accomplished by anti-angiogenic treatment which prevents the formation of a tumour neovasculature, or anti-vascular treatment, which aims at destruction of existent tumour vessels. The latter has received relatively little attention because there is a lack of specific tumour-endothelial markers. Instead, the current detailed knowledge on the factors and mechanisms, involved in angiogenesis, has enabled the development of a variety of angiogenesis inhibitors, especially those that target cellular signalling by vascular endothelial growth factor-A (VEGF-A), the most potent angiogenic factor known. These inhibitors have received lots of attention because they effectively inhibit tumour growth in pre-clinical models. However, in clinical trials these same inhibitors showed very poor anti-tumour activity. In this review we discuss this discrepancy, and we show that the tumour microenvironment is crucial to the sensitivity of tumours to anti-angiogenic therapy.

Tumor-Secreted Vascular Endothelial Growth Factor-C Is Necessary for Prostate Cancer Lymphangiogenesis, but Lymphangiogenesis Is Unnecessary for Lymph Node Metastasis

Dissemination to draining lymph nodes is a frequent first step in prostate cancer metastasis. Although tumors metastasize to lymph nodes via the lymphatics, the importance of lymphangiogenesis in mediating the process remains controversial. Here, we inhibit intratumoral lymphangiogenesis in s.c. and surgical orthotopic implantation mouse models of human prostate cancer using several strategies. Stable expression of small interfering RNAs (siRNA) targeted against human vascular endothelial growth factor-C (VEGF-C) in PC-3 cells reduced intratumoral lymphatics by 99% in s.c. tumors, indicating that tumor-secreted VEGF-C is necessary for lymphangiogenesis. Expression of siRNAs against human VEGF-A somewhat reduced tumor lymphangiogenesis. Secretion of a soluble VEGF receptor-3/Flt4 fusion protein by PC-3 cells reduced intratumoral lymphatics by 100% in s.c. tumors. Combination of soluble Flt4 and VEGF-C siRNA yielded >92% reduction of intratumoral lymphatics in orthotopic prostate tumors. However, metastasis to lymph nodes was not significantly affected regardless of intratumoral lymphatic vessel density. The abundance of marginal lymphatics at the tumor-stromal interface was unchanged in orthotopic tumors whose intratumoral lymphatics were inhibited, suggesting that these marginal vessels could be sufficient for lymph node metastasis. Hematogenous metastasis (blood tumor burden, lung metastasis) correlated with degree of lymph node invasion. We also analyzed the lymphatics in spontaneous transgenic adenocarcinomas of the mouse prostate which metastasize to lymph nodes. Progression from well-differentiated prostate intraepithelial neoplasia to metastatic, undifferentiated adenocarcinoma was accompanied by loss of lymphatics. These results suggest that tumor-secreted VEGF-C and, to a lesser extent, VEGF-A, are important for inducing prostate cancer intratumoral lymphangiogenesis but are unnecessary for lymph node metastasis.