The relation between cell proliferation and the vascular system in a transplanted mouse mammary tumour

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.

An In Vivo Dual-Observation Method to Monitor Tumor Mass and Tumor-Surface Blood Vessels for Developing Anti-Angiogenesis Agents against Submillimeter Tumors

Managing metastasis at the early stage and detecting and treating submillimeter tumors at early metastasis are crucial for improving cancer prognosis. Angiogenesis is a critical target for developing drugs to detect and inhibit submillimeter tumor growth; however, drug development remains challenging because there are no suitable models for observing the submillimeter tumor mass and the surrounding blood vessels in vivo. We have established a xenograft subcutaneous submillimeter tumor mouse model with HT-29-RFP by transplanting a single spheroid grown on radiation-crosslinked gelatin hydrogel microwells. Here, we developed an in vivo dual-observation method to observe the submillimeter tumor mass and tumor-surface blood vessels using this model. RFP was detected to observe the tumor mass, and a fluorescent angiography agent FITC-dextran was administered to observe blood vessels via stereoscopic fluorescence microscopy. The anti-angiogenesis agent regorafenib was used to confirm the usefulness of this method. This method effectively detected the submillimeter tumor mass and tumor-surface blood vessels in vivo. Regorafenib treatment revealed tumor growth inhibition and angiogenesis downregulation with reduced vascular extremities, segments, and meshes. Further, we confirmed that tumor-surface blood vessel areas monitored using in vivo dual-observation correlated with intratumoral blood vessel areas observed via fluorescence microscopy with frozen sections. In conclusion, this method would be useful in developing anti-angiogenesis agents against submillimeter tumors.

"Targeted plus controlled" - Composite nano delivery system opens the tumor vascular and microenvironment normalization window for anti-tumor therapy

The bottleneck of traditional anti-tumor therapy is mainly limited by the abnormal microenvironment of tumors. Leaky vessels are difficult for drugs or immune cells to penetrate deep into tumors, but tumor cells can easily escape through which and metastasize to other organs. Reprogramming the tumor microenvironment is one of the main directions for anti-cancer research, among which, tumor vascular normalization has received increasing attention. However, how to control the dose and time of anti-angiogenic drugs for stable vascular normalizing effect limits it for further research. We developed a composite nano delivery system, P-V@MG, with double delivery function of pH-responsibility and sustained drug release. The PHMEMA shell improves amphiphilicity of nano delivery system and prolongs in vivo retention, and releases V@MG in the weakly acidic tumor microenvironment, which slowly release anti-angiogenic drugs, Vandetanib. We found that P-V@MG not only prolonged the normalization window of tumor vascular but also reprogram tumor microenvironment with increased perfusion, immune cells infiltration and relieved hypoxia, which further opened the pathway for other anti-cancer therapeutics. This synergy was proved by the improving anti-tumor efficiency by combination of P-V@MG with the doxorubicin hydrochloride in 4 T1 breast cancer model suggesting the desirable value of pro-vascular normalization nano delivery systems in the field of anti-tumor combination therapy.

Cell proliferation, drug distribution and therapeutic effects in relation to the vascular system of solid tumours

In this perspective, the authors summarise some properties of the solid tumour micro-environment that have been explored during the last 55 years. It is well established that the concentrations of nutrients, including oxygen, decrease with increasing distance from tumour blood vessels, and that low extracellular pH is found in nutrient-poor regions. Cell proliferation is dependent on nutrient metabolites and decreases in regions distal from patent blood vessels. Proliferating cells cause migration of neighbouring cells further from blood vessels where they may die, and their breakdown products pass into regions of necrosis. Anticancer drugs reach solid tumours via the vascular system and establish concentration gradients such that drug concentration within tumours may be quite variable. Treatment with chemotherapy such as doxorubicin or docetaxel can kill well-nourished proliferating cells close to blood vessels, thereby interrupting migration toward necrotic regions and lead to re-oxygenation and renewed proliferation of distal cells, as can occur with radiotherapy. This effect leads to the paradox that cancer treatment can rescue cells that were destined to die in the untreated tumour. Renewed and sometimes accelerated repopulation of surviving tumour cells can counter the effects of cell killing from repeated treatments, leading to tumour shrinkage and regrowth without changes in the intrinsic sensitivity of cells to the administered treatment. Strategies to prevent these effects include the combined use of chemotherapy with agents that selectively kill hypoxic tumour cells, including inhibitors of autophagy, since this is a process that may allow recycling of cellular macromolecules from dying cells and improve their survival.

Hyperhydration of Cancers: A Characteristic Biophysical Trait Strongly Increasing O2, CO2, Glucose and Lactate Diffusivities, and Improving Thermophysical Properties of Solid Malignancies

Cancers are complex, heterogeneous, dynamic and aggressive diseases exhibiting a series of characteristic biophysical traits which complement the original biological hallmarks of cancers favouring progressive growth, metastasis, and contributing to immune evasion and treatment resistance. One of the prevalent differences between most solid tumors and their corresponding, healthy tissues is a significantly higher water content (hyperhydration) in cancers. As a consequence, cancers have distinctly higher (Fick's) diffusion coefficients D [cm2 s-1] for the respiratory gases O2 and CO2, the key substrate glucose, and for the oncometabolite lactate. In addition, cancers have (a) clearly increased specific heat capacities cp [J g-1 K-1], thus representing high-capacity-tissues upon therapeutic heating induced by electromagnetic irradiation, and (b) higher thermal conductivities k [W m-1 K-1], i.e., increased abilities to conduct heat. Therefore, in diffusion analyses (e.g., when describing critical O2 and glucose supplies or CO2 removal, and the development of hypoxic subvolumes) and for modeling temperature distributions in hyperthermia treatment planning, these specific cancer-related data must be considered in order to reliably reflect oncologic thermo-radiotherapy settings.

Anti-angiogenic nano-delivery system promotes tumor vascular normalizing and micro-environment reprogramming in solid tumor

Aberrant tumor vasculature leads to the malignant tumor microenvironment (TME) for tumor progression. Research has found temporary tumor vascular normalization after treated with low-dose anti-angiogenic agents, however, has paid little attention to prolonging the normalization window and its further influence on tumor tissue. Based on the dose- and time-dependent effect of anti-angiogenic agents, we developed V@LDL NPs, a nano-delivery system sustainedly releasing Vandetanib, an anti-VEGFR2 inhibitor, to control the dose of drug to the normalizing level, and prove its stable tumor vascular normalizing effect in 4 T1 breast cancer model. Furthermore, long-term normalized vasculature could improve tumor perfusion, then provide a circulation to reverse abnormalities in TME, such as hypoxia and heterogeneity, and also inhibit tumor progression. Our findings demonstrate that stable tumor vascular normalization could be a considerable strategy for long-term change to remodel TME and probably result in a therapeutic benefit to anti-cancer treatment, which could be achieved by anti-angiogenic nano-delivery system.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Transiently hypoxic tumour cell turnover and radiation sensitivity in human tumour xenografts

BACKGROUND

Solid tumour perfusion can be unstable, creating transiently hypoxic cells that can contribute to radiation resistance. We investigated the in vivo lifetime of transiently hypoxic tumour cells and chronically hypoxic tumour cells during tumour growth and following irradiation.

METHODS

Hypoxic cells in SiHa and WiDr human tumour xenografts were labelled using pimonidazole and EF5, and turnover was quantified as the loss of labelled cells over time. The perfusion-modifying drug pentoxifylline was used to reoxygenate transiently hypoxic cells prior to hypoxia marker administration or irradiation.

RESULTS

Chronically hypoxic cells constantly turnover in SiHa and WiDr tumours, with half-lives ranging from 42-82 h and significant numbers surviving >96 h. Transiently hypoxic cells constitute 26% of the total hypoxic cells in WiDr tumours. These transiently hypoxic cells survive at least 24 h, but then rapidly turnover with a half-life of 34 h and are undetectable 72 h after labelling. Transiently hypoxic cells are radiation-resistant, although vascular dysfunction induced by 10 Gy of ionising radiation preferentially kills transiently hypoxic cells.

CONCLUSIONS

Transiently hypoxic tumour cells survive up to 72 h in WiDr tumours and are radiation-resistant, although transiently hypoxic cells are sensitive to vascular dysfunction induced by high doses of ionising radiation.

Intrinsic Differences in Spatiotemporal Organization and Stromal Cell Interactions Between Isogenic Lung Cancer Cells of Epithelial and Mesenchymal Phenotypes Revealed by High-Dimensional Single-Cell Analysis of Heterotypic 3D Spheroid Models

The lack of inadequate preclinical models remains a limitation for cancer drug development and is a primary contributor to anti-cancer drug failures in clinical trials. Heterotypic multicellular spheroids are three-dimensional (3D) spherical structures generated by self-assembly from aggregates of two or more cell types. Compared to traditional monolayer cell culture models, the organization of cells into a 3D tissue-like structure favors relevant physiological conditions with chemical and physical gradients as well as cell-cell and cell-extracellular matrix (ECM) interactions that recapitulate many of the hallmarks of cancer in situ. Epidermal growth factor receptor (EGFR) mutations are prevalent in non-small cell lung cancer (NSCLC), yet various mechanisms of acquired resistance, including epithelial-to-mesenchymal transition (EMT), limit the clinical benefit of EGFR tyrosine kinase inhibitors (EGFRi). Improved preclinical models that incorporate the complexity induced by epithelial-to-mesenchymal plasticity (EMP) are urgently needed to advance new therapeutics for clinical NSCLC management. This study was designed to provide a thorough characterization of multicellular spheroids of isogenic cancer cells of various phenotypes and demonstrate proof-of-principle for the applicability of the presented spheroid model to evaluate the impact of cancer cell phenotype in drug screening experiments through high-dimensional and spatially resolved imaging mass cytometry (IMC) analyses. First, we developed and characterized 3D homotypic and heterotypic spheroid models comprising EGFRi-sensitive or EGFRi-resistant NSCLC cells. We observed that the degree of EMT correlated with the spheroid generation efficiency in monocultures. In-depth characterization of the multicellular heterotypic spheroids using immunohistochemistry and high-dimensional single-cell analyses by IMC revealed intrinsic differences between epithelial and mesenchymal-like cancer cells with respect to self-sorting, spatiotemporal organization, and stromal cell interactions when co-cultured with fibroblasts. While the carcinoma cells harboring an epithelial phenotype self-organized into a barrier sheet surrounding the fibroblasts, mesenchymal-like carcinoma cells localized to the central hypoxic and collagen-rich areas of the compact heterotypic spheroids. Further, deep-learning-based single-cell segmentation of IMC images and application of dimensionality reduction algorithms allowed a detailed visualization and multiparametric analysis of marker expression across the different cell subsets. We observed a high level of heterogeneity in the expression of EMT markers in both the carcinoma cell populations and the fibroblasts. Our study supports further application of these models in pre-clinical drug testing combined with complementary high-dimensional single-cell analyses, which in turn can advance our understanding of the impact of cancer-stroma interactions and epithelial phenotypic plasticity on innate and acquired therapy resistance in NSCLC.

Temporal and spatial topography of cell proliferation in cancer

Proliferation is a fundamental trait of cancer cells, but its properties and spatial organization in tumours are poorly characterized. Here we use highly multiplexed tissue imaging to perform single-cell quantification of cell cycle regulators and then develop robust, multivariate, proliferation metrics. Across diverse cancers, proliferative architecture is organized at two spatial scales: large domains, and smaller niches enriched for specific immune lineages. Some tumour cells express cell cycle regulators in the (canonical) patterns expected of freely growing cells, a phenomenon we refer to as 'cell cycle coherence'. By contrast, the cell cycles of other tumour cell populations are skewed towards specific phases or exhibit non-canonical (incoherent) marker combinations. Coherence varies across space, with changes in oncogene activity and therapeutic intervention, and is associated with aggressive tumour behaviour. Thus, multivariate measures from high-plex tissue images capture clinically significant features of cancer proliferation, a fundamental step in enabling more precise use of anti-cancer therapies.

Therapeutic Modification of Hypoxia

Regions of reduced oxygenation (hypoxia) are a characteristic feature of virtually all animal and human solid tumours. Numerous preclinical studies, both in vitro and in vivo, have shown that decreasing oxygen concentration induces resistance to radiation. Importantly, hypoxia in human tumours is a negative indicator of radiotherapy outcome. Hypoxia also contributes to resistance to other cancer therapeutics, including immunotherapy, and increases malignant progression as well as cancer cell dissemination. Consequently, substantial effort has been made to detect hypoxia in human tumours and identify realistic approaches to overcome hypoxia and improve cancer therapy outcomes. Hypoxia-targeting strategies include improving oxygen availability, sensitising hypoxic cells to radiation, preferentially killing these cells, locating the hypoxic regions in tumours and increasing the radiation dose to those areas, or applying high energy transfer radiation, which is less affected by hypoxia. Despite numerous clinical studies with each of these hypoxia-modifying approaches, many of which improved both local tumour control and overall survival, hypoxic modification has not been established in routine clinical practice. Here we review the background and significance of hypoxia, how it can be imaged clinically and focus on the various hypoxia-modifying techniques that have undergone, or are currently in, clinical evaluation.

Vascular normalisation as the stepping stone into tumour microenvironment transformation

A functional vascular system is indispensable for drug delivery and fundamental for responsiveness of the tumour microenvironment to such medication. At the same time, the progression of a tumour is defined by the interactions of the cancer cells with their surrounding environment, including neovessels, and the vascular network continues to be the major route for the dissemination of tumour cells in cancer, facilitating metastasis. So how can this apparent conflict be reconciled? Vessel normalisation-in which redundant structures are pruned and the abnormal vasculature is stabilised and remodelled-is generally considered to be beneficial in the course of anti-cancer treatments. A causality between normalised vasculature and improved response to medication and treatment is observed. For this reason, it is important to discern the consequence of vessel normalisation on the tumour microenvironment and to modulate the vasculature advantageously. This article will highlight the challenges of controlled neovascular remodelling and outline how vascular normalisation can shape disease management.

Direct phosphorylation and stabilization of HIF-1α by PIM1 kinase drives angiogenesis in solid tumors

Angiogenesis is essential for the sustained growth of solid tumors. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of angiogenesis and constitutive activation of HIF-1 is frequently observed in human cancers. Therefore, understanding the mechanisms governing the activation of HIF-1 is critical for successful therapeutic targeting of tumor angiogenesis. Herein, we establish a new regulatory mechanism responsible for the constitutive activation of HIF-1α in cancer, irrespective of oxygen tension. PIM1 kinase directly phosphorylates HIF-1α at threonine 455, a previously uncharacterized site within its oxygen-dependent degradation domain. This phosphorylation event disrupts the ability of prolyl hydroxylases to bind and hydroxylate HIF-1α, interrupting its canonical degradation pathway and promoting constitutive transcription of HIF-1 target genes. Moreover, phosphorylation of the analogous site in HIF-2α (S435) stabilizes the protein through the same mechanism, indicating post-translational modification within the oxygen-dependent degradation domain as a mechanism of regulating the HIF-α subunits. In vitro and in vivo models demonstrate that expression of PIM1 is sufficient to stabilize HIF-1α and HIF-2α in normoxia and stimulate angiogenesis in a HIF-1-dependent manner. CRISPR mutants of HIF-1α (Thr455D) promoted increased tumor growth, proliferation and angiogenesis. Moreover, HIF-1α-T455D xenograft tumors were refractory to the anti-angiogenic and cytotoxic effects of PIM inhibitors. These data identify a new signaling axis responsible for hypoxia-independent activation of HIF-1 and expand our understanding of the tumorigenic role of PIM1 in solid tumors.

In vitro effect of dibenzyl trisulfide on the p50 of the oxygen haemoglobin dissociation curve

OBJECTIVES

Dibenzyl trisulfide (DTS) has been reported to have cytotoxic and anti-inflammatory effects. It also affects erythrocyte deformability. We investigated the effects of DTS on the p50 of the oxygen haemoglobin dissociation curve.

METHODS

Blood samples from 10 healthy male volunteers with normal haemoglobin AA were exposed to 50, 100, 200 and 400 ng/mL, respectively, of DTS. A hemox-analyzer was used to obtain the p50 values.

RESULTS

The mean p50 value for the control samples was 25.89 ± 2.18 mm Hg. The values for the samples exposed to 50, 100, 200 and 400 ng/mL were 23.53 ± 1.81 mm Hg, 22.62 ± 1.61 mm Hg, 21.88 ± 1.67 mm Hg and 21.68 ± 1.88 mm Hg, respectively.

CONCLUSIONS

DTS caused a significant (p<0.001) reduction in p50 values indicating a shift of the oxygen- haemoglobin dissociation curve to the left in all the samples compared with control, suggesting that the administration of DTS could result in decrease in oxygen supply to tissues.

Occupancy and Fractal Dimension Analyses of the Spatial Distribution of Cytotoxic (CD8+) T Cells Infiltrating the Tumor Microenvironment in Triple Negative Breast Cancer

Favorable outcomes have been associated with high densities of tumor infiltrating lymphocytes (TILs) such as cytotoxic ([Formula: see text]) T cells. However, the clinical significance of the spatial distribution of TILs is less well understood. We have developed novel statistical techniques to characterize the spatial distribution of TILs at various length scales. These include a box counting method that we call “occupancy” and novel applications of fractal dimensions. We apply these techniques to the spatial distribution of [Formula: see text] T cells in the tumor microenvironment of tissue resected from 35 triple negative breast cancer patients. We find that there is a distinct difference in the spatial distribution of [Formula: see text] T cells between good clinical outcome (no recurrence within at least 5 years of diagnosis) and poor clinical outcome (recurrence within 3 years of diagnosis). The statistical significance of the difference between good and poor outcome in the occupancy, fractal dimension (FD), and FD difference of [Formula: see text] T cells is comparable to that of the [Formula: see text] T cell density. Even when we randomly exclude some of the cells so that the images have the same cell density, we still find that the fractal dimension at short length scales is correlated with cancer recurrence, implying that the actual spatial distribution of [Formula: see text] cells, and not just the [Formula: see text] cell density, is associated with clinical outcome. The occupancy and FD difference indicate that the [Formula: see text] T cells are more spatially dispersed in good outcome and more aggregated in poor outcome. We discuss possible interpretations.

Angiogenesis in Breast Cancer Progression, Diagnosis, and Treatment

Angiogenesis is a significant event in a wide range of healthy and diseased conditions. This process frequently involves vasodilation and an increase in vascular permeability. Numerous players referred to as angiogenic factors, work in tandem to facilitate the outgrowth of endothelial cells (EC) and the consequent vascularity. Conversely, angiogenic factors could also feature in pathological conditions. Angiogenesis is a critical factor in the development of tumors and metastases in numerous cancers. An increased level of angiogenesis is associated with decreased survival in breast cancer patients. Therefore, a good understanding of the angiogenic mechanism holds a promise of providing effective treatments for breast cancer progression, thereby enhancing patients' survival. Disrupting the initiation and progression of this process by targeting angiogenic factors such as vascular endothelial growth factor (Vegf)-one of the most potent member of the VEGF family- or by targeting transcription factors, such as Hypoxia-Inducible Factors (HIFs) that act as angiogenic regulators, have been considered potential treatment options for several types of cancers. The objective of this review is to highlight the mechanism of angiogenesis in diseases, specifically its role in the progression of malignancy in breast cancer, as well as to highlight the undergoing research in the development of angiogenesis-targeting therapies.

Preclinical murine tumor models: a structural and functional perspective

The goal of this review is to pinpoint the specific features, including the weaknesses, of various tumor models, and to discuss the reasons why treatments that are efficient in murine tumor models often do not work in clinics. In a detailed comparison of transplanted and spontaneous tumor models, we focus on structure-function relationships in the tumor microenvironment. For instance, the architecture of the vascular tree, which depends on whether tumor cells have gone through epithelial-mesenchymal transition, is determinant for the extension of the spontaneous necrosis, and for the intratumoral localization of the immune infiltrate. Another key point is the model-dependent abundance of TGFβ in the tumor, which controls the variable susceptibility of different tumor models to treatments. Grounded in a historical perspective, this review provides a rationale for checking factors that will be key for the transition between preclinical murine models and clinical applications.

Modelling of killer T-cell and cancer cell subpopulation dynamics under immuno- and chemotherapies

Each patient's cancer has a unique molecular makeup, often comprised of distinct cancer cell subpopulations. Improved understanding of dynamic processes between cancer cell populations is therefore critical for making treatment more effective and personalized. It has been shown that immunotherapy increases the survival of melanoma patients. However, there remain critical open questions, such as timing and duration of immunotherapy and its added benefits when combined with other types of treatments. We introduce a model for the dynamics of active killer T-cells and cancer cell subpopulations. Rather than defining the cancer cell populations based on their genetic makeup alone, we consider also other, non-genetic differences that make the cell populations either sensitive or resistant to a therapy. Using the model, we make predictions of possible outcomes of the various treatment strategies in virtual melanoma patients, providing hypotheses regarding therapeutic efficacy and side-effects. It is shown, for instance, that starting immunotherapy with a denser treatment schedule may enable changing to a sparser schedule later during the treatment. Furthermore, combination of targeted and immunotherapy results in a better treatment effect, compared to mono-immunotherapy, and a stable disease can be reached with a patient-tailored combination. These results offer better understanding of the competition between T-cells and cancer cells, toward personalized immunotherapy regimens.

Intratumoral distribution of YSNSG cyclopeptide in a mouse melanoma model using microdialysis

The YSNSG peptide is a synthetic cyclopeptide targeting α_vβ₃ integrin with antitumor activity. Previous study has determined main pharmacokinetic parameters in plasma and in tissue in healthy animals using microdialysis. First we aim to assess the impact of a 20 mg/kg dosage instead of 10 mg/kg in tumor growth inhibition. Secondly we aim to investigate the YSNSG peptide distribution in two different tumor regions in animals with melanoma. C57BL/6 mice were exposed at Days 8, 10 and 12 after melanoma cells implantation (B16F1) to different dosage of YSNSG peptide or control, respectively (n = 10 per group). Data analysis was performed at D16, 20 and 24 with a Nonlinear Mixed-Effects (NLME) approach. For pharmacokinetic study n = 8 mice (same disease condition) received YSNSG peptide by intravenous after insertion of two microdialysis probes in central peripheral region of tumor, respectively. Plasma and tissue samples were collected during 2 h. A non-compartmental analysis was performed to determine main pharmacokinetic parameters. There was a significant tumor growth inhibition in mice receiving 20 mg/kg vs Control (p < 0.02). Main plasma parameters were half-life elimination 25.8 ± 8.2 min, volume of distribution 11.9 ± 0.4 mL, clearance 19.8 ± 9.4 mL/h and area under the curve 1,173.6 µg.min/mL. Penetration rate of the YSNSG peptide from plasma to tumor tissue were 3.3 ± 2.1% and 3.4 ± 2.7% in central and peripheral, respectively. Contrary to subcutaneous distribution in healthy animals the distribution of the YSNSG peptide into tumoral tissue is low but seems non-heterogeneous between central and peripheral tumor region.

Quantitative Visualization of Hypoxia and Proliferation Gradients Within Histological Tissue Sections

The formation of hypoxic microenvironments within solid tumors is known to contribute to radiation resistance, chemotherapy resistance, immune suppression, increased metastasis, and an overall poor prognosis. It is therefore crucial to understand the spatial and molecular mechanisms that contribute to tumor hypoxia formation to improve the efficacy of radiation treatment, develop hypoxia-directed therapies, and increase patient survival. The objective of this study is to present a number of complementary novel methods for quantifying tumor hypoxia and proliferation in multiplexed immunofluorescence images, especially in relation to the location of perfused blood vessels. A standard marker analysis strategy is to take a positive pixel count approach, in which a threshold for positive stain is used to compute a positive area fraction for hypoxia. This work is a reassessment of that approach, utilizing not only cell segmentation but also distance to nearest blood vessel in order to incorporate spatial information into the analysis. We describe a reproducible pipeline for the visualization and quantitative analysis of hypoxia using a vessel distance analysis approach. This methodological pipeline can serve to further elucidate the relationship between vessel distance and microenvironment-linked markers such as hypoxia and proliferation, can help to quantify parameters relating to oxygen consumption and hypoxic tolerance in tissues, as well as potentially serve as a hypothesis generating tool for future studies testing hypoxia-linked markers.

Three-dimensional tumor growth in time-varying chemical fields: a modeling framework and theoretical study

Background

Contemporary biological observations have revealed a large variety of mechanisms acting during the expansion of a tumor. However, there are still many qualitative and quantitative aspects of the phenomenon that remain largely unknown. In this context, mathematical and computational modeling appears as an invaluable tool providing the means for conducting in silico experiments, which are cheaper and less tedious than real laboratory experiments.

Results

This paper aims at developing an extensible and computationally efficient framework for in silico modeling of tumor growth in a 3-dimensional, inhomogeneous and time-varying chemical environment. The resulting model consists of a set of mathematically derived and algorithmically defined operators, each one addressing the effects of a particular biological mechanism on the state of the system. These operators may be extended or re-adjusted, in case a different set of starting assumptions or a different simulation scenario needs to be considered.

Conclusion

In silico modeling provides an alternative means for testing hypotheses and simulating scenarios for which exact biological knowledge remains elusive. However, finer tuning of pertinent methods presupposes qualitative and quantitative enrichment of available biological evidence. Validation in a strict sense would further require comprehensive, case-specific simulations and detailed comparisons with biomedical observations.

Hematological Malignancy-Derived Small Extracellular Vesicles and Tumor Microenvironment: The Art of Turning Foes into Friends

Small extracellular vesicles (small EVs) are commonly released by all cells, and are found in all body fluids. They are implicated in cell to cell short- and long-distance communication through the transfer of genetic material and proteins, as well as interactions between target cell membrane receptors and ligands anchored on small EV membrane. Beyond their canonical functions in healthy tissues, small EVs are strategically used by tumors to communicate with the cellular microenvironment and to establish a proper niche which would ultimately allow cancer cell proliferation, escape from the immune surveillance, and metastasis formation. In this review, we highlight the effects of hematological malignancy-derived small EVs on immune and stromal cells in the tumor microenvironment.

Tissue "Hypoxia" and the Maintenance of Leukemia Stem Cells

The relationship of the homing of normal hematopoietic stem cells (HSC) in the bone marrow to specific environmental conditions, referred to as the stem cell niche (SCN), has been intensively studied over the last three decades. These conditions include the action of a number of molecular and cellular players, as well as critical levels of nutrients, oxygen and glucose in particular, involved in energy production. These factors are likely to act also in leukemias, due to the strict analogy between the hierarchical structure of normal hematopoietic cell populations and that of leukemia cell populations. This led to propose that leukemic growth is fostered by cells endowed with stem cell properties, the leukemia stem cells (LSC), a concept readily extended to comprise the cancer stem cells (CSC) of solid tumors. Two alternative routes have been proposed for CSC generation, that is, the oncogenic staminalization (acquisition of self-renewal) of a normal progenitor cell (the "CSC in normal progenitor cell" model) and the oncogenic transformation of a normal (self-renewing) stem cell (the "CSC in normal stem cell" model). The latter mechanism, in the hematological context, makes LSC derive from HSC, suggesting that LSC share SCN homing with HSC. This chapter is focused on the availability of oxygen and glucose in the regulation of LSC maintenance within the SCN. In this respect, the most critical aspect in view of the outcome of therapy is the long-term maintenance of the LSC subset capable to sustain minimal residual disease and the related risk of relapse of disease.

Active Role of the Necrotic Zone in Desensitization of Hypoxic Macrophages and Regulation of CSC-Fate: A hypothesis

Fast-proliferating cancer cells in the hypoxic region face a shortage of oxygen and nutrients, undergo necrotic cell death, and release numerous signaling components. Hypoxia-induced chemo-attractants signal for macrophages/monocytes to clear debris and return the system to steady state. Accordingly, macrophages arrange into pre-necrotic positions, where they are continuously exposed to stress signals. It can thus be hypothesized that gradual alteration of gene expression in macrophages eventually turns off their phagocytic machinery. Uncleared cell corpses within the hypoxic region potentially provide a rich source of building blocks for anaerobic metabolism of cancer stem cells via macropinocytosis, and are conceivably implicated in tumor progression and invasion.

The role of spatial variations of abiotic factors in mediating intratumour phenotypic heterogeneity

We present here a space- and phenotype-structured model of selection dynamics between cancer cells within a solid tumour. In the framework of this model, we combine formal analyses with numerical simulations to investigate in silico the role played by the spatial distribution of abiotic components of the tumour microenvironment in mediating phenotypic selection of cancer cells. Numerical simulations are performed both on the 3D geometry of an in silico multicellular tumour spheroid and on the 3D geometry of an in vivo human hepatic tumour, which was imaged using computerised tomography. The results obtained show that inhomogeneities in the spatial distribution of oxygen, currently observed in solid tumours, can promote the creation of distinct local niches and lead to the selection of different phenotypic variants within the same tumour. This process fosters the emergence of stable phenotypic heterogeneity and supports the presence of hypoxic cells resistant to cytotoxic therapy prior to treatment. Our theoretical results demonstrate the importance of integrating spatial data with ecological principles when evaluating the therapeutic response of solid tumours to cytotoxic therapy.

Morpho-Functional Study of Vascular Fluorochrome Delivery to Lung and Liver Metastases of Lewis Lung Carcinoma (3Ll)

The growth of 3LL liver and lung metastases related to Its vascular organization was studied by morphological and functional methods, using the Hoechst 33342 fluorescent DNA staining technique. Experimental liver and lung metastases were produced in syngeneic C57BL/6 mice by injection of 3LL tumor cells into a lateral tail vein or into the spleen, respectively. The resulting neoplasms were composed of large cells arranged in sheets with a thin irregularly distributed stroma. Scattered blood vessels with an open or closed lumen were observed within the tumor. Functional study of H33342 diffusion showed a single and reticular fluorescent pattern in liver metastases. In contrast, in lung metastases the fluorochrome diffusion revealed two different fluorescent patterns related to the location of the metastasis. Thus, parenchymal and subpleural metastasis presented a fluorescent pattern similar to that observed in the liver whereas metastases located around blood vessels and conducting airways never displayed fluorescence. In summary, our results suggest that the target metastatic organ and/or intra-organ location modulates the characteristics of metabolic exchange of the tumor cells In relation to the vascular organization of the metastatic focus.

Imatinib-mesylate enhances the maintenance of chronic myeloid leukemia stem cell potential in the absence of glucose

The introduction of BCR/Abl tyrosine kinase inhibitors (TKI), such as imatinib-mesylate (IM), has revolutioned the treatment of chronic myeloid leukemia (CML). However, although extremely effective in inducing CML remission, IM is unable to eliminate leukemia stem cells (LSC). This is largely due to the suppression of BCR/Abl protein, driven by the reduction of energy supply due to oxygen or glucose shortage, in stem cell niches of bone marrow. Here, we investigated whether, in K562 and KCL22 CML cell cultures, glucose shortage induces refractoriness of stem cell potential to IM. In the absence of glucose, IM, while maintaining its detrimental effect on CML cell bulk, actually enhanced colony formation ability and stem cell potential. This was paralleled by an increased expression of the Nanog and Sox-2 stem cell markers. These evidences stress further the importance of developing strategies alternative to TKI capable to target LSC of CML.

The promise and challenges of exploiting the proton-coupled folate transporter for selective therapeutic targeting of cancer

This review considers the "promise" of exploiting the proton-coupled folate transporter (PCFT) for selective therapeutic targeting of cancer. PCFT was discovered in 2006 and was identified as the principal folate transporter involved in the intestinal absorption of dietary folates. The recognition that PCFT was highly expressed in many tumors stimulated substantial interest in using PCFT for cytotoxic drug targeting, taking advantage of its high level transport activity under the acidic pH conditions that characterize many tumors. For pemetrexed, among the best PCFT substrates, transport by PCFT establishes its importance as a clinically important transporter in malignant pleural mesothelioma and non-small cell lung cancer. In recent years, the notion of PCFT-targeting has been extended to a new generation of tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine compounds that are structurally and functionally distinct from pemetrexed, and that exhibit near exclusive transport by PCFT and potent inhibition of de novo purine nucleotide biosynthesis. Based on compelling preclinical evidence in a wide range of human tumor models, it is now time to advance the most optimized PCFT-targeted agents with the best balance of PCFT transport specificity and potent antitumor efficacy to the clinic to validate this novel paradigm of highly selective tumor targeting.

Non-randomness of the anatomical distribution of tumors

Background

Why does a tumor start where it does within an organ? Location is traditionally viewed as a random event, yet the statistics of the location of tumors argues against this being a random occurrence. There are numerous examples including that of breast cancer. More than half of invasive breast cancer tumors start in the upper outer quadrant of the breast near the armpit, even though it is estimated that only 35 to 40% of breast tissue is in this quadrant. This suggests that there is an unknown microenvironmental factor that significantly increases the risk of cancer in a spatial manner and that is not solely due to genes or toxins. We hypothesize that tumors are more prone to form in healthy tissue at microvascular ‘hot spots’ where there is a high local concentration of microvessels providing an increased blood flow that ensures an ample supply of oxygen, nutrients, and receptors for growth factors that promote the generation of new blood vessels.

Results

To show the plausibility of our hypothesis, we calculated the fractional probability that there is at least one microvascular hot spot in each region of the breast assuming a Poisson distribution of microvessels in two-dimensional cross sections of breast tissue. We modulated the microvessel density in various regions of the breast according to the total hemoglobin concentration measured by near infrared diffuse optical spectroscopy in different regions of the breast. Defining a hot spot to be a circle of radius 200 μm with at least 5 microvessels, and using a previously measured mean microvessel density of 1 microvessel/mm², we find good agreement of the fractional probability of at least one hot spot in different regions of the breast with the observed invasive tumor occurrence. However, there is no reason to believe that the microvascular distribution obeys a Poisson distribution.

Conclusions

The spatial location of a tumor in an organ is not entirely random, indicating an unknown risk factor. Much work needs to be done to understand why a tumor occurs where it does.

Electronic supplementary material

The online version of this article (10.1186/s41236-017-0006-7) contains supplementary material, which is available to authorized users.

Downregulation of DNA repair proteins and increased DNA damage in hypoxic colon cancer cells is a therapeutically exploitable vulnerability

Surgical removal of colorectal cancer (CRC) liver metastases generates areas of tissue hypoxia. Hypoxia imposes a stem-like phenotype on residual tumor cells and promotes tumor recurrence. Moreover, in primary CRC, gene expression signatures reflecting hypoxia and a stem-like phenotype are highly expressed in the aggressive Consensus Molecular Subtype 4 (CMS4). Therapeutic strategies eliminating hypoxic stem-like cells may limit recurrence following resection of primary tumors or metastases.

Here we show that expression of DNA repair genes is strongly suppressed in CMS4 and inversely correlated with hypoxia-inducible factor-1 alpha (HIF1α) and HIF-2α co-expression signatures. Tumors with high expression of HIF signatures and low expression of repair proteins showed the worst survival. In human tumors, expression of the repair proteins RAD51, KU70 and RIF1 was strongly suppressed in hypoxic peri-necrotic tumor areas. Experimentally induced hypoxia in patient derived colonospheres in vitro or in vivo (through vascular clamping) was sufficient to downregulate repair protein expression and caused DNA damage. Hypoxia-induced DNA damage was prevented by expressing the hydroperoxide-scavenging enzyme glutathione peroxidase-2 (GPx2), indicating that reactive oxygen species mediate hypoxia-induced DNA damage. Finally, the hypoxia-activated prodrug Tirapazamine greatly augmented DNA damage and reduced the fraction of stem-like (Aldefluor^bright) tumor cells in vitro, and in vivo following vascular clamping.

We conclude that decreased expression of DNA repair proteins and increased DNA damage in hypoxic tumor areas may be therapeutically exploited with hypoxia-activated prodrugs, and that such drugs reduce the fraction of Aldefluor^bright (stem-like) tumor cells.

Microscale Mass Spectrometry Analysis of Extracellular Metabolites in Live Multicellular Tumor Spheroids

Extracellular compounds in tumors play critical roles in intercellular communication, tumor proliferation, and cancer cell metastasis. However, the lack of appropriate techniques leads to limited studies of extracellular metabolite. Here, we introduced a microscale collection device, the Micro-funnel, fabricated from biocompatible fused silica capillary. With a small probe size (∼25 μm), the Micro-funnel can be implanted into live multicellular tumor spheroids to accumulate the extracellular metabolites produced by cancer cells. Metabolites collected in the Micro-funnel device were then extracted by a microscale sampling and ionization device, the Single-probe, for real-time mass spectrometry (MS) analysis. We successfully detected the abundance change of anticancer drug irinotecan and its metabolites inside spheroids treated under a series of conditions. Moreover, we found that irinotecan treatment dramatically altered the composition of extracellular compounds. Specifically, we observed the increased abundances of a large number of lipids, which are potentially related to the drug resistance of cancer cells. This study provides a novel way to detect the extracellular compounds inside live spheroids, and the successful development of our technique can benefit the research in multiple areas, including the microenvironment inside live tissues, cell-cell communication, biomarker discovery, and drug development.

Three-dimensional tumor cell growth stimulates autophagic flux and recapitulates chemotherapy resistance

Current preclinical models in tumor biology are limited in their ability to recapitulate relevant (patho-) physiological processes, including autophagy. Three-dimensional (3D) growth cultures have frequently been proposed to overcome the lack of correlation between two-dimensional (2D) monolayer cell cultures and human tumors in preclinical drug testing. Besides 3D growth, it is also advantageous to simulate shear stress, compound flux and removal of metabolites, e.g., via bioreactor systems, through which culture medium is constantly pumped at a flow rate reflecting physiological conditions. Here we show that both static 3D growth and 3D growth within a bioreactor system modulate key hallmarks of cancer cells, including proliferation and cell death as well as macroautophagy, a recycling pathway often activated by highly proliferative tumors to cope with metabolic stress. The autophagy-related gene expression profiles of 2D-grown cells are substantially different from those of 3D-grown cells and tumor tissue. Autophagy-controlling transcription factors, such as TFEB and FOXO3, are upregulated in tumors, and 3D-grown cells have increased expression compared with cells grown in 2D conditions. Three-dimensional cultures depleted of the autophagy mediators BECN1, ATG5 or ATG7 or the transcription factor FOXO3, are more sensitive to cytotoxic treatment. Accordingly, combining cytotoxic treatment with compounds affecting late autophagic flux, such as chloroquine, renders the 3D-grown cells more susceptible to therapy. Altogether, 3D cultures are a valuable tool to study drug response of tumor cells, as these models more closely mimic tumor (patho-)physiology, including the upregulation of tumor relevant pathways, such as autophagy.

A review of the development of tumor vasculature and its effects on the tumor microenvironment

Background

The imbalance of angiogenic regulators in tumors drives tumor angiogenesis and causes the vasculature to develop much differently in tumors than in normal tissue. There are several cancer therapy techniques currently being used and developed that target the tumor vasculature for the treatment of solid tumors. This article reviews the aspects of the tumor vasculature that are relevant to most cancer therapies but particularly to vascular targeting techniques.

Materials and methods

We conducted a review of identified experiments in which tumors were transplanted into animals to study the development of the tumor vasculature with tumor growth. Quantitative vasculature morphology data for spontaneous human head and neck cancers are reviewed. Parameters assessed include the highest microvascular density (h-MVD) and the relative vascular volume (RVV). The effects of the vasculature on the tumor microenvironment are discussed, including the distributions of hypoxia and proliferation.

Results

Data for the h-MVD and RVV in head and neck cancers are highly varied, partly due to methodological differences. However, it is clear that the cancers are typically more vascularized than the corresponding normal tissue. The commonly observed chronic hypoxia and acute hypoxia in these tumors are due to high intratumor heterogeneity in MVD and lower than normal blood oxygenation levels through the abnormally developed tumor vasculature. Hypoxic regions are associated with decreased cell proliferation.

Conclusion

The morphology of the vasculature strongly influences the tumor microenvironment, with important implications for tumor response to medical intervention such as radiotherapy. Quantitative vasculature morphology data herein may be used to inform computational models that simulate the spatial tumor vasculature. Such models may play an important role in exploring and optimizing vascular targeting cancer therapies.

Development of an in silico stochastic 4D model of tumor growth with angiogenesis

PURPOSE

A stochastic computer model of tumour growth with spatial and temporal components that includes tumour angiogenesis was developed. In the current work it was used to simulate head and neck tumour growth. The model also provides the foundation for a 4D cellular radiotherapy simulation tool.

METHODS

The model, developed in Matlab, contains cell positions randomised in 3D space without overlap. Blood vessels are represented by strings of blood vessel units which branch outwards to achieve the desired tumour relative vascular volume. Hypoxic cells have an increased cell cycle time and become quiescent at oxygen tensions less than 1 mmHg. Necrotic cells are resorbed. A hierarchy of stem cells, transit cells and differentiated cells is considered along with differentiated cell loss. Model parameters include the relative vascular volume (2-10%), blood oxygenation (20-100 mmHg), distance from vessels to the onset of necrosis (80-300 μm) and probability for stem cells to undergo symmetric division (2%). Simulations were performed to observe the effects of hypoxia on tumour growth rate for head and neck cancers. Simulations were run on a supercomputer with eligible parts running in parallel on 12 cores.

RESULTS

Using biologically plausible model parameters for head and neck cancers, the tumour volume doubling time varied from 45 ± 5 days (n = 3) for well oxygenated tumours to 87 ± 5 days (n = 3) for severely hypoxic tumours.

CONCLUSIONS

The main achievements of the current model were randomised cell positions and the connected vasculature structure between the cells. These developments will also be beneficial when irradiating the simulated tumours using Monte Carlo track structure methods.

Downregulation of EGFR in hypoxic, diffusion-limited areas of squamous cell carcinomas of the head and neck

Background:

The receptor for the epidermal growth factor (EGFR) is widely considered to be one of the central drivers of oncogenesis in squamous cell carcinomas of the head and neck region (HNSCC). Inhibition of EGFR using monoclonal antibodies is established both in the curative and the palliative setting in this disease. HNSCCs are known to contain abundant hypoxic tissue areas and hypoxia has been shown to be involved in the (down)regulation of EGFR membrane expression.

Methods:

A novel method for multiplex immunofluorescence and single-cell segmentation (via DAPI-stained nuclei) was established, to study the expression of EGFR, the endogenous hypoxia marker CA IX, and intratumoural diffusion distances from microvessels (using CD34 staining) in 58 human HNSCCs and 9 normal/cancer adjacent tissues.

Results:

EGFR was found to be significantly downregulated with increasing distance from tumour microvessels, whereas the opposite was true for CA IX. Larger diffusion-limited areas were correlated with higher expression of CA IX.

Conclusions:

The hypoxic tumour microenvironment may have a major role in mediating resistance against anti-EGFR strategies by downregulating EGFR molecules on tumour cells.

Development of TRACER: tissue roll for analysis of cellular environment and response

The tumour microenvironment is heterogeneous and consists of multiple cell types, variable extracellular matrix (ECM) composition, and contains cell-defined gradients of small molecules, oxygen, nutrients and waste. Emerging in vitro cell culture systems that attempt to replicate these features often fail to incorporate design strategies to facilitate efficient data collection and stratification. The tissue roll for analysis of cellular environment and response (TRACER) is a novel strategy to assemble layered, three-dimensional tumours with cell-defined, graded heterogeneous microenvironments that also facilitates cellular separation and stratification of data from different cell populations from specific microenvironments. Here we describe the materials selection and development of TRACER. We find that cellulose fibre scaffolding is an ideal support to generate tissue constructs having homogenous cell seeding and consistent properties. We explore ECM remodeling and long-term cell growth in the scaffold, and characterize the tumour microenvironment in assembled TRACERs using multiple established analysis methods. Finally, we confirm that TRACERs replicate small molecule gradients of glucose and lactate, and explore cell phenotype associated with these gradients using confocal microscopy, flow cytometry, and quantitative PCR analysis. We envision this technology will provide a platform to create complex, yet controlled tumour microenvironments that can be easily disassembled for snapshot analysis of cell phenotype and response to therapy in relation to microenvironment properties.

The challenge of targeting metastasis

Metastases that are resistant to conventional therapy are the major cause of death from cancer. In most patients, metastasis has already occurred by the time of diagnosis. Thus, the prevention of metastasis is unlikely to be of therapeutic benefit. The biological heterogeneity of metastases presents a major obstacle to treatment. However, the growth and survival of metastases depend on interactions between tumor cells and host homeostatic mechanisms. Targeting these interactions, in addition to the tumor cells, can produce synergistic therapeutic effects against existing metastases.

Tumor necrosis is an important hallmark of aggressive endometrial cancer and associates with hypoxia, angiogenesis and inflammation responses

Aims

Tumor necrosis is associated with aggressive features of endometrial cancer and poor prognosis. Here, we investigated gene expression patterns and potential treatment targets related to presence of tumor necrosis in primary endometrial cancer lesions.

Methods and Results

By DNA microarray analysis, expression of genes related to tumor necrosis reflected multiple tumor-microenvironment interactions like tissue hypoxia, angiogenesis and inflammation pathways. A tumor necrosis signature of 38 genes and a related patient cluster (Cluster I, 67% of the cases) were associated with features of aggressive tumors such as type II cancers, estrogen receptor negative tumors and vascular invasion. Further, the tumor necrosis signature was increased in tumor cells grown in hypoxic conditions in vitro. Multiple genes with increased expression are known to be activated by HIF1A and NF-kB.

Conclusions

Our findings indicate that the presence of tumor necrosis within primary tumors is associated with hypoxia, angiogenesis and inflammation responses. HIF1A, NF-kB and PI3K/mTOR might be potential treatment targets in aggressive endometrial cancers with presence of tumor necrosis.

Optimal treatment and stochastic modeling of heterogeneous tumors

In this work we review past articles that have mathematically studied cancer heterogeneity and the impact of this heterogeneity on the structure of optimal therapy. We look at past works on modeling how heterogeneous tumors respond to radiotherapy, and take a particularly close look at how the optimal radiotherapy schedule is modified by the presence of heterogeneity. In addition, we review past works on the study of optimal chemotherapy when dealing with heterogeneous tumors.

REVIEWERS

This article was reviewed by Thomas McDonald, David Axelrod, and Leonid Hanin.

Modelling tumour cell proliferation from vascular structure using tissue decomposition into avascular elements

Computer models allow the mechanistically detailed study of tumour proliferation and its dependency on nutrients. However, the computational study of large vascular tumours requires detailed information on the 3-dimensional vessel network and rather high computation times due to complex geometries. This study puts forward the idea of partitioning vascularised tissue into connected avascular elements that can exchange cells and nutrients between each other. Our method is able to rapidly calculate the evolution of proliferating as well as dead and quiescent cells, and hence a proliferative index, from a given amount and distribution of vascularisation of arbitrary complexity. Applying our model, we found that a heterogeneous vessel distribution provoked a higher proliferative index, suggesting increased malignancy, and increased the amount of dead cells compared to a more static tumour environment when a homogenous vessel distribution was assumed. We subsequently demonstrated that under certain amounts of vascularisation, cell proliferation may even increase when vessel density decreases, followed by a subsequent decrease of proliferation. This effect was due to a trade-off between an increase in compensatory proliferation for replacing dead cells and a decrease of cell population due to lack of oxygen supply in lowly vascularised tumours. Findings were illustrated by an ectopic colorectal cancer mouse xenograft model. Our presented approach can be in the future applied to study the effect of cytostatic, cytotoxic and anti-angiogenic chemotherapy and is ideally suited for translational systems biology, where rapid interaction between theory and experiment is essential.

The Contribution of Angiogenesis to the Process of Metastasis

The role of angiogenesis in tumor growth has been studied continuously for over 45 years. It is now appreciated that angiogenesis is also essential for the dissemination and establishment of tumor metastases. In this review, we focus on the role of angiogenesis as a necessity for the escape of tumor cells into the bloodstream and for the establishment of metastatic colonies in secondary sites. We also discuss the role of tumor lymphangiogenesis as a means of dissemination of lymphatic metastases. Appropriate combination therapies may be used in the future to both prevent and treat metastatic disease through the rational use of antiangiogenic and antilymphangiogenic therapies in ways that are informed by the current and future work in the field.

The Biology of Brain Metastasis: Challenges for Therapy

Many patients with lung cancer, breast cancer, and melanoma develop brain metastases that are resistant to conventional therapy. The median survival for untreated patients is 1 to 2 months, which may be extended to 6 months with surgery, radiotherapy, and chemotherapy. The outcome of metastasis depends on multiple interactions of unique metastatic cells with host homeostatic mechanisms which the tumor cells exploit for their survival and proliferation. The blood-brain barrier is leaky in metastases that are larger than 0.5-mm diameter because of production of vascular endothelial growth factor by metastatic cells. Brain metastases are surrounded and infiltrated by microglia and activated astrocytes. The interaction with astrocytes leads to up-regulation of multiple genes in the metastatic cells, including several survival genes that are responsible for the increased resistance of tumor cells to cytotoxic drugs. These findings substantiate the importance of the "seed and soil" hypothesis and that successful treatment of brain metastases must include targeting of the organ microenvironment.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Pathophysiological Basis for the Formation of the Tumor Microenvironment

Poor microenvironmental conditions are a characteristic feature of solid tumors. Such conditions occur because the tumor vascular supply, which develops from the normal host vasculature by the process of angiogenesis, is generally inadequate in meeting the oxygen and nutrient demands of the growing tumor mass. Regions of low oxygenation (hypoxia) is believed to be the most critical deficiency, since it has been well documented to play a significant role in influencing the response to conventional radiation and chemotherapy treatments, as well as influencing malignant progression in terms of aggressive growth and recurrence of the primary tumor and its metastatic spread. As a result, significant emphasis has been placed on finding clinically applicable approaches to identify those tumors that contain hypoxia and realistic methods to target this hypoxia. However, most studies consider hypoxia as a single entity, yet we now know that it is multifactorial. Furthermore, hypoxia is often associated with other microenvironmental parameters, such as elevated interstitial fluid pressure, glycolysis, low pH, and reduced bioenergetic status, and these can also influence the effects of hypoxia. Here, we review the various aspects of hypoxia, but also discuss the role of the other microenvironmental parameters associated with hypoxia.