Intratumoral lymphatic vessels: a case of mistaken identity or malfunction?

Biochemical and mechanical signals in the lymphatic vasculature

Lymphatic vasculature is an integral part of the cardiovascular system where it maintains interstitial fluid balance. Additionally, lymphatic vasculature regulates lipid assimilation and inflammatory response. Lymphatic vasculature is composed of lymphatic capillaries, collecting lymphatic vessels and valves that function in synergy to absorb and transport fluid against gravitational and pressure gradients. Defects in lymphatic vessels or valves leads to fluid accumulation in tissues (lymphedema), chylous ascites, chylothorax, metabolic disorders and inflammation. The past three decades of research has identified numerous molecules that are necessary for the stepwise development of lymphatic vasculature. However, approaches to treat lymphatic disorders are still limited to massages and compression bandages. Hence, better understanding of the mechanisms that regulate lymphatic vascular development and function is urgently needed to develop efficient therapies. Recent research has linked mechanical signals such as shear stress and matrix stiffness with biochemical pathways that regulate lymphatic vessel growth, patterning and maturation and valve formation. The goal of this review article is to highlight these innovative developments and speculate on unanswered questions.

Optical Microscopy and Coherence Tomography of Cancer in Living Subjects

Intravital microscopy (IVM) and optical coherency tomography (OCT) are two powerful optical imaging tools that allow visualization of dynamic biological activities in living subjects with subcellular resolutions. Recent advances in labeling and label-free techniques empower IVM and OCT for a wide range of preclinical and clinical cancer imaging, providing profound insights into the complex physiological, cellular, and molecular behaviors of tumors. Preclinical IVM and OCT have elucidated many otherwise inscrutable aspects of cancer biology, while clinical applications of IVM and OCT are revolutionizing cancer diagnosis and therapies. We review important progress in the fields of IVM and OCT for cancer imaging in living subjects, highlighting key technological developments and their emerging applications in fundamental cancer biology research and clinical oncology investigation.

Radiomics analysis of magnetic resonance imaging improves diagnostic performance of lymph node metastasis in patients with cervical cancer

BACKGROUND AND PURPOSE

Robust parameters are needed to predict lymph node metastasis (LNM) in locally advanced cervical cancer patients in order to select optimal treatment regimen. The aim of this study is to utilize radiomics analysis of magnetic resonance imaging (MRI) to improve diagnostic performance of LNM in cervical cancer patients.

MATERIALS AND METHODS

A total of 189 cervical cancer patients were divided into a training cohort (n = 126) and a validation cohort (n = 63). For each patient, we extracted radiomic features from intratumoral and peritumoral tissues on sagittal T2WI and axial apparent diffusion coefficient (ADC) maps. Afterward, the radiomic features associated with LNM status were selected by univariate ROC testing and logistic regression with the least absolute shrinkage and selection operator (LASSO) penalty in the training cohort. Based on the selected features, a support vector machine (SVM) model was established to predict LNM status. To further improve the diagnostic performance, a decision tree which combines the radiomics model with clinical factors was built.

RESULTS

Radiomics model of the intratumoral and peritumoral tissues on T2WI (T2_tumor+peri) showed best sensitivity and clinical LN (c-LN) status showed best specificity to predict LNM. The decision tree that combines radiomics model of T2_tumor+peri and c-LN status achieved best diagnostic performance, with AUC and sensitivity of 0.895 and 94.3%, 0.847 and 100% in the training and validation cohort respectively.

CONCLUSIONS

The decision tree, which incorporates radiomics model of T2_tumor+peri and c-LN status can be potentially applied in the preoperative prediction of LNM in locally advanced cervical cancer patients.

Functional intratumoral lymphatics in patient-derived xenograft models of squamous cell carcinoma of the uterine cervix: implications for lymph node metastasis

Studies of cell line-derived human tumor xenografts have suggested that the lymphatics seen in immunohistochemical preparations from non-peripheral regions of tumors are nonfunctional. In this investigation, lymphangiogenesis, hemangiogenesis, and lymph node metastasis were studied in patient-derived xenograft (PDX) models of carcinoma of the uterine cervix. Lymph vessel density (LVD) and blood vessel density (BVD) were measured in immunohistochemical preparations. The expression of angiogenesis-related genes was investigated by quantitative PCR. Lymphatic functionality was assessed with the ferritin assay, and tumor interstitial fluid pressure (IFP) was measured with a Millar catheter. The PDX models mirrored the angiogenesis and aggressiveness of the donor patients' tumors, and two highly aggressive models developed functional lymphatics within the tumor mass. Tumors with functional intratumoral lymphatics showed low IFP, high LVD, high BVD, high expression of a large number of angiogenesis-related genes, and high incidence of lymph node metastases. LVD correlated with BVD, and lymph node metastasis was associated with high LVD and high BVD. Nine angiogenesis-related genes associated with the development of functional intratumoral lymhatics were identified. High expression of these genes, high LVD, and high BVD may be important biomarkers for poor outcome in cervix carcinoma.

Revealing elasticity of largely deformed cells flowing along confining microchannels

Deformability is a hallmark of malignant tumor cells. Characterizing cancer cell deformation can reveal how cancer cell metastasizes through tiny gaps in tissues. However, many previous reports only focus on the cancer cell behaviors under small deformation regimes, which may not be representative for the behaviors under large deformations as in the in vivo metastatic processes. Here, we investigate a wide range of cell elasticity using our recently developed confining microchannel arrays. We develop a relation between the elastic modulus and cell shape under different deformation levels based on a modified contact theory and the hyperelastic Tatara theory. We demonstrate good agreements between the model prediction and experimental results. Strikingly, we discover a clear ‘modulus jump’ of largely deformed cells compared to that of small deformed cells, offering further biomechanical properties of the cells. Likely, such a modulus jump can be considered as a label-free marker reflecting the elasticity of intracellular components including the nucleus during cell translocation in capillaries and tissue constrictions. In essence, we perform cell classification based on the distinct micromechanical properties of four cell lines, i.e. one normal cell line (MCF-10A) and three cancer cell lines (MCF-7, MDA-MB-231 and PC3) and achieved reasonable efficiencies (efficiency >65%). Finally, we study the correlation between large-deformational elasticity and translocation rates of the floating cells in the microchannels. Together, our results demonstrate the quantitative analysis of the biomechanical properties of single floating cells, which provide an additional label-free physical biomarker toward more effective cancer diagnosis.

Deformability is a hallmark of malignant tumor cells.

Lymphangiogenic Gene Expression Is Associated With Lymph Node Recurrence and Poor Prognosis After Partial Hepatectomy for Colorectal Liver Metastasis

OBJECTIVES

To investigate the relevance of lymphangiogenic gene expression in primary and liver metastasis of colorectal cancer (CRC) and identify determinants of lymphatic invasion.

BACKGROUND

Lymphatic development promoting vascular endothelial growth factor C (VEGFC) is associated with poor outcome in primary CRC. For colorectal liver metastasis (CRLM), intrahepatic lymph invasion and lymph node metastasis are poor prognostic factors. Exact biological factors promoting lymphatic involvement remain elusive, just as the association with molecular subtypes of CRC.

METHODS

We designed a lymphangiogenic gene set (VEGFC, Nrp-2, PDPN, LYVE-1, MRC1, CCL-21) and applied it to large datasets of CRC. Gene expression of the lymphangiogenic signature was assessed in resected CRLM specimens by Rt-QPCR. In vitro experiments were performed with colon cancer cell line Colo320 (high Nrp-2 expression) and human dermal microvascular lymphatic endothelial cells (LECs).

RESULTS

Lymphangiogenic gene expression was associated with poor prognosis in both primary and liver metastasis of CRC. CRLM with high expression of consensus molecular subtype-4 identifier genes also exhibited high lymphangiogenic gene expression. Lymph node recurrence following CRLM resection was associated with high expression of VEGFC and Nrp-2. Blocking Nrp-2 significantly reduced invasion of Colo320 cells through an LEC monolayer.

CONCLUSIONS

Lymphangiogenic gene expression is correlated with worse prognosis and consensus molecular subtype-4 in both primary and liver metastatic CRC. VEGFC and Nrp-2 expression may be predictive of lymph node involvement in recurrence after resection of CRLM. Nrp-2, expressed on both tumor and LECs, may have a mechanistic role in lymphatic invasion and is a potential novel target in CRC.

Effects of fatty acid synthase inhibitors on lymphatic vessels: an in vitro and in vivo study in a melanoma model

Fatty acid synthase (FASN) is responsible for the endogenous production of fatty acids from acetyl-CoA and malonyl-CoA. Its overexpression is associated with poor prognosis in human cancers including melanomas. Our group has previously shown that the inhibition of FASN with orlistat reduces spontaneous lymphatic metastasis in experimental B16-F10 melanomas, which is a consequence, at least in part, of the reduction of proliferation and induction of apoptosis. Here, we sought to investigate the effects of pharmacological FASN inhibition on lymphatic vessels by using cell culture and mouse models. The effects of FASN inhibitors cerulenin and orlistat on the proliferation, apoptosis, and migration of human lymphatic endothelial cells (HDLEC) were evaluated with in vitro models. The lymphatic outgrowth was evaluated by using a murine ex vivo assay. B16-F10 melanomas and surgical wounds were produced in the ears of C57Bl/6 and Balb-C mice, respectively, and their peripheral lymphatic vessels evaluated by fluorescent microlymphangiography. The secretion of vascular endothelial growth factor C and D (VEGF-C and -D) by melanoma cells was evaluated by ELISA and conditioned media used to study in vitro lymphangiogenesis. Here, we show that cerulenin and orlistat decrease the viability, proliferation, and migration of HDLEC cells. The volume of lymph node metastases from B16-F10 experimental melanomas was reduced by 39% in orlistat-treated animals as well as the expression of VEGF-C in these tissues. In addition, lymphatic vessels from orlistat-treated mice drained more efficiently the injected FITC-dextran. Orlistat and cerulenin reduced VEGF-C secretion and, increase production of VEGF-D by B16-F10 and SK-Mel-25 melanoma cells. Finally, reduced lymphatic cell extensions, were observed following the treatment with conditioned medium from cerulenin- and orlistat-treated B16-F10 cells. Altogether, our results show that FASN inhibitors have anti-metastatic effects by acting on lymphatic endothelium and melanoma cells regardless the increase of lymphatic permeability promoted by orlistat.

Overview of Methods for Overcoming Hindrance to Drug Delivery to Tumors, with Special Attention to Tumor Interstitial Fluid

Every drug used to treat cancer (chemotherapeutics, immunological, monoclonal antibodies, nanoparticles, radionuclides) must reach the targeted cells through the tumor environment at adequate concentrations, in order to exert their cell-killing effects. For any of these agents to reach the goal cells, they must overcome a number of impediments created by the tumor microenvironment (TME), beginning with tumor interstitial fluid pressure (TIFP), and a multifactorial increase in composition of the extracellular matrix (ECM). A primary modifier of TME is hypoxia, which increases the production of growth factors, such as vascular endothelial growth factor and platelet-derived growth factor. These growth factors released by both tumor cells and bone marrow recruited myeloid cells form abnormal vasculature characterized by vessels that are tortuous and more permeable. Increased leakiness combined with increased inflammatory byproducts accumulates fluid within the tumor mass (tumor interstitial fluid), ultimately creating an increased pressure (TIFP). Fibroblasts are also up-regulated by the TME, and deposit fibers that further augment the density of the ECM, thus, further worsening the TIFP. Increased TIFP with the ECM are the major obstacles to adequate drug delivery. By decreasing TIFP and ECM density, we can expect an associated rise in drug concentration within the tumor itself. In this overview, we will describe all the methods (drugs, nutraceuticals, and physical methods of treatment) able to lower TIFP and to modify ECM used for increasing drug concentration within the tumor tissue.

Numerical modeling of drug delivery in a dynamic solid tumor microvasculature

The complicated capillary network induced by angiogenesis is one of the main reasons of unsuccessful cancer therapy. A multi-scale mathematical method which simulates drug transport to a solid tumor is used in this study to investigate how capillary network structure affects drug delivery. The mathematical method involves processes such as blood flow through vessels, solute and fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. The effect of heterogeneous dynamic network on interstitial fluid flow and drug delivery is investigated by this multi-scale method. The sprouting angiogenesis model is used for generating capillary network and then fluid flow governing equations are implemented to calculate blood flow through the tumor-induced capillary network and fluid flow in normal and tumor tissues. Finally, convection-diffusion equation is used to simulate drug delivery. Three approaches are used to simulate drug transport based on the developed mathematical method: without a vascular network, using a static vascular network, and a dynamic vascular network. The avascular approach predicts more uniform and higher drug concentration than vascular approaches since the simplified assumptions are implemented in this method. The dynamic network which uses more realistic assumptions predicts more irregular blood vessels, high interstitial pressure, and more heterogeneity in drug distribution than other two approaches.

Pressing the right buttons: signaling in lymphangiogenesis

Lymphatic vasculature is increasingly recognized as an important factor both in the regulation of normal tissue homeostasis and immune response and in many diseases, such as inflammation, cancer, obesity, and hypertension. In the last few years, in addition to the central role of vascular endothelial growth factor (VEGF)-C/VEGF receptor-3 signaling in lymphangiogenesis, significant new insights were obtained about Notch, transforming growth factor β/bone morphogenetic protein, Ras, mitogen-activated protein kinase, phosphatidylinositol 3 kinase, and Ca2+/calcineurin signaling pathways in the control of growth and remodeling of lymphatic vessels. An emerging picture of lymphangiogenic signaling is complex and in many ways distinct from the regulation of angiogenesis. This complexity provides new challenges, but also new opportunities for selective therapeutic targeting of lymphatic vasculature.

The clinical implication of cancer-associated microvasculature and fibroblast in advanced colorectal cancer patients with synchronous or metachronous metastases

BACKGROUND

We aimed to evaluate the clinical significance of microvessel density (MVD), lymphatic vessel density (LVD), and cancer-associated fibroblasts (CAFs) in relation to tumor location in advanced colorectal cancer (CRC).

METHODS

Using immunohistochemistry, we examined 181 advanced CRC patients for CD31 and D2-40 to measure MVD and LVD, respectively, α-smooth muscle actin (SMA) and desmin to identify CAFs, and PTEN to examine genetic changes of CAFs. To evaluate the regional heterogeneity of these properties, we examined tissue from four sites (the center and periphery of the primary cancer, a distant metastasis, and a lymph node metastasis) in each patient.

RESULTS

MVD, LVD, and CAFs showed significant heterogeneity with respect to the tumor location. LVD was the greatest in the center of the primary cancers and the amount of CAFs was the lowest in distant metastases. In distant metastases, those from the lung had higher LVD and MVD, but fewer CAFs than those from the liver, peritoneum, or ovary. Patients with low MVD and LVD in the center of the primary cancer had worse outcomes and patients with few CAFs in distant metastases and in the primary tumor had a lower survival rate. PTEN expression in CAFs in distant metastases was lost in 11 of 181 CRC patients (6.1%), which was associated with a worse prognosis.

CONCLUSIONS

The microenvironment, including cancer-associated microvasculature and fibroblasts, is heterogeneous with respect to the tumor location in CRC patients. Therefore, heterogeneity of microenvironments should be taken into account when managing CRC patients.

Mechanisms of lymphatic metastasis

Malignant tumors release growth factors such as VEGF-C to induce lymphatic vessel expansion (lymphangiogenesis) in primary tumors and in draining sentinel LNs, thereby promoting LN metastasis. Surprising recent evidence suggests that lymphatic vessels do not merely represent passive channels for tumor spread, but that they may actively promote tumor cell recruitment to LNs, cancer stem cell survival, and immune modulation. New imaging approaches allow the sensitive visualization of the earliest LN metastases and the quantitative, noninvasive measurement of the function of tumor-draining lymphatic vessels, with potential applications in the development of biomarkers for prognosis and measurement of therapeutic response.

Normalizing tumor microenvironment to treat cancer: bench to bedside to biomarkers

For almost four decades, my work has focused on one challenge: improving the delivery and efficacy of anticancer therapeutics. Working on the hypothesis that the abnormal tumor microenvironment-characterized by hypoxia and high interstitial fluid pressure--fuels tumor progression and treatment resistance, we developed an array of sophisticated imaging technologies and animal models as well as mathematic models to unravel the complex biology of tumors. Using these tools, we demonstrated that the blood and lymphatic vasculature, fibroblasts, immune cells, and extracellular matrix associated with tumors are abnormal, which together create a hostile tumor microenvironment. We next hypothesized that agents that induce normalization of the microenvironment can improve treatment outcome. Indeed, we demonstrated that judicious use of antiangiogenic agents--originally designed to starve tumors--could transiently normalize tumor vasculature, alleviate hypoxia, increase delivery of drugs and antitumor immune cells, and improve the outcome of various therapies. Our trials of antiangiogenics in patients with newly diagnosed and recurrent glioblastoma supported this concept. They revealed that patients whose tumor blood perfusion increased in response to cediranib survived 6 to 9 months longer than those whose blood perfusion did not increase. The normalization hypothesis also opened doors to treating various nonmalignant diseases characterized by abnormal vasculature, such as neurofibromatosis type 2. More recently, we discovered that antifibrosis drugs capable of normalizing the tumor microenvironment can improve the delivery and efficacy of nano- and molecular medicines. Our current efforts are directed at identifying predictive biomarkers and more-effective strategies to normalize the tumor microenvironment for enhancing anticancer therapies.

Lymphatic vessels in health and disease

The lymphatic vasculature plays vital roles in tissue fluid balance, immune defense, metabolism, and cancer metastasis. In adults, lymphatic vessel formation and remodeling occur primarily during inflammation, development of the corpus luteum, wound healing, and tumor growth. Unlike the blood circulation, where unidirectional flow is sustained by the pumping actions of the heart, pumping actions intrinsic to the lymphatic vessels themselves are important drivers of lymphatic flow. This review summarizes critical components that control lymphatic physiology.

Overlapping biomarkers, pathways, processes and syndromes in lymphatic development, growth and neoplasia

Recent discoveries in molecular lymphology, developmental biology, and tumor biology in the context of long-standing concepts and observations on development, growth, and neoplasia implicate overlapping pathways, processes, and clinical manifestations in developmental disorders and cancer metastasis. Highlighted in this review are some of what is known (and speculated) about the genes, proteins, and signaling pathways and processes involved in lymphatic/blood vascular development in comparison to those involved in cancer progression and spread. Clues and conundra from clinical disorders that mix these processes and mute them, including embryonic rests, multicentric nests of displaced cells, uncontrolled/invasive "benign" proliferation and lymphogenous/hematogenous "spread", represent a fine line between normal development and growth, dysplasia, benign and malignant neoplasia, and "metastasis". Improved understanding of these normal and pathologic processes and their underlying pathomechanisms, e.g., stem cell origin and bidirectional epithelial-mesenchymal transition, could lead to more successful approaches in classification, treatment, and even prevention of cancer and a whole host of other diseases.

Lymph vessel density in seminomatous testicular cancer assessed with the specific lymphatic endothelium cell markers D2-40 and LYVE-1: correlation with pathologic parameters and clinical outcome

OBJECTIVES

To evaluate the role of lymph vessel density (LVD) and lymphangiogenesis in seminomatous testicular cancer (STC) by using the lymphatic endothelial cell (LEC) markers LYVE-1 and D2-40.

METHODS AND MATERIALS

Paraffin embedded tumor specimens from 40 patients with STC were stained by specific D2-40 and Lyve-1 antibodies. LVD was measured in different representative and standardized areas. Fluorescence double immunostaining for Lyve-1 and Ki-67 was performed and results were correlated with clinicopathologic data. The median follow-up period was 55 (range 10-135) months.

RESULTS

Mean intratumoral LVD (D2-40: 1.30 ± 1.99; Lyve-1: 1.82 ± 2.34) was significantly lower than peritumoral LVD (D2-40: 4.94 ± 2.58; Lyve-1: 4.62 ± 2.73) and LVD in nontumoral areas (D2-40: 4.81 ± 3.79; Lyve-1: 4.22 ± 3.19). There was no significant difference between LVD measures when using D2-40 or LYVE-1. Detection rates of lymphatic vascular invasion (LVI) were significantly higher than in conventional HE-stained sections (77.5% vs. 52.5%). No proliferating lymphatic vessels were found.

CONCLUSIONS

We found that LVD is decreased within tumor areas of STC. Despite a higher peritumoral LVD, no signs of proliferating endothelial cells were observed, suggesting a lack of lymphangiogenesis in STC. Detection of LVI can be optimized by specific D2-40 or LYVE-1 staining.

Prognostic value of lymphangiogenesis in supraglottic laryngeal carcinoma

Background:

Metastasis to regional lymph nodes via lymphatic microvessels plays a key role in cancer progression, and is an important prognostic factor in many cancers. Recent evidence suggests that tumour lymphangiogenesis promotes lymphatic metastasis.

Aims:

To investigate whether tumour lymphatic microvessel density correlates with clinicopathological factors and serves as a prognostic indicator of supraglottic laryngeal carcinoma progression.

Methods:

The lymphatics of 84 supraglottic laryngeal carcinoma cases were investigated by immunohistochemical staining for podoplanin (also termed D2-40). The relationships between (intra- and peritumoural) lymphatic microvessel density, clinicopathological parameters and clinical prognosis were analysed.

Results:

There was a significant relationship between high intratumoural lymphatic microvessel density and aggressive tumour node stage (p < 0.0001), distant metastasis (p = 0.037) and poor prognosis (p = 0.011), and between high peritumoural lymphatic microvessel density and node stage (p = 0.004) and poor prognosis (p = 0.029). Patients with high lymphatic microvessel density also had significantly worse disease-free survival (p = 0.003) and overall survival (p = 0.005). Intratumoural lymphatic microvessel density was found to be an independent prognostic factor for overall survival (p = 0.008) and disease-free survival (p = 0.005) (multivariate analysis).

Conclusion:

Lymphatic microvessel density (detected by podoplanin immunohistochemistry), especially intratumoural density, may be an independent predictor of lymphatic tumour spread and survival in supraglottic laryngeal carcinoma patients, and may be useful to guide decisions regarding additional surgery.

Deguelin--an inhibitor to tumor lymphangiogenesis and lymphatic metastasis by downregulation of vascular endothelial cell growth factor-D in lung tumor model

Deguelin, a rotenoid of the flavonoid family, has been reported to possess antiproliferative and anticarcinogenic activities in several cell lines and tumor models. However, it is still unclear whether deguelin effectively inhibits tumor-associated lymphangiogenesis and lymphatic metastasis. Since tumor production of vascular endothelial cell growth factor (VEGF)-D was associated with tumor lymphangiogenesis and lymphatic metastasis, we established the mouse lymphatic metastasis model by transfecting high expression VEGF-D into LL/2 Lewis lung cells (VEGF-D-LL/2) and explored the effects of deguelin on lymphatic metastasis in the immunocompetent C57BL/6 mice. Our results indicated that deguelin inhibited proliferation, migration of VEGF-D-LL/2 cells via downregulating AKT and mitogen-activated protein kinase pathway and interfered tube formation of lymphatic vascular endothelial cells on matrigel at nanomolar concentrations. Deguelin significantly downregulated the expression of VEGF-D both at mRNA and protein levels in VEGF-D-LL/2 cells in a dose-dependent manner. In the in vivo study, intraperitoneal administration of deguelin (4 mg/kg) remarkably inhibited the tumor-associated lymphangiogenesis and lymphatic metastasis. The rates of lymph node and lung metastasis in deguelin-treated mice were 0 and 16.7% compared with 58.3 and 83.3% in control group mice, respectively. Deguelin also resulted in a remarkable delay of tumor growth and prolongation of life span. Immunohistochemical staining with antibodies against VEGF-D, LYVE-1 and VEGFR-3 revealed fewer positive vessel-like structures in deguelin-treated mice compared with control group mice. Taken together, we demonstrate for the first time that deguelin suppresses tumor-associated lymphangiogenesis and lymphatic metastasis by downregulation of VEGF-D both in vitro and in vivo.

Pathophysiology of oral cancer in experimental animal models: a review with focus on the role of sympathetic nerves

Global increase in incidence and mortality as well as poor prognosis of oral cancer (OC) has intensified efforts towards early detection and prevention of this disfiguring disease. Several studies have been conducted using experimental animal models to understand the pathophysiology and molecular events involved in OC. Lack of identification of specific biomarkers during the multifaceted steps of oral carcinogenesis has hindered its diagnosis and treatment. Solid stress generated by growing tumors as well as abnormalities in tumor vasculature lead to increased interstitial fluid pressure, which could obstruct therapeutic drug delivery to tumors. Furthermore, the sympathetic nervous system is known to affect angiogenesis, vessel permeability, immune responses and carcinogenesis. Recent findings indicate that, in addition to angiogenic and lymphangiogenic factors, tumor cells release neurotrophic factors that initiate innervation. Interactions between cytokines and sympathetic neurotransmitters, and their respective receptors expressed by the nerve, immune and tumor cells appear to influence tumor growth. Thus, understanding the complex signaling processes and interrelationships between vascular, nervous and immune systems during oral carcinogenesis may prove vital for successful prevention and treatment of OC. This review aims at outlining the available knowledge on pathophysiology of OC in experimental animal models including evidence from our own findings.

Tumor microvasculature and microenvironment: novel insights through intravital imaging in pre-clinical models

Intravital imaging techniques have provided unprecedented insight into tumor microcirculation and microenvironment. For example, these techniques allowed quantitative evaluations of tumor blood vasculature to uncover its abnormal organization, structure and function (e.g., hyper-permeability, heterogeneous and compromised blood flow). Similarly, imaging of functional lymphatics has documented their absence inside tumors. These abnormalities result in elevated interstitial fluid pressure and hinder the delivery of therapeutic agents to tumors. In addition, they induce a hostile microenvironment characterized by hypoxia and acidosis, as documented by intravital imaging. The abnormal microenvironment further lowers the effectiveness of anti-tumor treatments such as radiation therapy and chemotherapy. In addition to these mechanistic insights, intravital imaging may also offer new opportunities to improve therapy. For example, tumor angiogenesis results in immature, dysfunctional vessels--primarily caused by an imbalance in production of pro- and anti-angiogenic factors by the tumors. Restoring the balance of pro- and anti-angiogenic signaling in tumors can "normalize" tumor vasculature and thus, improve its function, as demonstrated by intravital imaging studies in preclinical models and in cancer patients. Administration of cytotoxic therapy during periods of vascular normalization has the potential to enhance treatment efficacy.

Inflammatory breast cancer: novel preoperative therapies

The treatment of inflammatory breast cancer (IBC) has been hampered by the diagnostic rarity of the disease and its consequent inclusion in clinical trials of preoperative treatment for the more indolent locally advanced breast cancer (LABC). Patients with IBC have a 2-fold greater probability of dying of their disease compared with patients diagnosed with LABC. The aggressive clinical portrait of IBC supports the recent investigative focus on determining molecular changes specific to IBC and developing novel systemic therapies that will favorably affect its poor disease prognosis. A significant amount of laboratory research has been involved in defining a specific "inflammatory signature" for IBC, denoting molecular changes consistently found in IBC. This work has involved human IBC tissue and cell lines and has demonstrated overexpression of several molecules governing metastatic dissemination, such as overexpression of E-cadherin concurrent with a dysfunctional mucin 1. An increased prevalence of mutant TP53, overexpression of RhoC, and vascular endothelial growth factor-A has been found to contribute to the dominant influence of angiogenesis in this disease. A greater understanding of the molecular mechanisms governing the pathophysiology of IBC has led to the development and clinical application of novel targeting agents for preoperative therapy. This study reviews the advances in molecular understanding of IBC and focuses on the efficacy of therapies that target the epidermal growth factor pathway and angiogenesis as well as early investigational therapies involving RhoC and TP53.

Intratumoral as well as peritumoral lymphatic vessel invasion correlates with lymph node metastasis and unfavourable outcome in colorectal cancer

The aim of this study was to assess the intratumoral and peritumoral distribution of lymphatic vessel density (LVD) and lymphatic vessel invasion (LVI) in colorectal cancer and their relationships with patients' clinicopathological characteristics and survival. Paraffin sections of 81 primary colorectal cancers were examined by immunohistochemical staining using monoclonal antibody D2-40. Peritumoral LVD was significantly higher than intratumoral LVD (P = 0.000). Both intratumoral LVD and peritumoral LVD were correlated with the presence of LVI (P = 0.006 and P = 0.003, respectively). LVI, intratumoral LVI and peritumoral LVI were identified, respectively in 38, 28 and 32% of the samples investigated. Both intratumoral LVI and peritumoral LVI were correlated with lymph node metastasis (P = 0.030 and P = 0.014, respectively). Lymph node metastasis, the presence of intratumoral LVI and peritumoral LVI were adversely associated with the 5-year overall survival in a univariate analysis (P = 0.001, P = 0.011 and P = 0.017, respectively). Multivariate analysis using Cox proportional hazard model showed that neither intratumoral LVI nor peritumoral LVI was an independent prognostic factor of overall survival. The results of this study demonstrated that intratumoral as well as peritumoral LVI was associated with lymph node metastasis and adverse outcome in colorectal cancer.

Cyclooxygenase-2 enhances alpha2beta1 integrin expression and cell migration via EP1 dependent signaling pathway in human chondrosarcoma cells

Background

Cyclooxygenase (COX)-2, the inducible isoform of prostaglandin (PG) synthase, has been implicated in tumor metastasis. Interaction of COX-2 with its specific EP receptors on the surface of cancer cells has been reported to induce cancer invasion. However, the effects of COX-2 on migration activity in human chondrosarcoma cells are mostly unknown. In this study, we examined whether COX-2 and EP interaction are involved in metastasis of human chondrosarcoma.

Results

We found that over-expression of COX-2 or exogenous PGE₂ increased the migration of human chondrosarcoma cells. We also found that human chondrosarcoma tissues and chondrosarcoma cell lines had significant expression of the COX-2 which was higher than that in normal cartilage. By using pharmacological inhibitors or activators or genetic inhibition by the EP receptors, we discovered that the EP1 receptor but not other PGE receptors is involved in PGE₂-mediated cell migration and α2β1 integrin expression. Furthermore, we found that human chondrosarcoma tissues expressed a higher level of EP1 receptor than normal cartilage. PGE₂-mediated migration and integrin up-regulation were attenuated by phospholipase C (PLC), protein kinase C (PKC) and c-Src inhibitor. Activation of the PLCβ, PKCα, c-Src and NF-κB signaling pathway after PGE₂ treatment was demonstrated, and PGE₂-induced expression of integrin and migration activity were inhibited by the specific inhibitor, siRNA and mutants of PLC, PKC, c-Src and NF-κB cascades.

Conclusions

Our results indicated that PGE₂ enhances the migration of chondrosarcoma cells by increasing α2β1 integrin expression through the EP1/PLC/PKCα/c-Src/NF-κB signal transduction pathway.

Role of intratumoral lymphatic vessels in the lymph node dissemination of laryngopharyngeal squamous cell carcinoma

BACKGROUND

The development of new markers for lymphatic endothelium allowed the study of intratumoral lymphatic microcirculation, as well as its association with lymph node metastasis.

METHODS

In all, 120 patients with laryngopharyngeal squamous cell carcinoma (LPSCC) without previous treatment were retrospectively studied. The immunohistochemical determination of PA2.26 antigen/podoplanin was used to assess intratumoral lymphatic vessels (ILVs) in the primary tumor.

RESULTS

Multivariate analysis revealed that lymph node metastasis was associated with tumor location (p = .001), differentiation grade (p = .02), and ILV (p = .013). Hypopharyngeal and supraglottic locations, poor grade of differentiation, and ILV, respectively, increased the risk of developing lymph node metastasis 13.5-, 4.7-, 5.2-, and 3.2-fold.

CONCLUSIONS

In our series, the presence of ILV in the primary tumor was an independent risk factor for the development of lymph node metastasis. The incorporation of ILV assessment into routine clinicopathological study might improve the evaluation of patients with LPSCC.

Washout of small molecular contrast agent in carcinoma-derived experimental tumors

The use of contrast-enhanced magnetic resonance imaging (MRI) for the assessment of breast carcinomas reveals satisfactory sensitivity, but due to low specificity, it does not obviate the need for subsequent tissue sampling. Its capability to differentiate benign from malignant lesion is under continuous investigation. Dynamic contrast-enhanced MRI (DCE-MRI) could improve specificity of MRI through the analysis of the kinetic of contrast enhancement. In particular, the study of the washout pattern is considered a promising tool to improve in vivo diagnosis and even to evaluate the response under chemotherapy. To provide a comprehensive characterization of this parameter in malignant tumor models, in vivo mapping of the washout of small molecular contrast agent (Gd-DTPA, molecular weight 0.57 kDa) was carried out in three transplanted/spontaneous mammary tumors, which differed in their histopathological and microvascular features. It resulted that in all models around 40% of tumor volume lacks efficient washout; washout areas are frequently, but not always, restricted to the tumor periphery and that non-washout areas are not restricted to necrotic regions. Difference in the distribution of lymphatic vessels characterized spontaneous vs. transplanted tumors but did not produce a corresponding different washout pattern, confirming that Gd-DTPA drainage does not mainly depend on lymphatic architecture. Finally, the efficiency of washout is correlated with parameters obtainable during the earlier phases of the enhancement curve and in malignant tumors it could be indirectly estimated from them.

Mechanisms of lymphatic metastasis in human colorectal adenocarcinoma

The invasion of lymphatic vessels by colorectal cancer (CRC) and its subsequent spread to draining lymph nodes is a key determinant of prognosis in this common and frequently fatal malignancy. Although tumoural lymphangiogenesis is assumed to contribute to this process, review of the current literature fails to support any notion of a simple correlation between lymphatic vessel density and CRC metastasis. Furthermore, attempts to correlate the expression of various lymphangiogenic growth factors, most notably VEGF-C and VEGF-D, with the lymphatic metastasis of CRC have provided contradictory results. Recent evidence from animal and human models of tumour metastasis suggests that complex functional and biochemical interactions between the microvasculature of tumours and other cell types within the tumour microenvironment may play a pivotal role in the behaviour of commonly metastasizing tumours. Indeed, previous insights into tumoural blood vessels have provided candidate markers of tumoural angiogenesis that are currently the subject of intense investigation as future therapeutic targets. In this review article we survey the current evidence relating lymphangiogenesis and lymphangiogenic growth factor production to metastasis by CRC, and attempt to provide some insight into the apparent discrepancies within the literature. In particular, we also discuss some new and provocative insights into the properties of tumoural lymphatics suggesting that they have specific expression profiles distinct from those of normal lymphatic vessels and that appear to promote metastasis. These findings raise the exciting prospect of future biomarkers of lymphatic metastasis and identify potential targets for new generation anti-tumour therapies.

Tumor necrosis factor-mediated interactions between inflammatory response and tumor vascular bed

Solid tumor therapy with chemotherapeutics greatly depends on the efficiency with which drugs are delivered to tumor cells. The typical characteristics of the tumor physiology promote but also appose accumulation of blood-borne agents. The leaky tumor vasculature allows easy passage of drugs. However, the disorganized vasculature causes heterogeneous blood flow, and together with the often-elevated interstitial fluid pressure, this state results in poor intratumoral drug levels and failure of treatment. Manipulation of the tumor vasculature could overcome these barriers and promote drug delivery. Targeting the vasculature has several advantages. The endothelial lining is readily accessible and the first to be encountered after systemic injection. Second, endothelial cells tend to be more stable than tumor cells and thus less likely to develop resistance to therapy. Third, targeting the tumor vasculature can have dual effects: (i) manipulation of the vasculature can enhance concomitant chemotherapy, and (ii) subsequent destruction of the vasculature can help to kill the tumor. In particular, tumor necrosis factor alpha is studied. Its action on solid tumors, both directly through tumor cell killing and destruction of the tumor vasculature and indirectly through manipulation of the tumor physiology, is complex. Understanding the mechanism of TNF and agents with comparable action on solid tumors is an important focus to further develop combination immunotherapy strategies.

[The physiopathology of metastases: from primary to secondary]

Metastasis genesis is the result of a series of many steps which make a tumoral cell localised in a primary tumor move and graft onto another organ to form a new tumor. Tumoral cells must go through the following steps: primary tumor formation, proliferation and angiogenesis, deep tissue invasion and arrival in the circulatory system, preparation for travel, migration, embolization in an organ, attachment to the wall of blood vessel, exit from the vessel, adaptation to the micro-surrounding, anchorage and neo-angiogenesis which corresponds to the metastasis establishment. At each step, there are defence and regulation mechanisms which, when they fail, lead to metastatic dissemination.

Imaging angiogenesis and the microenvironment

Intravital microscopy has provided unprecedented insights into tumor pathophysiology, including angiogenesis and the microenvironment. Tumor vasculature shows an abnormal organization, structure, and function. Tumor vessels are leaky, blood flow is heterogeneous and often compromised. Vascular hyperpermeability and the lack of functional lymphatic vessels inside tumors causes elevation of interstitial fluid pressure in solid tumors. These abnormalities form physiological barriers to the delivery of therapeutic agents to tumors and also lead to a hostile microenvironment characterized by hypoxia and acidosis, which hinders 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, resulting in pathophysiological characteristics of the tumor. On the other hand, in a physiological setting, angiogenic vessels become mature and form long-lasting functional units. Restoring the balance of pro- and anti-angiogenic factors in tumors may "normalize" tumor vasculature and thus improve its function. Administration of cytotoxic therapy during the vascular normalization would enhance its efficacy.

Intratumoural lymphatics in benign and malignant soft tissue tumours

Soft tissue sarcomas do not generally metastasise via lymphatics, and the presence or absence of lymphatic vessels within sarcomas and benign soft tissue tumours is not known. In this study, we determined whether lymphatic vessels were present in a wide range of benign and malignant soft tissue lesions by examining intratumoural expression of the lymphatic endothelial cell markers, Lyve-1 and podoplanin. Intratumoural Lyve-1+/podoplanin+ lymphatics were not identified in sarcomas apart from all cases of epithelioid sarcoma (a tumour which is known to metastasise to lymph nodes) and a few cases of leiomyosarcoma, rhabdomyosarcoma and synovial sarcoma. Intratumoural lymphatics were also absent in most benign soft tissue tumours. Reparative and inflammatory soft tissue lesions contained lymphatics, as did all (pseudosarcomatous) proliferative myofibroblastic lesions including nodular, proliferative and ischaemic fasciitis, elastofibroma, nuchal fibroma and deep fibromatosis. Our results show that most soft tissue sarcomas do not contain intratumoural lymphatics, a finding which is consistent with the infrequent finding of sarcoma metastasis to lymph nodes. In contrast to fibrosarcoma and a number of other malignant spindle cell tumours, proliferative fibroblastic/myofibroblastic lesions of soft tissue contain intralesional lymphatic vessels.

Laboratory models of regional chemotherapy

Development of new treatment strategies and agents is a difficult and costly matter in oncology. Routinely drugs are tested in vitro on tumor cells which, however, may have limited predictive value for their activity in patients. Also, the pharmacokinetic behavior, intratumoral distribution, as well as toxic side effects, binding to other compounds and stability of an agent are very important in determining activity in the patient. More so, development and evaluation of surgical delivery methods, i.e. regional treatment strategies, cannot be tested in cell systems. Therefore animal models are crucial for the development of regional chemotherapy methodologies. To allow translation of the animal data to patients it is important that the animal model closely mimics the clinical setting as for instance is achieved with isolated limb perfusion. However, animal models remain limited in their use, as eventually the efficacy of the approach may be different in animals compared to patients. Here we describe the use of animal models for regional treatment of solid tumors.

Chapter 2. Color-coded fluorescent mouse models of cancer cell interactions with blood vessels and lymphatics

Several new strategies now exist for imaging cancer cell interactions with both blood vessels and lymphatics in living animals. Tumors labeled with fluorescent proteins allow the nonluminous capillaries and larger blood vessels to be clearly visualized against the bright tumor fluorescence via either intravital or whole-body imaging. Signal attenuation by overlying tissue can be markedly reduced by opening a reversible skin flap in the light path, increasing detection sensitivity. With this increase in observable depth of tissue, many previously obscured small tumor vessels can be imaged. In addition, dual-color fluorescence imaging, effected by using red fluorescent protein (RFP)-expressing tumors growing in green fluorescent protein (GFP)-expressing transgenic mice, can show with great clarity tumor-stroma interactions, including the developing tumor vasculature. The GFP-expressing host vasculature, both mature and nascent, can be distinguished from the RFP-expressing tumor itself in this model. Transgenic mice with GFP gene expression driven by the nestin promoter offer another way to image the developing tumor vasculature. In this model system, only nascent blood vessels express GFP, allowing newly developing blood vessels to be imaged against a background of RFP-expressing tumor cells. Finally, dual-color imaging technology can facilitate the imaging of cancer cell interactions with lymphatics. Delivery of FITC-dextran or fluorescent antibodies specific for lymphatic endothelium to the lymphatics around an RFP-expressing tumor allows imaging of tumor cell shedding into the lymphatic system. This imaging technology has the potential to visualize each step of tumor progress.

Lymphatic vessel endothelial hyaluronan receptor 1 immunocytochemical staining for pancreatic islets and pancreatic endocrine tumors

OBJECTIVES

Immunocytochemical staining for lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) is able to recognize lymphatic vessel endothelium and pancreatic endocrine cells (PETs). Pancreatic endocrine tumors were studied for LYVE-1 immunocytochemical staining compared with normal pancreatic islets to detect possible presence of LYVE-1 in PETs.

METHODS

Twenty-five cases of primary and metastatic PETs were immunocytochemically stained for LYVE-1, including insulinomas, glucagonomas, somatostatinoma, pancreatic polypeptidomas, gastrinomas, and nonfunctioning tumors. With routinely formalin-fixed and paraffin-embedded tissues, LYVE-1 immunostaining was performed with polyclonal goat antihuman LYVE-1.

RESULTS

All normal pancreatic islet cells were positive for LYVE-1, whereas 2 cases of 25 PETs, 1 each of gastrinoma and nonfunctioning tumor, were positive for LYVE-1, retaining immunocytochemical reactivity of islet cells.

CONCLUSIONS

Normal pancreatic islets were positive for LYVE-1, whereas only 2 of 25 PETs were positive, suggesting that most PETs lost LYVE-1 or contained below detectable levels of LYVE-1. The presence of LYVE-1 in pancreatic islets and in some PETs may suggest structure-function relationship of LYVE-1/lymphatic vessel in hormone synthesis and secretion.

Lymphatic vessel density, microvessel density and lymphangiogenic growth factor expression in colorectal cancer

OBJECTIVE

Microvessel density (MVD) has been studied as a prognostic marker in human cancers. Quantification of lymphatic vessel density (LVD) is now possible by using new antibodies. Expression of the lymphangiogenic growth factors, VEGF-C and VEGF-D, is associated with poorer clinicopathological outcomes in various tumours. The aim of this study was to quantify LVD and MVD in colorectal cancer, determine the relationship between LVD, MVD and clinicopathological variables and examine the relationship between LVD and tumour expression of VEGF-C and VEGF-D.

METHOD

Thirty primary colorectal cancers were immunostained for CD34, lymph vessel endothelial hyaluronan receptor-1 (LYVE-1), VEGF-A and VEGF-D using standard techniques. LVD and MVD were determined by Chalkley grid counting. Tumours were assessed for the presence or absence of LYVE-1 positive lymphatics at different areas within the tumour and the tumour was scored for VEGF-C and VEGF-D immunostaining intensity at the invading tumour edge. Non-parametric tests were used for statistical analysis and a P-value of <0.05 was taken as significant.

RESULTS

Lymph vessel endothelial hyaluronan receptor-1 was an excellent lymphatic vessel marker. Within normal bowel wall, lymphatic vessels were found rarely in the superficial colonic mucosa, but were numerous in the submucosa and muscularis propria. In the majority of tumours, lymphatic vessels were located in the peri-tumoural area, intra-tumoural vessels were sparse and tended to be narrow with closed lumina. At the invading tumour edge, VEGF-C expression was higher (P = 0.028) and VEGF-D expression lower (P = 0.011), in tumours in which lymphatic vessels were present. No significant differences between LVD and any clinicopathological variable or route of metastasis were identified.

CONCLUSION

Lymphatic vessel density and MVD can be quantified in colorectal carcinoma using immunohistochemical techniques. The balance between expression of VEGF-C and VEGF-D at the invading tumour edge may enhance lymphatic metastasis, by promoting tumour lymphangiogenesis or by activation of pre-existing lymphatic vessels. No relationship was identified between LVD and clinicopathological variables.

Investigation of intratumoural and peritumoural lymphatics expressed by podoplanin and LYVE-1 in the hybridoma-induced tumours

Tumour-associated lymphatics contribute to a key component of metastatic spread, however, the biological interaction of tumour cells with intratumoural and peritumoural lymphatics (ITLs and PTLs) has remained unclear. To address this important issue, we have focused on the morphological and molecular aspects of newly formed lymphatics (lymphangiogenesis) and pre-existing lymphatics in the intratumoural and peritumoural tissues by using a hybridoma-induced tumour model. In the present study, ITLs with very high vessel density within the tumour mass showed small and flattened contours that varied from non-solid-to-solid tumours, whereas PTLs were relatively disorganized and tortuous, and packed with a cluster of tumour cells at the tumour periphery. Lymphatic endothelial cells (LECs) both in ITLs and PTLs were expressed with LYVE-1 and podoplanin in various tumour tissues, in which initial lymphatics were extremely extended and dilated. The tumour cells were frequently detected adhering to or penetrating lymphatic walls, especially near the open junctions. In the metastatic tissues, lymphangiogenic vasculatures occurred within the tumour matrix, and collecting PTLs represented abnormal twisty valve leaflets. The Western blot and RT-PCR analysis showed local variations of LEC proliferating potentials and lymphatic involvement in metastasis by a distinct profile of the protein and mRNA expression by LYVE-1, podoplanin, Prox-1 and vascular endothelial growth factor-3 (VEGFR-3). These findings indicated that both ITLs and PTLs, including enlarged pre-existing and newly formed lymphatics, may play a crucial role in metastasis with an active tumour cell adhesion, invasion, migration and implantation.

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.

Sympathectomy decreases size and invasiveness of tongue cancer in rats

The sympathetic nervous system plays a role in carcinogenesis wherein locally released sympathetic neurotransmitters affect proliferation, angiogenesis, vessel permeability, lymphocyte traffic and cytokine production. The present in vivo study was designed to investigate whether surgical sympathectomy, both unilateral and bilateral, had an effect on tumor growth, interstitial fluid pressure (IFP) and lymphatics in rat tongue cancer. We used 4-nitroquinoline-1-oxide (4-NQO) in drinking water for 19 weeks to induce tongue cancer in 20 Dark Agouti rats. After 11 weeks, one group underwent unilateral sympathectomy and another underwent bilateral sympathectomy, while the third group underwent sham surgery. By 19 weeks, tumors in the bilaterally sympathectomized (BL-SCGx) rats were significantly smaller (P<0.05), more diffuse in appearance and less invasive (P<0.05) compared with the large exophytic tumors in the sham-operated rats. The relative lymphatic area was significantly decreased (P<0.05) in tumors in the BL-SCGx rats compared with the sham group. Interestingly, the tumors in rats that underwent unilateral or bilateral sympathectomy had a significantly lower (P<0.05) IFP than those in sham rats. Lack of tyrosine hydroxylase (TH) immunoreactive nerves and few neuropeptide Y (NPY) positive fibers indicate absence of sympathetic nerve fibers in the bilateral sympathectomized group. The peritumoral lymph vessel area was correlated with the tumor size (P<0.001), depth of invasion (P<0.001), weight of rats (P<0.005) and IFP (P<0.05). In conclusion, the present study presents evidence that deprivation of sympathetic nerves decreases tumor growth in rat tongue, probably caused by decreasing IFP and lymph vessel area.

Thermal Cycling Enhances the Accumulation of a Temperature-Sensitive Biopolymer in Solid Tumors

The delivery of anticancer therapeutics to solid tumors remains a critical problem in the treatment of cancer. This study reports a new methodology to target a temperature-responsive macromolecular drug carrier, an elastin-like polypeptide (ELP) to solid tumors. Using a dorsal skin fold window chamber model and intravital laser scanning confocal microscopy, we show that the ELP forms micron-sized aggregates that adhere to the tumor vasculature only when tumors are heated to 41.5 degrees C. Upon return to normothermia, the vascular particles dissolve into the plasma, increasing the vascular concentration, which drives more ELPs across the tumor blood vessel and significantly increases its extravascular accumulation. These observations suggested that thermal cycling of tumors would increase the exposure of tumor cells to ELP drug carriers. We investigated this hypothesis in this study by thermally cycling an implanted tumor in nude mice from body temperature to 41.5 degrees C thrice within 1.5 h, and showed the repeated formation of adherent microparticles of ELP in the heated tumor vasculature in each thermal cycle. These results suggest that thermal cycling of tumors can be repeated multiple times to further increase the accumulation of a thermally responsive polymeric drug carrier in solid tumors over a single heat-cool cycle. More broadly, this study shows a new approach--tumor thermal cycling--to exploit stimuli-responsive polymers in vivo to target the tumor vasculature or extravascular compartment with high specificity.

Tumor cell-organ microenvironment interactions in the pathogenesis of cancer metastasis

The process of cancer metastasis is sequential and selective and contains stochastic elements. The growth of metastases represents the endpoint of many lethal events that few tumor cells can survive. Primary tumors consist of multiple subpopulations of cells with heterogeneous metastatic properties, and the outcome of metastasis depends on the interplay of tumor cells with various host factors. The findings that different metastases can originate from different progenitor cells account for the biological diversity that exists among various metastases. Even within a solitary metastasis of proven clonal origin, however, heterogeneity of biological characteristics can develop rapidly. The pathogenesis of metastasis depends on multiple interactions of metastatic cells with favorable host homeostatic mechanisms. Interruption of one or more of these interactions can lead to the inhibition or eradication of cancer metastasis. For many years, all of our efforts to treat cancer have concentrated on the inhibition or destruction of tumor cells. Strategies both to treat tumor cells (such as chemotherapy and immunotherapy) and to modulate the host microenvironment (including the tumor vasculature) should offer additional approaches for cancer treatment. The recent advances in our understanding of the biological basis of cancer metastasis present unprecedented possibilities for translating basic research to the clinical reality of cancer treatment.