Premetastatic lung "niche": is vascular endothelial growth factor receptor 1 activation required?

Premetastatic Niche: A Novel Area for Research in Metastasis with a Potential as Therapeutic Targeting in Oral Cancer

Premetastatic niche (PMN) concept, introduced by David Lyden and colleagues, is an area that can support cancer cells to nurture in it, but the area itself being bereft of cancerous cells. It provides a microenvironment that is congenial for tumor invasion, endurance, and or proliferation of malignant cells to develop into metastasis. These are noncancerous variations in a tumor-free organ and are the most primitive indications of metastasis. These may have a potential to serve as a diagnostic aid, prognostic biomarkers, and therapeutic target. Nevertheless, there is still no clear elucidation on diverse trails of tumor metastasis via lymphatic or hematogenous route, especially in relationship with the PMN. In this review, contemporary knowledge associated with nodal premetastatic niche formation with forthcoming directions on translational and clinical research is deliberated.

Immunohistochemical expression of VEGFR1 in non small cell lung carcinomas: Lower VEGFR1 expression is asociated with squamous cell carcinoma subtype and high SUV max values in 18F-FDG PET

BACKGROUND

To study the possible relation between immunohistochemical expression of vascular endothelial growth factor receptor 1 (VEGFR1) and the maximum standardised uptake value (SUV max) of ¹⁸F-FDG PET in patients with non small cell lung cancer (NSCLC).

MATERIAL AND METHODS

The study included 39 patients with NSCLC (24 squamous cell carcinomas and 15 adenocarcinomas). According to the clinical stage, the patients were distributed as follows: 8 stage I, 7 stage II, 15 stage III and 9 stage IV. Immunohistochemical expression of VEGFR1 was studied through the technique of tissue-matrix using Tissue Arrayer Device (Beecher Instruments, Sun Prairie, WI), using the polyclonal antibody against VEGFR1 (Santa Cruz Biotechnology, California, USA).

RESULTS

Positive VEGFR1 immunohistochemical expression was noted in 23 cases (59%). The number of positive tumours was not related with clinical stage but there was a different statistically significant association (p:0,0009) between VEGFR1 positivity and histological type, corresponding the greater percentages of positive results to adenocarcinomas (93,3%) versus in squamous cell carcinomas (37,5%). Likewise, SUV max values were higher (p: 0,039) in negative VEGFR1 carcinomas than in positive VEGFR1 tumors (r: 4-32,1; 16,4+/-6,4 (median 16,1) vs r: 3-47; 14,5+/-8,6 (12,8)).

CONCLUSIONS

Our results led us to consider that in NSCLC, the negative VEGFR1 immunohistochemical expression is associated significantly with squamous cell carcinomas subtype and with higher SUV max values in ¹⁸F-FDG-PET.

Immunohistochemical expression of VEGFR1 in non small cell lung carcinomas: Lower VEGFR1 expression is asociated with squamous cell carcinoma subtype and high max SUV values in 18F-FDG PET

BACKGROUND

To study the possible relation between immunohistochemical expression of vascular endothelial growth factor receptor 1 (VEGFR1) and the maximum standardised uptake value (maxSUV) of 18F-FDG PET in patients with non small cell lung cancer.

MATERIAL AND METHODS

The study included 39 patients with NSCLC (24 squamous cell carcinomas and 15 adenocarcinomas). According to the clinical stage, the patients were distributed as follows: 8 stage I, 7 stage II, 15 stage III and 9 stage IV. Immunohistochemical expression of VEGFR1 was studied through the technique of tissue-matrix using tissue arrayer device (Beecher Instruments, Sun Prairie, WI), using the polyclonal antibody against VEGFR1 (Santa Cruz Biotechnology, California, USA).

RESULTS

Positive VEGFR1 immunohistochemical expression was noted in 23 cases (59%). The number of positive tumours was not related with clinical stage but there was a different statistically significant association (p:.0009) between VEGFR1 positivity and histological type, corresponding the greater percentages of positive results to adenocarcinomas (93.3%) versus in squamous cell carcinomas (37.5%). Likewise, maxSUV values were higher (p: .039) in negative VEGFR1 carcinomas than in positive VEGFR1 tumors (r: 4-32.1; 16.4+/-6.4 [median 16.1] vs. r: 3-47; 14.5+/-8.6 [12.8]).

CONCLUSIONS

Our results led us to consider that in NSCLC, the negative VEGFR1 immunohistochemical expression is associated significantly with squamous cell carcinomas subtype and with higher maxSUV values in 18F-FDG-PET.

A history of exploring cancer in context

The concept that progression of cancer is regulated by interactions of cancer cells with their microenvironment was postulated by Stephen Paget over a century ago. Contemporary tumour microenvironment (TME) research focuses on the identification of tumour-interacting microenvironmental constituents, such as resident or infiltrating non-tumour cells, soluble factors and extracellular matrix components, and the large variety of mechanisms by which these constituents regulate and shape the malignant phenotype of tumour cells. In this Timeline article, we review the developmental phases of the TME paradigm since its initial description. While illuminating controversies, we discuss the importance of interactions between various microenvironmental components and tumour cells and provide an overview and assessment of therapeutic opportunities and modalities by which the TME can be targeted.

Exosomal tetraspanins mediate cancer metastasis by altering host microenvironment

The metastases of malignant tumors develop through a cascade of events. The establishment of a pre-metastatic micro-environment is initiated by communication between tumors and host. Exosomes come into focus as the most potent intercellular communicators playing a pivotal role in this process. Cancer cells release exosomes into the extracellular environment prior to metastasis. Tetraspanin is a type of 4 times transmembrane proteins. It may be involved in cell motility, adhesion, morphogenesis, as well as cell and vesicular membrane fusion. The exosomal tetraspanin network is a molecular scaffold connecting various proteins for signaling transduction. The complex of tetraspanin-integrin determines the recruiting cancer exosomes to pre-metastatic sites. Tetraspanin is a key element for the target cell selection of exosomes uptake that may lead to the reprogramming of target cells. Reprogrammed target cells assist pre-metastatic niche formation. Previous reviews have described the biogenesis, secretion and intercellular interaction of exosomes in various tumors. However, there is a lack of reviews on the topic of exosomal tetraspanin in the context of cancer. In this review, we will describe the main characteristics of exosomal tetraspanin in cancer cells. We will also discuss how the cancer exosomal tetraspanin alters extracellular environment and regulates cancer metastasis.

Aggressive rat prostate tumors reprogram the benign parts of the prostate and regional lymph nodes prior to metastasis

In order to grow and spread tumors need to interact with adjacent tissues. We therefore hypothesized that small but aggressive prostate cancers influence the rest of the prostate and regional lymph nodes differently than tumors that are more indolent. Poorly metastatic (Dunning AT1) or highly metastatic (Dunning MLL) rat prostate tumor cells were injected into the ventral prostate lobe of immunocompetent rats. After 10 days—when the tumors occupied about 30% of the prostate lobe and lymph node metastases were undetectable—the global gene expression in tumors, benign parts of the prostate, and regional iliac lymph nodes were examined to define tumor-induced changes related to preparation for future metastasis. The tumors induced profound effects on the gene expression profiles in the benign parts of the prostate and these were strikingly different in the two tumor models. Gene ontology enrichment analysis suggested that tumors with high metastatic capacity were more successful than less metastatic tumors in inducing tumor-promoting changes and suppressing anti-tumor immune responses in the entire prostate. Some of these differences such as altered angiogenesis, nerve density, accumulation of T-cells and macrophages were verified by immunohistochemistry. Gene expression alterations in the regional lymph nodes suggested decreased quantity and activation of immune cells in MLL-lymph nodes that were also verified by immunostaining. In summary, even when small highly metastatic prostate tumors can affect the entire tumor-bearing organ and pre-metastatic lymph nodes differently than less metastatic tumors. When the kinetics of these extratumoral influences (by us named TINT = tumor instructed normal tissue) are more precisely defined they could potentially be used as markers of disease aggressiveness and become therapeutic targets.

Cancer and the metastatic substrate

Seventy percent of cancer patients have detectable metastases when they receive a diagnosis and 90% of cancer deaths result from metastases. These two facts emphasise the urgency for research to study the mechanisms and processes that enable metastasis. We need to develop a greater understanding of the cellular and molecular mechanisms that cause metastasis and also we need to do more. We must also consider the micro- and macro-environmental factors that influence this disease. Studying this environmental context has led us to update the ‘seed and soil’ hypothesis which dates back to the 19th century. This theory describes cancerous cells as seeds and the substrate as the soil in target organs though this may seem antiquated. Nonetheless, the tissue specificity that researchers have recently observed in metastatic colonisation supports the validity of the seed and soil theory. We now know that the metastatic potential of a tumour cell depends on multiple, reciprocal interactions between the primary tumour and distant sites. These interactions determine tumour progression. Studies of metastasis have allowed us to develop treatments that focus on therapeutic effectiveness. These new treatments account for the frequent metastasis of some tumours to target organs such as bones, lungs, brain, and liver. The purpose of this review is first to describe interactions between the cellular and molecular entities and the target organ tumour environment that enables metastasis. A second aim is to describe the complex mechanisms that mediate these interactions.

Exosomal Annexin II Promotes Angiogenesis and Breast Cancer Metastasis

Tumor-derived exosomes are emerging mediators of tumorigenesis and tissue-specific metastasis. Proteomic profiling has identified Annexin II as one of the most highly expressed proteins in exosomes; however, studies focused on the biological role of exosomal Annexin II (exo-Anx II) are still lacking. In this study, mechanistic insight was sought regarding exo-Anx II and its function in angiogenesis and breast cancer metastasis. Multiple in vitro and in vivo techniques were used to study the role of exo-Anx II in angiogenesis. Using atomic force microscopy and Western blotting, exo-Anx II expression was characterized in normal and breast cancer cells. In addition, organ-specific metastatic breast cancer cells and animal models were used to define the role exo-Anx II in breast cancer metastasis. Results revealed that exo-Anx II expression is significantly higher in malignant cells than normal and premetastatic breast cancer cells. In vitro and in vivo studies demonstrated that exo-Anx II promotes tPA-dependent angiogenesis. Furthermore, in vivo analysis indicated that metastatic exosomes create a favorable microenvironment for metastasis, and exo-Anx II plays an important role in this process, as priming with Anx II-depleted exosomes reduces brain (∼4-fold) and lung (∼2-fold) metastasis. Upon delineating the mechanism, it was discovered that exo-Anx II causes macrophage-mediated activation of the p38MAPK, NF-κB, and STAT3 pathways and increased secretion of IL6 and TNFα. These data demonstrate an important role for exo-Anx II in breast cancer pathogenesis.

IMPLICATIONS

Exosome-associated Annexin II plays an important role in angiogenesis and breast cancer metastasis, which can be exploited as a potential biomarker as well as a therapeutic target for diagnosis and treatment of metastatic breast cancer. Mol Cancer Res; 15(1); 93-105. ©2016 AACR.

The brain metastatic niche

Metastasizing cancer cells that arrest in brain microvessels have to face an organ microenvironment that is alien, and exclusive. In order to survive and thrive in this foreign soil, the malignant cells need to successfully master a sequence of steps that includes close interactions with pre-existing brain microvessels, and other nonmalignant cell types. Unfortunately, a relevant number of circulating cancer cells is capable of doing so: brain metastasis is a frequent and devastating complication of solid tumors, becoming ever more important in times where the systemic tumor disease is better controlled and life of cancer patients is prolonged. Thus, it is very important to understand which environmental cues are necessary for effective brain colonization. This review gives an overview of the niches we know, including those who govern cancer cell dormancy, survival, and proliferation in the brain. Colonization of pre-existing niches related to stemness and resistance is a hallmark of successful brain metastasis. A deeper understanding of those host factors can help to identify the most vulnerable steps of the metastatic cascade, which might be most amenable to therapeutic interventions.

PlGF/VEGFR-1 Signaling Promotes Macrophage Polarization and Accelerated Tumor Progression in Obesity

PURPOSE

Obesity promotes pancreatic and breast cancer progression via mechanisms that are poorly understood. Although obesity is associated with increased systemic levels of placental growth factor (PlGF), the role of PlGF in obesity-induced tumor progression is not known. PlGF and its receptor VEGFR-1 have been shown to modulate tumor angiogenesis and promote tumor-associated macrophage (TAM) recruitment and activity. Here, we hypothesized that increased activity of PlGF/VEGFR-1 signaling mediates obesity-induced tumor progression by augmenting tumor angiogenesis and TAM recruitment/activity.

EXPERIMENTAL DESIGN

We established diet-induced obese mouse models of wild-type C57BL/6, VEGFR-1 tyrosine kinase (TK)-null, or PlGF-null mice, and evaluated the role of PlGF/VEGFR-1 signaling in pancreatic and breast cancer mouse models and in human samples.

RESULTS

We found that obesity increased TAM infiltration, tumor growth, and metastasis in pancreatic cancers, without affecting vessel density. Ablation of VEGFR-1 signaling prevented obesity-induced tumor progression and shifted the tumor immune environment toward an antitumor phenotype. Similar findings were observed in a breast cancer model. Obesity was associated with increased systemic PlGF, but not VEGF-A or VEGF-B, in pancreatic and breast cancer patients and in various mouse models of these cancers. Ablation of PlGF phenocopied the effects of VEGFR-1-TK deletion on tumors in obese mice. PlGF/VEGFR-1-TK deletion prevented weight gain in mice fed a high-fat diet, but exacerbated hyperinsulinemia. Addition of metformin not only normalized insulin levels but also enhanced antitumor immunity.

CONCLUSIONS

Targeting PlGF/VEGFR-1 signaling reprograms the tumor immune microenvironment and inhibits obesity-induced acceleration of tumor progression. Clin Cancer Res; 22(12); 2993-3004. ©2016 AACR.

Primary Tumor-Secreted Lymphangiogenic Factors Induce Pre-Metastatic Lymphvascular Niche Formation at Sentinel Lymph Nodes in Oral Squamous Cell Carcinoma

OBJECTIVES

The objectives of this study were to evaluate the formation of lymphvascular niches in lymph nodes of patients with oral squamous cell carcinoma (OSCC), and investigate the roles of lymphangiogenic and angiogenic factors, such as vascular endothelial growth factor (VEGF)-A, VEGF-C, and VEGF-D, expressed in the primary tumors.

MATERIALS AND METHODS

Forty-four patients with previously untreated clinically late T2 or T3 OSCC of cN0 were evaluated for primary tumors and 166 sentinel lymph nodes (SLNs). Primary tumors were immunohistochemically analyzed for expressions of VEGFs. Densities of lymphatic vessels (LVDpodoplanin) and high endothelial venules (HEVD) in the SLNs were also calculated using antibodies for each marker, podoplanin and MECA-79, respectively.

RESULTS

In 25 patients, all lymph nodes were metastasis-negative, whereas, in 19 patients, metastasis was positive for at least one lymph node (either at SLN, non-SLN, or nodal recurrence). From the analyses of 140 SLNs without metastasis, LVDpodoplanin in 50 SLNs of metastasis-positive cases was significantly higher than that in 90 SLNs of metastasis-negative cases (p = 0.0025). HEVD was not associated with lymph node metastasis. The patients with VEGF-A-High or VEGF-D-High tumors had significantly higher LVDpodoplanin than patients with their Low counterparts (p = 0.0233 and p = 0.0209, respectively). In cases with lymph node metastasis, the VEGF-D-expression score was significantly higher than in those without lymph node metastasis (p = 0.0006).

CONCLUSIONS

These results suggest that lymph node lymphangiogenesis occurs before metastasis in OSCC. VEGF-A and VEGF-D play critical roles in this process. VEGF-D is a potential predictive marker of positive lymph node metastasis in cN0 patients.

The pre-metastatic niche: finding common ground

It is rapidly becoming evident that the formation of tumor-promoting pre-metastatic niches in secondary organs adds a previously unrecognized degree of complexity to the challenge of curing metastatic disease. Primary tumor cells orchestrate pre-metastatic niche formation through secretion of a variety of cytokines and growth factors that promote mobilization and recruitment of bone marrow-derived cells to future metastatic sites. Hypoxia within the primary tumor, and secretion of specific microvesicles termed exosomes, are emerging as important processes and vehicles for tumor-derived factors to modulate pre-metastatic sites. It has also come to light that reduced immune surveillance is a novel mechanism through which primary tumors create favorable niches in secondary organs. This review provides an overview of our current understanding of underlying mechanisms of pre-metastatic niche formation and highlights the common links as well as discrepancies between independent studies. Furthermore, the possible clinical implications, links to metastatic persistence and dormancy, and novel approaches for treatment of metastatic disease through reversal of pre-metastatic niche formation are identified and explored.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Vascular endothelial growth factor (VEGF) receptors: drugs and new inhibitors

The recent launch onto the market of five VEGFR inhibitors indicates the therapeutic value of these agents and the importance of the research in the field of angiogenesis inhibitors for future oncologic therapy. In this Perspective we briefly report the inhibitors that are in clinical use, while we dedicate two wider sections to the compounds that are in clinical trials and to the new derivatives appearing in the literature. We especially consider the medicinal chemistry aspect of the topic and report the structure-activity relationship studies and the binding mode of some inhibitors as well as the biological data of the compounds discovered in the past 5 years.

TIMP-2 targets tumor-associated myeloid suppressor cells with effects in cancer immune dysfunction and angiogenesis

Angiogenesis and inflammation are important therapeutic targets in non-small cell lung cancer (NSCLC). It is well known that proteolysis mediated by matrix metalloproteinases (MMPs) promotes angiogenesis and inflammation in the tumor microenvironment. Here, the effects of the MMP inhibitor TIMP-2 on NSCLC inflammation and angiogenesis were evaluated in TIMP-2-deficient (timp2-/-) mice injected subcutaneously (SC) with Lewis lung carcinoma cells and compared with the effects on tumors in wild-type mice. TIMP-2-deficient mice demonstrated increased tumor growth, enhanced expression of angiogenic marker αvβ3 in tumor and endothelial cells, and significantly higher serum vascular endothelial growth factor-A levels. Tumor-bearing timp2-/- mice showed a significant number of inflammatory cells in their tumors, upregulation of inflammation mediators, nuclear factor-kappaB, and Annexin A1, as well as higher levels of serum interleukin (IL)-6. Phenotypic analysis revealed an increase in myeloid-derived suppressor cell (MDSC) cells (CD11b+ and Gr-1+) that coexpressed vascular-endothelial-growth factor receptor 1 (VEGF-R1) and elevated MMP activation present in tumors and spleens from timp2-/- mice. Furthermore, TIMP-2-deficient tumors upregulated expression of the immunosuppressing genes controlling MDSC growth, IL-10, IL-13, IL-11, and chemokine ligand (CCL-5/RANTES), and decreased interferon-γ and increased CD40L. Moreover, forced TIMP-2 expression in human lung adenocarcinoma A-549 resulted in a significant reduction of MDSCs recruited into tumors, as well as suppression of angiogenesis and tumor growth. The increase in MDSCs has been linked to cancer immunosuppression and angiogenesis. Therefore, this study supports TIMP-2 as a negative regulator of MDSCs with important implications for the immunotherapy and/or antiangiogenic treatment of NSCLC.

PlGF: a multitasking cytokine with disease-restricted activity

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family that also comprises VEGF-A (VEGF), VEGF-B, VEGF-C, and VEGF-D. Unlike VEGF, PlGF is dispensable for development and health but has diverse nonredundant roles in tissue ischemia, malignancy, inflammation, and multiple other diseases. Genetic and pharmacological gain-of-function and loss-of-function studies have identified molecular mechanisms of this multitasking cytokine and characterized the therapeutic potential of delivering or blocking PlGF for various disorders.

Bone metastatic process of breast cancer involves methylation state affecting E-cadherin expression through TAZ and WWOX nuclear effectors

We investigated the involvement of Hippo-related pathways in bone metastasis from breast cancer, by evaluating E-cadherin expression downstream of WWdomain-containing oxidoreductase (Wwox) and transcriptional co-activator with PDZ-binding motif (TAZ). These nuclear effectors functioned in a context-specific fashion on transcriptome, depending on breast-cancer aggressiveness and methylation state. Wwox and E-cadherin were found in human specimens of bone metastasis but not in primary-ductal breast carcinoma, while TAZ showed a characteristic localisation in metastasis nuclei. Wwox and E-cadherin were higher in 1833-metastatic clone with bone avidity than in parental-MDA-MB231 cells, while only metastatic cells presented TAZ. In 1833 cells, a complex interplay of transcriptional signalling controlled E-cadherin transactivation. Wwox and TAZ activated Hypoxia inducible factor-1 (HIF-1) binding to E-cadherin promoter, while Peroxisome proliferator-activated receptor γ (PPARγ) intervened in E-cadherin transactivation favouring and preventing Wwox and TAZ functions, respectively. Methylation impinged on Hippo-related pathways through Wwox and TAZ, modifying metastatic phenotype. The protract exposure to 5-azacytidine (Aza), by affecting methylation state modified the shape of 1833 cells, becoming mesenchymal as that of MDA-MB231 cells and reduced spontaneous-Matrigel invasion. The underlying-molecular mechanisms were diminutions of E-cadherin, Wwox, matrix metalloproteases 2 and 9, HIF-1- and PPARγ-activities, inversely correlated to Snail and nuclear-TAZ accumulations. Exogenous WWOX restored 1833-Aza invasion. Thus, 1833-Aza cells permitted to study the role played by methylation in metastasis plasticity, being E-cadherin loss part of an entire-gene reprogramming. Of note, bone-metastasis formation in 1833-Aza xenograft was partially impaired, prolonging mice survival. In conclusion, the methylation-heritable changes seemed important for cancer progression to establish bone metastasis engraftment/growth, by affecting steps requiring homotipic and/or heterotypic-adhesive properties and matrix degradation.

The pre-metastatic niche: is metastasis random?

The metastasis of solid tumours is a vastly complex, dynamic and systemic process involving both primary tumour cells as well as a wide array of stromal and vascular cells. The recruitment and activation of host cells by tumours at both the primary and metastatic sites is crucial for successful metastatic dissemination highlighting the systemic nature of disease progression. The appropriation of distant metastatic sites by primary tumours and the generation of so-called pre-metastatic niches have gained much interest in the last decade complementing the century old 'seed and soil' hypothesis. The idea that tumours are capable of pre-defining future sites of metastasis is both exciting and terrifying as we try to understand the dynamic networks associated with solid tumour metastasis. Exactly how a tumour cell can alter the distant metastatic microenvironment is of great importance and will unlock novel strategies for successfully targeting these processes.

Bone marrow-derived proangiogenic cells in pancreatic cancer

Tumor-derived signals systemically induce an angiogenic switch that allows cancer cells to survive and grow. However, the vascular network in tumors is not well organized and fails to meet metabolic needs to maintain tissue homeostasis, resulting in significant hypoxia. Among various tumors, pancreatic ductal adenocarcinoma (PDAC) typically develops in an unusually disordered microenvironment, which contributes to its highly aggressive behavior. Since anti-vascular endothelial growth factor (VEGF) (Avastin) has failed to demonstrate a survival benefit in PDAC, we need to re-visit the basic biology of this disease and understand what makes it so refractory to the anti-angiogenic approaches that are clinically effective in other neoplasms. To address this issue, we specifically focused on the process of neovascularization where bone marrow-derived cells (BMDCs) play a role during pancreatic tumorigenesis. We have identified subsets of BMDCs that regulate key processes during development of the neovessels through paracrine Hedgehog signaling. Considering the importance of systemic responses occurring in tumor bearing hosts, we are currently using genetically engineered mice, which spontaneously develop PDAC, Pdx1-Cre;LSL-Kras(G12D);p53(lox/+) strain, to clarify critical events that can trigger aberrant angiogenesis in pancreatic cancer. These studies allow us to provide insights into the cellular and molecular mechanisms of pancreatic tumorigenesis and have an implication for the design of therapies against this difficult disease.

Molecular and functional imaging of invasion and metastasis: windows into the metastatic cascade

The ability of cancer cells to invade, metastasize, and form distant colonies, is one of the key characteristics that confers lethality to cancer. Metastatic cancer cells typically become refractory to treatment. The metastatic cascade is a multi-step process that is governed by events within the cancer cell, the tumor microenvironment, and the distant environments that are invaded and colonized by the cancer cells. Noninvasive imaging techniques are facilitating a close examination of the stepwise journey of the cancer cell from the primary tumor to the distant metastatic site. Here we have discussed the metastatic process, and how molecular and functional imaging of cancer are providing new insights into the metastatic cascade that can be exploited for treatment of metastatic disease.

Molecular mechanisms and clinical applications of angiogenesis

Blood vessels deliver oxygen and nutrients to every part of the body, but also nourish diseases such as cancer. Over the past decade, our understanding of the molecular mechanisms of angiogenesis (blood vessel growth) has increased at an explosive rate and has led to the approval of anti-angiogenic drugs for cancer and eye diseases. So far, hundreds of thousands of patients have benefited from blockers of the angiogenic protein vascular endothelial growth factor, but limited efficacy and resistance remain outstanding problems. Recent preclinical and clinical studies have shown new molecular targets and principles, which may provide avenues for improving the therapeutic benefit from anti-angiogenic strategies.

Initial steps of metastasis: cell invasion and endothelial transmigration

Metastasis is the leading cause of cancer mortality. The metastatic cascade represents a multi-step process which includes local tumor cell invasion, entry into the vasculature followed by the exit of carcinoma cells from the circulation and colonization at the distal sites. At the earliest stage of successful cancer cell dissemination, the primary cancer adapts the secondary site of tumor colonization involving the tumor–stroma crosstalk. The migration and plasticity of cancer cells as well as the surrounding environment such as stromal and endothelial cells are mandatory. Consequently, the mechanisms of cell movement are of utmost relevance for targeted intervention of which three different types have been reported. Tumor cells can migrate either collectively, in a mesenchymal or in an amoeboid type of movement and intravasate the blood or lymph vasculature. Intravasation by the interaction of tumor cells with the vascular endothelium is mechanistically poorly understood. Changes in the epithelial plasticity enable carcinoma cells to switch between these types of motility. The types of migration may change depending on the intervention thereby increasing the velocity and aggressiveness of invading cancer cells. Interference with collective or mesenchymal cell invasion by targeting integrin expression or metalloproteinase activity, respectively, resulted in an amoeboid cell phenotype as the ultimate exit strategy of cancer cells. There are little mechanistic details reported in vivo showing that the amoeboid behavior can be either reversed or efficiently inhibited. Future concepts of metastasis intervention must simultaneously address the collective, mesenchymal and amoeboid mechanisms of cell invasion in order to advance in anti-metastatic strategies as these different types of movement can coexist and cooperate. Beyond the targeting of cell movements, the adhesion of cancer cells to the stroma in heterotypic circulating tumor cell emboli is of paramount relevance for anti-metastatic therapy.