Unique ability of integrin alpha(v)beta 3 to support tumor cell arrest under dynamic flow conditions

Crosstalk between Circulating Tumor Cells and Plasma Proteins-Impact on Coagulation and Anticoagulation

Cancer metastasis is a complex process. After their intravasation into the circulation, the cancer cells are exposed to a harsh environment of physical and biochemical hazards. Whether circulating tumor cells (CTCs) survive and escape from blood flow defines their ability to metastasize. CTCs sense their environment with surface-exposed receptors. The recognition of corresponding ligands, e.g., fibrinogen, by integrins can induce intracellular signaling processes driving CTCs' survival. Other receptors, such as tissue factor (TF), enable CTCs to induce coagulation. Cancer-associated thrombosis (CAT) is adversely connected to patients' outcome. However, cancer cells have also the ability to inhibit coagulation, e.g., through expressing thrombomodulin (TM) or heparan sulfate (HS), an activator of antithrombin (AT). To that extent, individual CTCs can interact with plasma proteins, and whether these interactions are connected to metastasis or clinical symptoms such as CAT is largely unknown. In the present review, we discuss the biological and clinical relevance of cancer-cell-expressed surface molecules and their interaction with plasma proteins. We aim to encourage future research to expand our knowledge of the CTC interactome, as this may not only yield new molecular markers improving liquid-biopsy-based diagnostics but also additional targets for better cancer therapies.

Tumor Cell-Induced Platelet Aggregation as an Emerging Therapeutic Target for Cancer Therapy

Tumor cells have the ability to induce platelet activation and aggregation. This has been documented to be involved in tumor progression in several types of cancers, such as lung, colon, breast, pancreatic, ovarian, and brain. During the process, platelets protect circulating tumor cells from the deleterious effects of shear forces, shield tumor cells from the immune system, and provide growth factors, facilitating metastatic spread and tumor growth at the original site as well as at the site of metastasis. Herein, we present a wider view on the induction of platelet aggregation by specific factors primarily developed by cancer, including coagulation factors, adhesion receptors, growth factors, cysteine proteases, matrix metalloproteinases, glycoproteins, soluble mediators, and selectins. These factors may be presented on the surface of tumor cells as well as in their microenvironment, and some may trigger more than just one simple receptor–ligand mechanism. For a better understanding, we briefly discuss the physiological role of the factors in the platelet activation process, and subsequently, we provide scientific evidence and discuss their potential role in the progression of specific cancers. Targeting tumor cell-induced platelet aggregation (TCIPA) by antiplatelet drugs may open ways to develop new treatment modalities. On the one hand, it may affect patients’ prognosis by enhancing known therapies in advanced-stage tumors. On the other hand, the use of drugs that are mostly easily accessible and widely used in general practice may be an opportunity to propose an unparalleled antitumor prophylaxis. In this review, we present the recent discoveries of mechanisms by which cancer cells activate platelets, and discuss new platelet-targeted therapeutic strategies.

The Manifold Cellular Functions of von Willebrand Factor

The plasma glycoprotein von Willebrand factor (VWF) is exclusively synthesized in endothelial cells (ECs) and megakaryocytes, the precursor cells of platelets. Its primary function lies in hemostasis. However, VWF is much more than just a "fishing hook" for platelets and a transporter for coagulation factor VIII. VWF is a true multitasker when it comes to its many roles in cellular processes. In ECs, VWF coordinates the formation of Weibel-Palade bodies and guides several cargo proteins to these storage organelles, which control the release of hemostatic, inflammatory and angiogenic factors. Leukocytes employ VWF to assist their rolling on, adhesion to and passage through the endothelium. Vascular smooth muscle cell proliferation is supported by VWF, and it regulates angiogenesis. The life cycle of platelets is accompanied by VWF from their budding from megakaryocytes to adhesion, activation and aggregation until the end in apoptosis. Some tumor cells acquire the ability to produce VWF to promote metastasis and hide in a shell of VWF and platelets, and even the maturation of osteoclasts is regulated by VWF. This review summarizes the current knowledge on VWF's versatile cellular functions and the resulting pathophysiological consequences of their dysregulation.

Platelet-Cancer Interplay: Molecular Mechanisms and New Therapeutic Avenues

Although platelets are critically involved in thrombosis and hemostasis, experimental and clinical evidence indicate that platelets promote tumor progression and metastasis through a wide range of physical and functional interactions between platelets and cancer cells. Thrombotic and thromboembolic events are frequent complications in patients with solid tumors. Hence, cancer modulates platelet function by directly inducing platelet-tumor aggregates and triggering platelet granule release and altering platelet turnover. Also, platelets enhance tumor cell dissemination by activating endothelial cell function and recruiting immune cells to primary and metastatic tumor sites. In this review, we summarize current knowledge on the complex interactions between platelets and tumor cells and the host microenvironment. We also critically discuss the potential of anti-platelet agents for cancer prevention and treatment.

The role of von Willebrand factor in breast cancer metastasis

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VWF plays an important role in breast tumour progression and metastasis.

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Patients with metastatic breast cancer have significantly elevated plasma VWF.

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Increased levels of highly adhesive VWF may regulate platelet-tumour interactions.

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VWF may protect disseminated tumour cells from chemotherapy.

Breast cancer is the most common female cancer globally, with approximately 12% of patients eventually developing metastatic disease. Critically, limited effective treatment options exist for metastatic breast cancer. Recently, von Willebrand factor (VWF), a haemostatic plasma glycoprotein, has been shown to play an important role in tumour progression and metastasis. In breast cancer, a significant rise in the plasma levels of VWF has been reported in patients with malignant disease compared to benign conditions and healthy controls, with an even greater increase seen in patients with disseminated disease. Direct interactions between VWF, tumour cells, platelets and endothelial cells may promote haematogenous dissemination and thus the formation of metastatic foci. Intriguingly, patients with metastatic disease have unusually large VWF multimers. This observation has been proposed to be a result of a dysfunctional or deficiency of VWF-cleaving protease activity, ADAMTS-13 activity, which may then regulate the platelet-tumour adhesive interactions in the metastatic process. In this review, we provide an overview of VWF in orchestrating the pathological process of breast cancer dissemination, and provide supporting evidence of the role of VWF in mediating metastatic breast cancer.

In vitro analysis of the trajectories of adhesive microbubbles approaching endothelial cells

Adhesion is a key process when ultrasound contrast agents, i.e. microbubbles, approach pathological tissues. A way to accomplish tumour targeting is to tether surface engineered microbubbles to endothelial cells of the up-regulated vascularization of cancer tissues. This can be achieved by coupling the microbubbles surface with the Arginine-Glycine-Aspartate, RGD, sequence. Such molecule interacts with the integrin receptors placed on the endothelial cells. Stability and trajectories of RGD modified lipid shelled MBs have been analysed in vitro using microchannels coated with human umbilical vein endothelial cells, HUVEC. In the microchannels realistic conditions, close to the physiological ones, were reproduced replicating shear rate, roughness comparable to the endothelium and channel size mimicking the postcapillary venules. In these conditions, the analysis of the trajectories close to the walls highlights a substantial difference between the modified MBs and the plain ones. Moreover, MBs adhesion has dynamic features recalling the motion of neutrophils engaged near the substrate such as rolling, translations and transient detachments. These findings are useful for the optimization of in vivo imaging and targeting functions.

The Complexities of Metastasis

Therapies that prevent metastatic dissemination and tumor growth in secondary organs are severely lacking. A better understanding of the mechanisms that drive metastasis will lead to improved therapies that increase patient survival. Within a tumor, cancer cells are equipped with different phenotypic and functional capacities that can impact their ability to complete the metastatic cascade. That phenotypic heterogeneity can be derived from a combination of factors, in which the genetic make-up, interaction with the environment, and ability of cells to adapt to evolving microenvironments and mechanical forces play a major role. In this review, we discuss the specific properties of those cancer cell subgroups and the mechanisms that confer or restrict their capacity to metastasize.

Platelet-Based Drug Delivery for Cancer Applications

Platelets can be considered as the "guardian of hemostasis" where their main function is to maintain vascular integrity. In pathological conditions, the hemostatic role of platelets may be hijacked to stimulate disease progression. In 1865, Armand Trousseau was a pioneer in establishing the platelet-cancer metastasis relationship, which he eventually termed as Trousseau's Syndrome to describe the deregulation of the hemostasis-associated pathways induced by cancer progression (Varki, Blood. 110(6):1723-9, 2007). Since these early studies, there has been an increase in experimental evidence not only to elucidate the role of platelets in cancer metastasis but also to create novel cancer therapies by targeting the platelet's impact in metastasis. In this chapter, we discuss the contribution of platelets in facilitating tumor cell transit from the primary tumor to distant metastatic sites as well as novel cancer therapies based on platelet interactions.

Cyclin D1b Splice Variant Promotes αvβ3-mediated EMT Induced by LPS in Breast Cancer Cells

Epithelial-to-mesenchymal transition (EMT) plays a critical role in cancer metastasis, and is relevant to the inflammatory microenvironment. Lipopolysaccharide (LPS), a cell wall constituent of gram-negative bacteria, has been reported to induce EMT of cancer cells through TLR4 signal. We previously reported that LPS promoted metastasis of mesenchymallike breast cancer cells with high expression of cyclin D1b. However, the role of cyclin D1b in LPS-induced EMT has not been fully elucidated. In the present study, we described that cyclin D1b augmented EMT induced by LPS in MCF-7 breast cancer cells. Cyclin D1b markedly amplified integrin αvβ3 expression, which was further up-regulated under LPS stimulation. Our results showed ectopic expression of cyclin D1b promoted invasiveness of epithelial-like MCF-7 cells under LPS stimulation. Additionally, LPS-induced metastasis and EMT in MCF-7-D1b cells might depend on αvβ3 expression. Further exploration indicated that cyclin D1b cooperated with HoxD3, a transcription factor promoting αvβ3 expression, to promote LPSinduced EMT. Knockout of HoxD3 repressed LPS-induced EMT and αvβ3 over-expression in MCF-7 cells with high expression of cyclin D1b. Specifically, all these effects were in a cyclin Dla independent manner. Taken all together, LPS up-regulated integrin αvβ3 expression in MCF-7 cells with high expression of cyclin D1b and induced EMT in breast cancer cells, which highlights that cyclin D1b may act as an endogenous pathway participating in exogenous signal inducing EMT in breast cancer cells.

A novel microfluidic model can mimic organ-specific metastasis of circulating tumor cells

A biomimetic microsystem might compensate costly and time-consuming animal metastatic models. Herein we developed a biomimetic microfluidic model to study cancer metastasis. Primary cells isolated from different organs were cultured on the microlfuidic model to represent individual organs. Breast and salivary gland cancer cells were driven to flow over primary cell culture chambers, mimicking dynamic adhesion of circulating tumor cells (CTCs) to endothelium in vivo. These flowing artificial CTCs showed different metastatic potentials to lung on the microfluidic model. The traditional nude mouse model of lung metastasis was performed to investigate the physiological similarity of the microfluidic model to animal models. It was found that the metastatic potential of different cancer cells assessed by the microfluidic model was in agreement with that assessed by the nude mouse model. Furthermore, it was demonstrated that the metastatic inhibitor AMD3100 inhibited lung metastasis effectively in both the microfluidic model and the nude mouse model. Then the microfluidic model was used to mimick liver and bone metastasis of CTCs and confirm the potential for research of multiple-organ metastasis. Thus, the metastasis of CTCs to different organs was reconstituted on the microfluidic model. It may expand the capabilities of traditional cell culture models, providing a low-cost, time-saving, and rapid alternative to animal models.

Occult cancer detection in patients with hemostatic disorder and venous thromboembolism

There are physiologic ties between Von Willebrand Factor (VWF) and circulating tumor cells. VWF appears to play a role in tumor biology, but it is unclear whether cancer behavior differs in Von Willebrand Disease. In patients presenting with venous thromboembolism (VTE), occult cancer is frequently considered as an underlying cause. The prevalence of occult cancer after provoked VTE is low (3%); therefore, cancer screening in these patients is not routinely recommended. In those with unprovoked VTE, occult cancer is more prevalent, estimated between 4 and 10%. Due to this elevated risk, occult cancer screening is recommended in this population. Multiple studies have investigated whether a "limited" approach (including history and physical exam, basic labs, and chest X-ray) versus "extensive" approach (addition of advanced imaging, such as computer tomography) is more effective. Current data fails to demonstrate extensive screening strategies diagnose more occult cancer, miss fewer cancers during follow up, or improve cancer-related mortality. Furthermore, many patients may be needlessly exposed to unnecessary diagnostic procedures with their associated complications and costs, as well as significant anxiety. Therefore, the decision to perform additional testing should be made on a case-by-case basis. Additional studies are needed to identify subgroups of patients with unprovoked VTE at highest risk for occult cancer.

Increased von Willebrand factor over decreased ADAMTS-13 activity is associated with poor prognosis in patients with advanced non-small-cell lung cancer

BACKGROUND

Hypercoagulability induced by the imbalance between von Willebrand factor (VWF) secretion and its cleaving protease (ADAMTS-13) has been correlated with cancer metastasis. The aim of this study was to explore the prognostic significance of the VWF/ADAMTS-13 ratio in advanced non-small-cell lung cancer (NSCLC).

METHODS

Pre-treatment sera/plasma levels of VWF, ADAMTS-13, VWF/ADAMTS-13 ratio, factor (F) VIII, and other clinical/laboratory parameters were measured in 119 patients with advanced NSCLC and 102 healthy controls. All patients were followed up to determine the predictive value of these parameters for prognosis of advanced NSCLC.

RESULTS

Elevated VWF, VWF/ADAMTS-13 ratio, and reduced ADAMTS-13 were significantly correlated with the stage and grade of advanced NSCLC and the final status of disease (P<.05). VWF levels and the VWF/ADAMTS-13 ratio were also associated with response to chemotherapy (P<.05). Multivariate analysis identified the VWF/ADAMTS-13 ratio and D-dimer as significant independent predictors of patient mortality. The area under the curve showed that the VWF/ADAMTS-13 ratio was more useful than VWF, ADAMTS-13, and D-dimer to predict mortality. Kaplan-Meier analysis showed that a low VWF/ADAMTS-13 ratio was significantly predictive of improved survival (P=.004).

CONCLUSION

These results suggest that the imbalance between VWF secretion and ADAMTS-13 may play a critical role in the hypercoagulability state in advanced NSCLC. Moreover, elevation of the plasma VWF/ADAMTS-13 ratio may serve as an independent predictive factor for mortality in patients with advanced NSCLC.

Platelet GPIIb supports initial pulmonary retention but inhibits subsequent proliferation of melanoma cells during hematogenic metastasis

Platelets modulate the process of cancer metastasis. However, current knowledge on the direct interaction of platelets and tumor cells is mostly based on findings obtained in vitro. We addressed the role of the platelet fibrinogen receptor glycoprotein IIb (integrin αIIb) for experimental melanoma metastasis in vivo. Highly metastatic B16-D5 melanoma cells were injected intravenously into GPIIb-deficient (GPIIb^-/-) or wildtype (WT) mice. Acute accumulation of tumor cells in the pulmonary vasculature was assessed in real-time by confocal videofluorescence microscopy. Arrest of tumor cells was dramatically reduced in GPIIb^-/- mice as compared to WT. Importantly, we found that mainly multicellular aggregates accumulated in the pulmonary circulation of WT, instead B16-D5 aggregates were significantly smaller in GPIIb^-/- mice. While pulmonary arrest of melanoma was clearly dependent on GPIIb in this early phase of metastasis, we also addressed tumor progression 10 days after injection. Inversely, and unexpectedly, we found that melanoma metastasis was now increased in GPIIb^-/- mice. In contrast, GPIIb did not regulate local melanoma proliferation in a subcutaneous tumor model. Our data suggest that the platelet fibrinogen receptor has a differential role in the modulation of hematogenic melanoma metastasis. While platelets clearly support early steps in pulmonary metastasis via GPIIb-dependent formation of platelet-tumor-aggregates, at a later stage its absence is associated with an accelerated development of melanoma metastases.

Thrombin-unique coagulation system protein with multifaceted impacts on cancer and metastasis

The association between blood coagulation and cancer development is well recognized. Thrombin, the pleiotropic enzyme best known for its contribution to fibrin formation and platelet aggregation during vascular hemostasis, may also trigger cellular events through protease-activated receptors, PAR-1 and PAR-4, leading to cancer progression. Our pioneering findings provided evidence that thrombin contributes to cancer metastasis by increasing adhesive potential of malignant cells. However, there is evidence that thrombin regulates every step of cancer dissemination: (1) cancer cell invasion, detachment from primary tumor, migration; (2) entering the blood vessel; (3) surviving in vasculature; (4) extravasation; (5) implantation in host organs. Recent studies have provided new molecular data about thrombin generation in cancer patients and the mechanisms by which thrombin contributes to transendothelial migration, platelet/tumor cell interactions, angiogenesis, and other processes. Though a great deal is known regarding the role of thrombin in cancer dissemination, there are new data for multiple thrombin-mediated events that justify devoting focus to this topic with a comprehensive approach.

Activated tumor cell integrin αvβ3 cooperates with platelets to promote extravasation and metastasis from the blood stream

Metastasis is the main cause of death in cancer patients, and understanding mechanisms that control tumor cell dissemination may lead to improved therapy. Tumor cell adhesion receptors contribute to cancer spreading. We noted earlier that tumor cells can expressing the adhesion receptor integrin αvβ3 in distinct states of activation, and found that cells which metastasize from the blood stream express it in a constitutively high affinity form. Here, we analyzed steps of the metastatic cascade in vivo and asked, when and how the affinity state of integrin αvβ3 confers a critical advantage to cancer spreading. Following tumor cells by real time PCR, non-invasive bioluminescence imaging, intravital microscopy and histology allowed us to identify tumor cell extravasation from the blood stream as a rate-limiting step supported by high affinity αvβ3. Successful transendothelial migration depended on cooperation between tumor cells and platelets involving the high affinity tumor cell integrin and release of platelet granules. Thus, this study identifies the high affinity conformer of integrin αvβ3 and its interaction with platelets as critical for early steps during hematogenous metastasis and target for prevention of metastatic disease.

Development of a selective cell capture and release assay: impact of clustered RGD ligands

Clustered RGD compounds improve the selective capture and release of cells that express α_vβ₃ integrin.

ADAM9 silencing inhibits breast tumor cells transmigration through blood and lymphatic endothelial cells

ADAMs are transmembrane multifunctional proteins that contain disintegrin and metalloprotease domains. ADAMs act in a diverse set of biological processes, including fertilization, inflammatory responses, myogenesis, cell migration, cell proliferation and ectodomain cleavage of membrane proteins. These proteins also have additional functions in pathological processes as cancer and metastasis development. ADAM9 is a member of ADAM protein family that is overexpressed in several types of human carcinomas. The aim of this study was to investigate the role of ADAM9 in hematogenous and lymphatic tumor cell dissemination assisting the development of new therapeutic tools. The role of ADAM9 in the interaction of breast tumor cells (MDA-MB-231) and endothelial cells was studied through RNA silencing. ADAM9 silencing in MDA-MB-231 cells had no influence in expression of several genes related to the metastatic process such as ADAM10, ADAM12, ADAM17, cMYC, MMP9, VEGF-A, VEGF-C, osteopontin and collagen XVII. However, there was a minor decrease in ADAM15 expression but an increase in that of MMP2. Moreover, ADAM9 silencing had no effect in the adhesion of MDA-MB-231 cells to vascular (HMEC-1 and HUVEC) and lymphatic cells (HMVEC-dLyNeo) under flow condition. Nevertheless, siADAM9 in MDA-MB-231 decreased transendothelial cell migration in vitro through HUVEC, HMEC-1 and HMVEC-dLyNeo (50%, 40% and 32% respectively). These results suggest a role for ADAM9 on the extravasation step of the metastatic cascade through both blood and lymph vessels.

Radiolabeled cyclic RGD peptides as radiotracers for tumor imaging

The integrin family comprises 24 transmembrane receptors, each a heterodimeric combination of one of 18α and one of 8β subunits. Their main function is to integrate the cell adhesion and interaction with the extracellular microenvironment with the intracellular signaling and cytoskeletal rearrangement through transmitting signals across the cell membrane upon ligand binding. Integrin α_vβ₃ is a receptor for the extracellular matrix proteins containing arginine–glycine–aspartic (RGD) tripeptide sequence. The α_vβ₃ is generally expressed in low levels on the epithelial cells and mature endothelial cells, but it is highly expressed in many solid tumors. The α_vβ₃ levels correlate well with the potential for tumor metastasis and aggressiveness, which make it an important biological target for development of antiangiogenic drugs, and molecular imaging probes for early tumor diagnosis. Over the last decade, many radiolabeled cyclic RGD peptides have been evaluated as radiotracers for imaging tumors by SPECT or PET. Even though they are called “α_vβ₃-targeted” radiotracers, the radiolabeled cyclic RGD peptides are also able to bind α_vβ₅, α₅β₁, α₆β₄, α₄β₁, and α_vβ₆ integrins, which may help enhance their tumor uptake due to the “increased receptor population.” This article will use the multimeric cyclic RGD peptides as examples to illustrate basic principles for development of integrin-targeted radiotracers and focus on different approaches to maximize their tumor uptake and T/B ratios. It will also discuss important assays for pre-clinical evaluations of the integrin-targeted radiotracers, and their potential applications as molecular imaging tools for noninvasive monitoring of tumor metastasis and early detection of the tumor response to antiangiogenic therapy.

Nanoparticles coated with the tumor-penetrating peptide iRGD reduce experimental breast cancer metastasis in the brain

Metastasis is the main killer in cancer; consequently, there is great interest in novel approaches to prevent and treat metastatic disease. Brain metastases are particularly deadly, as the protection of the blood-brain barrier obstructs the passage of common anticancer drugs. This study used magnetic resonance imaging (MRI) to investigate the therapeutic effects of nanoparticles coated with a tumor-penetrating peptide (iRGD) against a preclinical model of breast cancer brain metastasis. Single doses of iRGD nanoparticle were administered intravenously, and the effect on tumor growth was observed over time. iRGD nanoparticles, when applied in the early stages of metastasis development, strongly inhibited tumor progression. Overall, this study demonstrated for the first time that a single dose of iRGD nanoparticle can have a significant effect on metastatic tumor progression and nonproliferative cancer cell retention when applied early in course of tumor development. These data suggest that iRGD nanoparticles may be useful in preventatively reducing metastasis after a cancer diagnosis has been established.

KEY MESSAGES

bSSFP MRI can be used to track nonproliferative iron-labeled cells and tumor development over time. iRGD-NW, when applied early, has a significant effect on metastatic tumor progression. Retained signal voids represent a subpopulation of nonproliferating tumor cells. Reduced cell retention and tumor burden show a role for iRGD-NW in metastasis prevention. iRGD target is universally expressed; thus, iRGD-NW should be clinically translatable.

Platelets in cancer. From basic research to therapeutic implications

Platelets are well-known for their major role in primary hemostasis and thrombosis. Cancer patients frequently manifest thrombotic events and present abnormalities in blood coagulation which appear to be linked to altered platelet function and turnover. Moreover, numerous studies indicate an intimate cross-talk between platelets and tumor growth, angiogenesis and metastatic dissemination. Finally, several experimental data and clinical trials suggest possible benefits of anti-platelet drugs on some cancers. Here, we will review the current state of basic biological research regarding the role of platelets in cancer progression. We also critically review the possible clinical applicability of some anti-platelet therapies to limit tumor growth and prevent metastatic dissemination.

Radiolabeled Cyclic RGD Peptide Bioconjugates as Radiotracers Targeting Multiple Integrins

Angiogenesis is a requirement for tumor growth and metastasis. The angiogenic process depends on vascular endothelial cell migration and invasion, and is regulated by various cell adhesion receptors. Integrins are such a family of receptors that facilitate the cellular adhesion to and migration on extracellular matrix proteins in the intercellular spaces and basement membranes. Among 24 members of the integrin family, αvβ3 is studied most extensively for its role in tumor angiogenesis and metastasis. The αvβ3 is expressed at relatively low levels on epithelial cells and mature endothelial cells, but it is highly expressed on the activated endothelial cells of tumor neovasculature and some tumor cells. This restricted expression makes αvβ3 an excellent target to develop antiangiogenic drugs and diagnostic molecular imaging probes. Since αvβ3 is a receptor for extracellular matrix proteins with one or more RGD tripeptide sequence, many radiolabeled cyclic RGD peptides have been evaluated as "αvβ3-targeted" radiotracers for tumor imaging over the past decade. This article will use the dimeric and tetrameric cyclic RGD peptides developed in our laboratories as examples to illustrate basic principles for development of αvβ3-targeted radiotracers. It will focus on different approaches to maximize the radiotracer tumor uptake and tumor/background ratios. This article will also discuss some important assays for preclinical evaluations of integrin-targeted radiotracers. In general, multimerization of cyclic RGD peptides increases their integrin binding affinity and the tumor uptake and retention times of their radiotracers. Regardless of their multiplicity, the capability of cyclic RGD peptides to bind other integrins (namely, αvβ5, α5β1, α6β4, α4β1, and αvβ6) is expected to enhance the radiotracer tumor uptake due to the increased integrin population. The results from preclinical and clinical studies clearly show that radiolabeled cyclic RGD peptides (such as (99m)Tc-3P-RGD2, (18)F-Alfatide-I, and (18)F-Alfatide-II) are useful as the molecular imaging probes for early cancer detection and noninvasive monitoring of the tumor response to antiangiogenic therapy.

Disintegrins from snake venoms and their applications in cancer research and therapy

Integrins regulate diverse functions in cancer pathology and in tumor cell development and contribute to important processes such as cell shape, survival, proliferation, transcription, angiogenesis, migration, and invasion. A number of snake venom proteins have the ability to interact with integrins. Among these are the disintegrins, a family of small, non-enzymatic, and cysteine-rich proteins found in the venom of numerous snake families. The venom proteins may have a potential role in terms of novel therapeutic leads for cancer treatment. Disintegrin can target specific integrins and as such it is conceivable that they could interfere in important processes involved in carcinogenesis, tumor growth, invasion and migration. Herein we present a survey of studies involving the use of snake venom disintegrins for cancer detection and treatment. The aim of this review is to highlight the relationship of integrins with cancer and to present examples as to how certain disintegrins can detect and affect biological processes related to cancer. This in turn will illustrate the great potential of these molecules for cancer research. Furthermore, we also outline several new approaches being created to address problems commonly associated with the clinical application of peptide-based drugs such as instability, immunogenicity, and availability.

FITC-conjugated cyclic RGD peptides as fluorescent probes for staining integrin αvβ3/αvβ5 in tumor tissues

This study sought to evaluate FITC-conjugated cyclic RGD peptides (FITC-RGD₂, FITC-3P-RGD₂, and FITC-Galacto-RGD₂) as fluorescent probes for in vitro assays of integrin α_vβ₃/α_vβ₅ expression in tumor tissues. FITC-RGD₂, FITC-3P-RGD₂, and FITC-Galacto-RGD₂ were prepared, and their integrin α_vβ₃/α_vβ₅ binding affinity was determined using the displacement assay against ¹²⁵I-echistatin bound to U87MG glioma cells. IC₅₀ values of FITC-Galacto-RGD₂, FITC-3P-RGD₂, and FITC-RGD₂ were calculated to be 28 ± 8, 32 ± 7, and 89 ± 17 nM, respectively. The integrin α_vβ₃/α_vβ₅ binding affinity followed a general trend: FITC-Galacto-RGD₂ ∼ FITC-3P-RGD₂ > FITC-RGD₂. The xenografted tumor-bearing models were established by subcutaneous injection of 5 × 10⁶ tumor cells into shoulder flank (U87MG, A549, HT29, and PC-3) or mammary fat pad (MDA-MB-435) of each athymic nude mouse. Three to six weeks after inoculation, the tumor size was 0.1–0.3 g. Tumors were harvested for integrin α_vβ₃/α_vβ₅ staining, as well as hematoxylin and eosin (H&E) staining. Six human carcinoma tissues (colon cancer, pancreatic cancer, lung adenocarcinoma, squamous cell lung cancer, gastric cancer, and esophageal cancer) were obtained from recently diagnosed cancer patients. Human carcinoma slides were deparaffinized in xylene, rehydrated with ethanol, and then used for integrin α_vβ₃/α_vβ₅ staining, as well as H&E staining. It was found that the tumor staining procedures with FITC-conjugated cyclic RGD peptides were much simpler than those with the fluorescence-labeled integrin α_vβ₃ antibodies. Since FITC-RGD₂, FITC-3P-RGD₂, and FITC-Galacto-RGD₂ were able to co-localize with the fluorescence-labeled integrin β₃ antibody, their tumor localization and tumor cell binding are integrin α_vβ₃-specific. Quantification of the fluorescent intensity in five xenografted tumors (U87MG, MDA-MB-435, A549, HT29, and PC-3) and six human carcinoma tissues revealed an excellent linear relationship between the relative integrin α_vβ₃/α_vβ₅ expression levels determined with FITC-Galacto-RGD₂ and those obtained with the fluorescence-labeled anti-human integrin β₃ antibody. There was also an excellent linear relationship between the tumor uptake (%ID/g) of ^99mTc-3P-RGD₂ (an integrin α_vβ₃/α_vβ₅-targeted radiotracer) and the relative integrin α_vβ₃/α_vβ₅ expression levels from the quantification of fluorescent intensity in the tumor tissues stained with FITC-Galacto-RGD₂. These results suggest that FITC-conjugated cyclic RGD peptides might be useful to correlate the in vitro findings with the in vivo imaging data from an integrin α_vβ₃/α_vβ₅-targeted radiotracer. The results from this study clearly showed that the FITC-conjugated cyclic RGD peptides (particularly FITC-3P-RGD₂ and FITC-Galacto-RGD₂) are useful fluorescent probes for assaying relative integrin α_vβ₃/α_vβ₅ expression levels in tumor tissues.

Nicotinamide phosphoribosyltransferase can affect metastatic activity and cell adhesive functions by regulating integrins in breast cancer

NAD(+) metabolism is an essential regulator of cellular redox reactions, energy pathways, and a substrate provider for NAD(+) consuming enzymes. We recently demonstrated that enhancement of NAD(+)/NADH levels in breast cancer cells with impaired mitochondrial NADH dehydrogenase activity, through augmentation of complex I or by supplementing tumor cell nutrients with NAD(+) precursors, inhibits tumorigenicity and metastasis. To more fully understand how aberrantly low NAD(+) levels promote tumor cell dissemination, we here asked whether inhibition of NAD(+) salvage pathway activity by reduction in nicotinamide phosphoribosyltransferase (NAMPT) expression can impact metastasis and tumor cell adhesive functions. We show that knockdown of NAMPT, the enzyme catalyzing the rate-limiting step of the NAD(+) salvage pathway, enhances metastatic aggressiveness in human breast cancer cells and involves modulation of integrin expression and function. Reduction in NAMPT expression is associated with upregulation of select adhesion receptors, particularly αvβ3 and β1 integrins, and results in increased breast cancer cell attachment to extracellular matrix proteins, a key function in tumor cell dissemination. Interestingly, NAMPT downregulation prompts expression of integrin αvβ3 in a high affinity conformation, known to promote tumor cell adhesive interactions during hematogenous metastasis. NAMPT has been selected as a therapeutic target for cancer therapy based on the essential functions of this enzyme in NAD(+) metabolism, cellular redox, DNA repair and energy pathways. Notably, our results indicate that incomplete inhibition of NAMPT, which impedes NAD(+) metabolism but does not kill a tumor cell can alter its phenotype to be more aggressive and metastatic. This phenomenon could promote cancer recurrence, even if NAMPT inhibition initially reduces tumor growth.

Integrin αvβ3 and fibronectin upregulate Slug in cancer cells to promote clot invasion and metastasis

The blood clotting cascade is selectively involved in lung metastasis, but the reason for this selectivity is unclear. Here, we show that tumor cells that metastasize predominantly to the lung, such as renal cell carcinoma (RCC) and soft tissue sarcoma (STS), have an inherent capacity to generate extensive invadopodia when embedded in a blood clot. Compared with other metastatic cancer cells tested, RCC and STS cells exhibited increased levels of expression of fibronectin and an activated form of the integrin αvβ3, which coordinately supported the generation of an elaborate fibronectin matrix and actin stress fibers in fibrin-embedded tumor cells. Together, fibronectin and αvβ3 induced upregulation of the transcription factor Slug, which mediates epithelial-mesenchymal transition as well as fibrin invasion and lung metastasis. This mechanism is clinically significant, because primary cancer cells from patients with metastatic RCC strongly invaded fibrin and this correlated with fibronectin matrix formation and Slug expression. In contrast, tumor cells from patients with localized RCC were largely noninvasive. Together, our findings establish that activated integrin αvβ3 and fibronectin promote lung metastasis by upregulating Slug, defining a mechanism through which cancer cells can colonize blood clots in the lung vasculature.

Plasma Fibronectin Promotes Tumor Cell Survival and Invasion through Regulation of Tie2

Our previous research has shown that plasma fibronectin promotes lung metastasis by facilitating tumor cell invasion in clotted plasma. To evaluate the role of clotted plasma for tumor cell survival, we treated B16F1 cells embedded in a 3-dimensional matrix of fibrin with tumor necrosis factor α (TNFα), a cytokine with anti-tumor activity. Under these conditions, TNFα caused significant cytotoxicity, which was prevented when we added plasma fibronectin to the fibrin clot. Fibronectin-mediated TNFα resistance was dependent on PI3-kinase, which also mediated the pro-adhesive and pro-invasive effects of plasma fibronectin on tumor cells. To further investigate the role of plasma fibronectin in tumor cell signaling, we performed a gene array that showed specific upregulation of Tie2 in B16F1 cells embedded in fibrin-fibronectin compared to fibrin. Importantly, inhibition of Tie2 resulted in decreased tumor cell invasion, reduced colony formation and increased tumor cell death in response to TNFα. Together, our findings indicate that plasma fibronectin induces tumor cell invasion and protects tumor cells from the cytotoxic effects of inflammatory mediators through up-regulation of Tie2.

Effect of ADAM28 on carcinoma cell metastasis by cleavage of von Willebrand factor

BACKGROUND

A disintegrin and metalloproteinase 28 (ADAM28) is implicated in tumor growth and metastasis in human breast and non-small cell lung carcinomas. We explored the mechanism of ADAM28-mediated metastasis by searching for new substrates of ADAM28.

METHODS

We used a yeast two-hybrid system to screen the human lung cDNA library for ADAM28-binding proteins and identified von Willebrand factor (VWF) as a potential candidate. Binding was confirmed using yeast two-hybrid and protein binding assays, and ADAM28-mediated cleavage of VWF was analyzed by immunoblotting. Exogenous VWF-induced apoptosis in vitro was examined in human lung carcinoma (PC-9 and Calu-3), breast carcinoma (MDA-MB231 and MCF-7), renal cell carcinoma (Caki-2 and 769P), and hepatocellular carcinoma (HepG2) cells, and expression of ADAM28 was assessed by reverse transcription-polymerase chain reaction and immunoblotting. Effect on lung metastasis of PC-9 and MDA-MB231 cells was assessed by knockdown of ADAM28 expression using short hairpin RNAs (ADAM28-shRNA) and small interfering RNAs (ADAM28-siRNA), and inhibition of activity using neutralizing anti-ADAM28 antibody, in a mouse xenograft model by in vivo imaging (n = 9 mice per group). All statistical tests were two-sided.

RESULTS

ADAM28 could bind to and cleave native VWF. Cells with very low ADAM28 expression (MCF-7, 769P, and HepG2) were susceptible to VWF-induced apoptosis, whereas cells with high expression (PC-9, Calu-3, MDA-MB231, and Caki-2) were resistant. Knockdown of ADAM28 expression in PC-9 and MDA-MB231 cells by shRNA showed increased carcinoma cell apoptosis mainly in lung blood vessels and statistically significantly decreased lung metastasis at week 3 after injection (PC-9-control [n = 9 mice] vs PC-9-ADAM28-shRNA [n = 9 mice]: mean count = 198 × 10(6) vs 37 × 10(6) photons/s, difference = 161 × 10(6) photons/s, 95% confidence interval = 134 × 10(6) to 188 × 10(6) photons/s, P < .001). Similar inhibition of lung metastasis was observed with ADAM28-siRNA and anti-ADAM28 antibody.

CONCLUSION

ADAM28 cleaves and inactivates proapoptotic VWF in carcinoma cells and enhances lung metastasis probably by promoting carcinoma cell survival within the blood vessels.

Fibrin serves as a divalent ligand that regulates neutrophil-mediated melanoma cells adhesion to endothelium under shear conditions

Elevated soluble fibrin (sFn) levels are characteristic of melanoma hematogeneous dissemination, where tumor cells interact intimately with host cells. Melanoma adhesion to the blood vessel wall is promoted by immune cell arrests and tumor-derived thrombin, a serine protease that converts soluble fibrinogen (sFg) into sFn. However, the molecular requirement for sFn-mediated melanoma-polymorphonuclear neutrophils (PMNs) and melanoma-endothelial interactions under physiological flow conditions remain elusive. To understand this process, we studied the relative binding capacities of sFg and sFn receptors e.g., α(v)β(3) integrin and intercellular adhesion molecule-1 (ICAM-1) expressed on melanoma cells, ICAM-1 on endothelial cells (EC), and CD11b/CD18 (Mac-1) on PMNs. Using a parallel-plate flow chamber, highly metastatic melanoma cells (1205Lu and A375M) and human PMNs were perfused over an EC monolayer expressing ICAM-1 in the presence of sFg or sFn. It was found that both the frequency and lifetime of direct melanoma adhesion or PMN-facilitated melanoma adhesion to the EC in a shear flow were increased by the presence of sFn in a concentration-dependent manner. In addition, sFn fragment D and plasmin-treated sFn failed to increase melanoma adhesion, implying that sFn-bridged cell adhesion requires dimer-mediated receptor-receptor cross-linking. Finally, analysis of the respective kinetics of sFn binding to Mac-1, ICAM-1, and α(v)β(3) by single bond cell tethering assays suggested that ICAM-1 and α(v)β(3) are responsible for initial capture and firm adhesion of melanoma cells. These results provide evidence that sFn enhances melanoma adhesion directly to ICAM-1 on the EC, while prolonged shear-resistant melanoma adhesion requires interactions with PMNs.

Triggering of Toll-like receptor 4 on metastatic breast cancer cells promotes αvβ3-mediated adhesion and invasive migration

Triggering of Toll-like receptor 4 (TLR4) on tumor cells has been found to promote tumor progression by promoting tumor cell proliferation and survival. So far, however, the effect of TLR4 signaling on tumor metastasis has not been well elucidated. Here, we report that triggering of TLR4 on metastatic breast cancer cells could reciprocally regulate the expression of αvβ3 and the expressions of TPM1 and maspin, and promote αvβ3-mediated adhesion and invasive migration of the cells. In metastatic breast cancer cells, TLR4 signaling increased the expression of integrin αvβ3 by activating NF-κB, resulting in the increased adhesion capacity of tumor cells to the ligand for αvβ3, and the increased polymerization of actin and production of MMP-9 in tumor cells in response to ECM. HoxD3 was required for the up-regulation of αv and β3 expressions by NF-κB. Moreover, TLR4 signaling increased the expression of miR-21 in breast cancer cells by activating NF-κB. Accordingly, the expressions of TPM1 and maspin were decreased at protein level, whereas the transcription activity of these genes was not influenced. Consistent with the promoting effect on αvβ3-mediated adhesion and invasive migration, TLR4 signaling promoted the arrest of metastatic breast cancer cells in circulation and following invasion. The effect of TLR4 signaling could be abrogated by inhibiting NF-κB. These findings suggest that metastatic breast cancer cells could acquire higher metastatic potential due to triggering of TLR4 and activation of NF-κB in the cells, and that both TLR4 and NF-κB could be therapeutic targets for preventing metastasis of breast cancer cells.

Sequential binding of αVβ3 and ICAM-1 determines fibrin-mediated melanoma capture and stable adhesion to CD11b/CD18 on neutrophils

Fibrin (Fn) deposition defines several type 1 immune responses, including delayed-type hypersensitivity and autoimmunity in which polymorphonuclear leukocytes (PMNs) are involved. Fn monomer and fibrinogen are multivalent ligands for a variety of cell receptors during cell adhesion. These cell receptors provide critical linkage among thrombosis, inflammation, and cancer metastasis under venous flow conditions. However, the mechanisms of Fn-mediated interactions among immune cells and circulating tumor cells remain elusive. By using a cone-plate viscometer shear assay and dual-color flow cytometry, we demonstrated that soluble fibrinogen and Fn had different abilities to enhance heterotypic aggregation between PMNs and Lu1205 melanoma cells in a shear flow, regulated by thrombin levels. In addition, the involvement of integrin α(v)β(3), ICAM-1, and CD11b/CD18 (Mac-1) in fibrin(ogen)-mediated melanoma-PMN aggregations was explored. Kinetic studies provided evidence that ICAM-1 mediated initial capture of melanoma cells by PMNs, whereas α(v)β(3) played a role in sustained adhesion of the two cell types at a shear rate of 62.5 s(-1). Quantitative analysis of the melanoma-PMN interactions conducted by a parallel-plate flow chamber assay further revealed that at a shear rate of 20 s(-1), α(v)β(3) had enough contact time to form bonds with Mac-1 via Fn, which could not otherwise occur at a shear rate higher than 62.5 s(-1). Our studies have captured a novel finding that leukocytes could be recruited to tumor cells via thrombin-mediated Fn formation within a tumor microenvironment, and α(v)β(3) and ICAM-1 may participate in multistep fibrin(ogen)-mediated melanoma cell adhesion within the circulation.

Plasma fibronectin promotes lung metastasis by contributions to fibrin clots and tumor cell invasion

The attachment of circulating tumor cells to the blood vessels of distant organs is an important step in metastasis. We show here that experimental lung metastasis by two cell lines, B16F1 melanoma and 3LL lung carcinoma, is greatly reduced in transgenic mice that lack plasma fibronectin. This multifunctional adhesive glycoprotein becomes cross-linked to fibrin during clotting. Here, we report that eliminating plasma fibronectin from the blood circulation reverses the prometastatic effects of blood clotting and tumor cell integrin alphavbeta3. In vitro studies showed that fibrin-fibronectin complexes, but not purified fibrin, supported tumor cell attachment and invasion. These functions correlate with the ability of fibrin-fibronectin complexes to induce the activation of integrin alphavbeta3. Our findings reveal an important contribution of plasma fibronectin in lung metastasis. Furthermore, they suggest that the previously noted effects of blood clotting on lung metastasis might be mediated in part by a fibronectin-alphavbeta3 integrin axis, in which plasma fibronectin has to be incorporated into the blood clot.

Acoustic driven flow and lattice Boltzmann simulations to study cell adhesion in biofunctionalized mu-fluidic channels with complex geometry

Accurately mimicking the complexity of microvascular systems calls for a technology which can accommodate particularly small sample volumes while retaining a large degree of freedom in channel geometry and keeping the price considerably low to allow for high throughput experiments. Here, we demonstrate that the use of surface acoustic wave driven microfluidics systems successfully allows the study of the interrelation between melanoma cell adhesion, the matrix protein collagen type I, the blood clotting factor von Willebrand factor (vWF), and microfluidic channel geometry. The versatility of the tool presented enables us to examine cell adhesion under flow in straight and bifurcated microfluidic channels in the presence of different protein coatings. We show that the addition of vWF tremendously increases (up to tenfold) the adhesion of melanoma cells even under fairly low shear flow conditions. This effect is altered in the presence of bifurcated channels demonstrating the importance of an elaborate hydrodynamic analysis to differentiate between physical and biological effects. Therefore, computer simulations have been performed along with the experiments to reveal the entire flow profile in the channel. We conclude that a combination of theory and experiment will lead to a consistent explanation of cell adhesion, and will optimize the potential of microfluidic experiments to further unravel the relation between blood clotting factors, cell adhesion molecules, cancer cell spreading, and the hydrodynamic conditions in our microcirculatory system.

The roles of platelet GPIIb/IIIa and alphavbeta3 integrins during HeLa cells adhesion, migration, and invasion to monolayer endothelium under static and dynamic shear flow

During their passage through the circulatory system, tumor cells undergo extensive interactions with various host cells including endothelial cells and platelets. Mechanisms mediating tumor cell adhesion, migration, and metastasis to vessel wall under flow condition are largely unknown. The aim of this study was to investigate the potential roles of GPIIb/IIIa and αvβ3 integrins underlying the HeLa-endothelium interaction in static and dynamic flow conditions. HeLa cell migration and invasion were studied by using Millicell cell culture insert system. The numbers of transmigrated or invaded HeLa cells significantly increased by thrombin-activated platelets and reduced by eptifibatide, a platelet inhibitor. Meanwhile, RGDWE peptides, a specific inhibitor of αvβ3 integrin, also inhibited HeLa cell transmigration. Interestingly, the presence of endothelial cells had significant effect on HeLa cell migration regardless of static or cocultured flow condition. The adhesion capability of HeLa cells to endothelial monolayer was also significantly affected by GPIIb/IIIa and αvβ3 integrins. The arrested HeLa cells increased nearly 5-fold in the presence of thrombin-activated platelets at shear stress condition (1.84 dyn/cm² exposure for 1 hour) than the control (static). Our findings showed that GPIIb/IIIa and αvβ3 integrins are important mediators in the pathology of cervical cancer and provide a molecular basis for the future therapy, and the efficient antitumor benefit should target multiple receptors on tumor cells and platelets.

Prion protein ablation increases cellular aggregation and embolization contributing to mechanisms of metastasis

Cellular Prion Protein (PrP(C)) is a cell surface protein highly expressed in the nervous system, and to a lesser extent in other tissues. PrP(C) binds to the extracellular matrix laminin and vitronectin, to mediate cell adhesion and differentiation. Herein, we investigate how PrP(C) expression modulates the aggressiveness of transformed cells. Mesenchymal embryonic cells (MEC) from wild-type (Prnp(+/+)) and PrP(C)-null (Prnp(0/0)) mice were immortalized and transformed by co-expression of ras and myc. These cells presented similar growth rates and tumor formation in vivo. When injected in the tail vein, Prnp(0/0)ras/myc cells exhibited increased lung colonization compared with Prnp(+/+)ras/myc cells. Additionally, Prnp(0/0)ras/myc cells form more aggregates with blood components than Prnp(+/+)ras/myc cells, facilitating the arrest of Prnp(0/0)ras/myc cells in the lung vasculature. Integrin alpha(v)beta(3) is more expressed and activated in MEC and in transformed Prnp(0/0) cells than in the respective Prnp(+/+) cells. The blocking of integrin alpha(v)beta(3) by RGD peptide reduces lung colonization in transformed Prnp(0/0) cells to similar levels of those presented by transformed Prnp(+/+) cells. Our data indicate that PrP(C) negatively modulates the expression and activation of integrin alpha(v)beta(3) resulting in a more aggressive phenotype. These results indicate that PrP(C) may have main implications in modulating metastasis formation.

Inhibition of platelets and tumor cell adhesion by the disintegrin domain of human ADAM9 to collagen I under dynamic flow conditions

This work aimed to investigate the role of the disintegrin domain of the human ADAM9 (ADAM9D) on the adhesion of breast tumor cells and platelets to collagen I, in a dynamic flow assay to simulate in vivo shear conditions. Recombinant ADAM9D was able to support tumor cell adhesion through binding to the beta1 integrin subunit and also to inhibit the invasion through matrigel in vitro. In a dynamic flow assay ADAM9D inhibited about 75% and 65% of MDA-MB-231 tumor cells and platelet adhesion to collagen I, respectively. In addition, it was demonstrated that alphaVbeta3 integrin is new interacting partner for ADAM9D. In conclusion, these results suggest a role for the disintegrin domain of ADAM9 in the metastatic process. Also, ADAM9D may be a tool for investigating the role of ADAMs in metastasis and cancer progression and for the design of selective inhibitors against the adhesion and extravasation of cancer cells.

Integrin alpha V polymorphisms and haplotypes in a Korean population are associated with susceptibility to chronic hepatitis and hepatocellular carcinoma

BACKGROUND/AIMS

Integrins are cell surface receptors for extracellular matrix (ECM) proteins that initiate signalling pathways that modulate proliferation, survival, invasion or metastasis. Consequently, integrins are potential targets for the treatment of cancer. In this study, we investigated whether single nucleotide polymorphisms (SNPs) in integrin alpha(V) (ITGAV) in a Korean population were associated with chronic hepatitis B virus (HBV) infection and HBV-infected hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

Thirteen ITGAV SNPs in 111 cases of chronic HBV infection, 86 cases of HBV-infected HCC and 107 cases of acute self-limited HBV infection were genotyped using Illumina's Sentrix array matrix (SAM) chip.

RESULTS

The ITGAV intron SNPs rs9333289 and rs11685758, the 3'-untranslated region SNP rs1839123 and haplotype 3 (T-T-A) were associated with enhanced susceptibility to HBV-infected HCC (OR=1.75-2.42; P=0.02-0.05), while the intron SNP rs2290083 was associated with both chronic infection and HBV-infected HCC (OR=1.73-2.01; P=0.01-0.04). In addition, both rs2290083 and ht1 (C-C-G) were associated with the age at which chronic infection occurred, as determined by Cox relative hazard analysis (RH=1.39-1.62, P=0.04-0.01)

CONCLUSION

ITGAV SNPs and haplotypes may be genetic factors that increase the susceptibility of Koreans to chronic HBV infection and HBV-infected HCC.

Mannose 6-phosphate/insulin-like growth factor 2 receptor limits cell invasion by controlling alphaVbeta3 integrin expression and proteolytic processing of urokinase-type plasminogen activator receptor

The multifunctional mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) is considered a tumor suppressor. We report here that RNA interference with M6P/IGF2R expression in urokinase-type plasminogen activator (uPA)/urokinase-type plasminogen activator receptor (uPAR) expressing human cancer and endothelial cells resulted in increased pericellular plasminogen activation, cell adhesion, and higher invasive potential through matrigel. M6P/IGF2R silencing led also to the cell surface accumulation of urokinase and plasminogen and enhanced expression of alphaV integrins. Genetic rescue experiments and inhibitor studies revealed that the enhanced plasminogen activation was due to a direct effect of M6P/IGF2R on uPAR, whereas increased cell adhesion to vitronectin was dependent on alphaV integrin expression and not uPAR. Increased cell invasion of M6P/IGF2R knockdown cells was rescued by cosilencing both uPAR and alphaV integrin. Furthermore, we found that M6P/IGF2R expression accelerates the cleavage of uPAR. M6P/IGF2R silencing resulted in an increased ratio of full-length uPAR to the truncated D2D3 fragment, incapable of binding most uPAR ligands. We conclude that M6P/IGF2R controls cell invasion by regulating alphaV integrin expression and by accelerating uPAR cleavage, leading to the loss of the urokinase/vitronectin/integrin-binding site on uPAR.

Melanoma and the tumor microenvironment

Melanoma arises through the accrual of mutations in genes critical for proliferation and survival. Although melanoma had been traditionally conceptualized as a cell-autonomous event, increasing evidence supports the notion that these tumors are not isolated entities but rather depend, interact with, and react to the adjacent microenvironment. Melanoma is composed of not only the malignant cells but also the supporting stroma, which includes fibroblasts, endothelial cells, immune cells, soluble molecules, and the extracellular matrix (ECM). Tumor cells actively interact with the microenvironment in a bidirectional manner through molecular signals that modulate the malignant phenotype. This article briefly reviews the molecular basis of melanomagenesis as well as the interplay of melanoma with other cells of the tumor microenvironment and components of the ECM. It also discusses the influence of the microenvironment on therapeutic targeting of melanoma, highlighting recent studies that propose novel strategies to target tumor-microenvironment interactions.

Integrin alpha(v)beta(3) on human endothelial cells binds von Willebrand factor strings under fluid shear stress

Acutely secreted von Willebrand factor (VWF) multimers adhere to endothelial cells, support platelet adhesion, and may induce microvascular thrombosis. Immunofluorescence microscopy of live human umbilical vein endothelial cells showed that VWF multimers rapidly formed strings several hundred micrometers long on the cell surface after stimulation with histamine. Unexpectedly, only a subset of VWF strings supported platelet binding, which depended on platelet glycoprotein Ib. Electron microscopy showed that VWF strings often consisted of bundles and networks of VWF multimers, and each string was tethered to the cell surface by a limited number of sites. Several approaches implicated P-selectin and integrin alpha(v)beta(3) in anchoring VWF strings. An RGDS peptide or a function-blocking antibody to integrin alpha(v)beta(3) reduced the number of VWF strings formed. In addition, integrin alpha(v) decorated the VWF strings by immunofluorescence microscopy. Furthermore, lentiviral transduction of shRNA against the alpha(v) subunit reduced the expression of cell-surface integrin alpha(v)beta(3) and impaired the ability of endothelial cells to retain VWF strings. Soluble P-selectin reduced the number of platelet-decorated VWF strings in the absence of Ca(2+) and Mg(2+) but had no effect in the presence of these cations. These results indicate that VWF strings bind specifically to integrin alpha(v)beta(3) on human endothelial cells.

Liver regeneration and tumor stimulation--a review of cytokine and angiogenic factors

Liver resection for metastatic (colorectal carcinoma) tumors is often followed by a significant incidence of tumor recurrence. Cellular and molecular changes resulting from hepatectomy and the subsequent liver regeneration process may influence the kinetics of tumor growth and contribute to recurrence. Clinical and experimental evidence suggests that factors involved in liver regeneration may also stimulate the growth of occult tumors and the reactivation of dormant micrometastases. An understanding of the underlying changes may enable alternative strategies to minimize tumor recurrence and improve patient survival after hepatectomy.

Role of von Willebrand factor in tumor metastasis

Von Willebrand factor (VWF) is a multimeric plasma glycoprotein that plays a critical role in primary hemostasis, allowing the adhesion of platelets to the exposed subendothelium. The key role played by VWF in platelet adhesion suggests a potential implication in various pathologies where this process is involved. In cancer metastasis development, tumor cells interact with platelets and the vessel wall to extravasate from the circulation. A number of potential receptors for VWF have been identified on tumor cells such as glycoprotein Ib or the alpha(IIb)beta(3) and alpha(v)beta(3) integrins and direct interactions between VWF and tumor cells have been reported. To address the role of VWF in an experimental metastasis model, we compared the formation of pulmonary metastatic foci in C57BL/6J wild-type and VWF-null mice following I.V. injection of murine melanoma B16-BL6 cells or Lewis lung carcinoma cells. Surprisingly we found a significant increase in the number of pulmonary metastatic foci in VWF-null mice. Restoration of VWF plasma levels by co-injection of VWF with the tumor cells led to the correction of this pro-metastatic phenotype. In vitro analysis revealed that VWF did not influence tumor cell proliferation or invasion but induced cellular death. This result was confirmed in vivo where analysis of the early survival of tumor cells in the lungs revealed that the presence of VWF led to a decreased survival of these cells during the first 24 hours after injection. Our results suggest that VWF plays a role in tumor metastasis, independently of its role in hemostasis.

A novel alpha(v)beta (3)-blocking disintegrin containing the RGD motive, DisBa-01, inhibits bFGF-induced angiogenesis and melanoma metastasis

The integrin alpha(v)beta(3) is involved in multiple aspects of malignant cancer, including tumor angiogenesis and metastasis, which makes the receptor a key target for the development of anti-cancer therapies. We report here on the production, the characterization and the in vivo anti-angiogenic and anti-metastatic properties of a novel alpha(v)beta(3)-binding disintegrin, DisBa-01, isolated from a cDNA library made with RNAs from the venom gland of Bothrops alternatus. The 11,637 Da-recombinant monomeric form of DisBa-01 displayed an RGD motif and interacted with purified alpha(v)beta(3) integrin in surface plasmon resonance studies, in a dose-dependent and cation sensitive manner. A three-dimensional molecular model of DisBa-01 in complex with alpha(v)beta(3) predicted a large surface of contacts with the beta(3) subunit. DisBa-01 inhibited the adhesion of alpha(v)beta(3)-expressing human microvascular endothelial cell line-1 (HMEC-1) and murine melanoma cell line B16F10 to vitronectin (IC(50) = 555 nM and 225 nM, respectively), and transiently inhibited their proliferation without direct cell toxicity, but did not affect the binding nor the proliferation of a human breast cancer-derived cell line (MDA-MB-231) not expressing alpha(v)beta(3). In vivo, DisBa-01 dose-dependently decreased bFGF-induced angiogenesis in a matrigel plug assay in athymic nude mice (IC(50) = 83 nM). When injected intravenously to C57BL/6 mice together with B16F10 melanoma cells, DisBa-01 time- and dose-dependently inhibited lung metastasis monitored by bioluminescent imaging. We conclude that DisBa-01 is a potent new inhibitor of alpha(v)beta(3)-dependent adherence mechanisms involved in neo-vascularization and tumor metastasis processes.

Phase I and pharmacokinetic study of etaracizumab (Abegrin), a humanized monoclonal antibody against alphavbeta3 integrin receptor, in patients with advanced solid tumors

This study assessed the safety, immunogenicity, and pharmacokinetics of etaracizumab, a monoclonal antibody directed against the alphavbeta3 integrin, in patients with advanced malignancies. Four cohorts of four patients received escalating dose of etaracizumab as a 30-min intravenous infusion, first as a single test dose, followed-up 2-5 weeks later by weekly doses. Sixteen patients with advanced solid tumors received a total of 309 cycles of etaracizumab at doses ranging 1-6 mg/kg. The mean number of weekly infusions was 19 (ranging 5-53). Frequently reported adverse events were grades 1-2 asthenia (15 patients) and infusion reactions (9 patients). At 1 mg/kg, one patient experienced grade 3 chills with the first infusion. Other grade 3 toxicities included reversible hyponatremia, hypophosphatemia and hyponatremia in one patient each at 1, 4 and 6 mg/kg, respectively. No patient experienced treatment delay/discontinuation due to an adverse event. The half-life of etaracizumab ranged 49-180 h with a nonlinear increase in terminal half-life with increasing doses. There was no objective response but five patients experienced a stable disease of >6-month duration. Etaracizumab was well-tolerated at doses up to 6 mg/kg with no evidence of immunogenicity. The safety profile of etaracizumab warrants further exploration in ongoing phase I/II trials.