Suppression of tumor angiogenesis through the inhibition of integrin function and signaling in endothelial cells: which side to target?

Peptide-Based Strategies for Targeted Tumor Treatment and Imaging

Cancer is one of the leading causes of death worldwide. The development of cancer-specific diagnostic agents and anticancer toxins would improve patient survival. The current and standard types of medical care for cancer patients, including surgery, radiotherapy, and chemotherapy, are not able to treat all cancers. A new treatment strategy utilizing tumor targeting peptides to selectively deliver drugs or applicable active agents to solid tumors is becoming a promising approach. In this review, we discuss the different tumor-homing peptides discovered through combinatorial library screening, as well as native active peptides. The different structure–function relationship data that have been used to improve the peptide’s activity and conjugation strategies are highlighted.

Detection of Pro- and Antiangiogenic Factors in the Human Sclera

PURPOSE

Avascular tissues can be used to identify antilymph- or antihemangiogenic factors. The human sclera-the outer covering layer of the eye, lacks lymphatic vessels and contains only a superficial network of blood vessels and was used here to identify endogenous antiangiogenic factors.

METHODS

Expression levels of a panel of 96 known pro- and antiangiogenic factors were analyzed in 12 scleral or conjunctival control samples from normal human donors using real-time PCR. In vitro, scleral homogenate was cocultured with blood- and lymphatic endothelial cells (BECs and LECs) and immunohistochemistry was performed of scleral fibroblasts and BECs.

RESULTS

Three antiangiogenic factors were significantly upregulated in the human sclera compared to the conjunctiva, including FBLN5 (fibulin 5), SERPINF1 (serpin peptidase inhibitor, clade F, member 1 = pigment epithelium derived factor) and TIMP2 (Tissue inhibitor of metalloproteinases 2). Six proangiogenic factors were significantly downregulated in the sclera, including FLT4 (Fms-related tyrosine kinase 4=VEGF-R3), HGF (hepatocyte growth factor), KIT (CD117 / c-kit), PROX1 (prospero homeobox 1), SEMA3F (semaphorin-3F) and TGFA (transforming growth factor alpha). In vitro, scleral homogenate inhibited the growth of both BECs and LECs. Immunohistochemistry labeling of three major antiangiogenic factors from scleral tissue confirmed TIMP3 and PEDF expression both in scleral fibroblasts and in blood endothelial cells, whereas TIMP2 was not detectable.

CONCLUSION

Balancing anti- and proangiogenic factors actively regulates human scleral avascularity, inhibits endothelial cell growth in vitro, and thus may help maintaining the vascular privilege of the inner eye.

Targeting of Tumor Neovasculature with GrB/VEGF121, a Novel Cytotoxic Fusion Protein

Angiogenesis is a critical process in numerous diseases, and intervention in neovascularization has therapeutic value in several disease settings, including ocular diseases, arthritis, and in tumor progression and metastatic spread. Various vascular targeting agents have been developed, including those that inhibit growth factor receptor tyrosine kinases, blocking antibodies that interfere with receptor signal transduction, and strategies that trap growth factor ligands. Limited anti-tumor efficacy studies have suggested that the targeted delivery of the human pro-apoptotic molecule Granzyme B to tumor cells has significant potential for cancer treatment. Here, we review biological vascular targeting agents, and describe a unique vascular targeting agent composed of Granzyme B and the VEGF receptor ligand VEGF₁₂₁. The fusion protein GrB/VEGF₁₂₁ demonstrates cytotoxicity at nanomolar or sub-nanomolar levels, excellent pharmacokinetic and efficacy profiles, and has significant therapeutic potential targeting tumor vasculature.

Design, preparation and characterization of cyclic RGDfK peptide modified poly(ethylene glycol)-block-poly(lactic acid) micelle for targeted delivery

Molecular targeted cancer therapy is a promising strategy to overcome the lack of specificity of anticancer drug. While the binding of c(RGDfK) (cyclic Arginine-Glycine-Aspartic acid-Phenylalanine-Lysine) to αvβ3 over-expressed on tumor cell has been validated, the underlying interaction remains poorly understood. In this work, docking calculation was applied to investigate the interactions between c(RGDfK)/c(RGDfK)-PEG and αvβ3. The calculated results indicated that c(RGDfK) interacted with αvβ3 mainly by electrostatic interaction, stabilization interaction, and hydrophobic interaction. Conjugation of PEG chain to the c(RGDfK) weakened the binding affinity of c(RGDfK) to αvβ3. Accordingly, docetaxel(DTX)-loaded target micelles (c(RGDfK)-PEG-PLA/PEG-PLA/DTX) were designed, characterized and evaluated using HeLa cells. In vitro release studies demonstrated both target and non-target micelles displayed almost the same profiles, which best fit in Ritger-Peppas model. Cellular uptake and MTT studies revealed that the target micelles with the presence of c(RGDfK) were more efficiently taken up by HeLa cells and significantly improved the cytotoxicity compared to that of non-target micelles. Cell inhibition rate of target micelles was improved by 20% after 24h. Our findings suggest that target micelles may be a potential anticancer drug delivery system in the treatment of integrin αvβ3 over-expressed on tumor cell.

Vagal efferent fiber stimulation ameliorates pulmonary microvascular endothelial cell injury by downregulating inflammatory responses

Electrical stimulation of the vagus nerve may have positive effects on many inflammatory diseases. This study determined the beneficial effects of vagus nerve stimulation and the mechanisms by which it attenuates lipopolysaccharide (LPS)-induced acute lung injury (ALI). Rats were intraperitoneally injected with 10 mg/kg LPS to induce ALI. The results showed that vagus nerve stimulation could improve lung injury, as evidenced by remarkable reductions in lung edema (wet-to-dry weight ratio), neutrophil infiltration (myeloperoxidase activity), and pulmonary permeability [total number of cells and protein concentrations in bronchoalveolar lavage fluid (BALF)]. In addition, vagus nerve stimulation not only decreased the expressions of Src-suppressed C kinase substrate and E-selectin proteins in lung tissue but also effectively attenuated the concentrations of the proinflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 in BALF. These suggest that vagus nerve stimulation is a suitable treatment for LPS-induced ALI and indicate that it helps ameliorate pulmonary microvascular endothelial cell injury by downregulating inflammatory responses.

IL-32 promotes angiogenesis

IL-32 is a multifaceted cytokine with a role in infections, autoimmune diseases, and cancer, and it exerts diverse functions, including aggravation of inflammation and inhibition of virus propagation. We previously identified IL-32 as a critical regulator of endothelial cell (EC) functions, and we now reveal that IL-32 also possesses angiogenic properties. The hyperproliferative ECs of human pulmonary arterial hypertension and glioblastoma multiforme exhibited a markedly increased abundance of IL-32, and, significantly, the cytokine colocalized with integrin αVβ3. Vascular endothelial growth factor (VEGF) receptor blockade, which resulted in EC hyperproliferation, increased IL-32 three-fold. Small interfering RNA-mediated silencing of IL-32 negated the 58% proliferation of ECs that occurred within 24 h in scrambled-transfected controls. Reduction of IL-32 neither affected apoptosis (insignificant changes in Bak-1, Bcl-2, Bcl-xL, lactate dehydrogenase, annexin V, and propidium iodide) nor VEGF or TGF-β levels, but siIL-32-transfected adult and neonatal ECs produced up to 61% less NO, IL-8, and matrix metalloproteinase-9, and up to 3-fold more activin A and endostatin. In coculture-based angiogenesis assays, IL-32γ dose-dependently increased tube formation up to 3-fold; an αVβ3 inhibitor prevented this activity and reduced IL-32γ-induced IL-8 by 85%. In matrigel plugs loaded with IL-32γ, VEGF, or vehicle and injected into live mice, we observed the anticipated VEGF-induced increase in neocapillarization (8-fold versus vehicle), but unexpectedly, IL-32γ was equally angiogenic. A second signal such as IFN-γ was required to render cells responsive to exogenous IL-32γ; importantly, this was confirmed using a completely synthetic preparation of IL-32γ. In summary, we add angiogenic properties that are mediated by integrin αVβ3 but VEGF-independent to the portfolio of IL-32, implicating a role for this versatile cytokine in pulmonary arterial hypertension and neoplastic diseases.

An easily accessible sulfated saccharide mimetic inhibits in vitro human tumor cell adhesion and angiogenesis of vascular endothelial cells

Oligosaccharides aberrantly expressed on tumor cells influence processes such as cell adhesion and modulation of the cell’s microenvironment resulting in an increased malignancy. Schmidt’s imidate strategy offers an effective method to synthesize libraries of various oligosaccharide mimetics. With the aim to perturb interactions of tumor cells with extracellular matrix proteins and host cells, molecules with 3,4-bis(hydroxymethyl)furan as core structure were synthesized and screened in biological assays for their abilities to interfere in cell adhesion and other steps of the metastatic cascade, such as tumor-induced angiogenesis.

The most active compound, (4-{[(β-D-galactopyranosyl)oxy]methyl}furan-3-yl)methyl hydrogen sulfate (GSF), inhibited the activation of matrix-metalloproteinase-2 (MMP-2) as well as migration of the human melanoma cells of the lines WM-115 and WM-266-4 in a two-dimensional migration assay. GSF inhibited completely the adhesion of WM-115 cells to the extracellular matrix (ECM) proteins, fibrinogen and fibronectin.

In an in vitro angiogenesis assay with human endothelial cells, GSF very effectively inhibited endothelial tubule formation and sprouting of blood vessels, as well as the adhesion of endothelial cells to ECM proteins. GSF was not cytotoxic at biologically active concentrations; neither were 3,4-bis{[(β-D-galactopyranosyl)oxy]methyl}furan (BGF) nor methyl β-D-galactopyranoside nor 3,4-bis(hydroxymethyl)furan, which were used as controls, eliciting comparable biological activity. In silico modeling experiments, in which binding of GSF to the extracellular domain of the integrin α_vβ₃ was determined, revealed specific docking of GSF to the same binding site as the natural peptidic ligands of this integrin. The sulfate in the molecule coordinated with one manganese ion in the binding site.

These studies show that this chemically easily accessible molecule GSF, synthesized in three steps from 3,4-bis(hydroxymethyl)furan and benzoylated galactose imidate, is nontoxic and antagonizes cell physiological processes in vitro that are important for the dissemination and growth of tumor cells in vivo.

Tumor immune surveillance and ovarian cancer: lessons on immune mediated tumor rejection or tolerance

In the past few years, cancer immunotherapies have produced promising results. Although traditionally considered unresponsive to immune therapy, increasing evidence indicates that ovarian cancers are, in fact, immunogenic tumors. This evidence comes from diverse epidemiologic and clinical data comprising evidence of spontaneous antitumor immune response and its association with longer survival in a proportion of ovarian cancer patients; evidence of tumor immune evasion mechanisms and their association with short survival in some ovarian cancer patients; and finally pilot data supporting the efficacy of immune therapy. Below we will discuss lessons learned on the biology underlying ovarian cancer immune rejection or tolerance and we will discuss its association with clinical outcome. We will discuss the role of angiogenesis and the tumor endothelium on regulation of the antitumor immune response with a special emphasis on the role of vascular endothelial growth factor (VEGF) in the suppression of immunological processes, which control tumor progression and its unique crosstalk with endothelin systems, and how their interactions may shape the antitumor immune response. In addition, we will discuss mechanisms of tumor tolerance through the suppression or exhaustion of effector cells and how these could be countered in the clinic. We believe that understanding these pathways in the tumor microenvironment will lead to novel strategies for enhancing ovarian cancer immunotherapy.

Immunohistochemical analysis of integrins αvβ3, αvβ5 and α5β1, and their ligands, fibrinogen, fibronectin, osteopontin and vitronectin, in frozen sections of human oral head and neck squamous cell carcinomas

Integrins mediate the interaction of cells with the extracellular matrix and are believed to be involved in tumor cell survival and metastasis, and in tumor angiogenesis. We used immunohistochemistry of fresh-frozen human tumor tissues to analyze the presence of integrins αvβ3, αvβ5 and α5β1, which are believed to be involved in tumor growth and migration, together with integrin ligands, vitronectin, osteopontin, fibronectin and fibrinogen, in human oral squamous cell carcinomas. Samples of squamous cell carcinomas and control tissues from patients without cancer undergoing oral or maxillofacial surgery were frozen in liquid nitrogen within 30 min of removal. Frozen sections were prepared, and the presence of integrins or ligands was visualized using standard immunohistochemistry (APAAP) with a blinded evaluation. Comparison of samples from the 40 oral cancer patients and the 20 controls revealed increased staining in tumors compared with the controls, and staining was demonstrated for αvβ3 in endothelia. αvβ5 staining was increased in the tumor samples, but this was associated with increased expression in stroma rather than in endothelia. Modestly increased expression of α5β1 was observed in the tumor samples, and this was associated with tumor cells, endothelia and stroma. Expression of ligands for the integrins varied between tissue types, with increased fibrinogen and fibronectin expression in tumor endothelia. Confirmation of the presence of these integrins and their association with tumor cells, endothelia or stroma suggests their potential for these integrins in human oral tumors. Overall, the increased expression of integrins within tumors, particularly expression associated with endothelial cells, supports the principle of selective integrin blockade as a novel anticancer strategy.

The tumor microenvironment: the making of a paradigm

What has been will be again, what has been done will be done again; there is nothing new under the sun

(Ecclesiastes 1:9)

Stephen Paget was the conceptual father of the role played by the Tumor Microenvironment (TME) in tumor progression. The focus of this essay is the developmental phase of the post Paget TME research. Attempts will be made to highlight some of the pioneering work of scientists from the late sixties through the eighties of last century who laid the foundations for the contemporary scientific achievements of TME research but whose ground breaking studies are rarely cited. This review should serve as a small tribute to their great work.

Regulation of angiogenesis: apoptotic cues from the ECM

The extracellular matrix (ECM) acts both as a physical scaffold for cells and as a repository for growth factors. Moreover, ECM structure and physical-chemical properties convey precise information to cells that profoundly influences their biology by interactions with cell surface receptors termed integrins. During angiogenesis, the perivascular ECM plays a critical role in determining the proliferative, invasive and survival responses of the local vascular cells to the angiogenic growth factors. Dynamic changes in both the ECM and the local vascular cells act in concert to regulate new blood vessel growth. The digestion of ECM components by proteolysis is critical for the invasive capacity of endothelial cells, but also creates ECM fragments, which antagonize the mechanosensory function of integrins, and can be apoptogenic. Here, we discuss the roles of integrins in modulating cellular responses to a changing ECM, in particular the regulation of survival and invasion among invasive endothelial cells.

The role of adhesion molecules, alpha v beta 3, alpha v beta 5 and their ligands in the tumor cell and endothelial cell adhesion

Tumor metastasis is a complex process involving the interaction between tumor cells and endothelial cells in which some adhesion molecules play an important role. It was our aim to investigate the role of the adhesion molecules, alpha v beta 3 and alpha v beta 5 and their ligands, developmental endothelial locus-1 (Del-1) and L1, in tumor cell adhesion to endothelial cells in vitro. In this study, the expression and regulation of alpha v beta 3, alpha v beta 5 and intercellular adhesion molecule -1 on liver sinusoidal endothelial cells and liver cancer endothelial cells (T3A) were analyzed by real-time PCR and fluorescent-activated cell sorter. The expression and regulation of the integrin ligands, Del-1 and L1, in six tumor cell lines were analyzed by real-time PCR and western blot. We found the expressions of alpha v beta 3 and alpha v beta 5 were higher on T3A than that on liver sinusoidal endothelial cells, whereas expression of intercellular adhesion molecule-1 was lower on T3A than that on liver sinusoidal endothelial cells. After 24 h hypoxia, the expressions of alpha v beta 3 and alpha v beta 5 were upregulated on T3A and liver sinusoidal endothelial cells; the expression of intercellular adhesion molecule-1 was increased on liver sinusoidal endothelial cells, but remained unchanged on T3A. Del-1 and L1 expression levels were obviously diverse in various tumor cell lines and differentially modulated after 12 h hypoxia. The adhesion of tumor cells with Del-1 and L1 expression was higher in T3A than that in liver sinusoidal endothelial cells, and was significantly increased under hypoxic conditions. Interestingly, the tumor cell adherence could be inhibited by antibodies against alpha v beta 5 and alpha v beta 5, but not by an antibody against intercellular adhesion molecule-1. The adhesion of tumor cells without Del-1 and L1 expression was also higher on T3A than that on liver sinusoidal endothelial cells, but the adhesion could not be inhibited by antibodies against alpha v beta 5, alpha v beta 5 or intercellular adhesion molecule-1, suggesting that other receptors are involved. In conclusion, alpha v beta 5, alpha v beta 5 and their ligands Del-1 and L1 play an important role in the process of tumor cells moving from the original place.

Functionalized micellar systems for cancer targeted drug delivery

Polymer micelles are rapidly becoming a powerful nanomedicine platform for cancer therapeutic applications due to their small size (10-100 nm), in vivo stability, ability to solubilize water insoluble anticancer drugs, and prolonged blood circulation times. Recent data from clinical trials with three micelle formulations have highlighted these and other pharmacokinetic advantages with reduced systemic toxicity and patient morbidity compared to conventional drug formulation. While the initial anti-tumor efficacy of these systems seems promising, a strong research impetus has been placed on micelle functionalization in order to achieve tumor targeting and site-specific drug release, with the hope of reaching a more pronounced tumor response. Hence, the purpose of this review is to draw attention to the new developments of multi-functional polymer micelles for cancer therapy with special focus on tumor targeting and controlled drug release strategies.

Inhibition of endothelial cell proliferation, in vitro angiogenesis, and the down-regulation of cell adhesion-related genes by genistein. Combined with a cDNA microarray analysis

Antiangiogenesis is presently one of the powerful strategies for treating cancer, and endothelial cells play a pivotal role in the process of angiogenesis. Genistein, a tyrosine kinase inhibitor, a major isoflavone plentiful in soybeans, is known to inhibit both tumor growth and angiogenesis. However, the precise molecular mechanism(s) by which genistein affects endothelial cells has yet to be elucidated. In the present study, a cDNA microarray was performed to investigate the targeted genes of human umbilical vein endothelial cells (HUVECs) affected by 10 microM genistein. As a result, a total of 256 genes showed an altered expression of more than twofold. Among them were the genes related to cell proliferation, adhesion, transcription, translation, metabolism, cytoskeleton, apoptosis, kinases, and functionally unknown. The down-regulation of mRNA or the protein expression of cell adhesion-related genes, including VE-cadherin, gap junction protein alpha 1 (connexin 43), integrin alpha V, and multimerin, were confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) or by immunofluorescence staining. The impaired cell-cell adhesion by genistein was also observed by electron microscopy. In addition, the antiangiogenesis role of genistein was confirmed on Matrigel using inverted microscopy and electron microscopy. In conclusion, genistein affects endothelial cells as a negative mediator of proliferation and angiogenesis in vitro, partially by down-regulating cell adhesion-related genes and impairing cell adhesions.

Simvastatin potentiates tumor necrosis factor α-mediated apoptosis of human vascular endothelial cells via the inhibition of the geranylgeranylation of RhoA

HMG-CoA reductase inhibitors (statins) are widely used in the treatment and prevention of atherosclerosis. Here we demonstrate that the HMG-CoA reductase inhibitor simvastatin potentiates TNFalpha-mediated apoptosis and TNFalpha signaling in human umbilical vein endothelial cells (HUVECs). While 2.5 microM simvastatin or 40 ng/ml TNFalpha alone had only a small effect on apoptosis in HUVECs, co-incubation with simvastatin and TNFalpha markedly increased apoptosis in a time- and dose-dependent manner as measured by FACS analysis of propidium iodide-stained cells. Geranylgeraniol, which serves as a substrate for the geranylgeranylation of small GTP binding proteins such as RhoA, which is required for the function and membrane localization of Rho, reversed the effect of simvastatin on apoptosis. GGTI, an inhibitor of protein geranylgeranylation, mimicked the effect of simvastatin on apoptosis and interfered with the membrane localization of RhoA. Furthermore, simvastatin increased the expression of the TNFalpha type I receptor (TNFalphaRI) with a dose dependence and a dependence on geranylgeranylation similar to that demonstrated for the potentiation of TNFalpha-mediated apoptosis. Adenoviral expression of a dominant-negative RhoA mimicked the effect of simvastatin on the expression of TNFalphaRI, while adenoviral expression of a dominant-activating RhoA mutant reversed the effect of simvastatin on the expression of TNFalphaRI. Simvastatin also potentiated TNFalpha signaling as determined by increased TNFalpha-mediated E-selectin expression. These data support the conclusion that TNFalpha signaling is under the negative control of RhoA and that statins potentiate TNFalpha signaling at least in part via interference with RhoA inhibition of TNFalpha type I receptor expression.

Cellular and molecular mechanisms of nicotine's pro-angiogenesis activity and its potential impact on cancer

The present study examined the mechanisms of nicotine's effect on angiogenesis and its impact on tumor growth. Nicotine demonstrated significant (P<0.01) stimulation of the release of endothelial cell growth factor, basic fibroblast growth factor (b-FGF) but not vascular endothelial growth factor (VEGF). In a concentration-dependent manner, nicotine induced endothelial cell tube formation. Additionally, in the chick chorioallantoic membrane (CAM) model of angiogenesis, nicotine effectively induced the generation of new blood vessels (P<0.01), an effect that is mediated via b-FGF. The pro-angiogenesis effect of nicotine in the CAM model was maximally blocked by either anti-integrin alphavbeta3 or inhibitor of mitogen activated protein kinase (MAPK, ERK 1/2). In the CAM tumor implant model, nicotine doubled (P<0.01) the growth rate of breast, colon, and lung cancer. These data indicated that the pro-angiogenesis effect is mediated via b-FGF and induced through the nicotinic receptor, alphavbeta3 integrin, and MAPK.

Circulating endothelial cells: a novel marker of endothelial damage

Circulating endothelial cells (CECs) were first described over 30 years ago in smears of peripheral blood. Since then, more sophisticated techniques for CEC isolation have become available. In particular, immunomagnetic isolation and fluorescence-activated cell sorting (FACS) have been employed with success. We provide a short historical perspective and a comprehensive review on the subject. We review isolation and enumeration of CECs with an emphasis on CD146-driven immunomagnetic isolation and FACS. We describe, in great detail, advantages and pitfalls of both approaches and compare their specificity. Moreover, we provide a comprehensive list of clinical studies in this field and describe the possible clinical use of CECs. We also describe the phenotype of these cells and list typical surface markers. In addition, we review the phenotype of CECs and discuss mechanisms of detachment. We speculate about potential interactions between CECs and other cell subsets. We also describe other serum markers of endothelial damage and compare CECs with these markers. Finally, we highlight differences between circulating endothelial cells and endothelial progenitor cells. In summary, CECs must now be regarded as a sensitive and specific marker of endothelial damage. We emphasize that use of CECs in a clinical setting is on the horizon and pathogenetic clues may also be obtained.

In silico analysis of angiogenesis associated gene expression identifies angiogenic stage related profiles

In vitro models have been extensively used to map gene expression in ECs but few studies have used cells from in vivo sources directly. Here, we compare different gene expression surveys on both cultured and fresh tissue derived ECs, and it emerges that gene expression profiles can be paralleled with the angiogenic stage of the cells. ECs stimulated with different growth factors in monolayer cultures exhibit gene expression profiles indicative of an active proliferative state, whereas gene expression in tube forming cells in vitro involves genes implicated in cell adhesion processes. Genes overexpressed in tumor ECs are biased towards extracellular matrix remodeling, a late event in angiogenesis. The elucidation of gene expression profiles under these different conditions will contribute to a better understanding of the molecular mechanisms during angiogenesis in both pathological and physiological circumstances and will have implications for the development of angiogenesis interfering treatment strategies.

FGF-2 binding to fibrin(ogen) is required for augmented angiogenesis

We have shown previously that fibrin(ogen) binds fibroblast growth factor 2 (FGF-2) and potentiates stimulation of endothelial-cell (EC) proliferation. We have now used 2 FGF-2 mutants differing only in the 5 residues constituting the binding site to characterize the importance of this interaction in angiogenesis. The nonbinding (2212) and binding (221*2) mutants stimulated EC proliferation by 2.2 +/- 0.4-fold and 2.9 +/- 0.3-fold over control, respectively, and both were similar to wild-type (wt) FGF-2 (2.5 +/- 0.3-fold). Proliferation was augmented by fibrinogen to 5.3 +/- 1.2-fold and 4.8 +/- 0.8-fold with wtFGF-2 and 221*2, whereas no augmentation occurred with 2212 and fibrinogen. Using a placental explant model in a fibrin matrix, wtFGF-2 resulted in 2.6 +/- 0.9-fold more growth over control, and 221*2 increased growth 3.3 plus or minus 0.9-fold. Vessel outgrowth with 2212 was minimal and comparable to control. Similarly, fibrinogen potentiated wtFGF-2 or 221*2-mediated angiogenesis in the chicken chorioallantoic membrane model. In a mouse Matrigel implant model, fibrinogen significantly increased angiogenesis with either wtFGF-2 or 221*2, whereas there was no augmentation with 2212. These results demonstrate that binding of FGF-2 to fibrin(ogen) mediated by the 5-residue FGF-2-fibrin(ogen) interactive site is required for augmented angiogenesis.

Targeted Measles Virus Vector Displaying Echistatin Infects Endothelial Cells via αvβ3 and Leads to Tumor Regression

Targeting tumor-associated vascular endothelium by replication-competent viral vectors is a promising strategy for cancer gene therapy. Here we describe the development of a viral vector based on the Edmonston vaccine strain of measles virus targeted to integrin alpha(v)beta3, which is expressed abundantly on activated but not quiescent vascular endothelium. We displayed a disintegrin, M28L echistatin that binds with a high affinity to integrin alpha(v)beta3 on the COOH terminus of the viral attachment (H) protein and rescued the replication-competent recombinant virus by reverse genetics. The new targeted virus was named measles virus echistatin vector (MV-ERV). Its native binding to CD46 was purposefully retained to allow virus infection of tumor cells expressing this receptor. MV-ERV correctly displayed echistatin on the outer surface of its envelope and produced interesting ring formation phenomena due to cell detachment upon infection of susceptible Vero cells in vitro. MV-ERV grew to 10(6) plaque-forming units/mL, slightly lower than the parental Edmonston strain of measles virus (MV-Edm), but it selectively infected Chinese hamster ovary cells expressing integrin alpha(v)beta3. It also selectively infected both bovine and human endothelial cells on matrigels and unlike MV-Edm, MV-ERV infected newly formed blood vessels in chorioallantoic membrane assays. In animal models, MV-ERV but not the control MV-Edm caused the regression of s.c. xenografts of resistant multiple myeloma tumors (MM1) in severe combined immunodeficient mice. The tumors were either completely eradicated or their growth was significantly retarded. The specificity, potency, and feasibility of MV-ERV infection clearly show the potential use of MV-ERV in gene therapy for targeting tumor-associated vasculature for the treatment of solid tumors.

Selection of recombinant phages binding to pathological endothelial and tumor cells of rat glioblastoma by in-vivo display

Pathological endothelial cells are attractive targets to selectively abrogate tumor growth. However, only a few cell surface molecules to address the endothelium of pathological blood vessels are known, but it could be anticipated that many more molecular addresses associated with abnormal endothelial function and proliferation could serve as potential candidates for development of drug delivery agents. To obtain a library of peptides mediating binding of recombinant M13 phages to endothelium of experimental rat brain tumors, in-vivo display of a combinatorial heptapeptide and a splenocyte M13 library was used. Phage clones were selected that bind to rat brain tumor endothelium in-vivo and phage proteins detected in tissues by immunohistochemistry. Some of the recombinant phages diffused or were transported far into the surrounding tumor tissue, where they persisted for several days. Sequence analysis of insertion peptides revealed surprising similarities to angiogenic and anti-angiogenic factors or matrix and guidance molecules that appear to be involved in glioblastoma pathology. In-vivo phage display of recombinant M13 phages is a tool to select peptides targeting pathological endothelium. Insertion peptides, their corresponding cellular proteins and ligands might have a variety of applications in providing molecular tools for targeting tumor vascular beds with diagnostic probes and therapeutic substances and might open new opportunities for treating frequently fatal glial tumors.

Human integrin alphavbeta5: homology modeling and ligand binding

The recently reported crystal structures of the extracellular domains of the alphavbeta3 integrin in its unligated state and in complex with the peptide cyclo(-RGDf[NMe]V-) have dramatically increased our understanding of ligand binding to integrins. Nonetheless, ligand selectivity toward different integrin subtypes is still a challenging problem complicated by the fact that 3D structures of most of the integrin subtypes remain unknown. In this study, a three-dimensional model for the human alphavbeta5 integrin was obtained using homology modeling based on the crystal coordinates of alphavbeta3 in its bound conformation as template. The modeled receptor was refined using energy minimization and molecular dynamics simulations in explicit solvent. The refined alphavbeta5 model was used to explore the interactions between this integrin and alphavbeta3/alphavbeta5 dual and alphavbeta3-selective ligands in the attempt to provide a preliminary rationalization, at the molecular level, of ligand selectivity toward the two alphav integrins. It was found that, in the RGD binding site of the alphavbeta5 receptor, a partial "roof" composed mainly of the SDL residues Tyr179 and Lys180 is present and hampers the binding of compounds containing bulky substituents in the proximity of the carboxylate group. This study provides a testable hypothesis for alphav integrins subtype ligand binding selectivity, in line with both mutagenesis data and SARs studies.

Pharmacokinetics and tumor retention of 125I-labeled RGD peptide are improved by PEGylation

Tumor growth and metastasis are angiogenesis dependent. Overexpression of integrin alphavbeta3 in angiogenic vessels as well as various malignant human tumors suggests the potential of suitably labeled antagonists of this adhesion receptor for radionuclide imaging and therapy of tumors. Small head-to-tail cyclic peptides including the Arg-Gly-Asp (RGD) amino acid sequence have been radiolabeled and studied in preclinical animal models. However, the fast blood clearance, high kidney and liver uptake, and rapid washout from tumors make this type of tracer ineffective for clinical applications. In this study we modified the cyclic pentapeptide c(RGDyK) with monofunctional methoxy-PEG (mPEG, M.W. = 2,000) and labeled the RGD-mPEG conjugate with 125I. We studied the tumor targeting efficacy and in vivo pharmacokinetic properties of 125I-RGD-mPEG by means of direct tissue sampling and autoradiography in mice xenografted subcutaneously with U87MG glioblastoma. Compared to the 125I-RGD analog, this PEGylated RGD peptide revealed faster blood clearance, lower kidney uptake, and prolonged tumor uptake without compromising the receptor targeting ability.

Docking studies on alphavbeta3 integrin ligands: pharmacophore refinement and implications for drug design

Starting from the first crystal structure of the extracellular segment of the alpha(v)beta(3) integrin receptor with a cyclic RGD ligand bound to the active site, structural models for the interactions of known ligands with the alpha(v)beta(3) integrin receptor were generated by automated computational docking. The obtained complexes were evaluated for their consistency with structure-activity relationships and site-directed mutagenesis data. A comparison between the calculated interaction free energies and the experimental biological activities was also made. All the possible interactions of the investigated compounds at the active site and the probable ligand binding conformations provide an improved basis for structure-based rational ligand design. Additionally, our docking results allow a further validation and refinement of the pharmacophore model previously postulated by us.

TNFalpha-based isolated perfusion for limb-threatening soft tissue sarcomas: state of the art and future trends

The management of limb-threatening soft tissue sarcomas has not yet been standardized. Although local disease control does not affect overall survival, amputation or highly mutilating surgery may be required, which impairs the patient's quality of life. Various neoadjuvant approaches have been proposed to allow limb-sparing surgery for these locally advanced tumors. With TNFalpha-based hyperthermic isolated limb perfusion, the majority of patients can be spared amputation, with acceptable rates of locoregional and systemic complications. As yet, no other available treatment seems to give comparable results when applied to limb-threatening soft tissue sarcomas. Nevertheless, several issues remain to be addressed, such as the type and dose of drugs, repeatability of the procedure, association with radiotherapy, further indications, and evaluation of response. The authors describe the principles underlying TNFalpha-based hyperthermic isolated limb perfusion, review the worldwide experience so far published, and discuss the above issues. The potential future developments of this locoregional therapeutic approach will also be reported.