Challenges facing antiangiogenic therapy for cancer: impact of the tumor extracellular environment

Role of berberine on angiogenesis and blood flow hemodynamics using zebrafish model

Angiogenesis and hemodynamic instability created by the irregular blood vessels causes hypoperfusion and angiogenesis-mediated diseases. Therefore, therapies focusing on controlling angiogenesis will be a valuable approach to treat a broad spectrum of diseases. In this study, we explored the anti-angiogenic potential of berberine (BBR) and also analyzed blood flow hemodynamics using zebrafish embryos. Zebrafish embryos treated with BBR (0.01-0.75 mM) at various doses at 1 hour post-fertilization (hpf) developed a variety of phenotypic variations including aberrant blood vessels, tail bending, edema, and hemorrhage. Survival rates were much lower at higher dosages, and hatching rates were almost 99%, whereas control group appeared normal. Heart rate is an essential measure that has a strong association with hemodynamics. We used ImageJ software to study the heart rate of embryos treated with BBR, preceded by video processing. The resultant graph shows a significant decrease in heart rate of embryos treated with BBR in dose-dependent manner. Also, RBC staining using o-Dianisidine confirms the anti-angiogenic potential of BBR by indicating the decrease in the intersegmental vessels at 0.5 and 0.75 mM treated embryos. Further, the gene expression study determined that the transcripts (vegf, vegfr2, nrp1a, hif-1α, nos2a, nos2b, cox-2a, and cox-2b) measured were found to be downregulated by BBR at 0.5 mM concentration, from which we conclude that enos/vegf signaling could play an important role in modulating angiogenesis. Our data imply that BBR may be an effective compound for suppressing angiogenesis in vivo, which might be helpful in the treatment of vascular disorders like cancer and diabetic retinopathy in future.

Anti-angiogenic and anti-metastatic activity of synthetic phosphoethanolamine

BACKGROUND

Renal cell carcinoma (RCC) is the most common type of kidney cancer, and represents the third most common urological malignancy. Despite the advent of targeted therapies for RCC and the improvement of the lifespan of patients, its cost-effectiveness restricted the therapeutic efficacy. In a recent report, we showed that synthetic phosphoethanolamine (Pho-s) has a broad antitumor activity on a variety of tumor cells and showed potent inhibitor effects on tumor progress in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

We show that murine renal carcinoma (Renca) is more sensitive to Pho-s when compared to normal immortalized rat proximal tubule cells (IRPTC) and human umbilical vein endothelial cells (HUVEC). In vitro anti-angiogenic activity assays show that Pho-s inhibits endothelial cell proliferation, migration and tube formation. In addition, Pho-s has anti-proliferative effects on HUVEC by inducing a cell cycle arrest at the G2/M phase. It causes a decrease in cyclin D1 mRNA, VEGFR1 gene transcription and VEGFR1 receptor expression. Pho-s also induces nuclear fragmentation and affects the organization of the cytoskeleton through the disruption of actin filaments. Additionally, Pho-s induces apoptosis through the mitochondrial pathway. The putative therapeutic potential of Pho-s was validated in a renal carcinoma model, on which our remarkable in vivo results show that Pho-s potentially inhibits lung metastasis in nude mice, with a superior efficacy when compared to Sunitinib.

CONCLUSIONS/SIGNIFICANCE

Taken together, our findings provide evidence that Pho-s is a compound that potently inhibits lung metastasis, suggesting that it is a promising novel candidate drug for future developments.

Receptor cross-talk in angiogenesis: mapping environmental cues to cell phenotype using a stochastic, Boolean signaling network model

Cancer invasion and metastasis depend on tumor-induced angiogenesis, the means by which cancer cells attract and maintain a blood supply. During angiogenesis, cellular processes are tightly coordinated by signaling molecules and their receptors. Understanding how endothelial cells synthesize multiple biochemical signals can catalyze the development of novel therapeutic strategies to combat cancer. This study is the first to propose a signal transduction model highlighting the cross-talk between key receptors involved in angiogenesis, namely the VEGF, integrin, and cadherin receptors. From experimental data, we construct a network model of receptor cross-talk and analyze its dynamics. We identify relationships between receptor activation combinations and cellular function, and show that cross-talk is crucial to phenotype determination. The network converges to a unique set of output states that correspond to known cell phenotypes: migratory, proliferating, quiescent, apoptotic, and it predicts one phenotype that challenges the "go or grow" hypothesis. Finally, we use the model to study protein inhibition and to suggest molecular targets for anti-angiogenic therapies.

Topography of extracellular matrix mediates vascular morphogenesis and migration speeds in angiogenesis

The extracellular matrix plays a critical role in orchestrating the events necessary for wound healing, muscle repair, morphogenesis, new blood vessel growth, and cancer invasion. In this study, we investigate the influence of extracellular matrix topography on the coordination of multi-cellular interactions in the context of angiogenesis. To do this, we validate our spatio-temporal mathematical model of angiogenesis against empirical data, and within this framework, we vary the density of the matrix fibers to simulate different tissue environments and to explore the possibility of manipulating the extracellular matrix to achieve pro- and anti-angiogenic effects. The model predicts specific ranges of matrix fiber densities that maximize sprout extension speed, induce branching, or interrupt normal angiogenesis, which are independently confirmed by experiment. We then explore matrix fiber alignment as a key factor contributing to peak sprout velocities and in mediating cell shape and orientation. We also quantify the effects of proteolytic matrix degradation by the tip cell on sprout velocity and demonstrate that degradation promotes sprout growth at high matrix densities, but has an inhibitory effect at lower densities. Our results are discussed in the context of ECM targeted pro- and anti-angiogenic therapies that can be tested empirically.

Integrins as "functional hubs" in the regulation of pathological angiogenesis

It is well accepted that complex biological processes such as angiogenesis are not controlled by a single family of molecules or individually isolated signaling pathways. In this regard, new insight into the interconnected mechanisms that regulate angiogenesis might be gained by examining this process from a more global network perspective. The coordination of signaling cues from both outside and inside many different cell types is required for the successful completion of angiogenesis. Evidence is accumulating that the multifunctional integrin family of cell adhesion receptors represent an important group of molecules that play active roles in sensing, integrating, and distributing a diverse set of signals that regulate many cellular events required for angiogenesis. Given the ability of integrins to bind numerous extracellular ligands and transmit signals in a bi-directional fashion, we will discuss the multiple ways by which integrins may serve as a functional hub during pathological angiogenesis. In addition, we will highlight potential imaging and therapeutic strategies based on the expanding new insight into integrin function.

Targeting of humanized antibody D93 to sites of angiogenesis and tumor growth by binding to multiple epitopes on denatured collagens

A humanized, affinity-matured IgG1 antibody, called D93, and its parental murine IgM HUI77 have been shown to specifically bind denatured collagens and thereby inhibit angiogenesis and tumor growth in various animal models. In this study, we have identified epitopes for both HUI77 and D93 on human collagen type IV. Several tryptic D93-binding peptides were identified by Western blot analysis and protein sequencing. Epitopes for D93 were ultimately identified by screening a synthetic 16-mer peptide array spanning immunoreactive tryptic peptides. D93 reacted with a peptide corresponding to alpha1(IV) P(1337)-Y(1352) that could inhibit binding of both D93 and HUI77 to denatured collagen IV in a concentration-dependent manner. A 9-mer peptide corresponding to alpha1(IV) G(1344)-Y(1352) showed maximum inhibition of D93 and HUI77 antibody binding to denatured collagen IV, and was critically dependent on the presence of hydroxyproline. D93 bound with similar affinity to denatured collagen IV and synthetic peptides with a K(D) of 1-10 microM for monovalent and of 30-63 nM for bivalent binding. Potential epitopes for D93 are highly repeated in multiple collagen types of diverse vertebrate species explaining reactivity of D93 with denatured collagens types I-V from chicken to man. Our data suggest that D93 inhibits angiogenesis and tumor growth by blockade of cryptic bioactive signals on proteolyzed collagens with importance for growth of tumors and new blood vessels.

Tetrathiomolybdate promotes tumor necrosis and prevents distant metastases by suppressing angiogenesis in head and neck cancer

Angiogenesis is well recognized as an essential process that influences not only the growth of head and neck squamous cell carcinoma (HNSCC) but also promotes its invasive and metastatic behavior. The critical role of copper in multiple facets of angiogenesis makes it an important therapeutic target. Tetrathiomolybdate is a potent copper chelator, which has shown remarkable ability to suppress angiogenesis. Although this may involve multiple mechanisms, the effects on vascular endothelial growth factor (VEGF) are pivotal. In previous work, tetrathiomolybdate suppressed production of several proangiogenic cytokines by HNSCC cell lines. Given these results, we hypothesized that tetrathiomolybdate would impair tumor growth and metastasis by HNSCC. To test this concept, we evaluated the effects of long-term tetrathiomolybdate treatment on the growth and metastatic progression of HNSCC using a xenograft animal model. The results showed that tetrathiomolybdate treatment is able to maintain effective inhibition of angiogenesis. There was a significant reduction in the tumor size and vascularity with evident gross necrosis in the tetrathiomolybdate-treated animals. These effects were highly correlated with suppression of human VEGF expressed in the developing tumors as well as the mouse VEGF levels detected in the plasma. Moreover, tetrathiomolybdate treatment drastically suppressed the development of lung metastases. Taken together, these results show that tetrathiomolybdate can act long-term as a suppressor of vascularity and inhibit the growth of metastasis in this model of HNSCC.

Targeting the vascular endothelial growth factor pathway in the treatment of multiple myeloma

Multiple myeloma is a clonal plasma cell malignancy within the bone marrow associated with bone loss, renal disease and immunodeficiency. Despite new insights into the pathogenesis of multiple myeloma and novel targeted therapies, the median survival remains 3-5 years. It is now well established that the intimate relation between the tumor cells and components of the microenvironment plays a key role in multiple myeloma pathogenesis. Specifically, tumor cells impact the bone marrow and thereby cause immune suppression and lytic bone lesions; conversely, components of the bone marrow provide signals that influence the behavior of multiple myeloma cells, including tumor cell growth, survival, migration and drug resistance. Important contributing effectors are tumor cell-stroma cell and cell-extracellular matrix contacts, the bone marrow vasculature, and a variety of cytokines and growth factors in the bone marrow milieu.

Lactate adversely affects the in vitro formation of endothelial cell tubular structures through the action of TGF-beta1

When lactate accumulation in a tumor microenvironment reaches an average concentration of 10-20 mM, it tends to reflect a high degree of malignancy. However, the hypothesis that tumor-derived lactate has a number of partially adverse biological effects on malignant and tumor-associated host cells requires further evidence. The present study attempted to evaluate the impact of lactate on the process of angiogenesis, in particular on the formation of tubular structures. The endothelial cell (EC) network in desmoplastic breast tumors is primarily located in areas of reactive fibroblastic stroma. We employed a fibroblast-endothelial cell co-culture model as in vitro angiogenesis system normally producing florid in vitro tubule formation to analyze this situation. In contrast to previous studies, we found that lactate significantly reduces EC network formation in a dose-dependent manner as quantified by semi-automated morphometric analyses following immunohistochemical staining. The decrease in CD31-positive tubular structures and the number of intersections was independent of VEGF supplementation and became more pronounced in the presence of protons. The number of cells, primarily of the fibroblast population, was reduced but cell loss could not be attributed to a decrease in proliferative activity or pronounced apoptotic cell death. Treatment with 10 mM lactate was accompanied by enhanced mRNA expression and release of TGF-beta1, which also shows anti-angiogenic activity in the model. Both TGF-beta1 and lactate induced myofibroblastic differentiation adjacent to the EC tubular structures. The lactate response on the EC network was diminished by TGF-beta1 neutralization, indicating a causal relationship between lactate and TGF-beta1 in the finely tuned processes of vessel formation and maturation which may also occur in vivo within tumor tissue.

Disruption of Endothelial Cell Interactions with the Novel HU177 Cryptic Collagen Epitope Inhibits Angiogenesis

PURPOSE

The importance of cellular communication with the extracellular matrix in regulating cellular invasion is well established. Selective disruption of communication links between cells and the local microenvironment by specifically targeting non-cellular matrix-immobilized cryptic extracellular matrix epitopes may represent an effective new clinical approach to limit tumor-associated angiogenesis. Therefore, we sought to determine whether the HU177 cryptic collagen epitope plays a functional role in regulating angiogenesis in vivo.

EXPERIMENTAL DESIGN

We examined the expression and characterized the HU177 cryptic collagen epitope in vitro and in vivo using immunohistochemistry and ELISA. We examined potential mechanisms by which this cryptic collagen epitope may regulate angiogenesis using in vitro cell adhesion, migration, proliferation, and biochemical assays. Finally, we examined the whether blocking cellular interactions with the HU177 cryptic epitope plays a role in angiogenesis and tumor growth in vivo using the chick embryo model.

RESULTS

The HU177 cryptic epitope was selectively exposed within tumor blood vessel extracellular matrix, whereas little was associated with quiescent vessels. An antibody directed to this cryptic site selectively inhibited endothelial cell adhesion, migration, and proliferation on denatured collagen type IV and induced increased levels of cyclin-dependent kinase inhibitor p27(KIP1). Systemic administration of mAb HU177 inhibited cytokine- and tumor-induced angiogenesis in vivo.

CONCLUSIONS

We provide evidence for a new functional cryptic regulatory element within collagen IV that regulates tumor angiogenesis. These findings suggest a novel and highly selective approach for regulating angiogenesis by targeting a non-cellular cryptic collagen epitope.

Potential of fibroblasts to regulate the formation of three-dimensional vessel-like structures from endothelial cells in vitro

The development of vessel-like structures in vitro to mimic as well as to realize the possibility of tissue-engineered small vascular networks presents a major challenge to cell biologists and biotechnologists. We aimed to establish a three-dimensional (3-D) culture system with an endothelial network that does not require artificial substrates or ECM compounds. By using human skin fibroblasts and endothelial cells (ECs) from the human umbilical vein (HUVECs) in diverse spheroid coculture strategies, we verified that fibroblast support and modulate EC migration, viability, and network formation in a 3-D tissue-like stromal environment. In mixed spheroid cultures consisting of human ECs and fibroblasts, a complex 3-D network with EC tubular structures, lumen formation, pinocytotic activity, and tight junction complexes has been identified on the basis of immunohistochemical and transmission electron microscopic imaging. Tubular networks with extensions up to 400 μm were achieved. When EC suspensions were used, EC migration and network formation were critically affected by the status of the fibroblast. However, the absence of EC migration into the center of 14-day, but not 3-day, precultured fibroblast spheroids could not be attributed to loss of F viability. In parallel, it was also confirmed that migrated ECs that entered cluster-like formations became apoptotic, whereas the majority of those forming vessel-like structures remained viable for >8 days. Our protocols allow us to study the nature of tubule formation in a manner more closely related to the in vivo situation as well as to understand the basis for the integration of capillary networks in tissue grafts and develop methods of quantifying the amount of angiogenesis in spheroids using fibroblast and other cells isolated from the same patient, along with ECs.

Recombinant alpha2(IV)NC1 domain inhibits tumor cell-extracellular matrix interactions, induces cellular senescence, and inhibits tumor growth in vivo

Cellular interaction with the extracellular matrix is thought to be a critical event in controlling angiogenesis and tumor growth. In our previous studies, genetically distinct noncollagenous (NC) domains of type-IV collagen were shown to interact with integrin receptors expressed on the surface of endothelial cells. Moreover, these NC1 domains were shown to inhibit angiogenesis in vivo. Here, we provide evidence that a recombinant form of the alpha2(IV)NC1 domain of type-IV collagen could bind integrins alpha1beta1 and alphavbeta3 expressed on melanoma cells and inhibit tumor cell adhesion in a ligand-specific manner. Systemic administration of recombinant alpha2(IV)NC1 domain potently inhibited M21 melanoma tumor growth within full thickness human skin and exhibited a dose-dependent inhibition of tumor growth in nude mice. Interestingly, alpha2(IV)NC1 domain enhanced cellular senescence in tumor cells in vitro and in vivo. Taken together, these results suggest that recombinant alpha2(IV)NC1 domain is not only a potent anti-angiogenic reagent, but it also directly impacts tumor cell behavior. Thus, alpha2(IV)NC1 domain represents a potent inhibitor of tumor growth by impacting both endothelial and tumor cell compartments.