Suppression of angiogenesis and tumor growth in vitro and in vivo using an anti-angiopoietin-2 single-chain antibody

The clinical value of angiopoietin-2 in liver diseases

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A Correlative Study Between IVIM-DWI Parameters and the Expression Levels of Ang-2 and TKT in Hepatocellular Carcinoma

Background

Noninvasive evaluation of the expression of angiopoietin-2 (Ang-2) and transketolase (TKT) in hepatocellular carcinoma (HCC) is of great significance for the clinical development of individualized treatment plans. However, the correlation between intravoxel incoherent motion diffusion weighted imaging (IVIM-DWI) and the expression of Ang-2 and TKT has not been reported. We sought to investigate the correlations between IVIM-DWI parameters and Ang-2 and TKT expression levels in HCCs.

Methods

Conventional non-enhanced magnetic resonance imaging (MRI) and IVIM-DWI and dynamic contrast MRI were performed for 61 patients with HCC before surgical treatment. Various IVIM-DWI parameters, such as apparent diffusion coefficient (ADC), slow apparent diffusion coefficient (D), fast apparent diffusion coefficient (D^*) and fraction of fast apparent diffusion coefficient (f), were calculated using Function-MADC software. Expression levels of Ang-2 and TKT in HCC were detected via immunohistochemical staining and classified into two grades. Independent sample t tests were used to compare differences in parameters between the two groups. The Spearman rank correlation test was used to analyze the correlations between IVIM-DWI parameters and Ang-2 and TKT expression levels in HCCs.

Results

The D^* and f values were significantly higher in the high Ang-2 group than in the low Ang-2 group; there were no obvious between-group differences in ADC and D. Ang-2 expression was positively correlated with D* and f but not with ADC and D. The ADC and D values were significantly lower in the high TKT group than in the low TKT group, whereas the between-group differences for D* and f were not significant. TKT expression was negatively correlated with ADC and D but not with D* and f.

Conclusions

IVIM-DWI can be used to evaluate Ang-2 and TKT expression in HCC.

The Angiopoietin/Tie2 Pathway in Hepatocellular Carcinoma

Due to the usually late diagnosis and lack of effective therapies, hepatocellular carcinoma (HCC), which poses a growing global health problem, is characterized by a poor prognosis. Angiogenesis plays an important role in HCC progression, and vascular endothelial growth factor (VEGF) and angiopoietins (Angs) are key drivers of HCC angiogenesis. VEGF-targeting strategies already represent an important component of today’s systemic treatment landscape of HCC, whereas targeting the Ang/Tie2 signaling pathway may harbor future potential in this context due to reported beneficial anticancer effects when targeting this pathway. In addition, a better understanding of the relation between Angs and HCC angiogenesis and progression may reveal their potential as predictive factors for post-treatment disease progression and prognosis. In this review, we give a comprehensive overview of the complex role of Ang/Tie2 signaling in HCC, pinpointing its potential value as biomarker and target for HCC treatments, aiding HCC diagnosis and therapy.

Integrative meta-modeling identifies endocytic vesicles, late endosome and the nucleus as the cellular compartments primarily directing RTK signaling

Recently, intracellular receptor signaling has been identified as a key component mediating cell responses for various receptor tyrosine kinases (RTKs). However, the extent each endocytic compartment (endocytic vesicle, early endosome, recycling endosome, late endosome, lysosome and nucleus) contributes to receptor signaling has not been quantified. Furthermore, our understanding of endocytosis and receptor signaling is complicated by cell- or receptor-specific endocytosis mechanisms. Therefore, towards understanding the differential endocytic compartment signaling roles, and identifying how to achieve signal transduction control for RTKs, we delineate how endocytosis regulates RTK signaling. We achieve this via a meta-analysis across eight RTKs, integrating computational modeling with experimentally derived cell (compartment volume, trafficking kinetics and pH) and ligand-receptor (ligand/receptor concentration and interaction kinetics) physiology. Our simulations predict the abundance of signaling from eight RTKs, identifying the following hierarchy in RTK signaling: PDGFRβ > IGFR1 > EGFR > PDGFRα > VEGFR1 > VEGFR2 > Tie2 > FGFR1. We find that endocytic vesicles are the primary cell signaling compartment; over 43% of total receptor signaling occurs within the endocytic vesicle compartment for these eight RTKs. Mechanistically, we found that high RTK signaling within endocytic vesicles may be attributed to their low volume (5.3 × 10^-19 L) which facilitates an enriched ligand concentration (3.2 μM per ligand molecule within the endocytic vesicle). Under the analyzed physiological conditions, we identified extracellular ligand concentration as the most sensitive parameter to change; hence the most significant one to modify when regulating absolute compartment signaling. We also found that the late endosome and nucleus compartments are important contributors to receptor signaling, where 26% and 18%, respectively, of average receptor signaling occurs across the eight RTKs. Conversely, we found very low membrane-based receptor signaling, exhibiting <1% of the total receptor signaling for these eight RTKs. Moreover, we found that nuclear translocation, mechanistically, requires late endosomal transport; when we blocked receptor trafficking from late endosomes to the nucleus we found a 57% reduction in nuclear translocation. In summary, our research has elucidated the significance of endocytic vesicles, late endosomes and the nucleus in RTK signal propagation.

Arid1a regulates response to anti-angiogenic therapy in advanced hepatocellular carcinoma

BACKGROUND & AIMS

AT-rich interaction domain 1a (Arid1a), a component of the chromatin remodeling complex, has emerged as a tumor suppressor gene. It is frequently mutated in hepatocellular carcinoma (HCC). However, it remains unknown how Arid1a suppresses HCC development and whether Arid1a deficiency could be exploited for therapy, we aimed to explore these questions.

METHODS

The expression of Arid1a in human and mouse HCCs was determined by immunohistochemical (IHC) staining. Gene expression was determined by quantitative PCR, ELISA or western blotting. Arid1a knockdown HCC cell lines were established by lentiviral-based shRNA. Tumor angiogenesis was quantified based on vessel density. The regulation of angiopoietin (Ang2) expression by Arid1a was identified by chromatin immunoprecipitation (ChIP) assay. The tumor promoting function of Arid1a loss was studied with a xenograft model in nude mice and diethylnitrosamine (DEN)-induced HCC in Arid1a conditional knockout mice. The therapeutic values of Ang2 antibody and sorafenib treatment were evaluated both in vitro and in vivo.

RESULTS

We demonstrate that Arid1a deficiency, occurring in advanced human HCCs, is associated with increased vessel density. Mechanistically, loss of Arid1a causes aberrant histone H3K27ac deposition at the angiopoietin-2 (Ang2) enhancer and promoter, which eventually leads to ectopic expression of Ang2 and promotes HCC development. Ang2 blockade in Arid1a-deficient HCCs significantly reduces vessel density and tumor progression. Importantly, sorafenib treatment, which suppresses H3K27 acetylation and Ang2 expression, profoundly halts the progression of Arid1a-deficient HCCs.

CONCLUSIONS

Arid1a-deficiency activates Ang2-dependent angiogenesis and promotes HCC progression. Loss of Arid1a in HCCs confers sensitivity to Ang2 blockade and sorafenib treatment.

LAY SUMMARY

AT-rich interaction domain 1a (Arid1a), is a tumor suppressor gene. Arid1a-deficiency promotes Ang2-dependent angiogenesis leading to hepatocellular carcinoma progression. Arid1a-deficiency also sensitizes tumors to Ang2 blockade by sorafenib treatment.

Vector-mediated Tum-5 expression in neovascular endothelial cells for treating hepatocellular carcinoma

Hypervascular hepatocellular carcinoma (HCC) is one of the leading causes of cancer-associated mortality. Angiogenesis is an important contributor to HCC progression and metastasis; therefore, inhibiting angiogenesis may be an effective method of treating HCC. Tumstatin is a novel type of efficient endogenous vascular endothelial cell growth inhibiting factor. The anti-angiogenic activity of tumstatin is localized to the 54-132 amino acid region (Tum-5). In a previous study performed by our group, the gene fragment encoding Tum-5 was cloned and inserted into a pLXSN retroviral vector. In the present study, the anti-angiogenic effects of Tum-5 and the antitumor effects exerted by the pLXSN-Tum-5 vector in vivo were investigated. The results demonstrated that pLXSN-Tum-5 significantly inhibited the growth of human umbilical vein endothelial cells compared with pLXSN, but had no obvious effect on HepG2 cell growth. Moreover, the antitumor and anti-angiogenic activity of Tum-5 was examined in vivo using a xenograft of H22 HCC cells. The results indicated that pLXSN-Tum-5 significantly inhibited tumor growth following 5 injections over 10 days. The size and weight of tumors in the pLXSN-Tum-5 group were lower than those in the saline and pLXSN groups. Furthermore, immunohistochemical analysis with CD31 antibodies indicated that the average microvessel density in the pLXSN-Tum-5 group were significantly lower than that in the saline and pLXSN groups. These results suggested that Tum-5 exerts its antitumor activity by suppressing vascular endothelial cells. The gene fragment of Tum-5 may be developed as an effective inhibitor of angiogenesis and used to treat patients with HCC.

Targeting the Angiopoietin-2/Tie-2 axis in conjunction with VEGF signal interference

Anti-angiogenic therapies target the tumor vasculature, impairing its development and growth. It was hypothesized over 40 years ago by the late Judah Folkman and Julie Denekamp that depriving a tumor of oxygen and nutrients, by targeting the tumor vasculature, could have therapeutic benefits. Identification of growth factors and signaling pathways important in angiogenesis subsequently led to the development of a series of anti-angiogenic agents that over the past decade have become part of the standard of care in several disease settings. Unfortunately not all patients respond to the currently available anti-angiogenic therapies while others become resistant to these agents following prolonged exposure. Identification of new pathways that may drive angiogenesis led to the development of second-generation anti-angiogenic agents such as those targeting the Ang-2/Tie2 axis. Recently, it has become clear that combination of first and second generation agents targeting the blood vessel network can lead to outcomes superior to those using either agent alone. The present review focuses on the current status of VEGF and Ang-2 targeted agents and the potential utility of using them in combination to impair tumor angiogenesis.

Metformin inhibits angiogenesis induced by interaction of hepatocellular carcinoma with hepatic stellate cells

Accumulated evidences indicate metformin is associated with reduced risk of hepatocellular carcinoma (HCC) in diabetic patients, which inspired researchers to explore its therapeutic potentials in HCC. Since Hepatic stellate cells (HSCs) are believed to be the key contributors to tumor microenvironment in HCC and promotes tumor development, here, we explored the effect of metformin on tumor angiogenesis induced by interplay of HCC and HSCs. Our results showed that conditional medium from co-culture of HCC/HSCs induced VEGF secretions and stimulated human umbilical vein endothelial cells (HUVEC) tube formation. However, 25 µM metformin could inhibit this angiogenesis effect. Furthermore, knockdown AMPK of HSCs, not HCC, could abolish inhibition caused by metformin. Our finding suggested that metformin could inhibit HCC angiogenesis through targeting on HSCs through AMPK pathway.

Update on implications and mechanisms of angiogenesis in liver fibrosis

Liver fibrosis occurs as a compensatory response to the process of tissue repair in a wide range of chronic liver injures. It is characterized by excessive deposition of extracellular matrix in liver tissues. As the pathogenesis progresses without effective management, it will lead to formation of liver fiber nodules and disruption of normal liver structure and function, finally culminating in cirrhosis and hepatocellular carcinoma. A new discovery shows that liver angiogenesis is strictly associated with, and may even favor fibrogenic progression of chronic liver diseases. Recent basic and clinical investigations also demonstrate that liver fibrogenesis is accompanied by pathological angiogenesis and sinusoidal remodeling, which critically determine the pathogenesis and prognosis of liver fibrosis. Inhibition of pathological angiogenesis is considered to be a new strategy for the treatment of liver fibrosis. This review summarizes current knowledge on the process of angiogenesis, the relationships between angiogenesis and liver fibrosis, and on the molecular mechanisms of liver angiogenesis. On the other hand, it also presents the different strategies that have been used in experimental models to counteract excessive angiogenesis and the role of angiogenesis in the prevention and treatment of liver fibrosis.

The E2F transcription factors regulate tumor development and metastasis in a mouse model of metastatic breast cancer

While the E2F transcription factors (E2Fs) have a clearly defined role in cell cycle control, recent work has uncovered new functions. Using genomic signature methods, we predicted a role for the activator E2F transcription factors in the mouse mammary tumor virus (MMTV)-polyomavirus middle T oncoprotein (PyMT) mouse model of metastatic breast cancer. To genetically test the hypothesis that the E2Fs function to regulate tumor development and metastasis, we interbred MMTV-PyMT mice with E2F1, E2F2, or E2F3 knockout mice. With the ablation of individual E2Fs, we noted alterations of tumor latency, histology, and vasculature. Interestingly, we noted striking reductions in metastatic capacity and in the number of circulating tumor cells in both the E2F1 and E2F2 knockout backgrounds. Investigating E2F target genes that mediate metastasis, we found that E2F loss led to decreased levels of vascular endothelial growth factor (Vegfa), Bmp4, Cyr61, Nupr1, Plod 2, P4ha1, Adamts1, Lgals3, and Angpt2. These gene expression changes indicate that the E2Fs control the expression of genes critical to angiogenesis, the remodeling of the extracellular matrix, tumor cell survival, and tumor cell interactions with vascular endothelial cells that facilitate metastasis to the lungs. Taken together, these results reveal that the E2F transcription factors play key roles in mediating tumor development and metastasis in addition to their well-characterized roles in cell cycle control.

A neutralizing recombinant single chain antibody, scFv, against BaP1, A P-I hemorrhagic metalloproteinase from Bothrops asper snake venom

BaP1 is a P-I class snake venom metalloproteinase (SVMP) relevant in the local tissue damage associated with envenomings by Bothrops asper, a medically important snake species in Central America and parts of South and North America. The main treatment for these accidents is the passive immunotherapy using antibodies raised in horses. In order to obtain more specific and batch-to-batch consistent antivenons, recombinant antibodies are considered a good option compared to animal immunization. We constructed a recombinant single chain variable fragment (scFv) from a monoclonal antibody against BaP1 (MABaP1) formerly secreted by a hybridoma clone. This recombinant antibody was cloned into pMST3 vector in fusion with SUMO protein and contains VH and VL domains linked by a flexible (G4S)3 polypeptide (scFvBaP1). The aim of this work was to produce scFvBaP1 and to evaluate its potential concerning the neutralization of biologically important activities of BaP1. The cytoplasmic expression of this construct was successfully achieved in C43 (DE3) bacteria. Our results showed that scFvBaP1-SUMO fusion protein presented an electrophoretic band of around 43 kDa from which SUMO alone corresponded to 13.6 kDa, and only the scFv was able to recognize BaP1 as well as the whole venom by ELISA. In contrast, neither an irrelevant scFv anti-LDL nor its MoAb partner recognized it. BaP1-induced fibrinolysis was significantly neutralized by scFvBaP1, but not by SUMO, in a concentration-dependent manner. In addition, scFvBaP1, as well as MaBaP1, completely neutralized in vivo hemorrhage, muscle necrosis, and inflammation induced by the toxin. Docking analyses revealed possible modes of interaction of the recombinant antibody with BaP1. Our data showed that scFv recognized BaP1 and whole B. asper venom, and neutralized biological effects of this SVMP. This scFv antibody can be used for understanding the molecular mechanisms of neutralization of SVMPs, and for exploring the potential of recombinant antibody fragments for improving the neutralization of local tissue damage in snakebite envenoming.