The dynamic roles of angiopoietins in tumor angiogenesis

An overview of the molecular and clinical significance of the angiopoietin system in leukemia

The angiogenesis efficacy in solid tumors and hematological malignancies has been identified for more than twenty years. Although the exact role of angiogenesis in leukemia as a common hematological malignancy has not yet been extensively studied, its effect is demonstrated on the initiation and maintenance of a favorable microenvironment for leukemia cell proliferation. The angiopoietin family is a defined molecular mediator for angiogenesis, which contributes to vascular permeability and angiogenesis initiation. They participate in the angiogenesis process by binding to tyrosine kinase receptors (Tie) on endothelial cells. Considering the role of angiogenesis in leukemia development and the crucial effects of the Ang-Tie system in angiogenesis regulation, many studies have focused on the correlation between the Ang-Tie system and leukemia diagnosis, monitoring, and treatment. In this study, we reviewed the Ang-Tie system's potential diagnostic and therapeutic effects in different types of leukemia in the gene expression level analysis approach. The angiopoietin family context-dependent manner prevents us from defining its actual function in leukemia, emphasizing the need for more comprehensive studies.

Angiogenic gene characterization and vessel permeability of dermal microvascular endothelial cells isolated from burn hypertrophic scar

Hypertrophic scar (HTS) formation is a common challenge for patients after burn injury. Dermal microvascular endothelial cells (DMVECs) are an understudied cell type in HTS. An increase in angiogenesis and microvessel density can be observed in HTS. Endothelial dysfunction may play a role in scar development. This study aims to generate a functional and expression profile of HTS DMVECs. We hypothesize that transcript and protein-level responses in HTS DMVECs differ from those in normal skin (NS). HTSs were created in red Duroc pigs. DMVECs were isolated using magnetic-activated cell sorting with ulex europaeus agglutinin 1 (UEA-1) lectin. Separate transwell inserts were used to form monolayers of HTS DMVECs and NS DMVECs. Cell injury was induced and permeability was assessed. Gene expression in HTS DMVECS versus NS DMVECs was measured. Select differentially expressed genes were further investigated. HTS had an increased area density of dermal microvasculature compared to NS. HTS DMVECs were 17.59% less permeable than normal DMVECs (p < 0.05). After injury, NS DMVECs were 28.4% and HTS DMVECs were 18.8% more permeable than uninjured controls (28.4 ± 4.8 vs 18.8 ± 2.8; p = 0.11). PCR array identified 31 differentially expressed genes between HTS and NS DMVECs, of which 10 were upregulated and 21 were downregulated. qRT-PCR and ELISA studies were in accordance with the array. DMVECs expressed a mixed profile of factors that can contribute to and inhibit scar formation. HTS DMVECs have both a discordant response to cellular insults and baseline differences in function, supporting their proposed role in scar pathology. Further investigation of DMVECs is warranted to elucidate their contribution to HTS pathogenesis.

Design, Cytotoxicity and Antiproliferative Activity of 4-Amino-5-methyl-thieno[2,3-d]pyrimidine-6-carboxylates against MFC-7 and MDA-MB-231 Breast Cancer Cell Lines

Novel 4-amino-thieno[2,3-d]pyrimidine-6-carboxylates substituted at the second position were prepared by cyclocondensation of 2-amino-3-cyano-thiophene and aryl nitriles in an acidic medium. The design of the target compounds was based on structural optimization. The derivatives thus obtained were tested in vitro against human and mouse cell lines. The examination of the compound effects on BLAB 3T3 and MFC-10A cells showed that they are safe, making them suitable for subsequent experiments to establish their antitumor activity. The photoirritancy factor of the compounds was calculated. Using the MTT test, the antiproliferative activity to MCF-10A, MCF-7 and MDA-MB-231 cell lines was estimated. The best antiproliferative effect in respect to the MCF-7 cell line revealed compound 2 with IC₅₀ 4.3 ± 0.11 µg/mL (0.013 µM). The highest selective index with respect to MCF-7 cells was shown by compound 3 (SI = 19.3), and to MDA-MB-231 cells by compound 2 (SI = 3.7). Based on energy analysis, the most stable conformers were selected and optimized by means of density functional theory (DFT). Ligand efficiency, ligand lipophilicity efficiency and the physicochemical parameters of the target 4-amino-thienopyrimidines were determined. The data obtained indicated that the lead compound among the tested substances is compound 2.

Pocket2Drug: An Encoder-Decoder Deep Neural Network for the Target-Based Drug Design

Computational modeling is an essential component of modern drug discovery. One of its most important applications is to select promising drug candidates for pharmacologically relevant target proteins. Because of continuing advances in structural biology, putative binding sites for small organic molecules are being discovered in numerous proteins linked to various diseases. These valuable data offer new opportunities to build efficient computational models predicting binding molecules for target sites through the application of data mining and machine learning. In particular, deep neural networks are powerful techniques capable of learning from complex data in order to make informed drug binding predictions. In this communication, we describe Pocket2Drug, a deep graph neural network model to predict binding molecules for a given a ligand binding site. This approach first learns the conditional probability distribution of small molecules from a large dataset of pocket structures with supervised training, followed by the sampling of drug candidates from the trained model. Comprehensive benchmarking simulations show that using Pocket2Drug significantly improves the chances of finding molecules binding to target pockets compared to traditional drug selection procedures. Specifically, known binders are generated for as many as 80.5% of targets present in the testing set consisting of dissimilar data from that used to train the deep graph neural network model. Overall, Pocket2Drug is a promising computational approach to inform the discovery of novel biopharmaceuticals.

1,3,5-Triazine Analogs: A Potent Anticancer Scaffold

Background:

This review presents the exhaustive exploration of 1,3,5-triazine scaffold for development of analogs of anticancer drugs, over the last century. In the recent years, striazine moiety has been one of the most studied moiety, showing broad-spectrum pharmacological activities such as antibacterial, antifungal, analgesic, anti-HIV, antileishmanial, antitrypanosomal, antimalarial and antiviral. Nowadays, many boffins are have become interested in novel synthesis of s-triazine derivatives because of low cost and ease of availability.

Methods:

This scaffold has been extensively investigated mainly in the past decade. Many products have been synthesized from different starting materials and these synthetic products possess anticancer potential against various cell lines.

Results:

Many 1,3,5-triazine analogs exhibited significant anticancer activity in various models and cell lines exhibiting different mechanisms. Some analogs have also shown good pharmacokinetic parameters with less IC50 values.

Conclusion:

Various 1,3,5-triazine analogs have shown potent activities and may be regarded as clinical candidates for future anticancer formulations. This review may be helpful to those researchers seeking required information with regard to the drug design and medicinal properties of 1,3,5-triazine derivatives for selected targets. This review may also offer help to find and improve clinically viable anticancer molecules.

Thieno[2,3-d]pyrimidine as a promising scaffold in medicinal chemistry: Recent advances

Thienopyrimidine scaffold is a fused heterocyclic ring system that structurally can be considered as adenine, the purine base that is found in both DNA and RNA-bioisosteres. Thienopyrimidines exist in three distinct isomeric forms. The current review discusses thieno[2,3-d]pyrimidine as a one of the opulent heterocycles in drug discovery. Its broad range of medical applications such as anticancer, anti-inflammatory, anti-microbial, and CNS protective agents has inspired us to study its structure-activity relationship (SAR), along with its relevant synthetic strategies. The present review briefly summarizes synthetic approaches for the preparation of thieno[2,3-d]pyrimidine derivatives. In addition, the promising biological activities of this scaffold are also illustrated with explanatory diagrams for their SAR studies.

LeadOp+R: Structure-Based Lead Optimization With Synthetic Accessibility

We previously described a structure-based fragment hopping for lead optimization using a pre-docked fragment database, “LeadOp,” that conceptually replaced “bad” fragments of a ligand with “good” fragments while leaving the core of the ligand intact thus improving the compound's activity. LeadOp was proven to optimize the query molecules and systematically developed improved analogs for each of our example systems. However, even with the fragment-based design from common building blocks, it is still a challenge for synthesis. In this work, “LeadOp+R” was developed based on 198 classical chemical reactions to consider the synthetic accessibility while optimizing leads. LeadOp+R first allows user to identify a preserved space defined by the volume occupied by a fragment of the query molecule to be preserved. Then LeadOp+R searches for building blocks with the same preserved space as initial reactants and grows molecules toward the preferred receptor-ligand interactions according to reaction rules from reaction database in LeadOp+R. Multiple conformers of each intermediate product were considered and evaluated at each step. The conformer with the best group efficiency score would be selected as the initial conformer of the next building block until the program finished optimization for all selected receptor-ligand interactions. The LeadOp+R method was tested with two biomolecular systems: Tie-2 kinase and human 5-lipoxygenase. The LeadOp+R methodology was able to optimize the query molecules and systematically developed improved analogs for each of our example systems. The suggested synthetic routes for compounds proposed by LeadOp+R were the same as the published synthetic routes devised by the synthetic/organic chemists.

Time course of the angiogenic response during normotrophic and hypertrophic scar formation in humans

Previous research suggests that in hypertrophic scars (HSs), an excess of microvessels is present compared with normotrophic scars (NSs). The aim of our study was to quantify vascular densities in HSs and normotrophic scars and to provide an insight into the kinetics of changes in the expression of angiogenic factors in time during wound healing and HS formation. Human presternal wound healing after cardiothoracic surgery through a sternotomy incision was investigated in a standardized manner. Skin biopsies were collected at consecutive time points, i.e., during surgery and 2, 4, 6, 12, and 52 weeks postoperatively. The expression levels of angiopoietin-1, angiopoietin-2, Tie-2, vascular endothelial growth factor, and urokinase-type plasminogen activator were measured by real-time reverse transcription-polymerase chain reaction. Quantification of angiogenesis and cellular localization of the proteins of interest were based on immunohistochemical analysis. Microvessel densities were higher in the HSs compared with the normotrophic scars 12 weeks (p=0.017) and 52 weeks (p=0.030) postoperatively. Angiopoietin-1 expression was lower in the hypertrophic group (p<0.001), which, together with a nonsignificant increase of angiopoietin-2 expression, represented a considerable decrease in the angiopoietin-1/angiopoietin-2 ratio in the hypertrophic group 4 weeks (p=0.053), 12 weeks (p<0.001), and 52 weeks (p<0.001) postoperatively. The expression of urokinase-type plasminogen activator was up-regulated during HS formation (p=0.008). Vascular endothelial growth factor expression was not significantly different when comparing both groups. In summary, the differential expression of angiopoietin-1, angiopoietin-2, and urokinase-type plasminogen activator in time is associated with an increased vascular density in HSs compared with normotrophic scars.

Context-dependent role of angiopoietin-1 inhibition in the suppression of angiogenesis and tumor growth: implications for AMG 386, an angiopoietin-1/2-neutralizing peptibody

AMG 386 is an investigational first-in-class peptide-Fc fusion protein (peptibody) that inhibits angiogenesis by preventing the interaction of angiopoietin-1 (Ang1) and Ang2 with their receptor, Tie2. Although the therapeutic value of blocking Ang2 has been shown in several models of tumorigenesis and angiogenesis, the potential benefit of Ang1 antagonism is less clear. To investigate the consequences of Ang1 neutralization, we have developed potent and selective peptibodies that inhibit the interaction between Ang1 and its receptor, Tie2. Although selective Ang1 antagonism has no independent effect in models of angiogenesis-associated diseases (cancer and diabetic retinopathy), it induces ovarian atrophy in normal juvenile rats and inhibits ovarian follicular angiogenesis in a hormone-induced ovulation model. Surprisingly, the activity of Ang1 inhibitors seems to be unmasked in some disease models when combined with Ang2 inhibitors, even in the context of concurrent vascular endothelial growth factor inhibition. Dual inhibition of Ang1 and Ang2 using AMG 386 or a combination of Ang1- and Ang2-selective peptibodies cooperatively suppresses tumor xenograft growth and ovarian follicular angiogenesis; however, Ang1 inhibition fails to augment the suppressive effect of Ang2 inhibition on tumor endothelial cell proliferation, corneal angiogenesis, and oxygen-induced retinal angiogenesis. In no case was Ang1 inhibition shown to (a) confer superior activity to Ang2 inhibition or dual Ang1/2 inhibition or (b) antagonize the efficacy of Ang2 inhibition. These results imply that Ang1 plays a context-dependent role in promoting postnatal angiogenesis and that dual Ang1/2 inhibition is superior to selective Ang2 inhibition for suppression of angiogenesis in some postnatal settings.

Angiopoietin-4 promotes glioblastoma progression by enhancing tumor cell viability and angiogenesis

Glioblastoma multiforme (GBM) is a highly invasive and vascularized aggressive brain tumor. Less than 10% of GBM patients survive >5 years after diagnosis. Angiogenesis plays an important role in GBM growth, and antiangiogenesis-based therapies have shown clinical efficacy for GBM patients. Unfortunately, therapeutic resistance often develops in these patients, suggesting that GBM cells are capable of switching their dependency on one proangiogenic signaling pathway to an alternative one. Therefore, it is important to identify novel angiogenic factors that play essential roles in tumor angiogenesis and GBM progression. Angiopoietins (Ang-1, Ang-2, and Ang-4) are the ligands of the Tie-2 receptor tyrosine kinase (RTK). The roles of Ang-1 and Ang-2 in tumor angiogenesis have been established. However, little is known about how Ang-4 affects tumor angiogenesis and GBM progression and the mechanism underlying its effects. In our current study, we establish that Ang-4 is upregulated in human GBM tissues and cells. We show that, like endothelial cells, human GBM cells express Tie-2 RTK. We first establish that Ang-4 promotes in vivo growth of human GBM cells by promoting tumor angiogenesis and directly activating extracellular signal-regulated kinase 1/2 (Erk1/2) in GBM cells. Our results establish the novel effects of Ang-4 on tumor angiogenesis and GBM progression and suggest that this pro-GBM effect of Ang-4 is mediated by promoting tumor angiogenesis and activating Erk1/2 kinase in GBM cells. Together, our results suggest that the Ang-4-Tie-2 functional axis is an attractive therapeutic target for GBM.

Thyroid hormone and angiogenesis

In models of thyroid hormone-induced cardiac hypertrophy, there is appropriate, supportive angiogenesis. Twenty years ago in one such model, angiogenesis in response to the hormone was observed before hypertrophy developed and it is now understood that iodothyronines induce neovascularization in a variety of settings, including the heart, ischemic striated muscle and tumor beds. The molecular mechanism of the proangiogenic action of thyroid hormone is both nongenomic and genomic. It is initiated nongenomically at the cell surface receptor for the hormone on integrin alphavbeta3. Kinase transduction of the hormone signal and, ultimately, transcription of several anagiogenesis-relevant genes result. The genes include basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). In addition, the integrin receptor for thyroid hormone (l-thyroxine, T(4), and 3, 5, 3'-triiodo-l-thyronine, T(3)) engages in crosstalk with the VEGF and bFGF receptors. Occlusion with tetraiodothyroacetic acid (tetrac) of the hormone receptor on the integrin in the absence of T(4) and T(3) suppresses the angiogenic effects of VEGF and bFGF. Tetrac also blocks the proangiogenic actions of T(4) and T(3). Other thyroid hormone analogues that are angiogenic include diiodothyropropionic acid (DITPA) and the nuclear thyroid hormone receptor-beta-selective agonist, GC-1. Thyroid hormone sustains angiogenesis and coronary blood flow about infarcted heart tissue in experimental models and blocks deleterious heart remodeling that otherwise is predictable in such tissue. The hormone may also induce expression of the hypoxia-inducible factor 1alpha (HIF1alpha) gene, a transcription factor important to coronary artery collateralization in the setting of hypoxia. The hormone also causes transcription of the matrix Gla protein (MGP) gene that opposes vascular smooth muscle calcification.

Effects of red light emitting diode on apoptosis of HeLa cells and suppression of implanted HeLa cells growth in mice

Low intensity irradiation of cells by laser was an effective method of biostimulation. Here, we have extended these actions to evaluate the apoptosis effects in red light emitting diode (RLED) exposure. Through morphological observation, flow cytometric analysis, intracellular calcium measurement and RT-PCR, we found that HeLa cells in 24 h RLED irradiation in in-vitro experiments would significantly affects the induction of cellular apoptosis, and morphological changes such as the loose arrangement of cells, the noticeable development of apoptotic bodies,and the accompaniment of arrested S phase and activated caspases-3,-6,-8. Moreover, intracellular calcium concentrations markedly increased 40.3 +/- 1.3% and 43.1 +/- 0.8% respectively, relative to an extracellular solution containing the Ca(2+) and Ca(2+) free unexposed group. In in-vivo tests, RLED irradiation decreased the growth of tumors on day 50 and attenuated the elevation of vascular endothelial growth factor (VEGF) expression in HeLa cell implanted BALB/c mice. Taken together, our results suggest that RLED could induce HeLa cell apoptosis and convey potential antitumor properties.

Matrix metalloproteinase-1 and thrombin differentially activate gene expression in endothelial cells via PAR-1 and promote angiogenesis

Many tumor types express matrix metalloproteinase-1 (MMP-1); its collagenase activity facilitates both tumor cell invasion and metastasis. MMP-1 expression is also associated with increased angiogenesis; however, the exact mechanism by which this occurs is not clear. MMP-1 proteolytically activates protease activated receptor-1 (PAR-1), a thrombin receptor that is highly expressed in endothelial cells. Thrombin is also present in the tumor microenvironment, and its activation of PAR-1 is pro-angiogenic. It is currently unknown whether MMP-1 activation of PAR-1 induces angiogenesis in a similar or different manner compared with thrombin. We sought to determine the mechanism by which MMP-1 promotes angiogenesis and to compare the effects of MMP-1 with those of thrombin. Our results demonstrate that via PAR-1, MMP-1 activates mitogen-activated protein kinase signaling cascades in microvessel endothelial cells. Although thrombin activation of PAR-1 also induces signaling through these pathways, the time-course of activation appears to vary. Gene expression analysis revealed a possible consequence of these signaling differences as MMP-1 and thrombin induce expression of different subsets of pro-angiogenic genes. Furthermore, the combination of thrombin and MMP-1 is more angiogenic than either protease alone. These data demonstrate that MMP-1 acts directly on endothelial cells as a pro-angiogenic signaling molecule and also suggest that the effects of MMP-1 may complement the activity of thrombin to better facilitate angiogenesis and promote tumor progression.

The angiogenic makeup of human hepatocellular carcinoma does not favor vascular endothelial growth factor/angiopoietin-driven sprouting neovascularization

Quantitative data on the expression of multiple factors that control angiogenesis in hepatocellular carcinoma (HCC) are limited. A better understanding of the mechanisms underlying angiogenesis in HCC will improve the rational choice of anti-angiogenic treatment. We quantified gene and protein expression of members of the vascular endothelial growth factor (VEGF) and angiopoietin systems and studied localization of VEGF, its receptors VEGFR-1 and VEGFR-2, Angiopoietin (Ang)-1 and Ang-2, and their receptor, in HCC in noncirrhotic and cirrhotic livers. We employed real-time reverse transcription polymerase chain reaction (RT-PCR), western blot, and immunohistology, and compared the outcome with highly angiogenic human renal cell carcinoma (RCC). HCC in noncirrhotic and cirrhotic livers expressed VEGF and its receptors to a similar extent as normal liver, although in cirrhotic background, VEGFR-2 levels in both tumor and adjacent tissue were decreased. Ang-1 expression was slightly increased compared with normal liver, whereas Tie-2 was strongly down-regulated in the tumor vasculature. Ang-2 messenger RNA (mRNA) levels were also low in HCCs of both noncirrhotic and cirrhotic livers, implying that VEGF-driven angiogenic sprouting accompanied by angiopoietin-driven vascular destabilization is not pronounced. In RCC, VEGF-A levels were one order of magnitude higher. At the same time, endothelially expressed Ang-2 was over 30-fold increased compared with expression in normal kidney, whereas Ang-1 expression was decreased.

CONCLUSION

In hepatocellular carcinoma, tumor vascularization is not per se VEGF/angiopoietin driven. However, increased CD31 expression and morphological changes representative of sinusoidal capillarization in tumor vasculature indicate that vascular remodeling is taking place. This portends that therapeutic intervention of HCC at the level of the vasculature is optional, and that further studies into the molecular control thereof are warranted.

Potential cellular and molecular causes of hypertrophic scar formation

A scar is an expected result of wound healing. However, in some individuals, and particularly in burn victims, the wound healing processes may lead to a fibrotic hypertrophic scar, which is raised, red, inflexible and responsible for serious functional and cosmetic problems. It seems that a wide array of subsequent processes are involved in hypertrophic scar formation, like an affected haemostasis, exaggerated inflammation, prolonged reepithelialization, overabundant extracellular matrix production, augmented neovascularization, atypical extracellular matrix remodeling and reduced apoptosis. Platelets, macrophages, T-lymphocytes, mast cells, Langerhans cells and keratinocytes are directly and indirectly involved in the activation of fibroblasts, which in turn produce excess extracellular matrix. Following the chronology of normal wound healing, we unravel, clarify and reorganize the complex molecular and cellular key processes that may be responsible for hypertrophic scars. It remains unclear whether these processes are a cause or a consequence of unusual scar tissue formation, but raising evidence exists that immunological responses early following wounding play an important role. Therefore, when developing preventive treatment modalities, one should aim to put the early affected wound healing processes back on track as quickly as possible.

Vascular changes in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most vascular solid tumors, in which angiogenesis plays an important role. The status of angiogenesis in HCC correlates with the disease progression and prognosis, and thus provides a potential therapeutic target. This review summarizes the vascular changes and molecular and cellular basis of angiogenesis in HCC. Development of HCC is characterized by arterialization of its blood supply and sinusoidal capillarization. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that plays a critical role in mediating angiogenesis in HCC. The VEGF can function on various types of cells, such as endothelial cells, hepatic stellate cells, endothelial progenitor cells and hemangiocytes, to induce vascular changes in HCC. Therefore, blockade of VEGF-mediated pathways, either by anti-VEGF neutralizing antibody or tyrosine kinase inhibitors that target VEGF receptors, suppresses carcinogenesis and angiogenesis in HCC. In addition to VEGF, several other angiogenic factors in HCC have recently been identified. These factors can also regulate angiogenic processes through interaction with VEGF or VEGF-independent pathways. Despite the fact that treatment of HCC remains a tough task due to lack of effective systemic therapy, antiangiogenic therapy has already entered clinical trials in HCC patients and sheds light on a promising novel treatment for this disease.

A software system for syntactic analysis of the EEG

This paper describes an interlocking set of programs used for syntactic analysis of the electroencephalogram. This system constitutes a basic set of programs in the Vanderbilt EEG analysis system (VEAS). The concepts underlying the methods are explained and examples of the use of the system are given. The algorithms employed for spatial, temporal and global parsing of 'EEG sentences' are presented and examples of the use of various grammatical rules are described.