Serum Angiopoietin Levels are Different in Acute and Chronic Myeloid Neoplasms: Angiopoietins do not only Regulate Tumor Angiogenesis

A comprehensive insight into the role of molecular pathways affected by the Angiopoietin and Tie system involved in hematological malignancies' pathogenesis

Angiogenesis has been recognized as a critical factor in developing solid tumors and hematological malignancies. How angiogenesis affects the molecular pathways in malignancies is still a mystery. The angiopoietin family, one of the known molecular mediators for angiogenesis, encourages angiogenesis by attaching to Tie receptors on cell surfaces. Angiopoietin, Tie, and particularly the molecular pathways they mediate have all been the subject of recent studies that have established their diagnostic, prognostic, and therapeutic potential. Here, we've reviewed the function of molecular pathways impacted by the Angiogenin and Tie system in hematological malignancies.

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.

Intracellular angiopoietin-1 promotes TKI-resistance via activation of JAK/STAT5 pathway in chronic myeloid leukemia

Drug resistance from BCR-ABL tyrosine kinase inhibitors (TKIs) and other chemotherapeutics results in treatment failure and disease progression in chronic myeloid leukemia (CML). However, the mechanism is still uncertain. In this study, we investigated the role of angiopoietin-1 (ANG-1) as a potential prognostic factor for drug resistance in CML. Both intracellular and secretory ANG-1 (iANG-1 and sANG-1) were overexpressed in multidrug-resistant CML samples. The IC₅₀ value was higher in primary CD34⁺ CD38^- cells with more ANG-1. Silencing ANG-1significantly sensitized three TKI-resistant CML cell lines to imatinib (IM) while recombinant human ANG-1 failed to retain cell survival in vitro. This indicated the important role of iANG-1 as opposed to sANG-1 in CML drug resistance. Moreover, a similar effect was observed in xenograft mice models bearing ANG-1-silenced CML cells. Subsequently, pathway analysis and protein validation experiments showed activation of the JAK/STAT pathway and augmentation of STAT5a phosphorylation in ANG-1 restored CML cells. Upstream Src phosphorylation, which plays a crucial role in CML drug resistance, was also upregulated as a key event in iANG-1-related JAK/STAT pathway activation. In conclusion, our study elucidated a new BCR-ABL independent molecular mechanism induced by intracytoplasmic ANG-1 overexpression as a potential strategy for overcoming CML resistance.

Investigating the expression pattern of the angiopoietin-Tie system in ALL and its correlation with baseline characteristics

Background

Acute lymphoblastic leukemia (ALL) is the most common type of leukemia in children. Several environmental and genetic factors are known to be involved in its development and progression. The angiopoietin-Tie system is one of the most critical factors in angiogenesis, and its possible role in solid tumors and leukemia has been previously investigated. In this study, we examined the expression of these genes in ALL patients (early pre-B-ALL and pre-B-ALL) and compared them with normal samples.

Methods

Bone marrow samples were collected from 40 patients (aged 0‒19 yr) newly diagnosed with early pre-B-ALL or pre-B-ALL using molecular and flow cytometric tests and from 15 control individuals. For molecular tests, RNA extraction and cDNA synthesis were performed, and Ang1, Ang2, Ang4, Tie1, and Tie2 gene expression was examined by real-time polymerase chain reaction.

Results

Ang2, Tie1, and Tie2 gene expression were significantly increased in patients with ALL, whereas Ang1 gene expression was decreased. The Ang4 gene did not show significant expression changes between the two groups.

Conclusion

Changes in the expression of the Ang-Tie system indicate a possible role of angiogenesis in ALL prognosis. Moreover, such changes can be considered as potential diagnostic biomarkers or therapeutic targets.

Clinical value of selected markers of angiogenesis, inflammation, insulin resistance and obesity in type 1 endometrial cancer

Background

It is a well-known fact show that the risk of developing endometrial cancer (type 1 EC) is strongly associated with obesity. In this study, selected markers, such as obesity, insulin resistance, angiogenesis and inflammation markers related to EC type 1 progression and patients’ survival data were analyzed.

Methods

To measure levels of adiponectin, C-reactive protein (CRP), vascular endothelial growth factor-A (VEGF-A), angiopoietin-2 (Ang-2), insulin-like growth factor-1 (IGF-1), insulin and C-peptide in 176 preoperative serum samples, the immunoassay technique (EMIT) has been applied.

Results

Angiopoietin-2 levels increase with age (P = 0.005), FIGO stage (p = 0.042), myometrial invasion (P = 0.009) and LVSI (P < 0.001). The CRP levels increase with age (P = 0.01), as well as the advancement of the FIGO stage (P < 0.001), higher tumor grade (P = 0.012), and myometrial invasion (P < 0.001). A positive correlation between serum Ang-2 and CRP levels was demonstrated (r = 0.44; p < 0.001). Kaplan-Meier survival analysis showed that patients with high CRP levels in serum and Ang-2 presented a worse outcome (P = 0.03 and P = 0.015, respectively). Cox regression analysis of individual predictors revealed that high serum levels of Ang-2, CRP, advanced clinical FIGO stage (P < 0.001, respectively), old age (P = 0.013) were all significant overall survival predictors. By means of multivariate analysis, their predictive significance was confirmed.

Conclusion

Our study provides evidence that serum levels of Ang-2 and CRP may serve as predictors for assessment of the clinical stage of type 1 EC and are significantly associated with poor prognosis. It is likely that angiogenesis and inflammation associated with obesity have a significant impact on EC type 1 progression and survival rate of patients.

Role of Angiopoietins in Development of Cancer and Neoplasia Associated with Viral Infection

Angiopoietin/tyrosine protein kinase receptor Tie-2 signaling in endothelial cells plays an essential role in angiogenesis and wound healing. Angiopoietin-1 (Ang-1) is crucial for blood vessel maturation while angiopoietin-2 (Ang-2), in collaboration with vascular endothelial growth factor (VEGF), initiates angiogenesis by destabilizing existing blood vessels. In healthy people, the Ang-1 level is sustained while Ang-2 expression is restricted. In cancer patients, Ang-2 level is elevated, which correlates with poor prognosis. Ang-2 not only drives tumor angiogenesis but also attracts infiltration of myeloid cells. The latter rapidly differentiate into tumor stromal cells that foster tumor angiogenesis and progression, and weaken the host’s anti-tumor immunity. Moreover, through integrin signaling, Ang-2 induces expression of matrix metallopeptidases (MMPs) to promote tumor cell invasion and metastasis. Many oncogenic viruses induce expression of Ang-2 to promote development of neoplasia associated with viral infection. Multiple Ang-2 inhibitors exhibit remarkable anti-tumor activities, further highlighting the importance of Ang-2 in cancer development.

Angiogenesis Status in Patients with Acute Myeloid Leukemia: From Diagnosis to Post-hematopoietic Stem Cell Transplantation

As already proven in solid tumors, increased angiogenesis leads to increased number of blood vessels, resulting in unfavorable outcomes and resistance to chemotherapy. It was previously thought that angiogenesis plays no role in the pathogenesis of acute myeloid leukemia (AML), due to the fact that AML is a liquid tumor. However, many studies have suggested that increased angiogenesis has important roles in patients with AML, including increased numbers of vessels in bone marrow and pro-angiogenic factors, as well as decreased anti-angiogenic factors. Also a large number of studies demonstrated that a two-way communication is established between leukemic and endothelial cells, as a component of the vessel wall, in the bone marrow of patients with AML. These two cells support the survival and proliferation of each other through a paracrine pathway, resulting in resistance to chemotherapy. In addition, It is well-established that increased angiogenesis is associated with unfavorable prognosis, lower survival rate, resistance to chemotherapy, and relapse. Furthermore, increased angiogenesis affects the response to treatment, hematopoietic stem cell transplantation (HSCT) outcome and graft versus host disease (GVHD) occurrence. In this regard, this review will address vascular endothelial growth factor (VEGF) and angiopoietin (Ang), two of the most important angiogenic factors, in patients with AML before and after HSCT. By increasing our understanding of the role of endothelial cells and angiogenic factors in patients with AML from diagnosis to post-HSCT, new therapeutic strategies can be developed to reduce angiogenesis, improve patients' survival and reduce complications.