Endogenous Vascular Endothelial Growth Factor-C Expression Is Associated with Decreased Drug Responsiveness in Childhood Acute Myeloid Leukemia

Far from Health: The Bone Marrow Microenvironment in AML, A Leukemia Supportive Shelter

Acute myeloid leukemia (AML) is the second most common leukemia among children. Although significant progress in AML therapy has been achieved, treatment failure is still associated with poor prognosis, emphasizing the need for novel, innovative therapeutic approaches. To address this major obstacle, extensive knowledge about leukemogenesis and the complex interplay between leukemic cells and their microenvironment is required. The tremendous role of this bone marrow microenvironment in providing a supportive and protective shelter for leukemic cells, leading to disease development, progression, and relapse, has been emphasized by recent research. It has been revealed that the interplay between leukemic cells and surrounding cellular as well as non-cellular components is critical in the process of leukemogenesis. In this review, we provide a comprehensive overview of recently gained knowledge about the importance of the microenvironment in AML whilst focusing on promising future therapeutic targets. In this context, we describe ongoing clinical trials and future challenges for the development of targeted therapies for AML.

VEGFC Antibody Therapy Drives Differentiation of AML

High expression of VEGFC predicts adverse prognosis in acute myeloid leukemia (AML). We therefore explored VEGFC-targeting efficacy as an AML therapy using a VEGFC mAb. VEGFC antibody therapy enforced myelocytic differentiation of clonal CD34⁺ AML blasts. Treatment of CD34⁺ AML blasts with the antibody reduced expansion potential by 30% to 50% and enhanced differentiation via FOXO3A suppression and inhibition of MAPK/ERK proliferative signals. VEGFC antibody therapy also accelerated leukemia cell differentiation in a systemic humanized AML mouse model. Collectively, these results define a regulatory function of VEGFC in CD34⁺ AML cell fate decisions via FOXO3A and serve as a new potential differentiation therapy for patients with AML.Significance: These findings reveal VEGFC targeting as a promising new differentiation therapy in AML. Cancer Res; 78(20); 5940-8. ©2018 AACR.

Effect of High VEGF-C mRNA Expression on Achievement of Complete Remission in Adult Acute Myeloid Leukemia

Although vascular endothelial growth factor-C (VEGF-C) is known to be expressed in acute myeloid leukemia (AML) blasts, the relevance of VEGF-C in the clinical setting remains to be fully explored. We examined the effect of VEGF-C on achievement of complete remission (CR) in adult de novo AML and immune cell population profiles according to VEGF-C mRNA expression. In comparison of VEGF-C expression between the no-CR and CR groups, the CR group showed a trend toward higher levels of plasma VEGF-C (P = .088), whereas mRNA expression of VEGF-C was downregulated (P = .008). Next, patients with continuous data for VEGF-C were divided into two groups (low vs. high) by a ROC curve analysis. The low- versus high-level groups for plasma VEGF-C (RR of 0.20, P = .030), mRNA expression of VEGF-C (RR of 18.75, P = .003), and the ratio of plasma level to mRNA expression (RR of 0.05, P = .007) were potential predictors of CR on univariate analysis. After adjusting for potential clinical factors including genetic group, multivariate analyses revealed that high VEGF-C mRNA expression was an independent risk factor for failure of induction chemotherapy. Furthermore, patients with high VEGF-C mRNA expression had a lower frequency of NKT and CD8+ cells and showed a trend for a lower frequency of NK cells. These results suggest that interruption of VEGF-C signaling might be a potential therapeutic target for antileukemic treatment in AML patients.

Gene Expression of VEGF-A and VEGF-C in Peripheral Blood Mononuclear Cells of Iranian Patients with Acute Myeloid Leukemia

Objective: The crucial role of angiogenesis in the pathophysiology of acute myeloid leukemia (AML) has been proposed. One of the key regulators of angiogenesis is the vascular endothelial growth factor (VEGF). Among the VEGF family, it has been observed that VEGF-A and VEGF-C are expressed by AML cells and mediate leukemic cell proliferation, survival, and resistance to chemotherapy. Emerging evidence, however, suggests that elevated levels of VEGF or a proangiogenic phenotype may impede, rather than promote, early tumor development and progression. As the significance of VEGF-A and VEGF-C levels in the pathogenesis of AML has not been clarified well, the aim of this study is to evaluate gene expression of these angiogenesis promoters and its possible prognostic value in peripheral blood mononuclear cells of Iranian patients with AML.

Materials and Methods: We investigated the mRNA expression of VEGF-A and VEGF-C in peripheral blood mononuclear cells of 27 patients with newly diagnosed AML and 28 healthy controls by quantitative real-time PCR.

Results: Expression of VEGF-C mRNA was significantly lower in AML patients than in healthy controls (p<0.001). However, there was no significant decrement in expression of VEGF-A mRNA of AML patients compared to the control group (p=0.861). VEGF-A and VEGF-C expression were not able to predict clinical outcome.

Conclusion: Our data showed that AML is associated with a decreased expression of VEGF-C mRNA. However, expression levels did not influence the clinical outcome in our study. It seems that angiogenesis is affected by different cytokines other than VEGF-C or VEGF-A, and VEGF is also affected by different cytokines. Taken together, these findings help to provide new insights into the investigation of other angiogenic factors and cytokines that may play roles in the pathogenesis of AML.

Conflict of interest:None declared.

Vascular endothelial growth factor-C modulates proliferation and chemoresistance in acute myeloid leukemic cells through an endothelin-1-dependent induction of cyclooxygenase-2

High-level expression of vascular endothelial growth factor (VEGF)-C is associated with chemoresistance and adverse prognosis in acute myeloid leukemia (AML). Our previous study has found that VEGF-C induces cyclooxygenase-2 (COX-2) expression in AML cell lines and significant correlation of VEGF-C and COX-2 in bone marrow specimens. COX-2 has been reported to mediate the proliferation and drug resistance in several solid tumors. Herein, we demonstrated that the VEGF-C-induced proliferation of AML cells is effectively abolished by the depletion or inhibition of COX-2. The expression of endothelin-1 (ET-1) rapidly increased following treatment with VEGF-C. We found that ET-1 was also involved in the VEGF-C-mediated proliferation of AML cells, and that recombinant ET-1 induced COX-2 mRNA and protein expressions in AML cells. Treatment with the endothelin receptor A (ETRA) antagonist, BQ 123, or ET-1 shRNAs inhibited VEGF-C-induced COX-2 expression. Flow cytometry and immunoblotting revealed that VEGF-C induces S phase accumulation through the inhibition of p27 and the upregulation of cyclin E and cyclin-dependent kinase-2 expressions. The cell-cycle-related effects of VEGF-C were reversed by the depletion of COX-2 or ET-1. The depletion of COX-2 or ET-1 also suppressed VEGF-C-induced increases in the bcl-2/bax ratio and chemoresistance against etoposide and cytosine arabinoside in AML cells. We also demonstrated VEGF-C/ET-1/COX-2 axis-mediated chemoresistance in an AML xenograft mouse model. Our findings suggest that VEGF-C induces COX-2-mediated resistance to chemotherapy through the induction of ET-1 expression. Acting as a key regulator in the VEGF-C/COX-2 axis, ET-1 represents a potential target for ameliorating resistance to chemotherapy in AML patients.

Vascular endothelial growth factor signaling in acute myeloid leukemia

This review is designed to provide an overview of the current literature concerning vascular endothelial growth factor signaling (VEGF) in acute myeloid leukemia (AML). Aberrant VEGF signaling operates in the bone marrow of AML patients and is related to a poor prognosis. The altered signaling pathway demonstrated to interfere in several autocrine and paracrine signaling pathways. VEGF signaling promotes autocrine AML blast cell proliferation, survival, and chemotherapy resistance. In addition, VEGF signaling can mediate paracrine vascular endothelial cell-controlled angiogenesis in AML. Both effects presumably explain the association of high VEGF levels and poor therapeutic outcome. More recently, researches focusing on bone marrow stem cell niches demonstrate a role for VEGF signaling in the preservation of several cell types within these niches. The bone marrow niches are proposed to be a protective microenvironment for AML cells that could be responsible for relapses in AML patients. This implies the need of sophisticated VEGF-targeted therapeutics in AML therapy strategies. This review highlights our current understanding of aberrant VEGF signaling in AML, appoints the interference of VEGF signaling in the AML-associated microenvironment, and reflects the novelty of current VEGF-targeted therapeutics used in clinical trails for the treatment of AML.

The role of the VEGF-C/VEGFRs axis in tumor progression and therapy

Vascular endothelial growth factor C (VEGF-C) has been identified as a multifaceted factor participating in the regulation of tumor angiogenesis and lymphangiogenesis. VEGF-C is not only expressed in endothelial cells, but also in tumor cells. VEGF-C signaling is important for progression of various cancer types through both VEGF receptor-2 (VEGFR-2) and VEGF receptor-3 (VEGFR-3). Likewise, both receptors are expressed mainly on endothelial cells, but also expressed in tumor cells. The dimeric VEGF-C undergoes a series of proteolytic cleavage steps that increase the protein binding affinity to VEGFR-3; however, only complete processing, removing both the N- and C-terminal propeptides, yields mature VEGF-C that can bind to VEGFR-2. The processed VEGF-C can bind and activate VEGFR-3 homodimers and VEGFR-2/VEGFR-3 heterodimers to elicit biological responses. High levels of VEGF-C expression and VEGF-C/VEGFRs signaling correlate significantly with poorer prognosis in a variety of malignancies. Therefore, the development of new drugs that selectively target the VEGF-C/VEGFRs axis seems to be an effective means to potentiate anti-tumor therapies in the future.

Vascular endothelial growth factor-C and its receptor type-3 expressed in acute lymphocytic leukemia cases with t(1;19)

The vascular endothelial growth factor (VEGF)-C system was analyzed in two cases of acute lymphocytic leukemia (ALL) with TCF3/PBX1 fusion to determine whether the VEGF-C system influences the growth of these ALL blasts. Bone marrow non-adherent mononuclear cells were prepared from the patients, and expressions of VEGFs and VEGF receptors (VEGFRs) were analyzed based on RNA and protein levels. Cell proliferation was also assayed with or without neutralizing antibodies to VEGFs. The patients' leukemic blasts expressed a significant amount of VEGF-C and VEGFR type-3. When anti-VEGF-C antibody was added to the blast cell cultures, cell proliferation was suppressed. These observations indicate that, in our ALL cases with TCF3/PBX1 fusion, VEGF-C autocrine stimulation plays an important role in the proliferation of ALL.

Vascular Endothelial Growth Factor A isoform mRNA expression in pediatric acute myeloid leukemia

In AML high VEGFA protein expression correlates with poor overall and relapse-free survival (OS/RFS). To date, the relevance of the various VEGFA isoforms is unclear. We determined VEGF121, VEGF145, VEGF148, VEGF165, VEGF183, and VEGF189 mRNA expression in pediatric AML samples and investigated the relation between VEGFA isoform expression and clinicopatholologic characteristics and outcome. A significant co-expression of VEGF121, VEGF165, VEGF183, and VEGF189 isoforms was apparent (mean rho = 0.716, P < 0.0001). This co-expression justifies measuring a single VEGFA isoform (e.g., 121, 165, 183, and 189) as representative expression of all VEGFA isoforms in future studies designed to determine the prognostic importance of VEGFA isoforms.

Hypoxia-inducible factor-1α protein expression is associated with poor survival in normal karyotype adult acute myeloid leukemia

We examined the predictive impact of HIF-1α protein expression on clinical outcome of 84 normal karyotype acute myeloid leukemia (NK-AML) patients (median age 66.5 years) at our institute. Thirty percent of NK-AML cells expressed cytoplasmic HIF-1α. In univariate analysis, low HIF-1α (≤ 5%, n = 66) was associated with improved event-free survival (p = 0.0453, HR = 0.22). Multivariate analysis incorporating age, complete remission, FLT3-ITD mutation, and marrow blast percentage demonstrated that HIF-1α was independently associated with poorer overall and event-free survival. HIF-1α expression correlated with VEGF-C but not VEGF-A, marrow angiogenesis, FLT3 ITD or NPM1 mutations. These results support HIF-1α as an outcome marker for NK-AML.

Does serum soluble vascular endothelial growth factor levels have different importance in pediatric acute leukemia and malignant lymphoma patients?

Vascular endothelial growth factor (VEGF) seems to play a central role in angiogenesis-lymphangiogenesis in hematological malignancies. There are limited data related to childhood hematologic malignancies. The aim of the study was to evaluate soluble VEGF (sVEGF) levels in children with acute leukemia and malignant lymphoma (ML) at diagnosis and in remission. The levels of serum sVEGF were measured by enzyme-linked immunosorbent assay (ELISA) in 20 children with acute leukemia, 33 children with different histopathological subtypes of ML, and 20 healthy controls. The levels of sVEGF at diagnosis (range 2 -1040 pg/mL; median 52 pg/mL) was significantly lower than in remission (range 136 -1960 pg/mL; median 630 pg/mL) in acute myeloid leukemia (AML) group (P = .018). The sVEGF levels at diagnosis (range: 2 -640 pg/mL; median 89 pg/mL) was significantly lower compared to remission values (range: 116 -1960 pg/mL; median 136 pg/mL) in patients with acute lymphoblastic leukemia (ALL) (P = .002). In ML group, including Burkitt's lymphoma (BL), T-cell non-Hodgkin's lymphoma (NHL), and Hodgkin's lymphoma (HL), sVEGF levels at diagnosis were higher than remission levels, but there was no statistically significant difference (P >.05). On the other hand, there were significant difference between levels in active disease and control group, ie, BL versus control, T-cell NHL versus control, and HL versus control (P = .008, P = .043, P = .007, respectively). The authors noticed that sVEGF levels showed distinct behavioral pattern in different childhood malignancies at diagnosis and in remission. In acute leukemia and ML patients, VEGF acts through different pathophysiological mechanisms, in both bone marrow (BM) angiogenesis and lymphoid tissue lymphangiogenesis.

High VEGFC expression is associated with unique gene expression profiles and predicts adverse prognosis in pediatric and adult acute myeloid leukemia

High VEGFC mRNA expression of acute myeloid leukemia (AML) blasts is related to increased in vitro and in vivo drug resistance. Prognostic significance of VEGFC on long-term outcome and its associated gene expression profiles remain to be defined. We studied effect of VEGFC on treatment outcome and investigated gene expression profiles associated with VEGFC using microarray data of 525 adult and 100 pediatric patients with AML. High VEGFC expression appeared strongly associated with reduced complete remission rate (P = .004), reduced overall and event-free survival (OS and EFS) in adult AML (P = .002 and P < .001, respectively). Multivariable analysis established high VEGFC as prognostic indicator independent of cytogenetic risk, FLT3-ITD, NPM1, CEBPA, age, and white blood cell count (P = .038 for OS; P = .006 for EFS). Also, in pediatric AML high VEGFC was related to reduced OS (P = .041). A unique series of differentially expressed genes was identified that distinguished AML with high VEGFC from AML with low VEGFC, that is, 331 up-regulated genes (representative of proliferation, vascular endothelial growth factor receptor activity, signal transduction) and 44 down-regulated genes (eg, related to apoptosis) consistent with a role in enhanced chemoresistance. In conclusion, high VEGFC predicts adverse long-term prognosis and provides prognostic information in addition to well-known prognostic factors.

Vascular endothelial growth factor-C (VEGF-C) promotes angiogenesis by induction of COX-2 in leukemic cells via the VEGF-R3/JNK/AP-1 pathway

Vascular endothelial growth factor (VEGF)-C is recognized as a tumor lymphangiogenic factor based on the effects of activated VEGF-R3 on lymphatic endothelial cells. Many tumor cells express VEGF-R3 but the function of this receptor in tumor cells is largely unknown. It has been reported that the VEGF-C/VEGF-R3 axis is activated in subsets of leukemia patients. Herein, we have shown that VEGF-C induces angiogenic activity in the tube formation assay invitro and Matrigel plug assay in vivo by upregulating an angiogenic factor, cyclooxygenase-2 (COX-2), through VEGF-R3 in the human acute myeloid leukemia (AML) cell line, THP-1. COX-2 induction by VEGF-C was also observed in other VEGF-R3(+) human AML cell lines (U937 and HL60). Moreover, immunohistochemical analysis of bone marrow specimens of 37 patients diagnosed with AML revealed that VEGF-C expression in specimens was associated with the expression of COX-2 (P < 0.001). The manner by which signaling pathways transduced by VEGF-C is responsible for COX-2 upregulation was further investigated. Blocking the p42/44 mitogen-activated protein kinase (MAPK) pathway with the MAPK kinase inhibitor, PD 98059, failed to inhibit VEGF-C-mediated COX-2 expression. However, VEGF-C-induced COX-2 upregulation was effectively abolished by overexpression of dominant-negative c-Jun N-terminal kinase (JNK) or treatment with the JNK inhibitor, SP 600125. VEGF-C induced JNK-dependent nuclear translocation of c-Jun. Furthermore, chromatin immunoprecipitation and reporter assays revealed that VEGF-C enhanced c-Jun binding to the cyclic adenosine 3',5'-monophosphate-response element of the COX-2 promoter and induced COX-2 expression. In sum, the data herein highlight the pathogenic role of VEGF-C in leukemia via regulation of angiogenesis through upregulation of COX-2.