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

Acute myeloid leukemia in the vascular niche

The greatest challenge in treating acute myeloid leukemia (AML) is refractory disease. With approximately 60-80% of AML patients dying of relapsed disease, there is an urgent need to define and target mechanisms of drug resistance. Unfortunately, targeting cell-intrinsic resistance has failed to improve clinical outcomes in AML. Emerging data show that cell-extrinsic factors in the bone marrow microenvironment protect and support AML cells. The vascular niche, in particular, regulates AML cell survival and cell cycling by both paracrine secretion and adhesive contact with endothelial cells. Moreover, AML cells can functionally integrate within vascular endothelia, undergo quiescence, and resist cytotoxic chemotherapy. Together, these findings support the notion of blood vessels as sanctuary sites for AML. Therefore, vascular targeting agents may serve to remit AML. Several early phase clinical trials have tested anti-angiogenic agents, leukemia mobilizing agents, and vascular disrupting agents in AML patients. In general, these agents can be safely administered to AML patients and cardiovascular side effects were reported. Response rates to vascular targeting agents in AML have been modest; however, a majority of vascular targeting trials in AML are monotherapy in design and indiscriminate in patient recruitment. When considering the chemosensitizing effects of targeting the microenvironment, there is a strong rationale to build upon these early phase clinical trials and initiate phase IB/II trials of combination therapy where vascular targeting agents are positioned as priming agents for cytotoxic chemotherapy.

Influence of pre-analytical variables on VEGF gene expression and circulating protein concentrations

BACKGROUND

The extended role of vascular endothelial growth factor (VEGF) in human pathophysiology led us to evaluate pre-analytical parameters possibly influencing its levels in peripheral blood and tissues. The effects on VEGF protein levels and mRNA expression were measured after storage delay (blood and tissue), use of different types of anticoagulants (blood), and after different numbers of freeze-thaw cycles (blood).

METHODS

Blood from healthy donors was sampled simultaneously in ethylene diamine tetraacetic acid (EDTA), acid citrate dextrose (ACD-A), hirudin, and serum separation tubes. For each anticoagulant, VEGF was measured by enzyme-linked immunosorbent assay (ELISA) with different conditions of delay at 4°C before centrifugation (2 h, 4 h, or 48 h) and of different numbers of freeze-thaw cycles (1, 2, and 10). The transcripts coding for the VEGF165 isoform were quantified in peripheral blood mononuclear cells by RT-PCR. Muscle biopsy samples were frozen with delays of 15, 30, or 60 min after surgery. VEGF expression was quantified on immunofluorescence stained slides.

RESULTS

The period of storage and the number of freeze-thaw cycles correlated with an increase in the levels of circulating VEGF (for each anticoagulant but not for serum) and its expression in PBMCs. VEGF expression measured from muscle biopsy sections was higher with freezing delays, with a peak at 30 and 60 min as compared to 15 min.

CONCLUSIONS

The most reliable conditions for measuring both circulating VEGF and its gene expression are to reduce time between blood collection and centrifugation, and to avoid multiple freeze-thaw cycles. Serum collection tubes with no additive and no separator were less sensitive to the pre-analytical variations analyzed in this study. Freezing delay had a significant influence on VEGF protein expression in tissue samples.

Vascular endothelial growth factor A (VEGFA) expression in mycosis fungoides

AIMS

High levels of vascular endothelial growth factor A (VEGFA) seem to herald a worse prognosis in mycosis fungoides (MF). In this study, we aimed to characterize more clearly VEGFA gene and protein expression in MF.

METHODS AND RESULTS

First, we compared VEGFA mRNA levels in MF and in normal T lymphocyte samples; significantly higher VEGFA levels were found in MF. We then studied VEGFA expression in different normal T cell subsets, focusing on CD4(+) , CD8(+) , resting and activated T lymphocytes. We applied the gene signatures of the normal T cell subsets to MF samples and found that activated T lymphocytes represented the closest normal counterpart of the tumour. However, VEGFA mRNA levels were significantly higher in MF than in activated normal T cells, suggesting that VEGFA overexpression in MF represents an attribute acquired during neoplastic transformation: no significant VEGFA expression differences were recorded between early and advanced stages. Gene expression profile results were supported by immunohistochemistry in routine sections from 27 MF cases.

CONCLUSIONS

For the first time, we demonstrate VEGFA expression in MF cells, suggesting that the VEGF pathway may be implicated in MF pathogenesis and can represent a novel therapeutic target.

Angiogenesis as a treatment target in leukemia

SUMMARY The importance of angiogenesis in the growth and survival of leukemia has been well established and confirmed by several studies. In the last 20 years, several antiangiogenic agents have been used in preclinical and clinical studies of the treatment of leukemia. This review article summarizes the literature focusing on the relationship between angiogenesis and disease progression, and the advantages and limits of the antiangiogenic treatment of leukemia.

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.

Angiogenesis in acute myeloid leukemia and opportunities for novel therapies

Acute myeloid leukemia (AML) arises from neoplastic transformation of hematopoietic stem and progenitor cells, and relapsed disease remains one of the greater challenges in treating this hematologic malignancy. This paper focuses on angiogenic aspects of AML including the significance and prognostic value of bone marrow microvessel density and circulating cytokine levels. We show three general mechanisms whereby AML exploits angiogenic pathways, including direct induction of angiogenesis, paracrine regulation, and autocrine stimulation. We also present early evidence that leukemia cells contribute directly to vascular endothelia. Novel treatment strategies are proposed, and a review of relevant antiangiogenic clinical trials is presented. By understanding how blood vessels can serve as a reservoir for refractory and relapsed AML, new diagnostics and promising treatment strategies can be developed.