Increased angiogenesis in bone marrow of children with acute lymphoblastic leukaemia has no prognostic significance

High BMP4 expression in low/intermediate risk BCP-ALL identifies children with poor outcomes

Pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL) outcome has improved in the last decades, but leukemic relapses are still one of the main problems of this disease. Bone morphogenetic protein 4 (BMP4) was investigated as a new candidate biomarker with potential prognostic relevance, and its pathogenic role was assessed in the development of disease. A retrospective study was performed with 115 pediatric patients with BCP-ALL, and BMP4 expression was analyzed by quantitative reverse transcription polymerase chain reaction in leukemic blasts at the time of diagnosis. BMP4 mRNA expression levels in the third (upper) quartile were associated with a higher cumulative incidence of relapse as well as a worse 5-year event-free survival and central nervous system (CNS) involvement. Importantly, this association was also evident among children classified as having a nonhigh risk of relapse. A validation cohort of 236 patients with BCP-ALL supported these data. Furthermore, high BMP4 expression promoted engraftment and rapid disease progression in an NSG mouse xenograft model with CNS involvement. Pharmacological blockade of the canonical BMP signaling pathway significantly decreased CNS infiltration and consistently resulted in amelioration of clinical parameters, including neurological score. Mechanistically, BMP4 favored chemoresistance, enhanced adhesion and migration through brain vascular endothelial cells, and promoted a proinflammatory microenvironment and CNS angiogenesis. These data provide evidence that BMP4 expression levels in leukemic cells could be a useful biomarker to identify children with poor outcomes in the low-/intermediate-risk groups of BCP-ALL and that BMP4 could be a new therapeutic target to blockade leukemic CNS disease.

The Bone Marrow Microenvironment in B-Cell Development and Malignancy

B lymphopoiesis is characterized by progressive loss of multipotent potential in hematopoietic stem cells, followed by commitment to differentiate into B cells, which mediate the humoral response of the adaptive immune system. This process is tightly regulated by spatially distinct bone marrow niches where cells, including mesenchymal stem and progenitor cells, endothelial cells, osteoblasts, osteoclasts, and adipocytes, interact with B-cell progenitors to direct their proliferation and differentiation. Recently, the B-cell niche has been implicated in initiating and facilitating B-cell precursor acute lymphoblastic leukemia. Leukemic cells are also capable of remodeling the B-cell niche to promote their growth and survival and evade treatment. Here, we discuss the major cellular components of bone marrow niches for B lymphopoiesis and the role of the malignant B-cell niche in disease development, treatment resistance and relapse. Further understanding of the crosstalk between leukemic cells and bone marrow niche cells will enable development of additional therapeutic strategies that target the niches in order to hinder leukemia progression.

Serum Levels of Vascular Endothelial Growth Factor and Its Receptor in Newly Diagnosed Paediatric Acute Lymphoblastic Leukemia

Autocrine and paracrine loop involving vascular endothelial growth factor (VEGF) and its receptor have been described in haematological malignancies. However, scarce literature is present on angiogenesis in paediatric acute lymphoblastic leukemia (ALL) with studies showing controversial results. The aim was to study serum levels of VEGF and its receptors in paediatric ALL at the time of diagnosis and at the end of induction phase and to compare these levels with clinico-haematological parameters in these patients. Serum VEGF, VEGFR-1 and VEGFR-2 levels were measured by enzyme-linked immunoabsorbant assay at diagnosis (day 0) and at the end of induction phase (day 35) in 30 newly diagnosed paediatric ALL patients and in 10 healthy controls. Median s-VEGF was significantly lower at day 0 as compared to day 35 (196.15 vs. 606.75 pg/ml: p < 0.001). s-VEGFR-1 levels were detectable only in 7 patients at day 0 and were below detection level at day 35 in all patients. Median s-VEGFR-2 at day 0 was significantly lower as compared to day 35 (17,577.5 vs. 20,507.5 pg/ml; p = 0.005). Median VEGF-R1 showed an inverse relationship with VEGF-R2 but was statistically insignificant. All patients were in remission at the end of induction. Thus, leukemic infiltration of bone marrow affects angiogenesis and reduces pro-angiogenic markers VEGF and VEGFR-2 in serum possibly due to increased local consumption by blasts. A successful induction leads to clearing of blasts causing restoration of normal hematopoiesis with normalization of VEGF and VEGFR-2 levels.

The Bone Marrow Niche in B-Cell Acute Lymphoblastic Leukemia: The Role of Microenvironment from Pre-Leukemia to Overt Leukemia

Genetic lesions predisposing to pediatric B-cell acute lymphoblastic leukemia (B-ALL) arise in utero, generating a clinically silent pre-leukemic phase. We here reviewed the role of the surrounding bone marrow (BM) microenvironment in the persistence and transformation of pre-leukemic clones into fully leukemic cells. In this context, inflammation has been highlighted as a crucial microenvironmental stimulus able to promote genetic instability, leading to the disease manifestation. Moreover, we focused on the cross-talk between the bulk of leukemic cells with the surrounding microenvironment, which creates a “corrupted” BM malignant niche, unfavorable for healthy hematopoietic precursors. In detail, several cell subsets, including stromal, endothelial cells, osteoblasts and immune cells, composing the peculiar leukemic niche, can actively interact with B-ALL blasts. Through deregulated molecular pathways they are able to influence leukemia development, survival, chemoresistance, migratory and invasive properties. The concept that the pre-leukemic and leukemic cell survival and evolution are strictly dependent both on genetic lesions and on the external signals coming from the microenvironment paves the way to a new idea of dual targeting therapeutic strategy.

Signaling and molecular basis of bone marrow niche angiogenesis in leukemia

Angiogenesis, the process of blood vessel formation, is necessary for tissue survival in normal and pathologic conditions. Increased angiogenesis in BM niche is correlated with leukemia progression and resistance to treatment. Angiogenesis can interfere with disease progression and several angiogenic (such as vascular growth factors) as well as anti-angiogenic factors (i.e. angiostatin) can affect angiogenesis. Furthermore, miRs can affect the angiogenic process by inhibiting angiogenesis or increasing the expression of growth factors. Given the importance of angiogenesis in BM for maintenance of leukemic clones, recognition of angiogenic and anti-angiogenic factors and miRs as well as drug resistance mechanisms of leukemic blasts can improve the therapeutic strategies. We highlight the changes in angiogenic balance within the BM niche in different leukemia types. Moreover, we explored the pathways leading to drug resistance in relation to angiogenesis and attempted to assign interesting candidates for future research.

Functional and Biological Role of Endothelial Precursor Cells in Tumour Progression: A New Potential Therapeutic Target in Haematological Malignancies

It was believed that vasculogenesis occurred only during embryo life and that postnatal formation of vessels arose from angiogenesis. Recent findings demonstrate the existence of Endothelial Precursor Cells (EPCs), which take partin postnatal vasculogenesis. EPCs are recruited from the bone marrow under the stimulation of growth factors and cytokines and reach the sites of neovascularization in both physiological and pathological conditions such as malignancies where they contribute to the “angiogenic switch” and tumor progression. An implementation of circulating EPCs in the bloodstream of patients with haematological malignancies has been demonstrated. This increase is strictly related to the bone marrow microvessel density and correlated with a poor prognosis. The EPCs characterization is a very complex process and still under investigation. This literature review aims to provide an overview of the functional and biological role of EPCs in haematological malignancies and to investigate their potential as a new cancer therapeutic target.

Angiogenesis and proliferation index in patients with acute leukemia: a prospective study

Angiogenesis and proliferation as measured by microvessel density (MVD) and proliferation index (PI) are essential correlates of malignancy. The aim of our study was to evaluate difference between these values in AML and ALL and also to study the modulation in these parameters following achievement of remission in acute lymphoblastic leukemia. Differences between adult and adolescent cases of acute leukemia in relation to these values were also studied. We also tried to assess the relationship between angiogenesis and proliferation. Fifty-five patients with acute leukemia were included in the study. Trephine biopsies were immunostained with CD34 and factor VIIIrAg to demonstrate angiogenesis measured as MVD. Immunostaining with PCNA and Ki-67 was done to study proliferation. We found a significant increase in MVD and PI in cases when compared with controls (P < 0.0001). In addition cases with ALL had a significantly higher MVD compared to those with AML (P < 0.01). The patients with ALL who went into remission showed a significant reduction in MVD; PI remained high. The cases which did not achieve remission showed no significant reduction in either MVD or PI. All adolescent cases of ALL were similar to adults with respect to MVD and PI.

Clinical nanomedicine: a solution to the chemotherapy conundrum in pediatric leukemia therapy

Although chemotherapy-based treatment of leukemia has tremendously improved survival rates in children, induction of treatment-related side effects is a major concern in clinical oncology. The development of nanotechnology-based drug delivery techniques to target clinically approved anticancer agents specifically to leukemic cells should diminish toxic side effects. This review aims to address the rational design of nanotherapeutics in treating hematologic malignancies with a focus on acute lymphoblastic leukemia (ALL)--the most prominent form of pediatric cancer.

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.

What role for angiogenesis in childhood acute lymphoblastic leukaemia?

The role of angiogenesis in acute leukaemia has been discussed since the cloning of the gene of vascular endothelial growth factor (VEGF) from the acute myelogenous leukemia cell line (HL60) and, thereafter, when the first studies reported increased bone marrow vascularity and elevation of angiogenic cytokines in acute lymphoblastic leukaemia (ALL). VEGF and basic fibroblast growth factor (bFGF) are the major proangiogenic cytokines that have been studied, and evaluation of their prognostic impact in childhood ALL has been reported in several studies, though with controversial results. The antiangiogenic response, contributing to the angiogenic balance, has scarcely been reported. The origin of the factors, their prognostic value, and their relevance as good markers of what really happens in the bone marrow are discussed in this paper. The place of antiangiogenic drugs in ALL has to be defined in the global treatment strategy.

Vascular endothelial growth factor levels in childhood acute lymphoblastic and myeloblastic leukemia

Angiogenesis has been associated with the growth, dissemination and metastasis and has been shown to be a prognostic. Although there are some data suggesting that angiogenesis may have a role in the pathophysiology of leukemia, its role in patient prognosis is yet to be defined. We analyzed the expression level of vascular endothelial growth factor (VEGF), an angiogenesis promoter and its possible- prognostic value in bone marrow samples at the time of diagnosis and remission of acute childhood leukemia patients. Besides 46 patients diagnosed as ALL or AML, 16 children were also included as a control group in the study. Our data have demonstrated that VEGF levels of AML patients were found higher than the control group statistically (P = 0.022). However we could not find any significant difference between VEGF levels of diagnosis and remission in both AML and ALL groups by blastic VEGF expression (P > 0.05). In this study the higher levels of VEGF in AML patients is one of the main findings although we were not able to assess any role of VEGF in predicting prognosis in pediatric leukemia patients by evaluating blastic cell VEGF expression. These results have demonstrated that the relationship between angiogenesis or angiogenesis promoters and hematological malignancies is not clear and simple as different methods or different cells beside different angiogenesis promotors are involved to these studies. So that not only tumor cells and their cytokines but also surrounding cells and their cytokines must be taken into consideration with the standardized study methods in the further studies to obtain a promising treatment approach.

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.

Vascular density in childhood acute lymphoblastic leukaemia correlates to biological factors and outcome

The issue of angiogenesis and its clinical relevance in childhood acute lymphoblastic leukaemia (ALL) is controversial. In the present study, microvessel density (MVD), analysed in 185 diagnostic bone marrow biopsies, was higher in T-cell ALL compared to B-cell precursor (BCP)-ALL (P = 0.013). In the BCP group, cases with t(12;21) were characterized by a low MVD while patients with high-hyperdiploid leukaemia (HeH, 51-61 chromosomes) showed a high MVD compared to other BCP patients (P = 0.001 and 0.002 respectively). There was a correlation between MVD and white blood cell (WBC) count in high-risk BCP patients (P = 0.021). In addition, BCP patients with a high marrow reticulin fibre density and high MVD had an unfavourable outcome compared to the other BCP patients (P = 0.002). The fraction of vessels in which lumina were filled with blasts (blast congested vessel fraction) correlated strongly with WBC count (P < 0.001). These findings indicate that the angiogenic process interacts with other stroma-factors, such as reticulin fibre density, in its effect on outcome, and is coupled to both the ALL genotype and phenotype. One possible implication is that different subtypes of childhood ALL may respond differently to anti-angiogenic drugs as a supplement in first-line treatment.

Clinical role of bone marrow angiogenesis in childhood acute lymphocytic leukemia

PURPOSE

Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are associated with increased angiogenesis, growth, and metastasis in solid tumors. But, until today, the importance of theses factors on leukemia, especially childhood acute lymphocytic leukemia (ALL) has received limited attention. Therefore, this study examined the bone marrow plasma VEGF and bFGF levels in ALL patients and normal controls.

PATIENTS AND METHODS

Bone marrow plasmas at diagnosis from 33 ALL patients (median age 5.9 years; range 1.8-13.9 years) were used for analysis. The bone marrow levels of bFGF and VEGF were determined by enzyme-linked immunosorbent assay (R & D Systems) and compared with the bone marrow levels of 7 healthy control subjects (median age 11.98 years; 6 months -13.6 years).

RESULTS

Average VEGF was higher in relapse ALL (N=7, 216.6 +/- 79.9pg/mL) compared to standard (N=9, 36.8 +/- 12.1pg/mL) (p=0.013) or high risk ALL (N=17, 80.0 +/- 12.2pg/mL) (p=0.023). bFGF levels were also significantly higher in relapse than standard-, or high-risk ALL patients (relapse ALL; 48.6 +/- 15.4pg/mL, standard risk ALL; 18.9 +/- 5.5pg/mL, high risk ALL; 19.0 +/- 3.5pg/mL, normal control; 18.6 +/- 4.0pg/mL) (p=0.003). Three patients with refractory relapse and death had much higher VEGF and bFGF values (VEGF; 420.0 +/- 81.6pg/ mL, bFGF; 85.6 +/- 3.2pg/mL).

CONCLUSION

Our data suggest that the increased levels of VEGF and bFGF in bone marrow may play an important role in prognosis of childhood ALL.

Expression of vascular endothelial growth factor receptor 3 and Tie1 tyrosine kinase receptor on acute leukemia cells

BACKGROUND

Recent data indicate a role for angiogenesis in hematologic malignancies. In addition to promoting new vessel growth in the bone marrow microenvironment, angiogenic factors are regulators of both hematopoietic and leukemic cells. Activation of vascular endothelial growth factor receptor 3 (VEGFR-3) and Tie1 tyrosine kinase receptor are known to promote leukemia cell survival. The details of this complex angiogenesis-related interaction are still uncertain.

PROCEDURE

We studied bone marrow samples from 73 patients with acute lymphoblastic (ALL) or myelogenous (AML) leukemia by using immunological methods.

RESULTS

Vascular endothelial growth factor receptor 3 expression was found in 15% of the samples, particularly in samples with pediatric lymphoblastic leukemias and monocytic AMLs. Tie1 protein expression was found in 11% of the samples, all of which were from adult AML patients.

CONCLUSIONS

Our findings suggest that there are angiogenesis-related differences between pediatric and adult lymphoblastic leukemias as well as between lymphoid and myeloid leukemias.

The Thalidomide Analogue, CC-4047, Induces Apoptosis Signaling and Growth Arrest in Childhood Acute Lymphoblastic Leukemia Cells In vitro and In vivo

PURPOSE

Thalidomide and its analogues have shown promise in the treatment of multiple myeloma but their therapeutic potential has not been evaluated in models of acute lymphoblastic leukemia (ALL).

EXPERIMENTAL DESIGN

We assessed the effects of the thalidomide analogue, CC-4047, on the growth and apoptosis signaling of human B cell precursor (BCP) ALL cell lines and freshly obtained childhood BCP-ALL cells grown with or without stromal cells. In addition, we studied the effects of CC-4047 on the progression and dissemination of xenotransplanted human BCP-ALL cells in nonobese diabetic/severe combined immunodeficiency mice.

RESULTS

CC-4047 reduced the proliferation of human BCP-ALL cell lines in vitro. In contrast with the antileukemic effect of cytarabin, this was more pronounced when cell lines or freshly obtained childhood BCP-ALL cells were cocultured with stromal cells. CC-4047 induced the cleavage of caspase-3, caspase-9, and poly(ADP-ribose) polymerase in stroma-cocultured BCP-ALL cells. The inhibition of tumor growth, caspase-3 cleavage, and reduced microvessel density was observed in nonobese diabetic/severe combined immunodeficiency mice inoculated s.c. with childhood BCP-ALL cells upon CC-4047 treatment. After i.v. BCP-ALL xenotransplantation, CC-4047 reduced splenic dissemination.

CONCLUSIONS

The thalidomide analogue, CC-4047, displays profound cytostatic effects on stroma-supported human ALL cells both in vitro and in vivo.

Leukemia-stimulated bone marrow endothelium promotes leukemia cell survival

Extensive endothelial cell proliferation and marked neovascularization are the most pronounced microenvironmental changes consistently observed in the bone marrow (BM) of patients with acute lymphoblastic leukemia (ALL). It is not known whether ALL cells induce this phenotype and whether they receive critical signals from the tumor-associated BM endothelium. Here, we show that leukemia cells actively stimulate BM endothelium, promote de novo angiogenesis, and induce neovascularization in the leukemic BM. Soluble factors, present in the leukemic BM microenvironment, promote the proliferation, migration, and morphogenesis of BM endothelial cells, which are critical processes in tumor angiogenesis. We also show in vitro that leukemia cells display directional motion towards assembled BM endothelium and following adherence exhibit cell polarization, pseudopodia, and ultrastructural features that suggest the existence of leukemia-endothelium cross-talk. Finally, we show that BM endothelium promotes leukemia cell survival through a mechanism mediated through the anti-apoptotic molecule bcl-2. These studies indicate that ALL cells actively recruit BM endothelium and mediate the leukemia-associated neovascularization observed in ALL. Therefore, disruption of interactions between leukemia cells and BM endothelium may constitute a valid therapeutic strategy.

Anti-leukemic and anti-angiogenesis efficacy of arsenic trioxide in new cases of acute promyelocytic leukemia

Arsenic trioxide is now considered the standard agent in treatment of refractory cases of acute promyelocytic leukemia (APL). This drug is also shown to have anti-angiogenesis effect against APL cells in vitro. This study evaluated clinical efficacy and anti-angiogenesis effect of arsenic trioxide in 17 new cases of APL. Arsenic trioxide was given in a dosage of 0.15 mg kg(-1) and remission rate, survival rate, toxicities and effect on vascular density of bone marrow was studied. The bone marrow vascular density was examined using immunohistochemistry for von Willebrand Factor (vWF) and CD31 markers. Bone marrow vascular density was determined by calculating mean vessel number in 3 hot spot, high power microscopic fields. Bone marrow vascular density was reduced as identified by anti-vWF immunohistochemical staining (Mean before treatment = 201.6 mm(-2) +/- 20.4 (SEM), mean after treatment = 109.4 +/- 17.2 (SEM), p < 0.001) and anti-CD31 immunostaining (mean before treatment = 199.17 mm(-2) +/- 21.5 (SEM), mean after treatment = 99.5 mm(-2) +/- 22.1 (SEM), p < 0.05). Treatment efficacy results showed 100% complete remission rate after median of 30 days and 72% survival rate after median 860 days of follow-up. Main toxicities included hyper-leukocytosis, hepatic toxicity and APL differentiation syndrome. The results imply that arsenic trioxide is an effective anti-leukemia and anti-angiogenesis agent in new cases of APL.

Angiogenic factors may have a different prognostic role in adult acute lymphoblastic leukemia

Angiogenesis plays an important role in solid tumors and hematologic malignancies. The prognostic significance of angiogenic factors in adult acute lymphoblastic leukemia (ALL) remains ambiguous. We therefore analyzed the impact of angiogenic factor levels on overall survival of newly diagnosed adult ALL patients. Plasma levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), interleukin-1 receptor alpha (IL-1Ralpha), IL-6, IL-8, VEGF receptors VEGFR1 and VEGFR2, and thrombopoietin (TPO) were measured in plasma samples of 95 patients by enzyme-linked immunosorbent assay (ELISA). In a univariate Cox proportional hazards model, higher levels of IL-1Ralpha, IL-8, VEGFR1, and VEGFR2 were predictive of poor survival. In contrast, higher levels of VEGF were predictive of longer survival, and higher levels of bFGF suggested a similar trend (P = .09). The multivariate model simultaneously included VEGF (relative risk [RR] for death, 8.01; P = .001 for levels less than or equal to 19.5 pg/mL), IL-1Ralpha (RR, 5.12; P = .007 for levels greater than 373 pg/mL), and VEGFR2 (RR, 4.01; P = .04 for levels greater than 8222 pg/mL) as independent factors for survival. Of interest is the association of high levels of VEGF with good prognosis and higher levels of VEGF receptors with poor outcome. These data reflect the complexity by which angiogenic factors may affect the clinical behavior of patients with ALL, and this complexity should be considered in any therapeutic strategy incorporating antiangiogenic agents.

A morphometric approach for the evaluation of angiogenesis in acute lymphoblastic leukemia of childhood

Angiogenesis was estimated in childhood acute lymphoblastic leukemia (ALL) by the use of a novel morphometric method. This was compared with the widely used one of microvessel density (MVD). Bone marrow biopsies were evaluated by immunostaining with anti-Factor VIII related antigen (FVIIIRAg). Angiogenesis was calculated as volume corrected microvessel density index (VC-MVDI), taking into account the bone marrow cellularity. According to our results both MVD and VC-MVDI were increased at diagnosis of ALL in comparison with the control group. However the VC-MVDI increment was not statistically significant. Therefore, VC-MVDI could be more representative of the true increase of angiogenesis, correlating better with the outcome of the disease.

The possible role of matrix metalloproteinase (MMP)-2 and MMP-9 in cancer, e.g. acute leukemia

In the past decades, a lot of effort has been put in identifying the role of matrix metalloproteinases (MMPs) in cancer. The main role of MMPs in angiogenesis, tumor growth and metastasis is degradation of extracellular matrix (ECM) and release and/or activation of growth factors through their degradative activity. The degradative activity finally results in cancer progression. MMP-inhibitors (MMPIs) have already been designed and tested, based on the degradative role of MMPs in cancer progression. First clinical trials with MMPIs have been performed with disappointing results, showing that in order to use MMP-inhibition the mechanisms underlying MMP-expression in cancer have to be further elucidated. This paper reviews the mechanisms of MMPs on molecular and cellular level and discusses the role for MMPs and MMP-inhibition in cancer with special focus on acute leukemia.

Bone marrow microvessel density and its prognostic significance in AML

Microvessel density reportedly is increased in various hematologic disorders including acute lymphatic and myeloid leukemias. In these patients the bone marrow microvessel density (BM-MVD) appears to be associated with an unfavorable prognosis. In the present study, we have retrospectively analyzed the BM-MVD (at diagnosis) in 31 patients with acute myeloid leukemia (AML) (median age: 38 years; range: 21-53 years; f:m-ratio: 1:1,4) who underwent conventional chemotherapy and consecutive allogeneic bone marrow transplantation (BMT). The median BM-MVD at diagnosis was 30/mm2 (range: 17-48/mm2) and thus was significantly higher compared to controls (n = 9; BM-MVD: median 7/mm2, range 2-11/mm2; P < 0.05). In patients who failed to achieve a complete remission (CR) in response to induction chemotherapy, the BM-MVD was significantly higher (median: 41.5/mm2) at diagnosis than in patients who entered CR (median: 28.5/mm2, P < 0.05). In addition, patients with high BM-MVD ( > 30 mm2) had a significantly shorter overall survival compared to patients with a lower BM-MVD ( < 30 mm2, P < 0.05). Moreover, patients with a high BM-MVD ( > 30 mm2) were found to have a significantly higher risk of relapse (P < 0.05). In 4 patients in whom a continuous complete remission was documented after BMT, the BM-MVD levels were analyzed at diagnosis as well as between day + 80 and day + 100 after BMT. In all 4 patients, the BM-MVD was found to decrease in response to BMT until day 100 (P < 0.05). Together, our data suggest that the BM-MVD could be a prognostic parameter concerning survival in patients with AML undergoing allogeneic BMT.

Hematopoietic Cancer and Angiogenesis

The growth of solid tumors is certainly angiogenesis dependent. However, the role of angiogenesis in the growth and survival of leukemias and other hematological malignancies has only been rendered evident since 1994 in a series of demonstrations showing that the progression of several forms is clearly related to their degree of angiogenesis. Here, we present an overview of the literature concerning the relationship between angiogenesis and disease progression in several hematological malignancies and the recent advances in antiangiogenesis in these diseases and we describe the most important active substances, preclinical and clinical data, and future perspectives.

Increased bone marrow angiogenesis in children with severe chronic neutropenia treated with granulocyte colony-stimulating factor

Severe chronic neutropenia (SCN) is a heterogeneous group of conditions characterized by chronically low neutrophil counts and recurrent infections. Granulocyte colony-stimulating factor (G-CSF) is the mainstay of treatment, and evidence exists that G-CSF may promote angiogenesis. To evaluate the effects of G-CSF on angiogenesis in children with SCN, the authors assessed microvessel density in bone marrow biopsies from nine children with SCN before starting G-CSF treatment and while receiving G-CSF. In all patients, microvessel density was greater in the on-treatment biopsy. Increased angiogenesis may result from a direct effect of G-CSF on endothelial cells or may be an indirect effect from increased neutrophils.

Activation of the HIF pathway in childhood ALL, prognostic implications of VEGF

Hypoxia-inducible factor 1 (HIF-1) controls angiogenesis and glycolysis, two leading characteristics of solid tumor invasion, metastasis, and lethality. Increased angiogenesis is also found in the bone marrow (BM) of leukemias. Less is known in leukemia about the role of HIF-1 and vascular endothelial growth factor (VEGF), the most important proangiogenic target gene of HIF-1. We show by immunohistochemistry that the oxygen-regulated component of HIF-1 (HIF-1alpha) is overexpressed in clusters of leukemic cells in BM specimens of childhood acute lymphoblastic leukemia (ALL) and absent in biopsies of normal BM. Half the HIF-1alpha-positive ALL biopsies exhibited VEGF coexpression. Among 96 children with relapsed ALL, diagnostic BM aspirates with high VEGF mRNA levels were associated with a significantly lower probability of event-free survival at 3 years (0.31+/-0.08 vs 0.65+/-0.07, P=0.003). Those with poor molecular response to therapy (evaluated by MRD assessment) had 2.2-fold higher VEGF levels than those responding well to chemotherapy (P=0.005). In conclusion, the data demonstrate activation of the HIF pathway in the BM of ALL patients and indicate that the expression of HIF target genes, such as VEGF, play an important role in leukemia progression, therapy response, and outcome.

Angiogenesis in acute and chronic lymphocytic leukemia

The bone marrow microenvironment plays a crucial role in leukemogenesis. Recent studies suggest that its vascularity changes significantly during this process and that angiogenic factors are of major importance in leukemia. This review summarizes the literature concerning the relationship between angiogenesis and the progression of acute and chronic lymphocytic leukemia. It is becoming increasingly evident that agents which interfere with angiogenesis also block tumor progression and anti-angiogenic management has become a prominent aspect of pre-clinical and clinical assessment. Recent applications of anti-angiogenic agents which interfere with or block leukemia progression are reviewed.

"In vitro" evaluation of bone marrow angiogenesis in myelodysplastic syndromes: a morphological and functional approach

In myelodysplastic syndromes (MDS), ineffective hematopoiesis and cytopenia may arise either from increased susceptibility to apoptosis of hematopoietic cells, or possibly from alterations of bone marrow stroma that contributes to defective development of marrow lineages. In order to test the significance of the endothelial growth in MDS patients, two in vitro assays are presented in this study: a long-term culture method for the detection of human bone marrow endothelial colonies (CFU-En) (77 patients) and a human primary model for the evaluation of the influence of a "bone marrow conditioned medium" on the formation of new vessels in a culture matrix ("angio-kit assay") (in 24 out 77 patients). The in vitro growth pattern of bone marrow CFU-En as well as the generation of microvessels in the angio-kit system was increased in RA, RARS and RAEB in comparison with controls. No CFU-En were detected in RAEB-T. The occurrence of large islands, formed by clusters of endothelial cells, unable to generate microcapillaries was also reported. Chromosomal abnormalities did not correlate with the angiogenetic pattern. These in vitro assays may constitute an useful approach to the analysis of angiogenesis in MDS.

Immature B cell malignancies synthesize VEGF, VEGFR-1 (Flt-1) and VEGFR-2 (KDR)

Expression of VEGF and VEGFR support a role for angiogenic pathways in the pathogenesis of some hematological malignances. Our goal was to determine if expression of these angiogenic molecules also extend to childhood precursor B cell acute lymphoblastic leukemia (pre-B ALL). We now show that transcripts of VEGF, and its receptors VEGFR-1 and VEGFR-2 are concomitantly expressed in both ALL cell lines and primary pre-B ALL. Western blot and ELISA consistently detected VEGF protein in the supernatants of the cell lines. Similarly, VEGFR-1 and VEGFR-2 proteins are also detectable by FACS analysis. Interestingly, the expression of the receptors in immature B cells is limited to the intra-cytoplasmic compartment and may suggest either internalization of the receptors or a block in trafficking of the receptor to the surface.