Human lymphoblastoid cells produce extracellular matrix-degrading enzymes and induce endothelial cell proliferation, migration, morphogenesis, and angiogenesis

The chorioallantoic membrane as a bio-barrier model for the evaluation of nanoscale drug delivery systems for tumour therapy

In 2010, the European Parliament and the European Union adopted a directive on the protection of animals used for scientific purposes. The directive aims to protect animals in scientific research, with the final goal of complete replacement of procedures on live animals for scientific and educational purposes as soon as it is scientifically viable. Furthermore, the directive announces the implementation of the 3Rs principle: "When choosing methods, the principles of replacement, reduction and refinement should be implemented through a strict hierarchy of the requirement to use alternative methods." The visibility, accessibility, and the rapid growth of the chorioallantoic membrane (CAM) offers a clear advantage for various manipulations and for the simulation of different Bio-Barriers according to the 3R principle. The extensive vascularisation on the CAM provides an excellent substrate for the cultivation of tumour cells or tumour xenografts which could be used for the therapeutic evaluation of nanoscale drug delivery systems. The tumour can be targeted either by topical application, intratumoural injection or i.v. injection. Different application sites and biological barriers can be examined within a single model.

The EGFL7-ITGB3-KLF2 axis enhances survival of multiple myeloma in preclinical models

Angiogenic factors play a key role in multiple myeloma (MM) growth, relapse, and drug resistance. Here we show that malignant plasma cells (cell lines and patient-derived MM cells) express angiocrine factor EGF like-7 (EGFL7) mRNA and protein. MM cells both produced EGFL7 and expressed the functional EGFL7 receptor integrin β 3 (ITGB3), resulting in ITGB3 phosphorylation and focal adhesion kinase activation. Overexpression of ITGB3 or EGFL7 enhanced MM cell adhesion and proliferation. Intriguingly, ITGB3 overexpression upregulated the transcription factor Krüppel-like factor 2 (KLF2), which further enhanced EGFL7 transcription in MM cells, thereby establishing an EGFL7-ITGB3-KLF2-EGFL7 amplification loop that supports MM cell survival and proliferation. EGFL7 expression was found in certain plasma cells of patients with refractory MM and of patients at primary diagnosis. NOD.CB17-Prkdc/J mice transplanted with MM cells showed elevated human plasma EGFL7 levels. EGFL7 knockdown in patient-derived MM cells and treatment with neutralizing antibodies against EGFL7 inhibited MM cell growth in vitro and in vivo. We demonstrate that the standard-of-care MM drug bortezomib upregulates EGFL7, ITGB3, and KLF2 expression in MM cells. Inhibition of EGFL7 signaling in synergy with BTZ may provide a novel strategy for inhibiting MM cell proliferation.

The CAM Assay as an Alternative In Vivo Model for Drug Testing

In the last decade, the chicken chorioallantoic membrane (CAM) assay has been re-discovered in cancer research to study the molecular mechanisms of anti-cancer drug effects. Literature about the CAM assay as an alternative in vivo cancer xenograft model according to the 3R principles has exploded in the last 3 years. Following a summary of the basic knowledge about the chicken embryo, we compare advantages and disadvantages with the classical mouse xenograft model, exemplify established and innovative imaging techniques that are used in the CAM model, and give examples of its successful utilization for studying major hallmarks of cancer such as angiogenesis, proliferation, invasion, and metastasis.

CDCA7 finely tunes cytoskeleton dynamics to promote lymphoma migration and invasion

Metastases, the major cause of death from cancer, require cells' acquisition of the ability to migrate and involve multiple steps, including local tumor cell invasion and basement membrane penetration. Certain lymphoid tumors are highly metastatic, but the mechanisms of invasion by lymphoma cells are poorly understood. We recently showed that CDCA7, a protein induced by MYC, is overexpressed in lymphoid tumors and that its knockdown decreases lymphoid tumor growth without inhibiting the proliferation of normal cells. Here we show that CDCA7 is critical for invasion and migration of lymphoma cells. Indeed, CDCA7 knockdown in lymphoma cells limited tumor cell invasion in matrigel-coated transwell plates and tumor invasion of neighboring tissues in a mouse xenograft model and in a zebrafish model of cell invasion. CDCA7 silencing markedly inhibited lymphoma cell migration on fibronectin without modifying cell adhesion to this protein. Instead, CDCA7 knockdown markedly disrupted the precise dynamic reorganization of actomyosin and tubulin cytoskeletons required for efficient migration. In particular, CDCA7 silencing impaired tubulin and actomyosin cytoskeleton polarization, increased filamentous actin formation, and induced myosin activation. Of note, inhibitors of actin polymerization, myosin II, or ROCK reestablished the migration capacity of CDCA7-silenced lymphoma cells. Given the critical role of CDCA7 in lymphoma-genesis and invasion, therapies aimed at inhibiting its expression or activity might provide significant control of lymphoma growth, invasion, and metastatic dissemination.

Models for Studying Angiogenesis in Vivo

In vivo and in vitro techniques are available for reseach on the functions of endothelial cells during angiogenesis. In this review we describe and evaluate the methodology and specific features of some of the most frequently used in vivo assays.

Impact of Chronic Viral Infection on T-Cell Dependent Humoral Immune Response

During the last decades, considerable efforts have been done to decipher mechanisms supported by microorganisms or viruses involved in the development, differentiation, and function of immune cells. Pathogens and their associated secretome as well as the continuous inflammation observed in chronic infection are shaping both innate and adaptive immunity. Secondary lymphoid organs are functional structures ensuring the mounting of adaptive immune response against microorganisms and viruses. Inside these organs, germinal centers (GCs) are the specialized sites where mature B-cell differentiation occurs leading to the release of high-affinity immunoglobulin (Ig)-secreting cells. Different steps are critical to complete B-cell differentiation process, including proliferation, somatic hypermutations in Ig variable genes, affinity-based selection, and class switch recombination. All these steps require intense interactions with cognate CD4⁺ helper T cells belonging to follicular helper lineage. Interestingly, pathogens can disturb this subtle machinery affecting the classical adaptive immune response. In this review, we describe how viruses could act directly on GC B cells, either through B-cell infection or by their contribution to B-cell cancer development and maintenance. In addition, we depict the indirect impact of viruses on B-cell response through infection of GC T cells and stromal cells, leading to immune response modulation.

CD24+ tumor-initiating cells from oral squamous cell carcinoma induce initial angiogenesis in vivo

BACKGROUND

In oral squamous cell carcinoma (OSCC), a minor subset of cancer stem cells has been identified using the surface marker CD24. The CD24+ cell population is involved in initiating, maintaining, and expanding tumor growth, but has not been reported to be involved in angiogenesis to date.

METHODS

NOD/SCID mice were equipped with dorsal skinfold chambers and gelatin sponges seeded with CD24+, CD24-, and unsorted cancer cells suspended in Matrigel® were implanted. Following intravital fluorescence microscopy, specimens were examined by immunohistology.

RESULTS

Sponges seeded with CD24+ cells showed a significantly higher functional capillary density than those seeded with CD24- cells. The presence of endothelial cells was confirmed by immunohistochemistry for CD31.

CONCLUSION

For the first time, CD24+ tumorigenic cells with angiogenic potential, which were isolated from OSCC, were characterized. Our findings provide a promising in vivo model to facilitate the development of therapeutic agents against cancer stem cells and their angiogenic pathways.

ASC, a bioactive steroidal saponin from Ophitopogin japonicas, inhibits angiogenesis through interruption of Src tyrosine kinase-dependent matrix metalloproteinase pathway

As angiogenesis is an important target for antitumour drugs, the agents that inhibit angiogenesis may help reduce the use of chemotherapy by blocking tumour blood supply. In this study, we investigated a potent angiogenesis inhibitor, ASC, a steroidal saponin compound, which has been purified from Ophitopogin japonicus (L.f) Ker.-Gawl. Our observations showed that ASC significantly suppressed human umbilical vein endothelial cell (HUVECs) growth both in vitro and in vivo. This may be resulted from the G2/M cell cycle arrest effects of ASC. Moreover, ASC inhibited HUVECs invasion and tube formation processes, which were associated with endothelial cells remodelling. A mechanism study indicated that ASC down-regulated the expression of Src tyrosine kinase, further leading to the blockage of Akt-dependent matrix metalloproteinases (mainly for MMP-9) signalling pathway, which was functionally associated with angiogenic blood vessels. Finally, ASC significantly inhibited angiogenesis and MMPs/VEGF expression in the subcutaneously injected matrigel in C57/BL mice. These findings suggest that ASC might be a potential drug candidate in anti-angiogenesis and anticancer therapies.

The chick chorioallantoic membrane as an in vivo xenograft model for Burkitt lymphoma

Background

Burkitt lymphoma (BL) is an aggressive malignancy that arises from B-cells and belongs to the group of Non-Hodgkin lymphomas (NHL). Due to the lack of appropriate in vivo models NHL research is mainly performed in vitro. Here, we studied the use of the chick chorioallantoic membrane (CAM) for the generation of human BL xenograft tumors, which we compared with known characteristics of the human disease.

Methods

In order to generate experimental BL tumors, we inoculated human BL2B95 and BL2-GFP cells on the CAM. BL2B95 xenograft-tumors were grown for seven days and subsequently analyzed with transmission electron and immunofluorescence microscopy, as well as histological staining approaches. BL2-GFP cells were studied at regular intervals up to seven days, and their metastatic behavior was visualized with intravital immunofluorescence techniques.

Results

Xenografted BL2B95 cells formed solid tumors in the CAM model with a Ki67-index greater than 90%, preservation of typical tumor markers (CD10, CD19, CD20), a ‘starry sky’ morphology, production of agyrophilic fibers in the stroma, formation of blood and lymphatic vessels and lymphogenic dissemination of BL2B95 to distant sites. We identified macrophages, lymphocytes and heterophilic granulocytes (chick homolog of neutrophils) as the most abundant immune cells in the experimental tumors. BL2-GFP cells could be traced in real-time during their distribution in the CAM, and the first signs for their dissemination were visible after 2-3 days.

Conclusions

We show that xenografted BL2B95 cells generate tumors in the CAM with a high degree of cellular, molecular and proliferative concord with the human disease, supporting the application of the CAM model for NHL research with a focus on tumor-stroma interactions. Additionally we report that BL2-GFP cells, grafted on the CAM of ex ovo cultured chick embryos, provide a powerful tool to study lymphogenic dissemination in real-time.

The evaluation of angiogenesis and matrix metalloproteinase-2 secretion in bone marrow of multiple myeloma patients before and after the treatment

PURPOSE

Angiogenesis appears to be a prominent feature of many hematological disorders, particularly in multiple myeloma (MM). Progression in MM also involves secretion of the metaloproteinases (MMPs). In this study, the expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and its receptor, in bone marrow trephine biopsy (TB) of thirty six MM patients before and after the treatment or during progression was examined. The MMP-2 secretion was assessed from the same patients.

MATERIAL/METHODS

Immunohistochemical staining of bone marrow specimens for angiogenic factors and microvessel density (MVD) and bone marrow aspirates for Western blot analysis of MMP-2 expression was performed.

RESULTS

In active, untreated MM patients, we found statistically significant differences in the expression of angiogenic factors according to the patients after the anti-angiogenic treatment. We found statistical differences of the expression of angiogenic factors between the group of patients with a response after the treatment and the patients who had progression during the treatment. The data showed statistically significant decreased MVD after the treatment. The results showed statistically significant differences between initial secretion of MMP-2 in active, untreated MM patients and patients with a response after the treatment and patients with progression during the treatment.

CONCLUSIONS

We showed that not only decreased expression of angiogenic cytokines is present after the anti-angiogenic treatment but also activity of MMP-2 in MM patients who responded to the treatment. Combination therapy with the inhibition of the activity of MMPs could represent an interesting therapeutical approach in MM.

The role of angiogenesis in human non-Hodgkin lymphomas

The role of angiogenesis in the growth of lymphomas and survival of patients with leukemias and other hematological malignancies has become evident since 1994. Angiogenic factors, such as vascular endothelial growth factor and its receptors together with other tumor microenvironment components, including myelo-monocytic cell, mast cells, endothelial progenitor cells, and circulating endothelial cells, have been shown to be important in the progression and maintenance of lymphoproliferative disorders. In this review article, we present an overview of the literature focusing on the relationship between angiogenesis and disease progression and the recent advantages in the antiangiogenic treatment in human non-Hodgkin lymphomas.

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.

Hypoxia and angiogenesis: regulation of hypoxia-inducible factors via novel binding factors

The mechanisms that regulate angiogenesis in hypoxia or hypoxic microenvironment are modulated by several pro- and antiangiogenic factors. Hypoxia-inducible factors (HIFs) have been established as the basic and major inducers of angiogenesis, but understanding the role of interacting proteins is becoming increasingly important to elucidate the angiogenic processes of a hypoxic response. In particular, with regard to wound healing and the novel therapies for vascular disorders such as ischemic brain and heart attack, it is essential to gain insights in the formation and regulation of HIF transcriptional machineries related to angiogenesis. Further, identification of alternative ways of inhibiting tumor growth by disrupting the growth-triggering mechanisms of increasing vascular supply via angiogenesis depends on the knowledge of how tumor cells develop their own vasculature. Here, we review our findings on the interactions of basic HIFs, HIF-1 alpha and HIF-2 alpha, with their regulatory binding proteins, histone deacetylase 7 (HDAC7) and translation initiation factor 6 (Int6), respectively. The present results and discussion revealed new regulatory interactions of HIF-related mechanisms.

Tax 1-independent induction of vascular endothelial growth factor in adult T-cell leukemia caused by human T-cell leukemia virus type 1

Adult T-cell leukemia (ATL) is caused by human T-cell leukemia virus type 1 (HTLV-1). Elevated expression of vascular endothelial growth factor (VEGF) in ATL patients is associated with leukemic cell invasion and infiltration in different organs. The regulatory protein Tax 1 encoded by HTLV-1 plays a pivotal role in T-cell transformation by deregulating the function and expression of several cellular factors. In the present study, we examined the effect of Tax 1 on VEGF expression at transcriptional and posttranscriptional levels in order to elucidate the regulatory mechanisms involved. Using functional assays, we demonstrate that Tax 1 downregulates the VEGF promoter through a cluster of Sp1 sites located close to the transcriptional start site. Using gel mobility shift assays, we show that Tax 1 reduced Sp1:DNA complex formation. We demonstrate that the level of secreted VEGF was significantly lower in Tax 1-transfected 293T cells compared to nontransfected cells, which is consistent with the observed downregulatory effect of Tax 1 at the transcription level. We showed that VEGF was secreted by HTLV-1-transformed and nontransformed cells, irrespective of Tax 1 expression. Overall our data indicate that, contrary to a previous report, Tax 1 downregulates VEGF expression and suggest there are Tax 1-independent mechanisms of VEGF activation in ATL.

A murine model of myeloma that allows genetic manipulation of the host microenvironment

Multiple myeloma, and the associated osteolytic bone disease, is highly dependent upon cellular interactions within the bone marrow microenvironment. A major limitation of existing myeloma models is the requirement for a specific host strain of mouse, preventing molecular examination of the bone marrow microenvironment. The aim of the current study was to develop a model of myeloma in which the host microenvironment could be modified genetically. The Radl 5T murine model of myeloma is well characterized and closely mimics human myeloma. In the current study, we demonstrate 5T myeloma establishment in recombination activating gene 2 (RAG-2)-deficient mice, which have improper B- and T-cell development. Importantly, these mice can be easily bred with genetically modified mice to generate double knockout mice, allowing manipulation of the host microenvironment at a molecular level. Inoculation of 5TGM1 myeloma cells into RAG-2(-/-) mice resulted in myeloma development, which was associated with tumor growth within bone and an osteolytic bone disease, as assessed by microcomputed tomography (microCT), histology and histomorphometry. Myeloma-bearing RAG-2(-/-) mice displayed many features that were similar to both human myeloma and the original Radl 5T model. To demonstrate the use of this model, we have examined the effect of host-derived matrix metalloproteinase 9 (MMP-9) in the development of myeloma in vivo. Inoculation of 5TGM1 myeloma cells into mice that are deficient in RAG-2 and MMP-9 resulted in a reduction in both tumor burden and osteolytic bone disease when compared with RAG-2-deficient wild-type myeloma-bearing mice. The establishment of myeloma in RAG-2(-/-) mice permits molecular examination of the host contribution to myeloma pathogenesis in vivo.

Evaluation of circulating endothelial cells, VEGF and VEGFR2 serum levels in patients with chronic myeloproliferative diseases

Authors evaluated some markers of angiogenetic activity in patients with chronic myeloproliferative diseases (CMDs). In this study by using a cytofluorimetric analysis we evaluated circulating endothelial progenitor cells (EPCs) in patients with chronic myeloproliferative disease. Moreover, in the same group of subjects, we evaluated serum levels of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor-2 (VEGFR2). In our patients, we have found an increase in the number of endothelial progenitor cells in primary myelofibrosis (PMF) and polycythaemia vera (PV) patients, while an increase of circulating endothelial cells (CECs) was found in all patients with CMD. Moreover, we found higher serum levels of VEGF with respect to control subjects in every group of patients with CMD, and a not significant reduction of VEGFR2 levels in essential thrombocythaemia (ET) patients. A correlation was also found in PV patients between VEGF levels and erythrocyte number and in PMF subjects with the count of white cells. Our data suggest that some markers of angiogenesis are activated in CMD patients and angiogenesis may have a role in the pathophysiology of chronic myeloproliferative disorders.

Transmembrane protein 18 enhances the tropism of neural stem cells for glioma cells

The failure of current glioma therapies is mainly due to the ability of the tumor cells to invade extensively the surrounding healthy brain tissue, hence escaping localized treatments. Neural stem cells (NSC) are able to home in on tumor foci at sites distant from the main tumor mass, possibly enabling treatment of scattered glioma clusters. To make the strategy more effective, we performed a cDNA expression library screening to identify the candidate genes that once overexpressed would enhance the tropism of NSCs for gliomas. Here, we show that a previously unannotated gene, the one encoding transmembrane protein 18 (TMEM18), is one such gene. Overexpression of TMEM18 was seen in the current study to provide NSCs and neural precursors an increased migration capacity toward glioblastoma cells in vitro and in the rat brain. Functional inactivation of the TMEM18 gene resulted in almost complete loss of the migration activity of these cells. Thus, TMEM18 is a novel cell migration modulator. Overexpression of this protein could be favorably used in NSC-based glioma therapy.

Artesunate inhibits angiogenesis and downregulates vascular endothelial growth factor expression in chronic myeloid leukemia K562 cells

Artesunate (ART), a semi-synthetic derivative of artemisinin extracted from the Chinese herb Artemisia annua, is a safe and effective antimalarial drug. In the present investigation, we analyzed the inhibitory effects of ART on angiogenesis and on VEGF production in chronic myeloid leukemia (CML) K562 cells in vitro and in vivo. In order to analyze the effect of ART on VEGF secretion in K562 cells, we examined the level of VEGF secreted in conditioned media (CM) by ELISA assay. The result showed that ART could decrease the VEGF level in CM of K562 cells, even at a lower concentration (2 micromol/l, P<0.01). The inhibitory effect of in vitro angiogenesis was tested on aortic sprouting in fibrin gel. ART could effectively suppress the stimulating angiogenic ability of CM by pretreated with K562 cells for 48 h in a time-dependent manner (days 3-14). The antiangiogenic effect of ART was further evaluated in vivo in chicken chorioallantoic membrane (CAM) neovascularization model. The result indicated that the stimulating angiogenic activity was decreased in response to the K562 cells treated with ART or the CM from K562 cells pretreated with ART in a dose-dependent manner (3-12 micromol/l). Furthermore, we analyzed the level of VEGF expression by western blot and detected the form of VEGF mRNA by RT-PCR in K562 cells. The experiments showed that ART could inhibit the VEGF expression, correlated well with the level of VEGF secreted in CM. These findings suggest that ART might present potential antileukemia effect as a treatment for CML therapy, or as an adjunct to standard chemotherapeutic regimens.

Dihydroartemisinin inhibits angiogenesis induced by multiple myeloma RPMI8226 cells under hypoxic conditions via downregulation of vascular endothelial growth factor expression and suppression of vascular endothelial growth factor secretion

Multiple myeloma remains incurable to date; therefore, new biologically target-based therapies are urgently needed. Our previous studies have showed that the antimalarial dihydroartemisinin possessed antiangiogenic activity in solid tumors. The present study evaluated the effect of dihydroartemisinin on human multiple myeloma-induced angiogenesis under hypoxia and elucidated its mechanism of action. An in-vivo chicken chorioallantoic membrane model was used to examine the effect of dihydroartemisinin on multiple myeloma-induced angiogenesis. Compared with conditioned medium of control, conditioned medium from human multiple myeloma RPMI8226 cells pretreated with 3 micromol/l dihydroartemisinin in hypoxia was observed to reduce microvessel growth on chicken chorioallantoic membranes by approximately 28.6% (P<0.05). The level of vascular endothelial growth factor in conditioned medium was determined by enzyme-linked immunosorbent assay. The results confirmed that 3 micromol/l dihydroartemisinin could significantly decrease vascular endothelial growth factor secretion by RPMI8226 cells (P<0.05), which correlated well with the reduction of multiple myeloma-induced angiogenesis on chicken chorioallantoic membranes. Western blot and reverse transcription-polymerase chain reaction results revealed that dihydroartemisinin downregulated the expression of vascular endothelial growth factor in RPMI8226 cells in hypoxia. In addition, we demonstrated that dihydroartemisinin reduced extracellular signal-regulated kinase 1/2 activation and inhibited growth of RPMI8226 cells under hypoxic conditions. Therefore, we concluded that dihydroartemisinin, which is already used to treat malaria and is well tolerated, possesses potential as an antiangiogenic drug in multiple myeloma therapy and thereby may improve patient outcome.

Resveratrol as a novel agent for treatment of multiple myeloma with matrix metalloproteinase inhibitory activity

AIM

To examine the in vitro antitumor activity of resveratrol against multiple myeloma (MM) cell lines (RPMI 8226, U266, and KM3), and the mechanisms involved.

METHODS

The growth inhibition of resveratrol was determined by 3-(4, 5-dimethyl-2-thiazyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The effect of resveratrol on the apoptosis was investigated by combined annexin V-propidium iodide staining. The effect of resveratrol on the invasion through Matrigel matrix was detected by transwell invasion analyses. The activity of matrix metalloproteinase (MMP)-2 and -9 proteins were determined by gelatin zymography analysis. The expression of MMP-2, MMP-9, Bcl-2, Bcl-x(L), XIAP and Bax protein were detected using Western blotting analysis.

RESULTS

Resveratrol inhibited proliferation of MM cells in a dose- and time-dependent manner. Incubation of MM cells with resveratrol resulted in apoptotic cell death. Resveratrol down-regulated the expression of the antiapoptotic proteins Bcl-2, Bcl-x(L) and XIAP and up-regulated the expression of the proapoptotic protein Bax. Furthermore, resveratrol inhibited invasion of RPMI 8226, U266, and KM3 cells with IC50 values of 64+/-8 micromol/L, 93+/-11 micromol/L, and 153+/-11 micromol/L, respectively. Resveratrol inhibited the constitutive expression of MMP-2 and -9 proteins of MM cells and suppressed its gelatinolytic activity.

CONCLUSION

Resveratrol inhibits the proliferation of MM cells by inducing apoptotic cell death. Resveratrol also inhibits MM cell invasion. The inhibition of invasion may be associated with the attenuation of the enzymatic activities of MMP-2 and -9.

The gelatin sponge–chorioallantoic membrane assay

Here we present a method for the quantification of angiogenesis and antiangiogenesis in the chick embryo chorioallantoic membrane (CAM) based on the implantation of a gelatin sponge on the top of the growing CAM on day 8 of development. After implantation, the sponge is treated with a stimulator of blood vessel formation in the absence or presence of an angiogenesis inhibitor. On day 12, blood vessels that are growing into the sponge are counted at macroscopic and microscopic levels. The estimated timeline for carrying out this protocol is 10 d. The presence of a vascular network in the CAM requires a careful analysis to distinguish new capillaries from pre-existing ones. This limitation does not occur in the avascular cornea assay, which may also take advantage of different genetic backgrounds when carried out in transgenic or knockout mice. Nevertheless, the gelatin sponge-CAM assay is simple, inexpensive and suitable for large-scale screening.

Epstein-Barr virus lytic infection is required for efficient production of the angiogenesis factor vascular endothelial growth factor in lymphoblastoid cell lines

Although Epstein-Barr virus (EBV)-associated malignancies are primarily composed of cells with one of the latent forms of EBV infection, a small subset of tumor cells containing the lytic form of infection is often observed. Whether the rare lytically infected tumor cells contribute to the growth of the latently infected tumor cells is unclear. Here we have investigated whether the lytically infected subset of early-passage lymphoblastoid cell lines (LCLs) could potentially contribute to tumor growth through the production of angiogenesis factors. We demonstrate that supernatants from early-passage LCLs infected with BZLF1-deleted virus (Z-KO LCLs) are highly impaired in promoting endothelial cell tube formation in vitro compared to wild-type (WT) LCL supernatants. Furthermore, expression of the BZLF1 gene product in trans in Z-KO LCLs restored angiogenic capacity. The supernatants of Z-KO LCLs, as well as supernatants from LCLs derived with a BRLF1-deleted virus (R-KO LCLs), contained much less vascular endothelial growth factor (VEGF) in comparison to WT LCLs. BZLF1 gene expression in Z-KO LCLs restored the VEGF level in the supernatant. However, the cellular level of VEGF mRNA was similar in Z-KO, R-KO, and WT LCLs, suggesting that lytic infection may enhance VEGF translation or secretion. Interestingly, a portion of the vasculature in LCL tumors in SCID mice was derived from the human LCLs. These results suggest that lytically infected cells may contribute to the growth of EBV-associated malignancies by enhancing angiogenesis. In addition, as VEGF is a pleiotropic factor with effects other than angiogenesis, lytically induced VEGF secretion may potentially contribute to viral pathogenesis.

Human mesenchymal stem cells (hMSCs) expressing truncated soluble vascular endothelial growth factor receptor (tsFlk-1) following lentiviral-mediated gene transfer inhibit growth of Burkitt's lymphoma in a murine model

BACKGROUND

Efficient gene transfer to bone marrow derived mesenchymal stem cells (MSC) would provide an important opportunity to express potent anticancer agents in the tumour microenvironment because of their contribution to the tumour stroma.

METHODS

HIV-based lentiviral vectors were pseudotyped with four different envelope proteins; amphotropic murine leukaemia virus (ampho), murine leukaemia virus (10A1), feline endogenous virus (RD114), and the vesicular stomatitis virus glycoprotein (VSVG). These pseudotypes were examined for transduction efficiency in human bone marrow derived MSC. The effect of lentiviral expression of truncated soluble vascular endothelial growth factor decoy receptor (tsFlk-1) in MSC on growth of Raji cells was determined, both in vitro and in vivo.

RESULTS

All lentiviral vectors produced significant levels of transduction at an multiplicity of infection (MOI) of 1, those bearing the RD114 envelope glycoprotein consistently produced higher transduction levels (mean 70 +/- 6%) compared with the other pseudotyped lentiviral vectors, although there was significant inter-donor variation. Stable transgene expression was achieved after multiple rounds of transduction with VSVG-pseudotyped particles, without alteration in the differentiative capacity of transduced cells. Co-injection of MSC stably expressing tsFlk-1 with Raji Burkitt's lymphoma cells significantly impaired subcutaneous tumour growth in immunodeficient mice when compared to controls where either unmanipulated MSC or GFP-expressing MSC were used.

CONCLUSIONS

Human MSC are easily transduced by pseudotyped lentiviral particles but there is inter-donor variation in transduction efficiency. Gene-modified MSC expressing a gene of therapeutic potential can moderate growth of haematological malignancies.

Targeting an MMP-9-activated prodrug to multiple myeloma-diseased bone marrow: a proof of principle in the 5T33MM mouse model

Multiple myeloma (MM) is an incurable B-cell cancer characterised by the monoclonal proliferation of tumour cells in the bone marrow (BM). It has been described that matrix metalloproteinases (MMPs) and especially MMP-9 is secreted by MM cells. In this study, we investigated the possibility to exploit MMP-9 activity to activate prodrugs and to target MM cells as a new tumour-specific therapy. Cleavage of the prodrug EV1-FITC by MMP-9 resulted in release of fluorescence which can be used as a measure of prodrug activation. The 5T33MM mouse model was used in this proof-of-principle study. The prodrug was activated in a higher amount by addition to MMP-9-producing 5T33MMvv cells, homogenates from tumour-bearing organs (BM, spleen) and isolated 5T33MM-diseased BM and spleen cells compared to non-MMP-9-producing 5T33MMvt cells and homogenates/cells from non-tumour-bearing organs/mice, as measured by fluorescence release. This fluorescence release could be inhibited by the MMP-2/MMP-9-specific inhibitor, CTT. Activation of the prodrug in the 5T33MM spleen and BM homogenates was confirmed by chromatography. EV1-fluorescein isothiocyanate injection into 5T33MM-diseased animals resulted in a higher fluorescence release by the isolated BM and spleen cells compared to injection into healthy animals. In conclusion, MMP-9 activity can be used to activate prodrugs that target MM.

Dihydroartemisinin downregulates vascular endothelial growth factor expression and induces apoptosis in chronic myeloid leukemia K562 cells

Dihydroartemisinin (DHA), a more water-soluble active metabolite of artemisinin derivatives, is safe and the most effective antimalarial analog of artemisinin. In the present investigation, we assessed the effect of DHA on vascular endothelial growth factor (VEGF) expression and apoptosis in chronic myeloid leukemia (CML) K562 cells. The results demonstrated that in addition to its antiproliferation effect on CML cells, DHA was also found to induce K562 cells apoptosis. The percentage of apoptotic cells was increased to 6.9 and 15.8% after being treated with 5 and 10 micromol/l DHA for 48 h, respectively (P<0.001). In order to analyze the effect of DHA on VEGF expression in K562 cells, we assessed the level of VEGF expression by western blot; detected the form of VEGF mRNA by RT-PCR and examined the level of VEGF secreted in conditioned media (CM) by ELISA assay. All these experiments suggested that DHA could inhibit the VEGF expression and secretion effectively in K562 cells, even at a lower concentration (2 micromol/l, P<0.05). Moreover, we further assessed the stimulating angiogenic activity of CM from K562 cells on CAM model. The angiogenic activity was decreased in response to the CM from K562 cells pretreated with DHA in a dose-dependent manner. Taken together, these results from our study together with its known low toxicity make it possible that DHA might present potential antileukemia effect as a treatment for CML therapy, or as an adjunct to standard chemotherapeutic regimens.

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.

B lymphocyte-specific c-Myc expression stimulates early and functional expansion of the vasculature and lymphatics during lymphomagenesis

Expression of the c-myc proto-oncogene is deregulated in many human cancers. We examined the role of c-Myc in stimulating angiogenesis and lymphangiogenesis in a highly metastatic murine model of Burkitt's lymphoma (E micro -c-myc), where c-Myc is expressed exclusively in B lymphocytes. Immunohistochemical analysis of bone marrow and lymph nodes from young (preneoplastic) E micro -c-myc transgenic mice revealed increased growth of blood vessels, which are functional by dye flow assay. Lymphatic sinuses also increased in size and number within the lymph nodes, as demonstrated by immunostaining for with a lymphatic endothelial marker 10.1.1. The 10.1.1 antibody recognizes VEGFR-2- and VEGFR-3-positive lymphatic sinuses and vessels within lymph nodes, and also recognizes lymphatic vessels in other tissues. Subcutaneously injected dye traveled more efficiently through draining lymph nodes in E micro -c-myc mice, indicating that these hypertrophic lymphatic sinuses increase lymph flow. Purified B lymphocytes and lymphoid tissues from E micro -c-myc mice expressed increased levels of vascular endothelial growth factor (VEGF) by immunohistochemical or immunoblot assays, which could promote blood and lymphatic vessel growth through interaction with VEGFR-2, which is expressed on the endothelium of both vessel types. These results indicate that constitutive c-Myc expression stimulates angiogenesis and lymphangiogenesis, which may promote the rapid growth and metastasis of c-Myc-expressing cancer cells, respectively.

Angiogenesis in health and disease

Blood vessels constitute the first organ in the embryo and form the largest network in our body but, sadly, are also often deadly. When dysregulated, the formation of new blood vessels contributes to numerous malignant, ischemic, inflammatory, infectious and immune disorders. Molecular insights into these processes are being generated at a rapidly increasing pace, offering new therapeutic opportunities that are currently being evaluated.

Endothelial stimulation by small lymphocytic lymphoma correlates with secreted levels of basic fibroblastic growth factor

Lymph nodes (LN) involved with small lympho- cytic lymphoma (SLL) reportedly contain increased numbers of microvessels that may constitute a therapeutic target in this disease. We investigated the secretion of the angiogenic growth factor, basic fibroblastic growth factor (bFGF), from primary tissue cultures of 15 LN with SLL and 10 reactive LN. bFGF was detected from the resulting conditioned media (CM) in 13/15 SLL samples (mean 92 +/- 30, range 5-420 pg/ml) but was undetectable in CM from all reactive lymph nodes. CM was also used in a 72-h human umbilical vein endothelial cell (HUVEC) proliferation assay. HUVEC proliferation increased in the presence of SLL CM (70 +/- 17%, range -4-194%), proportional to secreted levels of bFGF (R2 = 0.95), and was reversed by depleting bFGF from CM. Previous SLL studies have examined either patient serum samples or paraffin-embedded lymph node tissue sections. This is the first study to examine the secretion of an angiogenic growth factor from primary cultures of lymph node cells. Our results indicate that bFGF is probably the primary mediator responsible for increased angiogenesis in involved nodes. These findings may be pertinent to future investigation into the mechanisms of increased angiogenesis in SLL.

Angiogenesis and anti-angiogenesis in hematological malignancies

Although it is well established that the growth of solid tumors requires vigorous neovascularization, it has been assumed that leukemias and other hematological malignancies do not depend on angiogenesis. However, the role of angiogenesis in growth and survival of neoplastic cells of the hematopoietic system has recently been recognized, and provides a rationale for novel therapeutic approaches to hematological malignancy. This review summarizes the literature concerning the relationship between angiogenesis and disease progression of several hematological malignancies. It is becoming increasingly evident that agents that interfere with blood vessel formation also block tumor progression, and, accordingly, antiangiogenic therapy has gained much interest as a potential adjunct to conventional therapy of many hematological malignancies. Recent successful applications of antiangiogenic agents that interfere or block the progression of hematological malignancies are evaluated in light of recent demonstrations of potent angiogenic activity of several hematopoietic growth factors. A novel finding regarding the role of angiogenesis in hematological malignancies, which accounts for many clinical observations as well as the apparent independence of these tumors on marrow vascularity, is presented. The information presented in this review will facilitate the design of future clinical trials using antiangiogenic agents for the treatment of hematological malignancies and will provide a basis for the design of experiments undertaken to define the mechanisms involved, mechanisms that may shed new light on the pathology of hematological malignancies.

Doxycycline induces apoptosis by way of caspase-3 activation with inhibition of matrix metalloproteinase in human T-lymphoblastic leukemia CCRF-CEM cells

Evidence for nonantibiotic activity displayed by tetracycline has been extensively reported in the field of antiinflammation. Here, we report a growth-inhibitory effect of doxycycline on CCRF-CEM, a T-lymphoblastic human leukemic cell line. Cells were incubated with doxycycline at concentrations ranging from zero to 50 micromol/L. We examined the hypothesis that induction of apoptosis is one of the mechanisms by which doxycycline inhibits CCRF-CEM proliferation. Caspase-3 activity of cells grown in the presence of 10 micromol/L and 50 micromol/L doxycycline increased dose-dependently after 24 hours in culture. The demonstration that doxycycline induces APO 2.7 expression in CCRF-CEM cells in vitro also supports its capacity for induction of apoptosis. The level of matrix metalloproteinase-2 was significantly lower in the medium cultured with 50 micromol/L doxycycline than the control. These phenomena suggest that this well-tolerated oral agent has the potential to be of value in antileukemic therapy.

Upregulation of matrix metalloproteinase-9 in murine 5T33 multiple myeloma cells by interaction with bone marrow endothelial cells

MM is a B-cell malignancy mainly characterized by monoclonal expansion of plasma cells in the BM, presence of paraprotein in serum and occurrence of osteolytic bone lesions. MMPs are a family of proteolytic enzymes that can contribute to cancer growth, invasion, angiogenesis, bone degradation and other processes important in the pathogenesis of MM. We investigated MMP-9 production in the 5T33MM murine model. Expression of MMP-9 protein in supernatant and cell extracts was analyzed by gelatin zymography. The in vitro, stroma-independent variant 5T33MMvt showed no protein expression of MMP-9 in contrast to in vivo growing MM cells, 5T33MMvv. However, when 5T33MMvt cells were injected into naive mice and isolated after tumor take (5T33MMvt-vv), they secreted a significant amount of MMP-9. These results were confirmed by specific staining of cytospins with an anti-MMP-9 antibody. The MMP-9 production by 5T33MMvt-vv cells disappeared when the cells were recultured in vitro. These data demonstrated that upregulation of MMP-9 occurs in vivo and that this process is dependent on the microenvironment. Cocultures of 5T33MMvt cells with STR10 BMECs induced MMP-9 in MM cells, as determined by both gelatin zymography and flow-cytometric analysis. In conclusion, our results demonstrate that MMP-9 production by MM cells is upregulated in vivo by the interaction of MM cells with BMECs.

Anti-angiogenic activity of the purine analog 6-thioguanine

The antimetabolite 6-thioguanine (6-TG) is utilized in the management of acute myelogenous leukemia (AML). Angiogenesis is a possible therapeutic target in hematologic tumors. Thus, we addressed the possibility that 6-TG may also act as an anti-angiogenic molecule. 6-TG inhibited endothelial cell proliferation triggered by fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor (VEGF) and delayed the repair of a mechanically wounded endothelial cell monolayer. Also, 6-TG inhibited sprouting within fibrin gel, morphogenesis on Matrigel, and collagen gel invasion by endothelial cells. 2-Aminopurine was ineffective. In vivo, 6-TG inhibited basal, VEGF-induced, and FGF2-induced vascularization in the chick embryo chorioallantoic membrane and prevented neovascularization triggered by leukemia LIK cells or their conditioned medium. Finally, bone marrow vascularization in AML patients was decreased to control values in the early remission phase and persisted unvaried after 8-12 months of maintenance therapy with 6-TG. Thus, 6-TG inhibits different steps of the angiogenesis process in vitro and exerts a potent anti-angiogenic activity in vivo. Its anti-angiogenic activity, together with its antimetabolite activity towards tumor cells, may contribute to its action during maintenance therapy in AML. These results suggest a new rationale for the use of purine analogs in the management of AML.

Clinical relevance of vascular endothelial growth factor receptors 1 and 2 in acute myeloid leukaemia and myelodysplastic syndrome

We have previously reported that high levels of cellular vascular endothelial growth factor (VEGF) protein correlated with short survival of patients with acute myeloid leukaemia (AML). As VEGF exerts its effects via two receptors, VEGF receptor 1 (VEGFR-1) and VEGFR-2, we evaluated the significance of VEGFR-1 and VEGFR-2 protein levels in AML and myelodysplastic syndrome (MDS), and their relationship to VEGF protein levels. Western blot analysis and radioimmunoassay confirmed and quantified specific protein levels in bone marrow samples from 41 MDS and 66 AML previously untreated patients. VEGFR-1 levels were significantly higher in AML than in MDS (P = 0.0004), but no significant difference was found in the VEGFR-2 levels (P = 0.5). No significant correlation between VEGFRs levels and duration of survival was found. VEGF protein levels were significantly higher in MDS than in AML (P < 0.0001). A Cox proportional-hazard regression model showed increasing VEGF levels to significantly correlate with shorter survival of patients with MDS (P = 0.008), a finding similar to our previous report of the inverse relationship between VEGF levels and survival of AML patients. We found a significant correlation between VEGF and VEGFR-2 levels in both AML and MDS (P < 0.0000001 andP < 0.0002 respectively) but not between VEGF and VEGFR-1 levels. These data suggest that VEGF expression, rather than the expression of its receptors, is the determining factor in the biological behaviour of AML and MDS, and that VEGFRs are differentially expressed in AML and MDS.

Marrow matrix metalloproteinases (MMPs) and tissue inhibitors of MMP in acute leukaemia: potential role of MMP-9 as a surrogate marker to monitor leukaemic status in patients with acute myelogenous leukaemia

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) were demonstrated to have important implications in the progression and invasiveness of many malignant disorders. In contrast, the biological significance of these molecules in human leukaemias is not clear. We determined the levels of MMP-2, MMP-9, TIMP-1 and TIMP-2 in the bone marrow of 37 patients with acute myelogenous leukaemia (AML) and 18 patients with acute lymphoblastic leukaemia (ALL) before chemotherapy. Nineteen bone marrow donors served as normal controls. After chemotherapy, sequential measurements were done during the course in 19 AML patients. The levels of TIMP-1 and TIMP-2 were significantly higher and MMP-9 levels were significantly lower in the AML and ALL patients than in the normal controls. MMP-2 levels were higher in ALL, but not AML patients, compared with controls. Moreover, the levels of marrow MMP-2 and MMP-9 did not parallel the numbers of leukaemic blasts in the peripheral blood. MMP-9 levels were significantly lower in the AML patients who achieved a complete remission (CR) than in those who did not (8.71 +/- 8.15 ng/ml vs 26.13 +/- 27.75 ng/ml, P < 0.05). The AML patients with lower MMP-9 levels (< or = 4.4 ng/ml) tended to have longer survival time than those with higher levels (> 12 months vs 4 months, P = 0.12). In addition, MMP-9 levels in the AML patients at CR rose to the same range as the controls, but dropped again at relapse, demonstrating a close relationship of marrow MMP-9 with disease status of AML. Therefore, we conclude that the level of marrow MMP-9 may be a useful surrogate marker for monitoring disease status in AML and propose it as a potential prognostic factor.

Angiogenesis in hematologic malignancies and its clinical implications

Angiogenesis is defined as a neoformation of blood vessels of capillary origin. Hematopoiesis is closely linked with angiogenesis, for they share a common ancestor, the hemangioblast. Although it is well established that growth in solid tumors is dependent on angiogenesis, its role in hematologic malignancies has not yet been clarified. In this review, the direct evidence, ie, increased microvessel density, and the indirect evidence, ie, elevated level of angiogenic factors or overexpression of messenger RNA or protein of angiogenic factors, for and against the role of angiogenesis in the development and progression of hematologic malignancies are presented.

Murine 5T multiple myeloma cells induce angiogenesis in vitro and in vivo

Multiple myeloma is a B cell malignancy. Recently, it has been demonstrated that bone marrow samples of patients with multiple myeloma display an enhanced angiogenesis. The mechanisms involved seem to be multiple and complex. We here demonstrate that the murine 5T multiple myeloma models are able to induce angiogenesis in vitro by using a rat aortic ring assay and in vivo by determining the microvessel density. The rat aortic rings cultured in 5T multiple myeloma conditioned medium exhibit a higher number of longer and more branched microvessels than the rings cultured in control medium. In bone marrow samples from 5T multiple myeloma diseased mice, a statistically significant increase of the microvessel density was observed when compared to bone marrow samples from age-matched controls. The angiogenic phenotype of both 5T multiple myeloma cells could be related, at least in part, to their capacity to produce vascular endothelial growth factor. These data clearly demonstrate that the 5T multiple myeloma models are good models to study angiogenesis in multiple myeloma and will allow to unravel the mechanisms of neovascularisation, as well as to test new putative inhibitors of angiogenesis.

Fibroblast growth factors and their receptors in hematopoiesis and hematological tumors

Fibroblast growth factors (FGFs) belong to a family of pleiotropic heparin-binding growth factors. They exert multiple functions on various cell types of mesodermal and neuroectodermal origin, affecting cell proliferation, motility, survival, and differentiation. FGF's exert their activity by interacting with tyrosine kinase receptors (FGFRs) and cell-surface heparan sulfate proteoglycans. This article reviews recent studies on the role of the FGF/FGFR system in embryonic hematopoietic development, hematopoiesis, and hematological tumors. FGFs exert both autocrine and paracrine functions in these biological processes by acting on blood cells and their precursors and accessory cells in the bone marrow, including stromal and endothelial cells.

Angiogenic and lymphangiogenic molecules in hematological malignancies

In this review, the role of angiogenic and lymphangiogenic growth factors in hematological malignancies is summarized, alongside with possible therapeutic applications. Recent data demonstrate the importance of angiogenesis in hematologic malignancies including leukemia, lymphoma, and multiple myeloma. Expression of angiogenic polypeptides vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) associate with clinical characteristics in human leukemia and lymphoma, and their serum concentrations serve as predictors of poor prognosis. VEGF and VEGF-C also act as survival factors on leukemia. Furthermore, certain hematological malignancies both produce angiogenic or lymphangiogenic growth factors including VEGF and VEGF-C, and also express their receptors, resulting in the generation of autocrine loops that may support cancer cell survival and proliferation. Inhibition of the action of key regulators of endothelial cell growth, alone or in combination with other antiangiogenic drugs and/or established chemo- or immunotherapy regimens, is a potential target for therapeutic intervention in hematological malignancies.

alpha(v)beta(3) integrin engagement modulates cell adhesion, proliferation, and protease secretion in human lymphoid tumor cells

OBJECTIVE

The mechanisms used by human lymphoproliferative diseases to invade locally and metastasize are thought to be similar to those developed by solid tumors, including cell proliferation and secretion of extracellular matrix-degrading enzymes following adhesion to extracellular matrix proteins. Hence, the ability of Namalwa (Burkitt's lymphoma), U266 (multiple myeloma), and CEM (T-cell lymphoblastic leukemia) cells to interact with the extracellular matrix components vitronectin and fibronectin was determined. Fresh bone marrow plasma cells from patients with multiple myeloma also were studied.

MATERIALS AND METHODS

Engagement of alpha(v)beta(3) integrin, formation and protein composition of focal adhesion contacts on the cell surface, phosphorylation of several signal transduction proteins in the contacts, cell proliferation, and enzyme secretion were studied following adhesion to vitronectin and fibronectin.

RESULTS

All three lines adhered to immobilized vitronectin and fibronectin. Adhesion was fully prevented by neutralizing monoclonal anti-alpha(v)beta(3) integrin antibody. Integrin engagement caused the formation of phosphorylated pp60(src)/focal adhesion kinase complexes and the aggregation of focal adhesion plaques containing the beta(3) integrin subunit, the cytoskeletal proteins vinculin, cortactin, and paxillin, the tyrosine kinases focal adhesion kinase and pp60(src), the adapter protein Grb-2, and the mitogen-activated protein kinase ERK-2. Free and immobilized vitronectin and fibronectin stimulated the proliferation of cells under serum-free conditions and the production and release of urokinase-type plasminogen activator, and increased the release of the activated forms of matrix metalloproteinase-2 and matrix metalloproteinase-9 in an alpha(v)beta(3) integrin-dependent manner. Similar results were obtained in myeloma plasma cells.

CONCLUSIONS

The demonstrated ability of lymphoid tumor cells to interact with the extracellular matrix components vitronectin and fibronectin via alpha(v)beta(3) integrin can be interpreted as evidence of a novel mechanism for their invasion and spreading. This interaction allows them to adhere to the substratum and enhances their proliferation and protease secretion.

Angiogenesis in acute promyelocytic leukemia: induction by vascular endothelial growth factor and inhibition by all-trans retinoic acid

Recent studies indicate that angiogenesis is important in the pathogenesis of leukemias, apart from its well-established role in solid tumors. In this study, the possible role of angiogenesis in acute promyelocytic leukemia (APL) was explored. Bone marrow trephine biopsies from patients with APL showed significantly increased microvessel density and hot spot density compared with normal control bone marrow biopsies. To identify the mediators of angiogenesis in APL, quantitative and functional assays were performed using the NB4 APL cell line as a model system. Conditioned media (CM) from the NB4 cells strongly stimulated endothelial cell migration. CM from the NB4 cells contained high levels of vascular endothelial growth factor (VEGF) but not basic fibroblast growth factor (bFGF). Most important, the addition of neutralizing VEGF antibodies completely inhibited the ability of NB4 CM to stimulate endothelial cell migration, suggesting that APL angiogenesis is mediated by VEGF. The effect of all-trans retinoic acid (ATRA) on APL angiogenesis was then studied. ATRA therapy resulted in a decrease in bone marrow microvessel density and hot spot density. CM from ATRA-treated APL cells did not stimulate endothelial cell migration. Finally, quantitative assays showed that ATRA treatment resulted in the abrogation of VEGF production by the NB4 cells. These results show that there is increased angiogenesis and VEGF production in APL and that ATRA therapy inhibits VEGF production and suppresses angiogenesis. The addition of specific antiangiogenic agents to differentiation therapy or chemotherapy should be explored. (Blood. 2001;97:3919-3924)