An anti-vascular endothelial growth factor receptor 2/fetal liver kinase-1 Listeria monocytogenes anti-angiogenesis cancer vaccine for the treatment of primary and metastatic Her-2/neu+ breast tumors in a mouse model

Thirty years after angiogenesis was shown to play an enabling role in cancer, modern medicine is still trying to develop novel compounds and therapeutics to target the tumor vasculature. However, most therapeutics require multiple rounds of administration and can have toxic side effects. In this study, we use anti-angiogenesis immunotherapy to target cells actively involved in forming new blood vessels that support the growth and spread of breast cancer. Targeting a central cell type involved in angiogenesis, endothelial cells, we immunized against host vascular endothelial growth factor receptor 2 to fight the growth of Her-2/neu(+) breast tumors. Using the bacterial vector, Listeria monocytogenes (Lm), we fused polypeptides from the mouse vascular endothelial growth factor receptor 2 molecule (fetal liver kinase-1) to the microbial adjuvant, listeriolysin-O, and used Lm to deliver the Ags and elicit potent antitumor CTL responses. Lm-listeriolysin-O-fetal liver kinase-1 was able to eradicate some established breast tumors, reduce microvascular density in the remaining tumors, protect against tumor rechallenge and experimental metastases, and induce epitope spreading to various regions of the tumor-associated Ag Her-2/neu. Tumor eradication was found to be dependent on epitope spreading to HER-2/neu and was not solely due to the reduction of tumor vasculature. However, vaccine efficacy did not affect normal wound healing nor have toxic side effects on pregnancy. We show that an anti-angiogenesis vaccine can overcome tolerance to the host vasculature driving epitope spreading to an endogenous tumor protein and drive active tumor regression.

Expression of vascular endothelial growth factor receptors coincide with blood vessel in-growth and reactive bone remodelling in experimental intervertebral disc degeneration

OBJECTIVE

To analyze immunohistochemically the localization of the VEGF receptors in experimental intervertebral disc degeneration tissues in a pig model.

MATERIALS AND METHODS

In six domestic pigs, the cranial bony endplate of the L4 vertebra were perforated into the nucleus pulposus. Three months postoperatively, the animals were sacrificed and the experimental and control vertebrae, complete with intervertebral discs, were excised and subjected for immunohistochemical staining of vascular endothelial growth factor receptors (VEGFR) along with VEGF - A, -C, -D and blood and lymphatic vessel markers vWF and LYVE-1.

RESULTS

The results of immunohistochemical analysis of experimental samples showed VEGFR-1 (Flt-1) expression in intervertebral disc and all paradiscal tissues studied. In control samples expression of VEGFR-1 was lower and absent in the intervertebral discs. Comparatively less of VEGFR-2 (KDR/Flk-1) and VEGFR-3 (Flt-4) than VEGFR-1was found in degenerated intervertebral discs and paradiscal tissues. In contiguous control intervertebral discs and control paradiscal tissues VEGFR-2 and-3 receptors were expressed to a lower extent than in experimental tissues or were even totally absent. Also growth factors VEGF-A, -C, -D, as well as von Willebrand factor and to a much lower extent LYVE-1 were differently expressed in experimental and control intervertebral discs.

CONCLUSION

In experimental intervertebral disc degeneration, VEGF receptors were expressed in the damaged disc and paradiscal tissues. In the same tissues, VEGF-A, -C, and -D, signs of blood and lymphatic vessel in-growth and reactive/adaptive vertebral bone remodelling were found.

Positive feedback between vascular endothelial growth factor-A and autotaxin in ovarian cancer cells

Tumor cell migration, invasion, and angiogenesis are important determinants of tumor aggressiveness, and these traits have been associated with the motility stimulating protein autotaxin (ATX). This protein is a member of the ectonucleotide pyrophosphatase and phosphodiesterase family of enzymes, but unlike other members of this group, ATX possesses lysophospholipase D activity. This enzymatic activity hydrolyzes lysophosphatidylcholine to generate the potent tumor growth factor and motogen lysophosphatidic acid (LPA). In the current study, we show a link between ATX expression, LPA, and vascular endothelial growth factor (VEGF) signaling in ovarian cancer cell lines. Exogenous addition of VEGF-A to cultured cells induces ATX expression and secretion, resulting in increased extracellular LPA production. This elevated LPA, acting through LPA(4), modulates VEGF responsiveness by inducing VEGF receptor (VEGFR)-2 expression. Down-regulation of ATX secretion in SKOV3 cells using antisense morpholino oligomers significantly attenuates cell motility responses to VEGF, ATX, LPA, and lysophosphatidylcholine. These effects are accompanied by decreased LPA(4) and VEGFR2 expression as well as by increased release of soluble VEGFR1. Because LPA was previously shown to increase VEGF expression in ovarian cancer, our data suggest a positive feedback loop involving VEGF, ATX, and its product LPA that could affect tumor progression in ovarian cancer cells.

Metronomic chemotherapy dosing-schedules with estramustine and temozolomide act synergistically with anti-VEGFR-2 antibody to cause inhibition of human umbilical venous endothelial cell growth

The effects of 'metronomic' or extended chemotherapy dosing schedules (ECS) are mediated through poorly understood anti-angiogenic mechanisms. ECS combined with biological anti-angiogenic agents have produced promising pre-clinical results.

MATERIALS AND METHODS

We have expanded the list of agents with an in vitro ECS profile to include the methylating agent temozolomide (Temodal) and the anti-mitotic agent estramustine (Estracyt). These agents were also combined with a specific anti-angiogenic inhibitor IMC-1C11 and a non-specific agent with anti-angiogenic properties, Compound 5h. The in vitro HUVEC ECS model system was optimised and cell proliferation assays undertaken.

RESULTS

As a single agent, estramustine inhibited endothelial cell proliferation with an IC50 of 4.5 microM and was active at 10-33% of the maximum tolerated dose (MTD) from clinical schedules, whilst temozolomide had IC50 of 6.6 microM and was active at 1-6% of MTD. In combination, significant synergy was seen with IMC-1C11 in combination with either drug, whilst modest additive effects were observed with Compound 5h. None of the combinations resulted in significant cytotoxicity or apoptosis.

DISCUSSION

The results show that ECS of temozolomide and estramustine can be significantly enhanced when combined with specific anti-angiogenic inhibitors in an in vitro HUVEC system.

[Adenovirus vector encoding human KDR elicits immunity against hepatocellular carcinomas in mice]

OBJECTIVE

To investigate the effect of adenovirus vector encoding human vascular endothelial growth factor receptor-2 (hVEGFR-2 or hKDR) on breaking the immune tolerance and inducing immunity against murine hepatocellular carcinomas.

METHODS

Human and mouse KDR cDNA were cloned from human umbilical vein endothelial cells (HUVEC) and C57BL/6 mouse embryo cells respectively using RT-PCR, and then Ad hKDR and Ad mKDR were constructed. Seven days after immunization of the mice with Ad hKDR or Ad mKDR, an analysis of cytotoxic activity of antigen-specific cytotoxic T lymphocytes (CTL) was made by lactate dehydrogenase (LDH) release assay, in which splenocytes of the immunized mice acted as effectors and Hepa 1-6/mKDR cells as the targets. In addition, the survival of the mice immunized with Hepa 1-6 hepatoma cells was checked.

RESULTS

Seven days after immunization, the 6 h killing activities of CTL elicited by the Ad hKDR were 84.3%+/-6.7%, 71.5%+/-5.2%, and 44.6%+/-4.7% at the ratio of the effectors:targets (E:T) of 100:1, 50:1, and 25:1, respectively. Correspondingly, the CTL activities by Ad mKDR were 65.2%+/-6.1%, 46.7%+/-5.0%, and 22.6%+/-3.7%. Sixty percent of the Ad hKDR-immunized mice with 5*10(6) Hepa 1-6 hepatoma cells were still alive two months after the inoculation, whereas just 40% of the Ad mKDR-immunized mice with 2*10(6) Hepa 1-6 cells survived two months. When CD8+ or CD4+ T lymphocytes were deleted in the mice the above mentioned CTL activities and protection of the mice from tumors disappeared.

CONCLUSION

Adenovirus vector-mediated xenogeneic KDR can effectively break the immune tolerance to hepatocellular carcinomas in an animal model and induce a strong antigen-specific T cell response, which is dependent on CD8+ and CD4+ T cells.

[Vasculogenic potential of endothelial progenitor cells derived from human umbilical cord blood and their roles in neovascularization of malignant glioma]

OBJECTIVE

To investigate vasculogenic potential of endothelial progenitor cells (EPCs) derived from human umbilical cord blood and their contribution to the neovascularization of malignant glioma in vivo.

METHODS

EPCs were isolated from human umbilical cord blood by density gradient centrifugation. After 7-10 days of culture, EPCs were investigated for CD34 and VEGFR-2 expression by direct immunofluoresent staining. The proliferative activity, migratory capability and forming capillary-like tubules were also monitored after stimulation with VEGF(50 mg/L) in vitro. Moreover, EPCs were administered into tumor-bearing mice, and the tumor and mouse organs were examined under confocal laser scanning microscope to visualize the distribution and localization of transplanted EPCs. In order to quantity the incorporation of EPCs into tumor vessels, cryosections of the tumor tissue were double-labelled with antihuman CD31 and anti-mouse CD31.

RESULTS

After 7 to 10 days of culture, EPCs assumed cobblestone-like monolayer growth pattern with nearly complete confluence, and expressed CD34 and VEGFR-2. Significant proliferative activity, increased migratory capability and forming capillary-like tubules were observed when stimulated with VEGF. The transplanted EPCs in vivo specifically homed to solid tumor tissue and incorporated into the tumor's endothelium. Quantitative analysis revealed that human EPCs contributed significantly to tumor neovascularization by incorporation into tumor vasculature (18.68 +/- 1.32)% of the total vessels.

CONCLUSION

EPCs possess the potential to form neovascular network in tumor and play a role in the phenotypical heterogeneity of tumor microvascular architecture.

Review: monoclonal antibodies to the vascular endothelial growth factor receptor-2 in cancer therapy

Angiogenesis is a fundamental mechanism of cancer growth and invasion. Current translational approaches are using both small-molecule inhibitors and antibodies that modulate various steps of these processes, and several such compounds have already received regulatory approval for the therapy of specific indications in cancer. Among the many molecular targets involved in the control of angiogenesis, the vascular endothelial growth factor receptor-2 (VEGFR-2; or kinase insert domain-containing receptor) is attractive as shown in part by the efficacy of small-molecule inhibitors directed to this receptor. Two small-molecule inhibitors that target VEGFR-2 have recently been granted approval for the treatment of renal cell cancer and gastrointestinal stromal tumors. The development of antibodies that can selectively block VEGFR-2 could potentially result in improved potency or tolerability. Here, we discuss the role of VEGFR-2 in cancer and ongoing efforts to develop highly specific monoclonal antibodies for cancer therapy.

Imaging steps of lymphatic metastasis reveals that vascular endothelial growth factor-C increases metastasis by increasing delivery of cancer cells to lymph nodes: therapeutic implications

Preclinical and clinical studies positively correlate the expression of vascular endothelial growth factor (VEGF)-C in tumors and the incidence of lymph node metastases. However, how VEGF-C regulates individual steps in the transport of tumor cells from the primary tumor to the draining lymph nodes is poorly understood. Here, we image and quantify these steps in tumors growing in the tip of the mouse ear using intravital microscopy of the draining lymphatic vessels and lymph node, which receives spontaneously shed tumor cells. We show that VEGF-C overexpression in cancer cells induces hyperplasia in peritumor lymphatic vessels and increases the volumetric flow rate in lymphatics at the base of the ear by 40%. The increases in lymph flow rate and peritumor lymphatic surface area enhance the rate of tumor cell delivery to lymph nodes, leading to a 200-fold increase in cancer cell accumulation in the lymph node and a 4-fold increase in lymph node metastasis. In our model, VEGF-C overexpression does not confer any survival or growth advantage on cancer cells. We also show that an anti-VEGF receptor (VEGFR)-3 antibody reduces both lymphatic hyperplasia and the delivery of tumor cells to the draining lymph node, leading to a reduction in lymph node metastasis. However, this treatment is unable to prevent the growth of tumor cells already seeded in lymph nodes. Collectively, our results indicate that VEGF-C facilitates lymphatic metastasis by increasing the delivery of cancer cells to lymph nodes and therapies directed against VEGF-C/VEGFR-3 signaling target the initial steps of lymphatic metastasis.

Suppression of choroidal neovascularization by dendritic cell vaccination targeting VEGFR2

PURPOSE

To investigate whether the induction of cellular immunity against vascular endothelial growth factor receptor (VEGFR) 2 inhibits the development of choroidal neovascularization (CNV).

METHODS

H-2Db-restricted peptide corresponding to amino acids 400 to 408 of VEGFR2 was used as an epitope peptide. Dendritic cells (DCs) were harvested from bone marrow progenitors of C57BL/6 mice. Six-week-old C57BL/6 mice received subcutaneous injections of the epitope peptide-pulsed mature DCs three times at 6-day intervals. After the third immunization, laser photocoagulation was performed to induce CNV. One week after photocoagulation, mice were killed to harvest the choroid and splenocytes. CNV volume was evaluated by volumetric measurements. To confirm the specific immunogenicity of the epitope peptides in C57BL/6 mice, CD8 T cells isolated from harvested splenocytes were restimulated to measure interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha production through enzyme-linked immunospot assay and ELISA. To determine the T-cell subset responsible for the immunotherapy, mice were intraperitoneally injected with an anti-CD4 or anti-CD8 depletion antibody.

RESULTS

CNV volume was significantly lower in mice immunized with the VEGFR2 epitope peptide than in those not immunized or immunized with a control peptide gp70. Cytokine assays showed the peptide-specific production of IFN-gamma and TNF-alpha from the CD8 T cells in a dose-dependent manner. In vivo depletion of CD8, but not CD4, T cells significantly reversed the suppressive effect of the VEGFR2 peptide-pulsed DC vaccination on CNV to the level observed in nonimmunized or gp70-immunized animals.

CONCLUSIONS

These results indicate that the VEGFR2 peptide-specific induction of cellular immunity inhibits CNV through the cytotoxicity of CD8 T cells. Results of the present study suggested the possibility of DC vaccination targeting VEGFR2 as a novel therapeutic strategy for CNV.

The preparation and characterization of anti-VEGFR2 conjugated, paclitaxel-loaded PLLA or PLGA microspheres for the systemic targeting of human prostate tumors

PURPOSE

The objective of this study was to manufacture paclitaxel (PTX) loaded polymeric microspheres, that were surface conjugated with antibodies to vascular endothelial growth factor receptor 2 (anti-VEGFR2), for systemic targeting to angiogenic sites in prostate tumors.

METHODS

Microspheres were manufactured in the 1-3 microm size range from poly (l-lactic acid) (PLLA) or poly (lactide-co-glycolide) (PLGA) by a modified solvent evaporation method using Polytron homogenization followed by high speed dispersion in poly vinyl alcohol. Antibodies were conjugated to the surface of these microspheres using cyanogen bromide activation of the polymer surface. Cell Binding was determined using human umbilical vein endothelial cells (HUVECs) in vitro. Efficacy determinations were made using human prostate tumors (PC-3) grown subcutaneously in mice.

RESULTS

Antibodies were effectively bound to the surface of PLLA and PLGA microspheres. Anti-VEGFR2 conjugated PLLA microspheres bound strongly to HUVEC's. Pilot efficacy studies in mice showed variability but demonstrated a significant inhibition of tumor growth following the systemic administration of a single dose of PTX-loaded anti-VEGFR2 conjugated PLLA microspheres as compared to non-antibody-conjugated PTX-loaded microspheres.

CONCLUSION

Anti-VEGFR2 conjugated PLLA microspheres containing PTX may offer an effective way of administering a controlled release formulation of the drug to target prostate tumors.

Detecting vascular changes in tumour xenografts using micro-ultrasound and micro-ct following treatment with VEGFR-2 blocking antibodies

Blockade of vascular endothelial growth factor (VEGF) binding to its receptors on endothelial cells has been shown preclinically to induce tumour growth inhibition. Using ultrasound biomicroscopy (UBM) or micro-ultrasound imaging and micro-computed tomography (micro-CT) analysis, we have examined the effects of DC101, a highly specific vascular endothelial growth factor receptor-2 (VEGFR-2)-targeting antibody, in inducing growth inhibition and functional vascular changes in established melanoma (MeWo) xenografts in mice. Postprocessing of UBM imaging loops for speckle variance was introduced to estimate the level of functional blood flow in tumours. Perfused tumour area visualized by speckle variance revealed decreased blood flow within 48 h after DC101 injection (control versus DC101: 1.90 +/- 0.25% versus 1.01 +/- 0.11%, p < 0.01) and following a 3-wk DC101 therapy (control versus DC101: 0.76 +/- 0.14% versus 0.45 +/- 0.05%, p = 0.04), suggesting that VEGFR-2 blockade mediates both early and long-term effects on tumour blood flow. The growth of xenografts was significantly inhibited after treating with DC101 for 3 wk compared with controls. In addition to UBM, we examined the tumour vasculature in three-dimension (3D) using contrast-enhanced Micro-CT imaging, which displayed a reduction in the number of tumour vessels following extended VEGFR-2 blockade (vascular density of control versus DC101: 48.4 +/- 5.4% versus 20.6 +/- 1.8%). Lastly, decreased microvessel density (MVD) was noted in DC101-treated xenografts (3 wk) by performing immunohistochemical staining of endothelial marker CD34. Our study investigates tumour response to DC101 using complementing micro-ultrasound and micro-CT imaging tools.

Lymphocyte contributions to altered endometrial angiogenesis during early and midgestation fetal loss

Peri-implantation and midgestational fetal losses reduce potential litter sizes up to 40% in commercial swine. Peri-implantation studies [gestation days (gd)15-23] of porcine RNA from laser capture microdissected uterine lymphocytes and biopsies of mesometrial endometrium and trophoblast previously linked gd21-23 fetal arrest with transcriptional deficits in vascular endothelial growth factor (VEGF) and its regulatory factor, hypoxia inducible factor (HIF)-1alpha, and with elevations in IFN-gamma and TNF-alpha and suggested endometrial lymphocytes played a pivotal, proangiogenic role in fetal survival. Here, we address more comprehensively porcine endometrial angiogenesis by comparing transcription between endometrial endothelium and lymphocytes during early (gd20) and midgestation (gd50) losses and by incorporation of histopathology and protein immunolocalization of VEGF, placenta growth factor (PlGF), VEGF receptor I (VEGFRI), and VEGFRII. In healthy sites, endometrial lymphocytes transcribed more VEGF at gd50 than gd20, and transcripts were more abundant in lymphocytes than in endothelium or trophoblast. Arterial endothelial cells showed the most abundant transcription of PlGF. With fetal arrest, maternal transcripts for VEGF but not PlGF dropped, and fetal transcripts remained relatively stable. Maternal and fetal HIF-1alpha transcription declined. Lymphocytes preferentially transcribed VEGFRI over VEGFRII, and endometrial arterial endothelium and trophoblast preferentially transcribed VEGFRII. IFN-gamma and TNF-alpha transcripts were present in gd20 and gd50 healthy- and arresting-implantation sites. gd20 arrest was associated with greater transcription of IFN-gamma than TNF-alpha in maternal and fetal tissues. At gd50, this was reversed. Endometrial, vascular pathology was evident only at gd50. These data suggest the critical importance for lymphocyte-driven endometrial angiogenesis, which extends to midgestation.

Vaccination against VEGFR2 attenuates initiation and progression of atherosclerosis

OBJECTIVE

Vascular endothelial growth factor receptor 2 (VEGFR2)-overexpressing cells may form an interesting target for the treatment of atherosclerosis because of their involvement in processes that contribute to this disease, such as angiogenesis.

METHODS AND RESULTS

We vaccinated mice against VEGFR2 by an orally administered DNA vaccine, comprising a plasmid, encoding murine VEGFR2, carried by live attenuated Salmonella typhimurium. This vaccine induces cellular immunity against cells that overexpress VEGFR2. Vaccination of hypercholesterolemic mice against VEGFR2 resulted in a marked induction of CD8+ cytotoxic T cells specific for VEGFR2 and led to an inhibition of angiogenesis in a hindlimb ischemia model. Interestingly, VEGFR2 vaccination attenuated the progression of preexisting advanced atherosclerotic lesions in the brachiocephalic artery of apoE-/- mice. Furthermore, VEGFR2 vaccination strongly reduced the initiation of collar-induced atherosclerosis in the carotid arteries of LDLr-/- mice. In addition, denudation of the carotid artery, as a model for postinterventional lesion formation, resulted in delayed endothelial replacement and significantly increased neointima formation on VEGFR2 vaccination.

CONCLUSIONS

These data indicate the prominent role of VEGFR2+ cells in cardiovascular diseases and show that induction of cellular immunity against atherosclerosis-associated cells by means of DNA vaccination may contribute to the development of novel therapies against atherosclerosis.

Vascular endothelial growth factor inhibits the function of human mature dendritic cells mediated by VEGF receptor-2

Dendritic cells (DCs) are the most potent antigen-presenting cells and play a central role in the host-antitumor immunity. Since it has been reported that vascular endothelial growth factor (VEGF) inhibits the functional maturation of immature-DCs and impairs DC differentiation, it is important to elucidate the mechanisms of VEGF-induced DC-dysfunction. To investigate the effects of VEGF against human mature DCs, we investigated how VEGF affects mature DCs with regards to phenotype, induction of apoptosis, IL-12(p70) production and the antigen-presenting function evaluated by allogeneic mixed leukocyte reaction (allo-MLR). We generated monocyte-derived DCs matured with lipopolysaccharide, OK-432 or pro-inflammatory cytokine cocktails. As a result, VEGF treatment did not alter the mature DCs with regard to phenotype, IL-12(p70) production and induction of apoptosis. As a novel and important finding, VEGF inhibited the ability of mature DCs to stimulate allogeneic T cells. Furthermore, this VEGF-induced DC dysfunction was mainly mediated by VEGF receptor-2 (VEGF R2). These observations were confirmed by the findings that the VEGF-induced DC dysfunction was recovered by anti-human VEGF neutralizing mAb or anti-human VEGF R2 blocking mAb, and that placenta growth factor (PlGF), VEGF R1-specific ligand, did not have any effect against mature DCs. Some modalities aiming at reversing mature-DC dysfunction induced by VEGF will be needed in order to induce the effective antitumor immunity.

Anticancer therapies combining antiangiogenic and tumor cell cytotoxic effects reduce the tumor stem-like cell fraction in glioma xenograft tumors

Vascular endothelial cells have been identified as a critical component of the neural stem cell niche, raising the possibility that brain tumor stem-like cells (TSLC) may also rely on signaling interactions with nearby tumor vasculature to maintain their stem-like state. The disruption of such a TSLC vascular niche by an antiangiogenic therapy could result in loss of stemness characteristics associated with intrinsic drug resistance and, thus, preferentially sensitize TSLC to the effects of chemotherapy. Considering these possibilities, we investigated the impact of antiangiogenic anticancer therapy on the TSLC fraction of glioma tumors. Athymic nude mice bearing s.c. tumor xenografts of the C6 rat glioma cell line were treated with either a targeted antiangiogenic agent, antiangiogenic schedules of low-dose metronomic chemotherapy, combination therapies of antiangiogenic agents and chemotherapy, or, for the purpose of comparison, a conventional cytotoxic schedule of maximum tolerated dose chemotherapy using cyclophosphamide. Targeted antiangiogenic therapy or cytotoxic chemotherapy did not reduce the fraction of tumor sphere-forming units (SFU) in the tumor, whereas all treatment groups that combined both antiangiogenic and cytotoxic drug effects caused a significant reduction in SFU. This work highlights the possibility that selective eradication of TSLC may be achieved by targeting the tumor microenvironment (and potentially a supportive TSLC niche) rather than the TSLC directly. Furthermore, this work suggests a possible novel effect of antiangiogenic therapy, namely, as a chemosensitizer of TSLC, and thus represents a possible new mechanism to explain the ability of antiangiogenic therapy to enhance the efficacy of chemotherapy.

Using behavioral measurement to assess tumor progression and functional outcome after antiangiogenic treatment in mouse glioma models

The objective of the current study was to investigate the behavioral changes of glioma-bearing nude mice and functional outcome from treatment with a novel antiangiogenesis regimen, which is a combination of monoclonal antibodies against both vascular endothelial growth factor receptor (VEGFR)-1 (MF1) and VEGFR-2 (DC101). The reliability and responsiveness of behavioral measurement with the rearing test were first examined in nude mice bearing two kinds of gliomas--9L gliosarcoma and U87 human glioma, which have different growth rates. Using immunohistochemical staining and fluorescent imaging techniques, upregulation of the angiogenesis marker VEGF, coincident with the abnormal neovascular architecture, was confirmed in the human U87 glioma model. The behavioral measurement was then applied to assess functional outcome with the combination antibody treatment in the orthotopic mouse model of human U87 glioma. The combination antibody therapy retarded tumor progression and delayed the onset of significant behavioral deficits. Histologically, tumor necrosis and apoptosis were increased and tumor cell proliferation was decreased after treatment. In clinical trials for novel interventions, functional end points typically are included in the assessment of potential efficacy. Because certain interventions that successfully treat tumor progression in animal models might interfere with compensatory neuroplasticity, functional measurement may be valuable for improving the clinical relevance of translational brain tumor research.

An antibody directed against PDGF receptor beta enhances the antitumor and the anti-angiogenic activities of an anti-VEGF receptor 2 antibody

Platelet-derived growth factor (PDGF) and its receptors (PDGFR) play important roles in tumorigenesis through stimulating tumor growth and promoting angiogenesis via enhancing pericyte recruitment and vessel maturation. Here we produced a neutralizing antibody, 1B3, directed against mouse PDGFRbeta. 1B3 binds to PDGFRbeta with high affinity (9x10(-11)M) and blocks PDGF-BB from binding to the receptor with an IC(50) of approximately 1.2 nM. The antibody also blocks ligand-stimulated activation of PDGFRbeta and downstream signaling molecules, including Akt and MAPK p42/44, in tumor cells. In animal studies, 1B3 significantly enhanced the antitumor and the anti-angiogenic activities of DC101, an antibody directed against mouse vascular endothelial growth factor receptor 2, in a pancreatic (BxPC-3) and a non-small cell lung (NCI-H460) tumor xenograft models. Treatment with the combination of 1B3 and DC101 in BxPC-3 xenograft-bearing mice resulted in tumor regression in 58% of mice compared to that in 18% of mice treated with DC101 alone. Taken together, these results lend great support to use PDGFRbeta antagonists in combinations with other antitumor and/or anti-angiogenic agents in the treatment of a variety of cancers.

Impairment in immuno-modulatory function of Flk1(+)CD31(-)CD34(-) MSCs from MDS-RA patients

OBJECTIVE

Myelodysplastic syndromes are a group of hematopoietic disorders characterized by hematopoietic stem cell dysregulation and abnormalities in the immune system. Mesenchymal stem cells (MSCs) and their derived stromal cells constitute a bone marrow microenvironment, which is the niche for hematopoiesis and a key compartment for immune development and regulation. Existing evidence has shown that MSCs from MDS patients have impaired capacity in supporting hematopoiesis. Here, we conducted an investigation to determine whether the immuno-modulatory function of MSCs is also impaired in MDS-RA (refractory anemia) patients.

METHOD

Flk1(+)CD31(-)CD34(-) MSCs were isolated from 15 MDS-RA patients and cultured for testing biological and immunological characteristics.

RESULTS

MDS-RA patient-derived Flk1(+)CD31(-)CD34(-) MSCs showed normal morphology, phenotype and karyotype but appeared impaired in immuno-modulatory function. The capacity of patient Flk1(+)CD31(-)CD34(-) MSCs to inhibit T lymphocyte activation and proliferation was impaired in vitro. In conclusion, MDS-RA patient-derived MSCs have impaired immuno-modulatory functions, suggesting that the dysregulation of hematopoiesis and immune response may originate from MSCs rather than HSCs. MSCs might be a potential target for developing efficacious cures for MDS.

Neutralization of Endogenous Vascular Endothelial Growth Factor Depletes Primordial Follicles in the Mouse Ovary1

The regulation of early follicular growth and development involves a complex interaction of autocrine, paracrine, and endocrine signals. The ability of these factors to regulate follicle growth may depend in part on the extent of vascular delivery to and perfusion of the ovary. Vascular endothelial growth factor A (VEGFA) is a major regulator of vascular physiology in the ovary. VEGFA is produced in numerous ovarian compartments and likely plays a role in the regulation of all phases of follicular growth, from preantral through preovulatory. The aim of the present study was to further evaluate the role of VEGF in early follicle growth by neutralization of endogenous VEGF or VEGF receptors. Adult mice were injected systemically and prepubertal mice were injected directly under the ovarian bursa with antibodies designed to neutralize VEGF or block interaction with its receptors in the ovary. Both systemic and intrabursal injections of VEGF antibody significantly reduced the number of primordial follicles within 1-3 days after administration without affecting primary or secondary follicle numbers. Primordial follicle numbers were not different from control levels by 30 days after VEGFA antibody administration. Administration of antibodies to the kinase domain receptor (KDR), but not the FMS-like tyrosine receptor (FLT1), for VEGF also resulted in a significant decrease in primordial follicles. These data suggest that VEGF plays a vital role in the maintenance and growth of the primordial follicle pool.

Immunohistochemical analysis of growth mechanisms in juvenile nasopharyngeal angiofibroma

Angiogenic factors are discussed to participate in growth and promotion of juvenile nasopharyngeal angiofibroma (JNA). However, only few data are available and mechanisms remain unclear. In the presented study we analysed the expression and subcellular distribution of several angiogenic growth factors and receptors potentially involved in JNA-growth and -vascularisation. In a retrospective, descriptive, multicenter-study, we analysed 13 formalin-fixed, paraffin-embedded or cryopreserved JNA-tumors (eleven primary tumors and two recurrent ones) after immunohistochemical staining. We used monoclonal antibodies specific for transforming growth factor beta 1 (TGF-beta(1)), basic fibroblast growth factor (bFGF), the VEGF-receptors 1 and -2 (FLT-1 and FLK-1), and the hypoxia inducible factor (Hif-1alpha). Data were compared to the vessel density. Quantitative analysis of staining intensities was performed by a computer assisted quantification technique. Endothelial and stromal compartments of the samples were analysed separately. Data were compared to vessel densities and patients data. The VEGF-Receptor-2 (FLK) was frequently unregulated in the stroma and endothelium of those samples with high vessel densities. Similarly, we observed high bFGF- and TGF-beta(1) levels in the stroma of strong vascularised samples. No correlations of expression levels to patients' data were found. The reported data support the concept of JNA-growth and -vascularisation driven by factors released from stromal fibroblasts. Therefore, inhibition of these factors might be beneficial for the therapy of inoperable JNA.

FLK-1-based minigene vaccines induce T cell-mediated suppression of angiogenesis and tumor protective immunity in syngeneic BALB/c mice

Angiogenesis is a rate-limiting step in the development of tumors. Here, we demonstrate that oral minigene DNA vaccines against murine vascular endothelial growth factor receptor-2 (FLK-1), a self-antigen overexpressed on proliferating endothelial cells in the tumor vasculature, induced protection against tumors of different origin in syngeneic BALB/c mice. This protection is mediated by CD8 T cells, which specifically kill FLK-1(+) endothelial cells, resulting in marked suppression of tumor angiogenesis. More importantly, the minigene vaccine proved to be of similar efficacy as a vaccine encoding the whole FLK-1 gene. These data suggest a FLK-1 minigene vaccine provides a more flexible alternative to the whole gene vaccine and will facilitate their future design and clinical applications in cancer therapy and prevention.

Roles of nitric oxide synthase inhibition and vascular endothelial growth factor receptor-2 inhibition on vascular morphology and function in an in vivo model of pancreatic cancer

PURPOSE

Both nitric oxide (NO) and vascular endothelial growth factor (VEGF) mediate tumor vascular function. Because these molecules regulate one another's expression, we hypothesized that NO synthase (NOS) inhibition produces effects comparable to those of anti-VEGF therapy on human pancreatic cancer xenografts.

EXPERIMENTAL DESIGN

L3.6pl human pancreatic cancer cells were s.c. implanted in nude mice. On day 6, mice were randomized to receive (a) PBS (control), (b) DC101 [VEGF receptor 2 (VEGFR-2) antibody] by i.p. injection, (c) N-nitro-l-arginine (NNLA; NOS inhibitor) in the drinking water, or (d) both DC101 and NNLA. Mice were killed on day 20.

RESULTS

DC101 and NNLA as single agents inhibited tumor growth by approximately 50% to 60% (P < 0.008 for both). Furthermore, combined therapy inhibited mean tumor growth by 89% (P < 0.008). Combined inhibition of VEGFR-2 and NOS also decreased mean vessel counts by 65% (P < 0.03) and vessel area by 80% versus controls (P < 0.001). In contrast to DC101 where vessel diameter was similar to control, NNLA decreased mean vessel diameter by 42% (P < 0.001). NNLA also led to a 54% (P < 0.03) decrease in tumor uptake of the perfusion marker Hoechst 33342 versus controls whereas DC101 decreased Hoechst 33342 staining by 43% (P < 0.03). The combination of inhibitors decreased perfusion by 73% (P < 0.03).

CONCLUSIONS

Although VEGFR-2 can mediate NOS activity, the combination of VEGFR-2 and NOS inhibition significantly increased the antivascular effect over single agent therapy. The addition of NOS inhibition led to an even further alteration of tumor vessel morphology and vascular perfusion compared with VEGFR-2 blockade, suggesting that NO and VEGFR-2 have distinct but complementary effects on the tumor vasculature.

Enhanced natural-killer cell and erythropoietic activities in VEGF-A-overexpressing mice delay F-MuLV-induced erythroleukemia

We have previously reported that VEGF-A, in combination with MCP-5, contributes to leukemia progression within the splenic microenvironment of mice infected with F-MuLV. To study the influence of constitutively elevated VEGF-A levels on the progression of erythroleukemia, mice heterozygous for a VEGF-A "hypermorphic" allele (Vegfhi/+) were inoculated with F-MuLV. Unexpectedly, a significant delay in erythroleukemia was observed in Vegfhi/+ mice when compared with wild-type controls. These results suggested an altered physiologic response arising from elevated VEGF-A levels that decelerated erythroleukemic progression. Characterization of hematopoiesis in Vegfhi/+ spleens showed a higher natural killer cell activity, elevated B cells, and a decrease in T-cell number. Furthermore, higher erythroid progenitors (ie, CD34+, CD36+, and Ter119+ cells) were evident in the bone marrow, spleen, and peripheral blood of Vegfhi/+ mice. The CFU-E levels were significantly elevated in Vegfhi/+ bone marrow cultures, and this elevation was blocked by a neutralizing antibody to VEGF-A receptor (VEGFR-2). Moreover, erythroleukemic mice were treated with recombinant erythropoietin and, similar to diseased Vegfhi/+ mice, showed a delay in disease progression. We propose that a compensatory erythropoietic response combined with increased natural killer (NK) cell activity account for the extended survival of erythroleukemic, Vegfhi/+ mice.

Vascular Endothelial Growth Factor Receptor 2-Based DNA Immunization Delays Development of Herpetic Stromal Keratitis by Antiangiogenic Effects

Stromal keratitis (SK) is an immunoinflammatory eye lesion caused by HSV-1 infection. One essential step in the pathogenesis is neovascularization of the normally avascular cornea, a process that involves the vascular endothelial growth factor (VEGF) family of proteins. In this report, we targeted the proliferating vascular endothelial cells expressing VEGFR-2 in the SK cornea by immunization with recombinant Salmonella typhimurium containing a plasmid encoding murine VEGFR-2. This form of DNA immunization resulted in diminished angiogenesis and delayed development of SK caused by HSV-1 infection and also reduced angiogenesis resulting from corneal implantation with rVEGF. CTL responses against endothelial cells expressing VEGFR-2 were evident in the VEGFR-2-immunized group and in vivo CD8+ T cell depletion resulted in the marked reduction of the antiangiogenic immune response. These results indicate a role for CD8+ T cells in the antiangiogenic effects. Our results may also imply that the anti-VEGFR-2 vaccination approach might prove useful to control pathological ocular angiogenesis and its consequences.

Cellular and molecular surrogate markers to monitor targeted and non-targeted antiangiogenic drug activity and determine optimal biologic dose

Perhaps the most significant recent advance in oncology therapeutics has been the approval of various "molecularly targeted" anti-cancer drugs. Currently, there are a large number of similar drugs in early or late stage development, including antiangiogenic agents. Clinical development of such drugs suffers from several handicaps including determining whether a patient's cancer expresses the target and is functionally contributing to cancer growth, monitoring biologic activity, and determining optimal biologic dose. The last problem is related to the low frequency of objective tumor responses (tumor shrinkage) caused by such drugs, or the lack of dose limiting toxicities necessary to define a maximum tolerated dose (MTD), or expression of optimal therapeutic activity at doses below the MTD, when one can be defined. These problems necessitate the development of alternative pharmacodynamic surrogate markers. Here we summarize several such promising markers for monitoring targeted antiangiogenic activity, and establishing optimal therapeutic/biologic dosing. The first is molecular--plasma VEGF--levels of which are rapidly and significantly increased in a dose dependent manner after injection of normal or tumor bearing mice with anti-VEGFR-2 antibodies. The second is a cellular marker, and more generic in nature--circulating VEGF receptor-2 positive cells found in peripheral blood, some of which may be circulating endothelial progenitor cells. Levels of such cells are suppressed in a dose dependent manner which correlate with previously determined optimal biologic/therapeutic anti-tumor activity of various antiangiogenic drugs or treatments. Finally, another promising marker we discuss is soluble VEGFR-2.

Potent neutralization of VEGF biological activities with a fully human antibody Fab fragment directed against VEGF receptor 2

Compelling evidence suggest that vascular endothelial growth factor (VEGF) and its receptors, especially receptor 2 (VEGFR2, or kinase insert domain-containing receptor, KDR), play a critical role in angiogenesis under both physiological and pathological conditions, including cancer and angiogenic retinopathies such as age-related macular degeneration (AMD). To this end, inhibition of angiogenesis with antagonists to either VEGF or KDR has yielded significant therapeutic efficacy both in preclinical studies in animal models and in clinical trials in patients with cancer and AMD. We previously reported the identification of a high affinity, fully human anti-KDR antibody fragment, 1121B Fab, through a highly stringent affinity maturation process with a Fab originally isolated from a naïve human antibody phage display library. In this study, we demonstrate that 1121B Fab is able to strongly block KDR/VEGF interaction, resulting in potent inhibition of an array of biological activities of VEGF, including activation of the receptor and its signaling pathway, intracellular calcium mobilization, and migration and proliferation of endothelial cells. Taken together, our data lend strong support to the further development of 1121B Fab fragment as an anti-angiogenesis agent in both cancer and angiogenic retinopathies.

Targeted anti-vascular endothelial growth factor receptor-2 therapy leads to short-term and long-term impairment of vascular function and increase in tumor hypoxia

Because antiangiogenic therapies inhibit the growth of new tumor-associated blood vessels, as well as prune newly formed vasculature, they would be expected to reduce the supply of oxygen and thus increase tumor hypoxia. However, it is not clear if antiangiogenic treatments lead only to consistent and sustained increases in hypoxia, or transient decreases in tumor hypoxia along with periods of increased hypoxia. We undertook a detailed analysis of an orthotopically transplanted human breast carcinoma (MDA-MB-231) over a 3-week treatment period using DC101, an anti-vascular endothelial growth factor receptor 2 antibody. We observed consistent reductions in microvascular density, blood flow (measured by high-frequency micro-ultrasound), and perfusion. These effects resulted in an increase in the hypoxic tumor fraction, measured with an exogenous marker, pimonidazole, concurrent with an elevation in hypoxia-inducible factor-1alpha expression, an endogenous marker. The increase in tumor hypoxia was evident within 5 days and remained so throughout the entire course of treatment. Vascular perfusion and flow were impaired at days 2, 5, 7, 8, 14, and 21 after the first injection, but not at 4 hours. A modest increase in the vessel maturation index was detected after the 3-week treatment period, but this was not accompanied by an improvement in vascular function. These results suggest that sustained hypoxia and impairment of vascular function can be two consistent consequences of antiangiogenic drug treatment. The implications of the results are discussed, particularly with respect to how they relate to different theories for the counterintuitive chemosensitizing effects of antiangiogenic drugs, even when hypoxia is increased.

Inhibition of VEGFR-3 activation with the antagonistic antibody more potently suppresses lymph node and distant metastases than inactivation of VEGFR-2

Lymph nodes are the first site of metastases for most types of cancer, and lymph node status is a key indicator of patient prognosis. Induction of tumor lymphangiogenesis by vascular endothelial growth factor-C (VEGF-C) has been shown to play an important role in promoting tumor metastases to lymph nodes. Here, we employed receptor-specific antagonist antibodies in an orthotopic spontaneous breast cancer metastasis model to provide direct evidence for the key role of VEGFR-3 activation in metastasis. Inhibition of VEGFR-3 activation more potently suppressed regional and distant metastases than inactivation of VEGFR-2, although VEGFR-2 blockade was more effective in inhibiting angiogenesis and tumor growth. Despite prominent proliferation, metastases were not vascularized in any of the control and treatment groups, indicating that the growth of metastases was not dependent on angiogenesis at the secondary site for the duration of the experiment. Systemic treatment with either VEGFR-2 or VEGFR-3 antagonistic antibodies suppressed tumor lymphangiogenesis, indicating that VEGFR-3 signaling affects the rate of tumor cell entry into lymphatic vessels through both lymphangiogenesis-dependent and independent mechanisms. Combination treatment with the anti-VEGFR-2 and anti-VEGFR-3 antibodies more potently decreased lymph node and lung metastases than each antibody alone. These results validate the concept of targeting the lymphatic dissemination and thereby very early steps of the metastatic process for metastasis control and suggest that a combination therapy with antiangiogenic agents may be a particularly promising approach for controlling metastases.

Rapid vessel regression, protease inhibition, and stromal normalization upon short-term vascular endothelial growth factor receptor 2 inhibition in skin carcinoma heterotransplants

Vascular endothelial growth factor (VEGF) plays a key role in tumor angiogenesis, and blockade of VEGF receptor 2 (VEGFR-2), with the monoclonal antibody DC101, inhibits angiogenesis and tumor growth. To examine the short-term effects of DC101, we surface transplanted the squamous cell carcinoma cell line A5-RT3 onto nude mice. After short-term treatment with DC101, we observed rapid reduction in vascularization and reversion of the tumor phenotype. Beginning 24 hours after treatment, VEGFR-2 inhibition resulted in decreased vessel density within the tenascin-c-staining tumor-associated stroma and reduced endothelial cell proliferation. Stromal expression of matrix metalloproteinase-9 and -13 was drastically reduced 96 hours after VEGFR-2 inhibition as detected by in situ hybridization and in situ zymography. Moreover, the morphology of the tumor-stroma border changed from a highly invasive carcinoma to a well-demarcated, premalignant phenotype. The latter was characterized by the appearance of a regular basement membrane in immunostaining and ultrastructural analyses. These findings suggest that VEGFR-2 inhibition by DC101 evokes very rapid reduction of preformed vessels and decreases both stromal protease expression and gelatinolytic activity, resulting in the modulation of the tumor-stroma border zone and reversion of the tumor phenotype. Thus, short-term inhibition of VEGF signaling results in complex stromal alterations with crucial consequences for the tumor phenotype.

Identification of H-2Db-Specific CD8+ T-Cell Epitopes From Mouse VEGFR2 That Can Inhibit Angiogenesis and Tumor Growth

Vascular endothelial growth factor receptor 2 (VEGFR2/KDR) plays a crucial role in tumor-associated angiogenesis and vascularization. It has been established that monoclonal antibodies against VEGFR2 can inhibit angiogenesis. In this study, two naturally processed CD8 T-cell epitopes (VILTNPISM and FSNSTNDILI) were identified from murine KDR. Cytotoxic T lymphocytes targeting endothelial cells could be directly monitored by KDR2 and KDR3 Elispots or major histocompatibility complex class I tetramer staining. Immunization with these two peptides effectively reduced angiogenesis and inhibited tumor growth in mouse models. Thus, vaccination with KDR peptides alone or in combination with other anti-angiogenesis agents may afford a novel immunotherapy for inhibition of tumor growth.

The kinase insert domain-containing receptor is an angiogenesis-associated antigen recognized by human cytotoxic T lymphocytes

Antigen-specific cancer immunotherapy directed toward tumor-nourishing angiogenic blood vessels holds the promise of high efficacy, low toxicity, and ease of application. To evaluate whether the human angiogenic kinase insert domain-containing receptor (KDR) can serve as a target for cellular immunotherapy, 19 peptide sequences with HLA-A*0201 motifs were selected by computer-based algorithms. Five peptides (KDR82-90, KDR288-297, KDR766-774, KDR1093-1101, KDR1035-1044) stimulated specific cytotoxic T lymphocytes (CTLs) from peripheral-blood mononuclear cells (PBMCs) of 3 HLA-A*0201 donors. The decapeptide KDR288-297 was efficient in sensitizing target cells for recognition by a CTL clone at a concentration of 10 nM. More important, KDR288-297-specific CTLs lysed target cells transfected with HLA-A2/KDR cDNAs and a range of HLA-matched KDR+ angiogenic endothelial cells (aECs) and also recognized CD34+ endothelial progenitor cells. The specificity of CTLs was further confirmed by tetramer assay and cold-target inhibition assay. In addition, ex vivo exposure of aECs to the inflammatory cytokines enhanced CTL reactivity, which is in keeping with up-regulated KDR and HLA class 1 expression. In Matrigel assays, recognition of aECs by specific CTLs triggered an antivascular effect. These findings provide the first proof of the antigenic property of KDR protein and may be useful for devising new immunotherapeutic approaches to human cancers.

T cell–mediated suppression of angiogenesis results in tumor protective immunity

Antiangiogenic intervention is known to inhibit tumor growth and dissemination by attacking the tumor's vascular supply. Here, we report that this was achieved for the first time using an oral DNA minigene vaccine against murine vascular endothelial growth factor receptor 2 (FLK-1), a self-antigen overexpressed on proliferating endothelial cells in the tumor vasculature. Moreover, we identified the first H-2Db–restricted epitope, FLK400 (VILT-NPISM), specifically recognized by cytotoxic T lymphocytes (CTLs). Such CTLs were capable of killing FLK-1+ endothelial cells, resulting in suppression of angiogenesis and long-lived tumor protection. The specificity of this immune response was indicated because the DNA vaccine encoding the entire FLK-1 gene also induced a FLK400-specific CTL response. This minigene vaccine strategy provides a more flexible alternative to whole-gene vaccination and facilitates in-depth mechanism studies to tailor DNA vaccines for optimal T-cell activation and tumor protection.

Increased CD133 expression in bone marrow of myelodysplastic syndromes

Fresh frozen bone marrow biopsies were evaluated immunohistochemically, applying monoclonal antibodies against CD31, CD34, VEGFR-2 and CD133, a novel marker identifying human endothelial progenitor cells (EPCs). Specimens of 51 patients diagnosed with MDS were compared with 16 AML and 18 controls. The percentage of CD34 expressing cells was increased and CD31 expression was decreased in advanced stages of MDS compared with normal BM. VEGFR-2 expression was also raised in MDS. Here we show for the first time that increased numbers of CD133 positive cells are present in the majority of MDS patients. Additionally, those cells occasionally seem to contribute to capillary forming units in bone marrow.

Novel highly efficient intrabody mediates complete inhibition of cell surface expression of the human vascular endothelial growth factor receptor-2 (VEGFR-2/KDR)

The human vascular endothelial growth factor receptor-2 (VEGFR-2/KDR) and its ligand vascular endothelial growth factor (VEGF) play an essential role in tumor angiogenesis and in haematological malignancies. To inhibit VEGF induced signalling, intrabodies derived from two scFv fragments recognizing the VEGF receptor were generated. When these intrabodies were expressed in endothelial cells, they blocked the transport of KDR to the cell surface. We developed a cell culture model using porcine aortic endothelial cells overexpressing KDR for testing the efficiency of anti-KDR intrabodies. The two intrabodies were targeted to the ER and colocalized with the KDR receptor in an intracellular compartment. No degradation of the receptor was observed. An immature incomplete glycosylated protein of 195 kDa was detected, suggesting that the intrabodies affect the maturation of the receptor. Despite the presence of significant amounts of receptor protein, the inactivation by one of the two intrabodies was highly effective, resulting in complete functional inhibition of KDR and inhibition of in vitro angiogenesis. The new intrabody appears to be a powerful tool with which to inhibit KDR function.

Anti-angiogenic effects and regression of localized murine AML produced by anti-VEGF and anti-Flk-1 antibodies

Reducing the blood supply of tumors is one modality to combat cancer. The objective of this study was to evaluate such an approach in the treatment of localized murine AML (acute myelogenous leukemia). For this purpose we designed an experimental model in which leukemic cells were embedded in 1% agar discs before subcutaneous implantation in C57Bl female mice. The C-1498 AML cell line (Frederick Inst., NCI, MD, USA) was used. Thirty experimental mice received on alternate days injections of 5 x 2.5 microg anti-VEGF (vascular endothelial growth factor) and 5 x 2.5 microg anti-Flk-1 (VEGFR2) antibodies to the site of cell implantation over a period of 10 d. Fifteen control mice received daily PBS injections. All mice were sacrificed 16 d after AML implantation. Of the 30 experimental animals, macroscopic examination showed in 21 animals (70%) small sized, pale tumors (0.5 g); in six mice (20%) the tumors were replaced completely by necrotic tissue, while in three mice (10%), there were large (2.5 g), highly vascularized tumors. In all 15 control mice large highly vascularized tumors were seen. A separate group of mice was studied for total survival following AML implantation. While 12 mice in the control group not treated with antibodies survived for 16 d post-implantation, survival was prolonged in 15 antibody treated mice by approximate 30 d to a total survival time of 48 d. Tumor specimens were processed for histology, immunohistochemistry (IHC) for CD31 endothelial cell antigen, and tube-like formation assay. The small, pale tumors of antibody treated animals consisted of degenerate hyaline material with remnant nests of leukemic cells, whereas large tumors showed sheets of leukemic cells and numerous blood vessels. Specimens processed for CD31 antigen showed scarce or absence of blood vessels in the small, pale tumors in contrast to intensive staining from a rich network of blood vessels in the large, highly vascularized tumors. Tube-like formation assays disclosed rudimentary Grade 1 endothelial cell tubes in the small, pale tumors as opposed to polygonal Grade 4 tube formation in control animals. In conclusion, this murine model of localized AML allows assessment of anti-angiogenic tumor regression. Anti-angiogenic antibodies against VEGF and Flk-1 have therapeutic effects in murine AML.

Angiogenesis and radiation response modulation after vascular endothelial growth factor receptor-2 (VEGFR2) blockade

The formation of new blood vessels (angiogenesis) represents a critical factor in the malignant growth of solid tumors and metastases. Vascular endothelial cell growth factor (VEGF) and its receptor VEGFR2 represent central molecular targets for antiangiogenic intervention, because of their integral involvement in endothelial cell proliferation and migration. In the current study, we investigated in vitro and in vivo effects of receptor blockade on various aspects of the angiogenic process using monoclonal antibodies against VEGFR2 (cp1C11, which is human specific, and DC101, which is mouse specific). Molecular blockade of VEGFR2 inhibited several critical steps involved in angiogenesis. VEGFR2 blockade in endothelial cells attenuated cellular proliferation, reduced cellular migration, and disrupted cellular differentiation and resultant formation of capillary-like networks. Further, VEGFR2 blockade significantly reduced the growth response of human squamous cell carcinoma xenografts in athymic mice. The growth-inhibitory effect of VEGFR2 blockade in tumor xenografts seems to reflect antiangiogenic influence as demonstrated by vascular growth inhibition in an in vivo angiogenesis assay incorporating tumor-bearing Matrigel plugs. Further, administration of VEGFR2-blocking antibodies in endothelial cell cultures, and in mouse xenograft models, increased their response to ionizing radiation, indicating an interactive cytotoxic effect of VEGFR2 blockade with radiation. These data suggest that molecular inhibition of VEGFR2 alone, and in combination with radiation, can enhance tumor response through molecular targeting of tumor vasculature.

Rationale for antiangiogenic cancer therapy with vaccination using epitope peptides derived from human vascular endothelial growth factor receptor 2

Angiogenesis is a critical mechanism for tumor progression. Multiple studies have suggested that tumor growth can be suppressed if tumor angiogenesis can be inhibited using various types of antiangiogenic agents. Recent studies in mouse systems have shown that tumor angiogenesis can also be inhibited if cellular immune response could be induced against vascular endothelial growth factor receptor 2 (VEGFR2), which is one of the key factors in tumor angiogenesis. In this study, we examined the possibility of developing this novel immunotherapy in clinical setting. We first identified the epitope peptides of VEGFR2 and showed that stimulation using these peptides induces CTLs with potent cytotoxicity in the HLA class I-restricted fashion against not only peptide-pulsed target cells but also endothelial cells endogenously expressing VEGFR2. In A2/Kb transgenic mice that express alpha1 and alpha2 domains of human HLA-A*0201, vaccination using these epitope peptides in vivo was associated with significant suppression of the tumor growth and prolongation of the animal survival without fatal adverse effects. In antiangiogenesis assay, tumor-induced angiogenesis was significantly suppressed with the vaccination using these epitope peptides. Furthermore, CTLs specific to the epitope peptides were successfully induced in cancer patients, and the specificities of the CTLs were confirmed using functional and HLA-tetramer analysis. These results in vitro and in vivo strongly suggest that the epitope peptides derived from VEGFR2 could be used as the agents for antiangiogenic immunotherapy against cancer in clinical settings.

Inhibition of glioblastoma angiogenesis and invasion by combined treatments directed against vascular endothelial growth factor receptor-2, epidermal growth factor receptor, and vascular endothelial-cadherin

PURPOSE

Inhibition of angiogenesis can influence tumor cell invasion and metastasis. We previously showed that blockade of vascular endothelial growth factor receptor-2 (VEGFR-2) with the monoclonal antibody DC101 inhibited intracerebral glioblastoma growth but caused increased tumor cell invasion along the preexistent vasculature. In the present study, we attempted to inhibit glioma cell invasion using a monoclonal antibody against the epidermal growth factor receptor (EGFR), which in the context of human glioblastomas, has been implicated in tumor cell invasion. In addition, we analyzed whether blockade of vascular endothelial (VE)-cadherin as a different antiangiogenic target could also inhibit glioblastoma angiogenesis and growth.

EXPERIMENTAL DESIGNS

Nude mice who received intracerebral glioblastoma xenografts were treated using monoclonal antibodies against VEGFR-2 (DC101), EGFR (C225), and VE-cadherin (E4G10) either alone or in different combinations.

RESULTS

Increased tumor cell invasion provoked by DC101 monotherapy was inhibited by 50% to 66% by combined treatment with C225 and DC101. C225 inhibited glioblastoma cell migration in vitro, but had no effect on the volume of the main tumor mass or on tumor cell proliferation or apoptosis in vivo, either alone or in combination with DC101. The anti-VE-cadherin monoclonal antibody E4G10 was a weaker inhibitor of tumor angiogenesis and growth than DC101, and also caused a weaker increase in tumor cell invasion.

CONCLUSIONS

Inhibition of angiogenesis achieved by blocking either VEGFR-2 or VE-cadherin can cause increased glioma cell invasion in an orthotopic model. Increased tumor cell invasion induced by potent inhibition of angiogenesis with DC101 could be inhibited by simultaneous blockade of EGFR.

A recombinant, fully human, bispecific antibody neutralizes the biological activities mediated by both vascular endothelial growth factor receptors 2 and 3

Vascular endothelial growth factors (VEGF) and their receptors (VEGFR) have been implicated to play important roles in tumor-associated angiogenesis and lymphangiogenesis, and hence in tumor growth and metastasis. We previously produced a number of fully human antibodies directed against VEGF receptor 2 (VEGFR2) and VEGF receptor 3 (VEGFR3) and showed that these antibodies are capable of inhibiting growth factor (VEGF and VEGF-C)-induced receptor activation, migration, and proliferation of human endothelial cells. In this report, we constructed and produced a bispecific antibody, a diabody, using the variable domain genes of two neutralizing antibodies, IMC-1121 to VEGFR2 and hF4-3C5 to VEGFR3. The diabody binds to both VEGFR2 and VEGFR3 in a dose-dependent manner, and blocks interaction between VEGF/VEGFR2, VEGF-C/VEGFR2, and VEGF-C/VEGFR3. In cell-based assays, the diabody neutralized both VEGF and VEGF-C-stimulated activation of VEGFR2, VEGFR3, and p44/p42 mitogen-activated protein kinase in endothelial cells. Furthermore, the diabody was able to inhibit both VEGF and VEGF-C-induced migration of endothelial cells. Taken together, our results suggest that a dual blockade of both VEGFR2 and VEGFR3 simultaneously may represent a more potent approach to effective cancer therapy.

[Specific anti-glioma angiogenesis immune response induced by attenuated Salmonella typhimurium vaccine expressing vascular endothelial growth factor receptor-2]

BACKGROUND & OBJECTIVE

Vascular endothelial growth factor (VEGF) and its receptor (VEGFR-2) play important roles in tumor angiogenesis. This study was to investigate anti-vasculature and anti-glioma effects of attenuated Salmonella typhimurium vaccine expressing VEGFR2 gene.

METHODS

Plasmid pcDNA3.1-VEGFR2 was constructed, and electrotransfected into attenuated Salmonella typhimurium strain SL7207. C57BL/6J mice were immunized with gastrogavage of cDNA vaccine encoding VEGFR2 (vaccine group). C57BL/6J mice received gastrogavage of pcDNA3.1 or NaHCO3 were used as controls. Serum level of specific anti-VEGFR2-IgG antibody was detected by ELISA. Cytotoxic T lymphocytes (CTLs) activity was measured by MTT assay. Mouse models of intracranial Gl261 glioblastoma were treated with gastrogavage of attenuated Salmonella typhimurium expressing VEGFR2 gene. Tumor diameter was measuredu microvessel density (MVD) was detected by immunohistochemistryu tumor cell apoptosis was detected by TUNEL.

RESULTS

All mice immunized with the vaccine developed high levels of anti-VEGFR2-IgG antibody, and showed strong CTLs activities against VEGFR2. The vaccine substantially inhibited glioblastoma growth. MVD was significantly lower in vaccine group than in pcDNA3.1 group, and NaHCO3 group (8.8+/-1.9 vs. 27.2+/-4.5, and 26.5+/-5.8, P < 0.01)u while apoptotic cell count per visual field was significantly higher in vaccine group than in the rest 2 groups (23.4+/-4.7 vs. 3.1+/-1.0, and 4.4+/-1.2, P < 0.01).

CONCLUSION

Attenuated Salmonella typhimurium vaccine expressing VEGFR2 gene can break immunologic tolerance against self-VEGFR2 antigen, and specifically kill glioblastoma vascular endothelial cells by inducing specific anti-VEGFR2 immunoreaction.

Combined therapy with flk1-based DNA vaccine and interleukin-12 results in enhanced antiangiogenic and antitumor effects

In this study, we investigated the anti-vasculature effects and the antitumor effects of combining attenuated Salmonella typhimurium vaccine strain encoding murine vascular endothelial growth factor (VEGF) receptor-2 (flk1) with plasmid DNA vector encoding the murine interleukin-12 (mIL-12) gene. In combination, flk1 based DNA vaccine and mIL-12 slowed down tumor growth more effectively than either one alone. Splenocytes from the combined group were showed a strong CTL response against both the flk1 and tumor cells. Automated image analysis revealed that the mean microvessel density was significantly reduced after administering either flk1 based DNA vaccine or mIL-12. In addition, the combination of flk1 based DNA vaccine and mIL-12 appeared more effective at reducing the microvessel density of tumor (P<0.01, both comparisons). In summary, the antivasculature effect and the anti-tumor effect were better when the combination of flk1 based DNA vaccine and IL-12 was administered in comparison to the individual treatment groups, suggesting the synergistic action of flk1 based DNA vaccine and mIL-12.

[Antitumor effects of recombinant quail vascular endothelial growth factor receptor 2, as a vaccine, combined with cisplatin on LL/2 tumor model in mice]

BACKGROUND & OBJECTIVE

Bio-chemotherapy is a new trend in cancer therapy. Antiangiogenic therapy represents a new strategy of tumor biotherapy. This study was designed to explore antitumor effect of recombinant quail vascular endothelial growth factor receptor 2 (qVEGFR) combined with cisplatin.

METHODS

Lewis lung carcinoma model (LL/2) was established in C57BL/6 mice. Seven days after inoculation of tumor cells, mice were randomized into combination group, qVEGFR group, chemotherapy group, and normal saline (NS) group (10 mice/group), and received relevant treatments. Tumor growth, survival rate of mice, and side effects were observed. Anti-VEGFR-2 antibody-producing B cells (APBCs) was detected by enzyme-linked immunospot (ELISPOT), microvessel density (MVD) of tumor was detected by immunohistochemistry, and tumor cell apoptosis was also detected.

RESULTS

Tumor volume of mice was obviously smaller in combination group than in NS group. Complete regression of tumor growth was observed in 3 of the 10 mice in combination group. Seventy days after inoculation of tumor cells, survival rate of mice was significantly higher in combination group than in qVEGFR, cisplatin, and NS groups (90% vs. 60%, 0%, and 0%, P < 0.05). APBCs counts were (156.8+/-19.3)/10(6) spleen cells in combination group, and (143.6+/-18.6)/10(6) spleen cells in qVEGFR group. MVD was significantly lower in combination group than in cisplatin, and NS groups (11.4+/-1.3 vs. 33.4+/-4.5, and 45.5 +/- 4.5, P < 0.01), MVD in qVEGFR group was 16.4+/-1.6. Tumor cell apoptosis was significantly higher in combination group than in qVEGFR, cisplatin, and NS groups [(36.2+/-3.5)% vs. (15.4+/-2.4)%, (17.6+/-2.6)%, and (4.1+/-1.4)%, P < 0.05].

CONCLUSION

The combination therapy of qVEGFR and cisplatin has synergistic antitumor effect.

[Effect of monoclonal antibody against extracellular domain III of vascular endothelial growth factor receptor KDR on proliferation of vascular endothelial cells]

OBJECTIVE

To prepare a neutralizing monoclonal antibody (McAb) against vascular endothelial growth factor receptor KDR and study its biological activity.

METHODS

Extracellular immunoglobulin (Ig)-like domain III of KDR (KDR III) was expressed in E. coli and purified by affinity chromatograph. Monoclonal antibody against KDR III was prepared by hybridoma technique. ELISA and FACS analysis were used to identify its specificity. Immunoprecipitation and [(3)H]-TdR incorporation assay were also used to detect the activity of anti-KDR McAb blocking the phosphorylation of KDR tyrosine kinase receptor and the influence on VEGF-induced mitogenesis of human endothelial cells.

RESULTS

McAb Ycom1D3 against KDR III was prepared which bound specifically to both the soluble KDR III and the cell-surface expressed KDR. It effectively blocked VEGF/KDR interaction and inhibited VEGF-stimulated activation of KDR expression on human endothelial cells. Furthermore, Ycom1D3 efficiently neutralized VEGF-induced mitogenesis of human umbilical vascular endothelial cells.

CONCLUSION

McAb Ycom1D3 against KDR III may suppress the action of VEGF by blocking native vascular endothelial growth factor receptor KDR. It has potential clinical applications in the treatment of cancers and other diseases where pathological angiogenesis is involved.

Antibody phage display technologies with special reference to angiogenesis

The presence of blood vessels is a prerequisite for normal development, tissue growth, and tissue repair. However, its abnormal occurrence or absence can also potentiate disease processes. Angiogenic therapies have been used to stimulate blood vessel growth in ischemic conditions such as severe end-stage peripheral vascular disease, ischemic heart disease and stroke and for inhibition of angiogenesis in tumors. The targeting and identification of novel endothelial cell (EC) markers that can ultimately be used in angiogenic strategies is an expanding field but is limited by the availability of reagents. For instance repeated injection of mouse monoclonal antibodies (Mabs) against angiogenic EC, can result in the production of autoantibodies. Therefore, these mouse Mabs cannot be used for therapeutic purposes. Phage display technology was employed in this context to select antibodies, proteins, and peptides against known or novel EC antigens. Furthermore, technologies have been developed that enable the specific targeting of epitopes on cells including the endothelium with high-affinity/avidity antibodies. The focus for these antibody targeting strategies are markers that are unique or up-regulated on angiogenic EC including the vascular endothelial growth factor receptor (VEGFR) KDR, endoglin (CD105), and the extracellular domain B (ED-B) domain of fibronectin (FN). These markers are reviewed herein.

Enhanced antimetastatic effect of fetal liver kinase 1 extracellular domain and interferon-gamma fusion gene-modified dendritic cell vaccination

Antiangiogenic immunotherapy benefits from targeting antigens expressed on genetically stable endothelial cells and represents a novel modality for cancer treatment. Vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2, also known as flk1 in mouse) mediated VEGF signaling is the key rate-limiting step in angiogenesis. Blockade of the flk1 signaling pathway can significantly inhibit tumor cell-induced angiogenesis and lead to inhibition of tumor metastasis. Interferon-gamma (IFN-gamma) is a pleiotropic cytokine, which plays an important role in cell-mediated immunity. In this study, we tested the hypothesis that immunization of mice with soluble flk1 (sflk1) and IFN-gamma fusion gene-transfected dendritic cells (DC-sflk1-IFN-gamma) would induce a potent CTL response to flk1, leading to an inhibition of tumor-induced angiogenesis and metastasis. Our data show that immunization of mice with sflk1 gene-modified DC (DC-sflk1) could induce a CTL response to flk1, leading to profound inhibition of tumor-cell-induced angiogenesis and metastasis. However, more striking antimetastatic effects were achieved through induction of enhanced CTL response to flk1 and augmented inhibition of angiogenesis when mice were immunized with DC-sflk1-IFN-gamma. In vivo T-cell subset depletion experiments showed that CD8(+) T cells were mainly responsible for this antimetastatic effect. Our data extend the notion that DC-based active antiangiogenic immunotherapy is an effective modality for cancer treatment, and show that the antitumor efficacy of this strategy can be improved by combination with DC-based cytokine immunotherapy.

Angiogenesis Inhibition by Vascular Endothelial Growth Factor Receptor-2 Blockade Reduces Stromal Matrix Metalloproteinase Expression, Normalizes Stromal Tissue, and Reverts Epithelial Tumor Phenotype in Surface Heterotransplants

Inhibition of vascular endothelial growth factor (VEGF) signaling, a key regulator of tumor angiogenesis, through blockade of VEGF receptor (VEGFR)-2 by the monoclonal antibody DC101 inhibits angiogenesis, tumor growth, and invasion. In a surface xenotransplant assay on nude mice using a high-grade malignant squamous cell carcinoma cell line (A-5RT3), we show that DC101 causes vessel regression and normalization as well as stromal maturation resulting in a reversion to a noninvasive tumor phenotype. Vessel regression is followed by down-regulation of expression of both VEGFR-2 and VEGFR-1 on endothelial cells and increased association of α-smooth muscle actin–positive cells with small vessels indicating their normalization, which was further supported by a regular ultrastructure. The phenotypic regression of an invasive carcinoma to a well-demarcated dysplastic squamous epithelium is accentuated by the establishment of a clearly structured epithelial basement membrane and the accumulation of collagen bundles in the stabilized connective tissue. This normalization of the tumor-stroma border coincided with down-regulated expression of the stromal matrix metalloproteinases 9 and 13, which supposedly resulted in attenuated turnover of extracellular matrix components permitting their structural organization. Thus, in this mouse model of a human squamous cell carcinoma cell line, blockade of VEGF signaling resulted in the reversion of the epithelial tumor phenotype through stromal normalization, further substantiating the crucial role of stromal microenvironment in regulating the tumor phenotype.