Drug delivery strategies in maximizing anti-angiogenesis and anti-tumor immunity

Metronomic chemotherapy has been shown to elicit anti-tumor immune response and block tumor angiogenesis distinct from that observed with maximal tolerated dose (MTD) therapy. This review delves into the mechanisms behind anti-tumor immunity and seeks to identify the differential effect of dosing regimens, including daily low-dose and medium-dose intermittent chemotherapy (MEDIC), on both innate and adaptive immune populations involved in observed anti-tumor immune response. Given reports of VEGF/VEGFR blockade antagonizing anti-tumor immunity, drug choice, dose, and selective delivery determined by advanced formulations/vehicles are highlighted as potential sources of innovation for identifying anti-angiogenic modalities that may be combined with metronomic regimens without interrupting key immune players in the anti-tumor response. Engineered drug delivery mechanisms that exhibit extended and local release of anti-angiogenic agents both alone and in combination with chemotherapeutic treatments have also been demonstrated to elicit a potent and potentially systemic anti-tumor immune response, favoring tumor regression and stasis over progression. This review examines this interplay between various cancer models, the host immune response, and select anti-cancer agents depending on drug dosing, scheduling/regimen, and delivery modality.

Are antiangiogenics a good 'partner' for immunotherapy in ovarian cancer?

Ovarian cancer (OC) is associated with poor survival because there are a limited number of effective therapies. Two processes key to OC progression, angiogenesis and immune evasion, act synergistically to promote tumor progression. Tumor-associated angiogenesis promotes immune evasion, and tumor-related immune responses in the peritoneal cavity and tumor microenvironment (TME) affect neovascular formation. Therefore, suppressing the angiogenic pathways could facilitate the arrival of immune effector cells and reduce the presence of myeloid cells involved in immune suppression. To date, clinical studies have shown significant benefits with antiangiogenic therapy as first-line therapy in OC, as well as in recurrent disease, and the vascular endothelial growth factor (VEGF) inhibitor bevacizumab is now an established therapy. Clinical data with immunomodulators in OC are more limited, but suggest that they could benefit some patients with recurrent disease. The preliminary results of two phase III trials have shown that the addition of immunomodulators to chemotherapy does not improve progression-free survival. For this reason, it could be interesting to look for synergistic effects between immunomodulators and other active drugs in OC. Since bevacizumab is approved for use in OC, and is tolerable when used in combination with immunotherapy in other indications, a number of clinical studies are underway to investigate the use of bevacizumab in combination with immunotherapeutic agents in OC. This strategy seeks to normalize the TME via the anti-VEGF actions of bevacizumab, while simultaneously stimulating the immune response via the immunotherapy. Results of these studies are awaited with interest.

The Binding of CD93 to Multimerin-2 Promotes Choroidal Neovascularization

Purpose

The purpose of this study was to investigate the involvement of CD93 and Multimerin-2 in three choroidal neovascularization (CNV) models and to evaluate their contribution in the neovascular progression of age-related macular degeneration (AMD).

Methods

Choroidal neovascular membranes collected during surgery from AMD patients were analyzed by microscopy methods. Laser-induced CNV mouse models and choroid sprouting assays (CSAs) were carried out using the CD93 knockout mouse model. An original ex vivo CSA of vascular angiogenesis, employing choroid tissues isolated from human donors, was developed.

Results

In contrast to healthy choroid endothelium, hyperproliferative choroidal endothelial cells (ECs) of AMD patients expressed high levels of CD93, and Multimerin-2 was abundantly deposited along the choroidal neovasculature. CD93 knockout mice showed a significant reduced neovascularization after laser photocoagulation, and their choroidal ECs displayed a decreased ability to produce sprouts in ex vivo angiogenesis assays. Moreover, the presence of an antibody able to hamper the CD93/Multimerin-2 interaction reduced vascular sprouting in the human CSA.

Conclusions

Our results demonstrate that CD93 and its interaction with Multimerin-2 play an important role in pathological vascularization of the choroid, disclosing new possibilities for therapeutic intervention to neovascular AMD.

Meta-analysis of individual patient safety data from six randomized, placebo-controlled trials with the antiangiogenic VEGFR2-binding monoclonal antibody ramucirumab

BACKGROUND

Ramucirumab, the human immunoglobulin G1 monoclonal antibody receptor antagonist of vascular endothelial growth factor receptor 2, has been approved for treating gastric/gastroesophageal junction, non-small-cell lung, and metastatic colorectal cancers. With the completion of six global, randomized, double-blind, placebo-controlled, phase III trials across multiple tumor types, an opportunity now exists to further establish the safety parameters of ramucirumab across a large patient population.

MATERIALS AND METHODS

An individual patient meta-analysis across the six completed phase III trials was conducted and the relative risk (RR) and associated 95% confidence intervals (CIs) were derived using fixed-effects or mixed-effects models for all-grade and high-grade adverse events (AEs) possibly related to vascular endothelial growth factor pathway inhibition. The number needed to harm was also calculable due to the placebo-controlled nature of all six registration standard trials.

RESULTS

A total of 4996 treated patients (N = 2748 in the ramucirumab arm and N = 2248 in the control, placebo arm) were included in this meta-analysis. Arterial thromboembolic events [ATE; all-grade, RR: 0.8, 95% CI 0.5-1.3; high-grade (grade ≥3), RR: 0.9, 95% CI 0.5-1.7], venous thromboembolic events (VTE; all-grade, RR: 0.7, 95% CI 0.5-1.1; high-grade, RR: 0.7, 95% CI 0.4-1.2), high-grade bleeding (RR: 1.1, 95% CI 0.8-1.5), and high-grade gastrointestinal (GI) bleeding (RR: 1.1, 95% CI 0.7-1.7) did not demonstrate a definite increased risk with ramucirumab. A higher percentage of hypertension, proteinuria, low-grade (grade 1-2) bleeding, GI perforation, infusion-related reaction, and wound-healing complications were observed in the ramucirumab arm compared with the control arm.

CONCLUSIONS

Ramucirumab may be distinct among antiangiogenic agents in terms of ATE, VTE, high-grade bleeding, or high-grade GI bleeding by showing no clear evidence for an increased risk of these AEs in this meta-analysis of a large and diverse patient population. Ramucirumab is consistent with other angiogenic inhibitors in the risk of developing certain AEs. Clinical Trial Numbers: NCT00917384 (REGARD), NCT01170663 (RAINBOW), NCT01168973 (REVEL), NCT01183780 (RAISE), NCT01140347 (REACH), and NCT00703326 (ROSE).

Acute tumour response to a bispecific Ang-2-VEGF-A antibody: insights from multiparametric MRI and gene expression profiling

BACKGROUND

To assess antivascular effects, and evaluate clinically translatable magnetic resonance imaging (MRI) biomarkers of tumour response in vivo, following treatment with vanucizumab, a bispecific human antibody against angiopoietin-2 (Ang-2) and vascular endothelial growth factor-A (VEGF-A).

METHODS

Colo205 colon cancer xenografts were imaged before and 5 days after treatment with a single 10 mg kg(-1) dose of either vanucizumab, bevacizumab (anti-human VEGF-A), LC06 (anti-murine/human Ang-2) or omalizumab (anti-human IgE control). Volumetric response was assessed using T2-weighted MRI, and diffusion-weighted, dynamic contrast-enhanced (DCE) and susceptibility contrast MRI used to quantify tumour water diffusivity (apparent diffusion coefficient (ADC), × 10(6) mm(2) s(-1)), vascular perfusion/permeability (K(trans), min(-1)) and fractional blood volume (fBV, %) respectively. Pathological correlates were sought, and preliminary gene expression profiling performed.

RESULTS

Treatment with vanucizumab, bevacizumab or LC06 induced a significant (P<0.01) cytolentic response compared with control. There was no significant change in tumour ADC in any treatment group. Uptake of Gd-DTPA was restricted to the tumour periphery in all post-treatment groups. A significant reduction in tumour K(trans) (P<0.05) and fBV (P<0.01) was determined 5 days after treatment with vanucizumab only. This was associated with a significant (P<0.05) reduction in Hoechst 33342 uptake compared with control. Gene expression profiling identified 20 human genes exclusively regulated by vanucizumab, 6 of which are known to be involved in vasculogenesis and angiogenesis.

CONCLUSIONS

Vanucizumab is a promising antitumour and antiangiogenic treatment, whose antivascular activity can be monitored using DCE and susceptibility contrast MRI. Differential gene expression in vanucizumab-treated tumours is regulated by the combined effect of Ang-2 and VEGF-A inhibition.

The role of the prolactin/vasoinhibin axis in rheumatoid arthritis: an integrative overview

Rheumatoid arthritis (RA) is a chronic, autoimmune, inflammatory disease destroying articular cartilage and bone. The female preponderance and the influence of reproductive states in RA have long linked this disease to sexually dimorphic, reproductive hormones such as prolactin (PRL). PRL has immune-enhancing properties and increases in the circulation of some patients with RA. However, PRL also suppresses the immune system, stimulates the formation and survival of joint tissues, acquires antiangiogenic properties upon its cleavage to vasoinhibins, and protects against joint destruction and inflammation in the adjuvant-induced model of RA. This review addresses risk factors for RA linked to PRL, the effects of PRL and vasoinhibins on joint tissues, blood vessels, and immune cells, and the clinical and experimental data associating PRL with RA. This information provides important insights into the pathophysiology of RA and highlights protective actions of the PRL/vasoinhibin axis that could lead to therapeutic benefits.

Potent inhibition of angiogenesis by the IGF-1 receptor-targeting antibody SCH717454 is reversed by IGF-2

Previously, we reported that a predominant action of a type-1 insulin-like growth factor receptor (IGF-1R)-targeted antibody was through inhibiting tumor-derived VEGF, and indirectly, angiogenesis. Here, we examined the direct antiangiogenic activity of the IGF-1R-targeted antibody SCH717454 that inhibits ligand-receptor binding and the mechanism by which tumors circumvent its antiangiogenic activity. Inhibition of ligand-stimulated activation of IGF-1R, insulin receptor (IN-R), or downstream signaling [phosphorylation of Akt (Ser473)] was determined by receptor-specific immunoprecipitation and immunoblotting. Inhibition of angiogenesis was determined by proliferation and tube formation using human umbilical vein endothelial cells (HUVEC) in vitro and in Matrigel plugs implanted in mice. SCH717454 blocked IGF-1-stimulated but not IGF-2-stimulated phosphorylation of Akt in sarcoma cells. Immunoprecipitation using anti-IGF-1R and anti-IN-R antibodies revealed that SCH717454 equally blocked IGF-1-stimulated and IGF-2-stimulated IGF-1R phosphorylation, but not IGF-2-stimulated phosphorylation of IN-R. SCH717454 completely blocked VEGF-stimulated proliferation and tube formation of HUVECs, but exogenous IGF-2 and insulin circumvented these inhibitory effects. Coculture of HUVECs with IGF-2-secreting tumor cells completely abrogated SCH717454 inhibition of VEGF-stimulated HUVEC tube formation. In mice, SCH717454 inhibited angiogenesis in VEGF-infused Matrigel plugs, but had no inhibitory activity when plugs contained both VEGF + IGF-2. These results reveal for the first time, a role for IGF-1R signaling in VEGF-mediated angiogenesis in vitro and indicate direct antiangiogenic activity of SCH717454. Both in vitro and in vivo IGF-2 circumvented these effects through IN-R signaling. Many childhood cancers secrete IGF-2, suggesting that tumor-derived IGF-2 in the microenvironment maintains angiogenesis in the presence of IGF-1R-targeted antibodies allowing tumor progression.

Anti-vascular endothelial growth factor antibody bevacizumab reduced the risk of anemia associated with chemotherapy-A meta-analysis

INTRODUCTION

Vascular endothelial growth factor (VEGF) may play a role in erythropoiesis. We performed a meta-analysis of randomized controlled trials (RCT) to determine the effect of the anti-VEGF antibody bevacizumab on anemia in cancer patients treated with chemotherapy.

METHODS

Databases from PUBMED, the Web of Science, Embase, the Cochrane Library, and abstracts presented at the American Society of Clinical Oncology (ASCO) conferences until May 2010 were searched to identify relevant studies. Eligible studies included prospective RCTs in which the combination of bevacizumab and chemotherapy was compared with chemotherapy alone. Summary incidence rate, relative risk (RR), and 95% confidence interval (CI) were calculated.

RESULTS

A total of 6439 patients with a variety of solid tumors were included for analysis from 11 RCTs. Among those patients receiving bevacizumab and chemotherapy, the incidences of all-grade and high-grade (grade 3 and above) anemia were 17.8% (95% CI: 11.1-27.1%) and 2.8% (95% CI: 1.6-5.0%) respectively. In comparison with chemotherapy alone, bevacizumab significantly reduced all-grade (RR, 0.79; 95% CI: 0.66-1.0, p = 0.007) and high-grade anemia (RR, 0.72; 95% CI: 0.57-0.90, p = 0.005). The effect did not vary significantly among bevacizumab doses (p = 0.88), tumor types (p = 0.75) or chemotherapy regimens (p = 0.98).

DISCUSSION

Bevacizumab may significantly reduce the risk of anemia with chemotherapy in cancer patients.

CXCL10/IP-10 in infectious diseases pathogenesis and potential therapeutic implications

C-X-C motif chemokine 10 (CXCL10) also known as interferon γ-induced protein 10 kDa (IP-10) or small-inducible cytokine B10 is a cytokine belonging to the CXC chemokine family. CXCL10 binds CXCR3 receptor to induce chemotaxis, apoptosis, cell growth and angiostasis. Alterations in CXCL10 expression levels have been associated with inflammatory diseases including infectious diseases, immune dysfunction and tumor development. CXCL10 is also recognized as a biomarker that predicts severity of various diseases. A review of the emerging role of CXCL10 in pathogenesis of infectious diseases revealed diverse roles of CXCL10 in disease initiation and progression. The potential utilization of CXCL10 as a therapeutic target for infectious diseases is discussed.

Dendritic cells transduced with TEM8 recombinant adenovirus prevents hepatocellular carcinoma angiogenesis and inhibits cells growth

Recent evidence suggested that angiogenesis played a pivotal role in the development of hepatocellular carcinoma cells (HCC), thus the therapy strategy targeting antiangiogenesis has been regarded as promising method for HCC therapy. Tumor endothelial marker 8 (TEM8) is a recently described protein that is preferentially expressed within tumor endothelium. However, the antiangiogenesis therapy of HCC based on TEM8 has not been reported. In this study, the recombinant adenovirus encoding TEM8 was constructed, and the DCs were transduced with the Ad-TEM8. In addition, the modified DCs were transferred into the BALB/c mice to determine whether DCs transduced with TEM8 could elicit a potent antitumor immunogenic response in vivo. The results demonstrated that DCs transduced with Ad-TEM8 induced specific CTLs effectively, which could secrete IFN-γ and lyse HCC. Furthermore, the modified DCs could effectively protect BALB/c mice from lethal challenges against HCC, reduce tumor growth and increase the mice life span by decreasing tumor vasculature density. These data suggest that the Ad-TEM8 modified DCs may induce antitumor immunity by disrupting tumor vasculature and may thus be used as an efficient therapy strategy to influence tumor development in clinical applications.

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.

A phase I pharmacological and biological study of PI-88 and docetaxel in patients with advanced malignancies

PURPOSE

This study evaluated the safety, toxicity, pharmacological properties and biological activity of PI-88, a heparanase endoglycosidase enzyme inhibitor, with fixed weekly docetaxel in patients with advanced solid malignancies.

EXPERIMENTAL DESIGN

This was a phase I study to determine the maximal-tolerated dose of escalating doses of PI-88 administered subcutaneously for 4 days per week, along with docetaxel 30 mg/m(2) given on days 1, 8, 15 of a 28-day schedule.

RESULTS

Sixteen patients received a total of 42 courses of therapy. No dose-limiting toxicities were observed despite escalation to the highest planned dose level of PI-88 (250 mg/day). Frequent minor toxicities included fatigue (38%), dysgeusia (28.5%), thrombocytopenia (12%), diarrhea (14%), nausea (12%), and emesis (10%) in the 42 courses. No significant bleeding complications were observed. One patient developed a positive anti-heparin antibody test/serotonin releasing assay with positive anti-platelet factor 4/PI-88 antibodies and grade 1 thrombocytopenia in cycle 5, and was withdrawn from the study without any sequelae. PI-88 plasma concentrations (mirrored by APTT) and urinary elimination were linear and dose-proportional. Docetaxel did not alter the pharmacokinetic (PK) profile of PI-88, nor did PI-88 affect docetaxel PK. No significant relationship was determined between plasma or urine FGF-2, or plasma VEGF levels and PI-88 dose/response. Although no objective responses were observed; 9 of the 15 evaluable patients had stable disease for greater than two cycles of therapy.

CONCLUSION

PI-88 administered at 250 mg/day for 4 days each week for 3 weeks with docetaxel 30 mg/m(2) on days 1, 8 and 15, every 28 days, was determined to be the recommended dose level for phase II evaluation. This combination was well tolerated without severe toxicities or PK interactions.

Bioactivity, pharmacokinetics, and immunogenicity assays in preclinical and clinical trials for recombinant human endostatin

AIM

To determine the in vitro and in vivo bioactivity of recombinant human endostatin (rhEndostatin) and to analyze its pharmacokinetics and immunogenicity in rhesus monkeys and patients.

METHODS

The physical chemical characteristics of rhEndostatin were detected according to Pharmacopoeia of the People's Republic of China (2005 edition, part III). Its in vitro and in vivo bioactivities were assayed via proliferation-inhibition on human umbilical vein endothelial cells and their inhibitory effect on tumor-bearing mice models. Serum concentrations of rhEndostatin in monkeys and patients were determined by an enzyme immunoassay method.

RESULTS

The corresponding specific in vitro activities of rhEndostatin obtained from the cell counting method, 3-(4,5-dimethylthiazol-2- yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and lactate dehydrogenase assay, respectively, were 6.4 x 10(7), 6.7 x 10(7), and 3.8 x 10(8) U/mg, and the in vivo antitumoral potency was 4.04 x 10(7) U/mg. In rhesus monkeys, there were no gender differences in all pharmacokinetic parameters. Serum anti-rhEndostatin immunoglobulin (Ig)G antibodies were generated quickly after intravenous (iv) administration and decreased rapidly when therapy was stopped. In phase I clinical trials, linearity in the pharmacokinetics of rhEndostatin was indicated by dose-proportionate increases in the area under the curve and the maximum serum concentration. Serum rhEndostatin reached a steady-state level after 7 d of successive administration with the average concentration at a steady state of 272.44+/-91.98 ng/mL. Neither IgG nor IgM antibodies against rhEndostatin were observed in patients.

CONCLUSION

RhEndostatin exhibited a definite proliferation- inhibition effect on HUVEC, and significant antitumoral activity in mice. The immunoreactivity of rhesus monkeys to rhEndostatin is common, and rhEndostatin showed no immunogenicity in patients in this trial. The results provide a basis for further clinical trials.

Oligosaccharides as anti-angiogenic agents

BACKGROUND

Several studies of drugs that inhibit tumour angiogenesis have shown improvements in the survival of cancer patients, thus validating angiogenesis as a clinically relevant target. Both intracellular and extracellular approaches have shown promising results in clinical situations.

OBJECTIVES

To compare and contrast oligosaccharide therapies and other anti-angiogenic compounds for their benefits and toxicity.

METHODS

Analysis of the relevant literature including presentations at recent conferences.

RESULTS

Receptor tyrosine kinase inhibitors are orally available but have a broad spectrum of activity which is associated with toxicity. Antibodies are associated with different toxicities, however, they are administered parenterally. Oligosaccharides that act as competitive inhibitors of heparan sulfate (HS) are in the early and late phases of clinical development. The advantage of oligosaccharides should be that they can be designed to target several angiogenic molecules, that they are relatively safe and that they can be administered subcutaneously at home. The key questions concerning their development focus on whether compounds with sufficient affinity and relative specificity can be generated, whether they are active at doses that do not perturb the coagulation cascade to a clinically dangerous level, whether the synthetic routes are scalable and, whether the current Phase III trials will yield positive results.

CONCLUSIONS

Saccharides represent a novel and exciting therapeutic approach that targets a spectrum of angiogenic molecules that cannot be inhibited through established drug development programmes.

Adjuvant therapy of melanoma

PURPOSE

The purpose of this article was to review the current state of knowledge regarding the efficacy of adjuvant therapy for melanoma.

PATIENTS AND METHODS

We reviewed the published literature, focusing on randomized clinical trials.

RESULTS

There have been no meaningful trials addressing adjuvant chemotherapy in melanoma because all trials have been underpowered. Adjuvant interferon-alpha has been tested both at high dose and at lower doses. None of the trials have shown a reproducible benefit in survival, although the high-dose trials and some of the low-dose trials have shown improvement in time to relapse. These experiences raise the question of whether chronic administration is more important than dose. An adjuvant pegylated interferon-alpha trial using a 5-year treatment period is currently under investigation. At least 7 randomized adjuvant vaccine trials have been published, but none have shown a beneficial effect on relapse-free or overall survival except in subset analyses.

CONCLUSIONS

To date, no adjuvant therapy has resulted in improved overall survival. To be attractive as an adjuvant therapy, experience from other tumor types indicates that a chemotherapy regimen should have a response rate of at least 20% in metastatic melanoma. Currently, biochemotherapy is being tested as an adjuvant treatment but other, less toxic, regimens should be sought. Once such a regimen with acceptable toxicity is identified, it would be reasonable to test it as an adjuvant therapy in a properly powered randomized trial. High-dose interferon-alpha for 1 year remains the only U.S. Food and Drug Administration-approved adjuvant therapy for melanoma, but long-term chronic dosing of interferon-alpha may prove more effective than short-term dose schedules. Development of melanoma vaccines remains an appealing and important goal. New technologies and understanding of the immune response against melanoma are leading to novel vaccine strategies designed to break immunologic tolerance against melanoma.

VEGF Trap complex formation measures production rates of VEGF, providing a biomarker for predicting efficacious angiogenic blockade

VEGF is the best characterized mediator of tumor angiogenesis. Anti-VEGF agents have recently demonstrated impressive efficacy in human cancer trials, but the optimal dosing of such agents must still be determined empirically, because biomarkers to guide dosing have yet to be established. The widely accepted (but unverified) assumption that VEGF production is quite low in normal adults led to the notion that increased systemic VEGF levels might quantitatively reflect tumor mass and angiogenic activity. We describe an approach to determine host and tumor production of VEGF, using a high-affinity and long-lived VEGF antagonist now in clinical trials, the VEGF Trap. Unlike antibody complexes that are usually rapidly cleared, the VEGF Trap forms inert complexes with tissue- and tumor-derived VEGF that remain stably in the systemic circulation, where they are readily assayable, providing unprecedented capability to accurately measure VEGF production. We report that VEGF production is surprisingly high in non-tumor-bearing rodents and humans, challenging the notion that systemic VEGF levels can serve as a sensitive surrogate for tumor load; tumor VEGF contribution becomes significant only with very large tumor loads. These findings have the important corollary that anti-VEGF therapies must be sufficiently dosed to avoid diversion by host-derived VEGF. We further show that our assay can indicate when VEGF is optimally blocked; such biomarkers to guide dosing do not exist for other anti-VEGF agents. Based on this assay, VEGF Trap doses currently being assessed in clinical trials are in the efficacious range.

In vitro and in vivo characterization of 64Cu-labeled Abegrin, a humanized monoclonal antibody against integrin alpha v beta 3

Abegrin (MEDI-522 or Vitaxin), a humanized monoclonal antibody against human integrin alpha(v)beta(3), is in clinical trials for cancer therapy. In vivo imaging using Abegrin-based probes is needed for better treatment monitoring and dose optimization. Here, we conjugated Abegrin with macrocyclic chelating agent 1,4,7,10-tetra-azacylododecane N,N',N'',N'''-tetraacetic (DOTA) at five different DOTA/Abegrin ratios. The conjugates were labeled with (64)Cu (half-life = 12.7 hours) and tested in three human (U87MG, MDA-MB-435, and PC-3) and one mouse (GL-26) tumor models. The in vitro and in vivo effects of these (64)Cu-DOTA-Abegrin conjugates were evaluated. The number of DOTA per Abegrin varied from 1.65 +/- 0.32 to 38.53 +/- 5.71 and the radiolabeling yield varied from 5.20 +/- 3.16% to 88.12 +/- 6.98% (based on 2 mCi (64)Cu per 50 microg DOTA-Abegrin conjugate). No significant difference in radioimmunoreactivity was found among these conjugates (between 59.78 +/- 1.33 % and 71.13 +/- 2.58 %). Micro-positron emission tomography studies revealed that (64)Cu-DOTA-Abegrin (1,000:1) had the highest tumor activity accumulation (49.41 +/- 4.54% injected dose/g at 71-hour postinjection for U87MG tumor). The receptor specificity of (64)Cu-DOTA-Abegrin was confirmed by effective blocking of MDA-MB-435 tumor uptake with coadministration of nonradioactive Abegrin. (64)Cu-DOTA-IgG exhibited background level tumor uptake at all time points examined. Integrin alpha(v)beta(3)-specific tumor imaging using (64)Cu-DOTA-Abegrin may be translated into the clinic to characterize the pharmacokinetics, tumor targeting efficacy, dose optimization, and dose interval of Abegrin and/or Abegrin conjugates. Chemotherapeutics or radiotherapeutics using Abegrin as the delivering vehicle may also be effective in treating integrin alpha(v)beta(3)-positive tumors.

Prophylactic naked DNA vaccination with the human vascular endothelial growth factor induces an anti-tumor response in C57Bl/6 mice

Passive immunotherapy against soluble pro-angiogenic factors and/or their receptors in endothelial cells has become a promising approach in cancer therapeutics. There is also experimental evidence indicating that an active immunotherapy strategy directed towards these target molecules could also be effective. In this paper we show that it is possible to reduce tumor growth or increase the survival of tumor-bearing C57Bl/6 mice when animals are vaccinated with the human vascular endothelial growth factor (VEGF) isoform 121 gene (hVEGF(121)), and later challenged with melanoma or lung carcinoma tumor cells. Immunization was done with 10 microg DNA doses of the hVEGF121 gene, which is highly homologous to its mouse counterpart, administered on a weekly basis using a plasmid bearing 5 CpG bacterial motifs. Histopathology analyses of tumors of hVEGF(121) immunized animals showed a decrease in tumor cell density around vessels and in mitotic figures, as well as an increase in apoptotic tumor cells. A statistically significant cell cytotoxic response was found when spleen cells of immunized mice were co-cultured in vitro with mouse tumor VEGF-producing cells. Vaccination with an hVEGF121 gene mutated to make it deficient for VEGF receptor binding, produced similar in vitro and in vivo results, and significantly reduced the number of spontaneous metastases produced by the mouse Lewis lung carcinoma. Our results indicate that human VEGF DNA can be employed for anti-angiogenic active immunotherapy in mice, and that direct cell cytotoxicity is a contributor mechanism to the overall anti-tumor effects seen in immunized animals.

Novel anti-denatured collagen humanized antibody D93 inhibits angiogenesis and tumor growth: An extracellular matrix-based therapeutic approach

Matrix metalloproteases (MMPs) secreted by both tumor and endothelial cells proteolytically degrade collagen during tumor growth and neo-vascularization. This exposes cryptic binding sites on collagen with functional relevance for angiogenesis. In this report, we characterized a novel humanized monoclonal IgG1 antibody, D93. After humanization, the antibody retained the binding specificity of the parental murine IgM antibody for denatured (dn) collagen. D93 recognized dn-collagen but not native (nat) collagen of different species, including mouse, chicken, and human, indicating that its cryptic binding site(s) is conserved across species. In immunohistochemistry (IHC) studies, D93 stained the basement membrane of blood vessels in several xenograft human tumors or in surgically removed tumor tissues from patients with different types of malignancies. D93 staining was rarely or not present in normal blood vessels of healthy tissues. In in vivo experiments, D93 significantly inhibited basic fibroblast growth factor (bFGF)-induced angiogenesis in chick embryo chorioallantoic membrane (CAM) and the tumor growth of pre-established orthotopic human breast (MDA-MB-435) tumors in mice. D93 i.v. administered in mice was subsequently detected in the subendothelial basement membrane of tumor blood vessels but not blood vessels of normal tissues. Inhibition of growth of pre-established orthotopic human breast MDA-MB-435 tumors was more effective when D93 was combined with Taxol, than either treatment alone. In addition, tumors from animals treated with D93 and/or Taxol showed significantly reduced levels of the endothelial cell-marker CD31. Our data suggest that blockade of cryptic epitopes exposed on collagen IV during angiogenesis and tumor growth by a monoclonal antibody may provide a novel therapeutic modality for treatment of cancer and pathogenic neo-vascularization.

Immunological Characteristics of Amniotic Epithelium

We review recent experimental evidence of the immunosuppressive and immunogenic potential of amniotic epithelial cells. Since cryopreserved amniotic membrane (AM) has been used in clinical applications, much research has focused on the beneficial effects of amniotic stromal matrix rather than on the function of viable amniotic cells. However, viable human amniotic epithelial cells (HAECs) have been shown to elicit beneficial effects on secretion of anti-inflammatory factors. Topical application of culture supernatant from HAECs leads to profound suppression of suture-induced neovascularization in cornea and fewer major histocompatibility complex (MHC) class II antigen-presenting cells (APCs) in inflamed cornea after thermal cautery. Furthermore, expression of interleukin (IL)-1beta mRNA was suppressed in cauterized cornea. These results suggest that HAECs are a source of soluble anti-inflammatory factors that suppress corneal inflammation. However, viable amniotic epithelial cells display antigenicity and immunogenicity as allografts. Fresh allogeneic amniotic epithelium (AE) expresses MHC class I antigens and sensitizes recipients when placed in the eye, although long-term memory of allo-specific delayed hypersensitivity (DH) was not acquired. Allogeneic AE was clearly vulnerable to acute immune rejection in specifically sensitized recipients and recipients of repeated AE transplantation. We therefore suggest that immunogenicity of AE should not be ignored, and use of AM from different donor placentas should be emphasized when repeated AM transplantation is required in patients clinically.

Inhibition of tumor growth with antiangiogenic cancer vaccine using epitope peptides derived from human vascular endothelial growth factor receptor 1

PURPOSE

Antiangiogenic therapy is now considered to be one of promising approaches to treat various types of cancer. In this study, we examined the possibility of developing antiangiogenic cancer vaccine targeting vascular endothelial growth factor receptor 1 (VEGFR1) overexpressed on endothelial cells of newly formed vessels in the tumor.

EXPERIMENTAL DESIGN

Epitope-candidate peptides were predicted from the amino acid sequence of VEGFR1 based on their theoretical binding affinities to the corresponding HLAs. The A2/Kb transgenic mice, which express the alpha1 and alpha2 domains of human HLA-A*0201, were immunized with the epitope candidates to examine their effects. We also examined whether these peptides could induce human CTLs specific to the target cells in vitro.

RESULTS

The CTL responses in A2/Kb transgenic mice were induced with vaccination using identified epitope peptides restricted to HLA-A*0201. Peptide-specific CTL clones were also induced in vitro with these identified epitope peptides from peripheral blood mononuclear cells donated by healthy volunteers with HLA-A*0201. We established CTL clones in vitro from human peripheral blood mononuclear cells with HLA-A*2402 as well. These CTL clones were shown to have potent cytotoxicities in a HLA class I-restricted manner not only against peptide-pulsed target cells but also against target cells endogenously expressing VEGFR1. Furthermore, immunization of A2/Kb transgenic mice with identified epitope peptides restricted to HLA-A*0201 was associated with significant suppression of tumor-induced angiogenesis and tumor growth without showing apparent adverse effects.

CONCLUSIONS

These results strongly suggest that VEGFR1 is a promising target for antiangiogenic cancer vaccine and warrants further clinical development of this strategy.

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.

Selective blockade of vascular endothelial growth factor receptor 2 with an antibody against tumor-derived vascular endothelial growth factor controls the growth of human pancreatic adenocarcinoma xenografts

BACKGROUND

Vascular endothelial growth factor (VEGF), a key regulator of angiogenesis, is critical for growth of human pancreatic adenocarcinoma. Preclinical studies demonstrate that blockade of VEGF activity can control the growth of pancreatic tumors in mice. In this study, we evaluated the efficacy of 2C3, an antibody that inhibits VEGF receptor 2 activation by human VEGF, to inhibit the growth of human pancreatic adenocarcinoma in mice.

METHODS

Human pancreatic cancer cell lines (MiaPaca-2, Panc-1, and Capan-1) were used to establish xenografts in nu/nu mice. The expression of VEGF and its receptors was determined in each cell line. Proliferation of tumor cells in vitro and tumor growth in vivo in the presence of 2C3 or a control antibody was evaluated. The effect of 2C3 on tumor weight, total vessel density, number of pericyte-associated vessels, and tumor perfusion was determined, and the level of 2C3 in the serum of animals was measured by enzyme-linked immunosorbent assay.

RESULTS

2C3 did not affect the proliferation of cells in culture. 2C3 was present and active in the serum of tumor-bearing animals treated with 2C3, and these animals showed a decrease in tumor burden compared with control-treated mice. Therapy with 2C3 resulted in reduced vascular function, measured by a decrease in vessel density and in the percentage of vessels associated with pericytes. Furthermore, tumors derived from Capan-1 cells demonstrated decreased perfusion after treatment with 2C3.

CONCLUSIONS

Blockade of VEGF receptor 2 activation by tumor-derived VEGF decreases tumor vessel function and growth of some human pancreatic adenocarcinoma cell lines in mice.

[The antiangiogenic effect of DNA vaccine based on beta-defensin 2 fused with VE-cadherin]

OBJECTIVE

To explore the feasibility of generating beta defensin 2 fusion vaccine to break the immune tolerance of self antigens associated with angiogenesis.

METHODS

PCR amplification of mature beta defensin 2 (Def) and extracelluar segment of Vascular Endothelial Cadherin (Cad) was conducted. (GGGS)3 was used as linker peptide for fusion plasmid(Def-Cad). All the three segments were inserted into pSecTag2B plasmid (pSec), and CT26 tumor cells were transfected. Expression was verified by RT-PCR and chemotaxis assay. The alginate bead model was used to study the antiangiogenic effect of fusion plasmid vaccination.

RESULTS

All constructions were verified by sequencing and were found expressed in mammalian cell. The beta defensin 2 fusion protein had similar capacity to chemoattract dendritic cells as compared with nonfusion protein (P>0.05). The alginate bead assay revealed that the tumor-induced angiogenesis in fusion plasmid immunized mice was significantly suppressed when compared with that in nonfusion plasmid (P<0.01).

CONCLUSION

An active immunization strategy based on beta defensin 2 fused with angiogenesis related antigen of endothelial can inhibit angiogenesis and may be a useful approach for cancer therapy.

Cancer CXC chemokine networks and tumour angiogenesis

Chemokines have pleiotropic effects in regulating immunity, angiogenesis, stem cell trafficking, and mediating organ-specific metastases of cancer. In the context of angiogenesis, the CXC chemokine family is a unique group of cytokines known for their ability to behave in a disparate manner in the regulation of angiogenesis. The glutamic acid-leucine-arginine (ELR+) CXC chemokines are potent promoters of angiogenesis, and mediate their angiogenic activity via signal-coupling of CXCR2 on endothelium. By contrast, members of the CXC chemokine family, such as platelet factor-4 (PF4; CXCL4) and interferon-inducible CXC chemokines are potent inhibitors of angiogenesis, and use CXCR3 on endothelium to mediate their angiostatic activity. This review will discuss the biology of CXC chemokines in the context of angiogenesis related to cancer.

Antiangiogenic chimeric anti-endoglin (CD105) antibody: pharmacokinetics and immunogenicity in nonhuman primates and effects of doxorubicin

We generated a human/mouse chimeric antibody c-SN6j of human IgG1 isotype from a murine anti-human endoglin (EDG) monoclonal antibody (mAb) SN6j that suppressed angiogenesis, tumor growth and metastasis in mice. We determined pharmacokinetics (PKs) and immunogenicity of c-SN6j in monkeys after multiple i.v. injections. A dose-escalation study was performed by administration of c-SN6j into six monkeys at the dose of 1 mg, 3 mg and 10 mg per kg body weight. In addition, both c-SN6j (3 mg/kg) and doxorubicin (0.275 mg/kg) were injected into two monkeys. c-SN6j and doxorubicin were injected twice a week for 3 weeks. We developed a unique and sensitive ELISA by sequentially targeting the common and idiotypic epitopes of c-SN6j-Fv to quantify plasma c-SN6j. Application of the ELISA showed that increasing the c-SN6j dose resulted in a proportional increase in the circulating c-SN6j after the first injection. In addition, the estimated area under the curve (AUC) for the first injection of c-SN6j is proportional to dose. We carried out detailed analyses of PKs of c-SN6j during and after the repeated injections. Our model of PKs fitted the empirical data well. Addition of doxorubicin modulated the PK parameters. We developed two ELISAs to separately determine the immune responses to the murine part and the human part of c-SN6j in monkeys. Interestingly, the murine part induced a weaker immune response than the human part. Doxorubicin potentiated the immune responses. Increasing the dose of c-SN6j increased plasma levels of c-SN6j but did not increase the immune responses to c-SN6j.

Antibody-based antiangiogenic cancer therapy

Monoclonal antibodies are beginning to fulfil their potential as therapeutics in different pathological conditions, with a special focus on cancer. At the same time, antiangiogenic therapy has evolved into one of the most active fields in cancer research. The logical combination of both strategies has produced a growing number of antibodies aimed to interfere with tumour angiogenesis at different steps of the angiogenic process. This development has taken advantage of recombinant technologies that have revolutionised the selection and production of monoclonal antibodies, and gene therapy approaches that achieve sustained and effective concentrations of therapeutic antibodies in vivo. Here, the current knowledge about these antibody-based antiangiogenic strategies is summarised and the authors propose a novel therapeutic approach based on the blocking of crucial binding sites present in the extracellular matrix.

Imiquimod as an antiangiogenic agent

Imiquimod (imidazoquinoline 5%) is a topical immune response modifier agent that inhibits angiogenesis, the growth of new blood vessels. In addition to its stimulation of cell-mediated immunity, imiquimod's antiangiogenic activity contributes to its clinical efficacy by interfering with pathological neovascularization that promotes disease progression. The antiangiogenic mechanisms of imiquimod are due to its: 1) induction of cytokines that themselves inhibit angiogenesis (interferons, IL-10, IL-12); 2) local up-regulation of endogenous angiogenesis inhibitors (TIMP, TSP-1); 3) local down-regulation of pro-angiogenic factors (bFGF, MMP-9); and 4) promotion of endothelial cell apoptosis. This report discusses these mechanisms and the rationale for imiquimod's use as an antiangiogenic agent. Key principles of antiangiogenic therapy are presented to describe how imiquimod may be applied in a well-tolerated fashion to treat a broad range of angiogenesis-dependent dermatological conditions, including actinic keratosis (AK), basal cell carcinoma (BCC), squamous cell carcinoma (SCC), lentigo maligna, hemangiomas, Kaposi's sarcoma, pyogenic granuloma, and external genital warts.

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.

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.

Two Functional Epitopes of Pigment Epithelial–Derived Factor Block Angiogenesis and Induce Differentiation in Prostate Cancer

Pigment epithelial-derived factor (PEDF), an angiogenesis inhibitor with neurotrophic properties, balances angiogenesis in the eye and blocks tumor progression. Its neurotrophic function and the ability to block vascular leakage is replicated by the PEDF 44-mer peptide (residues 58-101). We analyzed PEDFs' three-dimensional structure and identified a potential receptor-binding surface. Seeking PEDF-based antiangiogenic agents we generated and tested peptides representing the middle and lower regions of this surface. We identified previously unknown antiangiogenic epitopes consisting of the 34-mer (residues 24-57) and a shorter proximal peptide (TGA, residues 16-26) with the critical stretch L19VEEED24 and a fragment within the 44-mer (ERT, residues 78-94), which retained neurotrophic activity. The 34-mer and TGA, but not the 44-mer reproduced PEDF angioinhibitory signals hinged on c-jun-NH2-kinase-dependent nuclear factor of activated T cell deactivation and caused apoptosis. Conversely, the ERT, but not the 34-mer/TGA induced neuronal differentiation. For the 44-mer/ERT, we showed a novel ability to cause neuroendocrine differentiation in prostate cancer cells. PEDF and the peptides bound endothelial and PC-3 prostate cancer cells. Bound peptides were displaced by PEDF, but not by each other, suggesting multiple receptors. PEDF and its active fragments blocked tumor formation when conditionally expressed by PC-3 cells. The 34- and 44-mer used distinct mechanisms: the 34-mer acted on endothelial cells, blocked angiogenesis, and induced apoptosis whereas 44-mer prompted neuroendocrine differentiation in cancer cells. Our results map active regions for the two PEDF functions, signaling via distinct receptors, identify candidate peptides, and provide their mechanism of action for future development of PEDF-based tumor therapies.

Soluble Expression of Recombinant Human Secondary Lymphoid Chemokine (SLC) in E. coli and Research on Its In Vitro and In Vivo Bioactivity

Secondary lymphoid tissue chemokine (SLC) is a CC chemokine that plays an important role in leukocytes homing to lymphoid tissues. The ability of SLC to co-localize both T cells and dendritic cells formed the rationale to evaluate its utility in cancer immunotherapy. The in vivo antitumor effect of murine SLC (mSLC) has been well documented, but little is known about that of human SLC (hSLC). To investigate the antitumor efficiency in vivo of hSLC, the hSLC gene was artificially synthesized and induced to express as a soluble form in Escherichia coli. After purification, the purity of the recombinant human SLC (rhSLC) protein was above 95% by SDS-PAGE analysis. The K(d) of rhSLC binding to peripheral blood lymphocytes (PBLs) was 0.2186 +/- 0.02675 microM as assessed by FACS, and the maximal chemotactic index of rhSLC was 9.49 at 100 nM as assessed by in vitro chemotaxis assay. Then genomic sequences of hSLC and mSLC, and of human CCR7 (hCCR7) and murine CCR7 (mCCR7), the receptor for SLC, were aligned. It was found that hSLC and mSLC share 70.72% identity and hCCR7 and mCCR7share 86.77% identity. Furthermore, we found that rhSLC could chemoattract murine peripheral blood mononuclear cells (PBMCs) in vitro. On the basis of these facts, immune competent mice inoculated with S180 sarcoma cells were chosen as an in vivo model. Intratumoral injections of rhSLC inhibited tumor growth and increased survival. These findings suggest that, despite its incapability to bind to either human or murine CXCR3, which is related to angiostasis, rhSLC can induce an antitumor response in vivo by another route. This report proves that rhSLC has a potent tumor-inhibition ability that makes it a promising candidate agent in cancer immunotherapy.

Anti-angiogenic vaccines as a treatment modality for cancer

Targeting angiogenesis to inhibit tumor development is now considered a valid approach to disease modulation. Recently, a number of laboratories have focused their research on the development of cancer vaccines that target modulators of angiogenesis. In this review we describe a number of novel vaccines that target mediators of angiogenesis and inhibit tumor progression in preclinical models.

Effect of Tinospora cordifolia on the cytokine profile of angiogenesis-induced animals

The antiangiogenic activity of Tinospora cordifolia was studied using in vivo as well as in vitro models. In vivo antiangiogenic activity was studied using B16F10 melanoma cell-induced capillary formation in animals. Intraperitoneal administration of the extract at a concentration of 20 mg/kg significantly inhibited the tumour directed capillary formation induced by melanoma cells. Analysis of the serum cytokine profile showed a drastic increase of proinflammatory cytokines such as IL-1beta, IL-6, TNF-alpha, granulocyte monocyte-colony stimulating factor (GM-CSF) and the direct endothelial cell proliferating agent vascular endothelial cell growth factor (VEGF) in the angiogenesis-induced control animals. Administration of Tinospora extract could differentially regulate these cytokine's elevation. The differential regulation is further evidenced by the increased production of antiangiogenic agents IL-2 and tissue inhibitor of metalloprotease-1 (TIMP-1) in the B16F10-injected, extract-treated animals. Moreover, using an in vitro rat aortic ring assay, it was observed that the extract at nontoxic concentrations inhibited the production of proangiogenic factors from B16F10 melanoma cells. Direct treatment of the extract also inhibits the microvessel outgrowth from the aortic ring. Hence, the observed antiangiogenic activity of the plant T. cordifolia is related, at least in part, to the regulation of the levels of these cytokines and growth factors in the blood of the angiogenesis-induced animal.

A monoclonal antibody that blocks VEGF binding to VEGFR2 (KDR/Flk-1) inhibits vascular expression of Flk-1 and tumor growth in an orthotopic human breast cancer model

Vascular endothelial growth factor (VEGF) is a primary stimulant of tumor angiogenesis. We previously raised a neutralizing anti-VEGF monoclonal antibody 2C3 that blocks the interaction of VEGF with VEGFR2 (KDR/Flk-1) but not with VEGFRI (FLT-1/flt-1). Here, we describe the therapeutic effects of 2C3 on tumor growth in an orthotopic model of MDA-MB-231 human breast carcinoma implanted in the mammary fat pads (MFP) of nude mice. Administration of 2C3 to mice with 100-150 mm3 tumors inhibited tumor growth by 75%, as compared to recipients of the isotype-matched irrelevant control IgG, C44. Treatment with 2C3 also inhibited the establishment of tumor colonies and reduced tumor burden in the lungs of mice injected intravenously with MDA-MB-231 cells. No toxicity was observed in these studies. The mean microvascular density (MVD) of tumors in 2C3-treated mice was 55 +/- 5 per mm2, as compared to 188 +/- 5 per mm2 in the C44-treated control group. The decrease in MVD closely correlated with the degree of inhibition of tumor growth. Treated tumors mostly contained mid-size and large vessels. Microvessels were mainly confined to the peripheral layer of tumor that bordered on the normal MFP epithelium. Tumor vessels had decreased expression of VEGFR2, indicating that neutralization of tumor-derived VEGF by 2C3 down-regulates the expression of VEGFR2 on tumor vasculature. This, in turn, may limit reinitiation of angiogenesis by either tumor-derived or stromal VEGF. These findings suggest that 2C3 is a candidate for treating primary cancer and for preventing the outgrowth of tumor metastases in cancer patients.

Immunological effects of thalidomide and its chemical and functional analogs

Thalidomide has recently shown considerable promise in the treatment of a number of conditions, such as leprosy and cancer. Its effectiveness in the clinic has been ascribed to wide-ranging properties, including anti-TNF-alpha, T-cell costimulatory and antiangiogenic activity. Novel compounds with improved immunomodulatory activity and side effect profiles are also being evaluated. These include selective cytokine inhibitory drugs (SelCIDs), with greatly improved TNF-alpha inhibitory activity, and immunomodulatory drugs (IMiDs) that are structural analogs of thalidomide, with improved properties. A third group recently identified within the SelCID group, with phosphodiesterase type 4-independent activity, is in the process of being characterized in laboratory studies. This review describes the emerging immunological properties of thalidomide, from a historical context to present-day clinical applications, most notably in multiple myeloma but also in other cancers, inflammatory disease, and HIV. We also describe the laboratory studies that have led to the characterization and development of SelCIDs and IMiDs into potentially clinically relevant drugs. Early trial data suggest that these novel immunomodulatory compounds may supercede thalidomide to become established therapies, particularly in certain cancers. Further evidence is required, however, to correlate the clinical efficacy of these compounds with their known immunomodulatory, antiangiogenic, and antitumor properties.

Infection and cancer: the common vein

The role of infectious agents in the development of cancer is well documented. The pathogenesis of various human neoplasms ranging from non-Hodgkin lymphoma (NHL) to cervical carcinoma frequently involves a chronic, most often viral, infection. At the same time, there is compelling evidence that certain acute infections result in the inhibition of neoplastic growth. The basis for this phenomenon is often thought to be concomitant anti-tumor immunity. Yet, experimental data supporting this hypothesis are scarce, and other non-immune anti-tumor factors could be involved. For instance, since virtually all aggressive tumors outstrip their blood supply, development of new vessels, or angiogenesis, is a limiting factor during neoplastic growth. In this review, we will discuss recent studies that implicate anti-angiogenesis in infection-mediated tumor suppression and suggest that this mechanism could also complement cytotoxic immunity arising from the use of cancer vaccines.

[The molecular mechanisms of neovascular age-related macular degeneration]

Age-related macular degeneration is the leading cause of irreversible vision loss in industrialized countries. While early forms of this disease with drusen and focal pigment alterations generally do not lead to relevant functional limitations, later forms of the disease, either through atrophy or choroidal neovascularization, are associated with significant visual impairment. A significant increase in knowledge about the molecular mechanisms of new vessel formation from the choriocapillaries has occurred over the past few years. This has already allowed for the clinical testing of pharmacological agents which inhibit the formation of new vessels in AMD. This article describes current research in the pathophysiology of choroidal neovascularization secondary to age-related macular degeneration.

Selective targeting of angiogenic tumor vasculature by vascular endothelial-cadherin antibody inhibits tumor growth without affecting vascular permeability

Vascular endothelial-cadherin (VE-cadherin) is an endothelial cell-specific adhesion molecule that is localized exclusively at cell-cell contacts referred to as adherens junctions. VE-cadherin-mediated adhesion is crucial for proper assembly of vascular structures during angiogenesis as well as for maintenance of a normal vascular integrity. We have shown previously that a monoclonal antibody (BV13) to VE-cadherin not only inhibits the formation of vascular tubes during tumor angiogenesis but also disrupts adherens junctions of normal vasculature with a concomitant increase in vascular permeability. The goal of the current studies was to block VE-cadherin function during angiogenesis without disrupting existing junctions on normal endothelium. Using in vitro screening assays to test for functional blocking of adherens junction formation and in vivo assays to detect antibody effects on vascular permeability in normal tissues, we have identified a novel blocking antibody (E4G10) that inhibits VE-cadherin function during angiogenesis but does not disrupt existing adherens junctions on normal vasculature. E4G10 inhibited formation of vascular tubes in vivo in the Matrigel plug and corneal micropocket assays. E4G10 also inhibited tumor growth in three models of mouse and human tumors via an antiangiogenic mechanism. Examination of normal mouse and tumor tissues showed that E4G10 bound to endothelial cells in a subset of tumor vasculature but not to normal vasculature. Bromodeoxyuridine labeling experiments showed that E4G10 specifically targeted a subset of tumor endothelium that is undergoing active cell proliferation, which likely reflects the activated, angiogenic endothelium. These findings indicate that VE-cadherin can be selectively targeted during states of pathological angiogenesis, despite its ubiquitous distribution throughout the entire vasculature. Our data also suggest that antibody E4G10 recognizes VE-cadherin epitopes that are only accessible on endothelial cells forming new adherens junctions, such as in angiogenic tumor vasculature.

Clinical experience with angiogenesis signaling inhibitors: focus on vascular endothelial growth factor (VEGF) blockers

Angiogenesis is required for tumor growth and metastasis and, therefore, represents an exciting target for cancer treatment. Angiogenesis is a complex process that is tightly regulated by pro- and anti-angiogenic growth factors. Physiologic angiogenesis takes place during tissue growth and repair, during the female reproductive cycle, and during fetal development. Pathologic angiogenesis is characterized by either excessive (eg, cancer) or inadequate (eg, coronary artery disease) neovascularization. Angiogenesis occurs in a series of complex and interrelated steps that involve the release of pro-angiogenic growth factors, such as vascular endothelial growth factor (VEGF). VEGF regulates both vascular proliferation and permeability, and functions as an anti-apoptotic factor for newly formed blood vessels. The biological effects of VEGF are mediated by two receptors, VEGF-1 and VEGF-2, whose expression is largely limited to the vascular endothelium. VEGF is often expressed in tumors at substantially increased levels. It is expressed in response to hypoxia, oncogenes, and other cytokines, and its expression is associated with poor prognosis in several types of cancer. Several different strategies have been used to inhibit VEGF, including anti-VEGF monoclonal antibodies (eg, bevacizumab) and agents that inhibit the VEGF receptor (eg, SU5416). Both types of agents have tolerable side effects and have shown promise when evaluated in a wide range of tumor types. Angiogenesis, the role of VEGF in angiogenesis and malignancy, and strategies for cancer treatment with VEGF inhibitors are discussed.

Thalidomide: new indications?

Thalidomide, which was developed as a nonbarbiturate sedative agent, was taken off the market in 1961 after it was linked to a spate of major birth defects. Gradually, thalidomide was reintroduced for the treatment of a few skin diseases including leprous erythema nodosum, severe mucosal ulcers (e.g., associated with HIV infection or Behçet's disease), lymphocytic skin infiltrations, cutaneous lupus erythematosus, and chronic graft-versus-host disease. Recent reports of original pharmacological properties including modulation of cytokine production (mainly reduced TNF-alpha production) and inhibition of angiogenesis have led to the suggestion that thalidomide may be useful in some inflammatory and neoplastic conditions. Several open-label studies and case reports have described the effects of thalidomide in Crohn's disease, rheumatoid arthritis, ankylosing spondylarthritis, systemic sclerosis, and a few other systemic disorders. In these indications, minor but dose-limiting side effects were apparently common. Thalidomide analogs with better acceptability profiles are under evaluation. The anti-angiogenic effects of thalidomide may make this compound valuable as single-drug therapy or as an adjunct to chemotherapy in patients with cancer, particularly those with metastases or multiple myeloma. This possibility requires further evaluation.

Antiangiogenic therapy of established tumors in human skin/severe combined immunodeficiency mouse chimeras by anti-endoglin (CD105) monoclonal antibodies, and synergy between anti-endoglin antibody and cyclophosphamide

Endoglin (EDG; CD105) is a proliferation-associated cell membrane antigen of endothelial cells and is strongly expressed on the tumor-associated angiogenic vascular endothelium. Furthermore, EDG is essential for angiogenesis and a component of the transforming growth factor (TGF)-beta receptor complex. The present three anti-EDG monoclonal antibodies (mAbs), SN6f, SN6j, and SN6k, react strongly with proliferating human endothelial cells but cross-react very weakly with murine endothelial cells. Analysis of Scatchard plot of direct binding of these mAbs to proliferating human umbilical vein endothelial cells showed equilibrium constants of 8.3 x 10(9), 3.1 x 10(9), and 1.0 x 10(9) liter/mol, respectively, for SN6f, SN6j, and SN6k. These mAbs did not react with MCF-7 human breast cancer cells. To facilitate antiangiogenic tumor therapy by these mAbs in animal models, we used human skin/severe combined immunodeficiency (SCID) mouse chimeras bearing tumors of MCF-7. Blood vessels in the chimeras were analyzed by immunostaining with species (human or mouse)-specific anti-CD31 and anti-EDG mAbs including an antihuman EDG mAb termed SN6h. Blood vessels in the completely healed grafted human skins consisted of a mixture of human (43.5%) and murine (56.5%) vessels, whereas only murine vessels were detected in the adjacent murine skins and s.c. tissues. Therefore, murine vessels infiltrate into the human skin grafts from the adjacent murine tissues, whereas the growth of human vessels is limited within the boundary of human skins. Growth of human MCF-7 tumors in the human skin grafts increased the ratio of human:murine vessels. Analyses of the grafted skins before and after tumor transplantation showed that SN6h reacted with tumor-induced angiogenic blood vessels but not with nonangiogenic vessels, whereas antihuman CD31 mAb reacted with both angiogenic and nonangiogenic vessels. The results show that SN6h is capable of distinguishing the tumor-induced angiogenic vasculature from the nonangiogenic vasculature in the present model. Antiangiogenic therapy of the chimeras bearing established MCF-7 tumors was carried out by i.v. administration of a mAb(s) via the tail vein of mice. SN6j and SN6k were effective for suppressing the established tumors, whereas tumor suppression was weaker with SN6f. The results indicate an absence of a direct correlation between antigen-binding avidity and in vivo antitumor efficacy of anti-EDG mAbs and suggest the importance of other factors (e.g., epitopes) in antitumor efficacy. No significant toxicity of the mAbs was detected. Combination of SN6f and SN6k that define mutually nonoverlapping epitopes showed an additive antitumor effect. Combination of SN6j and cyclophosphamide using an antiangiogenic schedule of drug dosing showed synergistic antitumor efficacy. The combination therapy induced lasting complete regression of the established tumors in two of the eight treated chimeras. We examined human and murine blood vessels in large human tumors from the chimeras at the end of therapeutic experiment. The test showed that SN6j therapy resulted in complete suppression of human vessels in the tumors but resulted in only weak suppression of murine vessels. Cyclophosphamide was not effective for suppressing human vessels and only weakly suppressive against murine vessels. Combination of SN6j and cyclophosphamide was effective for completely suppressing human vessels and also effective for partial (i.e., 35%) suppression of murine vessels. The results show that systemic administration of naked antihuman EDG mAbs can suppress established tumors, and the efficacy is markedly enhanced by combining a chemotherapeutic drug using an antiangiogenic schedule of drug dosing. These mAbs should show stronger antitumor efficacy in patients whose tumors depend entirely on human blood vessels.

Thalidomide: dual benefits in palliative medicine and oncology

Thalidomide is an immunomodulator, anti-angiogenic agent, anti-cytokine, and anti-integrin. Alone or in combination with other drugs, thalidomide has also demonstrated anti-cachexin and anti-neoplastic properties. Anorexia and cachexia are common symptoms of advanced cancer. Since certain cytokines also promote tumor growth, we may have a class of agents with palliative and anti-tumor benefits in combination with anti-neoplastics and anti-cytokines, such as thalidomide.

IFN-gamma-dependent inhibition of tumor angiogenesis by tumor-infiltrating CD4+ T cells requires tumor responsiveness to IFN-gamma

The importance of CD4(+) T cells in the induction of an optimal antitumor immune response has largely been attributed to their ability to provide costimulatory signals for the priming of MHC class I-restricted CD8(+) CTL. However, many reports have demonstrated a requirement for CD4(+) T cells in the effector phase of tumor rejection indicating a greater responsibility for CD4(+) T cells in controlling tumor outgrowth. We demonstrate here a critical role for CD4(+) T cells in restraining initial tumor development through the inhibition of tumor angiogenesis. Using a tumor variant that is unresponsive to IFN-gamma, we show that tumor responsiveness to IFN-gamma is necessary for IFN-gamma-dependent inhibition of tumor angiogenesis by CD4(+) T cells. These studies reveal a pivotal role for CD4(+) T cells in controlling early tumor development through inhibition of tumor angiogenesis.

Antibodies to endostatin in a multifocal glioblastoma patient

Endostatin, a C-terminal fragment of collagen XVIII is involved in the regulation of neovascularisation in solid tumours in mice. However, few data are available on the concentration of endostatin protein in patients with cancer. Paradoxical results obtained in this way prompted us to investigate an antibody to endostatin. We detected antibodies to endostatin in the serum and in the tumour brain tissue of a patient with a multifocal glioblastoma, and in the serum samples from two patients with aggressive tumours. These data suggest that endostatin overexpression by tumour tissue might induce a humoral immune response.

Antitumor effects of the mouse chemokine 6Ckine/SLC through angiostatic and immunological mechanisms

Mouse 6Ckine/SLC (secondary lymphoid tissue chemokine) is a chemotactic factor for dendritic cells, T cells, and NK cells in vitro. In addition, mouse 6Ckine/SLC interacts with the chemokine receptor CXCR3, as do several chemokines with antiangiogenic properties. These dual properties of mouse 6Ckine/SLC were tested for the induction of an antitumor response by transducing the C26 colon carcinoma tumor cell line with a cDNA encoding mouse 6Ckine/SLC. The C26-6CK-transduced cells showed reduced tumorigenicity in immunocompetent or in nude mice. Part of this effect was likely due to angiostatic mechanisms as shown by immunohistochemistry and Matrigel assay. C26-6CK tumors were also heavily infiltrated with leukocytes, including granulocytes, dendritic cells, and CD8+ T cells. In vivo, anti-CD8 treatment increased the tumorigenicity of the C26-6CK tumor cells, and tumor-infiltrating CD8+ T cells had the phenotype of memory effector cells, suggesting the induction of cytotoxic tumor-specific T lymphocytes. On the other hand, anti-asialo-GM1 depletion also increased the tumorigenicity of C26-6CK cells, supporting the participation of NK cells. Finally, tumor-infiltrating dendritic cells had the phenotype and functional features of immature dendritic cells. Overall, these results suggest that mouse 6Ckine/SLC has strong antitumor effects by inducing both angiostatic, CD8+ T cell-mediated, and possibly NK-mediated tumor resistance mechanisms.