Angiogenesis and Antiangiogenic Therapy

Correlation between the Expression of Angiogenic Factors and Stem Cell Markers in Human Uveal Melanoma

Uveal melanoma (UM) is the most common malignant tumor of the eye with extremely high metastatic potential. UM tumor cells can disseminate only hematogenously, thus, angiogenic signals have a particular role in the prognosis of the disease. Although the presence of cancer stem cells (CSCs) in densely vascularized UMs has been reported previously, their role in the process of hematogenous spread of UM has not been studied. In this study, we investigated the regulation of angiogenesis in UM in correlation with the presence of CSCs. Seventy UM samples were collected to analyze the expression of CSC markers and angiogenic factors. The expression of CSC markers was studied by RT-PCR, Western blotting techniques and IHC-TMA technique. RT-PCR showed high expression of CSC markers, particularly nestin, FZD6 and SOX10 and somewhat lower expression of NGFR. The protein expression of FZD6, HIF-1α and VEGFA was further evaluated in 52 UM samples by the IHC-TMA technique. We report here for the first time a significant correlation between FZD6 and VEGFA expression in UM samples. The observed correlation between FZD6 and VEGFA suggests the presence of CSCs in UM that are associated with the vascularization process.

The Development and Characterization of an HEK293-Derived Cell Line for Use in an Intratumoral Cytokine Delivery System

As part of ongoing work to develop a method of cytokine delivery for use as an intratumoral depot, we noted that HEK293 cells, encapsulated in alginate, died within 24–48 h after in vivo, intratumoral implantation. We hypothesized that the highly hypoxic and acidic conditions found inside the tumor was the cause of the cells' premature demise. Therefore, we set out to develop a cell line, derived from HEK293, that would survive these hostile conditions. The HEK293 line was selected in 0.3–0.5% oxygen conditions over several weeks, followed by a further 6-week period of culture in alternating hypoxic and normoxic conditions. The most rapidly growing clones were selected and grown in normoxic conditions for several weeks to ensure their stability. The clones were then compared to the original line in terms of cell proliferation in normoxia and hypoxia, colony-forming efficiency, and morphological characteristics. The resulting line was able to proliferate in the harshest of conditions and continues to release its biological payload after alginate microencapsulation.

Targeted therapies in early-stage breast cancer: achievements and promises

One of the most impressive changes in the therapeutic landscape of breast cancer in the past decade has been the advent of targeted therapies for specific subtypes. This article discusses the meaning of targeted therapy and examines the genomic basis for targeted therapy as it has emerged over the past decade. Human epidermal growth factor receptor 2 (HER2)-targeted therapy, the principle example of targeted therapy to enter the adjuvant arena in the past decade, is described in depth. Novel targeted therapies under development, many currently being examined in the adjuvant setting, are also explored, including anti-vascular endothelial growth factor therapy, poly (ADP ribose) polymerase (PARP) inhibition for triple-negative breast cancers, and agents targeting site-specific metastasis to the bone (receptor activator of NF-kB [RANK] ligand inhibition). Chemotherapy, the epitome of nonspecific anticancer therapy, is in the process of becoming targeted therapy as understanding of breast cancer biology improves.

Drug resistance associated with antiangiogenesis therapy

Neovascularization is one of the hallmarks associated with tumor growth. In the recent years, a number of angiogenesis inhibitors have been approved for clinical use in cancer patients. However, the efficacy of antiangiogenic therapy is in most cases short-lasting, with likely drug resistance developing within a few months. It is becoming clear also that there are a subset of malignant tumors that are inherently resistant to angiogenesis inhibition. The knowledge regarding resistance mechanisms towards angiogenesis inhibitors is still evolving and here we propose some theories and in some cases provide experimental evidence.

Inhibition of vascular endothelial growth factor receptor signaling in angiogenic tumor vasculature

Neovascularization takes place in a large number of pathologies, including cancer. Significant effort has been invested in the development of agents that can inhibit this process, and an increasing number of such agents, known as antiangiogenic drugs, are entering clinical trials or being approved for clinical use. The key players involved in the development and maintenance of tumor neovasculature are vascular endothelial growth factor (VEGF) and its receptors (VEGFRs), and therefore VEGF/VEGFR signaling pathways have been a focus of anticancer therapies for several decades. This review focuses on two main approaches designed to selectively target VEGFRs, inhibiting VEGFR with small molecule inhibitors of receptor tyrosine kinase activity and inhibiting the binding of VEGF to VEGFRs with specific antibodies or soluble decoy VEGF receptors. The major problem with these strategies is that they appeared to be effective only in relatively small and unpredictable subsets of patients. An alternative approach would be to subvert VEGFR for intracellular delivery of cytotoxic molecules. We describe here one such molecule, SLT-VEGF, a fusion protein containing VEGF121 and the highly cytotoxic catalytic subunit of Shiga-like toxin.

Alpha-v integrins as therapeutic targets in oncology

Integrins are heterodimeric cell adhesion receptors that mediate intercellular communication through cell-extracellular matrix interactions and cell-cell interactions. Integrins have been demonstrated to play a direct role in cancer progression, specifically in tumor cell survival, tumor angiogenesis, and metastasis. Therefore, agents targeted against integrin function have potential as effective anticancer therapies. Numerous anti-integrin agents, including monoclonal antibodies and small-molecule inhibitors, are in clinical development for the treatment of solid and hematologic tumors. This review focuses on the role of alpha(v) integrins in cancer progression, the current status of integrin-targeted agents in development, and strategies for the clinical development of anti-integrin therapies.

Phase I and pharmacokinetic study of etaracizumab (Abegrin), a humanized monoclonal antibody against alphavbeta3 integrin receptor, in patients with advanced solid tumors

This study assessed the safety, immunogenicity, and pharmacokinetics of etaracizumab, a monoclonal antibody directed against the alphavbeta3 integrin, in patients with advanced malignancies. Four cohorts of four patients received escalating dose of etaracizumab as a 30-min intravenous infusion, first as a single test dose, followed-up 2-5 weeks later by weekly doses. Sixteen patients with advanced solid tumors received a total of 309 cycles of etaracizumab at doses ranging 1-6 mg/kg. The mean number of weekly infusions was 19 (ranging 5-53). Frequently reported adverse events were grades 1-2 asthenia (15 patients) and infusion reactions (9 patients). At 1 mg/kg, one patient experienced grade 3 chills with the first infusion. Other grade 3 toxicities included reversible hyponatremia, hypophosphatemia and hyponatremia in one patient each at 1, 4 and 6 mg/kg, respectively. No patient experienced treatment delay/discontinuation due to an adverse event. The half-life of etaracizumab ranged 49-180 h with a nonlinear increase in terminal half-life with increasing doses. There was no objective response but five patients experienced a stable disease of >6-month duration. Etaracizumab was well-tolerated at doses up to 6 mg/kg with no evidence of immunogenicity. The safety profile of etaracizumab warrants further exploration in ongoing phase I/II trials.

Bevacizumab and non-small-cell lung cancer

Although platinum-based chemotherapy remains a mainstay of non-small-cell lung cancer treatment, its efficacy has probably reached a plateau. Increased understanding of cancer biology has allowed the identification of a number of possible molecular targets, including the EGF receptor and the angiogenesis pathway. ECOG-E4599 has randomised chemonaive patients to receive paclitaxel--carboplatin with and without bevacizumab, a humanised monoclonal antibody targeting the VEGF. The study is the first to show a survival advantage of adding a biological agent to chemotherapy in this setting: in particular, for the first time the survival of lung cancer patients has been extended beyond 1 year. The aim of this review is to describe the biological and clinical properties of bevacizumab and to discuss the evidence that has supported its approval for the first-line treatment of advanced non-squamous non-small-cell lung cancer.

The role of VEGF and EGFR inhibition: implications for combining anti-VEGF and anti-EGFR agents

Multiple cellular pathways influence the growth and metastatic potential of tumors. This creates heterogeneity, redundancy, and the potential for tumors to bypass signaling pathway blockade, resulting in primary or acquired resistance. Combining therapies that inhibit different signaling pathways has the potential to be more effective than inhibition of a single pathway and to overcome tumor resistance. Vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) inhibitors have become key therapies in several tumor types. Close relationships between these factors exist: VEGF signaling is up-regulated by EGFR expression and, conversely, VEGF up-regulation independent of EGFR signaling seems to contribute to resistance to EGFR inhibition. Therefore, inhibition of both pathways could improve antitumor efficacy and overcome resistance to EGFR inhibition. Preclinical studies have shown that VEGF and EGFR inhibitors can have additive effects and that combined inhibition is effective in EGFR inhibitor-resistant cell lines. Clinical trials have also produced promising data: combining the anti-VEGF monoclonal antibody bevacizumab with the anti-EGFR antibody cetuximab or the EGFR tyrosine kinase inhibitor erlotinib increases benefit compared with either of these anti-EGFR agents alone or combined with chemotherapy. The potential of this novel approach to anticancer therapy will be elucidated by large, ongoing clinical trials.

Vascular endothelial growth factor as a target for anticancer therapy

The development of a vascular supply is a critical factor in the growth and metastatic spread of malignant tumors. Of the multitude of growth factors that regulate physiological and pathological angiogenesis, vascular endothelial growth factor (VEGF) is believed to be the most important. There is evidence that overexpression of VEGF is correlated with an adverse prognosis, at least in some tumors. Tumor-expressed VEGF is particularly attractive as a target for anticancer therapy because its angiogenesis-promoting activity is at the level of the endothelial cell and, compared with agents that directly target tumor cells, tumor penetration is less critical for VEGF inhibitors. Moreover, recent work has shown that inhibiting tumor angiogenesis increases the effectiveness of coadministered chemotherapy and radiotherapy. This suggests that drugs that target VEGF or its receptors can be combined with traditional treatment modalities to ensure maximum effectiveness. A variety of agents aimed at blocking VEGF or its receptor-signaling system are currently being developed for the treatment of cancer. Of these, bevacizumab, a humanized monoclonal antibody directed at VEGF, is the most advanced in clinical development and has shown promising results in clinical trials.

VEGF-C expression in breast cancer: clinical importance

It is well known that angiogenesis and lymphangiogenesis play important roles in tumor occurrence and progression. The vascular endothelial growth factor (VEGF) family is the most important family of proteins involved in angiogenesis, and VEGF-C is the most important molecule in lymphangiogenesis. Lymphangiogenesis plays an important role in lymphovascular invasion, metastasis to regional lymph nodes, and distant organ metastasis. In this study, the rate of VEGF-C was investigated in 217 patients with breast cancer. VEGF-C was evaluated by immunohistochemistry and its expression was compared with that of well-known prognostic indicators, such as tumor stage and grade, axillary lymph node involvement, estrogen and progesterone receptor status, c-erb-B2 expression, and extent of lymphovascular invasion. The patient population included 8 men, in addition to women before (n=108), during (n=9), and after (n=92) menopause. Patients had been diagnosed with invasive ductal (n=181) or invasive lobular (n=22) carcinoma, mixed (n=8) or medullary (n=1) carcinoma, or ductal carcinoma in situ (n=5). Tumors ranged from stage 0 to IV and grade I to III and the distribution of estrogen-positive (n=100) and estrogen-negative (n=110) receptor tumors was almost equal. The number of patients with c-erbB2 tumors ranged from 21 to 49 for each tumor stage, and the number of patients with VEGF-C-negative tumors ranged from 28 to 59 for each tumor stage. No important association between VEGF-C expression and other prognostic indicators was found. However, this may be a result of the lack of standardization among the methods used to determine VEGF-C expression. Also, the lymphangiogenic effect may not be overt because of the variety of VEGFR-3 variants, which included nonfunctional variants. To determine the relationship among angiogenesis, lymphangiogenesis, and prognosis, more standardized methods to demonstrate the angiogenesis, and prospective studies to cover a larger, more homogenous patient population are needed.

Anti-vascular endothelial growth factor monoclonals in non-small cell lung cancer

There is an urgent need for new therapies to treat non-small cell lung cancer (NSCLC) because current chemotherapy regimens are of limited effectiveness. The role of vascular endothelial growth factor in promoting tumor angiogenesis, in maintaining existing vasculature, and in resistance to traditional therapies, together with its negative prognostic significance in NSCLC, make it an appropriate target for therapy. Bevacizumab (Avastin), a monoclonal antibody directed against vascular endothelial growth factor, has shown promise in treating a number of different cancers. In a recent Phase II trial in patients with advanced metastatic NSCLC, the addition of bevacizumab to standard carboplatin/paclitaxel chemotherapy significantly increased the time to progression and increased the response rate when compared with chemotherapy alone. This was particularly impressive in the subset of patients with non-squamous histology. Bevacizumab is generally well tolerated and did not appear to increase the incidence or severity of nausea/vomiting, neuropathy and renal toxicity, which are typically associated with carboplatin/paclitaxel chemotherapy. Adverse events in Phase I and II studies included hypertension, thrombosis, proteinuria (with occasional nephrotic syndrome), and epistaxis. Serious tumor-related bleeding episodes (hemoptysis/hematemesis) seem to be the main safety concern in patients with NSCLC, with squamous cell histology as a possible risk factor. Present ongoing studies are under way in NSCLC including (a) a Phase II neo-adjuvant study in combination with paclitaxel and carboplatin in patients with stage IB-IIA NSCLC; (b) a Phase I/II study of bevacizumab in combination with the epidermal growth factor receptor tyrosine kinase inhibitor agent, Tarceva, in patients with previously treated NSCLC; and (c) an Eastern Cooperative Group randomized Phase III study of paclitaxel and carboplatin with/without bevacizumab in patients with previously untreated IIIB (malignant pleural effusion) or metastatic NSCLC. These studies will help to establish the role of bevacizumab in NSCLC.

Non‐Small Cell Lung Cancer and Antiangiogenic Therapy: What Can Be Expected of Bevacizumab?

There is an urgent need for new therapies to treat non-small cell lung cancer (NSCLC), as progress with current chemotherapy regimens has been limited. The roles of vascular endothelial growth factor (VEGF) in promoting tumor angiogenesis, maintaining existing vasculature, and contributing to resistance to traditional therapies, together with its negative prognostic significance in NSCLC, make it an appropriate target for therapy. Bevacizumab (Avastin; Genentech Inc., South San Francisco, CA), a monoclonal antibody directed against VEGF, has shown promise in treating a number of different cancers. In a recent phase II trial in patients with advanced metastatic NSCLC, the addition of bevacizumab to standard carboplatin/paclitaxel chemotherapy produced a significantly longer time to progression (32.1 versus 18.4 weeks) and greater response rate (31% versus 19% [not significant]) than chemotherapy alone. In the subset of patients with nonsquamous histologies, response rates and survival were further enhanced, with a mean survival time of 17.9 months versus 12.3 months with chemotherapy alone. Bevacizumab was generally well tolerated and did not appear to increase the incidences or severities of the nausea/vomiting, neuropathy, and renal toxicity that are typically associated with carboplatin/paclitaxel chemotherapy. Adverse events in phase I and II studies included hypertension, thrombosis, proteinuria (with occasional nephrotic syndrome), and epistaxis. Serious tumor-related bleeding episodes (hemoptysis/hematemesis) appear to be the main safety concern in patients with NSCLC, with squamous cell histology as a possible risk factor. Further work is needed to identify the best way to use bevacizumab in NSCLC, including use in combination with other biologic agents and in the adjuvant setting.

The roles of vascular endothelial growth factor and angiopoietin-2 in the regression of pregnancy pyogenic granuloma

OBJECTIVES

The molecular mechanism for the regression of pregnancy pyogenic granuloma after parturition remains unclear. It has been proposed that, in the absence of vascular endothelial growth factor (VEGF), angiopoietin-2 (Ang-2) causes blood vessels to regress. Therefore, we investigated the roles of Ang-2 and VEGF in the regression of pregnancy pyogenic granuloma.

MATERIALS AND METHODS

The effects of tumor necrosis factor-alpha (TNF-alpha) on the transcription of Ang-2 were tested in endothelial cells by reverse transcriptase-polymerase chain reaction. A total of 15 specimens, including granulomas taken from five gravidas during pregnancy, five after parturition, and five from normal gingiva were compared by immunoblot assays for their relative expressions of Ang-1, Ang-2, Tie-2, VEGF, and beta-actin. Double staining, immunohistochemistry for Ang-2, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling for apoptotic cells, were used to evaluate their regression. Finally, a fibrin gel culture system was used to investigate whether the withdrawal of VEGF and addition of Ang-2 could cause newly grown microvessels to regress.

RESULTS

TNF-alpha upregulated the expression of Ang-2 in all endothelial cell types tested. The protein levels of Ang-2 and Tie-2 were highest in the granulomas in pregnancy, followed by those after parturition and normal gingiva, while Ang-1 and beta-actin exhibited no significant differences. The amount of VEGF was high in the granulomas in pregnancy and almost undetectable after parturition. Double staining on granulomas after parturition revealed more apoptotic cells and less Ang-2 than did those in pregnancy. In the fibrin gel assay, VEGF alone or in combination with Ang-2 could protect microvessels from apoptosis, while Ang-2 alone had no effect.

CONCLUSIONS

Our findings suggest that a lack of VEGF is associated with apoptosis of endothelial cells and regression of granuloma. The roles of Ang-2 require additional study.

The role of plasminogen in angiogenesis in vivo

Plasminogen, by virtue of its role in the degradation of extracellular matrix proteins and by facilitation of cell migration, may contribute to angiogenesis.

OBJECTIVE

the purpose of this study was to evaluate the contribution of plasminogen to angiogenesis in vivo.

METHODS

Angiogenesis was assessed in gene-targeted mice with deficiencies of plasminogen, urokinase plasminogen activator (uPA), and urokinase receptor (uPAR) in a mouse corneal model. In wild-type mice, female and young mice showed a trend toward increased angiogenesis compared to males and old mice. Because of this influence of age and gender on angiogenesis, young, female mice (6-13 weeks of age) were used for this study.

RESULTS

In response to angiogenic stimulation by basic fibroblast growth factor (bFGF), uPA deficient mice exhibited a decrease in new vessel formation as reflected by vessel length (0.47 in control vs. 0.33 mm in uPA-/- mice, P = 0.043), but new vessel formation was not altered (P = 0.107) in the uPAR deficient mice compared to control mice. A significantly decreased angiogenic response of new vessel formation to both vascular endothelial growth factor (VEGF) (P < 0.02) and bFGF (P < 0.007) was observed in Plg deficient (Plg-/-) mice (VEGF - 0.36 mm, bFGF - 0.67 mm) compared to Plg+/+ mice (VEGF - 0.56 mm, bFGF - 0.85 mm).

CONCLUSIONS

These results demonstrate the importance of plasminogen, as well as of uPA, in angiogenesis in vivo.

Anti-angiogenesis in cancer therapy

OBJECTIVE

To review tumor angiogenesis, identify potential targets for anti-angiogenic cancer therapy, and highlight certain anti-angiogenic agents in clinical trials.

DATA SOURCE

Research articles, abstracts, review articles, and book chapters.

CONCLUSION

Tumor angiogenesis is a complex, multistep process that provides a target for antineoplastic therapy whereby tumor neovasculature is interrupted at various steps in the angiogenic process. Clinical trials are investigating the application and efficacy of anti-angiogenic agents.

IMPLICATIONS FOR NURSING PRACTICE

Oncology nurses must continually increase their knowledge with the onset of newer, targeted agents. This will provide a background for educating and caring for the patient who is receiving anti-angiogenic therapy.

Effects of angiogenic regulators on in vitro proliferation and cytokine secretion by native human acute myelogenous leukemia blasts

Angiogenesis seems to be important in the pathogenesis of acute myelogenous leukemia (AML). The endothelial cell proliferation and microvessel formation are regulated by a wide range of soluble mediators, including angiogenin, angiopoietin-2, basic fibroblast growth factors, vascular endothelial growth factor (VEGF), VEGF-D, angiostatin and endostatin. In the present study, it has been investigated whether these mediators have an additional direct effect on the proliferation and cytokine release by native human AML blasts. AML cells derived from a large group of consecutive patients were investigated. All these mediators could alter the proliferation and cytokine release [interleukin (IL) 1beta, IL6, IL8, tumor necrosis factor alpha] for a minority of patients. Alteration of spontaneous proliferation by at least one mediator was detected in five of 38 patients; whereas, altered cytokine (Flt3-ligand, granulocyte-macrophage colony-stimulating factor, stem cell factor)-dependant proliferation was observed for 10 patients. Growth enhancement was most frequently observed, whereas growth inhibition was uncommon. The effects on AML blast proliferation were often dependant on or were modulated by the presence of the three hematopoietic growth factors. Based on the present results, it is concluded that angioregulatory mediators have additional growth-enhancing effects directly on the AML blasts for certain patients. However, based on the results from this investigation and previous studies it is suggested that their major contribution to the pathogenesis of AML is through their effects on regulation of bone marrow angiogenesis, and future studies of these mediators in AML should probably focus on these effects.

Antiangiogenic therapy against experimental glioblastoma using genetically engineered cells producing interferon-alpha, angiostatin, or endostatin

Inhibition of angiogenesis has been considered among the most promising approaches to treat highly vascularized solid tumors such as glioblastoma. In this study, we designed and validated a new in vitro assay system based on the implantation of tumor cells into organotypic brain slice cultures. We evaluated the effects of local production of three endogenous inhibitors of angiogenesis, angiostatin, endostatin, and interferon (IFN)-alpha(1), using stably transfected rat (9L) and human (GL15) glioblastoma cells on tumor vascularization and growth. Despite similar effectiveness of the three proteins in a classic in vitro endothelial cell migration assay, IFN-alpha(1) demonstrated the most potent antiangiogenic effect in organotypic brain slice cultures. In vivo, after intracerebral implantation of such genetically modified glioblastoma cells, IFN-alpha(1) caused a dramatic decrease in tumor volume revealed by magnetic resonance imaging and by postmortem histology. The mechanisms of this antitumor effect were most likely caused by the major antiangiogenic action of the cytokine, because IFN-alpha(1) expression provoked a pronounced decrease in blood vessel density, which was accompanied by extensive necrosis in the body mass of the tumors. The median survival time of rats implanted intracerebrally with IFN-alpha-expressing 9L cells tripled, and was still significantly increased when these constituted only 1% of transplanted tumor cells. A similar effect was seen when 50% of the transplanted cells were replaced by IFN-alpha-expressing bone marrow stromal cells. These data point to the local delivery of IFN-alpha(1) using cell vectors as a potent tool for the inhibition of tumor-induced angiogenesis.