Simultaneous blockade of VEGFR-1 and VEGFR-2 activation is necessary to efficiently inhibit experimental melanoma growth and metastasis formation

Expression of angiogenic and lymphangiogenic genes in primary cutaneous melanoma: relationship with angiolymphatic invasion and disease-free survival

Melanoma is one of the most common cancers in the world. The main routes of tumor progression are related to angiogenesis and lymphangiogenesis. These routes can occur by local invasion, which is called angiolymphatic invasion (ALI). In this study, we assess gene expression of relevant biomarkers of angiogenesis and lymphangiogenesis in 80 FFPE melanoma samples to determine a molecular profile that correlates with ALI, tumor progression, and disease-free survival. The results were enhanced by a posttranscriptional analysis by an immunofluorescence assay. Three SNPs in the VEGFR-2 gene were genotyped in 237 malignant melanoma (MM) blood DNA samples by qPCR. A significant correlation was found for LYVE -1 and ALI, qualitative ( P  = 0.017) and quantitative ( P  = 0.005). An increased expression of protein LIVE-1 in ALI samples supported these results ( P  = 0.032). VEGFR2 was lower in patients who showed disease progression ( P  = 0.005) and protein VEGFR2 posttranscriptional expression decreased ( P  = 0.016). DFS curves showed differences ( P  = 0.023) for VEGFR2 expression detected versus the absence of VEGFR2 expression. No significant influence on DFS was detected for the remaining analyzed genes. Cox regression analysis suggested that VEGFR2 expression has a protective role (HR = 0.728; 95% CI = 0.552-0.962; P  = 0.025) on disease progression. No significant association was found between any of the studied SNPs of VEGFR2 and DFS or progression rate. Our main results suggest that LYVE-1 gene expression is closely related to ALI; the relationship with the development of metastases in MM deserves further studies. Low expression of VEGFR2 was associated with disease progression and the expression of VEGFR2 correlates with an increased DFS.

Vascular Endothelial Growth Factor Receptors [VEGFR] as Target in Breast Cancer Treatment: Current Status in Preclinical and Clinical Studies and Future Directions

Breast cancer [BC] is one of the most common cancers among women, one of the leading causes of a considerable number of cancer-related death globally. Among all procedures leading to the formation of breast tumors, angiogenesis has an important role in cancer progression and outcomes. Therefore, various anti-angiogenic strategies have developed so far to enhance treatment's efficacy in different types of BC. Vascular endothelial growth factors [VEGFs] and their receptors are regarded as the most well-known regulators of neovascularization. VEGF binding to vascular endothelial growth factor receptors [VEGFRs] provides cell proliferation and vascular tissue formation by the subsequent tyrosine kinase pathway. VEGF/VEGFR axis displays an attractive target for anti-angiogenesis and anti-cancer drug design. This review aims to describe the existing literature regarding VEGFR inhibitors, focusing on BC treatment reported in the last two decades.

Apoptosis induction in human lung and colon cancer cells via impeding VEGF signaling pathways

There is ample evidence to suggest that vascular endothelial growth factor (VEGF) is a potent mitogen factor in vasculogenesis and angiogenesis and that blockade of VEGF-mediated signals can also prevent tumor growth via enforcing cell apoptosis. In the current study, we assessed the suppressing effect of VGB4, a VEGF antagonist peptide with the binding ability to both VEGF receptor1 and VEGF receptor2, on VEGF-induced proliferation and migration of the human lung adenocarcinoma cell line A549 and the human colon adenocarcinoma cell line HT29 using MTT assay, colony formation assay, and Scratch-wound assay. To evaluate the apoptotic inductive effect of VGB4 on A549 and HT29 cells, apoptosis analysis was carried out by flow cytometry and TUNEL assay. Likewise, p53 and PTEN expression level was examined by immunofluorescence microscopy. In addition, the level of proteins involved in VEGF signaling pathways related to apoptosis was investigated using western blot analysis. Our results indicated that VGB4 markedly inhibited VEGF-induced proliferation and migration, and induced apoptosis of A549 and HT29 cells dose dependently. Encouragingly, significant downregulation of B-cell lymphoma 2 (Bcl2), X-linked inhibitor of apoptosis, Procaspase9, and procaspase3, as well as upregulation of PTEN and P53 tumor suppressors, BCL2 associated X, Cytochrome c, cleaved caspase9, and cleaved caspase3 in VGB4-treated A549 and HT29 cells, further confirmed the profound inductive influence of VGB4 on apoptotic pathways. These findings along with the results from our previous studies show that VGB4 may be considerable for cancer therapy.

Anti-angiogenic Agents: A Review on Vascular Endothelial Growth Factor Receptor-2 (VEGFR-2) Inhibitors

Tumor growth inhibition can be achieved by inhibiting angiogenesis, which has been a field of great concern in recent years. Important targets to inhibit angiogenesis include vascular endothelial growth factor receptor (VEGFR) and its homologous tyrosine kinase receptor. Anti-angiogenic therapy based on inhibition of VEGFR-2 is an effective clinical treatment strategy. The research progress of VEGFR-2 inhibitors is reviewed in this paper from the aspects of drug development and chemical synthesis.

Design and synthesis of new 1,6-dihydropyrimidin-2-thio derivatives targeting VEGFR-2: Molecular docking and antiproliferative evaluation

A series of new 1,6-dihydropyrimidin-2-thiol derivatives (scaffold A) as VEGFR-2 inhibitors has been designed and synthesized. Compounds 3a, 3b, 3e and 4b have been selected for in vitro anticancer screening by the National Cancer Institute. Compound 3e showed remarkable anticancer activity against most of the cell lines tested, where a complete cell death against leukemia, non-small cell lung cancer, colon, CNS, melanoma, and breast cancer cell lines was observed. In vitro five dose tests showed that compound 3e had high activity against most of the tested cell lines with GI₅₀ ranging from 19 to 100 μM and selectivity ratios ranging between 0.75 and 1.71 at the GI₅₀ level. VEGFR-2-kinase was tested against 3a, 3b, 3e, 4b and sorafenib was used as a reference. Compounds 3a and 3e were the most potent analogues with IC₅₀ values of 386.4 nM and 198.7 nM against VEGFR-2, respectively, in comparison to sorafenib (IC₅₀ = 0.17 nM). The results of the docking study showed a good fitting of the new compounds to the active site of VEGFR-2 with binding free energies in the range of -9.80 to -11.25 kcal/mol compared to -12.12 kcal/mol for sorafenib. Compounds 4a-e with the hydroxyimino group had a higher affinity to VEGFR-2 than their parent derivatives 3a-e.

Targeting signaling pathways of VEGFR1 and VEGFR2 as a potential target in the treatment of breast cancer

Tumor angiogenesis allows tumor cells to grow and migrate toward the bloodstream and initiate metastasis. The interactions of vascular endothelial growth factors (VEGF) A and B, as the important regulating factors for blood vessel growth, with VEGFR1 and VEGFR2 trigger angiogenesis process. Thus, preventing these interactions led to the effective blockade of VEGF/VEGFRs signaling pathways. In this study, the inhibitory effect of a 23-mer linear peptide (VGB4), which binds to both VEGFR1 and VEGFR2, on VEGF-stimulated Human Umbilical Vein Endothelial Cells (HUVECs) and highly metastatic human breast cancer cell MDA-MB-231 proliferation was examined using MTT assay. To assess the anti-migratory potential of VGB4, HUVECs and also MDA-MB-231 cells wound healing assay was carried out at 48 and 72 h. In addition, downstream signaling pathways of VEGF associated with cell migration and invasion were investigated by quantification of mRNA and protein expression using real-time quantitative PCR and western blot in 4T1 tumor tissues and MDA-MB-231 cells. The results revealed that VGB4 significantly impeded proliferation of HUVECs and MDA-MB-231 cells, in a dose- and time-dependent manner, and migration of HUVECs and MDA-MB-231 cells for a prolonged time. We also observed statistically significant reduction of the transcripts and protein levels of focal adhesion kinase (FAK), Paxillin, matrix metalloproteinase-2 (MMP-2), RAS-related C3 botulinum substrate 1 (Rac1), P21-activated kinase-2 (PAK-2) and Cofilin-1 in VGB4-treated 4T1 tumor tissues compared to controls. The protein levels of phospho-VEGFR1, phospho-VEGFR2, Vimentin, β-catenin and Snail were markedly decreased in both VGB4-treated MDA-MB-231 cells and VGB4-treated 4T1 tumor tissues compared to controls as evidenced by western blotting. These results, in addition to our previous studies, confirm that dual blockage of VEGFR1 and VEGFR2, due to the inactivation of diverse signaling mediators, effectively suppresses tumor growth and metastasis.

Vessel co-option in cancer

All solid tumours require a vascular supply in order to progress. Although the ability to induce angiogenesis (new blood vessel growth) has long been regarded as essential to this purpose, thus far, anti-angiogenic therapies have shown only modest efficacy in patients. Importantly, overshadowed by the literature on tumour angiogenesis is a long-standing, but continually emerging, body of research indicating that tumours can grow instead by hijacking pre-existing blood vessels of the surrounding nonmalignant tissue. This process, termed vessel co-option, is a frequently overlooked mechanism of tumour vascularization that can influence disease progression, metastasis and response to treatment. In this Review, we describe the evidence that tumours located at numerous anatomical sites can exploit vessel co-option. We also discuss the proposed molecular mechanisms involved and the multifaceted implications of vessel co-option for patient outcomes.

A peptide mimicking the binding sites of VEGF-A and VEGF-B inhibits VEGFR-1/-2 driven angiogenesis, tumor growth and metastasis

Interfering with interactions of vascular endothelial growth factors (VEGFs) with their receptors (VEGFRs) effectively inhibits angiogenesis and tumor growth. We designed an antagonist peptide of VEGF-A and VEGF-B reproducing two discontinuous receptor binding regions of VEGF-B (loop 1 and loop3) covalently linked together by a receptor binding region of VEGF-A (loop3). The designed peptide (referred to as VGB4) was able to bind to both VEGFR1 and VEGFR2 on the Human Umbilical Vein Endothelial Cells (HUVECs) surface and inhibited VEGF-A driven proliferation, migration and tube formation in HUVECs through suppression of ERK1/2 and AKT phosphorylation. The whole-animal fluorescence imaging demonstrated that fluorescein isothiocyanate (FITC)-VGB4 accumulated in the mammary carcinoma tumors (MCTs). Administration of VGB4 led to the regression of 4T1 murine MCT growth through decreased expression of p-VEGFR1 and p-VEGFR2 and abrogation of ERK1/2 and AKT activation followed by considerable decrease of tumor cell proliferation (Ki67 expression) and angiogenesis (CD31 and CD34 expression), induction of apoptosis (increased p53 expression, TUNEL staining and decreased Bcl2 expression), and suppression of metastasis  (increased E-cadherin and decreased N-cadherin, NF-κB and MMP-9 expression). These findings indicate that VGB4 may be applicable for antiangiogenic and antitumor therapy.

Phase II study of pazopanib in combination with paclitaxel in patients with metastatic melanoma

PURPOSE

This phase II study evaluated the safety and clinical activity of pazopanib, a potent and mutlitargeted tyrosine kinase inhibitor (TKI) of vascular endothelial growth factor receptors (VEGFRs)-1, -2 and -3, platelet-derived growth factor receptor (PDGFR)-α and β, and cKit, in combination with metronomic paclitaxel in patients with metastatic melanoma.

EXPERIMENTAL DESIGN

Sixty chemotherapy-naive patients received pazopanib at a starting dose of 800 mg daily in combination with metronomic dosing of paclitaxel 80 mg/m² weekly thrice every 4 weeks. The primary endpoint was 6-month progression-free survival (PFS) rate, while secondary endpoints included 1-year overall survival rate, RECIST response rates, progression-free survival rates and median overall survival. Prior BRAF-targeted therapy or checkpoint inhibitors were permitted.

RESULTS

The 6-month PFS rate was 68%, with a 1-year OS rate of 48%. Objective response rate was 37% comprising one complete and 20 partial responses. Stable disease at 8 weeks was noted in 32 patients (55%) with an overall clinical benefit rate of 93%. Six-month median progression-free survival was 8 months and median OS was 12.7 months. The most frequently (> 15%) reported non-hematologic, treatment-related adverse events were fatigue, diarrhea, hypertension, transaminitis and peripheral neuropathy. Treatment-related non-fatal bowel perforation, a known class effect, occurred in one patient. No significant association was noted between plasma levels of pazopanib and response.

CONCLUSIONS

The combination of pazopanib and metronomic paclitaxel was well-tolerated, demonstrating significant activity in metastatic melanoma. Further evaluation of this combination is warranted.

Antagonist antibodies to vascular endothelial growth factor receptor 2 (VEGFR-2) as anti-angiogenic agents

Interaction of numerous signaling pathways in endothelial and mesangial cells results in exquisite control of the process of physiological angiogenesis, with a central role played by vascular endothelial growth factor receptor 2 (VEGFR-2) and its cognate ligands. However, deregulated angiogenesis participates in numerous pathological processes. Excessive activation of VEGFR-2 has been found to mediate tissue-damaging vascular changes as well as the induction of blood vessel expansion to support the growth of solid tumors. Consequently, therapeutic intervention aimed at inhibiting the VEGFR-2 pathway has become a mainstay of treatment in cancer and retinal diseases. In this review, we introduce the concepts of physiological and pathological angiogenesis, the crucial role played by the VEGFR-2 pathway in these processes, and the various inhibitors of its activity that have entered the clinical practice. We primarily focus on the development of ramucirumab, the antagonist monoclonal antibody (mAb) that inhibits VEGFR-2 and has recently been approved for use in patients with gastric, colorectal, and lung cancers. We examine in-depth the pre-clinical studies using DC101, the mAb to mouse VEGFR-2, which provided a conceptual foundation for the role of VEGFR-2 in physiological and pathological angiogenesis. Finally, we discuss further clinical development of ramucirumab and the future of targeting the VEGF pathway for the treatment of cancer.

Receptor tyrosine kinase inhibitors: Are they real tumor killers?

Inhibiting tumor growth by targeting the tumor vasculature was first proposed by Judah Folkman almost 40 years ago. Since then, different approaches and numerous drugs and agents have been developed to achieve this goal, either with the aim of inhibiting tumor neoangiogenesis or normalizing the tumor vasculature. Among the most promising therapeutic targets are receptor tyrosine kinases (RTKs), some of which are predominantly expressed on tumor endothelial cells, although they are sometimes also present on tumor cells. The majority of RTK inhibitors investigated over the past two decades competes with ATP at the active site of the kinase and therefore block the phosphorylation of intracellular targets. Some of these drugs have been approved for therapy, whereas others are still in clinical trials. Here, we discuss the scientific basis, current status, problems and future prospects of RTK inhibition in anti-tumor therapy.

Exogenous norepinephrine attenuates the efficacy of sunitinib in a mouse cancer model

Background

Sunitinib alone exhibits satisfactory efficacy in several mouse homografts and xenografts but unsatisfactory efficacy in many kinds of solid tumors in clinic. Different from animals, receiving a diagnosis of cancer impacts chronic stress on patients. Here, we examine whether norepinephrine (NE), one of the most potent stress related hormones, leads to the difference in the efficacy of sunitinib between clinical and preclinical trials.

Methods

The influence of NE on mouse melanoma B16F1 cells under sunitinib was evaluated in vitro and in vivo. The β-AR/cAMP/PKA (β-adrenoceptor/cyclic adenosine monophosphate/protein kinase A) signaling pathway was also evaluated in human lung adenocarcinoma cells.

Results

We found that NE upregulated the expression of VEGF, IL-8 and IL-6 in vitro and stimulated tumor growth in vivo, which was mediated by β-AR/cAMP/PKA signaling pathway and could be inhibited by propranolol, a β-blocker for hypertension for decades.

Conclusions

This research indicates exogenous norepinephrine attenuates the efficacy of sunitinib, and a combination of sunitinib and propranolol might be suggested as a new strategy in solid tumor in clinic.

TNF-alpha and melphalan modulate a specific group of early expressed genes in a murine melanoma model

BACKGROUND

Cutaneous melanoma displays high morbidity and mortality rates. Isolated limb perfusion with melphalan (Mel) is used for the treatment of non-resectable, locally advanced extremity melanomas. When combined with tumor necrosis factor alpha (TNF-alpha) treatment, the complete response varies between 70% and 90%. The mechanisms underlying the effects of Mel and TNF-alpha are not completely understood. We evaluated the impact of systemic Mel and TNF-alpha administration on tumor growth, analyzed the morphological changes promoted by each treatment, and identified early expressed genes in response to Mel and TNF-alpha treatment, either alone or in combination, in a murine melanoma model.

METHODS

Six- to eight-week-old male mice were subcutaneously inoculated with B16F10 melanoma cells and then intravenously injected with TNF-alpha, melphalan or a combination of both drugs when the tumors reached 1.0 cm(2). Tumor growth was monitored every other day, and histological analysis was performed when the tumors reached 3.0 cm(2). Total RNA was extracted from the resected tumors and submitted to amplification, labeling and hybridization on an oligonucleotide microarray (Fox Chase Cancer Center). Tumor growth and histological parameters were compared using ANOVA. Survival curves were calculated using the Kaplan-Meier method. Two-way ANOVA was used to identify differentially expressed genes among the various treatments, and Dunn's test was used for pair-wise comparisons.

RESULTS

Systemic administration of Mel impaired tumor growth (p<0.001), improved animal survival (p<0.001), and decreased mitotic rate (p=0.049). Treatment with TNF-alpha alone had no impact, neither on tumor growth, nor on survival, but it increased necrosis (p<0.024) and decreased mitotic rates (p=0.001) in the tumors. Combined treatment with Mel and TNF-alpha had similar effects in tumor growth, survival, necrosis and mitotic rate as observed with individual treatments. Moreover, 118 genes were found differentially expressed by microarray analysis and 10% of them were validated by RT- real time PCR. In our model we found that the treatments regulate genes that play important roles in tumorigenesis such as cell adhesion (Pard3, Pecam1, Ilk, and Dlg5), proliferation (Tcfe3 and Polr1e), cell motility (Kifap3, Palld, and Arhgef6), apoptosis (Bcl2l11), and angiogenesis (Flt1 and Ptprj).

CONCLUSIONS

Our data reproduces, in mice, some of the features observed in melanoma patients treated with the combination of Mel and TNF-alpha. The identification of genes with altered expression by these drugs both individually and in combination might help in the understanding of their mechanism of action and, as a consequence, improved strategies that could impact their clinical application.

Blockade of VEGFR-1 and VEGFR-2 enhances paclitaxel sensitivity in gastric cancer cells

PURPOSE

Hypoxia-inducible factor-1α (HIF-1α) increases transcription of the vascular endothelial growth factor (VEGF) gene. Inhibition of VEGF abolishes VEGF mediated induction of HIF-1α. Recent reports suggested that HIF-1α also mediated the induction of class III β-tubulin (TUBB3) in hypoxia. TUBB3 confers resistance to taxanes. Inhibition of VEGF may decrease the expression of HIF-1α and TUBB3. This study was undertaken to investigate the roles of vascular endothelial growth factor receptor (VEGFR) in gastric cancer cell behavior and to identify methods to overcome paclitaxel resistance in vitro.

MATERIALS AND METHODS

The protein expression levels of HIF-1α and TUBB3 were measured in human gastric cancer cell lines (AGS) under normoxic and hypoxic conditions. The relationship between TUBB3 and paclitaxel resistance was assessed with small interfering TUBB3 RNA. AGS cells were treated with anti-VEGFR-1, anti-VEGFR-2, placental growth factor (PlGF), bevacizuamb, and paclitaxel.

RESULTS

Hypoxia induced paclitaxel resistance was decreased by knockdown of TUBB3. Induction of HIF-1α and TUBB3 in AGS is VEGFR-1 mediated and PlGF dependent. Hypoxia-dependent upregulation of HIF-1α and TUBB3 was reduced in response to paclitaxel treatment. Expressions of HIF-1α and TUBB3 were most decreased when AGS cells were treated with a combination of paclitaxel and anti-VEGFR-1. AGS cell cytotoxicity was most increased in response to paclitaxel, anti-VEGFR-1, and anti-VEGFR-2.

CONCLUSION

We suggest that blockade of VEGFR-1 and VEGFR-2 enhances paclitaxel sensitivity in TUBB3-expressing gastric cancer cells.

Vascular endothelial growth factor (VEGF) receptors: drugs and new inhibitors

The recent launch onto the market of five VEGFR inhibitors indicates the therapeutic value of these agents and the importance of the research in the field of angiogenesis inhibitors for future oncologic therapy. In this Perspective we briefly report the inhibitors that are in clinical use, while we dedicate two wider sections to the compounds that are in clinical trials and to the new derivatives appearing in the literature. We especially consider the medicinal chemistry aspect of the topic and report the structure-activity relationship studies and the binding mode of some inhibitors as well as the biological data of the compounds discovered in the past 5 years.

Role of the VEGF/VEGFR axis in cancer biology and therapy

New vessel formation (angiogenesis) is an essential physiological process for embryologic development, normal growth, and tissue repair. Angiogenesis is tightly regulated at the molecular level; however, this process is dysregulated in several pathological conditions such as cancer. The imbalance between pro- and antiangiogenic signaling molecules within tumors creates an abnormal vascular network that is characterized by dilated, tortuous, and leaky vessels. The pathophysiological consequences of these vascular abnormalities include temporal and spatial heterogeneity in tumor blood flow, oxygenation, and increased tumor interstitial fluid pressure. The resultant microenvironment deeply impacts on tumor progression, and also leads to a reduction in therapy efficacy. The discovery of vascular endothelial growth factor (VEGF) as a major driver of tumor angiogenesis has led to efforts to develop novel therapeutics aimed at inhibiting its activity. Anti-VEGF therapy has become an important option for the management of several human malignancies; however, a significant number of patients do not respond to anti-VEGF therapy when used either as single agent or in combination with chemotherapy. In addition, the benefit of antiangiogenic therapy is relatively short lived and the majority of patients relapse and progress. An increasing amount of reports suggest several potential mechanisms of resistance to antiangiogenic therapy including, but not limited to, tumor hypoxia. This chapter discusses the role of the VEGF axis in tumor biology and highlights the clinical application of anti-VEGF therapies elaborating on pitfalls and strategies to improve clinical outcome.

Combining Bevacizumab with Radiation or Chemoradiation for Solid Tumors: A Review of the Scientific Rationale, and Clinical Trials

Radiation therapy or the combination of radiation and chemotherapy is an important component in the local control of many tumor types including glioblastoma, rectal cancer, and pancreatic cancer. The addition of anti-angiogenic agents to chemotherapy is now standard treatment for a variety of metastatic cancers including colorectal cancer and non-squamous cell lung cancer. Anti-angiogenic agents can increase the efficacy of radiation or chemoradiation for primary tumors through mechanisms such as vascular normalization and augmentation of endothelial cell injury. The most commonly used anti-angiogenic drug, bevacizumab, is a humanized monoclonal antibody that binds and neutralizes vascular endothelial growth factor A (VEGF-A). Dozens of preclinical studies nearly uniformly demonstrate that inhibition of VEGF-A or its receptors potentiates the effects of radiation therapy against solid tumors, and this potentiation is generally independent of the type or schedule of radiation and timing of VEGF-A inhibitor delivery. There are now several clinical trials combining bevacizumab with radiation or chemoradiation for the local control of various primary, recurrent, and metastatic tumors, and many of these early trials show encouraging results. Some added toxicities occur with the delivery of bevacizumab but common toxicities such as hypertension and proteinuria are generally easily managed while severe toxicities are rare. In the future, bevacizumab and other anti-angiogenic agents may become common additions to radiation and chemoradiation regimens for tumors that are difficult to locally control.

Overcoming evasive resistance from vascular endothelial growth factor a inhibition in sarcomas by genetic or pharmacologic targeting of hypoxia-inducible factor 1α

Increased levels of hypoxia and hypoxia-inducible factor 1α (HIF-1α) in human sarcomas correlate with tumor progression and radiation resistance. Prolonged antiangiogenic therapy of tumors not only delays tumor growth but may also increase hypoxia and HIF-1α activity. In our recent clinical trial, treatment with the vascular endothelial growth factor A (VEGF-A) antibody, bevacizumab, followed by a combination of bevacizumab and radiation led to near complete necrosis in nearly half of sarcomas. Gene Set Enrichment Analysis of microarrays from pretreatment biopsies found that the Gene Ontology category “Response to hypoxia” was upregulated in poor responders and that the hierarchical clustering based on 140 hypoxia-responsive genes reliably separated poor responders from good responders. The most commonly used chemotherapeutic drug for sarcomas, doxorubicin (Dox), was recently found to block HIF-1α binding to DNA at low metronomic doses. In four sarcoma cell lines, HIF-1α shRNA or Dox at low concentrations blocked HIF-1α induction of VEGF-A by 84–97% and carbonic anhydrase 9 by 83–93%. HT1080 sarcoma xenografts had increased hypoxia and/or HIF-1α activity with increasing tumor size and with anti-VEGF receptor antibody (DC101) treatment. Combining DC101 with HIF-1α shRNA or metronomic Dox had a synergistic effect in suppressing growth of HT1080 xenografts, at least in part via induction of tumor endothelial cell apoptosis. In conclusion, sarcomas respond to increased hypoxia by expressing HIF-1α target genes that may promote resistance to antiangiogenic and other therapies. HIF-1α inhibition blocks this evasive resistance and augments destruction of the tumor vasculature.

Vascular endothelial growth factor receptors and the therapeutic targeting of angiogenesis in cancer: where do we go from here?

Abstract Vascular Endothelial Growth Factor receptors (VEGFRs), the interactions with their ligands and the subsequent signalling pathways are known to play a vital role in tumour angiogenesis. Initial clinical trials of VEGFR inhibitors were disappointing but over the past decade some therapies have been successfully brought to market. At present, VEGFR inhibitors appear to be most promising as adjuvants to conventional chemotherapy. However, several interacting signalling molecules and downstream pathways have recently been shown to interact with VEGFR signalling and provide promising novel targets, such as the platelet-derived growth factor (PDGF), epithelial growth factor (EGF), human epithelial receptor-2, (HER-2) Tie-2 and oestrogen receptors. Elucidation of this web of signalling pathways may identify new therapeutic strategies which may be used in combination with VEGFR inhibitors to augment the efficacy of anti-angiogenic cancer treatments. This review assesses the role of modulating VEGFR activity in cancer and systematically examines current evidence and trials in this area.

Multicenter, phase II study of axitinib, a selective second-generation inhibitor of vascular endothelial growth factor receptors 1, 2, and 3, in patients with metastatic melanoma

PURPOSE

This multicenter, open-label, phase II study evaluated the safety and clinical activity of axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors (VEGFR)-1, 2, and 3, in patients with metastatic melanoma.

EXPERIMENTAL DESIGN

Thirty-two patients with a maximum of one prior systemic therapy received axitinib at a starting dose of 5 mg twice daily. The primary endpoint was objective response rate.

RESULTS

Objective response rate was 18.8% [95% confidence interval (CI), 7.2-36.4], comprising one complete and five partial responses with a median response duration of 5.9 months (95% CI, 5.0-17.0). Stable disease at 16 weeks was noted in six patients (18.8%), with an overall clinical benefit rate of 37.5%. Six-month progression-free survival rate was 33.9%, 1-year overall survival rate was 28.1%, and median overall survival was 6.6 months (95% CI, 5.2-9.0). The most frequently (>15%) reported nonhematologic, treatment-related adverse events were fatigue, hypertension, hoarseness, and diarrhea. Treatment-related fatal bowel perforation, a known class effect, occurred in one patient. Axitinib selectively decreased plasma concentrations of soluble VEGFR (sVEGFR)-2 and sVEGFR-3 compared with soluble stem cell factor receptor (sKIT). No significant association was noted between plasma levels of axitinib and response. However, post hoc analyses indicated potential relationships between efficacy endpoints and diastolic blood pressure of 90 mm Hg or higher as well as baseline serum lactate dehydrogenase levels.

CONCLUSIONS

Axitinib was well tolerated, showed a selective VEGFR-inhibitory profile, and showed single-agent activity in metastatic melanoma. Further evaluations of axitinib, alone and combined with chemotherapy, are ongoing.

Myeloid cell diversification and complexity: an old concept with new turns in oncology

Tumour development is accompanied by an enhanced haematopoiesis. This is not a widespread activation since only cells belonging to the myelo-monocytic compartment are expanded and mobilized from primary sites of haematopoiesis to other organs, reaching also the tumour stroma. This process occurs early during tumour formation but becomes more evident in advanced disease. Far from being a simple, unwanted consequence of cancer development, accumulation of myelo-monocytitc cells plays a role in tumour vascularization, local spreading, establishment of metastasis at distant sites, and contribute to create an environment unfavourable for the adoptive immunity against tumour-associated antigens. Myeloid populations involved in these process are likely different but many cells, expanded in primary and secondary lymphoid organs of tumour-bearing mice, share various levels of the CD11b and Gr-1 (Ly6C/G) markers. CD11b(+)Gr-1(+) cells are currently named myeloid-derived suppressor cells for their ability to inhibit T lymphocyte responses in tumour-bearing hosts. In this manuscript, we review the recent literature on tumour-conditioned myeloid subsets that assist tumour growth, both in mice and humans.

VEGFR-2 expression in human melanoma: revised assessment

Vascular endothelial growth factor (VEGF) is an angiogenic factor that also functions as an autocrine growth factor for VEGF receptor (VEGFR)-2(+) melanomas. In multiple studies, VEGFR-2 was detected by immunostaining in 78-89% of human melanoma cells, suggesting that most patients with melanoma would benefit from anti-VEGF therapy. Here, we evaluated 167 human melanoma specimens in a tissue microarray to verify the presence of VEGFR-2, but found disparities in staining with commercial antibodies A-3 and 55B11. Antibody A-3 stained melanoma cells in 79% of specimens, consistent with published results; however, we noted extensive nonspecific staining of other cells such as smooth muscle and histiocytes. In contrast, antibody 55B11 stained melanoma cells in only 7% (95% confidence interval: 3.3-11.5) of specimens. As an internal positive control for VEGFR-2 detection, vascular endothelial cells were stained with antibody 55B11 in all specimens. We compared VEGFR-2(+) and VEGFR-2(-) melanoma cell lines by immunoblotting and immunohistochemistry after small interfering RNA (siRNA) knockdown and transient overexpression of VEGFR-2 to validate antibody specificity. Immunoblotting revealed that A-3 primarily cross-reacted with several proteins in both cell lines and these were unaffected by siRNA knockdown of VEGFR-2. In contrast, 55B11 staining of VEGFR-2(+) cells was mostly eliminated by siRNA knockdown of VEGFR-2 and increased in VEGFR-2(-) melanoma cell lines following transfection to express ectopic VEGFR-2. Our results show that relatively few melanoma cells (<10%) express detectable levels of VEGFR-2, and therefore, the majority of patients with melanoma are unlikely to benefit from antiproliferative effects of anti-VEGF therapy.

Vascular endothelial growth factors and receptors: anti-angiogenic therapy in the treatment of cancer

Vascular endothelial growth factors (VEGFs) are critical regulators of vascular and lymphatic function during development, in health and in disease. There are five mammalian VEGF ligands and three VEGF receptor tyrosine kinases. In addition, several VEGF co-receptors that lack intrinsic catalytic activity, but that indirectly modulate the responsiveness to VEGF contribute to the final biological effect. This review describes the molecular features of VEGFs, VEGFRs and co-receptors with focus on their role in the treatment of cancer.

A unique and potent protein binding nature of liposome containing polyethylenimine and polyethylene glycol: a nondisplaceable property

Most of the currently available targeting vectors are produced via the linkage of targeting molecules. However, the coupling process is complicated, and the covalent linkage may attenuate the activity of certain targeting molecules. In this study, we have developed a cationic liposome complexed with polyethylenimine and polyethylene glycol polymers (LPPC) that can capture various proteins without covalent conjugation. Characterizations of prepared LPPC revealed that the maximal-binding capacity was about 170 µg of bovine serum albumin to 40 µg of sphere-shaped LPPC (180 nm). The proteins were essentially located at or near the surface when analyzed by atomic force or transmission electron microscopy. We demonstrate that polyethylenimine was an essential component to bind the proteins. Upon the saturation of captured proteins, a given protein could not be displaced by other additional proteins and still retained its biological activity. Using a variety of functional proteins, we show some typical examples of the utility of incorporated beta-glucuronidase and antibodies onto the LPPC. The beta-glucuronidase can be used for the study of antigen-antibody interactions, whereas in studies with the antibody complex, we used anti-CD3 as an agonist to stimulate the proliferation of peripheral blood mononuclear cells via a receptor-mediated mechanism and anti-VEGFR for cell staining. In conclusion, the prepared LPPC can provide a platform to capture biologically and biochemically functional proteins on its surface for various applications, such as cell signaling, cell profiling, noncovalent enzyme-linked immunoassays, and others not mentioned.

Cancer biomarker discovery: the entropic hallmark

Background

It is a commonly accepted belief that cancer cells modify their transcriptional state during the progression of the disease. We propose that the progression of cancer cells towards malignant phenotypes can be efficiently tracked using high-throughput technologies that follow the gradual changes observed in the gene expression profiles by employing Shannon's mathematical theory of communication. Methods based on Information Theory can then quantify the divergence of cancer cells' transcriptional profiles from those of normally appearing cells of the originating tissues. The relevance of the proposed methods can be evaluated using microarray datasets available in the public domain but the method is in principle applicable to other high-throughput methods.

Methodology/Principal Findings

Using melanoma and prostate cancer datasets we illustrate how it is possible to employ Shannon Entropy and the Jensen-Shannon divergence to trace the transcriptional changes progression of the disease. We establish how the variations of these two measures correlate with established biomarkers of cancer progression. The Information Theory measures allow us to identify novel biomarkers for both progressive and relatively more sudden transcriptional changes leading to malignant phenotypes. At the same time, the methodology was able to validate a large number of genes and processes that seem to be implicated in the progression of melanoma and prostate cancer.

Conclusions/Significance

We thus present a quantitative guiding rule, a new unifying hallmark of cancer: the cancer cell's transcriptome changes lead to measurable observed transitions of Normalized Shannon Entropy values (as measured by high-througput technologies). At the same time, tumor cells increment their divergence from the normal tissue profile increasing their disorder via creation of states that we might not directly measure. This unifying hallmark allows, via the the Jensen-Shannon divergence, to identify the arrow of time of the processes from the gene expression profiles, and helps to map the phenotypical and molecular hallmarks of specific cancer subtypes. The deep mathematical basis of the approach allows us to suggest that this principle is, hopefully, of general applicability for other diseases.

Sublethal total body irradiation leads to early cerebellar damage and oxidative stress

The present study aimed at identifying early damage index in the cerebellum following total body irradiation (TBI). Adult male CD2F1 mice (n=18) with or without TBI challenge (8.5 Gy irradiation) were assessed for histology and expression of selected immunohistochemical markers including malondiadehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OHdG), protein 53 (p53), vascular endothelial growth factor receptor 2 (VEGF-R2), CD45, calbindin D-28k (CB- 28) and vesicular glutamate transport-2 (VGLUT2) in cerebellar folia II to IV. Compared to sham-controls, TBI significantly increased vacuolization of the molecular layer. At high magnification, deformed fiber-like structures were found along with the empty matrix space. Necrotic Purkinje cells were identified on 3.5 days after TBI, but not on 1 day. Purkinje cell count was reduced significantly 3.5 days after TBI. Compared with sham control, overall intensities of MDA and 8-OHdG immunoreactivities were increased dramatically on 1 and 3.5 days after TBI. Expression of VEGF-R2 was identified to be co-localized with 8-OHdG after TBI. This validates microvessel endothelial damage. The p53 immunoreactivities mainly deposited in the granular layer and microvessels after TBI and co-localization of the p53 with the CD45, both which were found within the microvessels. After TBI, CB28 expression decreased whereas the VGLUT2 expression increased significantly; Purkinje cells exhibited a reduced body size and deformity of dendritic arbor, delineated by CB28 immunoreactivity. Substantial damage to the cerebellum can be detectable as early as 1- 3.5 days in adult animals following sublethal TBI. Oxidative stress, inflammatory response and calcium neurotoxicity-associated mechanisms are involved in radiation-induced neuronal damage.

Low-dose metronomic cyclophosphamide combined with vascular disrupting therapy induces potent antitumor activity in preclinical human tumor xenograft models

Vascular disrupting agents preferentially target the established but abnormal tumor vasculature, resulting in extensive intratumoral hypoxia and cell death. However, a rim of viable tumor tissue remains from which angiogenesis-dependent regrowth can occur, in part through the mobilization and tumor colonization of circulating endothelial progenitor cells (CEP). Cotreatment with an agent that blocks CEPs, such as a vascular endothelial growth factor pathway-targeting biological antiangiogenic drug, results in enhanced antitumor efficacy. We asked whether an alternative therapeutic modality, low-dose metronomic chemotherapy, could achieve the same result given its CEP-targeting effects. We studied the combination of the vascular disrupting agent OXi4503 with daily administration of CEP-inhibiting, low-dose metronomic cyclophosphamide to treat primary orthotopic tumors with the use of the 231/LM2-4 breast cancer cell line and MeWo melanoma cell line. In addition, CEP mobilization and various tumor characteristics were assessed. We found that daily p.o. low-dose metronomic cyclophosphamide was capable of preventing the CEP spike and tumor colonization induced by OXi4503. This was associated with a decrease in the tumor rim and marked suppression of primary 231/LM2-4 growth in nude as well as severe combined immunodeficient mice. Similar results were found in MeWo-bearing nude mice. The delay in tumor growth was accompanied by significant decreases in microvessel density, perfusion, and proliferation, and a significant increase in tumor cell apoptosis. No overt toxicity was observed. The combination of OXi4503 and metronomic chemotherapy results in prolonged tumor control, thereby expanding the list of therapeutic agents that can be successfully integrated with metronomic low-dose chemotherapy.

Cigarette smoking and risk of lung metastasis from esophageal cancer

BACKGROUND

Whereas extensive research has explored the effect of environmental factors on the etiology of specific cancers, the influence of exposures such as smoking on risk of site-specific metastasis is unknown. We investigated the association of cigarette smoking with lung metastasis in esophageal cancer.

METHODS

We conducted a case-control study of esophageal cancer patients from two centers, comparing cases with lung metastases to controls without lung metastases. Information was gathered from medical records on smoking history, imaging results, site(s) of metastasis, and other patient and tumor characteristics. We used logistic regression to assess association.

RESULTS

We identified 354 esophageal cancer cases; smoking status was known in 289 (82%). Among patients with lung metastases, 73.6% (39 of 53) were ever smokers, versus 47.8% (144 of 301) of patients without lung metastases [P=0.001; summary odds ratio (OR), 2.52; 95% confidence interval (95% CI), 1.17-5.45; stratified by histology]. Smoking was associated with a nonsignificant increased adjusted odds of lung metastasis (OR, 1.89; 95% CI, 0.80-4.46). Upper esophageal subsite (OR, 4.71; 95% CI, 1.20-18.5), but not histology (squamous OR 0.65,95% CI 0.27-1.60), was associated with lung metastasis. Compared with the combined never/unknown smoking status group, smoking was associated with a significantly increased odds of lung metastasis (OR, 2.35; 95% CI, 1.11-4.97). There was no association between liver metastasis and smoking (OR, 0.88; 95% CI, 0.42-1.83).

CONCLUSIONS

Smoking is associated with increased odds of lung metastasis from esophageal cancer, and this relationship seems to be site specific. Future studies are needed to determine whether smoking affects the tumor cell or the site of metastasis, and whether this changes the survival outcome.

FLT1 and its ligands VEGFB and PlGF: drug targets for anti-angiogenic therapy?

Less than 5 years ago, it was still not clear whether anti-angiogenic drugs would prove successful in the clinic. After numerous patients with cancer or age-related macular degeneration have been treated with these drugs, they have now become part of the standard range of therapeutic tools. Despite this milestone, anti-angiogenic therapy still faces a number of clinical hurdles, such as improving efficacy, avoiding escape and resistance, and minimizing toxicity. Hopefully, other agents with complementary mechanisms, such as those that target placental growth factor, will offer novel opportunities for improved treatment.

Lack of effect of SU1498, an inhibitor of vascular endothelial growth factor receptor-2, in a transgenic murine model of retinoblastoma

SU1498, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor 2 (VEGFR-2), has activity against retinal neovascular diseases. To determine if this drug might have clinical utility against retinoblastoma, we evaluated the effects of SU1498, as well as the expression of VEGFR-2, in a transgenic animal model of retinoblastoma. Optical coherence tomography (OCT) was evaluated as a technology to measure retinal tumors in vivo, in response to treatment. Immunofluorescence analysis was performed to evaluate the distribution and expression of VEGFR-2 in enucleated eyes from LHβTag transgenic mice and controls at 4, 8, 12, and 16 weeks of age. VEGFR-2 and phosphorylated (p)VEGFR-2 levels were quantitated by Western blot. OCT was used to pair 10-week-old animals based on tumor volume (n=10), and these animals were treated with 6 periocular injections of SU1498 (50mg/kg, given twice weekly) or vehicle for 3 weeks. Tumor burden was determined by histology and in vivo imaging by OCT. VEGFR-2 and pVEGFR-2 expression levels were upregulated during tumorigenesis. However, SU1498 did not significantly reduce tumor burden compared to vehicle (p=0.29). OCT imaging of one matched pair demonstrated equivalent, linear tumor growth despite treatment with SU1498. Retinal tumors can be followed non-invasively and quantitatively measured with OCT. VEGFR-2 is strongly upregulated during tumorigenesis in transgenic retinoblastoma; however, SU1498 does not decrease tumor volume in transgenic murine RB at the studied dose and route of administration.

Rational Design, Structure, and Biological Evaluation of Cyclic Peptides Mimicking the Vascular Endothelial Growth Factor

Angiogenesis is the development of a novel vascular network from a pre-existing structure. Blocking angiogenesis is an attractive strategy to inhibit tumor growth and metastasis formation. Based on structural and mutagenesis data, we have developed novel cyclic peptides that mimic, simultaneously, two regions of the VEGF crucial for the interaction with the VEGF receptors. The peptides, displaying the best affinity for VEGF receptor 1 on a competition assay, inhibited endothelial cell transduction pathway, migration, and capillary-like tubes formation. The specificity of these peptides for VEGF receptors was demonstrated by microscopy using a fluorescent peptide derivative. The resolution of the structure of some cyclic peptides by NMR and molecular modeling has allowed the identification of various factors accounting for their inhibitory activity. Taken together, these results validate the selection of these two regions as targets to develop molecules able to disturb the development of cancer and angiogenesis-associated diseases.