Targeting angiogenesis: progress with anti-VEGF treatment with large molecules

Lessons learned from adult clinical experience to inform evaluations of VEGF pathway inhibitors in children with cancer

Agents targeting the vascular endothelial growth factor (VEGF) pathway have been studied in adults with cancer for nearly two decades. It is important to assess the lessons learned from this adult experience and to see how these lessons can help inform pediatric development of agents in this class. The benefit achieved from the use of VEGF pathway targeted agents for adult cancers has primarily been to delay for several months disease progression and less commonly time to death for conditions in which cure is not a reasonable expectation. VEGF pathway targeted agents have shown no efficacy when applied in the adjuvant setting. For adults with advanced cancer, prolongation of survival by 2-3 months is considered an important achievement in some settings. However, the primary goal of pediatric oncology clinical research is to identify treatments that allow children to be cured of their cancer and to grow to adulthood without treatment-induced limitations that lower their quality of survival. An important question for the pediatric oncology research community, pharmaceutical companies, and regulatory agencies to address in planning for future clinical trials is whether existing data support a role for VEGF pathway targeted agents in contributing to a therapeutic pathway to cure for children with cancer.

Targeting angiogenesis and tumor microenvironment in metastatic colorectal cancer: role of aflibercept

In the last decades, we have progressively observed an improvement in therapeutic options for metastatic colorectal cancer (mCRC) treatment with a progressive prolongation of survival. mCRC prognosis still remains poor with low percentage of 5-year survival. Targeted agents have improved results obtained with standard chemotherapy. Angiogenesis plays a crucial role in colorectal cancer growth, proliferation, and metastasization and it has been investigated as a potential target for mCRC treatment. Accordingly, novel antiangiogenic targeted agents bevacizumab, regorafenib, and aflibercept have been approved for mCRC treatment as the result of several phase III randomized trials. The development of a tumor permissive microenvironment via the aberrant expression by tumor cells of paracrine factors alters the tumor-stroma interactions inducing an expansion of proangiogenic signals. Recently, the VELOUR study showed that addition of aflibercept to FOLFIRI regimen as a second-line therapy for mCRC improved significantly OS, PFS, and RR. This molecule represents a valid second-line therapeutic option and its peculiar ability to interfere with placental growth factor (PlGF)/vascular endothelial growth factor receptor 1 (VEGFR1) axis makes it effective in targeting angiogenesis, inflammatory cells and in overcoming resistances to anti-angiogenic first-line treatment. Here, we discuss about Aflibercept peculiar ability to interfere with tumor microenvironment and angiogenic pathway.

Synthesis and evaluation of 2,4-disubstituted quinazoline derivatives with potent anti-angiogenesis activities

A series of 2,4-disubstituted quinazoline derivatives were designed and synthesized. The biological results showed that most of quinazoline derivatives exhibited potent antiproliferative activities against a panel of three tumor cell lines and a good inhibitory effect against the adhesion and migration of human umbilical vein endothelial cells (HUVECs). Among these compounds, 11d was the most potent agent, that alsoexhibited the highest anti-angiogenesis activities in the chick embryo chorioallantoic membrane (CAM) assay.

The dominant role of IL-8 as an angiogenic driver in a three-dimensional physiological tumor construct for drug testing

The induction of angiogenesis and the promotion of tumor growth and invasiveness are processes critical to metastasis, and are dependent on reciprocal interactions between tumor cells and their microenvironment. The formation of a clinically relevant tumor requires support from the surrounding stroma, and it is hypothesized that three-dimensional (3D) tumor coculture models offer a microenvironment that more closely resembles the physiological tumor microenvironment. In this study, we investigated the effects of tissue-engineered 3D architecture and tumor-stroma interaction on the angiogenic factor secretion profiles of U2OS osteosarcoma cells by coculturing the tumor cells with immortalized fibroblasts or human umbilical vein endothelial cells (HUVECs). We also carried out Transwell migration assays for U2OS cells grown in monoculture or fibroblast coculture systems to study the physiological effect of upregulated angiogenic factors on endothelial cell migration. Anti-IL-8 and anti-vascular endothelial growth factor (VEGF)-A therapies were tested out on these models to investigate the role of 3D culture and the coculture of tumor cells with immortalized fibroblasts on the efficacy of antiangiogenic treatments. The coculture of U2OS cells with immortalized fibroblasts led to the upregulation of IL-8 and VEGF-A, especially in 3D culture. Conversely, coculture with endothelial cells resulted in the downregulation of VEGF-A for cells seeded in 3D scaffolds. The migration of HUVECs through the Transwell polycarbonate inserts increased for the 3D and immortalized fibroblast coculture models, and the targeted inhibition of IL-8 greatly reduced HUVEC migration despite the presence of VEGF-A. A similar effect was not observed when anti-VEGF-A neutralizing antibody was used instead, suggesting that IL-8 plays a more critical role in endothelial cell migration than VEGF-A, with significant implications on the clinical utility of antiangiogenic therapy targeting VEGF-A.

Impaired tumor angiogenesis and VEGF-induced pathway in endothelial CD146 knockout mice

CD146 is a newly identified endothelial biomarker that has been implicated in angiogenesis. Though in vitro angiogenic function of CD146 has been extensively reported, in vivo evidence is still lacking. To address this issue, we generated endothelial-specific CD146 knockout (CD146(EC-KO)) mice using the Tg(Tek-cre) system. Surprisingly, these mice did not exhibit any apparent morphological defects in the development of normal retinal vasculature. To evaluate the role of CD146 in pathological angiogenesis, a xenograft tumor model was used. We found that both tumor volume and vascular density were significantly lower in CD146(EC-KO) mice when compared to WT littermates. Additionally, the ability for sprouting, migration and tube formation in response to VEGF treatment was impaired in endothelial cells (ECs) of CD146(EC-KO) mice. Mechanistic studies further confirmed that VEGF-induced VEGFR-2 phosphorylation and AKT/p38 MAPKs/NF-κB activation were inhibited in these CD146-null ECs, which might present the underlying cause for the observed inhibition of tumor angiogenesis in CD146(EC-KO) mice. These results suggest that CD146 plays a redundant role in physiological angiogenic processes, but becomes essential during pathological angiogenesis as observed in tumorigenesis.

Critical role of histone demethylase RBP2 in human gastric cancer angiogenesis

Background

The molecular mechanisms responsible for angiogenesis and abnormal expression of angiogenic factors in gastric cancer, including vascular endothelial growth factor (VEGF), remain unclear. The histone demethylase retinoblastoma binding protein 2 (RBP2) is involved in gastric tumorgenesis by inhibiting the expression of cyclin-dependent kinase inhibitors (CDKIs).

Methods

The expression of RBP2, VEGF, CD31, CD34 and Ki67 was assessed in 30 human gastric cancer samples and normal control samples. We used quantitative RT-PCR, western blot analysis, ELISA, tube-formation assay and colony-formation assay to characterize the change in VEGF expression and associated biological activities induced by RBP2 silencing or overexpression. Luciferase assay and ChIP were used to explore the direct regulation of RBP2 on the promoter activity of VEGF. Nude mice and RBP2-targeted mutant mice were used to detect the role of RBP2 in VEGF expression and angiogenesis in vivo.

Results

RBP2 and VEGF were both overexpressed in human gastric cancer tissue, with greater microvessel density (MVD) and cell proliferation as compared with normal tissue. In gastric epithelial cell lines, RBP2 overexpression significantly promoted the expression of VEGF and the growth and angiogenesis of the cells, while RBP2 knockdown had the reverse effect. RBP2 directly bound to the promoter of VEGF to regulate its expression by histone H3K4 demethylation. The subcutis of nude mice transfected with BGC-823 cells with RBP2 knockdown showed reduced VEGF expression and MVD, with reduced carcinogenesis and cell proliferation. In addition, the gastric epithelia of RBP2 mutant mice with increased H3K4 trimethylation showed reduced VEGF expression and MVD.

Conclusions

The promotion of gastric tumorigenesis by RBP2 was significantly associated with transactivation of VEGF expression and elevated angiogenesis. Overexpression of RBP2 and activation of VEGF might play important roles in human gastric cancer development and progression.

Differential antitumor activity of aflibercept and bevacizumab in patient-derived xenograft models of colorectal cancer

The recombinant fusion protein aflibercept (ziv-aflibercept in the United States) binds VEGF-A, VEGF-B, and placental growth factor (PlGF). The monoclonal antibody bevacizumab binds VEGF-A. Recent studies hypothesized that dual targeting of VEGF/PlGF is more beneficial than targeting either ligand. We compared activity of aflibercept versus bevacizumab in 48 patient-derived xenograft (PDX) colorectal cancer models. Nude mice engrafted subcutaneously with PDX colorectal cancer tumors received biweekly aflibercept, bevacizumab, or vehicle injections. Differential activity between aflibercept and bevacizumab, determined by mouse (m), human (h), VEGF-A, and PlGF levels in untreated tumors, was measured. Aflibercept induced complete tumor stasis in 31 of 48 models and bevacizumab in 2 of 48. Based on statistical analysis, aflibercept was more active than bevacizumab in 39 of 48 models; in 9 of 39 of these models, bevacizumab was considered inactive. In 9 of 48 remaining models, aflibercept and bevacizumab had similar activity. Tumor levels of hVEGF-A (range 776-56,039 pg/mg total protein) were ∼16- to 1,777-fold greater than mVEGF-A (range 8-159 pg/mg total protein). Tumor levels of mPlGF (range 104-1,837 pg/mg total protein) were higher than hPlGF (range 0-543 pg/mg total protein) in 47 of 48 models. Tumor cells were the major source of VEGF; PlGF was primarily produced by tumor stroma. Because tumor levels of hVEGF-A were far greater than mVEGF-A, bevacizumab's inability to bind mVEGF-A is unlikely to explain higher and more consistent aflibercept activity. Neutralizing PlGF and VEGFR-1 activation may be a factor and should be investigated in future studies. In these colorectal cancer PDX models, aflibercept demonstrated greater antitumor activity than bevacizumab.

Diffuse alveolar hemorrhage as a fatal adverse effect of bevacizumab: an autopsy case

A 71-year-old female with Stage IIIB primary adenocarcinoma was administered a three-drug combination therapy consisting of docetaxel, cisplatin and bevacizumab as a first-line treatment based on the Phase II clinical trial. On the 32nd day after the fourth course of chemotherapy, the patient developed bloody sputum. She was found dead at home on the 34th day. Autopsy revealed a diffuse alveolar hemorrhage without diffuse alveolar damage. Endothelial cells of the small arteries and capillaries were swollen and desquamated, indicating that alveolar capillaries were injured. The similar pathological changes in blood vessels were also observed in the kidney and the digestive tract. Because diffuse alveolar hemorrhage caused by cisplatin and docetaxel has never been reported apart from interstitial pneumonitis, bevacizumab is the most suspicious drug for diffuse alveolar hemorrhage in our case. Chest physicians and oncologists should be aware that although it is very rare, diffuse alveolar hemorrhage can develop during any course of chemotherapy with bevacizumab.

Norcantharidin inhibits tumor growth and vasculogenic mimicry of human gallbladder carcinomas by suppression of the PI3-K/MMPs/Ln-5γ2 signaling pathway

BACKGROUND

Vasculogenic mimicry (VM) is a novel tumor blood supply in some highly aggressive malignant tumors. Recently, we reported VM existed in gallbladder carcinomas (GBCs) and the formation of the special passage through the activation of the PI3K/MMPs/Ln-5γ2 signaling pathway. GBC is a highly aggressive malignant tumor with disappointing treatments and a poor prognosis. Norcantharidin (NCTD) has shown to have multiple antitumor activities against GBCs, etc; however the exact mechanism is not thoroughly elucidated. In this study, we firstly investigated the anti-VM activity of NCTD as a VM inhibitor for GBCs and its underlying mechanisms.

METHODS

In vitro and in vivo experiments to determine the effects of NCTD on proliferation, invasion, migration, VM formation, hemodynamic and tumor growth of GBC-SD cells and xenografts were respectively done by proliferation, invasion, migration assays, H&E staining and CD31-PAS double stainings, optic/electron microscopy, tumor assay, and dynamic micro-MRA. Further, immunohistochemistry, immunofluorescence, Western blotting and RT-PCR were respectively used to examine expression of VM signaling-related markers PI3-K, MMP-2, MT1-MMP and Ln-5γ2 in GBC-SD cells and xenografts in vitro and in vivo.

RESULTS

After treatment with NCTD, proliferation, invasion, migration of GBC-SD cells were inhibited; GBC-SD cells and xenografts were unable to form VM-like structures; tumor center-VM region of the xenografts exhibited a decreased signal in intensity; then cell or xenograft growth was inhibited. Whereas all of untreated GBC-SD cells and xenografts formed VM-like structures with the same conditions; the xenograft center-VM region exhibited a gradually increased signal; and facilitated cell or xenograft growth. Furthermore, expression of MMP-2 and MT1-MMP products from sections/supernates of 3-D matrices and the xenografts, and expression of PI3-K, MMP-2, MM1-MMP and Ln-5γ2 proteins/mRNAs of the xenografts were all decreased in NCTD or TIMP-2 group; (all P < 0.01, vs. control group); NCTD down-regulated expression of these VM signaling-related markers in vitro and in vivo.

CONCLUSIONS

NCTD inhibited tumor growth and VM of human GBCs in vitro and in vivo by suppression of the PI3-K/MMPs/Ln-5γ2 signaling pathway. It is firstly concluded that NCTD may be a potential anti-VM agent for human GBCs.

A phase I study of the human monoclonal anti-NRP1 antibody MNRP1685A in patients with advanced solid tumors

The human monoclonal antibody MNRP1685A targets the VEGF binding domain of neuropilin-1 (NRP1), a multi-domain receptor necessary for neural development and blood vessel maturation. In nonclinical studies, MNRP1685A prevents vascular maturation by keeping blood vessels in an immature, highly VEGF-dependent state. We explored the safety and tolerability of MNRP1685A in patients with advanced solid tumors. Patients were treated with MNRP1685A given intravenously every 3 weeks using a 3 + 3 dose-escalation design with 7 dose-escalation cohorts. Twenty-four of 35 patients (69 %) experienced drug-related adverse events (AEs) of infusion-related reaction on the day of MNRP1685A administration. With premedication including dexamethasone, infusions were well-tolerated with main symptoms of pruritus and rash. Outside the day of infusion, most common (≥ 2 patients) related AEs were fatigue (17 %), pruritus (9 %), myalgia and thrombocytopenia (both 6 %) (all were Grade 1-2). MNRP1685A-related Grade ≥ 3 AEs consisted of one dose-limiting toxicity of Grade 3 upper gastrointestinal bleeding and one related Grade 3 thrombocytopenia, coinciding with unrelated Grade 3 fungemia and duodenal obstruction. MNRP1685A showed nonlinear PK with more-than-dose proportional increases in exposure, consistent with broad target expression. Transient platelet count reductions (≥ 30 % from predose) were observed in 56 % of evaluable patients. Nine patients were on study for ≥ 4 cycles, one colorectal cancer patient for one year. MNRP1685A was generally well-tolerated. The primary MNRP1685A-related AE was infusion-related reaction, which were attenuated by premedication including dexamethasone. Transient platelet count reductions were frequent but did not impact MNRP1685A dosing.

Metabolic effects of antiangiogenic drugs in tumors: therapeutic implications

Antiangiogenic therapy has become a mainstay of cancer therapeutics, but clinical responses are generally short-term owing to the development of secondary resistance. Tumor starvation by antiangiogenic drugs is largely attributed to increased hypoxia and impaired nutrients supply, suggesting that angiogenesis inhibition causes remarkable metabolic perturbations in the tumor microenvironment. We review here recent acquisitions concerning metabolic effects of angiogenesis blockade in tumors and discuss the possibility that some metabolic features of tumor cells - i.e. their dependency from glucose as primary energy substrate - might affect tumor responses to anti-vascular endothelial growth factor treatment. Moreover, we discuss the hypothesis that anti-angiogenic therapy might foster metabolic evolution of tumors. The therapeutic implications of this hypothesis will be discussed further here.

Antitumor efficacy of α-solanine against pancreatic cancer in vitro and in vivo

α-solanine, a steroidal glycoalkaloid in potato, was found to have proliferation-inhibiting and apoptosis-promoting effect on multiple cancer cells, such as clone, liver, melanoma cancer cells. However, the antitumor efficacy of α-solanine on pancreatic cancer has not been fully evaluated. In this study, we inquired into the anti-carcinogenic effect of α-solanine against human pancreatic cancer cells. In the present study, we investigated the anti-carcinogenic effect of α-solanine against human pancreatic cancer cells. In vitro, α-solanine inhibited proliferation of PANC-1, sw1990, MIA PaCa-2 cells in a dose-dependent manner, as well as cell migration and invasion with atoxic doses. The expression of MMP-2/9, extracellular inducer of matrix metalloproteinase (EMMPRIN), CD44, eNOS and E-cadherin were suppressed by α-solanine in PANC-1 cells. Moreover, significantly decreased vascular endothelial growth factor (VEGF) expression and tube formation of endothelial cells were discerned following α-solanine treatment. Suppressed phosphorylation of Akt, mTOR, and Stat3, and strengthen phosphorylation of β-catenin was found, along with markedly decreased tran-nuclear of NF-κB, β-catenin and TCF-1. Following the administration of α-solanine (6 µg/g for 2 weeks) in xenograft model, tumor volume and weight were decreased by 61% and 43% (p<0.05) respectively, showing decreased MMP-2/9, PCNA and VEGF expression. In conclusion, α-solanine showed beneficial effects on pancreatic cancer in vitro and in vivo, which may via suppressing the pathway proliferation, angiogenesis and metastasis.

Activation of the glutamate receptor GRM1 enhances angiogenic signaling to drive melanoma progression

Glutamate-triggered signal transduction is thought to contribute widely to cancer pathogenesis. In melanoma, overexpression of the metabotropic glutamate receptor (GRM)-1 occurs frequently and its ectopic expression in melanocytes is sufficient for neoplastic transformation. Clinical evaluation of the GRM1 signaling inhibitor riluzole in patients with advanced melanoma has demonstrated tumor regressions that are associated with a suppression of the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathways. Together, these results prompted us to investigate the downstream consequences of GRM1 signaling and its disruption in more detail. We found that melanoma cells with enhanced GRM1 expression generated larger tumors in vivo marked by more abundant blood vessels. Media conditioned by these cells in vitro contained relatively higher concentrations of interleukin-8 and VEGF due to GRM1-mediated activation of the AKT-mTOR-HIF1 pathway. In clinical specimens from patients receiving riluzole, we confirmed an inhibition of MAPK and PI3K/AKT activation in posttreatment as compared with pretreatment tumor specimens, which exhibited a decreased density of blood vessels. Together, our results demonstrate that GRM1 activation triggers proangiogenic signaling in melanoma, offering a mechanistic rationale to design treatment strategies for the most suitable combinatorial use of GRM1 inhibitors in patients.

CUX1: a modulator of tumour aggressiveness in pancreatic neuroendocrine neoplasms

Pancreatic neuroendocrine neoplasms (PNENs) constitute a rare tumour entity, and prognosis and treatment options depend on tumour-mediating hallmarks such as angiogenesis, proliferation rate and resistance to apoptosis. The molecular pathways that determine the malignant phenotype are still insufficiently understood and this has limited the use of effective combination therapies in the past. In this study, we aimed to characterise the effect of the oncogenic transcription factor Cut homeobox 1 (CUX1) on proliferation, resistance to apoptosis and angiogenesis in murine and human PNENs. The expression and function of CUX1 were analysed using knockdown and overexpression strategies in Ins-1 and Bon-1 cells, xenograft models and a genetically engineered mouse model of insulinoma (RIP1Tag2). Regulation of angiogenesis was assessed using RNA profiling and functional tube-formation assays in HMEC-1 cells. Finally, CUX1 expression was assessed in a tissue microarray of 59 human insulinomas and correlated with clinicopathological data. CUX1 expression was upregulated during tumour progression in a time- and stage-dependent manner in the RIP1Tag2 model, and associated with pro-invasive and metastatic features of human insulinomas. Endogenous and recombinant CUX1 expression increased tumour cell proliferation, tumour growth, resistance to apoptosis, and angiogenesis in vitro and in vivo. Mechanistically, the pro-angiogenic effect of CUX1 was mediated via upregulation of effectors such as HIF1α and MMP9. CUX1 mediates an invasive pro-angiogenic phenotype and is associated with malignant behaviour in human insulinomas.

The role of vascular endothelial growth factor in metastatic prostate cancer to the skeleton

Despite the clinical implication and high incidence of bone and spinal metastases, the molecular mechanisms behind prostate cancer metastasis to bone and spine are not well understood. In this review the molecular mechanisms that may contribute to the highly metastatic phenotype of prostate cancer are discussed. Proangiogenic factors such as vascular endothelial growth factor (VEGF) have been shown to not only aid in the metastatic capabilities of prostate cancer but also encourage the colonization and growth of prostate tumour cells in the skeleton. The importance of VEGF in the complex process of prostate cancer dissemination to the skeleton is discussed, including its role in the development of the bone premetastatic niche, metastatic tumour cell recognition of bone, and bone remodeling. The expression of VEGF has also been shown to be upregulated in prostate cancer and is associated with clinical stage, Gleason score, tumour stage, progression, metastasis, and survival. Due to the multifaceted effect VEGF has on tumour angiogenesis, tumour cell proliferation, and bone destruction, therapies targeting the VEGF pathways have shown promising clinical application and are being investigated in clinical trials.

Molecularly targeted drugs for metastatic colorectal cancer

The survival rate of patients with metastatic colorectal cancer (mCRC) has significantly improved with applications of molecularly targeted drugs, such as bevacizumab, and led to a substantial improvement in the overall survival rate. These drugs are capable of specifically targeting the inherent abnormal pathways in cancer cells, which are potentially less toxic than traditional nonselective chemotherapeutics. In this review, the recent clinical information about molecularly targeted therapy for mCRC is summarized, with specific focus on several of the US Food and Drug Administration-approved molecularly targeted drugs for the treatment of mCRC in the clinic. Progression-free and overall survival in patients with mCRC was improved greatly by the addition of bevacizumab and/or cetuximab to standard chemotherapy, in either first- or second-line treatment. Aflibercept has been used in combination with folinic acid (leucovorin)-fluorouracil-irinotecan (FOLFIRI) chemotherapy in mCRC patients and among patients with mCRC with wild-type KRAS, the outcomes were significantly improved by panitumumab in combination with folinic acid (leucovorin)-fluorouracil-oxaliplatin (FOLFOX) or FOLFIRI. Because of the new preliminary studies, it has been recommended that regorafenib be used with FOLFOX or FOLFIRI as first- or second-line treatment of mCRC chemotherapy. In summary, an era of new opportunities has been opened for treatment of mCRC and/or other malignancies, resulting from the discovery of new selective targeting drugs.

Ziv-aflibercept (Zaltrap) for the treatment of metastatic colorectal cancer

OBJECTIVE

Review pharmacology, pharmacokinetics, efficacy, and safety of ziv-aflibercept in combination with FOLFIRI for treatment of metastatic colorectal cancer (mCRC) resistant to or progressed following oxaliplatin-containing regimens.

DATA SOURCES

Articles indexed in PubMed (1948-August 2013), TOXLINE (2001-August 2013), and Google Scholar as well as meeting abstracts were identified using the search terms ziv-aflibercept and colorectal cancer.

STUDY SELECTION AND DATA EXTRACTION

Available English-language articles

DATA SYNTHESIS

Ziv-aflibercept, a selective vascular endothelial growth factor antagonist, was evaluated as monotherapy for treatment of mCRC in a phase 2 study and added to FOLFIRI in a phase 3 trial. Patient response to ziv-aflibercept as monotherapy did not reach statistical significance. Results suggest that response to ziv-aflibercept treatment is not influenced by prior bevacizumab therapy. A phase 3 trial compared the safety and efficacy of ziv-aflibercept plus FOLFIRI with placebo plus FOLFIRI in patients with mCRC who experienced disease progression on an oxaliplatin-containing regimen. Patients in the ziv-aflibercept arm had a median overall survival of 13.5 months, versus 12.06 months for those receiving placebo (hazard ratio [HR] = 0.817, 95% CI = 0.713 to 0.937). Progression-free survival for patients receiving ziv-aflibercept was higher compared with placebo (HR = 0.758; 95% CI = 0.661 to 0.869). The most common adverse effects observed were anemia, diarrhea, and neutropenia.

CONCLUSIONS

Ziv-aflibercept is a safe and effective option in combination with FOLFIRI for the treatment of mCRC in patients who progress on oxaliplatin-containing therapy. Superiority over other antiangiogenic treatment has not been established.

MicroRNA 329 suppresses angiogenesis by targeting CD146

CD146, an endothelial biomarker, has been shown to be aberrantly upregulated during pathological angiogenesis and functions as a coreceptor for vascular endothelial growth factor receptor 2 (VEGFR-2) to promote disease progression. However, the regulatory mechanisms of CD146 expression during angiogenesis remain unclear. Using a microRNA screening approach, we identified a novel negative regulator of angiogenesis, microRNA 329 (miR-329), that directly targeted CD146 and inhibited CD146-mediated angiogenesis in vitro and in vivo. Endogenous miR-329 expression was downregulated by VEGF and tumor necrosis factor alpha (TNF-α), resulting in the elevation of CD146 in endothelial cells. Upregulation of CD146 facilitated an endothelial response to VEGF-induced SRC kinase family (SKF)/p38 mitogen-activated protein kinase (MAPK)/NF-κB activation and consequently promoted endothelial cell migration and tube formation. Our animal experiments showed that treatment with miR-329 repressed excessive CD146 expression on blood vessels and significantly attenuated neovascularization in a mouse model of pathological angiogenesis. Our findings provide the first evidence that CD146 expression in angiogenesis is regulated by miR-329 and suggest that miR-329 could present a potential therapeutic tool for the treatment of angiogenic diseases.

Novel VEGF decoy receptor fusion protein conbercept targeting multiple VEGF isoforms provide remarkable anti-angiogenesis effect in vivo

VEGF family factors are known to be the principal stimulators of abnormal angiogenesis, which play a fundamental role in tumor and various ocular diseases. Inhibition of VEGF is widely applied in antiangiogenic therapy. Conbercept is a novel decoy receptor protein constructed by fusing VEGF receptor 1 and VEGF receptor 2 extracellular domains with the Fc region of human immunoglobulin. In this study, we systematically evaluated the binding affinity of conbercept with VEGF isoforms and PlGF by using anti-VEGF antibody (Avastin) as reference. BIACORE and ELISA assay results indicated that conbercept could bind different VEGF-A isoforms with higher affinity than reference. Furthermore, conbercept could also bind VEGF-B and PlGF, whereas Avastin showed no binding. Oxygen-induced retinopathy model showed that conbercept could inhibit the formation of neovasularizations. In tumor-bearing nude mice, conbercept could also suppress tumor growth very effectively in vivo. Overall, our study have demonstrated that conbercept could bind with high affinity to multiple VEGF isoforms and consequently provide remarkable anti-angiogenic effect, suggesting the possibility to treat angiogenesis-related diseases such as cancer and wet AMD etc.

Targeting angiogenesis and the tumor microenvironment

The role of the microenvironment during the initiation and progression of malignancy is appreciated to be of critical importance for improved molecular diagnostics and therapeutics. The tumor microenvironment is the product of a crosstalk between different cells types. Active contribution of tumor-associated stromal cells to cancer progression has been recognized. Stromal elements consist of the extracellular matrix, fibroblasts of various phenotypes, and a scaffold comprised of immune and inflammatory cells, blood and lymph vessels, and nerves. This review focuses on therapeutic targets in the microenvironment related to tumor endothelium, tumor associated fibroblasts, and the extracellular matrix.

Epigenetic silencing of miR-126 contributes to tumor invasion and angiogenesis in colorectal cancer

microRNAs (miRNAs) have been reported to play a crucial role in regulating a variety of genes pivotal for tumor metastasis. miR-126 is well known as one of the angiogenesis regulatory miRNAs. Recent studies have reported controversial roles of miR-126 in tumor progression. In this study, we sought to investigate the potential roles of miR-126 in colorectal cancer (CRC). By real-time PCR, miR-126 was shown to be downregulated in primary CRC tissues and cell lines. Restoration of miR-126 in CRC cells inhibited cell growth, migration and invasion. Using both in silico prediction and immunoblotting, we found that vascular endothelial growth factor (VEGF) was a target of miR-126. The interaction of miR-126 on the 3'UTR of VEGF mRNA was validated by luciferase reporter assay. Mechanistically, we found that the silencing of miR-126 was induced by promoter methyl-ation of its host gene, EGFL7. Treatment with 5-aza-CdR restored miR-126 expression and thereby led to a decline in VEGF expression. Functionally, due to suppression of VEGF, enhanced miR-126 expression inhibited tumor neovasculature triggered by CRC cells. In conclusion, our findings suggest that DNA methylation-induced silencing of miR-126 contributes, at least in part, to tumor invasion and angiogenesis in CRC, through upregulation of VEGF expression. miR-126 may be a potential target for the therapeutic strategy against CRC.

Dietary compound isoliquiritigenin inhibits breast cancer neoangiogenesis via VEGF/VEGFR-2 signaling pathway

Angiogenesis is crucial for cancer initiation, development and metastasis. Identifying natural botanicals targeting angiogenesis has been paid much attention for drug discovery in recent years, with the advantage of increased safety. Isoliquiritigenin (ISL) is a dietary chalcone-type flavonoid with various anti-cancer activities. However, little is known about the anti-angiogenic activity of isoliquiritigenin and its underlying mechanisms. Herein, we found that ISL significantly inhibited the VEGF-induced proliferation of human umbilical vein endothelial cells (HUVECs) at non-toxic concentration. A series of angiogenesis processes including tube formation, invasion and migration abilities of HUVECs were also interrupted by ISL in vitro. Furthermore, ISL suppressed sprout formation from VEGF-treated aortic rings in an ex-vivo model. Molecular mechanisms study demonstrated that ISL could significantly inhibit VEGF expression in breast cancer cells via promoting HIF-1α (Hypoxia inducible factor-1α) proteasome degradation and directly interacted with VEGFR-2 to block its kinase activity. In vivo studies further showed that ISL administration could inhibit breast cancer growth and neoangiogenesis accompanying with suppressed VEGF/VEGFR-2 signaling, elevated apoptosis ratio and little toxicity effects. Molecular docking simulation indicated that ISL could stably form hydrogen bonds and aromatic interactions within the ATP-binding region of VEGFR-2. Taken together, our study shed light on the potential application of ISL as a novel natural inhibitor for cancer angiogenesis via the VEGF/VEGFR-2 pathway. Future studies of ISL for chemoprevention or chemosensitization against breast cancer are thus warranted.

Second-line therapy in advanced biliary tract cancer: what should be the standard?

Biliary tract cancer is a rare malignant tumor. Accordingly, to perform prospective and randomized trials is difficult and the knowledge of its natural history and optimal management remains limited. Chemotherapy is commonly used to improve the outcome and to delay tumor progression in advanced disease. Only recently, cisplatin-gemcitabine combination was identified as the new standard first-line therapy. Despite the outcome improvement, disease progression is a constant and approximately half of patients failing upfront treatment maintain a good performance status and are willing to undergo further treatment. No standard salvage chemotherapy regimen has been identified yet. Experiences of salvage therapy in advanced biliary tract cancer are sparse and yielded disappointing results. Well designed multi-institutional randomized trials are warranted to clarify the role and the activity of a second-line therapy.

Anti-VEGF agents in metastatic colorectal cancer (mCRC): are they all alike?

Bevacizumab is a monoclonal antibody that binds and neutralizes vascular endothelial growth factor (VEGF)-A, a key player in the angiogenesis pathway. Despite benefits of bevacizumab in cancer therapy, it is clear that the VEGF pathway is complex, involving multiple isoforms, receptors, and alternative ligands such as VEGF-B, and placental growth factor, which could enable escape from VEGF-A-targeted angiogenesis inhibition. Recently developed therapies have targeted other ligands in the VEGF pathway (eg, aflibercept, known as ziv-aflibercept in the United States), VEGF receptors (eg, ramucirumab), and their tyrosine kinase signaling (ie, tyrosine kinase inhibitors). The goal of the current review was to identify comparative preclinical data for the currently available VEGF-targeted therapies. Sources were compiled using PubMed searches (2007 to 2012), using search terms including, but not limited to: “bevacizumab,” “aflibercept,” “ramucirumab,” and “IMC-18F1.” Two preclinical studies were identified that compared bevacizumab and the newer agent, aflibercept. These studies identified some important differences in binding and pharmacodynamic activity, although the potential clinical relevance of these findings is not known. Newer antiangiogenesis therapies should help further expand treatment options for colorectal and other cancers. Comparative preclinical data on these agents is currently lacking.

A phase II trial of frontline capecitabine and bevacizumab in poor performance status and/or elderly patients with metastatic colorectal cancer

OBJECTIVES

This study aims to determine the efficacy and tolerability of capecitabine (CAP) plus bevacizumab (BEV) as treatment for frontline metastatic colorectal cancer (mCRC) in frail and/or elderly patients.

MATERIALS AND METHODS

This was an open label, multi-site, single arm, phase II study in frontline mCRC. In this study, patients (pts) who were frail (ECOG 2) or older patients with ECOG 1 performance status (PS) received CAP (1000 mg/m(2) bid, 14 days of every 21 days) plus BEV (7.5mg/kg iv once every 21 days). The primary objective was progression free survival (PFS). Secondary objectives were overall response rate (ORR) and toxicity.

RESULTS

In terms of patients: 50 were enrolled; 5 withdrew consent prior to treatment; 45 were treated, and 41 were evaluable. The mean age was 75.9 (range 54-93) and 62% had an ECOG 2 PS. The median PFS was 6.87 months (95% CI, 5.1-11.5 months) and median overall survival was 12.7 months (95% CI, 6.9-12.7 months). The most common grades 3-4 toxicities were: diarrhea (17.8%), fatigue (13.3%), hand-foot syndrome (13.3%), dehydration (8.9%), hypertension (6.7%) and vomiting (6.7%).

CONCLUSIONS

The results of this trial support the use of CAP plus BEV as first-line treatment for frail/elderly patients with metastatic CRC. The ORR (40%) is comparable to pooled data in elderly on fluorouracil (5-FU)+BEV. The median PFS (7.2 months) in this study is slightly lower than that seen with 5-FU+BEV but this study had a high percentage of ECOG PS 2 patients. Side effects were manageable with no new safety signals.

Role of activated Rac1/Cdc42 in mediating endothelial cell proliferation and tumor angiogenesis in breast cancer

Angiogenesis is a well-established target in anti-cancer therapy. Although vascular endothelial growth factor (VEGF)-mediated angiogenesis apparently requires the Rho GTPases Rac1 and Cdc42, the relevant mechanisms are unclear. Here, we determined that activated Rac1/Cdc42 in MCF-7 breast cancer cells could decrease p53 protein levels and increase VEGF secretion to promote proliferation and tube formation of human umbilical vein endothelial cells (HUVECs). However, these effects are reversed after ubiquitin-proteasome breakage. In exploring potential mechanisms for this relationship, we confirmed that activated Rac1/Cdc42 could enhance p53 protein ubiquitination and weaken p53 protein stability to increase VEGF expression. Furthermore, in a xenograft model using nude mice that stably express active Rac1/Cdc42 protein, active Rac1/Cdc42 decreased p53 levels and increased VEGF expression. Additionally, tumor angiogenesis was inhibited, and p53 protein levels were augmented, by intratumoral injection of the ubiquitin-proteasome inhibitor MG132. Finally in 339 human breast cancer tissues, our analyses indicated that Rac1/Cdc42 expression was related to advanced TNM staging, high proliferation index, ER status, and positive invasive features. In particular, our data suggests that high Rac1/Cdc42 expression is correlated with low wt-p53 and high VEGF expression. We conclude that activated Rac1/Cdc42 is a vascular regulator of tumor angiogenesis and that it may reduce stability of the p53 protein to promote VEGF expression by enhancing p53 protein ubiquitin.

Adverse events associated with antiangiogenic agents in combination with cytotoxic chemotherapy in metastatic colorectal cancer and their management

Colorectal cancer (CRC) is the third most common cancer in men and women, and, despite advances in detection and treatment that result in a steadily decreasing incidence and mortality, remains a leading cause of death. The 5-year survival rate of persons with metastatic CRC (mCRC) is only 12%. With the recognition of vascularity as an important factor in tumor proliferation and growth, targeting angiogenesis pathways has been a major focus of research. The addition of bevacizumab, an inhibitor of the vascular endothelial growth factor (VEGF) pathway, to cytotoxic chemotherapy has improved response rates and survival of patients with mCRC. Aflibercept, a potent new multiple angiogenic factor trap that prevents not only VEGF-A but also VEGF-B and placental growth factor from activating their native receptors, has demonstrated efficacy in previously treated patients with mCRC. Phase I/II clinical trials and, more recently, a phase III clinical trial, have demonstrated effective antiangiogenic and cytotoxic activity with acceptable safety and tolerability. As is the case with bevacizumab, the optimal use of aflibercept requires appropriate management of the associated anti-VEGF adverse events and those associated with its use in combination with chemotherapy. These adverse events have previously been observed and are generally manageable with appropriate therapeutic intervention.

Arginase II expressed in cancer-associated fibroblasts indicates tissue hypoxia and predicts poor outcome in patients with pancreatic cancer

An adequate level of arginine in the tissue microenvironment is essential for T cell activity and survival. Arginine levels are regulated by the arginine-catabolizing enzyme, arginase (ARG). It has been reported that arginase II (ARG2), one of two ARGs, is aberrantly expressed in prostate cancer cells, which convert arginine into ornithine, resulting in a lack of arginine that weakens tumor-infiltrating lymphocytes and renders them dysfunctional. However, immune suppression mediated by ARG2-expressing cancer cells in lung cancer has not been observed. Here we studied the expression of ARG2 in pancreatic ductal carcinoma (PDC) tissue clinicopathologically by examining over 200 cases of PDC. In contrast to prostate cancer, ARG2 expression was rarely demonstrated in PDC cells by immunohistochemistry, and instead ARG2 was characteristically expressed in α-smooth muscle actin-positive cancer-associated fibroblasts (CAFs), especially those located within and around necrotic areas in PDC. The presence of ARG2-expressing CAFs was closely correlated with shorter overall survival (OS; P  = 0.003) and disease-free survival (DFS; P  = 0.0006). Multivariate Cox regression analysis showed that the presence of ARG2-expressing CAFs in PDC tissue was an independent predictor of poorer OS (hazard ratio [HR]  = 1.582, P  = 0.007) and DFS (HR  = 1.715, P  = 0.001) in PDC patients. In addition to the characteristic distribution of ARG2-expressing CAFs, such CAFs co-expressed carbonic anhydrase IX, SLC2A1, or HIF-1α, markers of hypoxia, in PDC tissue. Furthermore, in vitro experiments revealed that cultured fibroblasts extracted from PDC tissue expressed the ARG2 transcript after exposure to hypoxia, which had arginase activity. These results indicate that cancer cell-mediated immune suppression through ARG2 expression is not a general event and that the presence of ARG2-expressing CAFs is an indicator of poor prognosis, as well as hypoxia, in PDC tissue.

Mesenchymal stem cell-derived interleukin-6 and vascular endothelial growth factor promote breast cancer cell migration

Several different cytokines and growth factors secreted by mesenchymal stem cells (MSCs) have been hypothesized to play a role in breast cancer progression. By using a small panel of breast cancer cell lines (MCF-7, T47D, and SK-Br-3 cells), we analyzed the role of interleukin-6 (IL-6) and vascular endothelial growth factor A (VEGF) in the cross-talk between MSCs and breast cancer cells. We performed migration assays in which breast cancer cells were allowed to migrate in response to conditioned medium from MSCs (MSCs-CM), in absence or in presence of the anti-VEGF antibody bevacizumab or an anti-IL-6 antibody, alone or in combination. We found that anti-VEGF and anti-IL-6 antibodies inhibited the migration of breast cancer cells and that the combination had an higher inhibitory effect. We next evaluated the effects of recombinant VEGF and IL-6 proteins on breast cancer cell growth and migration. IL-6 and VEGF had not significant effects on the proliferation of breast carcinoma cells. In contrast, both VEGF and IL-6 significantly increased the ability to migrate of MCF-7, T47D and SK-Br-3 cells, with the combination showing a greater effect as compared with treatment with a single protein. The combination of VEGF and IL-6 produced in breast cancer cells a more significant and more persistent activation of MAPK, AKT, and p38MAPK intracellular signaling pathways. These results suggest that MSC-secreted IL-6 and VEGF may act as paracrine factors to sustain breast cancer cell migration.

p55PIK-PI3K stimulates angiogenesis in colorectal cancer cell by activating NF-κB pathway

Vascular growth factor (VEGF) is an important mediator of angiogenesis. PI3K plays essential roles in angiogenesis; however, the mechanisms and specific functions of individual isoforms of PI3K members in tumor angiogenesis regulation are still not fully understood. In this study, we evaluate the role of p55PIK, a PI3K regulatory subunit encoded by PIK3R3 gene, in tumor angiogenesis. We reported that overexpression of p55PIK in cancer cells up-regulated HIF-1α expression and increased VEGF expression. Furthermore, overexpression of p55PIK increased tumor angiogenesis in vivo and in vitro. Moreover, data indicated enhanced HIF-1α expression by p55PIK-PI3K depended on its ability to activate NF-кB signaling pathways, especially to increase the phosphorylation of p65 subunits of NF-κB. Our study suggested that p55PIK-PI3K was essential in regulating cancer cell-mediated angiogenesis and contributed to tumor growth and that the p55PIK provides a potential and specific target for new anti-angiogenesis drug development.

Molecular Biomarkers of Response to Antiangiogenic Therapy for Cancer

Antiangiogenic therapy for cancer has gone from an intriguing hypothesis in the 1970s to an accepted treatment approach for many cancer types. It has also become a standard of care for certain eye diseases. Yet, despite the use of molecularly targeted drugs with well defined targets, to date there are no biomarkers to guide the use of antiangiogenic therapy in patients. The mechanisms of action of these drugs are also being debated. This paper discusses some of the emerging biomarker candidates for this type of cancer therapy, which have provided mechanistic insight and might be useful in the future for optimizing cancer treatment.

Deletion of tetraspanin CD9 diminishes lymphangiogenesis in vivo and in vitro

Tetraspanins have emerged as key players in malignancy and inflammatory diseases, yet little is known about their roles in angiogenesis, and nothing is known about their involvement in lymphangiogenesis. We found here that tetraspanins are abundantly expressed in human lymphatic endothelial cells (LEC). After intrathoracic tumor implantation, metastasis to lymph nodes was diminished and accompanied by decreased angiogenesis and lymphangiogenesis in tetraspanin CD9-KO mice. Moreover, lymphangiomas induced in CD9-KO mice were less pronounced with decreased lymphangiogenesis compared with those in wild-type mice. Although mouse LEC isolated from CD9-KO mice showed normal adhesion, lymphangiogenesis was markedly impaired in several assays (migration, proliferation, and cable formation) in vitro and in the lymphatic ring assay ex vivo. Consistent with these findings in mouse LEC, knocking down CD9 in human LEC also produced decreased migration, proliferation, and cable formation. Immunoprecipitation analysis demonstrated that deletion of CD9 in LEC diminished formation of functional complexes between VEGF receptor-3 and integrins (α5 and α9). Therefore, knocking down CD9 in LEC attenuated VEGF receptor-3 signaling, as well as downstream signaling such as Erk and p38 upon VEGF-C stimulation. Finally, double deletion of CD9/CD81 in mice caused abnormal development of lymphatic vasculature in the trachea and diaphragm, suggesting that CD9 and a closely related tetraspanin CD81 coordinately play an essential role in physiological lymphangiogenesis. In conclusion, tetraspanin CD9 modulates molecular organization of integrins in LEC, thereby supporting several functions required for lymphangiogenesis.

The VEGF pathway in cancer and disease: responses, resistance, and the path forward

Antiangiogenesis was proposed as a novel target for the treatment of cancer 40 years ago. Since the original hypothesis put forward by Judah Folkman in 1971, factors that mediate angiogenesis, their cellular targets, many of the pathways they signal, and inhibitors of the cytokines and receptors have been identified. Vascular endothelial growth factor (VEGF) is the most prominent among the angiogenic cytokines and is believed to play a central role in the process of neovascularization, both in cancer as well as other inflammatory diseases. This article reviews the biology of VEGF and its receptors, the use of anti-VEGF approaches in clinical disease, the toxicity of these therapies, and the resistance mechanisms that have limited the activity of these agents when used as monotherapy.

Antiangiogenesis therapy in the treatment of metastatic colorectal cancer

The process of new blood vessel formation, or angiogenesis, has become an important target for therapeutic intervention in many cancers, including metastatic colorectal cancer (mCRC). The growth and metastasis of primary tumors is dependent upon their ability to acquire and maintain an adequate blood supply; however, angiogenesis in tumors is an irregular process leading to chaotic and hyperpermeable vessels that may result in increased intratumoral pressure and poor exchange of macromolecules and oxygen. It has been hypothesized that inhibition of angiogenesis in tumors can both impair the formation of new tumor blood vessels and possibly 'normalize' the existing tumor vasculature, causing a more efficient delivery of cytotoxic chemotherapies (CTs). Over the last decade, therapies that target vascular endothelial growth factor (VEGF) have become a component of treatment for several cancers. In particular, the combination of bevacizumab with established chemotherapeutic regimens for mCRC has been shown to improve overall and progression-free survival, as well as response rates, over CT alone. Agents that target various members of the VEGF family, as well as signaling by the VEGF receptors and their tyrosine kinase components, are currently under development and evaluation in clinical trials. Integration of these new therapies into the treatment of mCRC will ultimately increase the available therapeutic options for patients. Still, many challenges remain, including identifying and validating relevant biomarkers to guide the optimal use of antiangiogenesis agents.

Are epsins a therapeutic target for tumor angiogenesis?

Solid tumor growth requires the formation of new blood vessels to supply nutrients and oxygen to the malignant cells; one approach to cancer therapy is to block this process by inhibiting VEGF signaling. In this issue of the JCI, Pasula et al. demonstrate a surprising role of epsins--proteins involved in endocytosis--in tumor angiogenesis via their modulation of VEGF signaling. Their findings suggest that these proteins might represent a new target for the development of cancer therapeutics.

Tumor vessel-injuring ability improves antitumor effect of cytotoxic T lymphocytes in adoptive immunotherapy

Angiogenesis is required for normal physiologic processes, but it is also involved in tumor growth, progression and metastasis. Here, we report the development of an immune-based antiangiogenic strategy based on the generation of T lymphocytes that possess killing specificity for cells expressing vascular endothelial growth factor receptor 2 (VEGFR2). To target VEGFR2-expressing cells, we engineered cytotoxic T lymphocyte (CTL) expressing chimeric T-cell receptors (cTCR-CTL) comprised of a single-chain variable fragment (scFv) against VEGFR2 linked to an intracellular signaling sequence derived from the CD3ζ chain of the TCR and CD28 by retroviral gene transduction methods. The cTCR-CTL exhibited efficient killing specificity against VEGFR2 and a tumor-targeting function in vitro and in vivo. Reflecting such abilities, we confirmed that the cTCR-CTL strongly inhibited the growth of a variety of syngeneic tumors after adoptive transfer into tumor-bearing mice without consequent damage to normal tissue. In addition, CTL expressing both cTCR and tumor-specific TCR induced complete tumor regression due to enhanced tumor infiltration by the CTL and long-term antigen-specific function. These findings provide evidence that the tumor vessel-injuring ability improved the antitumor effect of CTLs in adoptive immunotherapy for a broad range of cancers by inducing immune-mediated destruction of the tumor neovasculature.

A complex of α6 integrin and E-cadherin drives liver metastasis of colorectal cancer cells through hepatic angiopoietin-like 6

Homing of colorectal cancer (CRC) cells to the liver is a non-random process driven by a crosstalk between tumour cells and components of the host tissue. Here we report the isolation of a liver metastasis-specific peptide ligand (CGIYRLRSC) that binds a complex of E-cadherin and α(6) integrin on the surface of CRC cells. We identify angiopoietin-like 6 protein as a peptide-mimicked natural ligand enriched in hepatic blood vessels of CRC patients. We demonstrate that an interaction between hepatic angiopoietin-like 6 and tumoural α(6) integrin/E-cadherin drives liver homing and colonization by CRC cells, and that CGIYRLRSC inhibits liver metastasis through interference with this ligand/receptor system. Our results indicate a mechanism for metastasis whereby a soluble factor accumulated in normal vessels functions as a specific ligand for circulating cancer cells. Consistently, we show that high amounts of coexpressed α(6) integrin and E-cadherin in primary tumours represent a poor prognostic factor for patients with advanced CRC.

The vascular disrupting agent STA-9584 exhibits potent antitumor activity by selectively targeting microvasculature at both the center and periphery of tumors

Vascular disrupting agents (VDAs) are an emerging class of therapeutics targeting the existing vascular network of solid tumors. However, their clinical progression has been hampered because of limited single-agent efficacy, primarily caused by the persistence of surviving cells at the well perfused "viable rim" of tumors, which allows rapid tumor regrowth to occur. In addition, off-target adverse events, including cardiovascular toxicities, underscore a need for compounds with improved safety profiles. Here, we characterize the mechanism of action, antitumor efficacy, and cardiovascular safety profile of (S)-2-amino-N-(2-methoxy-5-(5-(3,4,5-trimethoxyphenyl)isoxazol-4-yl)phenyl)-3-phenylpropanamide hydrochloride (STA-9584), a novel tubulin-binding VDA. In vitro, 2-methoxy-5-(5-(3,4,5-trimethoxyphenyl)isoxazol-4-yl)aniline (STA-9122) (active metabolite of STA-9584) displayed increased potency relative to other tubulin-binding agents and was highly cytotoxic to tumor cells. STA-9584 induced significant tumor regressions in prostate and breast xenograft models in vivo and, in an aggressive syngeneic model, demonstrated superior tumor growth inhibition and a positive therapeutic index relative to combretastatin A-4 phosphate (CA4P). It is noteworthy that histological analysis revealed that STA-9584 disrupted microvasculature at both the center and periphery of tumors. Compared with CA4P, STA-9584 induced a 73% increase in central necrotic area, 77% decrease in microvasculature, and 7-fold increase in tumor cell apoptosis in the remaining viable rim 24 h post-treatment. Ultrasound imaging confirmed that STA-9584 rapidly and efficiently blocked blood flow in highly perfused tumor regions. Moreover, cardiovascular effects were evaluated in the Langendorff assay and telemetered dogs, and cardiovascular toxicity was not predicted to be dose-limiting. This bioactivity profile distinguishes STA-9584 from the combretastatin class and identifies the compound as a promising new therapeutic VDA candidate.

Targeted therapy for metastatic colorectal cancer: role of aflibercept

Worldwide, colorectal cancer (CRC) is the third most commonly diagnosed cancer in male individuals and the second most commonly diagnosed cancer in female individuals. Survival outcomes are less than optimal for patients with metastatic disease, with a 5-year survival in the 5% to 8% range. The development of new chemotherapeutic agents and effective combination regimens for metastatic colorectal cancer (mCRC) has increased median overall survival (OS) to the 24- to 28-month range. Because of the recognition that vascular endothelial growth factors (VEGFs) and their receptors are primary regulators of physiologic and pathologic angiogenesis and lymphangiogenesis, leading to neovascularization and tumor growth, the targeting of the angiogenic pathway has become a focus of key therapeutic strategies in mCRC. Therapeutic regimens that include bevacizumab, an inhibitor of VEGF-A, in combination with cytotoxic chemotherapy, have resulted in improved response rate (RR) and survival in mCRC. However, the effects of VEGF-A inhibition are often temporary, with resistance and disease progression developing in most patients. Proposed models include intrinsic and adaptive resistance, mediated by factors other than VEGF-A. Aflibercept (known as ziv-aflibercept in the United States; Zaltrap®, Regeneron Pharmaceuticals; sanofi-aventis), a novel recombinant fusion protein, is an angiogenic factor trap that blocks the binding of VEGF-A, VEGF-B, and placental growth factor. Phase I/II clinical trials have demonstrated effective activity in mCRC, with acceptable safety and tolerability. A recent phase III randomized double-blind trial in patients previously treated with oxaliplatin reported significant improvement in OS, progression-free survival (PFS), and RR with aflibercept compared with placebo when administered in combination with irinotecan and fluorouracil. Adverse events were consistent with anti-VEGF therapy. Thus aflibercept represents a potential new treatment option for patients with mCRC.

Linking systemic angiogenic factors (VEGF, angiogenin, TIMP-2) and Doppler ultrasound to anti-inflammatory treatment in rheumatoid arthritis

OBJECTIVE

To evaluate an association between synovial Doppler flow and serum levels of vascular endothelial growth factor (VEGF), angiogenin and TIMP-2 in patients with rheumatoid arthritis during anti-inflammatory treatment with glucocorticoids and TNF-α inhibitors.

METHODS

Inflamed wrists of 15 patients with rheumatoid arthritis (RA) were examined by two independent ultrasound investigators prior to and at days 3, 7, 14 and 42 after the initiation of treatment with glucocorticoids in therapy-naïve patients or after the beginning of a therapy with a TNF-α inhibitor in patients with DMARD failure. Quantitative three-dimensional power Doppler ultrasonographic assessment of synovial vascularization was compared at each visit with serum levels of VEGF, angiogenin and TIMP-2.

RESULTS

In the glucocorticoid group, synovial Doppler signals decreased significantly at day 3 (-44%; P=0.003) in comparison to a delayed decrease in the TNF-α inhibitor group after 6 weeks (-46%; P=0.001). A significant reduction of serum VEGF levels could be determined with a delay of 1 week after the decrease of Doppler activity but no correlation was found between both parameters (rho: P=0.7; r=-0.03). Angiogenin concentrations decreased in the TNF group and increased in the GC group. Levels of TIMP-2 did not change significantly in both groups.

CONCLUSION

The decrease of serum VEGF levels under treatment with glucocorticoids or TNF-α inhibitors followed the reduction of the intra-articular synovial Doppler flow. This result supports the idea that the reduction of synovial perfusion due to anti-inflammatory treatment is not regulated by systemic VEGF, but that the inflamed joints are the source for circulating VEGF.

β-Catenin and peroxisome proliferator-activated receptor-δ coordinate dynamic chromatin loops for the transcription of vascular endothelial growth factor A gene in colon cancer cells

Vascular endothelial growth factor A (VEGFA) mRNA is regulated by β-catenin and peroxisome proliferator activated receptor δ (PPAR-δ) activation in colon cancer cells, but the detailed mechanism remains to be elucidated. As chromatin loops are generally hubs for transcription factors, we tested here whether β-catenin could modulate chromatin looping near the VEGFA gene and play any important role for PPAR-δ activated VEGFA transcription. First, we identified the far upstream site as an important site for VEGFA transcription by luciferase assay and chromatin immunoprecipitation in colorectal carcinoma HCT116 cells. Chromatin conformation capture analysis also revealed the chromatin loops formed by the β-catenin bindings on these sites near the VEGFA gene. Dynamic association and dissociation of β-catenin/TCF-4/PPAR-δ on the far upstream site and β-catenin/NF-κB p65 on the downstream site were also detected depending on PPAR-δ activation. Interestingly, β-catenin-mediated chromatin loops were relieved by PPAR-δ activation, suggesting a regulatory role of β-catenin for VEGFA transcription. Based on these data, we propose a model for PPAR-δ-activated VEGFA transcription that relies on β-catenin-mediated chromatin looping as a prerequisite for the activation. Our findings could extend to other β-catenin regulated target genes and could provide a general mechanism and novel paradigm for β-catenin-mediated oncogenesis.

CD146 is a coreceptor for VEGFR-2 in tumor angiogenesis

CD146 is a novel endothelial biomarker and plays an essential role in angiogenesis; however, its role in the molecular mechanism underlying angiogenesis remains poorly understood. In the present study, we show that CD146 interacts directly with VEGFR-2 on endothelial cells and at the molecular level and identify the structural basis of CD146 binding to VEGFR-2. In addition, we show that CD146 is required in VEGF-induced VEGFR-2 phosphorylation, AKT/p38 MAPKs/NF-κB activation, and thus promotion of endothelial cell migration and microvascular formation. Furthermore, we show that anti-CD146 AA98 or CD146 siRNA abrogates all VEGFR-2 activation induced by VEGF. An in vivo angiogenesis assay showed that VEGF-promoted microvascular formation was impaired in the endothelial conditional knockout of CD146 (CD146(EC-KO)). Our animal experiments demonstrated that anti-CD146 (AA98) and anti-VEGF (bevacizumab) have an additive inhibitory effect on xenografted human pancreatic and melanoma tumors. The results of the present study suggest that CD146 is a new coreceptor for VEGFR-2 and is therefore a promising target for blocking tumor-related angiogenesis.