Therapeutic implications of intrinsic or induced angiogenic growth factor redundancy in tumors revealed

Matrix stiffness in regulation of tumor angiogenesis

Angiogenesis is one of the most common malignant features of solid tumors such as liver cancer, pancreatic cancer, and gastrointestinal tumors, which is the basis of tumor growth, invasion, and metastasis. It is also an important target of anti-tumor therapy. Tumor angiogenesis is usually triggered by biochemical, hypoxic, and biomechanical factors in the microenvironment. The regulation of biochemical signals and hypoxic microenvironment in tumor angiogenesis have been widely documented, but the role of biomechanical signals in tumor angiogenesis has gradually begun to be uncovered in recent years. The vasculature system is naturally sensitive to mechanical stimuli. Recent studies have highlighted the important regulatory effects of biomechanical stimuli, such as matrix stiffness, fluid shear stress, and vascular lumen pressure, on the phenotype and functions of tumor blood vessels. In this paper, we summarize the new progress and internal mechanisms of matrix stiffness-mediated effects on tumor angiogenesis.

Apatinib in Patients with Relapsed or Refractory Diffuse Large B Cell Lymphoma: A Phase II, Open-Label, Single-Arm, Prospective Study

Purpose

Treatment options for relapsed or refractory diffuse large B-cell lymphoma (RR DLBCL) represent an unmet medical need. Apatinib is a new oral tyrosine kinase inhibitor mainly targeting vascular endothelial growth factor receptor-2 (VEGFR-2) to inhibit tumour angiogenesis. In the present study, we evaluated the efficacy and safety of apatinib for patients with RR DLBCL.

Patients and Methods

In this phase II, open-label, single-arm, prospective study, we enrolled patients aged 14–70 years with treatment failure of at least two chemotherapeutic regimens using Simon’s two-stage design. All patients were administered apatinib at an initial dose of 500 mg on a 4-week cycle at home and visited the outpatient clinic every two cycles to evaluate efficacy and to record adverse events. We considered objective response rate (ORR) as the primary end point, and progression-free survival (PFS), and overall survival (OS) plus duration of response (DoR) as the secondary end point. (This trial was registered at ClinicalTrials.gov, identifier: NCT03376958.).

Results

From January 2017 to February 2019, we screened 35 patients and enrolled 32 eligible patients. At the cutoff point (April 2019), we noted 2 (6.3%) complete responses, 12 (37.5%) partial responses, and 9 (28.1%) stable diseases, attributing to an ORR of 43.8% and a disease control rate of 71.9%. The median PFS and OS were 6.9 (95% confidence interval [CI], 5.8–7.9) and 7.9 months (95% CI, 7.0–8.7), respectively. The median DoR was 5.0 months (95% CI, 3.5–6.5) for patients who achieved PR. The most common grade 3–4 adverse events (AE) were hypertension (12.6%), hand–foot syndrome (9.4%), and leucopenia (6.3%). No apatinib-related deaths were noted.

Conclusion

Home administration of apatinib shows promising efficacy and manageable AEs in patients with RR DLBCL.

Synergy Between Low Dose Metronomic Chemotherapy and the pH-centered Approach Against Cancer

Low dose metronomic chemotherapy (MC) is becoming a mainstream treatment for cancer in veterinary medicine. Its mechanism of action is anti-angiogenesis by lowering vascular endothelial growth factor (VEGF) and increasing trombospondin-1 (TSP1). It has also been adopted as a compassionate treatment in very advanced human cancer. However, one of the main limitations of this therapy is its short-term effectiveness: 6 to 12 months, after which resistance develops. pH-centered cancer treatment (pHT) has been proposed as a complementary therapy in cancer, but it has not been adopted or tested as a mainstream protocol, in spite of existing evidence of its advantages and benefits. Many of the factors directly or indirectly involved in MC and anti-angiogenic treatment resistance are appropriately antagonized by pHT. This led to the testing of an association between these two treatments. Preliminary evidence indicates that the association of MC and pHT has the ability to reduce anti-angiogenic treatment limitations and develop synergistic anti-cancer effects. This review will describe each of these treatments and will analyze the fundamentals of their synergy.

Phase II evaluation of dalantercept in the treatment of persistent or recurrent epithelial ovarian cancer: An NRG Oncology/Gynecologic Oncology Group study

OBJECTIVE

To determine the efficacy of dalantercept, a soluble ALK1 inhibitor receptor fusion protein, in patients with persistent or recurrent ovarian carcinoma and related malignancies.

METHODS

Eligibility criteria included measurable disease, 1-2 prior cytotoxic regimens and GOG performance status (PS) ≤2. Dalantercept was administered subcutaneously at 1.2 mg/kg every 3 weeks until disease progression or development of unacceptable toxicity. The primary null hypothesis was the probability of response ≤0.10 and the probability of 6-month progression-free survival without receipt of non-protocol therapy (event-free survival at 6 months, EFS6) ≤0.15, using RECIST 1.1 criteria.

RESULTS

The first stage was closed after enrollment of 30 participants with median age of 56.5 years, high-grade serous histology in 76.7%, 2 prior regimens in 46.7%, and platinum-free interval <6 months in 73.3%. All participants discontinued dalantercept, 24 (80.0%), 5 (16.7%) and 1 (3.3%) due to progression, toxicity, and other reason, respectively. The median number of treatment cycles per patient was 2 (range 1-29). There were six treatment-related grade 3 AEs and no grade ≥4 AEs. There were no objective responses. EFS6 was reached in 20% (6 out of 30 participants, 90% CI 9.1% to 35.7%).

CONCLUSIONS

Though safe, dalantercept as administered had limited efficacy in this patient population overall.

Pharmacologic or Genetic Targeting of Glutamine Synthetase Skews Macrophages toward an M1-like Phenotype and Inhibits Tumor Metastasis

Glutamine-synthetase (GS), the glutamine-synthesizing enzyme from glutamate, controls important events, including the release of inflammatory mediators, mammalian target of rapamycin (mTOR) activation, and autophagy. However, its role in macrophages remains elusive. We report that pharmacologic inhibition of GS skews M2-polarized macrophages toward the M1-like phenotype, characterized by reduced intracellular glutamine and increased succinate with enhanced glucose flux through glycolysis, which could be partly related to HIF1α activation. As a result of these metabolic changes and HIF1α accumulation, GS-inhibited macrophages display an increased capacity to induce T cell recruitment, reduced T cell suppressive potential, and an impaired ability to foster endothelial cell branching or cancer cell motility. Genetic deletion of macrophagic GS in tumor-bearing mice promotes tumor vessel pruning, vascular normalization, accumulation of cytotoxic T cells, and metastasis inhibition. These data identify GS activity as mediator of the proangiogenic, immunosuppressive, and pro-metastatic function of M2-like macrophages and highlight the possibility of targeting this enzyme in the treatment of cancer metastasis.

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GS expression and activity are induced by M2 stimuli, especially under starvation

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Inhibition of GS activity skews M2 macrophages toward an M1-like phenotype

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Metabolic rewiring by GS loss favors immunostimulatory and antiangiogenic features

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GS ablation in macrophages blocks vessels, immunosuppression, and metastasis

Targeting tumor-infiltrating Ly6G+ myeloid cells improves sorafenib efficacy in mouse orthotopic hepatocellular carcinoma

Sorafenib, a multikinase inhibitor with antiangiogenic activity, is an approved therapy for hepatocellular carcinoma (HCC). It is unclear whether the proinflammatory and immunosuppressive mechanisms may limit the therapeutic efficacy of sorafenib in HCC. We used a syngeneic mouse liver cancer cell line to establish orthotopic liver or subcutaneous tumors to study how proinflammatory and immunosuppressive mechanisms impact on the efficacy of sorafenib. We found sorafenib exhibited a potent therapeutic effect in subcutaneous tumors, but a less potent effect in orthotopic liver tumors. The protein levels of interleukin-6 (IL-6) and vascular endothelial growth factor A (VEGF-A) were persistently elevated in orthotopic liver tumors, but not in subcutaneous tumors, treated with sorafenib. Likewise, the tumor-infiltrating Ly6G⁺ myeloid-derived suppressor cells (MDSCs) and immune suppressors were increased in orthotopic liver tumors, not in subcutaneous tumors, treated with sorafenib. The tumor-infiltrating Ly6G⁺ MDSCs of sorafenib-treated orthotopic liver tumors significantly induced IL-10 and TGF-β expressing CD4⁺ T cells, and downregulated the cytotoxic activity of CD8⁺ T cells. IL-6, but not VEGF-A, protected Ly6G⁺ MDSCs from sorafenib-induced cell death in vitro. The combination of anti-Ly6G antibody or anti-IL-6 antibody with sorafenib significantly reduced the cell proportion of Ly6G⁺ MDSCs in orthotopic liver tumors, enhanced the T cells proliferation and improved the therapeutic effect of sorafenib synergistically. Modulating tumor microenvironment through targeting tumor-infiltrating Ly6G⁺ MDSCs represents a potential strategy to improve the anti-HCC efficacy of sorafenib.

2-(&#969;-Carboxyethyl)pyrrole Antibody as a New Inhibitor of Tumor Angiogenesis and Growth

BACKGROUND

Angiogenesis is a fundamental process in the progression, invasion, and metastasis of tumors. Therapeutic drugs such as bevacizumab and ranibuzumab have thus been developed to inhibit vascular endothelial growth factor (VEFG)-promoted angiogenesis. While these anti-angiogenic drugs have been commonly used in the treatment of cancer, patients often develop significant resistance that limits the efficacy of anti-VEGF therapies to a short period of time. This is in part due to the fact that an independent pathway of angiogenesis exists, which is mediated by 2-(ω-carboxyethyl)pyrrole (CEP) in a TLR2 receptor-dependent manner that can compensate for inhibition of the VEGF-mediated pathway.

AIMS

In this work, we evaluated a CEP antibody as a new tumor growth inhibitor that blocks CEP-induced angiogenesis.

METHOD

We first evaluated the effectiveness of a CEP antibody as a monotherapy to impede tumor growth in two human tumor xenograft models. We then determined the synergistic effects of bevacizumab and CEP antibody in a combination therapy, which demonstrated that blocking of the CEP-mediated pathway significantly enhanced the anti-angiogenic efficacy of bevacizumab in tumor growth inhibition indicating that CEP antibody is a promising chemotherapeutic drug. To facilitate potential translational studies of CEP-antibody, we also conducted longitudinal imaging studies and identified that FMISO-PET is a non-invasive imaging tool that can be used to quantitatively monitor the anti-angiogenic effects of CEP-antibody in the clinical setting.

RESULTS

That treatment with CEP antibody induces hypoxia in tumor tissue WHICH was indicated by 43% higher uptake of [18F]FMISO in CEP antibody-treated tumor xenografs than in the control PBS-treated littermates.

Angiogenesis and Metabolism: Entwined for Therapy Resistance

Angiogenesis and metabolism are entwined processes that permit tumor growth and progression. Blood vessel supply is necessary for tumor survival not only by providing oxygen and nutrients for anabolism but also by removing waste products from cellular metabolism. On the other hand, blocking angiogenesis with antiangiogenic therapies shows clinical benefits in treating several tumor types. Nevertheless, resistance to therapy emerges over time. In this review we discuss a novel mechanism of adaptive resistance involving metabolic adaptation of tumor cells, and we also provide examples of tumor adaptation to therapy, which may represent a new mechanism of resistance in several types of cancer. Thus, targeting this metabolic tumor adaptation could be a way to avoid resistance in cancer patients.

Prognostic value of angiopoietin-2 in non-small cell lung cancer patients: a meta-analysis

Background

Non-small cell lung cancer (NSCLC) is the most frequent cause of cancer deaths worldwide. The targeted therapy had made important progress in recent years, but few potential predictive biomarkers for prognosis of NSCLC patients were identified. Angiopoietin-2 (Ang-2), a cytokine upregulated in tumor endothelial cells and some tumor cells including NSCLC, is a partial agonist and antagonist of angiopoietin-1 (Ang-1). Ang-1 is another ligand for the tyrosine kinase receptor Tie2; it promotes recruitment of pericytes and smooth muscle cells, stabilizing vascular networks by binding to Tie2. Although many studies mainly considered that Ang-2 correlated with progression and prognosis of NSCLC significantly, there are much conflicting and controversial data. Therefore, we conducted a meta-analysis to assess the relationship between Ang-2 and prognosis, a clinical outcome of NSCLC.

Methods

The search was based on major databases from PubMed, Cochrane Library, EMBASE, and CNKI, and 20 eligible publications (range from 2002 to 2015) are included in our meta-analysis with 2011 NSCLC patients in total. These studies illuminated the correlation between the expression of Ang-2 and NSCLC, based on either prognostic factors or clinicopathological features. Pooled calculations were carried out on the odds ratio (OR) and the corresponding 95 % confidence interval (CI) to perform this meta-analysis, and all statistical analyses were carried out by STATA 12.0 and Review Manager 5.3.

Results

According to our results, the expression of Ang-2 in NSCLC tissues was significantly higher than that in normal lung tissues, indicating that Ang-2 over-expression may be a predictive marker (pooled OR = 5.09, corresponding 95 % confidence interval (95 % CI) 3.10–8.36, p = 0.000). In addition, our pooled data showed that Ang-2 expression was positively correlated with tumor stages (pooled OR = 3.58, 95 % CI 2.40–5.35, p = 0.000), differentiation (pooled OR = 0.65, 95 % CI 0.45–0.94, p = 0.02), lymphatic invasion (pooled OR = 3.15, 95 % CI 1.97–5.03, p = 0.000), and poor survival (pooled OR = 1.93, 95 % CI 1.47–2.52, p = 0.000) of NSCLC, but seems to have no significant impact on tumor size (pooled OR = 1.09, 95 % CI 0.59–2.00, p = 0.78).

Conclusions

These results demonstrate that Ang-2 expression significantly correlated with poor prognosis for patients with NSCLC.

Systems pharmacology approaches for optimization of antiangiogenic therapies: challenges and opportunities

Targeted therapies have become an important therapeutic paradigm for multiple malignancies. The rapid development of resistance to these therapies impedes the successful management of advanced cancer. Due to the redundancy in angiogenic signaling, alternative proangiogenic factors are activated upon treatment with anti-VEGF agents. Higher doses of the agents lead to greater stimulation of compensatory proangiogenic pathways that limit the therapeutic efficacy of VEGF-targeted drugs and produce escape mechanisms for tumor. Evidence suggests that dose intensity and schedules affect the dynamics of the development of this resistance. Thus, an optimal dosing regimen is crucial to maximizing the therapeutic benefit of antiangiogenic agents and limiting treatment resistance. A systems pharmacology approach using multiscale computational modeling can facilitate a mechanistic understanding of these dynamics of angiogenic biomarkers and their impacts on tumor reduction and resistance. Herein, we discuss a systems pharmacology approach integrating the biology of VEGF-targeted therapy resistance, including circulating biomarkers, and pharmacodynamics to enable the optimization of antiangiogenic therapy for therapeutic gains.

Prostate cancer cell-stromal cell crosstalk via FGFR1 mediates antitumor activity of dovitinib in bone metastases

Bone is the most common site of prostate cancer (PCa) progression to a therapy-resistant, lethal phenotype. We found that blockade of fibroblast growth factor receptors (FGFRs) with the receptor tyrosine kinase inhibitor dovitinib has clinical activity in a subset of men with castration-resistant PCa and bone metastases. Our integrated analyses suggest that FGF signaling mediates a positive feedback loop between PCa cells and bone cells and that blockade of FGFR1 in osteoblasts partially mediates the antitumor activity of dovitinib by improving bone quality and by blocking PCa cell-bone cell interaction. These findings account for clinical observations such as reductions in lesion size and intensity on bone scans, lymph node size, and tumor-specific symptoms without proportional declines in serum prostate-specific antigen concentration. Our findings suggest that targeting FGFR has therapeutic activity in advanced PCa and provide direction for the development of therapies with FGFR inhibitors.

Phase Ib study of dovitinib in combination with gemcitabine plus cisplatin or gemcitabine plus carboplatin in patients with advanced solid tumors

PURPOSE

Dovitinib is a small molecule kinase inhibitor with activity against the fibroblast growth factor and vascular endothelial growth factor receptor families. The purpose of this phase Ib study was to define the recommended phase 2 dose of the combinations of gemcitabine and cisplatin or gemcitabine and carboplatin plus dovitinib.

METHODS

Patients with advanced solid tumors were enrolled in two parallel dose escalation arms (cisplatin- or carboplatin-based regimens). Treatment was administered with gemcitabine (1,000 mg/m(2) on days 1 and 8), cisplatin (70 mg/m(2)), or carboplatin (AUC 5) on day 1, and dovitinib (orally on days 1-5, 8-12, and 15-19), every 21 days. The starting dose of dovitinib was 300 mg and was dose escalated in successive cohorts using 3 + 3 dose escalation rules.

RESULTS

Fourteen patients with advanced solid tumors were enrolled, five to the cisplatin arm and nine to the carboplatin arm. Patients enrolled in the cisplatin arm received a median of two cycles of treatment (range 1-5), and patients enrolled in the carboplatin arm received a median of one cycle of treatment (range 1-4). There were no protocol-defined dose-limiting toxicities in the cisplatin arm. However, the cohort was closed due to the need for frequent dose delays and/or reductions and two patients experiencing severe thromboembolic events. There were two dose-limiting toxicities in the carboplatin arm at the starting dose level of dovitinib (both prolonged neutropenia), and the dose of dovitinib was de-escalated to 200 mg. Two additional dose-limiting toxicities (prolonged neutropenia and febrile neutropenia) occurred in the lower dose cohort, and the study was closed. No patients achieved an objective response to treatment.

CONCLUSIONS

Dovitinib in combination with gemcitabine plus cisplatin or gemcitabine plus carboplatin was poorly tolerated due to myelosuppression.

What could Nintedanib (BIBF 1120), a triple inhibitor of VEGFR, PDGFR, and FGFR, add to the current treatment options for patients with metastatic colorectal cancer?

Increasing knowledge of the pro-angiogenic processes involved in the progression of metastatic colorectal cancer (mCRC) has resulted in the clinical development of several anti-angiogenic agents, with bevacizumab currently being the only approved agent for mCRC. Nintedanib (BIBF 1120) has been shown to block the vascular endothelial growth factor receptor (VEGFR), the platelet-derived growth factor receptor (PDGFR), and the fibroblast growth factor receptor (FGFR). By targeting FGFR signaling, nintedanib may overcome resistance to previous anti-VEGF treatments, and may represent a better approach in patients with high basal levels of circulating FGFs. In this article, the angiogenic mechanisms implicated in mCRC are reviewed (focusing on the signaling pathways activated by VEGFR, PDGFR, and FGFR), along with the clinical data for nintedanib in the context of other anti-angiogenic tyrosine kinase inhibitors under clinical development for mCRC. Biomarkers that could predict response to nintedanib are also discussed.

The association of alternate VEGF ligands with resistance to anti-VEGF therapy in metastatic colorectal cancer

Background

Circulating angiogenic factors are altered in patients with mCRC receiving bevacizumab. Evaluation of alterations in levels of VEGF ligands may provide insights into possible resistance mechanisms.

Methods

PlGF, VEGF-A, VEGF-C, and VEGF-D were measured from two cohorts of patients. Sequential plasma samples were obtained from a discovery cohort of 42 patients treated with chemotherapy and bevacizumab. A validation cohort included plasma samples from a cross-sectional of 403 patients prior to chemotherapy, or after progression on a regimen with or without bevacizumab.

Results

In the discovery cohort, VEGF-C was increased prior to progression and at progression (+49% and +95%, respectively, p<0.01), consistent with previously reported elevations in PlGF. Levels of VEGF-D were increased (+23%) at progression (p=0.05). In the validation cohort, samples obtained from patients after progression on a regimen with bevacizumab had higher levels of PlGF and VEGF-D (+43% and +6%, p=0.02, p=0.01, respectively) compared to untreated patients, but failed to validate the increase in VEGF-C seen in the first cohort. Patients who progressed on chemotherapy with bevacizumab had significantly elevated levels of PlGF (+88%) but not VEGF-C and VEGF-D compared to patients treated with chemotherapy alone. Elevations of PlGF and VEGF-D appeared transient and returned to baseline with a half-life of 6 weeks.

Conclusions

Increases in PlGF and VEGF-D were observed after progression on chemotherapy with bevacizumab. These changes appear to be reversible after discontinuing therapy. These ligands are associated with resistance to bevacizumab-containing chemotherapy in mCRC, but causation remains to be established.

Marine algal carotenoids inhibit angiogenesis by down-regulating FGF-2-mediated intracellular signals in vascular endothelial cells

Discovery of natural compounds as effective angiogenesis inhibitors has become an important approach in the prevention of cancer. We previously demonstrated the anti-angiogenic potential of two marine algal carotenoids, fucoxanthin and siphonaxanthin. In this study, we evaluated the molecular mechanisms of the anti-angiogenic activity of those two carotenoids using human umbilical vein endothelial cells. This study showed that both fucoxanthin and siphonaxanthin suppress the mRNA expression of fibroblast growth factor 2 (FGF-2) and its receptor (FGFR-1) as well as their trans-activation factor, EGR-1. But, the mRNA expression of VEGFR-2 did not show significant effect by those two carotenoids. Further, those two marine algal carotenoids down-regulate the phosphorylation of FGF-2-mediated intracellular signaling proteins such as ERK1/2 and Akt. Inhibition of FGF-2-mediated intracellular signaling proteins by those carotenoids represses the migration of endothelial cells as well as their differentiation into tube-like structures on Matrigel. These results demonstrate for the first time the possible molecular mechanism underlying the anti-angiogenic effects of fucoxanthin and siphonaxanthin and suggest that these effects are due to the down-regulation of signal transduction by FGFR-1. Our findings imply a new insight into the novel bio-functional property of marine algal carotenoids which should improve current anti-angiogenic therapies in the treatment of cancer and other pro-angiogenic diseases.

Myeloid-derived suppressor cells adhere to physiologic STAT3- vs STAT5-dependent hematopoietic programming, establishing diverse tumor-mediated mechanisms of immunologic escape

The receptor tyrosine kinase inhibitor, sunitinib, is astonishingly effective in its capacity to reduce MDSCs in peripheral tissues such as blood (human) and spleen (mouse), restoring responsiveness of bystander T lymphocytes to TcR stimulation. Sunitinib blocks proliferation of undifferentiated MDSCs and decreases survival of more differentiated neutrophilic MDSC (n-MDSC) progeny. Ironically, sunitinib's profound effects are observed even in a total absence of detectable anti-tumor therapeutic response. This is best explained by the presence of disparate MDSC-conditioning stimuli within individual body compartments, allowing sensitivity and resistance to sunitinib to coexist within the same mouse or patient. The presence or absence of GM-CSF is likely the major determinant in each compartment, given that GM-CSF's capacity to preempt STAT3-dependent with dominant STAT5-dependent hematopoietic programming confers sunitinib resistance and redirects differentiation from the n-MDSC lineage to the more versatile monocytoid (m-MDSC) lineage. The clinical sunitinib experience underscores that strategies for MDSC and Treg depletions must be mindful of disparities among body compartments to avoid sanctuary effects. Ironically, m-MDSCs manifesting resistance to sunitinib also have the greatest potential to differentiate into tumoricidal accessory cells, by virtue of their capacity to respond to T cell-secreted IFN-γ or to TLR agonists with nitric oxide and peroxynitrate production.

Essential role for endocytosis in the growth factor-stimulated activation of ERK1/2 in endothelial cells

Vascular endothelial growth factor (VEGF) stimulates angiogenesis by binding to VEGF receptor 2 (VEGFR2) on endothelial cells (ECs). Downstream activation of the extracellular related kinases 1/2 (ERK1/2) is important for angiogenesis to proceed. Receptor internalization has been implicated in VEGFR2 signaling, but its role in the activation of ERK1/2 is unclear. To explore this question we utilized pitstop and dynasore, two small molecule inhibitors of endocytosis. First, we confirmed that both inhibitors block the internalization of VEGFR2 in ECs. We then stimulated ECs with VEGF in the presence and absence of the inhibitors and examined VEGFR2 signaling to ERK1/2. Activation of VEGFR2 and C-Raf still occurred in the presence of the inhibitors, whereas the activation of MEK1/2 and ERK1/2 was abrogated. Therefore, although internalization is not required for activation of either VEGFR2 or C-Raf in ECs stimulated with VEGF, internalization is necessary to activate the more distal kinases in the cascade. Importantly, inhibition of internalization also prevented activation of ERK1/2 when ECs were stimulated with other pro-angiogenic growth factors, namely fibroblast growth factor 2 and hepatocyte growth factor. In contrast, the same inhibitors did not block ERK1/2 activation in fibroblasts or cancer cells stimulated with growth factors. Finally, we show that these small molecule inhibitors of endocytosis block angiogenesis in vitro and in vivo. Therefore, receptor internalization may be a generic requirement for pro-angiogenic growth factors to activate ERK1/2 signaling in human ECs, and targeting receptor trafficking may present a therapeutic opportunity to block tumor angiogenesis.

Up-regulation of platelet-derived growth factor-A is responsible for the failure of re-initiated interferon alpha treatment in hepatocellular carcinoma

BACKGROUND

Postoperative interferon-α(IFN-α) treatment delays hepatocellular carcinoma(HCC) recurrence and prolongs patient survival, and may thus be an effective form of adjuvant therapy. However, clinical observations found that HCC recurs in some patients within 8 months of IFN-α treatment being discontinued. We investigated whether HCC regrowth appears after IFN-α is discontinued, whether re-initiated IFN-α is effective, and the underlying mechanisms of IFN-α treatment.

METHODS

The human HCC nude mouse model LCI-D20 was used to study the effects of IFN-α treatment, discontinued IFN-α treatment, and re-initiated IFN-α treatment on tumor growth. Tumor weight, microvessel density(MVD), serum vascular endothelial growth factor (VEGF), and tumor cell apoptosis were analyzed. Angiogenesis-related factors were studied using cDNA microarray in different tumor samples and confirmed using reverse transcription-polymerase chain reaction(RT-PCR) and Western blotting assays. Finally, imatinib was added with re-initiated IFN-α treatment to improve efficacy.

RESULTS

IFN-α (1.5 × 107 U/kg/day for 20 days) suppressed HCC growth by 60.3% and decreased MVD by 52.2% compared with the control. However, tumor regrowth occurred after IFN-α was discontinued, and re-initiated IFN-α treatment was not effective for inhibiting tumor growth or reducing MVD compared with a saline-treated group. cDNA microarray showed VEGF was down-regulated while platelet-derived growth factor-A (PDGF-A) was up-regulated when IFN-α treatment was re-initiated. These findings were further confirmed with RT-PCR and Western blotting assay. The combination of imatinib with re-initiated IFN-α reduced HCC weight by 30.7% and decreased MVD by 31.1% compared with IFN-α treatment only (P=0.003 and 0.015, respectively).

CONCLUSION

Tumor regrowth occurred after IFN-α treatment was discontinued. Re-initiated IFN-α treatment was not effective and was associated with up-regulation of PDGF-A, while the VEGF remained suppressed. The combination of a PDGF-receptor inhibitor with IFN-α improved the effect of the re-initiated treatment.

Antiangiogenic agents should be integrated into the standard treatment for patients with ovarian cancer

Tumor angiogenesis is a fundamental process driving the progression of epithelial ovarian cancer and related malignancies. The question is whether agents targeting tumor angiogenesis should at this time be integrated into standard treatment. In this article, the pro side of this question is presented. Multiple phase II trials have demonstrated efficacy for antiangiogenic agents in the treatment of women with recurrent ovarian cancer. Results of three phase III trials evaluating the antivascular endothelial growth factor antibody bevacizumab have been presented, all demonstrating significant increases in progression-free survival when combined with standard cytotoxic chemotherapy and continued beyond chemotherapy, with acceptable toxicity. Several other angiogenesis-targeted agents are undergoing phase III evaluation. Based on these data, it is concluded that antiangiogenic therapy, at least with bevacizumab, should be integrated into the standard clinical management of patients with this disease. Further investigation is needed to determine optimal utilization.

Regulator of G-protein signaling 5 (RGS5) protein: a novel marker of cancer vasculature elicited and sustained by the tumor's proangiogenic microenvironment

We previously identified regulator of G-protein signaling 5 (RGS5) among several genes expressed by tumor-derived endothelial cells (EC). In this study, we provide the first in vivo/ex vivo evidence of RGS5 protein in the vasculature of ovarian carcinoma clinical specimens and its absence in human ovaries. Consistent with this, we show higher amounts of Rgs5 transcript in EC isolated from human cancers (as opposed to normal tissues) and demonstrate that expression is sustained by a milieu of factors typical of the proangiogenic tumor environment, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2). Supporting these findings, we show elevated levels of Rgs5 mRNA in the stroma from strongly (as opposed to weakly) angiogenic ovarian carcinoma xenografts and accordingly, we also show more of the protein associated to the abnormal vasculature. RGS5 protein predominantly colocalizes with the endothelium expressing platelet/endothelial cell adhesion molecule-1 (PECAM-1/CD31) and to a much lesser extent with perivascular/mural cells expressing platelet-derived growth factor receptor-beta (PDGFR-β) or alpha smooth muscle actin (αSMA). To toughen the relevance of the findings, we demonstrate RGS5 in the blood vessels of other cancer models endowed with a proangiogenic environment, such as human melanoma and renal carcinoma xenografts; to the contrary, it was undetectable in the vasculature of normal mouse tissues. RGS5 expression by the cancer vasculature triggered and retained by the proangiogenic microenvironment supports its exploitation as a novel biomarker and opens the path to explore new possibilities of therapeutic intervention aimed at targeting tumor blood vessels.

Assessment of acute antivascular effects of vandetanib with high-resolution dynamic contrast-enhanced computed tomographic imaging in a human colon tumor xenograft model in the nude rat

Tumor size is not a reliable marker for the assessment of early antivascular effects of antiangiogenics. In the present study, we used 200-microm in-plane high-resolution dynamic contrast-enhanced computed tomography (DCE-CT) to noninvasively assess the immediate antivascular effects of vandetanib in a subcutaneous human colon cancer (LoVo) xenograft model in nude rats and to investigate correlation between changes in CT perfusion parameters and tumor volume or immunohistochemical end points. At 3 to 4 weeks after LoVo cell implantation, the animal was gavaged with either vandetanib (50 mg/kg) or vehicle twice (22 hours apart) and scanned with a preclinical DCE-CT scanner before (0 hour) and after treatment (24 hours). Quantitative maps of blood flow (BF) and volume (BV) of the tumor were calculated from the acquired DCE-CT images. The rats were divided into nonhypovascular, hypovascular, and combined (regardless of vascularity) groups. In the nonhypovascular group, significant decreases in both tumor BF and BV were observed in the vandetanib-treated rats compared with increases in the vehicle-treated rats. A significant decrease in BV was detected in the vandetanib-treated rats in the combined group as well. No differences in tumor growth, vascular endothelial growth factor expression, microvessel density, or apoptosis were observed between vandetanib- and vehicle-treated rats in all three groups. These results demonstrate that BF and BV imaging biomarkers from DCE-CT imaging can be used for rapid monitoring of immediate (24 hours after) antimicrovascular effects of vandetanib on tumors, even in the absence of significant changes of tumor volume or clinically relevant immunohistochemical end points.

The autophagic tumor stroma model of cancer or "battery-operated tumor growth": A simple solution to the autophagy paradox

The role of autophagy in tumorigenesis is controversial. Both autophagy inhibitors (chloroquine) and autophagy promoters (rapamycin) block tumorigenesis by unknown mechanism(s). This is called the "Autophagy Paradox". We have recently reported a simple solution to this paradox. We demonstrated that epithelial cancer cells use oxidative stress to induce autophagy in the tumor microenvironment. As a consequence, the autophagic tumor stroma generates recycled nutrients that can then be used as chemical building blocks by anabolic epithelial cancer cells. This model results in a net energy transfer from the tumor stroma to epithelial cancer cells (an energy imbalance), thereby promoting tumor growth. This net energy transfer is both unilateral and vectorial, from the tumor stroma to the epithelial cancer cells, representing a true host-parasite relationship. We have termed this new paradigm "The Autophagic Tumor Stroma Model of Cancer Cell Metabolism" or "Battery-Operated Tumor Growth". In this sense, autophagy in the tumor stroma serves as a "battery" to fuel tumor growth, progression and metastasis, independently of angiogenesis. Using this model, the systemic induction of autophagy will prevent epithelial cancer cells from using recycled nutrients, while the systemic inhibiton of autophagy will prevent stromal cells from producing recycled nutrients-both effectively "starving" cancer cells. We discuss the idea that tumor cells could become resistant to the systemic induction of autophagy, by the upregulation of natural endogenous autophagy inhibitors in cancer cells. Alternatively, tumor cells could also become resistant to the systemic induction of autophagy, by the genetic silencing/deletion of pro-autophagic molecules, such as Beclin1. If autophagy resistance develops in cancer cells, then the systemic inhibition of autophagy would provide a therapeutic solution to this type of drug resistance, as it would still target autophagy in the tumor stroma. As such, an anti-cancer therapy that combines the alternating use of both autophagy promoters and autophagy inhibitors would be expected to prevent the onset of drug resistance. We also discuss why anti-angiogenic therapy has been found to promote tumor recurrence, progression and metastasis. More specifically, anti-angiogenic therapy would induce autophagy in the tumor stroma via the induction of stromal hypoxia, thereby converting a non-aggressive tumor type to a "lethal" aggressive tumor phenotype. Thus, uncoupling the metabolic parasitic relationship between cancer cells and an autophagic tumor stroma may hold great promise for anti-cancer therapy. Finally, we believe that autophagy in the tumor stroma is the local microscopic counterpart of systemic wasting (cancer-associated cachexia), which is associated with advanced and metastatic cancers. Cachexia in cancer patients is not due to decreased energy intake, but instead involves an increased basal metabolic rate and increased energy expenditures, resulting in a negative energy balance. Importantly, when tumors were surgically excised, this increased metabolic rate returned to normal levels. This view of cachexia, resulting in energy transfer to the tumor, is consistent with our hypothesis. So, cancer-associated cachexia may start locally as stromal autophagy, and then spread systemically. As such, stromal autophagy may be the requisite precursor of systemic cancer-associated cachexia.

Understanding the "lethal" drivers of tumor-stroma co-evolution: emerging role(s) for hypoxia, oxidative stress and autophagy/mitophagy in the tumor micro-environment

We have recently proposed a new model for understanding how tumors evolve. To achieve successful "Tumor-Stroma Co-Evolution", cancer cells induce oxidative stress in adjacent fibroblasts and possibly other stromal cells. Oxidative stress in the tumor stroma mimics the effects of hypoxia, under aerobic conditions, resulting in an excess production of reactive oxygen species (ROS). Excess stromal production of ROS drives the onset of an anti-oxidant defense in adjacent cancer cells, protecting them from apoptosis. Moreover, excess stromal ROS production has a "Bystander-Effect", leading to DNA damage and aneuploidy in adjacent cancer cells, both hallmarks of genomic instability. Finally, ROS-driven oxidative stress induces autophagy and mitophagy in the tumor micro-environment, leading to the stromal over-production of recycled nutrients (including energy-rich metabolites, such as ketones and L-lactate). These recycled nutrients or chemical building blocks then help drive mitochondrial biogenesis in cancer cells, thereby promoting the anabolic growth of cancer cells (via an energy imbalance). We also show that ketones and lactate help "fuel" tumor growth and cancer cell metastasis and can act as chemo-attractants for cancer cells. We have termed this new paradigm for accelerating tumor-stroma co-evolution, "The Autophagic Tumor Stroma Model of Cancer Cell Metabolism". Heterotypic signaling in cancer-associated fibroblasts activates the transcription factors HIF1alpha and NFκB, potentiating the onset of hypoxic and inflammatory response(s), which further upregulates the autophagic program in the stromal compartment. Via stromal autophagy, this hypoxic/inflammatory response may provide a new escape mechanism for cancer cells during anti-angiogenic therapy, further exacerbating tumor recurrence and metastasis.

Potential relevance of bell-shaped and u-shaped dose-responses for the therapeutic targeting of angiogenesis in cancer

Tumor angiogenesis, the growth of new blood vessels into tumors, facilitates tumor growth and thus represents an attractive therapeutic target. Numerous experimental angiogenesis inhibitors have been characterised and subsequently trialled in patients. Some of these agents have failed to show any substantial activity in patients. In contrast, others have been more successful, but even these provide only a few months extra patient survival. Recent work has focused on understanding the effects of anti-angiogenic agents on tumor biology and has revealed a number of new findings that may help to explain the limited efficacy of angiogenesis inhibitors. Herein, I review the evidence that hormetic dose-responses (i.e. bell-shaped and U-shaped dose-response curves) are often observed with anti-angiogenic agents. Agents reported to exhibit these types of dose-response include: 5-fluorouracil, ATN-161, bortezomib, cisplatin, endostatin, enterostatin, integrin inhibitors, interferon-α, plasminogen activator-1 (PAI-1), rapamycin, rosiglitazone, statins, thrombospondin-1, TGF-α1 and TGF-α3. Hormesis may also be relevant for drugs that target the vascular endothelial growth factor (VEGF) signalling pathway and for metronomic chemotherapy. Here I argue that hormetic dose-responses present a challenge for the clinical translation of several anti-angiogenic agents and discuss how these problems might be circumvented.

P53-induced microRNA-107 inhibits HIF-1 and tumor angiogenesis

The pathway involving the tumor suppressor gene TP53 can regulate tumor angiogenesis by unclear mechanisms. Here we show that p53 regulates hypoxic signaling through the transcriptional regulation of microRNA-107 (miR-107). We found that miR-107 is a microRNA expressed by human colon cancer specimens and regulated by p53. miR-107 decreases hypoxia signaling by suppressing expression of hypoxia inducible factor-1beta (HIF-1beta). Knockdown of endogenous miR-107 enhances HIF-1beta expression and hypoxic signaling in human colon cancer cells. Conversely, overexpression of miR-107 inhibits HIF-1beta expression and hypoxic signaling. Furthermore, overexpression of miR-107 in tumor cells suppresses tumor angiogenesis, tumor growth, and tumor VEGF expression in mice. Finally, in human colon cancer specimens, expression of miR-107 is inversely associated with expression of HIF-1beta. Taken together these data suggest that miR-107 can mediate p53 regulation of hypoxic signaling and tumor angiogenesis.

Fibroblast growth factor signalling: from development to cancer

Fibroblast growth factors (FGFs) and their receptors control a wide range of biological functions, regulating cellular proliferation, survival, migration and differentiation. Although targeting FGF signalling as a cancer therapeutic target has lagged behind that of other receptor tyrosine kinases, there is now substantial evidence for the importance of FGF signalling in the pathogenesis of diverse tumour types, and clinical reagents that specifically target the FGFs or FGF receptors are being developed. Although FGF signalling can drive tumorigenesis, in different contexts FGF signalling can mediate tumour protective functions; the identification of the mechanisms that underlie these differential effects will be important to understand how FGF signalling can be most appropriately therapeutically targeted.

Antiangiogenic strategies for treatment of malignant gliomas

Numerous antiangiogenic agents with diverse mechanisms of action are currently under investigation for the treatment of patients with glioblastoma (GBM), a diagnosis that continues to carry a poor prognosis despite maximal conventional therapy. Early clinical trials suggest that antiangiogenic drugs, which target the blood vessels of these highly angiogenic tumors, may have clinical benefit in GBM patients. Antiangiogenic agents have potent antiedema and steroid-sparing effects in patients, and emerging data suggest that these drugs may modestly improve progression-free survival. Although these early results are encouraging, several issues arise regarding the use and efficacy of these agents. Interpretation of the radiographic changes that occur after treatment with antiangiogenic agents presents a major challenge. Still lacking are reliable radiographic and biologic markers that can predict which patients will benefit from treatment and that accurately indicate response and progression during therapy. In addition, most patients treated with antiangiogenic drugs eventually progress, and the mechanisms by which tumors escape from therapy are only beginning to be understood. Larger prospective trials that incorporate correlative biomarker studies will be required to address these challenges. Here, we summarize the clinical experience with antiangiogenic therapy in patients with malignant gliomas (MG), review the major issues concerning the use and development of these agents, and discuss strategies that may build upon the initial gains observed with antiangiogenic agents.

Angiogenesis as a therapeutic target in malignant gliomas

Currently, adult glioblastoma (GBM) patients have poor outcomes with conventional cytotoxic treatments. Because GBMs are highly angiogenic tumors, inhibitors that target tumor vasculature are considered promising therapeutic agents in these patients. Encouraging efficacy and tolerability in preliminary clinical trials suggest that targeting angiogenesis may be an effective therapeutic strategy in GBM patients. However, the survival benefits observed to date in uncontrolled trials of antiangiogenic agents have been modest, and several obstacles have limited their effectiveness. This article reviews the rationale for antiangiogenic agents in GBM, their potential mechanisms of action, and their clinical development in GBM patients. Although challenges remain with this approach, ongoing studies may improve upon the promising initial benefits already observed in GBM patients.

Myeloid-derived suppressor cells: a novel therapeutic target

Immunotherapy and angiogenic inhibitors, used alone or in combination with chemotherapy, represent two promising cancer treatment programs. Each is limited by myeloid-derived suppressor cells (MDSCs), which accumulate in tumor-bearing hosts. MDSCs inhibit effector T-cell function and thus prevent the formation and execution of an effective antitumor immune response. Recently reported studies have shown that MDSCs also function to promote tumor-dependent angiogenesis as well as tumor metastasis, and to provide tumor resistance to antiangiogenic drugs. Insights into tumor-imposed dynamic changes in bone marrow function and myeloid cell development should fuel novel drug developments and novel applications of drugs currently in use. Such insights suggest that multitargeted receptor tyrosine kinase inhibitors, such as sunitinib, may be useful adjunctive agents for use in immunotherapy trials treating several tumor types.

Modes of resistance to anti-angiogenic therapy

Angiogenesis inhibitors targeting the vascular endothelial growth factor (VEGF) signalling pathways are affording demonstrable therapeutic efficacy in mouse models of cancer and in an increasing number of human cancers. However, in both preclinical and clinical settings, the benefits are at best transitory and are followed by a restoration of tumour growth and progression. Emerging data support a proposition that two modes of unconventional resistance underlie such results: evasive resistance, an adaptation to circumvent the specific angiogenic blockade; and intrinsic or pre-existing indifference. Multiple mechanisms can be invoked in different tumour contexts to manifest both evasive and intrinsic resistance, motivating assessment of their prevalence and importance and in turn the design of pharmacological strategies that confer enduring anti-angiogenic therapies.

Developing and applying a gene functional association network for anti-angiogenic kinase inhibitor activity assessment in an angiogenesis co-culture model

Background

Tumor angiogenesis is a highly regulated process involving intercellular communication as well as the interactions of multiple downstream signal transduction pathways. Disrupting one or even a few angiogenesis pathways is often insufficient to achieve sustained therapeutic benefits due to the complexity of angiogenesis. Targeting multiple angiogenic pathways has been increasingly recognized as a viable strategy. However, translation of the polypharmacology of a given compound to its antiangiogenic efficacy remains a major technical challenge. Developing a global functional association network among angiogenesis-related genes is much needed to facilitate holistic understanding of angiogenesis and to aid the development of more effective anti-angiogenesis therapeutics.

Results

We constructed a comprehensive gene functional association network or interactome by transcript profiling an in vitro angiogenesis model, in which human umbilical vein endothelial cells (HUVECs) formed capillary structures when co-cultured with normal human dermal fibroblasts (NHDFs). HUVEC competence and NHDF supportiveness of cord formation were found to be highly cell-passage dependent. An enrichment test of Biological Processes (BP) of differentially expressed genes (DEG) revealed that angiogenesis related BP categories significantly changed with cell passages. Built upon 2012 DEGs identified from two microarray studies, the resulting interactome captured 17226 functional gene associations and displayed characteristics of a scale-free network. The interactome includes the involvement of oncogenes and tumor suppressor genes in angiogenesis. We developed a network walking algorithm to extract connectivity information from the interactome and applied it to simulate the level of network perturbation by three multi-targeted anti-angiogenic kinase inhibitors. Simulated network perturbation correlated with observed anti-angiogenesis activity in a cord formation bioassay.

Conclusion

We established a comprehensive gene functional association network to model in vitro angiogenesis regulation. The present study provided a proof-of-concept pilot of applying network perturbation analysis to drug phenotypic activity assessment.

NDRG2 is a new HIF-1 target gene necessary for hypoxia-induced apoptosis in A549 cells

The NDRG2 gene belongs to a family of N-Myc downstream-regulated genes (NDRGs) and is expressed in many normal tissues. NDRG2 gene expression has been shown to be regulated in the stress response of certain cells. However, its function is not yet fully understood. Many studies have demonstrated that hypoxia, one of the stress responses, induced apoptosis in several cell types. In the current study, we investigated NDRG2 involvement in hypoxia response and found that NDRG2 expression was markedly up-regulated in several tumor cell lines exposed to hypoxic conditions or similar stresses at the mRNA and protein level. We also observed that the expression of NDRG2 was regulated by Hypoxia-inducible factor 1 (HIF-1) in tumor cells under hypoxia. Three hypoxia-responsive elements (HREs) in the NDRG2 promoter were identified. HRE1 could directly bind Hif-1 in vivo. Importantly, we found that silencing or enforcing the expression of NDRG2 could strongly inhibit or increase apoptosis. In addition, our data also showed that Ndrg2 was able to be translocated from the cytoplasm to the nucleus, and the segment from 101 to 178 amino acids of Ndrg2 is responsible for its translocation. Taken together, this study suggests that NDRG2 is a Hif-1 target gene and closely related with hypoxia-induced apoptosis in A549 cells.

Chemotherapy: new uses for old drugs

Using chemotherapy drugs as antiangiogenic agents is a new use for drugs that have been around for a long time. The favorable toxicity profile and reduced cost make low-dose continuous "metronomic" chemotherapy trials appealing, but there is still much to be learned. Challenges ahead include determination of the optimal tumor types, drugs, doses, schedules, and response monitoring (end points). The measurement of angiogenic growth factors and inhibitors and of circulating endothelial progenitor cells or their precursors represents promising strategies in these areas.

Mouse dendritic-endothelial cell hybrids and 4-1BB costimulation elicit antitumor effects mediated by broad antiangiogenic immunity

Antiangiogenic immunotherapy, which targets molecules critical to tumor angiogenesis, is expected to counteract the negative effect of tumor cell genetic instability on the outcome of immunotherapy targeting tumor antigens. Previously, targeting of individual angiogenic molecules has been shown to inhibit tumor angiogenesis and limit tumor growth. Nevertheless, this approach may be bypassed by redundant angiogenic pathways. To overcome this limitation, we have developed an immunization strategy targeting multiple molecules critical to angiogenesis. To this end, hybrids of dendritic cells (DC) and syngeneic endothelial cells (EC) were used as immunogens, because (a) whole EC express multiple molecules involved in angiogenesis and (b) DC tumor cell hybrids are effective in generating self-antigen-specific immune responses. The immunization strategy included the administration of an agonist 4-1BB-specific monoclonal antibody (mAb), because it augments self-antigen-specific immune responses elicited by DC hybrids. Immunization of mice with DC-EC hybrids and 4-1BB-specific mAb inhibited the growth of B16.F10 melanoma and MC38 colon adenocarcinoma tumors. This effect is mediated by EC-specific CD4+ and CD8+ T-cell responses, which markedly inhibited tumor angiogenesis. No therapy-related side effects, except minor and transient hematologic changes, were observed. Our findings represent a useful background for the design of antiangiogenic immunotherapeutic strategies to control tumor growth in a clinical setting.

Antiangiogenic versus cytotoxic activity in analogues of aeroplysinin-1

A series of analogues of the potentially angiogenic inhibitor aeroplysinin-1 1 were synthesized and their in vitro antiangiogenic and cytotoxic activities evaluated. In the case of epoxy ketone 6 and azlactone 36 the relationship sprouting inhibition assay/cytotoxicity in BAE cells was enhanced by one order and two orders of magnitude, respectively, with respect to the reference. These results imply more specific antiangiogenic properties for the synthesized derivatives.

Philinopside E, a New Sulfated Saponin from Sea Cucumber, Blocks the Interaction between Kinase Insert Domain-Containing Receptor (KDR) and αvβ3 Integrin via Binding to the Extracellular Domain of KDR

Vascular endothelial growth factor (VEGF) signaling pathway is essential for tumor angiogenesis and has long been recognized as a promising target for cancer therapy. Current view holds that physical interaction between alpha(v)beta(3) integrin and kinase insert domain-containing receptor (KDR) is important in regulating angiogenesis and tumor development. We have reported previously that a new marine-derived compound, philinopside E (PE), exhibited the antiangiogenic activity via inhibition on KDR phosphorylation and downstream signaling. Herein, we have further demonstrated that PE specifically interacts with KDR extracellular domain, which is distinct from conventional small-molecule inhibitors targeting cytoplasmic kinase domain, to block its interaction with VEGF and the downstream signaling. We also noted that PE markedly suppresses alpha(v)beta(3) integrin-driven downstream signaling as a result of disturbance of the physical interaction between KDR and alpha(v)beta(3) integrin in HMECs, followed by disruption of the actin cytoskeleton organization and decreased cell adhesion to vitronectin. All of these findings substantiate PE to be an unrecognized therapeutic class in tumor angiogenesis and, more importantly, help appeal the interest of the therapeutic potential in angiogenesis and cancer development via targeting integrin-KDR interaction in the future.

Effects of Raf-1 siRNA on human cerebral microvascular endothelial cells: A potential therapeutic strategy for inhibition of tumor angiogenesis

The serine/threonine kinase Raf-1 is involved in the regulation of tumor cell survival, proliferation and metastasis formation, and has therefore emerged as a promising target for cancer therapy. In addition, Raf-1 activity mediates proliferation of endothelial cells thereby promoting angiogenesis and invasive growth of various tumors, including highly vascularized malignant glioblastoma. The aim of this study was to evaluate the effects of small inhibitory RNA (siRNA) directed against Raf-1 on viability, proliferation and motility in glioma cells and cerebral endothelial cells. Half-quantitative RT-PCR and Western blotting revealed efficient siRNA-mediated Raf-1 down regulation in glioma cells (U373, U251) and in human cerebral microvascular endothelial cells (HCMEC). Surprisingly, Raf-1 gene silencing failed to affect cell survival, proliferation or migration activity in the glioblastoma cell lines. In HCMEC, however, pronounced decrease of cell survival and significant inhibition of tube formation was achieved by Raf-1 siRNA compared to non-functional siRNA or vehicle controls. In conclusion, Raf-1 silencing appears as a potential therapeutic strategy to inhibit brain tumor angiogenesis and thereby outgrowth of highly vascularized glioblastoma multiforme, whereas direct cytotoxic effects of Raf-1 knockdown in tumor cells may vary.

Predicting benefit from anti-angiogenic agents in malignancy

A high probability of benefit is desirable to justify the choice of anti-angiogenic therapy from an ever-expanding list of expensive new anticancer agents. However, biomarkers of response to cytotoxic agents are not optimal for predicting benefit from anti-angiogenic drugs. This discussion will focus on both preclinical and clinical research to identify biomarkers for anti-angiogenic therapies that can inform dosing, early clinical benefit, initial drug choice, emerging resistance and second-line treatments.

VEGF-targeting therapy for breast cancer

Vascular Endothelial Growth Factor (VEGF) plays an important role in multiple physiologic and pathologic processes involving endothelial cells. Several preclinical and clinical sources of evidence suggest its importance in human breast cancer. Based on the presumed biologic relevance of VEGF in human breast cancer, clinical trials using agents targeting VEGF were launched beginning in the late 1990s. This clinical trial effort came to fruition in 2005 with the success of the first large, prospective randomized trial of anti-VEGF therapy in patients with front-line metastatic breast cancer, which demonstrated the benefit of adding the monoclonal anti-ligand antibody bevacizumab to the chemotherapeutic agent paclitaxel. Based upon this success, numerous anti-VEGF agents are now being tested in patients with breast cancer, and adjuvant therapy trials are in development. Nevertheless, important questions remain regarding the biology and clinical development of these agents in breast cancer.