Targeting VEGF-A to treat cancer and age-related macular degeneration

The connection between lymphangiogenic signalling and prostaglandin biology: a missing link in the metastatic pathway

Substantial evidence supports important independent roles for lymphangiogenic growth factor signaling and prostaglandins in the metastatic spread of cancer. The significance of the lymphangiogenic growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, is well established in animal models of metastasis, and a strong correlation exits between an increase in expression of VEGF-C and VEGF-D, and metastatic spread in various solid human cancers. Similarly, key enzymes that control the production of prostaglandins, cyclooxygenases (COX-1 and COX-2, prototypic targets of Non-steroidal anti-inflammatory drugs (NSAIDs)), are frequently over-expressed or de-regulated in the progression of cancer. Recent data have suggested an intersection of lymphangiogenic growth factor signaling and the prostaglandin pathways in the control of metastatic spread via the lymphatic vasculature. Furthermore, this correlates with current clinical data showing that some NSAIDs enhance the survival of cancer patients through reducing metastasis. Here, we discuss the potential biochemical and cellular basis for such anti-cancer effects of NSAIDs through the prostaglandin and VEGF signaling pathways.

A hybrid discrete-continuum mathematical model of pattern prediction in the developing retinal vasculature

Pathological angiogenesis has been extensively explored by the mathematical modelling community over the past few decades, specifically in the contexts of tumour-induced vascularisation and wound healing. However, there have been relatively few attempts to model angiogenesis associated with normal development, despite the availability of animal models with experimentally accessible and highly ordered vascular topologies: for example, growth and development of the vascular plexus layers in the murine retina. The current study aims to address this issue through the development of a hybrid discrete-continuum mathematical model of the developing retinal vasculature in neonatal mice that is closely coupled with an ongoing experimental programme. The model of the functional vasculature is informed by a range of morphological and molecular data obtained over a period of several days, from 6 days prior to birth to approximately 8 days after birth. The spatio-temporal formation of the superficial retinal vascular plexus (RVP) in wild-type mice occurs in a well-defined sequence. Prior to birth, astrocytes migrate from the optic nerve over the surface of the inner retina in response to a chemotactic gradient of PDGF-A, formed at an earlier stage by migrating retinal ganglion cells (RGCs). Astrocytes express a variety of chemotactic and haptotactic proteins, including VEGF and fibronectin (respectively), which subsequently induce endothelial cell sprouting and modulate growth of the RVP. The developing RVP is not an inert structure; however, the vascular bed adapts and remodels in response to a wide variety of metabolic and biomolecular stimuli. The main focus of this investigation is to understand how these interacting cellular, molecular, and metabolic cues regulate RVP growth and formation. In an earlier one-dimensional continuum model of astrocyte and endothelial migration, we showed that the measured frontal velocities of the two cell types could be accurately reproduced by means of a system of five coupled partial differential equations (Aubert et al. in Bull. Math. Biol. 73:2430-2451, 2011). However, this approach was unable to generate spatial information and structural detail for the entire retinal surface. Building upon this earlier work, a more realistic two-dimensional hybrid PDE-discrete model is derived here that tracks the migration of individual astrocytes and endothelial tip cells towards the outer retinal boundary. Blood perfusion is included throughout plexus development and the emergent retinal architectures adapt and remodel in response to various biological factors. The resulting in silico RVP structures are compared with whole-mounted retinal vasculatures at various stages of development, and the agreement is found to be excellent. Having successfully benchmarked the model against wild-type data, the effect of transgenic over-expression of various genes is predicted, based on the ocular-specific expression of VEGF-A during murine development. These results can be used to help inform future experimental investigations of signalling pathways in ocular conditions characterised by aberrant angiogenesis.

Tumour-secreted miR-9 promotes endothelial cell migration and angiogenesis by activating the JAK-STAT pathway

Angiogenesis plays a crucial role during tumorigenesis and much progress has been recently made in elucidating the role of VEGF and other growth factors in the regulation of angiogenesis. Recently, microRNAs (miRNAs) have been shown to modulate a variety of physiogical and pathological processes. We identified a set of differentially expressed miRNAs in microvascular endothelial cells co-cultured with tumour cells. Unexpectedly, most miRNAs were derived from tumour cells, packaged into microvesicles (MVs), and then directly delivered to endothelial cells. Among these miRNAs, we focused on miR-9 due to the strong morphological changes induced in cultured endothelial cells. We found that exogenous miR-9 effectively reduced SOCS5 levels, leading to activated JAK-STAT pathway. This signalling cascade promoted endothelial cell migration and tumour angiogenesis. Remarkably, administration of anti-miR-9 or JAK inhibitors suppressed MV-induced cell migration in vitro and decreased tumour burden in vivo. Collectively, these observations suggest that tumour-secreted miRNAs participate in intercellular communication and function as a novel pro-angiogenic mechanism.

Hypoxia inducible factor-1α is necessary for invasive phenotype in Vegf-deleted islet cell tumors

In the mouse model of pancreas endocrine tumor, loss of Vegf (VKO) results in dramatically decreased tumor progression; however, the residual microscopic lesions show increased invasion into surrounding exocrine tissue. Double KO mice of Vegf and hypoxia inducible factor-1α (Hif-1α) showed increased life span and suppressed tumor growth due to increased apoptosis. The increased invasiveness of tumors in VKO mice was diminished in DKO mice to the levels of wild-type mice. Compared to VKO mice, DKO mice also exhibited smaller changes in the expression levels of adhesion molecules, including E-cadherin, N-cadherin, and NCAM. These changes of adhesion molecules were not observed in the primary culture of the tumor cells under hypoxic conditions. Thus, the invasive phenotype observed under angiogenesis inhibition requires Hif-1α, but is not directly caused by acute hypoxia.

Workshop on immunotherapy combinations. Society for Immunotherapy of Cancer annual meeting Bethesda, November 3, 2011

Although recent FDA approvals on ipilimumab and sipuleucel-T represent major milestones, the ultimate success of immunotherapy approaches will likely benefit from appropriate combinations with other immunotherapeutic and/or non-immunotherapeutic approaches. However, implementation of ideal combinations in the clinic may still face formidable challenges in regulatory, drug-availability and intellectual property aspects. The 2011 SITC annual meeting hosted a workshop on combination immunotherapy to discuss: 1) the most promising combinations found in the laboratory; 2) early success of combination immunotherapy in clinical trials; 3) industry perspectives on combination approaches, and 4) relevant regulatory issues. The integrated theme was how to accelerate the implementation of efficacious combined immunotherapies for cancer patients. Rodent animal models are providing many examples of synergistic combinations that typically include more than two agents. However, mouse and human immunology differ in a significant number of mechanisms and hence we might be missing opportunities peculiar to humans. Nonetheless, incisive animal experimentation with deep mechanistic insight remains the best compass that we can use to guide our paths in combinatorial immunotherapy. Combination immunotherapy clinical trials are already in progress and preliminary results are extremely promising. As a key to translate promising combinations into clinic, real and “perceived” business and regulatory hurdles were debated. A formidable step forward would be to be able to test combinations of investigational agents prior to individual approval. Taking together the FDA and the industrial perspective on combinatorial immunotherapy, the audience was left with the clear message that this is by no means an impossible task. The general perception is that the road ahead of us is full of combination clinical trials which hopefully will bring clinical benefit to our cancer patients at a fast pace.

Biological, preclinical and clinical characteristics of inhibitors of vascular endothelial growth factors

Vascular endothelial growth factor (VEGF) plays an important role in the pathophysiology of several sight-threatening retinal disorders such as age-related macular degeneration, diabetic macular edema and proliferative diabetic retinopathy. The discovery of anti-VEGF agents has revolutionized our treatment of these conditions. There are 4 anti-VEGF agents that are either approved or in common use in ophthalmology, namely pegaptanib (Macugen, Pfizer), ranibizumab (Lucentis, Novartis), aflibercept or VEGF Trap-Eye (EYLEA, Bayer) and bevacizumab (Avastin, Roche). There are differences between them. In this review, the differences are discussed in detail. Furthermore, an attempt is made to explain some of the clinical trial data based on their differences in ocular efficacy, duration of action, and local and systemic safety concerns.

Induction of Bv8 expression by granulocyte colony-stimulating factor in CD11b+Gr1+ cells: key role of Stat3 signaling

Bv8, also known as prokineticin 2, has been characterized as an important mediator of myeloid cell mobilization and myeloid cell-dependent tumor angiogenesis. Bv8 expression is dramatically enhanced by G-CSF, both in vitro and in vivo. The mechanisms involved in such up-regulation remain unknown. Using pharmacological inhibitors that interfere with multiple signaling pathways known to be activated by G-CSF, we show that signal transducer and activator of transcription 3 (Stat3) activation is required for Bv8 up-regulation in mouse bone marrow cells, whereas other Stat family members and extracellular signal-regulated kinase (ERK) activation are not involved. We further identified CD11b(+) Gr1(+) myeloid cells as the primary cell population in which Stat3 signaling is activated by G-CSF. Bv8 expression induced by G-CSF was also significantly reduced by siRNA-mediated Stat3 knockdown. Moreover, chromatin immunoprecipitation studies indicate that G-CSF significantly induces binding of phospho-Stat3 to the Bv8 promoter, which was abolished by pretreatment with the Stat3 inhibitor WP1066. Luciferase assay confirmed that the phospho-Stat3 binding site is a functional enhancer of the Bv8 promoter. The key role of Stat3 signaling in regulating G-CSF-induced Bv8 expression was further confirmed by in vivo studies. We show that the regulation of Bv8 expression in human bone marrow cells is also Stat3 signaling-dependent. Stat3 is recognized as a key regulator of inflammation-dependent tumorigenesis. We propose that such a role of Stat3 reflects at least in part its ability to regulate Bv8 expression.

Unraveling the influence of endothelial cell density on VEGF-A signaling

Vascular endothelial growth factor-A (VEGF) is the master determinant for the activation of the angiogenic program leading to the formation of new blood vessels to sustain solid tumor growth and metastasis. VEGF specific binding to VEGF receptor-2 (VEGFR-2) triggers different signaling pathways, including phospholipase C-γ (PLC-γ) and Akt cascades, crucial for endothelial proliferation, permeability, and survival. By combining biologic experiments, theoretical insights, and mathematical modeling, we found that: (1) cell density influences VEGFR-2 protein level, as receptor number is 2-fold higher in long-confluent than in sparse cells; (2) cell density affects VEGFR-2 activation by reducing its affinity for VEGF in long-confluent cells; (3) despite reduced ligand-receptor affinity, high VEGF concentrations provide long-confluent cells with a larger amount of active receptors; (4) PLC-γ and Akt are not directly sensitive to cell density but simply transduce downstream the upstream difference in VEGFR-2 protein level and activation; and (5) the mathematical model correctly predicts the existence of at least one protein tyrosine phosphatase directly targeting PLC-γ and counteracting the receptor-mediated signal. Our data-based mathematical model quantitatively describes VEGF signaling in quiescent and angiogenic endothelium and is suitable to identify new molecular determinants and therapeutic targets.

Intrinsic therapeutic applications of noble metal nanoparticles: past, present and future

Biomedical nanotechnology is an evolving field having enormous potential to positively impact the health care system. Important biomedical applications of nanotechnology that may have potential clinical applications include targeted drug delivery, detection/diagnosis and imaging. Basic understanding of how nanomaterials, the building blocks of nanotechnology, interact with the cells and their biological consequences are beginning to evolve. Noble metal nanoparticles such as gold, silver and platinum are particularly interesting due to their size and shape dependent unique optoelectronic properties. These noble metal nanoparticles, particularly of gold, have elicited a lot of interest for important biomedical applications because of their ease of synthesis, characterization and surface functionalization. Furthermore, recent investigations are demonstrating another promising application of these nanomaterials as self-therapeutics. To realize the potential promise of these unique inorganic nanomaterials for future clinical translation, it is of utmost importance to understand a few critical parameters; (i) how these nanomaterials interact with the cells at the molecular level; (ii) how their biodistribution and pharmacokinetics influenced by their surface and routes of administration; (iii) mechanism of their detoxification and clearance and (iv) their therapeutic efficacy in appropriate disease model. Thus in this critical review, we will discuss the various clinical applications of gold, silver and platinum nanoparticles with relevance to above parameters. We will also mention various routes of synthesis of these noble metal nanoparticles. However, before we discuss present research, we will also look into the past. We need to understand the discoveries made before us in order to further our knowledge and technological development (318 references).

Inhibition of angiogenesis and the angiogenesis/invasion shift

Angiogenesis has become a major target in cancer therapy. However, current therapeutic strategies have their limitations and raise several problems. In most tumours, anti-angiogenesis treatment targeting VEGF (vascular endothelial growth factor) has only limited overall survival benefit compared with conventional chemotherapy alone, and reveals several specific forms of resistance to anti-VEGF treatment. There is growing evidence that anti-VEGF treatment may induce tumour cell invasion by selecting highly invasive tumour cells or hypoxia-resistant cells, or by up-regulating angiogenic alternative pathways such as FGFs (fibroblast growth factors) or genes triggering new invasive programmes. We have identified new genes up-regulated during glioma growth on the chick CAM (chorioallantoic membrane). Our results indicate that anti-angiogenesis treatment in the experimental glioma model drives expression of critical genes which relate to disease aggressiveness in glioblastoma patients. We have identified a molecular mechanism in tumour cells that allows the switch from an angiogenic to invasive programme. Furthermore, we are focusing our research on alternative inhibitors that act, in part, independently of VEGF. These are endogenous molecules that play a role in the control of tumour growth and may constitute a starting point for further development of novel therapeutic or diagnostic tools.

Targeting oncogenic serine/threonine-protein kinase BRAF in cancer cells inhibits angiogenesis and abrogates hypoxia

Carcinomas are comprised of transformed epithelial cells that are supported in their growth by a dedicated neovasculature. How the genetic milieu of the epithelial compartment influences tumor angiogenesis is largely unexplored. Drugs targeted to mutant cancer genes may act not only on tumor cells but also, directly or indirectly, on the surrounding stroma. We investigated the role of the BRAF(V600E) oncogene in tumor/vessel crosstalk and analyzed the effect of the BRAF inhibitor PLX4720 on tumor angiogenesis. Knock-in of the BRAF(V600E) allele into the genome of human epithelial cells triggered their angiogenic response. In cancer cells harboring oncogenic BRAF, the inhibitor PLX4720 switches off the ERK pathway and inhibits the expression of proangiogenic molecules. In tumor xenografts harboring the BRAF(V600E), PLX4720 extensively modifies the vascular network causing abrogation of hypoxia. Overall, our results provide a functional link between oncogenic BRAF and angiogenesis. Furthermore, they indicate how the tumor vasculature can be "indirectly" besieged through targeting of a genetic lesion to which the cancer cells are addicted.

Regulation of VEGF expression in human retinal cells by cytokines: implications for the role of inflammation in age-related macular degeneration

Chronic inflammation is implicated in the pathogenesis of age-related macular degeneration (AMD). Choroidal neovascularization (CNV) observed in exudative form of AMD results in vision loss. Human retinal pigment epithelial cell (HRPE) layer and choroidal tissue are the primary pathological sites in AMD. Pathological and therapeutic evidences have strongly indicated the vascular endothelial growth factor (VEGF) molecules as critical components in CNV pathogenesis. In these studies, we used human primary HRPE and choroidal fibroblast cells (HCHF) prepared from adult donor eyes. The effects of inflammatory cytokine (IFN-γ+ TNF-α+IL-1β) mix (ICM) on global gene expression profiles in HRPE cells, revealed 10- and 9-fold increase in VEGF-A and VEGF-C expression, respectively. The microarray results were validated by quantitative RT-PCR and secretion of VEGFs proteins. IL-1β is the most potent in inducing VEGFs secretion followed by IFN-γ and TNF-α, and the secretion was more effective in the presence of 2 and 3 cytokines. NF-κB and JAK-STAT pathway, but not HIF-1α, Sp-1, Sp-3, and STAT-3, transcription factors were upregulated and translocated to nucleus by ICM treatment. The mRNA levels of VEGF-A and VEGF-C and secretion of these proteins were also significantly enhanced by ICM in HCHF cells. The secretion of other angiogenic molecules, PEDF, SDF-1α, endostatin, and angiopoietins was not affected by ICM. Our results show that the inflammatory cytokines enhance secretion of VEGF-A and VEGF-C by HRPE and HCHF cells. These studies indicate that VEGFs secreted by these cells initiate and promote pathological choroidal and retinal noevascularization processes in AMD.

Molecular mechanisms of tumor angiogenesis

Tumors have been recently recognized as aberrant organs composed of a complex mixture of highly interactive cells that in addition to the cancer cell include stroma (fibroblasts, adipocytes, and myofibroblasts), inflammatory (innate and adaptive immune cells), and vascular cells (endothelial and mural cells). While initially cancer cells co-opt tissue-resident vessels, the tumor eventually recruits its own vascular supply. The process of tumor neovascularization proceeds through the combined output of inductive signals from the entire cellular constituency of the tumor. During the last two decades, the identification and mechanistic outcome of signaling pathways that mediate tumor angiogenesis have been elucidated. Interestingly, many of the genes and signaling pathways activated in tumor angiogenesis are identical to those operational during developmental vascular growth, but they lack feedback regulatory control and are highly affected by inflammatory cells and hypoxia. Consequently, tumor vessels are abnormal, fragile, and hyperpermeable. The lack of hierarchy and inconsistent investment of mural cells dampen the ability of the vessels to effectively perfuse the tumor, and the resulting hypoxia installs a vicious cycle that continuously perpetuates a state of vascular inefficiency. Pharmacological targeting of blood vessels, mainly through the VEGF signaling pathway, has proven effective in normalizing tumor vessels. This normalization improves perfusion and distribution of chemotherapeutic drugs with resulting tumor suppression and moderate increase in overall survival. However, resistance to antiangiogenic therapy occurs frequently and constitutes a critical barrier in the inhibition of tumor growth. A concrete understanding of the chief signaling pathways that stimulate vascular growth in tumors and their cross-talk will continue to be essential to further refine and effectively abort the angiogenic response in cancer.

Mitochondrial respiration inhibitors suppress protein translation and hypoxic signaling via the hyperphosphorylation and inactivation of translation initiation factor eIF2α and elongation factor eEF2

Over 20,000 lipid extracts of plants and marine organisms were evaluated in a human breast tumor T47D cell-based reporter assay for hypoxia-inducible factor-1 (HIF-1) inhibitory activity. Bioassay-guided isolation and dereplication-based structure elucidation of an active extract from the Bael tree (Aegle marmelos) afforded two protolimonoids, skimmiarepin A (1) and skimmiarepin C (2). In T47D cells, 1 and 2 inhibited hypoxia-induced HIF-1 activation with IC50 values of 0.063 and 0.068 μM, respectively. Compounds 1 and 2 also suppressed hypoxic induction of the HIF-1 target genes GLUT-1 and VEGF. Mechanistic studies revealed that 1 and 2 inhibited HIF-1 activation by blocking the hypoxia-induced accumulation of HIF-1α protein. At the range of concentrations that inhibited HIF-1 activation, 1 and 2 suppressed cellular respiration by selectively inhibiting the mitochondrial electron transport chain at complex I (NADH dehydrogenase). Further investigation indicated that mitochondrial respiration inhibitors such as 1 and rotenone induced the rapid hyperphosphorylation and inhibition of translation initiation factor eIF2α and elongation factor eEF2. The inhibition of protein translation may account for the short-term exposure effects exerted by mitochondrial inhibitors on cellular signaling, while the suppression of cellular ATP production may contribute to the inhibitory effects following extended treatment periods.

Antagonistic VEGF variants engineered to simultaneously bind to and inhibit VEGFR2 and alphavbeta3 integrin

Significant cross-talk exists between receptors that mediate angiogenesis, such as VEGF receptor-2 (VEGFR2) and α(v)β(3) integrin. Thus, agents that inhibit both receptors would have important therapeutic potential. Here, we used an antagonistic VEGF ligand as a molecular scaffold to engineer dual-specific proteins that bound to VEGFR2 and α(v)β(3) integrin with antibody-like affinities and inhibited angiogenic processes in vitro and in vivo. Mutations were introduced into a single-chain VEGF (scVEGF) ligand that retained VEGFR2 binding, but prevented receptor dimerization and activation. Yeast-displayed scVEGF mutant libraries were created and screened by high-throughput flow cytometric sorting to identify several variants that bound with high affinity to both VEGFR2 and α(v)β(3) integrin. These engineered scVEGF mutants were specific for α(v)β(3) integrin and did not bind to the related integrins α(v)β(5), α(iib)β(3), or α(5)β(1). In addition, surface plasmon resonance and cell binding assays showed that dual-specific scVEGF proteins can simultaneously engage both receptors. Compared to monospecific scVEGF mutants that bind VEGFR2 or α(v)β(3) integrin, dual-specific scVEGF proteins more strongly inhibited VEGF-mediated receptor phosphorylation, capillary tube formation, and proliferation of endothelial cells cultured on Matrigel or vitronectin-coated surfaces. Moreover, dual specificity conferred strong inhibition of VEGF-mediated blood vessel formation in Matrigel plugs in vivo, whereas monospecific scVEGF mutants that bind VEGFR2 or α(v)β(3) integrin were only marginally effective. Instead of relying on antibody associating domains or physical linkage, this work highlights an approach to creating dual-specific proteins where additional functionality is introduced into a protein ligand to complement its existing biological properties.

Safety and efficacy of a flexible dosing regimen of ranibizumab in neovascular age-related macular degeneration: the SUSTAIN study

OBJECTIVE

To evaluate the safety and efficacy of individualized ranibizumab treatment in patients with neovascular age-related macular degeneration.

DESIGN

Twelve-month, phase III, multicenter, open-label, single-arm study.

PARTICIPANTS

A total of 513 ranibizumab-naïve SUSTAIN patients.

INTERVENTION

Three initial monthly injections of ranibizumab (0.3 mg) and thereafter pro re nata (PRN) retreatment for 9 months based on prespecified retreatment criteria. Patients switched to 0.5 mg ranibizumab after approval in Europe.

MAIN OUTCOME MEASURES

Frequency of adverse events (AEs), monthly change of best-corrected visual acuity (BCVA) and central retinal thickness (CRT) from baseline, the time to first re-treatment, and the number of treatments were assessed.

RESULTS

A total of 249 patients (48.5%) reported ocular AEs, and 8 (1.5%) deaths, 5 (1.2%) patients with ocular serious AEs of the study eye (retinal hemorrhage, cataract, retinal pigment epithelial tear, reduced visual acuity [VA], vitreous hemorrhage), and 19 (3.7%) patients with arteriothromboembolic events were observed. Most frequent AEs in the study eye were reduced VA (18.5%), retinal hemorrhage (7.2%), increased intraocular pressure (7.0%), and conjunctival hemorrhage (5.5%). The average number of re-treatments from months 3 to 11 was 2.7. Mean best-corrected visual acuity increased steadily from baseline to month 3 to reach +5.8 letters, decreased slightly from month 3 to 6, and remained stable from month 6 to 12, reaching +3.6 at month 12. Mean change in CRT was -101.1 μm from baseline to month 3 and -91.5 μm from baseline to month 12.

CONCLUSIONS

The safety results are comparable to the favorable tolerability profile of ranibizumab observed in previous pivotal clinical studies; individualized treatment with less than monthly re-treatments shows a similar safety profile as observed in previous randomized clinical trials with monthly ranibizumab treatment. Efficacy outcomes were achieved with a low average number of re-treatments. Visual acuity in SUSTAIN patients with individualized re-treatment based on VA/optical coherence tomography assessment reached on average a maximum after the first 3 monthly injections, decreased slightly under PRN during the next 2 to 3 months, and was then sustained throughout the treatment period.

Rap1 promotes VEGFR2 activation and angiogenesis by a mechanism involving integrin αvβ₃

Vascular endothelial growth factor (VEGF) acting through VEGF receptor 2 (VEGFR2) on endothelial cells (ECs) is a key regulator of angiogenesis, a process essential for wound healing and tumor metastasis. Rap1a and Rap1b, 2 highly homologous small G proteins, are both required for angiogenesis in vivo and for normal EC responses to VEGF. Here we sought to determine the mechanism through which Rap1 promotes VEGF-mediated angiogenesis. Using lineage-restricted Rap1-knockout mice we show that Rap1-deficiency in endothelium leads to defective angiogenesis in vivo, in a dose-dependent manner. Using ECs obtained from Rap1-deficient mice we demonstrate that Rap1b promotes VEGF-VEGFR2 kinase activation and regulates integrin activation. Importantly, the Rap1b-dependent VEGF-VEGFR2 activation is in part mediated via integrin α(v)β(3). Furthermore, in an in vivo model of zebrafish angiogenesis, we demonstrate that Rap1b is essential for the sprouting of intersomitic vessels, a process known to be dependent on VEGF signaling. Using 2 distinct pharmacologic VEGFR2 inhibitors we show that Rap1b and VEGFR2 act additively to control angiogenesis in vivo. We conclude that Rap1b promotes VEGF-mediated angiogenesis by promoting VEGFR2 activation in ECs via integrin α(v)β(3). These results provide a novel insight into the role of Rap1 in VEGF signaling in ECs.

Long-term efficacy and safety of ranibizumab administered pro re nata in Japanese patients with neovascular age-related macular degeneration in the EXTEND-I study

PURPOSE

To evaluate the long-term efficacy and safety of ranibizumab administered pro re nata (PRN) in Japanese patients with choroidal neovascularization secondary to age-related macular degeneration during the extension phase of the EXTEND-I study.

METHODS

EXTEND-I, an open-label, multicenter, Phase I ⁄ II study comprised: a single-injection (Group A); a multiple-injection (Groups A and B; the latter consisted of patients who did not participate in the single-injection phase); and an extension phase. In the extension phase, a PRN regimen of ranibizumab (0.3 or 0.5 mg) guided by monthly best-corrected visual acuity (BCVA) score and other ophthalmic examinations was employed. The efficacy variables included the mean BCVA change from Month 12 to the last visit in Group B. Safety was assessed in all patients.

RESULTS

In the extension phase, efficacy was assessed only in Group B patients. The number of ranibizumab injections per year in the 0.3 and 0.5 mg Group B patients was 4.19 and 4.27, respectively. The mean BCVA change (SD) from Month 12 to the last visit was )3.6 (14.82) letters for 0.3 mg (n = 28) and )2.2 (7.92) letters for 0.5 mg groups (n = 33) in Group B. Conjunctival haemorrhage and nasopharyngitis were the most commonly reported adverse events. Of the 13 serious adverse events reported, cerebral infarction (two incidences) was suspected to be study-drug related.

CONCLUSIONS

Pro re nata regimen of ranibizumab guided by monthly BCVA and other ophthalmic examinations appears effective in sustaining the BCVA gained with 12 monthly injections while reducing the number of injections during the extension phase. Ranibizumab was well tolerated during the extension phase.

Pazopanib synergizes with docetaxel in the treatment of bladder cancer cells

OBJECTIVES

To investigate the efficacy of pazopanib, both alone and in combination with docetaxel, in bladder cancer cells. Bladder cancer expresses many potential therapeutic targets of biological agents, including the vascular endothelial growth factor receptor (VEGFR). Pazopanib is a small molecule inhibitor of VEGFR-1, -2-3, platelet-derived growth factor receptor (PDGFR), and c-Kit.

MATERIALS AND METHODS

Using human bladder cancer cells HTB3, HT1376, J82, RT4, CRL1749, T24, Sup, and HTB9, the treatment effect of pazopanib and cytotoxic chemotherapy was assessed using a tetrazolium-based assay. The combinatorial effect of these agents on clonogenic growth was further examined. Western blotting was used to assess changes in relevant downstream targets, including phospho-AKT, phospho-FAK, total AKT, and total FAK.

RESULTS

Single-agent pazopanib had modest activity. However, synergy was seen with the combination of docetaxel and pazopanib in these multiple cells lines. J82 and T24 cells were selected for additional clonogenic testing because of their resistance to single-agent docetaxel chemotherapy. 1.25 nM of docetaxel had little effect on clonogenic formation; however, in combination with pazopanib, significant inhibition of colony formation was observed. This combination treatment additionally decreased phospho-AKT, an important mediator of cell survival in all cell lines, whereas phospho-FAK expression was variably affected.

CONCLUSIONS

The present study demonstrates synergistic efficacy of pazopanib with docetaxel in docetaxel-resistant bladder cancer cells. This work supports future evaluation of pazopanib with docetaxel for the treatment of bladder cancer with the potential of improved efficacy and toxicity.

Comparing protein VEGF inhibitors: In vitro biological studies

VEGF inhibitors are widely used as a therapy for tumors and intravascular neovascular disorders, but limited and conflicting data regarding their relative biological potencies are available. The purpose of the study is to compare different protein VEGF inhibitors for their ability to inhibit VEGF-stimulated activities. We tested ranibizumab, the full-length variant of ranibizumab (Mab Y0317), bevacizumab, the VEGF-TrapR1R2 and Flt(1-3)-IgG in bioassays measuring VEGF-stimulated proliferation of bovine retinal microvascular endothelial cells or chemotaxis of human umbilical vein endothelial cells (HUVEC). The inhibitors were also compared for their ability to inhibit MAP kinase activation in HUVECs following VEGF addition. Ranibizumab, VEGF-TrapR1R2 and Flt(1-3)-IgG had very similar potencies in the bioassays tested. Bevacizumab was over 10-fold less potent than these molecules. Mab Y0317 was over 30-fold more potent than bevacizumab. The findings reported in this manuscript describe important intrinsic characteristics of several VEGF inhibitors that may be useful to design and interpret preclinical or clinical studies.

Infantile aphakic glaucoma: a proposed etiologic role of IL-4 and VEGF

PURPOSE

To identify the factors secreted by lens epithelial cells (LECs) responsible for the altered trabecular meshwork (TM) cells and to compare their effect on monocultured TM cells with that of TM cells co-cultured with LECs.

METHODS

Such factors were isolated using cytokine antibody array membranes, and their effect on TM cells was assessed by analyzing changes in morphology and gene expression. In addition, inhibition of the isolated factors was performed in the co-culture model by adding specific antibodies to the cell culture media.

RESULTS

Transforming growth factor beta-2, interleukin-4 (IL-4), and vascular endothelial growth factor (VEGF) are presented as candidate cytokines responsible for the observed changes in LEC-TM co-cultures. Culturing TM cells in the presence of VEGF and IL-4 triggered alterations closely reflecting those observed in the LEC-TM co-culture model, where their inhibition significantly hindered the alteration of the TM cells.

CONCLUSION

These findings suggest a possible explanation for the development of infantile aphakic glaucoma, based on residual LECs secreting IL-4 and VEGF after removal of congenital cataract, which then alter trabecular meshwork cell morphology and gene expression.

Natural and semisynthetic mammea-type isoprenylated dihydroxycoumarins uncouple cellular respiration

In an effort to identify natural product-based molecular-targeted antitumor agents, mammea-type coumarins from the tropical/subtropical plant Mammea americana were found to inhibit the activation of HIF-1 (hypoxia-inducible factor-1) in human breast and prostate tumor cells. In addition to the recently reported mammea E/BB (15), bioassay-guided fractionation of the active extract yielded 14 mammea-type coumarins including three new compounds, mammea F/BB (1), mammea F/BA (2), and mammea C/AA (3). The absolute configuration of C-1' in 1 was determined by the modified Mosher's method on a methylated derivative. These coumarins were evaluated for their effects on mitochondrial respiration, HIF-1 signaling, and tumor cell proliferation/viability. Acetylation of 1 afforded a triacetoxylated product (A-2) that inhibited HIF-1 activation with increased potency in both T47D (IC(50) 0.83 μM for hypoxia-induced) and PC-3 cells (IC(50) 0.94 μM for hypoxia-induced). Coumarins possessing a 6-prenyl-8-(3-methyloxobutyl) substituent pattern exhibited enhanced HIF-1 inhibitory effects. The O-methylated derivatives were less active at inhibiting HIF-1 and suppressing cell proliferation/viability. Mechanistic studies indicate that these compounds act as anionic protonophores that potently uncouple mitochondrial electron transport and disrupt hypoxic signaling.

Arterial thromboembolic events in patients with exudative age-related macular degeneration treated with intravitreal bevacizumab or ranibizumab

BACKGROUND/AIMS

To compare retrospectively the incidence of arterial thromboembolic events (ATEs) in patients treated with bevacizumab or ranibizumab for exudative age-related macular degeneration.

METHODS

Charts of 378 patients treated with at least 1 intravitreal injection of ranibizumab or bevacizumab were reviewed to calculate the incidence of ATEs. Only patients under monotherapy were analyzed.

RESULTS

ATEs occurred in 15 patients: 12 (12/97) with bevacizumab (12.4%) and 3 (3/219) with ranibizumab (1.4%) - odds ratio 10.16; 95% confidence interval 2.80-36.93; p < 0.0001. ATEs in the bevacizumab and ranibizumab cohorts included stroke, myocardial infarction, angina pectoris, peripheral thromboembolic disease, transient ischemic attack, sudden death and lethal stroke.

CONCLUSION

In this series, bevacizumab raised the risk of ATEs when compared to ranibizumab. In an elderly population with multiple cardiovascular risk factors, the new ATEs may not be attributed exclusively to the intravitreal bevacizumab administration. These findings raise an issue that must be confirmed in randomized clinical trials.

Efficacy and safety of monthly versus quarterly ranibizumab treatment in neovascular age-related macular degeneration: the EXCITE study

OBJECTIVE

To demonstrate noninferiority of a quarterly treatment regimen to a monthly regimen of ranibizumab in patients with subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD).

DESIGN

A 12-month, multicenter, randomized, double-masked, active-controlled, phase IIIb study.

PARTICIPANTS

Patients with primary or recurrent subfoveal CNV secondary to AMD (353 patients), with predominantly classic, minimally classic, or occult (no classic component) lesions.

INTERVENTION

Patients were randomized (1:1:1) to 0.3 mg quarterly, 0.5 mg quarterly, or 0.3 mg monthly doses of ranibizumab. Treatment comprised of a loading phase (3 consecutive monthly injections) followed by a 9-month maintenance phase (either monthly or quarterly injection).

MAIN OUTCOME MEASURES

Mean change in best-corrected visual acuity (BCVA) and central retinal thickness (CRT) from baseline to month 12 and the incidence of adverse events (AEs).

RESULTS

In the per-protocol population (293 patients), BCVA, measured by Early Treatment Diabetic Retinopathy Study-like charts, increased from baseline to month 12 by 4.9, 3.8, and 8.3 letters in the 0.3 mg quarterly (104 patients), 0.5 mg quarterly (88 patients), and 0.3 mg monthly (101 patients) dosing groups, respectively. Similar results were observed in the intent-to-treat (ITT) population (353 patients). The mean decrease in CRT from baseline to month 12 in the ITT population was -96.0 μm in 0.3 mg quarterly, -105.6 μm in 0.5 mg quarterly, and -105.3 μm in 0.3 mg monthly group. The most frequent ocular AEs were conjunctival hemorrhage (17.6%, pooled quarterly groups; 10.4%, monthly group) and eye pain (15.1%, pooled quarterly groups; 20.9%, monthly group). There were 9 ocular serious AEs and 3 deaths; 1 death was suspected to be study related (cerebral hemorrhage; 0.5 mg quarterly group). The incidences of key arteriothromboembolic events were low.

CONCLUSIONS

After 3 initial monthly ranibizumab injections, both monthly (0.3 mg) and quarterly (0.3 mg/0.5 mg) ranibizumab treatments maintained BCVA in patients with CNV secondary to AMD. At month 12, BCVA gain in the monthly regimen was higher than that of the quarterly regimens. The noninferiority of a quarterly regimen was not achieved with reference to 5.0 letters. The safety profile was similar to that reported in prior ranibizumab studies.

Mammea E/BB, an isoprenylated dihydroxycoumarin protonophore that potently uncouples mitochondrial electron transport, disrupts hypoxic signaling in tumor cells

The mammea-type coumarin mammea E/BB (1) was found to inhibit both hypoxia-induced and iron chelator-induced hypoxia-inducible factor-1 (HIF-1) activation in human breast tumor T47D cells with IC(50) values of 0.96 and 0.89 μM, respectively. Compound 1 suppressed the hypoxic induction of secreted VEGF protein (T47D cells) and inhibited cell viability/proliferation in four human tumor cell lines. Compound 1 (at 5 and 20 μM) inhibited human breast tumor MDA-MB-231 cell migration. While the mechanisms that underlie their biological activities have remained unknown, prenylated mammea coumarins have been shown to be cytotoxic to human tumor cells, suppress tumor growth in animal models, and display a wide variety of antimicrobial effects. Mechanistic studies revealed that 1 appears to exert an assemblage of cellular effects by functioning as an anionic protonophore that potently uncouples mitochondrial electron transport and disrupts mitochondrial signaling in human tumor cell lines.

VEGF receptor signaling links inflammation and tumorigenesis in colitis-associated cancer

Inflammation drives expression of VEGFR2, which is expressed on and drives growth of tumor cells in colitis-associated cancer.

Whereas the inhibition of vascular endothelial growth factor (VEGF) has shown promising results in sporadic colon cancer, the role of VEGF signaling in colitis-associated cancer (CAC) has not been addressed. We found that, unlike sporadic colorectal cancer and control patients, patients with CAC show activated VEGFR2 on intestinal epithelial cells (IECs). We then explored the function of VEGFR2 in a murine model of colitis-associated colon cancer characterized by increased VEGFR2 expression. Epithelial cells in tumor tissue expressed VEGFR2 and responded to VEGF stimulation with augmented VEGFR2-mediated proliferation. Blockade of VEGF function via soluble decoy receptors suppressed tumor development, inhibited tumor angiogenesis, and blocked tumor cell proliferation. Functional studies revealed that chronic inflammation leads to an up-regulation of VEGFR2 on IECs. Studies in conditional STAT3 mutant mice showed that VEGFR signaling requires STAT3 to promote epithelial cell proliferation and tumor growth in vivo. Thus, VEGFR-signaling acts as a direct growth factor for tumor cells in CAC, providing a molecular link between inflammation and the development of colon cancer.

Regulation of angiogenesis by histone chaperone HIRA-mediated incorporation of lysine 56-acetylated histone H3.3 at chromatin domains of endothelial genes

Angiogenesis is critically dependent on endothelial cell-specific transcriptional mechanisms. However, the molecular processes that regulate chromatin domains and thereby dictate transcription of key endothelial genes are poorly understood. Here, we report that, in endothelial cells, angiogenic signal-mediated transcriptional induction of Vegfr1 (vascular endothelial growth factor receptor 1) is dependent on the histone chaperone, HIRA (histone cell cycle regulation-defective homolog A). Our molecular analyses revealed that, in response to angiogenic signals, HIRA is induced in endothelial cells and mediates incorporation of lysine 56 acetylated histone H3.3 (H3acK56) at the chromatin domain of Vegfr1. HIRA-mediated incorporation of H3acK56 is a general mechanism associated with transcriptional induction of several angiogenic genes in endothelial cells. Depletion of HIRA inhibits H3acK56 incorporation and transcriptional induction of Vegfr1 and other angiogenic genes. Our functional analyses revealed that depletion of HIRA abrogates endothelial network formation on Matrigel and inhibits angiogenesis in an in vivo Matrigel plug assay. Furthermore, analysis in a laser-induced choroidal neovascularization model showed that depletion of HIRA significantly inhibits neovascularization. Our results for the first time decipher a histone chaperone (HIRA)-dependent molecular mechanism in endothelial gene regulation and indicate that histone chaperones could be new targets for angiogenesis therapy.

Inflammatory mediators and angiogenic factors in choroidal neovascularization: pathogenetic interactions and therapeutic implications

Choroidal neovascularization (CNV) is a common and severe complication in heterogeneous diseases affecting the posterior segment of the eye, the most frequent being represented by age-related macular degeneration. Although the term may suggest just a vascular pathological condition, CNV is more properly definable as an aberrant tissue invasion of endothelial and inflammatory cells, in which both angiogenesis and inflammation are involved. Experimental and clinical evidences show that vascular endothelial growth factor is a key signal in promoting angiogenesis. However, many other molecules, distinctive of the inflammatory response, act as neovascular activators in CNV. These include fibroblast growth factor, transforming growth factor, tumor necrosis factor, interleukins, and complement. This paper reviews the role of inflammatory mediators and angiogenic factors in the development of CNV, proposing pathogenetic assumptions of mutual interaction. As an extension of this concept, new therapeutic approaches geared to have an effect on both the vascular and the extravascular components of CNV are discussed.

Binding to the extracellular matrix and proteolytic processing: two key mechanisms regulating vascular endothelial growth factor action

Vascular endothelial growth factor (VEGF, VEGF-A) is a major regulator of physiological and pathological angiogenesis. One feature of VEGF is the existence of multiple isoforms arising from alternative exon splicing. Our initial biochemical and biological studies indicated that such isoforms are uniquely suited to generate angiogenic gradients by virtue of their differential ability to interact with the extracellular matrix (ECM). Although ECM-bound VEGF was bioactive, processing by physiologically relevant proteases such as plasmin was identified as a key mechanism to convert ECM-bound VEGF into freely diffusible forms. This retrospective article examines the early studies and also emphasizes the subsequent progress in our understanding of these processes in health and disease.

Cancer-associated myeloproliferation: old association, new therapeutic target

The association between malignancy and development of a paraneoplastic leukocytosis, the so-called leukemoid reaction, has long been appreciated. Although a leukemoid reaction has conventionally been defined as a peripheral blood leukocytosis composed of both mature and immature granulocytes that exceeds 50,000/microL, a less profound leukocytosis may be appreciated in many patients harboring a malignant disease. More recent insights have shed new light on this long-recognized association, because research performed in both murine models and cancer patients has uncovered multiple mechanisms by which tumors both drive myelopoiesis, sometimes leading to a clinically apparent leukocytosis, and inhibit the differentiation of myeloid cells, resulting in a qualitative change in myelopoiesis. This qualitative change leads to the accumulation of immature myeloid cells, which due to their immune suppressive effects have been collectively called myeloid-derived suppressor cells. More recently, myeloid cells have been shown to promote tumor angiogenesis. Cancer-associated myeloproliferation is not merely a paraneoplastic phenomenon of questionable importance but leads to the suppression of host immunity and promotion of tumor angiogenesis, both of which play an integral part in tumorigenesis and metastasis. Therefore, cancer-associated myeloproliferation represents a novel therapeutic target in cancer that, decades after its recognition, is only now being translated into clinical practice.

Biochemical and structural analysis of the binding determinants of a vascular endothelial growth factor receptor peptidic antagonist

Cyclic peptide antagonist c[YYDEGLEE]-NH(2), which disrupts the interaction between vascular endothelial growth factor (VEGF) and its receptors (VEGFRs), represents a promising tool in the fight against cancer and age-related macular degeneration. Furthermore, coupled to a cyclen derivative, this ligand could be used as a medicinal imaging agent. Nevertheless, before generating such molecular probes, some preliminary studies need to be undertaken in order to define the more suitable positions for introduction of the cyclen macrocycle. Through an Ala-scan study on this peptide, we identified its binding motif, and an NMR study highlights its binding sites on the VEGFR-1D2 Ig-like domain. Guided by the structural relationship results deduced from the effect of the peptides on endothelial cells, new peptides were synthesized and grafted on beads. Used in a pull-down assay, these new peptides trap the VEGFRs, thus confirming that the identified amino acid positions are suitable for further derivatization.

The marine sponge metabolite mycothiazole: a novel prototype mitochondrial complex I inhibitor

A natural product chemistry-based approach was applied to discover small-molecule inhibitors of hypoxia-inducible factor-1 (HIF-1). A Petrosaspongia mycofijiensis marine sponge extract yielded mycothiazole (1), a solid tumor selective compound with no known mechanism for its cell line-dependent cytotoxic activity. Compound 1 inhibited hypoxic HIF-1 signaling in tumor cells (IC(50) 1nM) that correlated with the suppression of hypoxia-stimulated tumor angiogenesis in vitro. However, 1 exhibited pronounced neurotoxicity in vitro. Mechanistic studies revealed that 1 selectively suppresses mitochondrial respiration at complex I (NADH-ubiquinone oxidoreductase). Unlike rotenone, MPP(+), annonaceous acetogenins, piericidin A, and other complex I inhibitors, mycothiazole is a mixed polyketide/peptide-derived compound with a central thiazole moiety. The exquisite potency and structural novelty of 1 suggest that it may serve as a valuable molecular probe for mitochondrial biology and HIF-mediated hypoxic signaling.

Antibody drug-conjugates targeting the tumor vasculature: Current and future developments

Reducing the blood supply of tumors is one modality to combat cancer. Monoclonal antibodies are now established as a key therapeutic approach for a range of diseases. Owing to the ability of antibodies to selectively target endothelial cells within the tumor vasculature, vascular targeting programs have become a mainstay in oncology drug development. However, the antitumor activity of single agent administration of conventional anti-angiogenic compounds is limited and the improvements in patient survival are most prominent in combinations with chemotherapy. Furthermore, prolonged treatment with conventional anti-angiogenic drugs is associated with toxicity and drug resistance. These circumstances provide a strong rationale for novel approaches to enhance the efficacy of mAbs targeting tumor vasculature such as antibody-drug conjugates (ADCs).Here, we review trends in the development of ADCs targeting tumor vasculature with the aim of informing future research and development of this class of therapeutics.

The alternative medicine pawpaw and its acetogenin constituents suppress tumor angiogenesis via the HIF-1/VEGF pathway

Products that contain twig extracts of pawpaw (Asimina triloba) are widely consumed anticancer alternative medicines. Pawpaw crude extract (CE) and purified acetogenins inhibited hypoxia-inducible factor-1 (HIF-1)-mediated hypoxic signaling pathways in tumor cells. In T47D cells, pawpaw CE and the acetogenins 10-hydroxyglaucanetin (1), annonacin (2), and annonacin A (3) inhibited hypoxia-induced HIF-1 activation with IC(50) values of 0.02 microg/mL, 12 nM, 13 nM, and 31 nM, respectively. This inhibition correlates with the suppression of the hypoxic induction of HIF-1 target genes VEGF and GLUT-1. The induction of secreted VEGF protein represents a key event in hypoxia-induced tumor angiogenesis. Both the extract and the purified acetogenins blocked the angiogenesis-stimulating activity of hypoxic T47D cells in vitro. Pawpaw extract and acetogenins inhibited HIF-1 activation by blocking the hypoxic induction of nuclear HIF-1alpha protein. The inhibition of HIF-1 activation was associated with the suppression of mitochondrial respiration at complex I. Thus, the inhibition of HIF-1 activation and hypoxic tumor angiogenesis constitutes a novel mechanism of action for these anticancer alternative medicines.

Tumor and stromal pathways mediating refractoriness/resistance to anti-angiogenic therapies

Identification and characterization of VEGF as an important regulator of angiogenesis, and FDA approval of the first anti-angiogenic drugs, has enabled significant advances in the therapy of cancer and neovascular age-related macular degeneration. However, similar to other therapies, inherent/acquired resistance to anti-angiogenic drugs may occur in patients, leading to disease recurrence. Recent studies in several experimental models suggest that tumor and non-tumor (stromal) cell types may be involved in the reduced responsiveness to the treatments. The present review examines the role of tumor- as well as stromal cell-derived pathways involved in tumor growth and in refractoriness to anti-VEGF therapies.

Angiogenesis inhibition in prostate cancer: current uses and future promises

Angiogenesis has been well recognized as a fundamental part of a multistep process in the evolution of cancer progression, invasion, and metastasis. Strategies for inhibiting angiogenesis have been one of the most robust fields of cancer investigation, focusing on the vascular endothelial growth factor (VEGF) family and its receptors. There are numerous regulatory drug approvals to date for the use of these agents in treating a variety of solid tumors. While therapeutic efficacy has been established, challenges remain with regards to overcoming resistance and assessing response to antiangiogenic therapies. Prostate cancer is the most common noncutaneous malignancy among American men and angiogenesis plays a role in disease progression. The use of antiangiogenesis agents in prostate cancer has been promising and is hereby explored.

Angiopoietin/Tie2 signaling transforms capillaries into venules primed for leukocyte trafficking in airway inflammation

Vascular endothelial growth factor (VEGF) is a key angiogenic factor in tumors, but less is known about what drives vascular remodeling in inflammation, where plasma leakage and leukocyte influx are prominent features. In chronic airway inflammation in mice infected by the bacterium Mycoplasma pulmonis (M. pulmonis), the segment of the microvasculature that supports leukocyte adhesion and migration expands through remodeling of capillaries into vessels with features of venules. Here, we report that the angiopoietin/Tie2 pathway is an essential driving force for capillary remodeling into venules in M. pulmonis-infected mouse airways. Similar to M. pulmonis infection, systemic overexpression of angiopoietin-1 (Ang1) resulted in remodeling of airway capillaries into venular-like vessels that expressed venous markers like P-selectin, ICAM-1, and EphB4 and were sites of leukocyte adhesion during lipopolysaccharide-induced acute inflammation. Ang1 and Ang2 protein increased in M. pulmonis-infected mouse airways but came from different cellular sources: Ang1 was expressed in infiltrating neutrophils and Ang2 in endothelial cells. Indeed, systemic administration of soluble Tie2 inhibited capillary remodeling, induction of venous markers, and leukocyte influx in M. pulmonis-infected mouse airways. Together, these findings suggest that blockade of the Ang/Tie2 pathway may represent a therapeutic approach in airway inflammation.

A human monoclonal anti-ANG2 antibody leads to broad antitumor activity in combination with VEGF inhibitors and chemotherapy agents in preclinical models

Localized angiopoietin-2 (Ang2) expression has been shown to function as a key regulator of blood vessel remodeling and tumor angiogenesis, making it an attractive candidate for antiangiogenic therapy. A fully human monoclonal antibody (3.19.3) was developed, which may have significant pharmaceutical advantages over synthetic peptide-based approaches in terms of reduced immunogenicity and increased half-life to block Ang2 function. The 3.19.3 antibody potently binds Ang2 with an equilibrium dissociation constant of 86 pmol/L, leading to inhibition of Tie2 receptor phosphorylation in cell-based assays. In preclinical models, 3.19.3 treatment blocked blood vessel formation in Matrigel plug assays and in human tumor xenografts. In vivo studies with 3.19.3 consistently showed broad antitumor activity as a single agent across a panel of diverse subcutaneous and orthotopic xenograft models. Combination studies of 3.19.3 with cytotoxic drugs or anti-vascular endothelial growth factor agents showed significant improvements in antitumor activity over single-agent treatments alone with no apparent evidence of increased toxicity. Initial pharmacokinetic profiling studies in mice and nonhuman primates suggested that 3.19.3 has a predicted human half-life of 10 to 14 days. These studies provide preclinical data for 3.19.3 as a potential new antiangiogenic therapy as a single agent or in combination with chemotherapy or vascular endothelial growth factor inhibitors for the treatment of cancer.

A dual-targeting PDGFRbeta/VEGF-A molecule assembled from stable antibody fragments demonstrates anti-angiogenic activity in vitro and in vivo

Targeting angiogenesis is a promising approach to the treatment of solid tumors and age-related macular degeneration (AMD). Inhibition of vascularization has been validated by the successful marketing of monoclonal antibodies (mAbs) that target specific growth factors or their receptors, but there is considerable room for improvement in existing therapies. Combination of mAbs targeting both the VEGF and PDGF pathways has the potential to increase the efficacy of anti-angiogenic therapy without the accompanying toxicities of tyrosine kinase inhibitors and the inability to combine efficiently with traditional chemotherapeutics. However, development costs and regulatory issues have limited the use of combinatorial approaches for the generation of more efficacious treatments. The concept of mediating disease pathology by targeting two antigens with one therapeutic was proposed over two decades ago. While mAbs are particularly suitable candidates for a dual-targeting approach, engineering bispecificity into one molecule can be difficult due to issues with expression and stability, which play a significant role in manufacturability. Here, we address these issues upstream in the process of developing a bispecific antibody (bsAb). Single-chain antibody fragments (scFvs) targeting PDGFRbeta and VEGF-A were selected for superior stability. The scFvs were fused to both termini of human Fc to generate a bispecific, tetravalent molecule. The resulting molecule displays potent activity, binds both targets simultaneously, and is stable in serum. The assembly of a bsAb using stable monomeric units allowed development of an anti-PDGFRB/VEGF-A antibody capable of attenuating angiogenesis through two distinct pathways and represents an efficient method for rapid engineering of dual-targeting molecules.

Pathways mediating VEGF-independent tumor angiogenesis

FDA approval of several inhibitors of the VEGF pathway has enabled significant advances in the therapy of cancer and neovascular age-related macular degeneration. However, similar to other therapies, inherent/acquired resistance to anti-angiogenic drugs may occur in patients, leading to disease progression. So far the lack of predictive biomarkers has precluded identification of patients most likely to respond to such treatments. Recent suggest that both tumor and non-tumor (stromal) cell types are involved in the reduced responsiveness to the treatments. The present review examines the role of tumor- as well as stromal cell-derived pathways involved in tumor growth and in refractoriness to anti-VEGF therapies.

The Caulerpa pigment caulerpin inhibits HIF-1 activation and mitochondrial respiration

The transcription factor hypoxia-inducible factor-1 (HIF-1) represents an important molecular target for anticancer drug discovery. In a T47D cell-based reporter assay, the Caulerpa spp. algal pigment caulerpin (1) inhibited hypoxia-induced as well as 1,10-phenanthroline-induced HIF-1 activation. The angiogenic factor vascular endothelial growth factor (VEGF) is regulated by HIF-1. Caulerpin (10 microM) suppressed hypoxic induction of secreted VEGF protein and the ability of hypoxic T47D cell-conditioned media to promote tumor angiogenesis in vitro. Under hypoxic conditions, 1 (10 microM) blocked the induction of HIF-1alpha protein, the oxygen-regulated subunit that controls HIF-1 activity. Reactive oxygen species produced by mitochondrial complex III are believed to act as a signal of cellular hypoxia that leads to HIF-1alpha protein induction and activation. Further mechanistic studies revealed that 1 inhibits mitochondrial respiration at electron transport chain (ETC) complex I (NADH-ubiquinone oxidoreductase). Under hypoxic conditions, it is proposed that 1 may disrupt mitochondrial ROS-regulated HIF-1 activation and HIF-1 downstream target gene expression by inhibiting the transport or delivery of electrons to complex III.