VEGF165b, an inhibitory vascular endothelial growth factor splice variant: mechanism of action, in vivo effect on angiogenesis and endogenous protein expression

Effects of receptor tyrosine kinase inhibitors on VEGF165 a- and VEGF165 b-stimulated gene transcription in HEK-293 cells expressing human VEGFR2

Background and Purpose

Receptor tyrosine kinase inhibitors (RTKIs) targeted at VEGF receptor 2 (VEGFR2) have proved to be attractive approaches to cancer therapy based on their ability to reduce angiogenesis. Here we have undertaken a quantitative analysis of the interaction of RTKIs and two VEGF splice variants, VEGF₁₆₅a and VEGF₁₆₅b, with VEGFR2 by studying nuclear factor of activated T-cells (NFAT) reporter gene activity in live HEK-293 cells.

Experimental Approach

HEK-293 cells expressing the human VEGFR2 and a firefly luciferase reporter gene regulated by an NFAT response element were used for quantitative analysis of the effect of RTKIs on VEGF₁₆₅a- and VEGF₁₆₅b-stimulated luciferase gene expression.

Key Results

VEGF₁₆₅a produced a concentration-dependent activation of the NFAT-luciferase reporter gene in living cells that was inhibited in a non-competitive fashion by four different RTKIs (cediranib, pazopanib, sorafenib and vandetanib). The potency obtained for each RTKI from this analysis was similar to those obtained in binding studies using purified VEGFR2 kinase domains. VEGF₁₆₅b was a lower-efficacy agonist of the NFAT-luciferase response when compared with VEGF₁₆₅a. Analysis of the concentration–response data using the operational model of agonism indicated that both VEGF₁₆₅ isoforms had similar affinity for VEGFR2.

Conclusions and Implications

Quantitative pharmacological analysis of the interaction of VEGF₁₆₅ isoforms and RTKIs with VEGFR2 in intact living cells has provided important insights into the relative affinity and efficacy of VEGF₁₆₅a and VEGF₁₆₅b for activation of the calcineurin- NFAT signalling pathway by this tyrosine kinase receptor.

The corneal pocket assay

The cornea in most species is physiologically avascular, and thus this assay allows the measurement of newly formed vessels. The continuous monitoring of neovascular growth in the same animal allows the evaluation of drugs acting as suppressors or stimulators of angiogenesis. Under anesthesia a micropocket is produced in the cornea thickness and the angiogenesis stimulus (tumor tissue, cell suspension, growth factor) is placed into the pocket in order to induce vascular outgrowth from the limbal capillaries. Neovascular development and progression can be modified by the presence of locally released or applied inhibitory factors or by systemic treatments. In this chapter the experimental details of the avascular cornea assay, the technical challenges, and advantages and disadvantages in different species are discussed. Protocols for local drug treatment and tissue sampling for histology and pharmacokinetic profile are reported.

Alternative splicing of TIA-1 in human colon cancer regulates VEGF isoform expression, angiogenesis, tumour growth and bevacizumab resistance

The angiogenic capability of colorectal carcinomas (CRC), and their susceptibility to anti-angiogenic therapy, is determined by expression of vascular endothelial growth factor (VEGF) isoforms. The intracellular protein T-cell Intracellular Antigen (TIA-1) alters post-transcriptional RNA processing and binds VEGF-A mRNA. We therefore tested the hypothesis that TIA-1 could regulate VEGF-A isoform expression in colorectal cancers. TIA-1 and VEGF-A isoform expression was measured in colorectal cancers and cell lines. We discovered that an endogenous splice variant of TIA-1 encoding a truncated protein, short TIA-1 (sTIA-1) was expressed in CRC tissues and invasive K-Ras mutant colon cancer cells and tissues but not in adenoma cell lines. sTIA-1 was more highly expressed in CRC than in normal tissues and increased with tumour stage. Knockdown of sTIA-1 or over-expression of full length TIA-1 (flTIA-1) induced expression of the anti-angiogenic VEGF isoform VEGF-A165b. Whereas flTIA-1 selectively bound VEGF-A165 mRNA and increased translation of VEGF-A165b, sTIA-1 prevented this binding. In nude mice, xenografted colon cancer cells over-expressing flTIA-1 formed smaller, less vascular tumours than those expressing sTIA-1, but flTIA-1 expression inhibited the effect of anti-VEGF antibodies. These results indicate that alternative splicing of an RNA binding protein can regulate isoform specific expression of VEGF providing an added layer of complexity to the angiogenic profile of colorectal cancer and their resistance to anti-angiogenic therapy.

Detection and Quantification of VEGF Isoforms by ELISA

Vascular endothelial growth factor (VEGF) is a potent mitogen for endothelial cells and plays an important role in physiological and tumor angiogenesis. The human VEGF gene has eight exons. Different VEGF isoforms are expressed via alternative RNA splicing and VEGF121 and VEGF165 are the major isoforms present in human tissues. The exact roles of these different VEGF isoforms are not totally clear. Assays to detect specific VEGF isoforms in biological samples are needed to understand the biological functions of these different VEGF isoforms and to better assess their potential use as predicative biomarkers for anti-angiogenic therapy. Because monoclonal antibodies specific to different VEGF isoforms are lacking, we used antibodies directed to different epitopes on VEGF165 in a set of three enzyme-linked immunosorbent assays (ELISAs) to assess the amount of VEGF121 and VEGF165 as well as VEGF110, which can be generated by plasmin cleavage in vivo. The first ELISA detects VEGF165. The second ELISA detects both VEGF121 and VEGF165. The third ELISA detects VEGF165, VEGF121, and VEGF110. The concentrations of VEGF121 can be assessed from the difference in VEGF concentrations measured by the second and the first ELISAs; the concentrations of VEGF110 can be assessed from the difference in VEGF concentrations measured by the third and the second ELISAs. The same assay strategy may be used to assess the amount of other VEGF isoforms if antibodies directed against the desired amino acids in those isoforms can be obtained.

VEGF Splicing and the Role of VEGF Splice Variants: From Physiological-Pathological Conditions to Specific Pre-mRNA Splicing

During this past decade, the vascular endothelial growth factor (VEGF) pathway has been extensively studied. VEGF is a paradigm of molecular regulation since its expression is controlled at all possible steps including transcription, mRNA stability, translation, and pre-mRNA splicing. The latter form of molecular regulation is probably the least studied. This field has been neglected; yet different forms of VEGF with different sizes and different physiological properties issued from alternative splicing have been described a long time ago. Recently a new level of complexity was added to the field of splicing of VEGF pre-mRNA. Whereas thousands of publications have described VEGF as a pro-angiogenic factor, an alternative splicing event generates specific anti-angiogenic forms of VEGF that only differ from the others by a modification in the last six amino acids of the protein. According to the scientists who discovered these isoforms, which are indistinguishable from the pro-angiogenic ones with pan VEGF antibodies, some of the literature on VEGF is at least inexact if not completely false. Moreover, the presence of anti-angiogenic forms of VEGF may explain the disappointing efficacy of anti-VEGF therapies on the overall survival of patients with different forms of cancers and with wet age-related macular degeneration. This review focuses on the existence of the different alternative splice variants of VEGF and the molecular mechanisms associated with their expression and function.

The great escape; the hallmarks of resistance to antiangiogenic therapy

The concept of antiangiogenic therapy in cancer treatment has led to the approval of different agents, most of them targeting the well known vascular endothelial growth factor pathway. Despite promising results in preclinical studies, the efficacy of antiangiogenic therapy in the clinical setting remains limited. Recently, awareness has emerged on resistance to antiangiogenic therapies. It has become apparent that the intricate complex interplay between tumors and stromal cells, including endothelial cells and associated mural cells, allows for escape mechanisms to arise that counteract the effects of these targeted therapeutics. Here, we review and discuss known and novel mechanisms that contribute to resistance against antiangiogenic therapy and provide an outlook to possible improvements in therapeutic approaches.

Serine-arginine protein kinase 1 (SRPK1) inhibition as a potential novel targeted therapeutic strategy in prostate cancer

Angiogenesis is required for tumour growth and is induced principally by VEGF-A. VEGF-A pre-mRNA is alternatively spliced at the terminal exon to produce two families of isoforms, pro- and anti-angiogenic, only the former of which is upregulated in prostate cancer. In renal epithelial cells and colon cancer cells, the choice of VEGF splice isoforms is controlled by the splicing factor SRSF1, phosphorylated by SRPK1. Immunohistochemistry staining of human samples revealed a significant increase in SRPK1 expression both in prostate intra-epithelial neoplasia lesions as well as malignant adenocarcinoma compared to benign prostate tissue. We therefore tested the hypothesis that the selective upregulation of pro-angiogenic VEGF in prostate cancer may be under the control of SRPK1 activity. A switch in the expression of VEGF₁₆₅ towards the anti-angiogenic splice isoform, VEGF₁₆₅b, was seen in PC-3 cells with SRPK1 knock-down (KD). PC-3 SRPK1-KD cells resulted in tumours that grew more slowly in xenografts, with decreased microvessel density. No effect was seen as a result of SRPK1-KD on growth, proliferation, migration and invasion capabilities of PC-3 cells in vitro. Small molecule inhibitors of SRPK1 switched splicing towards the anti-angiogenic isoform VEGF₁₆₅b in PC3 cells and decreased tumour growth when administered intraperitoneally in an orthotopic mouse model of prostate cancer. Our study suggests that modulation of SRPK1 and subsequent inhibition of tumour angiogenesis by regulation of VEGF splicing can alter prostate tumour growth and supports further studies into the use of SRPK1 inhibition as a potential anti-angiogenic therapy in prostate cancer.

The carboxyl terminus of VEGF-A is a potential target for anti-angiogenic therapy

Anti-VEGF-A therapy has become a mainstay of treatment for ocular neovascularisation and in cancer; however, their effectiveness is not universal, in some cases only benefiting a minority of patients. Anti-VEGF-A therapies bind and block both pro-angiogenic VEGF-Axxx and the partial agonist VEGF-Axxxb isoforms, but their anti-angiogenic benefit only comes about from targeting the pro-angiogenic isoforms. Therefore, antibodies that exclusively target the pro-angiogenic isoforms may be more effective. To determine whether C-terminal-targeted antibodies could inhibit angiogenesis, we generated a polyclonal antibody to the last nine amino acids of VEGF-A165 and tested it in vitro and in vivo. The exon8a polyclonal antibody (Exon8apab) did not bind VEGF-A165b even at greater than 100-fold excess concentration, and dose dependently inhibited VEGF-A165 induced endothelial migration in vitro at concentrations similar to the VEGF-A antibody fragment ranibizumab. Exon8apab can inhibit tumour growth of LS174t cells implanted in vivo and blood vessel growth in the eye in models of age-related macular degeneration, with equal efficacy to non-selective anti-VEGF-A antibodies. It also showed that it was the VEGF-Axxx levels specifically that were upregulated in plasma from patients with proliferative diabetic retinopathy. These results suggest that VEGF-A165-specific antibodies can be therapeutically useful.

Programmed translational readthrough generates antiangiogenic VEGF-Ax

Translational readthrough, observed primarily in less complex organisms from viruses to Drosophila, expands the proteome by translating select transcripts beyond the canonical stop codon. Here, we show that vascular endothelial growth factor A (VEGFA) mRNA in mammalian endothelial cells undergoes programmed translational readthrough (PTR) generating VEGF-Ax, an isoform containing a unique 22-amino-acid C terminus extension. A cis-acting element in the VEGFA 3' UTR serves a dual function, not only encoding the appended peptide but also directing the PTR by decoding the UGA stop codon as serine. Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 binds this element and promotes readthrough. Remarkably, VEGF-Ax exhibits antiangiogenic activity in contrast to the proangiogenic activity of VEGF-A. Pathophysiological significance of VEGF-Ax is indicated by robust expression in multiple human tissues but depletion in colon adenocarcinoma. Furthermore, genome-wide analysis revealed AGO1 and MTCH2 as authentic readthrough targets. Overall, our studies reveal a novel protein-regulated PTR event in a vertebrate system.

Regulation of placental angiogenesis

Ample interest has been evoked in using placental angiogenesis as a target for the development of diagnosis tools and potential therapeutics for pregnancy complications based on the knowledge of placental angiogenesis in normal and aberrant pregnancies. Although these goals are still far from reach, one would expect that two complementary processes should be balanced for therapeutic angiogenesis to be successful in restoring a mature and functional vascular network in the placenta in any pregnancy complication: (i) pro-angiogenic stimulation of new vessel growth and (ii) anti-angiogenic inhibition of vessel overgrowth. As the best model of physiological angiogenesis, investigations of placental angiogenesis provide critical insights not only for better understanding of normal placental endothelial biology but also for the development of diagnosis tools for pregnancy complications. Such investigations will potentially identify novel pro-angiogenic factors for therapeutic intervention for tissue damage in various obstetric complications or heart failure or anti-angiogenic factors to target on cancer or vision loss in which circulation needs to be constrained. This review summarizes the genetic and molecular aspects of normal placental angiogenesis as well as the signaling mechanisms by which the dominant angiogenic factor vascular endothelial growth factor regulates placental angiogenesis with a focus on placental endothelial cells.

Regulation of alternative VEGF-A mRNA splicing is a therapeutic target for analgesia

Vascular endothelial growth factor-A (VEGF-A) is best known as a key regulator of the formation of new blood vessels. Neutralization of VEGF-A with anti-VEGF therapy e.g. bevacizumab, can be painful, and this is hypothesized to result from a loss of VEGF-A-mediated neuroprotection. The multiple vegf-a gene products consist of two alternatively spliced families, typified by VEGF-A₁₆₅a and VEGF-A₁₆₅b (both contain 165 amino acids), both of which are neuroprotective. Under pathological conditions, such as in inflammation and cancer, the pro-angiogenic VEGF-A₁₆₅a is upregulated and predominates over the VEGF-A₁₆₅b isoform.

We show here that in rats and mice VEGF-A₁₆₅a and VEGF-A₁₆₅b have opposing effects on pain, and that blocking the proximal splicing event – leading to the preferential expression of VEGF-A₁₆₅b over VEGF₁₆₅a – prevents pain in vivo. VEGF-A₁₆₅a sensitizes peripheral nociceptive neurons through actions on VEGFR2 and a TRPV1-dependent mechanism, thus enhancing nociceptive signaling. VEGF-A₁₆₅b blocks the effect of VEGF-A₁₆₅a.

After nerve injury, the endogenous balance of VEGF-A isoforms switches to greater expression of VEGF-A_xxxa compared to VEGF-A_xxxb, through an SRPK1-dependent pre-mRNA splicing mechanism. Pharmacological inhibition of SRPK1 after traumatic nerve injury selectively reduced VEGF-A_xxxa expression and reversed associated neuropathic pain. Exogenous VEGF-A₁₆₅b also ameliorated neuropathic pain.

We conclude that the relative levels of alternatively spliced VEGF-A isoforms are critical for pain modulation under both normal conditions and in sensory neuropathy. Altering VEGF-A_xxxa/VEGF-A_xxxb balance by targeting alternative RNA splicing may be a new analgesic strategy.

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The different vegf-a splice variants, VEGF-A₁₆₅a and VEGF-A₁₆₅b have pro- and anti-nociceptive actions respectively.

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Pro-nociceptive actions of VEGF-A₁₆₅a are dependent on TRPV1.

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Alternative pre-mRNA splicing underpins peripheral sensitization by VEGF-A isoforms in normal and neuropathic animals.

Antiangiogenic actions of vascular endothelial growth factor-A165b, an inhibitory isoform of vascular endothelial growth factor-A, in human obesity

BACKGROUND

Experimental studies suggest that visceral adiposity and adipose tissue dysfunction play a central role in obesity-related cardiometabolic complications. Impaired angiogenesis in fat has been implicated in the development of adipose tissue hypoxia, capillary rarefaction, inflammation, and metabolic dysregulation, but pathophysiological mechanisms remain unknown. In this study, we examined the role of a novel antiangiogenic isoform of vascular endothelial growth factor-A (VEGF-A), VEGF-A165b, in human obesity.

METHODS AND RESULTS

We biopsied paired subcutaneous and visceral adipose tissue in 40 obese subjects (body mass index, 45±8 kg/m(2); age, 45±11 years) during bariatric surgery and characterized depot-specific adipose tissue angiogenic capacity using an established ex vivo assay. Visceral adipose tissue exhibited significantly blunted angiogenic growth compared with subcutaneous fat (P<0.001) that was associated with marked tissue upregulation of VEGF-A165b (P=0.004). The extent of VEGF-A165b expression correlated negatively with angiogenic growth (r=-0.6, P=0.006). Although recombinant VEGF-A165b significantly impaired angiogenesis, targeted inhibition of VEGF-A165b with neutralizing antibody stimulated fat pad neovascularization and restored VEGF receptor activation. Blood levels of VEGF-A165b were significantly higher in obese subjects compared with lean control subjects (P=0.02), and surgical weight loss induced a marked decline in serumVEGF-A165b (P=0.003).

CONCLUSIONS

We demonstrate that impaired adipose tissue angiogenesis is associated with overexpression of a novel antiangiogenic factor, VEGF-A165b, that may play a pathogenic role in human adiposopathy. Moreover, systemic upregulation of VEGF-A165b in circulating blood may have wider-ranging implications beyond the adipose milieu. VEGF-A165b may represent a novel area of investigation to gain further understanding of mechanisms that modulate the cardiometabolic consequences of obesity.

The role of mRNA splicing in prostate cancer

Alternative splicing (AS) is a crucial step in gene expression. It is subject to intricate regulation, and its deregulation in cancer can lead to a wide array of neoplastic phenotypes. A large body of evidence implicates splice isoforms in most if not all hallmarks of cancer, including growth, apoptosis, invasion and metastasis, angiogenesis, and metabolism. AS has important clinical implications since it can be manipulated therapeutically to treat cancer and represents a mechanism of resistance to therapy. In prostate cancer (PCa) AS also plays a prominent role and this review will summarize the current knowledge of alternatively spliced genes with important functional consequences. We will highlight accumulating evidence on AS of the components of the two critical pathways in PCa: androgen receptor (AR) and phosphoinositide 3-kinase (PI3K). These observations together with data on dysregulation of splice factors in PCa suggest that AR and PI3K pathways may be interconnected with previously unappreciated splicing regulatory networks. In addition, we will discuss several lines of evidence implicating splicing regulation in the development of the castration resistance.

Podocytes, signaling pathways, and vascular factors in diabetic kidney disease

Alterations and injury to glomerular podocytes play a key role in the initiation and progression of diabetic kidney disease (DKD). Multiple factors in diabetes cause abnormalities in podocyte signaling that lead to podocyte foot process effacement, hypertrophy, detachment, loss, and death. Alterations in insulin action and mammalian target of rapamycin activation have been well documented to lead to pathology. Reduced insulin action directly leads to albuminuria, increased glomerular matrix accumulation, thickening of the glomerular basement membrane, podocyte apoptosis, and glomerulosclerosis. In addition, podocytes generate factors that alter signaling in other glomerular cells. Prominent among these is vascular endothelial growth factor-A, which maintains glomerular endothelium viability but causes endothelial cell pathology when generated at too high a level. Finally, circulating vascular factors (eg, activated protein C) have a profound effect on podocyte stability and survival. This cytoprotective factor is critical for podocyte health, and its deficiency promotes podocyte injury and apoptosis. Thus, the podocyte sits in the center of a network of paracrine and hormonal signaling systems that in health keep the podocyte adaptable and viable, but in diabetes they can lead to pathologic changes, detachment, and death.

Potential Vascular Mechanisms of Ramipril Induced Increases in Walking Ability in Patients With Intermittent Claudication

Rationale:

We recently reported that ramipril more than doubled maximum walking times in patients with peripheral artery disease with intermittent claudication.

Objective:

Our aim was to conduct exploratory analyses of the effects of ramipril therapy on circulating biomarkers of angiogenesis/arteriogenesis, thrombosis, inflammation, and leukocyte adhesion in patients with intermittent claudication.

Methods and Results:

One hundred sixty-five patients with intermittent claudication (mean, 65.3 [SD, 6.7] years) were administered ramipril 10 mg per day (n=82) or matching placebo (n=83) for 24 weeks in a randomized, double-blind study. Plasma biomarkers of angiogenesis/arteriogenesis (vascular endothelial growth factor-A, fibroblast growth factor-2), thrombosis (D-dimer, von Willebrand factor, thrombin-antithrombin III), inflammation (high-sensitivity C-reactive protein, osteopontin), and leukocyte adhesion (soluble vascular cell adhesion molecule-1, soluble intracellular adhesion molecule-1) were measured at baseline and 24 weeks. Relative to placebo, ramipril was associated with increases in vascular endothelial growth factor-A by 38% (95% confidence interval [CI], 34%–42%) and fibroblast growth factor-2 by 64% (95% CI, 44–85%; P <0.001 for both), and reductions in D-dimer by 24% (95% CI, −30% to −18%), von Willebrand factor by 22% (95% CI, −35% to −9%), thrombin-antithrombin III by 16% (95% CI, −19% to −13%), high-sensitivity C-reactive protein by 13% (95% CI, −14% to −9%), osteopontin by 12% (95% CI, −14% to −10%), soluble vascular cell adhesion molecule-1 by 14% (95% CI, −18% to −10%), and soluble intracellular adhesion molecule-1 by 15% (95% CI, −17% to −13%; all P <0.001). With the exception of von Willebrand factor, all the above changes correlated significantly with the change in maximum walking time ( P =0.02−0.001) in the group treated with ramipril.

Conclusions:

Ramipril is associated with an increase in the biomarkers of angiogenesis/arteriogenesis and reduction in the markers of thrombosis, inflammation, and leukocyte adhesion. This study informs strategies to improve mobility in patients with intermittent claudication.

Clinical Trial Registration Information:

URL: http://clinicaltrials.gov . Unique identifier: NCT00681226.

TGF-β-activated kinase 1 is crucial in podocyte differentiation and glomerular capillary formation

TGF-β-activated kinase 1 (TAK1) is a key intermediate in signal transduction induced by TGF-β or inflammatory cytokines, such as TNF-α and IL-1, which are potent inducers of podocyte injury responses that lead to proteinuria and glomerulosclerosis. Nevertheless, little is known about the physiologic and pathologic roles of TAK1 in podocytes. To examine the in vivo role of TAK1, we generated podocyte-specific Tak1 knockout mice (Nphs2-Cre(+):Tak1(fx/fx); Tak1(∆/∆)). Targeted deletion of Tak1 in podocytes resulted in perinatal lethality, with approximately 50% of animals dying soon after birth and 90% of animals dying within 1 week of birth. Tak1(∆/∆) mice developed proteinuria from P1 and exhibited delayed glomerulogenesis and reduced expression of Wilms' tumor suppressor 1 and nephrin in podocytes. Compared with Tak1(fx/fx) mice, Tak1(∆/∆) mice exhibited impaired formation of podocyte foot processes that caused disruption of the podocyte architecture with prominent foot process effacement. Intriguingly, Tak1(∆/∆) mice displayed increased expression of vascular endothelial growth factor within the glomerulus and abnormally enlarged glomerular capillaries. Furthermore, 4- and 7-week-old Tak1(∆/∆) mice with proteinuria had increased collagen deposition in the mesangium and the adjacent tubulointerstitial area. Thus, loss of Tak1 in podocytes is associated with the development of proteinuria and glomerulosclerosis. Taken together, our data show that TAK1 regulates the expression of Wilms' tumor suppressor 1, nephrin, and vascular endothelial growth factor and that TAK1 signaling has a crucial role in podocyte differentiation and attainment of normal glomerular microvasculature during kidney development and glomerular filtration barrier homeostasis.

Effect of recombinant human VEGF165b protein and bevacizumab on expression of CD34 and cell apoptosis in human gastric carcinoma xenografts in nude mice

AIM: To investigate the effect of recombinant human VEGF₁₆₅b protein (rhVEGF₁₆₅b) and bevacizumab on expression of CD34 and cell apoptosis in human gastric carcinoma xenografts in nude mice.

METHODS: Thirty male nude mice were used to establish the human gastric carcinoma xenograft model. The mice were randomly divided into three groups: a rhVEGF₁₆₅b group (intraperitoneal injection, 10 μg/kg), a bevacizumab group (intraperitoneal injection, 5 mg/kg) and a control group. Tumor growth was detected by measuring tumor volume and weight. The expression of CD34 and apoptosis of tumor cells were detected by immunohistochemistry and TdT-mediated dUTP nick end labeling (TUNEL) assay at weeks 1, 2 and 3, respectively.

RESULTS: Tumor volume and weight at weeks 1 and 2 in the rhVEGF₁₆₅b group (week 1: 0.546 ± 0.132 vs 0.637 ± 0.084, 1.894 ± 0.599 vs 0.46 ± 0.093; week 2: 1.894 ± 0.599 vs 2.238 ± 0.29, 1.537 ± 0.568 vs 2.013 ± 0.833; P < 0.05 for all) and at weeks 1, 2 and 3 in the bevacizumab group (week 1: 0.453 ± 0.119 vs 0.637 ± 0.084, 0.320 ± 0.097 vs 0.460 ± 0.093; week 2: 1.691 ± 0.381 vs 2.238 ± 0.290, 1.168 ± 0.524 vs 2.013 ± 0.833; week 3: 1.709 ± 0.474 vs 4.872 ± 0.594, 1.747 ± 0.557 vs 3.463 ± 0.986, P < 0.05 for all) were significantly smaller than those in the control group. At week 3, tumor volume and weight were significantly larger in the rhVEGF₁₆₅b group than in the bevacizumab group (3.843 ± 1.339 vs 1.709 ± 0.474, 3.066 ± 1.281 vs 1.747 ± 0.557, P < 0.05 for both). Microvascular density (MVD) and apoptosis index (AI) at weeks 1, 2 and 3 in the rhVEGF₁₆₅b group and bevacizumab group were significantly different from those in the control group. MVD and AI also differed significantly between the rhVEGF₁₆₅b group and bevacizumab group.

CONCLUSION: Both rhVEGF₁₆₅b and bevacizumab can inhibit the growth of human gastric carcinoma cells possibly by inhibiting angiogenesis and inducing apoptosis, with rhVEGF₁₆₅b having a more significant effect in early stage.

Association of VEGF-A splice variant mRNA expression with outcome in bevacizumab-treated patients with metastatic breast cancer

BACKGROUND

The prognostic utility of vascular endothelial growth factor A (VEGF-A) splice variants in patients with advanced breast cancer treated with bevacizumab has not been studied.

PATIENTS AND METHODS

A total of 111 patients with metastatic breast cancer treated with weekly docetaxel or ixabepilone without bevacizumab (cohort A) and 100 treated with weekly paclitaxel and bevacizumab (cohort B) were studied. Formalin-fixed tumors were macrodissected for reverse transcription quantitative polymerase chain reaction relative quantification of VEGF-A165, -189, and -206 isoforms spliced at exon 8 proximal splice site (VEGF-Axxxa) and at exon 8 distal splice site (VEGF-Axxxb).

RESULTS

For high VEGF-Axxxa, the hazard ratios (HRs) for progression were 1.08 (P = .71) in non-bevacizumab-treated patients (cohort A) and 0.66 (P = .22) in bevacizumab-treated patients (cohort B), and the HRs for death were 1.45 (P = .13) and 0.50 (P = .049), respectively. The interaction of VEGF-Axxxa with bevacizumab administration was significant (P = .011) for overall survival (OS). High tissue VEGF-Axxxb was not prognostic in cohort A but was predictive for bevacizumab benefit in cohort B (HR for progression, 0.57 [P = .04]; HR for death, 0.51 [P = .02]). Exploratory analyses done only in cohort B suggested that abundance of VEGFR1 messenger RNA (mRNA) in peripheral blood and low VEGFR2 mRNA in tissue correlated with poor outcome. In multivariate analysis, high tissue mRNA of angiogenic VEGF-Axxxa in the presence of bevacizumab therapy predicted for favorable progression-free survival (HR for progression, 0.39; P = .0227) and OS (HR for death, 0.32; P = .0140).

CONCLUSION

Tissue mRNA expression of angiogenic VEGF-Axxxa isoforms was retrospectively associated with adverse prognosis in the absence of bevacizumab and with favorable outcome when bevacizumab was administered in patients with advanced breast cancer.

Transplantation of bone marrow stromal cells overexpressing human vascular endothelial growth factor 165 enhances tissue repair in a rat model of radiation-induced injury

BACKGROUND

The multilineage differentiation potential ability of bone marrow stromal cells (BMSCs) showed great potential in tissue engineering, while vascular endothelial growth factor 165 (VEGF165) promotes vasculogenesis and further promotes tissue regeneration. This study aimed to assess the ability of rat BMSCs expressing human VEGF A165 (hVEGF165) to promote tissue repair in rat model of radiation-induced injury.

METHODS

Rat BMSCs were isolated from the tibia. Plasmid DNA expressing hVEGF165 was stably transfected into BMSCs using liposomes. The right hindlimb muscle of 40 rats was irradiated using a (60)Co γ source (total dose 30 Gy). The animals were divided into four groups (n = 10): not injected with BMSCs (control; group 1) or intramuscularly injected two times (once in 2 weeks) with pcDNA(TM)3.1-transfected BMSCs (group 2), untransfected BMSCs (group 3), or hVEGF165-transfected BMSCs (group 4). Angiography was performed 1 week after the last injection of BMSCs; samples of the hindlimb muscle were subjected to transmission electron microscopy, ultrastructural analysis, reverse transcription-PCR (RT-PCR), Western blotting, and immunohistochemistry.

RESULTS

Rat BMSCs with multipotent differentiation capacity were isolated. hVEGF165-transfected BMSCs overexpressed hVEGF165 mRNA and protein. Injection of BMSCs (groups 2-4) increased the average vessel number, density, diameter, and cross-sectional area; mRNA expression of the myogenic markers including myoblast determination protein, myogenin, and a-smooth muscle actin; and CD31 protein expression; and promoted the repair of blood vessels and myofibers after radiation-induced injury compared to group 1; each of these parameters and hVEGF165 mRNA or protein expression were markedly improved in rats injected with hVEGF165-transfected BMSCs compared to groups 2 and 3.

CONCLUSIONS

BMSCs expressing hVEGF165 enhanced the repair of radiation-induced tissue injury by promoting vasculogenesis and muscle fiber regeneration. BMSCs expressing hVEGF165 may have potential clinical applications.

Vascular endothelial growth factor in acute lung injury and acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is the most severe form of lung injury, characterised by alveolar oedema and vascular permeability, in part due to disruption of the alveolar capillary membrane integrity. Vascular endothelial growth factor (VEGF) was originally identified as a vascular permeability factor and has been implicated in the pathogenesis of acute lung injury/ARDS. This review describes our current knowledge of VEGF biology and summarises the literature investigating the potential role VEGF may play in normal lung maintenance and in the development of lung injury.

Hallmarks of alternative splicing in cancer

The immense majority of genes are alternatively spliced and there are many isoforms specifically associated with cancer progression and metastasis. The splicing pattern of specific isoforms of numerous genes is altered as cells move through the oncogenic process of gaining proliferative capacity, acquiring angiogenic, invasive, antiapoptotic and survival properties, becoming free from growth factor dependence and growth suppression, altering their metabolism to cope with hypoxia, enabling them to acquire mechanisms of immune escape, and as they move through the epithelial-mesenchymal and mesenchymal-epithelial transitions and metastasis. Each of the 'hallmarks of cancer' is associated with a switch in splicing, towards a more aggressive invasive cancer phenotype. The choice of isoforms is regulated by several factors (signaling molecules, kinases, splicing factors) currently being identified systematically by a number of high-throughput, independent and unbiased methodologies. Splicing factors are de-regulated in cancer, and in some cases are themselves oncogenes or pseudo-oncogenes and can contribute to positive feedback loops driving cancer progression. Tumour progression may therefore be associated with a coordinated splicing control, meaning that there is the potential for a relatively small number of splice factors or their regulators to drive multiple oncogenic processes. The understanding of how splicing contributes to the various phenotypic traits acquired by tumours as they progress and metastasise, and in particular how alternative splicing is coordinated, can and is leading to the development of a new class of anticancer therapeutics-the alternative-splicing inhibitors.

Clinical Implications of VEGF, TGF-β1, and IL-1β in Patients with Advanced Non-small Cell Lung Cancer

PURPOSE

Vascular endothelial growth factor (VEGF)-A, VEGF165b, interleukin (IL)-1β, and transforming growth factor (TGF)-β1 are known to influence tumor angiogenesis. Clinical implications of these cytokines need to be elucidated.

MATERIALS AND METHODS

Using clinical data and baseline serum samples of 140 consecutive patients with advanced non-small cell lung cancer who received platinum-based combination chemotherapy, we investigated the association among serum cytokine levels, treatment outcomes, as well as leukocyte and platelet counts.

RESULTS

The median age of patients was 64 years (range, 26 to 86 years). The male to female ratio was 104:36. High TGF-β1 and IL-1β levels were associated with shorter progression-free survival, and high VEGF-A and IL-1β levels were associated with shorter overall survival in the univariate analysis. VEGF165b was not related to the treatment outcomes. Leukocytosis and thrombocytosis were associated with shorter overall survival. The multivariate analysis demonstrated that VEGF-A, IL-1β, and leukocytosis were significant prognostic factors (p=0.0497, p=0.047, and p<0.001, respectively). Leukocytosis was not associated with recent pneumonia (p=0.937) and correlated with VEGF-A (p<0.001) and TGF-β1 (p=0.020) levels.

CONCLUSION

Serum VEGF-A, TGF-1β, and IL-1β levels, in addition to leukocyte and platelet counts, are shown to be associated with clinical outcomes. Leukocyte and platelet counts are correlated with serum VEGF-A and TGF-β1 levels.

Increased intravitreal angiopoietin-2 levels associated with rhegmatogenous retinal detachment

PURPOSE

To explore factors related to pathogenesis of rhegmatogenous retinal detachment (RRD) and development of proliferative vitreoretinopathy (PVR), vitreous levels of angiopoietin-1 and -2 (Ang-1 and -2), previously undefined in RRD, transforming growth factor-(TGF) β1, vascular endothelial growth factor (VEGF), erythropoietin (EPO) and proteolytic mediators of extracellular matrix remodelling (MMP-2 and -9) were compared in eyes with RRD and eyes with idiopathic macular hole or pucker.

METHODS

Vitreous samples were collected from 117 eyes with RRD (study group) and 40 eyes with macular hole or pucker (control group). Growth factors were measured by ELISA and matrix metalloproteinases (MMPs) by gelatin zymography.

RESULTS

The mean vitreous concentrations of Ang-2, MMP-2, and MMP-9 were higher (all p < 0.01), whereas concentration of VEGF was lower (p = 0.01) in eyes with RRD relative to controls. Logistic regression analysis identified Ang-2 concentration as a novel marker of RRD (p = 0.0001, OR 48.7). Ang-1, EPO, and total TGF-β1 levels were not significantly different between the groups. However, TGF-β1 and MMP-2 were increased in eyes with total RRD compared to those with local RRD (p ≤ 0.05). In eyes with PVR, no differences were observed in any studied marker as compared with non-PVR eyes.

CONCLUSIONS

Current results reveal Ang-2 as a key factor upregulated in RRD. It may co-operate with fibrosis-associated factors and contribute to vascular complications such as breakdown of blood-eye barrier and PVR development.

A gene signature combining the tissue expression of three angiogenic factors is a prognostic marker in early-stage non-small cell lung cancer

BACKGROUND

Angiogenesis and lymphangiogenesis are key mechanisms for tumor growth and dissemination. They are mainly regulated by the vascular endothelial growth factor (VEGF) family of ligands and receptors. The aim of this study was to analyze relative expression levels of angiogenic markers in resectable non-small cell lung cancer patients in order to asses a prognostic signature that could improve characterization of patients with worse clinical outcomes.

METHODS

RNA was obtained from tumor and normal lung specimens from 175 patients. Quantitative polymerase chain reaction was performed to analyze the relative expression of HIF1A, PlGF, VEGFA, VEGFA165b, VEGFB, VEGFC, VEGFD, VEGFR1, VEGFR2, VEGFR3, NRP1 and NRP2.

RESULTS

Univariate analysis showed that tumor size and ECOG-PS are prognostic factors for time to progression (TTP) and overall survival (OS). This analysis in the case of angiogenic factors also revealed that PlGF, VEGFA, VEGFB and VEGFD distinguish patients with different outcomes. Taking into account the complex interplay between the different ligands of the VEGF family and to more precisely predict the outcome of the patients, we considered a new analysis combining several VEGF ligands. In order to find independent prognostic variables, we performed a multivariate Cox analysis, which showed that the subgroup of patients with higher relative expression of VEGFA plus lower VEGFB and VEGFD presented the poorest outcome for both TTP and OS.

CONCLUSIONS

The relative expression of these three genes can be considered as an angiogenic gene signature whose applicability for the selection of candidates for targeted therapies needs to be further validated.

Targeting tumor micro-environment for design and development of novel anti-angiogenic agents arresting tumor growth

Angiogenesis: a process of generation of new blood vessels has been proved to be necessary for sustained tumor growth and cancer progression. Inhibiting angiogenesis pathway has long been remained a significant hope for the development of novel, effective and target orientated antitumor agents arresting the tumor proliferation and metastasis. The process of neoangiogenesis as a biological process is regulated by several pro- and anti-angiogenic factors, especially vascular endothelial growth factor, fibroblast growth factor, epidermal growth factor, hypoxia inducible factor 1 and transforming growth factor. Every endothelial cell destined for vessel formation is equipped with receptors for these angiogenic peptides. Moreover, numerous other angiogenic cytokines such as platelet derived growth factor (PGDF), placenta growth factor (PGF), nerve growth factor (NGF), stem-cell factor (SCF), and interleukins-2, 4, 6 etc. These molecular players performs critical role in regulating the angiogenic switch. Couple of decade's research in molecular aspects of tumor biology has unraveled numerous structural and functional mysteries of these angiogenic peptides. In present article, a detailed update on the functional and structural peculiarities of the various angiogenic peptides is described focusing on structural opportunities made available that has potential to be used to modulate function of these angiogenic peptides in developing therapeutic agents targeting neoplastic angiogenesis. The data may be useful in the mainstream of developing novel anticancer agents targeting tumor angiogenesis. We also discuss major therapeutic agents that are currently used in angiogenesis associated therapies as well as those are subject of active research or are in clinical trials.

VEGF111b, a new member of VEGFxxxb isoforms and induced by mitomycin C, inhibits angiogenesis

Vascular endothelial growth factor (VEGF-A) stimulating angiogenesis is required for tumor growth and progression. The conventional VEGF-A isoforms have been considered as pro-angiogenic factors. Another family of VEGF-A isoforms generated by alternative splicing, termed VEGFxxxb isoforms, has anti-angiogenic property, exemplified by VEGF165b. Here, we identify a new number of VEGFxxx family-VEGF111b induced by mitomycin C, although not detected in mitomycin C-unexposed ovarian cancer cells. SKOV3 cells were transfected with pcDNA3.1 empty vector, pcDNA3.1-VEGF111b or pcDNA3.1-VEGF165b to collect conditioned mediums respectively. VEGF111b overexpression inhibits proliferation, migration and tube formation of endothelial cell by inhibiting VEGF-R2 phosphorylation and its downstream signaling, similar to VEGF165b but slightly lower than VEGF165b. The anti-angiogenic property depends on the six amino acids of exon 8b of the VEGFxxxb isoforms. Our results show that VEGF111b is a novel potent anti-angiogenic agent that can target the VEGF-R2 and its signaling pathway to inhibit ovarian tumor growth.

MicroRNA-dependent cross-talk between VEGF and HIF1α in the diabetic retina

Both HIF1α (hypoxia-inducible factor alpha) and VEGF (vascular endothelial growth factor) are implicated in the pathogenesis of diabetic retinopathy (DR). Competitive endogenous RNAs (ceRNAs) are messenger RNA (mRNA) molecules that affect each other expression through competition for their shared microRNAs (miRNA). However, little is known about the role of ceRNAs in DR. We assess whether the expression of HIF1α and VEGF in DR is interdependent through sequestration of common miRNAs. We used bioinformatics to identify potential miRNAs that affect both genes and validated the interdependence of the genes by silencing or overexpression of the genes and assessed the luciferase-HIF1α 3'UTR activity. We found that HIF1α and VEGF are targeted by 12 common miRNAs. Silencing either HIF1α or VEGF increased the availabilities of the shared miRNAs, therefore suppressed the luciferase-HIF1α 3'UTR activity, whereas over-expressing HIF1α or VEGF increased the luciferase activity. HIF1α was co-expressed with VEGF in-vivo and in-vitro in DR models. Silencing HIF1α transcripts resulted in a significant reduction in VEGF protein levels and vice versa. This interdependence was miRNA- and 3'UTR-dependent, as silencing Dicer abolished the interdependence. Over-expression of a common miRNA (miR-106a) significantly reduced the expression of HIF1α and VEGF and prevented high glucose-induced increased permeability. There is a cross-talk between HIF1α and VEGF through interactions with their common miRNAs. miRNA based therapy can affect the expression of both HIF1α and VEGF and may represent a therapeutic potential for the treatment of DR.

Topical antiangiogenic SRPK1 inhibitors reduce choroidal neovascularization in rodent models of exudative AMD

PURPOSE

Exudative AMD (wet AMD) is treated by monthly injection into the eye of anti-VEGF proteins. VEGF is alternatively spliced to produce numerous isoforms that differ in angiogenic activity. Serine-rich protein kinase-1 (SRPK1) has been identified as a regulator of pro-angiogenic VEGF splicing by phosphorylating serine-rich splicing factor-1 (SRSF1), which binds to VEGF pre-mRNA. We tested the hypothesis that topical (eye drop) SRPK1-selective inhibitors could be generated that reduce pro-angiogenic isoforms, and prevent choroidal neovascularization in vivo.

METHODS

Novel inhibitors were tested for SRPK inhibition in vitro, pro-angiogenic VEGF production in RPE cells by PCR and ELISA, and for inhibition of choroidal neovascularisation in mice and rats.

RESULTS

A novel disubstituted furan inhibitor was selective for the SRPK family of kinases and reduced expression of pro-angiogenic but not antiangiogenic VEGF isoforms. This inhibitor and previously identified SRPK inhibitors significantly reduced choroidal neovascularisation in vivo. Topical administration of SRPK inhibitors dose-dependently blocked CNV with an EC50 of 9 μM.

CONCLUSIONS

These results indicate that novel SRPK1 selective inhibitors could be a potentially novel topical (eye drop) therapeutic for wet AMD.

Alternative RNA splicing and cancer

Alternative splicing of pre-messenger RNA (mRNA) is a fundamental mechanism by which a gene can give rise to multiple distinct mRNA transcripts, yielding protein isoforms with different, even opposing, functions. With the recognition that alternative splicing occurs in nearly all human genes, its relationship with cancer-associated pathways has emerged as a rapidly growing field. In this review, we summarize recent findings that have implicated the critical role of alternative splicing in cancer and discuss current understandings of the mechanisms underlying dysregulated alternative splicing in cancer cells.

VEGF-A165b is an endogenous neuroprotective splice isoform of vascular endothelial growth factor A in vivo and in vitro

Vascular endothelial growth factor (VEGF) A is generated as two isoform families by alternative RNA splicing, represented by VEGF-A165a and VEGF-A165b. These isoforms have opposing actions on vascular permeability, angiogenesis, and vasodilatation. The proangiogenic VEGF-A165a isoform is neuroprotective in hippocampal, dorsal root ganglia, and retinal neurons, but its propermeability, vasodilatatory, and angiogenic properties limit its therapeutic usefulness. In contrast, a neuroprotective effect of endogenous VEGF-A165b on neurons would be advantageous for neurodegenerative pathologies. Endogenous expression of human and rat VEGF-A165b was detected in hippocampal and cortical neurons. VEGF-A165b formed a significant proportion of total VEGF-A in rat brain. Recombinant human VEGF-A165b exerted neuroprotective effects in response to multiple insults, including glutamatergic excitotoxicity in hippocampal neurons, chemotherapy-induced cytotoxicity of dorsal root ganglion neurons, and retinal ganglion cells (RGCs) in rat retinal ischemia-reperfusion injury in vivo. Neuroprotection was dependent on VEGFR2 and MEK1/2 activation but not on p38 or phosphatidylinositol 3-kinase activation. Recombinant human VEGF-A165b is a neuroprotective agent that effectively protects both peripheral and central neurons in vivo and in vitro through VEGFR2, MEK1/2, and inhibition of caspase-3 induction. VEGF-A165b may be therapeutically useful for pathologies that involve neuronal damage, including hippocampal neurodegeneration, glaucoma diabetic retinopathy, and peripheral neuropathy. The endogenous nature of VEGF-A165b expression suggests that non-isoform-specific inhibition of VEGF-A (for antiangiogenic reasons) may be damaging to retinal and sensory neurons.

SRPK1 inhibition modulates VEGF splicing to reduce pathological neovascularization in a rat model of retinopathy of prematurity

PURPOSE

We tested the hypothesis that recombinant human VEGF-A165b and the serine arginine protein kinase (SRPK) inhibitor, SRPIN340, which controls splicing of the VEGF-A pre-mRNA, prevent neovascularization in a rodent model of retinopathy of prematurity (ROP).

METHODS

In the 50/10 oxygen-induced retinopathy (50/10 OIR) model that exposes newborn rats to repeated cycles of 24 hours of 50% oxygen alternating with 24 hours of 10% oxygen, pups received intraocular injections of SRPIN340, vehicle, VEGF165b, anti-VEGF antibody, or saline. Whole mounts of retinas were prepared for isolectin immunohistochemistry, and preretinal or intravitreal neovascularization (PRNV) determined by clock hour analysis.

RESULTS

The anti-VEGF antibody (P < 0.04), rhVEGF165b (P < 0.001), and SRPIN340 (P < 0.05) significantly reduced PRNV compared with control eyes. SRPIN340 reduced the expression of proangiogenic VEGF165 without affecting VEGF165b expression.

CONCLUSIONS

These results suggest that splicing regulation through selective downregulation of proangiogenic VEGF isoforms (via SRPK1 inhibition) or competitive inhibition of VEGF signaling by rhVEGF165b has the potential to be an effective alternative to potential cyto- and neurotoxic anti-VEGF agents in the treatment of pathological neovascularization in the eye.

Vascular contributions to early ovarian development: potential roles of VEGFA isoforms

Vascularisation is an essential component of ovarian morphogenesis; however, little is known regarding factors regulating the establishment of vasculature in the ovary. Angiogenesis involving extensive endothelial cell migration is a critical component of vessel formation in the embryonic testis but vasculogenic mechanisms appear to play a prominent role in ovarian vascularisation. Vasculature has a strong influence on the formation of ovarian structures, and the early developmental processes of ovigerous cord formation, primordial follicle assembly and follicle activation are all initiated in regions of the ovary that are in close association with the highly vascular medulla. The principal angiogenic factor, vascular endothelial growth factor A (VEGFA), has an important role in both endothelial cell differentiation and vascular pattern development. Expression of VEGFA has been localised to ovigerous cords and follicles in developing ovaries and an increased expression of pro-angiogenic Vegfa isoform mRNA in relation to anti-angiogenic isoform mRNA occurs at the same time-point as the peak of primordial follicle assembly in perinatal rats. Elucidation of specific genes that affect vascular development within the ovary may be critical for determining not only the normal mechanisms of ovarian morphogenesis, but also for understanding certain ovarian reproductive disorders.

Detection of VEGF-A(xxx)b isoforms in human tissues

Vascular Endothelial Growth Factor-A (VEGF-A) can be generated as multiple isoforms by alternative splicing. Two families of isoforms have been described in humans, pro-angiogenic isoforms typified by VEGF-A165a, and anti-angiogenic isoforms typified by VEGF-A165b. The practical determination of expression levels of alternative isoforms of the same gene may be complicated by experimental protocols that favour one isoform over another, and the use of specific positive and negative controls is essential for the interpretation of findings on expression of the isoforms. Here we address some of the difficulties in experimental design when investigating alternative splicing of VEGF isoforms, and discuss the use of appropriate control paradigms. We demonstrate why use of specific control experiments can prevent assumptions that VEGF-A165b is not present, when in fact it is. We reiterate, and confirm previously published experimental design protocols that demonstrate the importance of using positive controls. These include using known target sequences to show that the experimental conditions are suitable for PCR amplification of VEGF-A165b mRNA for both q-PCR and RT-PCR and to ensure that mispriming does not occur. We also provide evidence that demonstrates that detection of VEGF-A165b protein in mice needs to be tightly controlled to prevent detection of mouse IgG by a secondary antibody. We also show that human VEGF165b protein can be immunoprecipitated from cultured human cells and that immunoprecipitating VEGF-A results in protein that is detected by VEGF-A165b antibody. These findings support the conclusion that more information on the biology of VEGF-A165b isoforms is required, and confirm the importance of the experimental design in such investigations, including the use of specific positive and negative controls.

Compartment model predicts VEGF secretion and investigates the effects of VEGF trap in tumor-bearing mice

Angiogenesis, the formation of new blood vessels from existing vasculature, is important in tumor growth and metastasis. A key regulator of angiogenesis is vascular endothelial growth factor (VEGF), which has been targeted in numerous anti-angiogenic therapies aimed at inhibiting tumor angiogenesis. Systems biology approaches, including computational modeling, are useful for understanding this complex biological process and can aid in the development of novel and effective therapeutics that target the VEGF family of proteins and receptors. We have developed a computational model of VEGF transport and kinetics in the tumor-bearing mouse, which includes three-compartments: normal tissue, blood, and tumor. The model simulates human tumor xenografts and includes human (VEGF121 and VEGF165) and mouse (VEGF120 and VEGF164) isoforms. The model incorporates molecular interactions between these VEGF isoforms and receptors (VEGFR1 and VEGFR2), as well as co-receptors (NRP1 and NRP2). We also include important soluble factors: soluble VEGFR1 (sFlt-1) and α-2-macroglobulin. The model accounts for transport via macromolecular transendothelial permeability, lymphatic flow, and plasma clearance. We have fit the model to available in vivo experimental data on the plasma concentration of free VEGF Trap and VEGF Trap bound to mouse and human VEGF in order to estimate the rates at which parenchymal cells (myocytes and tumor cells) and endothelial cells secrete VEGF. Interestingly, the predicted tumor VEGF secretion rates are significantly lower (0.007-0.023 molecules/cell/s, depending on the tumor microenvironment) than most reported in vitro measurements (0.03-2.65 molecules/cell/s). The optimized model is used to investigate the interstitial and plasma VEGF concentrations and the effect of the VEGF-neutralizing agent, VEGF Trap (aflibercept). This work complements experimental studies performed in mice and provides a framework with which to examine the effects of anti-VEGF agents, aiding in the optimization of such anti-angiogenic therapeutics as well as analysis of clinical data. The model predictions also have implications for biomarker discovery with anti-angiogenic therapies.

VEGF-A mRNA processing, stability and translation: a paradigm for intricate regulation of gene expression at the post-transcriptional level

Vascular Endothelial Growth Factor A (VEGF-A) is a potent secreted mitogen crucial for physiological and pathological angiogenesis. Post-transcriptional regulation of VEGF-A occurs at multiple levels. Firstly, alternative splicing gives rise to different transcript variants encoding diverse isoforms that exhibit distinct biological properties with regard to receptor binding and extra-cellular localization. Secondly, VEGF-A mRNA stability is regulated by effectors such as hypoxia or growth factors through the binding of stabilizing and destabilizing proteins at AU-rich elements located in the 3′-untranslated region. Thirdly, translation of VEGF-A mRNA is a controlled process involving alternative initiation codons, internal ribosome entry sites (IRESs), an upstream open reading frame (uORF), miRNA targeting and a riboswitch in the 3′ untranslated region. These different levels of regulation cooperate for the crucial fine-tuning of the expression of VEGF-A variants. This review will be focused on our current knowledge of the complex post-transcriptional regulatory switches that modulate the cellular VEGF-A level, a paradigmatic model of post-transcriptional regulation.

Antiangiogenic VEGF isoform in inflammatory myopathies

Objective. To investigate expression of vascular endothelial growth factor (VEGF) antiangiogenic isoform A-_165b on human muscle in idiopathic inflammatory myopathies (IIM) and to compare distribution of angiogenic/antiangiogenic VEGFs, as isoforms shifts are described in other autoimmune disorders. Subjects and Methods. We analyzed VEGF-A_165b and VEGF-A by western blot and immunohistochemistry on skeletal muscle biopsies from 21 patients affected with IIM (polymyositis, dermatomyositis, and inclusion body myositis) and 6 control muscle samples. TGF-β, a prominent VEGF inductor, was analogously evaluated. Intergroup differences of western blot bands density were statistically examined. Endomysial vascularization, inflammatory score, and muscle regeneration, as pathological parameters of IIM, were quantitatively determined and their levels were confronted with VEGF expression. Results. VEGF-A_165b was significantly upregulated in IIM, as well as TGF-β. VEGF-A was diffusely expressed on unaffected myofibers, whereas regenerating/atrophic myofibres strongly reacted for both VEGF-A isoforms. Most inflammatory cells and endomysial vessels expressed both isoforms. VEGF-A_165b levels were in positive correlation to inflammatory score, endomysial vascularization, and TGF-β. Conclusions. Our findings indicate skeletal muscle expression of antiangiogenic VEGF-A_165b and preferential upregulation in IIM, suggesting that modulation of VEGF-A isoforms may occur in myositides.

Cancer-Associated Perturbations in Alternative Pre-messenger RNA Splicing

For most of our 25,000 genes, the removal of introns by pre-messenger RNA (pre-mRNA) splicing represents an essential step toward the production of functional messenger RNAs (mRNAs). Alternative splicing of a single pre-mRNA results in the production of different mRNAs. Although complex organisms use alternative splicing to expand protein function and phenotypic diversity, patterns of alternative splicing are often altered in cancer cells. Alternative splicing contributes to tumorigenesis by producing splice isoforms that can stimulate cell proliferation and cell migration or induce resistance to apoptosis and anticancer agents. Cancer-specific changes in splicing profiles can occur through mutations that are affecting splice sites and splicing control elements, and also by alterations in the expression of proteins that control splicing decisions. Recent progress in global approaches that interrogate splicing diversity should help to obtain specific splicing signatures for cancer types. The development of innovative approaches for annotating and reprogramming splicing events will more fully establish the essential contribution of alternative splicing to the biology of cancer and will hopefully provide novel targets and anticancer strategies. Metazoan genes are usually made up of several exons interrupted by introns. The introns are removed from the pre-mRNA by RNA splicing. In conjunction with other maturation steps, such as capping and polyadenylation, the spliced mRNA is then transported to the cytoplasm to be translated into a functional protein. The basic mechanism of splicing requires accurate recognition of each extremity of each intron by the spliceosome. Introns are identified by the binding of U1 snRNP to the 5' splice site and the U2AF65/U2AF35 complex to the 3' splice site. Following these interactions, other proteins and snRNPs are recruited to generate the complete spliceosomal complex needed to excise the intron. While many introns are constitutively removed by the spliceosome, other splice junctions are not used systematically, generating the phenomenon of alternative splicing. Alternative splicing is therefore the process by which a single species of pre-mRNA can be matured to produce different mRNA molecules (Fig. 1). Depending on the number and types of alternative splicing events, a pre-mRNA can generate from two to several thousands different mRNAs leading to the production of a corresponding number of proteins. It is now believed that the expression of at least 70 % of human genes is subjected to alternative splicing, implying an enormous contribution to proteomic diversity, and by extension, to the development and the evolution of complex animals. Defects in splicing have been associated with human diseases (Caceres and Kornblihtt, Trends Genet 18(4):186-93, 2002, Cartegni et al., Nat Rev Genet 3(4):285-98, 2002, Pagani and Baralle, Nat Rev Genet 5(5):389-96, 2004), including cancer (Brinkman, Clin Biochem 37(7):584-94, 2004, Venables, Bioessays 28(4):378-86, 2006, Srebrow and Kornblihtt, J Cell Sci 119(Pt 13):2635-2641, 2006, Revil et al., Bull Cancer 93(9):909-919, 2006, Venables, Transworld Res Network, 2006, Pajares et al., Lancet Oncol 8(4):349-57, 2007, Skotheim and Nees, Int J Biochem Cell Biol 39:1432-1449, 2007). Numerous studies have now confirmed the existence of specific differences in the alternative splicing profiles between normal and cancer tissues. Although there are a few cases where specific mutations are the primary cause for these changes, global alterations in alternative splicing in cancer cells may be primarily derived from changes in the expression of RNA-binding proteins that control splice site selection. Overall, these cancer-specific differences in alternative splicing offer an immense potential to improve the diagnosis and the prognosis of cancer. This review will focus on the functional impact of cancer-associated alternative splicing variants, the molecular determinants that alter the splicing decisions in cancer cells, and future therapeutic strategies.

Angiogenesis in neuroendocrine tumors: therapeutic applications

The considerable research efforts devoted to the understanding of the mechanisms of tumor angiogenesis have resulted in the development of targeted anti-angiogenic therapies and finally in their introduction in clinical practice. Neuroendocrine tumors (NETs), which are characterized by a high vascular supply and a strong expression of VEGF-A, one of the most potent pro-angiogenic factors, are an attractive indication for these new treatments. However, several lines of evidence show that the dense vascular networks associated with low-grade NETs are more likely to be a marker of differentiation than a marker of aggressiveness, as in other epithelial tumors. These observations form the basis for the so-called 'neuroendocrine paradox', according to which the most vascularized are the most differentiated and the less angiogenic NETs. This must be kept in mind when discussing the role of anti-angiogenic strategies in the treatment of NETs. Nevertheless, several targeted therapies, with direct or indirect anti-angiogenic properties, including anti-VEGF antibodies, tyrosine kinase inhibitors (sunitinib) and mTOR inhibitors (everolimus), have recently proven to be of clinical benefit. In addition, some drugs already used in NET treatment, such as somatostatin analogues and interferon-α, may also have anti-angiogenic properties. The main challenges for the next future are to validate biomarkers for the selection of patients and the prediction of their response to refine the indications of anti-angiogenic targeted therapies and to overcome the mechanisms of resistance, which explain the limited duration of action of most of these treatments.

New prospects in the roles of the C-terminal domains of VEGF-A and their cooperation for ligand binding, cellular signaling and vessels formation

VEGF-A is a crucial growth factor for blood vessel homeostasis and pathological angiogenesis. Due to alternative splicing of its pre-mRNA, VEGF-A is produced under several isoforms characterized by the combination of their C-terminal domains, which determines their respective structure, availability and affinity for co-receptors. As controversies still exist about the specific roles of these exon-encoded domains, we systematically compared the properties of eight natural and artificial variants containing the domains encoded by exons 1-4 and various combinations of the domains encoded by exons 5, 7 and 8a or 8b. All the variants (VEGF111a, VEGF111b, VEGF121a, VEGF121b, VEGF155a, VEGF155b, VEGF165a, VEGF165b) have a similar affinity for VEGF-R2, as determined by Surface plasmon resonance analyses. They strongly differ however in terms of binding to neuropilin-1 and heparin/heparan sulfate proteoglycans. Data indicate that the 6 amino acids encoded by exon 8a must be present and cooperate with those of exons 5 or 7 for efficient binding, which was confirmed in cell culture models. We further showed that VEGF165b has inhibitory effects in vitro, as previously reported, but that the shortest VEGF variant possessing also the 6 amino acids encoded by exon 8b (VEGF111b) is remarkably proangiogenic, demonstrating the critical importance of domain interactions for defining the VEGF properties. The number, size and localization of newly formed blood vessels in a model of tumour angiogenesis strongly depend also on the C-terminal domain composition, suggesting that association of several VEGF isoforms may be more efficient for treating ischemic diseases than the use of any single variant.

Association between VEGF splice isoforms and progression-free survival in metastatic colorectal cancer patients treated with bevacizumab

PURPOSE

Bevacizumab improves survival for patients with metastatic colorectal cancer with chemotherapy, but no proven predictive markers exist. The VEGF-A splice form, VEGF(165)b, anti-angiogenic in animal models, binds bevacizumab. We tested the hypothesis that prolonged progression-free survival (PFS) would occur only in patients with low relative VEGF(165)b levels treated with bevacizumab.

EXPERIMENTAL DESIGN

Blinded tumor samples from the phase III trial of FOLFOX4 ± bevacizumab were assessed for VEGF(165)b and VEGF(total) by immunohistochemistry and scored relative to normal tissue. A predictive index (PI) was derived from the ratio of VEGF(165)b:VEGF(total) for 44 samples from patients treated with FOLFOX + bevacizumab (arm A) and 53 samples from patients treated with FOLFOX4 (arm B), and PFS, and overall survival (OS) analyzed on the basis of PI relative to median ratio.

RESULTS

Unadjusted analysis of PFS showed significantly better outcome for individuals with VEGF(165)b:VEGF(total) ratio scores below median treated with FOLFOX4 + bevacizumab compared with FOLFOX4 alone (median, 8.0 vs. 5.2 months; P < 0.02), but no effect of bevacizumab on PFS in patients with VEGF(165)b:VEGF(total) ratio >median (5.9 vs. 6.3 months). These findings held after adjustment for other clinical and demographic features. OS was increased in arm A (median, 13.6 months) compared with arm B (10.6 months) in the low VEGF(165)b group, but this did not reach statistical significance. There was no difference in the high VEGF(165)b:VEGF(total) group between FOLFOX + bevacizumab (10.8 months) and FOLFOX alone (11.3 months).

CONCLUSION

Low VEGF(165)b:VEGF(total) ratio may be a predictive marker for bevacizumab in metastatic colorectal cancer, and individuals with high relative levels may not benefit.

The role of VEGF 165b in pathophysiology

Anti-angiogenic vascular endothelial growth factor A (VEGF) 165b and pro-angiogenic VEGF 165 are generated from the same transcript, and their relative amounts are dependent on alternative splicing. The role of VEGF 165b has not been investigated in as much detail as VEGF 165, although it appears to be highly expressed in non-angiogenic tissues and, in contrast with VEGF 165, is downregulated in tumors and other pathologies associated with abnormal neovascularization such as diabetic retinopathy or Denys Drash syndrome. VEGF 165b inhibits VEGFR2 signaling by inducing differential phosphorylation, and it can be used to block angiogenesis in in vivo models of tumorigenesis and angiogenesis-related eye disease. Recent reports have identified three serine/arginine-rich proteins, SRSF1, SRSF2 and SRSF6, and studied their role in regulating terminal splice-site selection. Since the balance of VEGF isoforms is lost in cancer and angiogenesis-related conditions, control of VEGF splicing could also be used as a basis for therapy in these diseases.

Post-transcriptional regulation in cancer progression : Microenvironmental control of alternative splicing and translation

The microenvironment acts as a conduit for cellular communication, delivering signals that direct development and sustain tissue homeostasis. In pathologies such as cancer, this integral function of the microenvironment is hijacked to support tumor growth and progression. Cells sense the microenvironment via signal transduction pathways culminating in altered gene expression. In addition to induced transcriptional changes, the microenvironment exerts its effect on the cell through regulation of post-transcriptional processes including alternative splicing and translational control. Here we describe how alternative splicing and protein translation are controlled by microenvironmental parameters such as oxygen availability. We also emphasize how these pathways can be utilized to support processes that are hallmarks of cancer such as angiogenesis, proliferation, and cell migration. We stress that cancer cells respond to their microenvironment through an integrated regulation of gene expression at multiple levels that collectively contribute to disease progression.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

Androgen receptor (AR) aberrations in castration-resistant prostate cancer

Genetic aberrations affecting the androgen receptor (AR) are rare in untreated prostate cancers (PCs) but have been found in castration-resistant prostate cancers (CRPCs). Further, successful treatment with novel endocrine therapies indicates that CRPCs remain androgen-sensitive. Known AR aberrations include amplification of the AR gene leading to the overexpression of the receptor, point mutations of AR resulting in promiscuous ligand usage, and constitutively active AR splice variants. Gain, or amplification, of the AR gene is one of the most frequent genetic alterations observed in CRPCs. Up to 80% of CRPCs have been reported to carry an elevated AR gene copy number, and about 30% have a high-level amplification of the gene. AR mutations are also commonly observed and have been found in approximately 10-30% of the CRPC treated with antiandrogens; however, the frequency and significance of AR splice variants is still unclear. Because AR aberrations are found almost exclusively in CRPC, these alterations must have been selected for during therapy. Interestingly, these aberrations lead to activation of the receptor, despite treatment-induced emergence of therapy-resistant tumor clones. Therefore, future novel treatment strategies should focus on suppressing AR activity in CRPC.