PlGF blockade does not inhibit angiogenesis during primary tumor growth.

It has been recently reported that treatment with an anti-placenta growth factor (PlGF) antibody inhibits metastasis and primary tumor growth. Here we show that, although anti-PlGF treatment inhibited wound healing, extravasation of B16F10 cells, and growth of a tumor engineered to overexpress the PlGF receptor (VEGFR-1), neutralization of PlGF using four novel blocking antibodies had no significant effect on tumor angiogenesis in 15 models. Also, genetic ablation of the tyrosine kinase domain of VEGFR-1 in the host did not result in growth inhibition of the anti-VEGF-A sensitive or resistant tumors tested. Furthermore, combination of anti-PlGF with anti-VEGF-A antibodies did not result in greater antitumor efficacy than anti-VEGF-A monotherapy. In conclusion, our data argue against an important role of PlGF during primary tumor growth in most models and suggest that clinical evaluation of anti-PlGF antibodies may be challenging.

Stanniocalcin 1 is an autocrine modulator of endothelial angiogenic responses to hepatocyte growth factor.

Stanniocalcin 1 (STC1) is a secreted glycoprotein originally described as a hormone involved in calcium and phosphate homeostasis in bony fishes. We recently identified the mammalian homolog of this molecule to be highly up-regulated in an in vitro model of angiogenesis, as well as focally and intensely expressed at sites of pathological angiogenesis (e.g. tumor vasculature). In the present study, we report that STC1 is a selective modulator of hepatocyte growth factor (HGF)-induced endothelial migration and morphogenesis, but not proliferation. STC1 did not inhibit proliferative or migratory responses to vascular endothelial growth factor or basic fibroblast growth factor. The mechanism of STC1 inhibitory effects on HGF-induced endothelial migration seem to occur secondary to receptor activation because STC1 did not inhibit HGF-induced c-met receptor phosphorylation, but did block HGF-induced focal adhesion kinase activation. In the mouse femoral artery ligation model of angiogenesis, STC1 expression closely paralleled that of the endothelial marker CD31, and the peak level of STC1 expression occurred after an increase in HGF expression. We propose that STC1 may play a selective modulatory role in angiogenesis, possibly serving as a "stop signal" or stabilizing factor contributing to the maturation of newly formed blood vessels. HGF is a mesenchyme-derived pleiotropic factor with mitogenic, motogenic, and morphogenic activities on a number of different cell types. HGF effects are mediated through a specific tyrosine kinase, c-met, and aberrant HGF and c-met expression are frequently observed in a variety of tumors. Recent studies have shown HGF to be a potent growth factor implicated in wound healing, tissue regeneration, and angiogenesis.

Vascular endothelial growth factor-induced genes in human umbilical vein endothelial cells: relative roles of KDR and Flt-1 receptors.

OBJECTIVE: This study evaluated the relative roles of the vascular endothelial growth factor (VEGF) receptors KDR and Flt-1 in the mediation of altered gene expression elicited by VEGF. METHODS AND RESULTS: We used mutants of VEGF selective for the KDR and Flt-1 receptors to differentiate gene expression patterns mediated by wild-type VEGF (VEGFwt) in human umbilical vein endothelial cells. RNA was extracted from cells treated for 24 hours with 1 nmol/L of each ligand, and gene expression was monitored by using oligonucleotide arrays (Affymetrix U95A). We report that activation of KDR was sufficient to upregulate all the genes induced by VEGFwt. In contrast, there were no genes selectively upregulated by the Flt-selective mutant. However, high concentrations of the Flt-selective mutant could augment the expression of some genes induced by submaximal concentrations of VEGFwt but not the KDR-selective mutant. CONCLUSIONS: The binding of VEGF to its receptor, KDR, is necessary and sufficient to induce the gene expression profile induced by this growth factor. Furthermore, in human umbilical vein endothelial cells, the Flt-1 receptor appears to act as a decoy receptor, tempering the response to lower concentrations of VEGF.

In silico data filtering to identify new angiogenesis targets from a large in vitro gene profiling data set.

The objective of this study was to use gene expression data from well-defined cell culture models, in combination with expression data from diagnostic samples of human diseased tissues, to identify potential therapeutic targets and markers of disease. Using Affymetrix oligonucleotide array technology, we identified a common profile of genes upregulated during endothelial morphogenesis into tubelike structures in three in vitro models of angiogenesis. Rigorous data selection criteria were used to identify a list of over 1,000 genes whose expression was increased more than twofold over baseline at either 4, 8, 24, 40 or 50 h. To further refine and prioritize this list, we used standard bioinformatic algorithms to identify potential transmembrane and secreted proteins. We then overlapped this gene set with genes upregulated in colon tumors vs. normal colon, resulting in a subset of 128 genes in common with our endothelial list. We removed from this list those genes expressed in 6 different colon tumor lines, resulting in a list of 24 putative, vascular-specific angiogenesis-associated genes. Three genes, gp34, stanniocalcin-1 (STC-1), and GA733-1, were expressed at levels 10-fold or more in colon tumors compared with normal mucosa. We validated the vascular-specific expression of one of these genes, STC-1, by in situ hybridization. The ability to combine in vitro and in vivo data sets should permit one to identify putative angiogenesis target genes in various tumors, chronic inflammation, and other disorders where therapeutic manipulation of angiogenesis is a desirable treatment modality.

A dominant-negative p65 PAK peptide inhibits angiogenesis.

PAK1 is a protein kinase downstream of the small GTPases Rac and Cdc42 that previous work has implicated in endothelial cell migration via modulation of cell contraction. The first proline-rich region of PAK that binds to an SH3 domain from the adapter protein NCK was responsible for these dominant-negative effects. To test the role of PAK in angiogenesis, we prepared a peptide in which the proline-rich region was fused to the polybasic sequence from the HIV Tat protein to facilitate entry into cells. We show that the short peptide selectively binds NCK, whereas a mutant peptide does not. Treatment of cells with the PAK peptide but not the control peptide disrupts localization of PAK. This peptide specifically inhibited endothelial cell migration and contractility similarly to full-length dominant-negative PAK. In an in vitro tube-forming assay, the PAK peptide specifically blocked formation of multicellular networks. In an in vivo chick chorioallantoic membrane assay, the PAK peptide specifically blocked angiogenesis. These results, therefore, suggest a role for PAK in angiogenesis.