Factors promoting tumor angiogenesis

Blood vessels are regulators of growth, diagnostic markers and therapeutic targets in prostate cancer

The vasculature plays an important role in the normal and malignant prostate. Under basal conditions both glandular epithelial and stromal prostate cells produce an abundance of blood flow and angiogenesis regulating substances and the expression of these is generally increased in prostate tumors. The proportion of proliferating endothelial cells is high in the normal prostate compared to other tissues in the body. After castration effects on the vasculature, such as decreased blood flow and vascular regression, precede effects on the glandular compartment. Correspondingly, hormone induced prostate growth is characterized by early effects on the vasculature such as increased blood flow and endothelial cell proliferation, thus indicating that the vasculature may be involved in the androgenic regulation of the prostate. Prostatic intraepithelial neoplasia (PIN) and prostate cancer are associated with increased vascular density and in experimental models prostate cancer growth is apparently angiogenesis-dependent since tumor growth and progression can be inhibited by antiangiogenic treatment. Moreover, vascular density has been related to prognosis in prostate cancer patients. A better understanding of the pathways regulating angiogenesis in the normal prostate and how these pathways change during malignant transformation can hopefully lead to better prognostic markers and therapies for the large group of patients with prostate cancer. The purpose of this review is therefore to summarize the current knowledge on the role and regulation of the vasculature in the prostate and its potential clinical applications.

Role of heparan sulfate as a tissue-specific regulator of FGF-4 and FGF receptor recognition

FGF signaling uses receptor tyrosine kinases that form high-affinity complexes with FGFs and heparan sulfate (HS) proteoglycans at the cell surface. It is hypothesized that assembly of these complexes requires simultaneous recognition of distinct sulfation patterns within the HS chain by FGF and the FGF receptor (FR), suggesting that tissue-specific HS synthesis may regulate FGF signaling. To address this, FGF-2 and FGF-4, and extracellular domain constructs of FR1-IIIc (FR1c) and FR2-IIIc (FR2c), were used to probe for tissue-specific HS in embryonic day 18 mouse embryos. Whereas FGF-2 binds HS ubiquitously, FGF-4 exhibits a restricted pattern, failing to bind HS in the heart and blood vessels and failing to activate signaling in mouse aortic endothelial cells. This suggests that FGF-4 seeks a specific HS sulfation pattern, distinct from that of FGF-2, which is not expressed in most vascular tissues. Additionally, whereas FR2c binds all FGF-4-HS complexes, FR1c fails to bind FGF-4-HS in most tissues, as well as in Raji-S1 cells expressing syndecan-1. Proliferation assays using BaF3 cells expressing either FR1c or FR2c support these results. This suggests that FGF and FR recognition of specific HS sulfation patterns is critical for the activation of FGF signaling, and that synthesis of these patterns is regulated during embryonic development.

Kininostatin, an angiogenic inhibitor, inhibits proliferation and induces apoptosis of human endothelial cells

We recently reported that domain 5 (D5) of high-molecular-weight kininogen inhibited critical steps required for angiogenesis. Thus, it was named kininostatin. To understand its mechanism of action, we further investigated the effects of D5 on basic fibroblast growth factor (bFGF)-induced endothelial cell proliferation and cell viability. We report here that D5-inhibited cell proliferation of human endothelial cells stimulated by bFGF was associated with a significant reduction of cyclin D1 expression, which is a critical component required for the transition from G(1) to S phase of the cell cycle. However, inhibition of cell proliferation by D5 was not due to an inhibition of extracellular signal-regulated protein kinase activity. Endothelial cells underwent apoptosis when cultured in a serum-free medium, which was prevented by bFGF. D5 reversed the protective effect of bFGF by 80%. Cells treated with D5 in the presence of bFGF showed typical morphological features of apoptosis, which was further confirmed by 2 additional assays: Hoechst 33258 cell staining and DNA fragmentation analysis. We conclude that the inhibition of endothelial cell proliferation and induction of apoptosis together represent a major contribution to the antiangiogenic activity of D5.

Direct cell adhesion to the angiopoietins mediated by integrins

Genetic ablation of angiopoietin-1 (Ang-1) or of its cognate receptor, Tie2, disrupts angiogenesis in mouse embryos. The endothelial cells in growing blood vessels of Ang-1 knockout mice have a rounded appearance and are poorly associated with one another and their underlying basement membranes (Dumont, D. J., Gradwohl, G., Fong, G. H., Puri, M. C., Gertsenstein, M., Auerbach, A., and Breitman, M. L. (1994) Genes Dev. 8, 1897--1909; Sato, T. N., Tozawa, Y., Deutsch, U., Wolburg-Buchholz, K., Fujiwara, Y., Gendron-Maguire, M., Gridley, T., Wolburg, H., Risau, W., and Qin, Y. (1995) Nature 376, 70--74; Suri, C., Jones, P. F., Patan, S., Bartunkova, S., Maisonpierre, P. C., Davis, S., Sato, T. N., and Yancopoulos, G. D. (1996) Cell 87, 1171--1180). It is therefore possible that Ang-1 regulates endothelial cell adhesion. In this study we asked whether Ang-1 might act as a direct substrate for cell adhesion. Human umbilical vein endothelial cells (HUVECs) plated for a brief period on different substrates were found to adhere and spread well on Ang-1. Similar results were seen on angiopoietin-2 (Ang-2)-coated surfaces, although cells did not spread well on Ang-2. Ang-1, but not Ang-2, supported HUVEC migration, and this was independent of growth factor activity. When the same experiments were done with fibroblasts that either lacked, or stably expressed, Tie2, results similar to those with HUVECs were seen, suggesting that adhesion to the angiopoietins was independent of Tie2 and not limited to endothelial cells. Interestingly, when integrin-blocking agents were included in these assays, adhesion to either angiopoietin was significantly reduced. Moreover, Chinese hamster ovary-B2 cells lacking the alpha(5) integrin subunit did not adhere to Ang-1, but they did adhere to Ang-2. Stable expression of the human alpha(5) integrin subunit in these cells rescued adhesion to Ang-1 and promoted an increase in adhesion to Ang-2. We also found that Ang-1 and Ang-2 bind rather selectively to vitronectin. These results suggest that, beyond their role in modulating Tie2 signaling, Ang-1 and Ang-2 can directly support cell adhesion mediated by integrins.

Copper control as an antiangiogenic anticancer therapy: lessons from treating Wilson's disease

The search for new anticopper drugs for Wilson's disease is culminating in two excellent new drugs: zinc for maintenance therapy and tetrathiomolybdate (TM) for initial therapy. Both are effective and nontoxic. TM is a very potent, fast-acting new anticopper drug and its properties may be useful well beyond Wilson's disease. Angiogenesis (new blood vessel growth) is required for tumor growth, and a sufficient level of copper appears to be required for angiogenesis. We hypothesize that there is a "window" to which the copper level can be reduced that inhibits angiogenesis in tumors, but does not interfere with vital cellular functions of copper. Using TM therapy, this approach has worked to slow or stabilize tumor growth in several animal tumor models, and preliminary results are also very encouraging in human patients with a variety of advanced and metastatic malignancies. A hypothesis is advanced that copper availability has played a fundamental role in growth regulation throughout evolution and that is the reason that so many angiogenic promoters appear to be dependent upon copper levels.

Serum endostatin levels are elevated in patients with soft tissue sarcoma

BACKGROUND

Solid tumors are angiogenesis dependent, and elevated levels of proangiogenic cytokines have been reported in a variety of histologies. Endostatin is an antiangiogenic fragment of the basement membrane protein, collagen XVIII. Because antiangiogenic protein fragments may be generated by tumor-derived proteases, the authors sought to determine whether circulating levels of endostatin were elevated in patients with localized soft tissue sarcoma.

METHODS

The authors analyzed preoperative serum levels of endostatin, vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) in 25 patients (14 males and 11 females; mean age, 44 years) with soft tissue sarcoma. For each serum sample, two aliquots were assayed in duplicate using a competitive enzyme immunoassay. Serum levels were compared with levels from 34 age-matched and gender-matched volunteer blood donors.

RESULTS

Endostatin levels were significantly higher in sera from sarcoma patients than in sera from healthy controls (43.0 ng/mL vs. 25.8 ng/mL, respectively; P = 0.0002; Mann-Whitney U test). Significant elevations also were noted in VEGF and bFGF levels (P = 0.0002 and P = 0.0001, respectively). Furthermore, endostatin levels > 2 standard deviations above the control mean (55 ng/mL) were associated with an increased risk of tumor recurrence after resection (P = 0.047; log-rank test).

CONCLUSIONS

Serum endostatin, VEGF, and bFGF levels are elevated in patients with soft tissue sarcoma. Elevated endostatin levels appear to be associated with tumor aggressiveness. The role of these cytokines in sarcoma angiogenesis and as potential targets for therapy warrants further study.

Angiozyme: a novel angiogenesis inhibitor

Several inhibitors of angiogenesis are being developed for the treatment of cancer. One dominant strategy involves disruption of the vascular endothelial growth factor (VEGF) pathway by inhibition of the receptors for VEGF. Inhibition of the VEGF receptor activity can be accomplished using catalytic RNA molecules known as ribozymes, which downregulate VEGF receptor function by specifically cleaving the mRNAs for the primary VEGF receptors, Flt-1 and KDR. Significant inhibition of angiogenesis using ribozymes against both receptors has been demonstrated. In animal tumor models, antitumor effects are most pronounced with the anti-Flt-1 ribozyme known as Angiozyme (Ribozyme Pharmaceuticals, Boulder, CO). Extensive preclinical studies have demonstrated no significant toxicities. Clinical trials of Angiozyme are currently in progress for patients with advanced malignancy. Preliminary results demonstrate Angiozyme to be well tolerated, without significant side effects. Several phase II trials are underway for patients with advanced malignancy to test therapeutic efficacy.

Kinetics of tumorigenic vascular endothelial growth factor signalling and its significance in human hepatocellular carcinoma cells

Ras-VEGF-concerned angiogenesis is correlated with oncogene maintenance, tumorigenesis, metastasis and resistance to anti-cancer therapies; however, this association is not clearly elucidated by serum VEGF, due to VEGF signalling in blood cells themselves. The present study aimed to elucidate tumorigenic VEGF signalling in eight human HCC cell types and reveal the kinetics of tumorigenic VEGF signalling in three time intervals, thereby discovering the relationships of VEGF-concerned angiogenesis signalling with the extent of the human HCC cell growth, metastasis and resistance to anti-cancer drugs, by using the poorly metastatic SMMC7721, 7402/D+ (doxorubicin-resistance) and 7402/D- (doxorubicin-withdrawal), the highly metastatic MHCC1 non-transfected human HCC cell lines, and the highly metastatic A3-1, F8, F11 and E3 human HCC cell lines transfected with expressing green fluorescence protein into the phenotype of MHCC1 cells, and quantitative 'sandwich' ELISA analyses. The unique results indicated attributes and objective laws as follows. Human HCC cell growth requires time-dependent tumorigenic VEGF signalling; levels of VEGF signalling are positively correlated with each cell phenotype itself; and levels of VEGF signalling are inversely correlated with the possibility of metastasis and drug resistance. The contrast data first reveal important clues for exploring dual metastatic mechanisms via tumor cell-generated non-endothelium vasculogenesis and VEGF-endothelium-attached angiogenesis that may be essential for developing novel strategies aimed at VEGF-concerned signal networks in ischemic/metastatic diseases and transgenic models.

Current role of thalidomide in cancer treatment

Thalidomide (Thalidomid, Celgene, Warren, NJ) is a putative anti-angiogenesis and immunomodulatory agent that has demonstrated activity in various dermatologic and rheumatologic conditions in addition to Crohn's disease. The biologic effects of thalidomide and the clinical trials conducted in solid tumors, hematologic malignancies, chronic graft-versus-host disease (GVHD), and cancer-related cachexia are reviewed. A summary of the preliminary results of ongoing clinical trials is presented, and the future directions of thalidomide research in the oncology are discussed.