Anti-tumor activity of the novel angiogenesis inhibitor anginex
Introduction
Angiogenesis or neovascularization is the process through which new blood vessels develop from pre-existing vasculature [1]. The growth of solid tumors is dependent on angiogenesis, as tumors generally cannot grow beyond the size of 1–2 mm in diameter without formation of new blood vessels to supply nutrition and oxygen and remove waste products. Most tumors release angiogenesis-regulating factors, and neovasculatization occurs only when there are more positive than negative regulators of angiogenesis [2], [3].
A highly vascularized tumor is correlated with a poor clinical prognosis, not only because of the potential for uncontrolled tumor growth, but also because of the increased access of the tumor to capillaries, which contributes to increased metastatic potential [4], [5]. Consequently, methods that inhibit angiogenic sprouting provide a unique opportunity to arrest tumor growth and prevent metastasis formation. Many endogenous and exogenous anti-angiogenic agents have been identified, such as angiostatin [6], endostatin [7], thrombospondin [8], TNP-470 [9], platelet factor-4 [10], thalidomide [11], squalamine [12], bactericidal/permeability-increasing protein [13] and carboxyamino-imidazole [14].
Although preclinical testing of anti-angiogenic agents shows promise, the need for more and better angiogenesis inhibitors is driven by the absence of any major clinical breakthroughs (e.g. SU5416, BB2516, AG3340, Bay 12-9566, IM-862 [15]). The most successful angiostatic agents have been those that directly act by inhibiting endothelial cell proliferation. Anginex, a designed β-sheet-forming cytokine-like 33-mer peptide, which potently inhibits multiple steps in the angiogenesis process, is a member of this class of angiogenesis inhibitors. A family of homologous βpep peptides was designed by using basic folding principles and incorporating short sequences from the β-sheets domains of α-chemokine IL-8 and bactericidal/permeability increasing (BPI) protein [16]. The angiostatic activity of anginex is based primarily on apoptosis-induction via prevention of adhesion on and migration through the extracellular matrix of angiogenically-activated endothelial cells [16].
The aim of the present study was to test and to optimize the in vivo efficacy of anginex as an anti-cancer agent in mouse models. Various treatment regiments, i.e. dose response, mode and frequency of administration, were investigated. For other angiogenesis inhibitors, the literature reports that continuous, systemic administration of, for example endostatin [17], results in more effective tumor growth suppression at significantly reduced doses compared with bolus administration. Continuous systemic administration of anginex in a 10 mg/kg per day dose provided optimal efficacy. Efficacy was significantly improved by conjugating anginex to human serum albumin to improve its bioavailability. These results demonstrate that anginex is a promising pharmacological anti-cancer agent that should be developed for clinical testing.
Section snippets
Cell culture
The human epithelial ovarian carcinoma cell line, MA148, was kindly provided by Prof. Dr Ramakrishnan. MA148 cells were cultured at 37 °C in RPMI 1640 medium (Life Technologies, Grand Island, NY) supplemented with 10% fetal bovine serum (Cellgro, Mediatech, Washington, DC) and 1% penicillin/streptomycin (Cellgro, Mediatech). Cultures were grown in the presence of 5% CO2 and split 1:3 every 3 days. The human SK-OV-3 carcinoma cell line was kindly provided by Dr Rebecca Bagley (Genzyme).
Proliferation assay
Human
Anginex inhibits tumor growth dose dependently
The dose dependency of anginex was assessed in the MA148 human ovarian carcinoma xenograft model, whereby anginex was administered at 5, 10, and 20 mg/kg per day via osmotic mini-pumps. For this study, there were three control groups: one given PBS containing BSA and the other two given PBS containing homologous peptide βpep-28 (5 or 10 mg/kg per day). As a model for minimal residual disease, treatment was initiated immediately after inoculation of animals with tumor cells. Anginex was observed
Discussion
Anginex is a rationally designed, cytokine-like peptide of 33-mer, which has been shown in vitro to induce apoptosis specifically in angiogenically-activated endothelial cells (EC) by inhibiting EC from adhering to and migrating on the extracellular matrix [16]. The present paper reports the in vivo efficacy of this small peptide and its development as a therapeutic anti-cancer agent. We have shown here that anginex significantly inhibits the growth of ovarian carcinoma-derived tumors in
Acknowledgements
This research was supported by grants from the Department of Defense (DA/DAMD 17-99-1-9564) and the National Institutes of Health (R01 CA-96090) to K.H. Mayo.
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Present address: Department of Chemistry, Mathematics and Physical Sciences, St. Francis University, Loretto, PA, USA.