Targeted Inhibition of Tumour Vascularisation Using Anti-PDGF/VEGF Aptamers

Review Article

Austin J Nanomed Nanotechnol. 2014;2(5): 1027.

Targeted Inhibition of Tumour Vascularisation Using Anti-PDGF/VEGF Aptamers

Kislay Roy, Rupinder K Kanwar and Jagat R Kanwar*

Department of Health, Deakin University, Australia

*Corresponding author: Jagat R Kanwar, Department of Health, Deakin University, Nanomedicine-Laboratory of Immunology and Molecular Biomedical Research (NLIMBR), School of Medicine, Waurn Ponds, Victoria 3217, Australia

Received: May 20, 2014; Accepted: June 24, 2014; Published: June 27, 2014

Abstract

Platelet-derived growth factor (PDGF) is one of the numerous proteins growth factors that plays a significant role in embryonic development, cell proliferation, cell migration and particularly, in blood vessel formation (angiogenesis). Its sub-family, vascular endothelial growth factor (VEGF) is another important growth factor that functions in creating new blood vessels during embryonic development, new blood vessels after injury, muscle following exercise, and new vessels to bypass blocked vessels. Over expression of PDGF/VEGF can contribute to diseases such as vascular disease in the retina of the eye and other parts of the body, eventually leading to cancer. Thus, PDGF and VEGF antagonists for therapy of neo vascular disorders and cancer have become important research topics for scientists during the last decade. Recently it has been reported that aptamers or chemical antibodies can bind to and inhibit the activity of PDGF/VEGF with highly affinity and specificity.

The effect of anti-PDGF and anti-VEGF therapy to treat tumour vascularisation is discussed in this review. Besides that, the benefits and drawbacks of three commercialized drugs, namely Avastin, Macugenand Lucentis, and examples of anti-VEGF/PDGF aptamers, such as E10030 have also been elaborately discussed.

Introduction

Platelet-derived growth factor (PDGF) is one of the critical proteins growth factors that stimulates the division and proliferation of cells by binding to its receptors on cell surfaces [1-3]. It is also defined as a potent mitogen and chemotactic factor for many connective tissue cells, such as fibroblasts, smooth muscle cells, and inglial cells in culture [1-5]. Vascular endothelial growth factor (VEGF) is another signal protein from the sub-family of PDGF [5, 6]. It is a secreted disulfide-linked homodimer and considered as an important signalling protein that involved in vasculogenesis (the formation of new blood vessels by de novo production of endothelial cells without pre-existing vasculature) and angiogenesis (the growth of blood vessels from pre-existing vasculature) [6-9]. VEGF's normal function is to create new blood vessels during embryonic development [6], new blood vessels after injury [6,7], muscle following exercise [7,9], and new vessels (collateral circulation) to bypass blocked vessels [6-9]. On the other hand, PDGF plays similarly role in embryonic development [5], cell proliferation [1-3], cell migration [2,3] and particularly, in blood vessel formation (angiogenesis) [1-5]. When PDGF/VEGF is over expressed, it can contribute to disease such as vascular disease in the retina of the eye and other parts of the body [1-9,14,15].

Due to alternative the splicing of the VEGF gene, VEGF may occur in four isoforms including VEGF-121, VEGF-165, VEGF-189, and VEGF-206, all of which show different heparin-binding affinities [6-9]. VEGF-121 and VEGF-165 are diffusible whereas VEGF-189 and VEGF-206 remain predominantly localized to the cell membrane as a consequence of their high affinity for heparin [6,7]. In addition, VEGF-165 can also bind to heparin and it is the predominant isoforms in the body [7-9]. Only VEGF-121 is incapable in binding with heparin that appears to have a lower affinity for VEGF receptors as well as lower mitogenic potency [6-8]. All members of the VEGF family stimulate cellular responses by binding to receptors VEGFR- 1(Flt-1) and VEGFR-2 (Flk-1/KDR) on the cell surface, allowing them to dimerize and get activated via trans-phosphorylation [6-9]. These receptors are classified as a receptor tyrosine kinase (RTK), a type of high affinity cell surface receptors for polypeptide growthfactor [5]. The PDGF dimer on the other hand, stimulates responsive cells by cross linking two RTK receptor subunits [1-4]. In both mouse and human, the PDGF signalling network consists of four ligands, included A (PDGF-A), B (PDGF-B), C (PDGF-C), and D (PDGF-D), and two receptors, alpha (PDGFR α) and beta (PDGFR β) [1-5] (Table1).