Peptide ligand-mediated liposome distribution and targeting to EGFR expressing tumor in vivo

Abstract

Epidermal growth factor receptor (EGFR) is an important anti-cancer therapy target that is applicable to many cancer types. We had previously reported the screening and discovery of a novel peptide ligand against EGFR named GE11. It was shown to bind to EGFR competitively with EGF and mediate gene delivery to cancer cells with high-EGFR expression. In this study, we conjugated GE11 on to liposome surface and examined their binding and distribution to EGFR expressing cancer cells in vitro and in vivo using fluorescence imaging techniques. GE11 liposomes were found to bind specifically and efficiently to EGFR high-expressing cancer cells. In vivo in H1299 xenograft mouse model, GE11 liposomes also extravasated and accumulated into the tumor site preferentially, and demonstrated better targeting and drug delivery capacities.

Introduction

Liposomes have been increasingly developed as preferred drug carriers in anti-tumor treatments (Bangham et al., 1965, Bangham, 1968). PEG-conjugated liposomes can somewhat escape from the capture of reticuloendothelial system to circulate longer than conventional liposomes. So they have a tendency to traverse leaky vascular and passively accumulate in tumor tissues based on the so-called enhanced permeability and retention (EPR) effect (Allen et al., 1991, Lasic et al., 1991, Woodle and Lasic, 1992, Wu et al., 1993). Such stealth liposome formulations had been used to deliver anti-cancer drugs and attained significant therapy effect (Mayhew et al., 1992, Vaage et al., 1992). In addition, modification of liposomes with antibody or antibody fragment, or small molecular ligands has also been developed a promising strategy for tumor targeting. Drug-loaded liposomes with active targeting were shown to have more enhanced anti-cancer efficacy (Lopes de Menezes et al., 1998, Asai et al., 2002, Gabizon et al., 2003).

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase over-expressed on many human cancer cells surface. It is regarded as a significant target for tumor-targeted therapy. EGFR-targeted immunoliposomes were shown to promote efficient intracellular delivery of doxorubicin to tumor cells, and therefore resulted in superior anti-tumor effects in a series of animal xenograft models (Mamot et al., 2003, Mamot et al., 2005, Mamot et al., 2006). In addition to antibodies and antibody fragments, peptide ligands having specific interaction with receptors over-expressing in tumor or tumor neovasculature were utilized to direct chemotherapeutics, proteins, and gene constructs (Kok et al., 2002). Some peptides such as the RGD-derived peptides were widely used (Takikawa et al., 2000, Schiffelers et al., 2003, Maeda et al., 2004). Many other studies had attempted to find other effective ligands for various targets based on phage display screening, comparative sequence/structure analysis and so on (Morpurgo et al., 2002, Wu et al., 2004). We had previously reported the screening of a noval peptide ligand (GE11) for EGFR (Li et al., 2005). It was shown to bind effectively to EGFR over-expressing cancer cells-mediated target specific gene transfection when conjugated to a PEI vector.

In this study, we used this peptide ligand to construct an active targeting liposome drug delivery system towards EGFR positive cancer cells. We also examined the liposome distribution in vivo in tumor bearing mice. The aim of this study is to explore the feasibility of using peptide ligand-directed liposome as target therapeutics for cancer.