Abstract. Recent studies have revealed that the epidermal growth factor receptor (EGFR) and insulin-like growth factor-1 receptor (IGF-1R) are overexpressed in various types of human tumors and are attractive targets for anticancer drugs. In the present study, the expression of EGFR and IGF-1R in esophageal squamous cell carcinoma (ESCC) and adjacent normal tissues in a tissue microarray was firstly detected by immunohistochemical staining. In addition, their co-overexpression was observed in 48 out of 75 (64%) patients. Based on the findings, the antitumor activity of an EGFR/IGF-1R bispecific and enediyne-energized fusion protein EGF-LDP-IGF-AE, which we constructed recently by fusing two ligands (EGF and IGF-1) with an enediyne antibiotic lidamycin (LDM), on ESCC were evaluated. Binding assay indicated that the EGF-LDP-IGF protein bound to esophageal cancer cells, and then internalized into the cytoplasm. In vitro, the enediyne-energized fusion protein EGF-LDP-IGF-AE exhibited extremely potent cytotoxicity to ESCC cells with IC 50 values between 10 -10 and 10 -15 mol/l. In vivo, EGF-LDP-IGF-AE also markedly suppressed the growth of human KYSE450 xenografts by 75.1% when administered at 0.3 mg/kg in a nude mouse model, and its efficacy was significantly higher than that of LDM (at maximum tolerated dosage) and mono-specific counterparts. In addition, EGF-LDP-IGF-AE arrested cell cycle progression and it concentration-dependently induced cell apoptosis as well as inhibited the activation of EGFR/IGF-1R and two major downstream signaling pathways (PI3K/AKT and RAS/MAPK). These data imply the potential clinical application of EGF-LDP-IGF-AE for ESCC patients with EGFR and/or IGF-1R overexpression.
IntroductionThe morbidity and mortality of esophageal cancer rank the eighth and sixth among all malignant tumors worldwide (1). Esophageal cancer is classified into esophageal squamous cell carcinoma (ESCC) and adenocarcinoma (EAC) based on the histopathologic type. In Western countries, EAC represents the dominant subtype and the incidence has increased markedly over the past decades, whereas the northern regions of Henan Province, China, have the highest incidence of ESCC (2). Despite the great advances in early diagnosis and traditional treatment options (surgery, chemotherapy and radiotherapy), the prognosis of patients with advanced esophageal cancer remains poor with the 5-year survival rate ranging from 15 to 25% (3). During the past decade, the field of drug development has been transformed with the identification of and ability to direct treatment at specific molecular targets. The overexpression and aberrant function of epidermal growth factor receptor (EGFR) and insulin-like growth factor-1 receptor (IGF-1R) in a number of solid tumors including esophageal cancer, and the important roles in the development of tumors have provided a rationale for targeting the two receptors.EGFR/HER1 is a member of the ErbB receptor tyrosine kinase family, and there are three other members, HER2, HER3 and HER4, in this family...