cetuximab and panitumumab for the treatment of metastatic colorectal cancer, cetuximab for head and neck cancer, gefitinib for the treatment of refractive non-small cell lung cancer, erlotinib for advanced/metastatic lung cancer, erlotinib in combination with gemcitabine for advanced/metastatic pancreatic cancer

Inhibition of epidermal growth factor receptor (EGFR) signaling is a promising treatment strategy for malignant tumors. In this study, we evaluated the effectiveness of Tyrphostin AG1478, a potent and specific inhibitor of EGFR tyrosine kinase, on the growth, apoptosis and invasion of breast cancer cells. Western blotting demonstrated that AG1478 inhibited the phosphorylation of EGFR, ERK1/2 and AKT in a dose-dependent manner. Three proliferation analyses, MTT, cell counting, and clone formation assay, consistently showed that AG1478 significantly inhibited cell proliferation in a dose-dependent manner. FACS analysis demonstrated that AG1478 promoted cell apoptosis. In addition, TRAP assay exhibited that AG1478 significantly suppressed telomerase activity of tumor cells, which was parallel with growth inhibition. Semi-qantitative RT-PCR revealed that the suppression of telomerase activity was correlated with the decreased expression of human telomerase catalytic subunit (hTERT) mRNA, the rate-limiting determinant of its enzyme activity. These data suggest that AG1478 suppressed cellular growth by inhibiting cellular proliferation, inducing apoptosis and inhibiting telomerase activity. Furthermore, we also examined the effects of AG1478 on cellular invasion. Boyden chamber invasion assay showed that AG1478 significantly inhibited cell invasion in a dose-dependent manner. Western blotting revealed that AG1478 could down-regulate the expression of MMP-9, which may be one of the mechanisms by which AG1478 suppressed cellular invasion. In conclusion, this study demonstrated that Tyrphostin AG1478 effectively inhibited the proliferation and invasion of breast cancer cells. Tyrphostin AG1478 may be a potential EGFR-targeted therapeutic agent for breast cancer. Introduction EGFR is widely expressed in most cell types with the exception of hematopoietic cells (1). EGFR activation is important in normal cellular processes. However, aberrantly enhanced EGFR signaling is closely associated with the development and progression of a variety of malignant tumors including breast cancer (1,2). Overexpression or mutation of EGFR is often correlated with advanced tumor stages, metastasis, and poor clinical outcome of malignant tumors (3). Therefore, EGFR has become a promising molecular target for development of novel and effective anticancer agents. Two predominant classes of EGFR inhibitors, antiEGFR monoclonal antibodies and tyrosine kinase inhibitors, have been developed (4-6). Anti-EGFR antibodies such as cetuximab, panitumumab, matuzumab, MDX-447, nimutozumab, and mAb806, bind to the extracellular domain of the receptor and compete with ligand binding (5,7). EGFR selective tyrosine kinase inhibitors (TKIs) such as erlotinib, gefitinib, EKB-569, lapatinib (GW572016), PKI-166, and canertinib (CI-1033), target the adenosine triphosphate (ATP) binding site on the intracellular kinase domain and prevent tyrosin kinase activation (6,7). These agents have been studied for the treatment of colorectal, lung, breast, pancreatic, renal, head and neck, gynecologic, and prostate cancer (1,6,7). However, only a few of EGFR-targeted agents have been approved by FDA, such as cetuximab and panitumumab for the treatment of metastatic colorectal cancer, cetuximab for head and neck cancer, gefitinib for the treatment of refractive non-small cell lung cancer, erlotinib for advanced/metastatic lung cancer, erlotinib in combination with gemcitabine for advanced/metastatic pancreatic cancer treatment (8). Many studies on EGFR-targeted therapy in breast cancer have been performed. It has been demonstrated that inhibitors of the EGFR-signaling can abrogate or delay the emergence of anti-estrogen resistance or antiHER2 resistance in breast cancer (9,10). However, relative to HER2-targeted therapy with trastuzumab, studies of EGFR inhibitors in breast cancer are still in their infancy. The large part of research in this area has been focused on gefitinib. Selected published data from phase II studies failed to show that gefitinib has a significant disease control rate in heavily pre-treated metastatic breast cancer [11,12; Albain et al, Breast Cancer Res Treat 76 (Suppl. 1): abs. 20, 2002). INTERNATIONAL JOURNAL OF ONCOLOGY 33: 595-602, 2008 595 Tyrphostin AG1478 suppresses proliferation and invasion of human breast cancer cells YUN-GANG ZHANG1,2, QIANG DU1, WEI-GANG FANG1, MU-LAN JIN2 and XIN-XIA TIAN1 1Department of Pathology, Peking University Health Science Center, Beijing 100083; 2Department of Pathology, Beijing Chao-Yang Hospital, Capital Medical University, Beijing 100020, P.R. China Received March 24, 2008; Accepted May 15, 2008 DOI: 10.3892/ijo_00000045 _________________________________________ Correspondence to: Dr Xin-Xia Tian, Department of Pathology, Peking University Health Science Center, Beijing 100083, P.R. China E-mail: [email protected]