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Abstract

Introduction: Epidermal Growth Factor (EGF) stimulates target cells by binding to Epidermal Growth Factor Receptor (EGFR) and EGF-EGFR interaction regulates the expression level of a variety of transcription factors through multiple signaling pathways. These pathways are sometimes involved in cancer initiation, promotion, and/or progression. Now many kinds of EGFR inhibitors are developed and used in the clinic. But we noticed EGF-induced cancer cell death in several EGFRoverexpressing cancer cell lines while EGF-induced proliferation of normal fibroblast cell lines. I would like to introduce some possible clinical application of EGF in the management of head and neck cancer based on our experimental data. Materials & Methods: Two EGFR-over expressing cancer cell lines (AMC-HN3 and A431) and normal fibroblast were cultured with 0.01-1000 nM of recombinant human EGF (rhEGF), and clonogenic assay was performed. After culturing serum-starved cells with 10 nMrhEGF, the expression patterns of two apoptosis-associated proteins (cleaved caspase-3 and cleaved PARP) and PI3K/Akt/mTOR signaling pathway were measured using immunoblotting. Balb/c-nu mice, which were inoculated with A431 (human squamous cell carcinoma) cells at right hind legs were divided into five groups: I (no treatment), II (EGF for 6 days), III (EGF for 20 days), IV (radiotherapy (RT)), and V (RT plus concomitant EGF). EGF was administered intraperitoneally (5 mg/kg) once a day, and RT dose was 30 Gy in 6 fractions. Hematoxylin and eosin (H&E) staining sections of tumor, liver, lung, and kidney tissues were investigated. Immunohistochemistry staining of caspase-3 was performed in tumor tissues. Results: In the clonogenic assay, the number of colonies was decreased in a dose-dependent manner in cancer cell lines, whereas rhEGF treatment increased the number of colonies in normal fibroblast. The expression of cleaved caspase-3 and cleaved PARP was significantly induced in the cancer cell lines, whereas there was no expression in normal fibroblast. As for PI3K/Akt/mTOR signaling pathway, rhEGF treatment paradoxically suppressed the expression of PI3K, Akt, phospho-Akt, and mTOR in a time-dependent manner. EGF for 6 days decreased tumor volume since day 13, but it approached to the level of the control group on day 23 (P=0.550). The duration of tumor shrinkage was prolonged more in group V (RT + EGF), and the slope of tumor re-growth phase was steeper in group IV (RT) (P=0.034). EGF for 20 days decreased tumor volume until the end of follow-up (P<0.001).In the immunohistochemistry of caspase-3, mice treated with RT plus EGF showed stronger staining intensity than the RT group. There were no abnormal histologic findings in H&E staining of the normal organs. Conclusions: EGF treatment induced cell death in the two EGFR-overexpressing cancer cell lines, and the mode of cell death was apoptosis. And, the cell death might be associated with the paradoxical suppression of PI3K/Akt/mTOR signaling pathway. According to animal studies, we suggest EGF-induced anti-tumor effect in the xenograft mouse models with A431 cells. The concomitant use of EGF resulted in tumor growth delay more, and it shows the potential as a radiosensitizer in the design of fractionated irradiation.

Biography

Hong-Gyun Wu is currently Professor and Chairman of Department of Radiation Oncology, Seoul National University College of Medicine. He completed his graduation in 1990 and PhD in Medicine in 2001 both from Seoul National University College of Medicine.