Miyata 5-10

The signaling pathway that is initiated by binding of epidermal growth factor receptor (EGFR) and results in sustained signaling through PI3K plays an important role in a tumor's response to ionizing radiation. The current in vitro study explored both the effects of ZD1839 (Iressa), a highly selective EGFR tyrosine kinase inhibitor, as a radiosensitiser for bile duct carcinoma cell lines and ZD1839's general effects on cell growth in the same two lines. Secondly, we ensured suppression of radiation-induced phosphorylation of EGFR by ZD1839 using an immunoprecipitation technique. Furthermore, we examined radiation-induced phosphorylation of ERK, p38, JNK, and AKT with or without inhibitor with use of Western blot techniques and performed clonogenic assays to confirm radiosensitivity in the presence of a drug. ZD1839 inhibited cell growth of both cell lines and suppressed radiation-induced phosphorylation of EGFR. After exposure to radiation, there was an increase in phosphorylation of AKT as shown by Western blot. Treatment with either ZD1839 or LY294002 (the latter, a PI3K inhibitor) suppressed phosphorylation of AKT by Western blot. Both ZD1839 and LY294002 significantly suppressed colony formation by clonogenic assay; however, U0126 (a MEK1/2 inhibitor), SB203580 (a p38 inhibitor), and SP600125 (a JNK inhibitor) had no effect on colony formation. These results suggest that AKT may be a useful target molecule for enhancement of radiotherapy effect and that ZD1839 may have an important role in combination with radiotherapy for patients with bile duct carcinoma. Introduction Bile duct carcinoma (BDC) is a malignancy with a poor prognosis. Complete surgical resection is the only hope for long-term survival, but only a small fraction of patients are candidates for curative surgery. For patients with unresectable disease, management of obstructive jaundice associated with BDC is necessary. Use of an expanding metallic stent (EMS) has been applied as treatment of obstructive jaundice. In the effort to extend stent patency and patient survival, clinicians have employed radiation therapy using a remote afterloading system (RALS); reports indicate that durations of stent patency and patient survival after RALS radiotherapy are significantly longer than those associated with EMS treatment only (1-3). However, because most BDCs are histologically adenocarcinoma and are considered radioresistant cancers, further improvements in outcome require development of effective radiosensitisers. The epidermal growth factor receptor (EGFR) family consists of four closely related growth factor receptors, including EGFR, erbB-2, erbB-3, and erbB-4. Amplification of EGFR and erbB-2 occurs in a subset of human tumors including cancers of the breast, lung, and ovary (4). EGFR is expressed or overexpressed in a wide variety of solid human tumors, including non-small cell lung (NSCL) cancer, as well as cancer of the prostate, breast, stomach, colon and rectum, head and neck, bladder, and ovary (5). Activation of EGFR initiates the cascade of intracellular signaling events that leads to proliferation, cell survival, angiogenesis, and metastasis. EGFR expression has been observed in about 44.7% of cases of BDC and is considered to be a contributor to disease progression (6). Overexpression of erbB-2 in breast and ovarian cancer is associated with particularly aggressive clinical behavior and poor prognosis (7). In BDC, the frequency of overexpression of erbB-2 has been reported in the range from 26.3 to 52.6% (6,8-10). Activation of EGFR initiates signaling through two main downstream pathways, the Ras/Raf/MAPK pathway and the PI3K/AKT pathway. The Ras to MAPK pathway is perhaps the most extensively studied, and it consists of at least three sequential kinase cascades that include the Ras/Raf/MAPK (also known as ERK) pathway, the stress-activated SAPK/JNK INTERNATIONAL JOURNAL OF ONCOLOGY 28: 915-921, 2006 915 The effects of ZD1839 (Iressa), a highly selective EGFR tyrosine kinase inhibitor, as a radiosensitiser in bile duct carcinoma cell lines HIDEKI MIYATA, TAMITO SASAKI, KENICHI KUWAHARA, MASAHIRO SERIKAWA and KAZUAKI CHAYAMA Department of Medicine and Molecular Science, Division of Frontier Medical Science, Programs for Biochemical Research, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan Received October 5, 2005; Accepted November 29, 2005 _________________________________________ Correspondence to: Dr Hideki Miyata, Department of Medicine and Molecular Science, Division of Frontier Medical Science, Programs for Biochemical Research, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-