The Cooperative Effect Of Iressa Combined With Ionizing Radiation In Non-small Cell Lung A549 Cell Line

Growth factors control cellular proliferation and differentiation and are important in initiating and maintaining neoplastic transformation. Growth factors and its specific receptor, the EGFRs, have been implicated in the development and progression of the majority of human epithelial cancer types. EGFR activation is not only critical for cell proliferation but EGFR-mediated signals also contribute to other processes that are crucial to cancer progression, including angiogenesis, metastatic spread, and the inhibition of apoptosis. Agents such as monoclonal antibodies or small molecule inhibitors of the associated TK, which block the function of some receptors, particularly HER2/neu and EGFR, can have significant antitumor actions against human tumors both in vitro and in vivo. Several studies have shown that the interruption of signaling with various EGFR inhibitors that recognize the extracellular (monoclonal antibodies) or intracellulardomain of the receptor (small molecules) results in inhibition of tumor cell proliferation and/or viability. High expression of EGFR is associated with resistance to hormonal therapy, cytotoxic drugs, or radiotherapy. More specifically, high EGFR expression has been associated with reduced sensitivity or with resistance to ionizing radiation in several preclinical models. Treatment with ionizing radiation can induce the EGFR/ras/ra^mitogen-activated protein kinase (MAPK) proliferative pathway through the release of TGF a and the activation of the EGFR tyrosine kinase . EGFR activation could be a cell survival response to block apoptotic signals in cancer cells exposed to cytotoxic damage. This may have clinical relevance because it could represent a mechanism by which cancer cells escape radiation-induced cell death. Iressa is an orally active, the first selective EGFR- TK1 which has been approved in the management of patients with advanced, chemotherapy-refractory NSCLC in many countries. Recently, various EGFR- TKI that have been tested as anticancer drugs in several clinical trials to treat NSCLC patients in combination with radiotherapy. To date, however, little is known about that the therapeutic effects of EGFR- TKI combined with radiotherapy for NSCLC and its mechanism. The aim of this experiment is to elucidate the synergistic effects of Iressa combined with ionizing radiation in human non-small cell lung A549 cell line.Purpose: To investigate the cooperative effect of Iressa, a selective small molecule EGFR tyrosine kinase inhibitor, when combined with ionizing radiation in non-small cell lung A549 cell line. Methods: A549 cell line was engaged in this study, anti-proliferation effects were determined using MTT assay, cell cycle distribution and apoptosis was analyzed by flow cytometry, the clonogenic assay was used to test the clone forming efficency . Result: A dose-dependent growth inhibition of Iressa was observed in A549 cell line. IC50 at 48 h was 49.88 u g/ml. Enhanced inhibition effect of Iressa was observed when combined with radiation at the Iressa concentrations of 5-> 10> 15> 20 > 30^ 40 u g/ml. The results of clone forming efficiency showed enhanced anti-proliferation effect of Iressa (15 u g/ml) when combined with radiation . Compared with control untreated cells, after 72 hours incubation in Iressa, cells showed an accumulation in the Go-G] phases. The percentage of cells in Go-Gi phase increased from 67.51±2.56% to 73.63±1.62% , and that in G2-M phase drop from 8.39±0.61% to 7.02 ±1.1% and S phase fell from 24.1±2.65% to 19.36±1.63%, the apoptosis rate increased from 0.99+0.56% to 1.95±0.7%. Twenty-four h after ionizing radiation, the apoptosis rate of cells in I+R group was evidently enhanced to 4.34±1.13%, much more higher than that in the other groups. Conclusion: This study showed Iressa, with antiproliferative and the proapoptotic activity, mayenhance the inhibition effect of ionizing radiation in A549 cell line in vitro.This may provides a way to evaluate the combination of ionizing radiationand Iressa in cancer patients.