Search

Purpose: Erlotinib is a novel therapeutic agent for cancer treatment. This study was performed to investigate the role of c-MET-PI3K-AKT pathway in the regulation of erlotinib-induced radiosensitization., Methods: A973 lung adenocarcinoma cells treated with 6 Gy of radiation were incubated in the presence of erlotinib. The apoptotic rate after 24 hours, the colony-formating rate after 14 days, and changes in the c-MET expression levels after 14 days of irradiation were examined. Surviving fractions in different treatment groups (blank control, radiation alone, erlotinib alone, anti-c-MET monoclonal antibody alone, combined erlotinib and radiation, and combined erlotinib and radiation with anti-c-MET monoclonal antibody groups) were determined, the survival curves were plotted, and the sensitizer enhancement ratio was calculated using colony formation assays. Expressions of c-MET, p-c-MET, PI3K, AKT, and p-AKT in cells in different treatment groups were examined by Western blot analysis., Results: The apoptotic rate in the combined erlotinib and radiation group was higher than those in single treatment groups; however, the colony-forming rate remained approximately 2.04 ± 1.02%. The expression of c-MET in colony-forming cells in the combined group significantly increased, and the blockade of c-MET activity significantly enhanced the radiosensitizing effect of erlotinib. The expression of c-Met, p-c-MET, PI3K, AKT, and p-AKT among colony-forming cells significantly decreased upon the inhibition of c-MET., Conclusions: Upregulated activity of the c-MET-PI3K-AKT pathway was found to be important for cell survival under combined the treatment with erlotinib and radiation. The blockade of the c-MET-PI3K-AKT signaling pathway enhanced the radiosensitizing effect of erlotinib.

Background: Despite of the recent success of EGFR inhibitory agents, the primary drug-resistant becomes a major challenge for EGFR inhibitor therapies. PTEN gene is an important positive regulatory factor for response to EGFR inhibitor therapy. Low-expression of PTEN is clearly one of the important reasons why tumor cells resisted to tyrosine kinase inhibitors., Methods: To investigate the drug-resistance reversal to gefitinb and the mechanism in PTEN low expression cells which radiated with X-rays in vitro, We demonstrated that H-157 lung cancer cells (low-expression of PTEN but phospho-EGFR overexpressed tumor cells) exposed to X-rays. The PTEN expressions and radiosensitizing effects of tyrosine kinase inhibitor before and after irradiation were observed. The cell-survival rates were evaluated by colony-forming assays. The cell apoptosis was investigated using FCM. The expressions of phospho-EGFR and PTEN were determined by Western blot analysis., Results: The results showed that the PTEN expressions were significantly enhanced by X-rays. Moreover, the cell growth curve and survival curve were down-regulated in the gefitinib-treated groups after irradiation. Meanwhile, the radiation-induced apoptosis of tumor cells was increased by inhibition of the EGFR through up-regulation of PTEN., Conclusion: These results suggested that PTEN gene is an important regulator on TKI inhibition, and the resistance to tyrosine kinase inhibitors might be reversed by irradiation in PTEN low expression cancer cells.

Background: To investigate the effectiveness and mechanism of 125I seed continuous low-dose-rate irradiation on colonic cell line CL187 in vitro., Methods: The CL187 cell line was exposed to radiation of 60Cogamma ray at high dose rate of 2 Gy/min and 125I seed at low dose rate of 2.77 cGy/h. Radiation responses to different doses and dose rates were evaluated by colony-forming assay. Under 125I seed low dose rate irradiation, a total of 12 culture dishes were randomly divided into 4 groups: Control group, and 2, 5, and 10 Gy irradiation groups. At 48 h after irradiation, apoptosis was detected by Annexin and Propidium iodide (PI) staining. Cell cycle arrests were detected by PI staining. In order to investigate the influence of low dose rate irradiation on the MAPK signal transduction, the expression changes of epidermal growth factor receptor (EGFR) and Raf under continuous low dose rate irradiation (CLDR) and/or EGFR monoclonal antibodies were determined by indirect immunofluorescence., Results: The relative biological effect (RBE) for 125I seeds compared with 60Co gamma ray was 1.41. Apoptosis rates of CL187 cancer cells were 13.74% +/- 1.63%, 32.58% +/- 3.61%, and 46.27% +/- 3.82% after 2 Gy, 5 Gy, and 10 Gy irradiation, respectively; however, the control group apoptosis rate was 1.67% +/- 0.19%. G2/M cell cycle arrests of CL187 cancer cells were 42.59% +/- 3.21%, 59.84% +/- 4.96%, and 34.61% +/- 2.79% after 2 Gy, 5 Gy, and 10 Gy irradiation, respectively; however, the control group apoptosis rate was 26.44% +/- 2.53%. P < 0.05 vs. control groups by Student's t-test were found in every treated group both in apoptosis and in G2/M cell cycle arrest. After low dose rate irradiation, EGFR and Raf expression increased, but when EGFR was blocked by a monoclonal antibody, EGFR and Raf expression did not change., Conclusion: 125I seeds resulted in more effective inhibition than 60Co gamma ray high dose rate irradiation in CL187 cells. Apoptosis following G2/M cell cycle arrest was the main mechanism of cell-killing effects under low dose rate irradiation. CLDR could influence the proliferation of cells via MAPK signal transduction.