Establishment of radio-resistant cell line The method for establishing radio-resistant cell line by fractionated irradiation has been described previously[13]. Briefly, the cell line was first grown to approximately 60% confluence in 25-cm2 culture flasks. Cells were irradiated with 10 Gy of X-ray irradiation, from a linear accelerator (6-MV X-ray), at a rate of 3 Gy/min. One cm thick of tissue-equivalent bolus was placed on top of the plate to ensure homogeneity. And then cells were returned to the incubator. When they reached approximately 60% confluence,

the cells were again irradiated with 10 Gy of X-ray. The fractionated irradiations were continued until the total concentration reached 80 Gy. The radio-resistant cell subline was CP-868596 solubility dmso then established. The parental cells were subjected to identical trypsinization, replating, and culture conditions,

but were not irradiated. For all assays on irradiated cells, there was at least a four-week interval between the last 10 Gy fractionated irradiation and the experiment. Assay for radiosensitivity Cell survival after X-ray irradiation was measured by clonogenic assay. Cells were plated in six-well culture plates, and were irradiated at different concentration ranging from 0 to 12 Gy. The appropriate plating density was aimed to produce 20–100 surviving colonies in each well. These cells were incubated at 37°C for 10–14 days (three wells in each radiation concentration). After fixation with acetic acid-methanol (1:4) and staining with diluted crystal violet (1:30), colonies consisting of GSI-IX 50 cells or more were counted under a light microscope. The triplicate colonies were averaged and divided by initial seeded cells to yield survival rate of clones for each concentration, and the surviving fraction was determined. All survival curves represent

at least three independent experiments. Detection of apoptotic cells Apoptosis was evaluated using the Annexin V-FITC Apoptosis Detection Kit (BD Biosciences Pharmingen, San Jose, CA, USA) followed by FACS analysis. Cells were treated with trypsin-EDTA in PBS at pH 7.5, washed with normal Geneticin clinical trial medium and cold PBS, and then resuspended in 1× binding buffer. Five μl of annexin V and ten μl of propidium iodide were added to the cells, vortexed, and incubated for 15 minutes in the dark. Finally, 400 μl of 1× binding buffer Thalidomide was added, and samples were evaluated by flow cytometry. MTT cell viability assay Drug-induced cytotoxicity was evaluated by conventional MTT cell viability assay as previously reported [14, 15]. Briefly, 1 × 104/well EC109 or EC109/R cells were seeded in 96-well plates and cultured in DMEM media supplemented with 10% FBS for 8 h. They were exposed to various concentrations of cisplatin (3.33–63.3 μM), 5-fluorouracil (0.07–4.93 mM), doxorubicin (0.53–7.36 μM), paclitaxel (3.12–100 nM) or etoposide (1–16 μM) for 48 h in a CO2 incubator.