Identification of the genes that are differentially-expressed between radiosensitive and radioresistant cancer cells is important to the ability to predict the clinical effectiveness of radiotherapy. We established radioresistant human pancreatic cancer cell lines using fractionated irradiation in order to identify genes that are differentially-expressed between parental lines and radioresistant cell sublines. Six pancreatic cancer cell lines (PK-1, PK-8, PK-9, T3M4, MiaPaCa2 and PANC-1) were treated with 10 Gy fractionated irradiation at approximately two-week intervals (total dose 150-180 Gy). Five radioresistant sublines (PK-1, PK-8, PK-9, T3M4, and MiaPaCa2) were successfully established. Using oligonucleotide microarrays containing 17,086 genes, we identified 73 up-regulated genes and 55 down-regulated genes common to radioresistant sub-lines. Subsequent analysis by quantitative RT-PCR confirmed the reliability of our microarray strategy. Up-regulated genes were associated with growth factor (example, amphiregulin), cell-cycle check point (MAPKAPK2), intracellular signaling pathway (regucalcin), and angiogenesis stimulation (angiopoietin 2). Down-regulated genes were associated with apoptosis (caspase 8), retinoid esterification (lecithin retinol acyltransferase), and electron transport (calcium-activated chloride channel 1). Some of these genes have known association with response to radiation, such as caspase 8 and MAPKAPK2, but others are novel. Global gene analysis of radioresistant sublines may provide new insights into the mechanisms underlying clinical radioresistance and to improving the efficacy of radiotherapy for pancreatic cancer.

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