Prediction of gemcitabine resistance in patients with pancreatic cancer

4125 Background: Pancreatic cancer is the most lethal of all solid tumors partially because of its chemoresistance. Although a deoxycytidine analogue, gemcitabine, is widely used as a first selected and a single agent for the treatment of this disease despite low response rate, molecular mechanisms of gemcitabine resistance in pancreatic cancer still remain obscure. The purpose of this study is to identify the molecular marker for gemcitabine resistance in human pancreatic cancer. Methods: Gemcitabine resistant variants were established from human pancreatic cancer cell lines, MiaPaCa2. Gene expression changes between parental cells and resistant cells were assessed by an oligonucleotide microarray covering 30,000 human oligonucleotides, and candidate genes were validated by RT-PCR and Western blotting. The association to resistance was validated by RNAi assay. Clinical effects on 18 recurrent pancreatic cancer patients treated by gemcitabine were evaluated using mRNA of specimens resected at the primary operation. Results: The 81-fold gemcitabine resistant variant MiaPaCa2-RG was selected from pancreatic cancer cell line MiaPaCa2. By microarray analysis between parental and resistant MiaPaCa2 cells, 99.6% genes were altered expression of less than 2-fold. Among 43 genes with altered expression of more than 2-fold, the most up-regulated gene in MiaPaCa2-RG cells is ribonucleotide reductase M1 subunit (RRM1) with 4.5-fold up-regulation compared with MiaPaCa2 cells. Transfection with RRM1-specific RNAi suppressed more than 90% of RRM1 mRNA and protein expression both in MiaPaCa2 and MiaPaCa2-RG cells. After RRM1-specific RNAi transfection, gemcitabine chemoresistance of MiaPaCa2-RG was significantly reduced to the same level of MiaPaCa2. The 18 recurrent pancreatic cancer patients were divided into two groups by RRM1 mRNA expression levels. There was a significant association between gemcitabine response and RRM1 expression (p = 0.018). Furthermore, patients with high RRM1 levels had a poor survival times after gemcitabine treatment than those with low RRM1 levels (p = 0.016). Conclusions: RRM1 should be a key molecule in gemcitabine resistance in pancreatic cancer through both in vitro and clinical models. RRM1 should be considered as the predictor of gemcitabine resistance. No significant financial relationships to disclose.