Ribonucleotide reductase subunit M1 is a possible chemoresistance marker to gemcitabine in biliary tract carcinoma

Biliary tract carcinoma is a relatively rare tumor with a poor prognosis. Surgical resection is the only potential cure. However, the efficacy of chemotherapeutic agents is disappointing in advanced or recurrent cases. Gemcitabine (GEM) appears to be one of the most promising chemotherapeutic agents in biliary tract carcinoma, and ribonucleotide reductase subunit M1 (RRM1) plays an important role in GEM resistance. The aim of this study was to evaluate the correlation between the expression of RRM1 and the response to GEM in biliary tract carcinoma in vitro and in vivo. The drug sensitivity to GEM was assessed by MTT assay. The expression of RRM1 was evaluated by quantitative RT-PCR, a Western blot analysis and immunohistochemistry. RNAi assay was used to investigate the down-regulation of the expression of RRM1. After the RRM1-specific RNAi transfection, a cell growth assay was performed to evaluate the drug sensitivity to GEM, and flow cytometry and TUNEL assay were performed to evaluate apoptosis. The results showed that in 6 biliary tract carcinoma cell lines, a tendency for a positive correlation between the expression of RRM1 and IC50 for GEM exists (R=0.620, p=0.19). The transfection of the RRM1-specific RNAi suppressed the expression level of RRM1 in a dose-dependent manner. After the transfection of RRM1-specific RNAi into G-415, the drug sensitivity to GEM markedly increased (p<0.001), and apoptosis was highly induced according to flow cytometry and the TUNEL assay. In an analysis of cancer tissue specimens obtained from the 12 patients treated with GEM for biliary tract cancer, RRM1 immunostaining was strongly positive in all of the PD cases (3/3), while weakly positive in all of the PR cases except for one (4/5). In conclusion, RRM1 may be one of the key marker molecules for GEM chemotherapy that overcomes advanced and recurrent biliary tract carcinoma.