γ-aminobutyric acid B2 receptor:A potential therapeutic target for cholangiocarcinoma in patients with diabetes mellitus

BACKGROUND The association between diabetes mellitus(DM)and the increased risk and progression of cholangiocarcinoma(CCA)has been reported with unclear underlying mechanisms.Previous studies showed thatγ-aminobutyric acid(GABA)B2 receptor(GABBR2)was upregulated in CCA cells cultured in high glucose(HG)conditions.Roles of GABA receptors in CCA progression have also been studied,but their association with DM and hyperglycemia in CCA remains unclarified.AIM To investigate the effects of hyperglycemia on GABBR2 expression and the potential use of GABBR2 as a CCA therapeutic target.METHODS CCA cells,KKU-055 and KKU-213A,were cultured in Dulbecco Modified Eagle’s Medium supplemented with 5.6 mmol/L(normal glucose,NG)or 25 mmol/L(HG)glucose and assigned as NG and HG cells,respectively.GABBR2 expression in NG and HG cells was investigated using real-time quantitative polymerase chain reaction and western blot.Expression and localization of GABBR2 in CCA cells were determined using immunocytofluorescence.GABBR2 expression in tumor tissues from CCA patients with and without DM was studied using immunohistochemistry,and the correlations of GABBR2 with the clinicopathological characteristics of patients were analyzed using univariate analysis.Effects of baclofen,a GABA-B receptor agonist,on CCA cell proliferation and clonogenicity were tested using the MTT and clonogenic assays.Phospho-kinases arrays were used to screen the affected signaling pathways after baclofen treatment,and the candidate signaling molecules were validated using the public transcriptomic data and western blot.RESULTS GABBR2 expression in CCA cells was induced by HG in a dose-and time-dependent manner.CCA tissues from patients with DM and hyperglycemia also showed a significantly higher GABBR2 expression compared with tumor tissues from those with euglycemia(P<0.01).High GABBR2 expression was significantly associated with a poorer non-papillary histological subtype but with smaller sizes of CCA tumors(P<0.05).HG cells of both tested CCA cell lines were more sensitive to baclofen treatment.Baclofen significantly suppressed the proliferation and clonogenicity of CCA cells in both NG and HG conditions(P<0.05).Phospho-kinase arrays suggested glycogen synthase kinase 3(GSK3),β-catenin,and the signal transducer and activator of transcription 3(STAT3)as candidate signaling molecules under the regulation of GABBR2,which were verified in NG and HG cells of the individual CCA cell lines.Cyclin D1 and c-Myc,the common downstream targets of GSK3/β-catenin and STAT3 involving cell proliferation,were accordingly downregulated after baclofen treatment.CONCLUSION GABBR2 is upregulated by HG and holds a promising role as a therapeutic target for CCA regardless of the glucose condition.

Orotate phosphoribosyl transferase mRNA expression and the response of cholangiocarcinoma to 5-fluorouracil

AIM:To determine whether expression of certain enzymes related to 5-fluorouracil(5-FU)metabolism predicts 5-FU chemosensitivity in cholangiocarcinoma(CCA).METHODS:The histoculture drug response assay(HDRA)was performed using surgically resected CCA tissues.Tumor cell viability was determined morphologically with hematoxylin and eosin-and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling-stained tissues.The mRNA expression of thymidine phosphorylase(TP),orotate phosphoribosyl transferase(OPRT),thymidylate synthase(TS),and dihydropyrimidine dehydrogenase(DPD)was determined with realtime reverse transcriptase-polymerase chain reaction.The levels of gene expression and the sensitivity to 5-FU were evaluated.RESULTS:Twenty-three CCA tissues were obtained from patients who had been diagnosed with intrahepatic CCA and who underwent surgical resection at Srinagarind Hospital,Khon Kaen University from 2007 to 2009.HDRA was used to determine the response of these CCA tissues to 5-FU.Based on the dose-response curve,200μg/mL 5-FU was selected as the test concentration.The percentage of inhibition index at the median point was selected as the cut-off point to differentiate the responding and non-responding tumors to 5-FU.When the relationship between TP,OPRT,TS and DPD mRNA expression levels and the sensitivity of CCA tissues to 5-FU was examined,only OPRT mRNA expression was significantly correlated with the response to 5-FU.The mean expression level of OPRT was significantly higher in the responder group compared to the non-responder group(0.41±0.25 vs 0.22±0.12,P<0.05).CONCLUSION:OPRT mRNA expression may be a useful predictor of 5-FU chemosensitivity of CCA.Whether OPRT mRNA could be used to predict the success of 5-FU chemotherapy in CCA patients requires confirmation in patients.