Transport and metabolism of radiolabeled choline in hepatocellular carcinoma.
Altered choline (Cho) metabolism in cancerous cells can be used as a basis for molecular imaging with PET using radiolabeled Cho. In this study, the metabolism of tracer Cho was investigated in a woodchuck hepatocellular carcinoma (HCC) cell line (WCH17) and in freshly derived rat hepatocytes. The transporter responsible for [(11)C]-Cho uptake in HCC was also characterized in WCH17 cells. The study helped to define the specific mechanisms responsible for radio-Cho uptake seen on the PET images of primary liver cancer such as HCC. Cells were pulsed with [(14)C]-Cho for 5 min and chased for varying durations in cold media to simulate the rapid circulation and clearance of [(11)C]-Cho. Radioactive metabolites were extracted and analyzed by radio-HPLC and radio-TLC. The Cho transporter (ChoT) was characterized in WCH17 cells. WCH17 cells showed higher (14)C uptake than rat primary hepatocytes. [(14)C]-Phosphocholine (PC) was the major metabolite in WCH17. In contrast, the intracellular Cho in primary hepatocytes was found to be oxidized to betaine (partially released into media) and, to a lesser degree, phosphorylated to PC. [(14)C]-Cho uptake by WCH17 cells was found to have both facilitative transport and nonfacilitative diffusion components. The facilitative transport was characterized by Na(+) dependence and low affinity (K(m) = 28.59 ± 6.75 μM) with partial energy dependence. In contrast, ChoT in primary hepatocytes is Na(+) independent and low affinity. Our data suggest that transport and phosphorylation of Cho are responsible for the tracer accumulation during [(11)C]-Cho PET imaging of HCC. WCH17 cells incorporate [(14)C]-Cho preferentially into PC. Conversion of [(14)C]-PC into phosphatidylcholine occurred slowly in vitro. Basal oxidation and phosphorylation activities in surrounding hepatic tissue contribute to the background seen in [(11)C]-Cho PET images.
Kuang
Yu
Y
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Salem
Nicolas
N
Corn
David J
DJ
Erokwu
Bernadette
B
Tian
Haibin
H
Wang
Fangjing
F
Lee
Zhenghong
Z
D000818:Animals; D002250:Carbon Radioisotopes / Q000378:metabolism / Q000493:pharmacokinetics; D006528:Carcinoma, Hepatocellular / Q000175:diagnosis / Q000378:metabolism*; D002478:Cells, Cultured; D002794:Choline / Q000378:metabolism* / Q000493:pharmacokinetics; D004140:Dinitrophenols / Q000494:pharmacology; D006426:Hemicholinium 3 / Q000494:pharmacology; D007700:Kinetics; D008113:Liver Neoplasms / Q000175:diagnosis / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D049268:Positron-Emission Tomography; D051381:Rats; D013329:Structure-Activity Relationship
D002250:Carbon Radioisotopes; D004140:Dinitrophenols; D026901:Membrane Transport Proteins; C065637:choline transporter; D006426:Hemicholinium 3; D010042:Ouabain; D002794:Choline