title: A Continuously Infused Microfluidic Radioassay System for the Characterization of Cellular Pharmacokinetics.
abstract: Measurement of cellular tracer uptake is widely applied to learn the physiologic status of cells and their interactions with imaging agents and pharmaceuticals. In-culture measurements have the advantage of less stress to cells. However, the tracer solution still needs to be loaded, unloaded, and purged from the cell culture during the measurements. Here, we propose a continuously infused microfluidic radioassay (CIMR) system for continuous in-culture measurement of cellular uptake. The system was tested to investigate the influence of the glucose concentration in cell culture media on18F-FDG uptake kinetics.
  
  
  METHODS
  The CIMR system consists of a microfluidic chip integrated with a flow-control unit and a positron camera. Medium diluted with radioactive tracer flows through a cell chamber continuously at low speed. Positrons emitted from the cells and from tracer in the medium are measured with the positron camera. The human cell lines SkBr3 and Capan-1 were incubated with media of 3 different glucose concentrations and then measured with18F-FDG on the CIMR system. In addition, a conventional uptake experiment was performed. The relative uptake ratios between different medium conditions were compared. A cellular 2-compartment model was applied to estimate the cellular pharmacokinetics on CIMR data. The estimated pharmacokinetic parameters were compared with expressions of glucose transporter-1 (GLUT1) and hexokinase-2 measured by quantitative real-time polymerase chain reaction.
  
  
  RESULTS
  The relative uptake ratios obtained from CIMR measurements correlated significantly with those from the conventional uptake experiments. The relative SDs of the relative uptake ratios obtained from the CIMR uptake experiments were significantly lower than those from the conventional uptake experiments. The fit of the cellular 2-compartment model to the18F-FDG CIMR measurements was of high quality. For SkBr3, the estimated pharmacokinetic parameters k1and k3were consistent with the messenger RNA expression of GLUT1 and hexokinase-2: culturing with low glucose concentrations led to higher GLUT1 and hexokinase-2 expression as well as higher estimated k1and k3For Capan-1, the estimated k1and k3increased as the glucose concentration in the culture medium decreased, and this finding did not match the corresponding messenger RNA expression.
  
  
  CONCLUSIONS
  The CIMR system captures dynamic uptake within the cell culture and enables estimation of the cellular pharmacokinetics.
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and liu@lrz.tum.de.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Ziying
authors.initials: Z
authors.lastname: Jian
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Tao
authors.initials: T
authors.lastname: Cheng
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Feuerecker
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.affiliation: Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, California.
authors.forename: Sung-Cheng
authors.initials: SC
authors.lastname: Huang
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Sibylle I
authors.initials: SI
authors.lastname: Ziegler
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Munich, Germany; and.
authors.forename: Kuangyu
authors.initials: K
authors.lastname: Shi
mesh_terms: D045744:Cell Line, Tumor; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000235:genetics; D006593:Hexokinase / Q000235:genetics; D006801:Humans; D007700:Kinetics; D056656:Lab-On-A-Chip Devices
chemical_list: D051272:Glucose Transporter Type 1; D019788:Fluorodeoxyglucose F18; C000609700:HK2 protein, human; D006593:Hexokinase
keywords: cellular pharmacokinetics; glycolysis; microfluidic radioassay; positron imaging