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@INPROCEEDINGS{Schneider:1027700,
      author       = {Schneider, Daniela and Schulze, Annette and Humpert, Swen
                      and Holschbach, Marcus and Bier, Dirk and Neumaier, Bernd},
      title        = {{E}valuation of a multifunctional blood-brain barrier
                      co-culture model prepared from rat primary brain endothelial
                      cells and astrocytes: first results},
      issn         = {0969-8051},
      reportid     = {FZJ-2024-04010},
      year         = {2022},
      abstract     = {Objectives: The potential of a rodent endothelial
                      cell/astrocyteco-culture BBB model to predict in vivo brain
                      exposure ofCNS radiotracers was evaluated using three
                      18F-labeled xanthine-derived positron emission tomography
                      (PET) tracers foradenosine A1 receptor (A1AR) imaging,
                      namely
                      8-cyclopentyl-3-(3-[18F]Fluoropropyl)-1-propylxanthine
                      ([18F]CPFPX [1,2]),
                      8-cyclobutyl-3-(3-[18F]Fluoropropyl)-1-propylxanthine
                      ([18F]CBX [3]),
                      and3-(3-[18F]Fluoropropyl)-8-(1-methylcyclobutyl)-1-propylxanthine([18F]MCBX
                      [3]).Methods: Primary rat brain astrocytes (4x104 cells) and
                      primaryrat brain microvascular endothelial cells (BECs,
                      2x104 cells) wereplated on opposite sides of a polycarbonate
                      Transwell membrane(pore size 3.0 m) and cultured at 37°C in
                      a $5\%$ CO2 atmosphere for4 days [4]. Integrity of the
                      endothelial cell layer was assessed bytransendothelial
                      electrical resistance (TEER) measurements. Forpermeability
                      testing, the radiolabeled compounds (185 kBq/ml)were added
                      to the donor chamber (apical compartment), and
                      theirappearance in the receiver chamber (basolateral
                      compartment) wasmonitored with a gamma counter to calculate
                      apparent permeabilities(Papp). Papp values of the xanthines
                      were compared to Pin vivo valuesderived from PET kinetic
                      modeling data [5]. Additional experimentswere conducted to
                      investigate the influence of test compound concentrationand
                      addition of albumin on Papp values.Results: Figure 1
                      displays time dependent permeation of [18F]CPFPX, [18F]CBX,
                      and [18F]MCBX across the model BBB. Calculated Pappvalues
                      and the corresponding Pin vivo values obtained from PET
                      measurementsare listed in Table 1. Papp values proved to be
                      highly predictivefor in vivo brain penetration. Permeability
                      rankings in vivo andin vitro were comparable ([18F]MCBX >
                      [18F]CBX≈[18F]CPFPX).Papp values of [18F]CPFPX did not
                      show concentration dependence,indicating that passage of the
                      compound through the BBB proceedssolely via transmembrane
                      diffusion without involvement of saturabletransport
                      mechanism. However, addition of bovine serumalbumin (30
                      mg/ml, corresponding to a free ligand concentration $of7\%)$
                      significantly lowered Papp of [18F]CPFPX by about $30\%,$
                      which isconsistent with the free drug
                      hypothesis.Conclusions: This first study demonstrates a
                      strong agreementbetween in vitro cell-based permeability
                      data and in vivo brain penetrationmeasured by PET. If these
                      results can be confirmed withother classes of molecules that
                      exhibit different transport characteristicsat the BBB (e.g.,
                      P-glycoprotein substrates), the BBB modeldescribed here
                      should prove valuable for the development of novelCNS
                      radiotracers.Acknowledgments: We thank Prof. Dr. Dieter
                      Willbold andDominik Honold from the Institute of Structural
                      Biochemistry (IBI-7)at FZJ for their valuable
                      support.References:[1] Holschbach et al., J Med Chem. 2002,
                      45(23), 5150-5156.[2] Bauer et al., J Nucl Med. 2003,
                      44(10), 1682-1689.[3] Schneider et al., Pharmaceuticals.
                      2019, 12(2), 57.[4] Niego et al., J Vis Exp. 2013, 81,
                      e50934.[5] Schneider et al., Nucl Med Biol. 2020, 82-83,
                      1-8.},
      month         = {May},
      date          = {2022-05-29},
      organization  = {24th International Symposium on
                       Radiopharmaceutical Sciences, Nantes
                       (France), 29 May 2022 - 3 Jun 2022},
      subtyp        = {After Call},
      cin          = {INM-5},
      ddc          = {570},
      cid          = {I:(DE-Juel1)INM-5-20090406},
      pnm          = {5253 - Neuroimaging (POF4-525)},
      pid          = {G:(DE-HGF)POF4-5253},
      typ          = {PUB:(DE-HGF)6},
      doi          = {10.1016/S0969-8051(22)00233-5},
      url          = {https://juser.fz-juelich.de/record/1027700},
}