title: Estimation of binding rate constants using a simultaneous mixed-effects method: application to monoamine transporter reuptake inhibitor reboxetine.
abstract: OBJECTIVE
  Reboxetine is a clinically used antidepressant and is a racemic mixture of two enantiomers, SS- and RR-reboxetine. The aim of the work described in this manuscript was to determine the kinetics of binding of the RR- and SS-reboxetine to the human noradrenaline transporter (hNET).
  
  
  METHODS
  We have applied a simultaneous mixed-effects method to the analysis of the transient kinetics of binding of SS-, RR- and racemic reboxetine to hNET. This method allowed simultaneous modelling of multiple datasets, taking into account inter-experiment variability, thereby facilitating robust parameter estimation and minimizing the assumptions made.
  
  
  RESULTS
  The mixed-effects method proved simple and robust. SS-reboxetine bound to hNET according to a one-step binding model with the SS-enantiomer having 130-fold higher steady state affinity than the RR-enantiomer (K(d)= 0.076 +/- 0.009 nM vs. 9.7 +/- 0.8 nM respectively). The k(on) for SS-reboxetine was c. 1.4 x 10(5) M(-1).s(-1) and k(off) 1.05 x 10(-5) s(-1) (t(1/2) approximately 18 h). The k(on) for RR-reboxetine was c. 4.3 x 10(5) M(-1).s(-1) and k(off) 4.2 x 10(-3) s(-1) (t(1/2) approximately 3 min). The racemate behaved as expected for an equimolar mixture of RR- and SS-reboxetine, assuming mutually exclusive binding.
  
  
  CONCLUSIONS
  These data will be useful for the interpretation of the behaviour of reboxetine and its enantiomers in man and the method used could be applied to other candidate drugs.
authors.affiliation: Pfizer Global Research & Development, Department of Pharmacokinetics Dynamics and Metabolism, Modelling & Simulation, Kent, UK. neil.benson@pfizer.com <neil.benson@pfizer.com>
authors.forename: Neil
authors.initials: N
authors.lastname: Benson
authors.forename: Nelleke
authors.initials: N
authors.lastname: Snelder
authors.forename: Bart
authors.initials: B
authors.lastname: Ploeger
authors.forename: Carolyn
authors.initials: C
authors.lastname: Napier
authors.forename: Harriet
authors.initials: H
authors.lastname: Sale
authors.forename: Nigel J M
authors.initials: NJ
authors.lastname: Birdsall
authors.forename: Richard P
authors.initials: RP
authors.lastname: Butt
authors.forename: Piet H
authors.initials: PH
authors.lastname: van der Graaf
mesh_terms: D018759:Adrenergic Uptake Inhibitors / Q000378:metabolism*; D000928:Antidepressive Agents / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D009025:Morpholines / Q000378:metabolism*; D050484:Norepinephrine Plasma Membrane Transport Proteins / Q000378:metabolism*; D011485:Protein Binding; D000077593:Reboxetine; D013237:Stereoisomerism
chemical_list: D018759:Adrenergic Uptake Inhibitors; D000928:Antidepressive Agents; D009025:Morpholines; D050484:Norepinephrine Plasma Membrane Transport Proteins; D000077593:Reboxetine