title: Synergistic effects of sirolimus with cyclosporine and tacrolimus: analysis of immunosuppression on lymphocyte proliferation and activation in rat whole blood.
abstract: BACKGROUND
  Whole-blood analysis of lymphocyte function was used to investigate the pharmacodynamic (PD) interaction of sirolimus (SRL) with cyclosporine (CsA) or tacrolimus (TRL) in vitro and to determine the relation between PD and pharmacokinetics (PK) of SRL in an in vivo rat model.
  
  
  METHODS
  In vitro, experiments involved incubation of increasing concentrations (0.25-25 [corrected] nM) of SRL with either CsA or TRL in rat whole blood. For the in vivo study, rats were orally treated with different doses of SRL alone (1, 3, 5, or 8 mg/kg) or with a combination of 3 mg/kg SRL plus 2.5 or 5 mg/kg CsA. Blood was obtained before and at different times after dosing. Inhibition of lymphocyte proliferation (proliferating cell nuclear antigen [PCNA]) and activation (CD25, CD71, CD11a, CD134) in mitogen-stimulated blood was determined using fluorescence-activated cell sorter analysis. SRL and CsA blood concentrations were determined at the same time points by light chromatography tandem mass spectrometry (LC-MS).
  
  
  RESULTS
  In vitro, concentrations of SRL between 0.25-25 [corrected] nM acted synergistically in combination with CsA or TRL at concentrations between 0.25-1.0 [corrected] nM. Higher SRL concentrations did not further increase inhibition of lymphocyte function in these combinations. In vivo, good correlations (r=0.68-0.94) were observed between PD parameters of lymphocyte function and SRL-PK and dose. Increasing SRL doses produced higher blood concentrations, but SRL doses of 8 mg/kg did not further increase inhibition of lymphocyte function. PD effects on lymphocyte function were prolonged, but maximal inhibition was not increased when SRL was applied in combination with CsA as compared to SRL mono therapy.
  
  
  CONCLUSIONS
  The results suggest that analysis of lymphocyte function in whole blood may be useful to optimize dosing of SRL in combination with CsA or TRL and that PD monitoring of immunosuppressive drugs will enhance the value of PK monitoring.
authors.affiliation: University of Leipzig, Department of Cardiac Surgery, Heart Center Leipzig, Leipzig, Germany. bartenm@medizin.uni-leipzig.de
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Barten
authors.forename: Frank
authors.initials: F
authors.lastname: Streit
authors.forename: Martin
authors.initials: M
authors.lastname: Boeger
authors.forename: Stefan
authors.initials: S
authors.lastname: Dhein
authors.forename: Attila
authors.initials: A
authors.lastname: Tarnok
authors.forename: Maria
authors.initials: M
authors.lastname: Shipkova
authors.forename: Victor W
authors.initials: VW
authors.lastname: Armstrong
authors.forename: Friedrich W
authors.initials: FW
authors.lastname: Mohr
authors.forename: Michael
authors.initials: M
authors.lastname: Oellerich
authors.forename: Jan F
authors.initials: JF
authors.lastname: Gummert
mesh_terms: D000818:Animals; D016572:Cyclosporine / Q000008:administration & dosage*; D004357:Drug Synergism; D007166:Immunosuppressive Agents / Q000008:administration & dosage*; D066298:In Vitro Techniques; D008213:Lymphocyte Activation / Q000187:drug effects; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D008297:Male; D051381:Rats; D011917:Rats, Inbred Lew; D020123:Sirolimus / Q000008:administration & dosage*; D016559:Tacrolimus / Q000008:administration & dosage*
chemical_list: D007166:Immunosuppressive Agents; D016572:Cyclosporine; D020123:Sirolimus; D016559:Tacrolimus