title: Profiling of hepatic clearance pathways of Pittsburgh compound B and human liver cytochrome p450 phenotyping.
abstract: BACKGROUND
  11C-PiB has been developed as a positron-emission tomography (PET) ligand for evaluating fibrillar β-amyloid (Aβ) in the human brain. The ligand is rapidly metabolized, with approximately 10% of intact tracer remaining 30 min after injection. When 11C-PiB is used as a treatment endpoint in intervention studies for Alzheimer's disease (AD), a concern is whether the clearance of the tracer changes from one scan to the next, increasing within subject variability in the PET signal. Subjects enrolled in AD trials may start or stop medications that inhibit or induce xenobiotic metabolizing enzymes such as the cytochrome P450 (CYP) isozymes.
  
  
  RESULTS
  We conducted CYP phenotyping in recombinantly expressed systems, and in human liver microsomes, to evaluate CYP isozyme contributions to the metabolism of PiB (carrier) and profiled microsomal and hepatocyte incubations for metabolites. The metabolism of PiB appears to be polyzymic, with direct conjugation via UDP-glucuronosyltransferases (UGTs) also occurring.
  
  
  CONCLUSIONS
  It is unlikely that CYP inhibition or induction will significantly influence the clearance of 11C-PiB.
authors: Experimental Medicine, Janssen Research and Development, Division of Janssen Pharmaceutica, NV Turnhoutseweg 30, B-2340, Beerse, Belgium. mschmid4@its.jnj.com.
authors: Anne
authors: A
authors: Van Vlaslaer
authors: Russell J
authors: RJ
authors: Mortishire-Smith
authors: Claire
authors: C
authors: Mackie
authors: Xavier
authors: X
authors: Langlois
authors: Mark E
authors: ME
authors: Schmidt