title: Molecular imaging of phosphorylation events for drug development.
abstract: OBJECTIVE
  Protein phosphorylation mediated by protein kinases controls numerous cellular processes. A genetically encoded, generalizable split firefly luciferase (FL)-assisted complementation system was developed for noninvasive monitoring phosphorylation events and efficacies of kinase inhibitors in cell culture and in small living subjects by optical bioluminescence imaging.
  
  
  METHODS
  An Akt sensor (AST) was constructed to monitor Akt phosphorylation and the effect of different PI-3K and Akt inhibitors. Specificity of AST was determined using a non-phosphorylable mutant sensor containing an alanine substitution (ASA).
  
  
  RESULTS
  The PI-3K inhibitor LY294002 and Akt kinase inhibitor perifosine led to temporal- and dose-dependent increases in complemented FL activities in 293T human kidney cancer cells stably expressing AST (293T/AST) but not in 293T/ASA cells. Inhibition of endogenous Akt phosphorylation and kinase activities by perifosine also correlated with increase in complemented FL activities in 293T/AST cells but not in 293T/ASA cells. Treatment of nude mice bearing 293T/AST xenografts with perifosine led to a 2-fold increase in complemented FL activities compared to that of 293T/ASA xenografts. Our system was used to screen a small chemical library for novel modulators of Akt kinase activity.
  
  
  CONCLUSIONS
  This generalizable approach for noninvasive monitoring of phosphorylation events will accelerate the discovery and validation of novel kinase inhibitors and modulators of phosphorylation events.
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: C T
authors.initials: CT
authors.lastname: Chan
authors.forename: R
authors.initials: R
authors.lastname: Paulmurugan
authors.forename: R E
authors.initials: RE
authors.lastname: Reeves
authors.forename: D
authors.initials: D
authors.lastname: Solow-Cordero
authors.forename: S S
authors.initials: SS
authors.lastname: Gambhir
mesh_terms: D000818:Animals; D002460:Cell Line; D055808:Drug Discovery / Q000379:methods*; D005816:Genetic Complementation Test; D006801:Humans; D049409:Luciferases, Firefly / Q000235:genetics; D049449:Luminescence; D051379:Mice; D015336:Molecular Probe Techniques; D015335:Molecular Probes; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*
chemical_list: D015335:Molecular Probes; D047428:Protein Kinase Inhibitors; D011506:Proteins; D049409:Luciferases, Firefly; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt