title: Evaluation of efficacy of a new MEK inhibitor, RO4987655, in human tumor xenografts by [(18)F] FDG-PET imaging combined with proteomic approaches.
abstract: BACKGROUND
  Inhibition of mitogen-activated protein kinase (MEK, also known as MAPK2, MAPKK), a key molecule of the Ras/MAPK (mitogen-activated protein kinase) pathway, has shown promising effects on B-raf-mutated and some RAS (rat sarcoma)-activated tumors in clinical trials. The objective of this study is to examine the efficacy of a novel allosteric MEK inhibitor RO4987655 in K-ras-mutated human tumor xenograft models using [(18)F] FDG-PET imaging and proteomics technology.
  
  
  METHODS
  [(18)F] FDG uptake was studied in human lung carcinoma xenografts from day 0 to day 9 of RO4987655 therapy using microPET Focus 120 (CTI Concorde Microsystems, Knoxville, TN, USA). The expression levels of GLUT1 and hexokinase 1 were examined using semi-quantitative fluorescent immunohistochemistry (fIHC). The in vivo effects of RO4987655 on MAPK/PI3K pathway components were assessed by reverse phase protein arrays (RPPA).
  
  
  RESULTS
  We have observed modest metabolic decreases in tumor [(18)F] FDG uptake after MEK inhibition by RO4987655 as early as 2 h post-treatment. The greatest [(18)F] FDG decreases were found on day 1, followed by a rebound in [(18)F] FDG uptake on day 3 in parallel with decreasing tumor volumes. Molecular analysis of the tumors by fIHC did not reveal statistically significant correlations of GLUT1 and hexokinase 1 expressions with the [(18)F] FDG changes. RPPA signaling response profiling revealed not only down-regulation of pERK1/2, pMKK4, and pmTOR on day 1 after RO4987655 treatment but also significant up-regulation of pMEK1/2, pMEK2, pC-RAF, and pAKT on day 3. The up-regulation of these markers is interpreted to be indicative of a reactivation of the MAPK and activation of the compensatory PI3K pathway, which can also explain the rebound in [(18)F] FDG uptake following MEK inhibition with RO4987655 in the K-ras-mutated human tumor xenografts.
  
  
  CONCLUSIONS
  We have performed the first preclinical evaluation of a new MEK inhibitor, RO4987655, using a combination of [(18)F] FDG-PET imaging and molecular proteomics. These results provide support for using preclinical [(18)F] FDG-PET imaging in early, non-invasive monitoring of the effects of MEK and perhaps other Ras/MAPK signaling pathway inhibitors, which should facilitate a wider implementation of clinical [(18)F] FDG-PET to optimize their clinical use.
authors.affiliation: Karolinska Institutet and Department of Neuroradiology, R3:00, MicroPET and Clinical Neurosciences, Karolinska University Hospital, Stockholm, 17176, Sweden, tetyana.tegnebratt@ki.se.
authors.forename: Tetyana
authors.initials: T
authors.lastname: Tegnebratt
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Ruge
authors.forename: Sabine
authors.initials: S
authors.lastname: Bader
authors.forename: Nobuya
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authors.lastname: Ishii
authors.forename: Satoshi
authors.initials: S
authors.lastname: Aida
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yoshimura
authors.forename: Chia-Huey
authors.initials: CH
authors.lastname: Ooi
authors.forename: Li
authors.initials: L
authors.lastname: Lu
authors.forename: Nicholas
authors.initials: N
authors.lastname: Mitsios
authors.forename: Valerie
authors.initials: V
authors.lastname: Meresse
authors.forename: Jan
authors.initials: J
authors.lastname: Mulder
authors.forename: Michael
authors.initials: M
authors.lastname: Pawlak
authors.forename: Miro
authors.initials: M
authors.lastname: Venturi
authors.forename: Jean
authors.initials: J
authors.lastname: Tessier
authors.forename: Sharon
authors.initials: S
authors.lastname: Stone-Elander