title: Mechanistic interrogation of combination bevacizumab/dual PI3K/mTOR inhibitor response in glioblastoma implementing novel MR and PET imaging biomarkers.
abstract: OBJECTIVE
  Resistance to bevacizumab (BEV) in glioblastoma is believed to occur via activation of molecular networks including the mTOR/PI3K pathway. Using an MR/PET molecular imaging biomarker approach, we investigated the response to combining BEV with the mTOR/PI3K inhibitor BEZ235.
  
  
  METHODS
  Tumours were established by orthotopically implanting U87MG-luc2 cells in mice. Animals were treated with BEZ235 and/or BEV, and imaged using diffusion-weighted-MRI, T2-weighted and T2*-weighted before and after administration of superparamagnetic iron oxide contrast agent. Maps for changes in relaxation rates (ΔR2, ΔR2* and apparent diffusion coefficient) were calculated. Vessel size index and microvessel density index were derived. 3'-Deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) PET and O-(2-[(18)F]fluoroethyl)-L-tyrosine ([(18)F]FET) PET were further performed and tumour endothelium/proliferation markers assessed by immunohistochemistry.
  
  
  RESULTS
  Treatment with BEV resulted in a pronounced decrease in tumour volume (T2-weighted MRI). No additive effect on tumour volume was observed with the BEV/BEZ235 combination compared with BEV monotherapy. The Ki67 proliferation index and [(18)F]FLT uptake studies were used to support the observations. Using ΔR2* and ΔR2 values, respectively, the BEV/BEZ235 combination significantly reduced tumour microvessel volume in comparison to BEV alone. Decreased microvessel density index was further observed in animals treated with the combination, supported by von Willebrand factor (vWF) immunohistochemistry. [(18)F]FET uptake was decreased following treatment with BEV alone, but was not further reduced following treatment with the combination. vWF immunohistochemistry analysis showed that the mean tumour vessel size was increased in all cohorts.
  
  
  CONCLUSIONS
  Assessing MR imaging biomarker parameters together with [(18)F]FET and [(18)F]FLT PET provided information on mechanism of action of the drug combination and clues as to potential clinical responses. Following translation to clinical use, treatment with a BEV/BEZ235 combination could reduce peritumoral oedema obviating the requirement for steroids. The use of hypothesis-driven molecular imaging studies facilitates the preclinical evaluation of drug response. Studies of this kind may more accurately predict the clinical potential of the BEV/BEZ235 combination regimen as a novel therapeutic approach in oncology.
authors.affiliation: Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland.|National Neurosurgical Department, Beaumont Hospital, Dublin 9, Ireland.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: O'Halloran
authors.affiliation: European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.|PARCC, INSERM U970, Université Paris Descartes, Paris, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Viel
authors.affiliation: Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland.
authors.forename: David W
authors.initials: DW
authors.lastname: Murray
authors.affiliation: Department of Clinical Radiology, University Hospital Münster, Münster, Germany.
authors.forename: Lydia
authors.initials: L
authors.lastname: Wachsmuth
authors.affiliation: European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Schwegmann
authors.affiliation: Department of Nuclear Medicine, Münster University Hospital, Münster, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Wagner
authors.affiliation: Department of Nuclear Medicine, Münster University Hospital, Münster, Germany.|Radiopharmaceutical Chemistry, German Cancer Research Centre (dkfz), Heidelberg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Kopka
authors.affiliation: Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland.
authors.forename: Monika A
authors.initials: MA
authors.lastname: Jarzabek
authors.affiliation: Department of Epidemiology & Public Health, Royal College of Surgeons, Dublin 2, Ireland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Dicker
authors.affiliation: European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Hermann
authors.affiliation: Department of Clinical Radiology, University Hospital Münster, Münster, Germany.
authors.forename: Cornelius
authors.initials: C
authors.lastname: Faber
authors.affiliation: Department of Clinical Radiology, University Hospital Münster, Münster, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Klasen
authors.affiliation: European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.|Department of Nuclear Medicine, Münster University Hospital, Münster, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schäfers
authors.affiliation: National Neurosurgical Department, Beaumont Hospital, Dublin 9, Ireland.
authors.forename: David
authors.initials: D
authors.lastname: O'Brien
authors.affiliation: Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland.
authors.forename: Jochen H M
authors.initials: JH
authors.lastname: Prehn
authors.affiliation: European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.|Interdisciplinary Centre of Clinical Research (IZKF), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.|Department of Geriatric Medicine, Johanniter Krankenhaus, Bonn, Germany.
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Jacobs
authors.affiliation: Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland. annettebyrne@rcsi.ie.
authors.forename: Annette T
authors.initials: AT
authors.lastname: Byrne
mesh_terms: D000818:Animals; D000068258:Bevacizumab / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D014408:Biomarkers, Tumor / Q000378:metabolism; D045744:Cell Line, Tumor; D004347:Drug Interactions; D005260:Female; D005909:Glioblastoma / Q000098:blood supply / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D008279:Magnetic Resonance Imaging; D051379:Mice; D055806:Microvessels / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D064847:Multimodal Imaging; D000081082:Phosphoinositide-3 Kinase Inhibitors; D049268:Positron-Emission Tomography; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D047368:Tumor Burden / Q000187:drug effects; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D014408:Biomarkers, Tumor; D007093:Imidazoles; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011804:Quinolines; C545932:(18F)fluoroethyltyrosine; D000068258:Bevacizumab; D014443:Tyrosine; D058570:TOR Serine-Threonine Kinases; C531198:dactolisib
keywords: BEZ235; Bevacizumab; Glioblastoma; PET; T2-weighted MRI