title: Molecular imaging of EGFR and CD44v6 for prediction and response monitoring of HSP90 inhibition in an in vivo squamous cell carcinoma model.
abstract: OBJECTIVE
  Heat shock protein 90 (HSP90) is essential for the activation and stabilization of numerous oncogenic client proteins. AT13387 is a novel HSP90 inhibitor promoting degradation of oncogenic proteins upon binding, and may also act as a radiosensitizer. For optimal treatment there is, however, the need for identification of biomarkers for patient stratification and therapeutic response monitoring, and to find suitable targets for combination treatments. The aim of this study was to assess the response of surface antigens commonly expressed in squamous cell carcinoma to AT13387 treatment, and to find suitable biomarkers for molecular imaging and radioimmunotherapy in combination with HSP90 inhibition.
  
  
  METHODS
  Cancer cell proliferation and radioimmunoassays were used to evaluate the effect of AT13387 on target antigen expression in vitro. Inhibitor effects were then assessed in vivo in mice-xenografts. Animals were treated with AT13387 (5 × 50 mg/kg), and were imaged with PET using either (18)F-FDG or (124)I-labelled tracers for EGFR and CD44v6, and this was followed by ex-vivo biodistribution analysis and immunohistochemical staining.
  
  
  RESULTS
  AT13387 exposure resulted in high cytotoxicity and possible radiosensitization with IC50 values below 4 nM. Both in vitro and in vivo AT13387 effectively downregulated HSP90 client proteins. PET imaging with (124)I-cetuximab showed a significant decrease of EGFR in AT13387-treated animals compared with untreated animals. In contrast, the squamous cell carcinoma-associated biomarker CD44v6, visualized with (124)I-AbD19384 as well as (18)F-FDG uptake, were not significantly altered by AT13387 treatment.
  
  
  CONCLUSIONS
  We conclude that AT13387 downregulates HSP90 client proteins, and that molecular imaging of these proteins may be a suitable approach for assessing treatment response. Furthermore, radioimmunotherapy targeting CD44v6 in combination with AT13387 may potentiate the radioimmunotherapy outcome due to radiosensitizing effects of the drug, and could potentially lead to a lower dose to normal tissues.
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. diana.spiegelberg@igp.uu.se.
authors.forename: Diana
authors.identifier: http://orcid.org/0000-0002-1509-2142
authors.initials: D
authors.lastname: Spiegelberg
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Anja C
authors.initials: AC
authors.lastname: Mortensen
authors.affiliation: Preclinical PET Platform, Uppsala University, Uppsala, Sweden.
authors.forename: Ram K
authors.initials: RK
authors.lastname: Selvaraju
authors.affiliation: Preclinical PET Platform, Uppsala University, Uppsala, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Eriksson
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Bo
authors.initials: B
authors.lastname: Stenerlöw
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.|Unit of Otolaryngology and Head and Neck Surgery, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.
authors.forename: Marika
authors.initials: M
authors.lastname: Nestor
mesh_terms: D000818:Animals; D001549:Benzamides / Q000009:adverse effects / Q000493:pharmacokinetics* / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000378:metabolism*; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D002460:Cell Line; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D019788:Fluorodeoxyglucose F18; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D007457:Iodine Radioisotopes; D054833:Isoindoles / Q000009:adverse effects / Q000493:pharmacokinetics* / Q000627:therapeutic use; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D049268:Positron-Emission Tomography; D016499:Radioimmunotherapy; D019275:Radiopharmaceuticals
chemical_list: D001549:Benzamides; D014408:Biomarkers, Tumor; C112697:CD44v6 antigen; D018841:HSP90 Heat-Shock Proteins; D018960:Hyaluronan Receptors; D007457:Iodine Radioisotopes; D054833:Isoindoles; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D066246:ErbB Receptors; C552103:(2,4-dihydroxy-5-isopropylphenyl)-(5-(4-methylpiperazin-1-ylmethyl)-1,3-dihydroisoindol-2-yl)methanone
keywords: 124I; AT13387; CD44v6; EGFR; HSP90 inhibitor; PET