title: Measuring the pharmacodynamic effects of a novel Hsp90 inhibitor on HER2/neu expression in mice using Zr-DFO-trastuzumab.
abstract: BACKGROUND
  The positron-emitting radionuclide (89)Zr (t(1/2) = 3.17 days) was used to prepare (89)Zr-radiolabeled trastuzumab for use as a radiotracer for characterizing HER2/neu-positive breast tumors. In addition, pharmacodynamic studies on HER2/neu expression levels in response to therapeutic doses of PU-H71 (a specific inhibitor of heat-shock protein 90 [Hsp90]) were conducted.
  
  
  RESULTS
  Trastuzumab was functionalized with desferrioxamine B (DFO) and radiolabeled with [(89)Zr]Zr-oxalate at room temperature using modified literature methods. ImmunoPET and biodistribution experiments in female, athymic nu/nu mice bearing sub-cutaneous BT-474 (HER2/neu positive) and/or MDA-MB-468 (HER2/neu negative) tumor xenografts were conducted. The change in (89)Zr-DFO-trastuzumab tissue uptake in response to high- and low-specific-activity formulations and co-administration of PU-H71 was evaluated by biodistribution studies, Western blot analysis and immunoPET. (89)Zr-DFO-trastuzumab radiolabeling proceeded in high radiochemical yield and specific-activity 104.3+/-2.1 MBq/mg (2.82+/-0.05 mCi/mg of mAb). In vitro assays demonstrated >99% radiochemical purity with an immunoreactive fraction of 0.87+/-0.07. In vivo biodistribution experiments revealed high specific BT-474 uptake after 24, 48 and 72 h (64.68+/-13.06%ID/g; 71.71+/-10.35%ID/g and 85.18+/-11.10%ID/g, respectively) with retention of activity for over 120 h. Pre-treatment with PU-H71 was followed by biodistribution studies and immunoPET of (89)Zr-DFO-trastuzumab. Expression levels of HER2/neu were modulated during the first 24 and 48 h post-administration (29.75+/-4.43%ID/g and 41.42+/-3.64%ID/g, respectively). By 72 h radiotracer uptake (73.64+/-12.17%ID/g) and Western blot analysis demonstrated that HER2/neu expression recovered to baseline levels.
  
  
  CONCLUSIONS
  The results indicate that (89)Zr-DFO-trastuzumab provides quantitative and highly-specific delineation of HER2/neu positive tumors, and has potential to be used to measure the efficacy of long-term treatment with Hsp90 inhibitors, like PU-H71, which display extended pharmacodynamic profiles.
authors.affiliation: Radiochemistry Service, Department of Radiology, Memorial Sloan-Kettering Cancer Center, Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Holland
authors.forename: Eloisi
authors.initials: E
authors.lastname: Caldas-Lopes
authors.forename: Vadim
authors.initials: V
authors.lastname: Divilov
authors.forename: Valerie A
authors.initials: VA
authors.lastname: Longo
authors.forename: Tony
authors.initials: T
authors.lastname: Taldone
authors.forename: Danuta
authors.initials: D
authors.lastname: Zatorska
authors.forename: Gabriela
authors.initials: G
authors.lastname: Chiosis
authors.forename: Jason S
authors.initials: JS
authors.lastname: Lewis
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D052117:Benzodioxoles / Q000493:pharmacokinetics / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003676:Deferoxamine / Q000737:chemistry*; D005260:Female; D018734:Genes, erbB-2; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D011687:Purines / Q000493:pharmacokinetics / Q000494:pharmacology*; D014018:Tissue Distribution; D000068878:Trastuzumab; D015040:Zirconium / Q000737:chemistry*
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D052117:Benzodioxoles; D018841:HSP90 Heat-Shock Proteins; D011687:Purines; C526550:9H-purine-9-propanamine, 6-amino-8-((6-iodo-1,3-benzodioxol-5-yl)thio)-N-(1-methylethyl)-; D015040:Zirconium; D003676:Deferoxamine; D000068878:Trastuzumab