title: MRI of tumor-associated macrophages with clinically applicable iron oxide nanoparticles.
abstract: OBJECTIVE
  The presence of tumor-associated macrophages (TAM) in breast cancer correlates strongly with poor outcome. The purpose of this study was to develop a clinically applicable, noninvasive diagnostic assay for selective targeting and visualization of TAMs in breast cancer, based on magnetic resonanceI and clinically applicable iron oxide nanoparticles.
  
  
  METHODS
  F4/80-negative mammary carcinoma cells and F4/80-positive TAMs were incubated with iron oxide nanoparticles and were compared with respect to magnetic resonance signal changes and iron uptake. MMTV-PyMT transgenic mice harboring mammary carcinomas underwent nanoparticle-enhanced magnetic resonance imaging (MRI) up to 1 hour and 24 hours after injection. The tumor enhancement on MRIs was correlated with the presence and location of TAMs and nanoparticles by confocal microscopy.
  
  
  RESULTS
  In vitro studies revealed that iron oxide nanoparticles are preferentially phagocytosed by TAMs but not by malignant tumor cells. In vivo, all tumors showed an initial contrast agent perfusion on immediate postcontrast MRIs with gradual transendothelial leakage into the tumor interstitium. Twenty-four hours after injection, all tumors showed a persistent signal decline on MRIs. TAM depletion via αCSF1 monoclonal antibodies led to significant inhibition of tumor nanoparticle enhancement. Detection of iron using 3,3'-diaminobenzidine-enhanced Prussian Blue staining, combined with immunodetection of CD68, localized iron oxide nanoparticles to TAMs, showing that the signal effects on delayed MRIs were largely due to TAM-mediated uptake of contrast agent.
  
  
  CONCLUSIONS
  These data indicate that tumor enhancement with clinically applicable iron oxide nanoparticles may serve as a new biomarker for long-term prognosis, related treatment decisions, and the evaluation of new immune-targeted therapies.
authors.affiliation: Department of Radiology, Molecular Imaging Program at Stanford, Stanford University, Stanford, California, USA. heiked@stanford.edu
authors.forename: Heike E
authors.initials: HE
authors.lastname: Daldrup-Link
authors.forename: Daniel
authors.initials: D
authors.lastname: Golovko
authors.forename: Brian
authors.initials: B
authors.lastname: Ruffell
authors.forename: David G
authors.initials: DG
authors.lastname: Denardo
authors.forename: Rosalinda
authors.initials: R
authors.lastname: Castaneda
authors.forename: Celina
authors.initials: C
authors.lastname: Ansari
authors.forename: Jianghong
authors.initials: J
authors.lastname: Rao
authors.forename: Grigory A
authors.initials: GA
authors.lastname: Tikhomirov
authors.forename: Michael F
authors.initials: MF
authors.lastname: Wendland
authors.forename: Claire
authors.initials: C
authors.lastname: Corot
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Coussens
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D014408:Biomarkers, Tumor; D005260:Female; D016173:Macrophage Colony-Stimulating Factor / Q000276:immunology; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles; D008325:Mammary Neoplasms, Experimental / Q000175:diagnosis* / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D010587:Phagocytosis; D011379:Prognosis; D000097382:CD68 Molecule
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D014408:Biomarkers, Tumor; D016173:Macrophage Colony-Stimulating Factor; D058185:Magnetite Nanoparticles; C081026:CD68 protein, mouse; D000097382:CD68 Molecule