title: Visualizing implanted tumors in mice with magnetic resonance imaging using magnetotactic bacteria.
abstract: OBJECTIVE
  To determine if magnetotactic bacteria can target tumors in mice and provide positive contrast for visualization using magnetic resonance imaging.
  
  
  METHODS
  The ability of the magnetotactic bacterium, Magnetospirillum magneticum AMB-1 (referred to from here as AMB-1), to confer positive magnetic resonance imaging contrast was determined in vitro and in vivo. For the latter studies, AMB-1 were injected either i.t. or i.v. Bacterial growth conditions were manipulated to produce small (approximately 25-nm diameter) magnetite particles, which were observed using transmission electron microscopy. Tumor targeting was confirmed using 64Cu-labeled bacteria and positron emission tomography and by determination of viable cell counts recovered from different organs and the tumor.
  
  
  RESULTS
  We show that AMB-1 bacteria with small magnetite particles generate T1-weighted positive contrast, enhancing in vivo visualization by magnetic resonance imaging. Following i.v. injection of 64Cu-labeled AMB-1, positron emission tomography imaging revealed increasing colonization of tumors and decreasing infection of organs after 4 hours. Viable cell counts showed that, by day 6, the bacteria had colonized tumors but were cleared completely from other organs. Magnetic resonance imaging showed a 1.22-fold (P = 0.003) increased positive contrast in tumors on day 2 and a 1.39-fold increase (P = 0.0007) on day 6.
  
  
  CONCLUSIONS
  Magnetotactic bacteria can produce positive magnetic resonance imaging contrast and colonize mouse tumor xenografts, providing a potential tool for improved magnetic resonance imaging visualization in preclinical and translational studies to track cancer.
authors: Department of Microbiology and Immunology, Stanford University, Stanford, California 94305-5124, USA.
authors: Michael R
authors: MR
authors: Benoit
authors: Dirk
authors: D
authors: Mayer
authors: Yoram
authors: Y
authors: Barak
authors: Ian Y
authors: IY
authors: Chen
authors: Wei
authors: W
authors: Hu
authors: Zhen
authors: Z
authors: Cheng
authors: Shan X
authors: SX
authors: Wang
authors: Daniel M
authors: DM
authors: Spielman
authors: Sanjiv S
authors: SS
authors: Gambhir
authors: A
authors: A
authors: Matin
mesh_terms: D000818:Animals; D001422:Bacterial Adhesion / Q000502:physiology; D002478:Cells, Cultured; D002633:Chemotaxis / Q000502:physiology*; D005260:Female; D052203:Ferrosoferric Oxide / Q000737:chemistry / Q000378:metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D042201:Magnetospirillum / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000382:microbiology; D011859:Radiography; D014183:Transplantation, Heterologous
chemical_list: D052203:Ferrosoferric Oxide