title: Macrophages homing to metastatic lymph nodes can be monitored with ultrasensitive ferromagnetic iron-oxide nanocubes and a 1.5T clinical MR scanner.
abstract: BACKGROUND
  Due to the ability of macrophages to specifically home to tumors, their potential use as a delivery vehicle for cancer therapeutics has been suggested. Tracking the delivery and engraftment of macrophages into human tumors with a 1.5T clinical MR scanner requires the development of sensitive contrast agents for cell labeling. Therefore, this study aimed to determine whether intravenously injected macrophages could target a primary tumor as well as metastatic LNs, and whether these cells could be detected in vivo by MRI.
  
  
  METHODS
  Peritoneal macrophages were obtained from BALB/c nude mice. The viability, phagocytotic capacity and migratory activity of the macrophages were assessed. MR imaging was performed using a clinical 1.5 T MR scanner and we estimated the T2* of the labeled macrophages. Metastatic lymph nodes were produced in BALB/c nude mice. We administrated 2×10⁶ macrophages labeled with 50 µg Fe/mL FIONs intravenously into the mice. In the 3D T2* GRE MR images obtained one day after the injection of the labeled macrophages or FION solution, the percentages of pixels in the tumors or LNs below the minimum normalized SI (signal intensity) threshold were summated and reported as the black pixel count (%) for the FION hypointensity. Tumors in the main tumor model as well as the brachial, axillary and inguinal lymph nodes in the metastatic LN models were removed and stained. For all statistical analyses, single-group data were assessed using t test or the Mann-Whitney test. Repeated measurements analysis of variance (ANOVA) with Tukey-Kramer post hoc comparisons were performed for multiple comparisons.
  
  
  CONCLUSIONS
  The FION-labeled macrophages, which could be non-invasively monitored using a 1.5T clinical MR scanner, targeted both the main tumors and LN metastases. Overall, the results of this study suggest that the use of macrophages may have many future applications in the clinic for vectorizing therapeutic agents toward main tumors as well as LN metastases.
authors.affiliation: Department of Radiology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Hye Rim
authors.initials: HR
authors.lastname: Cho
authors.forename: Seung Hong
authors.initials: SH
authors.lastname: Choi
authors.forename: Nohyun
authors.initials: N
authors.lastname: Lee
authors.forename: Taeghwan
authors.initials: T
authors.lastname: Hyeon
authors.forename: Hyeonjin
authors.initials: H
authors.lastname: Kim
authors.forename: Woo Kyung
authors.initials: WK
authors.lastname: Moon
mesh_terms: D000818:Animals; D002465:Cell Movement; D002470:Cell Survival; D004195:Disease Models, Animal; D005290:Ferric Compounds; D005434:Flow Cytometry; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D008207:Lymphatic Metastasis / Q000175:diagnosis* / Q000473:pathology; D017737:Macrophages, Peritoneal / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000648:ultrastructure; D008297:Male; D008545:Melanoma / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D010587:Phagocytosis
chemical_list: D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; C000499:ferric oxide