title: The effect of cell cluster size on intracellular nanoparticle-mediated hyperthermia: is it possible to treat microscopic tumors?
abstract: OBJECTIVE
  To compare the measured surface temperature of variable size ensembles of cells heated by intracellular magnetic fluid hyperthermia with heat diffusion model predictions.
  
  
  METHODS
  Starch-coated Bionized NanoFerrite (Micromod Partikeltechnologie GmbH, Rostock, Germany) iron oxide magnetic nanoparticles were loaded into cultured DU145 prostate cancer cells. Cell pellets of variable size were treated with alternating magnetic fields. The surface temperature of the pellets was measured in situ and the associated cytotoxicity was determined by clonogenic survival assay.
  
  
  CONCLUSIONS
  For a given intracellular nanoparticle concentration, a critical minimum number of cells was required for cytotoxic hyperthermia. Above this threshold, cytotoxicity increased with increasing cell number. The measured surface temperatures were consistent with those predicted by a heat diffusion model that ignores intercellular thermal barriers. These results suggest a minimum tumor volume threshold of approximately 1 mm(3), below which nanoparticle-mediated heating is unlikely to be effective as the sole cytotoxic agent.
authors.affiliation: Department of Radiation Oncology & Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hedayati
authors.forename: Owen
authors.initials: O
authors.lastname: Thomas
authors.forename: Budri
authors.initials: B
authors.lastname: Abubaker-Sharif
authors.forename: Haoming
authors.initials: H
authors.lastname: Zhou
authors.forename: Christine
authors.initials: C
authors.lastname: Cornejo
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Michele
authors.initials: M
authors.lastname: Wabler
authors.forename: Jana
authors.initials: J
authors.lastname: Mihalic
authors.forename: Cordula
authors.initials: C
authors.lastname: Gruettner
authors.forename: Fritz
authors.initials: F
authors.lastname: Westphal
authors.forename: Alison
authors.initials: A
authors.lastname: Geyh
authors.forename: Theodore L
authors.initials: TL
authors.lastname: Deweese
authors.forename: Robert
authors.initials: R
authors.lastname: Ivkov
mesh_terms: D006801:Humans; D006979:Hyperthermia, Induced; D008297:Male; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D009369:Neoplasms / Q000628:therapy*; D011471:Prostatic Neoplasms / Q000473:pathology / Q000628:therapy*