Molecular Imaging and Biology

, Volume 13, Issue 2, pp 314–320

MRI with Magnetic Nanoparticles Monitors Downstream Anti-Angiogenic Effects of mTOR Inhibition

  • Alexander R. Guimaraes
  • Robert Ross
  • Jose L. Figuereido
  • Peter Waterman
  • Ralph Weissleder
Research Article



To study the effect of mammalian target of rapamycin (mTOR) inhibition on angiogenesis with magnetic resonance imaging (MRI) using magnetic iron oxide nanoparticles (MNP).


One million CAK-1 renal cell carcinoma cells were subcutaneously implanted into each of 20 nude mice. When tumors reached ∼750 μl, four daily treatment arms began and continued for 4 weeks: rapamycin (mTOR inhibitor) 10 mg/kg/day; sorafenib (VEGF inhibitor) high dose (80 mg/kg/day) and low dose (30 mg/kg/day); and saline control. Weekly MRI (4.7 T Bruker Pharmascan) was performed before and after IV MION-48, a prototype MNP similar to MNP in clinical trials. Vascular volume fraction (VVF) was quantified as ΔR2 (from multi-contrast T2 sequences) and normalized to assumed muscle VVF of 3%. Linear regression compared VVF to microvascular density (MVD) as determined by histology.


VVF correlated with MVD (R2 = 0.95). VVF in all treatment arms differed from control (p < 0.05) and declined weekly with treatment. VVF changes with rapamycin were similar to high-dose sorafenib.


This study demonstrates noninvasive, in vivo anti-angiogenic monitoring using MRI of mTOR inhibition.

Key words

Magnetic resonance imaging MRI Magnetic nanoparticle imaging Ultrasmall superparamagnetic iron oxide nanoparticle Renal cell cancer mTOR Angiogenesis 


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Copyright information

© Academy of Molecular Imaging and Society for Molecular Imaging 2010

Authors and Affiliations

  • Alexander R. Guimaraes
    • 1
    • 2
    • 4
  • Robert Ross
    • 3
  • Jose L. Figuereido
    • 1
    • 2
  • Peter Waterman
    • 1
    • 2
  • Ralph Weissleder
    • 1
    • 2
  1. 1.Center for Molecular Imaging Research, Department of RadiologyMassachusetts General HospitalCharlestownUSA
  2. 2.Center for Systems BiologyMassachusetts General HospitalBostonUSA
  3. 3.Lank Center for Genitourinary OncologyDana Farber Cancer InstituteBostonUSA
  4. 4.Division of Abdominal Imaging, Department of RadiologyMassachusetts General HospitalBostonUSA

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