MRI with magnetic nanoparticles monitors downstream anti-angiogenic effects of mTOR inhibition.

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

Procedures: 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.