Magnetic resonance imaging of high intensity focused ultrasound mediated drug delivery from temperature-sensitive liposomes: an in vivo proof-of-concept study.

Temperature-sensitive liposomes (TSLs) co-encapsulating doxorubicin and 250 mM [Gd(HPDO3A)(H₂O)] were evaluated for HIFU-mediated drug delivery under MR image guidance. In vitro studies showed simultaneous and quantitative release of the drug and the MRI contrast agent from the lumen of the TSLs at 42°C, while no leakage was observed over 1 h at 37°C. In a proof-of-concept study, local hyperthermia has been applied for 30 min in 9L rat tumors using a clinical MR-HIFU system. The local temperature-triggered release of [Gd(HPDO3A)(H₂O)] was monitored with interleaved T₁ mapping of the tumor tissue. A good correlation between the ΔR₁, the uptake of doxorubicin and the gadolinium concentration in the tumor was found, implying that the in vivo release of doxorubicin from TSLs can be probed in situ with the longitudinal relaxation time of the co-released MRI contrast agent.