Systemic Magnetic Targeting of Pure-Antiestrogen-Loaded Superparamagnetic Nanovesicles for Effective Therapy of Hormone- Dependent Breast Cancers

Systemic hormone therapy of breast cancer often suffers from severe side effects mainly due to non-specific drug delivery. To overcome this limitation, we propose an effective strategy based on the association of the selective estrogen receptor down-regulator RU-58668 (RU) that acts as a pure hormone antagonist, with magnetic-fluidloaded liposomes (MFLs) which can be driven selectively into the tumors by a magnetic field gradient. MFLs consisted in 200-nm unilamellar phospholipid vesicles entrapping superparamagnetic iron oxide nanocrystals, fluorescently labeled and coated by poly(ethylene glycol) (PEG) chains ensuring long plasmatic half-life. Significant antitumoral activity of antiestrogen at doses usually sub-therapeutic was demonstrated against MCF-7 tumors xenografts in nude mice after weekly intravenous administration of RU-loaded MFLs followed by 4-hour exposure to an external 0.44-T magnet (155 T/m magnetic field gradient). The magnetic accumulation of RU-MFLs at the origin of improved antitumor activity was checked in vivo by MRI using the magnetic fluid as intrinsic contrast agent, fibered confocal fluorescence microscopy to track the lipid vesicle structures, ex-vivo tumor histology by confocal fluorescence microscopy or iron oxide staining, and KI-67 immunostaining to reveal RU anti-proliferative activity. Our findings establish that magnetic targeting results in significant therapeutic benefit by highly concentrating RUloaded liposomes in the tumor tissue according to amplified EPR effect and significantly enhanced drug delivery at the intracellular level. The use of superparamagnetic liposomes to target magnetically estrogen antagonists offers a reliable direction to treat hormone-dependent breast tumors with possible combination of MRI diagnosis.