MRI Assessment of Prostate-Specific Membrane Antigen (PSMA) Targeting by a PSMA-Targeted Magnetic Nanoparticle: Potential for Image-Guided Therapy.

Magnetic nanoparticle (MNP)-induced hyperthermia is currently being evaluated for localized prostate cancer. We evaluated the feasibility of tumor-selective delivery of prostate-specific membrane antigen (PSMA)-targeted MNPs in a murine model with high-resolution magnetic resonance imaging (MRI) after intravenous administration of MNPs at a concentration necessary for hyperthermia. A PSMA-targeted MNP was synthesized and evaluated using T2-weighted MRI, after intravenous administration of 50 mg/kg of the MNP. Significant contrast enhancement ( P < 0.0002, n = 5) was observed in PSMA(+) tumors compared to PSMA(-) tumors 24 h and 48 h after contrast agent administration. Mice were also imaged with near-infrared fluorescence imaging, to validate the MRI results. Two-photon microscopy revealed higher vascular density at the tumor periphery, which resulted in higher  peripheral accumulation of PSMA-targeted MNPs. These results suggest that the delivery of PSMA-targeted MNPs to PSMA(+) tumors is both actively targeted and passively mediated.