Targeting and cellular trafficking of magnetic nanoparticles for prostate cancer imaging.

Antibody-conjugated iron oxide nanoparticles offer a specific and sensitive tool to enhance magnetic resonance (MR) images of both local and metastatic cancer. Prostate-specific membrane antigen (PSMA) is predominantly expressed on the neovasculature of solid tumors and on the surface of prostate cells, with enhanced expression following androgen deprivation therapy. Biotinylated anti-PSMA antibody was conjugated to streptavidin-labeled iron oxide nanoparticles and used in MR imaging and confocal laser scanning microscopic imaging studies using LNCaP prostate cancer cells. Labeled iron oxide nanoparticles are internalized by receptor-mediated endocytosis, which involves the formation of clathrin-coated vesicles. Endocytosed particles are not targeted to the Golgi apparatus for recycling but instead accumulate within lysosomes. In T(1)-weighted MR images, the signal enhancement owing to the magnetic particles was greater for cells with magnetic particles bound to the cell surface than for cells that internalized the particles. However, the location of the particles (surface vs internal) did not significantly alter their effect on T(2)-weighted images. Our findings indicate that targeting prostate cancer cells using PSMA offers a specific and sensitive technique for enhancing MR images.