Use of targeted magnetic nanoparticles for imaging in prostate cancer

Abstract Objective: Imaging techniques better than those conventionally used are needed to improve prostate cancer (PC) staging and read out of therapeutic effects in real time in treated patients. We aimed to perform preclinical evaluation of newly developed well-characterized, biocompatible, PC-targeted magnetic nanoparticles (MNPs) targeted to prostate cancer by conjugation with J591 (from N. Bander, Cornell, USA), an antibody which binds specifically to prostate specific membrane antigen (PSMA) which is expressed on the surface of ∼90% of PCs including castrate resistant prostate cancers; this binding results in internalization. The use of targeted MNPs should enhance the specificity and sensitivity of magnetic resonance imaging (MRI) to enable better staging of patients with PC and future targeted delivery of therapy. Methods: MNPs were prepared, engineered to the appropriate size and conjugated with J591. There was no compromise in J591 cell binding or specificity for PSMA positive cells due to the conjugation, and Inductively Coupled Plasma Optical Emission Spectrometry and Prussian blue staining for iron indicated increased uptake of MNPs that were conjugated with the antibody. In vivo studies were performed in immunodepressed nude mice with subcutaneous LNCaP-LN3 (PSMA-positive) xenografts (post euthanasia using an 11.7T NMR system) or on live mice with orthotopic LNCaP xenografts, using a 16.4T MRI imaging system following intravenous injection of MNPs. Results: Similar enhancement of MRI was obtained by NMR after injection of MNP or J591-MNP conjugates. Live imaging of mice given systemic J591-MNPs showed uptake into the prostate tumors. Conclusions: The data indicate the promise of this technique in enabling imaging of small clusters of human prostate cancer cells. This should enable the effects of therapy to be determined by imaging in real time, improving patient management