Visualizing tumour self-homing with magnetic particle imaging.

Due to their innate tumour homing capabilities, in recent years, circulating tumour cells (CTCs) have been engineered to express therapeutic genes for targeted treatment of primary and metastatic lesions. Additionally, previous studies have incorporated optical or PET imaging reporter genes to enable noninvasive monitoring of therapeutic CTCs in preclinical tumour models. An alternative method for tracking cells is to pre-label them with imaging probes prior to transplantation into the body. This is typically more sensitive to low numbers of cells since large amounts of probe can be concentrated in each cell. The objective of this work was to evaluate magnetic particle imaging (MPI) for the detection of iron-labeled experimental CTCs. CTCs were labeled with micro-sized iron oxide (MPIO) particles, administered via intra-cardiac injection in tumour bearing mice and were detected in the tumour region of the mammary fat pad. Iron content and tumour volumes were calculated. Ex vivo MPI of the tumours and immunohistochemistry were used to validate the imaging data. Here, we demonstrate for the first time the ability of MPI to sensitively detect systemically administered iron-labeled CTCs and to visualize tumour self-homing in a murine model of human breast cancer.