Contribution of macrophages in the contrast loss in iron oxide-based MRI cancer cell tracking studies

Area of Science:

• Biomedical Imaging
• Nanotechnology
• Cancer Research

Background:

• Magnetic resonance imaging (MRI) cell tracking uses superparamagnetic iron oxides (SPIO) to visualize metastatic cancer cells in preclinical models.
• A known limitation is the time-dependent decrease in MRI signal contrast caused by SPIO.
• The fate of SPIO and the role of macrophages in their metabolism remain unclear.

Purpose of the Study:

• To investigate the fate of iron oxide nanoparticles used in MRI cell tracking.
• To elucidate the role of macrophages in the metabolism of SPIO.
• To identify factors limiting long-term MRI cell tracking of metastatic cells.

Main Methods:

• In vivo MRI cell tracking of SPIO-labeled 4T1 breast cancer cells.
• In vitro characterization of iron pools using electron paramagnetic resonance (EPR) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS).
• Histology studies on 4T1 tumors and analysis of SPIO-labeled 4T1 cells and J774 macrophages.

Main Results:

• In vivo MRI revealed a rapid loss of T2* contrast after injecting SPIO-positive 4T1 cells.
• In vitro and histology studies demonstrated rapid degradation of iron oxides by macrophages.
• Macrophages were shown to uptake iron oxides released from dying cancer cells.

Conclusions:

• Macrophage-mediated degradation of SPIO and iron oxide uptake limit the long-term effectiveness of MRI cell tracking.
• These findings highlight the need for alternative imaging methods, such as (MR) reporter-gene imaging, for sustained tracking of metastatic cells.