Noninvasive imaging of tumor-associated macrophages in mice
Researchers co-led by Ludwig Lausanne’s Johanna Joyce and alumnus Davide Croci reported in an October issue of Science Translational Medicine a strategy to noninvasively track immune cells known as macrophages within brain and breast tumors in living mice. Cancers often recruit and reprogram these tumor-associated macrophages, or TAMs, to support their own growth and establish resistance to therapies. Johanna, Davide and their colleagues exploited a basic function of macrophages, which is to roam around the body, gobbling up particulate matter. They injected mouse models of gliomas, breast cancer and breast-to-brain metastases with two different types of nanoparticles, both labeled with a fluorine isotope, that each emits a discernible signal detectable by magnetic resonance imaging. Those signals are also distinct from the one transmitted by a hydrogen isotope, which is used to image tissue, including cancerous growths. The researchers demonstrate that the nanoparticles accumulate in TAMs, permitting a non-invasive means to ascertain with “multispectral” MR imaging not just the abundance, but also the location of the immune cells across the geography of tumors. The imaging approaches developed in this study could, with further development, help clinicians noninvasively identify brain tumor types, better monitor prognosis and drug resistance and thus improve the therapeutic management of brain tumors.