Smart Bacterial Magnetic Nanoparticles for Tumor-Targeting Magnetic Resonance Imaging of HER2-Positive Breast Cancers.

Supersensitive magnetic resonance (MR) imaging requires contrast with extremely high r2 values. However, synthesized magnetic nanoparticles generally have a relatively low r2 relaxivity. Magnetosomes with high saturation magnetization and good biocompatibility have shown potential value as MR imaging contrast agents. Magnetosomes that target human epidermal growth factor receptor-2 (HER2) were prepared using genetic technology and low-frequency sonication. Anti-HER2 affibody of the ability to target HER2 was displayed on membrane surface of the magnetosomes through the anchor protein MamC, allowing the bacterial nanoparticles to target tumors overexpressing HER2. The prepared nanoparticles exhibited a very high relaxivity of 599.74 mM-1 s-1, better dispersion and their ability to target HER2 was demonstrated both in vitro and in vivo. Also, the HER2-targeting magnetosomes significantly enhanced MR imaging of orthotopic breast cancer models with or without HER2 expression using a 7.0 T scanner. In particular, tumors overexpressing HER2 demonstrated better MR imaging than HER2-negative tumors after i.v. administration of HER2-targeting magnetosomes, and the MR signals of the augmented contrast could be detected from 3 h to 24 h. The magnetosomes did not cause any notably pathogenic effect in the animals. Therefore, we expect that non-invasive imaging of tumors using HER2-targeting magnetosomes has potential for clinical applications in the near future.