Bioengineered Magnetoferritin Nanoprobes for Single-Dose Nuclear-Magnetic Resonance Tumor Imaging Yanzhao Zhao, †,# Minmin Liang, ‡,# Xiao Li, † Kelong Fan, ‡ Jie Xiao, † Yanli Li, † Hongcheng Shi, † Fei Wang, ‡ Hak Soo Choi,* ,§ Dengfeng Cheng,* ,† and Xiyun Yan* ,‡ † Department of Nuclear Medicine, Zhongshan Hospital, Fudan University/Shanghai Institute of Medical Imaging, Shanghai 200032, China ‡ Key Laboratory of Protein and Peptide Pharmaceutical/Chinese Academy of Sciences-University of Tokyo Joint Laboratory of Structural Virology and Immunology/Beijing Translational Engineering Center of Biomacromolecular Drugs, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China § Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, United States * S Supporting Information ABSTRACT: Despite all the advances in multimodal imaging, it remains a significant challenge to acquire both magnetic resonance and nuclear imaging in a single dose because of the enormous difference in sensitivity. Indeed, nuclear imaging is almost 10 6 -fold more sensitive than magnetic resonance imaging (MRI); thus, repeated injections are generally required to obtain sufficient MR signals after nuclear imaging. Here, we show that strategically engineered magnetoferritin nanoprobes can image tumors with high sensitivity and specificity using SPECT and MRI in living mice after a single intravenous injection. The magnetoferritin nanoprobes composed of 125 I radionuclide-conjugated human H-ferritin iron nanocages ( 125 I-M-HFn) internalize robustly into cancer cells via a novel tumor-specific HFn-TfR1 pathway. In particular, the endocytic recycling characteristic of TfR1 transporters solves the nuclear signal blocking issue caused by the high dose nanoprobes injected for MRI, thus enabling simultaneous functional and morphological tumor imaging without reliance on multi-injections. KEYWORDS: multimodal imaging, diagnostic imaging, nuclear signal blocking, tumor targeting, magnetoferritin nanoparticles A combination of morphological imaging and nuclear medicine techniques has been required for compre- hensive understanding and characterization of human cancers. 1 In particular, synergizing magnetic resonance imaging (MRI) with positron emission tomography (PET) or single photon emission tomography (SPECT) offers highly comple- mentary information for tumor characterization in vivo. MRI provides high spatial resolution structural images with high soft- tissue contrast but low sensitivity and signal-to-noise ratios, 2 while SPECT and PET imaging modalities show very high sensitivity with relatively low imaging resolution. 3 The combination of SPECT-PET with MRI provides sufficient spatial and temporal resolutions as well as high sensitivity. Despite the clinical and preclinical availability of hybrid PET/ MRI and SPECT/MRI scanners, 4 no imaging agents can serve as dual modality imaging probes in clinical practice 5,6 because nuclear imaging is extremely more sensitive than MRI. For example, MRI would require >10 7 Gd atoms 7 or >10 6 high Received: November 25, 2015 Accepted: March 4, 2016 Published: March 9, 2016 Article www.acsnano.org © 2016 American Chemical Society 4184 DOI: 10.1021/acsnano.5b07408 ACS Nano 2016, 10, 4184-4191