Abstract
A unique hybrid protein ferritin–enhanced green fluorescent protein (EGFP) was built to serve as an endogenous dual reporter for both fluorescence and magnetic resonance imaging (MRI). It consists of a human ferritin heavy chain (an iron-storage protein) at the N terminus, a flexible polypeptide in the middle as a linker, and an EGFP at the C terminus. Through antibiotic screening, we established stable human glioma U251 cell strains that expressed ferritin–EGFP under the control of tetracycline. These cells emitted bright green fluorescence and were easily detected by a fluorescent microscope. Ferritin–EGFP overexpression proved effective in triggering obvious intracellular iron accumulation as shown by Prussian blue staining and by MRI. Further, we found that ferritin–EGFP overexpression did not cause proliferation differences between experimental and control group cells when ferritin–EGFP was expressed for <96 hours. Application of this novel ferritin–EGFP chimera has a promising future for combined optical and MRI approaches to study in vivo imaging at a cellular level.
Highlights
Glioma is among one of the most malignant tumors and is characterized by high levels of mortality and recurrence [1]
This proved that ferritin–enhanced green fluorescent protein (EGFP) was successfully expressed in cancer cells
Fluorescence detection showed that cells that expressed ferritin–EGFP emitted bright green fluorescence (Figure 2B), which indicated that the EGFP functioned well and was not impaired when linked with heavy-chain ferritin
Summary
Glioma is among one of the most malignant tumors and is characterized by high levels of mortality and recurrence [1]. Precise noninvasive imaging is of great importance in tumor localization, metastasis detection, and subsequent therapy. Fluorescence imaging can provide noninvasive real-time dynamic observation of tumors. Magnetic resonance imaging (MRI) is not affected by the depth of target tissues and has high spatial resolution. The sensitivity of MRI is not high enough for performing cellular or molecular imaging. To solve this problem, MRI contrast agents were invented using substances such as iron or gadolinium [2, 3]. Several MRI reporter genes have been introduced into cells by either plasmids or slow virus transfection to serve as endogenous reporters [7, 8]
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