Ferritin heavy chain as a molecular imaging reporter gene in glioma xenografts

Ferritin nanoparticles: new strategies for the diagnosis and treatment of central nervous system diseases

Ferritin nanoparticles, which can penetrate the blood-brain barrier (BBB), have gained significant research interest for the diagnosis and treatment of central nervous system (CNS) diseases, including gliomas, Alzheimer's disease, and brain metastases. In recent years, ferritin has been proved as a candidate to cross the BBB using receptor-mediated transport (RMT) mechanism through transferrin receptor 1 (TfR1) which is overexpressed in the cells of the BBB. Various types of cargo molecules, including therapeutics, imaging agents, nucleic acids, and metal nanoparticles, have been incorporated into ferritin nanocages for the diagnosis and treatment of CNS diseases. In particular, low immunogenicity of ferritin implies safety for its usage in clinical practices, and high biocompatibility add to the perspectives of its applications. Furthermore, contemporary strides in molecular biology have enabled some alteration in the configuration of the ferritin outer layers and surface characters so as to enhance the drug encapsulation capacity and conjugation affinity. Such modifications not only enhance the property of ferritin in crossing the BBB, but also enhance its efficacy when applied to CNS diseases. In summary, ferritin, as a drug delivery system, shows great potential for the treatment and diagnosis of CNS diseases.

Biogenic Imaging Contrast Agents

Imaging contrast agents are widely investigated in preclinical and clinical studies, among which biogenic imaging contrast agents (BICAs) are developing rapidly and playing an increasingly important role in biomedical research ranging from subcellular level to individual level. The unique properties of BICAs, including expression by cells as reporters and specific genetic modification, facilitate various in vitro and in vivo studies, such as quantification of gene expression, observation of protein interactions, visualization of cellular proliferation, monitoring of metabolism, and detection of dysfunctions. Furthermore, in human body, BICAs are remarkably helpful for disease diagnosis when the dysregulation of these agents occurs and can be detected through imaging techniques. There are various BICAs matched with a set of imaging techniques, including fluorescent proteins for fluorescence imaging, gas vesicles for ultrasound imaging, and ferritin for magnetic resonance imaging. In addition, bimodal and multimodal imaging can be realized through combining the functions of different BICAs, which helps overcome the limitations of monomodal imaging. In this review, the focus is on the properties, mechanisms, applications, and future directions of BICAs.

In vivo visualization of murine melanoma cells B16-derived exosomes through magnetic resonance imaging

BACKGROUND

Numerous studies demonstrated that exosomes play a powerful role in mediating intercellular communication to induce a pro-tumoral environment to promote tumor progression, including pre-metastatic niche formation and metastasis. Noninvasive imaging could determine the in vivo kinetics of exosomes in real time to provide better understanding of the mechanisms of the tumor formation, progression and metastasis. Magnetic resonance imaging (MRI) is an ideal technique which provides excellent anatomical resolution, intrinsic soft tissue contrast, unlimited penetration depth and no radiation exposure.

METHODS

A fusion protein composed of ferritin heavy chain (FTH1) and lactadherin was designed for visualizing exosomes through MRI. FTH1 was served as MRI reporter protein and lactadherin is a membrane-associated protein that is distributed on exosome surface. The characterizations of labeled exosomes were validated through transmission electron microscopy, western blot, nanoparticle tracking analysis and finally visualized in vitro and in vivo through MRI.

RESULTS

MR imaging showed that the labeled exosomes are able to be visualized in vitro and in vivo. Verification of the characterizations of exosomes observed no significant difference between labeled and unlabeled exosomes.

CONCLUSION

The proposed FTH1 labeling method was useful for visualizing exosomes through MRI.

GENERAL SIGNIFICANCE

The present study first reported a novel self-label method for imaging labeled exosomes of tumor cells in vivo through MR with cell endogenous MRI reporter protein. It may be further used as a tool to enhance understanding the role of exosomes in various pathophysiological conditions.

Dual-Effect of Magnetic Resonance Imaging Reporter Gene in Diagnosis and Treatment of Hepatocellular Carcinoma

Propose

The early diagnosis of hepatocellular carcinoma (HCC) with ferritin heavy chain (Fth) modified by alpha-fetoprotein (AFP) promoter has been studied. However, no study has focused on the considerable upregulation and specific targeting effects of transferrin receptors (TfR) caused by the transfection of plasmids encoded with the AFP promoter. Thus, the objective of our study was to investigate whether the transfection of Fth gene modified with AFP promoter (AFP@Fth) could be used for early diagnosis and enhanced treatment of HCC.

Methods

The AFP@Fth plasmid was transfected into AFP positive cells. The expression of intracellular Ferritin was verified by Western blot, and the upregulation of TfR was confirmed by immunofluorescence and flow cytometry analysis. Cellular iron accumulation resulting in decreased imaging signals was examined by magnetic resonance imagining. Doxorubicin liposome modified with transferrin (Tf-LPD) was prepared to investigate the efficiency of the subsequent treatment after transfection. The enhanced drug distribution and effects were investigated both in vitro and in vivo.

Results

Both Ferritin and TfR were overexpressed after transfection. The transfected cells showed higher intracellular iron accumulation and resulted in a lower MR T2-weighted imaging (T2WI) intensity, suggesting that the transfection of AFP@Fth could be a potential strategy for early diagnosis of liver cancer. The following treatment efficacy was revealed by Tf-LPD. As compared with un-transfected cells, transfected cells exhibited higher uptake of transferrin-modified liposomes (Tf-LP), which was due to the specific interaction between Tf and TfR overexpressed on the transfected cells. This is also the reason why Tf-LPD showed better in vitro and in vivo anticancer ability than doxorubicin loaded liposome (LPD). These results suggested that transfection of AFP@Fth could result in enhanced therapy of liver cancer.

Conclusion

Transfection of AFP@Fth could be used for early diagnosis and for enhanced treatment of live cancers.

Visualization of exosomes from mesenchymal stem cells in vivo by magnetic resonance imaging

BACKGROUND AND PURPOSE

We develop a method of imaging exosomes in vivo according to the vital role of exosomes in intercellular communication. This study aims to design a new label method that allows the visualization of labeled exosomes with magnetic resonance imaging (MRI).

METHODS

We designed a fusion protein consisting of two parts, namely, ferritin heavy chain (FTH1) and a truncated lactadherin. FTH1 is used as an MRI reporter. Lactadherin is a trans-membrane protein. The lactadherin protein are mostly located on the outer surface of exosomes. We replaced the outer membrane part of lactadherin with FTH1, infected mesenchymal stem cells with lentivirus carrying the fusion protein, and isolated exosomes from the labeled cells by ultracentrifugation. Labeled exosomes were validated by transmission electron microscopy images, Western blot, nanosight particle tracking, and visualized in vitro and in vivo by MRI.

RESULTS

FTH1 expression would suppress mesenchymal stem cell proliferation, whereas the characterization of labeled exosomes remains comparable with unlabeled exosomes. MR imaging shows that exosomes labeled with FTH1 can be visualized in vitro and in vivo.

CONCLUSION

This innovative reporter-imaging approach to track and visualize exosomes with MRI can be utilized as a tool for the study of the role of exosomes under different conditions.

MRI Tracking of SPIO- and Fth1-Labeled Bone Marrow Mesenchymal Stromal Cell Transplantation for Treatment of Stroke

We aimed to identify a suitable method for long-term monitoring of the migration and proliferation of mesenchymal stromal cells in stroke models of rats using ferritin transgene expression by magnetic resonance imaging (MRI). Bone marrow mesenchymal stromal cells (BMSCs) were transduced with a lentivirus containing a shuttle plasmid (pCDH-CMV-MCS-EF1-copGFP) carrying the ferritin heavy chain 1 (Fth1) gene. Ferritin expression in stromal cells was evaluated with western blotting and immunofluorescent staining. The iron uptake of Fth1-BMSCs was measured with Prussian blue staining. Following surgical introduction of middle cerebral artery occlusion, Fth1-BMSCs and superparamagnetic iron oxide- (SPIO-) labeled BMSCs were injected through the internal jugular vein. The imaging and signal intensities were monitored by diffusion-weighted imaging (DWI), T2-weighted imaging (T2WI), and susceptibility-weighted imaging (SWI) in vitro and in vivo. Pathology was performed for comparison. We observed that the MRI signal intensity of SPIO-BMSCs gradually reduced over time. Fth1-BMSCs showed the same signal intensity between 10 and 60 days. SWI showed hypointense lesions in the SPIO-BMSC (traceable for 30 d) and Fth1-BMSC groups. T2WI was not sensitive enough to trace Fth1-BMSCs. After transplantation, Prussian blue-stained cells were observed around the infarction area and in the infarction center in both transplantation models. Fth1-BMSCs transplanted for treating focal cerebral infarction were safe, reliable, and traceable by MRI. Fth1 labeling was more stable and suitable than SPIO labeling for long-term tracking. SWI was more sensitive than T2W1 and suitable as the optimal MRI-tracking sequence.

MR molecular imaging of HCC employing a regulated ferritin gene carried by a modified polycation vector

Purpose: Early diagnosis is essential for reducing liver cancer mortality, and molecular diagnosis by magnetic resonance imaging (MRI) is an emerging and promising technology. The chief aim of the present work is to use the ferritin gene, modified by the alpha-fetoprotein (AFP) promoter, carried by a highly safe vector, to produce signal contrast on T2-weighted MR imaging as an endogenous contrast agent, and to provide a highly specific target for subsequent therapy.

Methods: Polyethyleneimine-β-cyclodextrin (PEI-β-CD, PC) was synthesized as a novel vector. The optimal nitrogen/phosphorus ratio (N/P) of the PC/plasmid DNA complex was determined by gel retardation, biophysical properties and transmission electron microscopy morphological analysis. The transfection efficiency was observed under a fluorescence microscope and analyzed by flow cytometry. Cellular iron accumulation caused by ferritin overexpression was verified by Prussian blue staining, and the resulting contrast imaging effect was examined by MRI.

Results: The modified cationic polymer PC was much safer than high molecular weight PEI, and could condense plasmid DNA at an N/P ratio of 50 with suitable biophysical properties and a high transfection efficiency. Overexpression of ferritin enriched intracellular iron. The short-term iron imbalance initiated by AFP promoter regulation only occurred in hepatoma cells, resulting in signal contrast on MRI. The specific target TfR was also upregulated during this process.

Conclusion: These results illustrate that the regulated ferritin gene carried by PC can be used as an endogenous contrast agent for MRI detection of hepatocellular carcinoma (HCC). This molecular imaging technique may promote safer early diagnosis of HCC, and provide a more highly specific target for future chemotherapy drugs.

Glioma-Targeted Delivery of a Theranostic Liposome Integrated with Quantum Dots, Superparamagnetic Iron Oxide, and Cilengitide for Dual-Imaging Guiding Cancer Surgery

Herein, a theranostic liposome (QSC-Lip) integrated with superparamagnetic iron oxide nanoparticles (SPIONs) and quantum dots (QDs) and cilengitide (CGT) into one platform is constructed to target glioma under magnetic targeting (MT) for guiding surgical resection of glioma. Transmission electron microscopy and X-ray photoelectron spectroscopy confirm the complete coencapsulation of SPIONs and QDs in liposome. Besides, CGT is also effectively encapsulated into the liposome with an encapsulation efficiency of ∼88.9%. QSC-Lip exhibits a diameter of 100 ± 1.24 nm, zeta potential of -17.10 ± 0.11 mV, and good stability in several mediums. Moreover, each cargo shows a biphasic release pattern from QSC-Lip, a rapid initial release within initial 10 h followed by a sustained release. Cellular uptake of QSC-Lip is significantly enhanced by C₆ cells under MT. In vivo dual-imaging studies show that QSC-Lip not only produces an obvious negative-contrast enhancement effect on glioma by magnetic resonance imaging but also makes tumor emitting fluorescence under MT. The dual-imaging of QSC-Lip guides the accurate resection of glioma by surgery. Besides, CGT is also specifically distributed to glioma after administration of QSC-Lip under MT, resulting in an effective inhibition of tumors. The integrated liposome may be a potential carrier for theranostics of tumor.

Multimodality reporter gene imaging: Construction strategies and application

Molecular imaging has played an important role in the noninvasive exploration of multiple biological processes. Reporter gene imaging is a key part of molecular imaging. By combining with a reporter probe, a reporter protein can induce the accumulation of specific signals that are detectable by an imaging device to provide indirect information of reporter gene expression in living subjects. There are many types of reporter genes and each corresponding imaging technique has its own advantages and drawbacks. Fused reporter genes or single reporter genes with products detectable by multiple imaging modalities can compensate for the disadvantages and potentiate the advantages of each modality. Reporter gene multimodality imaging could be applied to trace implanted cells, monitor gene therapy, assess endogenous molecular events, screen drugs, etc. Although several types of multimodality imaging apparatus and multimodality reporter genes are available, more sophisticated detectors and multimodality reporter gene systems are needed.