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Background:
Recent studies have shown that human ferritin can be used as a reporter of gene expression for magnetic resonance imaging (MRI). Bacteria also encode three classes of ferritin-type molecules with iron accumulation properties.
Methods and Findings:
Here, we investigated whether these bacterial ferritins can also be used as MRI reporter genes and which of the bacterial ferritins is the most suitable reporter. Bacterial ferritins were overexpressed in probiotic E. coli Nissle 1917. Cultures of these bacteria were analyzed and those generating highest MRI contrast were further investigated in tumor bearing mice. Among members of three classes of bacterial ferritin tested, bacterioferritin showed the most promise as a reporter gene. Although all three proteins accumulated similar amounts of iron when overexpressed individually, bacterioferritin showed the highest contrast change. By site-directed mutagenesis we also show that the heme iron, a unique part of the bacterioferritin molecule, is not critical for MRI contrast change. Tumor-specific induction of bacterioferritin-expression in colonized tumors resulted in contrast changes within the bacteria-colonized tumors.
Conclusions:
Our data suggest that colonization and gene expression by live vectors expressing bacterioferritin can be monitored by MRI due to contrast changes.
Magnetic Resonance Imaging of Tumors Colonized with Bacterial Ferritin-Expressing Escherichia coli
(2011)
Background: Recent studies have shown that human ferritin can be used as a reporter of gene expression for magnetic resonance imaging (MRI). Bacteria also encode three classes of ferritin-type molecules with iron accumulation properties. Methods and Findings: Here, we investigated whether these bacterial ferritins can also be used as MRI reporter genes and which of the bacterial ferritins is the most suitable reporter. Bacterial ferritins were overexpressed in probiotic E. coli Nissle 1917. Cultures of these bacteria were analyzed and those generating highest MRI contrast were further investigated in tumor bearing mice. Among members of three classes of bacterial ferritin tested, bacterioferritin showed the most promise as a reporter gene. Although all three proteins accumulated similar amounts of iron when overexpressed individually, bacterioferritin showed the highest contrast change. By site-directed mutagenesis we also show that the heme iron, a unique part of the bacterioferritin molecule, is not critical for MRI contrast change. Tumor-specific induction of bacterioferritin-expression in colonized tumors resulted in contrast changes within the bacteria-colonized tumors. Conclusions: Our data suggest that colonization and gene expression by live vectors expressing bacterioferritin can be monitored by MRI due to contrast changes
Vaccinia virus plays an important role in human medicine and molecular biology ever since the 18th century after E. Jenner discovered its value as a vaccination virus against smallpox. After the successful eradication of smallpox, vaccinia virus, apart from its use as a vaccine carrier, is today mainly used as a viral vector in molecular biology and increasingly in cancer therapy. The capability to specifically target and destroy cancer cells makes it a perfect agent for oncolytic virotherapy. Furthermore, the virus can easily be modified by inserting genes encoding therapeutic or diagnostic proteins to be expressed within the tumor. The emphasis in this study was the diagnosis of tumors using different vaccinia virus strains. Viruses with metal-accumulating capabilities for tumor detection via MRI technology were generated and tested for their usefulness in cell culture and in vivo. The virus strains GLV-1h131, GLV-1h132, and GLV-1h133 carry the gene encoding the two subunits of the iron storage protein ferritin under the control of three different promoters. GLV-1h110, GLV-1h111, and GLV-1h112 encode the bacterial iron storage protein bacterioferritin, whereas GLV-1h113 encodes the codon-optimized version of bacterioferritin for more efficient expression in human cells. GLV-1h22 contains the transferrin receptor gene, which plays an important role in iron uptake, and GLV-1h114 and GLV-1h115 contain the murine transferrin receptor gene. For possibly better iron uptake the virus strains GLV-1h154, GLV-1h155, GLV-1h156, and GLV-1h157 were generated, each with a version of a ferritin gene and a transferrin receptor gene. GLV-1h154 carries the genes that encode bacterioferritin and human transferrin receptor, GLV-1h155 the human ferritin H-chain gene and the human transferrin receptor gene. GLV-1h156 and GLV-1h157 infected cells both express the mouse transferrin receptor and bacterioferritin or human ferritin H-chain, respectively. The virus strains GLV-1h186 and GLV-1h187 were generated to contain a mutated form of the ferritin light chain, which was shown to result in iron overload and the wildtype light chain gene, respectively. The gene encoding the Divalent Metal Transporter 1, which is a major protein in the uptake of iron, was inserted in the virus strain GLV-1h102. The virus strain GLV-1h184 contains the magA gene of the magnetotactic bacterium Magnetospirillum magnetotacticum, which produces magnetic nanoparticles for orientation in the earth’s magnetic field. Initially the infection and replication capability of all the virus strains were analyzed and compared to that of the parental virus strain GLV-1h68, revealing that all the viruses were able to infect cells of the human cancer cell lines A549 and GI-101A. All constructs exhibited a course of infection comparable to that of GLV-1h68. Next, to investigate the expression of the foreign proteins in GI-101A and A549 cells with protein analytical methods, SDS-gelelectrophoresis, Western blots and ELISAs were performed. The proteins, which were expressed under the control of the strong promoters, could be detected using these methods. To be able to successfully detect the protein expression of MagA and DMT1, which were expressed under the control of the weak promoter, the more sensitive method RT-PCR was used to at least confirm the transcription of the inserted genes. The determination of the iron content in infected GI-101A and A549 cells showed that infection with all used virus strains led to iron accumulation in comparison to uninfected cells, even infection with the parental virus strain GLV-1h68. The synthetic phytochelatin EC20 was also shown to enhance the accumulation of different heavy metals in bacterial cultures. In vivo experiments with A549 tumor-bearing athymic nude mice revealed that 24 days post infection virus particles were found mainly in the tumor. The virus-mediated expression of recombinant proteins in the tumors was detected successfully by Western blot. Iron accumulation in tumor lysates was investigated by using the ferrozine assay and led to the result that GLV-1h68-infected tumors had the highest iron content. Histological stainings confirmed the finding that iron accumulation was not a direct result of the insertion of genes encoding iron-accumulating proteins in the virus genome. Furthermore virus-injected tumorous mice were analyzed using MRI technology. Two different measurements were performed, the first scan being done with a seven Tesla small animal scanner seven days post infection whereas the second scan was performed using a three Tesla human scanner 21 days after virus injection. Tumors of mice injected with the virus strains GLV-1h113 and GLV-1h184 were shown to exhibit shortened T2 and T2* relaxation times, which indicates enhanced iron accumulation. In conclusion, the experiments in this study suggest that the bacterioferritin-encoding virus strain GLV-1h113 and the magA-encoding virus strain GLV-1h184 are promising candidates to be used for cancer imaging after further analyzation and optimization.
Background
Oncolytic virotherapy is a novel approach for the treatment of glioblastoma multiforme (GBM) which is still a fatal disease. Pathologic features of GBM are characterized by the infiltration with microglia/macrophages and a strong interaction between immune- and glioma cells. The aim of this study was to determine the role of microglia and astrocytes for oncolytic vaccinia virus (VACV) therapy of GBM.
Methods
VACV LIVP 1.1.1 replication in C57BL/6 and \(Foxn1^{nu/nu}\) mice with and without GL261 gliomas was analyzed. Furthermore, immunohistochemical analysis of microglia and astrocytes was investigated in non-, mock-, and LIVP 1.1.1-infected orthotopic GL261 gliomas in C57BL/6 mice. In cell culture studies virus replication and virus-mediated cell death of GL261 glioma cells was examined, as well as in BV-2 microglia and IMA2.1 astrocytes with M1 or M2 phenotypes. Co-culture experiments between BV-2 and GL261 cells and apoptosis/necrosis studies were performed. Organotypic slice cultures with implanted GL261 tumor spheres were used as additional cell culture system.
Results
We discovered that orthotopic GL261 gliomas upon intracranial virus delivery did not support replication of LIVP 1.1.1, similar to VACV-infected brains without gliomas. In addition, recruitment of \(Iba1^+\) microglia and \(GFAP^+\) astrocytes to orthotopically implanted GL261 glioma sites occurred already without virus injection. GL261 cells in culture showed high virus replication, while replication in BV-2 and IMA2.1 cells was barely detectable. The reduced viral replication in BV-2 cells might be due to rapid VACV-induced apoptotic cell death. In BV-2 and IMA 2.1 cells with M1 phenotype a further reduction of virus progeny and virus-mediated cell death was detected. Application of BV-2 microglial cells with M1 phenotype onto organotypic slice cultures with implanted GL261 gliomas resulted in reduced infection of BV-2 cells, whereas GL261 cells were well infected.
Conclusion
Our results indicate that microglia and astrocytes, dependent on their activation state, may preferentially clear viral particles by immediate uptake after delivery. By acting as VACV traps they further reduce efficient virus infection of the tumor cells. These findings demonstrate that glia cells need to be taken into account for successful GBM therapy development.
No abstract availableBackground: Glioblastoma multiforme (GBM) is one of the most aggressive forms of cancer with a high rate of recurrence. We propose a novel oncolytic vaccinia virus (VACV)-based therapy using expression of the bone morphogenetic protein (BMP)-4 for treating GBM and preventing recurrence.
Methods: We have utilized clinically relevant, orthotopic xenograft models of GBM based on tumor-biopsy derived, primary cancer stem cell (CSC) lines. One of the cell lines, after being transduced with a cDNA encoding firefly luciferase, could be used for real time tumor imaging. A VACV that expresses BMP-4 was constructed and utilized for infecting several primary glioma cultures besides conventional serum-grown glioma cell lines. This virus was also delivered intracranially upon implantation of the GBM CSCs in mice to determine effects on tumor growth.
Results: We found that the VACV that overexpresses BMP-4 demonstrated heightened replication and cytotoxic activity in GBM CSC cultures with a broad spectrum of activity across several different patient-biopsy cultures. Intracranial inoculation of mice with this virus resulted in a tumor size equal to or below that at the time of injection. This resulted in survival of 100% of the treated mice up to 84 days post inoculation, significantly superior to that of a VACV lacking BMP-4 expression. When mice with a higher tumor burden were injected with the VACV lacking BMP-4, 80% of the mice showed tumor recurrence. In contrast, no recurrence was seen when mice were injected with the VACV expressing BMP-4, possibly due to induction of differentiation in the CSC population and subsequently serving as a better host for VACV infection and oncolysis. This lack of recurrence resulted in superior survival in the BMP-4 VACV treated group.
Conclusions: Based on these findings we propose a novel VACV therapy for treating GBM, which would allow tumor specific production of drugs in the future in combination with BMPs which would simultaneously control tumor maintenance and facilitate CSC differentiation, respectively, thereby causing sustained tumor regression without recurrence.