SPECT/CT imaging of baculovirus biodistribution in rat

Comparative Biodistribution Study of Baculoviral and Adenoviral Vector Vaccines against SARS-CoV-2

Various types of vaccines have been developed against COVID-19, including vector vaccines. Among the COVID-19 vaccines, AstraZeneca's chimpanzee adenoviral vaccine was the first to be commercialized. For viral vector vaccines, biodistribution studies are critical to vaccine safety, gene delivery, and efficacy. This study compared the biodistribution of the baculoviral vector vaccine (AcHERV-COVID19) and the adenoviral vector vaccine (Ad-COVID19). Both vaccines were administered intramuscularly to mice, and the distribution of the SARS-CoV-2 S gene in each tissue was evaluated for up to 30 days. After vaccination, serum and various tissue samples were collected from the mice at each time point, and IgG levels and DNA copy numbers were measured using an enzyme-linked immunosorbent assay and a quantitative real-time polymerase chain reaction. AcHERV-COVID19 and Ad-COVID19 distribution showed that the SARS-CoV-2 spike gene remained predominantly at the injection site in the mouse muscle. In kidney, liver, and spleen tissues, the AcHERV-COVID19 group showed about 2-4 times higher persistence of the SARS-CoV-2 spike gene than the Ad-COVID19 group. The distribution patterns of AcHERV-COVID19 and Ad-COVID19 within various organs highlight their contrasting biodistribution profiles, with AcHERV-COVID19 exhibiting a broader and prolonged presence in the body compared to Ad-COVID19. Understanding the biodistribution profile of AcHERV-COVID19 and Ad-COVID19 could help select viral vectors for future vaccine development.

Application of Advanced Imaging Modalities in Veterinary Medicine: A Review

Veterinary anatomy has traditionally relied on detailed dissections to produce anatomical illustrations, but modern imaging modalities, now represent an enormous resource that allows for fast non-invasive visualizations in living animals for clinical and research purposes. In this review, advanced anatomical imaging modalities and their applications, safety issues, challenges, and future prospects of the techniques commonly employed for animal imaging would be highlighted. The quality of diagnostic imaging equipment in veterinary practice has greatly improved. Recent advances made in veterinary advanced imaging specifically about cross-sectional modalities (CT and MRI), nuclear medicine (PET, SPECT), and dual imaging modalities (PET/CT, PET/MR, and SPECT/CT) have become widely available, leading to greater demands and expectations from veterinary clients. These modalities allow for the creation of three-dimensional representations that can be of considerable value in the dissemination of clinical diagnosis and anatomical studies. Despite, the modern imaging modalities well established in developed countries across the globe, it is yet to remain in its infancy stage in veterinary practice in developing countries due to heavy initial investment and maintenance costs, lack of expert interpretation, a requirement of specialized technical staff and need of adjustable machines to accommodate the different range of animal sizes. Therefore, veterinarians should take advantage of these imaging techniques in designing future experiments by considering the availability of these varied imaging modalities and the creation of three-dimensional graphical representations of internal structures.

Visualizing and quantifying antimicrobial drug distribution in tissue

The biodistribution and pharmacokinetics of drugs are vital to the mechanistic understanding of their efficacy. Measuring antimicrobial drug efficacy has been challenging as plasma drug concentration is used as a surrogate for tissue drug concentration, yet typically does not reflect that at the intended site(s) of action. Utilizing an image-guided approach, it is feasible to accurately quantify the biodistribution and pharmacokinetics within the desired site(s) of action. We outline imaging modalities used in visualizing drug distribution with examples ranging from in vitro cellular drug uptake to clinical treatment of microbial infections. The imaging modalities of interest are: radio-labeling, magnetic resonance, mass spectrometry imaging, computed tomography, fluorescence, and Raman spectroscopy. We outline the progress, limitations, and future outlook for each methodology. Further advances in these optical approaches would benefit patients and researchers alike, as non-invasive imaging could yield more profound insights with a lower clinical burden than invasive measurement approaches used today.

Pseudotyped baculovirus is an effective gene expression tool for studying molecular function during axolotl limb regeneration

Axolotls can regenerate complex structures through recruitment and remodeling of cells within mature tissues. Accessing the underlying mechanisms at a molecular resolution is crucial to understand how injury triggers regeneration and how it proceeds. However, gene transformation in adult tissues can be challenging. Here we characterize the use of pseudotyped baculovirus (BV) as an effective gene transfer method both for cells within mature limb tissue and within the blastema. These cells remain competent to participate in regeneration after transduction. We further characterize the effectiveness of BV for gene overexpression studies by overexpressing Shh in the blastema, which yields a high penetrance of classic polydactyly phenotypes. Overall, our work establishes BV as a powerful tool to access gene function in axolotl limb regeneration.

Manufacturing of AcMNPV baculovirus vectors to enable gene therapy trials

Over the past two decades, baculoviruses have become workhorse research tools for transient transgene expression. Although they have not yet been used directly as a gene therapy vector in the clinical setting, numerous preclinical studies have suggested the highly promising potential of baculovirus as a delivery vector for a variety of therapeutic applications including vaccination, tissue engineering, and cancer treatment. As such, there is growing interest in using baculoviruses as human gene therapy vectors, which has led to advances in baculovirus bioprocessing methods. This review provides an overview of the current approaches for scaled-up amplification, concentration, purification, and formulation of AcMNPV baculoviruses, and highlights the key regulatory requirements that must be met before gene therapy clinical trials can be initiated.

Baculovirus-mediated gene delivery and RNAi applications

Baculoviruses are widely encountered in nature and a great deal of data is available about their safety and biology. Recently, these versatile, insect-specific viruses have demonstrated their usefulness in various biotechnological applications including protein production and gene transfer. Multiple in vitro and in vivo studies exist and support their use as gene delivery vehicles in vertebrate cells. Recently, baculoviruses have also demonstrated high potential in RNAi applications in which several advantages of the virus make it a promising tool for RNA gene transfer with high safety and wide tropism.

Biodistribution and antitumor effect of Cetuximab-targeted lentivirus

Viral vectors are central tools for gene therapy. Targeting of the vector to desired tissues followed by expression of the therapeutic gene forms one of the most critical points in effective therapy. In this study we used streptavidin-displaying lentivirus conjugated to biotinylated anti-epidermal growth factor receptor (EGFR) antibody (Cetuximab) to target vector specifically to ovarian tumors. Biodistribution of the targeted virus was studied in nude mice with orthotropic SKOV-3m human ovarian carcinoma xenografts. Radiolabeled antibodies were conjugated to streptavidin-displaying lentiviruses and biodistribution of the virus after the intravenous delivery to tumor-bearing mice was monitored up to 6 days using combined SPECT/CT imaging modality. Organ samples were collected post mortem and specific organ activities were measured. The integration of lentivirus vectors in collected tissue samples was analyzed using qPCR and the expression of green fluorescent protein (GFP)-transgene was tested by enzyme-linked immunosorbent assay. Our results showed that lentiviruses conjugated to Cetuximab (Cet-LV) or control human IgG (IgG-LV) accumulated mainly to the liver and spleen of the mice and to lower extent to lung, kidneys and tumors. Strikingly, in 50% of the mice injected with cetuximab-targeted lentivirus no tumor tissue was found, whereas the remaining half showed a significant decrease in tumor size. We hypothesize/present data that lentivirus-mediated INF-αβ production together with tumor targeting could function as an effective antitumor treatment.

Baculovirus as delivery system for gene transfer during hypothermic organ preservation

Concerns over the safety of conventional viral vectors have limited the translation of gene transfer from an exciting experimental procedure to a successful clinical therapy in transplantation. Baculoviruses are insect viruses, but have the ability to enter mammalian cells and deliver potential therapeutic molecules with no evidence of viral replication. This study provides evidence of the ability of recombinant baculovirus to enter mammalian kidneys and livers during cold preservation. Six kidneys and six liver lobules retrieved from large pigs were perfused with University of Wisconsin (UW) solution containing a baculovirus tagged with green fluorescent protein and preserved for 8 h. In addition, six kidneys were perfused with UW containing a baculovirus expressing red fluorescent protein and preserved for 24 h. Green fluorescent virus particles were detected within transduced kidneys and livers after 8 h standard cold storage and red fluorescent protein mRNA was detected in kidneys after 24 h of cold preservation. There were no significant differences in tissue architecture, cell morphology or ATP content between experimental organs and their controls. Ex vivo transduction of organs with recombinant baculovirus during conventional cold preservation was demonstrated with no evidence of additional injury or reduction in cell viability.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.

In vivo SPECT/CT imaging of human orthotopic ovarian carcinoma xenografts with 111In-labeled monoclonal antibodies

Epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor 3 (VEGFR-3) are expressed in the tumor area during the progression of ovarian carcinoma. Monoclonal antibodies developed against these receptors are potential diagnostic molecules for in vivo imaging of ovarian carcinoma.

METHODS

Biodistribution of the monoclonal antibodies cetuximab against EGFR and mF4-31C1 against VEGFR-3 was studied in nude mice with orthotopic SKOV-3m human ovarian carcinoma xenografts. The biodistribution of (111)Indium-labeled antibodies was followed up to 48 h postinjection using combined SPECT and CT imaging modality. Organ samples were collected postmortem and specific organ activity was measured. Accumulation of the intravenously injected antibodies in the tumor tissue and lymph nodes was verified using immunohistology.

RESULTS

Imaging studies with SPECT/CT showed clear accumulation of both antibodies into tumor area. The tumor uptake was 8.78 ± 0.74 %ID/g for cetuximab and 5.77 ± 0.62 %ID/g for mF4-31C1 after 48 h postinjection. Cetuximab had lower liver tropism and faster tumor homing rate. In addition, after 48 h two of five tumor-bearing mice showed a clear accumulation of the In-labeled mF4-31C1 at the left axillary area. Both intravenously administered antibodies could also be detected from the tumor sections by immunohistological staining but only mF4-31C1 forms in the lymph nodes.

CONCLUSION

These results demonstrate the accumulation of EGFR- and VEGFR-3-specific antibodies in orthotopic ovarian carcinoma tumors. Systemically administered they had slow pharmacokinetics which is typical for antibodies. Accumulation of mF4-31C1 antibody in the lymph nodes suggests the remote activation of VEGFR-3 by the primary tumor.

Whole animal imaging

Translational research plays a vital role in understanding the underlying pathophysiology of human diseases, and hence development of new diagnostic and therapeutic options for their management. After creating an animal disease model, pathophysiologic changes and effects of a therapeutic intervention on them are often evaluated on the animals using immunohistologic or imaging techniques. In contrast to the immunohistologic techniques, the imaging techniques are noninvasive and hence can be used to investigate the whole animal, oftentimes in a single exam which provides opportunities to perform longitudinal studies and dynamic imaging of the same subject, and hence minimizes the experimental variability, requirement for the number of animals, and the time to perform a given experiment. Whole animal imaging can be performed by a number of techniques including x-ray computed tomography, magnetic resonance imaging, ultrasound imaging, positron emission tomography, single photon emission computed tomography, fluorescence imaging, and bioluminescence imaging, among others. Individual imaging techniques provide different kinds of information regarding the structure, metabolism, and physiology of the animal. Each technique has its own strengths and weaknesses, and none serves every purpose of image acquisition from all regions of an animal. In this review, a broad overview of basic principles, available contrast mechanisms, applications, challenges, and future prospects of many imaging techniques employed for whole animal imaging is provided. Our main goal is to briefly describe the current state of art to researchers and advanced students with a strong background in the field of animal research.

Avidin-biotin technology in targeted therapy

IMPORTANCE OF THE FIELD

The goal of drug targeting is to increase the concentration of the drug in the vicinity of the cells responsible for disease without affecting healthy cells. Many approaches in cancer treatment are limited because of their broad range of unwanted side effects on healthy cells. Targeting can reduce side effects and increase efficacy of drugs in the patient.

AREAS COVERED IN THIS REVIEW

Avidin, originally isolated from chicken eggs, and its bacterial analogue, streptavidin, from Streptomyces avidinii, have extremely high affinity for biotin. This unique feature is the basis of avidin-biotin technology. This article reviews the current status of avidin-biotin systems and their use for pretargeted drug delivery and vector targeting.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the following approaches using the avidin-biotin system: i) targeting antibodies and therapeutic molecules are administered separately leading to a reduction of drug dose in normal tissues compared with conventional (radio)immunotherapies; ii) introducing avidin gene into specific tissues by local gene transfer, which subsequently can sequester and concentrate considerable amounts of therapeutic ligands; and iii) enabling transductional targeting of gene therapy vectors.

TAKE HOME MESSAGE

Avidin and biotin technology has proved to be an extremely versatile tool with broad applications, such as pretargeting, delivering avidin gene into cells enabling targeting of biotinylated compounds and targeting of viral vectors.

Concanavalin A affinity chromatography for efficient baculovirus purification

Baculovirus has emerged as a novel gene delivery and vaccine vector, and the demand for purified baculovirus is rising due to the increasing in vivo applications. Since the baculoviral envelope protein gp64 is a glycoprotein, we aimed to develop a concanavalin A (Con A) chromatography process, which harnessed the possible affinity interaction between gp64 and Con A, for simple and effective baculovirus purification. Throughout the purification process the virus stability and recovery were assessed by quantifying the virus transducing titers [TT, defined as transducing units (TU) per milliliter] and viral particles (VP). We found that baculovirus stability was sensitive to buffer conditions and diafiltration with a tangential flow filtration system LabScale using 300 K membranes yielded recoveries of approximately 75% in TT and 82% in VP. The diafiltered baculovirus strongly bound to the Con A column as evidenced by the low virus losses to the flow through and wash fractions. The wash steps eliminated >99% of protein impurities and elution with 0.6 M alpha-D-methylmannoside at room temperature led to the recoveries of approximately 16% in VP and approximately 15.3% in TU. The resultant VP/TU ratio was as low as 41.4, attesting the high quality of the purified virus. Further elution with 1 M alpha-D-methylmannoside recovered another 6% virus TU, yielding a cumulative recovery of approximately 21.3% in TU. These data demonstrated for the first time that Con A chromatography is suitable for baculovirus purification, and may be used for the purification of other viruses with surface glycoproteins.

(Strept)avidin-displaying lentiviruses as versatile tools for targeting and dual imaging of gene delivery

Lentiviruses have shown great promise for human gene therapy. However, no optimal strategies are yet available for noninvasive imaging of virus biodistribution and subsequent transduction in vivo. We have developed a dual-imaging strategy based on avidin-biotin system allowing easy exchange of the surface ligand on HIV-derived lentivirus envelope. This was achieved by displaying avidin or streptavidin fused to the transmembrane anchor of vesicular stomatitis virus G protein on gp64-pseudotyped envelopes. Avidin and streptavidin were efficiently incorporated on virus particles, which consequently showed binding to biotin in ELISA. These vectors, conjugated to biotinylated radionuclides and engineered to express a ferritin transgene, enabled for the first-time dual imaging of virus biodistribution and transduction pattern by single-photon emission computed tomography and magnetic resonance imaging after stereotactic injection into rat brain. In addition, vector retargeting to cancer cells overexpressing CD46, epidermal growth factor and transferrin receptors using biotinylated ligands and antibodies was demonstrated in vitro. In conclusion, we have generated novel lentivirus vectors for noninvasive imaging and targeting of lentivirus-mediated gene delivery. This study suggests that these novel vectors could be applicable for the treatment of central nervous system disorders and cancer.

Tumor targeting of baculovirus displaying a lymphatic homing peptide

BACKGROUND

Tumor-associated cells and vasculature express attractive molecular markers for site-specific vector targeting. To attain tumor-selective tropism, we recently developed a baculovirus vector displaying the lymphatic homing peptide LyP-1, originally identified by ex vivo/in vivo screening of phage display libraries, on the viral envelope by fusion to the transmembrane anchor of vesicular stomatitis virus G-protein.

METHODS

In the present study, we explored the specificity and kinetics of viral binding and internalization as well as in vivo tumor homing of the LyP-1 displaying virus to elucidate the applicability of baculovirus for targeted therapies.

RESULTS

We demonstrated that the LyP-1 peptide contributes to saturable binding of baculovirus in human MDA-MB-435 and HepG2 carcinoma cells and escalates the kinetics of viral internalization leading to earlier nuclear accumulation and enhanced transgene expression. The LyP-1 displaying virus also showed stronger competitiveness against transduction with wild-type baculovirus, suggesting involvement of a specific receptor in cellular attachment and entry. Following intravenous injections, the modified virus accumulated within the human MDA-MB-435 and MDA-MB-231 carcinoma xenografts in mice with higher specificity and efficiency than the control virus. Targeting of the modified virus was more specific in the MDA-MB-435 than in the MDA-MB-231 xenografts as demonstrated by higher tumor accumulation and lower distribution in nontarget organs. No apparent cytotoxicity was associated with the surface modification.

CONCLUSIONS

This first demonstration of in vivo tumor targeting of a systemically administered, tropism-modified baculoviral vector highlights the potential of baculovirus-mediated targeted therapies.

Inhibition of nasopharyngeal carcinoma growth by RTA-expressing baculovirus vectors containing oriP

BACKGROUND

Nasopharyngeal carcinoma (NPC) is closely associated with latent Epstein-Barr virus (EBV) infection. Activation of latent EBV into lytic replication by introducing viral lytic gene BRLF1 (RTA) has been shown to be a potential approach to suppress the growth of EBV-associated NPC tumor.

METHODS

The baculovirus vectors with RTA expression cassette (BV-R), RTA and the EBV latent replication origin (OriP, BV-RO), or RTA, OriP and EBNA-1 gene (BV-ROE-CMV), were constructed and examined for their ability to mediate RTA expression, initiate lytic replication and induce cell death in EBV-positive cell lines Hone1-EBV, HK1-EBV and C666-1 in vitro. Their effect to inhibit the growth of EBV-positive NPC tumors was also evaluated in nude mice.

RESULTS

The baculovirus vectors BV-RO and BV-ROE-CMV mediated efficient expression of RTA in EBV-positive NPC cells. Lytic EBV replication and cell death were observed in these infected cells. Both vectors also significantly inhibited the growth of EBV-positive NPC tumor in nude mice. EBV early lytic gene expression and tumor cell death were observed in these treated tumors.

CONCLUSIONS

The presence of OriP improved the performance of the RTA-expressing baculovirus vectors to induce EBV lytic replication and cell death in vitro, and suppress the growth of EBV positive NPC tumors in vivo. By confining RTA and EBNA-1 expression to EBV-positive cells, BV-RO is expected to be a better candidate in application than BV-ROE-CMV in the long term.

Targeting and purification of metabolically biotinylated baculovirus

Targeting viral entry is one of the major goals in the development of vectors for gene therapy. Ideally, the coupling of each new targeting motif would not require changes in vector structure. To achieve this, we developed novel metabolically biotinylated baculoviral vectors by displaying a small biotin acceptor peptide (BAP) fused either to different sites in the baculovirus glycoprotein gp64 or to the transmembrane anchor of vesicular stomatitis virus G protein. Baculoviral particles were biotinylated during vector production by coexpression of Escherichia coli biotin ligase (BirA). The insertion of BAP at amino acid position 283 of gp64 resulted in the most efficient biotin display. Unlike vectors with lower biotin display, these vectors also showed improved transduction when retargeted to transferrin, epidermal growth factor, and CD46 receptors overexpressed on rat glioma and human ovarian carcinoma cells. Biotinylated baculoviral vectors could also be concentrated by one-step magnetic particle-based capture to reach titers up to 10(10) plaque-forming units/ml. These results demonstrate the utility of metabolically biotinylated baculovirus for vector targeting and viral purification applications.

Non-invasive Imaging in Gene Therapy

Several methods are available for non-invasive imaging of gene delivery and transgene expression, including magnetic resonance imaging (MRI), single photon emission tomography (SPECT)/positron emission tomography (PET), and fluorescence and bioluminescence imaging. However, these imaging modalities differ greatly in terms of their sensitivity, cost, and ability to measure the signal. Whereas MRI can produce a resolution of approximately 50 mum, optical imaging achieves only 3-5 mm but outperforms MRI in terms of the cost of the imaging device. Similarly, SPECT and PET give a resolution of only 1-2 mm but provide for relatively easy quantitation of the signal and need only nanograms of probe, compared with the microgram or milligram levels required for MRI and optical imaging. To develop safer and more efficient gene delivery vectors, it is essential to perform rigorous in vivo experiments, to image particle biodistribution and transduction patterns, and to quantify the transgene expression profile. Differences between modalities have a significant effect on the resultant imaging resolution for gene therapy. This review describes the methodologies in use and highlights recent key approaches using the latest imaging modalities in gene therapy. Future trends in gene therapy imaging are also discussed.