Using Dual Fluorescence Reporting Genes to Establish an In Vivo Imaging Model of Orthotopic Lung Adenocarcinoma in Mice

Cell-Derived Allograft Models as a Solution to the Obstacles of Preclinical Studies under Limited Resources: A Systematic Review on Experimental Lung Cancer Animal Models

BACKGROUND

The use of appropriate animal models for cancer studies is a major challenge, particularly for investigators who lack the resources to maintain and use xenograft animals or genetically engineered mouse models (GEMM). In addition, several countries intending to incorporate these models must conduct importation procedures, posing an additional challenge.

OBJECTIVE

This review aimed to explore the use of cell-derived allograft or syngeneic models under limited resources. The results can be used by investigators, specifically from low-middle-income countries, to contribute to lung cancer eradication.

METHODS

A literature search was carried out on various databases, including PubMed, Web of Science, and Scopus. In addition, the publication year of the selected articles was set between 2013 and 2023 with different search components (SC), namely lung cancer (SC1), animal models (SC2), and preclinical studies (SC3).

RESULTS

This systematic review focused on selecting animals, cells, and methods that could be applied to generating allograft-type lung cancer animal models from 101 included articles.

CONCLUSION

Based on the results, the use of cell-derived allograft models in cancer studies is feasible and relevant, and it provides valuable insights regarding the conditions with limited resources.

Visualization of nonsmall-cell lung cancer by near-infrared fluorescence imaging with tumor-targeting peptide ABT-510

Nonsmall-cell lung cancer (NSCLC) is the most frequent type of lung cancer, with early surgical treatment proving vital for prolonged patient survival. However, precise visualization of NSCLC remains a challenge due to limited molecular imaging probes, the unique anatomical structure of the lungs, and respiratory movement interference. In this study, we investigated the potential utility of CD36, which is highly expressed in NSCLC, as an imaging target. A selective and water-soluble fluorescent probe, MPA-ABT-510, was successfully constructed by coupling ABT-510 with MPA, a near-infrared (NIR) fluorescent dye. Molecular docking analysis shows that MPA-ABT-510 possesses strong binding affinity to the CD36 protein, with specific hydrogen bond interactions at defined amino acid residues. In vitro assays reveals that the fluorescein isothiocyanate-labeled peptide ABT-510 specifically binds to the CD36-high expressing NSCLC cell lines H1299 and A549. In vivo imaging verifies that the MPA-ABT-510 efficiently accumulates in the tumor site with a distinct fluorescent signal. Ex vivo imaging revealed that tumor-to-lung fluorescence ratios for subcutaneous and orthotopic H1299 mouse models were 7.19 ± 0.73 and 1.91 ± 0.42, respectively, while those for A549 mice were 5.53 ± 0.64 and 1.77 ± 0.41, respectively. Biodistribution analysis demonstrated efficient MPA-ABT-510 uptake in H1299 and A549 liver metastases models with tumor-to-liver fluorescence ratios of 2.47 ± 0.48 and 2.19 ± 0.22, respectively. High MPA-ABT-510 accumulation was evident in A549 intestinal metastases models, as evidenced by tumor-to-colorectal fluorescence ratios of 4.27 ± 0.11. MPA-ABT-510 exhibits superior imaging capabilities with minimal safety concerns, so it is a promising candidate for NSCLC surgical navigation.

Current Trends of Bacterial and Fungal Optoproteins for Novel Optical Applications

Photoproteins, luminescent proteins or optoproteins are a kind of light-response protein responsible for the conversion of light into biochemical energy that is used by some bacteria or fungi to regulate specific biological processes. Within these specific proteins, there are groups such as the photoreceptors that respond to a given light wavelength and generate reactions susceptible to being used for the development of high-novel applications, such as the optocontrol of metabolic pathways. Photoswitchable proteins play important roles during the development of new materials due to their capacity to change their conformational structure by providing/eliminating a specific light stimulus. Additionally, there are bioluminescent proteins that produce light during a heatless chemical reaction and are useful to be employed as biomarkers in several fields such as imaging, cell biology, disease tracking and pollutant detection. The classification of these optoproteins from bacteria and fungi as photoreceptors or photoresponse elements according to the excitation-emission spectrum (UV-Vis-IR), as well as their potential use in novel applications, is addressed in this article by providing a structured scheme for this broad area of knowledge.

Fluorescence Microscopy-An Outline of Hardware, Biological Handling, and Fluorophore Considerations

Fluorescence microscopy has become a critical tool for researchers to understand biological processes at the cellular level. Micrographs from fixed and live-cell imaging procedures feature in a plethora of scientific articles for the field of cell biology, but the complexities of fluorescence microscopy as an imaging tool can sometimes be overlooked or misunderstood. This review seeks to cover the three fundamental considerations when designing fluorescence microscopy experiments: (1) hardware availability; (2) amenability of biological models to fluorescence microscopy; and (3) suitability of imaging agents for intended applications. This review will help equip the reader to make judicious decisions when designing fluorescence microscopy experiments that deliver high-resolution and informative images for cell biology.

Additive Antiproliferative and Antiangiogenic Effects of Metformin and Pemetrexed in a Non-Small-Cell Lung Cancer Xenograft Model

Lung cancer is heterogeneous and challenging to cope with once it has progressed. Chemotherapy is the first step once no active driver mutation has been discovered. Non-antitumor drugs have been found to be beneficial when used as adjuvants to chemotherapy. In this study, the additive effect and mechanism of metformin combined with pemetrexed in non-small-cell lung cancer (NSCLC) cells were elucidated. Three NSCLC cell lines, A549, H1975, and HCC827, were used to analyze tumor cell proliferation, colony formation and the cell cycle in vitro when exposed to metformin alone, pemetrexed alone or their combination. We found that combination treatment in three cell lines exerted antiproliferative effects through cell cycle arrest in the S phase. An ex vivo chicken chorioallantoic membrane (CAM) assay was used to examine the antiangiogenic effect of metformin combined with pemetrexed on vascular structure formation. We further created an A549 orthotopic xenograft model with an in vivo imaging system (IVIS) and explored the associated indicators involved in the tumorigenic process. The in vitro results showed that the combination of metformin and pemetrexed exhibited an antiproliferative effect in reducing cell viability and colony formation, the downregulation of cyclin D1 and A2 and the upregulation of CDKN1B, which are involved in the G1/S phase. For antiangiogenic effects, the combination therapy inhibited the vascular structure, as proven by the CAM assay. We elucidated that combination therapy could target VEGFA and Endoglin by RT-qPCR, ELISA and histopathological findings in an A549 orthotopic NSCLC xenograft model. Our research demonstrated the additive antiproliferative and antiangiogenic effects of the combination of metformin with pemetrexed in NSCLC and could be applied to clinical lung cancer therapy.

iRFP (near-infrared fluorescent protein) imaging of subcutaneous and deep tissue tumours in mice highlights differences between imaging platforms

BACKGROUND

In vivo imaging using fluorescence is used in cancer biology for the detection, measurement and monitoring of tumours. This can be achieved with the expression of fluorescent proteins such as iRFP, which emits light at a wavelength less attenuated in biological tissues compared to light emitted by other fluorescent proteins such as GFP or RFP. Imaging platforms capable of detecting fluorescent tumours in small animals have been developed but studies comparing the performance of these platforms are scarce.

RESULTS

Through access to three platforms from Xenogen, Bruker and Li-Cor, we compared their ability to detect iRFP-expressing subcutaneous tumours as well as tumours localised deeper within the body of female NSG mice. Each platform was paired with proprietary software for image analyse, but the output depends on subjective decisions from the user. To more objectively compare platforms, we developed an 'in house' software-based approach which results in lower measured variability between mice.

CONCLUSIONS

Our comparisons showed that all three platforms allowed for reliable detection and monitoring of subcutaneous iRFP tumour growth. The biggest differences between platforms became apparent when imaging deeper tumours with the Li-Cor platform detecting most tumours and showing the highest dynamic range.

Utilization of a novel Sendai virus vector in ex vivo gene therapy for hemophilia A

Sendai virus (SeV) vectors are being recognized as a superior tool for gene transfer. Here, we report the transfection efficacy of a novel, high-performance, replication-defective, and persistent Sendai virus (SeVdp) vector in cultured cells and in mice using a near-infrared fluorescent protein (iRFP)-mediated in vivo imaging system. The novel SeVdp vector established persistent infection, and strong expression of inserted genes was sustained indefinitely in vitro. Analysis of iRFP-expressing cells transplanted subcutaneously into NOG, nude, and ICR mice suggests that innate immunity was involved in the exclusion of the transplanted cells. We also evaluated the feasibility of this novel SeVdp vector for hemophilia A gene therapy. This system enabled insertion of full-length FVIII genes, and transduced cells secreted FVIII into the culture medium. Transient FVIII activity was detected in the plasma of mice after intraperitoneal transplantation of these FVIII-secreting cells. Further improvement in methods to evade immunity, such as simultaneous expression of immunomodulatory genes, would make this novel vector a very useful tool in regenerative medicine.

Intrapulmonary inoculation of multicellular spheroids to construct an orthotopic lung cancer xenograft model that mimics four clinical stages of non-small cell lung cancer

INTRODUCTION

Lung cancer leads in mortality among all types of cancer in US and Non-small cell lung cancer (NSCLC) is the major type of lung cancer. Mice models of lung cancer based on subcutaneous or orthotopic inoculation of cancer cell suspension do not adequately mimic the progression of lung cancer in clinic.

METHODS

A549-iRFP cells (human NSCLC adenocarcinoma) were cultured to form multicellular spheroids (MCS), which were then inoculated intrapulmonarily into male athymic nude mice. The xenograft cancer development was monitored by in vivo fluorescent imaging and validated by open-chest anatomy, ex vivo fluorescent imaging, and histological studies.

RESULTS

The newly developed orthotopic xenograft model of lung cancer simulated all four clinical stages of NSCLC progression over one month: Stage 1) localized tumor at the inoculation site, Stage 2) multiple tumor nodules or larger tumor nodule on the same side of the lung, Stage 3) cancer growth on heart surface, and Stage 4) metastatic cancer on both sides of the lung. The model yielded high rates of postoperative survival (100%) and parenchymal tumor establishment (88.9%). The roughness of the inoculated MCS associated negatively with the time needed to develop metastatic cancer (p = .0299).

DISCUSSION

This new orthotopic xenograft model of NSCLC would facilitate the development of medications to treat lung cancer.

Integration of nano- and biotechnology for beta-cell and islet transplantation in type-1 diabetes treatment

Regenerative medicine using human or porcine β‐cells or islets has an excellent potential to become a clinically relevant method for the treatment of type‐1 diabetes. High‐resolution imaging of the function and faith of transplanted porcine pancreatic islets and human stem cell–derived beta cells in large animals and patients for testing advanced therapy medicinal products (ATMPs) is a currently unmet need for pre‐clinical/clinical trials. The iNanoBIT EU H2020 project is developing novel highly sensitive nanotechnology‐based imaging approaches allowing for monitoring of survival, engraftment, proliferation, function and whole‐body distribution of the cellular transplants in a porcine diabetes model with excellent translational potential to humans. We develop and validate the application of single‐photon emission computed tomography (SPECT) and optoacoustic imaging technologies in a transgenic insulin‐deficient pig model to observe transplanted porcine xeno‐islets and in vitro differentiated human beta cells. We are progressing in generating new transgenic reporter pigs and human‐induced pluripotent cell (iPSC) lines for optoacoustic imaging and testing them in transplantable bioartificial islet devices. Novel multifunctional nanoparticles have been generated and are being tested for nuclear imaging of islets and beta cells using a new, high‐resolution SPECT imaging device. Overall, the combined multidisciplinary expertise of the project partners allows progress towards creating much needed technological toolboxes for the xenotransplantation and ATMP field, and thus reinforces the European healthcare supply chain for regenerative medicinal products.

Near-Infrared Fluorescent Proteins and Their Applications

High transparency, low light-scattering, and low autofluorescence of mammalian tissues in the near-infrared (NIR) spectral range (~650-900 nm) open a possibility for in vivo imaging of biological processes at the micro- and macroscales to address basic and applied problems in biology and biomedicine. Recently, probes that absorb and fluoresce in the NIR optical range have been engineered using bacterial phytochromes - natural NIR light-absorbing photoreceptors that regulate metabolism in bacteria. Since the chromophore in all these proteins is biliverdin, a natural product of heme catabolism in mammalian cells, they can be used as genetically encoded fluorescent probes, similarly to GFP-like fluorescent proteins. In this review, we discuss photophysical and biochemical properties of NIR fluorescent proteins, reporters, and biosensors and analyze their characteristics required for expression of these molecules in mammalian cells. Structural features and molecular engineering of NIR fluorescent probes are discussed. Applications of NIR fluorescent proteins and biosensors for studies of molecular processes in cells, as well as for tissue and organ visualization in whole-body imaging in vivo, are described. We specifically focus on the use of NIR fluorescent probes in advanced imaging technologies that combine fluorescence and bioluminescence methods with photoacoustic tomography.

A mini-pig model for evaluating the efficacy of autologous platelet patches on induced acute full thickness wound healing

Background

Autologous platelet concentrates are currently widely used across different areas of regenerative medicine in order to enhance the wound healing process. Although several protocols for platelet concentrates are available, their application remains difficult due to different protocols leading to distinct products with vary potential biological uses. In this study, we attempted to make a platelet patch (PP) using mixtures of platelet rich plasma (PRP) injection and platelet rich fibrin (PRF) to promote wound repair and regeneration.

Results

Experiments were performed using a full-thickness wound model in mini-pigs. Autologous PRP, PRF and PP were prepared immediately before creating four full-thickness skin wounds in pigs. We quantified concentrations of platelets, thrombin and various growth factors to ensure that the desired effect can be produced. After surgery, hydrocolloid dressing, PRP injection, PRF and PP was applied to experimentally induced wounds. Application efficacy was evaluated by measurement of wound sizes and histological examination. The results indicated that all wounds showed a significant size reduction. Wound repair efficacy in response to PP treatment exhibited enhanced re-epithelialization compared to PRP and PRF (P < 0.05) and higher wound contraction than did PRF application (P < 0.05). Another aspect, experiment using DsRed transgenic pigs as blood donors demonstrated that leucocytes in PP were incorporated into the wound bed at the end of the study, suggesting that leucocytes activity is stimulated in response to PP application. Safety of the experimental processes was also confirmed by examination of organ biopsies.

Conclusions

We used a mini-pig model to evaluate the efficacy of lab-made PP on induced full-thickness wound healing. Results demonstrated that application of one piece of PP was enough to obtain comparable efficacy versus general utilization of PRP or PRF for wound care. We also demonstrated that leucocytes in PP were incorporated into the wound bed and no safety concerns have been found in the whole experiment. This study provides a novel and feasible method for veterinary or clinical wound care.

Non-Invasive Fluorescent Monitoring of Ovarian Cancer in an Immunocompetent Mouse Model

Ovarian cancers (OCs) are the most lethal gynaecological malignancy, with high levels of relapse and acquired chemo-resistance. Whilst the tumour⁻immune nexus controls both cancer progression and regression, the lack of an appropriate system to accurately model tumour stage and immune status has hampered the validation of clinically relevant immunotherapies and therapeutic vaccines to date. To address this need, we stably integrated the near-infrared phytochrome iRFP720 at the ROSA26 genomic locus of ID8 mouse OC cells. Intrabursal ovarian implantation into C57BL/6 mice, followed by regular, non-invasive fluorescence imaging, permitted the direct visualization of tumour mass and distribution over the course of progression. Four distinct phases of tumour growth and dissemination were detectable over time that closely mimicked clinical OC progression. Progression-related changes in immune cells also paralleled typical immune profiles observed in human OCs. Specifically, we observed changes in both the CD8+ T cell effector (Teff):regulatory (Treg) ratio, as well as the dendritic cell (DC)-to-myeloid derived suppressor cell (MDSC) ratio over time across multiple immune cell compartments and in peritoneal ascites. Importantly, iRFP720 expression had no detectible influence over immune profiles. This new model permits non-invasive, longitudinal tumour monitoring whilst preserving host⁻tumour immune interactions, and allows for the pre-clinical assessment of immune profiles throughout disease progression as well as the direct visualization of therapeutic responses. This simple fluorescence-based approach provides a useful new tool for the validation of novel immuno-therapeutics against OC.

Near-Infrared Fluorescent Proteins: Multiplexing and Optogenetics across Scales

Since mammalian tissue is relatively transparent to near-infrared (NIR) light, NIR fluorescent proteins (FPs) engineered from bacterial phytochromes have become widely used probes for non-invasive in vivo imaging. Recently, these genetically encoded NIR probes have been substantially improved, enabling imaging experiments that were not possible previously. Here, we discuss the use of monomeric NIR FPs and NIR biosensors for multiplexed imaging with common visible GFP-based probes and blue light-activatable optogenetic tools. These NIR probes are suitable for visualization of functional activities from molecular to organismal levels. In combination with advanced imaging techniques, such as two-photon microscopy with adaptive optics, photoacoustic tomography and its recent modification reversibly switchable photoacoustic computed tomography, NIR probes allow subcellular resolution at millimeter depths.

A novel osteoporosis model with ascorbic acid deficiency in Akr1A1 gene knockout mice

The AKR1A1 protein is a member of the aldo-keto reductase superfamily that is responsible for the conversion of D-glucuronate to L-gulonate in the ascorbic acid (vitamin C) synthesis pathway. In a pCAG-eGFP transgenic mouse line that was produced by pronuclear microinjection, the integration of the transgene resulted in a 30-kb genomic DNA deletion, including the Akr1A1 gene, and thus caused the knockout (KO) of the Akr1A1 gene and targeting of the eGFP gene. The Akr1A1 KO mice (Akr1A1eGFP/eGFP) exhibited insufficient serum ascorbic acid levels, abnormal bone development and osteoporosis. Using micro-CT analysis, the results showed that the microarchitecture of the 12-week-old Akr1A1eGFP/eGFP mouse femur was shorter in length and exhibited less cortical bone thickness, enlargement of the bone marrow cavity and a complete loss of the trabecular bone in the distal femur. The femoral head and neck of the proximal femur also showed a severe loss of bone mass. Based on the decreased levels of serum osteocalcin and osteoblast activity in the Akr1A1eGFP/eGFP mice, the osteoporosis might be caused by impaired bone formation. In addition, administration of ascorbic acid to the Akr1A1eGFP/eGFP mice significantly prevented the condition of osteoporotic femurs and increased bone formation. Therefore, through ascorbic acid administration, the Akr1A1 KO mice exhibited controllable osteoporosis and may serve as a novel model for osteoporotic research.

Bacterial Phytochromes, Cyanobacteriochromes and Allophycocyanins as a Source of Near-Infrared Fluorescent Probes

Bacterial photoreceptors absorb light energy and transform it into intracellular signals that regulate metabolism. Bacterial phytochrome photoreceptors (BphPs), some cyanobacteriochromes (CBCRs) and allophycocyanins (APCs) possess the near-infrared (NIR) absorbance spectra that make them promising molecular templates to design NIR fluorescent proteins (FPs) and biosensors for studies in mammalian cells and whole animals. Here, we review structures, photochemical properties and molecular functions of several families of bacterial photoreceptors. We next analyze molecular evolution approaches to develop NIR FPs and biosensors. We then discuss phenotypes of current BphP-based NIR FPs and compare them with FPs derived from CBCRs and APCs. Lastly, we overview imaging applications of NIR FPs in live cells and in vivo. Our review provides guidelines for selection of existing NIR FPs, as well as engineering approaches to develop NIR FPs from the novel natural templates such as CBCRs.

Simple generation of hairless mice for in vivo imaging

The in vivo imaging of mice makes it possible to analyze disease progress non-invasively through reporter gene expression. As the removal of hair improves the accuracy of in vivo imaging, gene-modified mice with a reporter gene are often crossed with Hos:HR-1 mutant mice homozygous for the spontaneous Hr^hr mutation that exhibit a hair loss phenotype. However, it is time consuming to produce mice carrying both the reporter gene and mutant Hr^hr gene by mating. In addition, there is a risk that genetic background of the gene-modified mice would be altered by mating. To resolve these issues, we established a simple method to generate hairless mice maintaining the original genetic background by CRISPR technology. First, we constructed the pX330 vector, which targets exon 3 of Hr. This DNA vector (5 ng/µl) was microinjected into the pronuclei of C57BL/6J mice. Induced Hr gene mutations were found in many founders (76.1%) and these mutations were heritable. Next, we performed in vivo imaging using these gene-modified hairless mice. As expected, luminescent objects in their body were detected by in vivo imaging. This study clearly showed that hairless mice could be simply generated by the CRISPR/Cas9 system, and this method may be useful for in vivo imaging studies with various gene-modified mice.

In Vivo Follow-up of Brain Tumor Growth via Bioluminescence Imaging and Fluorescence Tomography

Reporter gene-based strategies are widely used in experimental oncology. Bioluminescence imaging (BLI) using the firefly luciferase (Fluc) as a reporter gene and d-luciferin as a substrate is currently the most widely employed technique. The present paper compares the performances of BLI imaging with fluorescence imaging using the near infrared fluorescent protein (iRFP) to monitor brain tumor growth in mice. Fluorescence imaging includes fluorescence reflectance imaging (FRI), fluorescence diffuse ^optical tomography (fDOT), and fluorescence molecular Imaging (FMT^®). A U87 cell line was genetically modified for constitutive expression of both the encoding Fluc and iRFP reporter genes and assayed for cell, subcutaneous tumor and brain tumor imaging. On cultured cells, BLI was more sensitive than FRI; in vivo, tumors were first detected by BLI. Fluorescence of iRFP provided convenient tools such as flux cytometry, direct detection of the fluorescent protein on histological slices, and fluorescent tomography that allowed for 3D localization and absolute quantification of the fluorescent signal in brain tumors.