Time course of bioluminescent signal in orthotopic and heterotopic brain tumors in nude mice

Fast Ultrasound Scanning is a Rapid, Sensitive, Precise and Cost-Effective Method to Monitor Tumor Grafts in Mice

In preclinical studies, accurate monitoring of tumor dynamics is crucial for understanding cancer biology and evaluating therapeutic interventions. Traditional methods like caliper measurements and bioluminescence imaging (BLI) have limitations, prompting the need for improved imaging techniques. This study introduces a fast-scan high-frequency ultrasound (HFUS) protocol for the longitudinal assessment of syngeneic breast tumor grafts in mice, comparing its performance with caliper, BLI measurements and with histological analysis. The E0771 mammary gland tumor cell line, engineered to express luciferase, was orthotopically grafted into immunocompetent C57BL/6 mice. Tumor growth was monitored longitudinally at multiple timepoints using caliper measurement, HFUS, and BLI, with the latter two modalities assessed against histopathological standards post-euthanasia. The HFUS protocol was designed for rapid, anesthesia-free scanning, focusing on volume estimation, echogenicity, and necrosis visualization. All mice developed tumors, only 20.6% were palpable at day 4. HFUS detected tumors as small as 2.2 mm in average diameter from day 4 post-implantation, with an average scanning duration of 47 s per mouse. It provided a more accurate volume assessment than caliper, with a lower average bias relative to reference tumor volume. HFUS also revealed tumor necrosis, correlating strongly with BLI in terms of tumor volume and cellularity. Notable discrepancies between HFUS and BLI growth rates were attributed to immune cell infiltration. The fast HFUS protocol enables precise and efficient tumor assessment in preclinical studies, offering significant advantages over traditional methods in terms of speed, accuracy, and animal welfare, aligning with the 3R principle in animal research.

Expression of tdTomato and luciferase in a murine lung cancer alters the growth and immune microenvironment of the tumor

Imaging techniques based on fluorescence and bioluminescence have been important tools in visualizing tumor progression and studying the effect of drugs and immunotherapies on tumor immune microenvironment in animal models of cancer. However, transgenic expression of foreign proteins may induce immune responses in immunocompetent syngeneic tumor transplant models and augment the efficacy of experimental drugs. In this study, we show that the growth rate of Lewis lung carcinoma (LL/2) tumors was reduced after transduction of tdTomato and luciferase (tdTomato/Luc) compared to the parental cell line. tdTomato/Luc expression by LL/2 cells altered the tumor microenvironment by increasing tumor-infiltrating lymphocytes (TILs) while inhibiting tumor-induced myeloid-derived suppressor cells (MDSCs). Interestingly, tdTomato/Luc expression did not alter the response of LL/2 tumors to anti-PD-1 and anti-CTLA-4 antibodies. These results suggest that the use of tdTomato/Luc-transduced cancer cells to conduct studies in immune competent mice may lead to cell-extrinsic tdTomato/Luc-induced alterations in tumor growth and tumor immune microenvironment that need to be taken into consideration when evaluating the efficacy of anti-cancer drugs and vaccines in immunocompetent animal models.

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.

Replication Study: Biomechanical remodeling of the microenvironment by stromal caveolin-1 favors tumor invasion and metastasis

As part of the Reproducibility Project: Cancer Biology we published a Registered Report (Fiering et al., 2015) that described how we intended to replicate selected experiments from the paper 'Biomechanical remodeling of the microenvironment by stromal caveolin-1 favors tumor invasion and metastasis' (Goetz et al., 2011). Here we report the results. Primary mouse embryonic fibroblasts (pMEFs) expressing caveolin 1 (Cav1WT) demonstrated increased extracellular matrix remodeling in vitro compared to Cav1 deficient (Cav1KO) pMEFs, similar to the original study (Goetz et al., 2011). In vivo, we found higher levels of intratumoral stroma remodeling, determined by fibronectin fiber orientation, in tumors from cancer cells co-injected with Cav1WT pMEFs compared to cancer cells only or cancer cells plus Cav1KO pMEFs, which were in the same direction as the original study (Supplemental Figure S7C; Goetz et al., 2011), but not statistically significant. Primary tumor growth was similar between conditions, like the original study (Supplemental Figure S7Ca; Goetz et al., 2011). We found metastatic burden was similar between Cav1WT and Cav1KO pMEFs, while the original study found increased metastases with Cav1WT (Figure 7C; Goetz et al., 2011); however, the duration of our in vivo experiments (45 days) were much shorter than in the study by Goetz et al. (2011) (75 days). This makes it difficult to interpret the difference between the studies as it is possible that the cells required more time to manifest the difference between treatments observed by Goetz et al. We also found a statistically significant negative correlation of intratumoral remodeling with metastatic burden, while the original study found a statistically significant positive correlation (Figure 7Cd; Goetz et al., 2011), but again there were differences between the studies in terms of the duration of the metastasis studies and the imaging approaches that could have impacted the outcomes. Finally, we report meta-analyses for each result.

Dual-selective photodynamic therapy with a mitochondria-targeted photosensitizer and fiber optic cannula for malignant brain tumors

Among brain tumors, glioblastoma multiforme (GBM) is the most common and aggressive form (WHO grade IV) with a median survival of only 14.6 months in adults. Photodynamic therapy (PDT) is a combination of a photosensitizer (PS), light and molecular oxygen, and considered a promising treatment for GBM. Therapeutic outcomes of PDT rely on ROS generation in a tumor microenvironment, which can be controlled with dual selectivity by localization of the photosensitizer and confinement of light to the targeted tumor microenvironment. We previously demonstrated the photodynamic anticancer efficacy of mitochondrial-targeted photosensitizer-loaded albumin nanoparticles (PS@chol-BSA NPs). In this study, the photodynamic therapeutic effect of PS@chol-BSA NPs was further enhanced by confinement of light using a fiber optic cannula in orthotopic GBM-xenografted mice. In vitro cellular uptake and phototoxicity of PS@chol-BSA NPs were evaluated in brain tumor (U87MG) and endothelial (bEnd.3) cells. In vivo biodistribution was determined by an in vivo imaging system (IVIS) and the photodynamic efficacy was evaluated with confined laser irradiation. PS@chol-BSA NPs showed higher cellular uptake and phototoxicity in U87MG cells than in bEnd.3 cells. PS@chol-BSA NPs showed a brain tumor accumulation of 0.2%ID within 2 h and remain in the brain tumor for 22 h. When compared to the control group, there was remarkable suppression in tumor growth by laser irradiation with and without the fiber optic cannula at a dose of 1 mg kg^-1, in which significant tumor suppression up to 40% was observed with confined laser irradiation. Together, dual-selective photodynamic therapy with a mitochondria-targeted photosensitizer and fiber optic cannula provides a promising therapeutic strategy for malignant brain tumors.

Synergistic effects of tetrandrine combined with ionizing radiation on a murine colorectal carcinoma‑bearing mouse model

Tetrandrine (TET), a traditional Chinese clinical agent, has been used for the treatment of many diseases, including cancers. The purpose of the present study was to investigate the combined effects of TET and ionizing radiation (IR) on murine CT26 colorectal adenocarcinoma cells in vitro and in vivo. A CT26 cell line transfected with dual HSV-1 thymidine kinase and firefly luciferase (luc) reporter genes was used. The half-maximal inhibitory concentration (IC₅₀) of TET in CT26/tk-luc cells was ~10 µM. An additive effect was observed after combination of both agents based on a colony formation assay. Apoptosis and cleaved caspase-3 levels were increased significantly in cells after combination treatment, as shown by flow cytometric analysis, DNA fragmentation and western blotting. However, tumor growth inhibition and therapeutic efficacy of TET combined with IR in vivo were identified to be synergistic, as monitored by tumor growth delay time, measured with a digital caliper. A significant inhibition of tumor growth was identified in the combination group compared with the radiation only group. Furthermore, non-invasive bioluminescent imaging (BLI) and gamma scintigraphy were also used to evaluate therapeutic efficacy. Both modalities revealed that the best tumor growth control was under combination treatment among all groups. The present study demonstrated that TET is not only beneficial for chemotherapy, but also has potential as a radiosensitizer for the treatment of cancer.

CCL2/CCL5 secreted by the stroma induce IL-6/PYK2 dependent chemoresistance in ovarian cancer

BACKGROUND

Minimal residual disease is the main issue of advanced ovarian cancer treatment. According to the literature and previous results, we hypothesized that Mesenchymal Stromal Cells (MSC) could support this minimal residual disease by protecting ovarian cancer cells (OCC) from chemotherapy. In vitro study confirmed that MSC could induce OCC chemoresistance without contact using transwell setting. Further experiments showed that this induced chemoresistance was dependent on IL-6 OCC stimulation.

METHODS

We combined meticulous in vitro profiling and tumor xenograft models to study the role of IL-6 in MSC/OCC intereactions.

RESULTS

We demonstrated that Tocilizumab® (anti-IL-6R therapy) in association with chemotherapy significantly reduced the peritoneal carcinosis index (PCI) than chemotherapy alone in mice xenografted with OCCs+MSCs. Further experiments showed that CCL2 and CCL5 are released by MSC in transwell co-culture and induce OCCs IL-6 secretion and chemoresistance. Finally, we found that IL-6 induced chemoresistance was dependent on PYK2 phosphorylation.

CONCLUSIONS

These findings highlight the potential key role of the stroma in protecting minimal residual disease from chemotherapy, thus favoring recurrences. Future clinical trials targeting stroma could use anti-IL-6 therapy in association with chemotherapy.

Prediction of bioluminescent proteins by using sequence-derived features and lineage-specific scheme

Background

Bioluminescent proteins (BLPs) widely exist in many living organisms. As BLPs are featured by the capability of emitting lights, they can be served as biomarkers and easily detected in biomedical research, such as gene expression analysis and signal transduction pathways. Therefore, accurate identification of BLPs is important for disease diagnosis and biomedical engineering. In this paper, we propose a novel accurate sequence-based method named PredBLP (Prediction of BioLuminescent Proteins) to predict BLPs.

Results

We collect a series of sequence-derived features, which have been proved to be involved in the structure and function of BLPs. These features include amino acid composition, dipeptide composition, sequence motifs and physicochemical properties. We further prove that the combination of four types of features outperforms any other combinations or individual features. To remove potential irrelevant or redundant features, we also introduce Fisher Markov Selector together with Sequential Backward Selection strategy to select the optimal feature subsets. Additionally, we design a lineage-specific scheme, which is proved to be more effective than traditional universal approaches.

Conclusion

Experiment on benchmark datasets proves the robustness of PredBLP. We demonstrate that lineage-specific models significantly outperform universal ones. We also test the generalization capability of PredBLP based on independent testing datasets as well as newly deposited BLPs in UniProt. PredBLP is proved to be able to exceed many state-of-art methods. A web server named PredBLP, which implements the proposed method, is free available for academic use.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-017-1709-6) contains supplementary material, which is available to authorized users.

Development of an inducible mouse model of iRFP713 to track recombinase activity and tumour development in vivo

While the use of bioluminescent proteins for molecular imaging is a powerful technology to further our understanding of complex processes, fluorescent labeling with visible light fluorescent proteins such as GFP and RFP suffers from poor tissue penetration and high background autofluorescence. To overcome these limitations, we generated an inducible knock-in mouse model of iRFP713. This model was used to assess Cre activity in a Rosa Cre-ER background and quantify Cre activity upon different tamoxifen treatments in several organs. We also show that iRFP can be readily detected in 3D organoid cultures, FACS analysis and in vivo tumour models. Taken together we demonstrate that iRFP713 is a progressive step in in vivo imaging and analysis that widens the optical imaging window to the near-infrared spectrum, thereby allowing deeper tissue penetration, quicker image acquisition without the need to inject substrates and a better signal to background ratio in genetically engineered mouse models (GEMMs).

Use of fluorescent proteins and color-coded imaging to visualize cancer cells with different genetic properties

Fluorescent proteins are very bright and available in spectrally-distinct colors, enable the imaging of color-coded cancer cells growing in vivo and therefore the distinction of cancer cells with different genetic properties. Non-invasive and intravital imaging of cancer cells with fluorescent proteins allows the visualization of distinct genetic variants of cancer cells down to the cellular level in vivo. Cancer cells with increased or decreased ability to metastasize can be distinguished in vivo. Gene exchange in vivo which enables low metastatic cancer cells to convert to high metastatic can be color-coded imaged in vivo. Cancer stem-like and non-stem cells can be distinguished in vivo by color-coded imaging. These properties also demonstrate the vast superiority of imaging cancer cells in vivo with fluorescent proteins over photon counting of luciferase-labeled cancer cells.

Application of GFP imaging in cancer

Multicolored proteins have allowed the color-coding of cancer cells growing in vivo and enabled the distinction of host from tumor with single-cell resolution. Non-invasive imaging with fluorescent proteins enabled the dynamics of metastatic cancer to be followed in real time in individual animals. Non-invasive imaging of cancer cells expressing fluorescent proteins has allowed the real-time determination of efficacy of candidate antitumor and antimetastatic agents in mouse models. The use of fluorescent proteins to differentially label cancer cells in the nucleus and cytoplasm can visualize the nuclear-cytoplasmic dynamics of cancer cells in vivo including: mitosis, apoptosis, cell-cycle position, and differential behavior of nucleus and cytoplasm that occurs during cancer-cell deformation and extravasation. Recent applications of the technology described here include linking fluorescent proteins with cell-cycle-specific proteins such that the cells change color from red to green as they transit from G1 to S phases. With the macro- and micro-imaging technologies described here, essentially any in vivo process can be imaged, giving rise to the new field of in vivo cell biology using fluorescent proteins.

Conventional in vivo irradiation procedures are insufficient to accurately determine tumor responses to non-uniform radiation fields

PURPOSE

To determine differences in overall tumor responses measured by volumetric assessment and bioluminescence imaging (BLI) following exposure to uniform and non-uniform radiation fields in an ectopic prostate tumor model.

MATERIALS AND METHODS

Bioluminescent human prostate tumor xenografts were established by subcutaneous implantation into male mice. Tumors were irradiated with uniform or non-uniform field configurations using conventional in vivo irradiation procedures performed using a 225 kVp generator with custom lead shielding. Tumor responses were measured using Vernier calipers and by BLI using an in vivo imaging system. Survival was defined as the time to quadroupling of pre-treatment tumor volume.

RESULTS

The correlation between BLI and tumor volume measurements was found to be different for un-irradiated (R = 0.61), uniformly irradiated (R = 0.34) and partially irradiated (R = 0.30) tumors. Uniformly irradiated tumors resulted in an average tumor growth delay of 60 days with median survival of 75 days, compared to partially irradiated tumors which showed an average growth delay of 24 days and median survival of 38 days.

CONCLUSIONS

Correlation between BLI and tumor volume measurements is lower for partially irradiated tumors than those exposed to uniform dose distributions. The response of partially irradiated tumors suggests non-uniformity in response beyond physical dose distribution within the target volume. Dosimetric uncertainty associated with conventional in vivo irradiation procedures prohibits their ability to accurately determine tumor response to non-uniform radiation fields and stresses the need for image guided small animal radiation research platforms.

Cellular uptake and cytotoxicity of a near-IR fluorescent corrole-TiO2 nanoconjugate

We are investigating the biological and biomedical imaging roles and impacts of fluorescent metallocorrole-TiO2 nanoconjugates as potential near-infrared optical contrast agents in vitro in cancer and normal cell lines. The TiO2 nanoconjugate labeled with the small molecule 2,17-bis(chlorosulfonyl)-5,10,15-tris(pentafluorophenyl)corrolato aluminum(III) (1-Al-TiO2) was prepared. The nanoparticle 1-Al-TiO2 was characterized by transmission electron microscopy (TEM) and integrating-sphere electronic absorption spectroscopy. TEM images of three different samples of TiO2 nanoparticles (bare, H2O2 etched, and 1-Al functionalized) showed similarity in shapes and sizes with an average diameter of 29nm for 1-Al-TiO2. Loading of 1-Al on the TiO2 surfaces was determined to be ca. 20-40mg 1-Al/g TiO2. Confocal fluorescence microscopy (CFM) studies of luciferase-transfected primary human glioblastoma U87-Luc cells treated with the nanoconjugate 1-Al-TiO2 as the contrast agent in various concentrations were performed. The CFM images revealed that 1-Al-TiO2 was found inside the cancer cells even at low doses (0.02-2μg/mL) and localized in the cytosol. Bioluminescence studies of the U87-Luc cells exposed to various amounts of 1-Al-TiO2 showed minimal cytotoxic effects even at higher doses (2-2000μg/mL) after 24h. A similar observation was made using primary mouse hepatocytes (PMH) treated with 1-Al-TiO2 at low doses (0.0003-3μg/mL). Longer incubation times (after 48 and 72h for U87-Luc) and higher doses (>20μg/mL 1-Al-TiO2 for U87-Luc and >3μg/mL 1-Al-TiO2 for PMH) showed decreased cell viability.

Optogenetic inhibition of neurons by internal light production

Optogenetics is an extremely powerful tool for selective neuronal activation/inhibition and dissection of neural circuits. However, a limitation of in vivo optogenetics is that an animal must be tethered to an optical fiber for delivery of light. Here, we describe a new method for in vivo, optogenetic inhibition of neural activity using an internal, animal-generated light source based on firefly luciferase. Two adeno-associated viruses encoding luciferase were tested and both produced concentration-dependent light after administration of the substrate, luciferin. Mice were co-infected with halorhodopsin- and luciferase-expressing viruses in the striatum, and luciferin administration significantly reduced Fos activity compared to control animals infected with halorhodopsin only. Recordings of neuronal activity in behaving animals confirmed that firing was greatly reduced after luciferin administration. Finally, amphetamine-induced locomotor activity was reduced in halorhodopsin/luciferase mice pre-injected with luciferin compared to controls. This demonstrates that virally encoded luciferase is able to generate sufficient light to activate halorhodopsin and suppress neural activity and change behavior. This approach could be used to generate inhibition in response to activation of specific molecular pathways.

Curcumin synergistically enhances the radiosensitivity of human oral squamous cell carcinoma via suppression of radiation-induced NF-κB activity

The anticancer effect of curcumin has been widely reported. However, whether curcumin can enhance the radiosensitivity of human oral squamous cell carcinoma (OSCC) remains to be elucidated. The aim of the present study was to evaluate the efficacy of curcumin combined with radiation against OSCC. SAS cells were transfected with the luciferase gene (luc) and named SAS/luc. NF-κB/DNA binding activity, the surviving fraction and NF-κB-regulated effector protein expression were determined by electrophoretic mobility shift assay, clonogenic survival assay and western blotting, respectively. The therapeutic efficacy was evaluated in SAS/luc tumor-bearing mice by caliper measurement and bioluminescence imaging. Curcumin enhanced SAS/luc radiosensitivity through the inhibition of radiation-induced NF-κB activity and expression of effector proteins both in vitro and in vivo. With 4 Gy or greater radiation doses, synergistic effects of curcumin were observed. The combination group (curcumin plus radiation) had significantly better tumor control compared with that of curcumin or radiation alone. No significant body weight change of mice was found throughout the entire study. In conclusion, curcumin is a radiosensitizer against OSCC with negligible toxicity.

Quantitative bioluminescence imaging of transgene expression in intact porcine antral follicles in vitro

BACKGROUND

The porcine oocyte maturation in vivo occurs within the ovarian follicle and is regulated by the interactions between oocytes and surrounding follicular components, including theca, granulosa, and cumulus cells, and follicular fluid. Therefore, the antral follicle is an essential microenvironment for efficient oocyte maturation and its developmental competence. Quantitative bioluminescence imaging of firefly luciferase reporter genes in an intact antral follicle would allow investigation of changes in cellular and molecular events and in the context of the whole follicles. In this study, we investigate factors influencing bioluminescence measurements as a first step towards developing a new bioluminescence imaging system for intact antral follicles.

METHODS

We analyzed the time course of bioluminescence emitted from transfected living intact follicles using a cationic lipid mediated gene transfer method with increasing doses (1-3 μg) of firefly luciferase reporter gene (pGL4). In addition, a standard luciferase assay was used to confirm the luciferase expression in granulosa cells in the transfected intact antral follicles. Finally, the dose effects of substrate, D-luciferin, were determined for optimal quantitative bioluminescence imaging of intact porcine antral follicles in vitro.

RESULTS

The level of luciferase activity of follicles with 3 μg pGL4 was significantly (P < 0.05) greater than the 1 μg and 2 μg groups at 1 min after D-luciferin injection. The bioluminescence intensity of transfected follicles reached a peak at 1 min, and then it was significantly (P < 0.05) reduced within 2 min after injection of D-luciferin; with the level of bioluminescence emission remained constant from 2.5 to 10 min. The bioluminescence emission was maximal with 300 μg of D-luciferin.

CONCLUSIONS

The results of this study suggested that the investigation of factors influencing bioluminescence measurements is a critical step toward developing a new bioluminescence imaging model. This study is the first to demonstrate that reporter genes can be transferred to intact granulosa cells with a lipid-mediated gene transfer method within intact follicles in vitro, and the level of transgene expression can be assessed by bioluminescence imaging in living intact antral follicles.

Low magnification confocal microscopy of tumor angiogenesis

Blood vessels are critical to normal mammalian development, tissue repair, and growth and treatment of cancer. Mouse research models enable mechanistic studies of blood vessels. We detail how to perfuse mice with fluorescent tomato lectin or the lipophilic fluorophore DiI. We provide details on how to image fluorescently labeled blood vessels.

Imageable clinically relevant mouse models of metastasis

In the past 10 years, we have developed a new approach to the development of a clinically accurate rodent model for human cancer based on our invention of surgical orthotopic implantation (SOI). The SOI models have been described in approx. 70 publications and in 4 patents.*SOI allows human tumors of all the major types of human cancer to reproduce clinical like tumor growth and metastasis in the transplanted rodents. The major features of the SOI models are reviewed here and also compared to transgenic mouse models of cancer.

In vivo imaging of trypanosome-brain interactions and development of a rapid screening test for drugs against CNS stage trypanosomiasis

HUMAN AFRICAN TRYPANOSOMIASIS (HAT) MANIFESTS IN TWO STAGES OF DISEASE: firstly, haemolymphatic, and secondly, an encephalitic phase involving the central nervous system (CNS). New drugs to treat the second-stage disease are urgently needed, yet testing of novel drug candidates is a slow process because the established animal model relies on detecting parasitemia in the blood as late as 180 days after treatment. To expedite compound screening, we have modified the GVR35 strain of Trypanosoma brucei brucei to express luciferase, and have monitored parasite distribution in infected mice following treatment with trypanocidal compounds using serial, non-invasive, bioluminescence imaging. Parasites were detected in the brains of infected mice following treatment with diminazene, a drug which cures stage 1 but not stage 2 disease. Intravital multi-photon microscopy revealed that trypanosomes enter the brain meninges as early as day 5 post-infection but can be killed by diminazene, whereas those that cross the blood-brain barrier and enter the parenchyma by day 21 survived treatment and later caused bloodstream recrudescence. In contrast, all bioluminescent parasites were permanently eliminated by treatment with melarsoprol and DB829, compounds known to cure stage 2 disease. We show that this use of imaging reduces by two thirds the time taken to assess drug efficacy and provides a dual-modal imaging platform for monitoring trypanosome infection in different areas of the brain.

Orthotopic mouse models expressing fluorescent proteins for cancer drug discovery

IMPORTANCE OF THE FIELD

Currently used rodent tumor models, including transgenic tumor models, or subcutaneously growing human tumors in immunodeficient mice, do not sufficiently represent clinical cancer, especially with regard to metastasis and drug sensitivity.

AREAS COVERED IN THIS REVIEW

To obtain clinically accurate models, we have developed the technique of surgical orthotopic implantation (SOI) to transplant histologically intact fragments of human cancer, including tumors taken directly from the patient, to the corresponding organ of immunodeficient rodents. SOI allows the growth and metastatic potential of the transplanted tumors to be expressed and reflects clinical cancer of all types. Effective drugs can be discovered and evaluated in the SOI models utilizing human tumor cell lines and patient tumors. Visualization of many aspects of cancer initiation and progression in vivo has been achieved with fluorescent proteins. Tumors and metastases in the SOI models that express fluorescent proteins can be visualized noninvasively in intact animals, greatly facilitating drug discovery.

WHAT THE READER WILL GAIN

This review will provide information on the imageable mouse models of cancer that are clinically relevant, especially regarding metastasis and their use for drug discovery and evaluation.

TAKE HOME MESSAGE

SOI mouse models of cancer reproduce the features of clinical cancer.

Orthotopic glioblastoma stem-like cell xenograft model in mice to evaluate intra-arterial delivery of bevacizumab: from bedside to bench

Bevacizumab (BV), a humanized monocolonal antibody directed against vascular endothelial growth factor (VEGF), is a standard intravenous (IV) treatment for recurrent glioblastoma multiforme (GBM), that has been introduced recently as an intra-arterial (IA) treatment modality in humans. Since preclinical models have not been reported, we sought to develop a tumor stem cell (TSC) xenograft model to investigate IA BV delivery in vivo. Firefly luciferase transduced patient TSC were injected into the cortex of 35 nude mice. Tumor growth was monitored weekly using bioluminescence imaging. Mice were treated with either intraperitoneal (IP) or IA BV, with or without blood-brain barrier disruption (BBBD), or with IP saline injection (controls). Tumor tissue was analyzed using immunohistochemistry and western blot techniques. Tumor formation occurred in 31 of 35 (89%) mice with a significant signal increase over time (p=0.018). Post mortem histology revealed an infiltrative growth of TSC xenografts in a similar pattern compared to the primary human GBM. Tumor tissue analyzed at 24 hours after treatment revealed that IA BV treatment with BBBD led to a significantly higher intratumoral BV concentration compared to IA BV alone, IP BV or controls (p<0.05). Thus, we have developed a TSC-based xenograft mouse model that allows us to study IA chemotherapy. However, further studies are needed to analyze the treatment effects after IA BV to assess tumor progression and overall animal survival.

Live cell imaging in live animals with fluorescent proteins

The discovery, cloning, and characterization of GFP and related proteins of many colors have enabled live cell imaging to an unprecedented extent and resolution. Essentially, any cellular process can be imaged with a fluorescent protein. These proteins serve as genetic reporters and therefore can be used to follow cellular processes over indefinite periods in vivo as well as in vitro. The brightness and specific spectra of fluorescent proteins allow them to be imaged in vivo, using specific filters, without interference from autofluorescence. This chapter describes the development of live imaging in live animals with subcellular resolution, emphasizing the study of in vivo cell biology of cancer growth, spread, and metastasis.

Transgenic nude mouse with green fluorescent protein expression-based human glioblastoma multiforme animal model with EGFR expression and invasiveness

Previously, we developed an orthotopic xenograft model of human glioblastoma multiforme (GBM) with high EGFR expression and invasiveness in Balb/c nu/nu nude mice. Now we also developed the same orthotopic xenograft model in transgenic nude mice with green fluorescent protein (GFP) expression. The present orthotopic xenografts labeled by phycoerythrin fluorescing red showed high EGFR expression profile, and invasive behavior under a bright green-red dual-color fluorescence background. A striking advantage in the present human GBM model is that the change of tumor growth can be observed visually instead of sacrificing animals in our further antitumor therapy studies.

Novel cell lines established from pediatric brain tumors

The paucity of cell culture models for childhood brain tumors prompted us to establish pediatric cell lines for use in biological experiments and preclinical developmental therapeutic studies. Three cell lines were established, CHLA-200 (GBM), CHLA-259 (anaplastic medulloblastoma) and CHLA-266 (atypical teratoid rhabdoid tumor, AT/RT). Consistent with an AT/RT origin, CHLA-266 lacked INI1 expression and had monosomy 22. All lines had unique DNA short tandem repeat "fingerprints" matching that of the patient's tumor tissue and were adherent on tissue culture plastic, but differed in morphology and doubling times. CHLA-200 had a silent mutation in TP53. CHLA-259 and CHLA-266 had wild-type TP53. All three lines were relatively resistant to multiple drugs when compared to the DAOY medulloblastoma cell line, using the DIMSCAN fluorescence digital image microscopy cytotoxicity assay. RNA expression of MYC and MYCN were quantified using RT-PCR (Taqman). CHLA-200 expressed MYC, DAOY and CHLA-259 expressed MYCN, and CHLA-266 expressed both MYCN and MYC. CHLA-200 was only tumorigenic subcutaneously, but CHLA-259 and CHLA-266 were tumorigenic both subcutaneously and in brains of NOD/SCID mice. Immunohistochemistry of the xenografts revealed GFAP staining in CHLA-200 and PGP 9.5 staining in CHLA-259 and CHLA-266 tumors. As expected, INI1 expression was lacking in CHLA-266 (AT/RT). These three new cell lines will provide useful models for research of pediatric brain tumors.

DNA nanoparticles: detection of long-term transgene activity in brain using bioluminescence imaging

In this study, we used bioluminescence imaging (BLI) to track long-term transgene activity following the transfection of brain cells using a nonviral gene therapy technique. Formulations of deoxyribonucleic acid (DNA) combined with 30-mer lysine polymers (substituted with 10 kDa polyethylene glycol) form nanoparticles that transfect brain cells in vivo and produce transgene activity. Here we show that a single intracerebral injection of these DNA nanoparticles (DNPs) into the rat cortex, striatum, or substantia nigra results in long-term and persistent luciferase transgene activity over an 8- to 11-week period as evaluated by in vivo BLI analysis, and single injections of DNPs into the mouse striatum showed stable luciferase transgene activity for 1 year. Compacted DNPs produced in vivo signals 7- to 34-fold higher than DNA alone. In contrast, ex vivo BLI analysis, which is subject to less signal quenching from surrounding tissues, demonstrated a DNP to DNA alone ratio of 76- to 280-fold. Moreover, the ex vivo BLI analysis confirmed that signals originated from the targeted brain structures. In summary, BLI permits serial analysis of luciferase transgene activity at multiple brain locations following gene transfer with DNPs. Ex vivo analysis may permit more accurate determination of relative activities of gene transfer vectors.

Tumor imaging with multicolor fluorescent protein expression

Imaging with fluorescent proteins has been revolutionary and has led to the new field of in vivo cell biology. Many new applications of this technology have been developed. Green fluorescent protein (GFP)-labeled or red fluorescent protein (RFP)-labeled HT-1080 human fibrosarcoma cells were used to determine clonality of metastasis by imaging of metastatic colonies after mixed implantation of the red and green fluorescent cells. Resulting pure red or pure green colonies were scored as clonal, whereas mixed yellow colonies were scored as nonclonal. Dual-color fluorescent cancer cells expressing GFP in the nucleus and RFP in the cytoplasm were engineered. The dual-color cancer cells enable real-time nuclear-cytoplasmic dynamics to be visualized in living cells in vivo, including mitosis and apoptosis. The nuclear and cytoplasmic behavior of dual-color cancer cells in real time in blood vessels was observed as they trafficked by various means or extravasated in an abdominal skin flap. Dual-color cancer cells were also visualized trafficking through lymphatic vessels where they were imaged via a skin flap. Seeding and arresting of single dual-color cancer cells in the lung, accumulation of cancer-cell emboli, cancer-cell viability, and metastatic colony formation were imaged in real time in an open-chest nude mouse model using assisted ventilation. Novel treatment was evaluated in these imageable models. UVC irradiation killed approximately 70% of the dual-color cancer cells in a nude mouse model. An RFP-expressing glioma was transplanted to the spinal cord of transgenic nude mice expressing nestin-driven green fluorescent protein (ND-GFP). In ND-GFP mice, GFP is expressed in nascent blood vessels and neural stem cells. ND-GFP cells staining positively for neuronal class III-β-tubulin or CD31 surrounded the tumor, suggesting that the tumor stimulated both neurogenesis and angiogenesis. The tumor caused paralysis and also metastasized to the brain. The Salmonella typhimurium A1-R tumor-targeting bacterial strain was administered in the orthotopic spinal cord glioma model. The treated animals had a significant increase in survival and decrease in paralysis. S. typhimurium A1-R was effective against primary bone tumor and lung metastasis expressing RFP in a nude mouse model. S. typhimurium A1-R was effective against both axillary lymph and popliteal lymph node metastases of human dual-color pancreatic cancer and fibrosarcoma cells, respectively, as well as lung metastasis of the fibrosarcoma in nude mice. Imaging with fluorescent proteins will reveal mechanisms of cancer progression and provide visual targets for novel therapeutics.

Luciferase expression and bioluminescence does not affect tumor cell growth in vitro or in vivo

Live animal imaging is becoming an increasingly common technique for accurate and quantitative assessment of tumor burden over time. Bioluminescence imaging systems rely on a bioluminescent signal from tumor cells, typically generated from expression of the firefly luciferase gene. However, previous reports have suggested that either a high level of luciferase or the resultant light reaction produced upon addition of D-luciferin substrate can have a negative influence on tumor cell growth. To address this issue, we designed an expression vector that allows simultaneous fluorescence and luminescence imaging. Using fluorescence activated cell sorting (FACS), we generated clonal cell populations from a human breast cancer (MCF-7) and a mouse melanoma (B16-F10) cell line that stably expressed different levels of luciferase. We then compared the growth capabilities of these clones in vitro by MTT proliferation assay and in vivo by bioluminescence imaging of tumor growth in live mice. Surprisingly, we found that neither the amount of luciferase nor biophotonic activity was sufficient to inhibit tumor cell growth, in vitro or in vivo. These results suggest that luciferase toxicity is not a necessary consideration when designing bioluminescence experiments, and therefore our approach can be used to rapidly generate high levels of luciferase expression for sensitive imaging experiments.

Therapeutic efficacy evaluation of curcumin on human oral squamous cell carcinoma xenograft using multimodalities of molecular imaging

Oral squamous cell carcinoma (OSCC) is the most common malignancy of the oral cavity; however the treatment approaches are still unsatisfactory. We used a luciferase-transfected animal model to evaluate the therapeutic effects of curcumin. Human oral squamous cell carcinoma SAS cell line was stably transfected with luc gene, named SAS/luc cells. For the in vivo study, they were inoculated subcutaneously to 6-week-old male NOD/SCID mice which were separated into four groups for intraperitoneal injection (i.p.) of curcumin: control, daily with 35 mg/kg, 70 mg/kg every 2 days, and 100 mg/kg every 3 days. We applied SAS/luc bearing animal model and bioluminescent imaging (BLI) to study the inhibition effect of curcumin on tumor growth. The cytotoxic effect of curcumin on SAS/luc cells was mainly at G2/M phase and a significant dose dependent increase of the apoptotic SAS/luc cells as represented by sub-G1 phase was shown. Therapeutic efficacy evaluated by both caliper assay and BLI showed a significant difference between curcumin-treated mice and the controls (p < 0.01). The significant inhibition effects of curcumin on the proliferation and the growth of human OSCC are observed both in vitro and in vivo. No significant body weight change (i.e. within 20%) was observed in all SAS/luc-bearing mice with or without curcumin treatment. This SAS/luc human OSCC bearing animal model combined with multimodalities of molecular imaging permits a sensitive and non-invasive approach to evaluate the therapeutic efficacy in vivo.

Bioluminescence imaging of invasive intracranial xenografts: implications for translational research and targeted therapeutics of brain tumors

Despite decades of study, the etiology of brain cancer remains elusive. However, extensive molecular characterization of primary brain tumors has been accomplished, outlining recurrent features that are proving useful for devising targeted therapies. There are far too few patients available for comparing the efficacy of therapeutic combinations, especially when variations in dosing, frequency, and sequencing are taken into account. Consequently, there is a substantial need for increasing preclinical testing throughput using clinically relevant models. We review luminescent optical imaging for its potential in facilitating in vivo assessment of intracranial tumor growth and response to therapy in rodent orthotopic xenograft models of primary brain malignancies. We review the rationale behind the need of an in vivo model, why orthotopic tumor models displaying an invasive phenotype may be a superior choice when compared to flank-implanted tumors, and what advantages may be drawn from the use of modified cells, suitable for sequential monitoring by in vivo optical imaging. Studies show that luminescent signal correlates highly both with tumor burden and Kaplan-Meier survival curves of rodents bearing intracranial xenografts. We conclude that bioluminescent imaging is a highly sensitive technique for assessment of tumor burden, response to therapy, tumor recurrence, and behavior to salvage therapy, making it a superior option for longitudinal monitoring in intracranial rodent models of primary brain tumors.

Timing of imaging after d-luciferin injection affects the longitudinal assessment of tumor growth using in vivo bioluminescence imaging

The peak signal or the signal at a predetermined, fixed time point after D-luciferin injection may be used for the quantitative analysis of in vivo bioluminescence imaging. We repeatedly performed sequential bioluminescence imaging after subcutaneous injection of D-luciferin in mice bearing subcutaneous tumors. The peak time in each measurement became shorter early after cell inoculation, presumably due to gradual establishment of intratumoral vasculature, and reached a plateau of about 10 min on day 10. Although the correlation between the signal at a fixed time point and the peak signal was high, the signal at 5 or 10 min normalized for the peak signal was lower for earlier days, which caused overestimation of tumor growth. The time course of the signals after D-luciferin injection may vary with time after cell inoculation, and this variation should be considered when determining the imaging protocol for quantitative bioluminescence tumor monitoring.

Firefly luciferase-based dynamic bioluminescence imaging: a noninvasive technique to assess tumor angiogenesis

OBJECTIVE

Bioluminescence imaging (BLI) is emerging as a cost-effective, high-throughput, noninvasive, and sensitive imaging modality to monitor cell growth and trafficking. We describe the use of dynamic BLI as a noninvasive method of assessing vessel permeability during brain tumor growth.

METHODS

With the use of stereotactic technique, 10 firefly luciferase-transfected GL26 mouse glioblastoma multiforme cells were injected into the brains of C57BL/6 mice (n = 80). After intraperitoneal injection of D-luciferin (150 mg/kg), serial dynamic BLI was performed at 1-minute intervals (30 seconds exposure) every 2 to 3 days until death of the animals. The maximum intensity was used as an indirect measurement of tumor growth. The adjusted slope of initial intensity (I90/Im) was used as a proxy to monitor the flow rate of blood into the vascular tree. Using a modified Evans blue perfusion protocol, we calculated the relative permeability of the vascular tree at various time points.

RESULTS

Daily maximum intensity correlated strongly with tumor volume. At postinjection day 23, histology and BLI demonstrated an exponential growth of the tumor mass. Slopes were calculated to reflect the flow in the vessels feeding the tumor (adjusted slope = I90/Im). The increase in BLI intensity was correlated with a decrease in adjusted slope, reflecting a decrease in the rate of blood flow as tumor volume increased (y = 93.8e-0.49, R2 = 0.63). Examination of calculated slopes revealed a peak in permeability around postinjection day 20 (n = 42, P < .02 by 1-way analysis of variance) and showed a downward trend in relation to both postinjection day and maximum intensity observed; as angiogenesis progressed, tumor vessel caliber increased dramatically, resulting in sluggish but increased flow. This trend was correlated with Evans blue histology, revealing an increase in Evans blue dye uptake into the tumor, as slope calculated by BLI increases.

CONCLUSION

Dynamic BLI is a practical, noninvasive technique that can semiquantitatively monitor changes in vascular permeability and therefore facilitate the study of tumor angiogenesis in animal models of disease.

Novel cancer vaccine based on genes of Salmonella pathogenicity island 2

Although tumors express potentially immunogenic tumor-associated antigens (TAAs), cancer vaccines often fail because of inadequate antigen delivery and/or insufficient activation of innate immunity. Engineering nonpathogenic bacterial vectors to deliver TAAs of choice may provide an efficient way of presenting TAAs in an immunogenic form. In this study, we used genes of Salmonella pathogenicity island 2 (SPI2) to construct a novel cancer vaccine in which a TAA, survivin, was fused to SseF effector protein and placed under control of SsrB, the central regulator of SPI2 gene expression. This construct uses the type III secretion system (T3SS) of Salmonella and allows preferential delivery of tumor antigen into the cytosol of antigen-presenting cells for optimal immunogenicity. In a screen of a panel of attenuated strains of Salmonella, we found that a double attenuated strain of Salmonella typhimurium, MvP728 (purD/htrA), was not toxic to mice and effectively expressed and translocated survivin protein inside the cytosol of murine macrophages. We also found that a ligand for CD1d-reactive natural killer T (NKT) cells, alpha-glucuronosylceramide (GSL1), enhanced MvP728-induced interleukin-12 production in human dendritic cells and that in vivo coadministration of a NKT ligand with MvP728-Llo or MvP728-survivin enhanced effector-memory cytotoxic T lymphocyte (CTL) responses. Furthermore, combined use of MvP728-survivin with GSL1 produced antitumor activity in mouse models of CT26 colon carcinoma and orthotopic DBT glioblastoma. Therefore, the use of TAA delivery via SPI-2-regulated T3SS of Salmonella and NKT ligands as adjuvants may provide a foundation for new cancer vaccines.

A transgenic red fluorescent protein-expressing nude mouse for color-coded imaging of the tumor microenvironment

The tumor microenvironment (TME) is critical for tumor growth and progression. We have previously developed color-coded imaging of the TME using a green fluorescent protein (GFP) transgenic nude mouse as a host. However, most donor sources of cell types appropriate for study in the TME are from mice expressing GFP. Therefore, a nude mouse expressing red fluorescent protein (RFP) would be an appropriate host for transplantation of GFP-expressing stromal cells as well as double-labeled cancer cells expressing GFP in the nucleus and RFP in the cytoplasm, thereby creating a three-color imaging model of the TME. The RFP nude mouse was obtained by crossing non-transgenic nude mice with the transgenic C57/B6 mouse in which the beta-actin promoter drives RFP (DsRed2) expression in essentially all tissues. In crosses between nu/nu RFP male mice and nu/+ RFP female mice, the embryos fluoresced red. Approximately 50% of the offspring of these mice were RFP nude mice. In the RFP nude mouse, the organs all brightly expressed RFP, including the heart, lungs, spleen, pancreas, esophagus, stomach, duodenum, the male and female reproductive systems; brain and spinal cord; and the circulatory system, including the heart, and major arteries and veins. The skinned skeleton highly expressed RFP. The bone marrow and spleen cells were also RFP positive. GFP-expressing human cancer cell lines, including HCT-116-GFP colon cancer and MDA-MB-435-GFP breast cancer were orthotopically transplanted to the transgenic RFP nude mice. These human tumors grew extensively in the transgenic RFP nude mouse. Dual-color fluorescence imaging enabled visualization of human tumor-host interaction. The RFP nude mouse model should greatly expand our knowledge of the TME.

Evaluation of bioluminescent imaging for noninvasive monitoring of colorectal cancer progression in the liver and its response to immunogene therapy

Background

Bioluminescent imaging (BLI) is based on the detection of light emitted by living cells expressing a luciferase gene. Stable transfection of luciferase in cancer cells and their inoculation into permissive animals allows the noninvasive monitorization of tumor progression inside internal organs. We have applied this technology for the development of a murine model of colorectal cancer involving the liver, with the aim of improving the pre-clinical evaluation of new anticancer therapies.

Results

A murine colon cancer cell line stably transfected with the luciferase gene (MC38Luc1) retains tumorigenicity in immunocompetent C57BL/6 animals. Intrahepatic inoculation of MC38Luc1 causes progressive liver infiltration that can be monitored by BLI. Compared with ultrasonography (US), BLI is more sensitive, but accurate estimation of tumor mass is impaired in advanced stages. We applied BLI to evaluate the efficacy of an immunogene therapy approach based on the liver-specific expression of the proinflammatory cytokine interleukin-12 (IL-12). Individualized quantification of light emission was able to determine the extent and duration of antitumor responses and to predict long-term disease-free survival.

Conclusion

We show that BLI is a rapid, convenient and safe technique for the individual monitorization of tumor progression in the liver. Evaluation of experimental treatments with complex mechanisms of action such as immunotherapy is possible using this technology.

Validation of bioluminescent imaging techniques

Bioluminescence imaging (BLI) is frequently cited for its ease of quantification. This fundamental strength of BLI has led to applications in cancer research, cell transplantation, and monitoring of infectious disease in which bioluminescence intensity is correlated with other metrics. However, bioluminescence measurements can be influenced by a number of factors, among them source location, tissue optical properties, and substrate availability and pharmacokinetics. Accounting for these many factors is crucial for accurate BLI quantification. A number of methods can be employed to ensure correct interpretation of BLI results and validate BLI techniques. This chapter summarizes the use of calibrated light-emitting standards, bioluminescence tomography, and post-mortem validation of luciferase expression for validating quantitative BLI measurements.

Noninvasive bioluminescent imaging of infections

Traditional studies of viral and bacterial infection and pathogenesis have generally relied on animal models that require the sacrifice of infected animals to determine viral or bacterial distributions and titers. The recent application of the in vivo bioluminescence imaging (BLI) to monitor the replication and tropism of pathogens expressing the luciferase (from firefly or Renilla) reporter proteins has been recently developed. This technology do not requires the sacrifice of the experimental animals, where the in vivo bioluminescence emissions in living animals permit the tracking of the infection. It has been demonstrated that the in vivo BLI is comparable to the classical approaches as measurements of in vitro light emission in organs of sacrificed animals. Moreover, molecular techniques such as PCR determinations show parallel results in pathogen quantification, where the concentrations of microbial DNA measured correlated with the magnitude of bioluminescence in vivo, and with the photon flux determined by the in vitro luciferase enzyme assay. These results show that BLI can be used for noninvasive, real-time monitoring of several infections of pathogens in living animals, supplying a new methodology in the study of pathogens in addition to conventional techniques for the characterization of infections.

A quantitative study of factors affecting in vivo bioluminescence imaging

In vivo bioluminescence imaging (BLI) has the advantages of high sensitivity and low background. By counting the number of photons emitted from a specimen, BLI can quantify biological events such as tumour growth, gene expression and drug response. The intensities and kinetics of the BL signal are affected by many factors and may confound the quantitative results acquired from consecutive imaging sessions or different specimens. We used three different mouse models of tumours to examine whether anaesthetics, positioning and tumour growth may affect the consistency of the BL signal. The results showed that BLI signal could be affected by different anaesthetics and repetitive positioning. Using the same anaesthetics produced consistent peak times, while other factors were held constant. However, as the tumours grew the peak times shifted and the time course of BL signals had different shapes, depending on the positioning of the mice. The data indicate that a carefully designed BLI experiment is required to generate optimal and consistent results.

Whole animal in vivo imaging after transient, nonviral gene delivery to the rat central nervous system

We previously showed that a vector:lipid delivery system, comprised of a plasmid DNA vector and cationic lipid (lipoplex), when injected into the cerebrospinal fluid (CSF) of rats can deliver reporter genes in vivo efficiently and with widespread expression to the Central Nervous System (CNS). To further characterize this delivery system, we now present experiments that demonstrate the in vivo time-to-peak expression of the reporter gene, firefly luciferase. We infused a formulated lipoplex containing the lipid MLRI [dissymmetric myristoyl (14:0) and lauroyl (12:1) rosenthal inhibitor-substituted compound formed from the tetraalkylammonium glycerol-based DORI] and pNDluc, a luciferase vector, into CSF in the cisterna magna (CM) of the rat. Luciferase activity was followed over time by bioluminescence imaging after injection of luciferin. Our results show that luciferase activity in the CNS of rats is widespread, peaks 72 hours after injection into CM and can be detected in vivo for at least 7-10 days after peak expression. We further show that in contrast to injection into CSF, enzyme activity is not widely distributed after injection of the vector into brain parenchyma, emphasizing the importance of CSF delivery to achieve widespread vector distribution. Finally, we confirm the distribution of firefly luciferase in brain by immunohistochemical staining from an animal that was euthanized at the peak of enzyme expression.

Molecular imaging of metastatic potential

If molecular imaging is to prove clinically useful it will have to surpass current, primarily anatomic techniques in terms of sensitivity and the ability to detect minimal changes in tissue. One of the most important tests for molecular imaging is to determine whether it can image the metastatic potential of tumors. Like all predictive endeavors, the imaging of such "potential" is a daunting task, but one that only molecular imaging--rather than standard, anatomic techniques--is likely to solve. Although difficult, imaging of metastatic potential is also arguably the most important task for molecular imaging of cancer because it is generally the dissemination of malignant tissue, not its prolonged residence in an inopportune site, which kills the patient. Below are examples of uses of molecular imaging of metastases as well as of metastatic potential, the former being a far more developed area of clinical inquiry.

Successful inhibition of intracranial human glioblastoma multiforme xenograft growth via systemic adenoviral delivery of soluble endostatin and soluble vascular endothelial growth factor receptor-2: laboratory investigation

OBJECT

Glioblastoma multiforme (GBM) is characterized by neovascularization, raising the question of whether angiogenic blockade may be a useful therapeutic strategy for this disease. It has been suggested, however, that, to be useful, angiogenic blockade must be persistent and at levels sufficient to overcome proangiogenic signals from tumor cells. In this report, the authors tested the hypothesis that sustained high concentrations of 2 different antiangiogenic proteins, delivered using a systemic gene therapy strategy, could inhibit the growth of established intracranial U87 human GBM xenografts in nude mice.

METHODS

Mice harboring established U87 intracranial tumors received intravenous injections of adenoviral vectors encoding either the extracellular domain of vascular endothelial growth factor receptor-2-Fc fusion protein (Ad-VEGFR2-Fc) alone, soluble endostatin (Ad-ES) alone, a combination of Ad-VEGFR2-Fc and Ad-ES, or immunoglobulin 1-Fc (Ad-Fc) as a control.

RESULTS

Three weeks after treatment, magnetic resonance imaging-based determination of tumor volume showed that treatment with Ad-VEGFR2-Fc, Ad-ES, or Ad-VEGFR2-Fc in combination with Ad-ES, produced 69, 59, and 74% growth inhibition, respectively. Bioluminescent monitoring of tumor growth revealed growth inhibition in the same treatment groups to be 62, 74, and 72%, respectively. Staining with proliferating cell nuclear antigen and with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling showed reduced tumor cell proliferation and increased apoptosis in all antiangiogenic treatment groups.

CONCLUSIONS

These results suggest that systemic delivery and sustained production of endostatin and soluble VEGFR2 can slow intracranial glial tumor growth by both reducing cell proliferation and increasing tumor apoptosis. This work adds further support to the concept of using antiangiogenesis therapy for intracranial GBM.

Hypoxia-induced human endonuclease G expression suppresses tumor growth in a xenograft model

We have developed a hypoxia-inducible gene therapy approach for the expression of the mature form of human endonuclease G to facilitate cell death in hypoxic regions of the tumor. The chimeric therapeutic gene is placed under the control of a hypoxia response element based promoter and contains a translocation motif linked in frame to an oxygen-dependent degradation domain and the endonuclease G gene. Transient expression of the chimeric therapeutic gene in breast and prostate cancer cell lines resulted in efficient cell death under hypoxia-mimetic conditions. Stable MDA-MB-435 cells expressing the chimeric therapeutic gene under 1% O2 showed an increase in stable HIF-1alpha protein levels and synthesis of the endonuclease G protein in a time-dependent manner. In normoxic conditions, these stable transgenic cells exhibited no change in growth rate, invasion and motility when compared to parental cells. Moreover, xenografts generated using the transgenic cells exhibited highly significant suppression of tumor growth in a preclinical cancer model compared to the parental cell line. Thus, the hypoxia-modulated endonuclease G expression has the potential to be used as a gene-based-therapy system to kill malignant cells within hypoxic regions of tumors.

Effects of the time dependence of a bioluminescent source on the tomographic reconstruction

There are two goals in this simulation study: (1) to show that the time variation of the bioluminescence source can cause artifacts in the tomographic images such that quantification and localization becomes impossible; and (2) to show that the a priori knowledge of the light kinetics can be used to eliminate these artifacts. These goals are motivated by the fact that the half-life of luciferase has been reported as 30 min to 2 h in vivo. We perform two-dimensional simulations. We consider a 40 mm diameter circular region with an inclusion of 6 mm diameter located 10 mm away from the center. The measurement data is simulated using a finite-element-based forward solver. We model the noncontact measurements such that four-wavelength data is collected from four 90 degrees apart views. The results show that the ratio of the total imaging time to the half-life of the exponentially decaying bioluminescent source is the deciding factor in the reconstruction of the source. It is also demonstrated that a priori knowledge of the source kinetics is required to perform tomographic bioluminescence imaging of short half-life bioluminescent sources and the use of spatial a priori information alone is not adequate.

Noninvasive molecular neuroimaging using reporter genes: part II, experimental, current, and future applications

SUMMARY

In this second article, we review the various strategies and applications that make use of reporter genes for molecular imaging of the brain in living subjects. These approaches are emerging as valuable tools for monitoring gene expression in diverse applications in laboratory animals, including the study of gene-targeted and trafficking cells, gene therapies, transgenic animals, and more complex molecular interactions within the central nervous system. Further development of more sensitive and selective reporters, combined with improvements in detection technology, will consolidate the position of in vivo reporter gene imaging as a versatile technique for greater understanding of intracellular biologic processes and underlying molecular neuropathology and will potentially establish a future role in the clinical management of patients with neurologic diseases.

Recent advances on in vivo imaging with fluorescent proteins

In vivo imaging with green fluorescent protein (GFP) and other fluorescent proteins is revolutionizing cancer biology and other fields of in vivo biology (Hoffman, 2005; Hoffman and Yang, 2006a,b,c). Our laboratory pioneered the use of GFP for in vivo imaging in 1997 (Chishima et al., 1997). This chapter highlights recent developments from our laboratory on both macro and micro in vivo imaging by using fluorescent proteins.