Transgenic nude mouse with ubiquitous green fluorescent protein expression as a host for human tumors

A Novel Ex Vivo Tumor Spheroid-Tissue Model for Investigating Microvascular Remodeling and Lymphatic Blood Vessel Plasticity

Biomimetic tumor microenvironment models bridge the gap between in vitro and in vivo systems and serve as a useful way to address the modeling challenge of how to recreate the cell and system complexity associated with real tissues. Our laboratory has developed an ex vivo rat mesentery culture model, which allows for simultaneous investigation of blood and lymphatic microvascular network remodeling in an intact tissue environment. Given that angiogenesis and lymphangiogenesis are key contributors to the progression of cancer, the objective of this study was to combine tissue and tumor spheroid culture methods to establish a novel ex vivo tumor spheroid-tissue model by verifying its use for evaluating the effects of cancer cell behavior on the local microvascular environment. H1299 or A549 tumor spheroids were formed via hanging drop culture and seeded onto rat mesenteric tissues harvested from adult male Wistar rats. Tissues with transplanted spheroids were cultured in serum-free media for 3 to 5 days. PECAM, NG2, CD11b, and αSMA labeling identified endothelial cells, pericytes, immune cells, and smooth muscle cells, respectively. Time-lapse imaging confirmed cancer cell type specific migration. In addition to increasing PECAM positive capillary sprouting and LYVE-1 positive endothelial cell extensions indicative of lymphangiogenesis, tumor spheroid presence induced the formation of lymphatic/blood vessel connections and the formation of hybrid, mosaic vessels that were characterized by discontinuous LYVE-1 labeling. The results support the application of a novel tumor spheroid microenvironment model for investigating cancer cell-microvascular interactions.

Color-Coded Imaging of the Tumor Microenvironment (TME) in Human Patient-Derived Orthotopic Xenograft (PDOX) Mouse Models

The tumor microenvironment (TME) contains stromal cells in a complex interaction with cancer cells. This relationship has become better understood with the use of fluorescent proteins for in vivo imaging, originally developed by our laboratories. Spectrally distinct fluorescent proteins can be used for color-coded imaging of the complex interaction of the tumor microenvironment in the living state using cancer cells expressing a fluorescent protein of one color and host mice expressing another color fluorescent protein. Cancer cells engineered in vitro to express a fluorescent protein were orthotopically implanted into transgenic mice expressing a fluorescent protein of a different color. Confocal microscopy was then used for color-coded imaging of the TME. Color-coded imaging of the TME has enabled us to discover that stromal cells are necessary for metastasis. Patient-derived orthotopic xenograft (PDOX) tumors were labeled by first passaging them orthotopically through transgenic nude mice expressing either green, red, or cyan fluorescent protein in order to label the stromal cells of the tumor. The colored stromal cells become stably associated with the PDOX tumors through multiple passages in transgenic colored nude mice or noncolored nude mice. The fluorescent protein-expressing stromal cells included cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Using this model, specific cancer cell or stromal cell targeting by potential therapeutics can be visualized. Color-coded imaging enabled the visualization of apparent fusion of cancer and stromal cells. Color-coded imaging is a powerful tool visualizing the interaction of cancer and stromal cells during cancer progression and treatment.

3D tumor angiogenesis models: recent advances and challenges

The development of blood vessels, referred to as angiogenesis, is an intricate process regulated spatially and temporally through a delicate balance between the qualitative and quantitative expression of pro and anti-angiogenic molecules. As angiogenesis is a prerequisite for solid tumors to grow and metastasize, a variety of tumor angiogenesis models have been formulated to better understand the underlying mechanisms and associated clinical applications. Studies have demonstrated independent mechanisms inducing angiogenesis in tumors such as (a) HIF-1/VEGF mediated paracrine interactions between a cancer cell and endothelial cells, (b) recruitment of progenitor endothelial cells, and (c) vasculogenic mimicry. Moreover, single-cell sequencing technologies have indicated endothelial cell heterogeneity among organ systems including tumor tissues. However, existing angiogenesis models often rely upon normal endothelial cells which significantly differ from tumor endothelial cells exhibiting distinct (epi)genetic and metabolic signatures. Besides, the existence of intra-individual variations necessitates the development of improved tumor vascular model systems for personalized medicine. In the present review, we summarize recent advancements of 3D tumor vascular model systems which include (a) tissue engineering-based tumor models; (b) vascular organoid models, and (c) organ-on-chips and their importance in replicating the tumor angiogenesis along with the associated challenges to design improved models.

Hyperthermia generated by magnetic nanoparticles for effective treatment of disseminated peritoneal cancer in an orthotopic nude-mouse model

Magnetic hyperthermia (MHT), which combines magnetic nanoparticles (MNPs) with an alternating magnetic field (AMF), holds promise as a cancer therapy. There have been many studies about hyperthermia, most of which have been performed by direct injection of MNPs into tumor tissues. However, there have been no reports of treating peritoneal disseminated disease with MHT to date. In the present study, we treated peritoneal metastasis of gastric cancer with MHT using superparamagnetic iron oxide (Fe3O4) nanoparticle (SPION) coated with carboxydextran as an MNP, in an orthotopic mouse model mimicking early peritoneal disseminated disease of gastric cancer. SPIONs of an optimal size were intraperitoneally administered, and an AMF (390 kHz, 28 kAm-1) was applied for 10 minutes, four times every three days. Three weeks after the first MHT treatment, the peritoneal metastases were significantly inhibited compared with the AMF-alone group or the untreated-control group. The results of the present study show that MHT can be applied as a new treatment option for disseminated peritoneal gastric cancer.Abbreviations: AMF: alternating magnetic field; Cy1: cytology-positive; DMEM: Dulbecco's Modified Eagle's Medium; FBS: fetal bovine serum; H&E: hematoxylin and eosin; HIPEC: hyperthermic intraperitoneal chemotherapy; MEM: Minimum Essential Medium; MHT: magnetic hyperthermia; MNPs: magnetic nanoparticles; P0: macroscopic peritoneal dissemination; RFP: red fluorescent protein; SPION: superparamagnetic iron oxide (Fe3O4) nanoparticle.

Color-Coded Imaging of Cancer and Stromal-Cell Interaction in the Pancreatic-Cancer Tumor Microenvironment (TME)

The tumor microenvironment (TME) contains stromal cells in a complex interaction with cancer cells. This relationship has become better understood with the use of fluorescent proteins for in vivo imaging, originally developed by our laboratories. Spectrally-distinct fluorescent proteins can be used for color-coded imaging of the complex interaction of the tumor microenvironment in the living state using cancer cells expressing a fluorescent protein of one color and host mice expressing another-color fluorescent protein. Cancer cells engineered in vitro to express a fluorescent protein were orthotopically implanted into transgenic mice expressing a fluorescent protein of a different color. Confocal microscopy was then used for color-coded imaging of the TME. Color-coded imaging of the TME has enabled us to discover that stromal cells are necessary for metastasis. Patient-derived orthotopic xenograft (PDOX) tumors were labeled by first passaging them orthotopically through transgenic nude mice expressing either green, red, or cyan fluorescent protein in order to label the stromal cells of the tumor (Yang et al., Cancer Res 64:8651-8656, 2004; Yang et al. J Cell Biochem 106: 279-284, 2009). The colored stromal cells become stably associated with the PDOX tumors through multiple passages in transgenic colored nude mice or non-colored nude mice. The fluorescent protein-expressing stromal cells included cancer-associated fibroblasts and tumor-associated macrophages. Color-coded imaging enabled the visualization of apparent fusion of cancer and stromal cells. Color-coded imaging is a powerful tool visualizing the interaction of cancer and stromal cells during cancer progression and treatment.

Novel enhanced GFP-positive congenic inbred strain establishment and application of tumor-bearing nude mouse model

Transgenic GFP gene mice are widely used. Given the unique advantages of immunodeficient animals in the field of oncology research, we aim to establish a nude mouse inbred strain that stably expresses enhanced GFP (EGFP) for use in transplanted tumor microenvironment (TME) research. Female C57BL/6-Tg(CAG-EGFP) mice were backcrossed with male BALB/c nude mice for 11 generations. The genotype and phenotype of novel inbred strain Foxn1nu .B6-Tg(CAG-EGFP) were identified by biochemical loci detection, skin transplantation and flow cytometry. PCR and fluorescence spectrophotometry were performed to evaluate the relative expression of EGFP in different parts of the brain. Red fluorescence protein (RFP) gene was stably transfected into human glioma stem cells (GSC), SU3, which were then transplanted intracerebrally or ectopically into Foxn1nu .B6-Tg(CAG-EGFP) mice. Cell co-expression of EGFP and RFP in transplanted tissues was further analyzed with the Live Cell Imaging System (Cell'R, Olympus) and FISH. The inbred strain Foxn1nu .B6-Tg(CAG-EGFP) shows different levels of EGFP expression in brain tissue. The hematological and immune cells of the inbred strain mice were close to those of nude mice. EGFP was stably expressed in multiple sites of Foxn1nu .B6-Tg(CAG-EGFP) mice, including brain tissue. With the dual-fluorescence tracing transplanted tumor model, we found that SU3 induced host cell malignant transformation in TME, and tumor/host cell fusion. In conclusion, EGFP is differentially and widely expressed in brain tissue of Foxn1nu .B6-Tg(CAG-EGFP), which is an ideal model for TME investigation. With Foxn1nu .B6-Tg(CAG-EGFP) mice, our research demonstrated that host cell malignant transformation and tumor/host cell fusion play an important role in tumor progression.

Temozolomide and Pazopanib Combined with FOLFOX Regressed a Primary Colorectal Cancer in a Patient-derived Orthotopic Xenograft Mouse Model

Purpose: The goal of the present study was to determine the efficacy of temozolomide (TEM) and pazopanib (PAZ) combined with FOLFOX (oxaliplatin, leucovorin and 5-fluorouracil) on a colorectal cancer patient-derived orthotopic xenograft (PDOX) mouse model. Materials and Methods: A colorectal cancer tumor from a patient previously established in non-transgenic nude mice was implanted subcutaneously in transgenic green fluorescence protein (GFP)-expressing nude mice in order to label the tumor stromal cells with GFP. Then labeled tumors were orthotopically implanted into the cecum of nude mice. Mice were randomized into four groups: Group 1, untreated control; group 2, TEM + PAZ; group 3, FOLFOX; group 4, TEM + PAZ plus FOLFOX. Tumor width, length, and mouse body weight were measured weekly. The Fluor Vivo imaging System was used to image the GFP-lableled tumor stromal cells in vivo. H&E staining and immunohistochemical staining were used for histological analysis. Results: All three treatments inhibited tumor growth as compared to the untreated control group. The combination of TEM + PAZ + FOLFOX regressed tumor growth significantly more effectively than TEM + PAZ or FOLFOX. Only the combination of TEM + PAZ + FOLFOX group caused a decrease in body weight. PAZ suppressed lymph vessels density in the colorectal cancer PDOX mouse model suggesting inhibition of lymphangiogenesis. Conclusion: Our results suggest that the combination of TEM + PAZ + FOLFOX has clinical potential for colorectal cancer patient.

Application of Highly Immunocompromised Mice for the Establishment of Patient-Derived Xenograft (PDX) Models

Patient-derived xenograft (PDX) models are created by engraftment of patient tumor tissues into immunocompetent mice. Since a PDX model retains the characteristics of the primary patient tumor including gene expression profiles and drug responses, it has become the most reliable in vivo human cancer model. The engraftment rate increases with the introduction of Non-obese diabetic Severe combined immunodeficiency (NOD/SCID)-based immunocompromised mice, especially the NK-deficient NOD strains NOD/SCID/interleukin-2 receptor gamma chain(IL2Rγ)null (NOG/NSG) and NOD/SCID/Jak3(Janus kinase 3)null (NOJ). Success rates differ with tumor origin: gastrointestinal tumors acquire a higher engraftment rate, while the rate is lower for breast cancers. Subcutaneous transplantation is the most popular method to establish PDX, but some tumors require specific environments, e.g., orthotropic or renal capsule transplantation. Human hormone treatment is necessary to establish hormone-dependent cancers such as prostate and breast cancers. PDX mice with human hematopoietic and immune systems (humanized PDX) are powerful tools for the analysis of tumor-immune system interaction and evaluation of immunotherapy response. A PDX biobank equipped with patients' clinical data, gene-expression patterns, mutational statuses, tumor tissue architects, and drug responsiveness will be an authoritative resource for developing specific tumor biomarkers for chemotherapeutic predictions, creating individualized therapy, and establishing precise cancer medicine.

Real-Time Determination of the Cell-Cycle Position of Individual Cells within Live Tumors Using FUCCI Cell-Cycle Imaging

Most cytotoxic agents have limited efficacy for solid cancers. Cell-cycle phase analysis at the single-cell level in solid tumors has shown that the majority of cancer cells in tumors is not cycling and is therefore resistant to cytotoxic chemotherapy. Intravital cell-cycle imaging within tumors demonstrated the cell-cycle position and distribution of cancer cells within a tumor, and cell-cycle dynamics during chemotherapy. Understanding cell-cycle dynamics within tumors should provide important insights into novel treatment strategies.

Surface-Modified Macrophages Facilitate Tracking of Breast Cancer-Immune Interactions

The immune system has been found to play key roles in cancer development and progression. Macrophages are typically considered to be pro-inflammatory cells but can also facilitate pro-oncogenic activities via associations with tumors and metastases. The study of macrophages and their interactions within the context of cancer microenvironments is stymied by the lack of a system to track them. We present a cell-based strategy for studying cancer-immune cell interactions by chemically modifying the surfaces of macrophages with fluorophores. Two widely used methods are employed, affecting cell surface proteins and glycans via NHS-ester and Staudinger ligation reactions, respectively. We show that these modifications do not interfere with macrophage responses to chemoattractants and that interactions with cancer cells can be readily monitored. This work describes the development of macrophage-based imaging agents for tumor detection and assessment of interactions between immune cells and cancers.

Advantages of patient-derived orthotopic mouse models and genetic reporters for developing fluorescence-guided surgery

Fluorescence-guided surgery can enhance the surgeon's ability to achieve a complete oncologic resection. There are a number of tumor-specific probes being developed with many preclinical mouse models to evaluate their efficacy. The current review discusses the different preclinical mouse models in the setting of probe evaluation and highlights the advantages of patient-derived orthotopic xenografts (PDOX) mouse models and genetic reporters to develop fluorescence-guided surgery.

Immunogenic cancer cell death selectively induced by near infrared photoimmunotherapy initiates host tumor immunity

Immunogenic cell death (ICD) is a form of cell death that activates an adaptive immune response against dead-cell-associated antigens. Cancer cells killed via ICD can elicit antitumor immunity. ICD is efficiently induced by near-infrared photo-immunotherapy (NIR-PIT) that selectively kills target-cells on which antibody-photoabsorber conjugates bind and are activated by NIR light exposure. Advanced live cell microscopies showed that NIR-PIT caused rapid and irreversible damage to the cell membrane function leading to swelling and bursting, releasing intracellular components due to the influx of water into the cell. The process also induces relocation of ICD bio markers including calreticulin, Hsp70 and Hsp90 to the cell surface and the rapid release of immunogenic signals including ATP and HMGB1 followed by maturation of immature dendritic cells. Thus, NIR-PIT is a therapy that kills tumor cells by ICD, eliciting a host immune response against tumor.

Overexpression of integrin α11 induces cardiac fibrosis in mice

AIM

To understand the role of the collagen-binding integrin α11 in vivo, we have used a classical approach of creating a mouse strain overexpressing integrin α11. A transgenic mouse strain overexpressing α11 in muscle tissues was analysed in the current study with special reference to the heart tissue.

METHODS

We generated and phenotyped integrin α11 transgenic (TG) mice by echocardiography, magnetic resonance imaging and histology. Wild-type (WT) mice were subjected to aortic banding (AB) and the expression of integrin α11 was measured in flow cytometry-sorted cardiomyocytes and non-myocytes.

RESULTS

TG mice developed left ventricular concentric hypertrophy by 6 months, with increased collagen deposition and reactivation of mRNA encoding foetal genes associated with cardiovascular pathological remodelling compared to WT mice. Masson's trichrome staining revealed interstitial fibrosis, confirmed additionally by magnetic resonance imaging and was found to be most prominent in the cardiac septum of TG but not WT mice. TG hearts expressed increased levels of transforming growth factor-β2 and transforming growth factor-β3 and upregulated smooth muscle actin. Macrophage infiltration coincided with increased NF-κB signalling in TG but not WT hearts. Integrin α11 expression was increased in both cardiomyocytes and non-myocyte cells from WT AB hearts compared to sham-operated animals.

CONCLUSION

We report for the first time that overexpression of integrin α11 induces cardiac fibrosis and left ventricular hypertrophy. This is a result of changes in intracellular hypertrophic signalling and secretion of soluble factors that increase collagen production in the heart.

Generation and Application of Male Mice with Specific Expression of Green Fluorescent Protein in Germ Cells

PURPOSE

The study aimed to generate a mouse line with green fluorescent protein (GFP) specifically expressed in male germ cells to assess testicular toxicity.

PROCEDURES

The mouse line with GFP specifically expressed in male germ cells was generated by mating a germ cell-specific transgenic Cre male mouse with a double-fluorescent reporter female mouse using Cre/loxP. The mouse line was administered ethylene glycol monomethyl ether (EGME) by oral gavage. Then, the green fluorescence intensity in the testes was used as an indicator to examine the potential for testicular toxicity testing by molecular biology, histopathology, and in vivo imaging techniques.

RESULTS

Specific testicular GFP expression was observed in mice. GFP was mainly expressed in the germ cell lineage and concentrated in secondary spermatocytes/spermatocytes and spermatozoa. After administration of EGME, at the organ level, the green fluorescent intensity of the testes was decreased by 11 days and had disappeared by 34 days. Frozen testicular sections stained with DAPI showed significantly decreased green fluorescence in secondary spermatocytes and sperm cells. These observations were consistent with the testis weight and results of testicular histopathology.

CONCLUSIONS

With the application of in vivo imaging becoming popular, this mouse line with GFP specifically expressed in the male germ cells may have some advantages for the study of reproductive toxicity.

Genetic Recombination Between Stromal and Cancer Cells Results in Highly Malignant Cells Identified by Color-Coded Imaging in a Mouse Lymphoma Model

The tumor microenvironment (TME) promotes tumor growth and metastasis. We previously established the color-coded EL4 lymphoma TME model with red fluorescent protein (RFP) expressing EL4 implanted in transgenic C57BL/6 green fluorescent protein (GFP) mice. Color-coded imaging of the lymphoma TME suggested an important role of stromal cells in lymphoma progression and metastasis. In the present study, we used color-coded imaging of RFP-lymphoma cells and GFP stromal cells to identify yellow-fluorescent genetically recombinant cells appearing only during metastasis. The EL4-RFP lymphoma cells were injected subcutaneously in C57BL/6-GFP transgenic mice and formed subcutaneous tumors 14 days after cell transplantation. The subcutaneous tumors were harvested and transplanted to the abdominal cavity of nude mice. Metastases to the liver, perigastric lymph node, ascites, bone marrow, and primary tumor were imaged. In addition to EL4-RFP cells and GFP-host cells, genetically recombinant yellow-fluorescent cells, were observed only in the ascites and bone marrow. These results indicate genetic exchange between the stromal and cancer cells. Possible mechanisms of genetic exchange are discussed as well as its ramifications for metastasis. J. Cell. Biochem. 118: 4216-4221, 2017. © 2017 Wiley Periodicals, Inc.

Color-coded intravital imaging demonstrates a transforming growth factor-β (TGF-β) antagonist selectively targets stromal cells in a human pancreatic-cancer orthotopic mouse model

Pancreatic cancer is a recalcitrant malignancy, partly due to desmoplastic stroma which stimulates tumor growth, invasion, and metastasis, and inhibits chemotherapeutic drug delivery. Transforming growth factor-β (TGF-β) has an important role in the formation of stromal desmoplasia. The present study describes the ability of color-coded intravital imaging to demonstrate the efficacy of a TGF-β inhibitor to target stroma in an orthotopic mouse model of pancreatic cancer. The BxPC-3 human pancreatic adenocarcinoma cell line expressing green fluorescent protein (GFP), which also has a high TGF-β expression level, was used in an orthotopic model in transgenic nude mice ubiquitously expressing red fluorescent protein (RFP). Fourteen mice were randomized into a control group (n = 7, vehicle, i.p., weekly, for 3 weeks) and a treated group (n = 7, SB431542 [TGF-β receptor type I inhibitor] 0.3 mg, i.p., weekly, for 3 weeks). Stromal cells expressing RFP and cancer cells expressing GFP were observed weekly for 3 weeks by real-time color-coded intravital imaging. The RFP fluorescence area from the stromal cells, relative to the GFP fluorescence area of the cancer cells, was significantly decreased in the TGF-β-inhibitor-treatment group compared to the control group. The present study demonstrated color-coded imaging in an orthotopic pancreatic-cancer cell-line mouse model can readily detect the selective anti-stromal-cell targeting of a TGF-β inhibitor.

Imaging the microenvironment of pancreatic cancer patient-derived orthotopic xenografts (PDOX) growing in transgenic nude mice expressing GFP, RFP, or CFP

We have developed a multi-color, imageable, orthotopic mouse model for individual patients with pancreatic cancer. The tumors are labeled by first passaging them orthotopically through transgenic nude mice expressing green fluorescent protein (GFP), red fluorescent protein (RFP), or cyan fluorescent protein (CFP). Passage of the tumors in these colored transgenic mice labels the stromal cells of the tumor. The cancer cells in the PDOX are labeled in situ with GFP by telomerase-dependent adenovirus OBP-401. The models are termed imageable patient-derived orthotopic xenografts (iPDOX). The tumors acquired brightly-fluorescent stromal cells from the transgenic host mice, which were stably associated with the tumors through multiple passages. The colored fluorescent protein-expressing stromal cells included cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). This model enables powerful color-coded imaging of the interaction of cancer and stromal cells during tumor progression and treatment.

From Gene Targeting to Genome Editing: Transgenic animals applications and beyond

Genome modification technologies are powerful tools for molecular biology and related areas. Advances in animal transgenesis and genome editing technologies during the past three decades allowed systematic interrogation of gene function that can help model how the genome influences cellular physiology. Genetic engineering via homologous recombination (HR) has been the standard method to modify genomic sequences. Nevertheless, nuclease-guided genome editing methods that were developed recently, such as ZFN, TALEN and CRISPR/Cas, opened new perspectives for biomedical research. Here, we present a brief historical perspective of genome modification methods, focusing on transgenic mice models. Moreover, we describe how new techniques were discovered and improved, present the paradigm shifts and discuss their limitations and applications for biomedical research as well as possible future directions.

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.

Color-Coded Imaging of Breast Cancer Metastatic Niche Formation in Nude Mice

We report here a color-coded imaging model in which metastatic niches in the lung and liver of breast cancer can be identified. The transgenic green fluorescent protein (GFP)-expressing nude mouse was used as the host. The GFP nude mouse expresses GFP in all organs. However, GFP expression is dim in the liver parenchymal cells. Mouse mammary tumor cells (MMT 060562) (MMT), expressing red fluorescent protein (RFP), were injected in the tail vein of GFP nude mice to produce experimental lung metastasis and in the spleen of GFP nude mice to establish a liver metastasis model. Niche formation in the lung and liver metastasis was observed using very high resolution imaging systems. In the lung, GFP host-mouse cells accumulated around as few as a single MMT-RFP cell. In addition, GFP host cells were observed to form circle-shaped niches in the lung even without RFP cancer cells, which was possibly a niche in which future metastasis could be formed. In the liver, as with the lung, GFP host cells could form circle-shaped niches. Liver and lung metastases were removed surgically and cultured in vitro. MMT-RFP cells and GFP host cells resembling cancer-associated fibroblasts (CAFs) were observed interacting, suggesting that CAFs could serve as a metastatic niche.

Tumor imaging technologies in mouse models

In this chapter, we describe protocols for tumor imaging technologies in mouse models. These models utilize human cancer cell lines which have been genetically engineered to selectively express high levels of green fluorescent protein (GFP) or red fluorescent protein (RFP). Tumors with fluorescent genetic reporters are established subcutaneously in nude mice, and fragments of the subcutaneous tumors are then surgically transplanted onto the orthotopic organ. Locoregional tumor growth and distant metastasis of these orthotopic implants occur spontaneously and rapidly throughout the abdomen in a manner consistent with clinical human disease. Highly specific, high-resolution, real-time quantitative fluorescence imaging of tumor growth and metastasis may be achieved in vivo without the need for contrast agents, invasive techniques, or expensive imaging equipment. Transplantation of RFP-expressing tumor fragments onto the pancreas of GFP- or cyan fluorescent protein (CFP)-expressing transgenic nude mice was used to facilitate visualization of tumor-host interaction between the pancreatic cancer cells and host-derived stroma and vasculature. Such in vivo models have enabled us to visualize in real time and acquire images of the progression of pancreatic cancer in the live animal, and to demonstrate the real-time antitumor and antimetastatic effects of several novel therapeutic strategies on a variety of malignancies. We discuss studies from our laboratory that demonstrate that fluorescence imaging in mice is complementary to other modalities such as magnetic resonance imaging (MRI) or ultrasound. These fluorescent models are powerful and reliable tools with which to investigate metastatic human cancer and novel therapeutic strategies directed against it.

Glioma initiating cells contribute to malignant transformation of host glial cells during tumor tissue remodeling via PDGF signaling

INTRODUCTION

Glioma initiating cells (GICs) play important roles in tumor initiation and progression. However, interactions between tumor cells and host cells of local tumor microenvironment are kept largely unknown. Besides GICs and their progeny cells, whether adjacent normal glial cells contribute to tumorigenesis during glioma tissue remodeling deserves further investigation.

METHODS

Red fluorescence protein (RFP) gene was stably transfected into human GIC cells lines SU3 and U87, then were transplanted intracerebrally into athymic nude mice with whole-body green fluorescence protein (GFP) expression. The interactions between GICs and host cells in vivo were observed during tissue remodeling processes initiated by hGICs. The biological characteristics of host glial cells with high proliferation capability cloned from the xenograft were further assayed.

RESULTS

In a SU3 initiated dual-fluorescence xenograft glioma model, part of host cells cloned from the intracerebral tumors were found acquiring the capability of unlimited proliferation. PCR and FISH results indicated that malignant transformed cells were derived from host cells; cell surface marker analysis showed these cells expressed murine oligodendrocyte specific marker CNP, and oligodendrocyte progenitor cells (OPCs) specific markers PDGFR-α and NG2. Chromosomal analysis showed these cells were super tetraploid. In vivo studies showed they behaved with high invasiveness activity and nearly 100% tumorigenic ratio. Compared with SU3 cells with higher PDGF-B expression, GICs derived from U87 cells with low level of PDGF-B expression failed to induce host cell transformation.

CONCLUSIONS

Primary high invasive GICs SU3 contribute to transformation of adjacent normal host glial cells in local tumor microenvironment possibly via PDGF/PDGFR signaling activation, which deserved further investigation.

Conditioning solid tumor microenvironment through inflammatory chemokines and S100 family proteins

Recently, there has been growing attention to the role of the tumor microenvironment (TME) in cancer growth, metastasis and emergence of chemotherapy resistance. Stromal and tumor cells make up the TME and interact with each other through a complex cross-talk manner. This interaction is facilitated by a variety of growth factors, cytokines, chemokines and S100 proteins. In this review, we focus on chemokines and their cognate receptors in regulating the tumorigenic process. Chemokines are cytokines that have chemotactic potential. Chemokine receptors are expressed on tumor cells and stromal cells. Chemokines and their cognate receptors modulate tumor growth and metastasis in a paracrine and autocrine manner. They play a major role in the modulation of stromal cell recruitment, angiogenic potential, cancer cell proliferation, survival, adhesion, invasion and metastasis to distant sites. In addition, a new class of calcium binding family S100 proteins has been getting attention as they play significant roles in tumor progression and metastasis by modulating TME. Here, we highlight recent developments regarding the inflammatory chemokine/S100 protein systems in the TME. We also focus on how chemokines/S100 proteins, through their role in the TME, modulate cancer cell ability to grow, proliferate, invade and metastasize to different organs. This review highlights the possibility of using the chemokine/chemokine receptor axis as a promising strategy in cancer therapy, the current difficulties in achieving this goal, and how it could be overcome for successful future therapeutic intervention.

Tumor-targeting Salmonella typhimurium A1-R prevents experimental human breast cancer bone metastasis in nude mice

Bone metastasis is a lethal and morbid late stage of breast cancer that is currently treatment resistant. More effective mouse models and treatment are necessary. High bone-metastatic variants of human breast cancer cells were selected in nude mice by cardiac injection. After cardiac injection of a high bone-metastatic variant of breast cancer, all untreated mice had bone metastases compared to only 20% with parental cells. Treatment with tumor-targeting Salmonella typhimurium A1-R completely prevented the appearance of bone metastasis of the high metastatic variant in nude mice (P < 0.001). After injection of the highly bone-metastatic breast cancer variant to the tibia of nude mice, S. typhimurium A1-R treatment significantly reduced tumor growth in the bone (P < 0.001). These data indicated that S. typhimurium A1-R is useful to prevent and inhibit breast cancer bone metastasis and should be of future clinical use for breast cancer in the adjuvant setting.

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.

A novel GFP nude rat model to investigate tumor-stroma interactions

BACKGROUD

A key strategy for the study of the tumor microenvironment is to implant human tumor cells in an immunodeficient rodent strain ubiquitously expressing a fluorescent marker. Here, a novel nude rat expressing a green fluorescent protein (GFP) transgene was established and engrafted with primary human tumor tissue in order to separate tumor from stromal cell populations for subsequent molecular analysis.

METHODS

SD-TG (GFP) 2BalRrrc transgenic rats were crossed with HsdHan™: rnu/rnu Rowett nude rats to develop a GFP expressing immunocompromised rat. PCR and flow cytometry were used to follow the GFP genotype and phenotype in newborns. After three to four generations, animals were implanted with 4 T1 dsRed murine breast cancer cells or primary human glioblastoma (GBM) biopsies to generate xenografts for subsequent separation by fluorescence-activated cell sorting (FACS).

RESULTS

Fluorecence microscopy and reverse transcription-PCR demonstrated that GFP, under the control of the human ubiquitin C promoter, was stably maintained and expressed in diverse organs over several generations. Immunophenotyping of blood samples by flow cytometry confirmed that the immunodeficient features of the parental rat strain, HsdHan™: rnu/rnu, were retained in the GFP nude rat. Both the murine cell line and human GBM biopsies engrafted, and stromal cell populations were isolated from dissociated xenografts by FACS to > 95% purity.

CONCLUSIONS

A GFP transgene was stably introduced into a nude rat background in which human and murine cancer cells successfully engrafted. This animal strain provides a novel in vivo system for detailed cellular and molecular characterization of tumor-stroma interactions.

Development and Evaluation of Transgenic Nude Mice Expressing Ubiquitous Green Fluorescent Protein

PURPOSE

Researchers had developed and characterized transgenic green/red fluorescent protein (GFP/RFP) nude mouse with ubiquitous RFP or GFP expression, but none has evaluated the level of immune cells and expression levels of GFP in this model.

PROCEDURE

The nude GFP mice were evaluated by imaging, hematological indices, and flow cytometry to compare the proportion of immune T cells. Quantitative real-time PCR (qRT-PCR) was done for evaluating the relative expression of GFP transcripts in few organs of the nude GFP mice.

RESULTS

The hematological and immune cells of nude GFP were within the range of nude mice. However, the gene expression levels were relatively less in various tissues compared with B6 GFP mice.

CONCLUSIONS

These findings suggest that nude GFP is an ideal model resembling normal nude mice; however, GFP expression in various tissues by fluorescence should be considered, as the expression of GFP differs in various organs.

Biological ablation of sentinel lymph node metastasis in submucosally invaded early gastrointestinal cancer

Currently, early gastrointestinal cancers are treated endoscopically, as long as there are no lymph node metastases. However, once a gastrointestinal cancer invades the submucosal layer, the lymph node metastatic rate rises to higher than 10%. Therefore, surgery is still the gold standard to remove regional lymph nodes containing possible metastases. Here, to avoid prophylactic surgery, we propose a less-invasive biological ablation of lymph node metastasis in submucosally invaded gastrointestinal cancer patients. We have established an orthotopic early rectal cancer xenograft model with spontaneous lymph node metastasis by implantation of green fluorescent protein (GFP)-labeled human colon cancer cells into the submucosal layer of the murine rectum. A solution containing telomerase-specific oncolytic adenovirus was injected into the peritumoral submucosal space, followed by excision of the primary rectal tumors mimicking the endoscopic submucosal dissection (ESD) technique. Seven days after treatment, GFP signals had completely disappeared indicating that sentinel lymph node metastasis was selectively eradicated. Moreover, biologically treated mice were confirmed to be relapse-free even 4 weeks after treatment. These results indicate that virus-mediated biological ablation selectively targets lymph node metastasis and provides a potential alternative to surgery for submucosal invasive gastrointestinal cancer patients.

The tumor-educated-macrophage increase of malignancy of human pancreatic cancer is prevented by zoledronic acid

We previously defined macrophages harvested from the peritoneal cavity of nude mice with subcutaneous human pancreatic tumors as “tumor-educated-macrophages” (Edu) and macrophages harvested from mice without tumors as “naïve-macrophages” (Naïve), and demonstrated that Edu-macrophages promoted tumor growth and metastasis. In this study, Edu- and Naïve-macrophages were compared for their ability to enhance pancreatic cancer malignancy at the cellular level in vitro and in vivo. The inhibitory efficacy of Zoledronic acid (ZA) on Edu-macrophage-enhanced metastasis was also determined. XPA1 human pancreatic cancer cells in Gelfoam co-cultured with Edu-macrophages proliferated to a greater extent compared to XPA1 cells cultured with Naïve-macrophages (P = 0.014). XPA1 cells exposed to conditioned medium harvested from Edu culture significantly increased proliferation (P = 0.016) and had more migration stimulation capability (P<0.001) compared to cultured cancer cells treated with the conditioned medium from Naïve. The mitotic index of the XPA1 cells, expressing GFP in the nucleus and RFP in the cytoplasm, significantly increased in vivo in the presence of Edu- compared to Naïve-macrophages (P = 0.001). Zoledronic acid (ZA) killed both Edu and Naïve in vitro. Edu promoted tumor growth and metastasis in an orthotopic mouse model of the XPA1 human pancreatic cancer cell line. ZA reduced primary tumor growth (P = 0.006) and prevented metastasis (P = 0.025) promoted by Edu-macrophages. These results indicate that ZA inhibits enhanced primary tumor growth and metastasis of human pancreatic cancer induced by Edu-macrophages.

A novel EGFP-expressing nude mice with complete loss of lymphocytes and NK cells to study tumor-host interactions

Enhanced green fluorescent protein (EGFP) expressing Balb/c nude mice strain with Rag-2 and Jak3 double mutants (Nude-R/J-EGFP mice) was established to improve the take rate of human tumors and to distinguish tumor and host cells. EGFP was ubiquitously expressed in all organs including the brain, lung, liver, heart, kidney, spleen, and gastrointestinal tract in Nude-R/J-EGFP mice. The mice showed complete loss of T lymphocytes, B lymphocytes, and NK cells, indicating a higher take rate of human tumor xenograft. M213-mCherry, an mCherry expressing the cholangiocarcinoma cell line, was successfully detected and tumor vessels derived from the host were clearly identified with fluorescence imager. Thus, dual-color fluorescence imaging visualizes the tumor-host interaction by non-invasive in vivo fluorescent imaging in Nude-R/J-EGFP mice. These finding suggests that Nude-R/J-EGFP mice are becoming a powerful tool to investigate human tumor-host interactions.

Preclinical whole body time domain fluorescence lifetime multiplexing of fluorescent proteins

The application of time domain (TD) fluorescence lifetime multiplexing for the detection of fluorescent proteins (FPs) in whole animals, in the presence of a strong background tissue autofluorescence and excitation light leakage is discussed. Tissue autofluorescence (AF) exhibits a nonexponential temporal response, distinct from the mono-exponential decay of FPs. This allows a direct separation of FP fluorescence from AF using a dual basis function approach. We establish the detection limits of this approach using in vitro and in vivo measurements. We also demonstrate, using an experimental model of lymph node metastasis, that FP-AF lifetime multiplexing provides a greater than 30-fold improvement in contrast-to-background ratio compared with continuous wave data. In addition, we show that TD detection can simultaneously discriminate between up to three red shifted FPs placed under the skin of a nude mouse based on their distinct fluorescence lifetimes.

Color-coded fluorescence imaging of lymph-node metastasis, angiogenesis, and its drug-induced inhibition

Lymph nodes are often the first target of metastatic cancer which can then remetastasize to distant organs. The progression of lymph node metastasis is dependent on sufficient blood supply provided by angiogenesis. In the present study, we have developed a color-coded imaging model to visualize angiogenesis of lymph nodes metastasis using green fluorescent protein (GFP) and red fluorescent protein (RFP). Transgenic mice carrying GFP under the control of the nestin promoter (ND-GFP mice) were used as hosts. Nascent blood vessels express GFP in these mice. B16F10-RFP melanoma cells were injected into the efferent lymph vessel of the inguinal lymph node of the ND-GFP nude mice, whereby the melanoma cells trafficked to the axillary lymph node. Three days after melanoma implantation, ND-GFP-expressing nascent blood vessels were imaged in the axillary lymph nodes. Seven days after implantation, ND-GFP-expressing nascent blood vessels formed a network in the lymph nodes. ND-GFP-positive blood vessels surrounded the tumor mass by 14 days after implantation. However, by 28 days after implantation, ND-GFP expression was diminished as the blood vessels matured. Treatment with doxorubicin significantly decreased the mean nascent blood vessel length per tumor volume. These results show that the dual-color ND-GFP blood vessels/RFP-tumor model is a powerful tool to visualize and quantitate angiogenesis of metastatic lymph nodes as well as for evaluation of its inhibition.

Novel enhanced green fluorescent protein-expressing NOG mouse for analyzing the microenvironment of xenograft tissues

The interaction between transplanted cells and host tissues is important for the growth and maintenance of transplanted cells. To analyze the mechanisms of these interactions, a systemic fluorescent protein-expressing mouse is a useful recipient. In this study, we generated a novel NOG strain, which strongly expresses enhanced green fluorescent protein (EGFP; PgkEGFP-NOG), especially in the liver, kidney, gastrointestinal tract, and testis. Because the host tissues expressed EGFP, xenotransplanted human cancer cells were clearly identified as EGFP-negative colonies in PgkEGFP-NOG mice. Immunohistochemical analysis revealed that EGFP-expressing stromal tissues formed a complicated tumor microenvironment within xenograft tissues. Moreover, a similar microenvironment was observed in human iPS cell-derived teratomas. Collectively, these results indicated that a suitable microenvironment is essential for the growth and maintenance of xenotransplanted cells and that PgkEGFP-NOG mice represent a useful animal model for analyzing the mechanisms of microenvironment formation.

Nestin-expressing stem cells from the hair follicle can differentiate into motor neurons and reduce muscle atrophy after transplantation to injured nerves

We have previously shown that nestin-expressing hair follicle stem cells from the mouse and human are multipotent and can differentiate into many cell types, including neurons and glial cells. The nestin-expressing hair follicle stem cells can effect nerve and spinal cord repair upon transplantation in mouse models. In the present study, nestin-expressing hair follicle stem cells expressing red fluorescent protein (RFP) were induced by retinoic acid and fetal bovine serum to differentiate and then transplanted together with Matrigel into the transected distal sciatic or tibial nerve stump of transgenic nude mice ubiquitously expressing green fluorescent protein (GFP). Control mice were transplanted with Matrigel only. The transplanted cells appeared neuron like, with large round nuclei and long extensions. Immunofluorescence staining showed that some of the transplanted cells in the distal nerve stump expressed the neuron marker Tuj1 as well as motor neuron markers Isl 1/2 and EN1. These transplanted cells contacted each other as well as host nerve fibers. Two weeks post-transplantation, nerve fibers in the distal sciatic nerve stump of the transplanted mice had greater expression of motor neuron markers and neurotrophic factor-3 than those in the Matrigel-only transplanted mice. Muscle fiber areas in the nestin-expressing stem cell plus Matrigel-transplanted animals were much bigger than that in the Matrigel-only transplanted animals after 4 weeks. The present results suggest that transplanted nestin-expressing hair follicle stem cells can differentiate into motor neurons and reduce muscle atrophy after sciatic nerve transection. This study demonstrates a new and accessible neuron source to reduce muscle atrophy after nerve injury.

Breast cancer metastasis progression as revealed by intravital videomicroscopy

Metastasis is the spread of cells from a primary tumor to a distant site, where they arrest and grow to form a secondary tumor. Conventional metastasis models have focused primarily on analysis of end point tumor formation following inoculation with tumor cells. This approach can be used to measure the metastatic potential of cell lines, the morphology of metastases and their vasculature and the overall effectiveness of treatment strategies. However, it cannot, reveal the dynamics of metastatic progression, tumor cell interactions with host tissues or the characteristics of blood flow within the tumor microvasculature. Intravital videomicroscopy has been developed to visualize and quantify the movement of tumor cells and their interactions with host tissues as they travel through metastatic pathways within the body and arrest at secondary sites. Intravital videomicroscopy can also be used to quantify the morphology and functional capacity of tumor microvasculature, as well as the timing and dynamic effects of drugs targeted to disrupt tumor vasculaturization. With the development of new fluorescent probes and reporter genes, intravital videomicroscopy has the potential to provide evidence of the timing and location of metabolic processes within the metastatic cascade that may serve as specific targets for the treatment of breast cancer.

Transgenic nude mice ubiquitously expressing fluorescent proteins for color-coded imaging of the tumor microenvironment

We have developed a transgenic green fluorescent protein (GFP) nude mouse with ubiquitous GFP expression. The GFP nude mouse was obtained by crossing nontransgenic nude mice with the transgenic C57/B6 mouse in which the β-actin promoter drives GFP expression in essentially all tissues. In the adult mice, many organs brightly expressed GFP, including the spleen, heart, lungs, spleen, pancreas, esophagus, stomach, and duodenum as well as the circulatory system. The liver expressed GFP at a lesser level. The red fluorescent protein (RFP) transgenic 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 the RFP nude mouse, the organs all brightly expressed RFP, including the heart, lungs, spleen, pancreas, esophagus, stomach, liver, 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. The cyan fluorescent protein (CFP) nude mouse was developed by crossing nontransgenic nude mice with the transgenic CK/ECFP mouse in which the β-actin promoter drives expression of CFP in almost all tissues. In the CFP nude mice, the pancreas and reproductive organs displayed the strongest fluorescence signals of all internal organs, which vary in intensity. The GFP, RFP, and CFP nude mice when transplanted with cancer cells of another color are powerful models for color-coded imaging of the tumor microenvironment (TME) at the cellular level.

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.

Novel approaches to glioma drug design and drug screening

INTRODUCTION

Gliomas are considered the most malignant form of brain tumors, and ranked among the most aggressive human cancers. Despite advance standard therapy the prognosis for patients with gliomas remains poor. Chemotherapy has played an important role as an adjuvant in treating gliomas. The efficacy of the chemotherapeutic drug is limited due to poor drug delivery and the inherent chemo- and radio-resistance. Challenges of the brain cancer therapy in clinical settings are; i) to overcome the chemo- and radio-resistance, ii) to improve drug delivery to tumors and iii) the development of effective drug screening procedures.

AREAS COVERED

In this review, the authors discuss clinically important chemotherapeutic agents used for treating malignant gliomas along with novel drug design approaches. The authors, furthermore, discuss the in vitro and in vivo drug screening procedures for the development of novel drug candidates.

EXPERT OPINION

The development of novel and highly potent chemotherapeutic agents for both glioma and glioma stem cells (GSCs) is highly important for future brain cancer research. Thus, research efforts should be directed towards developing innovative molecularly targeted antiglioma agents in order to reduce the toxicity and drug resistance which are associated with current forms of therapy. Development of novel pre-clinical drug screening procedures is also very critical for the overall success of brain cancer therapies in clinical settings.

Establishment of a novel dsRed NOD/Scid mouse strain to investigate the host and tumor cell compartments

Here we describe a NOD/Scid mouse strain expressing the dsRed transgene. The strain is maintained by inbreeding of homozygous dsRed NOD/Scid siblings, and expresses red fluorescence from various organs. The model allows engraftment of human tumor tissue, and engrafted tumors were separated into stromal and malignant cell compartments. Furthermore, we compared tumor-associated and normal fibroblast for expression of fibroblast-associated markers, and identified a marker panel that was upregulated in the tumor-associated fibroblasts. In conclusion, we propose that this model may be used in a variety of studies of tumor progression and to elucidate the role of the tumor microenvironment.

Major liver resection stimulates stromal recruitment and metastasis compared with repeated minor resection

BACKGROUND

The present study examined the effects of types of liver resection on the growth of liver and lung metastases.

METHODS

Experimental liver metastases were established by spleen injection of the Colon 26 murine adenocarcinoma cell line expressing green fluorescent protein (GFP) into transgenic nude mice expressing red fluorescent protein. Experimental lung metastases were established by tail-vein injection with Colon 26-GFP. Three days after cell injection, groups of mice underwent (35% + 35% repeated minor resection versus 70% major resection versus 35% minor resection). Metastatic tumor growth was measured by color-coded fluorescence imaging of the GFP-expressing cancer cells and red fluorescent protein-expressing stroma.

RESULTS

Although major and repeated minor resection removed the same total volume of liver parenchyma, the 2 procedures had very different effects on metastatic tumor growth. Major resection stimulated liver and lung metastatic growth and recruitment of host-derived stroma compared with repeated minor resection. Repeated minor resection did not stimulate metastasis or stromal recruitment. No significant difference was found in liver regeneration between the 2 groups. Host-derived stroma density, which was stimulated by major resection compared with repeated minor resection, might stimulate growth in the liver-metastatic tumor. Transforming growth factor-β is also preferentially stimulated by major resection and might play a role in stromal and metastasis stimulation.

CONCLUSIONS

The results of the present study indicate that when liver resection is necessary, repeated minor liver resection will be superior to major liver resection, because major resection, unlike repeated minor resection, stimulates metastasis. This should be taken into consideration in clinical situations that require liver resection.

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.

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.

Multi-color palette of fluorescent proteins for imaging the tumor microenvironment of orthotopic tumorgraft mouse models of clinical pancreatic cancer specimens

Pancreatic-cancer-patient tumor specimens were initially established subcutaneously in NOD/SCID mice immediately after surgery. The patient tumors were then harvested from NOD/SCID mice and passaged orthotopically in transgenic nude mice ubiquitously expressing red fluorescent protein (RFP). The primary patient tumors acquired RFP-expressing stroma. The RFP-expressing stroma included cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Further passage to transgenic nude mice ubiquitously expressing green fluorescent protein (GFP) resulted in tumors that acquired GFP stroma in addition to their RFP stroma, including CAFs and TAMs as well as blood vessels. The RFP stroma persisted in the tumors growing in the GFP mice. Further passage to transgenic nude mice ubiquitously expressing cyan fluorescent protein (CFP) resulted in tumors acquiring CFP stroma in addition to persisting RFP and GFP stroma, including RFP- and GFP-expressing CAFs, TAMs and blood vessels. This model can be used to image progression of patient pancreatic tumors and to visually target stroma as well as cancer cells and to individualize patient therapy.

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.

Potential utility of eGFP-expressing NOG mice (NOG-EGFP) as a high purity cancer sampling system

PURPOSE

It is still technically difficult to collect high purity cancer cells from tumor tissues, which contain noncancerous cells. We hypothesized that xenograft models of NOG mice expressing enhanced green fluorescent protein (eGFP), referred to as NOG-EGFP mice, may be useful for obtaining such high purity cancer cells for detailed molecular and cellular analyses.

METHODS

Pancreato-biliary cancer cell lines were implanted subcutaneously to compare the tumorigenicity between NOG-EGFP mice and nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. To obtain high purity cancer cells, the subcutaneous tumors were harvested from the mice and enzymatically dissociated into single-cell suspensions. Then, the cells were sorted by fluorescence-activated cell sorting (FACS) for separation of the host cells and the cancer cells. Thereafter, the contamination rate of host cells in collected cancer cells was quantified by using FACS analysis. The viability of cancer cells after FACS sorting was evaluated by cell culture and subsequent subcutaneous reimplantation in NOG-EGFP mice.

RESULTS

The tumorigenicity of NOG-EGFP mice was significantly better than that of NOD/SCID mice in all of the analyzed cell lines (p < 0.01). Sorting procedures enabled an almost pure collection of cancer cells with only slight contamination by host cells. Reimplantation of the sorted cancer cells formed tumors again, which demonstrated that cell viability after sorting was well maintained.

CONCLUSIONS

This method provides a novel cancer sampling system for molecular and cellular analysis with high accuracy and should contribute to the development of personalized medicine.

LIGHT EMITTING DIODES IN BIO-IMAGING

Light-emitting diodes (LEDs) can and are currently integrated into light microscopes. They have numerous advantages as illumination sources. Most notably, they provide intensity (brightness) and spectral control during bio-imaging. For transmitted light imaging, LEDs can replace the traditional tungsten filament bulb, while offering longer life, little-to-no color temperature shift resulting from an intensity change, reduced emission in the infrared region, (a property important for live cell imaging), and reduced cost of ownership. For fluorescent imaging, in which the typical illumination sources are mercury or xenon lamps, LEDs offer the advantages of a longer lifespan, greater spatial and temporal stability, elimination of the need for mechanical shutters and neutral density filters, significantly lower cost of ownership, and reduction of photon dose at the specimen. Additionally, LEDs permit vibration-free, high-speed spectral and temporal modulation. This modulation allows more information to be obtained for a given photon dose.

Orthotopic model of SHG-44 in the enhanced green fluorescent protein nude mouse

Naturally fluorescent proteins have been widely used in biological research. In this study, we found that the simple and effective way to obtain enhanced green fluorescent protein (EGFP) nude mice is to cross transgenic EGFP C57BL/6J mice with nude (nu/nu) mice. EGFP expression is identified by tail genotyping. Establishment of the orthotopic EGFP nude mouse model used surgical orthotopic implantation. The morphology and human glioma cell markers, such as glial fibrillary acidic protein (GFAP) and S-100, remain unchanged in this mouse model. The tumor blood vessels obtained from the orthotopic model show brilliant EGFP fluorescence as observed by fluorescence microscopy. These findings suggested that this is an ideal mouse model with which to study interaction among host, tumor, and tumor microenvironment; the findings also suggested that the host (EGFP nude mouse) was involved in tumor angiogenesis.