Establishment of fluorescent lung carcinoma metastasis model and its real-time microscopic detection in SCID mice

Real Time Metastatic Route Tracking of Orthotopic PC-3-GFP Human Prostate Cancer Using Intravital Imaging

The cellular basis of metastasis is poorly understood. An important step to understanding this process is to be able to visualize the routes by which cancer cells migrate from the primary tumor to various distant sites to eventually form metastasis. Our laboratory previously developed single-cell in vivo imaging using fluorescent proteins to label cancer cells. In the present study, using PC-3 human prostate cancer cells labeled with green fluorescent protein (GFP) and orthotopic tumor transplantation, we have imaged in live mice various highly diverse routes by which PC-3 cells metastasize superiorly and inferiorly to distant sites, including in the portal area, stomach area, and urogenital system. Imaging began at day 9, at which time distant metastasis had already occurred, and increased at each imaging point at days 10, 13, 14, and 16. Metastatic cells were observed migrating superiorly and inferiorly from the primary tumor as well as in lymphatic channels and trafficking in various organ systems demonstrating that PC-3 has multiple metastatic routes similar to hormone-independent advanced-stage prostate cancer in the clinic.

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.

CIP4 promotes lung adenocarcinoma metastasis and is associated with poor prognosis

Aberrant Epidermal growth factor receptor (EGFR) signaling in non-small cell lung cancer (NSCLC) is linked to tumor progression, metastasis, and poor survival rates. Here, we report the role of Cdc42-interacting protein 4 (CIP4) in the regulation of NSCLC cell invasiveness and tumor metastasis. CIP4 was highly expressed in a panel of NSCLC cell lines and normal lung epithelial cell lines. Stable knock-down (KD) of CIP4 in lung adenocarcinoma H1299 cells, expressing wild-type EGFR, led to increased EGFR levels on the cell surface, and defects in sustained activation of Erk kinase in H1299 cells treated with EGF. CIP4 localized to leading edge projections in NSCLC cells, and CIP4 KD cells displayed defects in EGF-induced cell motility and invasion through extracellular matrix. This correlated with reduced expression and activity of matrix metalloproteinase-2 (MMP-2) in CIP4 KD cells compared to control. In xenograft assays, CIP4 silencing had no effect on tumor growth, but resulted in significant defects in spontaneous metastases to the lungs from these subcutaneous tumors. This correlated with reduced expression of the Erk target gene Zeb1, and the Zeb1 target gene MMP-2 in CIP4 KD tumors compared to control. CIP4 also enhanced rates of metastasis to the liver and lungs in an intrasplenic experimental metastasis model. In human NSCLC tumor sections, CIP4 expression was elevated ≥ 2-fold in 43% of adenocarcinomas and 32% of squamous carcinomas compared to adjacent normal lung tissues. Analysis of microarray data for NSCLC patients also revealed that high CIP4 transcript levels correlated with reduced overall survival. Together, these results identify CIP4 as a positive regulator of NSCLC metastasis, and a potential poor prognostic biomarker in lung adenocarcinoma.

Imaging metastatic cell trafficking at the cellular level in vivo with fluorescent proteins

Fluorescent proteins have revolutionized biology, allowing what was formerly invisible to be clearly seen. The Nobel Prize in Chemistry was awarded in 2008 for the discovery and early use of green fluorescent protein (GFP) as a genetic reporter. Our laboratory pioneered the use of GFP for in vivo imaging. In this chapter we review the developments within our research on subcellular imaging of metastatic trafficking of cancer cells carried out in real time in mice. Dual-color fluorescent cells, with one color fluorescent protein in the nucleus and another color fluorescent protein in the cytoplasm, enable real-time nuclear-cytoplasmic dynamics to be visualized in living cells in vivo as well as in vitro. In the dual-color cells, red fluorescent protein (RFP) is expressed in the cytoplasm of cancer cells, and GFP is linked to histone H2B and is expressed in the nucleus. Nuclear GFP expression enables visualization of nuclear dynamics, whereas simultaneous cytoplasmic RFP expression allows visualization of nuclear cytoplasmic ratios in addition to simultaneous cell and nuclear shape changes. With the use of dual-color fluorescent cells, it is possible to achieve subcellular real-time imaging of cancer cell trafficking in live mice. Extravasation can also be imaged in real time. Dual-color imaging has shown that cytoplasmic processes of cancer cells exit the vessels first, with nuclei following along the cytoplasmic projections [Yamauchi et al., Cancer Res 66:4208-4214, 2006]. Dual-color in vivo cellular imaging was used to visualize cancer cell trafficking blood vessels, as well as in the lymphatic systems of the mice. The real-time imaging of cancer cell seeding on the lung has now been achieved with dual-color cells. Subcellular in vivo imaging confers great promise for understanding metastasis at the cellular level in vivo.

Fer protein-tyrosine kinase promotes lung adenocarcinoma cell invasion and tumor metastasis

Epidermal growth factor receptor (EGFR) is frequently amplified or mutated in non-small cell lung cancer (NSCLC). Although Fer protein-tyrosine kinase signals downstream of EGFR, its role in NSCLC tumor progression has not been reported. Here, Fer kinase was elevated in NSCLC tumors compared to normal lung epithelium. EGFR signaling in NSCLC cells fosters rapid Fer activation and increased localization to lamellipodia. Stable silencing of Fer in H1299 lung adenocarcinoma cells (Fer KD) caused impaired EGFR-induced lamellipodia formation compared to control cells. Fer KD NSCLC cells showed reduced Vav2 tyrosine phosphorylation that was correlated with direct Fer-mediated phosphorylation of Vav2 on tyrosine-172, which was previously reported to increase the guanine nucleotide exchange factor activity of Vav2. Indeed, Fer KD cells displayed defects in Rac-GTP localization to lamellipodia, cell migration, and cell invasion in vitro. To test the role of Fer in NSCLC progression and metastasis, control and Fer KD cells were grown as subcutaneous tumors in mice. Although Fer was not required for tumor growth, Fer KD tumor-bearing mice had significantly fewer numbers of spontaneous metastases. Combined, these data demonstrate that Fer kinase is elevated in NSCLC tumors and is important for cellular invasion and metastasis.

IMPLICATIONS

Fer protein-tyrosine kinase is a potential therapeutic target in metastatic lung cancer. Mol Cancer Res; 11(8); 952-63. ©2013 AACR.

Use of optical imaging to progress novel therapeutics to the clinic

There is an undisputed need for employment and improvement of robust technology for real-time analyses of therapeutic delivery and responses in clinical translation of gene and cell therapies. Over the past decade, optical imaging has become the in vivo imaging modality of choice for many preclinical laboratories due to its efficiency, practicality and affordability, while more recently, the clinical potential for this technology is becoming apparent. This review provides an update on the current state of the art in in vivo optical imaging and discusses this rapidly improving technology in the context of it representing a translation enabler or indeed a future clinical imaging modality in its own right.

Initial contact of glioblastoma cells with existing normal brain endothelial cells strengthen the barrier function via fibroblast growth factor 2 secretion: a new in vitro blood-brain barrier model

Glioblastoma multiforme (GBM) cells invade along the existing normal capillaries in brain. Normal capillary endothelial cells function as the blood-brain barrier (BBB) that limits permeability of chemicals into the brain. To investigate whether GBM cells modulate the BBB function of normal endothelial cells, we developed a new in vitro BBB model with primary cultures of rat brain endothelial cells (RBECs), pericytes, and astrocytes. Cells were plated on a membrane with 8 μm pores, either as a monolayer or as a BBB model with triple layer culture. The BBB model consisted of RBEC on the luminal side as a bottom, and pericytes and astrocytes on the abluminal side as a top of the chamber. Human GBM cell line, LN-18 cells, or lung cancer cell line, NCI-H1299 cells, placed on either the RBEC monolayer or the BBB model increased the transendothelial electrical resistance (TEER) values against the model, which peaked within 72 h after the tumor cell application. The TEER value gradually returned to baseline with LN-18 cells, whereas the value quickly dropped to the baseline in 24 h with NCI-H1299 cells. NCI-H1299 cells invaded into the RBEC layer through the membrane, but LN-18 cells did not. Fibroblast growth factor 2 (FGF-2) strengthens the endothelial cell BBB function by increased occludin and ZO-1 expression. In our model, LN-18 and NCI-H1299 cells secreted FGF-2, and a neutralization antibody to FGF-2 inhibited LN-18 cells enhanced BBB function. These results suggest that FGF-2 would be a novel therapeutic target for GBM in the perivascular invasive front.

Subcellular imaging in vivo: the next GFP revolution

The use of fluorescent proteins to differentially label cancer cells in the nucleus and cytoplasm and high-powered imaging technology have been used to visualize the nuclear-cytoplasmic dynamics of cancer-cell in vivo. Nuclear-cytoplasmic dynamics have been imaged in cancer cells trafficking in both blood vessels and lymphatic vessels as well as during seeding on organs and interacting with stroma in the live animal. Fluorescent proteins have also been used to color code the phases of the cell cycle which can now be followed in vivo. This technology has furthered our understanding of the spread of cancer at the subcellular level. Fluorescent proteins thereby provide the basis for the new field of in vivo cell biology.

Imaging cancer dynamics in vivo at the tumor and cellular level with fluorescent proteins

Whole-body imaging with fluorescent proteins has been shown to be a powerful technology to follow the dynamics of metastatic cancer. Whole-body imaging of fluorescent protein-expressing-cancer cells enables the facile determination of efficacy of candidate anti-tumor and anti-metastatic agents in mouse models. GFP-expressing transgenic mice transplanted with the RFP-expressing cancer cells enable the distinction of cancer and host cells and the efficacy of drugs on each type of cell. This is particularly useful for imaging tumor angiogenesis. Cancer-cell trafficking through the cardiovascular and lymphatic systems is the critical means of spread of cancer. The use of fluorescent proteins to differentially label cancer calls in the nucleus and cytoplasm and high-powered imaging technology are used to visualize the nuclear-cytoplasmic dynamics of cancer-cell trafficking in both blood vessels and lymphatic vessels in the live animal. This technology has furthered our understanding of the spread of cancer at the subcellular level in the live mouse. Fluorescent proteins thus enable both macro and micro imaging technology and thereby provide the basis for the new field of in vivo cell biology.

In vivo observation of pulmonary micrometastasis of colon cancer in normal rats

The initial kinetics of cancer cell metastasis to organs requires investigation to establish an effective strategy against malignant disease. In vivo observation of pulmonary micrometastasis at an extremely early stage is of particular importance, and it is desirable from a clinical perspective to use an animal model with a normal immune system. RCN-9 cells labeled with green fluorescent protein were injected into the liver parenchyma of Fischer F344 male rats and the lungs were observed using real-time confocal laser scanning microscopy from 3 to 10 weeks after injection. Metastasis at the single cell level was observed throughout this period, but the number of pulmonary micrometastases did not increase significantly with time. The largest metastasis was 300 mum in diameter, and the mean size of the metastases did not increase with time. There were two types of micrometastases in terms of shape: round and linear metastases, with the latter resembling the pulmonary microvasculature. The precise location of each pulmonary micrometastasis was revealed by acridine orange infusion. We could observe a single cancer cell and a small cancer mass in endothelial and interstitial locations in vivo, and we found proliferating cancer cells both inside and outside of microvessels. Most of the pulmonary micrometastases stayed dormant as a single cell or a cancer mass of less than 100 microm in diameter until 10 weeks after cancer-cell injection into the liver.

Subcellular imaging of cancer cells in live mice

Dual-color fluorescent cells, with one color in the nucleus and the other in the cytoplasm, enable real-time nuclear-cytoplasmic dynamics to be visualized in living cells in vivo as well as in vitro. To obtain the dual-color cells, red fluorescent protein (RFP) is expressed in the cytoplasm of cancer cells, and green fluorescent protein (GFP) linked to histone H2B is expressed in the nucleus. Nuclear GFP expression allows visualization of nuclear dynamics, whereas simultaneous cytoplasmic RFP expression allows visualization of nuclear-cytoplasmic ratios as well as simultaneous cell and nuclear shape changes. This methodology has allowed us to show that the cells and nuclei of cancer cells in the capillaries elongate to fit the width of these vessels. The average length of the major axis of the cancer cells in the capillaries increased to approximately four times their normal length. The nuclei increased their length 1.6 times. Cancer cells in capillaries over 8 microm in diameter were shown to migrate at up to 48.3 microm/h. With the use of dual-color fluorescent cells and the Olympus OV100, a highly sensitive whole-mouse imaging system with both macrooptics and microoptics, it is possible to achieve subcellular real-time imaging of cancer cell trafficking in live mice. Extravasation can also be imaged in real time. Dual-color imaging showed that cytoplasmic processes of cancer cells exited the vessels first, with nuclei following along the cytoplasmic projections. Dual-color in vivo cellular imaging was also used to visualize trafficking, nuclear-cytoplasmic dynamics, and the viability of cancer cells after their injection into the portal vein of mice.

The multiple uses of fluorescent proteins to visualize cancer in vivo

Naturally fluorescent proteins have revolutionized biology by enabling what was formerly invisible to be seen clearly. These proteins have allowed us to visualize, in real time, important aspects of cancer in living animals, including tumour cell mobility, invasion, metastasis and angiogenesis. These multicoloured proteins have allowed the colour-coding of cancer cells growing in vivo and enabled the distinction of host from tumour with single-cell resolution. Visualization of many aspects of cancer initiation and progression in vivo should be possible with fluorescent proteins.

In vivo cell biology of cancer cells visualized with fluorescent proteins

This chapter describes a new cell biology where the behavior of individual cells can be visualized in the living animal. Previously it has been demonstrated that fluorescent proteins can be used for whole-body imaging of metastatic tumor growth, bacterial infection, and gene expression. An example of the new cell biology is dual-color fluorescence imaging using red fluorescent protein (RFP)-expressing tumors transplanted in green fluorescent protein (GFP)-expressing transgenic mice. These models show with great clarity the details of tumor-stroma interactions and especially tumor-induced angiogenesis, tumor-infiltrating lymphocytes, stromal fibroblasts, and macrophages. Another example is the color coding of cells with RFP or GFP such that both cell types can be simultaneously visualized in vivo. Stem cells can also be visualized and tracked in vivo. Mice in which the regulatory elements of the stem cell marker nestin drive GFP expression enable nascent vasculature to be visualized interacting with transplanted RFP-expressing cancer cells. Nestin-driven GFP expression can also be used to visualize hair follicle stem cells. Dual-color cells expressing GFP in the nucleus and RFP in the cytoplasm enable real-time visualization of nuclear-cytoplasm dynamics including cell cycle events and apoptosis. Highly elongated cancer cells in capillaries in living mice were observed within skin flaps. The migration velocities of the cancer cells in the capillaries were measured by capturing images of the dual-color fluorescent cells over time. The cells in the capillaries elongated to fit the width of these vessels. The use of the dual-color cancer cells differentially labeled in the cytoplasm and nucleus and associated fluorescent imaging provide a powerful tool to understand the mechanism of cancer cell migration and deformation in small vessels.

Detection of micrometastasis of gastric carcinoma in peripheral blood circulation

AIM: To detect the micrometastasis of gastric carcinoma in peripheral blood circulation using immunomagnetic beads sorting technique and RT-PCR technique, and to discuss its significance and the difference between the two methods.

METHODS: Density gradient centrifugation was used to isolate mononuclear cells from peripheral blood, immunomagnetic beads sorting technique and RT-PCR technique were used to detect the disseminated carcinoma cells. HE, immunocytochemical and immunofluorescence staining were also used to identify the characteristics of the cells separated with immunomagnetic beads sorting technique.

RESULTS: Cells expressing cytokeratin were separated and enriched from the peripheral blood specimens of patients suffering from gastric carcinoma or chronic gastritis. After HE staining, two kinds of cells with little cytoplasm were found. Majority of these cells had small and round nuclei, even chromatins and the thickness of nuclear membrane was normal. Immunohistochemical staining indicated that there were CD34 and CD45 expression on the cell membrane of this kind of cells and these cells also showed expressed human telomerase reverse transcriptase by immunofluorescence staining, but the expression of carcinoembryonic antigen was absent. So, these cells might hematopoiesis precursors. Another kind of cells had larger and abnormal nuclei with thicker nuclear membranes. Massed chromatins and poly-nucleoli were found in the nuclei. These cells expressed human telomerase reverse transcriptase and carcinoembryonic antigen, but CD34 and CD45 were not found on the cell membrane. So, these cells were considered as gastric carcinoma cells escaping from the original focuses and existing in the peripheral blood circulation. Carcinoma cells were found in 25 of 60(41.7%) specimens of peripheral blood from patients with gastric carcinoma, while there were no such cells separated from the blood specimens of chronic gastritis patients. The difference of positive rates of disseminated carcinoma cells between two groups was markedly significant (P < 0.005). The expressions of CK20 mRNA in peripheral blood specimens were examinated with RT-PCR. CK20 mRNA was detected from 32 of 60(53.3%) peripheral blood specimens in the group of gastric carcinoma patients, while none of the specimens from patients suffering from chronic gastritis had CK20 mRNA. Significant difference was also found between two groups (P < 0.005). Statistic analyses also showed that there was a significant difference between the positive rates of two methods in detecting the disseminated carcinoma cells from the peripheral blood circulation of gastric carcinoma patients (P < 0.05).

CONCLUSION: The results demonstrated that there were disseminated carcinoma cells in the peripheral blood circulation of some patients with gastric carcinoma. Disseminated carcinoma cells can be detected from the peripheral blood samples with immunomagnetic beads sorting technique and RT-PCR technique. The positive rate of RT-PCR technique is higher than that of immunomagnetic beads sorting technique in detecting micrometastasis.

Gene transfer and expression of enhanced green fluorescent protein in variant HT-29c cells

AIM: To study the expression of enhanced green fluorescent protein (EGFP) gene in retrovirally transduced variant HT-29 cells.

METHODS: The retroviral vector prkat EGFP/neo was constructed and transfected into the 293T cell using a standard calcium phosphate precipitation method. HT-29c cells (selected from HT-29 cells) were transduced by a retroviral vector encoding the GEFP gene. The fluorescence intensity of colorectal carcinoma HT-29c cells after transduced with the EGFP bearing retrovirus was visualized using fluorescence microscope and fluorescence activated cell sorter (FACS) analysis. Multiple biological behaviors of transduced cells such as the proliferating potential and the expression of various antigens were comparatively analyzed between untransduced and transduced cells in vitro. EGFP expression of the fresh tumor tissue was assessed in vivo.

RESULTS: After transduced, HT-29c cells displayed a stable and long-term EGFP expression under the nonselective conditions in vitro. After cells were successively cultured to passage 50 in vitro, EGFP expression was still at a high level. Their biological behaviors, such as expression of tumor antigens, proliferation rate and aggregation capability were not different compared to untransduced parental cells in vitro. In subcutaneous tumors, EGFP was stable and highly expressed.

CONCLUSION: An EGFP expressing retroviral vector was used to transduce HT-29c cells. The transduced cells show a stable and long-term EGFP expression in vitro and in vivo. These cells with EGFP are a valuable tool for in vivo research of tumor metastatic spread.