Specific route mapping visualized with GFP of single-file streaming contralateral and systemic metastasis of Lewis lung carcinoma cells beginning within hours of orthotopic implantion

Metastasis is impaired by endothelial-specific Dll4 loss-of-function through inhibition of epithelial-to-mesenchymal transition and reduction of cancer stem cells and circulating tumor cells

Systemic inhibition of Dll4 has been shown to thoroughly reduce cancer metastasis. The exact cause of this effect and whether it is endothelial mediated remains to be clarified. Therefore, we proposed to analyze the impact of endothelial Dll4 loss-of-function on metastasis induction on three early steps of the metastatic process, regulation of epithelial-to-mesenchymal transition (EMT), cancer stem cell (CSC) frequency and circulating tumor cell (CTC) number. For this, Lewis Lung Carcinoma (LLC) cells were used to model mouse tumor metastasis in vivo, by subcutaneous transplantation into endothelial-specific Dll4 loss-of-function mice. We observed that endothelial-specific Dll4 loss-of-function is responsible for the tumor vascular regression that leads to the reduction of tumor burden. It induces an increase in tumoral blood vessel density, but the neovessels are poorly perfused, with increased leakage and reduced perivascular maturation. Unexpectedly, although hypoxia was increased in the tumor, the number and burden of macro-metastasis was significantly reduced. This is likely to be a consequence of the observed reduction in both EMT and CSC numbers caused by the endothelial-specific Dll4 loss-of-function. This multifactorial context may explain the concomitantly observed reduction of the circulating tumor cell count. Furthermore, our results suggest that endothelial Dll4/Notch-function mediates tumor hypoxia-driven increase of EMT. Therefore, it appears that endothelial Dll4 may constitute a promising target to prevent metastasis.

Downregulation of TRIM28 inhibits growth and increases apoptosis of nude mice with non‑small cell lung cancer xenografts

TRIM28 is a well-known transcriptional co-repressor of Kruppel-associated box zinc finger proteins. The authors previously demonstrated that TRIM28 small interfering (si)RNA decreases cell proliferation and inhibits cell cycle progression in non-small cell lung cancer (NSCLC) cell lines. The present study further demonstrated that the stable silencing of TRIM28 expression by a specific siRNA lentivirus vector significantly inhibited the growth and exerted obvious anti-tumor effects in nude mice. The results of the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay indicated that TRIM28 knockdown increased apoptosis. Furthermore, TRIM28 knockdown decreased the expression of B cell lymphoma (Bcl)-2 and increased the expression of Bcl-2 associated X, apoptosis regulator and p53 at the gene and protein levels. Auto-antibodies to TRIM28 were present in 12.32% of the sera of the patients with NSCLC. The results suggest that TRIM28 knockdown may be effective against NSCLC, and TRIM28 antibodies have the potential to act as novel diagnostic and therapeutic tools.

A spontaneous metastasis model reveals the significance of claudin-9 overexpression in lung cancer metastasis

Metastasis causes most cancer related mortality but the mechanisms governing metastatic dissemination are poorly defined. Metastasis involves egression of cancer cells from the primary tumors, their survival in circulation and colonization at the secondary sites. Cancer cell egression from the primary tumor is the least defined process of metastasis as experimental metastasis models directly seed cancer cells in circulation, thus bypassing this crucial step. Here, we developed a spontaneous metastasis model that retains the egression step of metastasis. By repeated in vivo passaging of the poorly metastatic Lewis lung carcinoma (3LL) cells, we generated a cell line (p-3LL) that readily metastasizes to lungs and liver from subcutaneous (s.c.) tumors. Interestingly, when injected intravenously, 3LL and p-3LL cells showed a similar frequency of metastasis. This suggests enhanced egression of p-3LL cells may underlie the enhanced metastatic spread from primary tumors. Microarray analysis of 3LL and p-3LL cells as well as the primary tumors derived from these cells revealed altered expression of several genes including significant upregulation of a tight junction protein, claudin-9. Increased expression of claudin-9 was confirmed in both p-3LL cells and tumors derived from these cells. Knockdown of claudin-9 expression in p-3LL cells by si-RNA significantly reduced their motility, invasiveness in vitro and metastasis in vivo. Conversely, transient overexpression of claudin-9 in 3LL cells enhanced their motility. These results suggest an essential role for claudin-9 in promoting lung cancer metastasis.

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.

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.