An Experimental Liver Metastasis Mouse Model Suitable for Short and Long-Term Intravital Imaging

The liver is a frequent site of cancer metastasis, but current treatment options for cancer patients with liver metastasis are limited, resulting in poor prognosis. Colonization of the liver by cancer cells is a multistep and temporally controlled process. Investigating this process in biological relevant settings in a dynamic manner may lead to new therapeutic avenues. Experimental mouse models of liver metastasis combined with high-resolution microscopy methods can facilitate study of the mechanisms that underlie the outgrowth of cancer cells in the liver. Intravital imaging can provide information on the behavior of tumor cells in their biological setting, in time frames of hours to days. In this unit, we describe the experimental induction of liver metastasis through administration of cancer cells into mice via mesenteric vein injection. The behavior of these injected cells can then be studied using intravital imaging by surgical exposure or through an abdominal imaging window. The approach is described for use with an upright multiphoton microscope, making it widely applicable. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Inducing liver metastasis through mesenteric vein injection Basic Protocol 2: Short-term imaging of tumor cells in mouse liver Basic Protocol 3: Long-term imaging of tumor cells in mouse liver using an abdominal imaging window.

Differences between epithelial and mesenchymal human tongue cancer cell lines in experimental metastasis

Distant metastasis represents the outcome with the worst prognosis for various types of malignant tumors, but little is known regarding the impact of interacting epithelial and mesenchymal phenotypic cancer cells within its etiopathogenesis. In a novel animal model, 48 male athymic Balb/c nude mice underwent subcutaneous and intravenous injection of human tongue cancer cell lines of green fluorescent mesenchymal and red fluorescent epithelial phenotypes, in order to visualize and monitor eventual phenotypic interaction in lung metastasis as well as experimental metastasis in in vivo, ex vivo and histopathological analyses. While the epithelial, but not the mesenchymal, phenotypic human tongue cancer cell line led to direct metastasis in the lungs when injected intravenously, neither of them, even when injected in combination, were able to establish distant metastasis. The results of the present study provide evidence regarding the role of epithelial phenotypic cancer cells in the release of experimental metastasis following tail vein injection in male athymic Balb/c nude mice, in addition to proving fluorescent human tongue cancer cells may be reliably detected under a fluorescence microscope even 8 weeks after the two injection types.

Comparison of GFP-Expressing Imageable Mouse Models of Human Esophageal Squamous Cell Carcinoma Established in Various Anatomical Sites

BACKGROUND/AIMS

Esophageal squamous cell carcinoma (ESCC) is a recalcitrant cancer. Mouse models of this disease could be used for discovery of more effective therapy for ESCC.

MATERIALS AND METHODS

The green fluorescent protein (GFP)-expressing human esophageal cancer EC1 cell line was established with a lentiviral expression system. Subsequently, nude mice were injected subcutaneously, intracardiac or intravenously, or orthotopically implanted with EC1-GFP cells. Tumor growth and metastasis were examined by fluorescence in vivo imaging or by open fluorescence imaging after autopsy.

RESULTS

Four different mouse xenograft models of ESCC expressing GFP were established. In the subcutaneous model, primary tumor growth was monitored in real-time by whole-body fluorescence imaging. No metastasis was observed in the subcutaneous or surgical orthotopic implantation model. By 55 days after implantation, all mice had developed orthotopic esophageal cancer, but without detectable metastasis. In contrast, experimental metastasis occurred in the intracardiac and intravenous models. In the intravenous injection model, the lung was the sole organ of experimental metastasis. In the intracardiac model, extensive experimental metastases occurred in the bone, brain and lung.

CONCLUSION

The mouse xenograft models of ESCC developed in the present study can provide a means of discovering more effective therapy of this recalcitrant type of cancer.

Cells shed from tumours show reduced clonogenicity, resistance to apoptosis, and in vivo tumorigenicity

The goal of this study was to compare growth characteristics of cells shed from a tumour with the native tumour cells. The human colon adenocarcinoma LS174T and its highly metastatic subline LS LiM 6 were grown as tissue-isolated tumours in nude mice and perfused to collect shed cells. The tumours were then excised and prepared into single-cell suspensions. Clonogenicity in 0.3-0.9% agarose, apoptotic fraction, and in vivo tumorigenicity were determined for each population. In both tumour lines, shed cells were less clonogenic, more apoptotic and less tumorigenic than cells isolated directly from their native tissue. These findings suggest that shed cells have a low metastatic potential compared to native tumour cells, most likely because they represent an apoptotic population.

Overexpressed human CD44s promotes lung colonization during micrometastasis of murine fibrosarcoma cells: facilitated retention in the lung vasculature

Normally nonmetastatic murine sis-transformed BALB/c 3T3 cells, transfected with human CD44s gene (hCD44s), acquire spontaneous metastatic capacity to the lung. The mechanism(s) of this facilitated micrometastasis was analyzed in an experimental metastasis model. Human CD44s overexpression promoted the earliest stages severalfold (initial implantation and subsequent stabilization of tumor cells) but was irrelevant for later stages (subsequent outgrowth) of lung experimental micrometastasis. By injecting mixed populations of parental (nonmetastatic) and CD44s-transfected cells, it was shown that cell-cell adhesion between tumor and parental cells was not promoted by hCD44s but that promotion of cell-cell adhesion to lung endothelium or specifically between transfected cells (via hyaluronan) are likely mechanisms. Results obtained with hCD44s-negative primary tumor cells and hCD44s-positive or -negative variants of lung micrometastatic cells (after s.c. injection of transfectants) confirmed the importance of CD44s overexpression for early but not late stages of experimental lung metastasis. Therefore, CD44s represents a metastasis-facilitating molecule that is irrelevant for primary tumor outgrowth but that promotes micrometastasis to the lungs at the very earliest stages.

Chemoimmunotherapy with cyclophosphamide and bestatin in experimental metastasis in mice

Bestatin has significant therapeutic activity (even following oral administration) for the treatment of metastatic disease, an activity which is limited by tumor burden. Therefore, the therapeutic potential of bestatin was examined in combination with chemotherapy to determine if there is additive activity for heavy tumor burdens. Bestatin significantly increased therapeutic activity and decreased the myelotoxicity of cyclophosphamide following a single injection of cyclophosphamide or split daily doses. In immune function studies, in tumor-bearing animals, bestatin increased the number of colony-forming units (granulocyte-macrophage) (CFU) and alveolar macrophage tumoricidal activity. However, when bestatin was combined with cyclophosphamide, which depressed bone marrow and macrophage activity, it did not show apparent augmentation of macrophage and NK cell activity, but did significantly increase bone marrow CFU activity. Thus, in combined chemoimmunotherapy, bestatin appears to enhance therapeutic activity by accelerating the recovery of hematopoiesis. We suggest, therefore, that a combination chemotherapy protocol, with oral bestatin, may facilitate myelorestoration following aggressive chemotherapy. The majority of biological response modifiers require parental administration; thus, the identification of an orally active, synthetic immunoaugmenting agent with a defined receptor is of particular interest.

Immunologic enhancement of experimental metastasis in the rat

Using a series of immunologically cross-reactive metastatic tumor variants, we demonstrate that serum from animals bearing pulmonary tumor colonies possesses enhancing properties in the experimental metastasis (lung colony) assay. Enhancement is produced by chronic serum administration and promotes the growth of tumor cells arrested in the lungs which would not otherwise proliferate to form grossly detectable lung nodules. Tumor-bearer serum from animals with lung colonies derived from the most highly metastatic variant examined is shown to possess enhancing properties in both BD-IX(H-1d) and BD-IV(H-1d) rat strains, while tumor-bearer serum from animals with lung colonies derived from the less metastatic parent tumor cell line possesses enhancing properties in the BD-IX rat strain only. Removal of immunoglobulin from enhancing serum by affinity column chromatography simultaneously removes the enhancing factor(s), and enhancing activity correlates with the presence of increased levels of Clq-binding immune complexes in the serum. Serum levels of immune complexes are shown to be more elevated in serum from animals bearing lung colonies derived from the most highly metastatic variant. The enhancing moieties are shown to bind to concanavalin A, but not to staphylococcal protein A, and the active fraction elutes from concanavalin A-Sepharose with alpha-methyl-mannoside. Consideration of immunoprecipitation studies on whole and fractionated enhancing sera, along with studies on affinity purified isotype fractions reveals that the activity resides with antibodies of IgG2b subclass.