Single-cell tumor dormancy model of uveal melanoma.

BACKGROUND: Ocular melanoma is easily treated by the removal of the eye or through plaque radiotherapy. However, after removal or control of the primary tumor, patients can develop fatal liver metastases up to 20 years later. It has been reported that difficulties in imaging single cells and the propensity for tumor cells to replicate rapidly in animal models account for the deficit of single-cell tumor dormancy models. METHODS: In this paper, we performed two animal experiments using green fluorescent-labeled uveal melanoma cells in nude mice. Cells were injected via tail-vein and the experiments ran 20 and 42 days, respectively. Labeled cells were imaged in vivo via skin-flap and epifluorescent microscopy. RESULTS: The first experiment exemplified the feasibility of a single-cell tumor dormancy model; cells were present in multiple organs post-injection, but persisted solely in the liver for the duration of the experiment. The second experiment, demonstrating the presence and viability of these single, metastatic seeds 6 weeks after injection. CONCLUSION: Due to the inherent difficulties in establishing single-celled tumor dormancy models, few exist. In this paper, we have successfully developed a single-cell dormancy model of uveal melanoma, a disease that, in patients, epitomizes tumor dormancy. This model has the potential to reveal the mechanisms behind dormancy, identify patients at high risk for metastatic development, and develop new serum biomarkers for micrometastasis detection.

Immunomagnetic isolation and in vitro expansion of human uveal melanoma cell lines.

PURPOSE: Uveal melanoma (UM) is the most common intra-ocular tumor in adults. Despite advances in diagnosis and treatment, the survival rate of UM has not increased in the last several decades. Approximately 50% of patients will die as a consequence of metastatic disease with the majority of metastases localized to the liver. Due to the lack of lymphatics in the eye, hematogenous dissemination is the predominant means by which UM cells escape the primary site. Our laboratory has recently demonstrated the presence of circulating malignant cells (CMCs) in the blood using both animal models and clinical trails involving UM patients. Current data suggests that all UM patients will be positive for CMCs after diagnosis. Furthermore, some of the phenotypic changes that are necessary for metastatic growth may occur while the cells are circulating in the blood. In this study, we evaluated the efficiency of a panel of antibodies to immunomagnetically isolate CMCs for the purpose of in vitro expansion and genetic, immunological, and phenotypic characterization. METHODS: In this study, five human uveal melanoma cell lines (92.1, MKT-BR, OCM-1, SP6.5, and UW-1) were immunostained with a panel of antibodies against known melanoma cell surface markers. Staining with monoclonal antibodies PAL M2, NKI C3, NKI/Beteb, and 9.2.27 permitted the generation of a cell surface expression profile in these cell lines. The five human UM cell lines and 92.1 transfected with GFP were subsequently spiked into human blood at concentrations ranging from 1x10(6) cells/ml to 10 cells/ml. Cells were immuno-magnetically isolated at concentrations as low as 10 cells/ml. RESULTS: Immunomagnetic isolation of all five human UM cell lines tested at concentrations down to 10 cells/ml human blood was achieved only when antibodies were used in combination. Individually, the antibodies did not permit isolation of cells at physiologically relevant concentrations. CONCLUSIONS: The immunomagnetic isolation method presented in this study can be used to isolate CMCs at physiologically relevant concentrations and at sensitivities comparable to those seen in polymerase chain reactions (PCR). In addition, our data suggests that our method is more efficient and reliable for the isolation of CMCs in UM than the methods currently used.

The effect of blue light exposure and use of intraocular lenses on human uveal melanoma cell lines.

Little is known about the effect of blue light on inducing melanocytic malignant transformation. We chose to investigate the effect of blue light (475 nm wavelength) on the proliferation rates of uveal melanoma cells. In addition, we tested two different intraocular lenses to determine the possible effects of ultraviolet absorbing and blue light filtering intraocular lenses on the changes in proliferation. Four human uveal melanoma cell lines (92.1, MKT-BR, OCM-1, SP6.5) were exposed to blue light with and without the presence of ultraviolet absorbing and blue light filtering intraocular lenses. Cells covered by aluminum foil were used as a control. The proliferation rate of the cells compared with the control was then assessed using the Sulforhodamine-B proliferation assay. Cells exposed to blue light showed a statistically significant (P<0.05) increase in proliferation. Those exposed to blue light through a standard ultraviolet absorbing intraocular lens showed a smaller increase in proliferation, whereas those exposed with a blue light filtering intraocular lens showed no increase in proliferation than the control in all four cell lines. The exposure of cells to blue light led to an increase in proliferation in all cell lines compared with the control. The use of blue light filtering intraocular lenses abolished these increases in proliferation in the four cell lines. These results indicate that blue light filtering intraocular lenses may have a protective effect on the proliferation rates of uveal melanoma cells exposed to blue light.

Characterization of ocular and metastatic uveal melanoma in an animal model.

PURPOSE: To characterize, in detail, tumor development, malignant cell dissemination, and metastasis in a 10-week animal model of uveal melanoma. METHODS: One million 92.1 human primary uveal melanoma cells were injected into the suprachoroidal space of the right eye of 27 immunosuppressed albino rabbits. Intraocular tumor growth was monitored weekly by fundoscopy and by ultrasonography at the end of the experiment. To document the progression of the disease, one animal per week was killed. The enucleated eyes, lungs, and livers were macroscopically examined and histopathologically studied by hematoxylin and eosin, periodic acid-Schiff, and immunohistochemistry. Mononuclear layers isolated from the rabbits' blood samples were cultured. RESULTS: Histopathology showed intraocular tumors in 89% of the animals. Tumor growth was found 1 week after cell inoculation, and by the end of the experiment large tumor masses were observed. Microscopic pulmonary metastatic foci were first observed 4 weeks after cell injection. By the end of the experiment, all the animals had metastasis to the lungs. Interestingly, 18% of the animals also had micrometastasis to the liver. Viable adherent uveal melanoma cells were successfully isolated from peripheral blood and grown in vitro. CONCLUSIONS: In this study, most rabbits developed intraocular tumors followed by lung metastasis, and some of these rabbits later developed liver micrometastases. This novel source of research material warrants a follow-up longer than 10 weeks to further explore the pathophysiologic bases of liver involvement commonly encountered in humans. The success in the isolation and culture of circulating malignant cells in this animal model suggests that it might be worthwhile to explore the application of this technique to the management of patients with primary uveal melanoma.

How in vitro techniques have increased our understanding of uveal melanoma cellular biology.

The past decade has seen a rapid increase in powerful in vitro techniques allowing for the specific study of the biologic properties of tumours. In this review we discuss the role of in vitro studies in providing insight into the biologic mechanisms involved in uveal melanoma. We also review the basis of these studies for the development of adjuvant therapies to aid in the treatment of systemic disease in patients with uveal melanoma.

Effect of inhibition of the lysophosphatidic acid receptor 1 on metastasis and metastatic dormancy in breast cancer.

BACKGROUND: Previous studies identified the human nonmetastatic gene 23 (NME1, hereafter Nm23-H1) as the first metastasis suppressor gene. An inverse relationship between Nm23-H1 and expression of lysophosphatidic acid receptor 1 gene (LPAR1, also known as EDG2 or hereafter LPA1) has also been reported. However, the effects of LPA1 inhibition on primary tumor size, metastasis, and metastatic dormancy have not been investigated. METHODS: The LPA1 inhibitor Debio-0719 or LPA1 short hairpinned RNA (shRNA) was used. Primary tumor size and metastasis were investigated using the 4T1 spontaneous metastasis mouse model and the MDA-MB-231T experimental metastasis mouse model (n = 13 mice per group). Proliferation and p38 intracellular signaling in tumors and cell lines were determined by immunohistochemistry and western blot to investigate the effects of LPA1 inhibition on metastatic dormancy. An analysis of variance-based two-tailed t test was used to determine a statistically significant difference between treatment groups. RESULTS: In the 4T1 spontaneous metastasis mouse model, Debio-0719 inhibited the metastasis of 4T1 cells to the liver (mean = 25.2 liver metastases per histologic section for vehicle-treated mice vs 6.8 for Debio-0719-treated mice, 73.0% reduction, P < .001) and lungs (mean = 6.37 lesions per histologic section for vehicle-treated mice vs 0.73 for Debio-0719-treated mice, 88.5% reduction, P < .001), with no effect on primary tumor size. Similar results were observed using the MDA-MB-231T experimental pulmonary metastasis mouse model. LPA1 shRNA also inhibited metastasis but did not affect primary tumor size. In 4T1 metastases, but not primary tumors, expression of the proliferative markers Ki67 and pErk was reduced by Debio-0719, and phosphorylation of the p38 stress kinase was increased, indicative of metastatic dormancy. CONCLUSION: The data identify Debio-0719 as a drug candidate with metastasis suppressor activity, inducing dormancy at secondary tumor sites.

The use of a cyclooxygenase-2 inhibitor (Nepafenac) in an ocular and metastatic animal model of uveal melanoma.

The expression of cyclooxygenase-2 (COX-2) has been reported as an indicator of poor prognosis in a wide variety of human tumors, including colon, breast and uveal melanoma (UM). COX-2 inhibitors have shown promise in controlling the malignancy of several types of tumors. Previous studies have demonstrated the efficacy of a COX-2 inhibitor on the proliferation rates of human UM cells. The goal of this experiment was to investigate the efficiency of Nepafenac, a topically administered COX-2 inhibitor, in a rabbit model of UM. The animals were divided into two groups of 14 animals for the duration of the 12-week experiment. One animal per group was killed each week to evaluate disease progression and for histopathological studies. The experimental group received drops containing 0.3% Nepafenac solution. Intraocular tumor growth was evaluated weekly by fundoscopic examination and each animal was weighed prior to examination. Blood samples were taken weekly from all rabbits to detect circulating malignant cells (CMCs) throughout the experiment. After the second week of inoculation, the experimental group weighed significantly more than the control group. The control group developed more intraocular tumors and presented with metastases and higher detectable levels of CMCs before the treated group. These results indicate that the topical administration of a COX-2 inhibitor delayed the progression of this malignancy in our animal model. A clinical trail using an anti-COX-2 inhibitor for patients with UM should be considered.