Governing step of metastasis visualized in vitro

Abstract

Metastasis is the ultimate life-threatening stage of cancer. The lack of accurate model systems thwarted studies of the metastatic cell's basic biology. To follow continuously the succeeding stages of metastatic colony growth, we heritably labeled cells from the human lung adenocarcinoma cell line ANIP 973 with green f luorescent protein (GFP) by transfection with GFP cDNA. Labeled cells were then injected intravenously into nude mice, where, by 7 days, they formed brilliantly f luorescing metastatic colonies on mouse lung [Chishima, T., Miyagi, Y., Wang, X., Yang, M., Tan Paget, more than 100 years ago, formulated his seed and soil hypothesis (i.e., the cells from a given tumor would ''seed'' only favorable ''soil'' offered by certain organs; ref. 1). He hypothesized that cancer cells must find a suitable ''soil'' in a target organ (i.e., one that supports colonization) for metastasis to occur. We recently reported that the ability of human colon cancer cells to colonize liver tissue governs whether a particular colon cancer will metastasize to the liver (2). In the model used in that study, human colon tumors were transplanted into the nude mouse colon as intact tissue blocks by surgical orthotopic implantation (i.e., to the corresponding organ). At the site of implantation in the mouse colon, all tumors were equally invasive locally into tissues and blood vessels. However, the metastatic behavior of implanted tumors closely depended on the metastatic behavior of the original human patient tumor. Only those tumors that originally metastasized to the liver in the donor patient did so in the mouse model. Furthermore, the cells of these metastasizing tumors could also colonize the liver directly after intrahepatic implantation. In contrast, cells from nonmetastatic colon tumors failed to engraft when implanted into liver tissue. Thus, the ability to colonize a distant organ is a critical aspect of metastatic spread in tumor progression. However, the colonization of distant tissues by micrometastasis formation and subsequent growth is still poorly understood due to lack of suitable experimental models.In this report, we describe a new system for the study of the metastatic process in vitro. Until now, envisioning an in vitro experimental system for replicating metastatic colony establishment and progression was not possible. Three recent developments make the described system realizable. One is the technology that underlies surgical orthotopic implantation. Tumor cells will closely replicate their original behavior in a heterologous species if implanted onto the corresponding organ. The experiments described here used human lung cancer cells growing on mouse lung. Another important technique is an in vitro culture system that closely mimics in vivo conditions. To this end, we took advantage of collagen spongegel matrix histoculture introduced by Leighton (3) in the 1950s and further developed by us (4-12). Finally, we sought a rapid, nondestructive means for examining the cultured lung tissue so that conti...

Direct external imaging of nascent cancer, tumor progression, angiogenesis, and metastasis on internal organs in the fluorescent orthotopic model

“…The greatest fidelity to donor cancer tissue was achieved with GFP models employing orthotopically implanted tumors (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). These tumors closely emulate the metastatic behavior of the donor in rate and seed similar target tissues.…”

It's not just about anatomy: In vivo bioluminescence imaging as an eyepiece into biology

“…Whole-body imaging of light that is generated within the body and transmitted through tissue is an exciting approach for studying biological processes in laboratory animals. Reporter genes that encode either fluorescent or bioluminescent proteins have been used to create internal biological light, and these reporter genes have been used broadly in the study of small animal models of human biology and disease (37,(41)(42)(43)(44). In the study of neoplasia, these strategies have enabled longitudinal studies of the disease course from minimal disease states to late stages of disease.…”

Whole-body optical imaging of green fluorescent protein-expressing tumors and metastases

“…Tracking of cancer cells that stably express GFP in vivo is far more sensitive and rapid than the traditional, cumbersome procedures of histopathological examination or immunohistochemistry. In particular, GFP labeling markedly improved the ability to visualize metastases in fresh soft organs and bone (11)(12)(13)(14)(15)(16)(17)(18).…”

“…A major advantage of GFP-expressing tumor cells is that imaging requires no preparative procedures and, therefore, is uniquely suited for visualizing in live tissue (11)(12)(13)(14)(15)(16)(17)(18). Using stable, high-GFP-expression tumor cells that we have selected (11)(12)(13)(14)(15)(16)(17)(18), Abbreviation: GFP, green fluorescent protein.…”

“…Using stable, high-GFP-expression tumor cells that we have selected (11)(12)(13)(14)(15)(16)(17)(18), Abbreviation: GFP, green fluorescent protein. ¶ To whom reprint requests should be addressed.…”