Noninvasive Assessment of Tumor Cell Proliferation in Animal Models

Abstract

Revealing the mechanisms of neoplastic disease and enhancing our ability to intervene in these processes requires an increased understanding of cellular and molecular changes as they occur in intact living animal models. We have begun to address these needs by developing a method of labeling tumor cells through constitutive expression of an optical reporter gene, and noninvasively monitoring cellular proliferation in vivo using a sensitive photon detection system. A stable line of HeLa cells that expressed a modified firefly luciferase gene was generated, and proliferation of these cells in irradiated severe combined immunodeficiency (SCID) mice was monitored. Tumor cells were introduced into animals via subcutaneous, intraperitoneal and intravenous inoculation and whole body images, that revealed tumor location and growth kinetics, were obtained. The number of photons that were emitted from the labeled tumor cells and transmitted through murine tissues was sufficient to detect 1x10(3) cells in the peritoneal cavity, 1x10(4) cells at subcutaneous sites and 1x10(6) circulating cells immediately following injection. The kinetics of cell proliferation, as measured by photon emission, was exponential in the peritoneal cavity and at subcutaneous sites. Intravenous inoculation resulted in detectable colonies of tumor cells in animals receiving more than 1x10(6) cells. Our demonstrated ability to detect small numbers of tumor cells in living animals noninvasively suggests that therapies designed to treat minimal disease states, as occur early in the disease course and after elimination of the tumor mass, may be monitored using this approach. Moreover, it may be possible to monitor micrometastases and evaluate the molecular steps in the metastatic process. Spatiotemporal analyses of neoplasia will improve the predictability of animal models of human disease as study groups can be followed over time, and this method will accelerate development of novel therapeutic strategies.

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

“…Models of photon diffusion through tissue have indicated that as few as one hundred bioluminescent cells should be detectable at subcutaneous tissue sites, and approximately 10 6 cells would be required to generate signals that are detectable through two cm of tissue (52). These predictions by Rice et al (52) were made with the assumption of a light output of 30 photons per cell per second at a wavelength of 650 nm, and have largely been supported empirically through a number of studies using different tumor cells at various tissue sites (5,37,43,(53)(54)(55). The levels of reporter gene expression in a given cell type will determine the extent to which it can be detected in vivo.…”

“…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.…”

Severe pulmonary metastasis in obese and diabetic mice

“…12,13 Then, metastatic processes in vivo were investigated by using B16-BL6 cells stably expressing luciferase (BL6-luc cells). Pulmonary metastasis in living mice was evaluated with the in vivo imaging system.…”

Noninvasive, quantitative imaging in living animals of a mutant dopamine D2 receptor reporter gene in which ligand binding is uncoupled from signal transduction

“…Non-invasive optical techniques for monitoring firefly luciferase 1,2 and green fluorescent protein (GFP) [3][4][5] expression in living animals have been developed and applied to in vivo gene transfer models. Luciferase and GFP in vivo imaging techniques provide the advantages of non-invasive and repetitive monitoring of reporter gene expression in living animals, but are primarily qualitative/semi-quantitative and do not provide tomo-graphic images.…”