Fluorescence can be used to report the location of biomolecules or tissue of interest in vivo with a high contrast-to-background ratio. By taking a series of fluorescent images at different time points, the development of diseases can be tracked in living organisms. Because of their endogenous expression, fluorescent proteins (FPs) allow observation with minimal disturbance to the subject.1 Cancer cells can be engineered to carry FPs stably and implanted into the subject to allow monitoring of metastasis and the effectiveness of treatment.
Through the use of fully automated large format optics, the UVP iBox Small Animal Imaging System can image a fluorescent tumor in vivo. The high-resolution camera and fast lens provides maximum imaging flexibility. The typical exposures are less than 50 ms, minimizing the effect of animal movement. The optics permits reproducible and rapid imaging with software presets and macros. Directed lighting with the use of filters allows imaging up to the near IR range for detection of fluorescent tumors labeled with green, cyan, and red fluorescent proteins. The illustration discusses the use of red fluorescent protein in cancer metastasis and treatment.
Evaluating Cancer Treatment
A time-controlled sequence of fluorescent images was taken on two groups of mice. Both groups received an injection of RFP-U87 brain cancer cells.2 Comparing the untreated control (A) to the treated group (B) at day 7 indicates that the tumor was targeted by Salmonella A1-R, which was administered intravenously via weekly injections. This resulted in a significant reduction in the tumor growth in the treatment group. The use of single color imaging of tumors is critical to time course studies and illustrates the importance of fluorescent protein imaging in cancer research.
The intensity and area of interest of the fluorescence signal can be used to quantify the progression of the disease, which is visualized by the fluorescent reporter. The 3D volume of the disease can be estimated from the area measured in two dimensional images. In a widespread cancer metastases study, the area measured was found to have an easily-formulated relationship with the volume of the tumor.3 UVP’s VisionWorks Software incorporates the formula and reports the volume in a graphical and tabular format.
Using fluorescent proteins to track small animal tumor growth in vivo provides the necessary indicators to visualize and detect effectiveness of cancer treatment.
1. Hoffman RM and Yang M. Whole-body imaging with fluorescent proteins. Nat Protoc. 2006;1(3):1429.
2. Kimura H, et al. Target therapy of spinal cord glioma with a genetically modified Salmonella typhimurium. Cell Prolif. 2010;43(1):41-8.
3. Katz MH, et al. A novel red fluorescent protein orthotopic pancreatic cancer model for the preclinical evaluation of chemotherapeutics. J Surg Res. 2003; 113(1):151-60.
This article was published in Drug Discovery & Development magazine: Vol. 13, No. 2, March 2010, p. 20.