In vivo imaging in cancer

Abstract

Imaging has become an indispensable tool in the study of cancer biology and in clinical prognosis and treatment. The rapid advances in high resolution fluorescent imaging at single cell level and MR/PET/CT image registration, combined with new molecular probes of cell types and metabolic states, will allow the physical scales imaged by each to be bridged. This holds the promise of translation of basic science insights at the single cell level to clinical application. In this article, we describe the recent advances in imaging at the macro- and micro-scale and how these advances are synergistic with new imaging agents, reporters, and labeling schemes. Examples of new insights derived from the different scales of imaging and relevant probes are discussed in the context of cancer progression and metastasis.

Figure 1.

Imaging technologies used in oncology. Several macroscopic imaging technologies (above date line) are in routine clinical use and have advanced tremendously in their capabilities to obtain anatomic and functional information. Microscopic and other intravital optical techniques (below date line) have evolved over the last decade and now allow experimental studies of genetic, molecular, and cellular events in vivo (reproduced with permission from Nature).

Figure 2.

Combination of MIW and photoconversion allows monitoring of the behavior of tumor cells in specific microenvironments. (A) An imaging box allows for reproducible animal positioning and environmental control (bottom, side, and full views). A mouse is placed in the box and the MIW is secured in place between two sliding doors on the bottom of the box. Anesthesia flow is established. (B) Photograph of the form fitting MIW. The MIW is cast in silicon molds from polyester resin. Scale bar, 4 mm. (C) Tumor cell behavior is controlled by the microenvironment. Images are shown of an area photoconverted next to a major blood vessel (white dotted line) taken at 0 h (left panel), 6 h (middle), and 24 h (right panel) after photoconversion. Photoconverted tumor cells disappear or move closer to the blood vessel at 24 h and appear in the lung (not shown). Scale bar, 50 µm (see Kedrin et al. 2008). (D) Four channel multiphoton imaging allows the visualization of interactions between macrophages and tumor cells in specific microenvironments. Images were taken after photoconversion of Dendra2 tumor cells. Channels collected: collagen (white, SHG), tumor cells (green and red, Dendra2), and macrophages (blue, AlexaFluor647 dextran 10 K). Scale bar, 10 µm. Figures courtesy of Bojana Gligorijevic of the Gruss-Lipper Biophotonics Center.

Figure 3.

Custom-built two-laser multiphoton microscope (TLMPM) provides excitation at 650–1040 nm and 1100–1600 nm and collection in four distinct channels. Optical Layout of TLMPM. Wavelengths <950 nm are excited by the Tsunami laser and 960–1040 nm by the Mai-Tai laser. For excitation at 1100–1600 nm, a flip mirror in the light path switches the Mai-Tai from being an illumination source to a pump beam for the OPO. Fluorescence is collected in one of four PMT detectors. Figures courtesy of David Entenberg of the Gruss-Lipper Biophotonics Center.

Figure 4.

Multiphoton imaging of mammary tumors in two color mice. The genotype of this mouse is MMTV-PyMT × MMTV-iCre/CAG-CAC-ECFP × c-fms-GFP where mice expressing CFP in tumor cells (white) and GFP in macrophages (green) allows the visualization of interactions between tumor cells and macrophages in living tumors. (A, B) Tumor cells interacting with macrophages in the invasion microenvironment. In the two sequences of still frames (left to right in time over 8 min) from two time lapse movies (A, B), interactions between tumor cells and macrophages (Ф) are observed during the macrophage-mediated initiation of tumor cell migration. Scale bars, A and B = 10 µm. (C) Tumor cells interact with peri-vascular macrophages in a relay pattern. In the first three panels (0, 4, 8 min) taken from a movie, a peri-vascular macrophage (Ф) adjacent to a blood vessel (line marks the wall of blood vessel [BV]) is attracting two tumor cells (arrows), which in turn attract another macrophage (* in second and third frame) all converging on the peri-vascular macrophage (pseudo coloring of tumor cells is purple; macrophages are green). (D) Tumor cells and their accompanying macrophages collectively migrate in single file in mammary tumors. In this sequence of still frames taken at 0, 7, and 14 min, a tumor cell (yellow outline) is followed closely by a macrophage (green outline), which in turn is followed by a tumor cell. This type of migration is believed to result from relay chemotaxis involving the EGF/CSF1 paracrine loop. Scale bars, C and D = 25 µm. Figure courtesy of Jeffrey Wyckoff, Gruss-Lipper Biophotonics Center.