January 2008 Update: IRDye 800CW 2-DG Optical Probe Now Available. Click for more information.
October 3, 2007, Lincoln, NE: LI-COR Biosciences recently presented two posters detailing research and development of two new IRDye® infrared dye optical agents for cancer research. IRDye 800CW 2DG can be used for studying tumor biology in mice and the IRDye 680 Bone Marker makes it possible to visualize bone anatomy/structures for an extended period and facilitates use of the bone targeting agent in conjunction with a second optical agent specific for a primary target (i.e, tumor tissue).
The products are planned for commercial availability in early 2008. Additional information is contained in the following abstracts:
IRDye® 800CW 2-deoxyglucose, a near infrared metabolic optical imaging agent?
Joy L Kovar, William Volcheck, D Michael Olive, and Melanie A Simpson
Cancer cells are often characterized by a high metabolic rate exemplified in dramatically elevated glucose uptake. This biological activity has been exploited for noninvasive imaging by positron emission tomography using glucose analogues such as 18F-2-deoxy-D-glucose to generate a tumor-localized signal. In this work, our goal was to adapt a similar methodology for optical imaging of tumors in mice. We selected a fluorophore with maximal excitation and emission wavelengths in the near infrared (NIR) spectral range (700-900 nm), where low absorption coefficients of tissues allow greater optical sensitivity, deeper tissue penetration, and low autofluorescence. The NIR fluorophore, IRDye 800CW (excitation/emission of 778 nm/794 nm), was covalently coupled to 2-deoxyglucose (2DG). The resultant conjugate was evaluated first for specificity and sensitivity in vitro. Specificity of the agent was assessed using an In-Cell Western assay, in which concentration dependence of label uptake was established by fluorescence changes in a high throughput microplate format. Uptake of the labeled agent was specifically blocked in a dose dependent manner by addition of unlabeled 2-deoxyglucose. Subsequent in vivo studies were conducted to optimize dosing, clearance, and the optimal time post-injection for signal capture in nude mice. A research prototype imager, optimized to detect IRDye 800CW signal, was used to characterize the IRDye 800CW 2DG optical agent in subcutaneous tumors derived from either an epithelial carcinoma (A431 cells), colorectal carcinoma (SW620 cells), or prostate carcinomas (PC3M-LN4 and 22Rv1). In all cases, the tumors were clearly imaged with good signal to noise characteristics. This pilot demonstration suggests IRDye 800CW 2DG will be an excellent general optical imaging tool for studying tumor biology in mice.
Effective bone labeling for in vivo NIR noninvasive imaging in nude mice
Joy L. Kovar, Xinshe Xu, Melanie Simpson, D. Michael Olive
ABSTRACT
Calcium-chelating compounds have been used effectively for the detection of bone mineralization, growth, and morphological changes, including tetracycline derivatives, xylenol orange, alizarin, calcein, and fluorescein. These compounds contain iminodiacetic acid groups that can form chelating complexes with apatite and provide a certain level of native fluorescence in the visible spectrum as the complexes become incorporated in mineralizing bone. We chose to exploit these characteristics to produce a near infrared (NIR) optical bone marker for small animal imaging. By conjugating compounds to IRDye® 800CW or IRDye 680, we have extended the effective fluorescence signal detection to the NIR region without affecting the compound’s ability to function as a marker of the mineralization process. Initial screening of multiple compounds was performed using MC3T3-E1 (osteoblasts) in an in vitro cell-based assay. Two of the seven compounds exhibited signal intensities approximately 3–6X higher than the others. Subsequent in vivo testing of Compounds A and F demonstrated effective skeletal labeling for imaging which is unabated several weeks post-administration. The ability to visualize bone anatomy/structures for an extended period will facilitate use of the bone targeting agent in conjunction with a second optical agent specific for a primary target (i.e, tumor tissue). We demonstrate a multiple probe application with the administration of IRDye 680 bone marker one week prior to implantation of prostate tumor cells in the flank of a nude mouse. Animals received weekly intravenous injections of IRDye 800CW 2-deoxyglucose and were imaged 24 hours post-injection over a six-week period, using a prototype small animal imaging system. The results provide evidence that NIR labeled conjugates are useful for multiple probe/localization applications in small animal imaging.
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