Figure 1. Images of IRDye 680 BoneTag 50 hours post
injection (intravenous delivery).
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 fluorescein1-3. In addition, near-infrared
(NIR) labeled pamidronate has been successfully used
for detection of arterial calcification in non-invasive
optical imaging.4
IRDye 680 BoneTag and IRDye 800CW BoneTag
are calcium-chelating compounds conjugated to either
IRDye 680 or IRDye 800CW NIR dyes. Use of IRDye NIR dyes
extends fluorescence signal detection to the NIR region
of the spectrum without affecting the compound’s
ability to function as a marker of the mineralization
process. NIR fluorescence detection improves depth of
penetration due to low tissue autofluorescence, translating
to low background interference.
The ability to visualize
bone anatomy and structures for an extended period facilitates
use of the IRDye BoneTag in conjunction with a second
optical agent specific for a primary target (i.e, tumor
tissue). In addition, IRDye 800CW BoneTag may prove effective
for studies dealing with bone metasteses and bone remodeling
studies.
Specificity
Bone-targeted binding was examined
using MC3T3 (osteoblast) cells in a cell-based assay.
MC3T3 cells exhibited a dose dependant increase in signal
when incubated with IRDye 680 BoneTag or IRDye 800CW
BoneTag. Incubation of either labeled bone tag with A431
cells (epidermoid carcinoma), a non-osteoblast cell line,
showed low non-specific binding.
