Bioluminescence imaging (BLI) has been an indispensable technique for noninvasive and highly sensitive observation of biological events in living tissues1-3. Firefly luciferase (Fluc) and D-luciferin have been a standard bioluminescence system for noninvasive small animal imaging. This bioluminescence system generates light signals within visible wavelength (λmax = 560 nm) where light is highly absorbed by hemoglobin and melanin4,5. This fact motivated us to develop a bioluminescence system generating near-infrared light that could penetrate living tissues deeply. Maki et al. evaluated synthetic substrate TokeOni (aka AkaLumine-HCl) (Product No. 808350) that emits near-infrared (λmax = 677 nm) in the reaction with native Fluc6. BLI imaging with TokeOni successfully achieved highly sensitive imaging of deep tissues7. However, poor solubility (< 1 mM) of TokeOni in neutral-buffered aqueous media limits its applications in some biological experiments.
We are now introducing a newly synthesized substrate, seMpai (Product No: 902268), a TokeOni analog that emits near-infrared bioluminescence in the reaction with Fluc, similar to TokeOni (Figure 1). In addition, seMpai offers high solubility (> 60 mM) in neutral-buffered aqueous media and is stable for several months under -80 ˚C.
Figure 1.Chemical structures and bioluminescent spectrums of SeMpai, D-luciferin and TokeOni.
Detection of lung metastasis in mice demonstrated that the detection sensitivity of seMpai is higher than that of D-luciferin (Figure 2) and is comparable with that of TokeOni8.
Figure 2.Highly-sensitive noninvasive imaging of lung metastasis with seMpai. The murine lung metastasis was established 2 weeks after intravenous injection of LLC/Fluc cells into B6 albino mice. The bioluminescence images were acquired 15 minutes after intraperitoneal administration of D-luciferin or seMpai (120 μMol / kg).
Overall results suggest that seMpai is a suitable substrate of near-infrared BLI for many biological experiments. Its high solubility in neutral buffer conditions further extends the bioluminescent application of TokeOni derivatives.
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