Abstract
NanoLuc luciferase recently gained popularity due to its small size and superior bioluminescence performance. For in vivo imaging applications, NanoLuc has been limited by its substrate furimazine, which has low solubility and bioavailability. Herein, we compared the performances of recently reported NanoLuc luciferase substrates for in vivo imaging in mice. Two substrates with improved aqueous solubility, hydrofurimazine and fluorofurimazine, were evaluated along with three stabilized O-acetylated furimazine analogues, the hikarazines. All 5 analogues, when tested in vitro, displayed greater signal intensity and reaction duration, in comparison to the standard NanoLuc substrate, furimazine. The two best-performing analogues from the in vitro study were selected for further in vivo testing. The NanoLuc/fluorofurimazine pair demonstrated the highest bioluminescence intensity, post intravenous administration. It was found to be around 9-fold brighter compared to the NanoLuc/furimazine and 11-fold more intense than the NanoLuc/hikarazine-003 pair, with an average of 3-fold higher light emission when the substrate was injected intraperitoneally, in a subcutaneous model. Excitingly, despite the fact that NanoLuc/fluorofurimazine emits mostly blue light, we prove that cells trapped in mice lungs vasculature could be visualised via the NanoLuc/fluorofurimazine pair and compare the results to the AkaLuc/AkaLumine system. Therefore, among the tested analogues, fluorofurimazine enables higher substrate loading and improved optical imaging sensitivity in small animals, upgrading the use of NanoLuc derived bioluminescent systems for deep tissue imaging.
Highlights
Bioluminescence imaging (BLI) is based on a biochemical reaction that is dependent on the oxidation of a luminophore containing sub strate by luciferase enzymes with light emission as a result
We found that peak light emission was highest with hikarazine-003, followed by hikarazine-001, hikarazine-097 and fluorofurimazine
The results demonstrated that the NanoLuc/fluorofurimazine pair was significantly brighter than the NanoLuc/furimazine pair and around 11.62 fold higher than the NanoLuc/hikarazine/003 pair (Fig. 3d) when adminis tered i.v. at equimolar doses
Summary
Bioluminescence imaging (BLI) is based on a biochemical reaction that is dependent on the oxidation of a luminophore containing sub strate (luciferin) by luciferase enzymes with light emission as a result. Luciferase enzymes and their substrates are extensively used as effective, non-invasive screening tools in diverse research fields and have become a prominent method for live-cell visualization. Several thousand bioluminescent species are represented by ~700 genera among which 90% originate from marine organisms [2,3]. Lu ciferases from marine luminous organisms primarily utilise as sub strates, coelenterazine [2], varguline [3] or analogues of these two. Coelenterazine (CTZ) is best-known as the substrate for luciferases derived from the sea pansy Renilla reniformis (RLuc), the luminous shrimp Oplophorus gracilirostris and the copepod Gaussia princeps (GLuc), yielding light with a fast enzymatic turnover and an emission maxima in the blue region (450–485 nm) of the visible spectrum
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