An allylated firefly luciferin analogue with luciferase specific response in living cells

A Comprehensive Exploration of Bioluminescence Systems, Mechanisms, and Advanced Assays for Versatile Applications

Bioluminescence has been a fascinating natural phenomenon of light emission from living creatures. It happens when the enzyme luciferase facilitates the oxidation of luciferin, resulting in the creation of an excited-state species that emits light. Although there are many bioluminescent systems, few have been identified. D-luciferin-dependent systems, coelenterazine-dependent systems, Cypridina luciferin-based systems, tetrapyrrole-based luciferins, bacterial bioluminescent systems, and fungal bioluminescent systems are natural bioluminescent systems. Since different bioluminescence systems, such as various combinations of luciferin-luciferase pair reactions, have different light emission wavelengths, they benefit industrial applications such as drug discovery, protein-protein interactions, in vivo imaging in small animals, and controlling neurons. Due to the expression of luciferase and easy permeation of luciferin into most cells and tissues, bioluminescence assays are applied nowadays with modern technologies in most cell and tissue types. It is a versatile technique in a variety of biomedical research. Furthermore, there are some investigated blue-sky research projects, such as bioluminescent plants and lamps. This review article is mainly based on the theory of diverse bioluminescence systems and their past, present, and future applications.

Synthesis and Bioluminescence of 'V'-Shaped Firefly Luciferin Analogues Based on A Novel Benzobisthiazole Core

The design of π-extended conjugation 'V'-shaped red shifted bioluminescent D-luciferin analogues based on a novel benzobisthiazole core is described. The divergent synthetic route allowed access to a range of amine donor substituents through an SN Ar reaction. In spectroscopic studies, the 'V'-shaped luciferins exhibited narrower optical band gaps, more red-shifted absorption and emission spectra than D-luciferin. Their bioluminescence characteristics were recorded against four different luciferases (PpyLuc, FlucRed, CBR2 and PLR3). With native luciferase PpyLuc, the 'V'-shaped luciferins demonstrated more red-shifted emissions than D-luciferin (λbl =561 nm) by 60 to 80 nm. In addition, the benzobisthiazole luciferins showed a wide range of bioluminescence spectra from the visible light region (λbl =500 nm) to the nIR window (>650 nm). The computational results validate the design concept which can be used as a guide for further novel D-luciferin analogues based upon other 'V'-shaped heterocyclic cores.

Bioluminescence, photophysical, computational and molecular docking studies of fully conformationally restricted enamine infraluciferin

A new rationally designed fully rotationally restricted luciferin has been synthesised. This synthetic luciferin, based upon the structure of infraluciferin, has two intramolecular H-bonds to reduce degrees of freedom, an amine group to enhance ICT process, and an alkenyl group to increase π-conjugation. In the spectroscopic measurements and computational calculations, enamine luciferin showed more red-shifted absorption and fluorescence emission than LH₂ and iLH₂. With PpyWT luciferase enamine luciferin gave bioluminescence at 564 nm which is similar to LH₂ at 561 nm. Further investigation by docking studies revealed that the emission wavelength of enamine luciferin might be attributed to the unwanted twisted structure caused by Asp531 within the enzyme. With mutant luciferase FlucRed, the major emission peak was shifted to 606 nm, a distinct shoulder above 700 nm, and 21% of its spectrum located in the nIR range.

Computational Investigation of Substituent Effects on the Fluorescence Wavelengths of Oxyluciferin Analogs

Oxyluciferin, which is the light emitter for firefly bioluminescence, has been subjected to extensive chemical modifications to tune its emission wavelength and quantum yield. However, the exact mechanisms for various electron-donating and withdrawing groups to perturb the photophysical properties of oxyluciferin analogs are still not fully understood. To elucidate the substituent effects on the fluorescence wavelength of oxyluciferin analogs, we applied the absolutely localized molecular orbitals (ALMO)-based frontier orbital analysis to assess various types of interactions (i.e. permanent electrostatics/exchange repulsion, polarization, occupied-occupied orbital mixing, virtual-virtual orbital mixing, and charge-transfer) between the oxyluciferin and substituent orbitals. We suggested two distinct mechanisms that can lead to red-shifted oxyluciferin emission wavelength, a design objective that can help increase the tissue penetration of bioluminescence emission. Within the first mechanism, an electron-donating group (such as an amino or dimethylamino group) can contribute its highest occupied molecular orbital (HOMO) to an out-of-phase combination with oxyluciferin's HOMO, thus raising the HOMO energy of the substituted analog and narrowing its HOMO-LUMO gap. Alternatively, an electron-withdrawing group (such as a nitro or cyano group) can participate in an in-phase virtual-virtual orbital mixing of fragment LUMOs, thus lowering the LUMO energy of the substituted analog. Such an ALMO-based frontier orbital analysis is expected to lead to intuitive principles for designing analogs of not only the oxyluciferin molecule, but also many other functional dyes.

Discovery of alkene-conjugated luciferins for redshifted and improved bioluminescence imaging in vitro and in vivo

The firefly luciferase system is the most extensively utilized bioluminescence system in the field of life science at the moment. In this work, we designed and synthesized a series of alkene-conjugated luciferins to develop new firefly bioluminescence substrates, and further evaluated their activities in vitro and in vivo. It is worth noting that the maximum biological emission wavelength of novel luciferin analogue AL3 ((S,E)-2-(6-hydroxy-5-(3-methoxy-3-oxoprop-1-en-1-yl)benzo[d]thiazol-2-yl)-4,5-dihydrothiazole-4-carboxylic acid) is 100 nm red-shifted compared with D-luciferin, while that of analogue AL4 ((S,E)-2-(5-(2-cyanovinyl)-6-hydroxybenzo[d]thiazol-2-yl)-4,5-dihydrothiazole-4-carboxylic acid) is 75 nm red-shifted. The new substrate AL2 ((S,E)-2-(6-hydroxy-7-(3-methoxy-3-oxoprop-1-en-1-yl)benzo[d]thiazol-2-yl)-4,5-dihydrothiazole-4-carboxylic acid) showed better bioluminescence performance in vivo.

From imines to amides via NHC-mediated oxidation

An efficient construction of amides through NHC-mediated oxidation of imines is described. This work has the advantages of wide scope, fast assembly and high yield, and can avoid the use of coupling agents, such as HATU, DCC, etc.

Molecular Design of d-Luciferin-Based Bioluminescence and 1,2-Dioxetane-Based Chemiluminescence Substrates for Altered Output Wavelength and Detecting Various Molecules

Optical imaging including fluorescence and luminescence is the most popular method for the in vivo imaging in mice. Luminescence imaging is considered to be superior to fluorescence imaging due to the lack of both autofluorescence and the scattering of excitation light. To date, various luciferin analogs and bioluminescence probes have been developed for deep tissue and molecular imaging. Recently, chemiluminescence probes have been developed based on a 1,2-dioxetane scaffold. In this review, the accumulated findings of numerous studies and the design strategies of bioluminescence and chemiluminescence imaging reagents are summarized.

Recent achievements of bioluminescence imaging based on firefly luciferin-luciferase system

Bioluminescence imaging (BLI) is a newly developed noninvasive visual approach which facilitates the understanding of a plethora of biological processes in vitro and in vivo due to the high sensitivity, resolution and selectivity, low background signal, and the lack of external light excitation. BLI based on firefly luciferin-luciferase system has been widely used for the activity evaluation of tumor-specific enzymes, for the detection of diseases-related bioactive small molecules and metal ions, and for the diagnosis and therapy of diseases including the studies of drug transport, the research of immune response, and the evaluation of drug potency and tissue distribution. In this review, we highlight the recent achievements in luciferin derivatives with red-shifted emission spectra, mutant luciferase-luciferin pairs, and the diagnostic and therapeutic application of BLI based on firefly luciferin-luciferase system. The development and application of BLI will expand our knowledge of the occurrence and development of diseases and shed light on the diagnosis and treatment of various diseases.

Ring-Fused Firefly Luciferins: Expanded Palette of Near-Infrared Emitting Bioluminescent Substrates

Firefly bioluminescence is broadly applied as a noninvasive imaging modality in the biomedical research field. One limitation in firefly bioluminescence imaging is the limited variety of luciferins emitting in the near-infrared (NIR) region (650-900 nm), where tissue penetration is high. Herein, we describe a series of structure-inherent NIR emitting firefly luciferin analogues, NIRLucs, designed through a ring fusion strategy. This strategy resulted in pH-independent structure-inherent NIR emission with a native firefly luciferase, which was theoretically supported by quantum chemical calculations of the oxidized form of each luciferin. When applied to cells, NIRLucs displayed dose-independent improved NIR emission even at low concentrations where the native d-luciferin substrate does not emit. Additionally, excellent blood retention and brighter photon flux (7-fold overall, 16-fold in the NIR spectral range) than in the case of d-luciferin have been observed with one of the NIRLucs in mice bearing subcutaneous tumors. We believe that these synthetic luciferins provide a solution to the longstanding limitation in the variety of NIR emitting luciferins and pave the way to the further development of NIR bioluminescence imaging platforms.

Light emission colour modulation study of oxyluciferin synthetic analogues via QM and QM/MM approaches

Study of emission spectra of three analogues of firefly oxyluciferin in gas phase, in water (PCM) and in protein.