Bioluminescence probe for γ-glutamyl transpeptidase detection in vivo

Luminescence Probes in Bio-Applications: From Principle to Practice

Bioanalysis based on optical imaging has gained significant progress in the last few decades. Luminescence probes are capable of detecting, monitoring, and tracing particular biomolecules in complex biological systems to figure out the roles of these molecules in organisms. Considering the rapid development of luminescence probes for bio-applications and their promising future, we have attempted to explore the working principles and recent advances in bio-applications of luminescence probes, in the hope of helping readers gain a detailed understanding of luminescence probes developed in recent years. In this review, we first focus on the current widely used luminescence probes, including fluorescence probes, bioluminescence probes, chemiluminescence probes, afterglow probes, photoacoustic probes, and Cerenkov luminescence probes. The working principles for each type of luminescence probe are concisely described and the bio-application of the luminescence probes is summarized by category, including metal ions detection, secretion detection, imaging, and therapy.

Advances and Perspectives of Responsive Probes for Measuring γ-Glutamyl Transpeptidase

Gamma-glutamyltransferase (GGT) is a plasma-membrane-bound enzyme that is involved in the γ-glutamyl cycle, like metabolism of glutathione (GSH). This enzyme plays an important role in protecting cells from oxidative stress, thus being tested as a key biomarker for several medical conditions, such as liver injury, carcinogenesis, and tumor progression. For measuring GGT activity, a number of bioanalytical methods have emerged, such as chromatography, colorimetric, electrochemical, and luminescence analyses. Among these approaches, probes that can specifically respond to GGT are contributing significantly to measuring its activity in vitro and in vivo. This review thus aims to highlight the recent advances in the development of responsive probes for GGT measurement and their practical applications. Responsive probes for fluorescence analysis, including "off-on", near-infrared (NIR), two-photon, and ratiometric fluorescence response probes, are initially summarized, followed by discussing the advances in the development of other probes, such as bioluminescence, chemiluminescence, photoacoustic, Raman, magnetic resonance imaging (MRI), and positron emission tomography (PET). The practical applications of the responsive probes in cancer diagnosis and treatment monitoring and GGT inhibitor screening are then highlighted. Based on this information, the advantages, challenges, and prospects of responsive probe technology for GGT measurement are analyzed.

An Efficient, Site-Selective and Spontaneous Peptide Macrocyclisation During in vitro Translation

Macrocyclisation provides a means of stabilising the conformation of peptides, often resulting in improved stability, selectivity, affinity, and cell permeability. In this work, a new approach to peptide macrocyclisation is reported, using a cyanobenzothiazole-containing amino acid that can be incorporated into peptides by both in vitro translation and solid phase peptide synthesis, meaning it should be applicable to peptide discovery by mRNA display. This cyclisation proceeds rapidly, with minimal by-products, is selective over other amino acids including non N-terminal cysteines, and is compatible with further peptide elaboration exploiting such an additional cysteine in bicyclisation and derivatisation reactions. Molecular dynamics simulations show that the new cyclisation group is likely to influence the peptide conformation as compared to previous thioether-based approaches, through rigidity and intramolecular aromatic interactions, illustrating their complementarity.

Novel furimazine derivatives for nanoluciferase bioluminescence with various C-6 and C-8 substituents

Nanoluciferase (NLuc) is the emerging commercially available luciferase considering its small size and superior bioluminescence performance. Nevertheless, this bioluminescence system has some limitations, including narrow emission wavelength and single substrate. Herein, a series of novel furimazine derivatives at the C-6 and C-8 positions of the imidazopyrazinone core have been designed and synthesized for extension of the bioluminescence substrates. It should be noted that two compounds, molecules A2 (2-(furan-2-ylmethyl)-6-(4-(hydroxymethyl)phenyl)-8-(phenylthio)imidazo[1,2-a]pyrazin-3(7H)-one) and A3 (2-(furan-2-ylmethyl)-6-(4-amino-3-fluorophenyl)-8-(phenylthio)imidazo[1,2-a]pyrazin-3(7H)-one), display reasonable bioluminescence properties for in vitro and in vivo biological evaluations. In particular, compound A3 can broaden the application of NLuc bioluminescence techniques, especially for in vivo bioluminescent imaging.

A bioluminescent probe for in vivo imaging of pyroglutamate aminopeptidase in a mouse model of inflammation

Pyroglutamate aminopeptidase (PGP) specifically cleaves the peptide bond of pyroglutamic acid linked to the N-terminal end of a polypeptide or protein. Previous studies showed that PGP was associated with several physiological processes and diseases especially those involving inflammation. Utilizing a 'caging' strategy, we designed and synthesized a bioluminescence probe (PBL) with a limit-of-detection of 3.7 * 10^-4 mU/mL. In vivo imaging in a mouse model of inflammatory liver disease revealed that the probe has excellent sensitivity and selectivity and provides a powerful tool for studying the physiological and pathological processes involving PGP.

Emerging tools for bioluminescence imaging

Bioluminescence (BL) relies on the enzymatic reaction between luciferase, a substrate conventionally named luciferin, and various cofactors. BL imaging has become a widely used technique to interrogate gene expression and cell fate, both in small and large animal models of research. Recent developments include the generation of improved luciferase-luciferin systems for deeper and more sensitive imaging as well as new caged luciferins to report on enzymatic activity and other intracellular functions. Here, we critically evaluate the emerging tools for BL imaging aiming to provide the reader with an updated compendium of the latest developments (2018-2020) and their notable applications.

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.

Sensitive and selective SERS probe for detecting the activity of γ-glutamyl transpeptidase in serum

γ-Glutamyl transpeptidase (GGT) has attracted considerable attention for its regulatory effect on glutathione metabolism in living organisms; further, its close relationship with physiological dysfunctions such as hepatitis and liver cancers has enhanced its applicability. Therefore, the accurate detection of GGT levels is particularly important for the early diagnosis of diseases. Thus, we herein report the development of a surface-enhanced Raman spectroscopic (SERS) probe, namely bis-s,s'-((s)-4,4'-thiolphenylamide-Glu) (b-(s)-TPA-Glu), that comprises of a γ-glutamyl moiety for detection of the GGT activity. In this system, detection was achieved by observing differences in the SERS spectral profiles of the b-(s)-TPA-Glu probe and its corresponding hydrolysis product that resulted from the catalytic action of GGT. This SERS probe system exhibited a high selectivity toward GGT due to a combination of its specific catalytic action and the distinctive spectroscopic fingerprint of the SERS technique. The developed SERS approach was also found to be approximately linear in the range of 0.2-200 U/L, and a limit of detection of 0.09 U/L was determined. Furthermore, the proposed SERS method was suitable for detection of the GGT activity of clinical serum samples and also for evaluation of the inhibitors of GGT. Consequently, this approach is considered to be a promising diagnostic and drug screening tool for GGT-associated diseases.

An Activatable Chemiluminescent Probe for Sensitive Detection of γ-Glutamyl Transpeptidase Activity in Vivo

Activatable chemiluminescent probes that show enhanced chemiluminescence upon interaction with a molecular target of interest have offered promising tools for sensing and bioimaging in terms of low background, high sensitivity, and improved penetration depth in biological tissues. Here, we reported a γ-glutamyl transpeptidase (GGT) activatable chemiluminescent probe for real-time detection of GGT activity in vitro and in living mice. The probe was designed by caging an electron-withdrawing acrylic group-substituted Schaap's phenoxy-dioxetane with a GGT-recognitive substrate (γ-Glu) and a self-immolative linker (p-aminobenzyl alcohol), which was initially chemiluminescence off. Upon interaction with GGT, strong chemiluminescence with a more than 800-fold turn-on ratio could be achieved in aqueous solution, allowing to specifically detect GGT activity with ultrahigh signal-to-background ratio and sensitivity in vitro and in live cells. We demonstrated that the probe was reliable to quantify the GGT in serum, permitting to accurately report the elevated levels of GGT in lipopolysaccharide-treated mouse serum. Moreover, through real-time chemiluminescence imaging of GGT activity, the designed probe was feasible to detect GGT-positive tumors in living mice after intravenous systemic administration. This study demonstrates the high potential of GGT-activatable chemiluminescent probe for serum assays and molecular imaging, which might find wide applications in diagnosis of GGT-related diseases.

Recent Advances in the Development of Optical Imaging Probes for γ-Glutamyltranspeptidase

γ-Glutamyltranspeptidase (GGT) is a cell-membrane-bound protease that participates in cellular glutathione and cysteine homeostasis, which are closely related to many physiological and pathological processes. The accurate measurement of GGT activity is useful for the early diagnosis of diseases. In the past few years, many efforts have been made to build optical imaging probes for the detection of GGT activity both in vitro and in vivo. In this Minireview, recent advances in the development of various optical imaging probes for GGT, including activatable fluorescence probes, ratiometric fluorescence probes, and activatable bioluminescence probes, are summarized. This review starts from the instruction of the GGT enzyme and its biological functions, followed by a discussion of activatable fluorescence probes that show off-on fluorescence in response to GGT. GGT-activatable two-photon fluorescence imaging probes with improved imaging depth and spatial resolution are also discussed. Ratiometric fluorescence probes capable of accurately reporting on GGT levels through a self-calibration mechanism are discussed, followed by describing GGT-activatable bioluminescence probes that can offer a high signal-to-background ratio to detect GGT in living mice. Finally, current challenges and further perspectives for the development of molecular imaging probes for GGT are addressed.

Bioluminescent Probe for Detection of Starvation-Induced Pantetheinase Upregulation

Pantetheinase, a glycosylphosphatidylinositol (GPI) anchored enzyme, overexpresses in intestine, liver, and kidney with various biological functions such as its linkage to the inflammation and some metabolic diseases. It can hydrolyze pantetheine to cysteamine, an antioxidant, and pantothenic acid (Vitamin B5) that is an essential component of coenzyme A (CoA). Until now, very few analytic methods were developed for this enzyme, hampering the further investigation of its biological functions. In this work, we report the design, synthesis, and biological examination of a highly sensitive bioluminogenic probe for pantetheinase with a limit of detection of 1.14 ng/mL. Furthermore, animal experiments validated that our probe can be applied to detect the endogenous pantetheinase activity. To the best of our knowledge, this is the first bioluminogenic probe achieving the detection of pantetheinase level in vivo.

Novel photoactivatable substrates for Renilla luciferase imaging in vitro and in vivo

To develop a photoactivatable bioluminescence imaging technique, a set of high and efficient photoactivatable substrates for Renilla luciferase has been well designed and synthesized. Surprisingly, all of them could release the free luciferin that presented robust bioluminescent signals ex vivo and in living animals after UV irradiation at 365 nm.