Multiplex quadruple bioluminescent assay system

Regiospecific Coelenterazine Analogs for Bioassays and Molecular Imaging

Bioluminescence (BL) generated by luciferase-coelenterazine (CTZ) reactions is broadly employed as an optical readout in bioassays and in vivo molecular imaging. In this study, we demonstrate a systematic approach to elucidate the luciferase-CTZ binding chemistry with a full set of regioisomeric CTZ analogs, where all the functional groups were regiochemically modified. When the chemical structures were categorized into Groups 1-6, the even-numbered Groups (2, 4, and 6) of the CTZ analogs are found to be exceptionally bright with NanoLuc enzyme. A CTZ analogue M2 was the brightest with NanoLuc and the reason was deciphered by a computational analysis of the binding modes. We also report that (i) the regioisomeric CTZ analogs collectively create unique intensity patterns according to each marine luciferase, (ii) the quantitative structure-activity relationship analysis revealed the roles of respective functional groups of CTZ analogs, and (iii) the regioisomeric CTZ analogs also exert red shifts of the BL spectra and color variation: that is, the λmax values are near 500 nm with NanoLuc, near 530 nm with ALuc16, and near 570 nm with RLuc86SG. The advantages of the regioisomeric CTZ analogs were finally demonstrated using (i) a dual-luciferase system with M2-specific NanoLuc and native CTZ-specific ALuc16, (ii) an estrogen activatable single-chain BL probe by imaging, and (iii) BL imaging of live mice bearing tumors expressing NanoLuc and RLuc8.6SG. This study is the first systematic approach to elucidate the regiochemistry in BL imaging studies. This study provides new insights into how CTZ analogs regiochemically work in BL reporter systems and guides the specific applications to molecular imaging.

Current advances in the use of bioluminescence assays for drug discovery: an update of the last ten years

INTRODUCTION

Bioluminescence is a well-established optical detection technique widely used in several bioanalytical applications, including high-throughput and high-content screenings. Thanks to advances in synthetic biology techniques and deep learning, a wide portfolio of luciferases is now available with tuned emission wavelengths, kinetics, and high stability. These luciferases can be implemented in the drug discovery and development pipeline, allowing high sensitivity and multiplexing capability.

AREAS COVERED

This review summarizes the latest advancements of bioluminescent systems as toolsets in drug discovery programs for in vitro applications. Particular attention is paid to the most advanced bioluminescence-based technologies for drug screening over the past 10 years (from 2013 to 2023) such as cell-free assays, cell-based assays based on genetically modified cells, bioluminescence resonance energy transfer, and protein complementation assays in 2D and 3D cell models.

EXPERT OPINION

The availability of tuned bioluminescent proteins with improved emission and stability properties is vital for the development of bioluminescence assays for drug discovery, spanning from reporter gene technology to protein-protein techniques. Further studies, combining machine learning with synthetic biology, will be necessary to obtain new tools for sustainable and highly predictive bioluminescent drug discovery platforms.

Coelenterazine Indicators for the Specific Imaging of Human and Bovine Serum Albumins

Albumin assays in serum are important for the prognostic assessment of many life-threatening diseases, such as heart failure, liver disease, malnutrition, inflammatory bowel disease, infections, and kidney disease. In this study, synthetic coelenterazine (CTZ) indicators are developed to quantitatively illuminate human and bovine serum albumins (HSA and BSA) with high specificity. Their functional groups were chemically modified to specifically emit luminescence with HSA and BSA. The CTZ indicators were characterized by assaying the most abundant serum proteins and found that the CTZ indicators S6 and S6h were highly specific to HSA and BSA, respectively. Their colors were dramatically converted from blue, peaked at 480 nm, to yellowish green, peaked at 535 nm, according to the HSA-BSA mixing ratios, wherein the origins and mixing levels of the albumins can be easily determined by their colors and peak positions. The kinetic properties of HSA and BSA were investigated in detail, confirming that the serum albumins catalyze the CTZ indicators, which act as pseudo-luciferases. The catalytic reactions were efficiently inhibited by specific inhibitors, blocking the drug-binding sites I and II of HSA and BSA. Finally, the utility of the CTZ indicators was demonstrated through a quantitative imaging of the real fetal bovine serum (FBS). This study is the first example to show that the CTZ indicators specify HSA and BSA with different colors. This study contributes to the expansion of the toolbox of optical indicators, which efficiently assays serum proteins in physiological samples. Considering that these CTZ indicators immediately report quantitative optical signals with high specificity, they provide solutions to conventional technical hurdles on point-of-care assays of serum albumins.

S-Series Coelenterazine-Driven Combinatorial Bioluminescence Imaging Systems for Mammalian Cells

A unique combinatorial bioluminescence (BL) imaging system was developed for determining molecular events in mammalian cells with various colors and BL intensity patterns. This imaging system consists of one or multiple reporter luciferases and a series of novel coelenterazine (CTZ) analogues named "S-series". For this study, ten kinds of novel S-series CTZ analogues were synthesized and characterized concerning the BL intensities, spectra, colors, and specificity of various marine luciferases. The characterization revealed that the S-series CTZ analogues luminesce with blue-to-orange-colored BL spectra with marine luciferases, where the most red-shifted BL spectrum peaked at 583 nm. The colors completed a visible light color palette with those of our precedent C-series CTZ analogues. The synthesized substrates S1, S5, S6, and S7 were found to have a unique specificity with marine luciferases, such as R86SG, NanoLuc (shortly, NLuc), and ALuc16. They collectively showed unique BL intensity patterns to identify the marine luciferases together with colors. The marine luciferases, R86SG, NLuc, and ALuc16, were multiplexed into multi-reporter systems, the signals of which were quantitatively unmixed with the specific substrates. When the utility was applied to a single-chain molecular strain probe, the imaging system simultaneously reported three different optical indexes for a ligand, i.e., unique BL intensity and color patterns for identifying the reporters, together with the ligand-specific fold intensities in mammalian cells. This study directs a new combinatorial BL imaging system to specific image molecular events in mammalian cells with multiple optical indexes.