Dual-color bioluminescent bioreporter for forensic analysis: evidence of androgenic and anti-androgenic activity of illicit drugs

Review on activity-based detection of doping substances and growth promotors in biological matrices: do bioassays deserve a place in control programs?

BACKGROUND

Control programs such as anti-doping control and growth promotor residue surveillance programs are challenged by the emergence of designer drugs and the use of low-level drug cocktails. In order to cope with these challenges, the use of bioassays, measuring biological activity in a matrix, has been explored over the past two decades as a universal means to detect (combinations of) unknown drugs, regardless of their chemical structure.

RESULTS

This review compiles the experience on the use of activity-based assays to detect doping substances and growth promotors in biological matrices of humans (athletes) or live animals (race and/or food-producing animals). The aim is to learn from the scientific progress, going from initial research to the recent revival of this topic. Bioassay improvements and remaining limitations are discussed, along with a rational evaluation of possible applications of bioassays in control programs at their current functionality. Limitations include the possible interference by endogenous compounds and the challenge to detect metabolically activated (pro-)drugs. Nevertheless, successful validation of bioassays has been achieved, ensuring robust, reliable and valid results.

SIGNIFICANCE

We conclude by proposing three applications of bioassays that provide added-value to the current testing procedures: (i) characterization of compounds to provide indisputable proof of biological effects and to prioritize legislative (cf. expansion of bans) and research endeavors (cf. method development), (ii) bioassay-based screening of biological samples to direct intelligent sample storage, sample retesting and targeted athlete testing, (iii) bioassay-guided identification of drugs to overcome the challenges of suspicious peak selection, related to high-resolution techniques.

Bioluminescence goes portable: recent advances in whole-cell and cell-free bioluminescence biosensors

Recent advancements in synthetic biology, organic chemistry, and computational models have allowed the application of bioluminescence in several fields, ranging from well established methods for detecting microbial contamination to in vivo imaging to track cancer and stem cells, from cell-based assays to optogenetics. Moreover, thanks to recent technological progress in miniaturized and sensitive light detectors, such as photodiodes and imaging sensors, it is possible to implement laboratory-based assays, such as cell-based and enzymatic assays, into portable analytical devices for point-of-care and on-site applications. This review highlights some recent advances in the development of whole-cell and cell-free bioluminescence biosensors with a glance on current challenges and different strategies that have been used to turn bioassays into biosensors with the required analytical performance. Critical issues and unsolved technical problems are also highlighted, to give the reader a taste of this fascinating and challenging field.

Prêt-à-porter nanoYESα and nanoYESβ bioluminescent cell biosensors for ultrarapid and sensitive screening of endocrine-disrupting chemicals

Cell-based assays utilizing reporter gene technology have been widely exploited for biosensing, as they provide useful information about the bioavailability and cell toxicity of target analytes. The long assay time due to gene transcription and translation is one of the main drawbacks of cell biosensors. We report the development of two yeast biosensors stably expressing human estrogen receptors α and β and employing NanoLuc as the reporter protein to upgrade the widely used yeast estrogen screening (YES) assays. A viability control strain was also developed based on a chimeric green-emitting luciferase, PLG2, expressed for the first time in Saccharomycescerevisiae. Thanks to their brightness, NanoLuc and PLG2 provided excellent sensitivity, enabling the implementation of these biosensors into low-cost smartphone-based devices. The developed biosensors had a rapid (1 h) response and reported on (anti)estrogenic activity via human estrogen receptors α and β as well as general sample toxicity. Under optimized conditions, we obtained LODs of 7.1 ± 0.4 nM and 0.38 ± 0.08 nM for E2 with nanoYESα and nanoYESβ, respectively. As a proof of concept, we analyzed real samples from plants showing significant estrogenic activity or known to contain significant amounts of phytoestrogens. Graphical abstract.

Luciferase Genes as Reporter Reactions: How to Use Them in Molecular Biology?

: The latest advances in molecular biology have made available several biotechnological tools that take advantage of the high detectability and quantum efficiency of bioluminescence (BL), with an ever-increasing number of novel applications in environmental, pharmaceutical, food, and forensic fields. Indeed, BL proteins are being used to develop ultrasensitive binding assays and cell-based assays, thanks to their high detectability and to the availability of highly sensitive BL instruments. The appealing aspect of molecular biology tools relying on BL reactions is their general applicability in both in vitro assays, such as cell cultures or purified proteins, and in vivo settings, such as in whole-animal BL imaging. The aim of this chapter is to provide the reader with an overview of state-of-the-art bioluminescent tools based on luciferase genes, highlighting molecular biology strategies that have been applied so far, together with some selected examples.

Dual-color bioluminescence imaging assay using green- and red-emitting beetle luciferases at subcellular resolution

Bioluminescence imaging is widely used to monitor cellular events, including gene expression in vivo and in vitro. Moreover, recent advances in luciferase technology have made possible imaging at the single-cell level. To improve the bioluminescence imaging system, we have developed a dual-color imaging system in which the green-emitting luciferase from a Brazilian click beetle (Emerald Luc, ELuc) and the red-emitting luciferase from a railroad worm (Stable Luciferase Red, SLR) were used as reporters, which were localized to the peroxisome and the nucleus, respectively. We clearly captured simultaneously the subcellular localization of ELuc in the peroxisome and SLR in the nucleus of a single cell using a high-magnification objective lens with 3-min exposure time without binning using a combination of optical filters. Furthermore, to apply this system to quantitative time-lapse imaging, the activation of nuclear factor triggered by tumor necrosis factor α was measured using nuclear-targeted SLR and peroxisome-targeted ELuc as the test and internal control reporters, respectively. We successfully quantified the kinetics of activation of nuclear factor κB using nuclear-targeted SLR and the transcriptional change of the internal control promoter using peroxisome-targeted ELuc simultaneously in a single cell, and showed that the activation kinetics, including activation rate and amplitude, differed among cells. The results demonstrated that this imaging system can visualize the subcellular localization of reporters and track the expressions of two genes simultaneously at subcellular resolution.

Multicolor bioluminescence boosts malaria research: quantitative dual-color assay and single-cell imaging in Plasmodium falciparum parasites

New reliable and cost-effective antimalarial drug screening assays are urgently needed to identify drugs acting on different stages of the parasite Plasmodium falciparum, and particularly those responsible for human-to-mosquito transmission, that is, the P. falciparum gametocytes. Low Z′ factors, narrow dynamic ranges, and/or extended assay times are commonly reported in current gametocyte assays measuring gametocyte-expressed fluorescent or luciferase reporters, endogenous ATP levels, activity of gametocyte enzymes, or redox-dependent dye fluorescence. We hereby report on a dual-luciferase gametocyte assay with immature and mature P. falciparum gametocyte stages expressing red and green-emitting luciferases from Pyrophorus plagiophthalamus under the control of the parasite sexual stage-specific pfs16 gene promoter. The assay was validated with reference antimalarial drugs and allowed to quantitatively and simultaneously measure stage-specific drug effects on parasites at different developmental stages. The optimized assay, requiring only 48 h incubation with drugs and using a cost-effective luminogenic substrate, significantly reduces assay cost and time in comparison to state-of-the-art analogous assays. The assay had a Z′ factor of 0.71 ± 0.03, and it is suitable for implementation in 96- and 384-well microplate formats. Moreover, the use of a nonlysing d-luciferin substrate significantly improved the reliability of the assay and allowed one to perform, for the first time, P. falciparum bioluminescence imaging at single-cell level.

Exploiting in vitro and in vivo bioluminescence for the implementation of the three Rs principle (replacement, reduction, and refinement) in drug discovery

Bioluminescence-based analytical tools are suitable for high-throughput and high-content screening assays, finding widespread application in several fields related to the drug discovery process. Cell-based bioluminescence assays, because of their peculiar advantages of predictability, possibility of automation, multiplexing, and miniaturization, seem the most appealing tool for the high demands of the early stages of drug screening. Reporter gene technology and the bioluminescence resonance energy transfer principle are widely used, and receptor binding studies of new agonists/antagonists for a variety of human receptors expressed in different cell lines can be performed. Moreover, bioluminescence can be used for in vitro and in vivo real-time monitoring of pathophysiological processes within living cells and small animals. New luciferases and substrates have recently arrived on the market, further expanding the spectrum of applications. A new generation of probes are also emerging that promise to revolutionize the preclinical imaging market. This formidable toolbox is demonstrated to facilitate the implementation of the three Rs principle in the early drug discovery process, in compliance with ethical and responsible research to reduce cost and improve the reliability and predictability of results.