Activity-based reporter assays for the screening of abused substances in biological matrices

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.

Untargeted Detection of HIF Stabilizers in Doping Samples: Activity-Based Screening with a Stable In Vitro Bioassay

Hypoxia-inducible factor (HIF) stabilizers are listed in the World Anti-Doping Agency's prohibited list as they can increase aerobic exercise capacity. The rapid pace of emergence of highly structurally diverse HIF stabilizers could pose a risk to conventional structure-based methods in doping control to detect new investigational drugs. Therefore, we developed a strategy that is capable of detecting the presence of any HIF stabilizer, irrespective of its structure, by detecting biological activity. Previously developed cell-based HIF1/2 assays were optimized to a stable format and evaluated for their screening potential toward HIF stabilizers. Improved pharmacological characterization was established by the stable cell-based formats, and broad specificity was demonstrated by pharmacologically characterizing a diverse set of HIF stabilizers (including enarodustat, IOX2, IOX4, MK-8617, JNJ-42041935). The methodological (in solvent) limit of detection of the optimal HIF1 stable bioassay toward detecting the reference compound roxadustat was 100 nM, increasing to 50-100 ng/mL (corresponding to 617-1233 nM in-well) in matching urine samples, owing to strong matrix effects. In a practical context, a urinary limit of detection of 1.15 μg/mL (95% detection rate) was determined, confirming the matrix-dependent detectability of roxadustat in urine. Pending optimization of a universal sample preparation strategy and/or a methodology to correct for the matrix effects, this untargeted approach may serve as a complementing method in antidoping control, as theoretically, it would be capable of detecting any unknown substance with HIF stabilizing activity.

A method for the sensitive targeted screening of synthetic cannabinoids and opioids in whole blood by LC-QTOF-MS with simultaneous suspect screening using HighResNPS.com

A sensitive method for the qualitative screening of synthetic cannabinoids and opioids in whole blood was developed and validated using alkaline liquid-liquid extraction (LLE) and liquid chromatography-time-of-flight mass spectrometry (LC-QTOF-MS). Estimated limits of detection for validated compounds ranged from 0.03 to 0.29 µg/L (median, 0.04 µg/L) for the 27 opioids and from 0.04 to 0.5 µg/L (median, 0.07 µg/L) for the 23 synthetic cannabinoids. Data processing occurred in two stages; first, a targeted screen was performed using an in-house database containing retention times, accurate masses and MS-MS spectra for 79 cannabinoids and 53 opioids. Suspect screening was then performed using a database downloaded from the crowd sourced NPS data website HighResNPS.com which contains mass, consensus MS-MS data and laboratory-specific predicted retention times for a far greater number of compounds. The method was applied to 61 forensic cases where synthetic cannabinoid or opioid screening was requested by the client or their use was suspected due to case information. CUMYL-PEGACLONE was detected in two cases and etodesnitazine, 5 F-MDMB-PICA, 4-cyano-CUMYL-BUTINACA and carfentanil were detected in one case each. These compounds were within the targeted scope of the method but were also detected through the suspect screening workflow. The method forms a solid base for expansion as more compounds emerge onto the illicit drug market.

Sensing an Oxygen Sensor: Development and Application of Activity-Based Assays Directly Monitoring HIF Heterodimerization

Conventionally, hypoxia-inducible factor (HIF) activation by prolyl hydroxylase domain enzyme (PHD) inhibition is monitored by gene reporter assays. The principle relies on the monitoring of an upstream event (HIF stabilization) by the downstream transcriptional activity. Here, we developed a novel approach to directly sense HIF activation by monitoring the heterodimerization of the HIFα/HIFβ subunits, constituting the functional HIF transcription factor. Two live cell-based biosensor assay setups were designed, utilizing functional complementation of split-nanoluciferase as a tool to measure HIFα/HIFβ protein-protein interaction resulting from the stabilization of HIF1α or HIF2α. The assay setup in a 96-well format was optimized for a duration of 2 h, and a HEK293T transfection protocol was introduced for the optimal configuration of HIFα/HIFβ-fusion proteins. These new bioassays outperformed hypoxia response element-based gene reporter assay, the current state-of-the-art assay, in terms of sensitivity. Applicability was demonstrated using a panel of PHD inhibitors, including roxadustat, molidustat, daprodustat, desidustat, vadadustat, and FG-2216, for which concentration-response curves were generated, allowing for the derivation of potency (EC₅₀) and efficacy (E_max) data. The broad applicability of the biosensors was established via applying hypoxia mimetic CoCl₂, iron chelator desferrioxamine, proteasome inhibitor MG-132, and 2-OG mimetic dimethyloxalylglycine on the assays, indicating concentration-dependent effects.

The Rise and Fall of Isotonitazene and Brorphine: Two Recent Stars in the Synthetic Opioid Firmament

Synthetic opioids constitute one of the fastest growing groups of new psychoactive substances (NPS) worldwide. With fentanyl analogues being increasingly controlled via class-wide scheduling, many non-fentanyl related opioids are now emerging on the recreational opioid market, rendering the landscape highly complex and dynamic. While new compounds are entering the supply in rapid and unpredictable manners, some recent patterns have become apparent. Many of these newly emerging opioids are being pirated from early patent literature and/or research papers, synthesized and sold online through various channels. Burdened by the identification of every newly emerging drug, many toxicology labs struggle to keep up. Moreover, by the time a "new" drug is controlled via legislative measures, illicit drug markets will have already adapted and diversified as manufacturers work to avoid the restricted product(s). Hence, the typical life-cycle of an NPS opioid is generally short (less than 6 months to one year), with only a few drugs escalating to significant numbers of detections. In this review, we summarize the key events in the emergence, rise, and subsequent decline of two non-fentanyl opioids - isotonitazene and brorphine. These two opioids sequentially dominated the NPS opioid market in 2019 and 2020. Both isotonitazene and brorphine remained in circulation for over a year, each contributing to hundreds of deaths and adverse events. By detailing the life-cycles of these opioids from their earliest synthesis as described in scientific literature to their subsequent rise and fall on recreational markets, this review illustrates the new characteristic life-cycle of synthetic opioids in the 'post-fentanyl-analogue' era.

Germaine DM, Iula DM, Stove CP. Synthesis, Chemical Characterization, and μ-Opioid Receptor Activity Assessment of the Emerging Group of "Nitazene" 2-Benzylbenzimidazole Synthetic Opioids

Several 2-benzylbenzimidazole opioids (also referred to as "nitazenes") recently emerged on the illicit market. The most frequently encountered member, isotonitazene, has been identified in multiple fatalities since its appearance in 2019. Although recent scheduling efforts targeted isotonitazene, many other analogues remain unregulated. Being structurally unrelated to fentanyl, little is known about the harm potential of these compounds. In this study, ten nitazenes and four metabolites were synthesized, analytically characterized via four different techniques, and pharmacologically evaluated using two cell-based β-arrestin2/mini-Gi recruitment assays monitoring μ-opioid receptor (MOR) activation. On the basis of absorption spectra and retention times, high-performance liquid chromatography coupled to diode-array detection (HPLC-DAD) allowed differentiation between most analogues. Time-of-flight mass spectrometry (LC-QTOF-MS) identified a fragment with m/z 100.11 for 12/14 compounds, which could serve as a basis for MS-based nitazene screening. MOR activity determination confirmed that nitazenes are generally highly active, with potencies and efficacies of several analogues exceeding that of fentanyl. Particularly relevant is the unexpected very high potency of the N-desethylisotonitazene metabolite, rivaling the potency of etonitazene and exceeding that of isotonitazene itself. Supported by its identification in fatalities, this likely has in vivo consequences. These results improve our understanding of this emerging group of opioids by laying out an analytical framework for their detection, as well as providing important new insights into their MOR activation potential.

Metabolism of 4F-MDMB-BICA in zebrafish by liquid chromatography-high resolution mass spectrometry

In this study, in vivo metabolic studies of the synthetic cannabinoid 4F-MDMB-BICA were investigated using zebrafish models. The metabolites were identified and structurally illustrated by liquid chromatography-high resolution mass spectrometry. Fourteen phase-I metabolites and four phase-II metabolites were generated from zebrafish. The main metabolic pathways of the phase-I metabolism included N-dealkylation, N-dealkylation combined with hydroxylation, amide hydrolysis, oxidative defluorination, oxidative defluorination to butyric acid, acetic acid formation at the indole side chain, hydroxylation, ester hydrolysis followed by hydroxylation, dehydrogenation, dehydrogenation, and N-dealkylation, and oxidative defluorination subsequently combined with dehydrogenation. The main biotransformations of the phase-II metabolism were glucuronidation and sulfation. Two phase-I metabolites (A1 and A11) and four phase-II metabolites (A2, A3, A4, and A12) were reported for the first time. A14, which was confirmed in human biological samples, was detected only in zebrafish samples but not found in human liver microsome incubation study. The current study indicates that the zebrafish model is a promising tool for elucidating the metabolism of NPS in the future.

The synthetic cannabinoids phenomenon: from structure to toxicological properties. A review

The word "cannabinoid" refers to every chemical substance, regardless of structure or origin, that joins the cannabinoid receptors of the body and brain and that have similar effects to those produced by the Cannabis plant and based on their source of production, cannabinoids can be classified into endocannabinoids, phytocannabinoids and synthetic cannabinoids. Synthetic cannabinoids represent the largest class of drugs detected through the EU Early Warning System with a total of 190 substances notified from 2008 to 2018 and about 280 have been reported worldwide to the United Nations Office on Drugs and Crime. Sprayed on natural herb mixtures with the aim to mimic the euphoria effect of cannabis and sold as "herbal smoking blends" or "herbal incense" under brand names like "Spice" or "K2", synthetic cannabinoids are available from websites for the combination with herbal materials or more recently, for the use in e-cigarettes. Currently labeled as "not for human consumption" to circumvent legislation, their legal status varies by country with many government institutions currently pushing for their control. However, due to the emergence of new substances, it requires a constant update of the list of controlled drugs. Little is known about how these substances work and their toxic effects in humans and the same product could vary not only in the amount and in the type of substance added. In the last years, synthetic cannabinoids have been associated with deaths and acute intoxications in Europe and, despite a range of new measures introduced in this area, continue to represent a challenge to current drug policy models. These synthetic substances are much more potent than natural cannabis, as well as displayed greater efficacy, acting as full agonists at the cannabinoid receptors. It is possible that, along with being highly potent, some may also have long half-lives, potentially leading to a prolonged psychoactive effect. The present work provides a review on existing literature about the development of synthetic cannabinoids as substances of abuse, current patterns of abuse and their legal status, chemical classification, and some pharmacological and toxicological properties.

Trends using biological target-based assays for drug detection in complex sample matrices

In vivo, drug molecules interact with their biological targets (e.g., enzymes, receptors, ion channels, transporters), thereby eliciting therapeutic effects. Assays that measure the interaction between drugs and bio-targets may be used as drug biosensors, which are capable of broadly detecting entire drug classes without prior knowledge of their chemical structure. This Trends article covers recent developments in bio-target-based screening assays for detecting drugs associated with the following areas: illicit products marketed as dietary supplements, food-producing animals, and bodily fluids. General challenges and considerations associated with using bio-target assays are also presented. Finally, future applications of these assays for drug detection are suggested based upon current needs.

Extraction of α-neurotoxins from equine plasma by receptor based affinity purification

Venoms were first identified as potential doping agents by the racing industry in 2007 when three vials of cobra venom were seized during an inspection of a stable at Keeneland Racecourse in the USA. Venoms are a complex mixture of proteins, peptides, and other substances with a wide range of biological effects, including inhibiting the transmission of nervous and muscular impulses. As an example of this, cobratoxin, an α-neurotoxin found in cobra venom, is claimed to be an effective treatment for pain. Recent analysis of seized samples identified venom from two different species of snake. Proteomic analysis identified the first sample as cobra venom, while the second sample, in a vial labeled "Conotoxin", was identified as venom from a many banded krait. Cobratoxin, conotoxins, and bungarotoxins (a component of krait venom) are all α-neurotoxins, suggesting a common application for all three venom proteins as potential pain blocking medications. Using a peptide based on the nicotinic acetylcholine receptor, a one-step affinity purification method was developed for the detection of α-neurotoxins in plasma.

Clinical value of analytical testing in patients presenting with new psychoactive substances intoxication

New psychoactive substances (NPS) have emerged worldwide in recent years, posing a threat to public health and a challenge to drug policy. NPS are usually derivatives or analogues of classical recreational drugs designed to imitate their effects while circumventing regulations. This article provides an overview of benefits and limitations of analytical screening in managing patients presenting with acute NPS toxicity. NPS typically cannot be analytically identified with the usual immunoassay tests. To detect NPS using an immunoassay, antibodies specifically binding to the new structures would have to be developed, which is complicated by the rapid change of the NPS market. Activity-based assays could circumvent this problem since no prior knowledge on the substance structure is necessary. However, classical recreational drugs activating the same receptors could lead to false positive results. Liquid or gas chromatography coupled with mass spectrometry is a valuable NPS analysis tool, but its costs (e.g. equipment), run time (results usually within hours vs minutes in case of immunoasssays) and the need for specialized personnel hinder its use in clinical setting, while factors such as lack of reference standards can pose further limitations. Although supportive measures are sufficient in most cases for adequate patient management, the detection and identification of NPS can contribute significantly to public health and safety in cases of e.g. cluster intoxications and outbreaks, and to the investigation of these novel compounds' properties. However, this requires not only availability of the necessary equipment and personnel, but also collaboration between clinicians, authorities and laboratories.

Enantiospecific Synthesis, Chiral Separation, and Biological Activity of Four Indazole-3-Carboxamide-Type Synthetic Cannabinoid Receptor Agonists and Their Detection in Seized Drug Samples

Synthetic cannabinoid receptor agonists (SCRAs) have been the largest group of illicit psychoactive substances reported to international monitoring and early warning systems for many years. Carboxamide-type SCRAs are amongst the most prevalent and potent. Enantiospecific synthesis and characterization of four indazole-3-carboxamides, AMB-FUBINACA, AB-FUBINACA, 5F-MDMB-PINACA (5F-ADB), and AB-CHMINACA is reported. The interactions of the compounds with CB1 and CB2 receptors were investigated using a G-protein coupled receptor (GPCR) activation assay based on functional complementation of a split NanoLuc luciferase and EC50 (a measure of potency) and Emax (a measure of efficacy) values determined. All compounds demonstrated higher potency at the CB2 receptor than at the CB1 receptor and (S)-enantiomers had an enhanced potency to both receptors over the (R)-enantiomers. The relative potency of the enantiomers to the CB2 receptor is affected by structural features. The difference was more pronounced for compounds with an amine moiety (AB-FUBINACA and AB-CHMINACA) than those with an ester moiety (AMB-FUBINACA and 5F-MDMB-PINACA). An HPLC method was developed to determine the prevalence of (R)-enantiomers in seized samples. Lux® Amylose-1 [Amylose tris(3,5-dimethylphenylcarbamate)] has the greatest selectivity for the SCRAs with a terminal methyl ester moiety and a Lux® i-Cellulose-5 column for SCRAs with a terminal amide moiety. Optimized isocratic separation methods yielded enantiomer resolution values (Rs) ≥ 1.99. Achiral GC-MS analysis of seized herbal materials (n = 16), found 5F-MDMB-PINACA (<1.0-91.5 mg/g herbal material) and AMB-FUBINACA (15.5-58.5 mg/g herbal material), respectively. EMB-FUBINACA, AMB-CHMICA, 5F-ADB-PINACA isomer 2, and ADB-CHMINACA were also tentatively identified. Analysis using chiral chromatography coupled to photodiode array and quadrupole time of flight mass spectrometry (chiral HPLC-PDA-QToF-MS/MS) confirmed that the (S)-enantiomer predominated in all samples (93.6-99.3% (S)-enantiomer). Small but significant differences in synthesis precursor enantiopurity may provide significant differences between synthesis batches or suppliers and warrants further study. A method to compare potency between samples containing different SCRAs at varying concentrations was developed and applied in this small preliminary study. A 10-fold difference in the "intrinsic" potency of samples in the study was noted. With the known heterogeneity of SCRA infused materials, the approach provides a simplified method for assessing and communicating the risk of their use.