Activity-Based Detection of Cannabinoids in Serum and Plasma Samples

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.

Interpreting mono- and poly-SCRA intoxications from an activity-based point of view: JWH-018 equivalents in serum as a comparative measure

Synthetic cannabinoid receptor agonists (SCRAs) are a class of synthetic drugs that mimic and greatly surpass the effect of recreational cannabis. Acute SCRA intoxications are in general difficult to assess due to the large number of compounds involved, differing widely in both chemical structure and pharmacological properties. The rapid pace of emergence of unknown SCRAs hampers on one hand the timely availability of methods for identification and quantification to confirm and estimate the extent of the SCRA intoxication. On the other hand, lack of knowledge about the harm potential of emerging SCRAs hampers adequate interpretation of serum concentrations in intoxication cases. In the present study, a novel comparative measure for SCRA intoxications was evaluated, focusing on the cannabinoid activity (versus serum concentrations), which can be measured in serum extracts with an untargeted bioassay assessing ex vivo CB1 activity. Application of this principle to a series of SCRA intoxication cases (n = 48) allowed for the determination of activity equivalents, practically entailing a conversion from different SCRA serum concentrations to a JWH-018 equivalent. This allowed for the interpretation of both mono- (n = 34) and poly-SCRA (n = 14) intoxications, based on the intrinsic potential of the present serum levels to exert cannabinoid activity (cf. pharmacological/toxicological properties). A non-distinctive toxidrome was confirmed, showing no relation to CB1 activity. The JWH-018 equivalent was partly related to the poison severity score (PSS) and causality of the clinical intoxication elicited by the SCRA. Altogether, this equivalent concept allows to comparatively and timely interpret (poly-)SCRA intoxications based on CB1 activity.

Activity-based detection of synthetic cannabinoid receptor agonists in plant materials

BACKGROUND

Since late 2019, fortification of 'regular' cannabis plant material with synthetic cannabinoid receptor agonists (SCRAs) has become a notable phenomenon on the drug market. As many SCRAs pose a higher health risk than genuine cannabis, recognizing SCRA-adulterated cannabis is important from a harm reduction perspective. However, this is not always an easy task as adulterated cannabis may only be distinguished from genuine cannabis by dedicated, often expensive and time-consuming analytical techniques. In addition, the dynamic nature of the SCRA market renders identification of fortified samples a challenging task. Therefore, we established and applied an in vitro cannabinoid receptor 1 (CB1) activity-based procedure to screen plant material for the presence of SCRAs.

METHODS

The assay principle relies on the functional complementation of a split-nanoluciferase following recruitment of β-arrestin 2 to activated CB1. A straightforward sample preparation, encompassing methanolic extraction and dilution, was optimized for plant matrices, including cannabis, spiked with 5 µg/mg of the SCRA CP55,940.

RESULTS

The bioassay successfully detected all samples of a set (n = 24) of analytically confirmed authentic Spice products, additionally providing relevant information on the 'strength' of a preparation and whether different samples may have originated from separate batches or possibly the same production batch. Finally, the methodology was applied to assess the occurrence of SCRA adulteration in a large set (n = 252) of herbal materials collected at an international dance festival. This did not reveal any positives, i.e. there were no samples that yielded a relevant CB1 activation.

CONCLUSION

In summary, we established SCRA screening of herbal materials as a new application for the activity-based CB1 bioassay. The simplicity of the sample preparation, the rapid results and the universal character of the bioassay render it an effective and future-proof tool for evaluating herbal materials for the presence of SCRAs, which is relevant in the context of harm reduction.

In vitro cannabinoid activity profiling of generic ban-evading brominated synthetic cannabinoid receptor agonists and their analogs

Following the enactment of a generic ban in China in 2021, the synthetic cannabinoid market has been evolving, now encompassing even wider structural diversity. Compounds carrying a brominated core such as ADB-5'Br-BUTINACA (ADMB-B-5Br-INACA) and tail-less analogs, such as ADB-5'Br-INACA (ADMB-5Br-INACA), MDMB-5'Br-INACA, and ADB-INACA (ADMB-INACA), have been detected since late 2021. This study investigated the cannabinoid receptor (CB) activation potential of synthesized (S)-enantiomers of these substances, as well as of two predicted analogs MDMB-5'Br-BUTINACA (MDMB-B-5Br-INACA) and ADB-5'F-BUTINACA (ADMB-B-5F-INACA), using CB1 and CB2 β-arrestin 2 recruitment assays and a CB1 intracellular calcium release assay. Surprisingly, the tail-less (S)-ADB-5'Br-INACA and (S)-MDMB-5'Br-INACA retained CB activity, albeit with a decreased potency compared to their tailed counterparts (S)-ADB-5'Br-BUTINACA and (S)-MDMB-5'Br-BUTINACA, respectively, which were potent and efficacious CB1 agonists. Also, at CB2, tail-less analogs showed a lower potency but increased efficacy. Removing the bromine substitution ((S)-ADB-INACA) resulted in a reduced activity at CB1; however, this effect was less prominent at CB2. Looking at tailed analogs, replacing the bromine with a fluorine substitution ((S)-ADB-5'F-BUTINACA) resulted in an increased potency and efficacy at both receptors. Furthermore, as ADB-5'Br-INACA and MDMB-5'Br-INACA have been frequently detected together in Scottish prisons, this study also evaluated the CB1 receptor activation potential of different mixtures of their respective reference standards, showing no unexpected cannabimimetic effect of combining both substances. Lastly, two powders seized by Belgian Customs and confirmed to contain ADB-5'Br-INACA and MDMB-5'Br-INACA, respectively, were assessed for CB activity. Based on the comparison with their reference standards, varying degrees of purity were suspected.

Synthesis and Functional Evaluation of Synthetic Cannabinoid Receptor Agonists Related to ADB-HEXINACA

ADB-HEXINACA has been recently reported as a synthetic cannabinoid receptor agonist (SCRA), one of the largest classes of new psychoactive substances (NPSs). This compound marks the entry of the n-hexyl tail group into the SCRA landscape, which has continued in the market with recent, newly detected SCRAs. As such, a proactive characterization campaign was undertaken, including the synthesis, characterization, and pharmacological evaluation of ADB-HEXINACA and a library of 41 closely related analogues. Two in vitro functional assays were employed to assess activity at CB1 and CB2 cannabinoid receptors, measuring Gβγ-coupled agonism through a fluorescence-based membrane potential assay (MPA) and β-arrestin 2 (βarr2) recruitment via a live cell-based nanoluciferase complementation reporter assay. ADB-HEXINACA was a potent and efficacious CB1 agonist (CB1 MPA pEC50 = 7.87 ± 0.12 M; Emax = 124 ± 5%; βarr2 pEC50 = 8.27 ± 0.14 M; Emax = 793 ± 42.5), as were most compounds assessed. Isolation of the heterocyclic core and alkyl tails allowed for the comprehensive characterization of structure-activity relationships in this compound class, which were rationalized in silico via induced fit docking experiments. Overall, most compounds assessed are possibly emerging NPSs.

In vitro cannabinoid receptor activity, metabolism, and detection in seized samples of CH-PIATA, a new indole-3-acetamide synthetic cannabinoid

The rapidly evolving synthetic cannabinoid receptor agonist (SCRA) market poses significant challenges for forensic scientists. Since the enactment of a generic ban in China, a variety of new compounds have emerged capable of evading the legislation by carrying new structural features. One recent example of a SCRA with new linker and head moieties is CH-PIATA (CH-PIACA, CHX-PIATA, CHX-PIACA). CH-PIATA bears an additional methylene spacer in the linker moiety between the indole core and the traditional carbonyl component of the linker. This study describes detections in 2022 of this new SCRA in the United States, Belgium, and Scottish prisons. CH-PIATA was detected once in a seized powder by Belgian customs and 12 times in Scottish prisons in infused papers or resin. The metabolites of CH-PIATA were investigated via in vitro human liver microsome (HLM) incubations and eight metabolites were identified, dominated by oxidative biotransformations. A blood sample from the United States was confirmed to contain a mixture of SCRAs including CH-PIATA via presence of the parent and at least five of the metabolites identified from HLM incubations. Furthermore, this paper evaluates the intrinsic in vitro cannabinoid 1 and 2 (CB1 and CB2) receptor activation potential of CH-PIATA reference material and the powder seized by Belgian customs by means of β-arrestin 2 recruitment assays. Both the reference and the seized powder showed a weak activity at both CB receptors with signs of antagonism found. Based on these results, the expected harm potential of this newly emerging substance remains limited.

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.

High-Performance Cannabinoid Sensor Empowered by Plant Hormone Receptors and Antifouling Magnetic Nanorods

The misuse of cannabinoids and their synthetic variants poses significant threats to public health, necessitating the development of advanced techniques for detection of these compounds in biological or environmental samples. Existing methods face challenges like lengthy sample pretreatment and laborious antifouling steps. Herein, we present a novel sensing platform using magnetic nanorods coated with zwitterionic polymers for the simple, rapid, and sensitive detection of cannabinoids in biofluids. Our technique utilizes the engineered derivatives of the plant hormone receptor Pyrabactin Resistance 1 (PYR1) as drug recognition elements and employs the chemical-induced dimerization (CID) mechanism for signal development. Additionally, the magnetic nanorods facilitate efficient target capture and reduce the assay duration. Moreover, the zwitterionic polymer coating exhibits excellent antifouling capability, preserving excellent sensor performance in complex biofluids. Our sensors detect cannabinoids in undiluted biofluids like serum, saliva, and urine with a low limit of detection (0.002 pM in saliva and few pM in urine and serum) and dynamic ranges spanning up to 9 orders of magnitude. Moreover, the PYR1 derivatives demonstrate high specificity even in the presence of multiple interfering compounds. This work opens new opportunities for sensor development, showcasing the excellent performance of antifouling magnetic nanorods that can be compatible with different recognition units, including receptors and antibodies, for detecting a variety of targets.

Current state-of-the-art approaches for mass spectrometry in clinical toxicology: an overview

INTRODUCTION

Hyphenated mass spectrometry (MS) has evolved into a very powerful analytical technique of high sensitivity and specificity. It is used to analyze a very wide spectrum of analytes in classical and alternative matrices. The presented paper will provide an overview of the current state-of-the-art of hyphenated MS applications in clinical toxicology primarily based on review articles indexed in PubMed (1990 to April 2023).

AREAS COVERED

A general overview of matrices, sample preparation, analytical systems, detection modes, and validation and quality control is given. Moreover, selected applications are discussed.

EXPERT OPINION

A more widespread use of hyphenated MS techniques, especially in systematic toxicological analysis and drugs of abuse testing, would help overcome limitations of immunoassay-based screening strategies. This is currently hampered by high instrument cost, qualification requirements for personnel, and less favorable turnaround times, which could be overcome by more user-friendly, ideally fully automated MS instruments. This would help making hyphenated MS-based analysis available in more laboratories and expanding analysis to a large number of organic drugs, poisons, and/or metabolites. Even the most recent novel psychoactive substances (NPS) could be presumptively identified by high-resolution MS methods, their likely presence be communicated to treating physicians, and be confirmed later on.

Dual-Acting Small Molecules: Subtype-Selective Cannabinoid Receptor 2 Agonist/Butyrylcholinesterase Inhibitor Hybrids Show Neuroprotection in an Alzheimer's Disease Mouse Model

We present the synthesis and characterization of merged human butyrylcholinesterase (hBChE) inhibitor/cannabinoid receptor 2 (hCB₂R) ligands for the treatment of neurodegeneration. In total, 15 benzimidazole carbamates were synthesized and tested for their inhibition of human cholinesterases, also with regard to their pseudoirreversible binding mode and affinity toward both cannabinoid receptors in radioligand binding studies. After evaluation in a calcium mobilization assay as well as a β-arrestin 2 (βarr2) recruitment assay, two compounds with balanced activities on both targets were tested for their immunomodulatory effect on microglia activation and regarding their pharmacokinetic properties and blood-brain barrier penetration. Compound 15d, containing a dimethyl carbamate motif, was further evaluated in vivo, showing prevention of Aβ_25-35-induced learning impairments in a pharmacological mouse model of Alzheimer's disease for both short- and long-term memory responses. Additional combination studies proved a synergic effect of BChE inhibition and CB₂R activation in vivo.

Off-target activity of NBOMes and NBOMe analogs at the µ opioid receptor

New psychoactive substances (NPS) are introduced on the illicit drug market at a rapid pace. Their molecular targets are often inadequately elucidated, which contributes to the delayed characterization of their pharmacological effects. Inspired by earlier findings, this study set out to investigate the µ opioid receptor (MOR) activation potential of a large set of psychedelics, substances which typically activate the serotonin (5-HT_2A) receptor as their target receptor. We observed that some substances carrying the N-benzyl phenethylamine (NBOMe) structure activated MOR, as confirmed by both the NanoBiT® βarr2 recruitment assay and the G protein-based AequoScreen® Ca²⁺ release assay. The use of two orthogonal systems proved beneficial as some aspecific, receptor independent effects were found for various analogs when using the Ca²⁺ release assay. The specific 'off-target' effects at MOR could be blocked by the opioid antagonist naloxone, suggesting that these NBOMes occupy the same common opioid binding pocket as conventional opioids. This was corroborated by molecular docking, which revealed the plausibility of multiple interactions of 25I-NBOMe with MOR, similar to those observed for opioids. Additionally, structure-activity relationship findings seen in vitro were rationalized in silico for two 25I-NBOMe isomers. Overall, as MOR activity of these psychedelics was only noticed at high concentrations, we consider it unlikely that for the tested compounds there will be a relevant opioid toxicity in vivo at physiologically relevant concentrations. However, small modifications to the original NBOMe structure may result in a panel of more efficacious and potent MOR agonists, potentially exhibiting a dual MOR/5-HT_2A activation potential.

Novel Receptor-Binding-Based Assay for the Detection of Opioids in Human Urine Samples

Consumption of opioids is a growing global health problem. The gold standard for drugs of abuse screening is immunochemical assays. However, this method comes with some disadvantages when screening for a wide variety of opioids. Detection of the binding of a compound at the human μ-opioid receptor (MOR) offers a promising alternative target. Here, we set up a urine assay to allow for detection of compounds that bind at the MOR, thus allowing the assay to be utilized as a screening tool for opioid intake. The assay is based on the incubation of MOR-containing cell membranes with the selective MOR-ligand DAMGO and urine. After filtration, the amount of DAMGO in the eluate is analyzed by liquid chromatography tandem mass spectroscopy (LC-MS/MS). The absence of DAMGO in the eluate corresponds to a competing MOR ligand in the urine sample, thus indicating opiate/opioid intake by the suspect. Sensitivity and specificity were determined by the analysis of 200 consecutive forensic routine casework urine samples. A pronounced displacement of DAMGO was observed in 29 of the 35 opiate/opioid-positive samples. Detection of fentanyl intake proved to be the most challenging aspect. Applying a cut-off value of, e.g., 10% DAMGO binding would lead to a sensitivity of 83% and a specificity of 95%. Consequently, the novel assay proved to be a promising screening tool for opiate/opioid presence in urine samples. The nontargeted approach and possible automation of the assay make it a promising alternative to conventional methods.

In vitro characterization of the pyrazole-carrying synthetic cannabinoid receptor agonist 5F-3,5-AB-PFUPPYCA and its structural analogs

The synthetic cannabinoid receptor agonist (SCRA) market is undergoing important changes since the enactment of the 2021 class-wide generic SCRA ban in China, one of the most important source countries for new psychoactive substances (NPS). Recently, various compounds with new structural features, synthesized to bypass this legislation, have entered the recreational drug market. Certain monocyclic pyrazole-carrying "FUPPYCA" SCRAs have been sporadically detected since 2015 without gaining further popularity. However, as evidenced by their recent detection in Scottish prisons, 5F-3,5-AB-PFUPPYCA and 3,5-ADB-4en-PFUPPYCA have re-emerged, potentially triggered by the new legislative ban. The aim of this study was to characterize the in vitro intrinsic CB₁ and CB₂ receptor activation potential of 5F-3,5-AB-PFUPPYCA and 3,5-ADB-4en-PFUPPYCA, as well as 4 analogs (5F-3,5-ADB-PFUPPYCA, 3,5-AB-CHMFUPPYCA, 5,3-AB-CHMFUPPYCA and 5,3-ADB-4en-PFUPPYCA) using live cell β-arrestin 2 recruitment assays. Most analogs were essentially inactive at either CB₁ or CB₂, with only 3,5-AB-CHMFUPPYCA, 5,3-AB-CHMFUPPYCA and 5,3-ADB-4en-PFUPPYCA showing a limited activation potential at CB₁. Furthermore, the importance of the position of the tail structure was demonstrated, with 5,3 regioisomers being more active than their 3,5 analogs. Moreover, all compounds exhibited antagonistic behavior at both receptors, which may be associated with their structural resemblance to cannabinoid antagonists and inverse agonists. Although the 3,5 regioisomers of these "FUPPYCA" SCRAs circumvent the Chinese ban, it is unlikely that these SCRAs will pose a major threat to public health, given the lack of pronounced CB receptor activity.

Comprehensive Characterization of a Systematic Library of Alkyl and Alicyclic Synthetic Cannabinoids Related to CUMYL-PICA, CUMYL-BUTICA, CUMYL-CBMICA, and CUMYL-PINACA

Over 200 synthetic cannabinoid receptor agonists (SCRAs) have been identified as new psychoactive substances. Effective monitoring and characterization of SCRAs are hindered by the rapid pace of structural evolution. Ahead of possible appearance on the illicit drug market, new SCRAs were synthesized to complete a systematic library of cumyl-indole- (e.g., CUMYL-CPrMICA, CUMYL-CPMICA) and cumyl-indazole-carboxamides (e.g., CUMYL-CPrMINACA, CUMYL-CPMINACA), encompassing butyl, pentyl, cyclopropylmethyl, cyclobutylmethyl, cyclopentylmethyl, and cyclohexylmethyl tails. Comprehensive pharmacological characterization was performed with three assay formats, monitoring the recruitment of either wild-type or C-terminally truncated (βarr2d366) β-arrestin2 to the activated cannabinoid 1 receptor (CB₁) or monitoring G_βγ-mediated membrane hyperpolarization. Altered compound characterization was observed when comparing derived potency (EC₅₀) and efficacy (E_max) values from both assays monitoring the same or a different signaling event, whereas ranges and ranking orders were similar. Structure-activity relationships (SAR) were assessed in threefold, resulting in the identification of the pendant tail as a critical pharmacophore, with the optimal chain length for CB₁ activation approximating an n-pentyl (e.g., cyclopentylmethyl or cyclohexylmethyl tail). The activity of the SCRAs encompassing cyclic tails decreased with decreasing number of carbons forming the cyclic moiety, with CUMYL-CPrMICA showing the least CB₁ activity in all assay formats. The SARs were rationalized via molecular docking, demonstrating the importance of the optimal steric contribution of the hydrophobic tail. While SAR conclusions remained largely unchanged, the differential compound characterization by both similar and different assay designs emphasizes the importance of detailing specific assay characteristics to allow adequate interpretation of potencies and efficacies.

A new cannabinoid receptor 1 selective agonist evading the 2021 "China ban": ADB-FUBIATA

Following the class-wide ban of synthetic cannabinoid receptor agonists (SCRAs) in China, SCRAs carrying new core and linker structures, aimed at circumventing the recent Chinese generic legislation, have appeared on the recreational drug market. A very recent example is (S)-2-(2-(1-(4-fluorobenzyl)-1H-indol-3-yl)acetamido)-3,3-dimethylbutanamide (ADB-FUBIATA), which is structurally closely related to the potent SCRA ADB-FUBICA, but carries an additional methylene in the linker region of the molecule. ADB-FUBIATA has recently been identified in seized materials in China, Russia, the United States, and also Belgium; however, its pharmacological characteristics were unknown. The aim of this study was to evaluate the intrinsic cannabinoid receptor (hCB₁ and hCB₂ ) activation potential of this previously unknown substance via two distinct yet similar in vitro β-arrestin2 recruitment assays, based on the NanoLuc Binary Technology®. At CB₁ , a potency of 635 nM (EC₅₀ ) was found, with an efficacy (E_max ) of 141% relative to the reference compound CP55,940. On the other hand, ADB-FUBIATA had almost no activity at CB₂ , indicative of a clear CB₁ selectivity. Interestingly, this activation pattern differs markedly from that observed for ADB-FUBICA, which was previously found to be potent and efficacious at both cannabinoid receptors. Additionally, the bioassays were applied to a seized powder containing ADB-FUBIATA, as analytically confirmed by high-performance liquid chromatography coupled to diode-array detection (HLPC-DAD), gas chromatography coupled to mass spectrometry (GC-MS), liquid chromatography couple to time-of-flight mass spectrometry (LC-QTOF-MS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The EC₅₀ and E_max values obtained for this powder were very similar to those of the ADB-FUBIATA analytical standard, suggesting a high purity of the powder, although analytical techniques did reveal that the sample was not entirely pure.

Development of an Indole-Amide-Based Photoswitchable Cannabinoid Receptor Subtype 1 (CB1R) "Cis-On" Agonist

Activation of the human cannabinoid receptor type 1 (hCB₁R) with high spatiotemporal control is useful to study processes involved in different pathologies related to nociception, metabolic alterations, and neurological disorders. To synthesize new agonist ligands for hCB₁R, we have designed different classes of photoswitchable molecules based on an indole core. The modifications made to the central core have allowed us to understand the molecular characteristics necessary to design an agonist with optimal pharmacological properties. Compound 27a shows high affinity for CB₁R (K_i (cis-form) = 0.18 μM), with a marked difference in affinity with respect to its inactive "trans-off" form (CB₁R K_i trans/cis ratio = 5.4). The novel compounds were evaluated by radioligand binding studies, receptor internalization, sensor receptor activation (GRABeCB2.0), Western blots for analysis of ERK1/2 activation, NanoBiT βarr2 recruitment, and calcium mobilization assays, respectively. The data show that the novel agonist 27a is a candidate for studying the optical modulation of cannabinoid receptors (CBRs), serving as a new molecular tool for investigating the involvement of hCB₁R in disorders associated with the endocannabinoid system.

Linking in vitro and ex vivo CB1 activity with serum concentrations and clinical features in 5F-MDMB-PICA users to better understand SCRAs and their metabolites

Synthetic cannabinoid receptor agonists (SCRAs) pose a danger to public health. This study focused on individuals experiencing recreational drug toxicity who had used 5F-MDMB-PICA.Patient records were evaluated regarding vital signs, Glasgow Coma Scale (GCS) and clinical features. Liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) confirmed and quantified the presence of 5F-MDMB-PICA (and/or metabolites) as the only SCRA present in the serum of 71 patients. Cannabinoid activity was evaluated by a cannabinoid receptor (CB₁) bioassay, to assess the relationship between serum concentrations and ex vivo human CB₁ activation potential. Furthermore, a link with the clinical presentation was appraised.5F-MDMB-PICA and five metabolites were pharmacologically profiled in vitro, revealing theoretically possible contributions of two active in vivo metabolites to overall cannabinoid activity. Serum concentrations of 5F-MDMB-PICA were correlated to the ex vivo cannabinoid activity, revealing a sigmoidal relationship. The latter could also be predicted based on pharmacological characterization of 5F-MDMB-PICA and its metabolites and an in-depth investigation of the bioassay outcome. Clinically, the GCS showed a significant trend (decrease) with increasing ex vivo cannabinoid activity.This is the first study to evaluate possible toxic effects of 5F-MDMB-PICA in a unique large patient cohort. It allows a better understanding of 5F-MDMB-PICA and metabolites in humans, suggesting a negligible contribution by 5F-MDMB-PICA metabolites to the overall cannabinoid activity in serum. Additionally, this work shows that in vitro pharmacological characterization allows close prediction of an individual's ex vivo CB₁ activity, the latter showing a relationship with the level of consciousness.

Affinity Assays for Cannabinoids Detection: Are They Amenable to On-Site Screening?

Roadside testing of illicit drugs such as tetrahydrocannabinol (THC) requires simple, rapid, and cost-effective methods. The need for non-invasive detection tools has led to the development of selective and sensitive platforms, able to detect phyto- and synthetic cannabinoids by means of their main metabolites in breath, saliva, and urine samples. One may estimate the time passed from drug exposure and the frequency of use by corroborating the detection results with pharmacokinetic data. In this review, we report on the current detection methods of cannabinoids in biofluids. Fluorescent, electrochemical, colorimetric, and magnetoresistive biosensors will be briefly overviewed, putting emphasis on the affinity formats amenable to on-site screening, with possible applications in roadside testing and anti-doping control.

Cannabinoid receptor activation potential of the next generation, generic ban evading OXIZID synthetic cannabinoid receptor agonists

In recent years, several nations have implemented various measures to control the surge of new synthetic cannabinoid receptor agonists (SCRAs) entering the recreational drug market. In July 2021, China put into effect a new generic legislation, banning SCRAs containing one of 7 general core scaffolds. However, this has driven manufacturers towards the synthesis of SCRAs with alternative core structures, exemplified by the recent emergence of "OXIZID SCRAs". Here, using in vitro β-arrestin2 recruitment assays, we report on the CB₁ and CB₂ potency and efficacy of five members of this new class of SCRAs: BZO-HEXOXIZID, BZO-POXIZID, 5-fluoro BZO-POXIZID, BZO-4en-POXIZID and BZO-CHMOXIZID. All compounds behaved as full agonists at CB₁ and partial agonists at CB₂ . Potencies ranged from 84.6 - 721 nM at CB₁ and 2.21 - 25.9 nM at CB₂ . Shortening the n-hexyl tail to a pentyl tail enhanced activity at both receptors. Fluorination of this pentyl analog did not yield a higher receptor activation potential, whereas an unsaturated tail resulted in decreased potency and efficacy at CB₁ . The cyclohexyl methyl analog BZO-CHMOXIZID was the most potent compound at both receptors, with EC₅₀ values of 84.6 and 2.21 nM at CB₁ and CB₂ , respectively. Evaluation of the activity of a seized powder containing BZO-4en-POXIZID suggested a high purity, in line with HPLC-DAD, GC-MS, LC-QTOF-MS and FTIR and NMR analysis. Furthermore, all tested compounds showed a preference for CB₂ , except for BZO-POXIZID. Overall, these findings inform public health officials, law enforcement agencies and clinicians on these newly emerging SCRAs.

Structure-activity relationships of valine, tert-leucine, and phenylalanine amino acid-derived synthetic cannabinoid receptor agonists related to ADB-BUTINACA, APP-BUTINACA, and ADB-P7AICA

Synthetic cannabinoid receptor agonists (SCRAs) remain one the most prevalent classes of new psychoactive substances (NPS) worldwide, and examples are generally poorly characterised at the time of first detection. We have synthesised a systematic library of amino acid-derived indole-, indazole-, and 7-azaindole-3-carboxamides related to recently detected drugs ADB-BUTINACA, APP-BUTINACA and ADB-P7AICA, and characterised these ligands for in vitro binding and agonist activity at cannabinoid receptor subtypes 1 and 2 (CB1 and CB2), and in vivo cannabimimetic activity. All compounds showed high affinity for CB1 (K i 0.299-538 nM) and most at CB2 (K i = 0.912-2190 nM), and most functioned as high efficacy agonists of CB1 and CB2 in a fluorescence-based membrane potential assay and a βarr2 recruitment assay (NanoBiT®), with some compounds being partial agonists in the NanoBiT® assay. Key structure-activity relationships (SARs) were identified for CB1/CB2 binding and CB1/CB2 functional activities; (1) for a given core, affinities and potencies for tert-leucinamides (ADB-) > valinamides (AB-) ≫ phenylalaninamides (APP-); (2) for a given amino acid side-chain, affinities and potencies for indazoles > indoles ≫ 7-azaindoles. Radiobiotelemetric evaluation of ADB-BUTINACA, APP-BUTINACA and ADB-P7AICA in mice demonstrated that ADB-BUTINACA and ADB-P7AICA were cannabimimetic at 0.1 mg kg-1 and 10 mg kg-1 doses, respectively, as measured by pronounced decreases in core body temperature. APP-BUTINACA failed to elicit any hypothermic response up to the maximally tested 10 mg kg-1 dose, yielding an in vivo potency ranking of ADB-BUTINACA > ADB-P7AICA > APP-BUTINACA.

Similarities and differences upon binding of naturally occurring Δ9-tetrahydrocannabinol-derivatives to cannabinoid CB1 and CB2 receptors

We have here assessed, using Δ⁹-tetrahydrocannabinol (Δ⁹-THC) for comparison, the effect of Δ⁹-tetrahydrocannabinolic acid (Δ⁹-THCA) and of Δ⁹-tetrahydrocannabivarin (Δ9-THCV) that is mediated by human versions of CB₁, CB₂, and CB₁-CB₂ receptor functional units, expressed in a heterologous system. Binding to the CB₁ and CB₂ receptors was addressed in living cells by means of a homogeneous assay. A biphasic competition curve for the binding to the CB₂ receptor, was obtained for Δ⁹-THCV in cells expressing the two receptors. Signaling studies included cAMP level determination, activation of the mitogen-activated protein kinase pathway and ß-arrestin recruitment were performed. The signaling triggered by Δ⁹-THCA and Δ⁹-THCV via individual receptors or receptor heteromers disclosed differential bias, i.e. the bias observed using a given phytocannabinoid depended on the receptor (CB₁, CB₂ or CB₁-CB₂) and on the compound used as reference to calculate the bias factor (Δ⁹-THC, a selective agonist or a non-selective agonist). These results are consistent with different binding modes leading to differential functional selectivity depending on the agonist structure, and the state (monomeric or heteromeric) of the cannabinoid receptor. In addition, on studying Gi-coupling we showed that Δ⁹-THCV and Δ⁹-THCA and Δ⁹-THCV were able to revert the effect of a selective CB₂ receptor agonist, but only Δ9-THCV, and not Δ9-THCA, reverted the effect of arachidonyl-2'-chloroethylamide (ACEA 100 nM) a selective agonist of the CB₁ receptor. Overall, these results indicate that cannabinoids may have a variety of binding modes that results in qualitatively different effects depending on the signaling pathway that is engaged upon cannabinoid receptor activation.

NNL-3: A Synthetic Intermediate or a New Class of Hydroxybenzotriazole Esters with Cannabinoid Receptor Activity?

Synthetic cannabinoid receptor agonists (SCRAs) remain a prolific class of new psychoactive substances (NPS) and continue to expand rapidly. Despite the recent identification of hydroxybenzotriazole (HOBt) containing SCRAs in synthetic cannabis samples, there is currently no information regarding the pharmacological profile of these NPS with respect to human CB₁ and CB₂ receptors. In the current study, a series consisting of seven HOBt indole-, indazole-, and 7-azaindole-carboxylates bearing a range of N-alkyl substituents were synthesized and pharmacologically evaluated. Competitive binding assays at CB₁ and CB₂ demonstrated that all analogues except a 2-methyl-substituted derivative had low affinity for CB₁ (K_i = 3.80-43.7 μM) and CB₂ (K_i = 2.75-18.2 μM). A fluorometric functional assay revealed that 2-methylindole- and indole-derived HOBt carboxylates were potent and efficacious agonists of CB₁ (EC₅₀ = 12.0 and 63.7 nM; E_max = 118 and 120%) and CB₂ (EC₅₀ = 10.9 and 321 nM; E_max = 91 and 126%). All other analogues incorporating indazole and 7-azaindole cores and bearing a range of N1-substituents showed relatively low potency for CB₁ and CB₂. Additionally, a reporter assay monitoring β-arrestin 2 (βarr2) recruitment to the receptor revealed that the 2-methylindole example was the most potent and efficacious at CB₁ (EC₅₀ = 131 nM; E_max = 724%) and the most potent at CB₂ (EC₅₀ = 38.2 nM; E_max = 51%). As with the membrane potential assay, the indazole and other indole HOBt carboxylates were considerably less potent at both receptors, and analogues comprising a 7-azaindole core showed little activity. Taken together, these data suggest that NNL-3 demonstrates little CB1 receptor activity and is unlikely to be psychoactive in humans. NNL-3 is likely an unintended SCRA manufacturing byproduct. However, the synthesis of NNL-3 analogues proved simple and general, and some of these showed potent cannabimetic profiles in vitro, indicating that HOBt esters of this type may represent an emerging class of SCRA NPS.

The Future of Analytical and Interpretative Toxicology: Where are We Going and How Do We Get There?

(Forensic) toxicology has faced many challenges, both analytically and interpretatively, especially in relation to an increase in potential drugs of interest. Analytical toxicology and its application to medicine and forensic science have progressed rapidly within the past centuries. Technological innovations have enabled detection of more substances with increasing sensitivity in a variety of matrices. Our understanding of the effects (both intended and unintended) have also increased along with determination and degree of toxicity. However, it is clear there is even more to understand and consider. The analytical focus has been on typical matrices such as blood and urine but other matrices could further increase our understanding, especially in postmortem (PM) situations. Within this context, the role of PM changes and potential redistribution of drugs requires further research and identification of markers of its occurrence and extent. Whilst instrumentation has improved, in the future, nanotechnology may play a role in selective and sensitive analysis as well as bioassays. Toxicologists often only have an advisory impact on pre-analytical and pre-interpretative considerations. The collection of appropriate samples at the right time in an appropriate way as well as obtaining sufficient circumstance background is paramount in ensuring an effective analytical strategy to provide useful results that can be interpreted within context. Nevertheless, key interpretative considerations such as pharmacogenomics and drug-drug interactions as well as determination of tolerance remain and in the future, analytical confirmation of an individual's metabolic profile may support a personalized medicine and judicial approach. This should be supported by the compilation and appropriate application of drug data pursuant to the situation. Specifically, in PM circumstances, data pertaining to where a drug was not/may have been/was contributory will be beneficial with associated pathological considerations. This article describes the challenges faced within toxicology and discusses progress to a future where they are being addressed.

Systematic evaluation of a panel of 30 synthetic cannabinoid receptor agonists structurally related to MMB-4en-PICA, MDMB-4en-PINACA, ADB-4en-PINACA, and MMB-4CN-BUTINACA using a combination of binding and different CB1 receptor activation assays-Part II: Structure activity relationship assessment via a β-arrestin recruitment assay

Synthetic cannabinoid receptor agonists (SCRAs) are the second largest class of new psychoactive substances (NPS) and are associated with serious adverse effects and even death. Despite this, little pharmacological data are available for many of the most recent SCRAs. This study consists of three different parts, aiming to systematically evaluate a panel of 30 SCRAs using binding and different in vitro human cannabinoid 1 receptor (CB₁ ) activation assays. The present Part II investigated the SCRA analogs for their CB₁ activation via a β-arrestin recruitment assay. The panel was systematically designed to include key structural sub-features of recent SCRAs. Thus, the 4-pentenyl tail of MMB-4en-PICA and MDMB-4en-PINACA was retained while incorporating varying head groups from other prevalent SCRAs, including amides and esters of L-valine, L-tert-leucine, and L-phenylalanine, and adamantyl and cumyl moieties. All 30 SCRAs activated CB₁ , with indazoles generally showing the greatest potency (EC₅₀  = 1.88-281 nM), followed by indoles (EC₅₀  = 11.5-2293 nM), and the corresponding 7-azaindoles (EC₅₀  = 62.4-9251 nM). Several subunit-linked structure-activity relationships were identified: (i) tert-leucine-functionalized SCRAs were more potent than the corresponding valine derivatives; (ii) no major difference in potency or efficacy was observed between tert-leucine/valine-derived amides and the corresponding methyl esters; however, phenylalanine analogs were affected by this change; and (iii) minor structural changes to the 4-pentenyl substituent had little influence on activity. These findings elucidate structural features that modulate the CB₁ activation potential of currently prevalent SCRAs and a systematic panel of analogs, some of which may appear in NPS markets in future.

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.

In Vitro Metabolic Profile Elucidation of Synthetic Cannabinoid APP-CHMINACA (PX-3)

Indazole carboxamide synthetic cannabinoids remain the most prevalent subclass of new psychoactive substances (NPS) reported internationally. However, the metabolic and pharmacological properties of many of these compounds remain unknown. Elucidating these characteristics allows members of the clinical and forensic communities to identify causative agents in patient samples, as well as render conclusions regarding their toxic effects. This work presents a detailed report on the in vitro phase I metabolism of indazole carboxamide synthetic cannabinoid APP-CHMINACA (PX-3). Incubation of APP-CHMINACA with human liver microsomes, followed by analysis of extracts via high-resolution mass spectrometry, yielded 12 metabolites, encompassing 7 different metabolite classes. Characterization of the metabolites was achieved by evaluating the product ion spectra, accurate mass and chemical formula generated for each metabolite. The predominant biotransformations observed were hydrolysis of the distal amide group and hydroxylation of the cyclohexylmethyl (CHM) substituent. Nine metabolites were amide hydrolysis products, of which five were monohydroxylated, one dihydroxylated and two were ketone products. The metabolites in greatest abundance in the study were products of amide hydrolysis with no further biotransformation (M1), followed by amide hydrolysis with monohydroxylation (M2.1). Three APP-CHMINACA-specific metabolites were generated, all of which were hydroxylated on the CHM group; one mono-, di- and tri-hydroxylated metabolite each was produced, with dihydroxylation (M6) present in the greatest abundance. The authors propose that metabolites M1, M2.1 and M6 are the most appropriate markers to determine consumption of APP-CHMINACA. The methods used in the current study have broad applicability and have been used to determine the in vitro metabolic profiles of multiple synthetic cannabinoids and other classes of NPS. This research can be used to guide analytical scientists in method development, synthesis of reference material, pharmacological testing of proposed metabolites and prediction of metabolic processes of compounds yet to be studied.

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.

Assessment of Biased Agonism among Distinct Synthetic Cannabinoid Receptor Agonist Scaffolds

Cannabinoid receptor 1 (CB₁) is a key drug target for a number of diseases, including metabolic syndromes and neuropathic pain. Most of the typical cannabinoid ligands provoke psychotropic side effects that impair their therapeutic utility. As of today, it is not yet clearly known which structural features of cannabinoid ligands determine a preference toward specific signaling pathways. Distinct bioassays are typically used to elucidate signaling preferences. However, these are often based on different cell lines and use different principles and/or read-outs, which makes straightforward assessment of "ligand bias" difficult. Within this context, this study is the first to investigate ligand bias among synthetic cannabinoid receptor agonists (SCRAs) in as closely analogous conditions as possible, by applying a new functional complementation-based assay panel to assess the recruitment of Gα_i protein or β-arrestin2 to CB₁. In a panel of 21 SCRAs, chosen to cover a broad diversity in chemical structures, distinct, although often subtle, preferences toward specific signaling pathways were observed. Relative to CP55940, here considered as a "balanced" reference agonist, most of the selected SCRAs (e.g., 5F-APINACA, CUMYL-PEGACLONE, among others) displayed preferred signaling through the β-arrestin2 pathway, whereas MMB-CHMICA could serve as a potential "balanced" agonist. Interestingly, EG-018 was the only SCRA showing a significant (10-fold) preference toward G protein over β-arrestin2 recruitment. While it is currently unclear what this exactly means in terms of abuse potential and/or toxicity, the approach proposed here may allow construction of a knowledge base that in the end may allow better insight into the structure-"functional" activity relationship of these compounds. This may aid the development of new therapeutics with less unwanted psychoactive effects.

In vitro Phase I metabolism of indazole carboxamide synthetic cannabinoid MDMB-CHMINACA via human liver microsome incubation and high-resolution mass spectrometry

Synthetic cannabinoids have proliferated over the last decade and have become a major public health and analytical challenge, critically impacting the clinical and forensic communities. Indazole carboxamide class synthetic cannabinoids have been particularly rampant, and exhibit severe toxic effects upon consumption due to their high binding affinity and potency at the cannabinoid receptors (CB₁ and CB₂ ). MDMB-CHMINACA, methyl 2-[1-(cyclohexylmethyl)-1H-indazole-3-carboxamido]-3,3-dimethylbutanoate, a compound of this chemical class, has been identified in forensic casework and is structurally related to several other synthetic cannabinoids. This study presents the first extensive report on the Phase I metabolic profile of MDMB-CHMINACA, a potent synthetic cannabinoid. The in vitro metabolism of MDMB-CHMINACA was determined via incubation with human liver microsomes and high-resolution mass spectrometry. The accurate masses of precursor and fragments, mass error (ppm), and chemical formula were obtained for each metabolite. Twenty-seven metabolites were identified, encompassing twelve metabolite types. The major biotransformations observed were hydroxylation and ester hydrolysis. Hydroxylations were located predominantly on the cyclohexylmethyl (CHM) moiety. Ester hydrolysis was followed by additional biotransformations, including dehydrogenation; mono- and dihydroxylation and ketone formation, each with dehydrogenation. Minor metabolites were identified and reported. The authors propose that CHM-monohydroxylated metabolites specific to MDMB-CHMINACA are the most suitable candidates for implementation into bioanalytical assays to demonstrate consumption of this synthetic cannabinoid. Due to the structural similarity of MDMB-CHMINACA and currently trending synthetic cannabinoids whose metabolic profiles have not been reported, the results of this study can be used as a guide to predict their metabolic pathways.

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.

Screening methods for rapid determination of new psychoactive substances (NPS) in conventional and non-conventional biological matrices

In the last years, a global awareness has arisen from the reported harmful effects and public health risks associated with the consumption of new psychoactive substances (NPSs). Improving efforts in the detection and identification of these substances have emerged as a global analytical challenge involving the large range of NPSs' chemical structures and the variety of conventional and non-conventional biological matrices. Indeed, detection capabilities and screening tools impact many fields and settings, including seized products analysis, workplace and roadside drug controls, emergency rooms, drug addiction treatment clinics, post-mortem and criminal caseworks, law enforcement and health interventions. Colorimetric, immunochemical and chromatographic-mass spectrometry techniques have been investigated and developed for the rapid identification of NPSs. Considering the continuous emergence of new substances, this review offers a panoramic view on the current status of analytical approaches for the rapid screening of NPSs, including, when available, data on conventional and non-conventional biological matrices. Although some of the presented methods are sound and promising, their applications are still limited, thus proving the importance of further investigations. New screening and sensitive targeted methods for NPS and their metabolites should be developed in different types of biological matrices, where concentration of substances and matrix effects can be significantly different.

Activity-Based Concept to Screen Biological Matrices for Opiates and (Synthetic) Opioids

BACKGROUND

Detection of new highly potent synthetic opioids is challenging as new compounds enter the market. Here we present a novel screening method for the detection of opiates and (synthetic) opioids based on their activity.

METHODS

A cell-based system was set up in which activation of the μ-opioid receptor (MOR) led to recruitment of β-arrestin 2, resulting in functional complementation of a split NanoLuc luciferase and allowing readout via bioluminescence. Assay performance was evaluated on 107 postmortem blood samples. Blood (500 μL) was extracted via solid-phase extraction. Following evaporation and reconstitution in 100 μL of Opti-MEM® I, 20 μL was analyzed in the bioassay.

RESULTS

In 8 samples containing synthetic opioids, in which no positive signal was obtained in the bioassay, quadrupole time-of-flight mass spectrometry revealed the MOR antagonist naloxone, which can prevent receptor activation. Hence, further evaluation did not include these samples. For U-47700 (74.5–547 ng/mL) and furanyl fentanyl (&lt;1–38.8 ng/mL), detection was 100% (8/8) for U-47700 and 95% (21/22) for furanyl fentanyl. An analytical specificity of 93% (55/59) was obtained for the opioid negatives. From an additional 10 samples found to contain other opioids, 5 were correctly scored positive. Nondetection in 5 cases could be explained by very low concentrations (&lt;1 ng/mL alfentanil/sufentanil) or presence of inactive enantiomers.

CONCLUSIONS

The MOR reporter assay allows rapid identification of opioid activity in blood. Although the cooccurrence of opioid antagonists is currently a limitation, the bioassay's high detection capability, specificity, and untargeted nature may render it a useful first-line screening tool to investigate potential opioid intoxications.