Novel halogenated derivates of JWH-018: Behavioral and binding studies in mice

Highlights

• JWH-018Cl and JWH-018Br are new halogenated cannabinoids seized in Internet Market.

• JWH-018-R compounds induced adverse effects through the stimulation of CB₁ receptor.

• JWH-018Br acts similarly to Δ⁹-THC and could replace JWH-018 in the illegal market.

Abstract

JWH-018 is a synthetic CB₁ and CB₂ agonist illegally marketed as products named “Spice” or “herbal blend” for its psychoactive effects which are much higher than those produced by cannabis. In the last year, the European Monitoring Centre for Drugs and Drug Addiction reported to the Italian National Early Warning System the seizure of plant material containing new halogenated derivatives of JWH-018 (JWH-018 Cl and JWH-018 Br). The present study aimed to investigate the in vitro and in vivo activity of these two new synthetic cannabinoids in mice. In vitro competition binding experiments performed on mouse and human CB₁ receptors revealed a high affinity and potency of the halogenated compounds. Synthetic cannabinoids (0.01–6 mg/kg i.p.) impaired motor activity and induced catalepsy in mice and their effects were more severe with respect to those evoked by Δ⁹-THC. Moreover, they increased the mechanical and thermal pain threshold and induced a marked hypothermia. It is interesting to note that whereas high doses of JWH-018 cause seizures, myoclonia and hyperreflexia, the halogenated compounds, in particular JWH-018Br, were less effective. Behavioral and neurological changes were prevented by the selective CB₁ receptor antagonist AM 251. These data demonstrate for the first time that JWH-018 Cl and JWH-018 Br act similarly to JWH-018 while inducing less convulsive episodes and myoclonias. These data support the hypothesis that the halogenated compounds may have been introduced onto market to produce similar intoxicating effects as JWH-018 while causing less side effects.

Introduction

JWH-018 (1-pentyl-3-(1-naphthoyl)indole) is a synthetic cannabinoid agonist developed in the early 1990's (Huffman et al., 1994) from a computational melding of the chemical structural features of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) with the prototypic aminoalkylindole WIN 55,212-2 (D'Ambra et al., 1992). JWH-018 binds and activates the CB₁ (Ki = 9 nM) and CB₂ (Ki = 3 nM) receptors in the low nanomolar range (Huffman et al., 1994, Wiley et al., 1998), showing approximately a four-fold increased activity at the CB₁ and about a ten-fold affinity at the CB₂ receptor compared with Δ⁹-THC (Auwarter et al., 2009). This aminoalkylindole is the first synthetic cannabinoid ever reported through the Early Warning System (EMCDDA, 2009, Uchiyama et al., 2010). JWH-018 mixtures are marketed as “Spice” and “herbal blend” for their psychoactive effects similar to those produced by cannabis. However, in addition to the “desired” psychoactive action, clinical data reported that JWH-018 induces significant psychiatric and physical adverse effects in consumers. The most common psychiatric effects reported were anxiety, psychosis, hallucinations and alterations in cognitive abilities, while physical effects reported ranged in severity from nausea to more serious sympathomimetic-like symptoms such as psychomotor agitation, diaphoresis, palpitations, tachycardia, tachyarrhythmia, hyperreflexia and generalized convulsions (Auwarter et al., 2009, Hermanns-Clausen et al., 2013, Seely et al., 2012).

In vivo animal studies revealed that JWH-018 reproduces the typical “tetrad” effects of Δ⁹-THC such as hypothermia, analgesia, hypolocomotion, akinesia (Brents et al., 2011, Macri et al., 2013, Wiebelhaus et al., 2012, Wiley et al., 2012) when delivered both via inhalation (Poklis et al., 2012, Wiebelhaus et al., 2012) or systemic injection (Fantegrossi et al., 2014, Wiley et al., 1998). In fact no differences were found in the final “tetrad” symptoms between the two routes of administration (Marshell et al., 2014). Moreover, JWH-018 produces anxiolysis and depressive-related behavior in mice (Macri et al., 2013), sensorimotor and cardio-respiratory alterations (Marti et al., 2013b, Marti, 2014) and impaired working memory in adult mice more potently than Δ⁹-THC (Marti et al., 2013a). In particular, the cannabinoid “tetrad” (Compton et al., 1992) has been extremely useful in the characterization of the biological activity of natural and synthetic agonists at CB₁ receptors. Ligands that fully activate cannabinoid receptors which produce maximal effects in a given system (i.e. “tetrad”) are referred to as high efficacy agonists. In contrast, agonists that result in reduced maximal effects when compared to full agonists are designated as low efficacy agonists. Interestingly, Δ⁹-THC, which is a partial agonist both in vitro (Govaerts et al., 2004) and in vivo (Paronis et al., 2012), tends to elicit tetrad effects of similar magnitude to higher efficacy cannabinoids such as WIN-55,212-2 and CP-55,940 (Fan et al., 1994).

In the last year, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) reported the seizure of plant material containing halogenated derivatives (N-(5-chloro-pentyl)- and N-(5-bromo-pentyl)) of JWH-018 to the Italian National Early Warning System (NEWS) (Fig. 1). The discovery of these new halogenated derivatives of JWH-018 on the illegal market and the lack of pharmacological and toxicological information suggested the need to rapidly study their in vitro and in vivo pharmacological profile to understand their main adverse effects. In fact, it is well known that halogenation of cannabinoid structures may lead to significant changes in compound potency and affinities for the CB₁ receptors (Nikas et al., 2004, Wiley et al., 2014) as well as potential changes in pharmacokinetic properties.

The present study was aimed at investigating the effects of acute exposure to JWH-018, JWH-018 Cl and JWH-018 Br on primary neurological changes, core and surface body temperature, modulation of acute thermal and mechanical pain stimuli and motor activity in CD-1 mice. Moreover, in vitro competition binding experiments were carried out to determine the selectivity and potency of the halogenated compounds for the CB₁ receptor. To better understand the behavioral profile of the JWH-018-R compounds, Δ⁹-THC was used as a reference molecule and the effects were monitored for over 5 h.