Effects of Bioisosteric Fluorine in Synthetic Cannabinoid Designer Drugs JWH-018, AM-2201, UR-144, XLR-11, PB-22, 5F-PB-22, APICA, and STS-135 Samuel D. Banister, †,‡ Jordyn Stuart, § Richard C. Kevin, ∥ Amelia Edington, § Mitchell Longworth, ‡ Shane M. Wilkinson, ‡ Corinne Beinat, †,‡ Alexandra S. Buchanan, ⊥,# David E. Hibbs, ∇ Michelle Glass, ¶ Mark Connor, § Iain S. McGregor, ∥ and Michael Kassiou* ,‡,◆ † Department of Radiology, Stanford University School of Medicine, Stanford, California 94305, United States ‡ School of Chemistry, The University of Sydney, Sydney, New South Wales 2006, Australia § Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales 2109, Australia ∥ School of Psychology, The University of Sydney, Sydney, New South Wales 2006, Australia ⊥ Center for Immersive and Simulation-based Learning, Stanford University School of Medicine, Stanford, California 94305, United States # Department of Anaesthesia, Prince of Wales Hospital, Randwick, New South Wales 2031, Australia ∇ Faculty of Pharmacy, The University of Sydney, Sydney, New South Wales 2006, Australia ¶ School of Medical Sciences, The University of Auckland, Auckland 1142, New Zealand ◆ Discipline of Medical Radiation Sciences, The University of Sydney, Sydney, New South Wales 2006, Australia * S Supporting Information ABSTRACT: Synthetic cannabinoid (SC) designer drugs featuring bioisosteric fluorine substitution are identified by forensic chemists and toxicologists with increasing frequency. Although terminal fluorination of N-pentyl indole SCs is sometimes known to improve cannabinoid type 1 (CB 1 ) receptor binding affinity, little is known of the effects of fluorination on functional activity of SCs. This study explores the in vitro functional activities of SC designer drugs JWH-018, UR-144, PB-22, and APICA, and their respective terminally fluorinated analogues AM-2201, XLR-11, 5F-PB-22, and STS- 135 at human CB 1 and CB 2 receptors using a FLIPR membrane potential assay. All compounds demonstrated agonist activity at CB 1 (EC 50 = 2.8−1959 nM) and CB 2 (EC 50 = 6.5−206 nM) receptors, with the fluorinated analogues generally showing increased CB 1 receptor potency (∼2−5 times). Additionally, the cannabimimetic activities and relative potencies of JWH-018, AM-2201, UR-144, XLR-11, PB-22, 5F- PB-22, APICA, and STS-135 in vivo were evaluated in rats using biotelemetry. All SCs dose-dependently induced hypothermia and reduced heart rate at doses of 0.3−10 mg/kg. There was no consistent trend for increased potency of fluorinated SCs over the corresponding des-fluoro SCs in vivo. Based on magnitude and duration of hypothermia, the SCs were ranked for potency (PB-22 > 5F-PB-22 = JWH-018 > AM-2201 > APICA = STS-135 = XLR-11 > UR-144). KEYWORDS: Cannabinoid, THC, JWH-018, AM-2201, XLR-11, PB-22 S ynthetic cannabinoids (SCs) are the most rapidly growing class of recreational “designer drugs”. The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) reports that, as of March 2015, 134 new SCs have been identified in the European Union (EU) since 2008, with 30 novel SCs formally notified in 2014 alone. 1 In the United States (US) in 2010, the Drug Enforcement Administration’s National Forensic Laboratory Information System (NFLIS) reported 19 distinct SCs across 3286 samples, but by 2012, there were 61 SC variants identified in 41 458 cases. 2 In the EU in 2013, there were over 21 000 seizures of SCs, a more than 200-fold increase since 2008. 1 Many SCs have no precedent in the scientific literature yet bear hallmarks of rational design. Like Δ 9 -tetrahydrocannabinol (Δ 9 -THC, 1; Figure 1), the principal bioactive component of cannabis, SCs typically exert agonist activity at both cannabinoid receptor subtypes, namely, Received: April 2, 2015 Accepted: April 28, 2015 Published: April 28, 2015 Research Article pubs.acs.org/chemneuro © 2015 American Chemical Society 1445 DOI: 10.1021/acschemneuro.5b00107 ACS Chem. Neurosci. 2015, 6, 1445−1458