Virginia Commonwealth University VCU Scholars Compass Theses and Dissertations Graduate School 2011 Discriminative stimulus properties of 3-substituent rimonabant analogs D. Matthew Walentiny Virginia Commonwealth University Follow this and additional works at: https://scholarscompass.edu/etd Part of the Psychology Commons © The Author Downloaded from https://scholarscompass.edu/etd/223 This Dissertation is brought to you for free and open access by the Graduate School at VCU Scholars Compass. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of VCU Scholars Compass. For more information, please contact libcompass@vcu.
DISCRIMINATIVE STIMULUS PROPERTIES OF 3-SUBSTITUENT RIMONABANT ANALOGS A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. by David Matthew Walentiny Master of Science, Virginia Commonwealth University, 2008 Director: Jenny L. Professor Department of Pharmacology & Toxicology Virginia Commonwealth University Richmond, Virginia May, 2011 ii Acknowledgments There are a number of people who deserve recognition for supporting my efforts on this dissertation and my time in graduate school. First, I wish to extend my heartfelt gratitude to my advisor, Dr.
Jenny Wiley, for offering me a position in her lab and all the training and support I have received from her since. I am also indebted to Dr. Robert Vann for taking a vested interest in my success and an active role in my development from the moment I began graduate school. I would also like to thank Dr.
Joseph Porter for giving me my first research opportunity as an undergraduate student working in his lab, and for subsequently serving as my master’s thesis advisor. In addition to these individuals, I am grateful for my other dissertation committee members, Dr. Aron Lichtman and Dr. Laura Sim-Selley, for providing their time and insight to improve this project.
Anu Mahadevan and Dr. Raj Razdan from Organix Inc. are also greatly appreciated for their efforts in developing and synthesizing the compounds of interest for this study. On a personal note, I also wish to thank my family for their love and support, especially my parents Stephen and Georgianna Walentiny and my grandparents George and Josefine Thompson.
I wish to dedicate this dissertation to the memory of my Dad for being my biggest fan and an immense source of motivation and encouragement. Finally, I owe a special thank you to my long-time girlfriend, Stefanie Gerwitz, for her constant love, and more importantly her patience throughout my undergraduate and graduate studies. iii Table of Contents Page Acknowledgements……………………………………………………………………………….ii List of Tables…………………………………………………………………………………….v List of Figures……………………………………………………. Introduction Cannabinoid pharmacology……………………………………………………………….1 Reinforcing properties of cannabinoids………………………………………………….2 Intoxicating properties of cannabinoid agonists………………………………………….9 Cannabinoid withdrawal…………………………………………………………………10 Discriminative stimulus properties of rimonabant……………………………………….12 Therapeutic potential for non-cannabinoid drug abuse disorders……………………….19 The case for rimonabant and further exploration of CB1 receptor antagonists.21 Pharmacological profile of rimonabant analogs…………………………………………21 II.34 Experiment 1—Cannabimimetic effects of 3-substituent rimonabant analogs…………34 Subjects………………………………………………………………………….36 Experiment 2—Discriminative stimulus effects of THC: evaluation of 3-substituent rimonabant analogs………………………………………………………………………36 Subjects………………………………………………………………………….40 Experiment 3—Discriminative stimulus effects of O-6629………………….42 iv Testing procedures……………………………………………………………….45 Experiment 1—Cannabimimetic effects of 3-substituent rimonabant analogs………….45 Pharmacological profile of O-6629 in the tetrad……………………………….45 Pharmacological profile of O-6658 in the tetrad……………………………….45 Experiment 2—Discriminative stimulus effects of THC: evaluation of 3-substituent rimonabant analogs………………….…46 THC’s discriminative stimulus: acquisition and generalization…………………46 Rimonabant challenge……………………………………………………………46 O-4332 generalization……………………………………………………………47 O-6629 generalization……………………………………………………………47 O-6629 challenge……………………………………………………………….48 O-6629 tolerance…………………………………………………………………48 Experiment 3—Discriminative stimulus effects of O-6629……………….…49 O-6629’s discriminative stimulus: acquisition and generalization………………49 O-6658 generalization……………………………………………………………50 Rimonabant generalization………………………………………………….…50 THC generalization………………………………………………………………50 Anandamide generalization…………………………………………………….50 Morphine generalization…………………………………………………………50 Nicotine generalization………………………………………………………….
List of References……………………………………………………………………………90 VII.103 v List of Tables Table Page 1. Pharmacological profiles of selected cannabinoid agents and pyrazole-derived rimonabant analogs………………………………………………………………….44 vi List of Figures Figure Page 1. Chemical structure of rimonabant……………………………………………………………. Pharmacological profile of O-6629 in the tetrad…………………………………………….
Pharmacological profile of O-6658 in the tetrad……………………………………………. Acquisition of THC’s discriminative stimulus………………………………………………. Evaluation of tolerance to the rate suppressant effects of O-6629…………………………. Acquisition of O-6629’s discriminative stimulus……………………………….73 Abstract DISCRIMINATIVE STIMULUS PROPERTIES OF 3-SUBSTITUENT RIMONABANT ANALOGS By David Matthew Walentiny, M.
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. Virginia Commonwealth University, 2011 Major Director: Jenny L. Professor Department of Pharmacology & Toxicology Cannabinoid agonists (e., THC) dose-dependently decrease locomotor activity and body temperature and produce antinociception and catalepsy. Drugs that produce this tetrad of effects within a limited dose range are likely to function as CB1 receptor agonists.
A structure activity relationship study from our laboratory investigating analogs of the CB1 antagonist rimonabant revealed that certain alterations in the 3-substituent of rimonabant’s pyrazole core conferred agonist-like properties in the tetrad. Interestingly, these effects were present in CB1 -/- mice, and were not reversed by rimonabant in wild-type mice. The present study evaluated two novel 3-substituent rimonabant analogs, O-6629 and O-6658 in the tetrad and drug discrimination, a preclinical model of drug subjective effects that possesses a high degree of pharmacological specificity. Drugs that elicit cannabinergic psychoactive effects in humans are likely to produce THC-like operant responding in animals trained to discriminate between the interoceptive stimuli produced by THC relative to vehicle.
O-6629 and O-6658 decreased locomotor activity and body temperature and produced catalepsy. O-6629, but not O-6658 produced significant antinociception. However, these drugs differed from THC in regard to the magnitude of tetrad effects observed. These analogs also failed to elicit THC-like discriminative stimulus effects, nor did they antagonize THC’s discriminative stimulus in mice discriminating 5.6 mg/kg THC from vehicle.
Finally, mice were trained to discriminate 5.6 mg/kg O-6629 from vehicle. O-6658 produced full substitution for O- 6629, whereas the cannabinoid agonists THC and anandamide did not. O-6629’s discriminative stimulus failed to generalize to rimonabant, cocaine or morphine, whereas WIN 55,212-2 and nicotine evoked partial substitution. These results suggest that these analogs might exert their pharmacological properties through a novel cannabinoid receptor, as has been proposed for WIN 55,212-2 and anandamide.
Additionally, O-6629’s discriminative stimulus may involve nicotinic acetylcholine or dopaminergic components. Future directions include determining whether the partial substitution observed with nicotine was mediated through a nicotinic mechanism. Tests with chlorpromazine, an antipsychotic that is a false positive in the tetrad, and diazepam, which produces partial substitution for THC’s discriminative stimulus through a GABAergic mechanism are also planned. Discriminative stimulus properties of 3-substituent rimonabant analogs Cannabinoid pharmacology The endogenous cannabinoid (hereto referred as endocannabinoid) system is comprised of two primary G-protein coupled receptors, cannabinoid 1 (CB1) and cannabinoid 2 (CB2), and two major endogenous ligands, anandamide and 2-arachidonoylglycerol (2-AG), which activate these receptors.
CB1 receptors are located primarily in the brain whereas CB2 receptors are located abundantly in the periphery suggesting functionally different roles for these receptors. Two decades of research have revealed much regarding anandamide’s role within the endocannabinoid system. Strong evidence suggests that membrane bound arachidonic acid is likely the precursor for anandamide formation though its synthesis has yet to be completely mapped or understood. Identification of anandamide’s degradative pathway has revealed that fatty acid amide hydrolase (FAAH) is primarily responsible for the rapid catabolism of anandamide (Cravatt et al.
Similarly, 2-AG is quickly degraded by a number of enzymes, with monoacylglycrol lipase (MAGL) serving as the primary catabolic enzyme (Long et al. Development of more stable endocannabinoid ligand analogs (e., methanandamide), selective inhibitors of FAAH and/or MAGL (e., URB597, JZL184, JZL195), and the development of various cannabinoid-related knockout mice (e., CB1 -/-, CB2 -/-, FAAH -/-, MAGL -/-) have facilitated further understanding of the endocannabinoid system and consequently have yielded valuable information regarding its impact on a multitude of biological processes. Accordingly, the endocannabinoid system has become a target of interest for a number of therapeutic purposes, such as management of pain, nausea and emesis. However, the abuse liability and intoxication associated with cannabis greatly limits its accepted therapeutic 1 use.
The following is a brief review of preclinical literature demonstrating the reinforcing efficacy and intoxicating properties of cannabinoids. Reinforcing properties of cannabinoids The reinforcing properties of cannabinoids have been especially challenging to demonstrate reliably in a preclinical setting. There have been numerous reports that Δ9- tetrahydrocannabinol (THC), the primary psychoactive chemical in marijuana (Gaoni & Mechoulam, 1964), fails to maintain self-administration behavior (Kaymakcalan, 1973; Leite & Carlini, 1974; Carney, Uwaydah, & Balster, 1977; Mansbach, Nicholson, Martin, & Balster, 1994), a preclinical model used to examine reinforcing efficacy of drugs (Balster, 1991). However, Tanda et al.
(2000) demonstrated that THC does indeed maintain self-administration using a lower dose range per infusion than had typically been studied. In that study, squirrel monkeys with prior experience self-administering cocaine ( as reported by Spear, Muntaner, Goldberg, & Katz, 1991) were given a 5 day saline replacement following their most recent cocaine exposure, during which operant responding for an infusion was nearly abolished. Following this extinction period, subjects then were able to respond for 2-4 µg/kg/infusion THC. This low dose infusion, described as comparable to the THC amount inhaled by a human per puff on a marijuana cigarette, readily maintained operant responding.
Further, these effects were reversed by pretreatment with selective CB1 antagonist/inverse agonist rimonabant (0.3 mg/kg), whereas responding for cocaine was not influenced by rimonabant, demonstrating CB1 mediation of the reinforcing properties of THC. Once rimonabant pretreatment was ceased, THC-maintained operant responding was reestablished and returned to baseline levels. Although rates of responding for THC and cocaine infusions were comparable, this does not necessarily imply that THC possesses the same degree of reinforcing efficacy as cocaine. A multitude of 2 procedural parameters, including dose, reinforcement schedule (e., FI, FR, second-order) and exposure (e.
limited exposure) can influence self-administration behavior. For these reasons, among others (e., subject drug history), determination of relative reinforcement efficacy between drugs can be arduous (Balster, 1991). A subsequent extension of these studies sought to determine whether previous exposure to cocaine might have influenced results reported by Tanda et al. Thus, drug naïve squirrel monkeys were employed in a similar paradigm and THC was evaluated for its ability to maintain self-administration behavior.
Monkeys were trained to lever press (FR10; 60 s timeout) for an infusion of 4 µg/kg THC, the dose that previously maintained self-administration behavior. This dose did indeed maintain self-administration behavior, and subjects responded at a near maximal rate given the reinforcement contingencies. Once baseline responding for this dose was established, a 5 day vehicle substitution was conducted in between each assessment in the dose effect determination (1-16 µg/kg/infusion). Only 2, 4 and 8 µg/kg/infusion doses resulted in a significantly higher number of infusions per session compared to vehicle.
Although rates of responding for THC 16 µg/kg/infusion were not significantly different than vehicle responding, subjects still responded for this high dose and administered a higher cumulative quantity of THC in the high dose condition relative to all other doses tested. In sum, THC is self- administered in humans, as well as non-human primates (under certain conditions), illustrating the reinforcing efficacy of cannabinoids. The synthetic cannabinoid WIN 55,212-2, a potent full agonist (compared to the plant- derived partial agonist THC) is self-administered in rodents. Both rats (Fattore, Cossu, Martellotta, & Fratta, 2001) and mice (Martellotta, Cossu, Fattore, Gessa, & Fratta, 1998) self- administer WIN 55,212-2 in a dose-dependent manner.
Microdialysis results from rats 3 demonstrate that WIN 55,212-2 self-administration also elevates extracellular dopamine in the shell and core of the nucleus accumbens (Lecca, Cacciapaglia, Valentini, & Di Chiara, 2006). Interestingly, onset of this elevation occurs more rapidly, persists longer and at a greater magnitude in the shell than the core (Lecca et al. Under extinction conditions, however, dopamine dialysate levels remain unchanged from baseline in both regions, despite the presence of lever-pressing behavior. These microdialysis findings conducted in animals self-administering cannabinoids support the role of the nucleus accumbens shell in the reinforcing properties of drugs with abuse liability (for review, see Di Chiara, 2002).
Intoxicating properties of cannabinoid agonists The drug discrimination paradigm has been used extensively as a preclinical model for the subjective effects produced by a drug. Based on the principle that certain drugs are capable of serving as discriminative stimuli (i., the interoceptive stimuli produced by one drug can be discerned from a non-drug or other drug state), this model typically features an animal trained to make one response (e.