A Preclinical Evaluation of the Discriminative And
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NP5101_proof ■ 12 June 2013 ■ 1/11 Neuropharmacology xxx (2013) 1e11 Contents lists available at SciVerse ScienceDirect Neuropharmacology journal homepage: www.elsevier.com/locate/neuropharm 1 56 2 A preclinical evaluation of the discriminative and reinforcing 57 3 58 4 properties of lisdexamfetamine in comparison to D-amfetamine, 59 5 fi 60 6 methylphenidate and moda nil 61 7 62 a,* a a a b 8 Q5 David J. Heal , Niki W. Buckley , Jane Gosden , Nigel Slater , Charles P. France , 63 9 David Hackett c 64 10 65 a 11 RenaSci Ltd, BioCity Nottingham, Pennyfoot Street, Nottingham NG1 1GF, UK 66 b University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA 12 c Shire Pharmaceutical Development Ltd, Hampshire International Business Park, Chineham, Basingstoke RG24 8EP, Hampshire, UK 67 13 68 14 69 15 article info abstract 70 16 71 17 Article history: Lisdexamfetamine dimesylate, which consists of L-lysine covalently bound to D-amfetamine, is the first 72 18 Received 12 December 2012 prodrug for treating ADHD. Its metabolic conversion to yield D-amfetamine by rate-limited, enzymatic 73 19 Received in revised form hydrolysis is unusual because it is performed by peptidases associated with red blood cells. Other 74 3 April 2013 20 stimulants shown to be effective in managing ADHD include D-amfetamine, methylphenidate and 75 Accepted 13 May 2013 21 modafinil. All have the potential for misuse or recreational abuse. The discriminative and reinforcing 76 effects of these compounds were determined in rats using a 2-choice, D-amfetamine (0.5 mg/kg, i.p.)- 77 22 Keywords: cued drug-discrimination test, and by substitution for intravenous cocaine in self-administration. Lis- 23 Lisdexamfetamine 78 dexamfetamine (0.5e1.5 mg/kg [D-amfetamine base], p.o.) generalised to saline when tested 15 min 24 D-Amfetamine 79 post-dosing, but dose-dependently generalised to D-amfetamine at 60 min. At 120 min, its D-amfet- 25 Methylphenidate 80 fi amine-like effects were substantially diminished. At 15 min, methylphenidate (3.0e10 mg/kg, p.o.) and 26 Moda nil 81 Drug discrimination D-amfetamine (0.1e1.5 mg/kg, p.o.) dose-dependently generalised to the intraperitoneal D-amfetamine 27 Discriminative effects cue. Switching to the intraperitoneal route reduced the interval required for lisdexamfetamine to be 82 28 Self-administration recognised as D-amfetamine-like, but did not alter its potency. Switching to intraperitoneal injection 83 Reinforcer 29 increased the potency of methylphenidate and D-amfetamine by 3.4Â and 2.2Â, respectively. Modafinil 84 30 (50e200 mg/kg, i.p.) generalised partially, but not fully, to D-amfetamine. Methylphenidate (0.1, 0.3, 85 31 1.0 mg/kg/injection, i.v.) maintained robust self-administration at the 2 highest doses. Neither lisdex- 86 32 amfetamine (0.05, 0.15 or 0.5 mg/kg/injection [D-amfetamine base], i.v.) nor modafinil (0.166, 0.498 or 87 33 1.66 mg/kg/injection, i.v.) served as reinforcers. The results reveal important differences between the 88 fi 34 pro les of these stimulants. Lisdexamfetamine did not serve as a positive reinforcer in cocaine-trained 89 fl 35 rats, and although it generalised fully to D-amfetamine, its discriminative effects were markedly in u- 90 enced by its unusual pharmacokinetics. 36 91 Ó 2013 Published by Elsevier Ltd. 37 92 38 93 39 94 40 95 41 1. Introduction 96 42 97 43 Attention deficit hyperactivity disorder (ADHD) is a childhood- 98 44 onset, psychiatric, cognitive and behavioural disorder that is 99 45 widely treated with the catecholaminergic stimulants, D-amfet- 100 amine and methylphenidate. These drugs are effective in managing 46 Abbreviations: ADHD, attention deficit hyperactivity disorder; AMF, amfet- 101 47 amine; C-II, Schedule 2 Controlled Drug; C-IV, Schedule 4 Controlled Drug; CD, the symptoms of approximately three quarters of children and 102 48 controlled drug; Cmax, maximum plasma drug concentration; DAT, dopamine re- adults (Spencer et al., 1996; Elia et al., 1999; Heal and Pierce, 2006; 103 49 uptake transporter; FR, fixed ratio; IACUC, Institutional Animal Care and Use Heal et al., 2009, 2012a; Buitelaar and Medori, 2010). Although 104 Committee; i.p., intraperitoneal; IR, immediate release; i.v., intravenous; PET, 50 these stimulants are undoubtedly effective, they have two major 105 positron emission tomography; PFC, prefrontal cortex; p.o., per os (oral); SAL, saline; 51 shortcomings. First, D-amfetamine and methylphenidate have 106 SR, sustained release; tmax, time to reach maximum plasma drug concentration. 52 * Corresponding author. Tel.: þ44 (0) 115 9124260; fax: þ44 (0) 115 9124263. relatively short half-lives that require the drugs to be administered 107 53 E-mail addresses: [email protected], [email protected] (D.J. Heal). several times a day, which makes them particularly unsuitable for 108 54 109 e Ó 55 0028-3908/$ see front matter 2013 Published by Elsevier Ltd. 110 http://dx.doi.org/10.1016/j.neuropharm.2013.05.021 Please cite this article in press as: Heal, D.J., et al., A preclinical evaluation of the discriminative and reinforcing properties of lisdexamfetamine in comparison to D-amfetamine, methylphenidate and modafinil, Neuropharmacology (2013), http://dx.doi.org/10.1016/ j.neuropharm.2013.05.021 NP5101_proof ■ 12 June 2013 ■ 2/11 2 D.J. Heal et al. / Neuropharmacology xxx (2013) 1e11 111 use by individuals whose disorder is characterised by inattention, cages with sawdust covered floors in a temperature and humidity controlled room. 176 112 distractibility and impulsivity. Second, when these catecholamin- Animals were maintained on 12 h:12 h lightedark cycle with free access to food and 177 tap water at all times when in their home cages. Rats were accustomed to these 113 ergic drugs are taken at doses above those recommended in the 178 conditions for 1 week before the start of training. 114 prescribing instructions and often by non-clinical routes, e.g. nasal For the self-administration study, 54 male, Sprague-Dawley rats (277e352 g at 179 115 insufflation (“snorting”) or intravenous injection, they have start of study) were purchased from Charles River UK, and 58 male, Sprague-Dawley 180 116 powerful psychostimulant and euphoriant properties which makes rats (277 ge342 g at start of study) from Harlan, USA. Rats were housed individually 181 117 them liable to diversion and recreational abuse. Both shortcomings in plastic cages containing rodent bedding and environmental enrichment on a 182 12 h:12 h lightedark cycle in a temperature and humidity controlled room. Animals 118 have to some extent been addressed by the development of long- were allowed to acclimatise to these conditions for at least 4 days before the study 183 119 acting formulations and by the use of novel delivery systems, e.g. commenced, during which time they underwent daily weighing and handling. Rats 184 120 osmotically controlled release or transdermal patches, that are also were allowed free access to tap water and standard rodent diet during the accli- 185 121 tamper deterrent (see reviews by Heal and Pierce, 2006; Heal et al., matisation period. After the acclimatisation period, food was restricted to 10 g/day 186 over 5 days, after which daily food intake was restricted to w90% of normal levels 122 2009, 2012a); nonetheless, all formulations of methylphenidate 187 (calculation based on the mean daily food intake during the acclimatisation period). 123 and D-amfetamine are classified as Schedule 2 Controlled Drugs Rats were given sufficient food to maintain age-appropriate growth. Body weights 188 124 (C-II) in the UK, USA and many other countries. were monitored and the amount of food given in home cages was altered when 189 Ò 125 Lisdexamfetamine dimesylate (Vyvanse ) is a relatively recent necessary. This regime was maintained throughout the remainder of the study, 190 except during the recovery period after surgery. 126 entry to the portfolio of ADHD medications. It is a D-amfetamine 191 In both studies, animals were tested in the light part of the lightedark cycle. 127 prodrug, which comprises the naturally occurring amino acid, L- 192 128 lysine, covalently bound to D-amfetamine via an amide linking 2.2. Drug-discrimination training and testing 193 129 group. Lisdexamfetamine is the first prodrug to have been 194 130 approved in the USA and Canada for the management of ADHD in D-Amfetamine-cued drug-discrimination testing in rats was based on the 195 fl 131 children (age 6e12), adolescents (age 13e17) and adults. It is method previously described by Heal et al. (1992). Brie y, female PVG rats were 196 trained to distinguish between D-amfetamine (0.5 mg/kg, i.p.) and saline (1 ml/kg, 197 132 currently undergoing evaluation for the treatment of ADHD in a i.p.) in a 2-choice lever-pressing task in response to a sweetened milk reward made 133 number of European countries. The metabolic route of conversion available on a FR-5 reward schedule (i.e. 5 lever-presses for 1 reward). Rats were 198 134 of lisdexamfetamine is unusual because after absorption into the randomly allocated one lever for D-amfetamine (0.5 mg/kg, i.p.) and the other for 199 135 bloodstream it is metabolised by red blood cells to yield D-amfet- saline. Once a rat had achieved approximately 60% correct lever-presses on most 200 trials, it began the test regime. 136 amine and the natural amino acid, L-lysine, by rate-limited, enzy- 201 On the test regime, rats were injected with drug cue or saline and then placed in 137 matic hydrolysis (Pennick, 2010). The prodrug is pharmacologically the test chamber.