Impact of Functional Group Modifications on Designer

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Impact of functional group modifications on designer phenethylamine induced hyperthermia Gregory G. Grecco, and Jon E Sprague Chem. Res. Toxicol., Just Accepted Manuscript • DOI: 10.1021/acs.chemrestox.6b00030 • Publication Date (Web): 08 Mar 2016 Downloaded from http://pubs.acs.org on March 10, 2016

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Chemical Research in Toxicology

Impact of functional group modifications on designer phenethylamine induced hyperthermia

Gregory G. Grecco and Jon E. Sprague

The Ohio Attorney General’s Center for the Future of Forensic Science, Bowling Green State University, Bowling Green, OH 43403, USA

Corresponding author: Jon E. Sprague, PhD Director and BCI Eminent Scholar Ohio Attorney General’s Center for the Future of Forensic Science Bowling Green State University Bowling Green, OH 43403 Phone: +1-419-372-0224 e-mail: [email protected]

Conflict of Interest: The authors declare no competing financial interest.

Keywords: Hyperthermia; MDMA; bath salts, phenethylamine, phenethylamines

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Abstract The popularity of designer phenethylamines such as synthetic cathinones (“bath salts”) has led to increased reports of life-threatening hyperthermia. The diversity of chemical modifications has resulted in the toxicological profile of most synthetic cathinones being mostly uncharacterized. Here, we investigated the thermogenic effects of six recently identified designer phenethylamines (4methylmethamphetamine, methylone, mephedrone, butylone, pentylone, and MDPV) and compared these effects to the established thermogenic agent 3,4-methylenedioxymethamphetamine (MDMA). Specifically, we determined the impact of a β-ketone, α-alkyl, or pyrrolidine functional group on corebody temperature changes. Sprague-Dawley rats (n=5-6) were administered a dose (30 mg/kg, sc) of a designer phenethylamine or MDMA, and core body temperature measurements were recorded at 30 minute intervals for 150 minutes post treatment. MDMA elicited the greatest maximum temperature change (∆Tmax), and this effect was significantly greater than its β-ketone analog, methylone. Temperature area under the curves (TAUCs) and ∆Tmax were also significantly different between 4methylmethamphetamine (4-MMA) and its β-ketone analog mephedrone. Lengthening the α-alkyl chain of methylone to produce butylone and pentylone significantly attenuated the thermogenic response on both TAUCs and ∆Tmax compared to methylone; however, butylone and pentylone were not different from each other. Pyrrolidine substitution on the N-terminus of pentylone produces 3,4-methylenedioxypyrovalerone (MDPV), which did not significantly alter core body temperature. Thermogenic comparisons of MDMA vs methylone and 4-MMA vs mephedrone indicate that oxidation at the benzylic position significantly attenuates the hyperthermic response. Furthermore, either extending the α-alkyl chain to ethyl and propyl (butylone and pentylone, respectively) or extending the α-alkyl chain and adding a pyrrolidine on the N-terminus (MDPV) significantly blunted the thermogenic effects of methylone. Overall, the present study provides the first structure-activity relationship in-vivo toxicological analysis of designer phenethylamines.


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Introduction Designer phenethylamines such as the synthetic cathinones (“bath salts”) are the latest versions of sympathomimetic compounds to emerge as abused drugs. Clandestine laboratories modify the chemical structures of the synthetic cathinone in order to circumvent the law.1 These chemical modifications have been demonstrated to alter the affinity of the synthetic cathinones for their primary pharmacologic target, the neurotransmitter reuptake proteins2 and intracranial self-administration in rats.3 The use of synthetic cathinones and/or 3,4-methylenedioxymethamphetamine (MDMA, Molly) can lead to tachycardia, hyperthermia and death.4 The National Forensic Laboratory Information System (NFLIS) recently reported that the number of Poison Control Center mentions for synthetic cathinone exposure increased from 303 in 2010 to 3,505 during the January through June 2011 period.5 The NFLIS report also outlined that synthetic cathinones reports increased from 142 reports during the first half of 2010 to 7,997 forensic reports during the first half of 2013. Mephedrone (54%) and methylenedioxypyrovalerone (MDPV) (38%) were the most commonly reported synthetic cathinones during the first half of 2010. By the first half of 2013, methylone accounted for 65% of those reports.5 The 2013 United Nations Office on Drugs and Crime report identified the use and spread of MDMA and synthetic cathinones worldwide as a major international problem.6 Furthermore, the growing popularity of synthetic cathinones and MDMA has resulted in increased reports of severe, life-threatening hyperthermia.7 Moreover, designer phenethylamine-induced hyperthermia has also been ostensibly linked to other adverse medical consequences such as rhabdomyolysis8,9 and death.10,11 The synthetic cathinones mephedrone, methylone, and MDPV are pharmacologically similar to MDMA in that they interact with the dopamine, norepinephrine and serotonin reuptake proteins.12,13 This might be expected because these compounds share the same cathinone and therefore phenethylamine pharmacophore for pharmacologic activity. However, while the effects of these three cathinones all result



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in increased neurotransmitter levels in the synapse, they do so through different mechanisms, functioning as releasing agents and/or (re)uptake inhibitors.2,12 Comparing the differences in hyperthermic responses generated by different designer phenethylamines will allow us to correlate the presence of key designer functional groups that are important for mediating designer stimulant induced thermogenesis. Experimental Procedure Animals Male Sprague-Dawley rats (284.6±2.4 g; Harlan, Indianapolis, IN) were used. Animals were housed two per cage (cage size: 21.0 x 41.9 x 20.3 cm), maintained on a 12:12 hr light/dark schedule and provided ad libitum access to food and water. In order to maximize a thermogenic response, animals were maintained on a minimum 10% fat diet, group housed two per cage and in a room maintained at 2425°C.14,15 Animal maintenance and research were conducted in accordance with the eighth edition of the Guide for the Care and Use of Laboratory Animals as adopted and promulgated by the National Institutes of Health and protocols were approved by the Bowling Green State University Animal Care and Use Committee. Study design Animals were randomly assigned to 8 groups (n=5-6) and treated with saline or a designer phenethylamine (30 mg/kg, sc). Synthetic cathinone doses were based on previous MDMA, methylone and mephedrone hyperthermia studies.16,17,18 Temperatures were taken rectally just prior to treatment (baseline) and every 30 min for 150 minutes post-treatment, using a Physiotemp Thermalert TH-8 thermocouple (Physitemp Instruments, Clifton, NJ) attached to a RET-2 rectal probe. Chemicals and reagents The 4-MMA (HCl salt) was synthesized in the laboratory of Dr. David E. Nichols (Purdue University, West Lafayette, IN) using standard methods. All other chemicals and reagents used were


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obtained as hydrochloride salts from Cayman Chemical (Ann Arbor, MI). On the day of the study, all drug solutions were made fresh at a concentration of 30 mg/mL in normal saline. Statistical analysis GraphPad InStat® v.6.0 software was used to complete all statistical analyses of data. Compounds were compared using one-way ANOVA with test drug as the main factor and in the presence of a significant main effect, a Student Newman Keuls post hoc test was conducted. In addition, a one-way repeated-measures ANOVA with time as the main factor was conducted, and in the presence of a significant time effect, a Dunnett’s post hoc test was conducted for comparisons to the corresponding baseline core temperature. When only two groups were compared, a Student’s t-test was used. Significance was set a priori at the 95% confidence level (p < 0.05). Statistical analysis and temperature area under the curve (TAUC) The temperature measurements were also converted to temperature area under the curve (TAUC) in a fashion similar to those described elsewhere.18 TAUC is a composite measurement of temperature and was determined for each animal by taking the temperatures measured at baseline (time of drug administration) and 30, 60, 90,120, and 150 min post-drug administration. This composite measure represents the area under the curve of a plot of temperature (1°C) versus time (min) and is expressed as °C x min. Maximum temperature change (∆Tmax) was calculated by comparing the maximum increase or decrease in core-body temperature to the individual animal’s baseline temperature. Results Effects of β-ketone substitutions on sympathomimetic-induced hyperthermia Following vehicle (saline control) administration, core body temperature did not significantly change over the 150-min monitoring period (Figure 1B, Figure 2B, Figure 3B, Figure 4B). 4-MMA significantly (p

Impact of Functional Group Modifications on Designer

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