Co-targeting the kappa opioid receptor and dopamine transporter reduces motivation to self-administer cocaine and partially reverses dopamine system dysregulation.

Cocaine disrupts dopamine (DA) and kappa opioid receptor (KOR) system activity, with long-term exposure reducing inhibiton of DA uptake by cocaine and increasing KOR system function. Single treatment therapies have not been successful for cocaine use disorder; therefore, this study focuses on a combination therapy targeting the dopamine transporter (DAT) and KOR. Sprague Dawley rats self-administered 5 days of cocaine (1.5 mg/kg/inf, max 40 inf/day, FR1), followed by 14 days on a progressive ratio (PR) schedule (0.19 mg/kg/infusion). Behavioral effects of individual and combined administration of phenmetrazine and nBNI were then examined using PR. Additionally, ex vivo fast scan cyclic voltammetry was then used to assess alterations in DA and KOR system activity in the nucleus accumbens before and after treatments. Chronic administration of phenmetrazine as well as the combination of phenmetrazine and nBNI-but not nBNI alone-significantly reduced PR breakpoints. In addition, the combination of phenmetrazine and nBNI partially reversed cocaine-induced neurodysregulations of the KOR and DA systems, indicating therapeutic benefits of targeting the DA and KOR systems in tandem. These data highlight the potential benefits of the DAT and KOR as dual-cellular targets to reduce motivation to administer cocaine and reverse cocaine-induced alterations of the DA system.

Target and suspect screening of (new) psychoactive substances in South Korean wastewater by LC-HRMS.

New psychoactive substances (NPS) are a type of abused drug designed to mimic the effects of the currently known illicit drugs, whose structures are constantly changing to escape surveillance. The quick identification of NPS use in the community therefore demands immediate action. This study aimed to develop a target and suspect screening method using LC-HRMS to identify NPS in wastewater samples. An in-house database of 95 traditional and NPS was built using the reference standards, and an analytical method was developed. Wastewater samples were collected from 29 wastewater treatment plants (WWTP) across South Korea, representing 50 % of the total population. The psychoactive substances in waste water samples were screened using in-house database and developed analytical methods. A total of 14 substances were detected in the target analysis, including three NPS (N-methyl-2-AI, 25E-NBOMe, and 25D-NBOMe) and 11 traditional psychoactive substances and their metabolites (zolpidem phenyl-4-COOH, ephedrine, ritalinic acid, tramadol, phenmetrazine, phendimetrazine, phentermine, methamphetamine, codeine, morphine, and ketamine). Out of these, N-methyl-2-AI, zolpidem phenyl-4-COOH, ephedrine, ritalinic acid, tramadol, phenmetrazine, and phendimetrazine were detected with a detection frequency of over 50 %. Primarily, N-methyl-2-Al was detected in all the wastewater samples. Additionally, four NPSs (amphetamine-N-propyl, benzydamine, isoethcathinone, methoxyphenamine) were tentatively identified at level 2b in a suspect screening analysis. This is the most comprehensive study to investigate NPS using target and suspect analysis methods at the national level. This study raises a need for continuous monitoring of NPS in South Korea.

Retrospective identification of new psychoactive substances in patient samples submitted for clinical drug analysis.

New psychoactive substances (NPS) are life threatening through unpredictable toxicity and limited analytical options for clinicians. We present the retrospective identification of NPS in raw data from a liquid chromatography-high resolution mass spectrometry (LC-HRMS)-based multidrug panel analysis on 14 367 clinical oral fluid samples requested during 2019 mainly by psychiatric and addiction care clinics. Retrospectively analysed NPS included 48 notified originally in 2019 by the European Union Early Warning System (EU EWS) and 28 frequently reported in Sweden. Of 88 included NPS, 34 (mitragynine, flualprazolam, 3F/4F-α-P(i)HP, etizolam, 4F-MDMB-BINACA, cyproheptadine, 5F-MDMB-PICA, isotonitazene, isohexedrone, MDPEP, N-ethylpentedrone, tianeptine, flubromazolam, 4'-methylhexedrone, α-P(i)HP, eutylone, mephedrone, N-ethylhexedrone, 5F-MDMB-PINACA, ADB-BUTINACA, 3-methoxy PCP, 4F-furanylfentanyl, 4F-isobuturylfentanyl, acrylfentanyl, furanylfentanyl, clonazolam, norfludiazepam, 3F-phenmetrazine, 3-MMC, 4-methylpentedrone, BMDP, ethylphenidate, methylone and α-PVP) were identified as 219 findings in 84 patients. Eight NPS notified in 2019 were identified, five before EWS release. NPS occurred in 1.20% of all samples and 1.53% of samples containing traditional drugs, and in 1.87% of all patients and 2.88% of patients using traditional drugs. NPS use was more common in men and polydrug users. Legal (not scheduled) NPS were more used than comparable illegal ones. Retrospective identification could be useful when prioritizing NPS for clinical routine analysis and when studying NPS epidemiology.

Organ distribution of diclazepam, pyrazolam and 3-fluorophenmetrazine.

The organ distribution of 3-fluorophenmetrazine (3-FPM), pyrazolam, diclazepam as well as its main metabolites delorazepam, lormetazepam and lorazepam, was investigated. A solid phase extraction (SPE) and a QuEChERS (acronym for quick, easy, cheap, effective, rugged and safe) - approach were used for the extraction of the analytes from human tissues, body fluids and stomach contents. The detection was performed on a liquid chromatography-tandem mass spectrometry system (LCMS/MS). The analytes of interest were detected in all body fluids and tissues. Results showed femoral blood concentrations of 10 µg/L for 3-FPM, 28 µg/L for pyrazolam, 1 µg/L for diclazepam, 100 µg/L for delorazepam, 6 µg/L for lormetazepam, and 22 µg/L for lorazepam. Tissues (muscle, kidney and liver) and bile exhibited higher concentrations of the mentioned analytes than in blood. Additional positive findings in femoral blood were for 2-fluoroamphetamine (2-FA, approx. 89 µg/L), 2-flourometamphetamine (2-FMA, hint), methiopropamine (approx. 2.2 µg/L), amphetamine (approx. 21 µg/L) and caffeine (positive). Delorazepam showed the highest ratio of heart (C) and femoral blood (P) concentration (C/P ratio = 2.5), supported by the concentrations detected in psoas muscle (430 µg/kg) and stomach content (approx. 210 µg/L, absolute 84 µg). The C/P ratio indicates that delorazepam displays susceptibility for post-mortem redistribution (PMR), supported by the findings in muscle tissue. 3-FPM, pyrazolam, diclazepam, lorazepam and lormetazepam did apparently not exhibit any PMR. The cause of death, in conjunction with autopsy findings was concluded as a positional asphyxia promoted by poly-drug intoxication by arising from designer benzodiazepines and the presence of synthetic stimulants.

Skin Delivery and Irritation Potential of Phenmetrazine as a Candidate Transdermal Formulation for Repurposed Indications.

Phenmetrazine, a selective dopamine and norepinephrine releaser, previously available as an oral anorectic, is prone to be abused. This study aimed to assess the feasibility of delivering phenmetrazine via the transdermal route for a new indication, while also minimizing its abuse potential. The passive permeation of phenmetrazine through dermatomed human cadaver skin was evaluated using static Franz diffusion cells at 10 mg/mL for the fumarate salt, and at 20, 40, and 80 mg/mL for the free base in propylene glycol for 24 h. Further, oleic acid (5% w/w), oleyl alcohol (5% and 10% w/w), and lauric acid (10% w/w) were investigated as chemical permeation enhancers to enhance the delivery. Skin irritation potential was assessed using EpiDerm™ in vitro reconstructed human epidermal model. The free base showed superior 24-h delivery (8.13 ± 4.07%, 10.6 ± 2.5%, and 10.4 ± 1.4% for groups with 20, 40, and 80 mg/mL of the free base, respectively) to phenmetrazine fumarate salt (undetectable). The successful screening of effective chemical enhancers, oleyl alcohol (5% and 10% w/w), oleic acid (5% w/w), and lauric acid (10% w/w) resulted in significant enhancement of delivery. The calculated therapeutic relevant flux for the potential indication, attention deficit hyperactivity disorder, 20 µg/cm2/h was met, where a 24-mg daily dose from a 50-cm2 patch was projected to be delivered to a 60-kg individual. Irritation study results suggest that formulations with therapeutically relevant delivery are likely to be non-irritant. In conclusion, it is feasible to deliver therapeutically relevant amounts of phenmetrazine via the transdermal route.

Validation of an LC-MS/MS method for the quantitative analysis of 1P-LSD and its tentative metabolite LSD in fortified urine and serum samples including stability tests for 1P-LSD under different storage conditions.

A variety of hallucinogens of the lysergamide type has emerged on the drug market in recent years and one such uncontrolled derivative of lysergic acid diethylamide (LSD) is 1-propionyl-LSD (1P-LSD). Due to the high potency of LSD and some of its derivatives (common doses: 50-200 µg), sensitive methods are required for the analysis of biological samples such as serum and urine. The occurrence of an intoxication case required the development of a fully validated, highly sensitive method for the quantification of 1P-LSD and LSD in urine and serum using LC-MS/MS. Given that LSD is unstable in biological samples when exposed to light or elevated temperatures, we also conducted stability tests for 1P-LSD in urine and serum under different storage conditions. The validation results revealed that the analysis method was accurate and precise with good linearity over a wide calibration range (0.015-0.4 ng mL-1). The limit of detection (LOD) and the lower limit of quantification (LLOQ) of 1P-LSD and LSD in serum and urine were 0.005 ng mL-1 and 0.015 ng mL-1, respectively. The stability tests showed no major degradation of 1P-LSD in urine and serum stored at -20 °C, 5 °C or at room temperature for up to five days, regardless of protection from light. However, LSD was detected in all samples stored at room temperature showing a temperature-dependent hydrolysis of 1P-LSD to LSD to some extent (up to 21% in serum). Serum samples were particularly prone to hydrolysis possibly due to enzymatically catalyzed reactions. The addition of sodium fluoride prevented the enzymatic formation of LSD. The method was applied to samples obtained from the intoxication case involving 1P-LSD. The analysis uncovered 0.51 ng mL-1 LSD in urine and 3.4 ng mL-1 LSD in serum, whereas 1P-LSD remained undetected. So far pharmacokinetic data of 1P-LSD is missing, but with respect to the results of our stability tests and the investigated case rapid hydrolysis to LSD in-vivo seems more likely than instabilities of 1P-LSD in urine and serum samples.

Method validation and preliminary pharmacokinetic studies on the new designer stimulant 3-fluorophenmetrazine (3-FPM).

Pharmaceutical research not only provides the basis for the development of new medicinal products but also for the synthesis of new drugs of abuse. 3-Fluorophenmetrazine (3-FPM), a fluorinated derivative of the anorectic phenmetrazine, was first patented in 2011 and appeared on the drug market in 2014. Though invented for potential medical purposes, pharmacokinetic data on this compound, crucial for interpreting forensic as well as clinical cases, are not available. Therefore, a liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method for the detection of 3-FPM in serum, urine, and oral fluid was developed, validated for urine and serum, and used to quantify 3-FPM in samples obtained during a controlled self-experiment. The method proved to be linear, selective and sufficiently sensitive. The limits of detection (LODs) were 0.1 ng/mL, 0.2 ng/mL, and 0.05 ng/mL in serum, urine, and oral fluid. Inter-day precision and intra-day precision (RSD) in serum samples were below 6.3% and below 8.5%, respectively. The highest serum concentration (cmax ) of 210 ng/mL was reached 2.5 hours (tmax ) after ingestion. The elimination half-life and the volume of distribution were calculated to be approx. 8.8 hours and 400 L (5.3 L/kg). 3-FPM could be detected in serum and urine up to 82 hours and 116 hours, respectively. It was still detected in the last oral fluid sample taken 55 hours after ingestion. 3-FPM was mainly excreted unchanged. Main metabolic reactions were aryl-hydroxylation and N-hydroxylation. Interestingly, the product of oxidative ring opening (2-amino-1-(3-fluorophenyl)propan-1-ol) showed the largest window of detection in the self-experiment.

Novel psychoactive substances: overdose of 3-fluorophenmetrazine (3-FPM) and etizolam in a 33-year-old man.

Though illegal in the UK, in many countries novel psychoactive substances are quasi-legal synthetic compounds that are widely available online under the guise of research chemicals. These substances are relatively cheap and are often undetectable in standard drug screens. Nearly 200 such compounds are introduced yearly, and little is usually known about their metabolism or physiological effects. Consequently, managing patients in overdose situations on largely unknown substances usually involves supportive care, however anticipating and managing atypical side effects are challenging in the absence of knowledge of these compounds. In this report, we discuss our encounter with a 33-year-old unconscious man presenting with coingestion of a novel stimulant 3-fluorophenmetrazine with a rarely used benzodiazepine etizolam. This patient developed seizure-like activity and delayed widespread T-wave inversions, both of which ultimately resolved without sequelae.

Synthesis, analytical characterization, and monoamine transporter activity of the new psychoactive substance 4-methylphenmetrazine (4-MPM), with differentiation from its ortho- and meta- positional isomers.

The availability of new psychoactive substances (NPS) on the recreational drug market continues to create challenges for scientists in the forensic, clinical and toxicology fields. Phenmetrazine (3-methyl-2-phenylmorpholine) and an array of its analogs form a class of psychostimulants that are well documented in the patent and scientific literature. The present study reports on two phenmetrazine analogs that have been encountered on the NPS market following the introduction of 3-fluorophenmetrazine (3-FPM), namely 4-methylphenmetrazine (4-MPM), and 3-methylphenmetrazine (3-MPM). This study describes the syntheses, analytical characterization, and pharmacological evaluation of the positional isomers of MPM. Analytical characterizations employed various chromatographic, spectroscopic, and mass spectrometric platforms. Pharmacological studies were conducted to assess whether MPM isomers might display stimulant-like effects similar to the parent compound phenmetrazine. The isomers were tested for their ability to inhibit uptake or stimulate release of tritiated substrates at dopamine, norepinephrine and serotonin transporters using in vitro transporter assays in rat brain synaptosomes. The analytical characterization of three vendor samples revealed the presence of 4-MPM in two of the samples and 3-MPM in the third sample, which agreed with the product label. The pharmacological findings suggest that 2-MPM and 3-MPM will exhibit stimulant properties similar to the parent compound phenmetrazine, whereas 4-MPM may display entactogen properties more similar to 3,4-methylenedioxymethamphetamine (MDMA). The combination of test purchases, analytical characterization, targeted organic synthesis, and pharmacological evaluation of NPS and their isomers is an effective approach for the provision of data on these substances as they emerge in the marketplace.

Fluorinated phenmetrazine "legal highs" act as substrates for high-affinity monoamine transporters of the SLC6 family.

A variety of new psychoactive substances (NPS) are appearing in recreational drug markets worldwide. NPS are compounds that target various receptors and transporters in the central nervous system to achieve their psychoactive effects. Chemical modifications of existing drugs can generate NPS that are not controlled by current legislation, thereby providing legal alternatives to controlled substances such as cocaine or amphetamine. Recently, 3-fluorophenmetrazine (3-FPM), a derivative of the anorectic compound phenmetrazine, appeared on the recreational drug market and adverse clinical effects have been reported. Phenmetrazine is known to elevate extracellular monoamine concentrations by an amphetamine-like mechanism. Here we tested 3-FPM and its positional isomers, 2-FPM and 4-FPM, for their abilities to interact with plasma membrane monoamine transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). We found that 2-, 3- and 4-FPM inhibit uptake mediated by DAT and NET in HEK293 cells with potencies comparable to cocaine (IC50 values < 2.5 µM), but display less potent effects at SERT (IC50 values >80 µM). Experiments directed at identifying transporter-mediated reverse transport revealed that FPM isomers induce efflux via DAT, NET and SERT in HEK293 cells, and this effect is augmented by the Na+/H+ ionophore monensin. Each FPM evoked concentration-dependent release of monoamines from rat brain synaptosomes. Hence, this study reports for the first time the mode of action for 2-, 3- and 4-FPM and identifies these NPS as monoamine releasers with marked potency at catecholamine transporters implicated in abuse and addiction. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Multiple Drug-Toxicity Involving Novel Psychoactive Substances, 3-Fluorophenmetrazine and U-47700.

3-Fluorophenmetrazine (3-FPM) is a stimulant-like novel psychoactive substance (NPS) and fluorinated analog of phenmetrazine that has recently appeared on the recreational drug market, with limited published information. Likewise, the synthetic opioid U-47700 has gained popularity among recreational drug users and is frequently detected in postmortem casework. We present the case history, autopsy and toxicological findings of a fatality involving the designer drugs 3-FPM and U-47700 for the first time in the literature. A sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the quantification of 3-FPM in whole blood, with a 0.001-0.100 mg/L analytical range. The method met the requirements for acceptable linearity, bias and precision. 3-FPM was detected along with U-47700 and other drugs including amitriptyline, nortriptyline, methamphetamine, amphetamine, diazepam, nordiazepam, temazepam, and the designer benzodiazepines flubromazolam and delorazepam. 3-FPM was quantified in the decedent's peripheral (femoral) and central (aortic) blood at 2.4 and 2.6 mg/L, respectively. These concentrations are similar to reported concentrations in non-fatal intoxications. U-47700 was present in peripheral blood at a semi-quantitative concentration of 0.36 mg/L, consistent with reported U-47700 postmortem concentrations. The cause of death was considered multiple drug-toxicity (3-FPM, U-47700, amitriptyline, methamphetamine, diazepam, temazepam, flubromazolam and delorazepam) and the manner of death ruled an accident. This case illustrates the dangers of polysubstance use and discusses the potential overlap between recreational and fatal concentrations for some NPS.

Test purchase, synthesis and characterization of 3-fluorophenmetrazine (3-FPM) and differentiation from its ortho- and para-substituted isomers.

The knowledge captured in patent and scientific research literature stimulates new ideas and fosters new drug development efforts. Manufacturers and entrepreneurs dedicated to the sale of 'research chemicals' and/or new psychoactive substances (NPS) also make use of access to information to identify, prepare, and launch a range of new substances. One of the most recent compounds to appear on the NPS market is the phenmetrazine analog 3-fluorophenmetrazine (3-FPM) which represents one of many phenylmorpholines designed to explore treatment options in areas such as obesity and drug dependence. The anorectic drug analogs phenmetrazine and phendimetrazine, used as prescription medicines before they were withdrawn, feature amphetamine-like properties associated with monoamine release. Available data on 3-FPM suggest that the effects might show mechanistic overlaps. This study describes the synthesis and extensive analytical characterization of 3-FPM and its differentiation from synthesized ortho- and para- substituted isomers, 2-FPM and 4-FPM, respectively. This study was triggered by the purchase of five powdered samples advertised as 3-FPM by five different Internet vendors based in the United Kingdom. The analytical data obtained for the vendor samples were consistent with the synthesized 3-FPM standard and differentiation between all three isomers was possible. The presence of positional isomers and the absence of suitable reference material can cause difficulties in the day-to-day operation of forensic work and given the rate at which many of the newly emerging NPS appear on the market, a comprehensive approach is needed when attempting to decipher the identity of NPS arriving onto the drug market. Copyright © 2016 John Wiley & Sons, Ltd.

Adverse events related to the new psychoactive substance 3-fluorophenmetrazine - results from the Swedish STRIDA project.

BACKGROUND: New psychoactive substances (NPS) are often poorly pharmacologically documented and the production is unregulated, implying high risks for toxic side effects. This report from the STRIDA project describes analytically confirmed non-fatal intoxications involving the phenmetrazine analogue 3-fluorophenmetrazine (3-FPM). STUDY DESIGN AND METHODS: Observational case series of patients with suspected acute NPS exposure requiring hospital care. Blood and urine samples were collected from patients presenting in emergency departments (ED) or intensive care units (ICU), after consultation with the Swedish Poisons Information Centre (PIC). Laboratory analysis was performed by multi-component liquid chromatography-mass spectrometry. Clinical data were collected during PIC consultations and retrieved from medical records. RESULTS: From November 2014 to October 2015, eight cases were registered as 3-FPM or "phenmetrazine" intoxications at the PIC after consultation. During the same period, analysis of STRIDA project samples confirmed 3-FPM use in a total of 19 patients (84% men) aged 22-54 (median 30) years. 3-FPM was detected in 15 out of 19 serum (2.7-1416 ng/mL) and in 14 out of 14 urine (1.0-6857 µg/mmol creatinine) samples. All patients were also tested positive for other psychoactive substances, with benzodiazepines being most common (57% of the cases). Ten patients were monitored in the ED for <4 h, while six needed ICU monitoring of which five were graded as severe intoxications (Poisoning Severity Score 3). Prominent clinical signs were tachycardia (47%), depressed consciousness (42%), agitation/anxiety (37%), delirium (37%), dilated pupils (26%), and seizures (16%). All patients survived. CONCLUSION: In 19 patients testing positive for 3-FPM, a high incidence of severe clinical features was demonstrated. However, as all patients had also used other psychoactive substances, it was difficult to identify a unique toxidrome for 3-FPM. The results further showed that many 3-FPM intoxications would have been missed, if relying solely on information from PIC consultations. These results emphasize the importance of performing bioanalytical investigation in cases of suspected NPS intoxication.

Dissociable effects of the prodrug phendimetrazine and its metabolite phenmetrazine at dopamine transporters.

Phendimetrazine (PDM) is a clinically available anorectic and a candidate pharmacotherapy for cocaine addiction. PDM has been hypothesized to function as a prodrug that requires metabolism to the amphetamine-like monoamine transporter substrate phenmetrazine (PM) to produce its pharmacological effects; however, whether PDM functions as an inactive prodrug or has pharmacological activity on its own remains unclear. The study aim was to determine PDM pharmacological mechanisms using electrophysiological, neurochemical, and behavioral procedures. PDM blocked the endogenous basal hDAT (human dopamine transporter) current in voltage-clamped (-60 mV) oocytes consistent with a DAT inhibitor profile, whereas its metabolite PM induced an inward hDAT current consistent with a DAT substrate profile. PDM also attenuated the PM-induced inward current during co-application, providing further evidence that PDM functions as a DAT inhibitor. PDM increased nucleus accumbens dopamine levels and facilitated electrical brain stimulation reinforcement within 10 min in rats, providing in vivo evidence supporting PDM pharmacological activity. These results demonstrate that PDM functions as a DAT inhibitor that may also interact with the pharmacological effects of its metabolite PM. Overall, these results suggest a novel mechanism for PDM therapeutic effects via initial PDM DAT inhibition followed by PM DAT substrate-induced dopamine release.

3-Fluorophenmetrazine, a fluorinated analogue of phenmetrazine: Studies on in vivo metabolism in rat and human, in vitro metabolism in human CYP isoenzymes and microbial biotransformation in Pseudomonas Putida and wastewater using GC and LC coupled to (HR)-MS techniques.

Wastewater-based epidemiology (WBE) as means to estimate illicit drug and new psychoactive substance (NPS) consumption with spatial and temporal resolution is gaining increasing attention. In order to evaluate a given NPS using WBE, in vivo metabolism and microbial biotransformation of excretion products and unchanged compounds need evaluation. The aims of this study were to identify in vivo phase I and II metabolites of the NPS 3-fluorophenmetrazine (3-FPM) in human and rat urine and study the in vitro contribution of Cytochrome P450 (CYP) isoenzymes in phase I metabolism. Additionally, to study microbial biotransformation products (MBPs) of 3-FPM from incubations in wastewater and in a wastewater isolated Pseudomonas Putida strain. To these aims gas chromatography and liquid chromatography coupled to mass spectrometry were applied. Metabolites and MBPs were isolated from urine and microbial incubations after solid phase extraction and precipitation with or without enzymatic conjungate cleaving. The main transformation pathways were N-oxidation, aryl hydroxylation and subsequent O-methylation, alkyl hydroxylation, oxidation, and degradation of the ethyl-bridge yielding the O/N-bis-dealkylated metabolite, combinations thereof and further glucuronidation or sulfations. The main excretion products in the human urine sample were the unchanged compound and the N-oxide, and the main MBPs were the N-oxide and hydroxylation with subsequent oxidations on the alpha-methyl position. Based on these findings, the proposed strategy for WBE analysis of 3-FPM is quantitative determination of unchanged 3-FPM together with qualitative verification of a number of selected metabolites to verify consumption and rule out discharge.

The individual and combined effects of phenmetrazine and mgluR2/3 agonist LY379268 on the motivation to self-administer cocaine.

BACKGROUND: The US Food and Drug Administration has not approved a treatment for cocaine addiction, possibly due in part to the fact that repeated cocaine use results in dysregulation of multiple neurotransmitter systems, including glutamate and dopamine, and an emergence of increased negative affective states and heightening motivation to take cocaine despite negative consequences. We used a combination therapy approach to assess whether modulation of both glutamate and dopamine transmission would reduce the motivation to self- administer cocaine compared to modulation of either system alone. METHODS: The metabotropic glutamate 2/3 receptor agonist, LY379268, and the monoamine releaser, phenmetrazine, were used to assess their individual and combined ability to decrease the reinforcing efficacy of cocaine because they modulate glutamate and dopamine levels, respectively. Cocaine breakpoints and cocaine intake was assessed, using a progressive ratio schedule, at baseline in three groups based on dose of cocaine (0.19, 0.38, 0.75mg/kg/infusion), and following LY379268 (0.03 or 0.30mg/kg; i.p.), phenmetrazine (25mg/kg/day; osmotic minipump), and a combination of the two drugs. RESULTS: LY379268 and phenmetrazine alone reduced breakpoints for all doses of cocaine. The combination of the two drugs showed a concerted effect in reducing breakpoints for all doses of cocaine, with the lowest dose of cocaine reduced by as much as 70%. CONCLUSIONS: These data support combination therapy of dopamine and glutamate systems as an effective means to reduce the motivation to take cocaine since a combination of drugs can address neurobiological dysfunction in multiple neurotransmitter systems compared to therapies using single drugs.

Cocaine-like discriminative stimulus effects of phendimetrazine and phenmetrazine in rats.

Phendimetrazine is a clinically available anorectic and candidate medication for the treatment of cocaine addiction. Phendimetrazine can be metabolized to the amphetamine-like monoamine releaser phenmetrazine, but it is unclear if phendimetrazine functions as an inactive prodrug or might have activity on its own. As one method to address this issue, the present study compared the potency and time course of phendimetrazine and phenmetrazine to produce cocaine-like discriminative stimulus effects in adult, male rats (N=5) trained to discriminate cocaine (5.6 mg/kg, intraperitoneally) from saline in a two-key food-reinforced discrimination procedure. We hypothesized that, if metabolism to phenmetrazine was required for phendimetrazine effects, then phendimetrazine would be less potent and have a slower onset and offset of effects than phenmetrazine. Both phendimetrazine and phenmetrazine produced dose-dependent cocaine-like discriminative stimulus effects, and phendimetrazine was 7.8-fold less potent than phenmetrazine. However, the time courses of discriminative stimulus effects produced by phendimetrazine and phenmetrazine were similar, with peak effects at 10 min and offset by 100 min. These results show the effectiveness of phendimetrazine to rapidly produce cocaine-like behavioral effects in rats and support other nonhuman primate evidence to suggest that metabolism to phenmetrazine may not be required for phendimetrazine effects.

Effects of the dopamine/norepinephrine releaser phenmetrazine on cocaine self-administration and cocaine-primed reinstatement in rats.

RATIONALE: Like other monoamine releasers such as D-amphetamine, chronic treatment with phenmetrazine can attenuate cocaine self-administration in monkeys. OBJECTIVES: The present studies extended this finding to rodents and to cocaine-primed reinstatement, a putative laboratory animal model of relapse. METHODS: In experiment 1, rats self-administered food pellets or injections of 0.19 mg/kg cocaine (i.v.) under a progressive-ratio schedule. When responding was stable, subcutaneous osmotic pumps were implanted containing saline or (+)-phenmetrazine (25 or 50 mg/kg per day). In experiment 2, rats self-administered injections of 0.75 mg/kg cocaine under a fixed-ratio 1 schedule in daily 6-h sessions. When responding was stable, rats were removed from the self-administration environment for 7 days and treated continuously with saline, 5 mg/kg per day D-amphetamine or phenmetrazine (25 or 50 mg/kg per day) via osmotic pumps. Rats were then returned to the self-administration context while treatment continued, and responding was extinguished by removing response-contingent stimulus changes and cocaine injections. Once responding was extinguished, reinstatement tests were conducted using cocaine injections (10 mg/kg i.p.). RESULTS: Phenmetrazine decreased self-administration of cocaine, but not food pellets, during the 14-day treatment period; effects persisted for several days after treatment was discontinued. Moreover, cocaine-induced increases in responding during the reinstatement test were attenuated by D-amphetamine and both phenmetrazine doses. CONCLUSIONS: These results extend the study of the effects of phenmetrazine on cocaine self-administration to a rodent model, and provide further support for the use of monoamine releasers as agonist medications for cocaine abuse.

A generalized matching law analysis of cocaine vs. food choice in rhesus monkeys: effects of candidate 'agonist-based' medications on sensitivity to reinforcement.

BACKGROUND: We have previously demonstrated reductions in cocaine choice produced by either continuous 14-day phendimetrazine and d-amphetamine treatment or removing cocaine availability under a cocaine vs. food choice procedure in rhesus monkeys. The aim of the present investigation was to apply the concatenated generalized matching law (GML) to cocaine vs. food choice dose-effect functions incorporating sensitivity to both the relative magnitude and price of each reinforcer. Our goal was to determine potential behavioral mechanisms underlying pharmacological treatment efficacy to decrease cocaine choice. METHODS: A multi-model comparison approach was used to characterize dose- and time-course effects of both pharmacological and environmental manipulations on sensitivity to reinforcement. RESULTS: GML models provided an excellent fit of the cocaine choice dose-effect functions in individual monkeys. Reductions in cocaine choice by both pharmacological and environmental manipulations were principally produced by systematic decreases in sensitivity to reinforcer price and non-systematic changes in sensitivity to reinforcer magnitude. CONCLUSIONS: The modeling approach used provides a theoretical link between the experimental analysis of choice and pharmacological treatments being evaluated as candidate 'agonist-based' medications for cocaine addiction. The analysis suggests that monoamine releaser treatment efficacy to decrease cocaine choice was mediated by selectively increasing the relative price of cocaine. Overall, the net behavioral effect of these pharmacological treatments was to increase substitutability of food pellets, a nondrug reinforcer, for cocaine.

Role of phenmetrazine as an active metabolite of phendimetrazine: evidence from studies of drug discrimination and pharmacokinetics in rhesus monkeys.

BACKGROUND: Monoamine releasers such as d-amphetamine that selectively promote release of dopamine/norepinephrine versus serotonin are one class of candidate medications for treating cocaine dependence; however, their clinical utility is limited by undesirable effects such as abuse liability. Clinical utility of these compounds may be increased by development of prodrugs to reduce abuse potential by slowing onset of drug effects. This study examined the behavioral and pharmacokinetic profile of the Schedule III compound phendimetrazine, which may serve as a prodrug for the N-demethylated metabolite and potent dopamine/norepinephrine releaser phenmetrazine. METHODS: Monkeys (n = 5) were trained in a two-key food-reinforced discrimination procedure to discriminate cocaine (0.32 mg/kg, IM) from saline, and the potency and time course of cocaine-like discriminative stimulus effects were determined for (+)-phenmetrazine, (-)-phenmetrazine, (+)-phendimetrazine, (-)-phendimetrazine, and (±)-phendimetrazine. Parallel pharmacokinetic studies in the same monkeys examined plasma phenmetrazine and phendimetrazine levels for correlation with cocaine-like discriminative stimulus effects. RESULTS: Both isomers of phenmetrazine, and the racemate and both isomers of phendimetrazine, produced dose- and time-dependent substitution for the discriminative stimulus effects of cocaine, with greater potency residing in the (+) isomers. In general, plasma phenmetrazine levels increased to similar levels after administration of behaviorally active doses of either phenmetrazine or phendimetrazine. CONCLUSIONS: These results support the hypothesis that phenmetrazine is an active metabolite that contributes to the effects of phendimetrazine. However, behavioral effects of phendimetrazine had a more rapid onset than would have been predicted by phenmetrazine levels alone, suggesting that other mechanisms may also contribute.