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Ilic M, Holy M, Jaentsch K, Liechti ME, Lubec G, Baumann MH, Sitte HH, Luethi D. Cell-Based Radiotracer Binding and Uptake Inhibition Assays: A Comparison of In Vitro Methods to Assess the Potency of Drugs That Target Monoamine Transporters. Front Pharmacol 2020; 11:673. [PMID: 32508638 PMCID: PMC7248194 DOI: 10.3389/fphar.2020.00673] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 04/24/2020] [Indexed: 01/10/2023] Open
Abstract
High-affinity monoamine transporters are targets for prescribed medications and stimulant drugs of abuse. Therefore, assessing monoamine transporter activity for candidate medications and newly-emerging drugs of abuse provides essential information for industry, academia, and public health. Radiotracer binding and uptake inhibition are the gold standard assays for determining drug–transporter interaction profiles. The combined results from such assays yield a unique biochemical fingerprint for each compound. Over time, different assay methods have been developed to assess transporter activity, and the comparability of data across various assay platforms remains largely unclear. Here, we compare the effects of six well-established stimulants in two different cell-based uptake inhibition assays, one method using adherent cells and the other using suspended cells. Furthermore, we compare the data from transfected cell lines derived from different laboratories and data reported from rat synaptosomes. For transporter inhibitors, IC50 values obtained by the two experimental methods were comparable, but using different transfected cell lines yielded disparate results. For transporter substrates, differences between the two cell lines were less pronounced but the drugs displayed different inhibition potencies when evaluated by the two methods. Our study illustrates the inherent limitations when comparing transporter inhibition data from different laboratories and stresses the importance of including appropriate control experiments with reference compounds when investigating new drugs of interest.
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Affiliation(s)
- Marija Ilic
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.,Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria.,Neuroproteomics, Paracelsus Private Medical University, Salzburg, Austria
| | - Marion Holy
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Kathrin Jaentsch
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Matthias E Liechti
- Division of Clinical Pharmacology and Toxicology, Department of Biomedicine, University Hospital Basel and University Basel, Basel, Switzerland
| | - Gert Lubec
- Neuroproteomics, Paracelsus Private Medical University, Salzburg, Austria
| | - Michael H Baumann
- Designer Drug Research Unit, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, United States
| | - Harald H Sitte
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Dino Luethi
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.,Division of Clinical Pharmacology and Toxicology, Department of Biomedicine, University Hospital Basel and University Basel, Basel, Switzerland
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Sotomayor-Zárate R, Jara P, Araos P, Vinet R, Quiroz G, Renard GM, Espinosa P, Hurtado-Guzmán C, Moya PR, Iturriaga-Vásquez P, Gysling K, Reyes-Parada M. Improving Amphetamine Therapeutic Selectivity:N,N-dimethyl-MTA has Dopaminergic Effects and does not Produce Aortic Contraction. Basic Clin Pharmacol Toxicol 2013; 114:395-9. [DOI: 10.1111/bcpt.12168] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 10/30/2013] [Indexed: 12/31/2022]
Affiliation(s)
- Ramón Sotomayor-Zárate
- Centro de Neurobiología y Plasticidad Cerebral; Departamento de Fisiología, Facultad de Ciencias; Universidad de Valparaíso; Valparaíso Chile
- Millennium Science Nucleus in Stress and Addiction; Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - Pablo Jara
- Faculty of Chemistry and Biology; University of Santiago de Chile; Santiago Chile
| | - Patricio Araos
- Centro Regional de Estudios en Alimentos y Salud (CREAS); Región de Valparaíso Chile
| | - Raúl Vinet
- Centro Regional de Estudios en Alimentos y Salud (CREAS); Región de Valparaíso Chile
- Laboratorio de Farmacología y Bioquímica; Facultad de Farmacia; Universidad de Valparaíso; Valparaíso Chile
| | - Gabriel Quiroz
- Department of Chemistry; Faculty of Sciences; University of Chile; Santiago Chile
| | - Georgina M. Renard
- Centro de Neurobiología y Plasticidad Cerebral; Departamento de Fisiología, Facultad de Ciencias; Universidad de Valparaíso; Valparaíso Chile
| | - Pedro Espinosa
- Centro de Neurobiología y Plasticidad Cerebral; Departamento de Fisiología, Facultad de Ciencias; Universidad de Valparaíso; Valparaíso Chile
| | | | - Pablo R. Moya
- Centro de Neurobiología y Plasticidad Cerebral; Departamento de Fisiología, Facultad de Ciencias; Universidad de Valparaíso; Valparaíso Chile
| | | | - Katia Gysling
- Millennium Science Nucleus in Stress and Addiction; Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - Miguel Reyes-Parada
- School of Medicine; Faculty of Medical Sciences; University of Santiago de Chile; Santiago Chile
- Facultad de Ciencias de la Salud; Universidad Autónoma de Chile; Santiago Chile
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Sainsbury P, Kicman A, Archer R, King L, Braithwaite R. Aminoindanes-the next wave of ‘legal highs’? Drug Test Anal 2011; 3:479-82. [DOI: 10.1002/dta.318] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 05/24/2011] [Indexed: 11/11/2022]
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Abstract
BACKGROUND The serotonin (5-HT) releasers (+/-)-fenfluramine and (+)-fenfluramine were withdrawn from clinical use owing to increased risk of valvular heart disease. One prevailing hypothesis (i.e., the '5-HT hypothesis') suggests that fenfluramine-induced increases in plasma 5-HT underlie the disease. OBJECTIVE Here, we critically evaluate the possible mechanisms responsible for fenfluramine-associated valve disease. METHODS Findings from in vitro and in vivo experiments performed in our laboratory are reviewed. The data are integrated with existing literature to address the validity of the 5-HT hypothesis and suggest alternative explanations. CONCLUSIONS The overwhelming majority of evidence refutes the 5-HT hypothesis. A more likely cause of fenfluramine-induced valvulopathy is activation of 5-HT(2B) receptors on heart valves by the metabolite norfenfluramine. Future serotonergic medications should be designed to lack 5-HT(2B) agonist activity.
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Affiliation(s)
- Richard B Rothman
- Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA.
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Abstract
The prevalence of obesity in the United States is a major health problem associated with significant morbidity, mortality, and economic burden. Although obesity and drug addiction are typically considered distinct clinical entities, both diseases involve dysregulation of biogenic amine neuron systems in the brain. Thus, research efforts to develop medications for treating drug addiction can contribute insights into the pharmacotherapy for obesity. Here, we review the neurochemical mechanisms of selected stimulant medications used in the treatment of obesity and issues related to fenfluramine-associated cardiac valvulopathy. In particular, we discuss the evidence that cardiac valve disease involves activation of mitogenic serotonin 2B (5-HT2B) receptors by norfenfluramine, the major metabolite of fenfluramine. Advances in medication discovery suggest that novel molecular entities that target 2 different neurochemical mechanisms, that is, "combination pharmacotherapy," will yield efficacious antiobesity medications with reduced adverse side effects.
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Rothman RB, Blough BE, Baumann MH. Dual dopamine/serotonin releasers: potential treatment agents for stimulant addiction. Exp Clin Psychopharmacol 2008; 16:458-74. [PMID: 19086767 PMCID: PMC2683464 DOI: 10.1037/a0014103] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
"Agonist therapy" for cocaine and methamphetamine addiction involves administration of stimulant-like medications (e.g., monoamine releasers) to reduce withdrawal symptoms and prevent relapse. A significant problem with this strategy is that many candidate medications possess abuse liability because of activation of mesolimbic dopamine (DA) neurons in the brain. One way to reduce DA-mediated abuse liability of candidate drugs is to add in serotonin (5-HT) releasing properties, since substantial evidence shows that 5-HT neurons provide an inhibitory influence over mesolimbic DA neurons. This article addresses several key issues related to the development of dual DA/5-HT releasers for the treatment of substance use disorders. First, the authors briefly summarize the evidence supporting a dual deficit in DA and 5-HT function during withdrawal from chronic cocaine or alcohol abuse. Second, the authors discuss data demonstrating that 5HT release can dampen DA-mediated stimulant effects, and the "antistimulant" role of 5-HT-sub(2C) receptors is considered. Next, the mechanisms underlying potential adverse effects of 5-HT releasers are described. Finally, the authors discuss recently published data with PAL-287, a novel nonamphetamine DA/5-HT releasing agent that suppresses cocaine self-administration but lacks positive reinforcing properties. It is concluded that DA/5-HT releasers could be useful therapeutic adjuncts for the treatment of cocaine and alcohol addictions, as well as for obesity, attention-deficit disorder, and depression.
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Affiliation(s)
- Richard B Rothman
- Clinical Psychopharmacology Section, IRP/NIDA/NIH, Clinical Psychopharmacology Section, Suite 4500, Triad Building, 333 Cassell Drive, Baltimore, MD 21224, USA.
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Rothman RB, Clark RD, Partilla JS, Baumann MH. (+)-Fenfluramine and its major metabolite, (+)-norfenfluramine, are potent substrates for norepinephrine transporters. J Pharmacol Exp Ther 2003; 305:1191-9. [PMID: 12649307 DOI: 10.1124/jpet.103.049684] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
(+/-)-Fenfluramine is an amphetamine analog that was once widely prescribed as an appetite suppressant. Although (+/-)-fenfluramine is no longer clinically available, the mechanisms underlying its anorectic properties are still of interest. Upon peripheral administration, stereoisomers of (+/-)-fenfluramine are N-deethylated to form the metabolites, (+)- and (-)-norfenfluramine. It is well accepted that isomers of (+/-)-fenfluramine and (+/-)-norfenfluramine interact with 5-hydroxytryptamine (serotonin, 5-HT) transporters to release 5-HT from neurons. However, the effects of these drugs on other monoamine transporters are not well characterized. In this study, we examined the interaction of stereoisomers of (+/-)-fenfluramine and (+/-)-norfenfluramine with transporters for 5-HT, norepinephrine (NE), and dopamine (DA). Results from in vitro assays confirmed these drugs are potent substrates for 5-HT transporters: (+)-fenfluramine, (-)-fenfluramine, (+)-norfenfluramine, and (-)-norfenfluramine released [3H]5-HT from synaptosomes with EC50 values of 52, 147, 59, and 287 nM, respectively. Importantly, (+)-fenfluramine and (+)-norfenfluramine released [3H]NE with EC50 values of 302 and 73 nM. Results from in vivo microdialysis experiments showed that intravenous injection of (+)-norfenfluramine elevates extracellular levels of 5-HT, NE, and DA in rat frontal cortex. The effects of (+)-norfenfluramine on NE and DA were antagonized by pretreatment with the NE uptake blocker nisoxetine. In summary, administration of fenfluramines can increase synaptic levels of 5-HT, NE, and DA in the cortex, and (+)-norfenfluramine likely contributes to these effects. Release of NE and DA evoked by (+)-norfenfluramine is at least partly mediated via NE transporters. Our results emphasize the potential involvement of noradrenergic mechanisms in the actions of fenfluramines.
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Affiliation(s)
- Richard B Rothman
- Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Dr., P.O. Box 5180, Baltimore, MD 21224, USA.
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Abstract
A variety of drugs release serotonin (5-HT, 5-hydroxytryptamine) from neurons by acting as substrates for 5-HT transporter (SERT) proteins. This review summarizes the neurochemical, therapeutic, and adverse actions of substrate-type 5-HT-releasing agents. The appetite suppressant (+/-)-fenfluramine is composed of (+) and (-) isomers, which are N-de-ethylated in the liver to yield the metabolites (+)- and (-)-norfenfluramine. Fenfluramines and norfenfluramines are potent 5-HT releasers. (+/-)-3,4-Methylenedioxymethamphetamine ((+/-)-MDMA, "ecstasy") and m-chlorophenylpiperazine (mCPP) are substrate-type 5-HT releasers. Fenfluramines, (+/-)-MDMA, and mCPP release neuronal 5-HT by a common non-exocytotic diffusion-exchange mechanism involving SERTs. (+)-Norfenfluramine is a potent 5-HT(2B) and 5-HT(2C) receptor agonist. The former activity may increase the risk of valvular heart disease, whereas the latter activity is implicated in the anorexic effect of systemic fenfluramine. Appetite suppressants that increase the risk for developing primary pulmonary hypertension (PPH) are all SERT substrates, but these drugs vary considerably in their propensity to increase this risk. For example, fenfluramine and aminorex are clearly linked to the occurrence of PPH, whereas other anorectics are not. Similarly, some SERT substrates deplete brain tissue 5-HT in animals (e.g., fenfluramine), while others do not (e.g., mCPP). In addition to the established indication of obesity, 5-HT releasers may help treat psychiatric disorders, such as drug and alcohol dependence, depression, and premenstrual syndrome. Viewed collectively, we believe new medications can be developed that selectively release 5-HT without increasing the risk for adverse effects of valvular heart disease, PPH, and neurotoxicity. Such agents may be useful for treating a variety of psychiatric disorders.
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Affiliation(s)
- Richard B Rothman
- Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, P. O. Box 5180, 5500 Nathan Shock Drive, Baltimore, MD 21224, USA.
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Baumann MH, Ayestas MA, Dersch CM, Partilla JS, Rothman RB. Serotonin transporters, serotonin release, and the mechanism of fenfluramine neurotoxicity. Ann N Y Acad Sci 2000; 914:172-86. [PMID: 11085319 DOI: 10.1111/j.1749-6632.2000.tb05194.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Administration of d,l-fenfluramine (FEN), or the more active isomer d-fenfluramine (dFEN), causes long-term depletion of forebrain serotonin (5-HT) in animals. The mechanism underlying FEN-induced 5-HT depletion is not known, but appears to involve 5-HT transporters (SERTs) in the brain. Some investigators have postulated that 5-HT release evoked by FEN is responsible for the deleterious effects of the drug. In the present work, we sought to examine the relationship between drug-induced 5-HT release and long-term 5-HT depletion. The acute 5-HT-releasing effects of dFEN and the non-amphetamine 5-HT agonist 1-(m-chlorophenyl)piperazine (mCPP) were evaluated using in vivo microdialysis in rat nucleus accumbens. The ability of dFEN and mCPP to interact with SERTs was assessed using in vitro assays for [3H]-transmitter uptake and release in rat forebrain synaptosomes. Drugs were subsequently tested for potential long-lasting effects on brain tissue 5-HT after repeated dosing (2.7 or 8.1 mg/kg, ip x 4). dFEN and mCPP were essentially equipotent in their ability to stimulate acute 5-HT release in vivo and in vitro. Both drugs produced very selective effects on 5-HT with minimal effects on dopamine. Interestingly, when dFEN or mCPP was administered repeatedly, only dFEN caused long-term 5-HT depletion in the forebrain at 2 weeks later. These data suggest that acute 5-HT release per se does not mediate the long-term 5-HT depletion associated with dFEN. We hypothesize that dFEN and other amphetamine-type releasers gain entrance into 5-HT neurons via interaction with SERTs. Once internalized in nerve terminals, drugs accumulate to high concentrations, causing damage to cells. The relevance of this hypothesis for explaining clinical side effects of FEN and dFEN, such as cardiac valvulopathy and primary pulmonary hypertension, warrants further study.
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Affiliation(s)
- M H Baumann
- Medications Development Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA.
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Rothman RB, Ayestas MA, Dersch CM, Baumann MH. Aminorex, fenfluramine, and chlorphentermine are serotonin transporter substrates. Implications for primary pulmonary hypertension. Circulation 1999; 100:869-75. [PMID: 10458725 DOI: 10.1161/01.cir.100.8.869] [Citation(s) in RCA: 166] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Coadministration of phentermine and fenfluramine (phen/fen) effectively treats obesity and possibly addictive disorders. The association of fenfluramine and certain other anorexic agents with serious side effects, such as cardiac valvulopathy and primary pulmonary hypertension (PPH), limits the clinical utility of these drugs. Development of new medications that produce neurochemical effects like phen/fen without causing unwanted side effects would be a significant therapeutic breakthrough. METHODS AND RESULTS We tested the hypothesis that fenfluramine (and other anorexic agents) might increase the risk of PPH through interactions with serotonin (5-HT) transporters. Because 5-HT transporter proteins in the lung and brain are identical, we examined, in rat brain, the effects of selected drugs on 5-HT efflux in vivo and monoamine transporters in vitro as a generalized index of transporter function. Our data show that drugs known or suspected to increase the risk of PPH (eg, aminorex, fenfluramine, and chlorphentermine) are 5-HT transporter substrates, whereas drugs that have not been shown to increase the risk of PPH are less potent in this regard. CONCLUSIONS We speculate that medications that are 5-HT transporter substrates get translocated into pulmonary cells where, depending on the degree of drug retention, their intrinsic drug toxicity, and individual susceptibility, PPH could develop as a response to high levels of these drugs or metabolites. Emerging evidence suggests that it is possible to develop transporter substrates devoid of adverse side effects. Such medications could have therapeutic application in the management of obesity, drug dependence, depression, and other disorders.
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Affiliation(s)
- R B Rothman
- Clinical Psychopharmacology Section, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, Md, USA.
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