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

Unlocking the Potential of High-Quality Dopamine Transporter Pharmacological Data: Advancing Robust Machine Learning-Based QSAR Modeling

The dopamine transporter (DAT) plays a critical role in the central nervous system and has been implicated in numerous psychiatric disorders. The ligand-based approaches are instrumental to decipher the structure-activity relationship (SAR) of DAT ligands, especially the quantitative SAR (QSAR) modeling. By gathering and analyzing data from literature and databases, we systematically assemble a diverse range of ligands binding to DAT, aiming to discern the general features of DAT ligands and uncover the chemical space for potential novel DAT ligand scaffolds. The aggregation of DAT pharmacological activity data, particularly from databases like ChEMBL, provides a foundation for constructing robust QSAR models. The compilation and meticulous filtering of these data, establishing high-quality training datasets with specific divisions of pharmacological assays and data types, along with the application of QSAR modeling, prove to be a promising strategy for navigating the pertinent chemical space. Through a systematic comparison of DAT QSAR models using training datasets from various ChEMBL releases, we underscore the positive impact of enhanced data set quality and increased data set size on the predictive power of DAT QSAR models.

Evaluation of Urea-Based Inhibitors of the Dopamine Transporter Using the Experimental Autoimmune Encephalomyelitis Model of Multiple Sclerosis

The dopaminergic system is involved in the regulation of immune responses in various homeostatic and disease conditions. For conditions such as Parkinson's disease and multiple sclerosis (MS), pharmacological modulation of dopamine (DA) system activity is thought to have therapeutic relevance, providing the basis for using dopaminergic agents as a treatment of relevant states. In particular, it was proposed that restoration of DA levels may inhibit neuroinflammation. We have recently reported a new class of dopamine transporter (DAT) inhibitors with high selectivity to the DAT over other G-protein coupled receptors tested. Here, we continue their evaluation as monoamine transporter inhibitors. Furthermore, we show that the urea-like DAT inhibitor (compound 5) has statistically significant anti-inflammatory effects and attenuates motor deficits and pain behaviors in the experimental autoimmune encephalomyelitis model mimicking clinical signs of MS. To the best of our knowledge, this is the first study reporting the beneficial effects of DAT inhibitor-based treatment in animals with induced autoimmune encephalomyelitis, and the observed results provide additional support to the model of DA-related neuroinflammation.

Evaluation of the Reinforcing Strength of Phendimetrazine Using a Progressive-Ratio Schedule of Reinforcement in Rhesus Monkeys

Stimulant abuse is a persistent public health problem with no Food and Drug Administration-approved pharmacotherapy. Although monoamine-releasing drugs such as d-amphetamine can decrease cocaine self-administration in human and animal laboratory studies, their potential for abuse limits clinical utility. "Abuse-deterrent" formulations of monoamine releasers, such as prodrugs, hold greater clinical promise if their abuse potential is, as theorized, lower than that of cocaine. In these studies, we determined the reinforcing strength of phendimetrazine (PDM), a prodrug for the amphetamine-like monoamine releaser phenmetrazine; both drugs have been shown to decrease cocaine self-administration in laboratory animals. To date, no study has directly compared PDM (Schedule III) with cocaine (Schedule II) under progressive-ratio (PR) schedules of reinforcement, which are better suited than fixed-ratio schedules to directly compare reinforcing strength of drugs. Dose-response curves for cocaine (saline, 0.001-0.3 mg/kg per injection) and PDM (0.1-1.0 mg/kg per injection) were generated in six cocaine-experienced male rhesus monkeys during 4-hour sessions with a 20-minute limited hold (LH). Under these conditions, the maximum number of injections was not significantly different between cocaine and PDM. The reinforcing strength of doses situated on the peaks of the cocaine and PDM dose-effect curves were redetermined with a 60-minute LH. The mean number of injections increased for both drugs, but not for saline. Cocaine presentations resulted in significantly higher peak injections than PDM with a 60-minute LH, which is consistent with the lower scheduling of PDM. These results support PDM as Schedule III and highlight the importance of schedule parameters when comparing reinforcing strength of drugs using a PR schedule of reinforcement. SIGNIFICANCE STATEMENT: One strategy for reducing cocaine use is to identify a treatment that substitutes for cocaine but has lower abuse potential. In a rhesus monkey model of drug abuse, this study compared the reinforcing strength of cocaine and phendimetrazine, a drug that has been shown to decrease cocaine use in some studies.

Morpholine as a privileged structure: A review on the medicinal chemistry and pharmacological activity of morpholine containing bioactive molecules

Morpholine is a heterocycle featured in numerous approved and experimental drugs as well as bioactive molecules. It is often employed in the field of medicinal chemistry for its advantageous physicochemical, biological, and metabolic properties, as well as its facile synthetic routes. The morpholine ring is a versatile and readily accessible synthetic building block, it is easily introduced as an amine reagent or can be built according to a variety of available synthetic methodologies. This versatile scaffold, appropriately substituted, possesses a wide range of biological activities. There are many examples of molecular targets of morpholine bioactive in which the significant contribution of the morpholine moiety has been demonstrated; it is an integral component of the pharmacophore for certain enzyme active-site inhibitors whereas it bestows selective affinity for a wide range of receptors. A large body of in vivo studies has demonstrated morpholine's potential to not only increase potency but also provide compounds with desirable drug-like properties and improved pharamacokinetics. In this review we describe the medicinal chemistry/pharmacological activity of morpholine derivatives on various therapeutically related molecular targets, attempting to highlight the importance of the morpholine ring in drug design and development as well as to justify its classification as a privileged structure.

Molecular Mechanisms of Amphetamines

There is a plethora of amphetamine derivatives exerting stimulant, euphoric, anti-fatigue, and hallucinogenic effects; all structural properties allowing these effects are contained within the amphetamine structure. In the first part of this review, the interaction of amphetamine with the dopamine transporter (DAT), crucially involved in its behavioral effects, is covered, as well as the role of dopamine synthesis, the vesicular monoamine transporter VMAT2, and organic cation 3 transporter (OCT3). The second part deals with requirements in amphetamine's effect on the kinases PKC, CaMKII, and ERK, whereas the third part focuses on where we are in developing anti-amphetamine therapeutics. Thus, treatments are discussed that target DAT, VMAT2, PKC, CaMKII, and OCT3. As is generally true for the development of therapeutics for substance use disorder, there are multiple preclinically promising specific compounds against (meth)amphetamine, for which further development and clinical trials are badly needed.

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.'