Linkers in Bitopic Agonists Shape Bias Profile among Transducers for the Dopamine D2 and D3 Receptors.

Bitopic ligands bind both orthosteric and allosteric or secondary binding sites within the same receptor, often resulting in an improvement of receptor selectivity, potency, and efficacy. In particular, for both agonists and antagonists of the dopamine D2 and D3 receptors (D2R and D3R), the primary therapeutic targets for several neurological and neuropsychiatric disorders, bitopic ligand design has proved advantageous in achieving better pharmacological profiles in vitro. Although the two pharmacophores within a bitopic ligand are typically considered the main drivers of conformational change for a receptor, the role of the linker that connects the two has not yet been systematically studied for its relevance in receptor activity profiles. Here, we present a comprehensive analysis of sumanirole and PF592,379-based indole-containing bitopic compounds in agonist activity at D2R and D3R, with a focus on linker chemical space and stereochemistry through testing six distinct chirally resolved linkers and a simple aliphatic linker. The structure activity relationships (SARs) of these linkers are examined extensively, beyond the conventional level, by characterizing the activation of all putative transducers over a 44 min time course. Our multiparametric analysis reveals previously unappreciated specific linker-dependent effects on primary pharmacophores, receptors, transducer activation kinetics, and bias, highlighting the utility of this comprehensive approach and the significance of the linker type in shaping transducer bias profiles.

Presynaptic and Postsynaptic Mesolimbic Dopamine D3 Receptors Play Distinct Roles in Cocaine Versus Opioid Reward in Mice.

BACKGROUND: Past research has illuminated pivotal roles of dopamine D3 receptors (D3R) in the rewarding effects of cocaine and opioids. However, the cellular and neural circuit mechanisms that underlie these actions remain unclear. METHODS: We employed Cre-LoxP techniques to selectively delete D3R from presynaptic dopamine neurons or postsynaptic dopamine D1 receptor (D1R)-expressing neurons in male and female mice. We utilized RNAscope in situ hybridization, immunohistochemistry, real-time polymerase chain reaction, voltammetry, optogenetics, microdialysis, and behavioral assays (n ≥ 8 animals per group) to functionally characterize the roles of presynaptic versus postsynaptic D3R in cocaine and opioid actions. RESULTS: Our results revealed D3R expression in ∼25% of midbrain dopamine neurons and ∼70% of D1R-expressing neurons in the nucleus accumbens. While dopamine D2 receptors (D2R) were expressed in ∼80% dopamine neurons, we found no D2R and D3R colocalization among these cells. Selective deletion of D3R from dopamine neurons increased exploratory behavior in novel environments and enhanced pulse-evoked nucleus accumbens dopamine release. Conversely, deletion of D3R from D1R-expressing neurons attenuated locomotor responses to D1-like and D2-like agonists. Strikingly, deletion of D3R from either cell type reduced oxycodone self-administration and oxycodone-enhanced brain-stimulation reward. In contrast, neither of these D3R deletions impacted cocaine self-administration, cocaine-enhanced brain-stimulation reward, or cocaine-induced hyperlocomotion. Furthermore, D3R knockout in dopamine neurons reduced oxycodone-induced hyperactivity and analgesia, while deletion from D1R-expressing neurons potentiated opioid-induced hyperactivity without affecting analgesia. CONCLUSIONS: We dissected presynaptic versus postsynaptic D3R function in the mesolimbic dopamine system. D2R and D3R are expressed in different populations of midbrain dopamine neurons, regulating dopamine release. Mesolimbic D3R are critically involved in the actions of opioids but not cocaine.

The Structural Basis of the Activity Cliff in Modafinil-Based Dopamine Transporter Inhibitors.

Modafinil analogs with either a sulfoxide or sulfide moiety have improved binding affinities at the human dopamine transporter (hDAT) compared to modafinil, with lead sulfoxide-substituted analogs showing characteristics of atypical inhibition (e.g., JJC8-091). Interestingly, the only distinction between sulfoxide and sulfide substitution is the presence of one additional oxygen atom. To elucidate why such a subtle difference in ligand structure can result in different typical or atypical profiles, we investigated two pairs of analogs. Our quantum mechanical calculations revealed a more negatively charged distribution of the electrostatic potential surface of the sulfoxide substitution. Using molecular dynamics simulations, we demonstrated that sulfoxide-substituted modafinil analogs have a propensity to attract more water into the binding pocket. They also exhibited a tendency to dissociate from Asp79 and form a new interaction with Asp421, consequently promoting an inward-facing conformation of hDAT. In contrast, sulfide-substituted analogs did not display these effects. These findings elucidate the structural basis of the activity cliff observed with modafinil analogs and also enhance our understanding of the functionally relevant conformational spectrum of hDAT.

Development of Novel Tools for Dissection of Central Versus Peripheral Dopamine D2-Like Receptor Signaling in Dysglycemia.

Dopamine (DA) D2-like receptors in both the central nervous system (CNS) and the periphery are key modulators of metabolism. Moreover, disruption of D2-like receptor signaling is implicated in dysglycemia. Yet, the respective metabolic contributions of CNS versus peripheral D2-like receptors, including D2 (D2R) and D3 (D3R) receptors, remain poorly understood. To address this, we developed new pharmacological tools, D2-like receptor agonists with diminished and delayed blood-brain barrier capability, to selectively manipulate D2R/D3R signaling in the periphery. We designated bromocriptine methiodide (BrMeI), a quaternary methiodide analog of D2R/D3R agonist and diabetes drug bromocriptine, as our lead compound based on preservation of D2R/D3R binding and functional efficacy. We then used BrMeI and unmodified bromocriptine to dissect relative contributions of CNS versus peripheral D2R/D3R signaling in treating dysglycemia. Systemic administration of bromocriptine, with unrestricted access to CNS and peripheral targets, significantly improved both insulin sensitivity and glucose tolerance in obese, dysglycemic mice in vivo. In contrast, metabolic improvements were attenuated when access to bromocriptine was restricted either to the CNS through intracerebroventricular administration or delayed access to the CNS via BrMeI. Our findings demonstrate that the coordinated actions of both CNS and peripheral D2-like receptors are required for correcting dysglycemia. Ultimately, the development of a first-generation of drugs designed to selectively target the periphery provides a blueprint for dissecting mechanisms of central versus peripheral DA signaling and paves the way for novel strategies to treat dysglycemia.

Involvement of dopamine D3 receptor in impulsive choice decision-making in male rats.

Impulsive decision-making has been linked to impulse control disorders and substance use disorders. However, the neural mechanisms underlying impulsive choice are not fully understood. While previous PET imaging and autoradiography studies have shown involvement of dopamine and D2/3 receptors in impulsive behavior, the roles of distinct D1, D2, and D3 receptors in impulsive decision-making remain unclear. In this study, we used a food reward delay-discounting task (DDT) to identify low- and high-impulsive rats, in which low-impulsive rats exhibited preference for large delayed reward over small immediate rewards, while high-impulsive rats showed the opposite preference. We then examined D1, D2, and D3 receptor gene expression using RNAscope in situ hybridization assays. We found that high-impulsive male rats exhibited lower levels of D2 and D3, and particularly D3, receptor expression in the nucleus accumbens (NAc), with no significant changes in the insular, prelimbic, and infralimbic cortices. Based on these findings, we further explored the role of the D3 receptor in impulsive decision-making. Systemic administration of a selective D3 receptor agonist (FOB02-04) significantly reduced impulsive choices in high-impulsive rats but had no effects in low-impulsive rats. Conversely, a selective D3 receptor antagonist (VK4-116) produced increased both impulsive and omission choices in both groups of rats. These findings suggest that impulsive decision-making is associated with a reduction in D3 receptor expression in the NAc. Selective D3 receptor agonists, but not antagonists, may hold therapeutic potentials for mitigating impulsivity in high-impulsive subjects.

The selective D3Receptor antagonist VK4-116 reverses loss of insight caused by self-administration of cocaine in rats.

Chronic psychostimulant use causes long-lasting changes to neural and cognitive function that persist after long periods of abstinence. As cocaine users transition from drug use to abstinence, a parallel transition from hyperactivity to hypoactivity has been found in orbitofrontal-striatal glucose metabolism and striatal D2/D3-receptor activity. Targeting these changes pharmacologically, using highly selective dopamine D3-receptor (D3R) antagonists and partial agonists, has shown promise in reducing drug-taking, and attenuating relapse in animal models of cocaine and opioid use disorder. However, much less attention has been paid to treating the loss of insight, operationalized as the inability to infer likely outcomes, associated with chronic psychostimulant use. Here we tested the selective D3R antagonist VK4-116 as a treatment for this loss in rats with a prior history of cocaine use. Male and female rats were first trained to self-administer cocaine or a sucrose liquid for 2 weeks. After 4 weeks of abstinence, performance was assessed using a sensory preconditioning (SPC) learning paradigm. Rats were given VK4-116 (15 mg/kg, i.p.) or vehicle 30 min prior to each SPC training session, thus creating four drug-treatment groups: sucrose-vehicle, sucrose-VK4-116, cocaine-vehicle, cocaine-VK4-116. The control groups (sucrose-vehicle, sucrose-VK4-116) showed normal sensory preconditioning, whereas cocaine use (cocaine-vehicle) selectively disrupted responding to the preconditioned cue, an effect that was reversed in the cocaine-VK4-116 group, which demonstrating responding to the preconditioned cue at levels comparable to controls. These preclinical findings demonstrate that highly selective dopamine D3R antagonists, particularly VK4-116, can reverse the long-term negative behavioral consequences of cocaine use.

Empowering Voices: Inspiring Women in Medicinal Chemistry.

As we celebrate International Women's Day 2024 with the theme "Inspire Inclusion", the women of the ACS Medicinal Chemistry Division (MEDI) want to foster a sense of belonging, relevance, and empowerment by sharing uplifting stories of what inspired them to become medicinal chemists. In this editorial, we are featuring female medicinal chemistry scientists to provide role models, encouragement, and inspiration to others. We asked women medicinal chemists to contribute a brief paragraph about what inspired them to become medicinal chemists or what inspires them today as medicinal chemists. The responses and contributions highlight their passions and motivations, such as their love of the sciences and their drive to improve human health by contributing to basic research and creating lifesaving drugs.

Dual DAT and sigma receptor inhibitors attenuate cocaine effects on nucleus accumbens dopamine dynamics in rats.

Psychostimulant use disorders (PSUD) are prevalent; however, no FDA-approved medications have been made available for treatment. Previous studies have shown that dual inhibitors of the dopamine transporter (DAT) and sigma receptors significantly reduce the behavioral/reinforcing effects of cocaine, which have been associated with stimulation of extracellular dopamine (DA) levels resulting from DAT inhibition. Here, we employ microdialysis and fast scan cyclic voltammetry (FSCV) procedures to investigate the effects of dual inhibitors of DAT and sigma receptors in combination with cocaine on nucleus accumbens shell (NAS) DA dynamics in naïve male Sprague Dawley rats. In microdialysis studies, administration of rimcazole (3, 10 mg/kg; i.p.) or its structural analog SH 3-24 (1, 3 mg/kg; i.p.), compounds that are dual inhibitors of DAT and sigma receptors, significantly reduced NAS DA efflux stimulated by increasing doses of cocaine (0.1, 0.3, 1.0 mg/kg; i.v.). Using the same experimental conditions, in FSCV tests, we show that rimcazole pretreatments attenuated cocaine-induced stimulation of evoked NAS DA release but produced no additional effect on DA clearance rate. Under the same conditions, JJC8-091, a modafinil analog and dual inhibitor of DAT and sigma receptors, similarly attenuated cocaine-induced stimulation of evoked NAS DA release but produced no additional effect on DA clearance rate. Our results provide the neurochemical groundwork towards understanding actions of dual inhibitors of DAT and sigma receptors on DA dynamics that likely mediate the behavioral effects of psychostimulants like cocaine.

Potential therapeutics for effort-related motivational dysfunction: assessing novel atypical dopamine transport inhibitors.

People with depression and other neuropsychiatric disorders can experience motivational dysfunctions such as fatigue and anergia, which involve reduced exertion of effort in goal-directed activity. To model effort-related motivational dysfunction, effort-based choice tasks can be used, in which rats can select between obtaining a preferred reinforcer by high exertion of effort vs. a low effort/less preferred option. Preclinical data indicate that dopamine transport (DAT) inhibitors can reverse pharmacologically-induced low-effort biases and increase selection of high-effort options in effort-based choice tasks. Although classical DAT blockers like cocaine can produce undesirable effects such as liability for misuse and psychotic reactions, not all DAT inhibitors have the same neurochemical profile. The current study characterized the effort-related effects of novel DAT inhibitors that are modafinil analogs and have a range of binding profiles and neurochemical actions (JJC8-088, JJC8-089, RDS3-094, and JJC8-091) by using two different effort-related choice behavior tasks in male Sprague-Dawley rats. JJC8-088, JJC8-089, and RDS3-094 significantly reversed the low-effort bias induced by the VMAT-2 inhibitor tetrabenazine, increasing selection of high-effort fixed ratio 5 lever pressing vs. chow intake. In addition, JJC8-089 reversed the effects of tetrabenazine in female rats. JJC8-088 and JJC8-089 also increased selection of high-effort progressive ratio responding in a choice task. However, JJC8-091 failed to produce these outcomes, potentially due to its unique pharmacological profile (i.e., binding to an occluded conformation of DAT). Assessment of a broad range of DAT inhibitors with different neurochemical characteristics may lead to the identification of compounds that are useful for treating motivational dysfunction in humans.

Development of novel tools for dissection of central versus peripheral dopamine D2-like receptor signaling in dysglycemia.

Dopamine (DA) D2-like receptors in both the central nervous system (CNS) and the periphery are key modulators of metabolism. Moreover, disruption of D2-like receptor signaling is implicated in dysglycemia. Yet, the respective metabolic contributions of CNS versus peripheral D2-like receptors including D2 (D2R) and D3 (D3R) receptors remain poorly understood. To address this, we developed new pharmacological tools, D2-like receptor agonists with diminished and delayed blood-brain barrier capability, to selectively manipulate D2R/D3R signaling in the periphery. We designated bromocriptine methiodide (BrMeI), a quaternary methiodide analogue of D2/3R agonist and diabetes drug bromocriptine, as our lead compound based on preservation of D2R/D3R binding and functional efficacy. We then used BrMeI and unmodified bromocriptine to dissect relative contributions of CNS versus peripheral D2R/D3R signaling in treating dysglycemia. Systemic administration of bromocriptine, with unrestricted access to CNS and peripheral targets, significantly improved both insulin sensitivity and glucose tolerance in obese, dysglycemic mice in vivo. In contrast, metabolic improvements were attenuated when access to bromocriptine was restricted either to the CNS through intracerebroventricular administration or delayed access to the CNS via BrMeI. Our findings demonstrate that the coordinated actions of both CNS and peripheral D2-like receptors are required for correcting dysglycemia. Ultimately, the development of a first-generation of drugs designed to selectively target the periphery provides a blueprint for dissecting mechanisms of central versus peripheral DA signaling and paves the way for novel strategies to treat dysglycemia.

Empowering Voices: Inspiring Women in Medicinal Chemistry.

As we celebrate International Women's Day 2024 with the theme "Inspire Inclusion", the women of the ACS Medicinal Chemistry Division (MEDI) want to foster a sense of belonging, relevance, and empowerment by sharing uplifting stories of what inspired them to become medicinal chemists. In this editorial, we are featuring female medicinal chemistry scientists to provide role models, encouragement, and inspiration to others. We asked women medicinal chemists to contribute a brief paragraph about what inspired them to become medicinal chemists or what inspires them today as medicinal chemists. The responses and contributions highlight their passions and motivations, such as their love of the sciences and their drive to improve human health by contributing to basic research and creating lifesaving drugs.

Development of a Fluorescently Labeled Ligand for Rapid Detection of DAT in Human and Mouse Peripheral Blood Monocytes.

The dopamine transporter (DAT) is one of the key regulators of dopamine (DA) signaling in the central nervous system (CNS) and in the periphery. Recent reports in a model of Parkinson's disease (PD) have shown that dopamine neuronal loss in the CNS impacts the expression of DAT in peripheral immune cells. The mechanism underlying this connection is still unclear but could be illuminated with sensitive and high-throughput detection of DAT-expressing immune cells in the circulation. Herein, we have developed fluorescently labeled ligands (FLL) that bind to surface-expressing DAT with high affinity and selectivity. The diSulfoCy5-FLL (GC04-38) was utilized to label DAT in human and mouse peripheral blood mononuclear cells (PBMCs) that were analyzed via flow cytometry. Selective labeling was validated using DAT KO mouse PBMCs. Our studies provide an efficient and highly sensitive method using this novel DAT-selective FLL to advance our fundamental understanding of DAT expression and activity in PBMCs in health and disease and as a potential peripheral biomarker.

Series of (([1,1'-Biphenyl]-2-yl)methyl)sulfinylalkyl Alicyclic Amines as Novel and High Affinity Atypical Dopamine Transporter Inhibitors with Reduced hERG Activity.

Currently, there are no FDA-approved medications for the treatment of psychostimulant use disorders (PSUD). We have previously discovered "atypical" dopamine transporter (DAT) inhibitors that do not display psychostimulant-like behaviors and may be useful as medications to treat PSUD. Lead candidates (e.g., JJC8-091, 1) have shown promising in vivo profiles in rodents; however, reducing hERG (human ether-à-go-go-related gene) activity, a predictor of cardiotoxicity, has remained a challenge. Herein, a series of 30 (([1,1'-biphenyl]-2-yl)methyl)sulfinylalkyl alicyclic amines was synthesized and evaluated for DAT and serotonin transporter (SERT) binding affinities. A subset of analogues was tested for hERG activity, and the IC50 values were compared to those predicted by our hERG QSAR models, which showed robust predictive power. Multiparameter optimization scores (MPO > 3) indicated central nervous system (CNS) penetrability. Finally, comparison of affinities in human DAT and its Y156F and Y335A mutants suggested that several compounds prefer an inward facing conformation indicating an atypical DAT inhibitor profile.

Population genomic structure of a widespread, urban-dwelling mammal: The eastern grey squirrel (Sciurus carolinensis).

Urbanization is a persistent and widespread driver of global environmental change, potentially shaping evolutionary processes due to genetic drift and reduced gene flow in cities induced by habitat fragmentation and small population sizes. We tested this prediction for the eastern grey squirrel (Sciurus carolinensis), a common and conspicuous forest-dwelling rodent, by obtaining 44K SNPs using reduced representation sequencing (ddRAD) for 403 individuals sampled across the species' native range in eastern North America. We observed moderate levels of genetic diversity, low levels of inbreeding, and only a modest signal of isolation-by-distance. Clustering and migration analyses show that estimated levels of migration and genetic connectivity were higher than expected across cities and forested areas, specifically within the eastern portion of the species' range dominated by urbanization, and genetic connectivity was less than expected within the western range where the landscape is fragmented by agriculture. Landscape genetic methods revealed greater gene flow among individual squirrels in forested regions, which likely provide abundant food and shelter for squirrels. Although gene flow appears to be higher in areas with more tree cover, only slight discontinuities in gene flow suggest eastern grey squirrels have maintained connected populations across urban areas in all but the most heavily fragmented agricultural landscapes. Our results suggest urbanization shapes biological evolution in wildlife species depending strongly on the composition and habitability of the landscape matrix surrounding urban areas.

Modifications to 1-(4-(2-Bis(4-fluorophenyl)methyl)sulfinyl)alkyl Alicyclic Amines That Improve Metabolic Stability and Retain an Atypical DAT Inhibitor Profile.

Atypical dopamine transporter (DAT) inhibitors have shown therapeutic potential in the preclinical models of psychostimulant use disorders (PSUD). In rats, 1-(4-(2-((bis(4-fluorophenyl)methyl)sulfinyl)ethyl)-piperazin-1-yl)-propan-2-ol (JJC8-091, 3b) was effective in reducing the reinforcing effects of both cocaine and methamphetamine but did not exhibit psychostimulant behaviors itself. Improvements in DAT affinity and metabolic stability were desirable for discovering pipeline drug candidates. Thus, a series of 1-(4-(2-bis(4-fluorophenyl)methyl)sulfinyl)alkyl alicyclic amines were synthesized and evaluated for binding affinities at DAT and the serotonin transporter (SERT). Replacement of the piperazine with either a homopiperazine or a piperidine ring system was well tolerated at DAT (Ki range = 3-382 nM). However, only the piperidine analogues (20a-d) showed improved metabolic stability in rat liver microsomes as compared to the previously reported analogues. Compounds 12b and 20a appeared to retain an atypical DAT inhibitor profile, based on negligible locomotor activity in mice and molecular modeling that predicts binding to an inward-facing conformation of DAT.

Ensuring Intervention Fidelity of an Attention Control Arm in a Multisite Randomized Controlled Trial.

BACKGROUND: Intervention fidelity is a critical element of randomized controlled trials, yet reporting of intervention fidelity among attention control arms is limited. Lack of fidelity to attention control procedures can affect study outcomes by either overestimating or underestimating the efficacy of the intervention under examination. OBJECTIVES: This brief report describes the approach researchers took to promote fidelity to the attention control arm of a pediatric palliative care randomized controlled trial funded by the National Institutes of Health. METHODS: The Informational Meetings for Planning and Coordinating Treatment trial aims to determine the efficacy of a communication intervention that uses care team dyads (i.e., physicians partnered with nurses or advanced practice providers) to engage parents of children with cancer who have a poor prognosis in structured conversations about prognostic information, goals of care, and care planning. The intervention is compared with an attention control arm, which provides parents with structured conversations on common pediatric cancer education topics, such as talking to their child about their cancer, clinical trials, cancer treatment, side effects, and so forth. National Institutes of Health guidelines for assessing and implementing strategies to promote intervention fidelity were used to design (a) the attention control arm of a randomized controlled trial, (b) related attention control arm training, and (c) quality assurance monitoring. RESULTS: Attention control study procedures were designed to mirror that of the intervention arm (i.e., same number, frequency, and time spent in study visits). Cluster randomization was used to allocate care team dyads to one arm of the randomized controlled trial. Care team dyads assigned to the attention control arm participated in online training sessions to learn attention control procedures, the different roles of research team members, and quality assurance methods. Fidelity to attention control procedures is assessed by both the interveners themselves and a quality assurance team. DISCUSSION: Study design, training, and delivery are all critical to attention control fidelity. Baseline training often needs to be supplemented with booster training when time gaps occur between study start-up and implementation. Quality assurance procedures are essential to determine whether interveners consistently deliver attention control procedures correctly.

Seasonal dynamics in the mammalian microbiome between disparate environments.

Host-associated bacterial microbiomes can facilitate host acclimation to seasonal environmental change and are hypothesized to help hosts cope with recent anthropogenic environmental perturbations (e.g., landscape modification). However, it is unclear how recurrent and recent forms of environmental change interact to shape variation in the microbiome. The majority of wildlife microbiome research occurs within a single seasonal context. Meanwhile, the few studies of seasonal variation in the microbiome often restrict focus to a single environmental context. By sampling urban and exurban eastern grey squirrel populations in the spring, summer, autumn, and winter, we explored whether seasonal rhythms in the grey squirrel gut microbiome differed across environments using a 16S amplicon sequencing approach. Differences in the microbiome between urban and exurban squirrels persisted across most of the year, which we hypothesize is linked to anthropogenic food consumption, but we also observed similarities in the urban and exurban grey squirrel microbiome during the autumn, which we attribute to engrained seed caching instincts in preparation for the winter. Host behaviour and diet selection may therefore be capable of maintaining similarities in microbiome structure between disparate environments. However, the depletion of an obligate host mucin glycan specialist (Akkermansia) during the winter in both urban and exurban squirrels was among the strongest differential abundance patterns we observed. In summary, urban grey squirrels showed different seasonal patterns in their microbiome than squirrels from exurban forests; however, in some instances, host behaviour and physiological responses might be capable of maintaining similar microbiome responses across seasons.

Palliative Care Interventions Among Adolescents and Young Adults with Serious Illness: A Scoping Review.

Objective: To map the range of multidisciplinary palliative care interventions that are available to adolescents and young adults (AYAs) with serious illness. Methods: Scoping review methodology as outlined by Arksey and O'Malley. Results: Twenty-two articles describing nine specific AYA-focused, multidisciplinary palliative care interventions were included in this review. Interventions focused on supporting advance care planning (ACP), facilitating treatment decision making, managing pain, and promoting resilience, psychosocial well-being, and quality of life. Interventions were delivered face-to-face and via different eHealth platforms and were targeted to AYAs with cancer, HIV/AIDS, and cystic fibrosis in both inpatient and outpatient settings. Conclusions: Few evidence-based multidisciplinary palliative care interventions have documented benefit for AYAs with serious illness. The limited work that has been done demonstrates that AYAs are open to engaging in palliative care interventions and suggests that individual members of the multidisciplinary team can implement these different interventions to support enhanced patient outcomes.

The selective D3-Receptor antagonist VK4-116 effectively treats behavioral inflexibility in rats caused by self-administration and withdrawal from cocaine.

Chronic psychostimulant use can cause long lasting changes to neural and cognitive function that persist even after long periods of abstinence. As cocaine users transition from drug use to abstinence, a parallel transition from hyperactivity to hypoactivity has been found in orbitofrontal-striatal glucose metabolism, and striatal D2/D3 receptor activity. Targeting these changes pharmacologically, using highly selective dopamine D3 receptor (D3R) antagonists and partial agonists, has shown significant promise in reducing drug-taking, and attenuating relapse in animal models of cocaine and opioid use disorder. However, much less attention has been focused on treating inflexible and potentially maladaptive non-drug behaviors following chronic psychostimulant use. Here we tested the selective D3R antagonist VK4-116 as a treatment for the long-term behavioral inflexibility in abstinent male and female rats with a prior history of chronic cocaine use. Rats were first trained to self-administer cocaine (0.75 mg/kg/reinforcer) or a sucrose liquid (10%, .04 mL/reinforcer) for 2 weeks (FR1 schedule, max 60 reinforcers in 3 hrs/ day), followed by 4 weeks of abstinence. Cognitive and behavioral flexibilities were then assessed using a sensory preconditioning (SPC) learning paradigm. Rats were given an VK4-116 (15 mg/kg, i.p.) or vehicle 30 mins prior to each SPC training session, thus creating four drug-treatment groups: sucrose-vehicle, sucrose-VK4-116, cocaine-vehicle, cocaine-VK4-116. The control groups (sucrose-vehicle, sucrose-VK4-116) demonstrated significant evidence of flexible SPC behavior, whereas cocaine use (cocaine-vehicle) disrupted SPC behavior. Remarkably, the D3R antagonist VK4-116 mitigated this cocaine deficit in the cocaine-VK4-116 group, demonstrating flexible SPC to levels comparable to the control groups. These preclinical findings demonstrate that highly selective dopamine D3R antagonists, particularly VK4-116, show significant promise as a pharmacological treatment for the long-term negative behavioral consequences of cocaine use disorder.