The Medication Development And Mechanistic Research On Dopamine D3 Receptors Antagonist In Drug Addiction

Drug addiction is characterized by drug-induced reward and relapse to drug use after abstinence. The mesolimbic dopamine (DA) system, which originates in the midbrain ventral tegmental area (VTA) and projects to the forebrain nucleus accumbens (NAc) and prefrontal cortex (PFC), has been shown to be critically involved in both drug reward and relapse. Thus, brain DA receptors have become important targets in medication development for the treatment of addiction. Five DA receptors (D1-D5) have been identified in the brain. DA D3 receptors are located primarily in the mesolimbic DA system, including the VTA, NAc, islands of Calleja, and olfactory tubercle. Growing evidence suggests that D3 receptors are critically involved in drug reward and in motivational and cognitive processes implicated in addiction and relapse to drug-seeking behavior. Based on this, it has been proposed that selective DA D3 receptor antagonists may be effective for the treatment of drug addiction. Several D3 receptor antagonists, such as BP-897, SB-277011A, NGB-2904, have been well studied in experimental animals for their potential utility for the treatment of addiction. However, the relatively poor pharmacokinetic properties (such as poor oral bioavailability, short half-life) and/or toxicity of these compounds have prevented further studies at both preclinical and clinical trials. Based on these developments, our purpose is to synthesize new structural compounds with higher selectivity, more stable pharmacokinetic properties and lower toxicity.Our findinga are as follows:1. Based on the 4-phenylpiperazine scaffold, we have developed new scaffolds sharing the following common features: two aromatic or heteroaromatic rings, one hydrogen donor, one hydrogen acceptor and one protonated center (basic group), formulated as A-L-B. Group A consisted of new structural units, including 2(3H)-benzox(thi)azolinone scaffolds, 4-hydroxy-quinoline, quinoline, and ferrocene. Group B was composed of 4-phenylpiperazines analogs. The new compounds included four series: respectively incorporating 2(3H)-benzox(thi)azolinone, 4-hydroxyquinoline, quinoline and ferrocene.2. We established 30 cell lines expressed G protein-coupled receptors, including dopamine receptors (D1-D5), adenosine receptors (A1 A2A), acetylcholine receptors (M1-M5), 5-HT receptors (5-HT1-5-HT6), histamine receptors (H1-H3), adrenaline receptors (?1???1), opiate receptors (???????) and cannabinoid receptors (CB1-CB2), for screening high selectivity D₃R ligands.?3. Using vitro receptor binding assays, we obtained a series of 2(3H)-benzox(thi)azolinones compounds with better D₃R affinity, including Y-QA14, Y-QA16, Y-QA20 and Y-QA29, for which the affinity of D₃R was Ki-High0.68×10-4 nM/Ki-Low2.11 nM, 26.5 nM, 14.8 nM and 6.89 nM respectively, and affinity for D₂R was 335.3 nM, 95.6 nM, 1990 nM and157.08 nM respectively. Thus the D₃R / D₂R selectivity was 4×106/158 fold, 3.6 fold, 134 fold and 23 fold respectively. Among them, Y-QA14 has higher affinity and the selectivity for D₃R over other DA receptors, and more than 1000-fold selectivity over 29 other G protein-coupled receptors.According to a potential model of receptor binding and molecular docking, the 2(3H)-benzox(thi)azolinones showed improved affinity and solubility; in addition the lactam served as an active functional structure ddetermining selectivity, yielding a consistent structure activity relationship.4. In vivo pharmacokinetic assays suggest that Y-QA14 has improved oral bioavailability (>40%) and longer half-life (>6 h) when compared to SB-277011A, the most well-characterized D3 receptor antagonist.5. To compare Y-QA14 with the well-characterised SB-277011A, further evaluated potentrial pharmacotherapeutic effects of Y-QA14 in multiple animal models of addiction. We found that Y-QA14 pretreatment significantly and dose-dependently inhibited the acute rewarding and psychomotor-stimulating effects of cocaine as assessed by intracranial electrical brain-stimulation reward, intravenous cocaine self-administration, conditioned place preference and cocaine-induced increases in locomotion. To determine whether such an effect is truly mediated by blockade of brain D3 receptors, we, for the first time, used D3 receptor gene-knockout mice and found that Y-QA14 significantly inhibits cocaine self-administration only in wild-type mice, but not in D3 receptor-knockout mice. Strikingly, Y-QA14 itself did not show any abuse liability because Y-QA14, unlike cocaine, was neither self-administered in drug na?ve rats, nor substituted for cocaine to maintain self-administration in rats previously trained for cocaine self-administration. In addition, Y-QA14 also dose-dependently inhibits incentive motivation (i.e., craving) for drug-taking and drug-seeking behavior observed during extinction sessions in which cocaine was replaced by saline. Pretreatment with Y-QA14 also significantly inhibits cocaine-induced locomotor sensitization, and inhibits cocaine priming- or cocaine-associated cue-induced reinstatement (relapse) to drug-seeking behavior. Importantly, Y-QA14, at doses that inhibit cocaine's actions as described above, inhibits neither locomotion nor oral sucrose-taking behavior, suggesting that Y-QA14 may not produce sedation or natural reward suppression when used for treatment of drug addiction. Such unwanted side effects have been repeated for other putative anti-cocaine medcations.Taken together, we have successfully developed and synthesized a series of 2-benzoxazolone compounds and screened their receptor binding affinities and selectivities. We found that Y-QA14, as leading compound in this category, is a novel highly potent and selective D3 receptor antagonist. In vivo pharmacokinetic studies suggest that Y-QA14 has significantly higher bioavailability and longer half-life than SB-277011A. In vivo behavioral studies with multiple animal models of addiction suggest that Y-QA14 is highly effective in attenuating cocaine's rewarding and psychomotor-stimulating effects and in attenuating motivation (or craving) for cocaine and relapse to drug-seeking behavior without significant unwanted side-effects. These findings suggest that Y-QA14 and other analogs in this drug category deserve further research as novel medications for the treatment of cocaine and/or other drug addiction.