ESG-1-60 and ESG-1-61: Novel dopamine D3 receptor-preferring partial agonists/antagonists that inhibit cocaine taking and seeking in rodents

Abstract

Background and purpose: Preclinical studies suggest that highly selective dopamine D₃ receptor (D₃R) antagonists or partial agonists hold promise for treating substance use disorders. However, their limited effectiveness in reducing cocaine self-administration is a major drawback. This study investigated whether cariprazine (D₃ receptor-preferring partial agonist) and its analogues ESG-1-60 and ESG-1-61 have enhanced efficacy in reducing cocaine-taking and cocaine-seeking behaviour.

Experimental approach: In vitro BRET experiments were used to characterize the functional efficacies of cariprazine and its analogues. Intravenous cocaine self-administration and reinstatement models were used to evaluate efficacy in reducing cocaine-taking and cocaine-seeking behaviour. Optical intracranial self-stimulation (oICSS) procedures assessed effects on dopamine-dependent behaviour. Open-field locomotion, oral sucrose self-administration and conditioned place-preference were used to evaluate potential unwanted side effects.

Key results: BRET functional assays indicated that cariprazine and ESG-1-60 are D₃ receptor-preferring partial agonists, while ESG-1-61 is a D₃ receptor-preferring antagonist/inverse agonist. All three compounds inhibited cocaine self-administration under both fixed-ratio and progressive-ratio reinforcement schedules and reduced cocaine-induced reinstatement of drug-seeking behaviour in both male and female rats. The compounds did not alter locomotor behaviour but suppressed sucrose intake and dopamine-dependent oICSS. Cariprazine and ESG-1-61 produced significant place aversion, while ESG-1-60 did not. Chronic administration of ESG-1-60 inhibited cocaine self-administration.

Conclusions and implications: Novel D₃ receptor-preferring compounds ESG-1-60 and ESG-1-61 were highly effective in reducing cocaine-taking and cocaine-seeking, under various reinforcement conditions. ESG-1-60 warrants further investigation as a new pharmacotherapy for treating cocaine use disorder as it is effective in these models and lacks unwanted behavioural effects.

Keywords: D3 receptor‐preferringpartial agonist; ESG‐1‐60; ESG‐1‐61; cariprazine; cocaine; dopamine.

FIGURE 1

Effects of cariprazine and analogues ESG-1–60 and ESG-1–61 on D₃R G_o activation (a) and β-arrestin2 recruitment (b) in bioluminescence resonance energy transfer (BRET) assays using transiently transfected HEK293T cells. Dose-dependent activities of cariprazine, ESG-1–60, ESG-1–61 and haloperidol (negative control) were normalized to the maximal response (E_max) elicited by the agonist quinpirole. Data shown in the curves are means ± SEM from n ≥ 6 for each experiment.

FIGURE 2

Chemical structures, receptor binding profiles and the effects of cariprazine and analogues ESG-1–60 and ESG-1–61 on cocaine self-administration in female rats. (a) Experimental timeline. Pretreatment with cariprazine (b), ESG-1–60 (c) and ESG-1–61 (d) dose-dependently reduced the total number of cocaine infusions and active lever presses but had no effect on inactive lever responses in female rats. (e–g) Comparisons of effects on cocaine self-administration between male and female rats. Pretreatment with cariprazine (e) and ESG-1–61 (g) resulted in similar inhibitory effects on cocaine self-administration, with no sex differences. In contrast, ESG-1–60 (f) produced more robust inhibitory effects in female rats on cocaine self-administration at a dose of 1 mg·kg⁻¹. The cocaine self-administration data for male rats were previously reported in Gogarnoiu et al. (2023) and are included here for comparison purposes. Data shown are individual values with means ± SEM. *P < 0.05, **P < 0.01, significantly different from vehicle control group; in (f), *P < 0.05, significantly different as indicated.

FIGURE 3

Effects of cariprazine and analogues ESG-1–60 and ESG-1–61 on cocaine self-administration under PR and multiple cocaine dose schedules of reinforcement. (a) Experimental timeline. Cariprazine, ESG-1–60 and ESG-1–61 reduced cocaine self-administration under PR schedule of reinforcement as assessed by the number of cocaine infusions (b) and active lever breakpoint (c). Cariprazine (d), ESG-1–60 (e) and ESG-1–61 (f) also dose-dependently inhibited cocaine self-administration under FR2 reinforcement maintained by a full dose range of cocaine. In (b, c), data shown are individual values with means ± SEM; in (d, e, f), data shown are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, significantly different from vehicle control group.

FIGURE 4

Effects of cariprazine, ESG-1–60 and ESG-1–61 on cocaine-induced reinstatement of cocaine-seeking behaviour in rats. (a) Experimental timeline. Cariprazine (b), ESG-1–60 (c) and ESG-1–61 (d) blocked cocaine-induced reinstatement of drug-seeking behaviour during the reinstatement test session. Data shown are individual values with means ± SEM. **P < 0.01, ***P < 0.001, significantly different from vehicle control group.

FIGURE 5

Effects of cariprazine, ESG-1–60 and ESG-1–61 on optical intracranial self-stimulation (oICSS) maintained by optogenetic stimulation of midbrain dopaminergic neurons in DAT-cre mice. (a) Scheme of optical ICSS procedures. (b) Representative image showing AAV-DIO-ChR2-EYFP expression in VTA dopaminergic neurons. (c) Representative oICSS records displaying stimulation frequency-dependent active lever responses. Pretreatment with cariprazine (d), ESG-1–60 (e) and ESG-1–61 (f) dose-dependently inhibited dopamine-dependent oICSS. Data shown are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, significantly different from baseline.

FIGURE 6

Effects of cariprazine, ESG-1–60 and ESG-1–61 on oral sucrose self-administration in mice. Cariprazine (a), ESG-1–60 (b) and ESG-1–61 (c) all dose-dependently inhibited sucrose self-administration as assessed by the total number of sucrose deliveries and active lever responses. Data shown are individual values with means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, significantly different from vehicle control group.

FIGURE 7

Effects of cariprazine and analogues ESG-1–60 and ESG-1–61 on open-field locomotion in mice and rats, and conditioned place preference in mice. Systemic administration of cariprazine (a, d), ESG-1–60 (b, e) and ESG-1–61 (c, f) failed to significantly alter locomotor activity as assessed by travelled distance in open-field locomotion chamber in mice (a–c, n = 7–8 per group) and rats (d-f, n = 8 per group). The CPP/CPA tests (g) indicated that cariprazine (h) (3 mg·kg⁻¹) and ESG-1–61 (h) (10 mg·kg⁻¹), but not ESG-1–60 (h) (3 mg/kg), induced significant conditioned place aversion (CPA). In (a-f), data shown are means ± SEM; in (h), data shown are individual values with means ± SEM. In (h), *P < 0.05, ***P < 0.001, significantly different from preconditioning.

FIGURE 8

Effects of chronic ESG-1–60 administration on cocaine self-administration under FR2 reinforcement conditions in rats. (a) ESG-1–60 reduces the total number of cocaine infusions during the duration of the treatment. (b) ESG-1–60 reduces the number of active lever presses during the duration of the treatment. Data shown are means ± SEM. *P < 0.05. **P < 0.01, ***P < 0.001, significantly different from baseline.