Psychedelic-like Properties of Quipazine and Its Structural Analogues in Mice

Abstract

Known classic psychedelic serotonin 2A receptor (5-HT_2AR) agonists retain a tryptamine or phenethylamine at their structural core. However, activation of the 5-HT_2AR can be elicited by drugs lacking these fundamental scaffolds. Such is the case of the N-substituted piperazine quipazine. Here, we show that quipazine bound to and activated 5-HT_2AR as measured by [³H]ketanserin binding displacement, Ca²⁺ mobilization, and accumulation of the canonical G_q/11 signaling pathway mediator inositol monophosphate (IP₁) in vitro and in vivo. Additionally, quipazine induced via 5-HT_2AR an expression pattern of immediate early genes (IEG) in the mouse somatosensory cortex consistent with that of classic psychedelics. In the mouse head-twitch response (HTR) model of psychedelic-like action, quipazine produced a lasting effect with high maximal responses during the peak effect that were successfully blocked by the 5-HT_2AR antagonist M100907 and absent in 5-HT_2AR knockout (KO) mice. The acute effect of quipazine on HTR appeared to be unaffected by serotonin depletion and was independent from 5-HT₃R activation. Interestingly, some of these features were shared by its deaza bioisostere 2-NP, but not by other closely related piperazine congeners, suggesting that quipazine might represent a distinct cluster within the family of psychoactive piperazines. Together, our results add to the mounting evidence that quipazine's profile matches that of classic psychedelic 5-HT_2AR agonists at cellular signaling and behavioral pharmacology levels.

Keywords: Psychedelics; animal models; pharmacology; piperazines; quipazine; serotonin receptors.

Figure 1.

Structures of quipazine, the position isomer isoquipazine, and the corresponding deaza isosteres 2-NP and 1-NP. The piperazine positions N_1′ and N_4′ are indicated in the structure of quipazine.

Figure 2.

(A) Time-course showing HTR counts in 15 min blocks corresponding to different doses of quipazine (n = 5–6). Black arrow shows the administration time point (t = 0). (B) HTR counts corresponding to the first 30 min after injection of quipazine. Two-way (A) and one-way (B) ANOVA Bonferroni’s post hoc test vs vehicle. *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 3.

Quipazine induced HTR time course (A–C, left panel) and sum of totals during the first 30 min (A–C, right panels) after different pretreatments. Quipazine was administered at t = 0 min (as indicated by the black arrow). (A) Effect of pretreatment with M100907 (0.1 mg/kg) or vehicle 5 min prior to the administration of quipazine (5 mg/kg) or vehicle (n = 3–10). (B) Effect of treatment with PCPA (100 mg/kg) or vehicle daily during the 4 previous days on quipazine (5 mg/kg) induced HTR on day 5 (n = 6). (C) Effect of pretreatment with ondansetron (1 mg/kg) or vehicle 5 min prior to the administration of quipazine (5 mg/kg, n = 6). (D) Feces count during the first 30 min after quipazine (5 mg/kg), ondansetron (1 mg/kg), or vehicle administration (n = 9). Two-way (A, left and D) and one-way ANOVA (A, right) Bonferroni’s post hoc. Studentťs t-test (B and C, right). ns = not significant, *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 4.

(A) In vivo IP1 accumulation by quipazine (5 mg/kg) and in the presence of the antagonist M100907 (0.1 mg/kg). Upper panel represents the timeline of the experiment: administration of LiCl (200 mg/kg, all animals), administration of the corresponding treatments or vehicle (Tx, n = 3 per group), and harvesting of tissue. (B) IEGs and housekeeping gene expression in the somatosensory cortices of 129S6/SvEv (A) wild-type (n = 12) and (B) 5-HT_2AR-KO (n = 5) mice 60 min after the administration of quipazine (5 mg/kg) or vehicle. One-way ANOVA Bonferroni’s post hoc vs vehicle (A). Multiple t-test with Bonferroni’s correction test for multiple comparisons (B). *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 5.

(A) [³H]Ketanserin binding displacement in membrane preparations from human post-mortem brain (n = 3) and mouse frontal cortices (n = 4). (B) Quipazine (hot pink carbon atoms) bound in the in the orthosteric binding site of the active (PDB: 6WHA) conformation of the 5-HT_2AR (green carbon atoms). Ligand and residues (shown within 5 Å from ligand) are rendered as capped sticks. Salt bridge and H-bond interactions (i.e., D155^3.32–N_4′, S159^3.36–N) are indicated by yellow dashed lines. (C) Schematic representation of the residues in the binding site relative to quipazine. F-test (A).

Figure 6.

(A) HTR-induced by different structural analogues of quipazine shown in Figure 1 (5 mg/kg all) during the first 30 min postinjection (n = 6–12) in wild-type and (B) 5-HT_2A-KO mice (n = 5–12). One-way ANOVA Bonferroni’s post hoc vs vehicle (A, B). *P < 0.05, ***P < 0.001.

Figure 7.

(A) HTR dose–response for 2-NP and 1-NP (n = 6). (B) Time-course of the effect of 2-NP and 1-NP on HTR (n = 6). (C) Effect of pretreatment with 5-HT_1AR antagonist WAY100635 (n = 3–6) on HTR induced by 2-NP or suppressed by 1-NP. (D) Effect of pretreatment with 5-HT_2CR antagonist SB242084 on HTR induced by 2-NP or suppressed by 1-NP (n = 6–12). One-way (A and C) and two-way ANOVA (B and D), Bonferroni’s post hoc vs vehicle (A and B), or vehicle pretreatment (C and D). *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 8.

(A) [³H]ketanserin binding displacement (n = 4–6; 2–3 independent experiments performed in duplicate) on membrane preparation from HEK293 cells stably expressing 5-HT_2AR. (B) In vitro IP₁ accumulation screening in HEK293 cells stably expressing 5-HT_2AR by different drugs (n = 2). Ca²⁺-mobilization on HEK293 cells with Fluo-4: (C) concentration-dependent Ca²⁺ mobilization for serotonin, quipazine P (n = 6–12; 3–4 independent experiments performed in duplicate or quadruplicate). (D) Antagonist concentration-dependent response of isoquipazine and 1-NP on serotonin (1 μM)-induced Ca²⁺ mobilization (n = 6–12; 3–4 independent experiments performed in duplicate or quadruplicate). (E) 5-HT_2AR antagonist M100907 blocking effect on Ca²⁺ release induced by 5-HT, quipazine, and 2-NP (n = 8–12; 2–3 independent experiments performed in duplicate or quadruplicate). (B) One-way ANOVA Bonferroni’s post hoc vs M100907 (B), M100907, ***P < 0.001. (E) Two-way ANOVA Bonferroni’s post hoc vs vehicle. *P < 0.05, ***P < 0.001.

Figure 9.

Effect of pretreatment with isoquipazine and 1-NP on quipazine induced HTR (n = 3). One-way ANOVA Bonferroni’s post hoc vs vehicle pretreatment. ***P < 0.001.