The HIV antiretroviral drug efavirenz has LSD-like properties

Abstract

Anecdotal reports have surfaced concerning misuse of the HIV antiretroviral medication efavirenz ((4S)-6-chloro-4-(2-cyclopropylethynyl)-4-(trifluoromethyl)-2,4-dihydro-1H-3,1-benzoxazin-2-one) by HIV patients and non-infected teens who crush the pills and smoke the powder for its psychoactive effects. Molecular profiling of the receptor pharmacology of efavirenz pinpointed interactions with multiple established sites of action for other known drugs of abuse including catecholamine and indolamine transporters, and GABAA and 5-HT(2A) receptors. In rodents, interaction with the 5-HT(2A) receptor, a primary site of action of lysergic acid diethylamine (LSD), appears to dominate efavirenz's behavioral profile. Both LSD and efavirenz reduce ambulation in a novel open-field environment. Efavirenz occasions drug-lever responding in rats discriminating LSD from saline, and this effect is abolished by selective blockade of the 5-HT(2A) receptor. Similar to LSD, efavirenz induces head-twitch responses in wild-type, but not in 5-HT(2A)-knockout, mice. Despite having GABAA-potentiating effects (like benzodiazepines and barbiturates), and interactions with dopamine transporter, serotonin transporter, and vesicular monoamine transporter 2 (like cocaine and methamphetamine), efavirenz fails to maintain responding in rats that self-administer cocaine, and it fails to produce a conditioned place preference. Although its molecular pharmacology is multifarious, efavirenz's prevailing behavioral effect in rodents is consistent with LSD-like activity mediated via the 5-HT(2A) receptor. This finding correlates, in part, with the subjective experiences in humans who abuse efavirenz and with specific dose-dependent adverse neuropsychiatric events, such as hallucinations and night terrors, reported by HIV patients taking it as a medication.

Figure 1

Profiling of the receptor psychopharmacology of efavirenz demonstrates its interaction with cloned serotonin 5-HT_2A receptors, catecholamine and indoleamine neurotransmitter transporters (dopamine (DAT), serotonin (SERT), and vesicular monoamine transporter 2 (VMAT2)), and γ-aminobutyric acid type A (GABA_A) (α₁,β₂, and γ₂) receptors in heterologous cellular expression systems. (a) Efavirenz (10 μM) displaces specifically bound [³H]radioligand from cloned serotonin 5-HT_2A and 5-HT_2C receptors expressed in HEK293 cells (n=3, *P<0.05 significant displacement compared to specific binding in the absence of efavirenz; one-way ANOVA with Bonferroni post hoc analysis), but not from CB₁ cannabinoid, dopamine D₁, D₂, D₃, and D₄, serotonin 5-HT_1A, opioid (μ, δ, and κ), histamine H₁, adrenergic α_2C, γ-hydroxybutyrate, or Sigma₁ receptors. (b) Agonist-stimulated Gq-coupled phospholipase C activity was measured as inositol phosphate accumulation. Efavirenz acts as a partial agonist of cloned serotonin 2A (5-HT_2A) receptors, and blockade of this receptor by pretreating with methysergide (10 μM) antagonizes its partial agonist effect (n=3–5, **P<0.01, ***P<0.001, NS means not significantly different from basal control levels; one-way analysis of variance (ANOVA) followed by a Dunnett's post hoc analysis). Lysergic acid diethylamine (LSD) (10 μM) acts as a full agonist of cloned 5-HT_2A receptors relative to the full agonist reference compound 5-HT (10 μM) effect (n=3, ***P<0.001, significantly greater levels than basal control). (c) Efavirenz (10 μM) significantly blocks the transport of DAT-mediated [³H]dopamine and SERT-mediated [³H]serotonin (n=2, *P<0.05, significant reduction in [³H]serotonin uptake compared with control uptake in the absence of test compound (defined as 100% uptake) and relative to complete inhibition by 10 μM nomifensine for DAT, and 10 μM fluoxetine for SERT; one-way ANOVA followed by Dunnett's post hoc analysis). (Inset) Efavirenz (10 μM) displaces tetrabenazine-displaceable specifically bound [³H]ketanserin to isoform 2 of the VMAT2 naturally expressed at high levels in rabbit platelets. Note that VMAT1 is not expressed in rabbit platelets. (d) Efavirenz is an allosteric potentiator of cloned α₁β₂γ₂ GABA_A receptors. Whole-cell chloride currents mediated by these receptors are potentiated by efavirenz (⩾10 μM), although efavirenz alone has no activity at the GABA_A receptor (*P<0.05 significantly different from control currents; Student's t-test).

Figure 2

Efavirenz dose-dependently depresses open-field locomotor activity in a novel environment in mice similar to lysergic acid diethylamine (LSD). The ambulation data are shown for groups of eight mice as mean (±SE) counts within 10-min periods for separate groups of eight mice injected intraperitoneally with vehicle, efavirenz, or LSD. (a) At a dose of 3 mg/kg, efavirenz had no effect on ambulation. (b) At a dose of 10 mg/kg, efavirenz decreased ambulation only during the first 10 min. (c) At a dose of 30 mg/kg, efavirenz produced near-maximal suppression of ambulation that was sustained for 40 min. (d) LSD (3 mg/kg) produces a more potent sustained decrease in ambulation similar to that produced by 30 mg/kg efavirenz. The asterisks (*) indicate a significant difference from vehicle control (P<0.05).

Figure 3

Efavirenz has discriminative stimulus effects that are similar to lysergic acid diethylamine (LSD) and consistent with serotonin 2A (5-HT_2A) receptor activity. (a) The data represent mean (±SEM) percent drug-appropriate responding (DAR) for eight rats discriminating 0.1 mg/kg LSD. Control data for vehicle and the training dose are shown to the left of the axis break, whereas substitution data for different doses of efavirenz alone and in combination with MDL100 907 are shown to the right. Drug-appropriate responding by efavirenz (30 mg/kg intraperitoneally) in rats discriminating LSD was fully blocked following pretreatment with a low dose of the 5-HT_2A-selective antagonist MDL100  907 (0.1 mg/kg intraperitoneally). The value n=5 indicates that three of the eight rats tested following 30 mg/kg efavirenz failed to complete the drug discrimination test. The asterisks (*) indicate the absence of a significant difference from the LSD control at P=0.05. Although rates of responding (responses per s) significantly decreased at all doses of efavirenz tested, a 58% decrease in rate of responses occurred at the 30 mg/kg dose (0.29±0.11 compared with 0.70±0.12 for the 0.1 mg/kg intraperitoneal training dose of LSD, P<0.05). The almost undetectable rates of responding at doses of efavirenz higher than 30 mg/kg precluded interpretation of the outcome of discrimination tests. MDL100 907 alone (0.1 mg/kg intraperitoneally) did not influence the rate of responding. (b) The graph shows efavirenz-appropriate lever responding as a function of discrimination training sessions in the presence of efavirenz (open squares) vs sessions with vehicle. With an 18 mg/kg intraperitoneal training dose, rats (n=6) reliably discriminated efavirenz from vehicle (⩾80% correct responding) within 20 training sessions, whereas a training dose of 10 mg/kg (the initial training dose) failed to yield evidence of stimulus control. *P<0.05, DAR is statistically different for vehicle vs efavirenz sessions. (c) LSD (0.1 mg/kg) occasioned drug-lever responding in rats discriminating efavirenz. *P<0.05, not statistically different from the training drug. All rats completed the first fixed ratio and there were no significant differences in the rates of responding (0.34±0.05 compared with 0.37±0.06 for the 18 mg/kg intraperitoneal training dose of efavirenz, P>0.05). (d) Efavirenz (15 mg/kg intraperitoneally) induces head-twitch in wild-type 129S6/SvEv mice, but not in 5-HT_2A-knockout (KO) littermates. Mice were injected with vehicle or efavirenz (15 mg/kg), and the head-twitch response was scored immediately after injection for 15 min. ***P<0.001; Bonferroni's post hoc test within two-way analysis of variance (ANOVA).

Figure 4

Efavirenz fails to exert positive reinforcing effects. (a) Efavirenz fails to maintain self-administration responding in rats that readily self-administer intravenous cocaine but not saline. The five of eight total rats that completed all phases of this study received an average of over three times the infusions of cocaine (dissolved in saline) per session (solid squares) than when saline was substituted for cocaine (open squares). When prepared in the 1 : 1 : 18 vehicle, cocaine maintained self-administration responding (dissolved in 1 : 1 : 18 vehicle) at the beginning (closed circles), middle (between the first two and the last two doses of efavirenz; data not shown), and end (solid circles, far right-hand side of graph) of the studies with efavirenz, respectively. When vehicle was substituted for cocaine, responding decreased markedly at the beginning and end of studies with efavirenz, respectively (open circles). At all doses tested, efavirenz (solid triangles) failed to maintain self-administration responding above what was obtained with vehicle (open circles). C(s), cocaine dissolved in saline (solid squares); sal, saline (open squares); C, cocaine dissolved in 1 : 1 : 18 (v/v/v) ethanol, emulphor, and 0.9% saline vehicle (solid circles); veh, 1 : 1 : 18 vehicle only (open circles); different doses of efavirenz dissolved in 1 : 1 : 18 vehicle (solid triangles). (b) Rats receiving place conditioning with cocaine (10 mg/kg intraperitoneally), but not efavirenz (5–20 mg/kg intraperitoneally), acquired a significant place preference (*P<0.05 significantly different from pretest; ^#P<0.05 significantly different from cocaine; one-way analysis of variance (ANOVA) with Bonferroni post hoc analysis). The data represent the mean (±SE) time spent on the drug-paired floor during the pretest for all rats tested (n=24), and during the post-test for groups of eight following acquisition under cocaine or efavirenz.