A Multifaceted GABAA Receptor Modulator: Functional Properties and Mechanism of Action of the Sedative-Hypnotic and Recreational Drug Methaqualone (Quaalude).

In the present study, we have elucidated the functional characteristics and mechanism of action of methaqualone (2-methyl-3-o-tolyl-4(3H)-quinazolinone, Quaalude), an infamous sedative-hypnotic and recreational drug from the 1960s-1970s. Methaqualone was demonstrated to be a positive allosteric modulator at human α1,2,3,5ß2,3γ2S GABAA receptors (GABAARs) expressed in Xenopus oocytes, whereas it displayed highly diverse functionalities at the α4,6ß1,2,3δ GABAAR subtypes, ranging from inactivity (α4ß1δ), through negative (α6ß1δ) or positive allosteric modulation (α4ß2δ, α6ß2,3δ), to superagonism (α4ß3δ). Methaqualone did not interact with the benzodiazepine, barbiturate, or neurosteroid binding sites in the GABAAR. Instead, the compound is proposed to act through the transmembrane ß((+))/α((-)) subunit interface of the receptor, possibly targeting a site overlapping with that of the general anesthetic etomidate. The negligible activities displayed by methaqualone at numerous neurotransmitter receptors and transporters in an elaborate screening for additional putative central nervous system (CNS) targets suggest that it is a selective GABAAR modulator. The mode of action of methaqualone was further investigated in multichannel recordings from primary frontal cortex networks, where the overall activity changes induced by the compound at 1-100 µM concentrations were quite similar to those mediated by other CNS depressants. Finally, the free methaqualone concentrations in the mouse brain arising from doses producing significant in vivo effects in assays for locomotion and anticonvulsant activity correlated fairly well with its potencies as a modulator at the recombinant GABAARs. Hence, we propose that the multifaceted functional properties exhibited by methaqualone at GABAARs give rise to its effects as a therapeutic and recreational drug.

DARK Classics in Chemical Neuroscience: Methaqualone.

Commonly known as "Quaaludes," methaqualone (1) is a sedative-hypnotic medication, with effects resembling barbiturates and other downers, that exerts its effects through modulation of γ-aminobutyric acid type A receptors (GABAAR). Following the discovery of the sedative and euphoric effects of methaqualone (1), it was quickly adopted by pharmaceutical companies and promoted by clinicians around the world as a "safe" sleeping pill option, and for a period it was available over the counter. The popularity of methaqualone (1) soared worldwide, and many people began to use it recreationally for its sedative-hypnotic-like psychoactive effects. Not long after its introduction, many individuals began to misuse the drug leading to overdoses and drug dependence which brought to light methaqualone's (1) addictive nature. In this review, the background, synthesis, pharmacology, metabolism, and pharmacokinetics of methaqualone (1) will be covered along with its discovery, history, and the derivatives that are currently available around the world through manufacture in clandestine laboratories.

Synthesis and anticonvulsant evaluation of some new 2,3,8-trisubstituted-4(3H)-quinazoline derivatives.

A new series of 2,3,8-trisubstituted-4(3H)-quinazoline derivatives were synthesized, evaluated for their anticonvulsant activity against electrically (MES) and chemically (PTZ, picrotoxin and Strychnine) induced seizures and compared with the standard drugs methaqualone and sodium valproate. Compounds 3, 17 and 22 proved to be the most potent compounds of this series with relatively low neurotoxicity and low toxicity in the median lethal dose test as compared with the reference drugs. The obtained results showed that the most active compounds could be useful as a template for future design, modification and investigation to produce more active analogs.

Functional properties and mechanism of action of PPTQ, an allosteric agonist and low nanomolar positive allosteric modulator at GABAA receptors.

The former sedative-hypnotic and recreational drug methaqualone (Quaalude) is a moderately potent, non-selective positive allosteric modulator (PAM) at GABAA receptors (GABAARs) (Hammer et al., 2015). In the present study, we have identified a novel methaqualone analog, 2-phenyl-3-(p-tolyl)quinazolin-4(3H)-one (PPTQ), in a screening of 67 analogs at five αß2γ2S GABAAR subtypes and delineated its functional properties and mechanism of action at wild-type and mutant GABAARs expressed in Xenopus laevis oocytes by two-electrode voltage clamp electrophysiology. PPTQ was found to be an allosteric agonist and a PAM (ago-PAM) at human α1ß2γ2S and α4ß2δ GABAARs, exhibiting intrinsic activity at micromolar concentrations and potentiating the GABA-evoked signaling through the receptors at concentrations down to the low-nanomolar range. Whereas PPTQ exclusively increased the potency of GABA at the α1ß2γ2S receptor, it increased both GABA potency and efficacy at α4ß2δ and displayed modest potency-based preference for α4ß2δ over α1ß2γ2S. In elaborate mutagenesis and competition experiments PPTQ was found to act through the same or an overlapping site as etomidate in the transmembrane ß(+)/α(-) subunit interfaces, whereas it did not seem to target the other three transmembrane interfaces in the GABAAR. Finally, the PPTQ site was shown to be allosterically linked with sites targeted by neurosteroids and barbiturates but not with the high-affinity benzodiazepine site in the α1ß2γ2S receptor. In conclusion, the development of a highly potent, bioavailable GABAAR ago-PAM by subtle modifications to the methaqualone scaffold demonstrates that derivatization of this infamous drug from the past can lead to modulators with distinct functional characteristics at the receptors.

Effects of methaqualone on blood platelet function.

To study the mechanism whereby toxic doses of methaqualone cause a bleeding tendency in humans, the effects of methaqualone, diphenhydramine, and the combination of methaqualone plus diphenhydramine on blood platelet function were investigated. Exposure of human platelets in platelet-rich plasma in vitro to final concentrations of methaqualone ranging from 1.1 to 4.5 X 10(-4)) M resulted in nearly complete inhibition of the secondary phase and significant inhibition of the primary phase of adenosine diphosphate (ADP)--induced aggregation. Both the slope and height of collagen-induced aggregation responses were reduced significantly in vitro by the drug. When methaqualone final concentrations of 1.1, 2.3, and 4.5 X 10(-4) M were studied in the presence of diphenhydramine (1.1, 2.3, and 4.5 X 10(-5) M, respectively), the degree of inhibition of ADP-induced aggregation was only slightly greater (not significant) than that observed with methaqualone. The platelets of rabbits injected intravenously with methaqualone, 10 mg/kg, demonstrated a significantly decreased ability to aggregate with ADP and collagen 30 and 60 min after administration of the drug. These results suggest that a drug-induced defect of blood platelet function may play a role in the bleeding associated with methaqualone toxicity.

Synthesis and central nervous system activity of quinazolones related to 2-methyl-3-(o-tolyl)-4(3H)-quinazolone (methaqualone).

A number of derivatives of 2-methyl-3-(o-tolyl)-4(3H)-quinazolone bearing new substituents on the 2-methyl group have been synthesized. It was established that most substitutions at this position reduce or remove the CNS depressant activity of methaqualone. From the series prepared only the 2-fluoromethyl derivative or certain isothiouronium salts, which could be hydrolyzed in vivo to the 2-mercaptomethyl derivative, showed activity of the same magnitude as methaqualone.

Studies on biologically active halogenated compounds. 1. Synthesis and central nervous system depressant activity of 2-(fluoromethyl)-3-aryl-4(3H)-quinazolinone derivatives.

Some 2-(fluoromethyl) analogues of 2-methyl-3-aryl-4-(3H)-quinazolinones have been synthesized and screened for CNS activities. It was shown that the 2-(fluoromethyl) analogues possess in general more potent CNS depressant activities and less toxicities than their parent compounds. Of particular interest were the 2-(fluoromethyl) analogues (22, 24, and 31) of methaqualone and 6-aminomethaqualone. Compound 24 was more potent in CNS depressant activity and less toxic than methaqualone. Compound 31 exhbited potent central muscle relaxing activity and markedly reduced toxicity as compared with 6-aminomethaqualone.

The muscle relaxant activity of methaqualone and its methyl congener.

Studies with methaqualone and dimethylquinazolone showed them to possess both central and peripheral muscle relaxant activity, the latter only at high dose levels. They selectively inhibited polysynaptic reflexes and were more potent than mephenesin.

Assessment of the abuse liability of buspirone in recreational sedative users.

The abuse potential of buspirone, a new dopaminergic antianxiety drug, was evaluated by assessing its subjective effects in standard (10 mg) and high (40 mg) doses. These were compared with methaqualone (300 mg), diazepam (20 mg and 10 mg), and placebo in 24 casual recreational sedative users. Addiction Research Center Inventory scales measuring euphoria, sedation, dysphoria, and abuse liability were used as dependent measures. Groups of subjects received all treatments in randomized order in six weekly 4-hour sessions. Compared to placebo, methaqualone caused elevated scores on euphoria, physical sedation, and abuse liability scales compared to placebo, while 40 mg buspirone caused increased physical sedation, increased physical and mental dysphoria, and lower abuse liability scores. Overall, buspirone at 40 mg appeared unlikely to be reinforcing to recreational illicit drug users; the 10 mg dose was not discriminable from placebo or 10 mg diazepam. Diazepam at 20 mg showed some euphoriant effect compared to placebo.

Dose effects of methaqualone on stimulus encoding in a memory scanning task.

Three task variables, stimulus quality, memory set size and response type, were used in a Sternberg binary classification task to define stimulus encoding, short-term memory scanning, and response selection stages within a serial stage reaction process. Mean reaction times, and the slopes and intercepts of the function relating reaction time to memory set size, were used to test the hypothesis that performance deficits seen at two doses of methaqualone (2.9 mg/kg and 5.9 mg/kg), in the range formerly in common clinical use, were specific to the stimulus encoding stage of the reaction process. Mean reaction times were increased significantly by the methaqualone at both doses, but the effects of the two doses did not differ from one another. The intercept of reaction time as a function of set size showed significant main effects of methaqualone, stimulus quality, and response type, and a significant hyper-additive interaction of methaqualone with stimulus quality. At 2.9 mg/kg, the intercept was increased by methaqualone but only with degraded stimuli. At 5.9 mg/kg, the intercept was increased by methaqualone for both high and low quality stimuli. These results suggested a dose-dependent selective effect of methaqualone on the stimulus encoding stage of the reaction process.

The effects of methaqualone on the seizure susceptibility of mice.

Methaqualone produces dose- and time-dependent decreases in susceptibility to electrically, chemically, and sound-induced seizures. The antagonism of methaqualone to electroconvulsive shock can be dissociated from its effects on temperature regulation and plasma corticosterone. Studies with SKF525A, a drug known to block enzymes in the liver that metabolize drugs, suggest that methaqualone, rather than a metabolite produced in the liver, is responsible for its anticonvulsant effects. Tolerance to the anticonvulsant effects of methaqualone is also demonstrated.

The effects of methaqualone on pituitary-adrenocortical activity in mice.

Methaqualone produces a dose- and time-dependent increase in plasma corticosterone concentration in mice. Acute studies showed that this effect is largely independent of methaqualone-induced hypothermia but can be blocked by pretreatment with dexamethasone, thus demonstrating that the adrenal cortex is not being directly stimulated. It is not clear whether the pituitary-adrenal activation is primarily caused by methaqualone itself or by a hepatic metabolite(s) since pretreatment with SKF 525-A failed either to potentiate or block the effect. Studies employing chronic methaqualone administration provided evidence for a rapid development of tolerance to the pituitary-adrenal effect of the drug. Dose- and time-response studies demonstrated a parallel between plasma concentrations of methaqualone and the stimulation of pituitary-adrenal activity. Furthermore, drug concentrations 1 h following methaqualone administration were diminished in chronically pretreated animals was compared to those previously untreated, suggesting that an altered metabolism of methaqualone may be responsible for the development of tolerance.

Involvement of gamma-amino butyric acid (GABA) in the anticonvulsant action of methaqualone.

The effects of methaqualone on isonicotinic acid hydrazide, 6-mercapto propionic acid, picrotoxin, and strychnine-induced convulsion were studied in mice and the results compared with diazepam. Methaqualone, like diazepam, was found to be a selective antagonist of isoniazid-induced convulsion and a much less effective inhibitor of strychnine convulsion. Methaqualone elicits muscle-relaxant, sedative, and anticonvulsant effects at different dose levels. At low, nonsedative doses the drug produces anticonvulsant effects, and at higher doses, muscle-relaxant and sedative effects. It appears that the mechanism(s) of action of methaqualone in on GABA deficiency or receptor blockade, rather than on glycine receptors.

Serotonin as a facilitatory neurotransmitter in the anticonvulsant activity of methaqualone.

The neuromodulatory role of serotonin in the anticonvulsant activity of methaqualone was investigated. A dose-dependent increase in the ability of methaqualone to provide protection against pentylenetetrazol (90 mg/kg SC)-induced convulsions in mice was observed. The ED50 value for the anticonvulsant activity of methaqualone was calculated and found to be 60 mg/kg, IP. Pretreatment of mice with 5-hydroxytryptophan (100 mg/kg, IP, 2 hr) and p-chlorophenylalanine (300 mg/kg, IP, 2 hr), causing an increase in brain serotonin levels, resulted in a 60% and 80% increase, respectively, in the anticonvulsant activity of methaqualone. Similar pretreatment with p-chlorophenylalanine (300 mg/kg, IP, 48 hr), causing a lowering of brain serotonin, and methysergide (10 mg/kg, IP, 0.5 hr), causing blockade of brain serotonin receptors, resulted in a 40% and 20% decrease, respectively, in the ability of methaqualone to provide protection against pentylenetetrazol-induced convulsions. These results suggest a facilitatory role of serotonin in the anticonvulsant activity of methaqualone.

Methaqualone.

Methaqualone is considered a sedative hypnotic drug with a pattern of pharmacological effects similar to those of barbiturates such as pentobarbital. It does have chemical similarities to the barbiturates but was, in fact, synthesized as part of an Indian program looking for antimalarial drugs (Brown and Goenechea, 1973). Methaqualone was selected for the focus of this study five years ago, because of its popularity as a euphoriant among casual recreational drug users in the Boston area. Methaqualone, instead of a barbiturate hypnotic, was therefore used to test our proposed methodology for the assessment of the abuse liability of sedative drugs. As one reviews the history of the clinical use and illicit abuse of methaqualone, it appears particularly unfortunate that a study of this sort was neither completed nor available to our Food and Drug Administration (FDA) and Drug Enforcement Agency (DEA) in 1965. It was at this time that the drug was approved for prescription use and placed in Schedule V, a schedule which essentially places no restrictions on the clinical use of a prescription drug (Falco, 1976). This paper will both review the development of methaqualone and present an experimental methodology for assessing its abuse liability under seminaturalistic conditions.

Effects of methaqualone on learning: a failure to observe tolerance.

The study was designed to assess the effects of Methaqualone (MTQ) on learning, as well as the effects of 15 days of pretask drug exposure on performance. Forty CFE rats were randomly divided into four groups: Group I received daily IP injections of MTQ for 15 days prior to and throughout the duration of the task; Group II served as a control for Group I, receiving injections of the carrier vehicle; Group III received MTO at the start and throughout the duration of the task; Group IV served as the control for Group III. The task consisted of two pretraining days of swimming down a straight, all-white alleyway, followed by 5 trials/day for 4 days on a black-white discrimination task in a water T maze, with the white side being reinforced for all animals. Analyses revealed that MTQ animals made significantly more errors than controls. Pretask drug exposure did not significantly alter Group I performance versus Group III. Furthermore, continued injections for half of the animals in Group I and II for eight days following the last learning day did not improve Group I performance when retested on the same task. Thus MTQ adversely affected learning with prolonged drug exposure failing to reverse such debilitation.

Effects of d-amphetamine, methaqualone, and phencyclidine on the reaction time of pigeons.

The effects of acute administrations of d-amphetamine (0.56, 1.0, 1.78, 3.2, and 5.6 mg/kg), methaqualone (5.6, 10, 18, 32, and 56 mg/kg), and phencyclidine (0.3, 0.56, 1.0, and 1.78 mg/kg) on the reaction time of pigeons were examined. In the reaction time assay, birds were trained to depress and hold a foot treadle until a stimulus change occurred. Releases within 2 s of the stimulus change were reinforced with food; premature releases or releases occurring after the 2-s limited hold were not reinforced. At relatively high doses, each of the drugs decreased the percentage of responses that were reinforced. Methaqualone and phencyclidine usually increased median reaction times at these doses, whereas the effects of d-amphetamine on reaction time were less clear.

Tolerance and cross-tolerance to central nervous system depressants after chronic pentobarbital or chronic methaqualone administration.

This study reports on tolerance and cross-tolerance to the rotarod (RR)-disrupting effects of various central nervous system (CNS) depressants. Female rats trained on the RR were fed ground chow containing pentobarbital (PB, 2.0 mg/g chow) or methaqualone (MQ, 1.0 mg/g chow) and were injected twice daily (PB) or daily MQ) with 30 mg/kg IP for 6 days. Control rats received ground chow and saline injections. On day 7 the subjects were tested with various doses of PB, MQ, diazepam (DZ), or ethanol (ET) for disruption of RR performance over the time-course of the drug effect (up to 12 hours). Control animals demonstrated a dose-dependent duration of impairment for all 4 agents. Both groups receiving chronic drug showed a prominent decrease in duration of RR impairment after PB, a less marked decrease after MQ, and even less of a decrease after DZ. However, neither chronic drug group showed an appreciable tolerance to the RR disruption of ET, relative to the control group. Based on the time of 50% recovery (RR performance recovering to 90 seconds or more), both chronic treatments resulted in a significant shift of the dose-response curves for PB, MQ and DZ to the right. Therefore, the degree of tolerance and cross-tolerance in rats chronically treated with PB or MQ was dramatic for PB and MQ, was significant for DZ, but was not demonstrable for ET.

Effect of methaqualone on plasma corticosterone in rats: possible sites of action.

Methaqualone produces large increases in plasma corticosterone in rats. This effect does not involve a direct stimulation of either the adrenal glands or pituitary, nor is it the result of a significant alteration in the clearance of circulating corticosterone. Methaqualone may therefore be influencing brain mechanisms which ultimately regulate hypothalamic CRH secretion, although a peripheral site of action has not yet been ruled out.

The effect of d-lysergic acid diethylamide (LSD), 2,5-dimethoxy-4-methylamphetamine (DOM), pentobarbital and methaqualone on punished responding in control and 5,7-dihydroxytryptamine-treated rats.

The purpose of the present study was to determine the role of central 5-hydroxytryptamine (5-HT) neuronal systems in the effects of d-lysergic acid diethylamide (LSD), 2,5-methoxy-4-methylamphetamine (DOM), pentobarbital (PB) and methaqualone (MQ) on punished responding in rats. Water-deprived rats were trained to drink from a tube that was electrified at intervals (variable interval 21 sec; 0.03 mA current intensity), electrification being signalled by a tone. In daily 10-min control sessions, these animals accepted a relatively constant number of shocks; water consumption was also quite stable. At maximally effective doses PB, and to a lesser extent MQ, produced large (400-600 percent of control) increases in punished responding with little decrease in water intake. Higher doses of these agents produced a significant depression of unpunished responding (water intake). The hallucinogens, on the other hand, produced only moderate (125-175 percent of control) increases in the number of shock received, yet a similar depression of unpunished responding. Selective destruction of 5-HT neurons by intracerebroventricular administration of the neurotoxin 5,7-dihydroxytryptamine per se produced little change in the number of shocks received or water consumed in controls sessions. This destruction of 5-HT neurons failed to alter the effects of PB or MQ on punished or unpunished responding. The increase in punished responding produced by the hallucinogens, however, was blocked by this destruction of 5-HT neurons. Furthermore, the capacity of the hallucinogens to decrease water intake was significantly potentiated by the neurotoxin pretreatment. These data demonstrate that the effects of the hallucinogens LSD and DOM on conditioned suppression are quite different from those of PB and MQ, and that this difference may be due to the extent of 5-HT involvement in the effects of these agents.