Reproductive toxicology studies supporting the safety of molindone, a dopamine receptor antagonist.

BACKGROUND: An extended-release molindone (a dopamine D2 and serotonin antagonist) is currently being developed as a novel treatment for impulsive aggression (IA) in patients optimally treated for ADHD. Oral Good Laboratory Practice reproductive toxicology studies (fertility and early embryonic [FEE], prenatal/postnatal [PPN], embryo-fetal development [EFD]) were conducted with molindone HCl using International Conference on Harmonisation (ICH) S5(R2)-compliant protocols. METHODS: In the FEE study, 0, 5, 15, or 30 mg kg-1 day-1 was administered to female (2 weeks premating through implantation) and male (4 weeks premating for 57 days) rats, and fertility parameters were evaluated. In the EFD studies, rats received 0, 5, 20, or 40 mg kg-1 day-1 on gestational days (GDs) 6-17; rabbits received 0, 5, 10, or 15 mg kg-1 day-1 on GDs 6-18. Ovarian/uterine and fetal parameters were evaluated at term. In the PPN study, F0 rats received 0, 5, 20, or 40 mg kg-1 day-1 (GD6-LD21); behavior and reproduction were evaluated in F1 offspring. RESULTS: Parental hypoactivity and reduced body weight gain occurred in all studies. In the FEE, prolonged estrous cycles and delayed mating occurred at ≥15 mg kg-1 day-1 , without effects on fertility or embryonic development. No developmental toxicity occurred in F1 fetuses. In F1 pups, reduced preweaning growth was observed at 40 mg kg-1 day-1 , but there were no effects on postweaning growth, behavior, or reproduction. CONCLUSIONS: Molindone was not developmentally toxic in rats or rabbits at 69X and 6X clinical exposures, confirming the reproductive safety of molindone. Changes in estrous cyclicity were related to species-specific pharmacological effects of molindone in rodents and are not considered relevant to human risk.

The use of molindone in the treatment of psychotic and delirious patients infected with the human immunodeficiency virus. Case reports.

Four patients with HIV infection and psychosis from various etiologies, refractory to standard treatments, and suffering from severe extrapyramidal symptoms (EPS), had a marked beneficial response to molindone. There was significant control of neuropsychiatric dysfunction without major adverse side effects. The results suggest that further evaluation is warranted of the use of molindone in treating severely ill, psychotic, or delirious HIV-infected patients.

Neuroleptics and learning: effects of haloperidol, molindone, mesoridazine and thioridazine on the behavior of pigeons under a repeated acquisition procedure.

The purpose of the present study was to examine the effects of haloperidol (0.3-10 mg/kg), molindone (0.3-5.6 mg/kg), mesoridazine (0.3-10) and thioridazine (0.3-25 mg/kg) on the behavior of pigeons exposed to a repeated acquisition procedure. At sufficiently high doses, each of these neuroleptics increased error rates (interfered with learning) and reduced rate of responding. When the drugs were compared on the basis of absolute doses administered, haloperidol disrupted behavior at doses considerably lower than the other drugs. If, however, chlorpromazine equivalent doses were examined, haloperidol was the least disruptive of the four drugs. Comparing the degree of behavioral disruption produced by the four drugs with their relative neuroreceptor affinities for dopamine D-2, cholinergic muscarinic, histamine H1, alpha-1 adrenergic and alpha-2 adrenergic receptors suggests that behavioral disruption cannot be attributed in any simple way to dopamine or acetylcholine receptor blockade. The relationship between the behavioral effects of neuroleptics and their simple neuropharmacological actions must be considered as highly tentative.

Effect of typical and atypical neuroleptic treatment on protachykinin mRNA levels in the striatum of the rat.

A significant population of striatal neurons synthesize the tachykinin peptides substance P and neurokinin A. The synthesis of these neuropeptides is under tonic stimulation by dopaminergic neurotransmission. Since typical and atypical neuroleptic drugs display differential effects on the activity of dopaminergic neurons, we evaluated the effect of typical (haloperidol and prolixin) and atypical (molindone, thioridazine and chlozapine) chronic neuroleptic treatment on protachykinin mRNA levels in the medial aspect of the caudate-putamen by in situ hybridization histochemistry. Both typical and atypical neuroleptics decreased protachykinin mRNA levels by 22-40% relative to saline-injected controls. Clozapine failed to affect protachykinin mRNA levels. The data suggest the hypothesis that decreased striatal protachykinin mRNA levels may not be directly linked to development of extrapyramidal side effects.

Down-regulation of tryptamine binding sites following chronic molindone administration. A comparison with responses of dopamine and 5-hydroxytryptamine receptors.

The present study assessed changes of tryptamine, dopamine D2, 5-HT1 and 5-HT2 binding sites in rat brain following chronic treatment with low (5 mg/kg/day) and high (40 mg/kg/day) doses of molindone, a clinically effective psychotropic drug. The high-dose molindone treatment produced a decrease in the number of tryptamine binding sites while both high and low doses caused an increase in the number of dopamine D2 binding sites in the striatum. No significant changes were observed in either 5-HT1 or 5-HT2 binding sites in the cerebral cortex. Competition binding experiments showed that molindone was a potent inhibitor at dopamine D2 but less effective at tryptamine, 5-HT1 and 5-HT2 binding sites. The inhibition activity of molindone towards type A monoamine oxidase produced a significant increase in endogenous tryptamine accumulation rate which was much higher than that of dopamine and 5-HT. These findings suggest that the reduction in the number of tryptamine binding sites produced by chronic molindone administration is related to monoamine oxidase inhibition and that the increase in the number of dopamine D2 binding sites is correlated to receptor blocking activity of the drug.

Molindone: effects in pigeons responding under conditional discrimination tasks.

Pigeons were trained to respond under three conditional discrimination procedures; 1) a fixed-consecutive-number procedure with (FCN 8-SD) and without (FCN 8) an added external discriminative stimulus, 2) a delayed matching-to-sample (DMTS) procedure using 0-sec, 2-sec and 8-sec delay intervals, and 3) a repeated acquisition of behavioral chains (RA) procedure using a four-link response chain with three stimulus keys. The atypical neuroleptic agent molindone decreased accuracy under the FCN 8 at doses that had no effect on accuracy under the FCN 8-SD. Under the DMTS procedure, molindone-induced decreases in accuracy were directly related to the delay interval, with the largest relative decrements obtained at the 8-sec delay and the smallest at the 0-sec delay. Under the RA procedure, molindone decreased accuracy at doses that had little or no effect on the number of correct responses emitted. Relative to control values, molindone-induced decreases in accuracy were smallest under the DMTS and FCN 8-SD procedures and largest under the FCN 8 and RA procedures. The differential effects obtained with molindone under each of these procedures illustrate the need to employ a variety of assays when determining the behavioral actions of neuroleptics. In addition, this battery of behavioral tests may provide a useful tool for assessing the different neurochemical actions of neuroleptic compounds.

Differences in the time course of dopaminergic supersensitivity following chronic administration of haloperidol, molindone, or sulpiride.

The onset and persistence of changes in 3H-spiroperidol binding to dopamine (DA) D2 receptors were examined in rat mesolimbic and striatal brain regions following daily administration of haloperidol, molindone, or sulpiride for 3, 7, 14, or 28 days. Neuroleptic dose equivalencies were determined by inhibition of 3H-spiroperidol in vivo binding in several rat brain regions. Changes in locomotor and stereotyped responses to the specific DA D2 agonist quinpirole were examined 3 days after the last treatment dose. Haloperidol or molindone administration increased mean stereotypy scores and striatal DA D2 receptor densities throughout the 28-day treatment period. In contrast, mesolimbic DA D2 receptor densities were transiently increased and returned to control values, after 28 days of haloperidol or molindone treatment. Sulpiride treatment increased mean stereotypy scores and striatal Bmax values, but had no effect on locomotion or mesolimbic dopamine receptor density. Additionally, the magnitude of change in the various measures of brain DA function varied among the three neuroleptic treatment groups. Results from this study suggest that mesolimbic and striatal brain regions differ in their response to long-term neuroleptic administration and that drug choice may influence the magnitude of neuroleptic-induced dopaminergic supersensitivity.

Potentiation of dopamine receptor-mediated responses by B-HT 920 in mice.

The effect of B-HT 920, an alpha 2-agonist, on postsynaptic dopamine receptor-mediated stereotypic behaviour, was studied in mice. Apomorphine produced typical stereotypic responses in mice such as sniffing, rearing, biting, licking and grooming. B-HT 920, when given alone, produced mild stereotypy. Pretreatment with B-HT 920 significantly potentiated the stereotypic behaviour of apomorphine. The specific alpha 2-blockers, idazoxan and yohimbine, failed to block the potentiating effect of B-HT 920. The specific D2-receptor blockers haloperidol and molindone, completely blocked the stereotypic responses due to B-HT 920 and apomorphine. On reserpinization of animals there was a 5-fold increase in stereotypy induced by the combination of apomorphine and B-HT 920. B-HT 920 also potentiated amphetamine-induced locomotor responses in mice in a haloperidol-sensitive way. These data imply an interaction of B-HT 920 with postsynaptic dopamine receptors.

D-1 and D-2 receptor blockade have additive cataleptic effects in mice, but receptor effects may interact in opposite ways.

The dopaminergic role of D-1 and D-2 receptors in catalepsy was evaluated using drugs with preferential receptor affinities. The D-1 antagonist, SCH 23390, caused distinct catalepsy in mice at 1, 2, and 10 mg/kg, IP, but not at two lower doses. The selective D-1 blocker, molindone, also caused catalepsy at 5 and 10 mg/kg; and blockade of both receptor types produced additive cataleptogenic effects. Apomorphine (4 mg/kg), which is an agonist for both receptors, potentiated SCH 23390-induced catalepsy much more than it did the catalepsy induced by molindone; the potentiation was produced by higher, not lower, doses of apomorphine. To determine if the apomorphine potentiation was mediated by D-1 or D-2 receptors, we tested selective agonists in mice that were concurrently injected with selective blockers. SCH 23390-induced catalepsy was potentiated by a large dose of the D-2 agonist, bromocriptine. The catalepsy of D-2 blockade with molindone was not potentiated by the D-1 agonist, SKF 38393, which slightly disrupted the catalepsy of D-2 blockade. We conclude that catalepsy is not a simple D-2 blockade phenomenon and that preferential antagonism of either receptor type can cause catalepsy. Catalepsy is most profound when both receptor types are blocked. Dopamine agonists, in large concentrations, are known to promote movements, and thus it is not surprising that they tend to disrupt catalepsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative determination of the effects of catecholaminergic agonists and antagonists on the rewarding efficacy of brain stimulation.

The effects of amphetamine, clonidine, molindone, pimozide and yohimbine on the rewarding efficacy of electrical stimulation of the medial forebrain bundle in the rat were determined from the effects of these drugs on the rate-frequency function, which is the plot of the rat's rate of pressing a lever against the frequency of the pulses in a rewarding train of fixed duration. These catecholaminergic agonists and antagonists produced dose-dependent alterations in the measurable rewarding efficacy, but only up to a factor of about 2, even though the method is capable of measuring 25-30-fold changes. At elevated doses, the effects on rewarding efficacy became unmeasurable, because the animals would not consistently self-stimulate at any parameters of stimulation. Amphetamine (0.5-3 mg/kg) enhanced rewarding efficacy. Clonidine (0.05-0.4 mg/kg), molindone (0.25-1 mg/kg) and pimozide (0.1-0.6 mg/kg) attenuated it. Pimozide and clonidine were equipotent despite their radically different receptor affinities. The effects of pimozide, clonidine and amphetamine were approximately additive (amphetamine cancelled the effects of pimozide and clonidine, while clonidine augmented the effect of pimozide). The alpha 2 antagonist yohimbine (0.05-10 mg/kg) had the same effect as the alpha 2 agonist clonidine (attenuation of rewarding efficacy), but these effects did not combine additively: yohimbine neither cancelled nor augmented the effect of clonidine. It is suggested that catecholaminergic agonists and antagonists do not alter the magnitude of the rewarding signal by acting on postsynaptic receptors in the reward pathway; rather, they may drive beyond functional limits a variable that is crucial to the proper recording of the magnitude of the rewarding signal.

3-Methoxytyramine accumulation: effects of typical neuroleptics and various atypical compounds.

The accumulation of 3-methoxytyramine (3-MT), the O-methylated metabolite of dopamine (DA), in rat striatum was used to assess the effects of drugs on dopaminergic activity. This was accomplished by pretreating rats with pargyline to completely inhibit 3-MT catabolism. Under the conditions used, 3-MT accumulation was linear over time for at least 90 minutes. Apomorphine and gamma-butyrolactone, drugs which depress the activity of DA-containing neurons, decreased striatal 3-MT accumulation; whereas typical neuroleptics (haloperidol, fluphenazine, chlorpromazine), which increase the activity of DA-containing neurons, increased striatal 3-MT accumulation. In addition, a number of other drugs which block DA receptors and exert various atypical actions on dopaminergic functioning were examined. These "atypical" compounds (clozapine, buspirone, molindone) also increased striatal 3-MT accumulation, but were generally less potent than the typical neuroleptics examined. Moreover, the potencies of the typical neuroleptics and "atypical" compounds that were tested appear to be somewhat related to their affinities for D-2 DA receptors, as measured by their abilities to displace 3H-spiperone from rat striatal membrane preparations. Interestingly, this relationship was less evident when NaCl was omitted from the 3H-spiperone binding assay buffer. The potential antipsychotic drugs, BW 234U and SCH 23390, were also investigated for their effects on 3-MT accumulation and 3H-spiperone binding, and they were relatively inactive in both of these measures of dopaminergic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of bromocriptine-induced cage climbing behaviour in mice by the selective D-2 dopamine receptor antagonists, metoclopramide and molindone.

Bromocriptine (5-30 mg/kg, ip), 2 hr after administration, induced cage climbing behaviour in mice. Pretreatment with haloperidol, an antagonist of both D-1 and D-2 dopamine receptors, metoclopramide and molindone, the selective D-2 dopamine receptor antagonists, effectively antagonised bromocriptine-induced climbing behaviour. The results indicate that bromocriptine most probably induces climbing behaviour in mice by stimulating the postsynaptic striatal D-2 dopamine receptors.

Neuroleptic-induced catalepsy: a D2 blockade phenomenon?

Typical neuroleptics, such as haloperidol, are cataleptogenic. But since such drugs block both D1 and D2 receptors, it is not clear if there is a differential receptor role in catalepsy. To test this issue in a mouse model of catalepsy, these experiments tested molindone, a D2-blocking neuroleptic with almost no ability to block D1 receptors. If D1 receptor blockade is necessary for catalepsy, molindone should not cause catalepsy. But molindone was cataleptogenic, albeit less potent than haloperidol. There was also a "training effect" with haloperidol, but not saline or molindone, in that the catalepsy produced by 5 mg/kg of haloperidol was much greater when tests were performed repeatedly at short intervals after injection. Concurrent administration of apomorphine (4 or 8 mg/kg) markedly potentiated haloperidol catalepsy, but had no effect on molindone catalepsy. Such results are not readily interpretable solely in terms of current concepts of D1 and D2 receptors.

Molindone and haloperidol in tardive dyskinesia.

Preliminary results are described from a study of 11 outpatients manifesting exacerbated tardive dyskinesia after tapering and withdrawal of neuroleptic medications. Patients were randomly assigned to molindone or haloperidol under double-blind placebo-controlled conditions to compare the masking effects of the two drugs. Haloperidol treatment masked withdrawal-exacerbated tardive dyskinesia more than molindone did; this difference (measured by percent change in AIMS scores) was significant (p = .04) when the dose was 200% but not 100% of the prestudy neuroleptic dose. Despite several limitations to the study, the results suggest that molindone may have less dyskinetogenic potential than haloperidol. Further research in the area of site-specificity of molindone is indicated.

Review of clinical and laboratory experiences with molindone hydrochloride.

The literature concerning the pharmacokinetics, pharmacodynamics, receptor physiology, and clinical use of molindone is reviewed. Unanswered questions about the drug are addressed. Although molindone is reputed to have a short half-life (1.5 hours), clinical observations report a prolonged effect from a once-daily dose. Early in treatment, some patients show intolerance due to akathisia or extrapyramidal symptoms. This may be withdrawal dyskinesia due to discontinuation of another drug or an early adverse effect of molindone. Different effects on dopamine receptors have been described, but the significance of these properties for the development of tardive dyskinesia remains unclear.

Effect of clozapine and molindone on plasma and brain levels of mescaline in mice.

Levels of unchanged mescaline were examined in the plasma and brain of albino Swiss-Webster mice pretreated with various doses of either clozapine or molindone. In clozapine treated mice, the mescaline levels were statistically significantly higher at 2 and 3 h with 7.5 and 15.0 mg/kg and at 1, 2 and 3 h with 30 mg/kg. Molindone at 4.0 and 8.0 mg/kg produced no significant effect; at 16.0 and 48.0 mg/kg, the levels were significantly higher at 1 and 2 h. Elevated brain levels of mescaline by clozapine and molindone indicate an adverse metabolic interaction between a hallucinogen and drugs that are commonly used to treat mescaline-induced psychosis.

Psychopharmacological investigation of the monoamine oxidase inhibitory activity of molindone, a dihydroindolone neuroleptic.

24 h pretreatment with molindone enhanced the behavioural effects of L-dopa and 5-HTP, precursors of biogenic amines (catecholamines and 5-HT respectively) preferentially deaminated by MAO-A, confirming that a metabolite of molindone inhibits MAO-A. 24 h pretreatment with molindone enhanced the behavioural effects of tryptamine and antagonized reserpine-induced ptosis, and in molindone-pretreated rats L-tryptophan induced behavioural effects, probably because of the MAO-A inhibitory activity exerted by a metabolite of molindone. Since 24 h pretreatment with molindone, unlike 30 min pretreatment with clomipramine, failed to antagonize fenfluramine and p-chloramphetamine-induced behavioural syndromes, it suggests that molindone and/or its metabolites most probably do not exert 5-HT neuronal uptake blocking activity and the potentiation of 5-HTP-induced behavioural syndrome is due to a metabolite's MAO-A inhibitory activity. As 2 h pretreatment with molindone induced catalepsy and antagonized apomorphine-induced climbing behaviour in mice and stereotypy in rats, while 24 h pretreatment failed to induce catalepsy and to antagonize apomorphine-induced behaviour, it appears that, at 24 h, the tissue levels of molindone are inadequate to block postsynaptic striatal and mesolimbic DA receptors and that, though a metabolite of molindone is biologically active so far as inhibition of MAO-A is concerned, the metabolites are devoid of neuroleptic activity. Further, since 2 h pretreatment with molindone failed to enhance the behavioural effects of L-dopa, it suggests that at 2 h the degree of MAO-A inhibition induced by molindone and/or the metabolite is not sufficient to counteract the neuroleptic activity of the parent compound.

Drug interactions on spontaneous locomotor activity in rats. Neuroleptics and amphetamine-induced hyperactivity.

The locomotor activity of female rats was recorded during 10-min sessions in a circular open-field apparatus after the administration of vehicle or drug. Dose-response curves were obtained for seven neuroleptic drugs both alone (spontaneous activity) and in combination with 1.0 mg/kg of d-amphetamine. Haloperidol, pimozide, loxapine, thiothixene, molindone and chlorpromazine all produced graded decreases in spontaneous locomotor activity. Haloperidol, pimozide, loxapine, thiothixene and molindone also produced graded reversals of the hyperactivity produced by d-amphetamine, while chlorpromazine did not. Clozapine neither altered spontaneous activity nor reversed the hyperactivity produced by d-amphetamine. The data indicate that measures of locomotor activity provide important additional information about the actions of neuroleptics and do not necessarily mirror the actions of these drugs on other measures of performance such as lever-pressing for brain stimulation.