Initial Clinical Experience of RP5063 Following Single Doses in Normal Healthy Volunteers and Multiple Doses in Patients with Stable Schizophrenia

RP5063 is a multimodal dopamine (D)‐serotonin (5‐HT) stabilizer with a high affinity for D_2/3/4 and 5‐HT_1A/2A/2B/7 receptors and moderate affinity for the serotonin transporter. Single‐dose (10 and 15 mg fasting, 15 mg fed) safety in healthy volunteers and multiple‐dose (10, 20, 50, and 100 mg fed, 10 days) safety and pharmacodynamics in patients with stable schizophrenia were defined in two phase I studies. In the single‐dose study, 32 treatment‐emergent adverse events (TEAEs) were observed. Orthostatic hypotension (n = 6), nausea (n = 5), and dizziness (n = 4) were the most common. One serious adverse event (SAE), seen in a patient who should not have been in the study due to a history of seizures, involved brief seizure‐like symptoms. In the multiple‐dose study, 75 TEAEs were reported. Akathisia (n = 20) and somnolence (n = 14) were the most frequent. No clinically significant changes were seen in glucose or prolactin levels, lipid profiles, weight, or electrocardiographic recordings. In both studies, all TEAEs resolved and none led to withdrawal from the study or death. A pharmacodynamic evaluation reflected significant improvements with RP5063 (P < 0.05) over placebo in an analysis of patients with a baseline Positive and Negative Syndrome Scale (PANSS) score ≥50 for positive subscale scores. Improvements of the Trail Making A and Trail Making B test results were observed for patients treated in the 50 mg dose group for days 5, 10, and 16. These findings indicate that RP5063 is well‐tolerated up to 100 mg and displays promising preliminary clinical behavioral and cognition activity signals in patients with stable disease over a 10‐day period.

Pharmacokinetics of RP5063 Following Single Doses to Normal Healthy Volunteers and Multiple Doses Over 10 Days to Stable Schizophrenic Patients

RP5063, a multimodal dopamine (D)-serotonin (5-HT) stabilizer, possesses high affinity for D_2/3/4 and 5-HT_{1A/2A/2B/2C/6/7} receptors and moderate affinity for the serotonin transporter. Two phase I studies characterized the pharmacokinetics of a single dose (10 and 15 mg fasting, 15 mg fed/fasting) in healthy volunteers and multiple doses (10, 20, 50, and 100 mg fed) over 10 days in patients with stable schizophrenia. RP5063 displayed a dose-dependent C_max at 4 to 6 h, linear dose proportionality for both C_max and AUC, and a half-life between 40 and 71 h. In the single-dose study, food slightly increased the extent of drug absorption. In the multiple-dose study, steady-state was approached after 120 h of daily dosing. Pooled data in the single-dose study indicate that the pharmacokinetic profile appears to be comparable between Japanese and Caucasians. RP5063 appears to have a straightforward pharmacokinetic profile that supports for phase II and III evaluation as a once-daily oral administered agent.

Dopamine serotonin stabilizer RP5063: A randomized, double-blind, placebo-controlled multicenter trial of safety and efficacy in exacerbation of schizophrenia or schizoaffective disorder

The study objectives were to evaluate the efficacy, safety, tolerability, and pharmacokinetics of RP5063 versus placebo. The study was conducted in adults with acute exacerbation of schizophrenia or schizoaffective disorder. This 28-day, multicenter, placebo-controlled, double-blind study randomized 234 subjects to RP5063 15, 30, or 50mg; aripiprazole; or placebo (3:3:3:1:2) once daily. The aripiprazole arm was included solely to show assay sensitivity and was not powered to show efficacy. The primary endpoint was change from baseline to Day 28/EOT (End-of-Treatment) in Positive and Negative Syndrome Scale (PANSS) total score; secondary endpoints included PANSS subscales, improvement ≥1 point on the Clinical Global Impressions-Severity (CGI-S), depression and cognition scales. The primary analysis of PANSS Total showed improvement by a mean (SE) of -20.23 (2.65), -15.42 (2.04), and -19.21 (2.39) in the RP5063 15, 30, and 50mg arms, versus -11.41 (3.45) in the placebo arm. The difference between treatment and placebo reached statistical significance for the 15mg (p=0.021) and 50mg (p=0.016) arms. Improvement with RP5063 was also seen for multiple secondary efficacy outcomes. Discontinuation for any reason was much lower for RP5063 (14%, 25%, 12%) versus placebo (26%) and aripiprazole (35%). The most common treatment-emergent adverse events (TEAE) in the RP5063 groups were insomnia and agitation. There were no significant changes in body weight, electrocardiogram, or incidence of orthostatic hypotension; there was a decrease in blood glucose, lipid profiles, and prolactin levels. In conclusion, the novel dopamine serotonin stabilizer, RP5063 is an efficacious and well-tolerated treatment for acute exacerbation of schizophrenia or schizoaffective disorder.

Comparative effects of rifabutin and rifampicin on cytochromes P450 and UDP-glucuronosyl-transferases expression in fresh and cryopreserved human hepatocytes

The aim of this study was to evaluate rifabutin (RBT) and rifampicin (RIF) capabilities in inducing various xenobiotic metabolizing enzymes such as cytochromes P450 (CYPs) and UDP-glucuronosyl-transferases (UGTs) in cultured fresh and cryopreserved human hepatocytes. Enzyme induction was assessed through the use of several diagnostic markers, i.e. testosterone, midazolam (MDZ), diazepam (DZP) and 7-ethoxyresorufin for CYP-dependent enzyme reactions; and AZT for UGT-dependent enzyme reactions. RBT concentrations (0.118, 0.708 microM) were selected according to previously published pharmacokinetic data in patients. The known CYP3A4 inducer in humans, RIF, was used as a positive control. At the concentrations used, no sign of cytotoxicity was evidenced. Both compounds were able to dose-dependently induce the overall metabolism of testosterone (approximately 2-fold for RBT, 4-fold for RIF) and the formation of the 6beta-hydroxylated-derivative (up to approximately 4-fold over control for RBT and approximately 10-fold for RIF), which is CYP3A4 dependent. The other hydroxylated metabolites (16alpha-OH and 2alpha-OH) were also enhanced. The metabolism of MDZ, which is specifically metabolized by CYP3A4 in humans, was also investigated following drug's exposure to hepatocytes. DZP one, which is governed by various CYPs, including CYP3A, was also investigated. RBT was shown to increase the biotransformation of both benzodiazepines (approximately 1.9-fold over control). Moreover, the effects of both drugs on ethoxyresorufin O-deethylase activity (EROD), which is representative of CYPIA1/2 isoforms, were tested. Results showed only a moderate induction of this marker (approximately 2-fold over control) when compared to the high effect observed after hepatocyte exposure to 3-methylcholantene (approximately 14-fold over control). Finally, the action of RBT and RIF on UGTs expression was investigated by using AZT as diagnostic substrate: glucuronides formation was not significantly affected by the two rifamycin derivatives. On the whole, exposure of fresh or cryopreserved human hepatocytes to RBT dose-dependently affected the levels of drug metabolizing enzymes in a dose-dependent manner. However, as already demonstrated by in vivo pharmacokinetic studies, its inducing properties towards CYPs, CYP3A in particular, are less pronounced than RIF.

Forebrain norepinephrine and neurobehavioral plasticity: neonatal 6-hydroxydopamine eliminates enriched-impoverished experience effects on maze performance

Newborn male rats were depleted of forebrain norepinephrine (NE) by systemic 6-hydroxydopamine injection and then reared from 25 to 60 days under either isolated or enriched conditions. They were subsequently tested for acquisition of either the Lashley III maze or the Hebb-Williams maze problems. Isolated rearing impaired Lashley maze performance of the controls but not the 6-OHDA injected rats. Similarly, for the Hebb-Williams maze, the isolation-reared controls made more errors than their enriched-reared counterparts while no differences were observed between the isolated and enriched reared, 6-OHDA injected rats. These results are consistent with the hypothesis that forebrain NE is permissive to the deleterious behavioral consequences of restricted experience during maturation.

Neonatal 6-hydroxydopamine lesion of spinal noradrenergic terminals: nociception, clonidine analgesia and spinal alpha two adrenoceptors

Newborn rats received intraspinal injections of 6-hydroxydopamine to enduringly deplete spinal norepinephrine (NE). When tested in adulthood for pain sensitivity with a hot water-tail immersion procedure, this neonatal spinal NE lesion lowered tail flick latencies of females but not males. It was postulated that this sexually dimorphic sparing or recovery of function reflected the development of denervation supersensitivity for males but not females. Contrary to expectation from such an hypothesis, females, not males, showed exaggerated sensitivity to the analgesic effects of a test dose of clonidine. Furthermore, neither males nor females showed an increased number of spinal cord binding sites for (3H)para-amino-clonidine [(3H)PAC]. These receptor binding data failed to indicate proliferation of the spinal alpha two adrenoceptor in either sex. That the lesioning of spinal NE terminals did not reduce (3H)PAC binding sites suggests that the spinal alpha two adrenoceptor does not reside exclusively on NE terminals. This is consistent with current conclusions concerning the alpha two adrenoceptor in the cerebral cortex.

Kinetics of intravenous and oral pentoxifylline in healthy subjects

The kinetics of a sustained-release formulation of pentoxifylline were compared with those of a capsule and an intravenous infusion. Ten healthy subjects received each of the oral pentoxifylline formulations (400 mg) three times a day for 9 days in a random crossover fashion. Pentoxifylline (200 mg) was also given intravenously on a separate day. After intravenous pentoxifylline, plasma levels declined in a biphasic manner, with a terminal t1/2 of 1.63 +/- 0.8 hr. Plasma clearance was 1333 +/- 481 ml/min and the volume of distribution was 168 +/- 82.3 l. Cumulation of pentoxifylline in plasma after repeated dosing was minimal. Plasma levels of the active 5-hydroxylated metabolite were generally higher than those of the parent drug after both routes of administration. Urinary excretion of two acid metabolites after oral and intravenous dosing indicated almost complete absorption of drug-related substances from both of the oral formulations, although bioavailability averaged 20% to 30%.

Acute exposure to pulsed microwaves affects neither pentylenetetrazol seizures in the rat nor chlordiazepoxide protection against such seizures

Three experiments failed to provide consistent evidence for an effect of 2.70 GHz pulsed microwave radiation up to 20 mW/cm2 on pentylenetetrazol-induced seizures or on the efficacy of chlordiazepoxide for counteracting such seizures. Microwave radiation counteracted the hypothermic effects of chlordiazepoxide without altering its antiseizure efficacy. This underscores the dissociation between thermal and pharmacological effects of microwaves.

Neonatal 6-hydroxydopamine attenuates the neural and behavioral effects of enriched rearing in the rat

Newborn male rats were administered subcutaneous 6-hydroxydopamine (6-OHDA) to deplete forebrain norepinephrine and after weaning were reared in normal or enriched environments. Subsequently the 6-OHDA treated rats and their vehicle controls were trained in a Lashley type III maze and then sacrificed for assay of regional brain weights and brain catecholamines. Whereas for the control rats, enriched rearing was found to: (1) increase hypothalamic and posterior cortical dopamine; (2) increase forebrain and decrease hypothalamic weight; and (3) to enhance maze acquisition, none of these consequences of enriched rearing was found in the 6-OHDA treated rats. We conclude that forebrain norepinephrine plays a permissive role in the neuroanatomical, neurochemical and behavioral alterations induced by the enriched rearing of weanling rats and that it is essential to at least some aspects of the shaping of the brain by experiential factors.

Neonatal intraspinal 6-hydroxydopamine, 5,7-dihydroxytryptamine or their combination: effects on nociception and morphine analgesia

Newborn rats received two injections of intraspinal 6-hydroxydopamine (6-OHDA, 10 micrograms) or 5,7-dihydroxytryptamine (5,7-DHT, 8 micrograms preceded by s.c. desmethylimipramine) or a 'cocktail' of both neurotoxins. The two injections were separated by 24 h. When assayed in adulthood, the 6-OHDA rats showed a substantial (about 80%) depletion of spinal norepinephrine (NE) but an elevation of brainstem NE. Conversely, the 5,7-DHT rats showed a modest (about 60%) loss of spinal serotonin (5-HT) but an elevation of brainstem 5-HT. Rats receiving combined 6-OHDA plus 5,7-DHT showed rostro-caudal, decreasing gradients of spinal NE and 5-HT depletions, with the largest loss in the lumbar cord. These depletions were much less than those observed after the respective single neurotoxin treatments. Neither the single nor combined neurotoxin treatments altered the tail-flick analgesia induced by morphine (1.0, 3.0 or 7.5 mg/kg s.c.). Basal nociception, however, was altered by the neurotoxins but in a sexually dimorphic manner. The 6-OHDA lowered baseline tail-flick latencies in females while 5,7-DHT elevated latencies in males. Like the 6-OHDA-only rats, the combined 6-OHDA plus 5,7-DHT lowered latencies in females. We conclude that neither spinal NE nor 5-HT are essential to morphine analgesia but do participate in nociception, seemingly in a sexually dimorphic fashion.

The ontogeny of spinal cord monoamines and the post-decapitation reflex

The ontogeny of the post-decapitation reflex (PDR) was examined in neonatal systemic 6-hydroxydopamine (6-OHDA) treated rats. The PDR was absent in the youngest (5 day) and oldest (60 day) 6-OHDA treated rats but present with attenuated characteristics at around 15 and 20 days. The reappearance of the PDR in these rats closely paralleled age-related fluctuations in spinal cord noradrenaline (NE) which increased until 15 days, then precipitously declined, but did not correlate with spinal dopamine (DA) or serotonin (5-HT). The failure of the alpha noradrenergic blocking agents chlorpromazine, phenoxybenzamine, prazosin, or yohimbine to eliminate the vestigial PDR in the 15-20-day-old, 6-OHDA-treated rats indicates that this is probably not mediated by remaining, undamaged spinal NE neurons at this age. Neither is it likely to be mediated by spinal 5-HT neurons since inhibition of 5-HT synthesis had no effect upon the PDR latency in normal or neonatal 6-OHDA-treated, 17-day-old rats. In contrast to NE levels which increased with age in normal rats, spinal cord 5-HT and DA levels at least as high at 5 days of age as at adulthood.

Neonatal intraspinal 6-hydroxydopamine: depletion of norepinephrine but not dopamine

Neonatal intraspinal 6-hydroxydopamine (6-OHDA), administered in two 10 microgram doses at 24 h intervals, severely depleted spinal norepinephrine (NE) for at least 200 days. This neurochemical lesions was accompanied by a functional loss of spinal NE neurotransmission, as measured by the absence of the post decapitation reflex. While these data contraindicated regeneration of spinal NE terminals, enhanced brainstem NE levels in these rats provided evidence for terminal arborization, possibly representing aborted regrowth of NE fibres into the cord. Neither 6-OHDA alone nor in combination with desmethylimipramine pretreatment depleted spinal cord dopamine of serotonin.

Intraventricular 6-hydroxydopamine in the newborn rat and locomotor responses to drugs in infancy: no support for the dopamine depletion model of minimal brain dysfunction

Bilateral intraventricular injections of 6-hydroxydopamine (6-OHDA) after desmethylimipramine (DMI) in rats 1 and 2 days of age, severely depleted brain dopamine (DA) particularly in the neostriatum, where levels in adulthood were about 7% of control. Compared to vehicle-injected controls these rats were hyperactive only at 15 and 20 days of age, and in adulthood were impaired in a two-way avoidance. Rats with similar 6-OHDA treatment but without DMI pretreatment showed severe depletion of brain norepinephrine (NE) as well as DA, and were behaviorally similar to the DA-depleted only rats. This behavioral syndrome is similar to that reported after intracisternal injection of 6-OHDA in 5-day-old rats, which has been argued as a model for minimal brain dysfunction (MBD). Contrary to expectation from this model, however, challenge doses of either d-amphetamine or methylphenidate did not reduce, but instead increased activity of these rats. The 6-OHDA treatments also did not alter the enhancement of locomotor activity by scopolamine, which was present at 30 days but not at 15 days.