Preclinical characterization of selective phosphodiesterase 10A inhibitors: a new therapeutic approach to the treatment of schizophrenia.

We have recently proposed the hypothesis that inhibition of the cyclic nucleotide phosphodiesterase (PDE) 10A may represent a new pharmacological approach to the treatment of schizophrenia (Curr Opin Invest Drug 8:54-59, 2007). PDE10A is highly expressed in the medium spiny neurons of the mammalian striatum (Brain Res 985:113-126, 2003; J Histochem Cytochem 54:1205-1213, 2006; Neuroscience 139:597-607, 2006), where the enzyme is hypothesized to regulate both cAMP and cGMP signaling cascades to impact early signal processing in the corticostriatothalamic circuit (Neuropharmacology 51:374-385, 2006; Neuropharmacology 51:386-396, 2006). Our current understanding of the physiological role of PDE10A and the therapeutic utility of PDE10A inhibitors derives in part from studies with papaverine, the only pharmacological tool for this target extensively profiled to date. However, this agent has significant limitations in this regard, namely, relatively poor potency and selectivity and a very short exposure half-life after systemic administration. In the present report, we describe the discovery of a new class of PDE10A inhibitors exemplified by TP-10 (2-{4-[-pyridin-4-yl-1-(2,2,2-trifluoro-ethyl)-1H-pyrazol-3-yl]-phenoxymethyl}-quinoline succinic acid), an agent with greatly improved potency, selectivity, and pharmaceutical properties. These new pharmacological tools enabled studies that provide further evidence that inhibition of PDE10A represents an important new target for the treatment of schizophrenia and related disorders of basal ganglia function.

Behavioral and neurochemical characterization of mice deficient in the phosphodiesterase-1B (PDE1B) enzyme.

PDE1B is a calcium-dependent cyclic nucleotide phosphodiesterase that is highly expressed in the striatum. In order to investigate the physiological role of PDE1B in the central nervous system, PDE1B knockout mice (C57BL/6N background) were assessed in behavioral tests and their brains were assayed for monoamine content. In a variety of well-characterized behavioral tasks, including the elevated plus maze (anxiety-like behavior), forced swim test (depression-like behavior), hot plate (nociception) and two cognition models (passive avoidance and acquisition of conditioned avoidance responding), PDE1B knockout mice performed similarly to wild-type mice. PDE1B knockout mice showed increased baseline exploratory activity when compared to wild-type mice. When challenged with amphetamine (AMPH) and methamphetamine (METH), male and female PDE1B knockout mice showed an exaggerated locomotor response. Male PDE1B knockout mice also showed increased locomotor responses to higher doses of phencyclidine (PCP) and MK-801; however, this effect was not consistently observed in female knockout mice. In the striatum, increased dopamine turnover (DOPAC/DA and HVA/DA ratios) was found in both male and female PDE1B knockout mice. Striatal serotonin (5-HT) levels were also decreased in PDE1B knockout mice, although levels of the metabolite, 5HIAA, were unchanged. The present studies demonstrate increased striatal dopamine turnover in PDE1B knockout mice associated with increased baseline motor activity and an exaggerated locomotor response to dopaminergic stimulants such as methamphetamine and amphetamine. These data further support a role for PDE1B in striatal function.

Disruption of the neurokinin-3 receptor (NK3) in mice leads to cognitive deficits.

RATIONALE: The structurally related neuropeptides, substance P, neurokinin A, and neurokinin B, belong to a family of molecules termed tachykinins and are widely distributed in the central and peripheral nervous systems. These peptides mediate their effects through three G protein coupled receptor subtypes, the neurokinin-1, neurokinin-2 and neurokinin-3 receptors, respectively. OBJECTIVE: To study the physiological functions of NK3, a line of NK3 knockout mice were generated and characterized in a broad spectrum of well-established behavioral tests. RESULTS: In several tests, including spontaneous locomotor activity, elevated plus maze, forced swim, and hot plate, wild-type and knockout mice performed similarly. However, in several cognition tests, including passive avoidance, acquisition of conditioned avoidance responding (CAR), and the Morris water maze, NK3 knockout mice displayed deficits compared to wild-type mice. Although NK3 wild-type and knockout mice performed similarly in the training phase of the passive avoidance test, knockout mice had shorter latencies to enter the dark compartment on days 3 and 4, suggesting impaired retention. In the acquisition phase of the conditioned avoidance responding assay, NK3 knockout mice acquired the CAR task at a slower rate than wild-type mice. Once the CAR test was acquired, both NK3 wild-type and knockout mice responded similarly to clozapine and risperidone, drugs which suppress responding in this test. In the Morris water maze, NK3 knockout mice showed increased latencies to find the escape platform on day 3 of training, suggesting a modest, but significant delay in acquisition compared to wild-type mice. CONCLUSION: These studies suggest a role for NK3 in learning and memory in mice.

Teaching sacrospinous colpopexy.

OBJECTIVE: A method is described by which residents can perform transvaginal sacrospinous colpopexy simply, quickly, safely, and effectively. STUDY DESIGN: Over 11 years, 134 sacrospinous suspension procedures have been performed, all or in part by residents, under the direct intraoperative supervision of the author. Minimum follow-up is 1 year. An operative technique has been developed with use of standard instruments and lights. The sitting resident, the attending physician, and the medical student are able to see the ligament penetrated by the suture. If necessary, the attending physician is able to perform the difficult steps of the operation without changing places with the resident. RESULTS: Results are known for 112 of the patients. There have been five recurrences of significant prolapse, and incontinence has developed in 8 patients. Ninety-nine patients felt the outcome to be satisfactory or excellent. There were two major complications and one postoperative death. CONCLUSIONS: This teaching method has provided our residents a direct-view, hands-on familiarity with sacrospinous colpopexy while achieving results for the patients consistent with the outcomes of other centers.

5,7-dihydro-3-[2-[1-(phenylmethyl)-4-piperidinyl]ethyl]-6H- pyrrolo[3,2-f]-1,2-benzisoxazol-6-one: a potent and centrally-selective inhibitor of acetylcholinesterase with an improved margin of safety.

A series of N-benzylpiperidines (2a-d, 10) with novel isoxazole-containing tricycles has been prepared. This series has shown potent in vitro inhibition of the enzyme acetylcholinesterase (AChE), with IC50S = 0.33 - 3.6 nM. Compound 2a was the most potent inhibitor with an IC50 = 0.33 +/- 0.09 nM. Derivatives 2a-d and 10 displayed weak in vitro inhibition of butyrylcholinesterase (BuChE) with IC50S = 600 - 23,000 nM. The most selective compound was 2a with a BuChE/AChE ratio in excess of 4 orders of magnitude (> 10,000). Pyrrolobenzisoxazole 2a also displayed a favorable profile in vivo. In microdialysis experiments, 2a produced a 200% increase in extracellular levels of acetylcholine (ACh) at a dose of 0.4 mg/kg in freely moving, conscious rats. Peripheral side effects (salivation ED50 = 26 +/- 1.5 mg/kg) and acute lethality (LD50[1 h] = 42 mg/kg) were observed at > 60-fold higher doses. These data indicate that 2a is an AChE inhibitor with good central selectivity and a favorable margin of safety. Compound 2a, designated as CP-118,954, is currently in clinical development for the treatment of cognitive disorders.

Novel benzisoxazole derivatives as potent and selective inhibitors of acetylcholinesterase.

A series of N-benzylpiperidine benzisoxazoles has been developed as potent and selective inhibitors of the enzyme acetylcholinesterase (AChE). The benzisoxazole heterocycle was found to be an appropriate bioisosteric replacement for the benzoyl functionality present in the N-benzylpiperidine class of inhibitors. The title compounds were synthesized by alkylating 3-methyl-1,2-benzisoxazoles with an iodo piperidine derivatives as the key step. Benzisoxazoles 1b-j,o displayed potent inhibition of AChE in vitro with IC50's = 0.8-14 nM. Particularly interesting were N-acetyl and morpholino derivatives 1g (IC50 = 3 nM) and 1j (IC50 = 0.8 nM), respectively, which displayed outstanding selectivity for acetyl-over butyrylcholinesterase, in excess of 3 orders of magnitude. N-Acetyl 1g also displayed a favorable profile in vivo. This analog showed a dose-dependent elevation of total acetylcholine in mouse forebrain after oral administration with an ED50 = 2.4 mg/kg. In addition, 1g was able to reverse amnesia in a mouse passive avoidance model at doses of 3.2 and 5.6 mg/kg with an average reversal of 89.7%. Molecular dynamics simulations were used to study the possible binding modes of N-benzylpiperidine benzisoxazoles to AChE from Torpedo californica. Key structural insights were obtained regarding the potency of this class of inhibitors. Specifically, Asp-72, Trp-84, Trp-279, Phe-288, and Phe-330 are implicated in the binding of these inhibitors. The N-benzylpiperidine benzisoxazoles may be suitable compounds for the palliative treatment of Alzheimer's Disease.

Sertraline, a serotonin-uptake inhibitor, reduces food intake and body weight in lean rats and genetically obese mice.

Sertraline was found to inhibit weight gain and decrease food intake without affecting locomotion in rats and genetically obese (ob/ob) mice. Doses of 10, 17.8, and 32 mg/kg, administered intraperitoneally, (bid) significantly reduced the time rats spent in contact with their feeders and body weight in a dose-related manner. During a 5-d bid treatment regimen, vehicle-treated rats gained 37 +/- 3 g (mean +/- SEM), whereas animals treated with 32 mg sertraline/kg lost 34 +/- 4 g. The effects of sertraline on feeding and body weight in rats appeared to be specific because locomotor activity was not altered. In ob/ob mice, sertraline (44 mg/kg, ip, bid) lowered body weight relative to vehicle-treated controls for the duration of a 12-d study. There was no evidence for tolerance to the hypophagic and weight-loss effects of sertraline during either of the chronic dosing studies. These results suggest a potential role for sertraline in the treatment of human obesity.

Structure-activity relationship of quinazolinedione inhibitors of calcium-independent phosphodiesterase.

A series of quinazolinediones and azaquinazolinediones is described which possess potent inhibitory activity toward the calcium-independent phosphodiesterase enzyme (CaIPDE). In vivo testing showed that this in vitro activity translates to animal models predictive of chronic diseases such as depression and inflammation. These results support the hypothesis that inhibition of CaIPDE may lead to useful activity in such chronic diseases.

Calcium-independent phosphodiesterase inhibitors as putative antidepressants: [3-(bicycloalkyloxy)-4-methoxyphenyl]-2-imidazolidinones.

The synthesis and biological properties of a novel series of selective calcium-independent phosphodiesterase inhibitors are described. These compounds also inhibit the specific binding of [3H]rolipram to rat brain membranes and exhibit efficacy in preclinical models of antidepressant activity in mice, such as reducing immobility in the forced-swim test and reversing reserpine-induced hypothermia. Imidazolidinones 4 and 16 were found to be the most potent compounds studied.

Exogenous tryptophan increases synthesis, storage, and intraneuronal metabolism of 5-hydroxytryptamine in the rat hypothalamus.

The effects of tryptophan administration on neurochemical estimates of synthesis [5-hydroxytryptophan (5-HTP) accumulation following administration of a decarboxylase inhibitor], storage [5-hydroxytryptamine (5-HT) concentrations], and metabolism [5-hydroxyindoleacetic acid (5-HIAA) concentrations] of 5-HT in selected regions of the hypothalamus were determined using HPLC coupled to an electrochemical detector. Tryptophan methyl ester HCl (30-300 mg/kg i.p.) produced a dose-dependent increase in the rate of 5-HTP accumulation throughout the hypothalamus but had no effect on the rate of accumulation of 3,4-dihydroxyphenylalanine. Peak 5-HTP levels were attained by 30 min following administration of tryptophan (100 mg/kg i.p.) and were maintained for an additional 60 min. Tryptophan also produced concomitant dose-dependent increases in 5-HT and 5-HIAA concentrations in these same regions without changes in the 5-HIAA/5-HT ratio. These results indicate that exogenous tryptophan administration selectively increases the synthesis, storage, and metabolism of 5-HT in the hypothalamus without altering the synthesis of catecholamines. Inhibition of 5-HT uptake with chlorimipramine or fluoxetine produced modest (10-40%) reductions in 5-HIAA concentrations throughout the hypothalamus, revealing that only a minor portion of 5-HIAA is derived from released and recaptured 5-HT, whereas the major portion of this metabolite reflects intraneuronal metabolism of unreleased 5-HT. In both chlorimipramine- and fluoxetine-treated rats, 5-HIAA concentrations were significantly increased by tryptophan administration, indicating that the increase in synthesis of 5-HT following precursor loading is accompanied by an increase in the intraneuronal metabolism of 5-HT.

Comparative effects of the neurotoxins N-chloroethyl-N-ethyl-2-bromobenzylamine hydrochloride (DSP4) and 6-hydroxydopamine on hypothalamic noradrenergic, dopaminergic and 5-hydroxytryptaminergic neurons in the male rat.

The intracerebroventricular (i.c.v.) administration of 6-hydroxydopamine (6-OHDA; 50 micrograms X 3) and the systemic administration of DSP4 (50 mg/kg X 2; i.p.), alone and in combination, were compared for their abilities to alter the concentrations of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and 5-hydroxytryptamine (5-HT) in selected hypothalamic and extra-hypothalamic (striatum, frontal cortex, hippocampus) regions of the male rat brain. DSP4 markedly lowered NE concentrations in extrahypothalamic regions, and within the hypothalamus produced a mild and variable reduction of NE without altering concentrations of DA, DOPAC or 5-HT. 6-OHDA markedly lowered NE concentrations in all brain regions, but was without effect on DA, DOPAC and 5-HT concentrations in any region analyzed. Combined treatment with DSP4 and 6-OHDA did not produce additional effects on levels of NE, DA and DOPAC over either drug alone, but did cause a mild reduction of 5-HT in several brain regions. These results indicate that systemic treatments with DSP4 per se are not as effective as i.c.v. 6-OHDA in depleting NE in the hypothalamus, and that when the two neurotoxins are administered there appears to be some destruction of 5-HT neurons.

The effects of continuous androgen secretion on the hypothalamic-pituitary axis in woman: evidence from a luteinized thecoma of the ovary.

Hyperandrogenic states in women are often accompanied by disruption of gonadotropin secretion. However, the role of androgens per se in the pathogenesis of this abnormality is poorly understood. We report a woman with a virilizing ovarian tumor in whom the effects of continuous androgen secretion on the hypothalamic-pituitary axis were investigated in detail. A 29-yr-old woman with previously normal reproductive function, including prior fertility, was evaluated for amenorrhea and hirsutism. She had elevated peripheral serum levels of testosterone (T; 337-500 ng/dl) and androstenedione (A; 258-353 ng/dl). Her serum LH level was above the normal follicular phase range and was hyperresponsive to LHRH, whereas the FSH level was below normal early follicular phase levels and increased minimally in response to LHRH. A luteinized thecoma of the left ovary, shown by catherization of the ovarian venous blood to be secreting both T and A, was removed. Postoperatively, serum T and A levels returned to normal, and the patient had a normal ovulatory menstrual cycle in the 30 days after the operation, documented by daily determinations of plasma estradiol, progesterone, and gonadotropin levels. A repeat LHRH test in the follicular phase of the second postoperative menstrual cycle was completely normal. This case indicates that the characteristic abnormalities of gonadotropin secretion observed in hyperandrogenic states such as polycystic ovarian disease can result from chronic androgen secretion by an ovarian tumor and that normal folliculogenesis and gonadotropin secretion can be promptly restored by the elimination of the androgen excess.

Differential effects of d-amphetamine, beta-phenylethylamine, cocaine and methylphenidate on the rate of dopamine synthesis in terminals of nigrostriatal and mesolimbic neurons and on the efflux of dopamine metabolites into cerebroventricular perfusates of rats.

The in vivo effects of four psychomotor stimulants (d-amphetamine, beta-phenylethylamine, cocaine and methylphenidate) were determined on: 1) the rate of dopamine (DA) synthesis, as measured by the accumulation of dihydroxyphenylalanine (DOPA) after aromatic L-amino acid decarboxylase inhibition, in the striatum (terminals of nigrostriatal neurons) and in the nucleus accumbens and olfactory tubercle (terminals of mesolimbic neurons) and 2) the efflux of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) into cerebroventricular perfusates of conscious, freely-moving rats. d-Amphetamine and beta-phenylethylamine produced biphasic responses with lower doses of each drug increasing both the efflux of DOPAC and the rate of DA synthesis in the striatum. Higher doses of each drug either had no effect or actually decreased the efflux of DOPAC and also decreased the rate of DA synthesis in the striatum. On the other hand, cocaine and methylphenidate only decreased the efflux of DOPAC and the rate of DA synthesis in the striatum. The effects of the drugs on the rate of DA synthesis in the nucleus accumbens and olfactory tubercle were similar to, but less pronounced than those seen in the striatum. These results are consistent with the following suggestions: 1) low doses of d-amphetamine and beta-phenylethylamine facilitate the neuronal release of DA while higher doses of both drugs facilitate release and inhibit neuronal reuptake of the amine, and 2) cocaine and methylphenidate preferentially block the neuronal reuptake of DA.

Immunity to antigens associated with primate C-type oncoviruses in pregnant women.

Cell-mediated and humoral immune responses against antigens associated with primate C-type oncoviruses were evaluated in humans by microcytotoxicity and radioimmunoprecipitation assays. Five of six women tested sequentially during pregnancy developed selective cell-mediated reactivity against baboon endogenous virus (BEV)--infected human fibroblasts. Responsiveness peaked during the second and third trimesters and corresponded temporally with elevated antibody levels to BEV antigens. Similar cell-mediated reactivity was not observed in nonpregnant individuals. Selective cell-mediated reactivity directed against cells infected with the simian sarcoma virus-simian sarcoma associated virus complex (SSV--SSAV) was observed in four of 20 healthy adults (three of 14 nonpregnant, one of six pregnant). These observations suggest that cell-mediated reactivity against primate C-type oncoviruses is occasionally detected in healthy nonpregnant adults, but that during pregnancy both cell-mediated and humoral reactivity against BEV may become selectively expressed.