Administration Of SCH Research Articles

The dopaminergic stabilizer pridopidine increases neuronal activity of pyramidal neurons in the prefrontal cortex

The dopaminergic stabilizer pridopidine demonstrates state-dependent effects on locomotor activity, counteracting both hypo- and hyperactivity in rats. Pridopidine has been shown to display both functional dopamine D2 receptor antagonist properties and increase in biomarkers associated with NMDA-mediated glutamate transmission in the frontal cortex. To further characterise the effects of pridopidine on prefrontal cortex (PFC) neurons, a series of in vivo electrophysiological studies were performed in urethane-anaesthetised rats. Pridopidine, administered at doses from 10 to 60 mg/kg (i.v.), dose dependently increased pyramidal cell firing in the majority of the neurons tested. Pridopidine induced a significant increase of 162 % in mean firing activity of PFC neurons, versus initial basal firing activity as the cumulative dose of 30 mg/kg, i.v., was administered. This enhancement of activity was due to increased firing frequency of already spontaneously active neurons, rather than an increase in population activity. The increase was partially reversed or prevented by a sub-threshold dose of the dopamine D1 receptor antagonist SCH23390 (0.5 mg/kg, i.v.). Microiontophoretic application of pridopidine had only moderate activating effects. The selective dopamine D1 receptor agonist A-68930 also had limited effects when administered by microiontophoretic application, but exerted a dose dependent (0.2-3 mg/kg, i.v.) activation of firing in the majority of neurons tested (10/16). However, inhibition of firing by systemic administration of A-68930 was also observed in a subgroup of neurons (6/16). Both activation and inhibition of firing induced by systemic administration of A-68930 were reversed by the systemic administration of SCH23390. The present data suggests that pridopidine enhances pyramidal cell firing via an indirect dopamine D1 receptor-mediated mechanism. These effects of pridopidine may serve to strengthen the cortico-striatal communication and to improve motor control in Huntington's disease for which pridopidine is currently in development.

Effects of Blockade of D1/D2 Dopamine Receptors on the Behavior of Rats with Different Levels of Impulsivity and Self-Control

Rats classified on the basis of preliminary experiments into “self-controlled” and “impulsive” groups were given selective D1/D2 dopamine receptor blockers (SCH 23390 and raclopride respectively). The concepts of impulsivity and self-control relate to preferences in the choice between a more valuable but timedelayed reinforcement and a less valuable but immediate reinforcement. The effects of administration of these agents on the selection of reinforcements of different value were studied: the greater time-delayed reinforcement or the smaller immediate reinforcement. The numbers of refusals to make a choice and the latent periods of responses were also measured. D1/D2 receptor blockers had different actions in the different groups of animals. In rats of the self-controlled group, both blockers produced statistically significant (p < 0.05) increases in the number presses on the pedal delivering the less valuable but immediate reinforcement, providing evidence of an increase in impulsivity. In impulsive animals, the behavioral strategy underwent virtually no change. Administration of SCH 23390 increased the number of missed presses in both groups, this being particularly marked in self-controlled animals. Raclopride also increased the number of missed reactions in self-controlled rats, though this action was seen only one day after administration. Administration of the dopamine blockers used here led to increases in the latent periods of responses, but only in impulsive animals.

Medial prefrontal cortex lesions impair decision-making on a rodent gambling task: Reversal by D1 receptor antagonist administration

Decision-making is a complex cognitive process that is impaired in a number of psychiatric disorders. In the laboratory, decision-making is frequently assessed using “gambling” tasks that are designed to simulate real-life decisions in terms of uncertainty, reward and punishment. Here, we investigate whether lesions of the medial prefrontal cortex (PFC) cause impairments in decision-making using a rodent gambling task (rGT). In this task, rats have to decide between 1 of 4 possible options: 2 options are considered “advantageous” and lead to greater net rewards (food pellets) than the other 2 “disadvantageous” options. Once rats attained stable levels of performance on the rGT they underwent sham or excitoxic lesions of the medial PFC and were allowed to recover for 1 week. Following recovery, rats were retrained for 5 days and then the effects of a dopamine D1-like receptor antagonist (SCH23390) or a D2-like receptor antagonist (haloperidol) on performance were assessed. Lesioned rats exhibited impaired decision-making: they made fewer advantageous choices and chose the most optimal choice less frequently than did sham-operated rats. Administration of SCH23390 (0.03mg/kg), but not haloperidol (0.015–0.03mg/kg) attenuated the lesion-induced decision-making deficit. These results indicate that the medial PFC is important for decision-making and that excessive signaling at D1 receptors may contribute to decision-making impairments.

Concerted Action of ANP and Dopamine D1-Receptor to Regulate Sodium Homeostasis in Nephrotic Syndrome

The edema formation in nephrotic syndrome (NS) is associated with a blunted response to atrial natriuretic peptide (ANP). The natriuretic effects of ANP have been related to renal dopamine D1-receptors (D1R). We examined the interaction between ANP and renal D1R in rats with puromycin aminonucleoside-induced NS (PAN-NS). Urinary sodium, cyclic guanosine monophosphate (cGMP) excretion, and D1R protein expression and localization in renal tubules were evaluated in PAN-NS and control rats before and during volume expansion (VE). The effects of zaprinast (phosphodiesterase type 5 inhibitor), alone or in combination with Sch-23390 (D1R antagonist), were examined in both groups. The increased natriuresis and urinary cGMP excretion evoked by acute VE were blunted in PAN-NS despite increased levels of circulating ANP. This was accompanied in PAN-NS by a marked decrease of D1R expression in the renal tubules. Infusion of zaprinast in PAN-NS resulted in increased urinary excretion of cGMP and sodium to similar levels of control rats and increased expression of D1R in the plasma membrane of renal tubular cells. Combined administration of Sch-23390 and zaprinast prevented natriuresis and increased cGMP excretion induced by zaprinast alone. We conclude that D1R may play a major role in the ANP resistance observed in PAN-NS.

Dopamine Regulation of Gonadotropin-Releasing Hormone Neuron Excitability in Male and Female Mice

Numerous in vivo studies have shown that dopamine is involved in the regulation of LH secretion in mammals. However, the mechanisms through which this occurs are not known. In this study, we used green fluorescent protein-tagged GnRH neurons to examine whether and how dopamine may modulate the activity of adult GnRH neurons in the mouse. Bath-applied dopamine (10-80 μm) potently inhibited the firing of approximately 50% of GnRH neurons. This resulted from direct postsynaptic inhibitory actions through D1-like, D2-like, or both receptors. Further, one third of GnRH neurons exhibited an increase in their basal firing rate after administration of SCH23390 (D1-like antagonist) and/or raclopride (D2-like antagonist) indicating tonic inhibition by endogenous dopamine in the brain slice. The role of dopamine in presynaptic modulation of the anteroventral periventricular nucleus (AVPV) γ-aminobutyric acid/glutamate input to GnRH neurons was examined. Exogenous dopamine was found to presynaptically inhibit AVPV-evoked γ-aminobutyric acid /glutamate postsynaptic currents in about 50% of GnRH neurons. These effects were, again, mediated by both D1- and D2-like receptors. Neither postsynaptic nor presynaptic actions of dopamine were found to be different between diestrous, proestrous, and estrous females, or males. Approximately 20% of GnRH neurons were shown to receive a dopaminergic input from AVPV neurons in male and female mice. Together, these observations show that dopamine is one of the most potent inhibitors of GnRH neuron excitability and that this is achieved through complex pre- and postsynaptic actions that each involve D1- and D2-like receptor activation.

Self-administration of propofol is mediated by dopamine D1 receptors in nucleus accumbens in rats

As a widely used intravenous short-acting anesthetic, propofol is recently indicated by clinical and animal studies for its abuse potential, but the mechanism underlying propofol abuse is largely unknown. This study examined the contribution of dopamine receptor subtype (D1 and D2 receptors) and neuroanatomical locus (i.e. nuclear accumbens) in the maintenance of propofol self-administration in rats. After the acquisition and maintenance of self-administration of propofol (1.7mg/kg/infusion) under a fixed ratio (FR1) schedule of reinforcement over 14days, rats were treated by either intraperitoneal injection or intra-nucleus accumbens (NAc) injection of D1 receptor antagonist (SCH23390) or D2 receptor antagonists (spiperone and eticlopride) 10min prior to the subsequent propofol self-administration. We demonstrated (i) systemic administration of SCH23390 (10, 30, 100μg/kg, i.p.) dose-dependently decreased the rate of propofol-maintained self-administration, suggesting a critical role of the D1 receptor in mediating propofol self-administration; (ii) the blockade of the propofol self-administration by SCH23390 was specific since spiperone and eticlopride did not affect propofol self-administration and SCH23390 at these doses did not affect food-maintained responding under an FR5 schedule; (iii) intra-accumbenal injection of SCH23390 (2.5μg/site) but not eticopride (3.0μg/site) attenuated the propofol self-administration, localizing nuclear accumbal D1 receptors as a critical locus in the reinforcement of propofol. Together, these findings provide the first direct evidence that D1 receptors in nuclear accumbens play an important role in the maintenance of propofol self-administration.

Orexin A in the ventral tegmental area induces conditioned place preference in a dose-dependent manner: Involvement of D1/D2 receptors in the nucleus accumbens

It has been shown that orexin A in the ventral tegmental area (VTA) is necessary for development of morphine place preference. Additionally, D1 and D2 dopamine receptors in the nucleus accumbens (NAc) have critical roles in motivation and reward. However, little is known about the function of orexin in conditioned place preference (CPP) in rats and involvement of D1/D2 receptors in the NAc. In the present study, we investigated the effect of direct administration of orexin A into the VTA, and examined the role of intra-accumbal dopamine receptors in development (acquisition) of reward-related behaviors in the rats. Adult male Wistar rats were unilaterally implanted by two separate cannulae into the VTA and NAc. The CPP paradigm was used, and, conditioning score and locomotor activity were recorded by Ethovision software. The results showed that unilateral intra-VTA administration of orexin A (27, 53 and 107ng/0.3μl saline) during conditioning phase induced CPP in a dose-dependent manner. The most effective dose of intra-VTA orexin-A in eliciting CPP was 107ng. However, intra-NAc administration of SCH 23390 (0.25, 1 and 4μg/0.5μl saline), a D1 receptor antagonist, and sulpiride (0.25, 1 and 4μg/0.5μl DMSO), a D2 receptor antagonist, inhibited the development of orexin-induced CPP. The inhibitory effect of D2 but not D1 receptor antagonist was exerted in a dose-dependent manner. It is supposed that the activation of VTA dopaminergic neuron by orexin impresses the D2 receptors more than D1 receptors in the NAc.

Suppression of Self-Stimulation of the Lateral Hypothalamus by Opiates and Opioids Administered into the Central Nucleus of the Amygdala in Rats

Bipolar electrodes were implanted into the lateral hypothalamus of male Wistar rats for investigation of self-stimulation responses in a Skinner box and microcannulae were implanted into the central nucleus of the amygdala for administration of pharmacological agents. Blockade of corticoliberin receptors (astressin, 1 μg) or influx Na + currents (lidocaine, 1 μg) by intra-amygdalar administration led to 29–55 % decreases in lateral hypothalamus self-stimulation responses. Inhibition of D1 and D2 receptors in the amygdala by administration of SCH23390 (1 μm) and sulpiride (1 μg) resulted in lower levels of inhibition of the self-stimulation reaction. On the background of blockade of corticoliberin receptors (astressin), dopamine receptors (sulpiride), and the influx Na + currents of amygdalar neurons (lidocaine), phenamine (1 mg/kg) and sodium ethaminal (5 mg/kg) retained their psychoactivating effects on self-stimulation (+30–37 %), while fentanyl (0.1 mg/kg) and leu-enkephalin (0.1 mg/kg) lost this effect. Fentanyl produced moderate activation of self-stimulation only after blockade of D1 receptors with SCH23390. On the background of blockade of corticoliberin receptors, leu-enkephalin potentiated its depressant action on selfstimulation reactions (–89 %). Thus, suppression of the modulatory influences of the amygdala on the hypothalamus blocked the reinforcing properties of opiates (fentanyl) and opioids (leu-enkephalin) without affecting the psychoactivating influence of the psychostimulators phenamine and the barbiturate sodium ethaminal.

Roles of dopamine D1 and D2 receptors in the acquisition and expression of fat-conditioned flavor preferences in rats

Sugars and fats elicit innate and learned flavor preferences with the latter mediated by flavor–flavor (orosensory) and flavor–nutrient (post-ingestive) processes. Systemic dopamine (DA) D1 (SCH23390: SCH) and D2 (raclopride: RAC), but not opioid antagonists blocked the acquisition and expression of flavor–flavor preferences conditioned by sugars. In addition, systemic D1, but not D2 or opioid antagonists blocked the acquisition of flavor–nutrient preferences conditioned by intragastric (IG) sugar infusions. Given that DA antagonists reduce fat intake, the present study examined whether systemic D1 or D2 antagonists altered the acquisition and/or expression of conditioned flavor preferences (CFP) produced by pairing one novel flavor (CS+, e.g., cherry) with a 3.5% corn oil (CO: fat) solution relative to another flavor (CS−, e.g., grape) paired with a 0.9% CO solution. In an expression study, food-restricted rats were trained to drink either flavored 3.5% or 0.9% CO solutions on alternate days. Subsequent two-bottle tests with the CS+ and CS− flavors mixed in 0.9% CO solutions occurred 0.5h after systemic administration of vehicle (VEH), SCH (50–800nmol/kg) or RAC (50–800nmol/kg). The rats displayed a robust CS+ preference following VEH treatment (87–88%) the expression of which was attenuated by treatment with moderate doses of RAC, and to a lesser degree, SCH. In an acquisition study, six groups of rats received VEH, SCH (25, 50, 200nmol/kg) or RAC (50, 200nmol/kg) 0.5h prior to 1-bottle training trials with CS+ flavored 3.5% and CS− flavored 0.9% (CS−) CO solutions. A seventh Limited VEH group was trained with its training intakes limited to that of the SCH and RAC groups. Subsequent two-bottle tests were conducted with the CS+ and CS− flavors presented in 0.9% CO without injections. Significant and persistent CS+ preferences were observed in VEH (75–82%), Limited VEH (70–88%), SCH25 (75–84%), SCH50 (64–87%), SCH200 (78–91%) and RAC200 (74–91%) groups. In contrast, the group trained with RAC50 displayed a significant initial CS+ preference (76%) which declined over testing to 61%. These data indicate limited DA D1 and D2 receptor signaling involvement in the expression and acquisition of a fat-CFP relative to previous robust effects for sugar-CFP.

Dopaminergic modulation of nitric oxide synthase activity in subregions of the rat nucleus accumbens

Nitric oxide (NO) is a gaseous neurotransmitter synthesized in the nucleus accumbens (NAc) by aspiny interneurons containing neuronal NO synthase (nNOS). nNOS activity is readily assayed using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) staining and is believed to be regulated by activation of dopamine (DA) D1- and D2-like receptors. However, the role of DA transmission in the regulation of nNOS activity in identified subregions of the NAc remains unexplored. In this study, the impact of pharmacological manipulations of D1, D2, and NMDA receptors on nNOS activity was determined using optical density measures of NADPH-d staining preformed in multiple subdivisions (core, medial shell, intermediate shell, and lateral shell) of the NAc. Awake behaving rats received systemic administration of vehicle and/or the following drugs ~25 min prior to tissue harvesting: the nNOS inhibitor N(G) -propyl-L-arginine (NPA), the D1 receptor agonist SKF 81297, the D1 receptor antagonist SCH 23390, the D2 receptor agonist quinpirole (QNP), the D2 receptor antagonist eticlopride (ETI), or the NMDA receptor antagonist 3-((±)2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP). In vehicle-treated animals, a distinct medial-lateral histochemical gradient of NADPH-d staining was observed, which was characterized by moderate staining in the core and medial shell and more robust staining in the intermediate and lateral shell. Administration of NPA, SCH 23390, QNP, and CPP attenuated staining preferentially in the intermediate and lateral shell. SKF 81297 and ETI administration consistently increased staining in the medial shell in a manner, which was attenuated following pretreatment with SCH 23390, QNP, NPA, and CPP. These observations demonstrate that nNOS activity measured in distinct subregions of the NAc is differentially modulated by DA D1 and D2 receptor activation. Moreover, these findings demonstrate for the first time that DA D1 and D2 receptor activation regulates the facilitatory influence of glutamatergic transmission on nNOS activity in the NAc medial shell via facilitation (D1) or suppression (D2) of NMDA receptor function.

SCH23390, a dopamine D1 receptor antagonist, suppressed scratching behavior induced by compound 48/80 in mice

To clarify the mechanisms by which compound 48/80 (C48/80) induces scratching behavior, the involvement of dopamine D(1) receptors was investigated. The intracisternal (i.t.) administration of SCH23390 (1.0 μg), a selective dopamine D(1) receptor antagonist, significantly decreased C48/80-induced scratching behavior in mice. These results suggest that dopamine D(1) receptors contribute to scratching behavior or the itch sensation induced by subcutaneous injection of C48/80 in mice. Co-administration of SCH23390 and C48/80 enhanced c-fos immunoreactivities in the peduncular part of the lateral hypothalamus (PLH), whereas the immunoreactivities in the other groups were unchanged. The dopaminergic system may be playing an important role in the suppression of C48/80-induced scratching behavior by SCH23390.

Functional correlation between GABAergic and dopaminergic systems of dorsal hippocampus and ventral tegmental area in passive avoidance learning in rats

The aim of the present study was to investigate the existence of possible functional correlation between GABA-A and dopamine (DA) receptors of the dorsal hippocampus and the ventral tegmental area (VTA) in passive avoidance learning. Two guide cannulas were stereotaxically implanted in the CA1 region of the dorsal hippocampus and the VTA of male Wistar rats. In order to measure memory retrieval, the animals were trained in a step-through type passive avoidance task and tested 24 h after training. Post-training intra-CA1 administration of a GABA-A receptor agonist, muscimol (0.01-0.02 μg/rat) dose-dependently impaired memory retrieval. Post-training intra-VTA administration of SCH23390 (a dopamine D1 receptor antagonist; 0.1-0.8 μg/rat) or sulpiride (a D2 receptor antagonist; 0.5-1.5 μg/rat) decreased the inhibitory effect of muscimol (0.02 μg/rat, intra-CA1) on memory retrieval. Intra-VTA administration of the same doses of SCH23390, but not sulpiride, decreased the step-through latencies. On the other hand, post-training administration of muscimol (0.02 μg/rat) into the VTA inhibited memory retrieval. The administration of SCH23390 (0.01-0.2 μg/rat) or sulpiride (0.1-1 μg/rat) into the CA1 region, immediately after training, had no effect on memory retrieval. Furthermore, the amnesic effect of intra-VTA administration of muscimol was significantly decreased by intra-CA1 administration of sulpiride (0.5 and 1 μg/rat, intra-CA1), but not SCH23390. The practical conclusion is that the relationship between the hippocampus and the VTA may regulate memory formation in passive avoidance learning. Also, the correlation between the hippocampus and VTA by a dopaminergic system may be involved in mediating muscimol-induced amnesia.

Roles of D1-like dopamine receptors in the nucleus accumbens and dorsolateral striatum in conditioned avoidance responses

Aversively motivated learning is more poorly understood than appetitively motivated learning in many aspects, including the role of dopamine receptors in different regions of the striatum. The present study investigated the roles of the D1-like DA receptors in the nucleus accumbens (NAc) and dorsolateral striatum (DLS) on learning and performance of conditioned avoidance responses (CARs). Adult male Wistar rats received intraperitoneal (i.p.), intra-NAc, or intra-DLS injections of the D1 dopamine receptor agonist SKF 81297 or the D1 receptor antagonist SCH 23390 20 min before or immediately after a training session in the CAR task two-way active avoidance, carried out 24 h before a test session. Pre-training administration of SCH 23390, but not SKF 81297, caused a significant decrease in the number of CARs in the test, but not in the training session, when injected into the DLS, or in either session when injected into the NAc. It also caused a significant increase in the number of escape failures in the training session when injected into the NAc. Systemic administration caused a combination of these effects. Post-training administrations of these drugs caused no significant effect. The results suggest that the D1-like receptors in the NAc and DLS play important, though different, roles in learning and performance of CAR.

Precision and Accuracy in the Quantitative Analysis of Biological Samples by Accelerator Mass Spectrometry: Application in Microdose Absolute Bioavailability Studies

Determination of the pharmacokinetics and absolute bioavailability of an experimental compound, SCH 900518, following a 89.7 nCi (100 μg) intravenous (iv) dose of (14)C-SCH 900518 2 h post 200 mg oral administration of nonradiolabeled SCH 900518 to six healthy male subjects has been described. The plasma concentration of SCH 900518 was measured using a validated LC-MS/MS system, and accelerator mass spectrometry (AMS) was used for quantitative plasma (14)C-SCH 900518 concentration determination. Calibration standards and quality controls were included for every batch of sample analysis by AMS to ensure acceptable quality of the assay. Plasma (14)C-SCH 900518 concentrations were derived from the regression function established from the calibration standards, rather than directly from isotopic ratios from AMS measurement. The precision and accuracy of quality controls and calibration standards met the requirements of bioanalytical guidance (U.S. Department of Health and Human Services, Food and Drug Administration, Center for Drug Evaluation and Research, Center for Veterinary Medicine. Guidance for Industry: Bioanalytical Method Validation (ucm070107), May 2001. http://www.fda.gov/downloads/Drugs/GuidanceCompilanceRegulatoryInformation/Guidances/ucm070107.pdf ). The AMS measurement had a linear response range from 0.0159 to 9.07 dpm/mL for plasma (14)C-SCH 900158 concentrations. The CV and accuracy were 3.4-8.5% and 94-108% (82-119% for the lower limit of quantitation (LLOQ)), respectively, with a correlation coefficient of 0.9998. The absolute bioavailability was calculated from the dose-normalized area under the curve of iv and oral doses after the plasma concentrations were plotted vs the sampling time post oral dose. The mean absolute bioavailability of SCH 900518 was 40.8% (range 16.8-60.6%). The typical accuracy and standard deviation in AMS quantitative analysis of drugs from human plasma samples have been reported for the first time, and the impact of these parameters on quantitative analysis was further assessed using the Z factor. The use of the lowest achievable LLOQ(Z=0) derived from statistical analysis of the control and low-concentration standards for AMS measurements is proposed in future studies.

Functional role of hypothalamic D1 and D2 receptors in organization of some forms of behavior of the common frog Rana temporaria

Dopamine is one of the most ancient, widely spread neurotransmitters. It performs a great number of neuromodulator effects in the vertebrates CNS. For the last few years there considerably increases an interest in study of functional role of this neurotransmitter in regulation of various forms of behavior of poikilothermal vertebrates. The present work deals with study of the role of the dopaminergic system, specifically of the hypothalamic dopaminergic system in providing some behavioral frog reactions. We studied behavior of the animals in the “open field” before and after administration to them of antagonists of D1 (SCH 23390) and D2 (haloperidol) receptors as well as of animals with destroyed anterior and posterior parts of hypothalamus. Administration of SCH 23390 to intact frogs caused a statistically significant decrease in the number of exploratory reactions and goal-oriented jumps, whereas haloperidol only moderately increased the number of the above reactions. Destruction of the posterior part of hypothalamus suppressed essentially all kinds of activity, while destruction of the anterior part inhibited them completely. Antagonist of D12 and D2 receptors of dopamine little changed the initial motor and emotional activity of the operated animals. The obtained data are discussed in terms of evolutionary origin of D1 and D2 receptors in vertebrates and allow concluding that D1 and D2 receptors of hypothalamic dopamine of the common frog are located predominantly in the anterior hypothalamic areas and that their effect on behavior can be mediated and is associated with other brain neurotransmitter systems in such brain structures as lateral hypothalamus, locus coereleus, and striatum that provide different aspects of wakefulness of amphibians.

The anxiolytic-like profile of the nociceptin receptor agonist, endo-8-[bis(2-chlorophenyl)methyl]-3-phenyl-8-azabicyclo[3.2.1]octane-3-carboxamide (SCH 655842): Comparison of efficacy and side effects across rodent species

The endogenous opioid-like peptide, nociceptin, produces anxiolytic-like effects that are mediated via the nociceptin (NOP) receptor. Similarly, synthetic, non-peptide NOP agonists produce robust anxiolytic-like effects although these effects are limited by marked side effects. In the present studies, the effects of a novel NOP receptor agonist, SCH 655842, were examined in rodent models sensitive to anxiolytic drugs and tests measuring potential adverse affects. Oral administration of SCH 655842 produced robust, anxiolytic-like effects in three species, i.e., rat, guinea pig, and mouse. Specifically, SCH 655842 was effective in rat conditioned lick suppression (3–10 mg/kg) and fear-potentiated startle (3–10 mg/kg) tests, a guinea pig pup vocalization test (1–3 mg/kg), as well as in mouse Geller–Seifter (30 mg/kg) and marble burying (30 mg/kg) tests. The anxiolytic-like effect of SCH 655842 in the conditioned lick suppression test was attenuated by the NOP antagonist, J-113397. In mice, SCH 655842 reduced locomotor activity and body temperature at doses similar to the anxiolytic-like dose and these effects were absent in NOP receptor knockout mice. In rats, SCH 655842 did not produce adverse behavioral effects up to doses of 70–100 mg/kg. Pharmacokinetic studies in the rat confirmed dose-related increases in plasma and brain levels of SCH 655842 across a wide oral dose range. Taken together, SCH 655842 may represent a NOP receptor agonist with improved tolerability compared to other members of this class although further studies are necessary to establish whether this extends to higher species.

Highlights of This Issue

Targeted CHK1 inhibition is an attractive approach with the potential for rational combination with multiple chemotherapies. The critical issue is the therapeutic index in combination, necessitating careful selection of compounds for progression. Guzi and colleagues identified SCH 900776 using a pathway-oriented functional approach and targeted medicinal chemistry. Mechanism-based biomarkers were used to quantitatively assay checkpoint override phenotypes. This strategy exposed the risk of functional antagonism, highlighting a need for sufficient CHK1 selectivity. The biomarkers were translated to preclinical animal species, allowing in vivo assessment of SCH 900776 mechanism engagement and tolerability. In xenograft models, doses of SCH 900776 associated with robust biomarker activation, and improved tumor response was not associated with enhanced toxicity of gemcitabine on hematological parameters in BALB/c mice. Administration of SCH 900776 presents a clinical opportunity to selectively enhance cell death responses in tumor cell backgrounds.Since its discovery, endostatin, an important regulator of angiogenesis, has failed to have significant clinical impact. In this issue, Shin and colleagues enhance endostatin performance by tethering a mutant human endostatin to an anti-HER2 antibody. The antibody-endostatin fusion protein has a longer half life than endostatin, localizes to the tumor, and shows superior antiangiogenic efficacy in vitro and antitumor activity in vivo in tumor xenograft models. This promising approach points the way to more effective endostatin use in the clinic for breast cancer and other solid tumors and represents a new class of antiangiogenic agents.Understanding mechanisms on leukemia differentiation may provide help for designing safe and specific differentiation therapy to treat leukemia. Yang and colleagues report that the induction of melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) and IL-24 delE5, a mda-7/IL-24 splice variant, contributes to 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced monocytic differentiation, and they also show the specific differentiation induction roles of mda-7/IL-24 and IL-24 delE5 in acute myeloid leukemia (AML) cells. These studies characterize mda-7/IL-24 and IL-24 delE5 as novel genes associated with leukemic cell differentiation and bring new insights into the regulation of AML cell differentiation.Genetic screens identifying molecules whose inactivation kills cancer cells carrying a specific genetic alteration (synthetic lethality) are widely used to select new therapeutic targets. Hattori and colleagues show an important limitation of synthetic lethal screens. They identify the checkpoint kinase CHK1 as a therapeutic target in cancers lacking the tumor suppressor BRCA2. However, CHK1 inhibition is rendered ineffective by additional mutations like activated KRAS or mutant TP53 typical of pancreatic cancers arising in BRCA2 mutation carriers. Gemcitabine overcomes this resistance. Synthetic lethal screens that fail to consider the full genetic context of specific malignancies may not identify valid therapeutic targets.

Differential response of A 68930 and sulpiride in stress-induced gastric ulcers in rats

Dopamine is linked to gastrointestinal functions. However, its exact nature in stress-induced gastric pathology is still not clear. In the present study, an attempt has been made to identify the effects of dopamine in stress-induced gastric ulcers, and concurrent alterations in various ulcer-influencing factors such as plasma corticosterone levels, gastric mucosal PGE 2 content and proton pump activity. The dopamine D 1 receptor agonist (A 68930) and antagonist (SCH 23390), and D 2 receptor agonist (quinpirole) and antagonist (sulpiride) were used to evaluate their effects on acute stress (single immobilization for 150 min) and chronic unpredictable stress (two different types of stressors for 7 days) induced gastric ulcers in rats. Acute and chronic unpredictable stress significantly increased the gastric ulcer severity, adrenal hypertrophy and corticosterone levels, while gastric mucosal dopamine levels were decreased. Pretreatment of sulpiride (60 mg/kg) significantly reverted the acute stress-induced alterations, while A 68930 (0.25 mg/kg) significantly restored the acute and chronic unpredictable stress-induced alterations. In contrast, administration of SCH 23390 (0.1–0.5 mg/kg) and quinpirole (0.1–0.5 mg/kg) failed to alter acute stress-induced alterations. Further, A 68930 and sulpiride showed different response on proton pump inhibition under in-vitro condition. A 68930 (10–50 μg/ml) inhibited the gastric H + K +-ATPase activity comparable to positive control omeprazole, while sulpiride (10–50 μg/ml) had no effect. A 68930 also normalized the decreased gastric PGE2 content observed during chronic unpredictable stress. The histopathological evaluation of gastric mucosal tissue supported the observations regarding the gastroprotective effect of sulpiride during acute stress and of A 68930 during both acute and chronic unpredictable stress conditions. Our results provide important insights into the mechanism of dopamine-regulated pathways, which cause an overall pathophysiology of gastric stress ulcers and implicating the importance of D 1 agonist in ulcer protection. Thus, current study highlights the need to evaluate anti-stress and anti-ulcer agents in terms of their ability to modulate dopaminergic transmissions.

Abstract 4533: In vivo activation of the p53 pathway leading to tumor regression by a novel and potent HDM2 antagonist SCH 1450206

Abstract The HDM2-p53 protein-protein interaction is well characterized through X-ray crystallography. Disrupting this HDM2-p53 protein-protein interaction by a small molecule would therefore release the p53 from the negative inhibition of HDM2 and restore its anti-tumor activities. Peptides, antisense oligonucleotides and small molecules have been identified which disrupt this interaction and result in the stabilization of p53 protein and activation of its downstream targets. We have recently discovered a novel, potent HDM2 antagonist (SCH 1450206) with mechanism-based activity both in vitro and in vivo. Oral administration of SCH 1450206 as a single agent resulted in tumor regression in the SJSA-1 osteosarcoma xenograft model without any observable toxicity. Analysis of the pharmacodynamic markers demonstrated that the anti-tumor activity of SCH 1450206 correlated with the robust activation of p53 pathway in vivo. In addition to its single agent anti-tumor activity, combination of HDM2 antagonist SCH 1450206 with various cytotoxics resulted in further tumor growth inhibition in various human cancer xenograft models. The activation of p53 pathway in vivo targets preferentially to tumor tissues compared to high proliferating and radio sensitive organs of the mouse at the efficacious dose. The lack of single agent toxicity at the efficacious dose and schedule would potentially allow the combination of this type of HDM2 antagonist with other anti-cancer agents at full dose in the clinic. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4533.

Enhancement of oral bioavailability of paclitaxel after oral administration of Schisandrol B in rats

Paclitaxel is a substrate of the efflux transporters such as P-glycoprotein, and is mainly metabolized by the liver. Schisandrol B (Sch B), one of the active components in Schisandra, has been reported to be able to inhibit the activity of P-gp and CYP3A. It might be possible that Sch B would alter the pharmacokinetic behavior of paclitaxel. Therefore, the purpose of this study was to investigate the effect of Sch B on the pharmacokinetics of paclitaxel administered orally and intravenously in rats. Paclitaxel were administered to rats orally (30 mg/kg) or intravenously (0.5 mg/kg) with or without the concomitant administration of Sch B (10 or 25 mg/kg). Oral pharmacokinetic parameters of paclitaxel were significantly altered when pretreated with Sch B. There were significant increases in AUC(0-24h) (from 297.7+/-110.3 to 838.9+/-302.1 h*ng/ml; p<0.05) and C(max) (from 51.7+/-20.1 to 136.4+/-35.5 ng/ml; p<0.05) in the presence of Sch B (25 mg/kg). The pharmacokinetic parameters for i.v. paclitaxel were not significantly affected by Sch B in contrast to that of oral administration. Since the presence of Sch B enhanced the systemic exposure of paclitaxel, their pharmacokinetic interaction should be taken into consideration. As the oral bioavailability of paclitaxel was increased about 3-fold in the presence of Sch B, the concomitant use of Sch B may provide a benefit in the oral delivery of paclitaxel.