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Characterization of a novel and selective V1B receptor antagonist
I.D. Neumann and R. Landgraf (Eds.) Progress in Brain Research, Vol. 170 ISSN 0079-6123 Copyright r 2008 Elsevier B.V. All rights reserved
CHAPTER 40
Characterization of a novel and selective V1B receptor antagonist Mark Craighead1,, Rachel Milne1, Leigh Campbell-Wan2, Lynn Watson1, Jeremy Presland1, Fiona J. Thomson1, Hugh M. Marston2 and Clı´ ona P. MacSweeney2 1
Department of Molecular Pharmacology, Organon Laboratories (a part of the Schering-Plough Corporation), Newhouse, UK 2 Department of Pharmacology, Organon Laboratories (a part of the Schering-Plough Corporation), Newhouse, UK
Abstract: It has been argued that hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is a major biological abnormality in patients suffering from psychiatric conditions such as major depression. Both arginine vasopressin (AVP) and corticotrophin releasing factor (CRF) are responsible for stimulating the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary. CRF is thought to be the predominant secretagogue under normal conditions but AVP may play a more important role in situations of aberrant/chronic stress. Studies in patients suffering from melancholic depression indicate a hyperresponsiveness to agonism at the vasopressin receptor type 1B (V1B); patients display a heightened ACTH release after challenge with the mixed V1B/V2 (vasopressin receptor type 2) agonist desmopressin in comparison to control subjects. A V1B antagonist has been developed which has significant selectivity for the human V1B receptor over the other members of the vasopressin receptor sub-family. The compound acts as an effective antagonist at both the human recombinant receptor (stably expressed in Chinese hamster ovary (CHO) cells) and the native rat V1B receptor (using isolated anterior pituitary cells), blocking the induction of luciferase and the release of ACTH, respectively. In vivo the compound can block the release of ACTH after challenge with a variety of V1B agonists. It can also attenuate the ACTH response to acute stressors in rats. Interestingly, this compound does not modulate the activity of the HPA axis under normal basal conditions. Keywords: vasopressin; depression; HPA; ACTH; V1B receptor; antagonist
front-line treatments for depression has focused almost solely upon modulation of monoamine levels in the central nervous system using first tricyclic anti-depressants (TCAs), then selective serotonin re-uptake inhibitors (SSRIs) and more recently serotonin and noradrenalin re-uptake inhibitors (SNRIs) (for a recent review of current treatments, see Nemeroff, 2007). However, these treatments still have a number of deficits including the lack of efficacy in a substantial percentage of
Introduction Psychiatric illnesses continue to place a major burden upon society both from an economic point of view and from the individual patient’s perspective (Kessler et al., 2005). The development of
Corresponding author. Tel.: +44 (0)1698 736000; Fax: +44 (0)1698 736003; E-mail: [email protected]
DOI: 10.1016/S0079-6123(08)00440-8
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patients, length of time for onset of action and unwanted side-effects such as sexual dysfunction (Fava, 2003). One of the most commonly described biological abnormalities associated with depression is a dysfunction in the hypothalamic-pituitary-adrenal (HPA) axis. It has been well documented that a significant percentage of patients suffering from depression demonstrate elevated levels of free cortisol (Carroll et al., 1976). Furthermore, a number of studies have indicated that these patients are resistant to the HPA feedback mechanism, which is mediated by the glucocorticoid receptor (GR). Using the dexamethasone (DEX) suppression test (DST), it was found that whereas administration of DEX (a synthetic GR agonist) at night can suppress morning plasma cortisol levels in normal subjects, a large percentage of depressed patients fail to show this response, indicating an impaired negative feedback control (Carroll et al., 1981). More recently a refined version of the DST using corticotrophin releasing factor (CRF), the DEX/CRF test, has been developed. In healthy volunteers, DEX can suppress the subsequent cortisol response to CRF, whereas in depressed patients there is an enhanced response to CRF (Heuser et al., 1994). Studies have indicated that the response to the DEX/CRF test becomes normalized as patients respond to treatment and that those patients who maintain an aberrant response to the test are more likely to subsequently relapse (Holsboer-Trachsler et al., 1991). A number of approaches to the treatment of depression by attempting to normalize the overactive HPA axis have been explored. These include the use of GR antagonists, cortisol synthesis inhibitors and CRF receptor type 1 (CRF1) antagonists (for a recent review, see Norman and Burrows, 2007). More recently there has been growing interest in the vasopressinergic system as a means of targeting the HPA axis dysfunction. The role of vasopressin in affective disorders Arginine vasopressin (AVP) is a nonapeptide which acts upon a series of closely related receptors (for a review, see Thibonnier et al., 2002). AVP released from the parvocellular cells of the hypothalamus
acts upon the anterior pituitary to stimulate the release of adrenocorticotropic hormone (ACTH) via the vasopressin receptor type 1B (V1B) receptor. ACTH subsequently induces the release of cortisol (corticosterone in rodents) from the adrenal glands. It is believed that under normal basal conditions CRF is the major secretagogue for ACTH, whereas under situations of chronic or prolonged stress AVP gains more prominence in the control of ACTH release (Scott and Dinan, 1998). This has important implications for the feedback control on the HPA axis because whilst CRF and CRF1 levels are negatively regulated by GR activation (Ochedalski et al., 1998), AVP signalling via V1B has been reported to be enhanced by glucocorticoids (Rabadan-Diehl and Aguilera, 1998). Indeed there is increasing clinical evidence to support this hypothesis; for example post-mortem studies have demonstrated an increase in the number of AVPexpressing neurons in the paraventricular nucleus (PVN) of the hypothalamus (Purba et al., 1996). Dinan and colleagues have also carried out a number of studies probing the role of V1B in depressed patients. In an initial report it was found that in comparison to healthy volunteers, depressed patients demonstrated a reduced ACTH response to a CRF challenge. However, when CRF was combined with desmopressin (dDAVP), a vasopressin analogue which activates the V1B and V2 receptors, a similar response was observed between both groups, indicating a shift in control of ACTH release towards control by AVP in depressed patients (Dinan et al., 1999). In a separate cohort of patients Dinan et al. (2004) found that infusion of dDAVP caused an enhanced release of both ACTH and cortisol in depressed patients compared to age-matched control subjects. Development of V1B antagonists The evidence for a role of AVP/V1B in depressed patients has led to an interest in the development of selective V1B antagonists for the treatment of depression. The most advanced compound thus far identified, SSR149415, has been shown to be efficacious in a variety of behavioural paradigms. It demonstrates activity in the rat forced swim test, mouse tail suspension test and mouse model
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of chronic mild stress (Griebel et al., 2005), tests in which monoaminergic anti-depressants have demonstrated efficacy. More recently, chronic treatment with the compound has been reported to reduce hyperemotionality in a mouse olfactory bulbectomy model (Iijima and Chaki, 2007). SSR149415 has also been reported to be efficacious in anxiety tests including the elevated plusmaze and a number of conflict paradigms (Griebel et al., 2005). SSR149415 is currently undergoing clinical trials to determine efficacy in both depression and anxiety. However, it has been recently reported that besides antagonizing the V1B receptor the compound also acts as an antagonist at the closely related oxytocin (OT) receptor (Griffante et al., 2005).
In vitro characterization of the Organon V1b antagonist A high-throughput screening approach was carried out by Organon in collaboration with Pharmacopeia, Inc., using a cell line stably expressing the human V1B receptor to identify an initial compound with efficacy at the V1B receptor, and further rounds of optimization yielded the compound. Radio-ligand binding experiments demonstrated that the compound had high affinity for the human V1B receptor (approximately 4 nM) and its selectivity against other members of the vasopressin/OT receptor sub-family was found to be greater than 1000-fold (Table 1). Screening at a panel of other receptors and ion-channels indicated that the compound did not demonstrate any significant affinity (W50% binding) at a concentration of 2.5 mM. Next the degree of functional antagonism was determined using a reporter cell line stably expressing the human V1B receptor as well as a luciferase reporter gene linked to a cyclic adenosine monophosphate (cAMP) response element. Cells were stimulated with 250 nM AVP in the presence of increasing levels of the compound. The compound was able to completely block the activity of AVP at the receptor with a calculated median inhibition concentration (concentration that reduces the effect by 50%) (IC50) of approximately 50 nM. Having demonstrated that it could act as an
Table 1. Binding affinities for the Organon V1b antagonist at the human vasopressin sub-family of receptors Receptor
pKi7SEM
V1B V1A V2 OT
8.470.1 o5 o5 o5
Note: CHO cells (V1B and OT) or membranes prepared from CHO cells (V1A and V2) expressing the human versions of the receptors were incubated with tritiated ligand ([3H] AVP for V1A, V1B and V2; [3H] oxytocin for OT) and increasing concentrations of the compound. Nonspecific binding was determined in the presence of 10 mM lysine vasopressin for V1A, V1B and V2; 10 mM oxytocin for OT. The concentration of compound was plotted against specific binding and data were analysed by non-linear regression to calculate affinities of the compound for each receptor. Each determination was carried out in triplicate on at least three separate occasions. pKi, negative logarithm of the inhibition constant; SEM, standard error of the mean.
antagonist against the recombinantly expressed human receptor the next step was to determine the compound’s activity at the native rat receptor. Anterior pituitary cells were prepared from female Sprague-Dawley rats. Treatment of the cells with AVP (3 nM) induced a robust release of ACTH. As can be seen in Fig. 1, the compound was able to dose-dependently block the release of ACTH (IC50 ¼ 20 nM) when the cells were co-treated with AVP and antagonist.
In vivo characterization of the Organon V1b antagonist Blockade of V1B agonist-induced HPA stimulation The ability of the compound to antagonize the V1B receptor in vivo was demonstrated by measuring ACTH release in rats following administration of CRF and dDAVP. Male adult Sprague-Dawley rats were implanted with jugular vein catheters and after a 2-day recovery period, CRF (0.3 mg/kg, intravenous (i.v.)) was administered followed by dDAVP (0.5 mg/kg, i.v.) 20 min later. After a further 10 min a blood sample was collected from each animal and plasma ACTH concentrations were measured by ELISA. As shown in Fig. 2, oral treatment with the compound two hours prior to the challenge caused a dose-related reduction in
530 8000
ACTH (pg/ml)
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AVP 3nM
10
30
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10000
Organon compound (nM) Fig. 1. The compound is able to functionally antagonize the native rat V1B receptor. Isolated rat anterior pituitary cells were incubated with 3 nM AVP for 2 h in the presence of increasing concentrations of the compound. ACTH release was determined by ELISA (IDS, UK). A pIC50 was determined by plotting the percent antagonism against the concentration of compound (pIC50 ¼ 7.770.2). Each treatment was carried out in quadruplicate and the whole experiment was repeated on at least three separate occasions. The figure is a representative result from one experiment.
Plasma ACTH (pg /ml)
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CRF + dDAVP
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Fig. 2. The compound can antagonize the V1B receptor in vivo. Male Sprague-Dawley rats (7–8 per group) were treated with the compound (3–30 mg/kg, p.o.) and then challenged with CRF (0.3 mg/kg, i.v.) and dDAVP (0.5 mg/kg, i.v.). The graph represents the mean+SEM (standard error of the mean) plasma ACTH levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Tukey’s post hoc analysis. po0.05 versus group treated with CRF and dDAVP alone.
ACTH release, with a minimal effective dose of 5 mg/kg, per os (p.o.). The in vivo efficacy of the compound was further confirmed using a selective agonist for the V1B receptor, [1-deamino-4-cyclohexylalanine] arginine vasopressin (d[Cha4]AVP), combined with CRF (Derick et al., 2002). A preliminary
experiment was performed to investigate the effects of CRF and d[Cha4]AVP, alone and in combination, on ACTH and corticosterone release. Using male Sprague-Dawley rats implanted with jugular vein catheters, CRF (0.3 mg/kg, i.v.) or vehicle was administered followed by d[Cha4]AVP (5 or 25 mg/ kg, i.v.) or vehicle 20 min later. Blood samples were
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collected 10 and 30 min post-administration of d[Cha4]AVP for the measurement of plasma ACTH and corticosterone, respectively. Both peptides caused a significant increase in plasma ACTH levels when administered alone (see Fig. 3a). However, when administered together the resulting increase in ACTH concentrations demonstrated that the peptides were acting in a synergistic rather than additive manner. In contrast to the effect on ACTH release, d[Cha4]AVP alone caused a substantial increase in plasma corticosterone concentrations and the addition of CRF appeared to only
have an additive effect on corticosterone release (see Fig. 3b). As displayed in Fig. 4a and b, oral treatment with the compound (30 mg/kg) effectively antagonized the release of both ACTH and corticosterone following administration of CRF and d[Cha4]AVP. Since the synergistic action of CRF and d[Cha4]AVP in stimulating the HPA axis is proposed to be mediated by the V1B receptor, these results confirm that the compound can effectively antagonize the V1B receptor in vivo. In addition to its ability to block the effects of CRF combined with dDAVP or d[Cha4]AVP,
(a) Plasma ACTH (pg/ml)
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CRF
d[Cha]AVP (5µg/kg)
Plasma corticosterone (pg/ml)
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d[Cha]AVP (25µg/kg)
1000 † *
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CRF + d[Cha]AVP (25µg/kg)
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600 * 400 200 0 Vehicle
CRF
d[Cha]AVP (5µg/kg)
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d[Cha]AVP (25µg/kg)
CRF + d[Cha]AVP (25µg/kg)
Fig. 3. (a) CRF and d[Cha4]AVP act synergistically to increase plasma ACTH concentrations. Male Sprague-Dawley rats (7–9 per group) were treated with CRF (0.3 mg/kg, i.v.), d[Cha4]AVP (at 5 or 25 mg/kg, i.v.), alone or in combination. The graph represents the mean+SEM plasma ACTH levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Tukey’s post hoc analysis. po0.05 versus vehicle-treated group; wpo0.05 versus CRF-treated group. (b) CRF and d[Cha4]AVP increase plasma corticosterone concentrations. Male Sprague-Dawley rats (7–9 per group) were treated with CRF (0.3 mg/kg, i.v.), d[Cha4]AVP (at 5 or 25 mg/kg, i.v.), alone or in combination. The graph represents the mean+SEM plasma corticosterone levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Tukey’s post hoc analysis. po0.05 versus vehicle-treated group; wpo0.05 versus CRF-treated group.
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(a)
Plasma ACTH (pg/ml)
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Fig. 4. (a) The compound blocks CRF and d[Cha4]AVP-induced plasma ACTH release. Male Sprague-Dawley rats (8 per group) were treated with the compound (30 mg/kg, p.o.) and then challenged with CRF (0.3 mg/kg, i.v.) and d[Cha4]AVP (25 mg/kg, i.v.). The graph represents the mean+SEM plasma ACTH levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Dunnett’s post hoc analysis. po0.05 versus group treated with CRF and d[Cha4]AVP alone. (b) the compound blocks CRF and d[Cha4]AVP-induced plasma corticosterone release. Male Sprague-Dawley rats (8 per group) were treated with the compound (3–30 mg/kg, p.o.) and then challenged with CRF (0.3 mg/kg, i.v.) and d[Cha4]AVP (25 mg/kg, i.v.). The graph represents the mean+SEM plasma corticosterone levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Dunnett’s post hoc analysis. po0.05 versus group treated with CRF and d[Cha4]AVP alone.
a recent study by Spiga et al. (2007) reported that the compound (30 mg/kg, subcutaneous (s.c.)) could partially antagonize the effect of AVP on ACTH secretion. Interestingly, the release of corticosterone by AVP was attenuated to a lesser extent than that observed for ACTH. The decreased magnitude of effect in blocking the corticosterone release may be a consequence of the failure to completely block ACTH release, which, albeit at low levels, could be
sufficient to trigger the subsequent corticosterone release. It was of interest to assess whether the compound would demonstrate efficacy following chronic treatment. Rats were treated with the compound for 14 days at 2.7 mg/kg/day via a subcutaneous minipump and then administered CRF and dDAVP i.v. by a jugular vein catheter (as described above). Blood samples were taken prior to the challenge and again 10 and 30 min post-administration of dDAVP
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Fig. 5. (a) The compound attenuates CRF and dDAVP-induced ACTH release following chronic infusion via subcutaneous minipump. Male Sprague-Dawley rats (7–9 per group) received the compound (2.7 mg/kg/day) over 14 days by a subcutaneous minipump. They were then challenged with CRF (0.3 mg/kg, i.v.) and dDAVP (0.5 mg/kg, i.v.). The graph represents the mean+SEM plasma ACTH levels before (basal) and after the CRF and dDAVP challenge. Statistical analysis on log-transformed data using a twoway ANOVA (General Linear Model) revealed no significant effect of treatment (vehicle or Organon compound), a main effect of sample (basal or following CRF/dDAVP; po0.001) and an interaction between treatment and sample (wp ¼ 0.01). This interaction demonstrated that the drug treatment significantly attenuated the response to the CRF and dDAVP challenge. (b) the compound does not attenuate CRF and dDAVP-induced corticosterone release following chronic infusion via subcutaneous minipump. Male SpragueDawley rats (7–9 per group) received the compound (2.7 mg/kg/day) over 14 days by a subcutaneous minipump. They were then challenged with CRF (0.3 mg/kg, i.v.) and dDAVP (0.5 mg/kg, i.v.). The graph represents the mean+SEM plasma corticosterone levels before (basal) and after the CRF and dDAVP challenge. Statistical analysis on log-transformed data using a two-way ANOVA (general linear model) revealed no significant effect of treatment (vehicle or Organon compound) or sample (basal or following CRF/ dDAVP; po0.001).
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for the measurement of plasma ACTH and corticosterone, respectively. Chronic treatment with the compound clearly reduced ACTH release (see Fig. 5a), demonstrating that the compound was effective as a V1B antagonist following chronic treatment. Corticosterone release (Fig. 5b), on the other hand, was not reduced, which may be due to the only partial attenuation of the ACTH response. Effects on HPA axis function In a recent study, Spiga et al. (2007) investigated whether the compound could modulate HPA axis function under normal basal conditions. Using an automated blood sampling system, diurnal pulsatile patterns of corticosterone secretion were recorded in rats following treatment with the compound, injected acutely during the diurnal peak of the hormone secretion. The compound did not alter either the frequency or amplitude of corticosterone secretory pulses. In a separate experiment, both plasma ACTH and corticosterone levels were measured for 3 h following administration of the compound at the peak phase and no effect of the compound was observed. These data suggest that the V1B receptor is not involved in basal regulation of the HPA axis. Spiga et al. (2007) also explored the effects of the compound on HPA responses to various acute stressors in rats. Plasma ACTH and corticosterone levels were measured following an acute immunological stressor (i.v. injection of lipopolysaccharide) and after a 30 min restraint stress. The compound pre-treatment partially blocked the ACTH responses to both types of acute stressor, whereas the corticosterone response remained unaltered. Conclusion The compound is a highly selective and potent V1B receptor antagonist. It demonstrates significant binding selectivity for the human V1B receptor over other members of the vasopressin receptor sub-family, as well as efficacy as an antagonist both in vitro (at the human recombinant receptor and native rat V1B receptor) and in vivo, blocking ACTH release in response to challenges with various V1B agonists in the rat.
The effects of the compound on HPA axis function were studied under normal basal and stressful conditions. The compound had no effect on basal circulating ACTH or corticosterone levels but it did reduce ACTH release in response to acute stressors. Plasma corticosterone levels were not reduced to the same extent; this may be due to an amplification of the corticosterone signal which only requires a sub-maximal level of ACTH to elicit a corticosterone response. Importantly, these data provide evidence that the HPA system can maintain an intact appropriate response to stressful situations in the presence of a V1B antagonist. The absence of any effects on the diurnal corticosterone release in naı¨ ve animals also confirms that blockade of the V1B receptor should not result in potentially harmful endocrine effects. In summary, this compound has been shown to act at the V1B receptor without disturbing the integrity of the HPA axis. Thus, the Organon V1b antagonist could provide a novel approach for the treatment of anxiety and depression.
Abbreviations ACTH AVP cAMP CHO CRF CRF1 d[Cha4]AVP dDAVP DEX DST GR HPA i.v. IC50
OT p.o. pKi PVN
adrenocorticotropic hormone arginine vasopressin cyclic adenosine monophosphate Chinese hamster ovary corticotrophin releasing factor CRF receptor type 1 [1-deamino-4-cyclohexylalanine] arginine vasopressin desmopressin dexamethasone dexamethasone suppression test glucocorticoid receptor hypothalamic-pituitary-adrenal intravenous median inhibition concentration (concentration that reduces the effect by 50%) oxytocin per os negative logarithm of the inhibition constant paraventricular nucleus
535
s.c. SEM SNRI SSRI TCA V1A V1B V2
subcutaneous standard error of the mean serotonin and noradrenalin re-uptake inhibitor selective serotonin re-uptake inhibitor tricyclic anti-depressant vasopressin receptor type 1A vasopressin receptor type 1B vasopressin receptor type 2
Acknowledgements We thank our colleagues at Pharmacopeia Inc., Dr. Jeffrey Letourneau, Dr. Christopher Riviello, Dr. Koc-Kan Ho, Dr. Jui-Hsiang Chan, Dr. Michael Ohlmeyer, Dr. Patrick Jokiel and Dr. Irina Neagu. We are very grateful for the support we have received from Dr. Susan Napier, Dr. James Baker and Dr. Stuart Best at Organon. Thanks are also due to Dr. Greti Aguilera and Dr. Maurice Manning for providing us with d[Cha4]AVP.
References Carroll, B.J., Curtis, G.C., Davies, B.M., Mendels, J. and Sugerman, A.A. (1976) Urinary free cortisol excretion in depression. Psychol. Med., 6: 43–50. Carroll, B.J., Feinberg, M., Greden, J.F., Tarika, J., Albala, A.A., Haskett, R.F., James, N.M., Kronfol, Z., Lohr, N., Steiner, M., de Vigne, J.P. and Young, E. (1981) A specific laboratory test for the diagnosis of melancholia. Standardization, validation and clinical utility. Arch. Gen. Psychiatry, 38: 15–22. Derick, S., Cheng, L.L., Voirol, M.J., Stoev, S., Giacomini, M., Wo, N.C., Szeto, H.H., Ben Mimoun, M., Andres, M., Gaillard, R.C., Guillon, G. and Manning, M. (2002) [1-deamino-4-cyclohexylalanine] arginine vasopressin: a potent and specific agonist for vasopressin V1b receptors. Endocrinology, 143: 4655–4664. Dinan, T.G., Lavelle, E., Scott, L.V., Newell-Price, J., Medbak, S. and Grossman, A.B. (1999) Desmopressin normalizes the blunted adrenocorticotropin response to corticotropin-releasing hormone in melancholic depression: evidence of enhanced vasopressinergic responsivity. J. Clin. Endocrinol. Metab., 84: 2238–2240. Dinan, T.G., O’Brien, S., Lavelle, E. and Scott, L.V. (2004) Further neuroendocrine evidence of enhanced vasopressin V3 receptor responses in melancholic depression. Psychol. Med., 34: 169–172.
Fava, M. (2003) Diagnosis and definition of treatment-resistant depression. Biol. Psychiatry, 53: 649–659. Griebel, G., Stemmelin, J., Gal, C.S. and Soubrie, P. (2005) Non-peptide vasopressin V1b receptor antagonists as potential drugs for the treatment of stress-related disorders. Curr. Pharm. Des., 11: 1549–1559. Griffante, C., Green, A., Curcuruto, O., Haslam, C.P., Dickinson, B.A. and Arban, R. (2005) Selectivity of d[Cha(4)]AVP and SSR149415 at human vasopressin and oxytocin receptors: evidence that SSR149415 is a mixed vasopressin V(1b)/oxytocin receptor antagonist. Br. J. Pharmacol., 146: 744–751. Heuser, I., Yassouridis, A. and Holsboer, F. (1994) The combined dexamethasone/CRH test: a refined laboratory test for psychiatric disorders. J. Psychiatr. Res., 28: 341–356. Holsboer-Trachsler, E., Stohler, R. and Hatzinger, M. (1991) Repeated administration of the combined dexamethasonehuman corticotropin releasing hormone stimulation test during treatment of depression. Psychiatry Res., 38: 163–171. Iijima, M. and Chaki, S. (2007) An arginine vasopressin V1b antagonist, SSR149415 elicits antidepressant-like effects in an olfactory bulbectomy model. Prog. Neuropsychopharmacol. Biol. Psychiatry, 31: 622–627. Kessler, R.C., Chiu, W.T., Demler, O., Merikangas, K.R. and Walters, E.E. (2005) Prevalence, severity and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication. Arch. Gen. Psychiatry, 62: 617–627. Nemeroff, C.B. (2007) The burden of severe depression: a review of diagnostic challenges and treatment alternatives. J. Psychiatr. Res., 41: 189–206. Norman, T.R. and Burrows, G.D. (2007) Emerging treatments for major depression. Expert Rev. Neurother., 7: 203–213. Ochedalski, T., Rabadan-Diehl, C. and Aguilera, G. (1998) Interaction between glucocorticoids and corticotropin releasing hormone (CRH) in the regulation of the pituitary CRH receptor in vivo in the rat. J. Neuroendocrinol., 10: 363–369. Purba, J.S., Hoogendijk, W.J., Hofman, M.A. and Swaab, D.F. (1996) Increased number of vasopressin- and oxytocinexpressing neurons in the paraventricular nucleus of the hypothalamus in depression. Arch. Gen. Psychiatry, 53: 137–143. Rabadan-Diehl, C. and Aguilera, G. (1998) Glucocorticoids increase vasopressin V1b receptor coupling to phospholipase C. Endocrinology, 139: 3220–3226. Scott, L.V. and Dinan, T.G. (1998) Vasopressin and the regulation of hypothalamic-pituitary-adrenal axis function: implications for the pathophysiology of depression. Life Sci., 62: 1985–1998. Spiga, F., Harrison, L., MacSweeney, C., Craighead, M., Thomson, F. and Lightman, S.L. (2007) Effect of the V1b antagonist Org 52186 on arginine vasopressin-induced and stress-induced hypothalamic-pituitary-adrenal axis activity. Society for Neurosciences. Abstract of the 37th Annual Meeting of the Society for Neuroscience, 3–7, November 2007, San Diego, CA, USA. Thibonnier, M., Coles, P., Thibonnier, A. and Shoham, M. (2002) Molecular pharmacology and modeling of vasopressin receptors. Prog. Brain Res., 139: 179–196.
CHAPTER 40
Characterization of a novel and selective V1B receptor antagonist Mark Craighead1,, Rachel Milne1, Leigh Campbell-Wan2, Lynn Watson1, Jeremy Presland1, Fiona J. Thomson1, Hugh M. Marston2 and Clı´ ona P. MacSweeney2 1
Department of Molecular Pharmacology, Organon Laboratories (a part of the Schering-Plough Corporation), Newhouse, UK 2 Department of Pharmacology, Organon Laboratories (a part of the Schering-Plough Corporation), Newhouse, UK
Abstract: It has been argued that hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is a major biological abnormality in patients suffering from psychiatric conditions such as major depression. Both arginine vasopressin (AVP) and corticotrophin releasing factor (CRF) are responsible for stimulating the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary. CRF is thought to be the predominant secretagogue under normal conditions but AVP may play a more important role in situations of aberrant/chronic stress. Studies in patients suffering from melancholic depression indicate a hyperresponsiveness to agonism at the vasopressin receptor type 1B (V1B); patients display a heightened ACTH release after challenge with the mixed V1B/V2 (vasopressin receptor type 2) agonist desmopressin in comparison to control subjects. A V1B antagonist has been developed which has significant selectivity for the human V1B receptor over the other members of the vasopressin receptor sub-family. The compound acts as an effective antagonist at both the human recombinant receptor (stably expressed in Chinese hamster ovary (CHO) cells) and the native rat V1B receptor (using isolated anterior pituitary cells), blocking the induction of luciferase and the release of ACTH, respectively. In vivo the compound can block the release of ACTH after challenge with a variety of V1B agonists. It can also attenuate the ACTH response to acute stressors in rats. Interestingly, this compound does not modulate the activity of the HPA axis under normal basal conditions. Keywords: vasopressin; depression; HPA; ACTH; V1B receptor; antagonist
front-line treatments for depression has focused almost solely upon modulation of monoamine levels in the central nervous system using first tricyclic anti-depressants (TCAs), then selective serotonin re-uptake inhibitors (SSRIs) and more recently serotonin and noradrenalin re-uptake inhibitors (SNRIs) (for a recent review of current treatments, see Nemeroff, 2007). However, these treatments still have a number of deficits including the lack of efficacy in a substantial percentage of
Introduction Psychiatric illnesses continue to place a major burden upon society both from an economic point of view and from the individual patient’s perspective (Kessler et al., 2005). The development of
Corresponding author. Tel.: +44 (0)1698 736000; Fax: +44 (0)1698 736003; E-mail: [email protected]
DOI: 10.1016/S0079-6123(08)00440-8
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patients, length of time for onset of action and unwanted side-effects such as sexual dysfunction (Fava, 2003). One of the most commonly described biological abnormalities associated with depression is a dysfunction in the hypothalamic-pituitary-adrenal (HPA) axis. It has been well documented that a significant percentage of patients suffering from depression demonstrate elevated levels of free cortisol (Carroll et al., 1976). Furthermore, a number of studies have indicated that these patients are resistant to the HPA feedback mechanism, which is mediated by the glucocorticoid receptor (GR). Using the dexamethasone (DEX) suppression test (DST), it was found that whereas administration of DEX (a synthetic GR agonist) at night can suppress morning plasma cortisol levels in normal subjects, a large percentage of depressed patients fail to show this response, indicating an impaired negative feedback control (Carroll et al., 1981). More recently a refined version of the DST using corticotrophin releasing factor (CRF), the DEX/CRF test, has been developed. In healthy volunteers, DEX can suppress the subsequent cortisol response to CRF, whereas in depressed patients there is an enhanced response to CRF (Heuser et al., 1994). Studies have indicated that the response to the DEX/CRF test becomes normalized as patients respond to treatment and that those patients who maintain an aberrant response to the test are more likely to subsequently relapse (Holsboer-Trachsler et al., 1991). A number of approaches to the treatment of depression by attempting to normalize the overactive HPA axis have been explored. These include the use of GR antagonists, cortisol synthesis inhibitors and CRF receptor type 1 (CRF1) antagonists (for a recent review, see Norman and Burrows, 2007). More recently there has been growing interest in the vasopressinergic system as a means of targeting the HPA axis dysfunction. The role of vasopressin in affective disorders Arginine vasopressin (AVP) is a nonapeptide which acts upon a series of closely related receptors (for a review, see Thibonnier et al., 2002). AVP released from the parvocellular cells of the hypothalamus
acts upon the anterior pituitary to stimulate the release of adrenocorticotropic hormone (ACTH) via the vasopressin receptor type 1B (V1B) receptor. ACTH subsequently induces the release of cortisol (corticosterone in rodents) from the adrenal glands. It is believed that under normal basal conditions CRF is the major secretagogue for ACTH, whereas under situations of chronic or prolonged stress AVP gains more prominence in the control of ACTH release (Scott and Dinan, 1998). This has important implications for the feedback control on the HPA axis because whilst CRF and CRF1 levels are negatively regulated by GR activation (Ochedalski et al., 1998), AVP signalling via V1B has been reported to be enhanced by glucocorticoids (Rabadan-Diehl and Aguilera, 1998). Indeed there is increasing clinical evidence to support this hypothesis; for example post-mortem studies have demonstrated an increase in the number of AVPexpressing neurons in the paraventricular nucleus (PVN) of the hypothalamus (Purba et al., 1996). Dinan and colleagues have also carried out a number of studies probing the role of V1B in depressed patients. In an initial report it was found that in comparison to healthy volunteers, depressed patients demonstrated a reduced ACTH response to a CRF challenge. However, when CRF was combined with desmopressin (dDAVP), a vasopressin analogue which activates the V1B and V2 receptors, a similar response was observed between both groups, indicating a shift in control of ACTH release towards control by AVP in depressed patients (Dinan et al., 1999). In a separate cohort of patients Dinan et al. (2004) found that infusion of dDAVP caused an enhanced release of both ACTH and cortisol in depressed patients compared to age-matched control subjects. Development of V1B antagonists The evidence for a role of AVP/V1B in depressed patients has led to an interest in the development of selective V1B antagonists for the treatment of depression. The most advanced compound thus far identified, SSR149415, has been shown to be efficacious in a variety of behavioural paradigms. It demonstrates activity in the rat forced swim test, mouse tail suspension test and mouse model
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of chronic mild stress (Griebel et al., 2005), tests in which monoaminergic anti-depressants have demonstrated efficacy. More recently, chronic treatment with the compound has been reported to reduce hyperemotionality in a mouse olfactory bulbectomy model (Iijima and Chaki, 2007). SSR149415 has also been reported to be efficacious in anxiety tests including the elevated plusmaze and a number of conflict paradigms (Griebel et al., 2005). SSR149415 is currently undergoing clinical trials to determine efficacy in both depression and anxiety. However, it has been recently reported that besides antagonizing the V1B receptor the compound also acts as an antagonist at the closely related oxytocin (OT) receptor (Griffante et al., 2005).
In vitro characterization of the Organon V1b antagonist A high-throughput screening approach was carried out by Organon in collaboration with Pharmacopeia, Inc., using a cell line stably expressing the human V1B receptor to identify an initial compound with efficacy at the V1B receptor, and further rounds of optimization yielded the compound. Radio-ligand binding experiments demonstrated that the compound had high affinity for the human V1B receptor (approximately 4 nM) and its selectivity against other members of the vasopressin/OT receptor sub-family was found to be greater than 1000-fold (Table 1). Screening at a panel of other receptors and ion-channels indicated that the compound did not demonstrate any significant affinity (W50% binding) at a concentration of 2.5 mM. Next the degree of functional antagonism was determined using a reporter cell line stably expressing the human V1B receptor as well as a luciferase reporter gene linked to a cyclic adenosine monophosphate (cAMP) response element. Cells were stimulated with 250 nM AVP in the presence of increasing levels of the compound. The compound was able to completely block the activity of AVP at the receptor with a calculated median inhibition concentration (concentration that reduces the effect by 50%) (IC50) of approximately 50 nM. Having demonstrated that it could act as an
Table 1. Binding affinities for the Organon V1b antagonist at the human vasopressin sub-family of receptors Receptor
pKi7SEM
V1B V1A V2 OT
8.470.1 o5 o5 o5
Note: CHO cells (V1B and OT) or membranes prepared from CHO cells (V1A and V2) expressing the human versions of the receptors were incubated with tritiated ligand ([3H] AVP for V1A, V1B and V2; [3H] oxytocin for OT) and increasing concentrations of the compound. Nonspecific binding was determined in the presence of 10 mM lysine vasopressin for V1A, V1B and V2; 10 mM oxytocin for OT. The concentration of compound was plotted against specific binding and data were analysed by non-linear regression to calculate affinities of the compound for each receptor. Each determination was carried out in triplicate on at least three separate occasions. pKi, negative logarithm of the inhibition constant; SEM, standard error of the mean.
antagonist against the recombinantly expressed human receptor the next step was to determine the compound’s activity at the native rat receptor. Anterior pituitary cells were prepared from female Sprague-Dawley rats. Treatment of the cells with AVP (3 nM) induced a robust release of ACTH. As can be seen in Fig. 1, the compound was able to dose-dependently block the release of ACTH (IC50 ¼ 20 nM) when the cells were co-treated with AVP and antagonist.
In vivo characterization of the Organon V1b antagonist Blockade of V1B agonist-induced HPA stimulation The ability of the compound to antagonize the V1B receptor in vivo was demonstrated by measuring ACTH release in rats following administration of CRF and dDAVP. Male adult Sprague-Dawley rats were implanted with jugular vein catheters and after a 2-day recovery period, CRF (0.3 mg/kg, intravenous (i.v.)) was administered followed by dDAVP (0.5 mg/kg, i.v.) 20 min later. After a further 10 min a blood sample was collected from each animal and plasma ACTH concentrations were measured by ELISA. As shown in Fig. 2, oral treatment with the compound two hours prior to the challenge caused a dose-related reduction in
530 8000
ACTH (pg/ml)
6000
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0
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0 CON
AVP 3nM
10
30
100
300
1000
3000
10000
Organon compound (nM) Fig. 1. The compound is able to functionally antagonize the native rat V1B receptor. Isolated rat anterior pituitary cells were incubated with 3 nM AVP for 2 h in the presence of increasing concentrations of the compound. ACTH release was determined by ELISA (IDS, UK). A pIC50 was determined by plotting the percent antagonism against the concentration of compound (pIC50 ¼ 7.770.2). Each treatment was carried out in quadruplicate and the whole experiment was repeated on at least three separate occasions. The figure is a representative result from one experiment.
Plasma ACTH (pg /ml)
1000 800 600
* *
400 * 200 0 CON
CRF + dDAVP
3
5
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Organon compound (nM)
Fig. 2. The compound can antagonize the V1B receptor in vivo. Male Sprague-Dawley rats (7–8 per group) were treated with the compound (3–30 mg/kg, p.o.) and then challenged with CRF (0.3 mg/kg, i.v.) and dDAVP (0.5 mg/kg, i.v.). The graph represents the mean+SEM (standard error of the mean) plasma ACTH levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Tukey’s post hoc analysis. po0.05 versus group treated with CRF and dDAVP alone.
ACTH release, with a minimal effective dose of 5 mg/kg, per os (p.o.). The in vivo efficacy of the compound was further confirmed using a selective agonist for the V1B receptor, [1-deamino-4-cyclohexylalanine] arginine vasopressin (d[Cha4]AVP), combined with CRF (Derick et al., 2002). A preliminary
experiment was performed to investigate the effects of CRF and d[Cha4]AVP, alone and in combination, on ACTH and corticosterone release. Using male Sprague-Dawley rats implanted with jugular vein catheters, CRF (0.3 mg/kg, i.v.) or vehicle was administered followed by d[Cha4]AVP (5 or 25 mg/ kg, i.v.) or vehicle 20 min later. Blood samples were
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collected 10 and 30 min post-administration of d[Cha4]AVP for the measurement of plasma ACTH and corticosterone, respectively. Both peptides caused a significant increase in plasma ACTH levels when administered alone (see Fig. 3a). However, when administered together the resulting increase in ACTH concentrations demonstrated that the peptides were acting in a synergistic rather than additive manner. In contrast to the effect on ACTH release, d[Cha4]AVP alone caused a substantial increase in plasma corticosterone concentrations and the addition of CRF appeared to only
have an additive effect on corticosterone release (see Fig. 3b). As displayed in Fig. 4a and b, oral treatment with the compound (30 mg/kg) effectively antagonized the release of both ACTH and corticosterone following administration of CRF and d[Cha4]AVP. Since the synergistic action of CRF and d[Cha4]AVP in stimulating the HPA axis is proposed to be mediated by the V1B receptor, these results confirm that the compound can effectively antagonize the V1B receptor in vivo. In addition to its ability to block the effects of CRF combined with dDAVP or d[Cha4]AVP,
(a) Plasma ACTH (pg/ml)
1600
† *
1200
† *
800 *
* 400
*
0 Vehicle
CRF
d[Cha]AVP (5µg/kg)
Plasma corticosterone (pg/ml)
(b)
CRF + d[Cha]AVP (5µg/kg)
d[Cha]AVP (25µg/kg)
1000 † *
800
† *
† *
CRF + d[Cha]AVP (25µg/kg)
† *
600 * 400 200 0 Vehicle
CRF
d[Cha]AVP (5µg/kg)
CRF+ d[Cha]AVP (5µg/kg)
d[Cha]AVP (25µg/kg)
CRF + d[Cha]AVP (25µg/kg)
Fig. 3. (a) CRF and d[Cha4]AVP act synergistically to increase plasma ACTH concentrations. Male Sprague-Dawley rats (7–9 per group) were treated with CRF (0.3 mg/kg, i.v.), d[Cha4]AVP (at 5 or 25 mg/kg, i.v.), alone or in combination. The graph represents the mean+SEM plasma ACTH levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Tukey’s post hoc analysis. po0.05 versus vehicle-treated group; wpo0.05 versus CRF-treated group. (b) CRF and d[Cha4]AVP increase plasma corticosterone concentrations. Male Sprague-Dawley rats (7–9 per group) were treated with CRF (0.3 mg/kg, i.v.), d[Cha4]AVP (at 5 or 25 mg/kg, i.v.), alone or in combination. The graph represents the mean+SEM plasma corticosterone levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Tukey’s post hoc analysis. po0.05 versus vehicle-treated group; wpo0.05 versus CRF-treated group.
532
(a)
Plasma ACTH (pg/ml)
1000 800 600 400
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CRF + d[Cha]AVP
(b)
Organon compound + CRF + d[Cha]AVP
Plasma corticosterone (ng/ml)
1000
800 600
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*
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0 Vehicle
CRF + d[Cha]AVP
Organon compound + CRF + d[Cha]AVP
Fig. 4. (a) The compound blocks CRF and d[Cha4]AVP-induced plasma ACTH release. Male Sprague-Dawley rats (8 per group) were treated with the compound (30 mg/kg, p.o.) and then challenged with CRF (0.3 mg/kg, i.v.) and d[Cha4]AVP (25 mg/kg, i.v.). The graph represents the mean+SEM plasma ACTH levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Dunnett’s post hoc analysis. po0.05 versus group treated with CRF and d[Cha4]AVP alone. (b) the compound blocks CRF and d[Cha4]AVP-induced plasma corticosterone release. Male Sprague-Dawley rats (8 per group) were treated with the compound (3–30 mg/kg, p.o.) and then challenged with CRF (0.3 mg/kg, i.v.) and d[Cha4]AVP (25 mg/kg, i.v.). The graph represents the mean+SEM plasma corticosterone levels. Statistical analysis was carried out on log-transformed data using a one-way ANOVA followed by Dunnett’s post hoc analysis. po0.05 versus group treated with CRF and d[Cha4]AVP alone.
a recent study by Spiga et al. (2007) reported that the compound (30 mg/kg, subcutaneous (s.c.)) could partially antagonize the effect of AVP on ACTH secretion. Interestingly, the release of corticosterone by AVP was attenuated to a lesser extent than that observed for ACTH. The decreased magnitude of effect in blocking the corticosterone release may be a consequence of the failure to completely block ACTH release, which, albeit at low levels, could be
sufficient to trigger the subsequent corticosterone release. It was of interest to assess whether the compound would demonstrate efficacy following chronic treatment. Rats were treated with the compound for 14 days at 2.7 mg/kg/day via a subcutaneous minipump and then administered CRF and dDAVP i.v. by a jugular vein catheter (as described above). Blood samples were taken prior to the challenge and again 10 and 30 min post-administration of dDAVP
533
(a)
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Organon compound
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Basal CRF/dDAVP
Plasma corticosterone (ng/ml)
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Fig. 5. (a) The compound attenuates CRF and dDAVP-induced ACTH release following chronic infusion via subcutaneous minipump. Male Sprague-Dawley rats (7–9 per group) received the compound (2.7 mg/kg/day) over 14 days by a subcutaneous minipump. They were then challenged with CRF (0.3 mg/kg, i.v.) and dDAVP (0.5 mg/kg, i.v.). The graph represents the mean+SEM plasma ACTH levels before (basal) and after the CRF and dDAVP challenge. Statistical analysis on log-transformed data using a twoway ANOVA (General Linear Model) revealed no significant effect of treatment (vehicle or Organon compound), a main effect of sample (basal or following CRF/dDAVP; po0.001) and an interaction between treatment and sample (wp ¼ 0.01). This interaction demonstrated that the drug treatment significantly attenuated the response to the CRF and dDAVP challenge. (b) the compound does not attenuate CRF and dDAVP-induced corticosterone release following chronic infusion via subcutaneous minipump. Male SpragueDawley rats (7–9 per group) received the compound (2.7 mg/kg/day) over 14 days by a subcutaneous minipump. They were then challenged with CRF (0.3 mg/kg, i.v.) and dDAVP (0.5 mg/kg, i.v.). The graph represents the mean+SEM plasma corticosterone levels before (basal) and after the CRF and dDAVP challenge. Statistical analysis on log-transformed data using a two-way ANOVA (general linear model) revealed no significant effect of treatment (vehicle or Organon compound) or sample (basal or following CRF/ dDAVP; po0.001).
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for the measurement of plasma ACTH and corticosterone, respectively. Chronic treatment with the compound clearly reduced ACTH release (see Fig. 5a), demonstrating that the compound was effective as a V1B antagonist following chronic treatment. Corticosterone release (Fig. 5b), on the other hand, was not reduced, which may be due to the only partial attenuation of the ACTH response. Effects on HPA axis function In a recent study, Spiga et al. (2007) investigated whether the compound could modulate HPA axis function under normal basal conditions. Using an automated blood sampling system, diurnal pulsatile patterns of corticosterone secretion were recorded in rats following treatment with the compound, injected acutely during the diurnal peak of the hormone secretion. The compound did not alter either the frequency or amplitude of corticosterone secretory pulses. In a separate experiment, both plasma ACTH and corticosterone levels were measured for 3 h following administration of the compound at the peak phase and no effect of the compound was observed. These data suggest that the V1B receptor is not involved in basal regulation of the HPA axis. Spiga et al. (2007) also explored the effects of the compound on HPA responses to various acute stressors in rats. Plasma ACTH and corticosterone levels were measured following an acute immunological stressor (i.v. injection of lipopolysaccharide) and after a 30 min restraint stress. The compound pre-treatment partially blocked the ACTH responses to both types of acute stressor, whereas the corticosterone response remained unaltered. Conclusion The compound is a highly selective and potent V1B receptor antagonist. It demonstrates significant binding selectivity for the human V1B receptor over other members of the vasopressin receptor sub-family, as well as efficacy as an antagonist both in vitro (at the human recombinant receptor and native rat V1B receptor) and in vivo, blocking ACTH release in response to challenges with various V1B agonists in the rat.
The effects of the compound on HPA axis function were studied under normal basal and stressful conditions. The compound had no effect on basal circulating ACTH or corticosterone levels but it did reduce ACTH release in response to acute stressors. Plasma corticosterone levels were not reduced to the same extent; this may be due to an amplification of the corticosterone signal which only requires a sub-maximal level of ACTH to elicit a corticosterone response. Importantly, these data provide evidence that the HPA system can maintain an intact appropriate response to stressful situations in the presence of a V1B antagonist. The absence of any effects on the diurnal corticosterone release in naı¨ ve animals also confirms that blockade of the V1B receptor should not result in potentially harmful endocrine effects. In summary, this compound has been shown to act at the V1B receptor without disturbing the integrity of the HPA axis. Thus, the Organon V1b antagonist could provide a novel approach for the treatment of anxiety and depression.
Abbreviations ACTH AVP cAMP CHO CRF CRF1 d[Cha4]AVP dDAVP DEX DST GR HPA i.v. IC50
OT p.o. pKi PVN
adrenocorticotropic hormone arginine vasopressin cyclic adenosine monophosphate Chinese hamster ovary corticotrophin releasing factor CRF receptor type 1 [1-deamino-4-cyclohexylalanine] arginine vasopressin desmopressin dexamethasone dexamethasone suppression test glucocorticoid receptor hypothalamic-pituitary-adrenal intravenous median inhibition concentration (concentration that reduces the effect by 50%) oxytocin per os negative logarithm of the inhibition constant paraventricular nucleus
535
s.c. SEM SNRI SSRI TCA V1A V1B V2
subcutaneous standard error of the mean serotonin and noradrenalin re-uptake inhibitor selective serotonin re-uptake inhibitor tricyclic anti-depressant vasopressin receptor type 1A vasopressin receptor type 1B vasopressin receptor type 2
Acknowledgements We thank our colleagues at Pharmacopeia Inc., Dr. Jeffrey Letourneau, Dr. Christopher Riviello, Dr. Koc-Kan Ho, Dr. Jui-Hsiang Chan, Dr. Michael Ohlmeyer, Dr. Patrick Jokiel and Dr. Irina Neagu. We are very grateful for the support we have received from Dr. Susan Napier, Dr. James Baker and Dr. Stuart Best at Organon. Thanks are also due to Dr. Greti Aguilera and Dr. Maurice Manning for providing us with d[Cha4]AVP.
References Carroll, B.J., Curtis, G.C., Davies, B.M., Mendels, J. and Sugerman, A.A. (1976) Urinary free cortisol excretion in depression. Psychol. Med., 6: 43–50. Carroll, B.J., Feinberg, M., Greden, J.F., Tarika, J., Albala, A.A., Haskett, R.F., James, N.M., Kronfol, Z., Lohr, N., Steiner, M., de Vigne, J.P. and Young, E. (1981) A specific laboratory test for the diagnosis of melancholia. Standardization, validation and clinical utility. Arch. Gen. Psychiatry, 38: 15–22. Derick, S., Cheng, L.L., Voirol, M.J., Stoev, S., Giacomini, M., Wo, N.C., Szeto, H.H., Ben Mimoun, M., Andres, M., Gaillard, R.C., Guillon, G. and Manning, M. (2002) [1-deamino-4-cyclohexylalanine] arginine vasopressin: a potent and specific agonist for vasopressin V1b receptors. Endocrinology, 143: 4655–4664. Dinan, T.G., Lavelle, E., Scott, L.V., Newell-Price, J., Medbak, S. and Grossman, A.B. (1999) Desmopressin normalizes the blunted adrenocorticotropin response to corticotropin-releasing hormone in melancholic depression: evidence of enhanced vasopressinergic responsivity. J. Clin. Endocrinol. Metab., 84: 2238–2240. Dinan, T.G., O’Brien, S., Lavelle, E. and Scott, L.V. (2004) Further neuroendocrine evidence of enhanced vasopressin V3 receptor responses in melancholic depression. Psychol. Med., 34: 169–172.
Fava, M. (2003) Diagnosis and definition of treatment-resistant depression. Biol. Psychiatry, 53: 649–659. Griebel, G., Stemmelin, J., Gal, C.S. and Soubrie, P. (2005) Non-peptide vasopressin V1b receptor antagonists as potential drugs for the treatment of stress-related disorders. Curr. Pharm. Des., 11: 1549–1559. Griffante, C., Green, A., Curcuruto, O., Haslam, C.P., Dickinson, B.A. and Arban, R. (2005) Selectivity of d[Cha(4)]AVP and SSR149415 at human vasopressin and oxytocin receptors: evidence that SSR149415 is a mixed vasopressin V(1b)/oxytocin receptor antagonist. Br. J. Pharmacol., 146: 744–751. Heuser, I., Yassouridis, A. and Holsboer, F. (1994) The combined dexamethasone/CRH test: a refined laboratory test for psychiatric disorders. J. Psychiatr. Res., 28: 341–356. Holsboer-Trachsler, E., Stohler, R. and Hatzinger, M. (1991) Repeated administration of the combined dexamethasonehuman corticotropin releasing hormone stimulation test during treatment of depression. Psychiatry Res., 38: 163–171. Iijima, M. and Chaki, S. (2007) An arginine vasopressin V1b antagonist, SSR149415 elicits antidepressant-like effects in an olfactory bulbectomy model. Prog. Neuropsychopharmacol. Biol. Psychiatry, 31: 622–627. Kessler, R.C., Chiu, W.T., Demler, O., Merikangas, K.R. and Walters, E.E. (2005) Prevalence, severity and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication. Arch. Gen. Psychiatry, 62: 617–627. Nemeroff, C.B. (2007) The burden of severe depression: a review of diagnostic challenges and treatment alternatives. J. Psychiatr. Res., 41: 189–206. Norman, T.R. and Burrows, G.D. (2007) Emerging treatments for major depression. Expert Rev. Neurother., 7: 203–213. Ochedalski, T., Rabadan-Diehl, C. and Aguilera, G. (1998) Interaction between glucocorticoids and corticotropin releasing hormone (CRH) in the regulation of the pituitary CRH receptor in vivo in the rat. J. Neuroendocrinol., 10: 363–369. Purba, J.S., Hoogendijk, W.J., Hofman, M.A. and Swaab, D.F. (1996) Increased number of vasopressin- and oxytocinexpressing neurons in the paraventricular nucleus of the hypothalamus in depression. Arch. Gen. Psychiatry, 53: 137–143. Rabadan-Diehl, C. and Aguilera, G. (1998) Glucocorticoids increase vasopressin V1b receptor coupling to phospholipase C. Endocrinology, 139: 3220–3226. Scott, L.V. and Dinan, T.G. (1998) Vasopressin and the regulation of hypothalamic-pituitary-adrenal axis function: implications for the pathophysiology of depression. Life Sci., 62: 1985–1998. Spiga, F., Harrison, L., MacSweeney, C., Craighead, M., Thomson, F. and Lightman, S.L. (2007) Effect of the V1b antagonist Org 52186 on arginine vasopressin-induced and stress-induced hypothalamic-pituitary-adrenal axis activity. Society for Neurosciences. Abstract of the 37th Annual Meeting of the Society for Neuroscience, 3–7, November 2007, San Diego, CA, USA. Thibonnier, M., Coles, P., Thibonnier, A. and Shoham, M. (2002) Molecular pharmacology and modeling of vasopressin receptors. Prog. Brain Res., 139: 179–196.