EP1212048A1

EP1212048A1 - Use of sigma receptor agonists for the treatment of depression

Info

Publication number: EP1212048A1
Application number: EP00962406A
Authority: EP
Inventors: Tangui Maurice; François Roman
Original assignee: Warner Lambert Co LLC
Current assignee: Warner Lambert Co LLC
Priority date: 1999-08-27
Filing date: 2000-08-25
Publication date: 2002-06-12
Also published as: AU7414700A; CA2388036A1; JP2003508432A; MXPA02002120A; EP1078630A1; WO2001015685A1

Abstract

Method for the prevention or treatment of depression comprising administering to a steroid-depleted patient suffering therefrom and in need of treatment an effective amount of a sigma 1 receptor agonist.

Description

NOVEL USES OF SIGMA RECEPTOR AGONISTS

BACKGROUND OF THE INVENTION

Depression is a serious illness associated with a high morbidity resulting from physical disorders and an increased mortality resulting from accidents and suicide. Major depression recurs in about half the patients. Thus depressed patients may be treated with antidepressants continuously for years. There are, however, important drawbacks to the use of available drugs. Twenty-five to 35 % of patients show only minimal improvement, and side effects and toxicity can occur: tricyclic antidepressants (TCAs) are especially bothersome in elderly patients, with postural hypotension being a particularly severe problem; selective serotonin reuptake inhibitors (SSRIs) may induce nausea, vomiting, diarrhea, headache and sexual dysfunctions. Severe drug interactions can also result from the co-administration of monoamine oxidase inhibitors and either TCAs or SSRIs.

As a consequence, there is a need for antidepressant drugs that would be active at doses intended to be as low as possible in order to minimize the risk of side effects and drug interactions, especially in elderly patients, often exposed to several drugs concurrently. Sigma 1 (σi) receptor ligands show clear antidepressant effects in several animal models: the selective σi receptor agonists (+)-pentazocine, (+)-SKF- 10,047, igmesine, OPC 14523 , DTG or SA4503 reduce the immobility time in the forced swim test or are active in the tail suspension test (Ukai et al. 1998, Matsuno et al, 1996, Tottori et al. 1997, Kinsora et al. 1998). United States patent 5,034,419 describes N-cycloalkylalkylamines, which are sigma 1 receptor agonists.

SUMMARY OF THE INVENTION

It has now been found that the antidepressant effect of selective σi receptor agonists is affected by the level of endogenous steroids. More particularly, σi receptor agonists, in particular the compounds described in US 5,034,419, are useful for the prevention or treatment of depression, especially in steroid-depleted patients. This invention therefore provides a method for preventing or treating depression, said method comprising administering to a steroid-depleted patient in need of such treatment an effective amount of a sigma 1 receptor agonist. Preferred sigma 1 receptor agonists include those of Formula I, described in US 5,034,419,

wherein:

Rl is phenyl optionally mono-, di- or trisubstituted by halogen, lower alkyl, lower haloalkyl or lower alkoxy,

R2 is lower alkyl, R3 is hydrogen or lower alkyl,

R4 is cycloalkyl -CH(CH2)_n wherein n has a value of 2, 3, 4 or 5 and wherein a carbon atom of

R4 optionally carries a radical R_x wherein R_x is lower alkyl or phenyl,

R5 is phenyl optionally mono-, di- or trisubstituted by halogen or lower alkoxy,

Q represents an ethylene-l,2-yl group -CH=CH- or a cyclopropane- 1,2-diyl group

H H C— C —

\ / C H ² and m has a value of 1 or 2, the pharmaceutically acceptable salts thereof and the optically active forms thereof.

This invention also concerns the use of a sigma receptor agonist for the preparation of a medicament useful for preventing or treating depression in steroid-depleted patients.

BRIEF DESCRIPTION OF FIGURES

Figure 1 shows the antidepressant effect of igmesine in the forced swim test in Swiss mice (A), lack of effect of NE-100 (B), and antagonism by NE-100 of the igmesine-induced effect (C). Drugs were injected i.p. 30 min before the session on day 2. NE-100 was administered i.p. 15 min before igmesine, which was given 30 min before the session on day 2. The duration of immobility was recorded during the last 5 min over a 6-min session. Values are expressed as mean ± S.E.M. of the number of animals indicated inside each column. *P < 0.05, " P < 0.01 vs. the Vehicule-treated group; ^## P < 0.01 vs. the igmesine-treated group (Dunnett's test).

Figure 2 shows the antidepressant effect in the forced swim test in Swiss mice of desipramine (A) and fluoxetine (B). Drugs were injected i.p. 30 min before the session on day 2. Values are expressed as mean ± S.E.M. of the number of animals indicated inside each column. ^** P < 0.01 vs the Vehicle-treated group (Dunnett's test).

Figure 3 shows the antidepressant effect of neurosteroids in the forced swim test in Swiss mice: dose-response effect of DHEAS (A), PREGS (B), PROG (C), and antagonism by PROG of the

DHEAS-induced effect (D).

The steroids were injected i.p. 30 min before the session on day 2. PROG was administered i.p.

15 min before DHEAS, which was given 30 min before the test. Values are expressed as mean ±

S.E.M. of the number of animals indicated inside each column. P < 0.05, P < 0.01 vs. the Veh-treated group; ^# P < 0.01 vs. the DHEAS-treated group (Dunnett's test).

Figure 4 shows the antagonism of the antidepressant effect of igmesine by PROG (A) and of the DHEAS-induced effect by NE-100 (B).

PROG or NE-100 was administered i.p. 15 min before igmesine or DHEAS, respectively, which was given 30 min before the test. Values are expressed as mean ± S.E.M. of the number of animals indicated inside each column. ^* P < 0.05, ^** P < 0.01 vs. the Veh-treated group; ^# P < 0.01 vs. the igmesine- or DHEAS-treated group (Dunnett's test). Figure 5 shows the antidepressant effect of igmesine in the forced swim test in AdX/CX Swiss mice. Half of experimental groups were treated with fmasteride (25 mg/kg, s.c.) 14 and 2 hr before the session on day 2. The σi ligands were injected i.p. 30 min before the session. Values are expressed as mean ± S.E.M. of the number of animals indicated inside each column. ^** P < 0.01 vs. the Veh-treated group; ^m P < 0.01 vs. the igmesine- or PRE-084-treated group (Dunnett's test).

Figure 6 shows the antidepressant effect of DHEAS in the forced swim test in AdX/CX Swiss mice. Half of experimental groups were treated with fmasteride (25 mg/kg, s.c.) 14 and 2 hr before the session on day 2. The steroid was injected i.p. 30 min before the session. Values are expressed as mean ± S.E.M. of the number of animals indicated inside each column. ^** P < 0.05, ^** P < 0.01 vs. the Vehicle-treated group (Dunnett's test).

Figure 7 shows the antagonism of the antidepressant effect of igmesine (A) or DHEAS (B) by NE-100 in AdX/CX Swiss mice. NE-100 was administered i.p. 15 min before igmesine or DHEAS, which was given 30 min before the test. Values are expressed as mean ± S.E.M. of the number of animals indicated inside each column. P < 0.01 vs. the Veh-treated group; ^# P < 0.01 vs. the igmesine- or DHEAS-treated group (Dunnett's test).

Figure 8 shows the time course of the in vivo (+)-[³H]SKF- 10,047 binding levels after a swim stress in Swiss mice. Binding levels in the hippocampus (A), cortex (B), cerebellum (C), and immobility time of each experimental group (D).

Animals were submitted to forced swim during 15 min on day one and 6 min on day two, immobility being recorded during the last 5 min. The in vivo binding assays were performed at varying intervals after swim, the radioligand being injected 30 min before decapitation. Open circles: non-stressed control animals (n = 3). The number of animals per group is indicated within the column in (D). * P < 0.05, ** P < 0.01 vs non-stressed controls (Dunnett's test).

Figure 9 shows the time course of the in vivo (+)-[³H]SKF-l 0,047 binding levels after a swim stress in the of AdX/CX mice. Binding levels in the hippocampus (A), cortex (B), cerebellum (C), and immobility time of each experimental group (D). Animals were submitted to forced swim during 15 min on day one and 6 min on day two, immobility being recorded during the last 5 min. The in vivo binding assays were performed at varying intervals after swim, the radioligand being injected 30 min before decapitation. Open circles: non-stressed animals (n = 5). The number of animals per group is indicated within the column in (D). * P < 0.05, ** P < 0.01 vs non-stressed controls (Dunnett's test).

Figure 10 shows the brain contents in PROG in the hippocampus (A), cortex (B), cerebellum (C) and whole brain (D) of Swiss mice.

PROG levels were measured in intact, AdX/CX mice or AdX/CX mice treated for 7 days with trilostane and levels in non-stressed (D) or stressed (■) mice are compared. Stressed animals were sacrificed 30 min after swim. The number of samples was n = 4-8. P < 0.05, P < 0.01 vs non-stressed controls; * P< < 0.05, ** P < 0.01 vs the corresponding AdX/CX group (Welch's test).

Figure 11 shows the brain contents in PREG (A~D), PREGS (E~H), DHEA (I~L) and DHEAS (M~P) levels in hippocampus (A, E, I, M), cortex (B, F, J, N), cerebellum (C, G, K, L) and whole brain (D, H, L, P) of Swiss mice.

The neurosteroids levels were measured in intact, AdX/CX mice or AdX/CX mice treated for 7 days with trilostane and levels in non-stressed (D) or stressed (■) mice are compared. Stressed animals were sacrificed 30 min after swim. The number of samples was n = 4-8. P < 0.05, P < 0.01 vs non-stressed controls (Welch's test).

Figure 12 shows the correlation between the increases in PROG levels after swim stress and the inhibition of in vivo (+)-[³H]SKF-10,047 binding to σi sites in the mouse hippocampus, after different endocrine manipulations. Data for the inhibition of in vivo (+)-[³H]SKF- 10,047 binding correspond to the levels measured 30 min after stress in Fig. 9 for intact mice, Fig. 10 for AdX/CX mice and Fig. 11 for AdX/CX mice treated with trilostane. The corresponding PROG levels are presented in Fig. 12. The curve fitting correlation factor is r = 0.986. 6

DETAILED DESCRIPTION

Neurosteroids are steroids that are synthesized in the brain from sterol precursors (Baulieu, 1981). Neurosteroids include: - progesterone (PROG),

- 5 -pregnane-3β-ol-20-one (allopregnanolone),

- pregnenolone (PREG),

- dehydroepiandrosterone (DHEA), and

- PREG and DHEA sulfate esters (PREGS and DHEAS respectively). Apart from their well-known effects on the control of gene expression, neurosteroids modulate several neurotransmission systems, in an excitatory or inhibitory way (Rupprecht et al. 1996). PREGS and DHEAS act as excitatory neurosteroids, since they antagonize the activation of γ-aminobutyric acid type A (GABA_A) receptors, whereas they potentiate the activation of the N- methyl-D-aspartate (NMDA)-type of glutamatergic receptors. Other neurosteroids including PROG and allopregnanolone act as inhibitory neurosteroids, being very potent agonists of GABA_A receptors with affinities comparable to those of benzodiazepines. Neurosteroids are involved in several physiopathological events, such as response to stress, depression, anxiety, sleep, epilepsy and memory formation (for a review, see Schumacher et al. 1997). The interaction between neurosteroids and the σi receptor have been uncovered in binding studies (Maurice et al. 1996; Su et al. 1988; Yamada et al. 1994), then reported in physiological studies regarding several neuronal responses (Bergeron et al. 1994; Debonnel et al. 1996; Monnet et al. 1995). However the exact nature of this interaction, and how it can be used to influence disease states, still remained to be determined. The inventors have now shown that in steroid-depleted mammals, the antidepressant effect of o\ receptor agonists is optimized when endogenous steroid levels are low.

The compounds used in the invention are σ\ receptor agonists.

Preferred compounds are those of Formula I wherein

Rl is phenyl optionally mono-, di- or trisubstituted by halogen, lower alkyl, lower haloalkyl or lower alkoxy, R2 is lower alkyl,

R3 is hydrogen or lower alkyl,

R4 optionally carries a radical R_x wherein R_x is lower alkyl or phenyl,

R5 is phenyl optionally mono-, di- or trisubstituted by halogen or lower alkoxy, Q represents an ethylene-l,2-yl group -CH=CH- or a cyclopropane- 1,2-diyl group

H H C— C —

\ / C

² and m has a value of 1 or 2, the pharmaceutically acceptable salts thereof and the optically active forms thereof.

Other preferred compounds are those of Formula I wherein Rl is phenyl, R2 is lower alkyl and in particular ethyl, R3 is methyl, R4 is cycloalkyl -CH(CH2)_n which is unsubstituted and wherein n has a value of 2, 3, 4 or 5, R5 is phenyl and Q is an ethylene-l,2-yl group -CH=CH-.

The lower alkyl groups of the compounds used in the invention include straight, branched, or cyclic carbon chains of from 1 to 5 carbon atoms except where specifically stated otherwise. Representative groups are methyl, ethyl, isopropyl, «-propyl, «-butyl, wø-butyl, sec-butyl, tert- butyl, «-pentyl, 1-methylbutyl, 2,2-dimethylpropyl, and the like.

By haloalkyl and lower alkoxy, there are understood, preferably, the trifluoromethyl and methoxy radicals respectively.

The term "halogen" is intended to include fluorine, bromine and ,preferably, chlorine.

A more preferred compound is (E)-(+)-N-(cyclopropylmethyl)-α-ethyl-N-methyl-α-(3-phenyl-2- propenyl)benzenemethanamine hydrochloride, also known as igmesine hydrochloride (INN). The compounds used in the present invention can have multiple chiral centers in the above Formula I depending on their structure. In particular, the compounds used in the present invention may exist as diastereomers, mixtures of diastereomers, or as the mixed or the individual optical enantiomers. The present invention contemplates use of all such forms of the compounds.

The compounds utilized in the invention include solvates, hydrates, pharmaceutically acceptable salts, and polymorphs (different crystalline lattice descriptors) of the compounds of Formula I. Where it is appropriate to form a salt, the pharmaceutically acceptable salts include acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, calcium acetate, camsylate, carbonate, chloride, citrate, dihydrochloride, edetate, edisylate, estolate, esylate, fumarate, gluceptate, gluconate, glutamate, glycoloylarsanilate, hexylresorcinate, hydrabamine, hydrobromide, hydrochloride, hydroxynaphthoate, iodide, isethionate, lactate, lactobionate, malate, maleate, mandelate, mesylate, methylbromide, methylnitrate, methylsulfate, mucate, napsylate, nitrate, pamoate (embonate), panto thenate, phosphate/diphosphate, polygalacturonate, salicylate, stearate, subacetate, succinate, sulfate, tannate, tartrate, theoclate, triethiodide, benzathine, chloroprocaine, choline, diethanolamine, ethylenediamine, meglumine, procaine, aluminum, calcium, lithium, magnesium, potassium, sodium, and zinc. (See also "Pharmaceutical salts" by Berge S.M. et al. (1997) J. Pharm. Sci. 66: 1-19, which is incorporated herein by reference.) Use of a prodrug of a compound of the invention, such as would occur to one skilled in the art (see Bundgaard, et al, Acta Pharm. Suec, 1987; 24: 233-246), is also contemplated.

The terms "patient" and "subject" is intended to include a mammal, especially a human. It should also be noted that the method of the present invention can be used in patients presenting either low levels of neurosteroids, low levels of circulating steroids, or both, such as elderly patients (particularly patients of age 50 and over, more particularly of age 55 and over) and post- menopausal women, who are particularly sensitive to treatment with a sigma 1 receptor agonist. Since it has been shown in the literature for example that an elderly of 80 years old has a steroids level corresponding only to 10% of the level recorded in a young person aged of 25 years, low levels of (neuro)steroids are understood as decreased levels and preferably as a depletion of the said levels. The methods of this invention are carried out by administering to a mammal an effective amount of a σi receptor agonist, preferably a compound of Formula I, or a pharmaceutically acceptable salt thereof, to treat the disorders hereinbefore described.

Such effective amount will generally be from about 1 to about 400 mg per day. Preferred doses will be from about 10 mg to about 100 mg per day for an adult of 70 kg. More generally, the dose to be administered to steroid-depleted subjects will be about 5 to 50 % and preferably about 10 to 40 % of the average dose used for non steroid-depleted subjects.

In a further aspect of the present invention, there is provided a pharmaceutical composition for the treatment or prevention of depression comprising a sigma 1 receptor agonist of Formula I, together with at least one pharmaceutically acceptable carrier or excipient. For preparing pharmaceutical compositions from the compounds used in this invention, inert, pharmaceutically acceptable carriers can be either solid or liquid. Solid form preparations include powders, tablets, dispersible granules, capsules, cachets, and suppositories. A solid carrier can be one or more substances which may also act as diluents, flavoring agents, solubilizers, lubricants, suspending agents, binders, or tablet disintegrating agents; it can also be an encapsulating material. In powders, the carrier is a finely divided solid which is in a mixture with the finely divided active component. In tablets, the active component is mixed with the carrier having the necessary binding properties in suitable proportions and compacted in the shape and size desired. For preparing suppository preparations, a low-melting wax such as a mixture of fatty acid glycerides and cocoa butter is first melted and the active ingredient is dispersed therein by, for example, stirring. The molten homogeneous mixture is then poured into convenient sized molds and allowed to cool and solidify. The powders and tablets preferably contain 5% to about 70% of the active component. Suitable carriers are magnesium carbonate, magnesium stearate, talc, lactose, sugar, pectin, dextrin, starch, tragacanth, methyl cellulose, sodium carboxymethyl cellulose, a low-melting wax, cocoa butter, and the like.

The term "preparation" is intended to include the formulation of the active component with encapsulating material as a carrier providing a capsule in which the active component (with or without other carriers) is surrounded by a carrier which is thus in association with it. Similarly, cachets are included. Tablets, powders, cachets, and capsules can be used as solid dosage forms suitable for oral administration. Liquid form preparations include solutions, suspensions, and emulsions. Sterile water or water-propylene glycol solutions of the active compounds may be mentioned as an example of liquid preparations suitable for parenteral administration. Liquid preparations can also be formulated in solution in aqueous polyethylene glycol solution.

Aqueous solutions for oral administration can be prepared by dissolving the active component in water and adding suitable colorants, flavoring agents, stabilizers, and thickening agents as desired. Aqueous suspensions for oral use can be made by dispersing the finely divided active component in water together with a viscous material such as natural synthetic gums, resins, methyl cellulose, sodium carboxymethyl cellulose, and other suspending agents known to the pharmaceutical formulation art. Preferably the pharmaceutical preparation is in unit dosage form. In such form, the preparation is divided into unit doses containing appropriate quantities of the active component. The unit dosage form can be a packaged preparation, the package containing discrete quantities of the preparation, for example, packeted tablets, capsules, and powders in vials or ampoules. The unit dosage form can also be a capsule, cachet, or tablet itself, or it can be the appropriate number of any of these packaged forms.

A further aspect of the present invention is the use of a sigma 1 receptor agonist for the preparation of a medicament useful for preventing or treating depression in steroid-depleted patients. Since the examples show that the effect of the antidepressant drugs fluoxetine and desipramine failed to be affected by the removal of circulating steroids, clearly indicating that the mechanism of the antidepressant effect mediated by σi receptors does not involve an indirect inhibition of the monoamine transporters. Therefore, sigma 1 receptor agonists, which have a different mechanism of action from that of serotonin reuptake inhibitors (or other monoamine transporter inhibitors), may be of benefit in depressed patients not responsive to these monoamine transporter inhibitors. In hence, the present invention also concerns the use of a sigma 1 receptor agonist for the preparation of a medicament useful for preventing or treating depression in patients not responsive to monoamine transporter inhibitors.

Medicament should be understood in its broadest definition including particularly a pharmaceutical composition which is defined above as well as the term "preparation". The invention also concerns the use of igmesine which is a preferred sigma 1 receptor agonist for the preparation of a medicament useful for preventing or treating depression in steroid-depleted patients and/or in patients not responsive to monoamine transporter inhibitors .

Examples show that patients with lower levels of steroids (circulating steroids and/or neurosteroids), such as elderly patients (particularly patients of age 50 and over, more particularly of age 55 and over) and post-menopausal women, are particularly sensitive to treatment with a sigma 1 receptor agonist. Therefore the present invention also concerns the use of a sigma 1 receptor agonist or igmesine for the preparation of a medicament useful for preventing or treating depression in patients having neurosteroids levels depleted and/or in patients having circulating steroids levels depleted.

Accordingly, the invention relates also to the use of a sigma 1 receptor agonist or igmesine for the preparation of a medicament useful for preventing or treating depression in elderly steroid- depleted patients and/or in elderly patients not responsive to monoamine transporter inhibitors and /or in post-menopausal women.

The present invention will be further disclosed in the following examples without limiting the scope of the invention.

EXAMPLES The compounds of the instant invention are useful in the treatment of depression in steroid- depleted patients as demonstrated by means of the following pharmacological procedures.

A/ Influence of endogenous steroidal levels on the antidepressant effect of σi receptor agonists

Using the forced swim test in mice, through several endocrine manipulations — adrenalec- tomy/castration and inhibition of the 5α-reductase responsible for the formation of progesterone — it is demonstrated that endogenous steroidal levels have a major influence on the antidepressant effect of σi receptor agonists. Animals

Male Swiss OF1 mice (Breeding center of the Faculty of Pharmacy, Montpellier, France), aged 5-6 weeks and weighing 30 ± 2 g are used throughout the study. Animals are housed in plastic cages in groups. They have free access to laboratory chow and water, except during behavioral experiments, and they are kept in a regulated environment (23 ± 1°C, 40-60% humidity) under a 12-hr light/dark cycle (light on at 7:00 a.m.). Experiments are carried out between 9:00 a.m. and 6:00 p.m., in a soundproof and air-regulated experimental room, to which mice are habituated at least 30 min before each experiment.

Drugs PROG and fmasteride are suspended in sesame oil ; other drugs are solubilized in distilled water or saline solution. Drugs are injected subcutaneously (s.c.) or intraperitoneally (i.p.), in a volume of 100 μl per 20 g of body weight.

Forced swim test

Each mouse is placed individually in a glass cylinder (diameter 12 cm, height 24 cm) filled with water at a height of 12 cm. Water temperature is maintained at 22-23°C. The animal is forced to swim for 15 min on the first day. Animals are then allowed to return to their home cage. On the second day, each mouse is placed again into the water and forced to swim for 6 min. The session is videotaped and the duration of immobility during the last 5 min is measured. The mouse is considered as immobile when it stops struggling and moves only to remain floating in the water, keeping its head above water. Drugs are administered 30 min before the session on the second day. Finasteride is administered twice, 14 and 2 hr before the session on day 2.

Adrenalectomy (AdX) / castration (CX)

About one week after habituation to the animal facilities, animals are anaesthetized with sodium pentobarbital 2%, 100 μl/30 g body weight i.p. Both adrenal glands are removed, through incisions in the back of the animal, just below the breast ribs. The skin is sutured. Then, both testes are ligatured and cut, through an incision in the scrotum. Animals received an injection of gentamycine 10 mg/kg i.p. and recovered within few hours from surgery. After surgery, drinking tap water is replaced by saccharose 1%, NaCl 0.9% solution. Animals are used for behavioral experiments six days after surgery.

Statistical analysis Results are expressed as means ± S.E.M. Data are analyzed using the Dunnett's multiple comparisons test after an analyzis of variance (ANOVA, F values). The criterion for statistical significance is P < 0.05.

Effects ofσj receptor agonists on the immobility time in the forced swim test

Mice rapidly develop a marked behavioral despair during the forced swim, with an immobility time of 180 ± 4 s (n = 18) on the first day. This immobility time significantly increases up to 227 ± 5 s on the second day (t = 7.92, P < 0.01, paired t-test). The selective σi receptor agonist igmesine significantly shortens the immobility time in the forced swim test at the dose of 60 mg/kg i.p. (F(₄₎₇₅₎ = 4.43, P < 0.01; Fig. 1A).

The selective σi receptor antagonist NE-100 (Ukai et al., 1998), tested in the 1-10 mg/kg i.p. dose-range, does not affect the immobility time by itself (F( _?2η = 1.52, P > 0.05; Fig. IB). However, pre-administration of NE-100, at 10 mg/kg, completely antagonizes the reduction of immobility time induced by igmesine (F_{(4>4 )} = 24.75, P < 0.001; Fig. 1C), confirming that the drug acts through the involvement of the σj receptor.

The effects of the σi receptor agonists are compared to those exhibited by the antidepressant drugs desipramine and fluoxetine (Fig. 2). Both drugs shortened the immobility time, at the doses of 30 and 60 mg/kg i.p. (desipramine: F_{(4> )} = 17.76, P < 0.001; Fig. 2A; fluoxetine: F(₄₎₃9) = 8.00,P < 0.001; Fig. 2B).

Effects of neurosteroids on the immobility time in the forced swim test

DHEAS, administered in the 5-60 mg/kg dose range, slightly but significantly shortens the immobility time, at the 10 mg/kg dose (F_(5>89) = 2.80, P < 0.05; Fig. 3A). At lower or higher dosages, the steroid is devoid of effect. PREGS fails to affect the immobility time, in the 5-40 mg/kg dose range (F₍₄₎₇₄₎ = 1.74, P > 0.05; Fig. 3B).

PROG does not affect the immobility time by itself, in the 5-60 mg/kg dose range (F_(5j68) = 0.21, P > 0.05; Fig. 3C). However, pre-administration of PROG (20-60 mg/kg) before the DHEAS (10 mg/kg)-treatment leads to a significant antagonism of its effect as shown in Fig. 3D (F_(3>55)=6.46, P < 0.001).

Interestingly, a crossed pharmacology is observed between the effects induced by the σi receptor ligands and the steroids. First, the pre-administration of PROG fully blocks the igmesine-induced reduction of immobility (F_{(6>7 )} = 15.75, P < 0.001; Fig. 4A). Second, the selective σi receptor antagonist NE-100 also prevents the DHEAS-induced diminution of immobility time

Effects of σj receptor ligands on the immobility time in the forced swim test in AdX/CX animals AdX/CX animals show an immobility time of 178 ± 12 s (n = 12) on the first day, which significantly increases up to 242 ± 5 s on the second day (t = 4.26, P < 0.01, paired t-test). These values do not differ from those in control animals (P > 0.05 on each day). Igmesine shortens significantly the immobility time in AdX/CX animals, in a dose-dependent manner at 20 and 60 mg/kg (F_{( >49)} = 18.70, P < 0.001; Fig. 5), thus in a more efficient manner as compared to non- operated animals (Fig. 1A). Finasteride pretreatment, which leads to an increase in the endogenous levels of PROG, does not affect the immobility time exhibited by vehicle-treated AdX/CX mice, but significantly alters the diminution induced by igmesine, at 60 mg/kg (Fig. 5).

Effects of neurosteroids on the immobility time in the forced swim test in AdX/CX animals

In AdX/CX animals, DHEAS significantly shortens the immobility time, as shown in Fig. 6. The DHEAS treatment leads to significant diminution of the immobility time at all the doses examined, within the 5-60 mg/kg dose-range (F(_5?56) = 10.86, P < 0.001; Fig. 6) , thus in a more efficient manner as compared to non-operated animals (Fig. 3 A). The facilitation of the effect observed in AdX/CX mice can be clearly linked to a facilitation of the σi receptor-mediated effect, as confirmed using a pretreatment with NE-100 (Fig. 7). Indeed, NE-100 fully antagonizes both the antidepressant effect of igmesine in AdX/CX mice (F₍₃,₃₉₎ = 71.40, P < 0.001; Fig. 7A) and that of DHEAS (F(3,41) = 19.48, P < 0.001; Fig. 7B).

The effect of igmesine is enhanced in AdX/CX animals, as compared to non-operated mice. Igmesine is active at 10 mg/kg whereas in intact animals the effect occurs only at 60 mg/kg.

Such observations show that circulating steroids exert a tonic modulatory effect on the σi receptor-mediated antidepressant effect. They indicate that endogenous steroids tonically interfere with the antidepressant activity of igmesine, and that the efficacy of igmesine is optimized when endogenous steroidal levels are low.

Furthermore, selective σi receptor antagonist NE-100 antagonized the igmesine-mediated effect, clearly demonstrating the involvement of the σi receptor. As a consequence, patients with lower levels of steroids, such as elderly patients (particularly patients of age 50 and over, more particularly of age 55 and over) and post-menopausal women, are particularly sensitive to treatment with a sigma 1 receptor agonist.

Interestingly, the effect of the antidepressant drugs fluoxetine and desipramine failed to be affected by the removal of circulating steroids, clearly indicating that the mechanism of the antidepressant effect mediated by σj receptors does not involve an indirect inhibition of the monoamine transporters. Therefore, sigma 1 receptor agonists, which have a different mechanism of action from that of serotonin reuptake inhibitors (or other monoamine transporter inhibitors), may be of benefit in depressed patients not responsive to these monoamine transporter inhibitors.

B/ effect of swim stress on the σi receptor/neurosteroidal systems

The effect of swim stress is examined on the σ receptor/neurosteroidal systems, through in vivo and in vitro (+)-[³H]SKF- 10,047 binding to σi sites and measurements of (neuro)steroid contents in different brain structures of mice. Different endocrine conditions are used: intact vs AdX CX, non-stressed vs stressed, and treatment with the PROG synthesis inhibitor trilostane.

Animals

Male Swiss OF1 mice (Breeding center of the Faculty of Pharmacy, Montpellier, France), aged 5-6 weeks and weighing 30 ± 2 g were used. Animals are housed in plastic cages with free access to laboratory chow and water. They are kept in a regulated environment (23 ± 1°C, 40-60% humidity) under a 12-hr light/dark cycle (light on at 7:00 a.m.). All animal procedures are conducted in strict adherence of European Community Council Directives of 24 November 1986 (86-609/EEC).

Adrenalectomy/castration (AdX/CX)

About 1 week after habituation to the animal facilities, animals are anaesthetized with sodium pentobarbital 2% i.p., 100 μl/20 g body weight. Both adrenal glands are removed, through incisions in the back of the animal, just below the breast ribs. The skin is sutured. Both testes are ligatured and cut, trough an incision in the scrotum. After surgery, drinking water is replaced by saccharose 1%, NaCl 0.9%. Animals are used for experiments 6 days after surgery. AdX/CX mice treated with trilostane (10 mg/kg) are injected s.c. for 6 days every 12 h, from the day after the surgery.

Compounds

(+)-[³H]SKF- 10,047 (1820 GBq/mmol, 37 MBq/ml); [l,2,6,7-³H(N)]progesterone ([³H]PROG, 3589 GBq/mmol, 37 MBq/ml) ; [7-³H(N)]pregnenolone ([³H]PREG, 777 GBq/mmol, 37 MBq/ml) ; [l,2,6,7-³H(N)]dehydroepiandrosterone ([³H]DHEA, 2220 GBq/mmol, 37 MBq/ml) and [7-³H(N)]dehydroepiandrosterone sulfate ([³H]DHEAS, 592 GBq/mmol, 37 MBq/ml) are from New England Nuclear (Boston, MA, USA). The PREG antibody is from AbCys (Paris, France), PROG and DHEA antibodies are from Biovalley (Marne-la-Vallee, France). Trilostane is a generous gift from Dr G. Margetts (Stegram Pharmaceuticals, Billinghurst, UK).

Swim stress Each mouse is placed individually in a glass cylinder (diameter 12 cm, height 24 cm) filled with water at a height of 12 cm. Water temperature is maintained at 22-23°C. The animal is forced to swim for 15 min on the first day. Animals are then allowed to return to their home cage. Twenty- four hours later, each mouse is placed again into the water and forced to swim for 6 min.

In vivo (+)-[³H]SKF-l 0,047 binding measures after the swim stress

Mice are injected in a tail vein with 150 kBq of (+)-[³H]SKF- 10,047 and sacrificed 30 min later by decapitation. The hippocampi, cerebrum and cerebellum dissected out on ice, homogenized in a 5 mM Tris-HCl pH = 7.4 buffer at 4°C. Two 1 ml aliquots are filtered under vacuum through GF/C filters, presoaked in 0.05% polyethyleneimine (Sigma, Saint Louis, MO, U.S.A.). The total radioactivity is determined by counting 200 μl aliquots of the homogenates. Preliminary experiments show that the nonspecific binding, defined as the binding levels measured after the pre-administration of haloperidol, 2 mg/kg i.p., 10 min before the tracer, represents between 5 to 9% of the total binding [Maurice, 1996 #14; Phan, 1999 #627]. Therefore, results are expressed as total binding and calculated as bound to free radioactivity ratios [Maurice, 1996 #14; Phan, 1999 #627].

Extraction, purification and measurements of neurosteroids

Mice are sacrificed by decapitation, and the brains were quickly removed, dissected and pooled obtain approximately 500 mg of tissue. Samples are frozen immediately in dry ice until analysis. The samples are then weighed, and homogenized in ice-cold 10 mM phosphate buffer saline, pH 7.4 (PBS). Recovery tracers ([³H]PROG, [³H]PREG, [³H]DHEA, [³H]DHEAS, 50 Bq each) are added. Then, 10 ml of ethylacetate/isooctane, 1/1 vol/vol, is added and the tubes are vigorously stirred for 8 min. After centrifugation at 4,000 g for 5 min, the organic phase is removed and the extraction step is repeated twice. This organic phase is then defatted with a MeOH 90%/isooctane separation. The aqueous extracts containing unconjugated steroids are further purified by reverse-phase chromatography on Cι₈ cartridges (Amersham, Les Ulis, France). The isooctane phases containing lipoidal derivatives are thrown away. Sulfate esters are solvolyzed. The aqueous phase from the first separation is brought to pH = 1.0 with a few drops of sulfuric acid and to a NaCl concentration of 20%> by adding 2/1 vol vol of a 30%> NaCl solution. Extraction with ethylacetate is again performed as described above, and this extract, which contained steroid sulfates, is solvolyzed at 37°C for 16 h. Ethylacetate extracts are washed once with 1 N NaOH (0.25 vol.) and twice with water (0.25 vol.). The extracts are taken to dryness.

The different steroids are separated using partition chromatography on Celite⁵ (Prolabo, Fontenay-sous-Bois, France) microcolumns, with propanediol, 1 g, as the stationary phase.

Impregnated celite is settled in 5 ml disposable glass pipettes. Extracts are taken up in 1 ml of isooctane saturated with propanediol, and deposited onto the columns. PROG is eluted with 19 ml isooctane, PREG with 15 ml of isooctane/benzene (7/3 vol/vol) and DHEA with 20 ml of isooctane/benzene (1/1 vol vol). The recovery of the different steroids added as tracers is routinely 60-80%.

Results are expressed as means ± S.E.M. Data are analyzed using the Dunnett's multiple comparisons test after analysis of variance (ANOVA, F values). For the neurosteroid measurement, statistical comparison of the data is made using the Welch's test. The criteria for statistical significance were P < 0.05, P < 0.01, P < 0.001.

The availability of the σi receptor after stress and following different endocrine manipulations is examined in brain structures selected for: (i) their involvement in the response to stress, (ii) their role in mediating the cognitive effects of σi agonists, and (iii) the possibility to measure the neurosteroid levels using the extraction/purification/RIA technique, i.e., the hippocampi and cortex, plus a control structure, the cerebellum. In control animals submitted to a swim stress (Fig. 8), a significant reduction of the in vivo (+)-[³H]SKF- 10,047 binding level is observed in the hippocampus (F(_{4j 2}) = 5.74, P < 0.001; Fig. 8A). The inhibition is observed immediately after the stress and at the 30 min time-point, when a 27% reduction was measured. No change is observed in the cortex (F₍₄,₂₂₎ = 1.01, P > 0.05; Fig. 8B) and cerebellum (F₍₄,₂₂₎ = 0.10, P > 0.05; Fig. 8C). The immobility duration is checked and not differs among each experimental group (F(₃,i9) = 1.41, P > 0.05; Fig. 8D). In AdX/CX animals submitted to a swim stress (Fig. 9), the in vivo (+)-[³H]SKF- 10,047 binding level significantly decreases in the hippocampus (F_{( j23)} = 5.62, P < 0.001; Fig. 9 A). The inhibition is observed immediately after the stress and remains significant until the 60 min time-point. At 30 min after the swim stress, a 48%> reduction is measured. No change is observed in the cortex (F_(4ι23) = 1.08, P > 0.05; Fig. 9B) and cerebellum (F₍₄₍₂₃₎ = 0.44, P > 0.05; Fig. 9C). In addition, the immobility duration not differs among each experimental group (F_(3;ι₉₎ = 2.30, P > 0.05; Fig. 9D).

The neurosteroid measurements are limited to the steroids known to interact with the σi receptor, namely PROG, PREG, DHEA, and their respective sulfate esters. The PROG levels measurements in the different experimental conditions and in the different brain structures are summarized in Fig. 10. In control mice, no significant difference is observed between structures, with an average

PROG content of 3 ng/g of tissue. The swim stress resulted in a significant increase of PROG levels in the hippocampus (P < 0.05; Fig. 10A). This effect is not observed in the cortex (Fig. 10B) or cerebellum (Fig. 10C), but remained significant in the whole brain (Fig. 10D). The measurements of the other neurosteroids led to less consistent differences, as detailed in Fig. 11. The surgery not affects the levels of all the neurosteroids examined. Only mild effects of stress are evidenced. PREG levels increased in the whole brain of intact animals (P < 0.05; Fig. 11D) and significant increases in DHEAS contents are observed in the cortex (P < 0.01; Fig. UN) and whole brain (P < 0.01; Fig. I IP) of intact animals, and in the cortex of AdX/CX animals (P < 0.05; Fig. UN).

In AdX/CX mice, PROG levels are unchanged as compared with the levels of intact animals. The PROG level was significantly increased after stress in the hippocampus (P < 0.01; Fig. 10A). This increase is greater than in intact mice: +150% vs +80%. This effect is not observed in the cortex (Fig. 10B) or cerebellum (Fig. 10C), but remained significant in the whole brain (P < 0.05; Fig. 10D). The treatment with trilostane resulted in a significant decrease of PROG levels in each structure examined and in the whole brain. In addition, stress failed to affect the PROG levels in trilostane-treated AdX CX mice (Fig. 10A-D).

In summary, and as shown in Fig. 12, a strong correlation is observed between the extent of the increases in PROG levels observed 30 min after stress and the extent of the inhibition of in vivo (+)-[³H]SKF- 10,047 binding in the hippocampus.

In conclusion, this study illustrated also a particularity of the mechanism of the antidepressant- like effect induced by the σi receptor agonists, due to their interaction with the neurosteroid hormonal system. An acute stress induces the release of PROG from the peripheral and central sources, which in turn interacts transiently with the σi receptor. This negative regulation, since PROG behaves as a potent σi antagonist, must be overridden by the selective synthetic σi agonists to exert their antidepressant-like effect. These observations, first, strengthen the hypothesis that PROG is a good candidate to be the endogenous σi receptor ligand, or at least a potent endogenous modulator, and, second, confirm that selective σi agonists present a particular therapeutic interest to alleviate the cognitive deficits, including response to stress and depression, in populations of patients with identified hormonal deficits and particularly the aged.

References

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Bergeron R, De Montigny C, Debonnel G (1994) Progesterone suppresses the potentiation of the NMDA response induced by selective sigma ligands. Soc Neurosci Abstr 20: 748 Debonnel G, Bergeron R, de Montigny C (1996) Potentiation by dehydroepiandrosterone of the neuronal response to N- methyl-D-aspartate in the CA3 region of the rat dorsal hippocampus: an effect mediated via s (sigma) receptors. J Endocrinol 150 Suppl: S33-42

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Claims

1) A method for treating depression comprising administering to a steroid-depleted patient suffering therefrom and in need of treatment an effective amount of a sigma 1 receptor agonist.

2) A method according to Claim 1 wherein the sigma 1 receptor agonist is a compound of

Formula I

wherein:

R2 is lower alkyl,

R3 is hydrogen or lower alkyl, R4 is cycloalkyl -CH(CH2)_n wherein n has a value of 2, 3, 4 or 5 and wherein a carbon atom of R4 optionally carries a radical R_x wherein R_x is lower alkyl or phenyl,

Q represents an ethyl ene-l,2-yl group -CH=CH- or a cyclopropane- 1,2-diyl group

H H C— C

\ / C

3) A method according to Claim 1 wherein the sigma 1 receptor agonist is igmesine.

4) A method according to Claim 1 wherein the steroid-depleted patient is an elderly patient.

5) A method according to Claim 4 wherein the elderly patient is a human of age 50 or older. 6) A method according to Claim 1 wherein the steroid-depleted patient is a post-menopausal woman.

7) A method according to Claim 1 wherein the steroid-depleted patient is not responsive to monoamine transporter inhibitors.

8) A method according to Claim 1 wherein the steroid-depleted patient has depleted neurosteroid levels.

9) A method according to Claim 1 wherein the steroid-depleted patient has depleted circulating steroid levels.

10) A method for preventing depression in a steroid-depleted patient comprising administering to a subject at risk thereof and in need of prophylaxis an effective amount of a sigma 1 receptor agonist.

11) The use of a sigma 1 receptor agonist for the preparation of a medicament useful for preventing or treating depression in steroid-depleted patients and/or in patients not responsive to monoamine transporter inhibitors.

12) The use of igmesine for the preparation of a medicament useful for preventing or treating depression in steroid-depleted patients and/or in patients not responsive to monoamine transporter inhibitors.

13) The use of a sigma 1 receptor agonist according to claim 11 or igmesine according to claim 12 for the preparation of a medicament useful for preventing or treating depression in patients having neurosteroids levels depleted and/or in patients having circulating steroids levels depleted. 14) The use of a sigma 1 receptor agonist according to claim 11 or igmesine according to claim 12 for the preparation of a medicament useful for preventing or treating depression in elderly steroid-depleted patients and/or in elderly patients not responsive to monoamine transporter inhibitors.

15) The use of a sigma 1 receptor agonist according to claim 11 or igmesine according to claim 12 for the preparation of a medicament useful for preventing or treating depression in post- menopausal woman.