Patent Application
20070282007
The present invention provides several embodiments of a method for treating pain disorders, such as neuropathic pain disorders and fibromyalgia. The method encompasses administering enantiomerically enriched P or enantiomerically enriched Q, or any mixture or pharmaceutically acceptable salt thereof. Thus, in one embodiment, the present invention is a method for treating a pain disorder in a human, the method comprising administering to a person in need of therapy for a pain disorder a therapeutically effective amount of a compound chosen from (1R,4S)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-naphthalenamine (P); (1S,4R)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-naphthalenamine (Q); mixtures of P and Q; and pharmaceutically acceptable salts thereof.
When the method encompasses administering a therapeutic amount of either enantiomerically enriched P or enantiomerically enriched Q, or pharmaceutically acceptable salt thereof, the term “enantiomerically enriched” refers to about 80% to about 100% enantiomeric excess of P or Q, respectively. Thus, the present invention is also a method for treating a pain disorder in a human, the method comprising administering to a person in need of therapy for a pain disorder a therapeutically effective amount of a compound chosen from (1R,4S)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-naphthalenamine (P); (1S,4R)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-naphthalenamine (Q); and pharmaceutically acceptable salts thereof; wherein P or Q is present in about 80% to about 100% enantiomeric excess. In one preferred embodiment, P or Q is present in about 90% to about 100% enantiomeric excess. In another preferred embodiment, P or Q is present in about 95% to about 100% enantiomeric excess. In yet another preferred embodiment, P or Q is present in about 99% to about 100% enantiomeric excess. The pain disorder may be neuropathic pain disorders or fibromyalgia.
The term “enantiomeric excess” is well known in the art and is defined for a resolution of ab into a+b as
The term “enantiomeric excess” is related to the older term “optical purity” in that both are measures of the same phenomenon. The value of ee will be a number from 0 to 100, zero being racemic and 100 being pure, single enantiomer. A compound which in the past might have been called 98% optically pure is now more precisely described as 96% ee.; in other words, a 90% e.e. reflects the presence of 95% of one enantiomer and 5% of the other in the material in question.
The term “treating” when used in connection with one or more pain disorders means amelioration, prevention, or relief from one or more of the symptoms and/or effects associated with a pain disorder, and includes the prophylactic administration of P or Q, or a mixture thereof, or pharmaceutically acceptable salt thereof, to substantially diminish the likelihood or seriousness of the condition or disorder.
The term “pharmaceutically acceptable salt” refers to salts prepared from pharmaceutically acceptable non-toxic acids including inorganic acids and organic acids. Exemplary acids that form pharmaceutically acceptable salts with the amines of the invention and that may be used in the compositions of the present invention are acetic acid, benzenesulfonic (besylate) acid, benzoic acid, isethionic acid, camphorsulfonic acid, citric acid, ethenesulfonic acid, fumaric acid, gluconic acid, glutamic acid, hydrobromic acid, hydrochloric acid, lactic acid, maleic acid, malic acid, mandelic acid, methanesulfonic acid, mucic acid, nitric acid, pamoic acid, pantothenic acid, phosphoric acid, succinic acid, sulfuric acid, p-toluenesulfonic acid and tartaric acid. The hydrochloric acid salt is particularly preferred.
Preparation of compounds of the present invention is illustrated below in Scheme 1 and its accompanying narrative.
In the compound
of Scheme 1,
wherein R1, R2 and R3 are each independently alkyl. In a preferred embodiment of the compounds, R is tert-butyl.
N-[4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydronaphthalen-1-yl]formamide, the intermediate in the synthesis shown in Scheme 1, exists in four stereoisomeric forms:
When N-[4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydronaphthalen-1-yl]formamide is synthesized from achiral starting materials via non-stereoselective syntheses, all four isomers will be produced. The mixture can be readily separated into a racemic cis diastereomer and a racemic trans diastereomer by means, such as recrystallization or chromatography on achiral media, that rely on chemical and physical differences.
The trans diastereomer, represented as E below, is a 1:1 mixture of A and B. When E is hydrolyzed, PQ is produced, when A is hydrolyzed, P is produced, when B is hydrolyzed, Q is produced. The cis diastereomer, represented as F below, is a 1:1 mix of C and D.
The graphic representations of racemic, ambiscalemic and scalemic or enantiomerically pure compounds used herein are taken from Maehr, J. Chem. Ed., 62:114-120 (1985): solid and broken wedges are used to denote the absolute configuration of a chiral element; wavy lines indicate disavowal of any stereochemical implication which the bond it represents could generate; solid and broken bold lines are geometric descriptors indicating the relative configuration shown but not implying any absolute stereochemistry; and wedge outlines and dotted or broken lines denote enantiomerically pure compounds of indeterminate absolute configuration.
Thus, formula PQ above indicates any mixture of the individual isomers P and Q, which share the trans relative configuration. Clearly, the most convenient mixture is the 1:1 racemate.
According to the present invention, a therapeutically effective amount of N-[4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydronaphthalen-1-yl]formamide, which may be a pure isomer or a mixture of any or all of A, B, C and D, may also be administered to a person in need of therapy. Accordingly, the present invention encompasses a method for treating a pain disorder in a human, the method comprising administering to a person in need of treatment for a pain disorder, a therapeutically effective amount of a compound of formula K:
wherein A, B, C, or D is present in about 80% to about 100% enantiomeric excess. In one embodiment, A, B, C, or D is present in about 90% to about 100% enantiomeric excess. In another embodiment, A, B, C, or D is present in about 95% to about 100% enantiomeric excess. In yet another embodiment, A, B, C, or D is present in about 99% to about 100% enantiomeric excess.
In one embodiment, the compound of formula K is a mixture of A and B.
In another embodiment, the compound of formula K is a mixture of C and D.
Pain disorders treatable with the compounds of the invention include, but are not limited to neuropathic pain and fibromyalgia.
Neuropathic pain disorders treatable with the compounds of the invention include, but are not limited to: burning and tingling sensations, hypersensitivity to touch and cold, phantom limb pain, postherpetic neuralgia, diabetic peripheral neuropathy, and chronic pain syndrome. In one particular embodiment, chronic pain syndrome is reflex sympathetic dystrophy or causalgia.
Current approaches to treating neuropathic pain disorders in man are the selective inhibition of a single monoamine uptake mechanism or the dual inhibition of two of these molecular targets. Inhibition of neuronal uptake of all three of 5-HT, NE and DA using the methods of the present invention provides the clinician with the ability to treat the neuropathic pain disorders more effectively by elevating all of the monoamine levels in the nervous system simultaneously and over the same dose-range without the need to titrate separate drugs.
Fibromyalgia disorders treatable with the compounds of the invention include, but are not limited to: generalized fibromyalgia, primary fibromyalgia syndrome, secondary fibromyalgia syndrome, localized fibromyalgia, and myofascial pain syndrome.
Current approaches to treating fibromyalgia disorders in man are by increase of 5-HT and NE levels by use of reuptake inhibitors. Since the compounds of the present invention are potent 5-HT and NE reuptake inhibitors they are useful in increasing 5-HT and NE levels, which has a beneficial effect on symptoms associated with fibromyalgia disorders. Furthermore, the compounds of the present invention exhibit equipotent selective inhibition of neuronal uptake of an additional monoamine, DA. The capability to selectively elevate all of the monoamine levels simultaneously and over the same do se-range is an advantageous quality of the compounds used in the methods of the present invention.
Administration of compounds of the present invention results in a broad therapeutic profile. Due to the ability of the compounds of the present invention to inhibit monoamine uptake without affecting other receptors or ion channels, their administration can avoid or ameliorateside-effects that are associated with an Imbalance in the distribution of activity among 5-HT, NE and DA receptors. Such side effects may include extrapyramidal symptoms, elevated serum prolactin levels, sexual dysfunction (decreased libido, anorgasmia, ejaculatory dysfunction), breast pain, weight gain and insomnia.
The magnitude of a prophylacetic or therapeutic dose of a compound of formula A-F, P or Q will vary with the nature and severity of the condition to be treated and the route of administration. The dose will also vary according to the age, body weight and response of the individual patient. In general, the total daily dose ranges of compounds of the present invention will be from about 0.5 mg per day to about 100 mg per day, preferably about 1 mg per day to about 25 mg per day, in single or divided doses. It may be necessary to use dosages outside these ranges in some cases, as will be apparent to those in the art. Further, it is noted that the clinician or treating physician knows how and when to interrupt adjust or terminate therapy in conjunction with an individual patient's response.
Any suitable route of administration may be employed. For example, oral, rectal, intranasal, and parenteral (including trans- or subcutaneous, intramuscular, and intravenous) routes may be employed. Dosage forms can include tablets, troches, dispersions, suspensions, solutions, capsules and patches.
Pharmaceutical compositions of the present invention include, as active ingredient, a single compound, or a mixture of compounds, of formula A-F, P or Q, or a pharmaceutically acceptable salt of P or Q, together with a pharmaceutically acceptable carrier and, optionally, with other therapeutic ingredients.
Compositions suitable for oral, rectal, and parenteral administration are encompassed by the present invention. A preferred route of administration is oral. The compositions may be conveniently presented in unit dosage form and prepared by any of the methods well known in the art of pharmacy. Preferred unit dosage formulations are those containing a therapeutically effective dose, or an appropriate fraction thereof, of the active ingredient(s).
The compositions of the present invention will also include a pharmaceutically acceptable carrier. The carrier may take a wide variety of forms, depending on the route desired for administration, for example, oral or parenteral (including intravenous). In preparing the composition for oral dosage form, any of the usual pharmaceutical media may be employed, such as, water, glycols, oils, alcohols, flavoring agents, preservatives, and coloring agents in the case of oral liquid preparation, including suspension, elixirs and solutions. Carriers such as starches, sugars, microcrystalline cellulose, diluents, granulating agents, lubricants, binders and disintegrating agents may be used in the case of oral solid preparations such as powders, capsules and caplets, with the solid oral preparation being preferred over the liquid preparations. Preferred solid oral preparations are tablets or capsules, because of their ease of administration. If desired, tablets may be coated by a standard aqueous or nonaqueous techniques. Oral and parenteral sustained release dosage forms may also be used.
Oral syrups, as well as other oral liquid formulations, are well known to those skilled in the art, and general methods for preparing them are found in any standard pharmacy school textbook for example Remington: The Science and Practice of Pharmacy. Chapter 86 of the 19th edition of Remington entitled “Solutions, Emulsions, Suspensions and Extracts” describes in complete detail the preparation of syrups (pages 1503-1505) and other oral liquids.
Similarly, sustained release formulation is well known in the art, and Chapter 94 of the same reference, entitled “Sustained-Release Drug Delivery Systems,” describes the more common types of oral and parenteral sustained-release dosage forms (pages 1660-1675.) The relevant disclosure of each of these chapters is incorporated herein by reference. Because they reduce peak plasma concentrations, as compared to conventional oral dosage forms, controlled release dosage forms are particularly useful for providing therapeutic plasma concentrations while avoiding the side effects associated with high peak plasma concentrations that occur with conventional dosage forms.
To a solution of 4-((3,4-dichlorophenyl)-3,4-dihydro-1-naphthalene (12 g) in THF (40 mL) was added (R)-t-butanesulfinamide (5.2 g) and Ti(OEt)4 (85 mL 20%) in EtOH. The reaction mixture was heated to 60° C. for 13 h. The reaction mixture was cooled to rt, and poured into a brine solution (100 mL) with stirring. The suspension was then added to EtOAc (300 mL) and stirred for 10 min. The suspension was filtered and the filtrate was concentrated to ca 50 mL. One hundred milliliters of EtOAc was added and the organic phase was separated and concentrated to give a crude reaction mixture. The final products were isolated from the crude products by careful flash column chromatography using EtOAc and hexane (3:7 to 1:1) to give ca 3 g starting ketone, and (1R,4S)-4-(3,4-dichlorophenyl)-3,4-dihydro-1-naphthalenone tert-butanesulfinimine (2.5 g, first product) as an oil that solidified on standing. 1H NMR (CDCl3) δ 1.33 (S,9H), 2.10-2.20 (m, 1H), 2.28-2.38 (m, 1H) 2.88-2.98 (m, 1H), 3.34-3.44 (m 1H), 4.12-4.24 (m, 1H), 6.84-6.88 (m, 2H), 7.20 (s,1H), 7.25-7.40 (m, 3H), 8.22-8.28 (m, 1H). The other product (1R,4R)-4-(3,4-dichloro phenyl)-3-4-dihydro-1-naphthalenone tert-butanesulfinimine (3.0 g, second product, lower Rf) was isolated also as an oil that solidified on standing. 1H NMR (CDCl3) δ 1.34 (S, 9H), 2.05-2.18 (m, 1H), 2.28-2.38 (m, 1H), 3.15-3.25 (m, 2H), 4.16-4.22(m,1H), 6.84-6.88(m,2H), 7.20(s,1H), 7.25-7.40(m,3H), 8.22-8.28(m, 1H).
(1R,4R)-4-(3,4-dichlorophenyl)3,4-dihydro-1-naphthalenone t-butanesulfinimine (3.0 g, second product in Example 1.1 above) was dissolved in MeOH (20 mL) and concentrated HCl (4 mL) at rt. The reaction mixture was stirred at rt to give a suspension. It was filtered and the solids were washed with hexane to give 1.2 g product. The enantiomeric purity was determined to be >99.3% by HPLC analysis with a ChiralPak AS 10:m, 4.6×250 mm, Hexane/IPA (90:10), TV 220 nm, R-isomer 8.23 min. S-isomer 12.25 min. 1H NMR (CDCl3) δ 2.20-2.32 (m, 1H), 2.42-2.53 (m, 1H) 2.57-2.78 (m,2H), 4.28 (dd=4.6, 8.1 Hz, 1H), 6.95 (dd, J=2.1, 7.6 Hz, 2H), 7.23 (d J=2.0 Hz, 1H), 7.37-50 (m, 3H), 8.13 (d, J=7.6 Hz, 1H). [α]=−66E (c=1, acetone).
The previous procedure of Example 1.2 was used, except that the starting material was the (1R,4S)-4-(3,4-dichlorophenyl)-3,4-dihydro-1-naphthalenone tert-butanesulfinimine product of Example 1.1. 1.7 g of product (>99% ee) was obtained.
[α]=+62 (c=1, acetone). 1H NMR spectrum of the product is the same as that of its enantiomer.
(R)-4-(3,4-dichlorophenyl)-3,4-dihydro-1-naphthalenone (1.2 g) was added formic acid (3 mL) and formamide (3 mL). The reaction mixture was heated to 160-165° C. for 15 h under nitrogen atmosphere. The reaction mixture was cooled to room temperature and decanted the solvent. The residue solid was passed through flash column using EtOAc:Hexane (3:7 to 1:1) to give the (1R,4R)-formamide (400 mg, first spot), and the (1S,4R)-formamide (360 mg). 1H NMR of the first product [(1R,4R)-isomer]: (CDCl3) δ 1.80-2.10 (m, 3H), 2.10-2.20 (m, 1H), 4.00-4.10 (m, 1H), 5.22-5.30 (m, 1H), 6.10-6.20 (m, 1H), 6.80-6.90 (M, 1H), 6.90-6.96 (m, 1H), 7.10-7.40 (m, 5H), 8.22 (s, 1H). M+320. 1H NMR of the second product [(1S,4R)-isomer: δ 1.64-1.90 (m, 2H), 2.10-2.28 (m, 2H), 4.10 (m, 1H), 5.38-5.42 (m, 1H), 5.82-6.05 (m, 1H), 6.80-6.90 (m, 2H), 7.10-40 (m, 5H), 8.28 (s, 1H). Mass Spec. M+ 320.
(1S,4R) formamide (ca 300 mg) from Example 1.4 above was dissolved in MeOH (5 mL) followed by addition of 6N HCl (6 mL). The reaction mixture was heated to 80° C. for 2 h. The reaction mixture was cooled to rt for 1 h and filtered to collect the solid. It washed with acetone (3 mL) and dried to give the product (280 mg). Enantiomeric purity was determined to be >99.8% by HPLC analysis with a ChiralPak AD 10 μm, 4.6×250 mm, Hexane/IPA/DEA (99:1:0.1), UV 220 nm, (1R,4S)-isomer, 11.00 min. (1S,4R)-isomer 11.70 min [α]=−51° (C=1, MeOH). 1H NMR (CD3OD) δ 1.86-1.97 (m, 2H), 2.20-2.42 (m, 2H), 4.30 (broad s, 1H), 4.67 (broad s, 1H), 4.87 (s, 3H), 6.95-6.99 (m, 2H), 7.18 (s, 1H), 7.28-7.50 (m, m, 4H). M+ 293.
(1R,4S)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamine HCl was obtained similarly from (1R,4S) formamide with HCl hydrolysis. Ee of the product is >99.8% based on HPLC analysis with a ChiralPak AD 10:m, 4.6×250 mm, Hexane/IPA/DEA (99:1:0.1), UV 220 nm, (1R,4S)-isomer 11.00 min. (1S,4R)-isomer 11.70 min.
The experimental data presented below demonstrates that compound P and compound Q are potent inhibitors of the reuptake of NE, DA and 5-HT. The monoamine reuptake inhibitory properties of compounds P and Q make them useful in treatment of pain disorders and reduce side effects associated with imbalance in monoamine levels. The triple monoamine reuptake inhibition properties of compounds P and Q give them advantage in treatment of various pain disorders.
Furthermore, present studies demonstrated that compound P has potential for rapid onset of action and long duration of action. Compound P was shown to be a specific monoamine reuptake inhibitor with little additional pharmacologic activity. The lack of additional activity significantly improves its side effect profile over current compounds used in treatment of neuropathic pain, such as tricyclic antidepressants. Present experiments demonstrated no effect on ECG, heart rate, or blood pressure at doses up to those maximally tolerated in dogs. This shows an improved cardiovascular effect profile over other agents used to treat neuropathic pain.
Studies were performed to obtain and compare Ki (inhibition constant) values of (1R,4S)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamine (Compound P) and sertraline (ZOLOFT™ in radiolabeled binding assays.
The assays measured the affinity of the two compounds for transporters of the monoamines 5-HT, NE and DA. The assay for affinity to the 5-HT transporter was performed essentially as outlined in Tatsumi M. et al., Eur. J. Pharmacol. 340 249 (1997). The assay for affinity to the NE transporter was performed essentially as outlined in Pacholczyk T. et al., Nature, 350: 350 (1991). The assay for affinity to the DA transporter was performed essentially as outlined in Andersen P. H., J. Neurochem, 48: 1887 (1987). The transporters were human recombinant proteins expressed in mammalian cells. Binding to the 5-HT transporter was assessed by evaluating displacement of [3H]paroxetine (0.1 nM). Binding to the DA transporter was assessed by evaluating displacement of [3H]GBR 12935 (0.5 nM). Binding to the NE transporter was assessed by evaluating displacement of [3H]nisoxetine (0.3 nM). The results of the assays are presented in Table 1
As could be seen in Table 1, (1R,4S)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamme (Compound P) has high affinity to human recombinant 5-HT, NE and DA transporters. Unlike sertraline, a 5-HT specific reuptake inhibitor, Compound P has high and approximately equal affinity for all three transporters.
(1R,4S)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamine (Compound P), (1S,4R)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamine (Compound Q), and a mixture of the two were tested for their ability to inhibit the functional uptake of radiolabeled 5-HT, NE, and DA into synaptosomes prepared from rat whole brain, hypothalamus, or corpus striatum, respectively. The 5-HT and NE assays were performed essentially as outlined in Perovic S. & Müller W. E. G., Arzneim.-Forsch. Drug Res., 45: 1145 (1995). The DA assay was performed essentially as outlined in Janowsky A. et al., Neurochem., 46: 1272 (1986).
IC50 values (concentration inhibiting control activity by 50%) for Compounds P, Q, a mixture of the two, and some known monoamine reuptake inhibitors are shown in Table 2. Fluoxetine (PROZAC®) IC50 values were taken from Wong et al., Neuropsychopharmacology, Jun, 8(4):337-44 (1993).
Unlike the 5-HT specific reuptake inhibitors (sertraline, fluoxetine and citalopram) and the “dual” reuptake inhibitors (venlafaxine and bupropion), Compounds P and Q potently inhibit the uptake of all three monoamines. Compound P is approximately equipotent in inhibiting the uptake of all three monoamines. Compound Q is approximately ten-fold less potent in inhibiting 5-HT reuptake, and three to four-fold less potent in inhibiting NE and DA reuptake when compared to Compound P.
(1R,4S)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamine (Compound P) and (1S,4R)-trans 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-napthalenamine (Compound Q) were also tested for their ability to inhibit functional uptake of radiolabeled 5-HT, NE, and DA into cells expressing recombinant human transporters. Cells expressing recombinant human transporters were obtained following the protocols of Gu H. et al., J. Biol. Chem., 269(10): 7124 (1994). Testing of the uptake inhibition was performed following protocols disclosed by Galli A. et al., J. Exp. Biol., 198: 2197 (1995), Giros B. et al., Mol. Pharmacol., 42: 383 (1992), Pristupa Z. B. et al., Mol. Pharmacol., 45: 125 (1994), and Gu H. et al., J. Biol. Chem., 269(10): 7124 (1994).
Consistent with the results obtained using rat brain as source material, both Compound P and Compound Q potently inhibited the functional uptake of 5-HT, NE, and DA.
Compound P and sertraline were compared in a broad in vitro screen of radioligand binding assays, which included 68 receptors. At a concentration of 10 μM, less than 50% inhibition of specific binding was observed in most of these receptors and the assays in which this was seen are listed in Table 4 below.
In thirteen assays, greater than 50% inhibition of specific binding was seen at a concentration of 10 μM. With the exception of the muscarinic (M3) receptor, all Ki values were 1 μM or higher and/or comparable to sertraline. The results are summarized in Table 5. The Ki at M3 is approximately 10-fold higher than Ki values at the monoamine transporters (see Table 1) and 25 to 50-fold higher than effective concentrations in functional assays (see Table 2).
To determine whether Compound P is a muscarinic agonist or antagonist, its effects on the isolated Guinea pig ileum were evaluated and compared to those of sertraline. The assays were performed following protocols described by Clague et al., Brit. J. Pharmacol., 86: 163 (1985). To evaluate for possible agonist effects, graded concentrations of compound P or sertraline alone were tested. To evaluate for possible antagonist effects, the ability to antagonize carbachol-induced contraction was examined at different concentrations of test article (added before re-challenge with carbachol). The experiments demonstrated that Compound P is no an M3 agonist. The results of experiments examining M3 antagonism are presented in Table 6 below.
Both Compound P and sertraline inhibited carbachol induced contractions, and with approximately equal potency. The results demonstrate that, although Compound P has a higher affinity for the M3 receptor, its functional M3 antimuscrianic activity is comparable to that of sertraline.
Performance in the Porsolt forced swim test was evaluated for sertraline and Compound P following protocols outlined in Porsolt R. D., et al., Arch. Int. Pharmacodyn., 229: 327 (1997).
The Porsolt forced swim test is a model of “behavioral despair”, which has been used as an in vivo model for assessing potential antidepressant-like activity. Both test articles were dissolved in physiological saline (vehicle) and administered intraperitoneally. Doses for Compound P were 1.25, 2.5, and 5.0 mg/kg (N=3-6/dose/group). Doses for sertraline were 2.5, 5.0 and 10 mg/kg (N=2-6/group). Long-Evans derived rats were used. Table 7 shows results from the Porsolt swim test in which Compound P was administered twice daily starting 2 days prior to testing (for a total of 3 administrations) or 4 days prior to testing (for a total of 7 administrations).
#Error value is std dev since N = 2;
Compound P was active and significantly different than controls at 2.5 and 5.0 mg/kg (i.p.) in both the two-day and four-day Porsolt forced swim tests. It is noteworthy that a subchromic protocol, whereby animals receive a number of drug administrations over a period of at least 4-days, must be used to show antidepressant like activity for SSRIs (i.e. fluoxetine, as shown in Vazquez-Palacios et al. Pharmacol Biochem Behav 78: 165 (2004) and Lifschytz et al. Eur Neuropsychopharmacol 16: 115 (2006)), whereas atypical anti-depressants (i.e. desipramine, data not shown) demonstrate activity after only 3 drug administrations over 2-days. Therefore, the triple uptake activity of Compound P may provide features of both typical and atypical antidepressants, and may have a faster onset of action than the SSRIs. Although not a model of neuropathic pain, efficacy in this model demonstrates that Compound P crosses the blood-brain barrier and has the anticipated effects on monoamine reuptake in vivo. In addition, the rapid onset of the effects suggests that Compound P will exert beneficial effects semi-acutely.
The effects on locomotor activity were studied in Long-Evans derived rats following protocol outlined in Dews P., Br. J. Pharmacol., 8: 46 (1953).
Table 8 shows the results from the locomotor activity study. Both sertraline and Compound P increased spontaneous locomotor activity above controls following a single intraperitoneal dose of 2.5 mg/kg (measurements initiated 10 minutes following dosing). This effect was still evident 2 hours following drug administration. On the basis of these studies, CNS effects and long duration of action may be anticipated at sufficient clinical doses.
577 ± 541
559 ± 572
1p < 0.056;
2p < 0.085 vs. vehicle.
Studies were conducted to determine effects on IKr, the rapidly activating delayed rectifier cardiac potassium current in the human heart. In order to determine the effects of Compound P on IKr, its effect on HERG channel current in stably transfected HEK293 cells was evaluated. In this assay system, HERG channel current serves as a surrogate for IKr. The results for Compound P are summarized and compared to those of known antidepressants in Table 9 below. Results for citalopram are from Witchel et al., FEBS Lett., 512(1-3): 59 (2002).
In studies evaluating the effect of Compound P on hERG channel current in stably transfected BEK293 cells, Compound P was found to inhibit hERG channel current in a concentration-dependent manner, with an IC50 between 0.7 and 0.8 μM. Sertraline, as a comparator control, also inhibited hERG channel current, with an IC50 of 1.1 μM. Their effects on HERG channel current are similar to those of fluoxetine and citalopram.
A cardiovascular safety study was conducted with Compound P in conscious dogs. The purpose was to assess any effects of Compound P on heart rate, blood pressure and ECG parameters at tolerated doses, and compare any effects to those of sertraline.
Conscious, telemetered Beagle dogs were orally administered single doses of either Compound P or sertraline at 0.5, 1.5 and 5 mg/kg. There were four animals/compound and each animal within the treatment group was exposed to the three doses (plus a empty capsule control), in a dose ramp-up manner with a minimum of 72 hours between doses.
Both Compound P and sertraline had no effect on heart rate, blood pressure or ECG parameters (including QTc) at the doses evaluated.
These results demonstrate that Compound P's effects on HERG channel current (a surrogate for IKr) did not translate into an effect on QTc in vivo at doses up to those maximally tolerated in dogs, and that it does not have effects on heart rate or blood pressure, issues shared by the tricyclic antidepressants.
The Spinal Nerve Ligation (SNL) model [Kim and Chung, Pain 50, 355-363 (1992)] was used to induce chronic neuropathic pain. The animals were anesthetized with isoflurane, the left L5 transverse process was removed, and the L5 and L6 spinal nerves were tightly ligated with 6-0 silk suture. The wound was then closed with internal sutures and external staples. Wound clips were removed 10-11 days following surgery.
Mechanical allodynia testing: Baseline, post-injury and posttreatment values for non-noxious mechanical sensitivity were evaluated using 8 Semmes-Weinstein filaments (Stoelting, Wood Dale, Ill., USA) with varying stiffness (0.4, 0.7, 1.2, 2.0, 3.6, 5.5, 8.5, and 15 g) according to the up-down method (Chaplan et al., 1994). Animals were placed on a perforated metallic platform and allowed to acclimate to their surroundings for a minimum of 30 minutes before testing. The mean and standard error of the mean (SEM) were determined for each animal in each treatment group. Since this stimulus is normally not considered painful, significant injury-induced increases in responsiveness in this test are interpreted as a measure of mechanical allodynia. Mechanical allodynia was evaluated 14 days post-surgery.
Mechanical hyperalgesia testing: Baseline, post-injury and post-treatment values for non-noxious mechanical sensitivity were evaluated using a Paw Pressure Analgesymeter (7200, Ugo Basile, Comerio, Italy) which generates a linearly increasing mechanical force. The mechanical nociceptive stimulus was applied to the plantar surface of the hind paws by a dome-shaped plastic tip placed between the 3rd and 4th metatarsus. To avoid tissue damage, a cutoff pressure was set at 390 g. Mechanical thresholds were defined as the force in grams at the first pain behavior, which includes paw withdrawal, struggle and/or vocalization. Paw pressure test was performed on each hind paw for each animal. The mean and standard error of the mean (SEM) were determined for each paw, in each treatment group. Mechanical hyperalgesia was evaluated 24 days post-surgery.
Ten rats were studied per group and the tests were performed blind. (1R,4S)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-naphthalenamine (P) was evaluated at 3 doses (5, 10 and 15 mg/kg), administered orally and compared with a vehicle control group. Gabapentin (100 mg/kg) and duloxetine (30 mg/kg) administered orally under the same experimental conditions, were used as comparator substances. Mechanical allodynia and hyperalgesia testing were conducted at baseline and 1, 2 and 4 hours after test article administration.
Results: The results for P on mechanical allodynia and mechanical hyperalgesia are summarized in Tables 10 and 11, respectively. The mechanical allodynia results showed that P reduced allodynia at the highest dose level tested (15 mg/kg) during the 4 hour test period. Efficacy of P appeared to be similar to gabapentin. Duloxetine showed modest anti-allodynic effects; however, effects were not statistically significant. The mechanical hyperalgesia results showed that P significantly reduced mechanical hyperalgesia at all dose levels. Gabapentin and Duloxetine also produced robust and sustained anti-hyperalgesic effects at all time points tested.
Additional studies were conducted to test Compound P (same doses as those of the above described SNL model of neuropathic pain study) in a formalin model of persistent pain. The method, which detects analgesic/anti-inflammatory activity, followed that described by Wheeler-Aceto et al. (Psychopharmacology, 104, 35-44, 1991). Rats were given an intraplantar injection of 5% formalin (50 μl) into the posterior left paw. This treatment induced a recognizable flinching response in control animals. The number of flinches was counted for 15 minutes, beginning 20 minutes after injection of formalin. Eight rats were studied per group. The test was performed blind. Compound P was evaluated at 3 doses (5, 10 and 15 mg/kg), administered orally 60 minutes before the test (i.e. 40 minutes before formalin), and compared with a vehicle control group. Morphine (128 mg/kg) and duloxetine (30 mg/kg) administered orally under the same experimental conditions, were used as comparator substances. Data were analyzed by comparing treated groups with vehicle control using unpaired Mann-Whitney U tests.
Results The results for P are summarized in Table 12. In summary, P dose-dependently reduced the number of flinches observed during the late phase (20-25 minutes after formalin injection) of the formalin test. Morphine also significantly reduced flinching behavior; however, duloxetine had no effect under the testing conditions.
In a second test, flinching behaviors were measured for 90 minutes after formalin injection using an automated detection system. Animals were tested for paw movement responses to injection of a 5% formalin solution (50 μl in saline) using the Automated Nociception Analyzer (Yaksh et al. J Appl Physiol 90:2386-402, 2001). This device used a magnetic detection system to measure paw movements, called “flinches”. Small metal bands were attached to the left hind paw of rats just before placement into individual circular test chambers 30 minutes prior to formalin injection. Rats were injected with P (5, 10 and 15 mg/kg,), duloxetine (30 mg/kg) or vehicle 60 minutes prior to formalin injection. In addition to duloxetine, morphine (6 mg/kg, subcutaneously) was used as a comparator substance. Animals were treated with morphine 30 minutes prior to the formalin injection. To initiate the experiment, the rats were injected with formalin subcutaneously on the dorsal surface of the left hind paw and placed in the test chambers. The instrument subsequently recorded rapid foot movements counted in one minute epochs.
The results for P in this second test are summarized in Table 13. In summary, P appeared to dose-dependently increase the number of flinches observed during the late phase (10-60 minutes after formalin injection) of the formalin test. Morphine significantly reduced flinching behavior; however, duloxetine had no effect on late phase flinching behavior. P and duloxetine had no effect on the acute phase of the formalin test (0-10 minutes after formalin injection). In contrast, morphine significantly reduced acute phase flinching behavior.
Conclusion for formalin tests: While P dose-dependently reduced flinching behavior in one experiment, dose-dependent increases in flinching were observed in a second experiment. The reason for the discrepancy is likely related to the different scoring techniques used in each experiment. In the study that observed increases in flinching behavior, P dose-dependently increased baseline locomotor activity. Furthermore, an automated flinching apparatus was used to record flinching and the increases in flinching responses appeared to be correlated with the dose-dependent increases in locomotor activity. The automated detection apparatus is not able to distinguish between flinching behavior and overall increased locomotor activity. In the experiment where P exhibited a dose-dependent suppression of late phase formalin flinch behavior, a manual scoring technique was used to record flinching. Taken together, the findings support efficacy of P in the formalin flinch test.
Compound P (or other compound of the invention) and silicon dioxide are dry mixed, the first portion of croscarmellose is added and the mixture is further dry mixed. The magnesium stearate is added, dry mixed and the mixture is run through a roller compactor and mill. The resulting dry granulate is mixed with the remaining three ingredients and compressed into tablets.
Compound P, lactose and cornstarch, in the proportions shown above, are blended until uniform and then the magnesium stearate is blended into the resulting powder, which is sieved and filled into suitably sized, two-piece, hard gelatin capsules using conventional machinery. Other doses may be prepared by altering the fill weight and, if necessary, changing the capsule size to suit.
Pharmaceutical formulations of the formamides A-F may be prepared in similar fashion.
The present invention has been described with regard to preferred embodiments. However, it will be obvious to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described in the following claims.
All patents, publications, or other references that are listed herein are hereby incorporated by reference.
This application claims priority from U.S. provisional application 60/809,649, filed May 31, 2006, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60809649 | May 2006 | US |
